impact of gprs-edge on rf network planning

8/6/2019 Impact of GPRS-EDGE on RF Network Planning

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Impact of GPRS/EDGE on RF network planning

DATE: 27/10/99

SUBJECT: Impact of GPRS/EDGE on RF network planning

AUTHOR: Silvia Martin-Leon (RF Systems & CapacityGroup)

TELEPHONE: +44-1793-776826FAX: +44-1793-776867EMAIL: [email protected]

Critical reviewers:

NAME EMAIL ADDRESS

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History

Version Date Author Change Description

00.00 7/10/98 S. Martin-Leon First draft

00.01 20/10/98 S. Martin-Leon Revision


1.00 30/6/99 S. Martin-Leon EDGE added - revision


1.02 27/10/99 S. Martin-Leon Comments from some reviewers

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Contents

1 Abstract......................................................................................................................8

2 Glossary of terms and abbreviations.......................................................................8

3 Introduction to GPRS...............................................................................................9

3.1 Logical and physical channels..............................................................................93.2 Coding schemes..................................................................................................103.3 Link adaptation (code switching).......................................................................113.4 Resource allocation.............................................................................................123.5 Mobility and resource management models.......................................................123.6 GPRS mobile station classes...............................................................................13

5 Impact on coverage planning.................................................................................14

6 Impact on conventional frequency planning........................................................17

9 Impact on Radio Link Control procedures..........................................................19

10.1 6.1 .....................................................................................................................2010.2 Cell re-selection and handover..........................................................................2010.3 Power control....................................................................................................2710.4 Link Adaptation (Code Switching)...................................................................32

11 Impact on capacity enhancement techniques.....................................................35

11.1 Frequency hopping............................................................................................3511.2 Directed retry and load sharing features ..........................................................3711.3 Concentric cells.................................................................................................3711.4 Cell splitting, hierarchical structures and dual band ........................................3811.5 Dynamic channel allocation..............................................................................3811.6 Adaptive antennas.............................................................................................38

12 Impact on capacity planning................................................................................38

12.1 Simple traffic model.........................................................................................4012.2 Simple traffic mix.............................................................................................41

12.3 Other models.....................................................................................................4112.4 Impact on overall capacity................................................................................41

13 EDGE/EGPRS.......................................................................................................42

16 Key:.........................................................................................................................42

17 Series 1 - A mix of vertical applications, telemetry and some Web/FTP users......................................................................................................................................42


19 Series 3 - Exclusive Web/FTP usage....................................................................42

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21 It is important to note that this model does not estimate the load of controlchannels and hence cannot be used to calculate how many timeslots should bededicated to GPRS control channels. ......................................................................42

23 The average number of timeslots per cell can be seen as Erlangs per cell.Making the assumption that circuit switched Erlangs can be linearly added toGPRS Erlangs (this implies they have the same traffic model: exponentialarrivals and length), and imposing a GoS requirement of 2% blocking to bothservices, the capacity per cell in terms of number of circuit and packet switchedservices can be calculated. ........................................................................................42

25 The following graphs show the results for systems with different allocated

bandwidths, using conventional 4/12 reuse or VIPtwo with 30% (conservative)and 50% (maximum) fractional load (it has been considered that frequency

hopping is used in all transceivers in a cell except the BCCH one). A traffic perspeech user of 25 mErlangs has been assumed........................................................42

26 ................................................................................................................................43

28 ................................................................................................................................43

37 G..............................................................................................................................43

38.1 Introduction.......................................................................................................4338.2 Impact on coverage planning............................................................................4638.3 Impact on conventional frequency planning.....................................................4738.4 Impact on radio link control procedures...........................................................48

1 Abstract......................................................................................................................8



3.1 Logical and physical channels..............................................................................93.2 Coding schemes..................................................................................................103.3 Link adaptation (code switching).......................................................................113.4 Resource allocation.............................................................................................123.5 Mobility and resource management models.......................................................12

3.6 GPRS mobile station classes...............................................................................13




10.1 6.1 .....................................................................................................................2010.2 Cell re-selection and handover..........................................................................2010.3 Power control....................................................................................................2710.4 Link Adaptation (Code Switching)...................................................................32


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11.1 Frequency hopping............................................................................................3511.2 Directed retry and load sharing features ..........................................................3711.3 Concentric cells.................................................................................................3711.4 Cell splitting, hierarchical structures and dual band ........................................38

11.5 Dynamic channel allocation..............................................................................3811.6 Adaptive antennas.............................................................................................38


12.1 Simple traffic model.........................................................................................4012.2 Simple traffic mix.............................................................................................4112.3 Other models.....................................................................................................4112.4 Impact on overall capacity................................................................................41

13 EDGE/EGPRS.......................................................................................................42

16 Key:.........................................................................................................................42




21 It is important to note that this model does not estimate the load of controlchannels and hence cannot be used to calculate how many timeslots should be

dedicated to GPRS control channels. ......................................................................42


25 The following graphs show the results for systems with different allocatedbandwidths, using conventional 4/12 reuse or VIPtwo with 30% (conservative)and 50% (maximum) fractional load (it has been considered that frequency


26 ................................................................................................................................43

28 ................................................................................................................................43

37 G..............................................................................................................................43

38.1 Introduction.......................................................................................................4338.2 Impact on coverage planning............................................................................4638.3 Impact on conventional frequency planning.....................................................47

38.4 Impact on radio link control procedures...........................................................48

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1 Abstract......................................................................................................................8



3.1 Logical and physical channels..............................................................................93.2 Coding schemes..................................................................................................103.3 Link adaptation (code switching).......................................................................113.4 Resource allocation.............................................................................................123.5 Mobility and resource management models.......................................................123.6 GPRS mobile station classes...............................................................................13




10.1 6.1 .....................................................................................................................2010.2 Cell re-selection and handover..........................................................................20

10.2.1 Mobile station controlled cell re-selection.........................................................................2010.2.2 Network controlled cell re-selection...................................................................................23

10.3 Power control....................................................................................................2710.3.1 Uplink power control...........................................................................................................2710.3.2 Downlink power control......................................................................................................31

10.4 Link Adaptation (Code Switching)...................................................................32


11.1 Frequency hopping............................................................................................3511.2 Directed retry and load sharing features ..........................................................3711.3 Concentric cells.................................................................................................3711.4 Cell splitting, hierarchical structures and dual band ........................................3811.5 Dynamic channel allocation..............................................................................3811.6 Adaptive antennas.............................................................................................38


12.1 Simple traffic model.........................................................................................4012.2 Simple traffic mix.............................................................................................4112.3 Other models.....................................................................................................4112.4 Impact on overall capacity................................................................................41

13 EDGE/EGPRS.......................................................................................................42

16 Key:.........................................................................................................................42




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21 It is important to note that this model does not estimate the load of controlchannels and hence cannot be used to calculate how many timeslots should bededicated to GPRS control channels. ......................................................................42


25 The following graphs show the results for systems with different allocated

bandwidths, using conventional 4/12 reuse or VIPtwo with 30% (conservative)and 50% (maximum) fractional load (it has been considered that frequency


26 ................................................................................................................................43

28 ................................................................................................................................43

37 G..............................................................................................................................43

38.1 Introduction.......................................................................................................4338.1.1 Modulation and coding schemes.........................................................................................4338.1.2 Link adaptation and incremental redundancy.....................................................................4538.1.3 Transmission power.............................................................................................................45

38.2 Impact on coverage planning............................................................................46

38.3 Impact on conventional frequency planning.....................................................4738.4 Impact on radio link control procedures...........................................................48

38.4.1 Cell re-selection and handover............................................................................................4838.4.2 Power control.......................................................................................................................4838.4.3 Link adaptation (Code Switching).......................................................................................49

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1 Abstract

This document details the foreseeable impact on RF network planning of the deployment of packetservices (GPRS and EDGE/EGPRS) on a GSM system. In particular, the document covers theimpacts on coverage planning, parameter setting, frequency planning, capacity enhancementtechniques and capacity of the system

It assumes a basic understanding of RF planning issues, in particular coverage and capacity related.However, general sections on GPRS and EDGE have been introduced to familiarise the reader withall the aspects of GPRS and EDGE that are being studied in the document.

