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Half Rate Feature

1.

2.

Document Scope:

This document describes the Nokia feature Half Rate and explains why and how it's recommended to activate.

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Contents1. INTRODUCTION................................................................................................................. 4

1.1. GENERAL DESCRIPTION......................................................................................................41.2. SCOPE............................................................................................................................... 5

2. FEATURE DESCRIPTION...................................................................................................6

2.1. DUAL RATE PENETRATION...................................................................................................62.2. TRAFFIC CHANNEL ALLOCATION IN THE ASSIGNMENT PROCEDURE........................................7

2.2.1. General Requirements...........................................................................................................................72.2.2. Channel Rate Allocation based on Cell Load.........................................................................................72.2.3. Basic Assignment Procedure.................................................................................................................82.2.4. TCH Allocation and Load Calculation with Dual Rate Resources..........................................................9

2.3. TRAFFIC CHANNEL RATE CONTROL IN THE HANDOVER PROCEDURE...................................142.3.1. Inter-Cell Handovers............................................................................................................................142.3.2. Intra-Cell Handovers............................................................................................................................15

2.4. NETWORK ELEMENT SUPPORT..........................................................................................152.5. ABIS, ATER AND A INTERFACES CONFIGURATION................................................................16

2.5.1. A bis Interface (BTS to BSC)...............................................................................................................162.5.2. A & A ter Interfaces (BSC to MSC)......................................................................................................16

3. INTERACTIONS WITH OTHER FEATURES....................................................................17

3.1. TANDEM FREE OPERATION AND NOISE SUPPRESSION........................................................173.2. DIRECTED RETRY.............................................................................................................173.3. QUEUING AND PREEMPTION..............................................................................................18

3.3.1. Queuing...............................................................................................................................................183.3.2. Pre-emption.........................................................................................................................................18

3.4. DL & UL POWER CONTROL..............................................................................................183.5. GPRS.............................................................................................................................. 183.6. MEASUREMENT REPORTING..............................................................................................193.7. UPLINK DTX.....................................................................................................................193.8. FREQUENCY HOPPING.......................................................................................................203.9. DYNAMIC SDCCH............................................................................................................203.10. TANDEM PREVENTION FEATURE.....................................................................................20

4. IMPACT ON THE SPEECH QUALITY..............................................................................21

4.1. GENERAL RESULTS...........................................................................................................214.2. TANDEM & NON-TANDEM RESULTS....................................................................................224.3. MOS IMPACT EVALUATION.................................................................................................244.4. RESULTS IN CLEAN AND NOISY ENVIRONMENTS..................................................................25

5. NEW PARAMETERS AND RECOMMENDED VALUES...................................................26

5.1. TRANSCEIVER (TRX) PARAMETERS...................................................................................275.2. BASE TRANSCEIVER STATION (BTS) PARAMETERS.............................................................275.3. BASE STATION CONTROLLER (BSC) PARAMETERS.............................................................28

6. NEW COUNTERS.............................................................................................................29

6.1. TRAFFIC COUNTERS..........................................................................................................296.2. RESOURCE AVAILABILITY COUNTERS.................................................................................31

7. NEW ALARMS.................................................................................................................. 32

8. FEATURE BENEFITS.......................................................................................................33

9. FEATURE DRAWBACKS.................................................................................................33

10. INSTRUCTIONS.............................................................................................................34

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10.1. ACTIVATION OF HALF RATE ON BSC & TRANSCODER LEVEL...........................................3410.1.1. New PRFILE........................................................................................................................................3410.1.2. TCSM2, Ater and A Interfaces Configuration.......................................................................................3410.1.3. Activation of Acoustic Echo Cancellation (AEC) for Half Rate..............................................................34

10.2. ACTIVATION OF HALF RATE ON TRX LEVEL....................................................................3410.2.1. 32 kbps TRX Signalling........................................................................................................................3410.2.2. Dual Rate Traffic Channel Definition....................................................................................................3410.2.3. Number of TRX's to activate in Half Rate.............................................................................................3410.2.4. Which TRX to activate in Half Rate ?...................................................................................................34

10.3. RECOMMENDED PARAMETERS.......................................................................................35

11. References.................................................................................................................... 36

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1. Introduction

1.1. General Description

This document explains how to implement Half Rate, and also the benefits and the drawbacks of the feature. Only Nokia BSS Network with its current Release S9, DF5.0 & T12 has been considered because on the Motorola Network, Half Rate is planned not before GSR7 (end of 2002). Our Siemens MSC with its current Release SR8 is compatible with Half Rate.

