Collection of GSM RNP technical problems and replies(No.2)-20040604-A-1.0.pdf

Collection of GSM RNP technical problems and replies(Issue 2) Internal Open

2004-06-04 Confidential Information of Huawei. No Spreading without Permission

Page1, Total18

Document number Product name

Applicable for Product version

Drafted by Wireless Network planning Dept.

Document version V1.0

Collection of GSM RNP technical problems and replies(No. 2)

(For internal use only)

Prepared by: Date:

Reviewed by: Date:

Reviewed by: Date:

Approved by: Date:

Huawei Technologies Co., Ltd.

All rights reserved



Page2, Total18

Contents

Problem 21 Inter-BSC PBGT handover ............................... Problem 22 Meaning of the parameter UO signal intensity difference.............4

Problem 23 What are the causes for trigger handover require for the better cell?

.................................................................................................................................5

Problem 24 How to enable a handover for a better cell?........................................5

Problem 25 Whether can the using of the omni antenna with inbuilt tilt angle

ensure the coverage nearby ? ..................................................................................5

Problem 26 Causes for handover failure with the reason value of Equipment

Failure .....................................................................................................................6

Problem 27 Distance between half- power point and BTS.....................................7

Problem 28 Call-drop rate increases suddenly........................................................7

Problem 29 Outgoing inter-BSC handover success rate is decreased by 3%-4%. .8

Problem 30 How to calculate BSC capacity ...........................................................8

Problem 31 MS is allocated with SDCCH repeatedly when acting as a called party

.................................................................................................................................8

Problem 32 Cell initialization fails after BCCH is configured to participate

baseband hopping. ................................................................................................9

Problem 33 Effect of TTA(Tower Top Amplifer) on noise factor .....................9

Problem 34 Which items is the GSM receiver sensitivity (Pmin) relate to? ........11

Problem 35 Cell reselection is slow and handover also fails................................11

Problem 36 The first paging success rate decreases after the network replacement .

...............................................................................................................................12

Problem 37 Which does the NCC Permitted' parameter affect, cell

selection/reselection or handover?........................................................................13

Problem 38 which attention when replacing Ss equipment ..............................13

Problem 39 Is the inter-layer handover threshold useful for load and interference

handover?..............................................................................................................14



Page3, Total18

Problem 40 TCH seizure failure times is different between two measurement tasks

...............................................................................................................................15

Problem 41 Meaning of radio interface failure, reversion to previous channel 15

Problem 42 How to predict the coverage distances under different environments?

...............................................................................................................................15

Problem 43 Differences in network performance between asynchronous &

synchronous site....................................................................................................16

Problem 44 which mean it does when CCCH overload alarm occurs..................17

Problem 45 Meaning of electrical tilt angle antenna ............................................18



Page4, Total18

Problem 21 Inter-BSC PBGT handover

Problem Whether it is possible to make an inter-BSC PBGT handover? Detail Description

Whether it is possible to make an inter-BSC PBGT handover?

Reply The conditions to trigger a PBGT handover include: 1. The receiving levels of the serving cell and the destination cell and the configuration of associated parameters must satisfy the PBGT value configured and P/N principles. 2. The destination cell and the serving cell are in the same layer and the same level. 3. The destination cell is prior to the serving cell in the list of handover candidate cells. Even for cells of different BSCs or MSCs, if they are the same in priority, they are also available for PBGT handover(satisfying Huawei 16 BIT order algorithm).

Problem 22 Meaning of the parameter UO signal intensity difference

Problem What does the parameter UO signal intensity difference mean? Detail Description

According to the Guide, the signal intensity of the underlay subcell differs from that of the overlay subcell due to the differences in transmission power and path loss. The UO signal intensity difference means a power compensation value for the overlay subcell. Since the handover decision procedure is based on the level after power compensation for the overlay subcell, the configuration of this parameter must be accurate. Otherwise, the PBGT/border handover may be delayed or advanced, thus causing handover failure. As we know, BCCH is generally distributed in the underlay subcell, and TCH in overlay subcell. It makes no sense to compensate power for the overlay subcell by the parameter UO signal intensity difference because only BCCH level instead of TCH level is involved in the handover decision procedure. Each cell has only one BCCH, which is in either the overlay subcell or the underlay subcell. If the BCCH is distributed in the underlay subcell, the parameter does not make any sense in the handover decision procedure.

Reply Indeed, BCCH is only distributed in the underlay subcell to ensure a satisfactory coverage, and the handover decision procedure depends on only BCCH level. In a handover decision procedure of a call undergoing in a overlay subcell, the signal intensity at the time is not the actual signal intensity of the IUO cell. It is



Page5, Total18

necessary to add RX_level of a overlay subcell and UO signal intensity difference and then compare the sum with the BCCH level of another cell to make a handover decision. IUO handover (handover from the overlay subcell to the underlay subcell or contrarily) depends on the IUO handover threshold configured, and the destination cell should be a concentric cell.


Problem What is the causes for trigger handover require for the better cell? Detail Description

What is the causes for trigger handover require for the better cell?

Reply 1. For cells of the same layer and the same level, the handover is triggered by PBGT. 2. For cells of different layers and different levels, the handover is triggered for layer handover(from lower layer cell to upper layer cell).

Problem 24 How to enable a handover for a better cell?

Problem How to enable a handover for a better cell? Detail Description

What are the terms to enable a handover for a better cell (that is, a handover from an M900 cell to an M1800 cell)?

Reply 1. The destination cell takes priority of the serving cell in the handover. 2. The level of the destination cell > Inter-layer HO Thrsh.+ Inter-layer HO hysteresis. 3. The destination cell is the first (certainly ahead of the serving cell) in the candidates queue.

Problem 25 Whether can the using of the omni antenna with inbuilt tilt angle ensure the coverage nearby ?

Problem The antenna height of the BTS is about 80m. Whether will the using of the omni-directional antenna with inbuilt 6-tilt angle make the area about 90m away from the BTS blind spots?

Detail Description

The antenna height of the BTS is about 80m. Whether will the using of the omni-directional antenna with inbuilt 6-tilt angle make the area about 90m away from the BTS blind spots?

Reply Coverage also depends on field environment. Generally, signals attenuate by over 10dB when passing through the outdoor



Page6, Total18

to the indoor, and the amount of attenuation varies from buildings to buildings. The signal intensity indoors must be higher than the receiving sensitivity of an MS (generally -102dBm), so the signal intensity outdoors must be higher than -80dBm to keep the MS attached, and over -65dBm to achieve a satisfactory coverage. Therefore, the coverage depends on gain of the side-lobe and zero deep filling position.

Problem 26 Causes for handover failure with the reason value of Equipment Failure

Problem What are the causes for incoming BSC handover failure with the reason

value of Equipment Failure?