The main conclusion of the document is that GPRS has been designed so that its deployment causesthe least disruption to an already established network. In particular it will not require a change incoverage and frequency planning.

However, there is at the time of writing no practical experience in the deployment of GPRS. Hencesome issues are still open and require further study and consideration:

New GPRS parameter settings for cell re-selection. Impact of the use of hierarchical networks with GPRS.New GPRS power control algorithms and achievable capacity gains.New GPRS parameter setting for the code switching algorithm. Impact of the use of frequency hopping and GPRS. GPRS radio resource planning and impact on capacity.

It is important to note that especially in the case of EDGE, standards are still under construction andchanges are expected. The information contained in this document reflects their status at the date ofwriting.

2 Glossary of terms and abbreviations

AMR Adaptive Multi RateBCCH Broadcast ChannelBCS Block Check SequenceBTS Base Transceiver StationCS1-4 Coding Scheme 1 to 4DRX Discontinuous ReceptionDTX Discontinuous TransmissionEDGE Enhanced Data Rates for GPRS EvolutionGoS Grade of ServiceGPRS General Packet Radio ServiceHCS Hierarchical Cell StructuresHSN Hopping Sequence Number IR Incremental Redundancy

LA Link AdaptationLCA Local Configuration AreaMAIO Mobile Allocation Index Order MCS1-8 Modulation and Coding scheme 1 to 8MS Mobile StationOMC Operations and Management CentrePACCH Packet Associated Control ChannelPAGCH Packet Access Grant ChannelPBCCH Packet Broadcast ChannelPCCCH Packet Common Control ChannelPCU Packet Control UnitPDTCH Packet Data Traffic ChannelPPCH Packet Paging Channel

PRACH Packet Random Access ChannelPTCH Packet Traffic ChannelRA Routing Area

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SDCCH Slow Dedicated Control ChannelSNDCP SubNetwork Dependent Convergence ProtocolTCH Traffic ChannelTDMA Time Division Multiple AccessTS Training Sequence

USF Uplink Status FlagVIPone Variable Interference Plan 1VIPtwo Variable Interference Plan 2

3 Introduction to GPRS

GPRS (General Packet Radio Service) tries to enlarge the limited range of existing GSM dataservices. To enable support of new data applications with a convenient quality of service, the GPRSconcept foresees bit rates of around 170 kb/s i that can be flexibly allocated according to actual userdemands. It uses packet switched access mechanisms that are known to give better utilisation of thetransmission medium than circuit switched ones due to the bursty nature of data communications.

3.1 Logical and physical channels

When a network operator decides to offer GPRS-based services within a cell, one or several physicalchannels from the pool of available channels are reserved to packet mode transfer. Each of these socalled packet data channels (PDCH) is mapped onto one physical timeslot. According to therequirement for flexible adaptation to different traffic conditions, allocation of PDCHs is based ondemand. This means that GPRS does not require permanently allocated PDCHs. The allocation ofcapacity for GPRS can be based on the needs of the actual packet transfers. This holds for bothcontrol channels and packet channels. If packet control channels are not available, GPRS will use theexisting GSM control channels for broadcasting, random access, paging and access grant.

GPRS logical channels can be divided in three groups according to their functions:

Packet Broadcast Control Channel (PBCCH):

The PBCCH transmits system information to all GPRS terminals in a cell. If the PBCCH is notallocated, the packet data specific system information is broadcast on BCCH.

Packet Common Control Channels (PCCCH):

The Packet Random Access Channel (PRACH) is used by MSs to initiate packet transfers orrespond to paging messages.

The Packet Paging Channel (PPCH) is used to page an MS prior to downlink packet transfer.

The Packet Access Grant Channel (PAGCH) is used to send resource assignment to an MSprior to the packet transfer.

If not allocated, common signalling will be conveyed on CCCH.

Packet Timing advance Control Channels (PTCCH):

These channels are used to derive the correct value for timing advance to be used while themobile station is in Packet Transfer mode (see 3.5). There are two types: PTCCH/U andPTCCH/D.

Packet Traffic Channels (PTCH):

The Packet Data Traffic Channel (PDTCH) is allocated for data transfer. One MSmay use more than one PDTCH in parallel (multislot operation) for individual packettransfers. Also up to eight different PDTCH can be multiplexed on the same physical channel

i Achieved with CS-4, 8 timeslots and without retransmissions. Protocol overheads will reduce theavailable bit rate to less than 160 kb/s.

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(PDCH). In the uplink this is achieved thanks to the Uplink State Flag (USF) sent in thedownlink, which specifies who is allowed to transmit in the next uplink block.

The Packet Associated Control Channel (PACCH) is used to convey signallinginformation related to a given MS such as measurements, acknowledgements, power control

orders, RLC parameters One PACCH is associated with one or several PDTCHsconcurrently assigned to one MS.

Lucents first GPRS release (known as GPRS BSS R1.0) will not support PCCCH channels. Allcommon signalling will be carried on exiting GSM CCCH. Support for PCCCH is expected in R2.0.

3.2 Coding schemes

Four different coding schemes, CS-1 to CS-4, are defined for the radio blocks carrying datainformation. The following figure shows how data is encoded for CS-1, CS-2 and CS3.

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CS-1 is the same coding scheme as specified for SDCCH. It consists of a half rate convolutional codefor forward error correction and a 40 bit FIRE code for BCS (Block Check Sequence). CS-2 and CS3

are punctured versions of the same half rate convolutional code. CS-4 has no forward error correctingcapabilities.

The stealing bits are used to indicate the actual code scheme (shown in the figure as Code).

The details of the codes are shown in the table below:

Signalling information can only use CS-1.

Lucent GPRS R1.0 will only offer CS-1and CS-2. The introduction of higher coding schemes is stillunder study.

3.3 Link adaptation (code switching)

Higher level coding schemes are more sensitive to noise and interference. Therefore, they can beused with less probability. An adaptive selection of the coding scheme to be used has to be provided

in order to take advantage of the increased efficiency of higher coding schemes. The selection of the

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USF BCS

Rate 1/2 convolutional coding

Puncturing

456 bits

Segmentationand

interleaving

114 bits

Normal burst Normal burst Normal burst Normal burst

114 bits 114 bits 114 bits

Normal GSM burst

Tail3 bits

Information57 bits

Code1 bit

Code1 bit

Information57 bits

Tail3 bits

TS26 bits

Scheme Code rate USF Pre-codedUSF

Radio Block excl.USF and BCS

BCS Tail Codedbits

Punctured

bits

Air int.rate Kb/s

CS-1 1/2 3 3 181 40 4 456 0 9.05

CS-2 2/3 3 6 268 16 4 588 132 13.4

CS-3 3/4 3 6 312 16 4 676 220 15.6

CS-4 1 3 12 428 16 - 456 - 21.4


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most appropriate coding scheme for coming transmissions, according to the estimated link quality, iscalled Link Adaptation or Code Switching.

Link Adaptation in GPRS presents the following problems:

Radio block retransmissions have to be done on the same coding scheme. In thecase the radio conditions deteriorate quickly, this could mean to loss of the connection

because the coding scheme previously selected can be not good enough to correct all theerrors. The system will react by breaking the connection if the number of retransmissionsreaches a certain limit.

Before switching all the pending acknowledgements have to be received. Thismakes the code switching procedure slow and useless in the case of short transmissions.

As it will be seen later GPRS available measurements are not the optimum.

Code switching between CS-1 and CS-2 will be introduced in GPRS R1.0. The algorithm used willbe described in section 10.4.

3.4 Resource allocation

GPRS has been specified such that it will provide a very flexible multiplexing of resources todifferent mobile stations on the same time slot. The basic solution, called dynamic allocation,multiplexes the uplink resources on a block basis, using the Uplink State Flag (USF) to determinewhich of up to 8 mobile stations shall transmit on the next block. For the downlink, the temporaryflow indicator (TFI) within each block controls the multiplexing, also on a block basis.

For the uplink, additional options are included: extended dynamic allocation, where the multiplexingis made on a four block basis, and fixed assignment, where the multiplexing is predefined in theassignment for a certain time (up to 88 blocks). Since these options work with units of more blocks,they are less flexible in terms of fast adaptation to the traffic with different priority.

