Synthesis Ed Frequency Hopping_implementation Strategy

Synthesised Frequency HoppingEdition 01 09/07/97MCD AIMS.DOC 3DF 00976 0001 TQZZA 1/105

SiteVELIZY

CELLULAR OPERATIONS DEPARTMENT

Originator(s)C. HELMER

Synthesised Frequency Hopping

Implementation strategy

Domain : MCD

Division : Operations

Rubric : Radio Network Planning/Optimisation

Type : Guide line

Abstract:This document is the report of Synthesised Frequency Hopping field trial in AbuDhabi. It gives an overview on Synthesised Frequency hopping possibilities onmicrocells and proposes a densification strategy for capacity enhancement.

ApprovalName C. Guetin

Signature

Table of contents1 EXECUTIVE SUMMARY ..................................................................................................................5

2 INTRODUCTION................................................................................................................................6

3 THEORETICAL BACKGROUND.....................................................................................................7

3.1 SLOW FREQUENCY HOPPING ...............................................................................................................73.2 HOPPING MODES .................................................................................................................................83.3 BENEFITS OF SLOW FREQUENCY HOPPING..........................................................................................10

3.3.1 Frequency Diversity ...............................................................................................................103.3.2 Interferer Diversity.................................................................................................................10

3.4 NETWORK IMPROVEMENTS................................................................................................................133.4.1 In principle ............................................................................................................................133.4.2 Definitions .............................................................................................................................13

3.5 FREQUENCY HOPPING IN MICROCELLS ................................................................................................153.6 FER CONTRA RXQUAL REGARDING VOICE QUALITY.........................................................................16

4 BSS AND CAE PARAMETER AND IMPLEMENTATION AT THE ALCATEL BSS.................17

4.1 BSS AND CAE PARAMETER FOR SFH................................................................................................174.2 IMPLEMENTED ALCATEL BTS CONCEPTS ...........................................................................................19

5 FIELD TRIAL RESULTS .................................................................................................................21

5.1 INTRODUCTION.................................................................................................................................215.2 FREQUENCY DIVERSITY ....................................................................................................................225.3 INTERFERENCE DIVERSITY ................................................................................................................23

5.3.1 Macrocell to microcell Reuse .................................................................................................235.3.1.1 Introduction and test conditions ....................................................................................................... 235.3.1.2 Interference evaluation..................................................................................................................... 23

5.3.1.2.1 Case Study ............................................................................................................................ 235.3.1.2.2 Interference evaluation........................................................................................................... 245.3.1.2.3 Examples :case study - conclusion.......................................................................................... 25

5.3.1.3 Unitary tests .................................................................................................................................... 255.3.1.3.1 Hopping sequence length : 4 .................................................................................................. 255.3.1.3.2 Description of field tests ........................................................................................................ 25

5.3.1.3.2.1 Global Results .................................................................................................................... 325.3.1.3.2.2 Comments on result and first conclusion ............................................................................. 33

5.3.1.3.3 Hopping sequence length : 8 .................................................................................................. 335.3.1.3.3.1 Description of field tests ..................................................................................................... 335.3.1.3.3.2 Global Results .................................................................................................................... 355.3.1.3.3.3 Comments on result and first conclusion ............................................................................. 36

5.3.1.3.4 Hopping sequence length: 15 ................................................................................................. 365.3.1.3.4.1 Description of field tests ..................................................................................................... 365.3.1.3.4.2 Global Results .................................................................................................................... 375.3.1.3.4.3 Comments on result and first conclusion ............................................................................. 38

5.3.1.3.5 Conclusion and radio rules..................................................................................................... 385.3.2 Micro to micro Re-use............................................................................................................40

5.3.2.1 Introduction ..................................................................................................................................... 405.3.2.2 microcells in line of sight................................................................................................................. 40

5.3.2.2.1 Environment description – E15PH1 and E16PH2................................................................... 405.3.2.2.2 Interference pattern................................................................................................................ 415.3.2.2.3 Unitary tests results ............................................................................................................... 41

5.3.2.2.3.1 Hopping Sequence Length: 13 – from 50 to 62 (contiguous frequencies).............................. 415.3.2.2.3.2 Hopping Sequence Length: 10............................................................................................. 45

5.3.2.2.4 Conclusion ............................................................................................................................ 475.3.2.3 microcells separated by a street corner ............................................................................................. 47

5.3.2.3.1 Environment description: E10PH2 and E10PH5..................................................................... 475.3.2.3.2 Interference pattern................................................................................................................ 485.3.2.3.3 Unitary tests results ............................................................................................................... 50

5.3.2.3.3.1 Hopping Sequence Length: 10............................................................................................. 505.3.2.3.4 Conclusion ............................................................................................................................ 53

5.3.2.4 Three microcells:2 pairs in LOS and one pair in NLOS.................................................................... 545.3.2.4.1 Introduction ........................................................................................................................... 545.3.2.4.2 Environment description........................................................................................................ 545.3.2.4.3 Interference pattern................................................................................................................ 545.3.2.4.4 Tests results – N (Hop)=13.................................................................................................... 55

5.3.2.4.4.1 OMC data........................................................................................................................... 55Abis interface ....................................................................................................................................... 575.3.2.4.4.3 Air interface ....................................................................................................................... 57

5.3.2.4.5 Conclusion ............................................................................................................................ 585.3.2.5 Three microcells:3 pairs in LOS....................................................................................................... 60

5.3.2.5.1 Environment description........................................................................................................ 605.3.2.5.2 Interference pattern................................................................................................................ 605.3.2.5.3 Tests results .......................................................................................................................... 61

5.3.2.5.3.1 OMC data........................................................................................................................... 615.3.2.5.3.2 Abis interface ..................................................................................................................... 615.3.2.5.3.3 Air interface ....................................................................................................................... 61

5.3.2.5.4 Conclusion ............................................................................................................................ 635.3.2.6 Conclusion on unitary tests .............................................................................................................. 63

5.4 GENERALISATION ON SOUQ AREA ....................................................................................................645.4.1 Introduction ...........................................................................................................................645.4.2 Environment description ........................................................................................................645.4.3 Synthesised Frequency hopping results...................................................................................65

5.4.3.1 OMC data........................................................................................................................................ 655.4.3.1.1 SOUQ BSC ........................................................................................................................... 655.4.3.1.2 Microcell data ....................................................................................................................... 685.4.3.1.3 Macrocell data....................................................................................................................... 69

5.4.3.2 Abis interface .................................................................................................................................. 705.4.3.3 Air interface .................................................................................................................................... 725.4.3.4 QVOICE.......................................................................................................................................... 74

5.4.4 Conclusion .............................................................................................................................75

6 INTERFERENCE REDUCTION......................................................................................................76

6.1 HO_MARGIN AND ANTI PING-PONG PROCESS IN B4.........................................................................776.1.1 HO_MARGIN 0......................................................................................................................776.1.2 Anti Ping-Pong process ..........................................................................................................80

6.2 LOAD MANAGEMENT AND SPEED DISCRIMINATION .............................................................................816.2.1 Speed discrimination ..............................................................................................................816.2.2 Load in the umbrella cell........................................................................................................81

6.2.2.1 General principles ........................................................................................................................... 816.2.2.2 Computation of the load in the umbrella cell.................................................................................... 816.2.2.3 Adaptation of MIN_DWELL_TIME - "power control" mechanism ................................................... 81

6.2.3 Trade-off between speed discrimination and overload of the umbrella cell .............................836.3 POWER CONTROL AND DTX .............................................................................................................84

6.3.1 Power control.........................................................................................................................846.3.2 DTX uplink.............................................................................................................................84

7 ALCATEL INTEGRATED MULTILAYER SOLUTION...............................................................85

7.1 PRINCIPLES ......................................................................................................................................85

7.2 CONDITIONS.....................................................................................................................................867.2.1 Re-use one between microcells ...............................................................................................867.2.2 Macro frequency re-use conditions.........................................................................................86

7.3 FRACTIONAL RE-USE (1/3 OR 1/1) ON THE MACRO LAYER....................................................................917.3.1 Principles...............................................................................................................................917.3.2 Frequency hopping in GSM....................................................................................................91

7.3.2.1 External Parameters......................................................................................................................... 927.3.2.2 Internal parameters .......................................................................................................................... 93

7.3.3 Constraints.............................................................................................................................947.3.3.1 “Intra-site” constraint ...................................................................................................................... 947.3.3.2 “Inter-site” constraint ...................................................................................................................... 967.3.3.3 Conclusion ...................................................................................................................................... 97

7.3.4 Densification comparison – simple 1/3 re-use Vs A I M S .......................................................977.3.5 Densification strategy ..........................................................................................................100

8 CONCLUSION ................................................................................................................................102

9 REFERENCES.................................................................................................................................103

10 ABBREVIATIONS ..........................................................................................................................104

1 Executive summary

• Frequency diversity starts to be efficient when the hopping sequence containsat least 8 frequencies (in accordance to the theory).

• In a microcellular environment, re-use one is possible between 2 TRXmicrocells hopping on 13 frequencies (RFLoad=8%). Each microcell beinginterfered by other at 70 % and having a full traffic on their second hopping FU (6Erl).

• An interference reduction process has been set by tuning radio parametersand by using fully our new features available in B4.

• When M4M microcells (4 watts and 4 TRX) are available, it will be possible toswitch on the hopping FU by re-using frequencies from the macrolayer.Those TRXs will be then considered as “free”.

• A full hopping network is the final act to enhance capacity and to make frequencyplan easier. 1/3 re-use and 1/1 re-use are discussed in this documentintroducing two types of constraints: “intra-site” and “inter-site”.

2 IntroductionGSM introduced antenna diversity and slow frequency hopping (SFH) to improve thetransmission quality, as described in GSM Rec. 04.08, 05.01, and 05.02. Whileantenna diversity combats multipath fading only, frequency hopping additionallyaverages the effects of interference.This allows a tighter frequency reuse; thus carrier upgrading can be performed,resulting in an increased capacity while maintaining network performance andquality.Alternatively, if no carrier upgrading is performed, frequency hopping allows qualityand performance to be improved while maintaining capacity.

The field trial in Abu Dhabi has shown the feasibility of a reuse 1 on Abu Dhabimicrocellular network.Moreover, interferences are hard to predict in microcellular networks, makingfrequency planning tricky in very dense areas.This brings important benefits for the customer without any Quality of Servicedegradation:- Provision of high capacity with limited engineering efforts- Very simple frequency planning for the 2nd FU of micro-BTSs- Fast deployment of a large amount of microcells

This experience allowed us to have a better view of Synthesised Frequency Hoppingtopic. An implementation method has been set and is proposed in this document.

3 Theoretical Background

3.1 Slow Frequency Hopping

Frequency hopping consists in changing the frequency used by a channel at regularintervals. One distinguishes fast frequency hopping (FFH), where the frequencychanges quicker than the modulation rate, from slow frequency hopping (SFH), whichis used in GSM. GSM uses a TDMA system with 8 timeslots. In slow frequencyhopping each mobile transmits or receives on a fixed frequency during one timeslotand hops to another frequency before the next timeslot will be transmitted orreceived, resulting in 217 hops per second for the MS. This technique can be appliedon all traffic and signalling channels, except the BCCH channel, which must transmiton a fixed frequency, to make correct RXLEV measurements for the neighbour cellmobiles possible. Moreover, the BCCH channel has to transmit full power on alltimeslots. Thus SFH, PC and DTX is not allowed on the BCCH carrier.