Detail Description

In a local network (containing both Es equipment and Huaweis), the incoming BSC handover seldom succeeds according to the result of traffic statistics. After tracing A interface signaling, we find the reason value of incoming BSC handover failure is Equipment Failure. What are the causes for incoming BSC handover failure with the reason value of Equipment Failure?

Reply The reasons for incoming BSC handover failure with the reason value of Equipment Failure include: 1. The target BSC processes the HANDOVER REQUEST message in the course of inter-BSC handover. It is either speech service or data service while the associated CIC number is invalid. 2. The target BSC processes the Inter CCB Change Complete message in the course of inter-BSC handover. It is an SDCCH handover and the BSC fails to search for the buffered Inter Into BSC Handover Request message. 3. The target BSC processes the Inter Path Ack message in the course of inter-BSC handover. Both decoding and searching for the buffered Inter Into BSC Handover Request message fail. 4. The target BSC receives a Inter Path Rej message. 5. The target BSC checks the conditions of incoming-BSC handover in the course of inter-BSC handover and finds equipment failure. 6. In the course of inter-BSC handover, the target BSC fails to connect with the radio channel over the Abis interface or fails to send a CHAN ACT message. 7. In the course of inter-BSC handover, the target BSC begins handover queueing procedure due to lack of available channels. Upon receipt of an Inter Ret Res message, the target BSC obtains idle channels, but it fails to send a CHAN ACT message, search the buffered HANDOVER COMMAND



Page7, Total18

message, and fetch the frequency of the carrier. 8. In the course of inter-BSC handover, the target BSC receives a CHAN ACT NACK message. 9. In the course of inter-BSC handover, the target BSC receives a HANDOVER DETECTION message and then a CONN FAIL IND message. 10. In the course of inter-BSC handover, the target BSC fails to receive a CHAN ACT message before the timer expires.

Problem 27 Distance between half- power point and BTS

Problem Distance between half- power point and BTS Detail Description

After site survey, we find the antenna is extremely high. The tower is 50m high and positioned on a hill. The altitude difference between the antenna and the town is nearly 120m. According to further study to sampling data, the antenna used at this site is omni-directional, with antenna gain of 11dBi and vertical half power angle of 7. The half power point of the antenna main lobe is about 2000m away from the site if the valid antenna height is 120m. Therefore, the town is not within the area covered by the antenna main lobe. How does the result 2000m (the distance between the half power point and the site) come? I think it is 977m (tan(907)120=977M).

Reply It is worry, and the correct formula is: Distance = 120/tan(7/2)=1961M

Problem 28 Call-drop rate increases suddenly

Problem Call-drop rate increases suddenly Detail Description

TCH call-drop rate of the BTS A increased suddenly (up to 100%) .

Reply According the traffic statistics, the call-drop rate of the site A is normal before, but increases up to 80% suddenly.The traffic statistic shows that TCH call drop times are nearly equal to inter-BSC incoming handover require times ,It indicates the requests for inter-BSC incoming cell handover all fail. After analyzing the traffic statistics of incoming cell handover of the site A, we found handover attempts from cells with CGI of 46001469189A0 to the site A all fail. Check the associated handover data.

The BSC host version is BSC07.0520B, for which incoming handover failures due to expiration are included in the call-drop measurement, but for the BSC02.1120A and later, they will not be included.



Page8, Total18

Conclusion: After checking the associated handover data, we found there are neighboring cells of the same frequency and the same BSIC. Modify the handover data, then both the number of handover failures and TCH call-drop rate become normal.

Problem 29 Outgoing inter-BSC handover success rate is decreased by 3%-4%.

Problem The success rate of M1800 outgoing inter-BSC handover decreases by 3 to 4 percentage points.

Detail Description

The success rate of M1800 outgoing inter-BSC handover decreased by 3 to 4 percentage points, and that of dual-frequency handover also decreased. The customer said no modification was done to M900(which other vendor provides) .

Reply After checking data , we found that the frequency or BSIC of eight external cells were inconsistent with that of M900. We then modified the associated data and then found the handover resumed normal.

Problem 30 How to calculate BSC capacity

Problem How to calculate BSC capacity Detail Description

How to figure out the capacity for the BSC if the total number of channels of the BSC is greater than 100, when there is not any information available in the Erlang B Table for capacity calculation.

Reply According to GOS and number of TCHs in each cell, it is possible to find the traffic volume that can be supported by the cell. The total capacity of the BSC equals to the sum of the traffic volume of various cells of this BSC.


Problem MS is allocated with SDCCH repeatedly when acting as a called party Detail Description

The customer complained that in the course of call tests, the test MS acting as the called party occupies the SDCCH first, then goes back in idle mode, and then occupies the SDCCH again and complete the call normally. Such event occurs frequently.

Reason According to drive test data, the MS receives a Channel release message with the reason value of the timer expiration by the network immediately after occupying the SDCCH channel. After further study, such event occurs to only VPN subscribers. The reason is that the PSI function makes the network page the MS twice. The first is for the purpose of fetching CGI for cell and time division



Page9, Total18

charging.

Problem 32 Cell initialization fails after BCCH is configured to participate baseband hopping.

Problem Cell initialization fails after BCCH of a cell is configured to participate

baseband frequency hopping.

Detail

Description

Cell initialization fails after BCCH of a cell is configured to participate

baseband frequency hopping. Cell initialization fails, prompting data

error. All channels of this cell are blocked. It is module 2 cell 19 whose

BCCH is configured on site to participate the baseband frequency

hopping. It is a 3-TRX M1800 cell. The version of the BSC is 08.0520B.

Reply The fault is error data configuration instead of BSC version. Both cell

BCCH mutual aid and cell TRX mutual aid are not closed.

NOTE:

1. BSC08.0520B and later Versions can support BCCH participating

base-band timeslot frequency hopping:

2. In BSC04120bB and before versions, BCCH participating base-band

frequency hopping conflicts with BCCH mutual aid, both cell BCCH

mutual aid and cell BCCH mutual aid must be closed during BCCH

participating baseband frequency hopping.

Problem 33 Effect of TTA(Tower Top Amplifer) on noise factor

Problem Effect of TTA(Tower Top Amplifer) on noise factor

Detail

Description

Effect of TTA(Tower Top Amplifer) on noise factor

Reply The TTA gain may make the noise factor smaller.

Since the TTA gain is high, the noise factor when a TTA is added is 3dB

smaller than that when a TTA is not added (suppose the TTA gain is



Page10, Total18

12dB, the noise factor is 2.2dB, and the feeder loss is 4dB). Therefore, the

uplink sensitivity is improved by about 3dB.

The calculation formulas of noise factor are given below:

The amplifying factor of the TTA gain is great (TTA gain is high), which

makes the cascading added value of the noise factor of the mode behind

the TTA is reversely proportional to the amplifying factor.