The basic principle of the GSM Half Rate Codec is the following: it allows to put 2 Half Rate TCH (TCH/HR) per Time Slot instead of 1 Full Rate TCH (TCH/FR) per Time Slot.

The major drawback of the feature is that the speech quality is slightly worse with Half Rate than with Enhanced Full Rate in general conditions. In MS to MS Call (what we call tandem conditions), the speech quality with Half Rate is worse and even much worse than with Enhanced Full Rate1.

The major advantage of Half Rate is that extra Capacity can be dynamically allocated depending on the load of the cell. By choosing at which cell load to begin allocation of half rate channels we have the possibility to balance the cell capacity against the potential degradation in speech quality.

1 The speech quality of a Half Rate to Half Rate call is worse and even much worse than an Enhanced Full Rate to Enhanced Full Rate call.

1 TRX

8 TCH/FR

1 TRXTCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCH TCHHR HR HR HR HR HR HR HR HR HR HR HR HR HR HR HR

16 TCH/HR

TS 4 TS 5 TS 6 TS 7TS 0 TS 1 TS 2 TS 3

TS 4 TS 5 TS 6 TS 7TS 0 TS 1 TS 2 TS 3

TCH/FR TCH/FR TCH/FR TCH/FRTCH/FR TCH/FR TCH/FR TCH/FR

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1.2. Scope

The Half Rate Feature is an efficient way to reduce the investment we need to make in network capacity:

1st Strategy: Half Rate for more capacity

All users would certainly prefer a slightly less than optimum speech quality call rather than no call at all, which make the customers frustrated with ‘network busy’. The dynamic capacity of Half Rate allows to decrease the number of blocked calls and the % CSDC.

This strategy is particularly useful in the following cases:

Where extra capacity is needed for a short period each day (i.e. traffic jams, …). Where temporary capacity is needed during some periods (i.e. summer Holidays on the

coast). Where specific or recurrent events take place (i.e. festival, concert, …). Where it's no more possible to add other TRX's (i.e. the cabinet is already full with 6TRX's,

or the impossibility to put new sites, …). Also before adding extension cabinets, it should be better to activate Half Rate on some TRX's.

2nd Strategy: Half Rate for TRX Efficiency

The objective of this strategy is to replace an add TRX by the activation of an Half Rate TRX, or in other terms, remove some TRX's and activate Half Rate on some TRX's. As the real compromise is Speech Quality versus Price Benefits (i.e. the best quality/cost balance), we will search for the best configuration (i.e. the best price benefits) which will lead to a determined Half Rate Traffic (in order to reduce the impact on speech quality). This strategy makes sense if and only if we can reuse the removed TRX's in another place.

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2. Feature Description

2.1. Dual Rate Penetration

With the activation of Half Rate at BSC level, we have been able to evaluate the average Dual Rate Traffic Penetration in the involved BSC's even if there are no Half Rate Traffic. In July - September 2001, the Dual Rate Traffic Penetration, i.e. the percentage of traffic generated by the Dual Rate Mobiles, was the following:

Dual Rate Traffic Penetration (%) July 2001Average on 1800MHz Only 85%Average on 900MHz in Dual Band Sites

72%

Global Average 75%

We can remark that the average Dual Rate Traffic Penetration in the 1800MHz Cells is clearly higher than the global average. This confirms that the majority of the Dual Band Mobiles are also Dual Rate.

The BSC counter TCH_FULL_REQ_SUCC_UNSUCC (P_NBSC_TRAFFIC n° 001103) is updated when the

channel rate of the TCH requested is defined to be FR only by the MSC which occurs in 2 cases (in all other cases, the MSC gives only an order of preference):

When the MS has no Dual Rate capabilities. When it's a Mobile-to-Mobile Call with the calling MS in Half Rate, then the MSC request stricly the called

MS to be EFR/FR. The two Mobile Stations must be in the same MSC.

