Eng, GPRS - Eng Guide, Radio 060426-2

CELTEL INTERNATIONAL B.V.

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GPRS/EDGE Radio – Celtel Deployment Engineering Guidelines

Document Category: GUIDELINE Information Category: NETWORK-PLANNING-RF Development Status: FINAL Document Owner: CI TCH

File Name: 1 (22) 28/08/2006 Eng, GPRS - Eng Guide, Radio 060426-2.doc

GPRS/EDGE Radio Deployment – Celtel Engineering Guidelines

Key Words

Distribution

Purpose Addressees

TO OpCo Planning and Technical Personnel

CC Document Control

Date [dd/mm/yyyy]

Description Of Change Author Version No.

27/02/2006 Initial Guidelines Bayan Monadjem 0 10/04/2006 Update, correction and expansion of Intial release Bayan Monadjem 1 26/04/2006 Update Alcatel BTS EDGE capability Bayan Monadjem 2


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Contents 1 GENERAL ................................................................................................................................... 3 2 RADIO NETWORK DIMENSIONING.......................................................................................... 4

2.1 PDCH Configuration.......................................................................................................... 4 2.1.1 Dynamic (on-demand) vs Dedicated (static) PDCHs ................................................... 4 2.1.2 Packet Control Channel Configuration ......................................................................... 5

2.1.2.1 PBCCH (Packet Broadcast Control Channel)...................................................... 5 DESIGN and SPECTRUM ISSUES ................................................................................................... 6

2.2 On which TRX should the PDCHs be configured? ........................................................... 6 2.2.1 Channel Allocation Strategy ......................................................................................... 6

2.3 In which band (900P, 900E or 1800) should the PDCH be configured? .......................... 7 2.4 Impact on GSM network capacity plan ............................................................................. 8 2.5 Dynamic PDCH & Pre-emption......................................................................................... 9 2.6 Impact on cell design ........................................................................................................ 9 2.7 Link Adaptation and Incremental Redundancy ................................................................. 9

2.7.1 GPRS............................................................................................................................ 9 2.7.2 EDGE.......................................................................................................................... 10

2.8 Routing Areas ................................................................................................................. 12 2.9 Impact on A-bis ............................................................................................................... 13

3 PERFORMANCE MEASUREMENT THROUGH BSS COUNTERS ........................................ 14 3.1 Data Volume ................................................................................................................... 14 3.2 IP Throughput ................................................................................................................. 14

3.2.1 Interference................................................................................................................. 15 3.2.1.1 Radio Link Bitrate ................................................................................................... 15

3.2.2 Capacity...................................................................................................................... 15 3.2.2.1 PCU Congestion..................................................................................................... 15 3.2.2.2 Multi-slot Utilisation ................................................................................................ 16 3.2.2.3 PDCH Allocation..................................................................................................... 16

3.2.3 Mobility........................................................................................................................ 16 4 PERFORMANCE MEASUREMENT THROUGH TEST MOBILE............................................. 17

4.1 Possible Test Applications .............................................................................................. 17 4.2 Celtel Recommended Test Process ............................................................................... 18 4.3 Test Mobile KPIs to be extracted .................................................................................... 19

5 DEPLOYMENT.......................................................................................................................... 20 5.1 Planning for EDGE.......................................................................................................... 20

6 HUMAN RESOURCES, PROCESSES & TOOLS.................................................................... 22 6.1 RF Engineering HR issues.............................................................................................. 22 6.2 RF Engineering Tools ..................................................................................................... 22 6.3 Training ........................................................................................................................... 22



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1 GENERAL This document outlines the Celtel group strategy for radio network preparation for the deployment of GPRS/EDGE services and covers the follows subject areas:

Dimensioning

Design & Spectrum Issues

Performance

Deployment

Human Resource & Tools

Additionally, there are sections that are not covered in this document but that will need future attention. Principally are:

Default parameters (vendor and BSS s/w release specific)



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2 RADIO NETWORK DIMENSIONING

In depth dimensioning of PDCHs (Packet Data Channels) is complex and multiple inputs have to be considered, such as

Initial configuration, i.e. frequency reuse (C/I environment) and # TRX and capabilities.

Circuit switched traffic and grade of service requirements.

Volume and characteristics (object size) of GPRS/EGPRS data traffic (dependant of subscribers and applications used).

Throughput requirements for GPRS/EGPRS data traffic (dependant on type of application being planned for).

Mobile multislot class that the system is to be dimensioned for (handset dependant).

In order to reduce the complexity of the exercise (especially for the start-up phase), a set of default guidelines will be used in configuring the network. In future, these will be optimised according to need.

2.1 PDCH Configuration 2.1.1 Dynamic (on-demand) vs Dedicated (static) PDCHs

Dynamic (on-demand) PDCH:

A timeslot, i.e. traffic channel, temporary allocated for packet data traffic. Circuit switched traffic is prioritised. Pre-emption is possible (channel changes from PDCH to TCH when voice traffic demand requires the resources).

All can be allocated as on-demand PDCHs except the timeslots used for BCCH and SDCCH.

Dedicated (static) PDCH:

A timeslot, i.e. traffic channel, reserved for packet data traffic.

A maximum of 8 dedicated PDCH per cell is possible (Ericsson implementation).