3.2 Hopping modes

As shown in figure 1, frequency hopping can be performed in two modes:t Cyclic hopping modet Random hopping mode While in cyclic hopping mode the same hopping sequence will be used periodically,in random hopping mode a pseudo random sequence will be used in order toachieve uncorrelated hopping sequences.

Principle of cyclic and random SFH on Timeslot 1 on F1, F2 and F3 From the BTS point of view one distinguishest Baseband Hopping (BBH)t Synthesiser frequency hopping (or Radio Frequency Hopping = RFH)

In baseband hopping (BBH) each transceiver (TRX) is transmitting on one fixedfrequency. Hopping is performed by switching the mobiles from burst to burst todifferent TRXs. Within the BTS the baseband part (FU) is separated from the RF-part(CU). Thus SFH is realised by switching the FU to the respective CU via an internalswitch. This concept is implemented in the Alcatel G2 BTS. The amount of hoppingfrequencies N (hop) is determined by the number of TRXs N (TRX): N (hop) <= N(TRX). Note that a BTS equipped with only one TRX cannot perform basebandhopping.

In synthesiser frequency hopping (RFH) the TRX do not get fixed frequencyassignments, they may change their frequency from TS to TS according to apredefined hopping sequence. In such a system the number of applicable hoppingfrequencies may be larger then the number of equipped TRXs: N (hop) ≥ N (TRX).Since the Alcatel micro BTS is usually equipped with one or two TRX, synthesiserfrequency hopping has to be used.

Since no hopping on the BCCH frequency is allowed, synthesiser frequency hoppingmust not be performed on the BCCH TRX. Figure 2 shows both hopping modes. TRX1represents the BCCH frequency, where the BCCH information is transmitted ontimeslot 0. Note that mobiles being connected to TRX1 can only hop in baseband

F1F2F3

Timeslot

Cyclichoppingmode

Randomhoppingmode

hopping mode. However, the implemented solution at the Alcatel micro BTS (1 TRX),makes synthesiser frequency hopping possible, by transmitting a dummy burst withan additional transmitter. This special concept will be explained in chapter 8.

0 1 2 3 4 5 6 7TRX1

Baseband hopping (left) and synthesiser frequency hopping (right)

3.3 Benefits of Slow Frequency Hopping

Frequency hopping has been included in the GSM specification, mainly in order todeal with two specific aspects, which affect the transmission quality:t Frequency diversityt Interferer diversity

3.3.1 Frequency Diversity

Considering urban environments, radio signals reach the receiver due to reflectionsand diffraction on different paths resulting in fading effects. The received signal levelsare varying dependent on the applied frequency and on the receiver location. SlowMS may stay in a fading notch for a long period of time and suffer from a severe lossof information. Frequency hopping introduces frequency diversity and combatsmultipath fading: Different frequencies experience different fadings, thus the mobilewill experience different fadings at each burst and will not stay in a deep minima fora long period of time.The error correction algorithms of the equaliser can reduce fading effects. But thesealgorithms only work effectively, if the signal interrupt is shorter than the period oftime over which the codeword is spread with interleaving. Therefore SFH will improvethe transmission quality, because too long fading holes will then be avoided.Since fast moving mobiles do not stay in long and deep fading holes, they do notsuffer severe from this type of fading. Thus especially slowly moving mobiles willbenefit from frequency diversity.The improvement results in increased receiver sensitivity under fading conditions (notunder non-fading propagation conditions) and therefore in improved quality in uplinkand downlink direction compared to a non-hopping configuration.3.3.2 Interferer Diversity

Without SFH, some receivers (MS or BTS) are not interfered, while others, receiving onanother frequency, will experience strong interference. This interference can bepermanent such as BCCH frequencies in downlink direction or some fixed interferersincorrectly radiating in the GSM band.With random SFH, the interfering scenario will change from TS to TS, due to ownhopping and uncorrelated hopping of potential interferers. Thus all receivers (MS andBTS) experience an averaged level of interference. This is called interferer averagingor interferer diversity.The average C/I in the network <C/I> remains unchanged but the „standard“deviation σ is reduced (see figure 3). Therefore the number of MS and BTS that willhave a C/I above a certain threshold (e.g. C/ITHR1=9dB) is increased. Note that this isonly true, as long as the mean C/I in the network is above the specified threshold. Ifthe mean C/I is below that threshold, SFH will therefore make the

situation worse! Figure 3 illustrates this situation: The diagram shows an arbitraryC/I distribution of eight mobiles.Let us first assume that C/IThr is C/IThr1 (mean C/I is above C/IThr): Without SFH 3 C/Ivalues are below C/IThr1, with SFH no C/I value is below C/IThr1. The situation isimproved, when introducing SFH.Let us now assume that C/IThr is C/IThr2 (mean C/I is below C/IThr): Without SFH 5 C/Ivalues are below C/IThr2, with SFH 7 C/I values are below C/IThr2. The situation isgetting worse, when using SFH.

Improved C/I due to reduced standard deviation based on interferer diversity, as longthe mean <C/I> is above the threshold C/IThr1. Left no SFH, right with SFH.

We can therefore conclude, that benefit out of SFH is taken only in well-designed andwell-tuned networks.Since the benefit of frequency diversity is based on the principle that differentfrequencies experience different depths of fading, it is recommended to separate thefrequencies within the hopping sequence as far as possible. An offset of typicallythree channels is automatically defined by the required co-cell separation (e.g.600kHz = 3 channels).

It can further be concluded, that the drawback of cyclic hopping is, that it does notprovide interferer diversity since the interfering and the interfered carriers do not hopuncorrelated. Therefore random hopping is recommended, since more benefit canbe expected from interferer diversity.Figure 4 summarises the effects of frequency and interferer diversity.

C/IThr1

C/IThr2 C/IThr2

C/IThr1

C/IWithout SFH With SFH

MS number

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

MS number

MS1BS1

F1,F2,F3

MS1BS1 MS2

F2,F3,F1

Interference Diversity

Frequency Diversity

NoHopping

FrequencyHopping

Effects of frequency and interferer diversity

3.4 Network improvements

3.4.1 In principle

Frequency diversity and Interferer diversity result in an improved network quality.Thus introducing SFH in a mature network is a feature for network qualityimprovement.Network capacity increase can be performed in a second step after the introductionof SFH. Due to the fact, that the same quality level with a lower C/Idesign ratio can behandled, a SFH network can be planned with a tighter reuse cluster size. Thereforemore carriers per site can be used.In order to evaluate possible capacity increases with SFH, simulations have beenperformed [10]. Within the following section three different simulation results will bepresented and discussed. Approach 1 and 2 are based on [10], whereas the thirdsimulation has been performed with the RNP Tool A955.

3.4.2 Definitions

The following definitions are required for the discussion of the simulation results.

ARCS:A key parameter is the average reuse cluster size ARCS, defined as:

ARCSBandwidth

Average amount of TRX per cell=

Fractional Reuse:Applying synthesiser frequency hopping, additionally fractional reuse techniquescan be applied. The principle of fractional frequency reuse is, to use morefrequencies in a cell than TRX are equipped: N(hop)>N(TRX). This technique can onlybe realised by applying synthesiser hopping (RFH).

The following effects of fractional reuse have to be considered in comparison to abaseband hopping system, where only N(hop)<=N(TRX) is possible:

t Hopping over more frequencies provides more diversity, whereas only neglectiblefrequency diversity gain can be expected, when going above 4 hoppingfrequencies.

t The classical definition of ARCS=BW/N(TRX) is no longer valid, a FrequencyAverage Reuse Cluster Size FARCS needs to be defined as:

FARCSBandwidth

Average amount of Frequencies per cell=

t Only N(TRX) frequencies are on air at one time (equal to BBH), which can be

defined by the RF Load = N(TRX)/N(hop)=FARCS/ARCS, resulting in a reducedcollision probability for each frequency.

t The reuse (FARCS) of the frequencies is smaller compared to an according BBHsystem (ARCS).

t Therefore to contrary effects have to be considered:1. Fractional reuse increases the level of interference, since FARCS<=ARCS,

each frequency is planned with a smaller reuse.2. Fractional reuse reduces the collision probability (RF Load) for each

frequency.

Example: BW=36, N (TRX)=3, N(Hop)=12 results in ARCS=36/3=12 (Reuse ofBBH system) and FARCS=36/12=3 (Reuse of a RFH system with fractional reuse), RFLoad=25%

Hard- and Softblocking:The smaller the ARCS for a constant bandwidth, the more TRX are available per celland accordingly more traffic can be handled. But with increasing amount of TRX percell the level of interference also increases, due to reduced ARCS. Thus the capacity ofa cellular network is basically restricted either by available hardware capacity or byinterference, depending on the ARCS. Accordingly a hard blocking and a softblocking limit can be defined as:

1. Hard blocking is determined by the amount of available channels. This type ofblocking occurs in conventional traffic systems, with a low interference probability.The blocking is defined by the blocking probability, e.g. Pblock=2%. Mobiles will notget access to the network, since all channels are in use (100% traffic load).

2. Soft blocking occurs due to high interference or due to an unacceptable calldrop rate. This type of blocking occurs in a network design with a low reuse clustersize, resulting in a high level of interference. The traffic load can define the softblocking limit, when the quality in the network becomes unacceptable. E.g. when10% of the mobiles will suffer from a C/I < C/IThr or when the call drop rate reaches5%. With increasing traffic load, the capacity will be limited due to soft blockingbefore the hard blocking limit is reached (traffic load <100%).

3.5 Frequency hopping in microcells

Due to increased signal fluctuations (fading or mobiles turning around the corneretc.) in microcells, more benefit is taken from frequency and interferer diversity thanin macrocells, which suffer less from fading. Thus SFH in microcellular environmentswill be more effective.Since microcells usually are introduced in capacity and therefore in interferencelimited environments, introducing SFH without carrier upgrading can improve thenetwork quality in microcellular networks very effective.Thus the ARCS can be further reduced after the introduction of SFH. Not only areduction of the ARCS between the microcells becomes possible, but also betweenmacro and microcells.

3.6 FER contra RXQUAL regarding voice quality

In a GSM system, the number of frames that are not erased are sent as an input tothe voice decoder (Figure 9).

DEMOD DECODER

ENCODER

FrameErasureDecision

VoiceDecoder

RXQUAL Frame Erasure Rate

DeinterleaveError correct.

Inside the mobile stationAir

The signal decoding process

Although in non hopping networks the RXQUAL and voice quality are correlated, thisis not the case in hopping networks, where two mobiles with similar RXQUAL canhave different voice qualities. The voice quality is rather correlated to the FER. This isdue to interferer averaging and due to the non-linear mapping of BER to RXQUALvalues (for more details see chapter 6). Thus, in SFH networks, the Frame ErasureRate (FER) is a better estimate of the voice quality than RXQUAL.

4 BSS and CAE Parameter and Implementation at the AlcatelBSS

In this chapter an overview about the BSS and CAE parameter, which need to bemodified for introduction of SFH, will be given. Further the implemented Alcatel BTSconcepts will be discussed.

4.1 BSS and CAE Parameter for SFH

Table 2 gives an overview about the relevant BSS parameter and a brief descriptionof their meanings.

Parameter name DescriptionFHSmax 16 freq.