As no counter exist for the second case, we can only give the "Dual Rate Traffic Penetration At least". For instance during an event, there are a lot of MTM calls within the same cells and so the Dual Rate Traffic Penetration indicated should be higher than given by the formula below.

The Dual Rate Traffic Penetration (%) is calculated following this formula:

(100*(1-[TCH_FULL_REQ_SUCC_UNSUCC]/[TCH_REQUEST]))

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2.2. Traffic Channel Allocation in the Assignment Procedure

2.2.1. General Requirements

Introduction of Half Rate to the network has significant effects on the Traffic Channel allocation algorithm of the BSC. The channel rate of the TCH to be allocated is initially determined by the Channel Type IE of the Assignment or Handover Request message received from the A interface . When it is not specified uniquely to be either FR or HR and only the preferred channel rate is given, the BSS makes the final decision on which kind of TCH radio resource is allocated for the call.

The following factors can affect the TCH channel rate determination (Handover or Call Setup):

TCH configuration of the BTS Actual traffic load of a cell Optimised allocation of the Dual Rate TCH resources Channel quality requirements stated either by the MSC or the BSC itself Pool of the A interface circuit when a resource is requested for speech or data Actual Circuit Pool Configuration on the A interface The Mobile Station

2.2.2. Channel Rate Allocation based on Cell Load

We have the possibility to determine the distribution between full rate and half rate traffic channels according to the cell load in TCH allocation from the dual rate TCH resources. This kind of TCH allocation control is possible if the A interface does not determine the channel rate uniquely but gives only the preferred rate, that is, half rate or full rate.

We have two cases for the Half Rate TCH allocation:

If HR represents the preferred channel rate of the resource request, the corresponding available permanent HR TCH resource is allocated primarily, regardless of whether the cell-load-based TCH allocation has been activated or not (In the specification, mobiles with Half Rate as 1 st preference can exist, but for the moment, we haven't yet found mobiles with this order of preference. It should be very rare).

A HR TCH is allocated always if the cell load requires , regardless of possible existing available permanent FR resources or preferred FR TCH requirement of the TCH resource request.

As shown on the figure below, the parameters for this feature consist of two threshold values, which are given as relative amount of available full rate TCH resources per working full rate TCH resources (%)2:

Full rate TCHs are allocated from the cell until the number of available full rate resources are reduced below a specific lower limit; the half rate resources are then allocated.

When the number of the available full rate resources of the cell increases above a specific upper limit, full rate TCHs are allocated again.

2 Please refer to § 2.2.4 for the calculation of the Free FR TCH (%).

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The function is controlled with two-level parameters, both consisting in the two threshold values mentioned just above:

At the BSS level with the aid of the BSC object class parameter btsLoadDepTCHRate (HRL & HRU): the values are valid in each BTS of the BSS area.

At the BTS level with the aid of BTS object class parameter btsSpLoadDepTCHRate (FRL & FRU): we can overwrite the BSS level values of the upper and lower limits by determining new values to the corresponding BTS-specific limits.

These threshold parameters determine the effect on quality: Half Rate is only activated when the load of the cell requires it. We can prohibit the effect of either parameter by setting the lower limit of the parameter higher than the upper limit. The feature is disabled in specific BTSs when The default values of both parameters are 100% for the lower limit and 0% for the upper limit, that is, the feature is disabled.

This allocation applies both to new calls started on the cell and also to calls in progress handed over to the cell. Hence calls can switch between half rate, full rate and EFR as they are handed between differently loaded cells but switching, for example, from half rate transcoded speech to transmission in a full rate TCH by using Channel Mode Modify is not supported. This is possible only during handovers but an handover is not started merely in order to change the TCH channel rate.

2.2.3. Basic Assignment Procedure

Initially the MS informs the network of its transcoding capabilities. It sends this information in two phases of the call set-up.