Using dedicated PDCH’s has some advantages: and disadvantages:

Advantages:

increase throughput & decreased user perceived delay due to less channel reconfigurations – can take 50 - 100ms to convert an idle TCH to an on-demand PDCH (vendor and s/w release dependant)

secure incessant GPRS traffic in each cell. If no dedicated PDCHs are configured, under peak load conditions the situation can arise were all time slots are occupied for CS traffic (voice) and no data service is available at all.

Reduce BSC load (although the effect of PDCH/TCH re-configuration is typically low (approx 1%)



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allow use of PBCCH (Packet Broadcast Control Channel). This allows greater control of cell reselection (eg separate CS/PS neighbour lists, etc)

Disadvantages:

less capacity for CS voice traffic

Less efficient pooling of PCU resources. Each dedicated PDCH has a GSL (GPRS Signalling Layer) device permanently attached to it. (Note: in Ericsson R11, semi-dedicated PDCHs allow a work-around to this limitation)

As the data traffic at the start of the service is not likely to be great, a cost trade-off is required to efficiently implement the data service with a minimum impact on cost (TRX upgrades, cabinet upgrades, capacity relief sites) and the minimum negative impact on the circuit switched voice service (this remains the core business of Celtel).

Hence, the recommendation for starting the service is:

URBAN ENVIRONMENT: A single dedicated PDCH should be configured, with 3 dynamic PDCHs configured on the same TRX as initial configuration for launching the services. This rule should be applied to ALL cells in the urban environment.

RURAL ENVIRONMENT: Cells with 2 TRXs or more should be configured with a single dedicated PDCH and 3 dynamic PDCHs (as in the urban scenario). Cells with only 1 TRX should be configured with 4 dynamic PDCHs and no dedicated PDCHs.

Please note the impact on A-bis Transmission Requirements (see 2.9, Impact on A-bis).

In future, dimensioning rules will be developed to assist in the dimensioning of the required no of dedicated and dynamic PDCH.

2.1.2 Packet Control Channel Configuration 2.1.2.1 PBCCH (Packet Broadcast Control Channel) Initially a PBCCH should not be configured. The GPRS MS will listen to the GSM BCCH (contains new SI 13) and PCH. The GPRS MS will use the GSM CS PCH, RACH and AGCH.

This allows for slightly greater capacity (no TS reserved for PBCCH) and allows sufficient mobility for data users. Even though NACC (network assisted cell change) works more efficiently with a PBCCH, the benefit is seen to be negligible as most heavy data usage will not be mobile.



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DESIGN and SPECTRUM ISSUES 2.2 On which TRX should the PDCHs be configured? Data services require a high C/I in order to deliver high data throughput (as the seen in the performance curves in Figure 3 for GPRS (with Link Adaptation) and EDGE (with Link Adaptation and Incremental Redundancy). Celtel’s approach to frequency planning – a dedicated BCCH block of 13-15ARFCN) and the rest of the carriers arranged with a tighter re-use (synthesised or base band hopping ) with means that the BCCH TRX experiences the best C/I environment.

Hence it is recommended to implement the 4 PDCHs (1 dedicated and 3 dynamic) on the BCCH TRX as the BCCH carrier is usually the least interfered carrier.

Also, as the uptake of the data service expands, so the BCCH block can be expanded (to between 15-21ARFCN) to improve the C/I environment for the PDCHs and hence improve the data throughput. This will avoid having to have 2 sets of relaxed frequency re-use blocks (1 for BCCH and 1 for PDCH). Guidelines will be provided for any such change in frequency planning strategy in the future.

2.2.1 Channel Allocation Strategy It is important to have a traffic allocation strategy that minimises disruptions to PS connections. This is to avoid situations where the current PSET (Set of PDCHs) cannot be expanded to cater for a new user as it is blocked by a TCH; there is only one PSET per TRX and only PDCHs in the same PSET can be used for the same PS connection. The result is that a new PSET is created on another TRX. In some cases the new PSET may only be one time slot as there are no TRXs with more than one TS available. This will have a large impact on the throughput for multi-slot mobiles. The recommended channel allocation strategy is shown in Figure 1 (CHGR being an Ericsson definition, but the overall concept applies to all BSS equipment). This allocation strategy prioritises CS traffic allocations on the BCCH TRX (for Ericsson, set CHALLOC=2). Also, the SDCCH allocations allows only one SDCCH on the BCCH frequency, with the rest of the SDCCH allocations being made on the TCH TRXs. In this way if the TCH TRXs become unavailable then there is still an SDCCH on the BCCH TRX so the entire cell does not become unavailable. In the Ericsson BSS, in order to configure the PDCHs on the BCCH, the parameter PDCHALLOC must set to prioritise PDCH allocations on the BCCH frequency. This results in the timeslots on the BCCH frequency only being used for CS traffic when all of the TCH timeslots are in use. The timeslots on the BCCH TRX will then be available for PS connections. Some Ericsson parameters to look at: CHALLOC=2 PDCHALLOC=FIRST SAS=MULTI SDCCH allocations (SDCCH, TN, BCCHTYPE)=according to Figure 1



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B S P P P P

B = BCCH S = SDCCH T = TCH P = PDCH

S S T T T T T

T T T T T T T

T T T T T T T

CHGR0

CHGR1

CHALLOC=2 (BCCH last) PDCHALLOC=FIRST

Figure 1: Recommended channel allocation strategy

Note 1: This implementation requires that one SDCCH channel be configured on the BCCH TRX, and all further SDCCHs be configured on non-BCCH TRXs.