Frequency Hopping Sequence: Set of frequencies to be used in thehopping sequence. Example: {F10,F30,F45,F34}

HSNRange:0...63

Hopping Sequence Number: Order of the frequencies defined inthe FHS. Cyclic: HSN = 0, Random: HSN = 1...63

MAIORange: 1...16

Mobile Allocation Index Offset: First frequency to be used in thehopping sequence. Example: MAIO = 2 ⇒ First freq.: F30

FHS_IDRange: 1...16

Identifier of a specific frequency hopping system. E.g. in TS 0 adifferent FHS and thus a different FHS_ID needs to be used than inthe other TS, since the BCCH frequency has to be excluded formthe FHS.

L_RXQUAL_UL_H Lower threshold for triggering a quality HO based on uplinkL_RXQUAL_DL_H Lower threshold for triggering a quality HO based on downlink

Relevant BSS Parameter for introduction of SFH

When using random hopping, cells which can potential interfere each other, shoulduse different HSNs in order to provide maximum interferer diversity.When using cyclic hopping, all cells will use the same HSN (HSN = 0).Within the same cells, different MS will use the same HSN but a different MAIO. Thisguarantees that there will be no collisions within one cell.In general TS 0 must not hop on the BCCH frequency. Thus a different FHS_ID has tobe defined for TS 0. Therefore the Customer Data Population Programs (CDPP) willautomatically populate two-frequency hopping systems [6]:FHS_ID 1 with all associated frequencies of the BTS except BCCH frequency for TS 0FHS_ID 2 with all associated frequencies of the BTS inclusive BCCH frequency

Once a HSN and the FHSs are defined, the FHS_ID and the MAIO defines thefrequency to use in each TS of each frequency unit. Instead of the ARFCN the FHS_IDand MAIO separated by a comma, will be inserted as the channel value in theaccording OMC screen. The following table illustrates a possible set-up with four FUs.

TS 0 TS 1 TS 2 TS 3 TS 4 TS 4 TS 5 TS 6 TS 7FU 1 bc/sd4

orbcch

TCH TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio freq 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0FU 2 TCH SD/8 TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 0 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1FU 3 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 1 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2FU 4 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 2 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3

Possible set-up for a frequency-hopping scenario, at 4 TRX BTS

Since the network quality is deteriorated by one digit, the thresholds ofL_RXQUAL_XX_H need to be tuned, when introducing SFH (increment by on value).

4.2 Implemented Alcatel BTS concepts

Macro BTS:G2 BTS: Maximum 8 carriers, baseband hopping.G3 BTS: Baseband and synthesiser hopping is possible. Real baseband hopping isplanned for a second step, when RTCs will be used instead of WBC.

Micro BTS [7]:

Realisation of synthesiser hopping in the 1 TRX micro BTSAs shown in figure 12 the basic unit of the micro BTS is equipped with 2 transmitter(TCH-TX and BCCH-TX). The BCCH-TX transmits the BCCH information of TS0 anddummy bursts on TS1-7. Traffic data is transmitted on the TCH-TX. Since bothtransmitter are equipped with one synthesiser (TXSYN 1 and TXSYN 2) the BCCH andTCH can be tuned on different frequencies. Therefore it is possible to performsynthesiser hopping on the 1 TRX micro BTS, while transmitting a dummy burst on theBCCH frequency. The hopping synthesiser TXSYN 2 and RXSYN are equipped withtwo oscillators, making synthesiser hopping possible, switching from TS to TS betweenboth oscillators.If frequency hopping is deactivated, the TCH-TX will not be used. Therefore thecombiner inside the BTS will not be used and the transmission power is increased bythe absence of combiner loss of 3dB to 26 dBm.

1 and 2 TRX micro BTS: synthesiser hopping:

1 TRX µ-BTS• without frequency hopping• with synthesiser hopping on TS1-TS7• TS0: BCCH/CCCH Bursts on BCCH-TX, TS1-TS7: Dummy Bursts on BCCH-TX• TS1-TS7: TCHs with frequency hopping on TCH-TX 2 TRX µ-BTS• First TRX: no frequency hopping (BCCH-Frequency)• Second TRX synthesiser hopping (TCH-Frequencies)

TCH-TX

BCCH-TX

BCCH/TCH-RX

Tx data

Rx data

TXSYN 1

TXSYN 2

TX/RX Antenna

Architecture of the 1TRX µ-BTS (basic unit), for the realisation of synthesiser hopping

5 Field Trial Results

5.1 Introduction

This trial took place in Abu Dhabi from 21st of March to 29th of May 1998.Each time we have activated Synthesised Frequency hopping on the field, it was arandom sequence: HSN? 0. Moreover, to improve interference diversity, HSN have tobe chosen different for neighbour cells.The schedule of this trial is described below:

5.2 Frequency Diversity

The tests that we have conducted did not point out any significant results on frequencydiversity. 15 configurations have been tested but air traces were not enough long todetect a real difference in the received level from the BTS.Anyway, the generalisation on SOUQ has shown that the frequency diversity gainwas not neglectible.

5.3 Interference Diversity

5.3.1 Macrocell to microcell Reuse

5.3.1.1 Introduction and test conditions

This study is based on tests performed by using firstly air traces results and in theworst case. Those tests were based on the introduction of continuous interferers(BCCH frequencies) in order to get rid of any traffic load effect on the interferers.Each tests last 20 minutes at least and were based on subjective quality and airtraces.

5.3.1.2 Interference evaluation

The content of this paragraph is the way each frequency need to be evaluated as aninterferer on another.

With Abis traces, Air traces and scanning, we can collect many samples of fieldstrength of the potential interferer and potential interfered frequencies. This resultsthat, during a test, we have C on I ratio samples. The issue is how to evaluatethese samples in order to evaluate a frequency (Very strong interferer,strong interferer, and clean frequency… ).

Two variables have to be taken into account: the C/I mean value and the distributionof the samples.1. C/I mean value: easy to collect.2. Distribution of samples: the first tests were based on it. We have defined a

threshold for C/I co-channel interferer: 9dB (GSM Standard). Then, we process thepercentage of samples with a C/I ratio worse than 9 dB.

5.3.1.2.1 Case Study

During the first tests, we realised that taking only this percentage into account was notprecise enough. Indeed, we had sometimes the same interfering percentage whereasthe interferer were completely different:

102030405060

-8 -6 -4 -2 0 2 4 6 8 10 12 14 16

Interferer1Interferer2

In this configuration, Interferer 1 is interfering at 100% and Interferer 2 is interferingat 98% whereas they are definitely different: the first one has a C/I average value of -3dB and the second has a C/I average value of 9dB!Moreover, when a frequency has a C/I always around 9dB, this percentage willchange each time a scan is performed:

-11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 17

C/I ratio

Interfere1 at time 1Interfere1 at time 2

At time 1, the interference is 61 %. At time 2, the interference is 90 %. We can see onthis case that this percentage varies a lot according to scanning time.

Conclusion of this case study: We need also to take into account C/I mean value.

5.3.1.2.2 Interference evaluation

We need to introduce in the interference percentage the notion of C/I mean value.That is what we do with the following function:At the end, we want to have, for 100% of samples inferior to 9dB

• for a mean C/I of 9dB, interference_percentage = 100%• for a mean C/I of 0dB, interference_percentage = 200%• for a mean C/I of –9dB, interference_percentage = 300 %

Assuming that x = C/I mean value

( ) = −29

This function is introduced as a weight in the interfering percentage:

3-9 -7 -5 -3 -1 1 3 5 7 9 11 13 15 17

Assuming that Distribution_percentage is the percentage of C/I samples worse than9dB and that C/I mean is the mean value of C/I during all the scanning, wehave

percentageonDistributieanCFpercentagegInterferin _)Im/(_ ×=

5.3.1.2.3 Examples :case study - conclusion

• For the previous configuration shown in the case study, we had 100 % and 98 %.With the new formulae, we get 300 % for the first and 160 % for the second.

We make the difference between both.• For the second configuration, with the new formula, we get 70 % for the first and

80 % for the second instead of 61% and 90%.The differences, due to field strength fluctuation, are smoothed.

5.3.1.3 Unitary tests

The unitary tests aim was to assess the maximum level of interference tolerated withina sequence and the effect of the hopping sequence length. Two aspects have beenconsidered: the average value of interference and the maximum level of interference(number of super frequencies, more than 50% interfering)

5.3.1.3.1 Hopping sequence length : 4

5.3.1.3.2 Description of field tests

The different interference patterns in the Hopping Sequence that have been testedare the following.Before each test, a scan has been performed to get, at the moment of the test, thereal interference percentage of the BCCH frequencies used in the hopping sequence.Some changes with the latest scan have been noticed, due to 4 or 5 meters ofdifferences. Find in Annex the scanning at test time.

Test Name ofconfiguration

State Hopping sequence interferences

1 C1 Referencetest

0% 0% 0% 0%

2 C51 Fair 15% 20% 20% 40%

3 C5 Fair 10% 25% 25% 40%

4 C4 Fair 10% 25% 25% 50%

5 C52 Fair - Bad 15% 20% 40% 50%

6 C53 Fair - Bad 15% 20% 50% 70%

7 C3 Fair - Bad 25% 25% 50% 75%

8 C54 Fair - Bad 20% 40% 50% 70%

9 C2 Fair - Bad 25% 50% 50% 75%

10 C57 Bad 15% 20% 40% 100%

11 C55 Very Bad 40% 50% 70% 100%

• Test 1 : Reference testHopping Sequence: 52, 56, 60, 64Those frequencies are clean ones.• Test 2Hopping Sequence: 78, 82, 84, 87Interference pattern

• Test 3Hopping Sequence : 81, 82, 84, 87Interference pattern

• Test 4Hopping Sequence: 81, 82, 85, 87Interference pattern

Edition 01 09/07/97MCD AIMS.DOC 3DF 00976 0001 TQZZA

5.3.1.3.2.1 Global Results

Test Configuration

Rxlevfull

Rxqualfull

F.E.R CRLTO BCCH Freq_List Interfering %

1 Conf1 -63,19 1,46 0,01 19,99 67 52 56 60 64 0% 0% 0% 0%2 Conf5.1 -69,14 3,15 0,83 19,95 67 78 82 84 87 15% 20% 20% 40%3 Conf5 -66,97 3,54 2,48 19,59 67 81 82 84 87 10% 25% 25% 40%4 Conf4 -67,77 3,29 0,87 19,93 67 81 82 85 87 10% 25% 25% 50%5 Conf5.2 -64,04 1,82 0,15 19,98 67 78 82 84 86 10% 20% 40% 50%6 Conf5.3 -66,58 4,08 1,56 19,78 67 78 82 83 86 15% 20% 50% 70%7 Conf3 -64,65 2,15 0,23 19,98 67 81 85 93 87 25% 25% 50% 75%8 Conf5.4 -66,39 4,11 2,17 19,78 67 78 80 83 86 20% 40% 50% 70%9 Conf2 -61,16 0,63 0,08 19,98 67 76 81 85 93 25% 50% 50% 75%10 Conf5.7 -58,58 5,09 4,35 19,15 67 79 82 84 87 15% 20% 40% 100%11 Conf5.5 -66,95 6,16 12,83 13,82 67 79 80 83 86 40% 50% 70% 100%

5.3.1.3.2.2 Comments on result and first conclusionSome interesting information appeared from those tests.

1. No need of any clean frequencies on the hopping sequence2. We can see that F.E.R is linked to voice quality whereas RXQUAL does not correspond

to any subjective consideration.3. The result of those tests is

For N-HOP = 4, quality does support, with a security margin, until a configuration10% 25% 25% 50%

(28%; 1) is the characteristic couple that models the interference pattern.