NFS=NF1+L1(NF2-1)/G1+

Examples:

For the case when the TTA is not added:

Jumper loss before the point where the TTA is intervened: L1=-0.4dB,

NF1=0.4dB

Loss over the parts after the point where the TTA is intervened:

L2=+13dB(with gain), NF2=6dB

Therefore, the noise factor when the TTA is not added is:

NFS (without TTA)=NF1+L1(NF2-1)(absolute value)=6.4dB


Jumper loss before the point where the TTA is intervened: L1=-0.4dB,

NF1=0.4dB

TTA gain: G3=12dB, NF3=2.2dB

Loss over the parts after the point where the TTA is intervened:

L2=+13dB(with gain), NF2=6dB

Therefore, the noise factor when the TTA is added is:

NFS (with TTA)=NF1+L1(NF3-1)+L1(NF2-1)/G3(absolute

value)=3.07dB

The figures above are only based on estimation.

Obviously, the noise factor when the TTA is added is smaller than that

when the TTA is not added.



Page11, Total18

Problem 34 Which items is the GSM receiver sensitivity (Pmin) relate to?

Problem Which items is the GSM receiver sensitivity (Pmin) relate to? Detail Description

Pnoise is 121dBm based on the heat noise formula P=KTW, but Pmin specified by the GSM protocol is 104dBm. Is the difference (17dBm) for protection? Can the noise factor of the BTS receiver be smaller?

Reason (Refer to GSM (0550) for details)

Signals received at the inputting end of the receiver include normal signal and noise(Pmin and Pnoise). Since the circuit in the receiving channel also occurs noise, the ratio of Pmin to Pnoise during demodulation is:

Eb/Nt=PminPnoiseNf ----------(1)

Where Nf is the noise factor at the circuit in the receiving channel, Eb/Nt is a ratio of average bit energy to the noise/ interference power spectrum density. It is also called demodulation threshold, equaling to C/I (ratio of carrier to interface) in FM modulation. It is a standard to measure digital modulation and encoding quality. The expected value of Eb/Nt depends on modulation mode and modulation algorithm of the system. Theoretically, Eb/Nt of GSM system is 9dB (with margin considered), and the demodulation threshold of the receiver can be lower than 7dB (Eb/Nt=7dB) if the demodulation algorithm is of good performance.

Pnoise is thermal noise signals at the inputting end of the receiver.

Pnoise =10Log(KT0 BW)

Wherein, K is Boldzmann constant (K=1.3810-23 J/K). T0 is standard noise temperature (T0=290K).

Therefore, Pnoise=10Log(KT0)+10LogBW= 174dBm+10LogBW --------(2)

Wherein, BW is channel bandwidth of the system. For the GSM system, BW=210+5 Hz.

Based on the equation (1) and (2), the static reference sensitivity Pmin of the GSM receiver is:

Pmin =174dBm +10LogBW+Nf+Eb/Nt

=121dBm+Nf+Eb/Nt (constant temperature)

Problem 35 Cell reselection is slow and handover also fails

Problem Cell reselection is slow and handover also fails Detail In a drive test, Cell reselection is slow and handover also fails



Page12, Total18

Description Reason 1. According to the message received, the duration of cell reselection is so short

that the MS cannot identify the BSIC. Since the system information delivered by the BTS is correct, the cause for the failure may be great clock deviation.

2. In the course of asynchronous handover, there are not any physical messages delivered. The reasons may be:

a). When detecting a handover access at the new channel, the BTS did not deliver a physical information. It was asynchronous handover judging by the Abis interface message traced, but whether the corresponding channel was activated was unknown according to the message. Since the handover command had been delivered normally and the BTS had reset, the corresponding channel must be activated properly. b). The handover detection message could not be decoded due to clock fault, thus leading to handover failure since there was no physical message to be delivered or it was hard to decode the physical message properly. Later it is confirmed that the clock is faulty.


Problem The first paging success rate decreases after the network is replaced with Huawei equipments

Detail Description

After NS equipment is replaced with Huaweis , the first paging success rate decreases from 86% to 75%, but the secondary is normal, and even up to 30%. Ns MSC initiates a paging twice at most, and the interval between the two paging actions is five seconds. The location updating period of the MSC is 24 hours, and that of the BSC is 2 hours, and they do not vary after the move. For Huaweis equipment, if the MSC initiate a paging, the BSC then follows. While for Ns equipment, the BSC can initiates the paging for three times by default. Therefore, the paging success rate of Ns equipment is obviously higher than that of Huaweis. At present, the parameters of the BSC mainly adopt default configuration. Which parameters of the BSC/MSC are to be modified to raise the first paging success rate?

Reply 1. View the traffic statistic first to find out the number of overloads and the status of SDCCH to locate whether the paging messages lost or no response to paging message.

2. Check the coverage of the Huaweis network. 3. If both are normal, then the reason may be related to the paging strategic of

Huaweis BSS



Page13, Total18

4. As described above, Ns BSC pages more than Huaweis does, So the paging success rate of Ns equipment is higher than that of Huaweis.

Currently, you can take the following measures to handle the trouble 1. check the BTS hardware and data configuration , including consistency

between cell module information table and cell description table. 2. Modify the number of extended transmission timeslots to lessen RACH

collisions. 3. Decrease RACH minimum access level (to 2 or 3). This action may has

impact upon the call-drop rate. 4. Modify the location updating period of the MSC to 2 or 3. 5. Identify those MS out of touch as recessively detached to raise the paging

success rate. 6. Increase the number of MS MAX Resent when the load over RACH and

SDCCH is light.

Problem 37 Which does the NCC Permitted' parameter affect, cell selection/reselection or handover?

Problem Which does the NCC Permitted' parameter affect, cell selection/reselection or handover?

Detail description

Which does the NCC Permitted' parameter affect, cell selection/reselection or handover?

Reply As described in the chapter 10.5.2.27 of the GSM 0408 protocol. The purpose of the NCC Permitted information element is to provide a definition of the allowed NCCs on the BCCH carriers to be reported in the MEASUREMENT REPORT message by the mobile stations in the cell.

Therefore, this information element affects only the MEASUREMENT

REPORT message.

After further verification by experiment, it is proved that the NCC Permitted

parameter has impact only upon handover instead of cell selection/reselection.

Problem 38 which attention when replacing Ss equipment

Problem Points of attention for coverage and handover when replacing Ss equipment with Huaweis

Detail Since we still use Ss antenna and feeder system after the replacement, we should



Page14, Total18

description mainly concern TRX output power and combiner loss to ensure a satisfactory coverage. What should we give special attention so that the coverage after replacement is satisfactory? Are there any requirements for the handover parameters?

Reply In respect of coverage, it is necessary to obtain information of Ss equipment, such as combination mode, combination loss, Power over cabinet top of typical configuration, coverage effect and so on. Perform driving test in areas which involve complaints and bad coverage. In respect of handover, refer to Guide to Parameter Configuration and Algorithm presented by S for details. Get some knowledge about Ss current network state and analyze the traffic statistics on busy hours before making a promise about Huaweis future network specifications.