When the MS requires a channel for starting the connection establishment to the network, it sends a specific establishment cause in the message which tells the network the reason for the call attempt 3. The BSC can use the establishment cause information when it makes a decision on the first DCCH to be allocated for the call, for example in a FACCH call set-up.

When the connection to the network has been established, the MS sends on the main DCCH information its half rate capabilities.

3 Phase 2 mobile stations can also inform of the required type of traffic channel, whether the HR TCH is sufficient or the FR TCH is the only alternative. This is possible in MOC cases only when the new establishment causes are supported by the network (NECI is set ON in the BTS); in MTC cases the type of the channel needed can be indicated to the MS in the paging request.

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- The information is transferred in the BC (Bearer Capability) IE of the set-up or call confirmation messages, depending on whether the call is a mobile originating or terminating one, to the MSC. Actually two alternatives are possible: either the MS supports full rate only (phase 1 MS) or the MS is capable of both full rate and half rate transcoding; in the latter case the MS also states which TCH channel rate is preferred, either full rate or half rate.

- The BC IE can also contain information of the speech codec versions the MS supports. The MS gives all speech codec versions in order of preference, which further determines the requirement of the channel rate preference.

The BSC receives from the MSC the TCH channel type and rate requirement in the Channel Type IE of the Assignment Request message; in the external handover case the Channel Type IE is also received in the Handover Request message.

The MSC can request a strictly full rate or half rate traffic channel ; the former choice is the only possibility when the MS supports only full rate transcoding. When the MS can handle half rate in most cases, the MSC can let the BSC make the final decision on the TCH type; it then gives only the preference for the channel rate, either full rate or half rate.

The BTS does not allow reconfiguration of an active channel from half rate to full rate or vice versa by using the Mode Modify procedure. This is possible only during handover which is not started merely in order to change the TCH channel rate.

The BSC can change the initial preference of the TCH channel rate stated in the Channel Type IE due to resources reasons of a specific BTS, i.e.- The actual TCH configuration- The traffic load of a cell - Constraints determined for the TCH channel rate at the time of internal handovers.

2.2.4. TCH Allocation and Load Calculation with Dual Rate Resources

Full Rate Calls are allocated on dedicated FR resources (TCHF) preferably to Dual Rate Resources (TCHD) when both kind of resources are available.

TCH Allocation: Free FR TCH (%) calculation

The Percentage of Free FR TCH, used for the TCH Allocation based on Cell Load, is calculated as follows:

The following Timeslots are ignored in the Free FR TCH (%) calculation:-Signalling Timeslot(s)-Blocked Timeslot(s)-Dedicated, additional and default GPRS Timeslots(s)

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The Available FR Resources is the sum of -All working Full Rate Timeslot(s) which are free-All working Dual Rate Timeslot(s) which are completely free (a TCHD at least 1/2 occupied by a HR call

is not counted anymore as an available FR Resource)

The Working FR Resources is the sum of-All Full Rate and Dual Rate Timeslot(s) which are not ignored as specified above.

The threshold parameters HRL, HRU, FRL & FRU are compared to Free FR TCH (%) in order to activate or not Half Rate. We will illustrate the calculations with some examples below but we will first specify the way for calculating the BTS LOAD.

BTS LOAD (%) Calculation

The BTS LOAD (%) is used in the Handover Control for different features: for instance, AmhUpperLoadThreshold, AmhLowerLoadThreshold, AmhMaxLoadOfTgtCell and BTSLoadThreshold (used in DADL/B4 and also Target Cell Prioritisation) have to be compared with the BTS LOAD. The formula to compute the BTS LOAD (%), used in Handover Allocation is the following:

The following Timeslots are ignored in the BTS LOAD (%) calculation:-Signalling Timeslot(s)-Blocked Timeslot(s)-Dedicated GPRS Timeslots(s)

The Reserved Resource s is the sum of -All busy TCHF which are not ignored as specified above-All busy TCHH which are not ignored as specified above (1 busy Dual Rate TSL = 2 reserved TCHH; 1/2

busy Dual Rate TSL = 1 reserved TCHH)-The additional and default GPRS Timeslots are not considered as reserved!

The Working Resources is the sum of-All TCHF and TCHH which are not ignored as specified above.-The additional and default GPRS Timeslots are considered as working!

