ETSI TC SMG Tdoc SMG 1015 / 97 Meeting No. 24 Agenda item 5.3 Madrid, Spain 15-19 December 1997

Source SMG2

EDGE Feasibility Study Work Item 184;

Improved Data Rates through Optimised Modulation Version 1.0

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Contents

0. SUMMARY ........................................................................................................................................ 3

1. INTRODUCTION.............................................................................................................................. 5

2. RADIO INTERFACE REQUIREMENTS....................................................................................... 6

3. SYSTEM CONCEPT......................................................................................................................... 7

4. LINK PERFORMANCE ................................................................................................................. 12

5. SYSTEM PERFORMANCE........................................................................................................... 21

6. PHYSICAL LAYER ASPECTS...................................................................................................... 28

7. COMPLEXITY ASPECTS ............................................................................................................. 34

8. LINK ADAPTATION...................................................................................................................... 37

9. NETWORK INTERFACE ASPECTS ........................................................................................... 39

10. DOCUMENT HISTORY............................................................................................................... 41

11. GLOSSARY.................................................................................................................................... 41

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0. Summary In December 1996 a work item for “Improved Data Rates through Optimised Modulation” was proposed by SMG2. This work item includes a feasibility study, where the introduction of a new modulation shall be evaluated. In May 1997 the first version of the feasibility study was presented on SMG2 #22, the second version on SMG2 WPB #1. The current version is presented on SMG2 WPB #2.

The basic concept of EDGE is to provide higher data rate transmission per radio time slot than with GMSK modulation. This allows the support of existing services with a lower number of time slots. In addition it allows the introduction of new services with up to 64kbps per timeslot or over 64kbps in multislot constellation, offering hence an evolution path for GSM to support multimedia applications. The feasibility study presented in this document investigates different aspects of introducing a linear, higher level modulation scheme. Additionally a second linear modulation is introduced to ease link adaptation. Quaternary Offset Quadrature Amplitude Modulation (Q-O-QAM) and Binary Offset Quadrature Amplitude Modulation are proposed as the new modulation schemes (other modulation schemes may also be considered, when the actual standardisation begins). Combined with a symbol rate of 361 ksps new services like Enhanced General Packet Radio Service (EGPRS) and Enhanced Circuit Switched Data (ECSD) with significantly higher data rates can be achieved The Enhanced Data rates for GSM Evolution (EDGE) concept can be seen as an extension of today’s GSM. Efficient link adaptation is a key feature for EDGE and should be jointly developed with EDGE.. Three different types of services are evaluated in this study: EGPRS, ECSD NT, where NT stands for non transparent and ECSD T, where T stands for transparent services. EGPRS EGPRS shows very good performance results on both link and system level. Since packet data is expected to be one of the most used data services in the future, this makes EDGE an attractive candidate for a GSM evolution. The services proposed here allows a maximal data throughput range from 11.2 to 65.2 kbps per time slot. On link level the Q-O-QAM based coding schemes show a loss of 3-4 dB sensitivity and 6-7 dB loss of C/I performance. However, in a coverage limited system as well as in an interference limited system a user will always gain in throughput, when EGPRS is selected. Simulations of an ideal 3/9 reuse system show that 50 % of the users in a cell can double their throughput by selecting EGPRS. The simulations have been performed with the same ideal assumptions for GPRS and EGPRS. ECSD/NT The transmission type is similar for EGPRS and non-transparent CSD, allowing re-transmissions, and the increase in radio interface rates due to Q-O-QAM is similar. Hence, an increase in spectral efficiency of the same magnitude as for EGPRS can be expected. ECSD/T The feasibility study proposes two transparent services, 28.8 and 38.4 kbps. On link level a bit error rate of 10-5 can be reached at 22 dB C/I for 28.8 kbps and 27.5 db C/I for 38.4 kbps. At this error rate a 28.8 kbps service could be offered in 40 % of a cell and a 38.4 kbps service could be offered in 19% of an interference limited cell, compared to 71% for 9.6 kbps and 58% for 14.4 kbps for GSM data services. Due to the high requirements concerning bit error rates, transparent services using EDGE are not as advantageous as packet data services, but the service could be offered in a micro, pico or hotspot cell environment. Beside the service oriented simulations several robustness investigations are made. With the selected modulation schemes, burst shape and symbol rate, the requirements from GSM concerning adjacent channel suppression and frequency mask can be fulfilled. This assumes a power amplifier (PA) being available today and a reasonable back off. Frequency error simulations show, that the selected modulation in EDGE is more sensitive to frequency errors than GSM’s modulation, but by applying a

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frequency error tracking algorithm the resulting error and performance degradation can be well compensated. Performance degradation for high speed can be compensated by using link adaptation in EGPRS. For transparent services the speed may be restricted to lower speeds, but this has not been simulated yet. A special focus has been laid on the working assumption to introduce as few changes to the existing GSM standards as possible. It is anticipated though that there will be an impact on mobile stations, the BSS and other network elements. The level of impact (hard- and/or software) is service and implementation dependent Also an asymmetrical air interface allowing to ease mobile complexity by using higher level modulation in the downlink only, but to have GMSK in the uplink is of interest. With the simulation results presented in this study, higher level modulation is shown to be a promising evolution path for GSM and especially interesting for the development of packet based services. Since EDGE is designed as an extension of today’s GSM system, the changes can be introduced gradually. On the other hand EDGE promises through its advanced data services to give GSM a good market share for future mobile multimedia applications.

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1. Introduction This document presents a concept where the use of Higher Level Modulation (HLM) is integrated into the overall GSM structure. Introducing higher level modulation allows higher data rates on a single time slot. Already today GSM has evolved within Phase 2+ to higher data rates for HSCSD and GPRS. The primary way of increasing the data rate has been allocation of multiple slots. The data rate within each time slot has also been increased through the introduction of new coding schemes. The use of higher level modulation and a higher symbol rate increases the air interface grossrate by factor 3 which enables significantly higher data rates. The new concept is called EDGE (Enhanced Data rates for GSM Evolution) and should be viewed as an extension to the GSM standard in the same way as GPRS and HSCSD. In order to achieve the data rates certain restrictions on the radio environment have to be taken into account. The main application environment for EDGE is an urban environment with quasi stationary or slowly moving mobiles. The purpose of this feasibility study is to investigate the performance of the concept and the impact on existing GSM nodes. The current version of the document covers now also transparent and non transparent data services. Additionally comments from SMG2 #22 and SMG2 WPB #1 have been taken into account and are discussed such as for instance linearity aspects, frequency and adjacent channel requirements. The feasibility study focuses on packet and circuit switched data services. Other services, like high quality speech, are also interesting and can be considered when the work on the actual specifications starts. The feasibility study is organised as follows. Different requirements on the new concept are listed in Chapter 2, while Chapter 3 gives an overview of the system concept and principle operation. Link level simulations for the new high level modulation are provided in Chapter 4. The results are compared to existing GSM traffic channels. Chapter 5 presents different system performance aspects, like the percentage of the service area where the higher level modulation can be used and the potential increase in capacity. Chapter 6 provides more details on the physical layer, while complexity issues of terminals and infrastructure are addressed in Chapter 7. Chapter 8 and 9 provide more details regarding the link adaptation and network aspects.

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2. Radio Interface Requirements Since EDGE is meant as an extension to the existing GSM standard, certain requirements have to be met. 2.1 Spectrum Requirements The spectrum requirements for GSM are defined in GSM 05.05, Section 4.2 RF Spectrum. When a new modulation is introduced into the GSM system, this will obviously have an effect on “Spectrum due to modulation and wide band noise”. The spectrum characteristics are however also related to the reference interference levels defined for adjacent channel interference (section 6.3 of GSM 05.05.) A fundamental requirement is that channels using higher level modulation (HLM) have to coexist with connections using the GMSK modulation. This implies several requirements on the HLM: 1. In a GMSK/HLM adjacent channel situation, a HLM carrier should not create more interference to

a GMSK carrier than a GMSK carrier would do in the same position. 2. In a GMSK/HLM adjacent channel situation, the interference from a GMSK carrier to a HLM

carrier should give a reasonable performance degradation. This should be further investigated, but the suppression of adjacent carriers could provisionally be set to the levels implied by section 6.3 in GSM 05.05.

3. An additional spectrum requirement for a HLM carrier is for a HLM/HLM adjacent channel situation. This requirement will depend on the expected link level performance and system scenarios for deploying HLM.

In order to fulfil requirement 1 it is necessary to define a spectrum mask for the new modulation. Since the modulation is different compared to GMSK it is not clear that the spectrum mask defined for GMSK is sufficient (or necessary). 2.2 TDMA Frame Structure The coexistence requirement for EDGE is also a requirements on the TDMA structure. In order to provide easy coexistence between EDGE and GSM the same TDMA frame structure should be used. It is therefore proposed that the multiple access and time slot structure described in GSM 05.01 Section 5 is kept for EGDE, except for modulation symbol rate, type of modulation and burst structure. 2.3 Logical Channel Structure Compatibility with the GSM logical channel structure is also a requirement. GSM signalling should be reused as far as possible. 2.4 Propagation Conditions Mobiles with EDGE capability can provide higher data rates per time slot at the cost of somewhat decreased receiver performance due to the HLM. It is therefore assumed that the MS to BTS distance is smaller than in normal GSM operation. This can either be achieved by smaller cells or by restricting the use of EDGE to central parts of the cell through link adaptation. Realistic environments are indoor pico cells of different kinds (office, corridor, etc.) and urban micro cells (street cells, campus). The requirements for receiver operation will thus be restricted to environments with limited time dispersion and mobile speeds. EDGE operation would not be restricted to such environments, but the coverage would not be complete in large cell, high time dispersion or high mobile speed cases. Of the current GSM channel models, the TU model with excess time dispersion of 5 µs and mobile speeds up to 50 km/h is a realistic environment for evaluation of EDGE.