Problem 39 Is the inter-layer handover threshold useful for load and interference handover?

Problem Is the inter-layer handover threshold useful for load handover and interference handover?

Detail description

When the receiving level of the candidate cell is smaller than the sum of the inter-layer receiving level threshold and the inter-layer hysteresis , the inter-layer handover cannot be triggered. Is it also true for load handover and interference handover?

Reply Conditions required to trigger an interference handover: 1. Neighboring cell level > inter-layer handover threshold + inter-layer handover hysteresis 2. The destination cell satisfies the corresponding thresholds for handover quality and receiving level. Conditions required to trigger a load handover: 1. The signaling flow of the destination cell is under the threshold specified. 2. The signaling flow of the serving cell is over the threshold specified. 3. The signaling flow of the destination cell is lower than the receiving threshold, and the receiving level of the serving cell is higher than the outgoing handover threshold specified. 4. The level of the destination cell is higher than the sum of the inter-layer handover threshold and the hysteresis. 5. Both the destination cell and the serving cell belong to the same BSC. 6. Within the load handover band. According to the handover triggering conditions above, both interference handover and load handover are not necessarily for a cell of higher receiving level. Therefore, it is necessary to set inter-layer handover threshold to prevent from handing over to a cell of lower receiving level.



Page15, Total18


Problem Number of TCH seizure failures in cell performance measurement differs task from number of TCH assignment failures in BSC general performance measurement task

Detail description

Number of TCH seizure failures in cell performance measurement task differs from number of TCH assignment failures in BSC general performance measurement task. Do the two measurement results contradict each other?

Reply Number of TCH seizure failures in cell performance measurement task includes the cases of handover, while number of TCH assignment failures in BSC general performance measurement task does not. Therefore, the two measurement result are different.

Problem 41 Meaning of radio interface failure, reversion to previous channel

Problem What does the parameter radio interface failure, reversion to previous channel means?

Detail description

According to the traffic statistic result, TCH assignment failures times are too many , with the reason value of radio interface failure, reversion to previous channel. The measurement object is the number of ASSIGNMENT FAILURE of ECV_NORM_A_REVERT_TO_OLD_CH. What's the cause of the trouble, and how to handle it?

Reply The assignment failure with the reason value of radio interface failure, reversion to previous channel means that MS has been allocated with a TCH channel, but it fails to access it and then returns back to the previous SDCCH channel. The reason for this failure may be: 1. Network quality is poor. Check frequency planning first. 2. Network coverage is dissatisfactory. Check both indoor and outdoor coverage first. 3. Check whether the antenna system and TRXs in cells are installed properly. 4. The TRX hardware is faulty (without alarming information).


Problem How to predict the coverage distances under different environments? Detail description

How to predict the coverage distances under different environments based on common propagation models?

Reply It is possible to predict the coverage distance based on Okumura-Hata model,



Page16, Total18

which is fit for 900MHz micro-cellular system. 1. Urban The medium value of the path loss in urban area can be figured out based on the following approximate analytic equation.

lglg

lglg lglg

Lp = 69.55 + 26.16 f 13.82 hb

+ (44.9 65.5 hb ) d Ahm

lglg

Wherein: Lp path loss between BTS and MS (unit: dB)

f carrier frequency (unit: MHz)

hb

hm

height of BTS antenna (unit: m)

height of MS antenna (unit: m)

d distance between BTS and MS (unit: km)

For medium cities: Am = (1.1 f 0.7)hm (1.56 f 0.8)lglg lglg ; For big cities: Am = 3.2( (11.75hm))2 4.97logloglog 2. Suburb In suburb, the propagation models can be modified as:

2[ (f /28)]2 5.4Lps = Lp lglg 3. Open area In open area, the propagation models can be modified as: Lps = Lp 4.78( f )2 5.4 + 18.33 f 40.94

Lp = 69.55 + 26.16 f 13.82 hb+ (44.9 65.5 hb ) d Ahm

lglg lglg

lglg

lglg lglg

lglg

Therefore, it is possible to predict out the coverage distance based on the Okumura-Hata model, BTS transmission power, antenna gain, combiner loss, feeder loss, land form and so on.

Problem 43 Differences in network performance between asynchronous & synchronous site

Problem Can you describe the differences in network performance between asynchronous S1/1/1 and synchronous S1/1/1?

Detail At present, the BTS3002C does not support several cabinets connecting for



Page17, Total18

description synchronous cells, so we configure a site of over two TRXs by cascading multiple BTSs at co-location. Can you describe the differences in network performance between asynchronous S1/1/1 and synchronous S1/1/1?

Reply 1. In respect of transmission Asynchronous S1/1/1 is composed of multiple BTSs, and it is configured as multiple sites accordingly. Therefore, multiple OML links are required for transmission, thus causing waste of transmission resources. The cascading connection may has impact upon network security.

2. In respect of handover Handover between cells of different BTSs is referred to as asynchronous handover. Handover between cells of the same BTS is referred to as synchronous handover. In the case of asynchronous networking, the system maintenance is complex. Cells at the same site address must be treated as different sites in maintenance and upgrade. When each cell is configured with over one TRX, it is hard to avoid co-channel or adjacent channel because different frames if with compact frequency reuse.

Problem 44 which mean it does when CCCH overload alarm occurs

Problem CCCH overload alarm occurs not only on busy hours, but also on wee hours. Is MS out of service cell because of the occurrence of CCCH overload alarm?

Detail description

CCCH overload alarm occurs not only on busy hours, but also on wee hours. Is MS out of the serving cell because of the occurrence of CCCH overload alarm?

Reply CCCH OVERLOAD includes PCH overload and RACH overload. It is mainly the former case on busy hours, and the latter on wee hours ( the BTS always detects RACH level frequently due to interfere). The MS may become out of the serving cell due to CCCH overload. Check the following parameter in this case. 1. Check RACH busy threshold. It is hard for an MS to access if the setting of the RACH busy threshold of the BTS2.0 is incorrect. 2. Check the configuration of the CCCH. Generally, the settings of CCCHs in the same location area must be consistent so that various cells in this location area are of the same capability in the paging procedure. If the settings of the CCCHs in the same location area are inconsistent, PCH overload tends to occur to some cells due to different capability in the paging procedure. That is to say, since the number of TRXs in urban area differs from that in rural area, so does the configuration of CCCHs. Therefore, the location area of urban area must be different from that of rural area. 3. Increase PCH sub-channels by setting a smaller value for



Page18, Total18

BS_AG_BLKS_RES, thus to expand the capacity of the paging channel. 4. Decrease BS-PA-MFRAMS to raising the frequency of sending paging message. The CCCH alarm report threshold is set 80 generally, but it can be set higher if necessary.

Problem 45 Meaning of electrical tilt angle antenna

Problem How to calculate the down tilt of the electrical tilt antenna Detail description

If an antenna is configured with a 7 electrical tilt, the actual down tilt of the antenna is 1, then is the tilt of the antenna lobe is 8?