Note 2: Some of the vendors BSS parameters allow the operator to select the preferred TRX for calls to be established on (BCCH & non-BCCH). For voice services (normal circuit-switched), this should be set to prefer establishing calls on the non-BCCH TRX (e.g. Ericsson parameter CHALLOC should be set to 2 with the command: RAEPC:PROP=CHALLOC-2).

Note 3: The output power of the BTS can be different for the 8PSK (EDGE) and GMSK (GSM voice, GPRS, signalling) modulation. However, as the proportion of the EDGE traffic is low, and the TRX power in urban areas is not set to the maximum, the impact of this is considered to be negligible

Note 4: Intracell Handovers (IHO) in the Ericsson BSS, triggered by poor RxQual, will attempt to handover the call to a different channel group. Therefore, dynamic PDCHs on the BCCH TRX (CHGR-0) risk being pre-empted by incoming IHO CS traffic from the TCH TRXs (CHGR-1). The impact of this on throughput has to be evaluated as this is a potential risk to high data throughput by evaluating the data throughput & preemptions vs no of IHOs. This risk should be managed through optimisation.

2.3 In which band (900P, 900E or 1800) should the PDCH be configured?

At the moment the only one Celtel operation (TZ) has E-GSM spectrum, and then in a limited quantity (2.5MHz), making the use of E-GSM for data services impractical at the moment. However this position can be revised in future should Celtel succeed in acquiring E-GSM spectrum in a bigger blocks (min 3MHz and up to 5MHz ideally).

Also, the cell grid plans of all Celtel networks is based on 900MHz inter-site distances, and 1800MHz cells are deployed on top of the 900MHz cells as a capacity layer only, meaning that the primary coverage layer remains on the 900MHz band, with no contiguous 1800MHz coverage. Hence, only the 900MHz primary band (P-GSM) can, at the moment, be realistically considered for data services.

In future, when the 1800MHz deployment blanket covers the main cities, a different strategy can be followed in cities where 1800MHz spectrum is available in large blocks (especially where 900MHz band is tight).

The major problem with this configuration is that dualband mobiles camping on the 1800 band will not detect any packet service and the user will perceive a loss/lack of GPRS/EDGE service. In order to overcome this, the strategy on idle mode behaviour has to be revised as described below:



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Mobiles should always camp on the 900MHz band and at call setup; the appropriate band is selected through the TCH assignment process. This situation will require all the SDCCH channels (required by the co-sector 900 and 1800 cells) be configured on the 900 band, and only 1 SDCCH be configured on the 1800 (this can be started as a combined BCCH + SDCCH/4 and expanded to a dedicated SDCCH/8 if required). For Ericsson BSS, this will require activation of the feature “Increased SDCCH Capacity” (FAJ 121 355). The other parameters required to force the mobiles to camp on the 900 band are described below. Further parameterisation is required to prioritise the 1800 band for traffic but this described in the celtel default parameters database as it is beyond the scope of this document.

Ericsson: ASSOC-ON (enable Assignment to other cell at BSC level) HNDSDCCHTCH=0 (Disable inter-BSC assignment to other cell) HNDBEFOREBANSW=0 (Disable inter MSC HO from taking place before answer from B party) SSLENSI=2 AW=ON (as per Celtel default parameter recommendation) CAND=BOTH (as per Celtel default parameter recommendation) AWOFFSET (as per Celtel default parameter recommendation) ACCMIN=110 (900 & 1800) CRO=0 (900); CRO=10 (1800) PT=0 (900) = 31 (1800) CBQ=HIGH (900); CBQ=LOW (1800) Siemens: RXLEVAMI=110 (900 & 1800) CRESOFF=0 (900); CRESOFF=10 (1800) PENTIME=0 (900); PENTIME=10 (1800) CBQ=0 (900); CBQ=1 (1800); ALcatel: RXLEV_ACCESS_MIN =110 (900 & 1800) CELL_RESELECT_OFFSET=0 (900); CELL_RESELECT_OFFSET =10 (1800) PENALTY_TIME =0 (900); PENALTY_TIME =10 (1800) CELL_BAR_QUALIFY=0 (900); CELL_BAR_QUALIFY=1 (1800);

2.4 Impact on GSM network capacity plan Celtel uses in-house tools to drive a dimensioning method based on circuit-switched traffic load per cell to dimension the radio network capacity. Introducing data services requires the planner to add 1 dedicated timeslot (TS) to the radio network capacity of each cell for data services. A mechanism to implement this crudely has been integrated into the new capacity planning tool and will be refined in future versions.

Note that when planning for capacity, the effect of the dynamic PDCHs is not considered as these can be pre-empted by circuit switched traffic (voice). Only the effect of dedicated PDCHs has to be taken into account.

Operations must nonetheless monitor – specifically following commercial launch – the development in demand for and usage of data services during Cell BH and determine whether additional TRX upgrades would be required to cater for reasonable data throughput and services availability, while maintaining required QoS for voice services (2% Air Interface blocking). It would be valuable to understand the traffic patterns of both voice and data services, monitoring separate and combined 24hr traffic distribution for both. As mentioned previously, a dimensioning mechanism will be introduced to cater to data traffic in the Celtel capacity planning tool.

