edge training

1 © NOKIA Impact of EDGE on the BSS.PPT / MRi Company Confidential

Impact of EDGE on the BSS

Manuel [email protected]

972 374 0646


Introduction :• Name :• Position :• Past experience :• Expectation from EDGE training:


Contents and Preliminary Agenda

• Impact of EDGE in the Base Station Subsystem (BSS)

•The Abis interface

• The Dynamic Abis feature

• Dynamic Abis pool modeling & dimensioning

•Abis branching tables with dynamic Abis pool

• PCU dimensioning with EDGE

• Gb interface considerations

• Conclusions


• EDGE = Enhanced Data Rates for GSM (or Global) Evolution• Enhancement results from introduction of new

modulation (8-PSK) + channel coding schemes

• EGPRS (Enhanced GPRS): packet switched channels/ services

• New modulation triples the nominal bit rates

• Update of the GSM Standard towards 3rd generation networks/mobiles

What is EDGE?


Impact of EDGE in GSM/GPRS network

8-PSK coverage

EDGE capable TRX,GSM compatible

GMSK coverage

A-bisBTS

BTS

MSC

Gn

GGSN

EDGE capableterminal,GSM compatible

More capacity in interfacesto support higher data usage

GbBSC

A

SGSN

EDGE functionality inthe network elements


The PCU in the BSC


Impact of EDGE in the BSS• In the air interface, higher rates are achieved through the use 8-PSK. Achievable transmission rates are in the order of 59.2 Kbit/s per Radio Timeslot (RTSL).

• Higher Capacity is needed in the Abis interface

• The Dynamic Abis Pool (EDAP) is a shared extra Abis resource for EGPRS channels and TRX’s.

• The increased data traffic volume and the use of EDAP puts additional requirements of PCU and Gb capacity

AbisBSC

SGSNBTS

Um Gb

PCU

Impact


The Abis Interface

• The Abis interface is also used for GPRS services. •In a “traditional” GSM/GPRS system, each TRX channel is mapped statically to Abis PCM timeslots.

AbisBSC

SGSNBTS

Um Gb

PCU

The Abis interface is situated between the BSC and the Base Station sites


GSM/GPRS Abis Interface

PCM frame structure

•The figure shows the PCM frame structure for the T1

•Each frame of 192 payload bits includes 8 bits for each 64-kbps timeslot or 2 bits for each 16-kbps sub-timeslot.

•Each 2 bits “sub-channel” is going to be called an “Abis-channel”

•The sub-timeslots of 160 PCM frames form a TRAU or PCU frame that has 320 bits and includes the data for a radio block of 20 ms.

TS Bits used in timeslots1 2 3 4 5 6 7 8

123456789

101112131415161718192021222324

64-kbit/s timeslots

1

24

192-bitPCM frame,repeat rate8000 Hz


Static (traditional) Abis allocation principle

• One RF traffic channel reserves a 2 bit – 16 Kbit/s Abis channel in the PCM

•Two entire 64Kbit/s timeslots per each TRX.

• One 16 kbit/s, 32 Kbit/s or 64 Kbit/s LAPD signaling channel per each TRX. These can be allocated in ¼, ½ or one (1) 64 Kbit/s timeslot.

• One 16 kbit/s, 32 Kbit/s or 64 Kbit/s LAPD signaling channel per each BCF. These can be allocated in ¼, ½ or one (1) 64 Kbit/s timeslot

TS Bits used in timeslots1 2 3 4 5 6 7 8

123456789

101112131415161718192021222324 Reserved

TRX 2

TRX 5

TRX 6

TRX 9

TRX 10

BCFSIG16K:BCF1 TRXSIG16K:1:2TRXSIG16K:1:1 TRXSIG16K:1:6TRXSIG16K:1:5 TRXSIG16K:1:10TRXSIG16K:1:9

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


New requirements for EDGE

• In the air interface, higher rates are achieved through the use 8-PSK. Achievable transmission rates are in the order of 59.2 Kbit/s per Radio Timeslot (RTSL).