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3. System Concept This chapter introduces a proposal for a new physical layer and describes how new services can be realised with respect to changes in higher layer protocols, network interfaces and nodes. A discussion on the principle operation of a GSM system using the EDGE extension is also included. 3.1 Physical Layer In order to achieve a higher gross rate, new modulation has to be introduced. Q-O-QAM (Quaternary Offset QAM) is proposed for EDGE, since Q-O-QAM can provide higher data rates and good spectral efficiency 1 2. An offset modulation has is proposed, because it causes smaller amplitude variations than 16QAM, which can be beneficial when using not completely linear amplifiers. The mapping of symbols onto the I/Q plane has been illustrated in Figure 1 . For each symbol two bits are transmitted and consecutive symbols are shifted by π/2 .

Figure 1: Principle symbol mapping for Q-O-QAM A linear modulation, as Q-O-QAM, is more spectrum efficient than GMSK, if a proper pulse shape is selected. Therefore higher symbol rates can be achieved within the same channel bandwidth. The symbol rate is set to 361.111 ksps. Considering the need of training sequence and tail symbols the resulting payload (bit to be used for user data) per burst is increased to 326 bit/burst compared to 114 bit/burst in existing GSM. Additionally a second reduced modulation has been introduced, which has the same symbol rate of 361.111 ksps, but where only the outer signal points of the Q-O-QAM modulation are used. The mapping of symbols onto the I/Q plane has been illustrated in Figure 2. For each symbol one bit is transmitted and consecutive symbols are shifted by π/2 .

Figure 2: Principle symbol mapping for B-O-QAM

1 J. Sköld et. al, “Cellular Evolution into Wideband Services”, Proc. Of VTC ’97, Phoenix, pp. 485-489 2 TDOC SMG2 13/97 “The use of higher level modulation for improved data rates in EDGE”

I

Q

t

T

I

Q

t

T

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This type of modulation can be seen as B-O-QAM. A second modulation scheme with the characteristic of being a subset of the first modulation scheme and having the same symbol rate as the first modulation has several advantages. For link adaptation it allows seamless switching between the two modulation types between bursts. But both modulation types can be used even in one and the same burst. This can be facilitated in an enhanced GPRS solution, where the up link state flag (USF) is modulated with B-O-QAM and user data in Q-O-QAM. B-O-QAM is used here for broadcast purposes and facilities the characteristic of being robust and therefore available in the whole GSM coverage area. The characteristic of being a subset of the first modulation is for enhanced circuit switched services important. Under the assumption to modulate the FACCH in B-O-QAM the FACCH can be detected by just one equalisation. When selecting another symbol rate than the first modulation or a modulation not being a subset of the first modulation, the FACCH detection will get complicated. From a complexity point of view the addition of a modulation, which is subset to the first modulation, adds no new requirements for the transmitter or receiver. A square root raised cosine pulse shape with a roll off factor α = 0.5 has been chosen as illustrated in Figure 3. With the chosen symbol rate and pulse form the spectrum will fulfil the GMSK spectrum mask as shown in section 4.4.1.

−8 −6 −4 −2 0 2 4 6 8

0

0.2

0.4

0.6

0.8

1

Pulse in time domain

Symbol

Am

plitu

de

Figure 3: RRC Impulse with roll off D = 0.5

The following table shows a comparison of fundamental physical layer parameters between EDGE and GSM:

EDGE GSM Modulation Q-O-QAM, 2 bit/sym B-O-QAM, 1 bit/sym GMSK, 1 bit/sym Symbol rate 361.111 ksps 361.111 ksps 270.833 ksps Payload/burst 326 bit 162 bit 114 bit Gross rate/time slot 65.2 kbps 32.4 kbps 22.8 kbps

Table 1: Physical layer parameter comparison

A more detailed description of the physical layer can be obtained in Chapter 6. 3.2 Service Examples The concept of EDGE is exemplified by looking at three different services: • Packet switched services (EGPRS) • Transparent circuit switched data services (ECSD T) • Non-transparent circuit switched data services (ECSD NT)

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3.2.1 Enhanced GPRS Enhanced GPRS offers eight additional coding schemes, which are defined as in Table 3. An EGPRS capable user will have 8 modulation and coding schemes available, compared to 4 for GPRS.

Service name Code rate Modulation Gross rate Radio interface rate*) GPRS CS-1 0.49 GMSK 22.8 kbps 11.2 kbps GPRS CS-2 0.64 GMSK 22.8 kbps 14.5 kbps GPRS CS-3 0.73 GMSK 22.8 kbps 16.7 kbps GPRS CS-4 1 GMSK 22.8 kbps 22.8 kbps

*) The radio interface rate includes the signalling overhead for the RLC/MAC layer.

Table 2: Overview of packet data services for GSM

Service name Code rate Modulation Gross rate Radio interface rate*) EGPRS ECS-1 0.51 Q-O-QAM 65.2 kbps 33.0 kbps EGPRS ECS-2 0.63 Q-O-QAM 65.2 kbps 41.0 kbps EGPRS ECS-3 0.74 Q-O-QAM 65.2 kbps 48.0 kbps EGPRS ECS-4 1 Q-O-QAM 65.2 kbps 65.2 kbps EGPRS ECS-5 0.35 B-O-QAM 32.4 kbps 11.2 kbps EGPRS ECS-6 0.45 B-O-QAM 32.4 kbps 14.5 kbps EGPRS ECS-7 0.52 B-O-QAM 32.4 kbps 16.7 kbps EGPRS ECS-8 0.70 B-O-QAM 32.4 kbps 22.8 kbps

*) The radio interface rate includes the signalling overhead for the RLC/MAC layer.

Table 3: Overview of packet data services for EDGE

As shown in Table 3, the same Radio Interface Rates for B-O-QAM have been selected as for GPRS. This has been done, in order to provide a smooth transition from B-O-QAM to GPRS. Beside the changes in the physical layer modifications in the protocol structure have to be done. The lower layers of user data plane which is specially designed for GPRS is reflected in the protocol stack comprising Physical, RLC/MAC and LLC layers (see Figure 4).While the LLC layer can be used without modifications when EDGE functionality is introduced, the RLC/MAC layer has to be somewhat redesigned to accommodate features for efficient multiplexing and link adaptation procedures that support the basically new Physical layer in EDGE. The RLC/MAC layer is currently defined in the GSM 03.64 specification. The basic modifications needed for EDGE consider the form of the data blocks that are being transferred across the radio interface. For the enhanced GPRS several combinations of interleaving and coding can be envisioned. In the current proposal the interleaving depth has been set to 4 bursts as in GPRS. Link adaptation offers mechanisms for choosing the best modulation and coding alternative for the current radio link. Today, in GPRS only the the coding scheme can be altered between two consecutive LLC frames. In EGPRS a more refined link adaptation concept can be used, since beside coding schemes the modulation can be changed (for details see Chapter 8).

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Figure 4: GPRS Transmission plane

Further the influence on the employed nodes with GPRS functionality have to be investigated. The overall GPRS system architecture can be seen in Figure 5. The most important nodes involved in providing GPRS are GGSN (Gateway GPRS Support Node) and SGSN (Serving GPRS Support Node), together with the functionality in BTS and BSC. The packet data switching and trunking principles in GPRS avoid the fixed bandwidth allocation (supporting connections across the radio interface) already on the Gb interface (i.e. between BSS and SGSN). It limits the influence of introducing EDGE only to BSS. The only open interface that is affected on the network side is the Abis interface. New solutions have to be found to accommodate data rates that exceed 16 kbps per time slot.

GGSN

X.25

Internet

MS MSC

SGSN

BTS

HLR

ISDN

PSTN

BSC

Modifications needed for EDGE

Abis

Gb

Figure 5: GPRS architecture

3.2.2 Enhanced Circuit Switched Data The services proposed here are single time slot proposals. 3.2.2.1 Enhanced Transparent Data Services (ECSD/T) Table 4 shows available circuit switched services in GSM. Table 5 shows the proposals for ECSD/T.

MS

PL

RLC/MAC

LLC

RLC/MAC

LLC RelayLLC

L2bis

L1bis

L2bis

L1bisPL

IP/X.25

Appl.

SNDCP SNDCP

BSS SGSNUm Gb

Modifications needed for EDGE

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Service name Code rate Modulation Gross rate Radio interface rate TCH/F2.4 0.16 GMSK 22.8 kbps 3.6 kbps TCH/F4.8 0.26 GMSK 22.8 kbps 6.0 kbps TCH/F9.6 0.53 GMSK 22.8 kbps 12.0 kbps TCH/F14.4 0.64 GMSK 22.8 kbps 14.5 kbps

Table 4: Overview of transparent services in GSM

Service name Code rate Modulation Gross rate Radio interface rate *) TCH/F ECS-9 0.44 Q-O-QAM 65.2 kbps 28.8 kbps TCH/F ECS-10 0.59 Q-O-QAM 65.2 kbps 38.4 kbps

*) The radio interface rate includes the signalling overhead Table 5: Overview of transparent services in EDGE

The radio interface rates mentioned in Table 5 have to be adjusted to meet a reasonable service rate on the network side. For transparent services link adaptation from Q-O-QAM to B-O-QAM can be feasible, but this is not discussed here. 3.2.2.2 Enhanced Non Transparent Services (ECSD/NT) As in GSM, the non transparent services can be derived from the transparent services, but special care has to be taken to adjust the RLP protocol and coding schemes. Proposals for different service rates should be left to the standardisation process. 3.2.3 Enhanced High Speed Circuit Switched Data In order to provide even higher data rates, multi slot solutions like in GSM HSCSD could be provided in EDGE. Since this has no impact on link or system performance, proposals for different timslot configuration should be left to the standardisation process. 3.3 Principle Operation An operator can gradually upgrade his GSM system to support EGDE in more and more cells. Channels with EDGE functionality should be able to operate dynamically on a slot by slot bases in either existing GSM or EDGE mode. Therefore a fixed partition of GSM and EDGE resources is not necessary. All terminals supporting EDGE will also be able to use existing GSM channels. When an EGDE capable user experience changing C/I conditions the link adaptation will adjust the coding and modulation in order to maximise the quality of the service. Details about link adaptations are provided in chapter 8. In principle the frequency plan can be kept unchanged and also the BCCH carrier planning will not be affected. If an operator wishes to offer the EDGE service with continuous coverage in a special area (office, conference centre, SMG2 meetings, …) consideration of the higher C/I requirement for EDGE has to be taken into account when planning the system. It should be noted that EGPRS and ECSD are extensions to GPRS and current circuit switched services. Hence, e.g. the basic GPRS functions are required for implementation of EGPRS.