This result is the worst case. Only “half gain” is considered (the interferer does not hop).Higher level of interference may be expected in case of hopping TCH introduction.

5.3.1.3.3 Hopping sequence length : 8

5.3.1.3.3.1 Description of field tests

The different interference patterns in the Hopping Sequence that have been tested arethe following.Before each test, a scan has been performed to get, at the moment of the test, the realinterference percentage of the BCCH frequencies used in the hopping sequence. Somechanges with the latest scan have been noticed, due to 4 or 5 meters of differences.

Test State Hopping sequence interferences

1 Fair-Bad 341% 100% 10% 10% 133% 5% 5% 0%

2 Fair 341% 10% 10% 0% 133% 5% 0% 0%

3 Good 10% 0% 0% 15% 10% 0% 130% 0%

5 Excellent 0% 0% 5% 10% 10% 20% 20% 130%

6 Excellent 0% 0% 0% 0% 5% 5% 15% 20%

Conf. Rxlev RxQual F.E.R CRLTO Freq_List Average Superfreq.

Interfering %

8_HOP -57,87 0,22 0,02 19,98 76 77 78 85 8788 89 95

74% 3 341% 100% 10% 10% 133%

8_HOP -59,77 3,65 0,7 19,95 77 78 85 86 8789 91 95

62% 2 341% 10% 10% 0% 133%

8_HOP -59,7 0,55 0,03 19,99 78 80 85 86 8889 91 92

21% 1 10% 0% 0% 15%

8_HOP -58,8 0,91 0,13 19,99 79 81 82 84 8586 87 91

25% 1 0% 0% 5% 10%

8_HOP -60,05 0,61 0,03 19,99 80 80 81 82 8488 89 92

6% 0 0% 0% 0% 0%

5.3.1.3.3.3 Comments on result and first conclusionSome interesting information appeared from those tests comparing to a hoppingsequence length of 4:1. In Abu Dhabi, interferences from the macro layer are almost binary. Either the

frequency is highly interfering (more than 100%), either the frequency is quite clean(less than 10 %)

2. Whereas the averaged level of interference tolerated is 30% with a hopping sequencelength of 4, we can reach an averaged level of interference of 60 % with 8frequencies!

5.3.1.3.4 Hopping sequence length: 15

5.3.1.3.4.1 Description of field tests

The different interference patterns in the Hopping Sequence that have been tested arethe following.Before each test, a scan has been performed to get, at the moment of the test, the realinterference percentage of the BCCH frequencies used in the hopping sequence. Somechanges with the latest scan have been noticed, due to 4 or 5 meters of differences.Please find in Annex the scanning at test time.

State Hopping sequence interferences

1 Verybad

0 0 50 65 295 125 70 15 20 100 85 145 30 35 0

2 Fair 0 0 0 50 65 125 70 15 20 100 85 145 30 35 0

3 Good 0 0 0 0% 50 65 130 70 15 20 100 85 30 35 0

4 Excellent

341 100 10 0% 20 0 5 15 10 0 130 5 5 0 0

Test Rxlev RxQual F.E.R CRLTO Freq_List Average

1 -72,06 5,55 5,67 19,48 52 54 77 78 79 80 81 82 83 84 85 87 93 94 95

2 -73,87 4,43 1,77 19,84 52 54 56 77 78 80 8182 83 84 85 87 93 94 95

3 -71,02 3,59 0,36 19,97 52 54 56 58 77 78 80 81 82 83 84 85 93 94 95

4 -58,07 2,71 0,59 19,96 76 77 78 80 81 82 83 84 85 86 87 88 89 91 94

Test Interfering %1 0% 0% 50% 65% 295% 125% 70% 15% 20% 100% 85% 145% 30% 35% 0%2 0% 0% 0% 50% 65% 125% 70% 15% 20% 100% 85% 145% 30% 35% 0%3 0% 0% 0% 0% 50% 65% 130% 70% 15% 20% 100% 85% 30% 35% 0%4 341% 100% 10% 0% 20% 0% 5% 15% 10% 0% 130% 5% 5% 0% 0%

5.3.1.3.4.3 Comments on result and first conclusionSome interesting information appeared from those tests comparing to a hoppingsequence length of 8 and 4:1. In Abu Dhabi, interferences from the macro layer are almost binary. Either the

frequency is highly interfering (more than 100%), either the frequency is quite clean(less than 10 %)

2. Whereas the averaged level of interference tolerated is 30% with a hoppingsequence length of 4 and 60 % with 8 frequencies, we can notice that we can’tincrease this averaged level even if the hopping sequence length increases (15frequencies). 67% is really bad.

5.3.1.3.5 Conclusion and radio rules

Introducing interfered frequencies from the macro layer involves two constraints:

• Averaged level of interference tolerated: the variation according to thehopping sequence length is not linear. This variation follows a logarithmic curve.

• Introduction of super frequencies: the number of very high-interfered

frequencies that can be introduced does not vary linearly. The variation follows anexponential curve:

4 freq 8 freq 15 freq

Averaged Level of Interference

4 freq 8 freq 15 freq

Number of Super frequencies

As a conclusion, a compromise has to be found between those both limitations. If thenumber of ‘super frequencies’ to introduce is high, we must have a long hoppingsequence length BUT, as the averaged level of interference tolerated is to be less than60 %, the other frequencies of the hopping sequence have to be very clean!

Note: One can be surprised that the averaged level of interference grows with thenumber of frequencies in the hopping sequence. We can argue that this is the effect offrequency diversity. Indeed, as each encoded word is interleaved on 8 consecutivebursts, the ideal hopping sequence in terms of frequency diversity may contain exactly8 “perfectly uncorrelated” frequencies.

5.3.2 Micro to micro Re-use

5.3.2.1 Introduction

There might be two approaches:• Re-use pattern of 1• Multiple Re-use PatternA quick overview of Abu Dhabi network design made us realise that it was impossibleto try a re-use cluster different from 1. Indeed, as far as Abu Dhabi microcellularnetwork is concerned, the second approach was non-sense because the patternshould have been at least 4. It involves too many frequencies to assign to themicrocells’ 2nd TRX.

5.3.2.2 microcells in line of sight

5.3.2.2.1 Environment description – E15PH1 and E16PH2

Two microcells in Line of Sight interfere each other. Those interferences are symmetricregarding radio aspect. The cell load has to be taken into account to determine thereal interferences between the cells.As far as E15PH1 is concerned, the traffic load is quite low: about 3 Erl on the secondFU at Busy Hour, whereas E16PH2 has an important traffic on its second FU: about 6Erl at Busy Hour (obtained by barring the microcells and within first FU TS blocked).Special care has to be taken on E15PH1 because this cell is supposed to be the mostinterfered regarding radio and load aspects.

E16PH2 and E15PH1

E16PH2

E15PH1

5.3.2.2.2 Interference pattern

Thanks to Abis traces, we can obtain the interference pattern of this cell pair:

Serving cell: E16PH2 – Interfering cell: E15PH1

Serving cell: E15PH1– Interfering cell: E16PH2

As the charts show, E16PH2 is 73%-interfered by E15PH1 and E15PH1 is 60%-interfered by E16PH2.

5.3.2.2.3 Unitary tests results

During the testing period, the First FU TS were blocked in order to increase the loadon the second FU.

5.3.2.2.3.1 Hopping Sequence Length: 13 – from 50 to 62 (contiguous frequencies)

-24 -21 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 38

-32 -28 -23 -19 -16 -13 -10 -7 -4 -1 2 5 8 11 14 17 20 23 26 29 32 35 39

5.3.2.2.3.1.1 OMC data

E16PH2 E15PH1

• Traffic:Mean value : 6 ErlPeak value : 8 Erl

• Traffic:Mean value : 1 ErlPeak value : 7 Erl

• Call Drop : 0 % • Call Drop : 0 %

According to OMC-R, hopping on 13 common frequencies provides a very goodquality of service. The load was very important on E16PH2 and quality on E15PH1 hasnot been degraded.

5.3.2.2.3.1.2 Abis interface

This chart shows the evolution of DL RxQual of the serving cell according to C/I ratio.

Correlation coefficient consideration:

The correlation coefficient between those two data sets is –80%! Therefore, RxQual ishighly correlated to C/I ratio (E15PH1 and E16PH2).This was obvious in this case because the possible interference causes occur from SFHbetween our microcells but this kind of study will become very useful when severalmicrocells or macrocells are involved in the Synthesised Frequency Hopping planningin order to identify the interferer (see chapter 7)

As a conclusion, even if RxQual values are degraded by Synthesised FH (C/I=-4dB,RxQual_mean=3.5), the final result of this experiment is that the quality is very good.

5.3.2.2.3.1.3 QVoice data

Some Ascom tests have been performed. They show a good voice quality:

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Moyenne RxQual_DL

RxQual_DL

68,40%

15,80%

10,50%

ExcellentGoodFairPoor

5.3.2.2.3.1.4 Air Traces

Best Server Map – N (Hop)=13

The best Server map shows that we did not notice any problem concerningmicrocellular algorithms. The behaviour of microcells and umbrellas is normal.

Best Server Map – N (Hop)=13In the quality map, we have removed the RxQual of 0. The RxQual value is degradedin the overlapping area. Anyway, voice quality and quality of service are very good.

5.3.2.2.3.1.5 Conclusion

For two microcells in Line of Sight, hopping on 13 common frequencies provides avery good quality of service regarding OMC-R, Ascom tests and Air traces.

5.3.2.2.3.2 Hopping Sequence Length: 10

5.3.2.2.3.2.1 OMC Data

The Call Drop Rate has been slightly improved during this period (5 Days).

This chart shows the evolution of RxQual_DL according to C/I ratio.

Comparing to N(Hop)=13, we can notice a degradation of RxQual when C/I ratiobecomes bad.

CALL DROP RATE

25-mars-98 26-mars-98 27-mars-98 28-mars-98 29-mars-98 30-mars-98 31-mars-98 01-avr-98

-7 -6 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 14 15

Moyenne RxQual

Max RxQualC/I

RxQual_DL

Correlation coefficient consideration:

The correlation coefficient between those two data sets is – 79 %! Therefore, RxQual isstill highly correlated to C/I ratio (E15PH1 and E16PH2).

As a conclusion, RxQual values are degraded by Synthesised FH (C/I=-4dB,RxQual_mean=4.5).

5.3.2.2.3.2.3 QVoice data

Some Ascom tests have been performed. They show a good voice quality:

5.3.2.2.3.2.4 Air Traces

Best Server Map – N (Hop)=10The best Server map shows that we did not notice any problem concerningmicrocellular algorithms. The behaviour of microcells and umbrellas is normal.

ExcellentGoodFairPoorBad

Quality Map – N (Hop)=10

In this quality map, we notice quite well that RxQual is bad in the overlapping area.

5.3.2.2.4 Conclusion

Concerning a pair of microcells in Line of Sight, the hopping sequence length advisedis 13 common frequencies (Re-use 1). The limit is reached with N (Hop)=10.