• Higher data rates don’t fit in 16 kbit/s A-bis channels. • 32, 48, 64 or 80 kbit/s Abis links are needed• Fixed Abis allocation of such links would be expensive and would lack flexibility.

• The Dynamic Abis Pool is a shared extra Abis resource for EGPRSchannels and TRX’s.

• The Dynamic Abis functionality allocates Abis transmission capacity to cells when needed instead of reserving full fixed transmission link per TRX.


Dynamic Abis

PCU frame types

• PCU data frame• used when TRX not in EDGE mode• only able to carry CS-1 and CS-2

• PCU master data frame• used when TRX is in EDGE mode• carries CS-1 or MCS-1 on its own and CS-2...CS-4

and MCS-2...MCS-9 with the help of slave frame(s)• includes pointers to the slave frames

• PCU slave data frame• carries additional data that does not fit in PCU

master data frames

MCS-1 M

MM

MMM

MMM

SS

S

CS-4CS-3

CS-2

CS-1

MCS-2MCS-3

MCS-4MCS-5MCS-6

MCS-7MCS-8MCS-9

SS

SSS

S

SSS

M

MMM

SSS

SSS

SS

CS-2

CS-1

D

D

non-EDGE TRXEDGE TRX

DM

S

PCU data framePCU master data frame

PCU slave data frame

+++

++

+++

+++

retrans M


Fixed channels and EDAP

• For each GPRS radio timeslot on each EDGE TRX, one fixed 16-kbps channel is allocated on the Abis for the transfer for PCU master data frames.

• PCU slave data frames are allocated in a common pool, the EDAP (EDGE Dynamic Abis Pool).

• We are still going to make a static allocation of 16 kbit/s per TCH, (used for voice or data)

• In a PSD call, this sub TS is called as a master Abis channel and if required system can allocate up to 4 extra slaveAbis sub-timeslots for same master from dynamic pool

Dynamic Abis (2) TS Bits used in timeslots

1 2 3 4 5 6 7 8123456789101112131415161718192021222324

Master

Slave

Reserved

Dynamic Abis Pool


Dynamic Abis pointers

• Each downlink PCU master data frame includes a pointer to downlink slave frames on the same block period, and a pointer to uplink slave frames on the next block period.

M M

S S S

S S S S

downlink PCMframes during

one block period

uplink PCMframes during

next block period

Dynamic Abis (3)


Transmission requirement for EGPRS coding schemes in Abis - interface

Abis PCM allocation (fixed + pool)

Coding Scheme Bit rate (bps)

CS-1 8,000CS-2 12,000CS-3 14,400CS-4 20,000

MCS-1 8,800MCS-2 11,200MCS-3 14,800MCS-4 17,600MCS-5 22,400MCS-6 29,600MCS-7 44,800MCS-8 54,400MCS-9 59,200

When EDGE is activated, CS-2 uses the pool

Slave Groups


Management of the Dynamic Abis pool (1)

• The Dynamic Abis is managed by the PCU (i.e. resource allocation and scheduling of EDAP channels)

• The management is necessary because of the EDAP is a limited resource to be shared between EDGE-TRX’s and EGPRS channels

• The management functions include:

• EDAP based EGPRS scheduling for EDGE TRX’s.

• Resource Management

•In the DL the MCS can be limited for RTSL’s if not enough EDAP resources are available.

•In the UL a transmission turn will be skipped for RTSLs if not EDAP resources are available.

•Pointer re-transmission used for EGPRS retransmissions to optimize Abis.


Management of the Dynamic Abis pool (2)

•The pool does not represent a “hard” blocking bottleneck. A pool not big enough to assign slave EDAP channels to every RTSL as requested reduces the MCS scheme granted for transmission.

• In practice PCU shares capacity evenly with users who will experience “rate reduction”.