In future, optimised techniques will be introduced that dimension based on:



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Cell TS resources available (difference between installed TS capacity and CS traffic demand)

Circuit switched traffic load in the cell

Packet switch traffic load in the cell

2.5 Dynamic PDCH & Pre-emption Dynamic PDCHs can be pre-empted (ie converted to CS TCHs) if no time slots are available for voice. The criteria for pre-emption can be specified. For example, in the Ericsson R10, the following pre-emption criteria are supported: Pre-emption of:

Only idle PDCHs

Only non essential PDCHs (not carrying TAI) and idle PDCH

Only on-demand PDCHs that are not marked as `used for streaming' or are non-essential

Only on-demand PDCHs that are not marked as `used for streaming'

All PDCHs

As the network is dimensioned primarily for CS voice traffic, the recommendation is that pre-emption of all PDCHs should be configured. When the volume of data on the networks increases, then this recommendation can be reviewed.

2.6 Impact on cell design Data services are sensitive to C/I and general better performance will be experience closer to the cell site, and in areas with good cell dominance. GPRS CS3 &4 will be allocated in high C/I environments, whereas typically, CS2 (and equally low MCS schemes) will be used at the cell borders. Hence, high priority areas where high speed and high volume data throughput are required should be served by a clean BCCH carrier, which in practice, often means that a cells site should be deployed close to such areas. This demand will have to be identified together with the marketing team, and will only come into play when the usage of the packet data service increases considerably.

At the start of the service, there is no impact on cell design and no sites need to be added to specifically cater for data services.

In general, the Celtel cell plan philosophy should aim to improve Celtel networks in areas where there is no dominance from a single cell/site as these areas are likely to experience lower C/I (which also may affect voice services) and hence lower data throughput rates (assuming of course a significant amount of data usage in the area).

Also, there is a difference between the EDGE and GSM/GPRS link budget and in future the design criteria and frequency plan targets will be developed as a guide for cell and frequency planning to accommodate EDGE data services.

2.7 Link Adaptation and Incremental Redundancy 2.7.1 GPRS GPRS is a packet switched service in GSM. The smallest entity is called a radio block and it consists of four normal bursts. A radio block can be transmitted over the radio interface using any of the four coding schemes that are available. The coding schemes are CS-1 to CS-4. The lower



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coding schemes have a high amount of channel coding and give a low data rate. The higher coding schemes have less channel coding and give a higher data rate.

The most robust coding scheme (CS-1) is used for transmission of all radio blocks that carry RLC/MAC control messages. Radio blocks can also carry RLC data blocks, and in such case any of the four coding schemes can be used. The coding schemes are summarized in Table 1 below:

Coding scheme RLC data block size (Bytes) RLC data bit rate (kbps) CS-1 20 8.0 CS-2 30 12.0 CS-3 36 14.4 CS-4 50 20.0 Table 1: The GPRS coding schemes

The objective of GPRS Link Adaptation is to dynamically select the most optimal coding scheme for downlink transmission of data over the radio interface. This is illustrated in Figure 2.

Figure 2: Link Adaptation in GPRS CS1-4

2.7.2 EDGE For optimizing the data rates, the EGPRS protocol uses the Modulation and Coding Schemes (MCS-1 to MCS-9).The algorithm used to optimize the data speed in EGPRS is the so called Link Quality Control (LQC). This LQC algorithm adapts the protection of the data to the channel quality, by modifying the coding rate used. In EGPRS, a hybrid Automatic Repeat request (ARQ) scheme is used for performing LQC. Two methods for adapting the hybrid ARQ scheme to the radio conditions can be distinguished. A pure Link Adaptation (LA, as known from GPRS) algorithm selects the MCS maximizing the data rate, depending on the estimate of the current C/I. Another method is Incremental Redundancy (IR), which arbitrarily starts by sending a block of data with some low rate Forward Error Control (FEC) code. For erroneously decoded blocks, transmission of additional redundancy subblocks (with increasing coding rates) is requested, received and combined to the first block. This procedure is repeated until decoding succeeds, giving a stepwise increment of the amount of redundancy.



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Compared to a pure link adaptation solution, this combination of link adaptation and incremental redundancy mechanisms significantly improves performance as shown in Figure 3 below.

Figure 3: Performance curves for the GPRS and the EGPRS curves

Link adaptation uses the radio link quality, measured either by the mobile station in a downlink transfer or by the base station in an uplink transfer, to select the most appropriate modulation coding scheme for transmission of the next sequence of packets. For an uplink packet transfer, the network informs the mobile station which coding scheme to use for transmission of the next sequence of packets. The modulation coding scheme can be changed for each radio block (four bursts), but a change is usually initiated by new quality estimates. The practical adaptation rate is therefore decided by the measurement interval.