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4. Link Performance This chapter contains link performance results for the proposed coding schemes for EDGE as described in chapter 6. Section 4.3 deals with conventional, service oriented simulations. Section 4.4 focuses on the robustness of the chosen modulation scheme and results are presented showing the impact from • non-linear power amplifiers • adjacent channel interference • frequency error • velocity When appropriate, corresponding simulation results for GSM are provided. 4.1 Simulation Assumptions The TU3 (Typical Urban) channel model in GSM 05.05 is used in all simulations. Ideal frequency hopping is assumed, which means that no correlation exists between the fading of any consecutive bursts. The channel is fading according to 3 km/h during the burst. The results are obtained without antenna diversity. Identical simulation assumptions for EDGE and GSM have been chosen. Two different types of simulation results are presented: 1. The link is only disturbed by white noise, hence yielding the performance versus Eb/N0. Eb is here

defined as the bit energy per modulated bit. These results are mainly aimed for coverage estimations.

2. The link is disturbed by one single interferer, hence yielding the performance versus C/I. These results are aimed for capacity estimations. No additional noise is added.

In the EDGE-receiver, a 7 tap channel estimate and synchronisation position is obtained from the mid-amble part of each burst. The equaliser used in the simulations is a sub optimal equaliser with a signal processing complexity, which is approximately 4 times more complex than a conventional MLSE for GSM. The results presented below show a loss in performance of only ~0.5 dB compared to results for a 7 tap MLSE equaliser3. 4.2 Measured Quantities For packet data services the block error rate, BLER, is the most appropriate link performance measure. A block error occurs if one or more bits in a coding block (1 block = 4 bursts) is erroneous after decoding. Perfect error detection is assumed for the simulations. All comparisons between coding and modulation schemes are made at a BLER of 20%, which can be considered as a realistic point of operation in a loaded system. For transparent services the bit error rate, BER, after decoding is presented. 4.3 Simulation Results (Service Oriented) All results in this section are based on simulation of 10000 blocks. 4.3.1 Packet Switched Services 4.3.1.1 EDGE ECS-1 to 8 versus GSM/GPRS CS-1 to 4 Figure 6 and Figure 8 show the BLER versus Eb/N0 for the coding schemes in EDGE for Q-O-QAM and B-O-QAM respectively. Figure 10 shows the corresponding BLER for the coding schemes in GPRS. Comparing ECS-1 to 3 with CS-1 to 3 at 20 % BLER show a sensitivity loss of 3-4 dB for EDGE.

3 Tdoc SMG2 150/97 “EDGE Feasibility Study, Work Item 184; Improved Data Rates through Optimised Modulation”

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When comparing ECS-5 to 8 (B-O-QAM) with CS-1 to 4, which results in the same radio interface rates, there is a gain in sensitivity between 3 and 9 dB. However, note that Eb is the energy per modulated bit and that the higher symbol rate in EDGE results in lower coding rate for the same radio interface rate. The raw BER (not shown) is about the same for the two modulation schemes. BLER versus C/I for ECS-1 to 8 and CS-1 to 4 are shown in Figure 7, Figure 9 and Figure 11 respectively. Comparing corresponding coding schemes for GSM and EDGE at 20 % BLER, show a loss of 6-7 dB in C/I performance for ECS-1 to 3 and an gain between 2 and 4 dB for ECS-5 to 7. The gain is even larger for ECS-8 compared to CS-4.

0 5 10 15 20 25 30 3510

−4

10−3

10−2

10−1

100

Eb/No [dB] (Eb=Energy per modulated bit)

BLE

R

ECS−1 (33.0 kbps)

ECS−2 (41.0 kbps)

ECS−3 (48.0 kbps)

ECS−4 (65.2 kbps)

Figure 6: BLER versus Eb/N0 for EGPRS (Q-O-

QAM)

0 5 10 15 20 25 30 3510

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10−3

10−2

10−1

100

C/I [dB]

BLE

R

ECS−1 (33.0 kbps)

ECS−2 (41.0 kbps)

ECS−3 (48.0 kbps)

ECS−4 (65.2 kbps)

Figure 7: BLER versus C/I for EGPRS (Q-O-

QAM)

0 5 10 15 20 25 30 3510

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10−3

10−2

10−1

100

Eb/No [dB] (Eb=Energy per modulated bit)

BLE

R

ECS−5 (11.2 kbps)

ECS−6 (14.5 kbps)

ECS−7 (16.7 kbps)

ECS−8 (22.8 kbps)

Figure 8: BLER versus Eb/N0 for EGPRS (B-O-

QAM)

0 5 10 15 20 25 30 3510

−4

10−3

10−2

10−1

100

C/I [dB]

BLE

R

ECS−5 (11.2 kbps)

ECS−6 (14.5 kbps)

ECS−7 (16.7 kbps)

ECS−8 (22.8 kbps)

Figure 9: BLER versus C/I for EGPRS (B-O-

QAM)

0 5 10 15 20 25 30 3510

−4

10−3

10−2

10−1

100

Eb/No [dB] (Eb=Energy per modulated bit)

BLE

R

CS−1 (11.2 kbps)

CS−2 (14.5 kbps)

CS−4 (22.8 kbps)

CS−3 (16.7 kbps)

Figure 10: BLER versus Eb/N0 for GPRS

(GMSK)

0 5 10 15 20 25 30 3510

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C/I [dB]

BLE

R

CS−1 (11.2 kbps)

CS−2 (14.5 kbps)

CS−4 (22.8 kbps)

CS−3 (16.7 kbps)

Figure 11: BLER versus C/I for GPRS (GMSK)

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4.3.2 Transparent Circuit Switched Data Services 4.3.2.1 EDGE/T versus GSM/T The proposed coding schemes for transparent services include an inner interleaving over 4 TDMA-frames and an outer interleaving over 6 20ms-blocks (See Chapter 6). The GSM/T services have an inner interleaving over 19 TDMA-frames. The assumptions of ideal frequency hopping and slow mobile stations result in optimistic performance for these coding schemes due to the large interleaving depths. More realistic results can be obtained if the number of frequencies is limited. Therefore the results below are obtained by assuming frequency hopping over 4 uncorrelated frequencies. Both carrier and interferer is using frequency hopping. The velocity is, as before, set to 3 km/h. The next figures compare the GSM/T and EDGE/T coding schemes for BER versus Eb/N0 and BER versus C/I. The required Eb/N0 and C/I for a BER of 10-5 are summarised in Table 6. The inner interleaving depths for EDGE/T are not optimised and better performance may be achieved with a larger inner interleaving depths. Further the outer interleaving may be adjusted to delay requirements.

Service Required Eb/N0 for BER=10-5 Required C/I for BER=10-5 TCH/F9.6 (12.0 kbps) ~14 dB ~15.5 dB

TCH/F14.4 (14.5 kbps) ~16 dB ~18 dB ECS-9 (28.8 kbps) ~15 dB ~22 dB

ECS-10 (38.4 kbps) ~19.5 dB ~27.5 dB Table 6: Performance requirements for GSM/T and EDGE/T services

0 5 10 15 20 25 3010

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10−2

10−1

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Eb/No [dB] (Eb=energy per modulated bit)

BE

R

ECS−9 (28.8 kbps)ECS−10 (38.4 kbps)

Figure 12: BER versus Eb/N0 for EDGE/T

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10−4

10−3

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C/I [dB]

BE

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28.8 kbps (ECS−9) 38.4 kbps (ECS−10)

Figure 13: BER versus C/I for EDGE/T

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Eb/No [dB] (Eb=Energy per modulated bit)

BE

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TCH/F9.6 (12.0 kbps)TCH/F14.4 (14.5 kbps)

Figure 14: BER versus Eb/N0 for GSM/T

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10−3

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C/I [dB]

BE

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TCH/F9.6 (12.0 kbps)TCH/F14.4 (14.5 kbps)

Figure 15: BER versus C/I for GSM/T

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4.3.3 Non-Transparent Circuit Switched Data Services The radio interface rate for non-transparent services, has to be adjusted to both maximum user data rate and protocol overhead. Other aspects on this choice is reuse of coding schemes for other services, transmission etc. Since these parameters and aspects are not investigated from this point of view at this stage, results for non-transparent services are not presented. However, the link performance can be estimated from the EGPRS results presented previously.

16

4.4 Simulation Results (Robustness Investigation) This section contains some investigations of the robustness of the Q-O-QAM modulation scheme in EDGE. Emphasis is put on the co- and adjacent channel interference performance when an existing non linear power amplifier is used in the transmitter. In addition, the effects from velocity and frequency offset between the transmitter and the receiver are presented. When feasible, corresponding results for GSM are presented for comparison. 4.4.1 Non-Linear PA Simulations In contrast to GSM, the linear modulation proposed for EDGE will put requirements on the linearity of the power amplifier. A typical practicable amplifier is close to linear over a large region. However, when the output power increases the amplifier will sooner or later be saturated. In order to prevent a large amount of clipping of the output signal, it is necessary to limit the mean power to a value lower than the maximum output power. This back off value depends on the PA characteristics and is hence a design parameter. There are two different back off values, the input back off and the output back off. In this document the input back off is defined as the difference between the mean power of the input and the 1 dB compression point. From that definition follows that the output back off will be 1 dB less than the input back-off. The method of defining the two different back off values is depicted in Figure 16.

Figure 16: The method of defining input and output back off given the 1 dB compression point. Figure 17 and Figure 18 show measured amplitude and phase characteristics of the power amplifier RF2108 from RF Micro Devices which is used as the PA-model in the simulations. The model hence take into account both amplitude and phase distortion.