In GPRS R1.0 only dynamic allocation will be supported.

3.5 Mobility and resource management models

Because GPRS is a packet service, nocontinuous physical circuits are allocatedto mobiles.

Before a mobile station is able to senddata, it has to attach to a GPRS. With thisattachment procedure a logical link contextis established.

During the GPRS session, the location ofan MS is tracked according to the three-state model shown in the accompanyingfigure. While the mobile station informsabout every cell change when in Readystate, location information is updated instandby state only if the Routing Area (RA)is changed. This Routing Area is a subsetof the GSM Location Area.

12

PDUtransmission

GPRSAttach

READYtimer expiry

orForce toSTANDBY

STANDBYtimer

expiry

GPRSDetach

MMState Model of MS

IDLE

READY

STANDBY


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In terms of resource management (allocation of transmission resources) on the air interface themobile and the base station can be on two different operating modes:

Packet Idle mode: no transmission resources are allocated to the connection. Themobile station listens to the paging sub-channel.

Packet Transfer mode: the mobile station is allocated a radio resource on one ormore physical channels (time slots). Transfer of data is possible.

The following table shows the correspondence between radio resource states and mobilitymanagement states:

Radio Resource BSS PacketTransfer mode

Measurementreportreception

No stateNo state

Radio Resource MS PacketTransfer mode

Packet Idle mode Packet idle mode

Mobility ManagementNSS and MS

Ready Standby

In Packet Idle mode the mobile station can perform discontinuous reception (DRX), where the pagingchannels are subdivided in sub-channels, and mobile stations restrict their monitoring of pagingmessages to their own sub-channel. In this way they increase significantly the lifetime of their

battery, at the expense of a small increase in delay for the setting up of incoming connections.

3.6 GPRS mobile station classes

Three GPRS MS classes are identified:

Class A:The mobile user can make and/or receive calls on the two services simultaneously subject to theQoS requirements.

Class B:Simultaneous traffic shall not be supported. The mobile user can make and/or receive calls oneither of the two services sequentially but not simultaneously. The selection of the appropriateservice is performed automatically, i.e. an active GPRS virtual connection is put on hold, if theuser accepts an incoming circuit switched call or establishes an outgoing circuit switched call.

Class C:Alternate use only. If both services (GPRS and Circuit Switched) are supported then a Class CMS can make and/or receive calls only from the manually or default selected service, i.e., eitherGPRS or Circuit Switched service.

Additionally, mobile stations can also be classified according to their multi-slot capability, which canbe up to 8 timeslots in the uplink and in the downlink.

In Lucent GPRS R1.0 the maximum configuration supported is 2 timeslots in the uplink and 4 in thedownlink. In R2.0 the capability will be enhanced to support 4 timeslots in the uplink and 8 in thedownlink.

3.7

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3.8

3.9

4

4.1

5 Impact on coverage planning

The following table shows the reference sensitivity (input signal level at reference performance: 10%block error rate) of GPRS channels (GSM 05.05):

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NOTE 1:The specification for PDTCH/CS-1 applies also for PACCH, PBCCH, PAGCH, PPCH,PTCCH/D, PNCH.

NOTE 2:Ideal FH case assumes perfect decorrelation between bursts. This case may only be

tested if such a decorrelation is ensured in the test. For TU50 (ideal FH), sufficientdecorrelation may be achieved with 4 frequencies spaced over 5 MHz.

NOTE 3: PDTCH/CS-4 can not meet the reference performance for some propagation conditions(*).

NOTE 4 : The complete conformance should not be restricted to the logical channels and channelmodels identified with (x)

In a GSM900 TU50 environment without frequency hopping, the minimum reference sensitivity levelfor CS-1 is -103 dBm, which corresponds to USF/CS-1.The reference sensitivity level for circuit services for a normal BTS, which is -104 dBm.There is, therefore, a 1 dB difference between the reference sensitivity values needed for circuit and

packet switched services, when using at least CS-1 in the latter.

An already existing GSM900 network offering circuit switched services would have typically beenplanned for 95% area coverage with minimum sensitivity of -104 dBm. In such a network the areacoverage for a minimum sensitivity value of -103 dBm would be 2-3% lower, assuming a combinedslow fading deviation of 7.0 dB ii.

This result does not restrict the use of the rest of coding schemes in a dynamic way.

It has to be pointed out, though, that the comparison between these values is a little misleading. Forcircuit services one sensitivity value is given and then its performance calculated for the different

propagation environments.For packet services, the performance is fixed: BLER=10% and then the necessary input signal levelcalculated for the different propagation environments. Values for the same propagation environment

ii These results assume the uplink is the limiting link.

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GSM 900Type of Propagation conditionschannel static TU50

(no FH)TU50

(ideal FH)RA250(no FH)

HT100(no FH)

PDTCH/CS-1 dBm -104(x) -104 -104(x) -104(x) -103

PDTCH/CS-2 dBm -104(x)

-100 -101 -101 -99PDTCH/CS-3 dBm -104(x) -98 -99 -98 -96

PDTCH/CS-4 dBm -101 -90 -90 * *

USF/CS-1 dBm -104(x) -103 -104(x) -104(x) -104

USF/CS-2 to 4 dBm -104(x) -104(x)

-104(x) -104(x) -104

PRACH/11 bits dBm -104(x) -104 -104 -103 -103

PRACH/8 bits dBm -104(x) -104 -104 -103 -103

DCS 1 800Type of Propagation conditionschannel static TU50

(no FH)TU50


HT100(no FH)

PDTCH/CS-1 dBm -104(x) -104 -104 -104(x) -103PDTCH/CS-2 dBm -104(x) -100 -100 -101 -99

PDTCH/CS-3 dBm -104(x) -98 -98 -98 -94

PDTCH/CS-4 dBm -101 -88 -88 * *

USF/CS-1 dBm -104(x) -104(x) -104(x) -104(x) -104

USF/CS-2 to 4 dBm -104(x) -104(x) -104(x) -104(x) -104

PRACH/11 bits dBm -104(x) -104 -104 -103 -103

PRACH/8 bits dBm -104(x) -104 -104 -103 -103


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and relative equal performance should have been compared, but, since they were not available, theones provided by the standard have been used.

Also, one characteristic of non-transparent radio link protocols, like the ones used in GPRS, is that alow radio link quality only results in lower bit rate for the user. Hence low signal level for a user does

no result in a dropped call as for speech, but in a temporary decrease of user bit rate

iii

.

In reality receiving equipment generally improve reference sensitivity values. In the case of Lucentmacro BTS, a sensitivity value of -108 dBm is quoted for circuit switched channels in a GSM900TU50 environment. Simulations have shown an improvement of 4 dB in the required signal levels ofall the coding schemes at reference performance. This gives a minimum sensitivity value for GPRSof 107 dB.

The following tables show in more detail the results of the simulations:

GSM 900

Differences of the simulation results compared with the GSM rec. 05.05

concerning reference sensitivity performance (10% FER)

propagation conditions

Type of channel static TU50

(no FH)

TU50

(ideal FH)

RA130

(no FH)

HT100

(no FH)

PDTCH/CS-1 >8 3.17 3.83 4.0 2.3

PDTCH/CS-2 7.05 4.63 3.92 3.8 2.3

PDTCH/CS-3 5.62 4.37 3.48 3.4 0.7

PDTCH/CS-4 4.03 3.93 3.73 * *

PRACH/11bit >7 4.08 4.08 5.3 3.9

PRACH/8 bit >7 4.8 4.8 6.0 4.8

Differences to GSM 05.05 in [dB]+ sign = better then GSM 05.05- sign = worse then GSM 05.05

(*) PDTCH/CS-4 can not meet the reference performance for some propagation conditions .Noise floor for simulation: -115dBm within 200kHz bandwith

DCS 1800

Differences of the simulation results for the BTS2000 compared with the GSM rec.05.05

concerning reference sensitivity performance (10% FER)

propagation conditions

Type of channel static TU50

(no FH)

TU50

(ideal FH)

RA130

(no FH)

HT100

(no FH)

PDTCH/CS-1 >8 3.44 3.82 4.08 1.98

PDTCH/CS-2 7.05 4.68 4.88 3.75 1.4

PDTCH/CS-3 5.62 4.28 4.35 2.9 -0.2

PDTCH/CS-4 4.03 4.64 4.85 * *

PRACH/11bit >7 4.08 4.08 6.0 3.7

PRACH/8 bit >7 4.8 4.8 6.2 4.6

iii Up to a certain limit because the number of retransmissions is limited.