For EDGE, the set of coding schemes is shown in Table 2

MCS Modulation Coding family RLC data block size (Bytes)

RLC data bit rate (kbps)

MCS-1 GMSK C 22 8.8 MCS-2 GMSK B 28 11.2 MCS-3 GMSK A 37 14.8 MCS-4 GMSK C 2x22 17.6 MCS-5 8-PSK B 2x28 22.4 MCS-6 8-PSK A 2x37 29.6



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MCS-7 8-PSK B 4x28 44.8 MCS-8 8-PSK A 4x34 54.4 MCS-9 8-PSK A 4x37 59.2 Table 2: The EDGE coding schemes

Incremental Redundancy (IR) is an approach to adapt the amount of channel coding to the channel quality. The data is encoded with a low rate code and divided into several subblocks, each separately decodable. If decoding of the first transmitted subblock, corresponding to a high rate code, failed a new subblock is transmitted. The receiver can combine the two subblocks using joint decoding. The procedure continues until decoding is successful. For each of the subblocks the information is stored as soft values. If the same subblock has to be retransmitted, the soft values from the first transmission is combined with the retransmission using soft combining.

In Link Adaptation/Incremental redundancy mode, EDGE also allows for adaptation of the link under packet re-transmission conditions (when packet loss occurs due to poor link quality). However, under retransmission conditions, a coding scheme change can only be triggered within a family of coding schemes. The coding scheme families are shown in Figure 4. For example, if a session being coded with MCS9 is degraded and packets are lost, for retransmission of the lost packets the link can adapt to MC8, 6 and finally 3, whereas a session being coded with MCS7 can adapt to 5 and 2 only.

Figure 4: EDGE Coding schemes and coding scheme families

The recommended configuration for GPRS is to have Link Adaptation enabled and the initial coding scheme should be set to CS2 (giving a conservative but safe starting point for transmissions. Link Adaptation will adapt the CS upwards if the radio conditions are good).

For EDGE the recommendation is to enable both Link Adaptation and Incremental redundancy.

2.8 Routing Areas The routing area is the equivalent of the location area in that the SGSN sends a paging request to all BSSs serving the routing area where the mobile is currently located. The timer T3313 is started. Upon expiry of the timer, if no paging response is received, the SGSN repeats the procedure up to five times before the procedure is considered to be unsuccessful and stopped.



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The recommendation is to set the Routing Areas along the same boundaries as the location areas. The recommended value for the T3313 timer set in the SGSN is T3313= 5 seconds

2.9 Impact on A-bis In GPRS/EDGE the coding is performed using coding schemes. For GPRS, four different coding schemes, designated CS1 through CS4, are defined. For EGPRS, nine modulation coding schemes, designated MCS1 through MCS9, are introduced.

The lower coding schemes of GPRS (CS1 & 2) use the standard GSM 16kbps A-bis configuration and so implementing data services at GPRS CS1 and CS2 has no impact on the transmission network capacity. However, GPRS CS3 and CS4 and all EDGE coding schemes require a 64kbps A-bis configuration and so the A-bis capacity may be severely affected by the deployment of say, 4 PDCHs all operating at CS3 or higher. When increasing the requirement on the A-bis it must be verified that sufficient transmission resources are available.

As an example, for the recommended start-up configuration of 1 dedicated + 3 dynamic PDCH in urban areas, A-bis resources would require to be increased by 4 x (64kbps – 16kbps) = 192kbps (or 3TS) over regular A-bis dimensioning (8 x 16kbps = 128kbps or 2TS/ TRX). For the purposes of effective A-bis utilization, an even number of PDCH shall be assigned (e.g. 4 PDCH, resulting in 4 fully utilized 64kbps TS on A-bis when combined with requirements for remaining voice channels; as opposed to 4.5 TS if 5 PDCH are assigned).

Until such time as Dynamic A-bis (for GPRS) or A-bis over IP features become widely deployed, the transmission capacity will have to be upgraded to match the radio network coding schemes enabled, or the radio network coding schemes will have to be limited to CS1 and 2 if there is a short term shortage of A-bis capacity.

With the exception of catering for any immediate transmission shortages prior to upgrades, the Celtel policy is to enable higher order coding schemes (CS3, 4, and EDGE coding schemes) as the incremental cost per kbps of throughput is always lower with higher coding schemes. However, for rural areas where only dynamic PDCHs are configured and no significant data traffic is expected, if there is a shortage of Abis capacity then it is recommended that initially the coding scheme be limited to CS2 and the data traffic monitored. Over times, cells carrying data traffic can be prioritised for Abis expansion to allow for support of higher rate coding schemes (Cs3 and upwards).

Operations are required to carry out an end-to-end capacities audit from TRX to CPU prior to launch of data services, defining capacity requirements on an A-bis basis, assigning extra A-bis TS as required, or where this is not immediately possible – define upgrade plan and limit initially the coding schemes of affected cells to CS1 and 2.

This impact will require the RF and TRM teams to work together closely to determine the PDH and A-bis capacities and upgrades required to support the data service.



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3 PERFORMANCE MEASUREMENT THROUGH BSS COUNTERS

3.1 Data Volume Packet data volume per cell (in Kbytes/hour; kB/h) is a primary KPI indicator that gives visibility into the level of packet traffic load (equivalent to Erlang in the CS network). The main KPIs for packet data volume are:

Key Performance Indicator (kB/h) IP Data Volume Downlink GPRS IP Data Volume Uplink GPRS IP Data Volume Downlink EDGE IP Data Volume Uplink EDGE

Table 3: KPI-Data Volume (kB/h) As data volumes vary greatly from operation to operation, it is difficult to reference data volume. However, as a rough benchmarck, downlink data volume per cell that is greater than 100 kB/h may be considered significant; and greater than 1 MB/h may be considered large.