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.040

0.2

0.4

0.6

0.8

1

1.2

In amplitude [V]

Out

am

plitu

de [V

]

PA characteristicIdeal PA

Figure 17: Measured amplitude

characteristics of RF2108.

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0494

94.5

95

95.5

96

96.5

97

97.5

98

98.5

99

In amplitude [V]

Out p

hase

[deg

rees

]

Figure 18: Measured phase characteristics of RF2108.

Figure 19 shows the link performance for Q-O-QAM with different back off values. The performance for an ideal power amplifier is also showed as reference. The results show that the impact on performance from non-linearity in the PA is only significant for an input back off less than 5 dB. In the following 5 dB has been chosen as a reasonable input back off value for this PA-model.

Pin

Pout

1dB

Back-offin

1 dB

Back-offout

17

Non-linearity in the PA will also affect the spectrum of the transmitted signal. Especially the spectrum leakage into adjacent channels can be significant if the back off is chosen too small. However, with a 5 dB input back off value, this leakage is about the same as for GMSK, which is shown in Figure 20. It should be noted that the implementation of the pulse shaping will also affect the spectrum leakage and the spectrum in Figure 20 is obtained using a Hanning-windowed RRC-pulse. Further, the chosen amplifier and windowing act only as an example and larger margins to the GSM spectrum mask can be achieved with other alternatives. Similar results for B-O-QAM show that the input back-off can be decreased with at least 2 dB. A reasonable input back off for B-O-QAM is hence 3 dB in order to fulfil performance and spectrum requirements.

6 8 10 12 14 16 18 20 22 24 26

10−2

10−1

C/I [dB]

Raw

BER

3 dB back−off

7 dB back−off

Ideal PA

5 dB back−off

Figure 19: Link performance degradation

due to non linear PA.

−100 0 100 200 300 400 500 600−80

−70

−60

−50

−40

−30

−20

−10

0

frequency [kHz]

P.S

.D. [

dB]

GSM spectrum mask

3 dB back−off

5 dB back−off

7 dB back−off

Ideal PA

Figure 20: Spectrum of transmitted signal.

4.4.2 Adjacent Channel Interference Simulations This section presents results showing the amount of adjacent channel protection achieved when EDGE is introduced in a GSM system. It is important from a co-existence point of view that the same adjacent channel protection as in GSM can be achieved. This ensures that EDGE can be introduced in an already planned system without increasing the adjacent channel interference. Different scenarios can be identified where maybe the most important is when a GSM-carrier is disturbed by an adjacent EDGE-carrier. Results are also presented for the other combinations of a GSM/EDGE carrier and a GSM/EDGE adjacent channel interferer. The measured quantity is the adjacent channel protection which here is defined as the ratio between the strength of an adjacent channel interferer and a co-channel interferer which results in the same performance in terms of BER. In the same way, the adjacent channel protection (ACP) is defined for an interferer separated a certain number of channels from the carrier. ACP-1 is the adjacent channel protection with respect to the first adjacent channel (200kHz), while ACP-2 is the adjacent channel protection with respect to the second adjacent channel (400kHz). Figure 21 schematically shows the used definition of adjacent channel protection (ACP). Note that an ACP is measured at a certain BER. However, in practice the slopes of the graphs are about the same which makes the ACP almost independent of the BER.

Figure 21: Definition of adjacent channel protection.

BER

C/Ix [dB]

C/Ic

C/Ia1C/Ia2

ACP-1

ACP-2

18

The reference interference ratios in GSM 05.05 result in an ACP-1 of 9 dB + 9 dB = 18 dB and an ACP-2 of 9 dB + 41 dB = 50 dB. Simulations have been performed for EDGE/Q-O-QAM estimating the ACP-1 and 2 from the raw BER. The simulations include use of the power amplifier specified in the previous section. Four different scenarios are simulated: first an GMSK carrier with an Q-O-QAM interferer (GMSK/Q-O-QAM), second a Q-O-QAM carrier with an Q-O-QAM interferer (Q-O-QAM/Q-O-QAM). The third scenario is a Q-O-QAM carrier with a GMSK interferer (Q-O-QAM/GMSK) and finally a GMSK carrier with a GMSK interferer is simulated for comparison purpose. The results from the simulations are summarised in Table 7.

Adjacent chan protection ACP-1, 1st adjacent channel (200 kHz)

ACP-2, 2nd adjacent channel (400 kHz)

GSM 05.05 18 dB 50 dB GMSK/Q-O-QAM ~20 dB ~56 dB

Q-O-QAM/Q-O-QAM ~20 dB ~54 dB Q-O-QAM/GMSK ~20 dB ~58 dB

GMSK-GMSK ~20 dB ~64 dB Table 7: Adjacent channel protection for EDGE and/or GSM.

The large adjacent channel protection in the GMSK/GMSK case for the second (400 kHz) adjacent channel might be explained by the fact that an ideal implementation of the GMSK transmitter is assumed. Further, when EDGE is used as interferer, the level of the adjacent channel protection for the first (200 kHz) adjacent channel mainly depends on the spectrum of the modulation pulse, while the level of the adjacent channel protection for the second (400 kHz) adjacent channel mainly depends on the power amplifier characteristics. The conclusion from the adjacent channel protection study is that EDGE fulfils the GSM requirements and hence it is possible to introduce EDGE in an already cell planned system without increasing the adjacent channel interference. The results also show that an adjacent channel interferer (GMSK or Q-O-QAM) is suppressed as much as an adjacent channel interferer in GSM today.

19

4.4.3 Frequency Error Simulations This section contains simulation results showing the performance degradation due to frequency mismatch between transmitter and receiver. Frequency errors can result from both Doppler shift and frequency synchronisation errors between the transmitter and the receiver. Realistic Doppler shift in the EDGE environment can be estimated for the 900 MHz band up to 50 Hz (60 km/h) and for the 1900 MHz band up to 100 Hz. GSM 05.10 allows for a frequency error of 0.1 ppm in the mobile station, which results in about 100 Hz for GSM900 and 200 Hz for PCS1900. The impact from frequency error can be reduced by introducing an AFC (Automatic Frequency Control) algorithm in the equaliser. Simulations are performed with a non-optimised algorithm which acts on burst basis, i.e. the frequency correction is made independently between any consecutive bursts. Performance improvement is expected if the AFC-algorithm takes into account the estimated frequency error from previous bursts. Figure 22 shows the link performance for frequency errors between 0 and 300 Hz. By introducing the AFC-algorithm the performance without frequency error is degraded with approximately 0.1-0.2 dB at a BER of 1%. With a frequency error of 300 Hz the performance degradation is ~1.5 dB at 1% BLER.

0 5 10 15 20 25 30 3510

−4

10−3

10−2

10−1

100

C/I [dB]

Raw

BE

R

Freq error = 0 Hz Freq error = 100 Hz Freq error = 200 Hz Freq error = 300 Hz Freq error = 0 Hz, No AFC

Figure 22: RawBER with AFC for ECS-3

20

4.4.4 Velocity Simulations Although the primary application environment for EDGE is best described by TU3, simulation results for TU with different velocities are shown below. The results are obtained for a 900 MHz system without AFC (Automatic Frequency Correction). Note that an AFC algorithm is expected to improve the performance for channels with low time dispersion. In the following figures BLER versus C/I for the ECS-3 coding scheme in EDGE and the CS-3 coding scheme in GSM/GPRS are shown for the velocities 3km/h, 10km/h, 50km/h and 100km/h.

0 5 10 15 20 25 3010

−3

10−2

10−1

100

C/I [dB]

Blo

ck E

rror

Rat

e, B

LER

TU3

TU10

TU50

TU100

Figure 23: BLER versus C/I for EDGE/EGPRS

ECS-3

0 5 10 15 20 25 3010

−4

10−3

10−2

10−1

100

C/I [dB]B

lock

Err

or R

ate,

BLE

R

TU3

TU10

TU50

TU100

Figure 24: BLER versus C/I for GSM/GPRS

CS-3 As expected the curves for TU3 and TU10 are almost identically for EDGE and GSM. At higher speeds like 100 km/h, the EDGE performance at 20 % BLER - a typical point of operation for packet switched services - degrades by 2 dB compared to TU3, whereas the degradation for GSM is negligible.

21

5. System Performance This chapter shows examples of simulated system performance characteristics for selected Enhanced GPRS and Enhanced CSD services. Coverage and capacity figures are compared with those of standard GPRS and standard circuit switched services. It is seen that the spectral efficiency of the system is increased when EDGE is introduced, for EGPRS it is more than doubled. 5.1 System Simulation Models and Assumptions The simulation environment includes a regular cellular layout consisting of a large number of equally sized 3-sector macro cells. The distance attenuation is calculated according to the formula L = C + 35 * log(d). Lognormal fading with 6 dB standard deviation is assumed. Cell selection is performed based on least path loss, apart from an uncertainty of 3 dB due to the handover margin. No antenna diversity is used. Only the downlink is studied. Further, the simulations are static, i.e. snapshots of the system are taken, in which non-moving mobiles are placed randomly according to a uniform distribution. The link level results from section 4.3, assuming ideal frequency hopping, are used. Both coverage limited systems (no co-channel interference) and interference limited systems (co-channel interference >> thermal noise) are analyzed. The cell size in the coverage limited system evaluation is set to obtain an Eb/N0 distribution that corresponds to 95% coverage for GSM full rate speech, which requires Eb/N0 = 6 dB. The interference limited system uses a standard 3/9 frequency reuse, and is assumed to be fully loaded. Full load is an unlikely situation in a real system, but for the purpose of comparison it is still relevant. The available spectrum is 14.4 MHz, resulting in 8 carriers per sector. For simplicity, the pessimistic assumption that no power control is used is made, which has a negative effect on the results of the interference limited system. The simple models and assumptions used here may result in uncertain absolute values, but since the same models and assumptions are used for both standard GSM and EDGE, a fair comparison can be made. 5.2 System Simulation Results The system simulations for the coverage and interference limited systems result in CDFs of Eb/N0 and C/I respectively (Figure 25 and Figure 26). These distributions are the basis of the system performance evaluations below. Notice the difference in the Eb/N0 distributions for the new modulation schemes, assuming the same transmitter output power, the difference is only due to the different gross bitrates compared to GMSK.