DL Data Scheduling Example – “adequate resources available”

Requests

Grants- - CS-2 MCS-9 MCS-7 MCS-1 MCS-7

RTSL

TRX 10 1 2 3 4 5 6 7

- - CS-2 MCS-9 MCS-7 MCS-1 MCS-7

• There are enough EDAP resources to handle adequately all the data transfers and MCS requests. (e.g PS Active EGPRS ch. =< EDAP PCM TSL)

PC

M T

SL

PCM subTSL1 2 3 4

8

11109

5

2

5

-

5

-

-

-7 7 7 -4 4 4 4

12 - - - -


4

• Because EDAP is a shared resource between a higher number of EGPRS TSL it is possible to encounter the situation where there are not enough EDAP resources to handle “adequately” all the data transfers (e.g PS Active EGPRS ch > EDAP PCM TSL)

DL Data Scheduling Example “adequate resources not available”

Grants

RTSLRequestsTRX 1

0 1 2 3 4 5 6 7

- - CS-2 MCS-5 MCS-9 MCS-8 MCS-1 MCS-7

- - CS-2 MCS-5 MCS-7 MCS-7 MCS-1 MCS-6PCU-TRX 0

53

5 5

74 4 -P

CM

TS

L

PCM subTSL1 2 3 4

1112

10

-72


Abis Pool Features and Limitations

• The Dynamic pool (EDAP) is used only for PSD

• The maximum pool size is of 12 PCM timeslots

• DAP can be shared for multiple TRXs in the same base station cabinet

• Only EDGE TRXs can use EDAP

• Several pools can be created in to the same PCM.

• The traffic and signaling timeslots including the dynamic pool for each TRX

must be located in the same T1 frame and can’t be distributed across different

T1s.

• All timeslots that make the pool should be contigous

• The actual size and number of DAPs needed for a site depend on the amount

of traffic that is expected to be handled by the site as well as the site

configuration.


How big should EDAP be?

• EDAP is a common resource shared dynamically among several TRXs:

•More data traffic à More EGPRS active channels à Larger pool needed.

• Different MCS make use of the pool differently• Some savings are achieved thanks to pointer retransmissions• What are the performance targets for the pool? à How often can we tolerate that the pool can’t grant the requested MCS? à (e.g. Target below 2% of the time)


EDAP Modeling (1)

• In its basic form, the EDAP can be modeled by understanding the rate at which RTSL will be requesting EDAP resources. Rate = RTLS data utilization

TRX 1 TS TS TS TS TSTS TS TSPBCCHBCCH

TS

TS

EGPRS TSL

Voice

TRX 2TS TS TS TS TSTS TS TSPBCCHBCCH

PC

M T

SL

PCM subTSL

1 2 3 4

11109

- - - -- - - -- - - -

4 RTSL contending for 3 PCM TSL


EDAP Modeling (2)

When we know the pool size and how many air-timeslots are competing of the usage of the pool we can calculate the Abisoverflow value. Pool overflow can be calculated using the binomial distribution.

,where x is the number of successes in trials, p is the utilization of the slave (E)GPRS channels (CS-1, CS-2, MCS-1 and re-transmission are not included in it), n are the EGPRS RF-timeslots in use. Probability of pool overflow (blocking) will be:

B(n,N,p)=

, where N is the available pool size.

xnx ppxn

xP −−⋅⋅

= )1()(

∑+=

n

Nx

xP1

)(


EDAP Modeling (3)Example:

•RTSL utilization• 3 EGPRS RTSLs (Dedicated + Default territory)• Data Traffic = 1.5 Data Erlangs traffic• RTSL utilization = 30% (Channel_utilization = Erlang_PS / Available_TLS)