3.2 IP Throughput In the packet environment, IP throughput can be considered as the single most important quality KPI as all problems areas reflect in a degraded IP throughput. Drilling down further helps identification of the source of problem areas, and 3 groupings are recommended; Interference, Capacity & Mobility, as shown in Figure 5.

Figure 5: Packet KPI Structure IP Throughput is defined as the average IP throughput per TBF (LLC throughput per TBF) during the measurement period

Key Performance Indicator Average Throughput (kbps) IP Throughput Downlink GPRS 30 → 36 IP Throughput Uplink GPRS 11 → 12.5 IP Throughput Downlink EDGE 50 → 95 IP Throughput Uplink EDGE 22 → 35

Table 4: KPI-Average data throughput per TBF, with average acceptable rates (source: Ericsson NetQB, 2005)



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In addition to IP Throughput, IP Interrupts can be used to access the overall performance of the packet network. IP Interrupt performance indicators are intend to cover Retainability and Accessibility problems for the user. The reason for why they are combined is that from a user perspective they are quite similar (as interrupts in the routing functionality of the GPRS packet network). IP interrupts UL is valuable for trouble shooting but perhaps not yet a trustworthy indicator for comparisons due to incorrect counter stepping and MS behaviour. There is also a large difference between UL and DL measured interrupts. Reasons for this are:

• The included counters are stepped more often due to functionality (UL is normally first attempt from MS which leads to higher interrupt counter values)

• TBFs are shorter on UL.

Key Performance Indicator Typical Values (TBF min/interrupt) IP Transfer Interrupt DL 5 → 50 (>30 is good) IP Transfer Interrupt UL 0.2 → 0.8

Table 5: KPI-TBF min/interrupt, with typical value ranges

3.2.1 Interference 3.2.1.1 Radio Link Bitrate The radio link bit rate provides an indication of the interference level in the radio environment. It is defined as the average RLC throughput per PDCH.

Key Performance Indicator (RLC throughput per PDCH) Reference Values (kbps) GPRS CS1-2 DL > 11.8 good; < 11 poor GPRS CS1-4 DL > 16 good; < 12 poor EGPRS MSC1-9 DL > 40 good GPRS CS1-2 UL > 6 good; < 4 poor EGPRS MSC1-9 UL > 30 good; < 20 poor Abnormally released TBFs due to radio reasons (%) < 2%

Table 6: KPI-Radio Link Bitrate (kbps) with typical reference values Abnormally released TBFs due to radio reasons

3.2.2 Capacity 3.2.2.1 PCU Congestion The following performance indicators provide an indication of when a review of PCU dimensioning is required. Note: Temporary relief may be obtained by lowering the timer that defines the time delay before converting an inactive dynamic PDCH to a TCH (eg in the Ericsson BSS, this timer is called PILTIMER and the recommended default is 20s. This can be reduced to 10s in order to reduce PCU load until an expansion of PCU capacity Key Performance Indicator (%) Reference Values (%) Failed PDCH allocation due to Processor/GSL congestion Should be 0% Processor load over 90% (also possible to get the distribution) Should be 0% Average Processor load in system BH for packet data Vendor defined GSL load over 90% (also possible to get the distribution) Should be 0% Average GSL Utilization in system BH for packet data < 80%

Table 7: KPIs-Capacity, with reference values



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3.2.2.2 Multi-slot Utilisation This performance indicator provides an indication of whether users are being assigned the number of PDCHs their mobiles are capable of; i.e. percentage of traffic allocated according to maximum multi-slot class. It is also possible to get a distribution of slot allocations for 4-, 3- and 2-slot capable mobiles.

Key Performance Indicator (%) Reference Value Full Multi-slot Utilization > 80% good

Table 8: KPI-Full Multi-slot Utilization , with typical reference value 3.2.2.3 PDCH Allocation PDCH allocation gives an indication of accessibility to the packet data network. The main KPIs are recommended below, with typical reference values.

Key Performance Indicator Reference Values

PDCH Sharing: Average number of simultaneous DL TBFs of any mode per any PDCH (in cell busy hour)

< 2 good

Average number of PDCHs carrying packet traffic (in cell busy hour) >3 good Total number of pre-empted PDCHs carrying packet traffic (can average per hour) N/A Number of pre-empted PDCHs carrying packet traffic per UL+DL TBF minute <0.25 acceptable

for starting point. Can be reduced to <0.1 when traffic picks up and we dimension more aggressively for

PS traffic Percentage rejected packet channel allocation attempts due to no PDCH (%) <2% Blocked access attempts due to complete congestion as percent of total attempts < 2%

Table 9: KPIs- PDCH Allocation, with typical reference values

3.2.3 Mobility The following performance indicators provide an indication of how mobile the data users are. It is difficult to provide a reference value for such an indicator, but an average DL TBF minutes between cell reselections (CRS) of greater than 20 minutes may be considered a relatively long time. If values are too low (in selected cells), then a review the CRS parameters may be required.