0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

70

80

90

100

Q−O−QAM

B−O−QAM

GMSK

Eb/N0 [dB]

C.D

.F. [%

]

Figure 25. The Eb/N0 distributions for GMSK, B-O-QAM and Q-O-QAM in a system designed

for 95% speech coverage

0 5 10 15 20 25 30 35 40 45 500

10

20

30

40

50

60

70

80

90

100

C.D

.F. [%

]

Downlink C/I [dB] Figure 26. The C/I distribution in a fully

loaded system with 3/9 reuse

22

The Eb/N0 differences for Q-O-QAM and B-O-QAM compared to GMSK can easily be calculated as:

∆ Eb Q O QAMGMSK

Q O QAM

R

RdB− −

− −= = = −

270 833

722 2224 3

.

..

∆ Eb B O QAMGMSK

B O QAM

R

RdB− −

− −= = = −

270 833

36111113

.

..

Thus, only the Eb/N0 distribution for GMSK is simulated, the distributions for B-O-QAM and Q-O-QAM are then derived using the above formulas. The C/I distribution is not affected by the choice of modulation scheme. 5.3 Enhanced GPRS For GPRS, it is further assumed that each communication link can always choose the modulation and coding combination that achieves the highest throughput for the current link quality, i.e. ideal link adaptation. The selection of modulation and coding in an interference limited system is illustrated by Figure 27, which is based on link level BLER simulation results. The principle is the same in coverage limited systems. The throughput Sc for each coding scheme c is simply defined as:

( )S R BLERc c= −1

where Rc and BLERc are the radio interface rate and block error rates respectively for coding scheme c.

0 5 10 15 20 25 30 35 40 45 500

10

20

30

40

50

60

70

C/I [dB])

Thr

ough

put S

[kbp

s]

ECS−4 (65.2 kbps)

ECS−3 (48.0 kbps)

ECS−2 (41.0 kbps)

ECS−1 (33.0 kbps)

ECS−8 (22.8 kbps)

ECS−7 (16.7 kbps)

ECS−6 (14.5 kbps)

ECS−5 (11.2 kbps)

Ideal Link Adaptation

Figure 27. Throughput with different modulation and coding schemes as a function of channel

quality. For each link the scheme with highest throughput is selected. By combining the above throughput results with the Eb/N0 and C/I distributions, throughput distributions can be derived using simple formulas, where the link quality of each user is mapped on a corresponding maximum throughput. The maximum throughput Si for each user in a coverage limited system is defined as:

( )( )[ ]{ }S R BLER E Nic

c c b i= −max /1 0

and in an interference limited system as:

( )( )[ ]{ }S R BLER C Iic

c c i= −max /1

23

where (Eb/N0)i is the Eb/N0 for user i, and (C/I)i is the C/I for user i. Throughput CDFs are shown in Figure 28 and Figure 29. These figures show that all users in both the coverage limited and interference limited system achieve a higher throughput when EDGE is used; the median throughput, read at 50% on the vertical axis in the CDFs, is approximately doubled, from 15 -20 kbps to 35 - 40 kbps.

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

100

C.D

.F. [%

]

Throughput S [kbps]

GPRS EGPRS

Figure 28. Throughput CDFs for GPRS and

EGPRS in a coverage limited system

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

100

C.D

.F. [%

]

GPRS EGPRS

Throughput S [kbps] Figure 29. Throughput CDFs for GPRS and EGPRS in an interference limited system

The relative usage of the different EDGE realizations is given in Figure 30 and Figure 31. It is seen that 80% of the users in the coverage limited system and 95% of the users in the interference limited system use the HLM realizations (ECS-1 - ECS-4). Notice that even the fraction of the EDGE users using B-O-QAM realizations, below 20% and 5% in Figure 28 and Figure 29 respectively, achieve a higher throughput than the standard GPRS users. Thus, the introduction of B-O-QAM not only simplifies link adaptation, but also increases the throughput.

ECS−5 ECS−6 ECS−7 ECS−8 ECS−1 ECS−2 ECS−3 ECS−40

5

10

15

20

25

30

35

Usa

ge o

f diff

eren

t cha

nnel

type

s [%

]

Figure 30. The relative usage of the EGPRS

channels in a coverage limited system

ECS−5 ECS−6 ECS−7 ECS−8 ECS−1 ECS−2 ECS−3 ECS−40

5

10

15

20

25

30

35

Usa

ge o

f diff

eren

t cha

nnel

type

s [%

]

Figure 31. The relative usage of the EGPRS channels in an interference limited system

Figure 32 and Figure 33 show the usage of the standard GPRS realizations. From these figures it can be seen that the majority of the users choose the least robust realization CS-4, even in the fully loaded interference limited system. This motivates the introduction of the less robust HLM realizations.

24

CS−1 CS−2 CS−3 CS−40

10

20

30

40

50

60

70

Usa

ge o

f diff

eren

t cha

nnel

type

s [%

]

Figure 32. The relative usage of the standard GPRS channels in a coverage limited system

CS−1 CS−2 CS−3 CS−40

10

20

30

40

50

60

70

Usa

ge o

f diff

eren

t cha

nnel

type

s [%

]

Figure 33. The relative usage of the standard

GPRS channels in an interference limited system

Finally, the spectrum efficiency for the interference limited system can be calculated as:

[ ]υ = =∑ S

MWkbps cell MHz

ii

N

1 / /

where Si is the throughput of user i, N is the number of served users, M is the number of cells and W is the total available spectrum. A comparison of interesting standard GPRS and EDGE services is given Table 8. It is seen that the spectral efficiency is more than doubled, from 79 kbps/cell/MHz for standard GPRS to 168 kbps/cell/MHz when using EDGE.

Service Peak bit rate (kbps) Spectral efficiency (kbps/cell/MHz)

3-slot GPRS 3*22.8 = 68.4 79 1 slot EGPRS 65.2 168

Table 8. Spectral efficiency for some GPRS and EGPRS services. 5.3.1 The System Performance Impact of Different Reuse Patterns and System Loads Table 9 shows how the mean throughput and spectral efficiency of EGPRS in an interference limited system is affected by different frequency reuse patterns and different system loads. Notice how the mean throughput per user decreases as the interference in the system is increased, i.e. heavier load and tighter reuse. However, also notice that the spectral efficiency increases as the reuse is tightened and the load is increased, since more user now are served by the system.

EGPRS Standard GPRS Reuse Load Smean

[kbps] ν

[kbps/MHz/cell] Smean

[kbps] ν

[kbps/MHz/cell] Smean and ν increase

4/12 50% 50 82 21 35 137% 100% 45 140 20 63 122% 3/9 50% 46 100 20 45 122% 100% 40 168 19 79 113% 1/3 50% 33 218 16 108 102% 100% 26 326 14 174 87%

Table 9. Mean throughput and spectral efficiency for some different reuse patterns and system loads.

5.4 Enhanced CSD Enhanced CSD can operate in both a transparent and a non-transparent mode. This section focuses mainly on the performance of the transparent Enhanced CSD mode.

25

5.4.1 Transparent ECSD For the transparent services, the performance measures are coverage and availability. Coverage is defined as the fraction of users having an Eb/N0 value high enough to fulfill the required bit error ratio, whereas availability is defined as the fraction of users having a C/I value high enough to fulfill the required bit error ratio. Availability can also be defined by means of the often used term outage, as Availability = 1-Outage. To determine the coverage and availability of the transparent services, the bit error rate results from the link simulations is combined with the Eb/N0 and C/I distributions from the system simulations. Figure 34 and Figure 35 show the coverage and the availability of the different transparent CSD and ECSD services in a coverage and interference limited system respectively. For example: if a bit error rate of 10-5 is required, it is seen that the ECS-9 service is available to 32% of the users in the coverage limited system, and 40% of the users in the interference limited system. The corresponding figures for TCH/F14.4 (14.5 kbps) are 48% and 58% in the coverage limited and interference limited systems respectively. As expected, in the studied macro cellular systems, the HLM realizations have a reduced coverage and availability compared to the ones using GMSK. However, this does not mean that EDGE is not suitable for use with transparent services. Better coverage is easily obtained by using smaller cells, whereas better availability can be achieved by placing system hot spots where higher data rates are needed. For macro cells, link adaptation could be employed. Users in central parts of the cell use EDGE channels, requiring fewer time slots for a certain service, compared to more remote users using standard channels.

10−7

10−6

10−5

10−4

10−3

10−2

10−1

100

0

10

20

30

40

50

60

70

80

90

100

TCH/F9.6 (12 kbps)

TCH/F14.4(14.5 kbps)

ECS−9 (28.8 kbps)

ECS−10 (38.4 kbps)

Required Bit Error Rate

Co

vera

ge

[%

]

Figure 34. The coverage of the CSD and

ECSD services as a function of required bit error rate for a coverage limited system

10−7

10−6

10−5

10−4

10−3

10−2

10−1

100

0

10

20

30

40

50

60

70

80

90

100

TCH/F9.6 (12 kbps)TCH/F14.4

(14.5 kbps)

ECS−9 (28.8 kbps)

ECS−10 (38.4 kbps)

Required Bit Error Rate

Ava

ilab

ility

(1

−O

uta

ge

) [%

]

Figure 35. The availability of the CSD and ECSD services as a function of required bit

error rate for an interference limited system For the interference limited system, it is also possible to calculate the spectral efficiency for different bit error rate requirements. For transparent services, the definition of spectral efficiency is somewhat different to the one for non-transparent services: only the fraction of users fulfilling its specified BER requirement contributes to the spectral efficiency. This leads to the following definition of spectral efficiency:

( ) ( ) [ ]υ BERR A BER N

MWusers cell MHz=

⋅ ⋅/ /

where R denotes the bit rate on the radio interface, and A(BER) is the availability as a function of bit error rate requirement, see Figure 35. The spectral efficiency for the different CSD and ECSD services is shown in Figure 36. It is seen that the ECS-9 (28.8 kbps) service is the most spectral efficient for most practically usable bit error rates.