5.3.2.3 microcells separated by a street corner

5.3.2.3.1 Environment description: E10PH2 and E10PH5

Two microcells in Non Line of Sight interfere each other in a non-symmetric way,regarding radio aspect. E10PH2 is far from the street corner whereas E10PH5 is closeto this corner. As the interference zone is the street corner, E10PH2 is supposed to bethe most interfered microcell.The cell load has to be taken into account to determine the real interferences betweenthe cells.As far as E10PH5 is concerned, the traffic load is quite low: about 1 Erl on the secondFU at Busy Hour, whereas E10PH2 has an quite important traffic on its second FU:about 4 Erl at Busy Hour.Special care has to be taken on E10PH2 because this cell is supposed to be the mostinterfered regarding radio aspect, and on E10PH5 because this cell is supposed to bethe most interfered regarding load aspects.

Thanks to Abis traces, we can obtain the interference pattern of this cell pair:

E10PH5

E10PH2

Serving cell: E10PH5 – Interfering cell: E10PH2

Serving cell: E10PH2– Interfering cell: E10PH5

As the charts show, E10PH2 is 70%-interfered by E10PH5 and E10PH5 is only 10%-interfered by E10PH2.

-29 -26 -20 -17 -12 -9 -6 -3 0 3 6 9 12 15 18 21 24 27 30 33 36 39

-25 -21 -13 -4 0 3 6 9 12 15 18 21 24 27 30 33 36 40 43 46 49 55

5.3.2.3.3 Unitary tests results

As this case is supposed to be better than the Line of Sight microcells, we have startedour investigation with a hopping sequence length of 10 and devoted those tests todecrease the length.

5.3.2.3.3.1 Hopping Sequence Length: 10

5.3.2.3.3.1.1 OMC data

E10PH2 DATABefore Synthesised Frequency Hopping, the average call drop rate is 0.98%. We reach0.73% thanks to SFH!

E10PH5 DATABefore Synthesised Frequency Hopping, the average call drop rate is 3.56%. We reach1.12% thanks to SFH!

CALL DROP & CALL SETUP SUCCESSFULL RATE

100,0%

27-mars-98 28-mars-98 29-mars-98 30-mars-98 31-mars-98 01-avr-98 02-avr-98 03-avr-980,0%

CALL SETUPSUCC.

CALL DROP

100,0%

27-mars-98 28-mars-98 29-mars-98 30-mars-98 31-mars-98 01-avr-98 02-avr-98 03-avr-980,0%

CALL SETUPSUCC.

CALL DROP

As a conclusion, we notice that Synthesised Frequency Hopping bring, in this case, aquality of service really better than before.

This chart below shows the evolution of RxQual_DL according to C/I ratio on E10PH2.

Correlation coefficient consideration:The correlation coefficient between those two data sets is –65%.The chart below shows the evolution of RxQual_DL according to C/I ratio on E10PH5.

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

C/I ratio

MoyenneRxQual_DL

We can notice that E10PH5 is not interfered at all, since almost none C/I samples isinferior to 4 dB. Moreover, the correlation coefficient is only –30%. It means that theinterference is so low that some other events have more impact on the RxQual values.

5.3.2.3.3.1.3 QVoice Data

Some ASCOM tests have been performed. They show a good voice quality.

5.3.2.3.3.1.4 Air traces

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

MoyenneRxQual_DL

6%5% 1%

Excellent

Best Server Map – N (Hop)=10

The best Server map shows that we did not notice any problem concerningmicrocellular algorithms. The behaviour of microcells and umbrellas is normal.

Quality Map – N (Hop)=10

In this quality map, we notice quite well that RxQual is good, even in the overlappingarea.

Concerning a pair of microcells in Non Line of Sight, the hopping sequence lengthadvised is 10 common frequencies (Re-use 1).

5.3.2.4 Three microcells:2 pairs in LOS and one pair in NLOS

5.3.2.4.1 Introduction

Those first results obtained, we need to assess the behaviour of three microcellshopping on common frequencies.

5.3.2.4.2 Environment description

Those tests have been done in E10 block. Three microcells were involved: E10PH2,E10PH5 and E10PH1. This area is a confined area, the streets are very small.Therefore, the conditions to use Synthesised Frequency hopping are good.

E10 block

With Abis traces, we were able to build an interference matrix:

Interferencematrix E10PH1 E10PH2 E10PH5

E10PH1 75 % 5 %

E10PH2 70 % 10 %

E10PH5 60 % 70 %

E10PH2 E10PH1

E10PH5

: LOS microcell pair

: NLOS microcell pair

Because of the interference non-symmetry, it is very easy to distinguish LOS microcellsfrom NLOS microcells.

5.3.2.4.4 Tests results – N (Hop)=13

5.3.2.4.4.1 OMC data

E10PH1 data

E10PH2 data

27-mars

28-mars

29-mars

30-mars

31-mars

1-avr 2-avr 3-avr 4-avr 10-avr 11-avr 12-avr 13-avr 14-avr 16-avr0,0%

CALL SETUPSUCC.

CALL DROP

27-mars

28-mars

29-mars

30-mars

31-mars

1-avr 2-avr 3-avr 4-avr 10-avr 11-avr 12-avr 13-avr 16-avr 17-avr0,0%

CALL SETUPSUCC.

CALL DROP

E10PH5 data

The results are described in the following table

Call drop average Before AfterE10PH1 1.15 % 1.21 %E10PH2 0.91 % 1.16 %E10PH5 2.45 % 0.71 %

We notice a slight degradation on E10PH1 and E10PH2 whereas E10PH5’s call dropis highly improved. Those results are not surprising because E10PH2 is interfered byE10PH1 (LOS pair, 13 frequencies are advised) and E10PH5 (NLOS pair, 10frequencies are advised)

90%91%

92%93%94%

95%96%97%98%99%

27-mars

28-mars

29-mars

30-mars

31-mars

1-avr 2-avr 3-avr 4-avr 10-avr 11-avr 12-avr 13-avr 14-avr 16-avr0%1%1%2%2%3%3%4%4%5%5%6%6%7%

CALL SETUPSUCC.

CALL DROP

5.3.2.4.4.2 Abis interface

E10PH1 on E10PH2

E10PH5 on E10PH2Correlation coefficient considerationRxQual values are correlated to C/I ratio between E10PH1 and E10PH2 at –35 %.RxQual values are correlated to C/I ratio between E10PH5 and E10PH2 at –25 %.We can conclude that E10PH1 is a bigger interferer than E10PH5. This result wasobvious but, when the number of microcells increases, it will be very useful to identifythe strongest interferer.

5.3.2.4.4.3 Air interfaceAir traces have shown that no problem has been noticed after Synthesised FrequencyHopping activation

Moyenne RxQual_DL

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18

MoyenneRxQual_DL

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18MoyenneRxQual_DL

Best Server Map – N(Hop)=10

Quality Map – N(Hop)=10

The quality is very good. Some areas are bad but it is due to coverage defaults insome streets covered only by the umbrellas.

For three microcells with one pair in LOS and two pairs in NLOS, hopping on 10frequencies is the possible limit we have reached. We advise to hop on 13frequencies to improve quality of service.

BTS 1 BTS 2

5.3.2.5 Three microcells:3 pairs in LOS

5.3.2.5.1 Environment description

Those tests have been done in the E15 and E16 area. Three microcells in LOS:E15PH1, E16PH1 and E16PH2.

E15 and E16 area

Interferencematrix E15PH1 E16PH1 E16PH2

E15PH1 50 % 73 %

E16PH1 45 % 55 %

E16PH2 60 % 70 %

: LOS microcell pair: NLOS microcell pair

5.3.2.5.3 Tests results

5.3.2.5.3.1 OMC dataThe test period only lasted two days because of tight schedule. We have noticed thatthe call drop rate came from 1.75% to 1.79%.

No degradation has been observed, whereas it was the worst case (themicrocells had a very important traffic: about 6 Erl on the second FU!)

5.3.2.5.3.2 Abis interface

E16PH1 on E16PH2

Correlation coefficient considerationRxQual values are correlated to C/I ratio between E16PH1 and E16PH2 at – 60 %.RxQual values are correlated to C/I ratio between E16PH2 and E15PH1 at – 25 %.We can conclude that E16PH1 is a bigger interferer than E15PH1. This is due to theinter-site distance.

5.3.2.5.3.3 Air interface

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16

MoyenneRxQual_DL

Best Server Map – N(Hop)=13

Quality Map – N(Hop)=13This quality map shows that quality is good (RxQual=0 samples have been removed).

For three microcells in full LOS, hopping on 13 frequencies is the possible limit wehave reached. We advise to hop on 15 frequencies to improve quality of service.

5.3.2.6 Conclusion on unitary tests

• “Block” microcells and “street” microcells have to be distinguish in term of1. Radio Engineering2. Default Parameter Setting3. Macro frequency Re-use

• For simplicity sake, the main rule concerning micro to micro re-use is:

Each microcells can hop on 13 common frequencies

13 commonfrequencies

5.4 Generalisation on SOUQ area

5.4.1 Introduction

The first step was to change the default radio parameters to have a significant trafficon the microcells, for the generalisation. Indeed, the microcells had a poor trafficwhereas the umbrellas were congested (20%).With a new parameter setting, the traffic on the microcells has increased by 220%and no more congestion was noticed on the umbrellas SOUQ_B and SOUQ_C.The second step was to introduce Synthesised Frequency Hopping on the 15 microcellsselected for the generalisation.5.4.2 Environment description

SOUQ area is the densest area of Abu Dhabi network. Proving thatSynthesised Frequency Hopping results are adapted to SOUQ means that a wholenetwork generalisation is possible without any problem at all.

As the Synthesised Frequency hopping needs a new frequency plan structure, we havemodified the micro BCCH and TCH plan as well. A Clean BCCH plan has beenintroduced and 13 contiguous frequencies have been reserved for the second FU.

5.4.3 Synthesised Frequency hopping results

The Synthesised Frequency Hopping has been implemented during one week. Theresult obtained was good and encourages us to continue in this way.

5.4.3.1 OMC data

5.4.3.1.1 SOUQ BSC

We have to compare three phases.1. Old frequency plan (From 12th to 17th of April)2. New frequency plan structure – Separated BCCH plan and TCH plan (From 28th of

April to 5th of May) – very clean frequency plan – NO INTERFERENCES3. New frequency plan structure and Synthesised Frequency hopping (From 21st to

27th of April)

1. Old frequency plan:Micro: 52-67BCCH and TCH interleaved:

52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67BCCH TCH BCCH TCH BCCH TCH BCCH TCH BCCH TCH BCCH TCH BCCH BCCH BCCH Jocker

In very dense area like Souq, more frequencies are needed: around a tenth ofadditional frequencies are stolen from the macrolayer. This requires importantplanning effort to find clean frequencies and becomes more and moretricky considering the current macrolayer densification process (extensionof 6/6/6 configuration with configurations up to 8/8/6).This solution is no more feasible for the deployment of 300 microcells in parallel to themacrolayer capacity increase.

2. New frequency plan structure: NO INTERFERENCEBCCH Micro: 10TCH Micro: 13

Total: 23 frequencies are needed for dense areas.This is the band required for the deployment of the 300 microcells if no synthesisedhopping is introduced on the microlayer and if no macro frequency is reused, this lastsolution becoming more and more critical.Note that in this case, all frequencies are not adjacent (no continuous bandwidth). Thissolution is very frequency consuming. The TCH plan was the following{27,28,30,35,40,41,42,43,45,48,50,67,75}.