Reply Electrical tilt is used to change the directional diagram of the antenna system. It plays an important role in controlling the coverage scope of a BTS and clearing the blind spots around a BTS. For an antenna system configured with electrical tilt, the actual down tilt equals to the sum of the electrical tilt and the mechanical tilt. The waveform becomes distorted when the mechanical tilt is greater than 10. Therefore, it is necessary to use antennas with electrical tilt angle if the intervals between two neighboring sites are short.

/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False

/Description > /Namespace [ (Adobe) (Common) (1.0) ] /OtherNamespaces [ > /FormElements false /GenerateStructure true /IncludeBookmarks false /IncludeHyperlinks false /IncludeInteractive false /IncludeLayers false /IncludeProfiles true /MultimediaHandling /UseObjectSettings /Namespace [ (Adobe) (CreativeSuite) (2.0) ] /PDFXOutputIntentProfileSelector /NA /PreserveEditing true /UntaggedCMYKHandling /LeaveUntagged /UntaggedRGBHandling /LeaveUntagged /UseDocumentBleed false >> ]>> setdistillerparams> setpagedevice

Collection of GSM RNP technical problems and replies(Issue 2)

Internal Open

Document number

Product name

Applicable for

Product version

Drafted by

Wireless Network planning

Dept.

Document version

V1.0

Collection of GSM RNP technical problems and replies(No. 2)

(For internal use only)

Prepared by:

Date:

Reviewed by:

Date:

Reviewed by:

Date:

Approved by:

Date:

Huawei Technologies Co., Ltd.

All rights reserved

Contents

4Problem 21 Inter-BSC PBGT handover

4Problem 22 Meaning of the parameter UO signal intensity difference

5Problem 23 What are the causes for trigger handover require for the better cell?

5Problem 24 How to enable a handover for a better cell?

6Problem 25 Whether can the using of the omni antenna with inbuilt tilt angle ensure the coverage nearby ?

6Problem 26 Causes for handover failure with the reason value of Equipment Failure

7Problem 27 Distance between half- power point and BTS

8Problem 28 Call-drop rate increases suddenly

8Problem 29 Outgoing inter-BSC handover success rate is decreased by 3%-4%.

9Problem 30 How to calculate BSC capacity

9Problem 31 MS is allocated with SDCCH repeatedly when acting as a called party

9Problem 32 Cell initialization fails after BCCH is configured to participate baseband hopping.

10Problem 33 Effect of TTA(Tower Top Amplifer) on noise factor

11Problem 34 Which items is the GSM receiver sensitivity (Pmin) relate to?

12Problem 35 Cell reselection is slow and handover also fails

13Problem 36 The first paging success rate decreases after the network replacement .

14Problem 37 Which does the NCC Permitted' parameter affect, cell selection/reselection or handover?

14Problem 38 which attention when replacing Ss equipment

15Problem 39 Is the inter-layer handover threshold useful for load and interference handover?

16Problem 40 TCH seizure failure times is different between two measurement tasks

16Problem 41 Meaning of radio interface failure, reversion to previous channel

16Problem 42 How to predict the coverage distances under different environments?

18Problem 43 Differences in network performance between asynchronous & synchronous site

18Problem 44 which mean it does when CCCH overload alarm occurs

19Problem 45 Meaning of electrical tilt angle antenna

Problem 21 Inter-BSC PBGT handover

Problem


Detail Description


Reply

The conditions to trigger a PBGT handover include:

1. The receiving levels of the serving cell and the destination cell and the configuration of associated parameters must satisfy the PBGT value configured and P/N principles.

2. The destination cell and the serving cell are in the same layer and the same level.

3. The destination cell is prior to the serving cell in the list of handover candidate cells.

Even for cells of different BSCs or MSCs, if they are the same in priority, they are also available for PBGT handover(satisfying Huawei 16 BIT order algorithm).

Problem 22 Meaning of the parameter UO signal intensity difference

Problem

What does the parameter UO signal intensity difference mean?

Detail Description

According to the Guide, the signal intensity of the underlay subcell differs from that of the overlay subcell due to the differences in transmission power and path loss. The UO signal intensity difference means a power compensation value for the overlay subcell. Since the handover decision procedure is based on the level after power compensation for the overlay subcell, the configuration of this parameter must be accurate. Otherwise, the PBGT/border handover may be delayed or advanced, thus causing handover failure.

As we know, BCCH is generally distributed in the underlay subcell, and TCH in overlay subcell. It makes no sense to compensate power for the overlay subcell by the parameter UO signal intensity difference because only BCCH level instead of TCH level is involved in the handover decision procedure.

Each cell has only one BCCH, which is in either the overlay subcell or the underlay subcell. If the BCCH is distributed in the underlay subcell, the parameter does not make any sense in the handover decision procedure.

Reply

Indeed, BCCH is only distributed in the underlay subcell to ensure a satisfactory coverage, and the handover decision procedure depends on only BCCH level. In a handover decision procedure of a call undergoing in a overlay subcell, the signal intensity at the time is not the actual signal intensity of the IUO cell. It is necessary to add RX_level of a overlay subcell and UO signal intensity difference and then compare the sum with the BCCH level of another cell to make a handover decision.

IUO handover (handover from the overlay subcell to the underlay subcell or contrarily) depends on the IUO handover threshold configured, and the destination cell should be a concentric cell.


Problem


Detail Description


Reply

1. For cells of the same layer and the same level, the handover is triggered by PBGT.

2. For cells of different layers and different levels, the handover is triggered for layer handover(from lower layer cell to upper layer cell).

Problem 24 How to enable a handover for a better cell?

Problem

How to enable a handover for a better cell?

Detail Description

What are the terms to enable a handover for a better cell (that is, a handover from an M900 cell to an M1800 cell)?

Reply

1. The destination cell takes priority of the serving cell in the handover.

2. The level of the destination cell > Inter-layer HO Thrsh.+ Inter-layer HO hysteresis.

3. The destination cell is the first (certainly ahead of the serving cell) in the candidates queue.

Problem 25 Whether can the using of the omni antenna with inbuilt tilt angle ensure the coverage nearby ?

Problem

The antenna height of the BTS is about 80m. Whether will the using of the omni-directional antenna with inbuilt 6(-tilt angle make the area about 90m away from the BTS blind spots?

Detail Description

The antenna height of the BTS is about 80m. Whether will the using of the omni-directional antenna with inbuilt 6(-tilt angle make the area about 90m away from the BTS blind spots?

Reply

Coverage also depends on field environment.

Generally, signals attenuate by over 10dB when passing through the outdoor to the indoor, and the amount of attenuation varies from buildings to buildings. The signal intensity indoors must be higher than the receiving sensitivity of an MS (generally -102dBm), so the signal intensity outdoors must be higher than -80dBm to keep the MS attached, and over -65dBm to achieve a satisfactory coverage.