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Differences to GSM 05.05 in [dB]+ sign = better then GSM 05.05- sign = worse then GSM 05.05noise floor for simulation: -115dBm within 200kHz bandwith

If higher peak data rates than those offered by CS-1 were to be offered all over the network, i.e.higher coding schemes were to be used all over the network, the appropriate sensitivity values wouldneed to be enforced at the cell edge. In capacity limited networks, where there is a certain degree ofcell splitting, it is possible that the higher signal strength allows for these codes. However,interference limitations need also be taken into account, as it will be described in the next section.

A complexity of 14 MIPS can be considered as well suited for mobiles and a complexity of 26 MIPSis still moderate to be implemented in a BTS.

In order to translate from Eb/No to sensitivity values, the following formula can be used:Ss = Eb/No + NF 1

6 Impact on conventional frequency planning

7

8

The following table show the interference ratio at reference performance for a normal BTS (GSM05.05):

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As it can be seen, in a GSM900 TU50 propagation environment without frequency hopping, theinterference ratio at reference performance for CS-1 is 10 dB. This value increases for the moreefficient coding schemes: 14dB for CS-2, 16 dB for CS-3, 23 dB for CS-4. These results take intoaccount multipath propagation effects by means of a 2 dB implementation margin.

The reference interference ratio for circuit switched channels is 9 dB (co-channel interference).

As the standard deviation of the mean signal level is estimated to be 7 dB in a dense urban, a shadowmargin of 7 dB is required to ensure that the outage probability is better or equal to 10%. Taking intoaccount the 2 dB implementation margin the reference interference ratio assumes, a C/I of 15 dB isrequired at the edge of the cell to give the required GPRS CS-1 grade of service.

In GSM, conventional frequency planning, based on regular reuse patterns, typically uses a 4/12reuse. This reuse, for an inverse 3.5 exponent law, realises a mean C/I ratio at the cell edge of ~18dB.

It can be seen that a 4/12 reuse pattern is sufficient when at least CS-1 is supported and the rest of thecoding schemes are only used when the interference situation of the particular communication isgood enough, i.e. when there is dynamic coding scheme allocation.

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GSM 900Type of Propagation conditionschannel TU3

(no FH)TU3

(ideal FH)TU50

(no FH)TU50


PDTCH/CS-1 dB 13 9 10 9 9

PDTCH/CS-2 dB 15 13 14 13 13

PDTCH/CS-3 dB 16 15 16 15 16

PDTCH/CS-4 dB 19 23 23 23 *

USF/CS-1 dB 16 9 10 9 9

USF/CS-2 to 4 dB 15 8 9 8 7

PRACH/11 bits dB 8 8 8 8 10


DCS 1 800

Type of Propagation conditionschannel TU1,5

(no FH)TU1,5

(ideal FH)TU50

(no FH)TU50


PDTCH/CS-1 dB 13 9 9 9 9

PDTCH/CS-2 dB 15 13 13 13 13

PDTCH/CS-3 dB 16 15 16 16 16

PDTCH/CS-4 dB 19 23 25 25 *

USF/CS-1 dB 16 9 9 9 9

USF/CS-2 to 4 dB 15 8 8 8 7



NOTE 1:The specification for PDTCH/CS-1 applies also for PACCH, PBCCH, PAGCH, PPCH,PTCCH/D, PNCH.

NOTE 2:Ideal FH case assumes perfect decorrelation between bursts. This case may only betested if such a decorrelation is ensured in the test. For TU50 (ideal FH), sufficientdecorrelation may be achieved with 4 frequencies spaced over 5 MHz. The TU3 (idealFH) and TU1.5 (ideal FH), sufficient decorrelation cannot easily be achieved. Theseperformance requirements are given for information purposes and need not be tested.

NOTE 3: PDTCH/CS-4 can not meet the reference performance for some propagation conditions(*).


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If an operator wants to offer higher data rates all over its network, it would have to move to a looserreuse. For example, a 7/21 reuse allows CS-3 to be used all over the network, which at reference

performance offers approximately 50% more throughput than CS-1 with a 4/12 reuse.

On the other side, the use information retransmission procedures allows GPRS to support tighterreuses (1/3), even if reference performance cannot be achieved at the cell edge. The maximumthroughput available per user will decrease but the spectrum efficiency (throughput/spectrum) doesnot. This supports the on-going trend towards tighter frequency reuse in GSM.

The following figure shows the maximum throughput available to the users depending on the reusepattern (ideal link adaptation based on compromise threshold values has been used see section10.4).

In reality, regular reuse patterns are not normally used because of the irregularities of the network.Frequency planning procedures are generally based on interference and separation matrixes, i.e.matrixes that define the probability of the interference being higher than a certain value and theseparation between frequencies assigned to different base stations.

Following these procedures, the 1 dB difference between the reference interference ratio for circuitand packet channels could have a impact in the achievable average reuse in the network. However, asit was pointed out in the previous section, the comparison between the values given for circuit and

packet channels is not direct. C/I threshold values normally used by operators are also conservative.

The conclusion is that it is expected that the initial introduction of GPRS on a network will have nomajor impact on conventional frequency planning. Different approaches will only be needed whenthere is demand for high bandwidth data services.

9 Impact on Radio Link Control procedures

9.1

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10

The radio link control procedures for GPRS are different to the ones for circuit switched services.

This is mainly because there is no continuous two-way connection to allow the network to havecomplete control over them. More information about the procedures can be found in GSM 05.08.

10.1 6.1

10.2 Cell re-selection and handover

In GPRS there is no handover as it is normally known in GSM. There are only the so-called cellselection and re-selection procedures.

In idle mode these procedures are the same as for circuit switched services and they use the same setof parameters.

In GPRS connected mode, which corresponds to Ready and Standby states (see section 3.5), GPRScell re-selection is implemented, instead of handovers. The only exception are class A mobile stationswhile in dedicated mode of a circuit switched connection, in which case the cell is determined by thenetwork according to the handover procedures. When the circuit switched connection is released, themobile station resumes cell re-selection.

In Ready state the GPRS cell re-selection can be controlled by the mobile station or by the network.This is indicated by the parameter NETWORK_CONTROL_ORDER. This parameter is broadcast onthe PBCCH, or BCCH if the former does not exist. It can also be sent to individual mobile station

using a Packet Measurement Order message on a PCCCH or PACCH. This message overrides theparameters sent on the BCCH/PBCCH.

The meaning of the different parameter values of NETWORK_CONTROL_ORDER is specified asfollows:

NC0 Normal MS controlThe MS shall perform autonomous cell re-selection

NC1 MS control with measurement reportsThe MS shall send measurement reports to the networkThe MS shall perform autonomous cell re-selection

NC2 Network controlThe MS shall send measurement reports to the networkThe MS shall not perform autonomous cell re-selection

RESET The MS shall return to the broadcast parameters. Only sent on PCCCH or PACCH

In Standby, GPRS cell re-selection can only be controlled by the mobile station.

Only mobile station controlled cell re-selection will be implemented in Lucent GPRS R1.0 and R2.0.Measurement reports will also not be supported. For this reason, parameter

NETWORK_CONTROL_ORDER is always set to NC0.

10.2.1 Mobile station controlled cell re-selection

Mobile station controlled cell re-selection means that the mobile station autonomously performs thecell re-selection. The algorithm for cell re-selection depends on whether the PBCCH exists or not,

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and whether the GPRS cell re-selection parameters are provided to mobile stations in a PacketMeasurement Order message:

PBCCH does not exist and Packet Measurement Order messages are not supported

This is the case of Lucent GPRS R1.0.

When no PBCCH is present the mobile station controlled cell re-selection follows the samealgorithm as in idle mode.

The mobile station continuously monitors all BCCH carriers indicated by the BA(BCCH) list,which is broadcast on the BCCH, and the BCCH carrier of the serving cell, updating the list ofthe 6 strongest non-serving carriers. For the serving cell and the list of non-serving cells themobile evaluates the path loss criterion parameter C1 and the reselection criterion C2.