26

10−7

10−6

10−5

10−4

10−3

10−2

10−1

100

0

20

40

60

80

100

120

140

160

TCH/F9.6 (12 kbps)

TCH/F14.4 (14.5 kbps)

ECS−9 (28.8 kbps)

ECS−10 (38.4 kbps)

Required Bit Error Rate

Spe

ctra

l Effi

cien

cy [k

bit/s

/MH

z/ce

ll]

Figure 36. The spectral efficiency of the different CSD and ECSD services as a function of bit error

rate requirement 5.4.2 Non-Transparent ECSD No system level simulations have been run for the non-transparent ECSD services. However, an increase in spectral efficiency of the same magnitude as for EGPRS can be expected. This is based on that the transmission type is mainly the same for EGPRS and non-transparent ECSD, allowing retransmissions; and that the increase in radio interface rates for ECSD compared to standard CSD is approximately the same as for EGPRS compared to standard GPRS. 5.5 The Effect of Transmitter Back-Off in a Coverage Limited System Transmitter back-off is defined in section 4. The result of the back-off is that a lower average output power has to be used for B-O-QAM and Q-O-QAM compared to GMSK, assuming the same peak output power. This immediately influences the Eb/N0 distribution of the system, Figure 37 shows Eb/N0 distributions when the back-off is introduced. In this section input power back-off values of 5 dB for Q-O-QAM and 3 dB for B-O-QAM are assumed. This corresponds to a decrease of the output power by 4 dB for Q-O-QAM and 2 dB for B-O-QAM .

−5 0 5 10 15 20 25 30

10

20

30

40

50

60

70

80

90

100

Downlink Eb/No [dB]

C.D

.F. [

%]

Q−O−QAM 5 dB back−offQ−O−QAM no back−off B−O−QAM 3 dB back−offB−O−QAM no back−off GMSK

Figure 37. Eb/N0 distributions when transmitter back-off is introduced.

For non-transparent services, the effect off the back-off is given in Figure 38. It is seen that the throughput is significantly lowered; but still, 92% of the users achieve a higher throughput when EDGE is introduced. Notice however also that B-O-QAM performs slightly worse than GMSK for the

27

remaining 8% of the users, switching to GMSK instead of B-O-QAM could thus be considered in this case. The relative usage of the channels is given in Figure 39, where it is seen that as the back-off is introduced, the more robust realizations are used more often. Notice that the transmitter back-off has no effect on the C/I distribution, i.e. in an interference limited system the system performance is not affected.

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

100

C.D

.F. [%

]

EGPRS3 dB / 5 dB back−off

GPRS

EGPRS0 dB back−off

Throughput S [kbps] Figure 38. Throughput CDFs with and

without transmitter back-off

ECS−5 ECS−6 ECS−7 ECS−8 ECS−1 ECS−2 ECS−3 ECS−40

5

10

15

20

25

Usa

ge o

f diff

eren

t cha

nnel

type

s [%

]

no back−off 3 dB / 5 dB back−off

Figure 39. The relative usage of the EGPRS

channels with and without transmitter back-off

28

6. Physical Layer Aspects The link level simulations in chapter 4 have been based on a specific implementation of the physical layer. EDGE supports two type of modulation Q-O-QAM and B-O-QAM, which is specified in more detail in this chapter. 6.1 TDMA Frame Structure The TDMA frame format and the time slot structure is kept like defined in GSM05.02. 6.2 Symbol Rate As in the GSM, the symbol rate has been derived from a 13 MHz clock but in the case of EDGE with a divisor of 36. This results in a symbol rate of 361.111 ksps. For Q-O-QAM the modulating bit rate in EDGE corresponds to 722.222 kbps, since 2 bits per symbol are used. For B-O-QAM, where only one bit per symbol is used, a modulating bit rate of 361.111 kbps is used. In a time slot allocated to a mobile transmitting in EDGE mode, 361.111 ksps * 576.92 µs or 208.333 symbols can be transmitted per burst, in contrast to 156.25 symbols in the GSM case. One TDMA frame hence comprises 1666.666 symbols for EDGE, compared to 1250 symbols in GSM, as shown in Table 10.

EDGE (Q-O-QAM) EDGE (B-O-QAM) GSM Time slot duration 576.92 µs 576.92 µs 576.92 µs 13 MHz divisor 36 36 48 Symbol rate 361.111 ksps 361.111 ksps 270.833 ksps Symbol period, T 2.769 µs 2.769 µs 3.692 µs Modulating bit rate 722.222 kbps 361.111 kbps 270.833 kbps Symbols per burst 208.333 208.333 156.25 Symbols per TDMA frame 1666.666 1666.666 1250

Table 10: Comparison of basic EDGE and GSM parameters 6.3 Burst Structure Figure 40 shows the principle format of a normal burst in GSM as defined in GSM 05.02.

Figure 40: Normal burst format in EDGE and GSM

TSS IS IS GP TS TS

576.92 µs

29

In EDGE the same principle format is used, but adapted to the higher symbol rate as shown in Table 11:

EDGE (Q-O-QAM) EDGE (B-O-QAM) GSM Tail symbols (TS) 2 2 3 Information symbols (IS) 82 82 58 Training sequence symbols (TSS)

28 28 26

Guard period (GP) 12.333 (34.153 µs) 12.333 (34.153 µs) 8.25 (30.462 µs) Table 11: Burst structure of EDGE and GSM

In EDGE the training sequences are derived from those used in GSM, by taking the sequences and adding one symbol on each side using cyclic repetition. Hence 8 training sequences are available in EDGE. The guard period in EDGE has been dimensioned at least as large as the GSM period. The information symbols contain as in GSM 2 stealing bits. Table 12 shows, that with EDGE significantly more information bits can be transmitted.

EDGE (Q-O-QAM) EDGE (B-O-QAM) GSM Information bits per burst 326 + 2 stealing bits 162 + 2 stealing bits 114 +2 stealing bits Gross rate (exclusive stealing bits)

65.2 kbps 32.4 kbps 22.8 kbps

Table 12: Grossrate and information bits for EDGE and GSM 6.4 Modulation 6.4.1 Mapping of Q-O-QAM Symbols The input signal of the modulator is a burst of modulating bits d(i). Two consecutive bits {d(2k),d(2k+1)}are mapped to one symbol a(k). The mapping of modulating bits to symbols is defined in Table 13:

{d(2k),d(2k+1)} a(k)

(0 , 0) +3

(0 , 1) +1

(1 , 0) -3

(1 , 1) -1

Table 13: Mapping of bits to Q-O-QAM symbols The symbols a(k) are multiplied with ejkπ/2 to generate the symbols b(k) which are given by:

b(k) = a(k) ejkπ/2

6.4.2 Mapping of B-O-QAM Symbols The input signal of the modulator is a burst of modulating bits d(i). One bit d(k) is mapped to one symbol a(k). The mapping of modulating bits to symbols is defined in Table 13.

{d(k)} a(k)

(0) +3

(1) -3

Table 14: Mapping of bits to symbols

The symbols are multiplied with ejkπ/2 to generate the symbols b(k) which are given by:

b(k) = a(k) ejkπ/2

30

6.4.3 Filtering The symbols a(k) are fed into a linear square root raised cosine pulse shaping filter with an impulse response given by:

h tt T t T t T

t t T( )

( / ( )) cos( ( ) / ( )) sin( ( ) / ( ))

( ( / ( )) )=

+ + −−

4 2 1 2 1 2

1 4 2 2

α π α π απ α

where α denotes the roll-off factor, which is defined by α = 0.5. Figure 41 shows the impulse response of h(t) in the time domain.

−8 −6 −4 −2 0 2 4 6 8

0

0.2

0.4

0.6

0.8

1

Pulse in time domain

Symbol

Am

plitu

de

Figure 41: RRC impulse with D = 0.5

The generated complex-valued baseband signal is given by

~( ) ( ) ( )x t b k h t kTk

= −∑

6.4.4 Frequency Translation

The modulated RF carrier may be expressed as:

x t E T x t f tc( ) / ~( ) cos( )= +2 0 0π ϕ

where Ec is the average energy per symbol, f0 is the carrier frequency, and ϕ 0 is a random phase,

which is constant during one burst. 6.5 Channel Coding 6.5.1 Enhanced General Packet Radio Services (EGPRS) Four coding schemes for EDGE and Q-O-QAM modulation are specified, as well as four coding schemes for EDGE and B-O-QAM modulation. 6.5.1.1 Q-O-QAM Coding Schemes (ECS-1-ECS-4) Figure 42 shows the channel coding structure for Q-O-QAM.

31

Conv. Coding

Class 1 Class 0

PuncturingP1

Grouping

Interleaving

Burst N Burst N+1 Burst N+2 Burst N+3

PuncturingP2

Figure 42: Channel coding structure The incoming bits are first convolutionally encoded. The resulting bits are split in two classes according to the different error protection requirements for the two levels of the 4-ary symbols. The two classes are then individually punctured and their contents grouped into dibits, with one bit from class 0 and one bit from class 1. Then the dibits are interleaved rectangularly over 4 bursts and mapped accordingly. Table 15 shows the coding and puncturing parameters for the different coding schemes.