Therefore, the coverage depends on gain of the side-lobe and zero deep filling position.

Problem 26 Causes for handover failure with the reason value of Equipment Failure

Problem

What are the causes for incoming BSC handover failure with the reason value of Equipment Failure?

Detail Description

In a local network (containing both Es equipment and Huaweis), the incoming BSC handover seldom succeeds according to the result of traffic statistics.

After tracing A interface signaling, we find the reason value of incoming BSC handover failure is Equipment Failure.

What are the causes for incoming BSC handover failure with the reason value of Equipment Failure?

Reply

The reasons for incoming BSC handover failure with the reason value of Equipment Failure include:

1. The target BSC processes the HANDOVER REQUEST message in the course of inter-BSC handover. It is either speech service or data service while the associated CIC number is invalid.

2. The target BSC processes the Inter CCB Change Complete message in the course of inter-BSC handover. It is an SDCCH handover and the BSC fails to search for the buffered Inter Into BSC Handover Request message.

3. The target BSC processes the Inter Path Ack message in the course of inter-BSC handover. Both decoding and searching for the buffered Inter Into BSC Handover Request message fail.

4. The target BSC receives a Inter Path Rej message.

5. The target BSC checks the conditions of incoming-BSC handover in the course of inter-BSC handover and finds equipment failure.

6. In the course of inter-BSC handover, the target BSC fails to connect with the radio channel over the Abis interface or fails to send a CHAN ACT message.

7. In the course of inter-BSC handover, the target BSC begins handover queueing procedure due to lack of available channels. Upon receipt of an Inter Ret Res message, the target BSC obtains idle channels, but it fails to send a CHAN ACT message, search the buffered HANDOVER COMMAND message, and fetch the frequency of the carrier.

8. In the course of inter-BSC handover, the target BSC receives a CHAN ACT NACK message.

9. In the course of inter-BSC handover, the target BSC receives a HANDOVER DETECTION message and then a CONN FAIL IND message.

10. In the course of inter-BSC handover, the target BSC fails to receive a CHAN ACT message before the timer expires.

Problem 27 Distance between half- power point and BTS

Problem

Distance between half- power point and BTS

Detail Description

After site survey, we find the antenna is extremely high. The tower is 50m high and positioned on a hill. The altitude difference between the antenna and the town is nearly 120m.

According to further study to sampling data, the antenna used at this site is omni-directional, with antenna gain of 11dBi and vertical half power angle of 7(.

The half power point of the antenna main lobe is about 2000m away from the site if the valid antenna height is 120m. Therefore, the town is not within the area covered by the antenna main lobe.

How does the result 2000m (the distance between the half power point and the site) come? I think it is 977m (tan(907)(120=977M).

Reply

It is worry, and the correct formula is: Distance = 120/tan(7/2)=1961M

Problem 28 Call-drop rate increases suddenly

Problem

Call-drop rate increases suddenly

Detail Description

TCH call-drop rate of the BTS A increased suddenly (up to 100%) .

Reply

According the traffic statistics, the call-drop rate of the site A is normal before, but increases up to 80% suddenly.The traffic statistic shows that TCH call drop times are nearly equal to inter-BSC incoming handover require times ,It indicates the requests for inter-BSC incoming cell handover all fail.

After analyzing the traffic statistics of incoming cell handover of the site A, we found handover attempts from cells with CGI of 46001469189A0 to the site A all fail. Check the associated handover data.

The BSC host version is BSC07.0520B, for which incoming handover failures due to expiration are included in the call-drop measurement, but for the BSC02.1120A and later, they will not be included.

Conclusion: After checking the associated handover data, we found there are neighboring cells of the same frequency and the same BSIC. Modify the handover data, then both the number of handover failures and TCH call-drop rate become normal.

Problem 29 Outgoing inter-BSC handover success rate is decreased by 3%-4%.

Problem

The success rate of M1800 outgoing inter-BSC handover decreases by 3 to 4 percentage points.

Detail Description

The success rate of M1800 outgoing inter-BSC handover decreased by 3 to 4 percentage points, and that of dual-frequency handover also decreased. The customer said no modification was done to M900(which other vendor provides) .

Reply

After checking data , we found that the frequency or BSIC of eight external cells were inconsistent with that of M900. We then modified the associated data and then found the handover resumed normal.

Problem 30 How to calculate BSC capacity

Problem

How to calculate BSC capacity

Detail Description

How to figure out the capacity for the BSC if the total number of channels of the BSC is greater than 100, when there is not any information available in the Erlang B Table for capacity calculation.

Reply

According to GOS and number of TCHs in each cell, it is possible to find the traffic volume that can be supported by the cell. The total capacity of the BSC equals to the sum of the traffic volume of various cells of this BSC.


Problem

MS is allocated with SDCCH repeatedly when acting as a called party

Detail Description

The customer complained that in the course of call tests, the test MS acting as the called party occupies the SDCCH first, then goes back in idle mode, and then occupies the SDCCH again and complete the call normally. Such event occurs frequently.

Reason

According to drive test data, the MS receives a Channel release message with the reason value of the timer expiration by the network immediately after occupying the SDCCH channel.

After further study, such event occurs to only VPN subscribers.

The reason is that the PSI function makes the network page the MS twice. The first is for the purpose of fetching CGI for cell and time division charging.

Problem 32 Cell initialization fails after BCCH is configured to participate baseband hopping.

Problem

Cell initialization fails after BCCH of a cell is configured to participate baseband frequency hopping.

Detail Description

Cell initialization fails after BCCH of a cell is configured to participate baseband frequency hopping. Cell initialization fails, prompting data error. All channels of this cell are blocked. It is module 2 cell 19 whose BCCH is configured on site to participate the baseband frequency hopping. It is a 3-TRX M1800 cell. The version of the BSC is 08.0520B.

Reply

The fault is error data configuration instead of BSC version. Both cell BCCH mutual aid and cell TRX mutual aid are not closed.

NOTE:

1. BSC08.0520B and later Versions can support BCCH participating base-band timeslot frequency hopping:

2. In BSC04120bB and before versions, BCCH participating base-band frequency hopping conflicts with BCCH mutual aid, both cell BCCH mutual aid and cell BCCH mutual aid must be closed during BCCH participating baseband frequency hopping.

Problem 33 Effect of TTA(Tower Top Amplifer) on noise factor

Problem


Detail Description


Reply

The TTA gain may make the noise factor smaller.

Since the TTA gain is high, the noise factor when a TTA is added is 3dB smaller than that when a TTA is not added (suppose the TTA gain is 12dB, the noise factor is 2.2dB, and the feeder loss is 4dB). Therefore, the uplink sensitivity is improved by about 3dB.

The calculation formulas of noise factor are given below:

The amplifying factor of the TTA gain is great (TTA gain is high), which makes the cascading added value of the noise factor of the mode behind the TTA is reversely proportional to the amplifying factor.