• 3 sectors X 3 EGPRS channels = 9 EGPRS channels

• EDAP = 5 PCM TSLs

• 9 EGPRS channels contending for 5 PCM TSLs

TRX 2

TRX 1

TS TS TS TS TS TS

TS TS T TS TSTS TS TSSSDCCHBCCH

TSTS

TS

TS

Dedicated EGPRS TSL

Default territory EGPRS TSL


97.5%

Probability of not having enough DL EDAP resources

Probability of pool not suffering overflow

Pool slave utilizationPCM RTSL 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8

4 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14 5 1 1 1 1 0.999 0.998 0.995 0.99 0.982 0.969 0.95 0.922 0.884 0.832 0.763 0.6724 6 1 1 1 0.998 0.995 0.989 0.978 0.959 0.931 0.891 0.836 0.767 0.681 0.58 0.466 0.3454 7 1 1 0.999 0.995 0.987 0.971 0.944 0.904 0.847 0.773 0.684 0.58 0.468 0.353 0.244 0.1484 8 1 1 0.997 0.99 0.973 0.942 0.894 0.826 0.74 0.637 0.523 0.406 0.294 0.194 0.114 0.0564 9 1 0.999 0.994 0.98 0.951 0.901 0.828 0.733 0.621 0.5 0.379 0.267 0.172 0.099 0.049 0.02

5 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15 6 1 1 1 1 1 0.999 0.998 0.996 0.992 0.984 0.972 0.953 0.925 0.882 0.822 0.7385 7 1 1 1 1 0.999 0.996 0.991 0.981 0.964 0.938 0.898 0.841 0.766 0.671 0.555 0.4235 8 1 1 1 0.999 0.996 0.989 0.975 0.95 0.912 0.855 0.78 0.685 0.572 0.448 0.321 0.2035 9 1 1 0.999 0.997 0.99 0.975 0.946 0.901 0.834 0.746 0.639 0.517 0.391 0.27 0.166 0.0865 10 1 1 0.999 0.994 0.98 0.953 0.905 0.834 0.738 0.623 0.496 0.367 0.249 0.15 0.078 0.0335 11 1 1 0.997 0.988 0.966 0.922 0.851 0.753 0.633 0.5 0.367 0.247 0.149 0.078 0.034 0.0125 12 1 0.999 0.995 0.981 0.946 0.882 0.787 0.665 0.527 0.387 0.261 0.158 0.085 0.039 0.014 0.004

MCS-9


EDAP MCS adjustment

MCS-7 44,800

MCS-7 coding scheme uses EDAP ¾ of the EDAP PCM TSL (3*16kbit/s sub-channels)

For example: EDAP pool of size 4 PCM timeslots is big enough to accommodate 4*4/3 = 5 MCS-7 calls

PC

M T

SL

PCM subTSL1 2 3 4

8

11109

1

5

1

5

1

5

2

63 4 4 42 2 3 3


EDAP Modeling (3)Example:

•RTSL utilization• 3 EGPRS RTSLs (Dedicated + Default territory)• Data Traffic = 1.5 Data Erlangs traffic• RTSL utilization = 30% (Channel_utilization = Erlang_PS / Available_TLS)

• 3 sectors X 3 EGPRS channels = 9 EGPRS channels

• EDAP = 5 PCM TSLs

• 9 EGPRS channels contending for 5 PCM TSLs

•Avg. MCS used in the network: MCS-7

TRX 2

TRX 1

TS TS TS TS TS TS

TS TS T TS TSTS TS TSSSDCCHBCCH

TSTS

TS

TS

Dedicated EGPRS TSL

Default territory EGPRS TSL


99.6%

Probability of not having enough DL EDAP resources

7 3 Pool slave utilizationPCM TSL RTSL 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8

4 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14 6 1 1 1 1 1 0.999 0.998 0.996 0.992 0.984 0.972 0.953 0.925 0.882 0.822 0.7384 7 1 1 1 1 0.999 0.996 0.991 0.981 0.964 0.938 0.898 0.841 0.766 0.671 0.555 0.4234 8 1 1 1 0.999 0.996 0.989 0.975 0.95 0.912 0.855 0.78 0.685 0.572 0.448 0.321 0.2034 9 1 1 0.999 0.997 0.99 0.975 0.946 0.901 0.834 0.746 0.639 0.517 0.391 0.27 0.166 0.086