Coding scheme ECS-4 ECS-3 ECS-2 ECS-1 Radio Interface Rate (kbps) 65.2 48.0 41.0 33.0

Input bits (per 20ms block) 1304 960 820 660

Convolutional coding rate n.a. ½ ½ 1/3

Polynoms n.a. G0, G1 G0, G1 G0, G1, G2

Tail bits n.a. 6 6 6

Number of class 0 bits 652 712 892 774

Number of class 1 bits 652 940 1040 1224

Remaining class 0 bits after puncturing

n.a 652 652 652

Remaining class 1 bits after puncturing

n.a 652 652 652

Output bits 1304 1304 1304 1304

G0 = 1 + D2 + D3 + D5 + D6 ,G1 = 1 + D + D2 + D3 + D6 ,G2 = 1 + D + D4 + D6

Table 15: Coding and puncturing parameters 6.5.1.2 B-O-QAM Coding Schemes (ECS-5 - ECS-8) Figure 43 shows the channel coding structure for B-O-QAM.

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Figure 43: Channel coding structure The incoming bits, delivered in 20ms blocks, are convolutionally encoded, punctured and rectangular interleaved over 4 bursts. Table 16 shows the coding and puncturing parameters for the different coding schemes.

Coding schemes ECS-8 ECS-7 ECS-6 ECS-5 Radio interface rate 22.8 16.7 14.5 11.2

Input bits 456 334 290 224

Tail bits 6 6 6 6

Convolutional coding rate ½ ½ 1/3 1/3

Polynoms as ECS-2 as ECS-2 as ECS-1 as ECS-1

Nr of punct. bits 276 32 240 42

Ouput bits 648 648 648 648

Table 16: Coding and puncturing parameters The 648 output bits are equivalent to 4 x 162 bits, which are block rectangular interleaved over 4 bursts. 6.5.2 Transparent Circuit Switched Data Services (ECSD/T) The transparent services are designed with an inner and an outer coding. In order to provide as low bit error as possible Reed Solomon coding is used for outer coding. Otherwise the same coding principle is used for the inner coding as for EGPRS. The transparent services work with an inner rectangular interleaving over 4 bursts.

Figure 44: Principle coding schema for transparent services The following parameters characterise the data services, as show in Table 17.

Conv. Coding

Puncturing

Interleaving

Burst N Burst N+1 Burst N+2 Burst N+3

Conv. CodingaccordingEGPRS

Symb. interleav.

RS Coding

33

ECS-9 ECS-10 Radio Interface rate 28.8 kbps 38.4 kbps

Input bits 576 768

Outer interleaving 6 6

Bit per RS symbol 8 8

RRS 0.71 0.8

RCC 0.63

0.74

Rtotal 0.45 0.59

Inner coding scheme ECS-2 ECS-3

Table 17: Coding and puncturing parameters for ECSD/T 6.5.3 Non Transparent Circuit Switched Data Services (ECSD/NT) The non transparent services should be derived from the transparent services and are left for the standardisation process. 6.6 Ciphering With the selected modulation and coding schemes, the same ciphering algorithms as for GSM can be employed. The only difference is that more bits have to be ciphered per bursts.

34

7. Complexity Aspects This section presents the expected complexity impacts on mobiles and base station radio interface. Network aspects are covered in Section 9. 7.1 General Aspects Introducing EDGE has several impacts on the mobile complexity. The major changes in the specifications that will have impact are 1. The higher data rate requires more processing power and memory 2. New coding and interleaving schemes 3. New burst formats, including training sequences 4. New modulation schemes, including a new symbol rate 5. Link adaptation schemes. The changes impact several parts of the mobile, such as memory requirements, signal processing and RF parts. An important issue is that all changes need to be done considering the “dual mode” requirements, i.e. that both GSM and EDGE are implemented in the same terminal without major implications. 7.1.1 Modulation Rate and Clock Rate The modulation rate in EDGE is chosen to be 361.111 ksymb/s, which is 13 MHz divided by 36. There are three symbol rates that are easily generated in the range 320-360 ksymb/s and they all have different impacts on complexity. Table 18 gives a summary of the Rx and Tx clocks and timing, together with reference figures for the GMSK modulation. Modulation Symbol rate Burst length TDMA frame length Symbol rate 4x symbol rate Q-O-QAM 361111 208 1/3 symbols 1666 2/3 symbols 13 MHz / 36 13 MHz / 9 Q-O-QAM 346667 200 symbols 1600 symbols 26 MHz / 75 26 MHz / 15 = 5x Q-O-QAM 325000 187 1/2 symbols 1500 symbols 13 MHz / 40 13 MHz / 10 GMSK 270833 156 1/4 symbols 1250 symbols 13 MHz / 48 13 MHz / 12

Table 18: Interesting symbol rates for EDGE

The highest symbol rate is the most desirable, but as can be seen in the table, it has a slight disadvantage in terms of the burst and TDMA frame lengths. The odd 1/3 symbol means that the burst lengths are defined to be 208, 208 and 209 in groups of three bursts (similar to the GMSK bursts). A consequence is that they do not add up to an integer number of symbols over a TDMA frame. This problem is believed to be small. The ease of generating the symbol rate plus an over-sampled symbol rate from a 13 MHz clock is more important and in this aspect, the 361 ksymb/s rate is a good choice compared to 347 kbps, which does not have these advantages. Together with the higher user bit rate possible to achieve, this therefore weights over to the advantage of 361 ksymb/s as the choice of symbol rate. 7.1.2 Memory Due to the high data rates the memory consumption for interleaving and buffering increases. A data frame in EDGE coming into the interleaver consists of a maximum of 1304 bits per time slot. At de-interleaving it results into 1304 soft decision values, each consisting of e.g. 4 bits. This is not a high memory requirements compared to GSM, which has diagonal interleaving over 19 bursts. For multislot solutions the amount has to be multiplied with the number of allocated time slots. For transparent services the outer interleaver requires memory for more bits, but the stored bits will then be hard decisions, each requiring only one bit of memory.

35

7.1.3 Transmitter Baseband Processing The HLM is a linear modulation, also with a different constellation than the non-linear GMSK and will therefore require changes to the modulator. The symbol rate change and the doubling of the bit rate (2 bits/symbol) will also impact Tx baseband complexity. The introduction of B-O-QAM in addition to Q-O-QAM does not add any extra complexity on the baseband modulator, since it uses the same pulse shaping and is a subset of the higher level modulation. The coding and interleaving schemes are new and of different structure compared to GSM. The schemes also involve larger blocks of data with increased memory requirement as a consequence. 7.1.4 Power Amplifier Requirements The linear modulation will require a higher linearity of the power amplifier in contrast to GMSK. This implies a different amplifier implementation and a back-off for the amplified signal. The back-off will depend on the Crest factor for the modulated signal. The back-off means that a PA has to be dimensioned for higher power than it will be used for. The non-linearity of the PA will cause a modulation error and a widening of the modulated spectrum. The latter effect is more critical because of the spectrum mask and out-of band emission limitations. Since the new modulation schemes are offset schemes, the Crest factor of the modulated signal is reduced and especially the need for dynamic range down to low amplitude is minimised. This will ease both the generation and amplification of the modulated signal. The power amplifier requirements for the Q-O-QAM modulation is studied in section 4.4. A realistic back-off for the PA is found to be 5 dB. The B-O-QAM modulation has a lower Crest factor and will need on the order of 3 dB back-off. This implies that B-O-QAM can operate at approximately 2 dB higher peak power than Q-O-QAM using the same amplifier. 7.1.5 Receiver Filter In order to keep the complexity of the mobile at a minimum, it is desirable that EDGE and GSM can operate with the same receiver filter. The impacts of this should be investigated. 7.1.6 Receiver Baseband Processing The receiver requirements will be different from GMSK modulation, because of HLM and higher symbol rates. An equaliser will be needed that can equalise up to 3 Q-O-QAM symbols of time dispersion, depending on the required propagation conditions. Because of the Inter Symbol Interference (ISI) introduced by modulation and receiver filtering, it is expected that at least a 6 tap equaliser is needed. An optimal MLSE equaliser will then have 1024 states, which is most likely too complex. Sub optimal algorithms can be used to reduced complexity. The simulations in Section 4 of this report are performed with a sub optimal 7-tap equaliser which is approximately 4 times more complex than a conventional GSM equaliser. The performance however is only approximately 0.5 dB below that of an optimal 7-tap (4096-state) MLSE equaliser. Since the B-O-QAM modulation is a subset of the Q-O-QAM modulation and has the same symbol rate it can use the same receiver structure including the equaliser. This implies that no additional receiver complexity is introduced. The decoding schemes are also new and have constraint length 7, which makes decoding 4 times more complex per decoded bit than for GSM. The basic increase in data rate is an obvious complexity increase.

36

7.2 Mobile Station Aspects 7.2.1 Multi-Slot Mobile Stations The mobile station RF complexity increases in case of duplex operation rapidly if more than 2+2 or 3+1 time slots (up + down link) is to be implemented. A considerable advantage with EDGE is that a certain peak user data rate can be achieved using fewer time slots. With rate 3/4 convolutional coding, EDGE can provide 48 kbps radio interface rate per time slot, while GPRS (with GMSK modulation) provides 16.7 kbps. With this coding, a 3+1 slot mobile using EDGE makes possible peak rates of 144+48 kbps. Using GPRS (GMSK), a 8+3 slot mobile would give 133.6+50.1 kbps, which is still not as good. Such a mobile would require duplex filter and an extra receiver for MAHO measurements. EDGE has thus a considerable advantage in making higher bit rates possible at a lower RF complexity cost. 7.2.2 Comparison HSCSD - EDGE An comparison of complexity issues for a mobile station shows Table 19. Compared are an EDGE mobile in an asymmetric mode (EDGE in the downlink, GMSK in to uplink) and an HSCSD mobile with a 3+1 time slot constellation. EDGE (asymmetrical service) HSCSD (3+1) Max gross bit rate downlink uplink

65.2 kbps 22.8 kbps

68.4 kbps 22.8 kbps

Memory Due to short inner interleaving lower than for single slot GSM data service (19 interleaving)

Higher than in single slot GSM data service due to buffering of 3 slots

RF transmitter Same as GSM Same as GSM RF receiver More complex compared to GSM

due to the fact that two symbol rates have to be handled

Same complexity as GSM

Power consumption Lower power consumption, RF components have to be active for one time slot