3. New frequency plan structure and Synthesised Frequency HoppingBCCH micro: 10Synthesised hopping on 2nd FU: 13 frequencies

In this case, 2 separated bandwidths are assigned to micro BCCH and micro TCH (nointerleaving).Solution 2 and 3 are equivalent in term of bandwidth, with the following advantagesfor solution 3:

- Easier planning: only BCCH frequencies planning- Faster deployment- More flexibility

Phase 1 – Phase 3 comparison:

The Call Drop has been improved between those two phases. The new frequencyplan, introducing Synthesised frequency hopping, has brought a quality of servicebenefit. Another benefit is the planning of the microcells second FUs.

100,0%

12-avr 13-avr 14-avr 15-avr 16-avr 17-avr 21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr0,0%

CALL SETUPSUCC.

CALL DROP

Phase 1Call Drop: 1.48%

12-avr 13-avr 14-avr 15-avr 16-avr 17-avr 21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr0

Avg TCHSeized

Peak Value

TCH Avail

The chart above shows the traffic status on Souq1 BSC. It shows that the traffic wasconstant during the testing period: around 200 Erl at peak hour.

Phase 3 – Phase 2 comparison

We can notice than the Call Drop rate between the two phases is almost the same.The benefits that bring Phase 3 is the simplicity and the flexibility if a new microcell isto be deployed on SOUQ: the planning will be changed only for BCCH consideration.

For any new microcell, the 2nd FU will be “free”!

The chart below shows the traffic during the phase 2 and 3 period.

100,0%

21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr 28-avr 29-avr 30-avr 1-mai 2-mai 3-mai 5-mai0,0%

CALL SETUPSUCC.

CALL DROP

21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr 28-avr 29-avr 30-avr 1-mai 2-mai 3-mai 5-mai0

Avg TCHSeized

Peak Value

TCH Avail

5.4.3.1.2 Microcell data

A detailed study has been conducted on the most interfered microcell of Souq area:E2PH7:Phase 1 – Phase 3 comparison:

E2PH7 Data

Phase 2 – Phase 3 comparison:

Those data shows that the problem in phase 1 was due to the BCCH plan. BUT, wecan notice that the call drop rate on E7PH2 microcell, the most interfered microcell inSOUQ, has been decreased by 30% with Synthesised FH introduction!

100,0%

21-avr 22-avr

23-avr

24-avr

25-avr

26-avr

27-avr

28-avr

29-avr

30-avr

1-mai 2-mai 3-mai 5-mai0,0%

CALL SETUPSUCC.

CALL DROP

100,0%

12-avr 13-avr 14-avr 15-avr 16-avr 17-avr 21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr0,0%

CALL SETUPSUCC.

CALL DROP

The same study has been done on each microcell. The results are summarised in thefollowing table:

Phase 2 – No SynthesisedFrequency Hopping

Phase 3 –SynthesisedFrequency Hopping

SFHGain

Delma_1 0.73% 0.66% 10%Delma_2 0.77% 0.69% 10%Delma_3 0.50% 0.39% 22%E2PH2 0.66% 0.76% -15%E2PH4 0.8% 1.1% -40%E2PH5 0.72% 0.57% 20%E2PH6 1.50% 1.30% 15%E2PH7 0.65% 0.46% 30%E2PH8 1.9% 2% -5%E1PH1 1% 1% 0%E1PH2 1.1% 1.3% -15%E1PH3 0.7% 0.6% 15%

Compared to a very clean frequency plan, we notice that Synthesised Frequencyhopping improves the quality of service on the microcells.

As a conclusion, the call drop has been decreased by 5% on all the microcells thanksto Synthesised Frequency Hopping

5.4.3.1.3 Macrocell data

SOUQ_B macro has been studied in detail.Phase 2 – Phase 3 comparison:

100,0%

21-avr 22-avr 23-avr 24-avr 25-avr 26-avr 27-avr 28-avr 29-avr 30-avr 1-mai 2-mai 3-mai 5-mai0,0%

CALL SETUPSUCC.

CALL DROP

The Call Drop on SOUQ_B, the real umbrella of our microcells, has beendecreased by 10% (from 1.43% to 1.31%)! The explanation is that, thanks to fadingprotection, there is less Rescue handover from the microcells

In the same way, SOUQ_C ‘s call drop rate has gone from 1.46% to 1.43% (Gain :0%).

In fact, only SOUQ_A which is not an umbrella of our microcells (we can suppose thatits call drop evolution is not linked to Synthesised frequency hopping implementation)has a bad call drop evolution: from 1.3% to 1.4%. This rate is enough to changeSOUQ1 BSC call drop evolution!

As a conclusion, comparing Synthesised frequency hopping to a very clean frequencyplan,• The Call Drop rate on the microcells is decreased by 5 % thanks to frequency

diversity• The Call Drop rate on the real umbrellas is also decreased by 5 %.

5.4.3.2 Abis interface

The interference matrix of Souq area has been obtained thanks to Abis traces:E2PH7 is the most interfered microcell. As an average, its micro to micro interferenceis 295%!That is why a special care has been done on this microcell.

Interference Matrix in SOUQ area

E1PH1 E1PH2 E1PH3 E2PH2 E2PH4 E2PH5 E2PH6 E2PH7 E2PH8 CHINESE_MIC

AL MANARA

E1PH1 20% 25% 10% 0% 0% 0% 0% 0% 0% 0%

E1PH2 30% 45% 45% 15% 0% 0% 0% 0% 0% 0%

E1PH3 20% 15% 5% 25% 0% 0% 25% 0% 40% 0%

E2PH2 25% 55% 10% 10% 60% 15% 5% 0% 10% 30%

E2PH4 0% 10% 20% 15% 0% 15% 60% 0% 0% 0%

E2PH5 0% 0% 0% 45% 0% 55% 0% 55% 0% 0%

E2PH6 0% 0% 0% 45% 15% 65% 25% 45% 0% 0%

E2PH7 0% 0% 20% 50% 55% 0% 60% 80% 0% 0%

E2PH8 0% 0% 0% 0% 0% 30% 90% 55% 0% 0%

CHINESE_MIC 0% 0% 5% 25% 30% 0% 0% 0% 0% 0%

AL MANARA 10% 15% 5% 25% 0% 0% 0% 0% 0% 0%

DELMA_MIC_1 0% 0% 0% 0% 0% 45% 75% 10% 5% 0% 0%

DELMA_MIC_3 0% 0% 0% 0% 0% 45% 30% 0% 70% 0% 0%

5.4.3.3 Air interface

Best Server Map – N(Hop)=13Walk tests have been performed on SOUQ area when Synthesised frequency hoppingwas activated. The results show a very good coverage and a good quality.

Coverage Map – N(Hop)=13

Quality Map – N(Hop)=13When the quality becomes bad (red points), we are not connected on a microcellanymore. In the real microcell area, the quality is really good.

5.4.3.4 QVOICE

Some ASCOM tests have been performed on two microcells. The results are thefollowing:E1PH1:

E2PH8:96%

Excellent

94,00%

ExcellentFair

5.4.4 Conclusion

The generalisation on SOUQ has proven that Synthesised Frequency hopping was agood solution for Abu Dhabi network. The main gains will be:

1- High speed microcells deployment2- No more frequency planning on micro TCHs – Re-use 13- Frequency diversity gain (5%)4- High density in the microcellular layer (300 microcells)

The generalisation on the whole network will involve some modifications in term ofRadio Engineering, Parameter settings and frequency plan structure. An “interferencereduction” process is also to be activated to minimise the collision probability. Then, aoptimisation methodology has to be set to monitor the “new” network.

6 Interference ReductionAs we have noticed during the very first tests on E15PH1 and E16PH2, mutualinterference is really important when two microcells are in Line of Sight but also whentwo microcells are not in Line of Sight. Alcatel algorithms allowed us to reduce thoseinterferences and B4 release new radio features will help us also in that way.

6.1 HO_MARGIN and anti Ping-Pong process in B4

6.1.1 HO_MARGIN 0

The more we can reduce HO_MARGIN, the more we reduce the mutual interferencebetween two microcells.We have used Abis traces to tune this parameter. Indeed, the evolution of RxQual_DLaccording to C/I ratio between both microcells is really useful.Let’s take E15-E16 example:

Until now, HO_MARGIN default value was 4dB. With this value, we can see with thechart above that a better cell handover is triggered when RxQual_DL is about 3 as anaverage. (Some other Abis traces showed an average RxQual_DL of 4). It means thateither a better cell handover is triggered in bad condition, either a quality handover(rescue HO) is triggered before a PBGT HO. Of course, a quality handover should beavoided as often as possible.That is why we advise a HO_MARGIN default value of 0dB. According to the chartabove, the RxQual_DL average value is 1!HO_MARGIN parameter has a very important influence on the mutual interferencepattern.

Some tests have been made with HO_MARGIN = 0 dB!

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Moyenne RxQual_DL

RxQual_DL

Interference pattern with HO_MARGIN=4dB (old value)

Interference pattern with HO_MARGIN=0dB

-34 -29 -25 -21 -17 -13 -9 -5 -1 3 7 11 15 19 23 27 31 35 39 43

The gain of this optimisation is very important: the mutual interference came from 73%to 40%:

Special care has been taken on possible Ping-Pong handover. Many air traces showedthat, thanks to the sliding averaging window, this phenomenon was not detectable:

Moreover, counters at OMC-R did not show any increase of the number of Better Cellhandover.

-34 -30 -27 -24 -21 -18 -15 -12 -9 -6 -3 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

HO_MARGIN=0dB HO_MARGIN=4dB (old)

Anyway, in B4 release, a new feature is introduced: Anti Ping-Pong process.6.1.2 Anti Ping-Pong process

A new tuning of Handover margin between adjacent cells is implemented in B4 inorder to avoid the following situations:

• Low HO margin : Important risk of Ping-Pong handovers for stationarymobiles situated at the limit of the cells (fluctuation of signal)

• High HO margin : HO is delayed and risk of interference is big

The new tuning mechanism temporary increases the handover margin of thepreceding cell and during a limited duration after the HO: thus this preceding cell ishandicapped and the mobile stays in the new cell; this mechanism is effective on a callbasis.The Ping-Pong handicap value and duration are modifiable at OMC-R with thePING_PONG_HCP parameter (range 0 dB to 20 dB) with a 1db step size. Thisparameter is validated on a cell basis.

Two parameters have to be tuned to activate this process.

PING_PONG_HCP = 4dBT_HCP = 30secCombining these new features to an HO_MARGIN of 0 between microcells will be veryhelpful in the interference reduction process

6.2 Load Management and speed discrimination

Those new features in B4 will be very helpful when G3 BTS are deployed in thenetwork and Synthesised frequency hopping implemented on the macro layer. Alcatelalgorithms will control the load of umbrella cells.6.2.1 Speed discrimination

To avoid a high rate of handovers fast moving mobiles are sent and kept in the upperlayer cells.This speed discrimination is based on the dwell time of a mobile in an overlaid cell.A mobile handled by overlaid cells is sent to the umbrella cell if the delay betweensuccessive handovers becomes small.Furthermore a mobile handled by an umbrella cell is sent to an overlaid cell if itreceives from this cell a high level of signal for a sufficient time. This is based on a"leaky bucket" mechanism.6.2.2 Load in the umbrella cell

The saturation of an umbrella cell is very serious and much more annoying than thesaturation of an overlaid cell. As there is no reservation of TCH channels for handoverthere is an important risk of loosing calls when a handover is required from anoverlaid cell or another umbrella cell.