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15 7 1 1 1 1 1 1 0.999 0.998 0.996 0.992 0.985 0.972 0.951 0.918 0.867 0.795 8 1 1 1 1 1 0.999 0.996 0.991 0.982 0.965 0.937 0.894 0.831 0.745 0.633 0.4975 9 1 1 1 1 0.999 0.996 0.989 0.975 0.95 0.91 0.85 0.768 0.663 0.537 0.399 0.2625 10 1 1 1 0.999 0.996 0.989 0.974 0.945 0.898 0.828 0.734 0.618 0.486 0.35 0.224 0.1215 11 1 1 1 0.998 0.992 0.978 0.95 0.901 0.826 0.726 0.603 0.467 0.332 0.21 0.115 0.055 12 1 1 0.999 0.996 0.986 0.961 0.915 0.842 0.739 0.613 0.473 0.335 0.213 0.118 0.054 0.019

MCS7MCS-7


Dynamic Abis counters

• The counters of Dynamic Abis Measurement give information about the usage of Dynamic Abis Pools.

TOTAL NUMBER OF PCM SUB-TSLs IN EDAPAVERAGE DL EDAP USAGE AVERAGE UL EDAP USAGE

PEAK DL EDAP USAGE PEAK UL EDAP USAGEUL TBFs WITHOUT EDAP RESOURCESDL TBFs WITHOUT EDAP RESOURCES

DL TBFs WITH INADEQUATE EDAP RESOURCES

Approximation to pool overflow


How can I plan the branching tables with EDAP

1. Understand the site configuration (TRXs, Cabinets, EDGE TRXs)2. Identify the EDGE TRXs that need to be connected to a DAP (GTRX=Y)3. Remember:

• DAP can be shared for multiple TRXs in the same base station cabinet• The traffic and signaling timeslots including the dynamic pool for

each TRX must be located in the same T1 frame and can’t be

distributed across different T1s.

• All timeslots that make the pool should be contigous

4. A ball park number:• Depending on the pool size, we may be able to transport about 6 TRXs

with a pool and signaling in the same T1


2+2+2 site structure

24V

Cabinet # 1

TRX#1TRX#2 A: 1900*

TRX#5TRX#6 B: 1900*

TRX#9TRX#10 C: 1900*

1900 TRX

Transmission Unit: FXC E1/T1

Cabinet 1

T1-1


2+2+2 site structure (2)Name: E222A

Configuration of BTSs: Timeslot allocation:BTS: Actual config: Forecasted config:BCF sig: TS Bits used in timeslotsBCF 1 2,2,2 16k 1 2 3 4 5 6 7 8

123

TRX numbering: 4TRX numbers: 5

BTS: Segment BTS actual: 6BCF 1 1 1,2 7

2 5,6 83 9,10 9

10111213

Legend: 14cross-connect TimeSlot 15unused TimeSlot 16

1718

TRX Legend: TRX A-B 19A: BCF # 20B: TRX # 21

22BCFSIG Legend: BCFSIG:X:Y 23TRXSIG Legend: TRXSIG:X:Y:Z 24X: Bit RateY: BCF # EDAP Pool Cabinet TRX # Band