NFS=NF1+L1(NF2-1)/G1+

Examples:


Jumper loss before the point where the TTA is intervened: L1=-0.4dB, NF1=0.4dB

Loss over the parts after the point where the TTA is intervened: L2=+13dB(with gain), NF2=6dB

Therefore, the noise factor when the TTA is not added is:

NFS (without TTA)=NF1+L1(NF2-1)(absolute value)=6.4dB


Jumper loss before the point where the TTA is intervened: L1=-0.4dB, NF1=0.4dB

TTA gain: G3=12dB, NF3=2.2dB

Loss over the parts after the point where the TTA is intervened: L2=+13dB(with gain), NF2=6dB

Therefore, the noise factor when the TTA is added is:

NFS (with TTA)=NF1+L1(NF3-1)+L1(NF2-1)/G3(absolute value)=3.07dB

The figures above are only based on estimation.

Obviously, the noise factor when the TTA is added is smaller than that when the TTA is not added.

Problem 34 Which items is the GSM receiver sensitivity (Pmin) relate to?

Problem

Which items is the GSM receiver sensitivity (Pmin) relate to?

Detail Description

Pnoise is 121dBm based on the heat noise formula P=KTW, but Pmin specified by the GSM protocol is 104dBm. Is the difference (17dBm) for protection? Can the noise factor of the BTS receiver be smaller?

Reason

(Refer to GSM (0550) for details)

Signals received at the inputting end of the receiver include normal signal and noise(Pmin and Pnoise). Since the circuit in the receiving channel also occurs noise, the ratio of Pmin to Pnoise during demodulation is:

Eb/Nt=PminPnoiseNf ----------(1)

Where Nf is the noise factor at the circuit in the receiving channel, Eb/Nt is a ratio of average bit energy to the noise/ interference power spectrum density. It is also called demodulation threshold, equaling to C/I (ratio of carrier to interface) in FM modulation. It is a standard to measure digital modulation and encoding quality. The expected value of Eb/Nt depends on modulation mode and modulation algorithm of the system. Theoretically, Eb/Nt of GSM system is 9dB (with margin considered), and the demodulation threshold of the receiver can be lower than 7dB (Eb/Nt=7dB) if the demodulation algorithm is of good performance.

Pnoise is thermal noise signals at the inputting end of the receiver.

Pnoise =10Log(KT0 BW)

Wherein, K is Boldzmann constant (K=1.38(10-23 J/K). T0 is standard noise temperature (T0=290K).

Therefore, Pnoise=10Log(KT0)+10LogBW= 174dBm+10LogBW --------(2)

Wherein, BW is channel bandwidth of the system. For the GSM system, BW=2(10+5 Hz.

Based on the equation (1) and (2), the static reference sensitivity Pmin of the GSM receiver is:

Pmin =174dBm +10LogBW+Nf+Eb/Nt

=121dBm+Nf+Eb/Nt (constant temperature)

Problem 35 Cell reselection is slow and handover also fails

Problem

Cell reselection is slow and handover also fails

Detail Description

In a drive test, Cell reselection is slow and handover also fails

Reason

1. According to the message received, the duration of cell reselection is so short that the MS cannot identify the BSIC. Since the system information delivered by the BTS is correct, the cause for the failure may be great clock deviation.

2. In the course of asynchronous handover, there are not any physical messages delivered. The reasons may be:

a). When detecting a handover access at the new channel, the BTS did not deliver a physical information. It was asynchronous handover judging by the Abis interface message traced, but whether the corresponding channel was activated was unknown according to the message. Since the handover command had been delivered normally and the BTS had reset, the corresponding channel must be activated properly.

b). The handover detection message could not be decoded due to clock fault, thus leading to handover failure since there was no physical message to be delivered or it was hard to decode the physical message properly.

Later it is confirmed that the clock is faulty.


Problem

The first paging success rate decreases after the network is replaced with Huawei equipments

Detail Description

After NS equipment is replaced with Huaweis , the first paging success rate decreases from 86% to 75%, but the secondary is normal, and even up to 30%.

Ns MSC initiates a paging twice at most, and the interval between the two paging actions is five seconds. The location updating period of the MSC is 24 hours, and that of the BSC is 2 hours, and they do not vary after the move.

For Huaweis equipment, if the MSC initiate a paging, the BSC then follows. While for Ns equipment, the BSC can initiates the paging for three times by default.

Therefore, the paging success rate of Ns equipment is obviously higher than that of Huaweis.

At present, the parameters of the BSC mainly adopt default configuration. Which parameters of the BSC/MSC are to be modified to raise the first paging success rate?

Reply

1. View the traffic statistic first to find out the number of overloads and the status of SDCCH to locate whether the paging messages lost or no response to paging message.

2. Check the coverage of the Huaweis network.

3. If both are normal, then the reason may be related to the paging strategic of Huaweis BSS

4. As described above, Ns BSC pages more than Huaweis does, So the paging success rate of Ns equipment is higher than that of Huaweis.

Currently, you can take the following measures to handle the trouble

1. check the BTS hardware and data configuration , including consistency between cell module information table and cell description table.

2. Modify the number of extended transmission timeslots to lessen RACH collisions.

3. Decrease RACH minimum access level (to 2 or 3). This action may has impact upon the call-drop rate.

4. Modify the location updating period of the MSC to 2 or 3.

5. Identify those MS out of touch as recessively detached to raise the paging success rate.

6. Increase the number of MS MAX Resent when the load over RACH and SDCCH is light.

Problem 37 Which does the NCC Permitted' parameter affect, cell selection/reselection or handover?

Problem


Detail description


Reply

As described in the chapter 10.5.2.27 of the GSM 0408 protocol.

The purpose of the NCC Permitted information element is to provide a definition of the allowed NCCs on the BCCH carriers to be reported in the MEASUREMENT REPORT message by the mobile stations in the cell.

Therefore, this information element affects only the MEASUREMENT REPORT message.

After further verification by experiment, it is proved that the NCC Permitted parameter has impact only upon handover instead of cell selection/reselection.

Problem 38 which attention when replacing Ss equipment

Problem

Points of attention for coverage and handover when replacing Ss equipment with Huaweis

Detail description

Since we still use Ss antenna and feeder system after the replacement, we should mainly concern TRX output power and combiner loss to ensure a satisfactory coverage. What should we give special attention so that the coverage after replacement is satisfactory? Are there any requirements for the handover parameters?

Reply

In respect of coverage, it is necessary to obtain information of Ss equipment, such as combination mode, combination loss, Power over cabinet top of typical configuration, coverage effect and so on. Perform driving test in areas which involve complaints and bad coverage.

In respect of handover, refer to Guide to Parameter Configuration and Algorithm presented by S for details. Get some knowledge about Ss current network state and analyze the traffic statistics on busy hours before making a promise about Huaweis future network specifications.

Problem 39 Is the inter-layer handover threshold useful for load and interference handover?