6.2.2.1 General principles

• Based on the dwell time in an overlaid cell: depends on the reportedmeasurements from neighbour overlaid cells.The counter used to estimate this dwell time is based on a "leaky bucket" mechanism.• Reduction of the minimum dwell time (MIN_DWELL_TIME) in case of high loadin the serving umbrella cell.

6.2.2.2 Computation of the load in the umbrella cell

For each umbrella cell, the load of the umbrella is averaged continuously over aperiod of LOAD_EV_PERIODLet this average load be noted L:L

Nb_ busy_ TCHTot_Nb_ TCH

= *100

With Tot_Nb_TCH being the total number of TCH in the umbrella cell.

6.2.2.3 Adaptation of MIN_DWELL_TIME - "power control" mechanism

Too high load: decrease MIN_DWELL_TIME step by step, with a minimum ofL_MIN_DWELL_TIMEL > H_LOAD_OBJ ⇒ MIN_DWELL_TIME= max (MIN_DWELL_TIME -DWELL_TIME_STEP, L_MIN_DWELL_TIME)

Too low load: increase MIN_DWELL_TIME step by step, with a maximum ofH_MIN_DWELL_TIMEL < L_LOAD_OBJ ⇒ MIN_DWELL_TIME= min (MIN_DWELL_TIME +DWELL_TIME_STEP, H_MIN_DWELL_TIME)

L_MIN_DWELL_TIME

load in umbrella cell

H_LOAD_OBJ

L_LOAD_OBJmacrocellwith little traffic

macrocellsaturated

Traffic regulation

MIN_DWELL_TIMEH_MIN_DWELL_TIME

L_MIN_DWELL_TIME: minimum dwell time used to have confidence in the stability ofthe reported parameters: this parameter is used in case of saturationH_MIN_DWELL_TIME: maximum delay to send slow MS to the overlaid cells.The default value of MIN_DWELL_TIME will be H_MIN_DWELL_TIME.

L_MIN_DWELL_TIME H_MIN_DWELL_TIME

load in umbrella cell

H_LOAD_OBJ

L_LOAD_OBJ

beginning : low traffic

end : low traffic

regulation of traffic peak

DWELL_TIME_STEP

6.2.3 Trade-off between speed discrimination and overload of theumbrella cell

The algorithm proposes a trade-off between speed discrimination and overload of theumbrella cell: when the load increases, the speed limit is increased too: quickermobiles are kept in the overlaid cells. With a very high load, the speed discriminationis disabled ⇒ there is a priority given to the load in the umbrella cell.

6.3 Power Control and DTX

Those features in Uplink as in Downlink improve the interference pattern betweencells.6.3.1 Power control

PC UplinkEven if the microcellular radio conditions are less predictable than in macrocell, it isalways better to reduce the UL interference in an environment with high cell density,especially to optimise the number of frequencies to hop on and the reuse cluster size.PC DownlinkThis features, which has never been tested in a microcell environment, could beexperimented in microcell area in order to decrease the average DL interference leveland then take much more advantage of synthesised frequency hoppingAnyway, the most important feature to implement quickly is the power control uplinksince the mobile transmission power is 33dBm and the station transmission power is27dBm!6.3.2 DTX uplink

Since this feature is implemented on macro layer, it can be used on the microcells withthe benefits to reduce the UL interference level, especially with synthesised frequencyhopping.

7 Alcatel Integrated Multilayer Solution

7.1 Principles

The aim is to integrate a very easy frequency planning solution, based on Synthesisedfrequency hopping, in a multilayer network.The principles are the followings:

• First step: Very secure fractional re-use 1/3 on the macro layer. (Inter-site distancefar from the limit… )

• Second step: introduction of microcells. Re-use 1 on the microcellular network,using for each microcell the two groups of macro frequency not used by the realumbrella.

This solution will allow any operator to adapt very accurately and quickly its network totraffic demand and traffic distribution:

Re-use oneWith a hopping

sequence:Group1+Group2

400 Erl/km²

200 Erl/km²

100 Erl/km²

7.2 Conditions

7.2.1 Re-use one between microcells

As the number of frequencies used by the microcells is equal to the number offrequencies used in Group1 added to the number of frequencies used in Group2 (forexample), and as the minimum number of frequencies to set on the microcells is 13,we have the following conditions:

#Group1 + #Group2 = 13And

Number of declared frequencies/cell = 64 (GSM standard)

This is directly connected with the BCCH bandwidth required in the network and thetotal bandwidth available. The following table gives the relation between the BCCHbandwidth and the total bandwidth required for the re-use one on 2TRXs microcells,3TRXs microcells and 4 TRXs microcells:

BCCHbandwidth

Total bandwidthrequired for 2TRXs

microcells

Total bandwidthrequired for 3TRXs

microcells

Total bandwidthrequired for

4TRXs microcells18 ch 7.8MHz 11.4 MHz 15.6 MHz20 ch 8.2 MHz 11.8 MHz 16 MHz22 ch 8.6 MHz 12.2 MHz 16.4 MHz24 ch 9 MHz 12.6 MHz 16.8 MHz

7.2.2 Macro frequency re-use conditions

Re-using frequencies from the macro layer requires a hopping sequence interferencepattern.

This pattern can be modelled with two parameters:

• Averaged interference percentage• Number of “super frequencies” (more than 50% interfering)

Those conditions was not achieved in Abu Dhabi because of:• The specific network design• The very low (27dBm) transmitting power of the M1M

Anyway, some Abis traces coming from several Alcatel microcellular networks pointedout that these tight re-use becomes possible when the transmitting power of themicrocells becomes upper than 36dBm (4W):

Antwerpen case:

Some Abis traces made on the microcell ATM (marked by the white ring) allowed us toprove that 36dBm was a necessary value for our AIMS solution.This mini G2 cell, configured as a microcell, was indeed transmitting 36dBm. Theresults of Abis traces analysis are the following:

ATM – Transmission power: 36dBm

Umbrella: CEN2, P(C/I<9dB) = 34%

Umbrella Neighbouring cells: CEN1 P(C/I<9dB) = 13 %

0%10%20%30%40%50%60%70%80%90%

-16 -13 -10 -7 -4 -1 2 5 8 11 14 17 20 23 26 29 32

4 Watts

0.5 Watt

0%10%20%30%40%50%60%70%80%90%

-23 -18 -14 -10 -6 -2 2 6 10 14 18 22 26 30 34 38 42 46 50

0.5 Watt

4 Watts

CEN3 P(C/I<9dB) = 2 %

DIA0 P(C/I<9dB) = 15 %

Those values mean that re-using a frequency from CEN1, CEN2 and DIA0 is possibleif the transmitting power is 4 Watts.Nevertheless, it is important to check if interferences from the microcell are notdamageable for the macrolayer.

Conclusion:

0%10%20%30%40%50%60%70%80%90%

-22 -15 -11 -7 -3 1 5 9 13 17 21 25 29 33 37 41 45

0.5 Watt

4 Watts

0%10%20%30%40%50%60%70%80%90%

-2 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 50

0.5 Watt

4 Watts

We need a 4-Watts transmitting microcell

7.3 Fractional re-use (1/3 or 1/1) on the macro layer

7.3.1 Principles

Fractional re-use (1/3 or 1/1) introduces a regular pattern in the network in term offrequency planning. BCCH plan is taken apart and achieved with the traditionalstrategy whereas TCH plan will be achieved with this new approach:• Creating only 3 groups of frequencies and applying them on the sectors of each

site. (1/3 re-use)• Using only one group of frequency and applying it on the sectors of each site. (1/1

re-use)

7.3.2 Frequency hopping in GSM

The algorithm describing the frequency hopping used in GSM is displayed in GSM05.02. Two type of frequency hopping are considered:

1. Cyclic hopping where the frequencies are used one after the other in order;2. Pseudo-random hopping where the frequencies are used according to an

algorithm described in GSM 05.02. Those sequences have been chosen becausethey have statistical properties similar to random sequence.

3. Between many parameters introduced in the algorithm, we may distinguish twoparameter families: “externals” and “internals”.

7.3.2.1 External Parameters

We consider as external parameters the parameters that can be modified by theoperator.In GSM standard, the maximum number of frequencies that can be used in a cell islimited to 64. We may define the following parameters:

v MA (Mobile allocation): ordered group of N frequencies attributed to a givencell (N integer ; 1=N=64) that is to say the whole frequencies available for thehopping sequence.

v MAI (Mobile Allocation Index): Index of each frequency in the ordered groupMA previously defined. We have 0=MAI=N-1

Usually, in GSM, the MAI is used to describe the hopping sequence.

Example: The GSM primary bandwidth (for uplink, from 890MHz to 915 MHz) iscomposed by 124 frequencies spaced by 200 kHz. Those frequencies are numberedfrom 1 to 124 by the ARFCN parameter (Absolute Radio Frequency Channel Number).

ARFCN=1 for 890.2 MHzARFCN=2 for 890.4 MHz, etc… and ARFCN=124 for 914.8 MHz.

If the operator allocates 5 frequencies (N=5) whose ARFCN are 1,2,64,100,123 to acell, the group MA ordered of this cell will be noted f0=890.2 MHz, f1=890.4 MHz,f2=902.8 MHz, f3=910 MHz, f4=914.6 MHz. We note MA={f0, f1, f2, f3 andf4}.Then:

MAI=0 for the first frequency of the indexed MA group: f0=890.2 MHzMAI=1 for the second frequency of the indexed MA group: f1=890.4 MHzMAI=2 for the third frequency of the indexed MA group: f2=902.8 MHzMAI=3 for the fourth frequency of the indexed MA group: f3=910 MHzMAI=4 for the fifth frequency of the indexed MA group: f4=914.6 MHz

For a given group of N frequencies, the operator can propose the SFH law byspecifying two parameters: HSN (Hopping Sequence Number) and MAIO (MobileAllocation Index Offset)

v HSN (Hopping Sequence Number): parameters defining the hopping law.The range of HSN is [0, 63].For HSN=0, we get the cyclic SFH law on N frequencies;For HSN? 0, we get a pseudo-random SFH law (still on those N frequencies)characterised by the HSN value.

Attention: Because of procedure used by the mobile for the measurement reportingwhen DTX (Discontinuous transmission) is activated, the cyclic law (HSN=0) isforbidden if N modulo (13)=0.

v The MAIO (Mobile Allocation Index Offset) is integer contained between 0and 64. This parameter is used to shift the hopping sequences using thesame HSN and the same group of N frequencies (that is to say the same MA).The interest of this parameter is to limit the adjacent and co-channelinterference.

Example: for HSN=0 and if N modulo (13)? 0, we have a cyclic SFH on N frequencies.Note that we usually use MAI to describe the hopping sequence.For MAIO=0 (the operator wants to start with the first frequency), the hoppingsequence will be:

0,1,2,3,4,5… N-3, N-2, N-1, 0,1,2,3,4,5… N-3, N-2, N-1… etc.For MAIO=2 (the operator wants to start with the third frequency), the hoppingsequence will be:

2,3,4,5… N-3, N-2, N-1, 2,3,4,5… N-3, N-2, N-1… etc.If the two hopping sequences are synchronised, the co-channel interference isremoved.