Key Performance Indicator DL TBF minutes between all cell reselections (between Flush-LL messages) DL TBF minutes between Intra PCU/BSC cell reselections (between Flush-LL messages with buffer moved) DL TBF minutes between Inter PCU/BSC cell reselections (between Flush-LL messages with buffer discard)

Table 10: KPIs-Mobility



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4 PERFORMANCE MEASUREMENT THROUGH TEST MOBILE

This section describes a procedure for measuring GPRS performance using a test mobile as a means of measuring the radio network quality as experienced by a GPRS user. The following test applications can be tested using a test mobile:

4.1 Possible Test Applications Attach / Detach Attach procedure is when the MS is activating mobility management for GPRS, i.e. going from GMM Idle state. When this is done the SGSN node will continuously handle location information for the mobile, knowing the routing area that the mobile belongs and in some cases also the specific cell (when the MS is in Ready state). The main purpose of GPRS Attach tests is to test the functionality of the GPRS core network. The procedure is so short that radio environment has limited impact on performance. These tests are best performed with automated GPRS Attach and GPRS Detach commands in the Command sequence handler. Activate / De-activate PDP context PDP Context activation / de-activation is session management procedures used when the MS communicates with the GGSN node and receives a user IP address (at activation). It is only after the PDP context activation is performed that any real user data can be sent. Prior to this only GPRS Mobility Management messages and SMS over GPRS will be sent (when MS is attached). The main purpose of Activate / De-activate PDP context is to test the functionality of the GPRS core network. The procedure is so short that radio environment has limited impact on performance. These tests are best performed with automated dial up and hang up commands (which is the “computer” commands generating PDP context activation) in the Command sequence handler. Ping Ping is an Internet control message that is sent to a server and a response back is expected. The main purpose of the ping is to check accessibility to a specific server and the roundtrip time to that server (which is a quality indicator of the network). The procedure is so short that radio environment has limited impact on performance. The time to transfer the ping message over the air interface is normally the main contributor, which makes the result BSS implementation dependant (thus different between vendors). These tests are best performed with automated ping commands in the Command sequence handler. HTTP Load HTTP load corresponds to a user browsing the web and downloading a web page. This includes signaling through the GPRS core network and IP network between MS and HTTP server. It is important to remember that the actual design of the web page will impact the measured performance. Number of objects in a webpage, what servers these objects resides on and used HTTP version are some factors contributing to how efficient the download will be. HTTP load is thus useful in order to investigate performance of a specific web page or to do repetitive tests of downloading a standardized/default webpage. Most web pages will however not provide sufficiently stable throughput to be useful for radio network evaluation (note that a web page could also be designed to give a stable throughput suitable similar to FTP). These tests are best performed with automated HTTP load commands in the Command sequence handler.

FTP Get/Put



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FTP Get and Put are commands for downloading and uploading data to FTP servers. This includes signaling through the GPRS core network and IP network between MS and FTP server. FTP Get and Put is normally used to initiate data transfer in downlink and uplink direction. This data transfer uses TCP and will try to maximize the throughput from the beginning to the end of the file transfer. It is thus a good choice when evaluating the radio network performance. There will be a small set-up time in the beginning of FTP Get and Put applications due to: connection to server, providing username and password, setting directory etc. These tests are best performed with automated FTP Get and Put commands in the Command sequence handler.

4.2 Celtel Recommended Test Process As the user experience is defined by the round trip response time (tested by PING) and data throughput rate (tested by FTP), it is recommended that the test mobile be scripted to do to the following process:

1) GPRS Attach 2) 1 minute FTP download from a national/international FTP server that will allow relative

comparison of Celtel and competitor throughput performance (if a local Celtel opco FTP server is used, then the competitor’s throughput rate cannot be compared directly with Celtel throughput rates). If required, a Celtel International FTP server can be made available for such testing.

3) PING a highly visited web page (eg www.yahoo.com, etc) with the following PING parameters (again, note that this should not be an IP address within the local Celtel opco, in order to allow direct comparison between Celtel and the competitors):

a. PING packet size = 32bytes b. Number of echo requests to send =10 c. Timeout=5 secs d. Time between echoes = 100ms

4) GPRS Detach 5) Continue looping steps 1 to 4 above for the whole duration of the TEMS drive.

Figure 6 shows an example An example of a command sequence for performing repetitive Ping tests with TEMS Investigation.

Figure 6: Example of TEMS command sequence for repetitive Ping tests The test route should be selected to be the same as the standard route driven for voice benchmarking, and the measurements should be carried out in the test vehicle.

The testing should be carried out with a test mobile capable of at least 4+1 (DL+UL) timeslots.


http://www.yahoo.com/


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4.3 Test Mobile KPIs to be extracted The KPIs of interest (this will be reflected in future releases of the engineering pack) should be extracted from the Test Mobile log and used to benchmark Celtel’s network performance over time, as well as Celtel’s network performance against the main competitors. The main KPIs to be extracted are:

Data throughput rate (kbps)

o Application layer

o LLC Layer

o RLC Layer

Ping round-trip time (ms)

Ping success rate (%)

GPRS attach time (s)

GPRS attach success rate (%)

Activate PDP Context time (ms)



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5 DEPLOYMENT

5.1 Planning for EDGE EDGE introduces only changes to the BTS part of the GPRS BSS network, as can be seen in the figure below.

Figure 7: Basic architecture of GPRS/EDGE enabled BSS

Both the BTS and the TRX have to EDGE capable. Table 11 summarises the BTS, TRX and BSS software release dependencies for GPRS and EDGE capability for the main BSS vendors of Celtel.