Problem

Is the inter-layer handover threshold useful for load handover and interference handover?

Detail description

When the receiving level of the candidate cell is smaller than the sum of the inter-layer receiving level threshold and the inter-layer hysteresis , the inter-layer handover cannot be triggered. Is it also true for load handover and interference handover?

Reply

Conditions required to trigger an interference handover:

1. Neighboring cell level > inter-layer handover threshold + inter-layer handover hysteresis

2. The destination cell satisfies the corresponding thresholds for handover quality and receiving level.

Conditions required to trigger a load handover:

1. The signaling flow of the destination cell is under the threshold specified.

2. The signaling flow of the serving cell is over the threshold specified.

3. The signaling flow of the destination cell is lower than the receiving threshold, and the receiving level of the serving cell is higher than the outgoing handover threshold specified.

4. The level of the destination cell is higher than the sum of the inter-layer handover threshold and the hysteresis.

5. Both the destination cell and the serving cell belong to the same BSC.

6. Within the load handover band.

According to the handover triggering conditions above, both interference handover and load handover are not necessarily for a cell of higher receiving level. Therefore, it is necessary to set inter-layer handover threshold to prevent from handing over to a cell of lower receiving level.


Problem

Number of TCH seizure failures in cell performance measurement differs task from number of TCH assignment failures in BSC general performance measurement task

Detail description

Number of TCH seizure failures in cell performance measurement task differs from number of TCH assignment failures in BSC general performance measurement task. Do the two measurement results contradict each other?

Reply

Number of TCH seizure failures in cell performance measurement task includes the cases of handover, while number of TCH assignment failures in BSC general performance measurement task does not. Therefore, the two measurement result are different.

Problem 41 Meaning of radio interface failure, reversion to previous channel

Problem

What does the parameter radio interface failure, reversion to previous channel means?

Detail description

According to the traffic statistic result, TCH assignment failures times are too many , with the reason value of radio interface failure, reversion to previous channel. The measurement object is the number of ASSIGNMENT FAILURE of ECV_NORM_A_REVERT_TO_OLD_CH.

What's the cause of the trouble, and how to handle it?

Reply

The assignment failure with the reason value of radio interface failure, reversion to previous channel means that MS has been allocated with a TCH channel, but it fails to access it and then returns back to the previous SDCCH channel. The reason for this failure may be:

1. Network quality is poor. Check frequency planning first.

2. Network coverage is dissatisfactory. Check both indoor and outdoor coverage first.

3. Check whether the antenna system and TRXs in cells are installed properly.

4. The TRX hardware is faulty (without alarming information).


Problem

How to predict the coverage distances under different environments?

Detail description

How to predict the coverage distances under different environments based on common propagation models?

Reply

It is possible to predict the coverage distance based on Okumura-Hata model, which is fit for 900MHz micro-cellular system.

1. Urban

The medium value of the path loss in urban area can be figured out based on the following approximate analytic equation.

Wherein:

path loss between BTS and MS (unit: dB)

carrier frequency (unit: MHz)

height of BTS antenna (unit: m)

height of MS antenna (unit: m)

distance between BTS and MS (unit: km)

For medium cities:

;

For big cities:

2. Suburb

In suburb, the propagation models can be modified as:

3. Open area

In open area, the propagation models can be modified as:

Therefore, it is possible to predict out the coverage distance based on the Okumura-Hata model, BTS transmission power, antenna gain, combiner loss, feeder loss, land form and so on.

Problem 43 Differences in network performance between asynchronous & synchronous site

Problem

Can you describe the differences in network performance between asynchronous S1/1/1 and synchronous S1/1/1?

Detail description

At present, the BTS3002C does not support several cabinets connecting for synchronous cells, so we configure a site of over two TRXs by cascading multiple BTSs at co-location. Can you describe the differences in network performance between asynchronous S1/1/1 and synchronous S1/1/1?

Reply

1. In respect of transmission

Asynchronous S1/1/1 is composed of multiple BTSs, and it is configured as multiple sites accordingly. Therefore, multiple OML links are required for transmission, thus causing waste of transmission resources. The cascading connection may has impact upon network security.

2. In respect of handover

Handover between cells of different BTSs is referred to as asynchronous handover. Handover between cells of the same BTS is referred to as synchronous handover.

In the case of asynchronous networking, the system maintenance is complex. Cells at the same site address must be treated as different sites in maintenance and upgrade. When each cell is configured with over one TRX, it is hard to avoid co-channel or adjacent channel because different frames if with compact frequency reuse.

Problem 44 which mean it does when CCCH overload alarm occurs

Problem

CCCH overload alarm occurs not only on busy hours, but also on wee hours. Is MS out of service cell because of the occurrence of CCCH overload alarm?

Detail description

CCCH overload alarm occurs not only on busy hours, but also on wee hours. Is MS out of the serving cell because of the occurrence of CCCH overload alarm?

Reply

CCCH OVERLOAD includes PCH overload and RACH overload. It is mainly the former case on busy hours, and the latter on wee hours ( the BTS always detects RACH level frequently due to interfere).

The MS may become out of the serving cell due to CCCH overload. Check the following parameter in this case.

1. Check RACH busy threshold. It is hard for an MS to access if the setting of the RACH busy threshold of the BTS2.0 is incorrect.

2. Check the configuration of the CCCH. Generally, the settings of CCCHs in the same location area must be consistent so that various cells in this location area are of the same capability in the paging procedure. If the settings of the CCCHs in the same location area are inconsistent, PCH overload tends to occur to some cells due to different capability in the paging procedure.

That is to say, since the number of TRXs in urban area differs from that in rural area, so does the configuration of CCCHs. Therefore, the location area of urban area must be different from that of rural area.

3. Increase PCH sub-channels by setting a smaller value for BS_AG_BLKS_RES, thus to expand the capacity of the paging channel.

4. Decrease BS-PA-MFRAMS to raising the frequency of sending paging message.

The CCCH alarm report threshold is set 80 generally, but it can be set higher if necessary.

Problem 45 Meaning of electrical tilt angle antenna

Problem

How to calculate the down tilt of the electrical tilt antenna

Detail description

If an antenna is configured with a 7( electrical tilt, the actual down tilt of the antenna is 1(, then is the tilt of the antenna lobe is 8(?

Reply

Electrical tilt is used to change the directional diagram of the antenna system. It plays an important role in controlling the coverage scope of a BTS and clearing the blind spots around a BTS. For an antenna system configured with electrical tilt, the actual down tilt equals to the sum of the electrical tilt and the mechanical tilt. The waveform becomes distorted when the mechanical tilt is greater than 10(.

Therefore, it is necessary to use antennas with electrical tilt angle if the intervals between two neighboring sites are short.

2004-6-4

Confidential Information of Huawei. No Spreading without Permission

Page1, Total18

Documents

Collection of GSM RNP technical problems and replies(No.2)-20040604-A-1.0.pdf