Overview and examples

1 working DR TSL = 1 working TCHF = Available FR Resources = 2 working TCHH

1 reserved DR TSL = 1 reserved TCHF = Not Available FR Resources= 2 reserved TCHH

1/2 reserved DR TSL = 1 reserved TCHF = Not Available FR Resources= 1 reserved TCHH

1 GPRS DEF DR TSL = 1 working TCHF = 2 working TCHH = Not Reserved Resources = Nor Working Nor Available FR Resources

Let's illustrate the complexity with some examples:

4 DADL/B : Direct Access to Desired Layer/Band

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Example 1

1 TRX with 8 DR TS, no GPRS TSthe 8 DR TS are HALF used (only 1/2 TS is used for each)

Free FR TCH (%) Calculation:

amount of available FR Resources is 0amount of working FR Resources is 8----------------------------------------------------

Free FR TCH = 0/8 = 0%

BTS LOAD (%) Calculations:

amount of reserved TCHF is 8amount of reserved TCHH is 8---------------------------------------total amount of reserved resources 16

amount of working TCHF is 8amount of working TCHH is 16-----------------------------------------total amount of working resources 24

BTS LOAD = 16/24 = 66.66%

Example 2

1 TRX with 8 DR TS, no GPRS TSall the DR TS are busy except 1/2 TS



Free FR TCH = 0/8 = 0%


amount of reserved TCHF is 8amount of reserved TCHH is 15---------------------------------------total amount of reserved resources 23

amount of working TCHF is 8

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amount of working TCHH is 16-----------------------------------------total amount of working resources 24

BTS LOAD = 23/24 = 95.83%

Example 3

1 TRX with 6 DR TS and 2 GPRS DEFthe 6 DR TS are used but not the GPRS DEF TS



Free FR TCH = 1/6 = 16,67%


amount of reserved FTCH 5 amount of reserved HTCH 10 -------------------------------------------------- total amount of reserved resources 15 amount of working FTCH 8 amount of working HTCH 16 -------------------------------------------------- total amount of reserved resources 24

BTS LOAD = 15/24 = 62,5%

2 GPRS DEFDR TSL

1 completely freeDR TSL

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Channel Search

Channels in both permanent HR and DR type RTSLs can be allocated for the TCH/H use, but the latter generally only in the case where no channels in permanent HR type RTSLs are left. Within DR resources RTSL's with only one HR subchannel occupied are preferred to totally free DR RTSL's . As we will implement only Dual Rate Resources, we will focus on this.

The Channel search differs slighlty depending on the type of the RTSL where the channel is to be allocated:

- TCH/H search: channel in a half occupied DR RTSL expected

1. The TRX search is started from the TRX where a TCH/H was seized last because of the high probability for a half occupied RTSL being found in that TRX.

2. After a TRX with a half occupied DR RTSL has been found, a suitable free TCH/H is searched for from the TRX. The search for the TCH/H is started from the RTSL where a TCH/H was seized last because of the high probability for the other HR subchannel in the RTSL being idle.

3. The first half occupied RTSL that contains an idle TCH/H whose interference level equals the expected one is selected.

- TCH/H search: channel in an idle DR RTSL expected

1. An attempt is made to allocate the channel from another TRX than that where a TCH/H was last seized by starting the search from the TRX following it in the list of working TRXs.

2. After a TRX with a free DR RTSL has been found, a suitable free TCH/H is searched for from the TRX. If possible, the channel is selected from another RTSL than that containing the last seized TCH/H.

3. The TCH/H is allocated from the first DR RTSL with both subchannels idle and at least one of them on the selected interference level. If both of the HR subchannels are on the requested interference level, the one that has been seized fewer times is selected.

With the Dual Rate Channels, the Channel Allocation is more efficient than with the fixed Half Rate Channels. Indeed, we can still afford a Full Rate Call or a GPRS Call on a completely free Dual Rate Timeslot and the channel search is optimised so that a new Half Rate call will be put on a half occupied Dual Rate Timeslot.