Z: TRX # 1 1 1,2,5,6,9,10 1900

TRXSIG16K:1:5 TRXSIG16K:1:6

Reserved


T1-1

TRX 1-9

EDAP Pool 1

TRX 1-1

TRX 1-2

TRX 1-10

TRX 1-6

TRX 1-5

TRXSIG16K:1:1 TRXSIG16K:1:2BCFSIG16K:1

TRXs connected to EDAP


5+5+5 site structure

Cell ASEG 1BTS1

Cell CSEG 3BTS 3

Cell CSEG 2BTS 2

Cabinet 1 Cabinet 2

Cell Cell Ch Cabinet TRX Cell Cell Ch Cabinet TRXA 1 1 C 1 1

A 2 2 C 2 2

A 3 3 C 3 3

A 4 4 C 4 4

A 5 5 C 5 5

B 1 7

B 2 8

B 3 9

B 4 10

B 5 11


5+5+5 site structure (2)Timeslot allocation: Timeslot allocation:TS Bits used in timeslots TS Bits used in timeslots

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 81 12 23 34 45 56 67 78 89 9

10 1011 1112 1213 1314 1415 1516 1617 1718 1819 1920 2021 2122 2223 2324 24

EDAP Pool Cabinet TRX # Band1 1 1,2,3,7,8,91900/8502 2 1,2,3,4 1900/850

EDAP 2

T1-1

TRX 1-3

TRX 1-8

TRX 1-7

TRX 1-2

Reserved for Cingular

TRXSIG16K:1:8TRXSIG16K:1:2

BCFSIG16K:BCF1

TRX 1-9

TRX 1-1

TRXSIG16K:1:1

TRXSIG16K:1:3TRXSIG16K:1:7


EDAP 1

T1-2

TRX 2-1

TRX 2-2

TRX 2-3

TRX 2-4

TRX 1-4

TRX 1-10

TRX 1-11


TRXSIG16K:1:11


Reserved for CingularBCFSIG16K:BCF2 TRXSIG16K:2:1TRXSIG16K:2:2 TRXSIG16K:2:3

TRX 2-5TRX 1-5

TRXs connected to EDAP


5+5+5 site structure (3)

Transmission Unit: FXC E1/T1

T1-1

To BSC

T1 A-BCabinet 1 Cabinet 2

To BSC

T1-2


PCU Dimensioning - 1Each BSC can now have up to 16 PCUs installed.

00253244

LEGEND:

1. Extension 4th SW64B Plug in Unit2. Extensions GPRS/EDGE3. Cartridges 8 & 9

GSWB 192-> 256

2nd PCU cards, 8+1

EXTRA 2*ET5Cs

2nd PCU for GPRS/EDGE

GSWB extension kit (192->256 PCMs)

External PCM extensions to increasePCMs in BSC2i from 112 to 144, ET5Cs 8 & 9, requires GSWB (256)

PSA20PSFP

PSA20PSFP

SW

1CM

CM

US

D3C

-S

OM

UM

CM

U

BC

SU

BC

SU

BC

SU

BC

SU

BC

SU

BC

SU

ET5

C

ET5

C

ET5

C

ET5

C

ET5

C

ET5

C

BC

SU

BC

SU

BC

SU

SW

1C

CLO

C

CLA

C

ET5

C

ET5

C

ET5

C

1

2

2

2

2

2

2

2

33

2

2

1


PCU Dimensioning - 2The PCUs have the following dimensioning criteria

• PCU connectivity towards the Abis interface supports 256 Abis channels, including (including PBCCH/PCCCH +default GPRS + EDAP channels and additional GPRS territory)•PCU supports 128 Abis channels, including: PBCCH/PCCCH +default GPRS + and additional GPRS territory•PCU connectivity towards the Gb interface is 31*64 Kbit/s channels. Data throughput up to full Gb capacity utilization (31*64K = 1984 Kbit/s) is supported.


PCU Dimensioning - 3• PCU supports up to 128 TRXs• 64 BTS (Note that BTS is defined as a group of TRXs sharing a same configuration, a sector which is now defined as a SEGMENT, starting in S.10) •The theoretical maximum number of TRXs per DAP is 20. However, since TRXs using DAP resources must be allocated to the same AbisETPCM line with EDAP, the maximum TRX count for a DAP about 7-8 in the ANSI environment.•The serving PCU must be the same for all the TRXs under one segment


PCU Dimensioning - 4Internal PCU restrictions:•A PCU has 16 DSP cores. One DSP core can handle only one EDAP, butone EDAP can be shared by several DSP cores. The maximum number of EDAPs per PCU is 16.