In Packet Idle mode, at least one measurement sample on each BCCH carrier is taken for eachpaging block monitored by the mobile station according to its current DRX mode and its paginggroup. In Packet Transfer mode, at least one measurement sample is taken on at least one of theBCCH carriers in every TDMA frame.

The mobile station performs cell re-selection if the pathloss criterion (C1) of the current cell fallsbelow zero for a period of 5 seconds, or the calculated value of C2 for a non-serving cell exceedsthe value of C2 for the serving cell for a period of 5 seconds.

The mobile station selects as new cell the cell with the highest C2.

Within a Routing Area, the mobile station will use hysteresis when re-selecting a cell while inReady state (it resembles the handover margin). This hysteresis, CELL_RESELECTIONHYSTERESIS, is applied to the C2 parameter of the non-serving cells.

If the new cell is in a different Routing Area to the serving cell, then the mobile station willapply a hysteresis, independent of whether the mobile station is in Ready or Standby state. This

hysteresis is given by the parameter CELL_RESELECTION_HYSTERESIS and it is applied tothe C2 criterion of the cells in a different Routing Area.

Additionally, a 5 dB hysteresis to the C2 of non-serving cells is applied if a cell re-selection hasoccurred in the previous 15 seconds.

In this case, the assignment of mobiles to the correct cell will depend on the proper setting of the parameters governing the C1 and C2 criteria: RXLEV_ACCESS_MIN, MS_TXPWR_MAX,CELL_RESELECT_OFFSET, TEMPORARY_OFFSET, PENALTY_TIME andCELL_RESELECTION_HYSTERESIS.

The C1 criteria will implement a form of mandatory cell re-selection based on signal strengthand the C2 a form of power budget where the parameter CELL_RESELECTION_HYSTERESIScould behave as the handover margin, preventing ping-pong effects.

In the case of dual band operation, CELL_RESELECT_OFFSET can be used to overcome theadditional path loss in the 1800 band and even to favour this band.

Parameters CELL_RESELECT_OFFSET, TEMPORARY_OFFSET and PENALTY_TIME ofthe C2 criteria can also be used to implement a hierarchical structure, encouraging slowmobiles to select a lower layer cell and fast mobiles an upper layer cell. By setting a largevalue for TEMPORARY_OFFSET for lower layer cells, mobiles can be directed to re-select anupper layer cell, putting any lower layer cells in the strongest server list at a disadvantage untilthe mobile can be considered slow moving. Once this has been achieved, i.e. PENALTY_TIMEhas expired, the TEMPORARY_OFFSET is removed, the C2 value for lower cells has to becomemore favourable so that lower layer cells are re-selected. This is done by setting theCELL_RESELECT_OFFSET accordingly.

More information about how to set this parameters can be found in the Dual Band andHierarchical Cell Structures Engineering Guidelines.

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PBCCH exits or the Packet Measurement Order message is supported

The mobile station continuously monitors all BCCH carriers indicated by the BA(GPRS) list andthe BCCH carrier of the serving cell, updating the list of the 6 strongest non-serving carriers.

Othe mobile station verifies the BSIC of the BCCH carriers and only the cells with the sameBSIC as broadcast together with the BA(GPRS) are considered for cell re-selection.

The BA(GPRS) list is broadcast on PBCCH. If PBCCH does not exist, BA(GPRS) is equal toBA(BCCH). The parameter NC_FREQUENCY_LIST may also be sent individually to a mobilestation through a Packet Measurement Order message. This list adds/deletes frequencies to theBA(GPRS). For added frequencies, the corresponding cell re-selection parameters are included.If the PBCCH does not exist, the NC_FREQUENCY_LIST contains the GPRS cell re-selection

parameters of all the BA(GPRS).

In Packet Idle mode, at least one measurement sample on each BCCH carrier is taken for eachpaging block monitored by the mobile station according to its current DRX mode and its paginggroup. In Packet Transfer mode, at least one measurement sample is taken on at least one of theBCCH carriers in every TDMA frame.

For the serving cell and the list of non-serving cell the mobile evaluates the pathloss criterionparameter C1, and the new C31 and C32 parameters.

The C1 criterion is the same as for GSM idle mode, except that parametersGPRS_RXLEV_ACCESS_MIN and GPRS_MS_TXPWR_MAX_CCH, broadcast on thePBCCH, are used instead of RXLEV_ACCESS_MIN and MS_TXPWR_MAX_CCH.Additionally no POWER_OFFSET is used.

C31 is the signal strength threshold criterion parameter for hierarchical cell structures (HCS)which is used to determine whether prioritised hierarchical cell re-selection shall apply. It isdefined as:

C31(s) = Averaged Received Level(s) - HCS_THR(s) (serving cell)C31(n) = Averaged Received Level(n) - HCS_THR(n) - TO(n)*L(n) (neighbour cell)

whereHCS_THR is the signal threshold for applying HCS re-selectionTO(n) = TEMPORARY_OFFSET(n) * H(PENALTY_TIME(n) - T(n))L(n) = 0 if PRIORITY_CLASS(n) = PRIORITY_CLASS(s)

1 if PRIORITY_CLASS(n) PRIORITY_CLASS(s)H(x) = 0 for x< 0

1 for x 0

C32 is an improvement of C2. It applies an individual offset and hysteresis value to each pair ofcells, as well as the same temporary offsets as for C2. Additional hysteresis values apply for acell re-selection that requires cell or routing area update.

C32 is also known as the cell ranking criterion parameter. It is used to select cells among thosewith the same priority and is defined as:

C32(s) = C1(s) (serving cell)C32(n) = C1(n) + GPRS_RESELECT_OFFSET(n) - TO(n) * (1-L(n)) (neighbour cell)

whereTO(n) = TEMPORARY_OFFSET(n) * H(PENALTY_TIME(n) - T(n))L(n) = 0 if PRIORITY_CLASS(n) = PRIORITY_CLASS(s)

1 if PRIORITY_CLASS(n) PRIORITY_CLASS(s)H(x) = 0 for x< 0

1 for x 0

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The mobile station performs cell re-selection if the pathloss criterion (C1) of the current cell fallsbelow zero for a period of 5 seconds, or non-serving cell is evaluated to be better than theserving cell for a period of 5 seconds.

The mobile station will select the best cell, which is the one that has the highest C32 value

among those that have the highest priority class among those that fulfil the criterion C31

0. The priority classes may correspond to different HCS layers. They may also be used for otherpurposes.

If no cell fulfils the criterion C31 0, the best cell is the one having the highest C32 value amongall cells.

If the parameter C32_QUAL is set, positive GPRS_RESELECT_OFFSET values are onlyapplied to the neighbour cell with the highest Averaged Receive Level value of those cells forwhich C32 is compared.

Within a Routing Area, the mobile station will use hysteresis when re-selecting a cell while inReady state (it resembles the handover margin). This hysteresis is applied to the C32 criteria. As

an option, the network operator may decide to use this hysteresis for the C31 criteria. The valueof the hysteresis is given by the parameter GPRS_CELL_RESELECT_HYSTERESIS.

If the new cell is in a different Routing Area to the serving cell, then the mobile station willapply a hysteresis, independent of whether the mobile station is in Ready or Standby state. Thishysteresis is given by the parameter RA_RESELECTION_HYSTERESIS.

Additionally, a 5 dB hysteresis to the C32 of non-serving cells is applied if a cell re-selection hasoccurred in the previous 15 seconds.

The C31 and C32 criteria are very similar to C2 except that they include prioritisation of cellsand uses parameter GPRS_RESELECT_OFFSET for each of the non-serving cells. The

prioritisation of cells allows a greater flexibility in defining hierarchical structures with more

than two layers, and proper dual band behaviour.

The main means to accomplish hierarchical cell structures is the use of PRIORITY_CLASS,TEMPORARY_OFFSET and PENALTY_TIME. An umbrella cell would be given a lowPRIORITY_CLASS. A micro cell would be given a high PRIORITY_CLASS and also aTEMPORARY_OFFSET with an associated PENALTY_TIME to keep fast moving mobilestations away. Also, the threshold for when a cell should be considered is set with the parameterHCS_THR.