7.3.2.2 Internal parameters

The parameter FN (TDMA Frame Number) and its “derivatives”: T1, T1R, T2 and T3(time parameters) are independent from the operator. We must consider them asinternal parameters of the network.

v FN (TDMA Frame Number) is the “internal clock”. It is a periodic counter(from 0 to (26*51*204 8)-1= 2.715.647). This counter is triggered each timea TDMA frame is transmitted (8 consecutive TS). The FN period is exactly anhyperframe length, that is to say 3h28mn53s760ms.The time parameters are defined as follows:

T1 = FN DIV (1326)=FN DIV (51*26);T1R = T1 modulo (64)T2 = FN modulo (26)T3 = FN modulo (51)

v T1 parameter is triggered each time a superframe (51*26 TDMA frames) istransmitted, that is to say 6.12s. It is a periodic counter (from 0 to 2047). T1is a superframe counter.

v T1R parameter (R: reduced) is a periodic counter (from 0 to 63) and it is alsotriggered each time a superframe is transmitted. The period is thus 64superframes, that is to say (51*26)*64 TDMA frames, in other words6.12s*24˜6mn 32 s. Note that this duration (64 superframes) corresponds tothe repetition period of the pseudo-random hopping sequence in GSM.

v T2 parameter is a periodic counter from 0 to 25 that is triggered each “26-multiframe” (120 ms) transmission. T2 is a 26-multiframe counter.

v T3 parameter is a periodic counter from 0 to 50 that is triggered each “51-multiframe” (235 ms) transmission. T3 is a 51-multiframe counter.

We don’t go further in the details of SFH algorithm that takes into account eachparameter quoted above. Please refer to 05.02 specification.7.3.3 Constraints

As far as it is possible, we must take advantage of synchronised BTSs or TRXs. As athree-sector contains three synchronised cells (in fact, it is the same cell – G3technology), we must reach a collision probability of 0%.

7.3.3.1 “Intra-site” constraint

This constraint on the number of frequencies in the hopping sequence is a matter ofalgorithms (MAIO allocation with constant HSN). We have to optimize the number ofrequired frequencies to reach a P coll = 0 %.Example: if we have a 3*(p+1) TRX site (one BCCH TRX and p hopping TCH TRX), theintra-site constraint will be the following:

For a 1/3 re-use:

1. Assuming the following FHS structure:• Group1: 1 4 7 … 3n-2• Group2: 2 5 8 … 3n-1• Group3: 3 6 9 … 3n2. The constraint on the MAIO will be:For each TRX of a same sector, we have to choose different MAIO: ∆MAIO ? 0.For TRX belonging to different sectors (where adjacencies can be avoided), theconstraints are the followings:Between sector 1 and 2: to avoid adjacencies, we have to take different MAIO:∆MAIO ? 0Between sector 1 and 3: to avoid adjacencies, we must forget MAIO_1 on one TRXand MAIO_1+1 on another TRX: ∆MAIO ? 1Between sector 2 and 3: to avoid adjacencies, we have to take different MAIO:∆MAIO ? 0

Those constraints are displayed in the following table:

∆MAIO ? from Sector 1 Sector 2 Sector 3Sector 1 0 0 1Sector 2 0 0 0Sector 3 1 0 0

3. The solution is written as followed ({each hopping TRX of sector1}; {each hoppingTRX of sector2}; { each hopping TRX of sector3})The solution is: ({0,2,4… 2p-2}; {1,3,5… 2p-1]}; {0,2,4… 2p-2}) for example.We thus need 2p MAIO to satisfy this co-site constraint and then n=2pfrequencies per group are required.

4. Conclusion:The maximum RF Load necessary to satisfy this first constraint is

%502/__

sec/__ ===pp

groupfreqofnbrtorTRXofnbr

Please note that if we assume another FHS structure [for example: group1: (1,2,3… n);group2: (n+1,n+2… 2n) and group3: (2n+1,2n+2… 3n)], we reach the same limit.

For a 1/1 re-use:

1. Assuming the following FHS structure: contiguous frequencies{1,2,3,4,5,6,7… n}2. The constraint on the MAIO will be:

∆MAIO ? from Sector 1 Sector 2 Sector 3Sector 1 (0;1) (0;1) (0;1)Sector 2 (0;1) (0;1) (0;1)Sector 3 (0;1) (0;1) (0;1)

3. The solution is written as followed ({each hopping TRX-sector1};{each hoppingTRX-sector2};{each hopping TRX-sector3})The solution is: ({0; 2; 4… 2p-2}; {2p… 4p-2}; {4p… 6p-2}).We thus need 6p-1 MAIO to satisfy this co-site constraint and then n=6p-1frequencies per group are required.

4. Conclusion:The maximum RF Load necessary to satisfy this first constraint is

%6.166/__

sec/__ ===pp

groupfreqofnbrtorTRXofnbr

Conclusion on intra-site constraint:It is quite easy to optimise this constraint by hand when the number of TRX ishomogeneous on a sector basis.

When we have 4/4/6 or 6/6/8 configurations, the optimisation is trickier and needa real tool to get the most adapted FHS, and MAIO allocation.

7.3.3.2 “Inter-site” constraint

This second constraint on the number of frequencies in the hopping sequence is amatter of radio and traffic aspects, as collision probability can’t be zero.Fractional re-use is a matter of compromise!Three parameters have to be optimised to increase capacity:

1- RF Load tolerated2- Interference probability P(C/I<9dB)

3- Real traffic distribution

Moreover, interference probability is directly connected with the re-use pattern (4/12,1/3, 1/1, A I M S… ), the inter-site distance, the network morpho-structure andtopography…The result that we need for optimising this constraint is a three variable function:

)_,9)/(,( ondistributiTrafficICPRFloadf <

This is thus a question of optimising a multi-variable function.For example, during the field trial in Abu Dhabi, we have defined two points of thisfunction:(8%, 70%, 75%) and (15%, 70%, 12.5%). Of course, we are far from knowing thisfunction.

P(C/I<9dB)Traffic

RF Loadtolerated

7.3.3.3 Conclusion

Two constraints are facing each other and we must, of course, take the most importantone.7.3.4 Densification comparison – simple 1/3 re-use Vs A I M S

The macrocellular network deployed with a 1/3 re-use is very uniform and does nottake into account the traffic distribution. RF load of 50% can be reached on the macrolayer provided that the inter-site distance limit is not reached. Let’s assume that thislimit corresponds to a macrocellular density of 1.3 site / km².Assuming that the total bandwidth is 12.6 MHz, the BCCH plan takes 16 channels andthe macrolayer density is 1.3 site/km², the 1/3 re-use can reach 200 Erl / km²:

Fractional re-use 1/3 – up to 200 Erl / km² at 50% RF Load

But, if the traffic is located in a very small area, this solution has no way to solve thiscurrent problem because the traffic non-homogeneity can not be taken into account.A.I.M. Solution is well adapted to this kind of densification problem. With the previousassumptions, we want to introduce 9 microcells in a city. After re-organising the BCCHplan for multi layer network (24 channels instead of 16), the solution will be to remove1 TRX on the macrocells involved in the dual layer network (here 7*3 macrocells) andto add our 9 microcells with 3 TRXs switched on. This part is only a comparison studyand does not provide a strategy for AIMS.

We reach in the microcellular area a capacity of 400 Erl / km² in the orange area:

The following table gives the calculation of the previous study.

7.3.5 Densification strategy

As A.I.M.S is a powerful solution for densification problems, we need to set a realdensification strategy that would be easy to implement in a real network.A.I.M.S is composed by two phases:

1. 1*3 re-use on the macrolayer2. Introduction of microcells with a re-use one on the second TRX.

The real issue is when can we introduce the microcells. A 1*3 re-use is possible until a50% RF Load, but we have noticed that introducing microcells implies that we free upsome frequencies (about 6 or 8) for the BCCH planning.We thus advise to have a RF load of 40% on the macrolayer (1*3 re-use) when themicrocell introduction is decided in order not to remove TRX from the macrolayer. Withthe same assumptions, the schedule of an ideal network evolution would be:

• First phase:

Classical 4*12 re-use. The capacity obtained reaches 80 Erl / km²

• Second phase:

1*3 re-use with the same number of site and a RF load of 40 %. The capacity obtainedreaches then 170 Erl / km²

• Third phase: A.I.M.S

1*3 re-use with the same number of site and a RF load of 50 % to free up abandwidth for BCCH micro plan.Introduction of 3 TRXs microcells (9 µcells / km²).The capacity reached in the microcellular area reaches then 410 Erl / km². (Thiscalculation is very simplistic because, in a dual layer network, we should not add themacrolayer capacity to the microlayer capacity).

Of course, this solution has not been validated on the field yet.

The following table gives the calculation of the previous strategy:

8 ConclusionThe document gave an overview about Synthesised Frequency Hopping benefits inmobile radio networks. At first time based on a theoretical discussion, and then basedon the pilot performed in Abu Dhabi, the following conclusions have been drawn:

General benefits of SFH :

The main benefits of SFH are frequency diversity for slowly moving mobiles andinterferer diversity, which occurs due to own hopping and uncorrelated hopping of theinterferer in random hopping mode

SFH can be performed in cyclic or random mode, whereas random hopping providesbetter interferer diversity and should be preferred to cyclic hopping HSN≠0.

Synthesised Frequency Hopping with fractional loading allows cluster reduction as thecollision probability is reduced, the key parameters being the real traffic load of thecell and the level of interference between neighbouring cell

Power Control and DTX are more effective in hopping networks and thusrecommended.

SFH should be introduced in well planned, optimised and mature networks, in orderto improve the network quality or in order to increase the capacity

9 References[1] U. BIRKEL “SLOW FREQUENCY HOPPING - Position paper”3DF 00995 0000 UDZZA

[2] R. RAVOALAVOSON “Default Radio Parameters”3DF 00942 0001 PQZZA

[3] JP Charles, A Vo Viet, D. Duponteil, L. Delaunay-ledter “Technical Note onFrequency Hopping” from Centre National d’Etudes des Télécommunications(CNET)

[4] M. HAHN, C. HELMER “Activation Strategy for Microcellular network”3DF 00 968 0001 TQZZA

10 Abbreviations

ARCS Average Reuse Cluster SizeARFCN Absolute Radio Frequency Channel NumberBBH Baseband hoppingBCCH Broadcast Control ChannelBER Bit Error RateBSS Base Station SubsystemBTS Base Transceiver StationC/I Signal to Interferer RatioC/ITHR Threshold of Signal to Interferer RatioCAE Customer Application EngineeringCCCH Common Control ChannelCDPP Customer Data Population ProgramCU Carrier UnitDTX Discontinuous TransmissionFER Frame Erasure RateFFH Fast Frequency HoppingFHS Frequency Hopping SystemFHS_ID Identifier of a FHSFU Frame UnitGSM Global System of Mobile CommunicationHO HandoverHSN Hopping Sequence NumberMAIO Mobile Allocation Index OffsetMS Mobile StationOMC Operation and Maintenance CentrePblock Blocking probability (Hard blocking)PC Power ControlPint Interference ProbabilityQoS Quality of ServiceRFH Radio Frequency HoppingRX ReceiverRXSYN Synthesiser of the ReceiverSACCH Slow Associated Control ChannelSFH Slow Frequency HoppingSTCH Super Traffic ChannelTCH Traffic ChannelTDMA Time Division Multiple AccessTRX TransceiverTS TimeslotTU3, TU50TU2

Typical Urban with 3, 50, 2km/h mobile speed

TX TransmitterTXSYN Synthesiser of the Transmitter

END OF DOCUMENT

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