Higher power consumption, RF components have to active for 3 time slots

Channel decoding Complexity is highly depending on the selected constraint length and is higher compared to a HSCSD solution

Lower complexity compared to EDGE

EQ 4 times more complex than GSM single slot data

3 times more complex than GSM single slot data

Table 19: Comparison between an EDGE and HSCSD mobile

37

8. Link Adaptation Link adaptation consists in adapting modulation and channel coding in response to changes of the radio link characteristics, particularly propagation and interference conditions. The related topic of adaptive source coding will not be handled here (SMG11 has a separate work item on this topic). Different coding and modulation schemes enable adjustment of the robustness of the transmission according to the environment. HLM (Q-O-QAM) allows for high data rate throughput, but requires slightly more energy per bit and a significantly higher carrier-to-noise or interference ratio compared to LLM (GMSK and B-O-QAM). This chapter focuses on link adaptation for EGPRS, although link adaptation should be made possible for all intended services including transparent and non-transparent ECSD. The chapter aims at outlining the functionality needed for supporting fast and efficient link adaptation. Improvements in terms of measurements and signalling compared to existing GPRS are proposed. Adaptation between channel coding schemes CS1-CS4 is already defined in GPRS. With the introduction of the new channels ECS1-ECS8, adaptation between all twelve schemes should be made possible. However, to simplify the switch of modulation, ECS5-ECS8 schemes should be used instead of CS1-CS4 whenever possible. As for GPRS, where all mobile stations are assumed to support all coding schemes, it is assumed that all EDGE mobile stations support all the EDGE (and GPRS) realisations. 8.1 Improved Channel Quality Measurements Actual performance of the used scheme together with channel characteristics form the basis for link adaptation. Actual performance for a non-transparent service is typically BLER. In GPRS, BLER is available through the ACK/NACK message. However, sufficient measurements for determining the channel characteristics do not exist in GPRS. Channel characteristics are needed to estimate the effects of a switch to another scheme. These characteristics include an estimated C/I ratio, but also time dispersion and fading characteristics (that affects the efficiency of interleaving). Hence, improvements relative GPRS should include measurements of time dispersion, and preferably measurements of channel quality on each burst. The variance of the latter measure could be used to estimate efficiency of the interleaving. 8.2 Channel Quality Reporting In standard GPRS, a channel quality report from the mobile station to the network is sent on three occasions: • In the transfer state, the channel quality report is included in the GPRS ACK/NACK message, which is

sent when polled for by the network. • In the wait state, the channel quality report may be sent when entering the transfer state, if the two phase

access method is used. • Also in the wait state, a channel quality report may be sent at an arbitrary time, on command from the

network. For EGPRS, channel quality reports could be sent at these occasions as well. However, the channel quality report for EGPRS should be extended to include the new channel quality measures defined above.

38

8.3 Principles for Switch Command A notification to switch coding or modulation scheme is always issued by the network and sent to the mobile station, for both downlink and uplink transmission. The notification may be sent using either in-burst signalling, or using a separate command message. For the GPRS downlink, the used coding scheme is simply indicated in each burst, using in-burst signalling on the GSM stealing flag bits. A special switch command is thus not needed. It would be advantageous if this simplicity could be maintained for EGPRS, despite the introduction of new modulation schemes. One solution for switching between B-O-QAM and Q-O-QAM on the EGPRS downlink is to still use in-burst signalling. Some symbols are reserved for indicating which modulation and coding scheme is used. In order to enable demodulation, these symbols are always transmitted using B-O-QAM. The training sequence is also always transmitted using B-O-QAM. It is also assumed that the two modulation schemes use the same symbol rate, pulse shaping and burst format. Furthermore, B-O-QAM uses a reduced signal set of Q-O-QAM. The commands for switching between GMSK and the new modulation schemes requires a separate message, such as the MAC Packet Reassignment message in GPRS. For the uplink data transfer, both GPRS and EGPRS always need a separate command message.

39

9. Network Interface Aspects 9.1 Introduction Increased user data rates over the radio interface require redesign of the physical transmission methods, frame formats, and signalling protocols in different network interfaces. The extent of modification needed is dependent on the user rate requirements, i.e., whether the support of higher data rates is required or merely a more efficient usage of the radio time slot to support current data services. This chapter outlines the changes required for EDGE in different GSM interfaces. For EGPRS the modifications on the network side are smaller compared to ECSD, since most of the changes on the radio interface are transparent to higher layer protocols as presented in figure 4 (chapter 3.2). 9.2 A-bis Interface Transmission Several alternatives for covering the increased radio interface data rates on the A-bis interface for EGPRS and ECSD can be envisioned. The existing physical structure can be reused as much as possible or new transmission method optimised can be specified for EDGE. Similar optimisation problem has already occurred in GPRS where coding schemes CS-3 and CS-4 can not use the existing A-bis interface. However, these GPRS changes may not be enough for EDGE. 9.2.1 Minimum Implementation Fast introduction of EGPRS/ESCD services is possible by reusing several times the existing TRAU formats and 16 kbps channel structure on the A-bis interface. Since the data rates above 14.4 kbps cannot be rate adapted to fit into one 14.4 kbps TRAU frame, TRAU frames on several 16 kbps channels have to be used in order to meet the increased capacity requirement. In this case the BTS is required to handle higher number of 16 kbps A-bis channels than time slots used on the radio interface, e.g., 2 TS connection with ECS-9 (28.8 kbps) would require 4 16 kbps A-bis channels with 14.4k TRAU format. The benefit of using the current TRAU formats is that the introduction of new channel codings does not have on impact on the A-bis transmission, but it makes it possible to hide the new codings from the TRAU unit. On the other hand, some additional complexity is introduced in BTS due to modified data frame handling. 9.2.2 Optimised Transmission Methods The current TRAU formats utilise 16 kbps channels between BTS and remotely located transcoders. Instead of reusing the current A-bis transmission formats for EDGE new TRAU formats and rate adaptations optimised for increased capacity could be specified. For example, 32 kbps TRAU format suited for ECS-7/8/9 or similar codings, could be defined. . The physical layer could be dimensioned statically for the maximum user rate specified for particular EDGE service or more dynamic reservation of A-bis transmission resources could be applied. In case of dynamic reservation, the A-bis channels could be reserved more dynamically, e.g., with 16 or 32 kbps increments call by call basis depending on the selected channel coding and the user data rate. The A-bis resources could even be released and reserved dynamically during the call, if link adaptation is applied. This is a new requirement for A-bis transmission and requires more investigation. More flexible and optimised handling of A-bis resources would be achieved with packet switched transmission methods. For GPRS the A-bis transmission is currently not specified and it would probably be even more difficult to specify packet switched transmission method for circuit switched EDGE services.

40

9.3 A and E Interface Transmission 9.3.1 Minimum Implementation The same multiplexing methods and rate adaptation functions as currently defined for CSD can be utilised for ECSD on the A and E interfaces. The frames coming from the A-bis interface could be multiplexed in the TRAU on 64 kbps A interface circuits. Depending on the A-bis transmission method, in the simpliest case the existing 16 kbps sub-channels are reused for EDGE.

MSC 1/ IWF

MS

32kBSS 1

64k 64kMSC 2

A

E

32k

32k

32k

64k

HOBSS 2

TRAU 1

TRAU 2

Figure 45: Enhanced HSCSD multiplexing with 32 kbps TRAU formats.

9.3.2 Optimised Transmission Methods As in A-bis interface new 32 kbps sub-channels (for ECS-7/8/9 or similar) could be specified for A interface as well (see Figure 45). Depending on the service requirements multi-circuit connections may be required on the A and E interfaces to cover the higher rate ECSD services. This is particularly the case for multi-slot connections with higher rate channel codings (ECS-9/10). Multi-circuit connections could use the same multiplexing methods as currently defined for non-transparent services, where the inter working towards other networks is done in the IWF. For the transparent services direct inter working from the TRAU towards ISDN could be used for higher user rates. Altogether, the impact on the TRAU is going to be service dependent. 9.4 Signalling Modifications New EDGE related parameters need to be defined for signalling messages to enable traffic channels to be activated with new modulation and channel codings. This affects particularly A-bis and RR level signalling protocols. New user rates (if introduced) and channel codings require additions to A-interface and CC-level parameters for ECSD. Changes in the classmark information, i.e., information of the mobile capabilities to support new modulation may also be needed for EGPRS and possibly for ESCD. A and E interface signalling need to be further adapted, if multi-circuit reservation for one connection is required. The changes include handling of resources and different error cases. If link adaptation is applied dynamic handling of the A and E interface resources, i.e., the reservation and release of circuits during the call, could be implemented to optimise the use of resources instead of reserving the maximum resourced during the whole call.

41

10. Document history Version 0.1 12th of May 1997 First version for SMG 2 #22 Version 0.2 15th of September 1997 Following additions have been made - B-O-QAM introduced for link adaptation

- ECSD NT & T services introduced - Network aspects for A, Abis interface added

- Linearity, frequency and phase error simulations - Simulations based on a sub optimal EQ

Version 0.3 30th of October 1997 Following additions have been made - Delay for ECSD/T reduced - Explanation of input and output back off - System simulation with reduced output back off

- Paragraph for different load and reuse introduced - Paragraph Comparison EDGE - HSCSD introduced

Version 1.0 5th of November 1997 Following changes have been made in SMG2 WPB meeting - Chapter 9 (Network interface aspects) restructured - Chapter 0 (Summary) updated

11. Glossary BER Bit error rate BLER Block error rate B-O-QAM Binary offset quadrature amplitude modulation CS Coding scheme CSD Circuit switched data ECS Enhanced coding scheme ECSD Enhanced circuit switched data EDGE Enhanced data rates for GSM evolution EGPRS Enhanced general packet radio service EHSCSD Enhanced high speed circuit switched data EQ Equaliser GPRS General packet radio service HLM Higher level modulation LLM Lower level modulation PA Power amplifier Q-O-QAM Quaternary offset quadrature amplitude modulation RLP Radio link protocol RRC Root raised cosine USF Uplink state flag