•One DSP core can handle 0…20 channels (16 kbit/s) including activeEDAP channels, EGPRS channels, GPRS channels and PBCCH/PCCCHs.

Some possible but bad configuration examples:

• One EDAP containing 12 TSLs and 15 EDAPs containing 2 TSLs each areconfigured to one PCU. The first EDAP is handled in one DSP core, andthe EDAP has 48 channels. Only 16 EDAP channels of the first EDAP canbe used by 4 EGPRS channels.

• 16 EDAPs that each contain 3 TSLs are configured to a PCU. The TRXsthat are connected to one EDAP have 20 default GPRS channels (totalcount). No single EDAP channel can be used and only MCS 1 or CS 1traffic is possible in the TRXs.


How many PCUs do I need?

• We need to understand the kind of sites that I will be connecting, different sites produce different “load”

•For example, 2+2+2 site

Site type 222

GPRS Defaul territory (includes dedicated) 0Number of BTSs per site 0Abis channels for GPRS territory 0

EGPRS Defaul territory (includes dedicated) 3Number of BTSs per site 3Abis channels for EGPRS territory 9EDAP 1 Pool size (DS0s) 5Abis channels for EDAP 1 20EDAP 2 Pool size (DS0s) 0Abis channels for EDAP 2 0

Total fixed Abis channels per site 29


How many PCUs do I need? (2)

• Don’t forget to leave a margin to allow for GPRS territory upgrades !!•If we expect to utilize additional territory channels for example 15% of the time, then we need to adjust the PCU planning capacity limit

PCU Abis channel capacity 256PCU utilization factor (to account for additional territory and possible addition of PBCCH) 85%PCU planning capacity 218

• Calculate how many sites can be supported with one PCU and withdifferent sets

BSC Utilization 100% 75%Number of sites per PCU 7Number of sites per 8 PCUs 8 56 42Number of sites per 12 PCUs 12 84 63Number of sites per 16 PCUs 16 112 84

Leave an additional margin to support site additions without need to modify PCU count and Gb plan


Gb interface considerations

• The number of PCUs selected has an impact on the Gb interface and SGSN dimensioning

BSC

PCU

SGSN

Frame Relay

Gb

PAPUBSS GPRS


GPRS logical to physical channels mapping

NSVC1

NSVC2

PCU1/NSE100

NSVC1

DLCI 16 CIR=384 Kbit/s

AR= 384 Kbit/sNSVC5

NSVC6

PCU2/NSE101

NSVC9

NSVC10

PCU3/NSE102

NSVC13

NSVC14

PCU4/NSE103

BSC1

T1-1

BCH1

NSVC5

DLCI 18 CIR= 384 Kbit/s

AR= 384 Kbit/s

BCH3

NSVC9


AR= 384 Kbit/s

BCH5

NSVC13


AR= 384 Kbit/s

BCH7

• With 4 PCUs and 1 T1, F.R. Bearer Channel size is 384 Kbit/s = 6 x 64 Kbit/s

• Bearer channel size should as be able to transport as an absolute minimum: Mobile Max RTSL * 64kbit/s• e.g: If we plan to have 3 TSL mobiles in the network, the absolute minimum size for the bearer channels should be 3*64k = 192 Kbit/s


CONCLUSIONS

• With EDGE it is necessary to activate a new feature called Dynamic Abis• The Dynamic Abis functionality allocates Abis transmission capacity to cells when needed instead of reserving full fixed transmission link per TRX. • It is necessary to properly size the EDAP to achieve good BSS transmission performance• The size and number of EDAPs in a BSC has an impact on the PCU dimensioning• It is necessay to optimize the whole chain: RF + EDAP + PCU dimensioning + Gb

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