C31 and C32 parameters (or C1 and C2) are evaluated by the mobile station every 5 seconds. Thismeans that cell re-selection can only take place every 5 seconds.

From a network point of view, mobile station controlled cell re-selection is the simplest option, but insome situations is not the best in terms of quality and spectrum efficiency. This is because it is only

based on the downlink, i.e. it assumes a high correlation between the downlink and the uplink, whichin some situations (heavily shadowed areas) might not be the case.

Also, no quality based re-selection and intra-cell handover will be available in this mode ofoperation. This implies that the only way the system would have to react against interference

problems is by either changing the coding scheme, or by retransmission of badly sent frames. Thiscould impact the efficiency of the system.

10.2.2 Network controlled cell re-selection

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Network controlled cell re-selection means that the network can order an individual mobile station inREADY state to perform cell re-selection to a cell appointed by the network, overriding the mobilestation originated cell selection.

The network command (Cell Change Order) can be sent both in Packet Idle and Packet Transfer

mode. It should normally rely on the measurement reports sent by the mobile station.

A mobile station is ordered to send measurement results when NETWORK_CONTROL_ORDER isNC1 or NC2. In this case the mobile station continuously monitors all carriers in BA(GPRS) or asindicated by the parameter NC_FREQUENCY_LIST and the BCCH carrier of the serving cell.

In Packet Idle mode, at least one measurement sample on each BCCH carrier is taken for each pagingblock monitored by the mobile station according to its current DRX mode and its paging group. InPacket Transfer mode, at least one measurement sample is taken on at least one of the BCCH carriersin every TDMA frame.

The time interval between measurement reports is given by the parametersNC_REPORTING_PERIOD_I and NC_REPORTING_PERIOD_T, for mobiles in Packet Idle andPacket Transfer mode respectively. They can take values of 0.48, 0.96, 1.92, , 61.44.

The measurement reports include the following information:

Average RXLEV in reporting period of serving cell.;

In Packet Idle mode, the average interference signal level for the serving cell measured onthe monitored PCCCH if a valid value is available. The average is calculated using a runningfilter with forgetting factor 1/NAVG_I.

; Average RXLEV in reporting period for the non-serving cells. Carriers are only reported ifthey are among the 6 strongest carriers and BSIC is successfully decoded and equal to theBSIC of the list.

T1.

2.

his mode of operation allows the implementation of cell re-selection algorithms similar to the onesavailable for handover in circuit switched services. These algorithms would take into account themeasurements reported by the mobile stations, and the ones performed by the base station.

The effectiveness and speed of reaction of the algorithms will depend on how often measurementsare reported. Studies are required to find the best value for parameters NC_REPORTING_PERIOD_I

and NC_REPORTING_PERIOD_T so that there are enough number of measurements withoutoverloading the air interface and/or the PCU.

Quality cell re-selection could be implemented by taking into account the interference measurements.Even though they will probably be a better estimate than the RXQUAL measurements present incircuit switched connections, the impact of interference diversity when deploying frequency hoppingneeds to be addressed.

The following table summarises the parameters required for GPRS cell re-selection.

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(*) These parameters for the serving cell occur also on BCCH.(**) These parameters occur also on BCCH if PBCCH does not exist.

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((s) and (n) denote serving cell and non-serving cell respectively)Parameter name Description Range Bits Channel

BA(GPRS) BCCH Allocation for GPRS re-selectionNote: If PBCCH does not exist,

BA(GPRS) = BA(BCCH)

- - PBCCH D/L

BSIC(s+n) Base station Identification Code

for carriers in BA(GPRS) and the servingBCCH carrier

0-63 6 PBCCH D/L

BA_GIND Sequence number of BA(GPRS) 0/1 1 PBCCH D/LMS_TXPWR_MAX_CCH Maximum transmit power 0-31 5 BCCH D/L

POWER OFFSET(s) Power offset for DCS 1800.Not required for PBCCH

0-3 2 BCCH D/L

RXLEV_ACCESS_MIN Minimum received level at the MS requiredfor access to the system.

0-63 6 BCCH D/L

GPRS_MS_TXPWR_MAX_CCH(s+n) The maximum TX power level an MS mayuse when accessing the system

0-31 5 PBCCH D/L

GPRS_RXLEV_ACCESS_MIN(s+n) Minimum received signal level at the MSrequired for access to the system.

0-63 6 PBCCH D/L

GPRS_RESELECT_OFFSET(n)

Applies an offset and hysteresis to the C32re-selection criterion.

-52, -48,..., -12, -10,..., 12, 16, ...,48 dB

0-31 5 PBCCH D/L

PRIORITY_CLASS (s+n) The HCS priority for the cells 0-7 3 PBCCH D/LHCS_THR(s+n) HCS signal level threshold

-110, -108,..., -48 dBm0-31 5 PBCCH D/L

GPRS_TEMPORARY_OFFSET(n) Applies a negative offset to C32 for theduration of PENALTY_TIME.

0, 10,..., 60 dB, infinity

0-7 3 PBCCH D/L

GPRS_PENALTY_TIME(n) Gives the duration for which the temporaryoffset is applied.

10, 20,..., 320 seconds

0-31 5 PBCCH D/L

GPRS_CELL_RESELECT_HYSTERESIS

Additional hysteresis applied in Ready statefor cells in the same RA.

0, 2,..., 14 dB

0-7 3 PBCCH D/L

RA_RESELECT_HYSTERESIS Additional hysteresis applied for cells indifferent RAs.0, 2,..., 14 dB

0-7 3 PBCCH D/L

CELL_RESELECT_HYSTERESIS Additional hysteresis applied for cells indifferent RAs if PCCCH does not exist.

0-7 3 BCCH D/L

C32_QUAL Flag indicating an exception rule for GPRS_RESELECT_OFFSET

1/0 1 BBCCH D/L

C31_HYST Flag indicating if hysteresis shall be appliedto C31.

1/0 1 PBCCH D/L

NETWORK_CONTROL_ORDER Controls cell re-selection and measurementreporting

0-3 2 PBCCH D/L(**)

PCCCH D/LPACCH D/L

NC_FREQUENCY_LIST Frequency list for cell re-selectionmeasurement reporting

- - PCCCH D/LPACCH D/L

NC_REPORTING_PERIOD_I

NC_REPORTING_PERIOD_T

Time period for measurement reporting

0.48, 0.96, 1.92, ..., 61.44 seconds

0-7 3 PBCCH D/L

PCCCH D/LPACCH D/L

(**) These parameters occur also on BCCH if PBCCH does not exist.

The cell reselection procedure in GPRS is very slow, because it involves closing and creating a newconnection. This implies a lot of signalling and in many cases information needs to be re-sent.Durations of more than 5 seconds are expected. This is the reason why GPRS is not suited for realtime applications. Also the standards do not contemplate inter SGSN cell re-selection.

Note: There is an open issue in the deployment of GPRS in an already existing hierarchical network.Even if the PBCCH is supported it will not always be active, because if the demand for packet

services is low there is no need for it. However, in the cases the PBCCH is not active BA(GPRS) isequal to BA(BCCH).

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Initially an operator will only deploy GPRS in the macrocells for efficiency reasons. However, in ahierarchical network, a cell, regardless of whether it is macro or micro, has neighbour cells which are

both macro and micro. A GPRS mobile will hence camp sometimes in a macro and some other timesin a micro and there is nowhere in the standards that says that the GPRS mobile should re-select acell where GPRS is active.

If this problem is not solved in standards it will mean that macrocells will only be able to havemacrocell neighbours broadcast on the BCCH and the system will need to relay on a differentneighbour list sent to circuit switched mobiles when they are connected (BA(SDCCH)).

T

10.3 Power control

GPRS supports power control in order to improve the spectrum efficiency and to reduce the powerconsumption in the MS.

10.3.1 Uplink power control

In the uplink, the mobile station calculates the power value to be used on each channel as:

PCH = min(0 - CH - * (C + 48), PMAX),

whereCH is an MS and channel specific power control parameter, sent to

the MS in any resource assignment parameter. Further, thenetwork can, at any time during a packet transfer, send new CHvalues to the mobile station on the downlink PACCH iv.