BTS/TRX Type BSS S/w release

GPRS Capability

EDGE Capability

Ericsson RBS2202 - TRU with DXU-1, DXU- 2, DXU-3 or DXU-11 R9.1 or later CS1-2 Not EDGE capable

Ericsson RBS2202 – sTRU with DXU-21 R9.1 or later CS1-4 MCS1-9

Ericsson RBS2206 – dTRU with DXU-21 R9.1 or later CS1-4 MCS1-9

Siemens BS60 with BBSIG44 BR5.5 CS1-2 Not EDGE capable

Siemens BS60 with BBSIG44 BR6 CS1-2 Not EDGE capable

Siemens BS60 with BBSIG44 BR7 CS1-4 Not EDGE capable

Siemens BS240 with GCU BR6 CS1-2 Not EDGE capable

Siemens BS240 with ECU BR6 CS1-2 Not EDGE capable

Siemens BS240 with ECU BR7 CS1-4 MCS1-9

Alcatel BTS Evolium G3 (MEDI/MINI) or G4 (MBI/MBO) with TRX (TRGM or TRDM, TRAG or TRAD, TRAGE or TRADE)

B7 CS1-2 Not EDGE capable

Alcatel BTS Evolium G3 (MEDI/MINI) with TRX (TRGM or TRDM) B8 CS1-CS4 Not EDGE capable

Alcatel BTS Evolium G3 (MEDI/MINI) with TRX (TRAG or TRAD) B8 CS1-CS4 MCS1-9

Alcatel BTS Evolium G3 (MEDI/MINI) with TRX (TRAGE or TRADE) B8 CS1-CS4 MCS1-9

Alcatel BTS Evolium G4 (MBI/MBO) with TRX (TRGM or TRDM) B8 CS1-CS4 Not EDGE capable

Alcatel BTS Evolium G4 (MBI/MBO)with TRX (TRAG or TRAD) B8 CS1-CS4 MCS1-9

Alcatel BTS Evolium G4 (MBI/MBO) with TRX (TRAGE or TRADE) B8 CS1-CS4 MCS1-9

Table 11: BTSs and TRXs commonly used in Celtel, with GPRS/EDGE capability

The modulation type is used in GSM/GPRS is the Gaussian minimum shift keying (GMSK), which maps 1 bit per symbol. Higher coding schemes of EDGE (MCS5-9), however, use a difference modulation type (8-phase shift keying (8PSK)) to map 3 bits per symbol. This increases the data throughput per timeslot, but increases the sensitivity to misinterpretation (poorer robustness against File Name: 20 (22) 28/08/2006 Eng, GPRS - Eng Guide, Radio 060426-2.doc


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interference). In order to counter the sensitivity to interference, error correction bits are added to the data stream and this has the effect of reducing the overall user data throughput. In very poor radio conditions, GMSK out-performs 8-PSK (with heavy error correction) and so the lower EDGE coding schemes (MCS1-4) use GMSK.

Since EDGE achieves greater data throughput per timeslot, it is, from a radio capacity perspective, a more efficient way of carrying data traffic (less timeslots needed per mbps of traffic throughput). However, low penetration of EDGE capable handsets (at least at the start-up phase) will prevent a wide-scale usage of and hence limit the reasons for deployment of EDGE until handsets on the market will be supporting this. As urban areas accommodate a greater density of high end users, Celtel will first target the main cities for the deployment of EDGE services, and thereafter the smaller towns and rural areas.

Therefore it is imperative that all expansion plans put in place consider the capability of the BTSs and TRXs in the main cities in terms of EDGE. Plans should be put in place to enable all cells on the 900MHz band in the main cities with at least 1 EDGE capable TRX so that EDGE services can be enabled in the main cities when required.

In general, all the latest generation equipment is EDGE capable, but as most of Celtel’s main cities are covered by older generation equipment (first rolled out in urban areas, and then started to expand to rural) and is not EDGE capable. So when new equipment is delivered, the new EDGE capable TRXs should be installed in the main cities (on the basis of 1 EDGE capable TRX per cell), re-deploying the non-EDGE capable TRXs to the rural areas. The next phase will be to target the next level of town or high data use area (e.g. farming communities, etc) for EDGE deployment.



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6 HUMAN RESOURCES, PROCESSES & TOOLS 6.1 RF Engineering HR issues At the start of data services, the loads on the RF engineering teams will be absorbed by existing staff and no additional headcount will be required. However, as the number of customers increases it may, in future, become necessary to increase the field measurement technicians, optimisation engineers, and the engineers/technicians who attend to customer complaints. This will depend on the extra work load generated by tuning the and GPRS/EDGE network performance and attending to customer complaints.

6.2 RF Engineering Tools At the start of the service, a test mobile capable of GPRS CS1-4, EDGE MC1-9, and 4+1 TS multislot operation (multislot class 8, 10, 11 or 12) is required (eg Sony Ericsson T610, Nokia 6230, Nokia 6680). Guidelines and recommendations for Test Mobile will not be covered in any further details, but will be distributed separately.

6.3 Training The RF planning and optimisation engineers will have to increase their knowledge of data services, GPRS/EDGE planning and optimisation. This can be co-ordinated at the group level, or managed locally with the main BSS vendor.


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