0 = 39 dBm for GSM900= 36 dBm for DCS1800

is a system parameter, broadcast on BCCH/PBCCH. Optionally, mobile station and channelspecific values can be sent to the mobile station together with the

CH.C is the normalised received signal level at the mobile station as

defined below.PMAX is the maximum allowed output power in the cell =

GPRS_MS_TXPWR_MAX_CCH if PBCCH existsMS_TXPWR_MAX_CCH otherwise. POWER_OFFSET will beadded to the later in the case of class 3 DCS1800 mobiles

Packet Idle mode

When the mobile is not transmitting or receiving data (Packet Idle mode) C is measured on thePCCCH or, if PCCCH is not available, the BCCH. The mobile station measures the received

iv The CH values are transferred to the MS in the Packet Assignment command, the Ack/Nackmessages or in Power Control commands.

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signal level of each paging block monitored by the mobile station according to its current DRXmode.

The normalised C value for each radio block is calculated:

Cblock n = SSblock n + Pb

whereSSblock n is the mean of the received signal level of the four normal bursts that compose the

block

Pb is the BTS output power reduction (relative to the output power used on BCCH) used onthe channel on which the measurements are performed. For PCCCH, Pb is

broadcast on PBCCH. If frequency hopping is being used on the associatedphysical channel, Pb is reduced by 25% for each burst in the block which isreceived on the BCCH frequency. For BCCH, Pb =0 (not broadcast)

Finally, the Cblock n values are filtered with a running average filter:Cn = (1-a) Cn-1 + a Cblock n

where a is the forgetting factor: a = 1/MIN(n, MAX(5, TAVG_W/TDRX)

TDRX = DRX period for the MS

TAVG_W is broadcast on PBCCH or, if PBCCH does not exist, on BCCH. BS_PA_MFRMS isbroadcast on BCCH. SPLIT_PG_CYCLE is defined at GPRS attach

n is the iteration index

The signal level filter period TAVG_W should ideally be tuned to the RF environment in each cell:

- At large values of TAVG_W ,a mobile station can make accurate estimates of the receivedsignal strength at the expense of slow adaptation of the estimate to variations in receivedsignal strength. Larger values of TAVG_W are suitable in suburban and rural environments,

where received signal strength is slowly varying. Received signal strength measurements insuburban-rural environments are strongly correlated over distances on the order of 1 km ormore.

- At small values of TAVG_W, the received signal strength estimate can quickly respond tochanges in received signal strength. The quick response time has a downside: since fewersamples are used in the averaging process, the received power estimate is less accurate. Lowvalues of TAVG_W are suitable in urban environments, where received signal strengthfluctuates. Received signal strength measurements in urban environments may only bestrongly correlated over distances on the order of 100 m. Roughly speaking, thecharacteristics of the airlink change dramatically on the order of every 100 m.

When a mobile station is in DRX mode, it will take at least one signal strength measurement on

each BCCH carrier indicated in the BA(GPRS) list every time it monitors a paging block. Whenthe mobile station is listening to a CCCH (no PBCCH available), the mobile is receiving a

paging block one every 0.47-2.12 seconds (TDRX), depending on the value selected for DRX(BS_PA_MFRMS parameter). In the worst case, (when BA_PA_MFRMS = 9), the mobilestation makes only one BCCH carrier measurement every 2.12 seconds.

In an urban cell, at an average speed of 36 kmph, a mobile station crosses 100m the urbanairlinks correlation distance, in roughly 10 seconds. If one signal strength measurement is madeevery 2.12 seconds (worst case), 10 seconds is roughly enough time for the mobile to make 5received signal strength measurements. In this environment, these 5, highly correlatedmeasurements should be used to estimate the received signal strength. Hence, a filter period of5*2.12 (approx. 10) seconds 45 multiframes is a reasonable filter period. This filter period isattained at TAVG_W = 16.

In a suburban-rural cell, at an average speed of 100 kph, a mobile station crosses 1 km thesuburban-rural airlinks correlation distance, - in 36 seconds. A filter period of 17*2.12 (approx.

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36) seconds 153 multiframes is a reasonable filter period. This filter period is attained atTAVG_W = 19-20.

The OMC default parameter value for TAVG_W is 16 (urban environment).

Packet Transfer mode

If the mobile is transmitting or receiving (Packet Transfer mode), the mobile station uses the same received signal level measurements on the BCCH carrier ofthe serving cell as made for cell reselection. The measurements are filtered with a runningaverage filter:

Cn = (1-b) Cn-1 + b SS n

where SSn is the received signal level of the measurement samples

b is the forgetting factor: b = 1/(6*TAVG_T)


If indicated by the parameter PC_MEAS_CHAN, the mobile station instead measures thereceived signal level of each radio block on one of the PDCH monitored by the mobile stationfor PACCH. For each downlink radio block Cblock n is derived (if PBCCH does not exist, Pb = 0).Finally, the Cblock n values are filtered with a running average filter:

Cn = (1-c) Cn-1 + c Cblock n,

where c is the forgetting factor: c = 1/(12*TAVG_T)


This method is suitable in the case where BCCH is in another frequency band than the usedPDCHs. It requires that constant output power is used on all downlink PDCH blocks.

Because in Packet Transfer mode the mobile station makes at least 6 signal strengthmeasurements of the serving cells BCCH every multiframe (25 measurements per second), ashorter filter period can be used without causing too much degradation in the accuracy of theestimate. A filter period of 2 seconds (9 multiframes) captures 50 measurements. Thiscorresponds to TAVG_T = 12, and it is the default value that can be changed via the OMC.

The current Cn value is used to update the power control formula each time a new C n value isobtained or whenever the MS applies new CH orvalues.

When the mobile station receives new CH orvalues, it will use them to update PCH according to theequation 2 radio blocks after the end of the last timeslot of the message block containing the newvalues.

The mobile station uses the same output power on all four bursts within one radio block.

When accessing a cell on the PRACH or RACH (random access) and before receiving the first powercontrol parameters during packet transfer on PDCH, the mobile station uses the output power defined

by PMAX.

The GPRS power control formula is a flexible tool that can be used for different power controlalgorithms (note that the constants 0 and 48 are included only for optimising the coding ofCH), openloop and closed loop.

Lucent GPRS R1.0 supports only open loop power control. Support for closed loop is scheduled forR2.0.

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10.3.1.1 Open loop power control

In an open loop power control algorithm the output power is based on the received signal levelmeasured by the mobile station C, assuming the same pathloss in uplink and downlink.

Different types of open loop power control algorithms can be implemented using the GPRS powercontrol formula. The first one and most common is the pathloss compensation algorithm where thetransmission power changes as the pathloss changes. If in the GPRS power control formula C issubstituted by PBTS-L the result can be expressed as PMS=constant+ *L, which is the formula thatcorresponds to a pathloss compensation algorithm.

A full pathloss compensation algorithm aims to achieve a constant receive signal level at the basestation. It can be achieved by setting = 1 and CH = 0 - PBTS - SSb 48, where SSb is the requiredconstant received signal level in the uplink

Simulation studies have shown that partial pathloss compensation algorithms ( (0,1)) are moreefficient in terms of interference reduction, especially the case of= 0.5.

Quality based power control, which also tries to compensate the change in interference levels, is alsopossible with the GPRS power control formula.

An example of a quality based power control algorithm is Pn+1 = Pref - (C/In - Pn), which can also bewritten as Pn+1 = P ref + (In + L). This algorithm can be implemented using the GPRS power controlformula by substituting C for PBTS-L, and setting CH to Pref + (PBTS + IBTS), where IBTS is theinterference level measured at the BTS.

Lucent GPRS R1.0 only supports the full pathloss compensation option ( is hard coded and set to 1).The target signal level SSb si configurable via the OMC. The system then calculates the appropriateCH parameter.

Currently there is also no interference level measurement capability for GPRS in the base station.

There exists the possibility of adding the Idle Channel Measurement functionality of the circuitswitched system to GPRS. However, the precision of the C/I measurements is too low, as theinterference is only classified within 5 classes with boundaries 106, -101, -95, -90, -62 dBm, andonly the boundary value is signalled to the BSS. This is why quality based open loop power controlhas not yet been implemented.

It is important to note that in GPRS higher or lower signal levels or quality mean higher or lowerthroughput. Hence the optimisation of the power control parameters, for example the set up of SSb inthe case of full pathloss compensation, remains a complex problem which depends on the codingschemes available and the interaction between the code switching and the power control algorithms.More studies are required to solve this problem.

In general, an open loop algorithm is the simplest uplink power control option, but in some situations

is not the best in terms of quality and spectrum efficiency. This is because it is based on an estimateof the downlink path loss and therefore only suitable in areas where the downlink and the uplink

path-loss show a high correlation. However, it is especially useful in the beginning of a packettransmission, when there are not enough signal level measurements in the uplink.

10.3.1.2

10.3.1.3 Closed loop power control

A pure closed loop is achieved by setting = 0 and setting CH to the required value.

With this method the output power is commanded by the network based on received signal levelmeasurements made in the BTS in a similar way as for a circuit switched connection. Power controlcommands are sent when required in order to achieve the target received signal level.

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Both pathloss and quality based algorithms are possible. The closed loop power control algorithm tobe implemented in Lucent GPRS R2.0 is still under study.

10.3.2 Downlink power control

In the downlink, the base station has to use constant power on the PDCH timeslots with PCCCHfunctionality, which may be lower than the power used on the BCCH. The power reduction (Pb) usedon the PCCCH, relative to the output power used on the BCCH, is broadcast on the PBCCH.

On PTCCH/D, the base station has to use the same output power as for the PBCCH, or BCCH ifPBCCH does not exist.

For synchronisation purposes, the network also ensures that each mobile station in Packet Transfermode in uplink or downlink receives at least one block every 78 TDMA frames with sufficient

power, by transmitting the block at maximum power.

If the operator wants to limit as much as possible the interference produced by the constanttransmission power of PCCCH channels, if downlink power control is used, PCCCH channels shouldbe allocated where possible on the BCCH frequency.

On the rest of the timeslots, downlink power control may be used. The base station will transmit thesame output power on all four bursts within a radio block except for bursts transmitted on the BCCHcarrier.

The procedure is based on the measurements from the mobile stations. The measurements (known asChannel Quality Report) include the following information:

C value, which is running average of the received signal strength, with forgetting factor 1/(6*TAVG_T) when transmitting (Packet Transfer mode), and 1/(TAVG_W/TDRX) when nottransmitting (Packet Idle Mode)

SIGN_VAR, which is an average of the variance of the received signal level

Interference signal level of serving cell, which is averaged using a running average filterwith forgetting factor 1/NAVG_I .;The interference levels are measured on the same carrier as theassigned PDCH in packet transfer mode or on the carriers indicated by theINT_MEAS_CHANNEL_LIST in packet idle mode. If INT_MEAS_CHANNEL_LIST doesnot exist, the mobile station is not required to perform any interference measurements

RXQUAL value, which is a running average of the received signal quality with forgettingfactor 1/NAVG_I, measured on successfully decoded blocks intended for that mobile station

Two methods of downlink power control exist. Power control mode A can be used for any resourceallocation method (see 3.4). Power control mode B can only be used for fixed allocation. The methodused is determined by the BTS_PWR_CTRL_MODE sent to the mobile station in the assignmentcommand. An additional parameter is used in both modes: P0 is defined as a power reduction relativeto BCCH and it is also included in the assignment message.

In power control mode A, the base station limits its output power on blocks addressed to a particularmobile station to levels between PBCCH - P0 dB and PBCCH -P0 dB - 10 dB, where PBCCH is the powerused to transmit the BCCH. The output power has to be enough for the mobile for which the data isintended as well as the mobiles for which the USF is intended.

In power control mode B, the full base station output range can be used. However, the base stationoutput power much comply with the following rules:

-The initial output power is PBCCH P0 dB

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- The same power is used on all blocks addressed to a particular multislot mobilestation within a TDMA frame

- The output power cannot change faster than on power control step every 60 ms

-

When the network changes the base station output power from level X to level Yfor a particular mobile station, the network has to transmit at least one block at each basestation power output level between X and Y on at least one of the PDCHs allocated to thismobile station

- The output power must be sufficient for the mobile station for which the data isintended (the USF is not used for fixed allocation)

- The output power on the timeslot immediately preceding each burst of a blockaddressed to one mobile station and belonging to the same multislot allocation, must notexceed the output power of that block by more than 10 dB

Mode A downlink power control will be implemented in Lucent GPRS R2.0. Until then, the settingof the NAVG_I parameter, which is broadcast on the BCCH/PBCCH, is irrelevant, since interferencemeasurements are not used.

The following table summarises the parameters required for GPRS power control:

Parameter name Description Range Bits Channel Power control parameter

0,0.1,...,10-10 4 PBCCH D/L

(**)Pb Power reduction used by BTS on PBCCH

blocks, relatively to the output power usedon BCCH

0, -2,..., -20 dB

0-15 4 PBCCH D/L

PC_MEAS_CHAN Flag that indicates whether the downlinkmeasurements for power control shall be

made on BCCH or PDCH.

0/1 1 PBCCH D/L(**)

TAVG_W Signal strength filter period for power controlin packet idle mode

2(k/2)/ 6 multiframes, k = 0,1,..., 25

0-25 5 PBCCH D/L(**)

TAVG_T Signal strength filter period for power controlin packet transfer mode

2(k/2)/ 6 multiframes, k = 0,1,..., 25

0-25 5 PBCCH D/L(**)

NAVG_I Interference signal strength filter constant forpower control

2(k/2), k = 0,1,..., 15

0-15 4 PBCCH D/L(**)

INT_MEAS_CHANNEL_LIST Channel list for interference measurements

in packet idle mode

- - PBCCH D/L

(**)NETWORK_CONTROL_ORDER Controls cell re-selection and measurement

reporting0-3 2 PBCCH D/L

PACCH D/L

(**) These parameters occur also on BCCH if PBCCH does not exist.

10.4 Link Adaptation (Code Switching)

10.4.1

In order to provide LA a Link Quality Control (LQC) mechanism (algorithm) is required. Thismechanism should be able to take decisions on which modulation/coding scheme is the most

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appropriate to use under the existing channel conditions and therefore it provides a switching methodbetween the alternative modulation/coding schemes.

The theoretically optimum LA algorithm would select the coding scheme that maximises thethroughput of the connection.

There are a few schemes proposed for LA in GPRS. The simplest approach is to define staticthresholds (switching points) in terms of C/I ratios or BER estimations. The major drawback of thisapproach is that it is very difficult to define switching points in terms of C/I or BER since theirselection depends on a variety of parameters that are not a priori known to the system. These are the

propagation environment, the speed of the mobile stations, the use or not of frequency hopping, toname a few.

The following figure shows the results of simulations performed for different propagationenvironments: TU3 and TU50 with FH. It can be seen how the optimum switching points in terms ofthroughput vary with the propagation environment.

It also varies with the traffic model:

The following table shows for each of the propagation environments the derived switching points interms of C/I, BER and RXQUAL. It can be seen that none of the parameters offer optimum switching

points that are independent of the environment.

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Propagation Profile Switching Points C/I in dB BER RXQUAL

TU3 no FH CS1/CS2 5.47 11.82 % RXQUAL_6



TU3 FH CS1/CS2 8.27 6.3 % RXQUAL_5

TU3 FH CS2/CS3 17.43 0.59 % RXQUAL_2

TU3 FH CS3/CS4 24.96 0.034 % RXQUAL_0




TU50 FH CS1/CS2 8.69 5.7 % RXQUAL_5

TU50 FH CS2/CS3 17.10 0.84 % RXQUAL_3

TU50 FH CS3/CS4 TBD

Therefore, a particular selection of C/I or BERv switching points based on specific radio propagation parameters does not necessarily lead to good system performance when these parameters change(which is very common in radio environments). Hence, there is always a performance compromiseinvolved when this simplistic LA approach is adopted. A set of compromise thresholds in terms ofC/I could be (7,14,23) dB.

The use of parameter SIG_VAR has also been proposed as a measure of the type of channel.However, this is only valid in a coverage limited environment, since SIG_VAR only measures thereceived signal, No indication can be obtained of the interference conditions, in particular in the

presence of random frequency hopping.

Another po

impact of gprs-edge on rf network planning

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