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2.3. Traffic Channel Rate Control in the Handover Procedure

The channel rate from FR to HR, and vice versa, as well as the speech version can alter in handovers. We have the possibility to determine extra constraints for the channel rate and codec changes in inter-cell handovers at the BSC site and in intra-cell handovers at the BTS site.

2.3.1. Inter-Cell Handovers

The following parameterisation, determined at the BSS level, is applied to each handover for which the type of the source TCH and the source speech version of the handover is known, that is:

to all the BSC-controlled, internal inter-cell and intra-cell handovers.

to the MSC-controlled, external handovers.If radio conditions for handovers are met and that amongst potential target cells, the best one (as regards radio conditions) is under another BSC, the value of HRI doesn't affect the selection of the target cell (in case several cells would simultaneously be valid candidates). An handover will be attempted towards the best (radio) candidate of other BSC5. Although HRI on source BSC doesn't affect the selection of target cell, the value of HRI on target BSC (once target cell is selected) influences the choice of the Codec to be activated on target cell.

We have 4 alternatives in the selection of the Handover Candidate Cells for the speech connections and 1

alternative for data calls. Half Rate offers no capacity benefit to data traffic and anyway, our MSC won't allow a request for half rate channels in case of data calls. We will only focused on the value we recommend for the BSC level parameter tchRateInternalHO (=HRI). For more details about the other value parameters, please refer to [5]6.

HRI= 5: "Best Candidate"

The TCH has to be allocated primarily from the best BTS of the handover candidates, which has the available TCH resources. The priorities are depicted in the figure below:

5 Even if several cells of adjacent BSC are valid candidates and passed over to the MSC in the "cell identifier list" of HORQD, only 1 cell is passed over to the target BSC in "cell identifier" of the HOREQ6 [5] Half Rate Feature Description, Raphaël De Beys, Version 2.0, 26 June 2001.

Same Type of TCH (HR - FR) as used in the source cell

Possible ?

Same Type of Speech Version as used in the source cell

Other Type of TCH is allocated

Yes No

The “Best” Possible Candidate Cells are allocated

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The traffic load of the best cell can affect the type of the target TCH when the call is maintained in FR TCH in the source cell. The full rate TCH is allocated when the cell is not overloaded. If the cell is overloaded, a HR TCH is allocated.

When the type of the source TCH is HR, the actual traffic load of the cell does not have an effect at all; the HR TCH is allocated if one is available7. We would have preferred that the traffic load of the cell have always an effect. The reason, given by Nokia, is to avoid as much as possible the changes of Codec

We recommend this value because it's the best (among the proposed configurations) from the quality point of view.

2.3.2. Intra-Cell Handovers

Though the channel rate control is valid at the BSS level for all the internal handovers, these constraints can be readjusted for internal intra-cell handovers in each BTS with the parameter tchRateIntraCellHO (=TRIH). For more details about the other value parameters, please refer to [5]8. We didn't see any advantages to have other constraints, that's why we recommend to set TRIH = 0:

TRIH= 0: "No constraints"

No extra constraints are given for intra-cell handovers (default value). This means that constraints given by the general parameter tchRateInternalHO (= HRI) are followed.

2.4. Network Element Support

The minimum HW and SW requirements per Nokia BSS network element to support half rate are given in the table below:

Our Nokia BSS Network with its current Release S9, DF5.0 & T12 is compatible with the Half Rate Feature.Except the Nokia 2nd Generation BTS (which is not present in our network), all the other types of BTS are HW compatible with Half Rate i.e. Talk-Family, PrimeSite, Insite, MetroSite, Ultra Site BTS.

The Siemens MSC with the current release SR8 is compatible with the Half Rate Feature.

7 With the new Multi-layer strategy, the Power Budget Handovers from 900MHz to 1800MHz are allowed only if the BTS LOAD in 900MHz > 40% and the load in 1800MHz < 85%. If the TCH source in 900MHz is Half Rate because the load of the cell requires it (80-90 % depending on the parameters FRL, FRU, HRL, HRU), the handovers to 1800MHz shouldn't be allowed because the Load in 1800MHz should be higher than 85%. Thus, a Half Rate Call on 1800MHz with low cell load shouldn't exist.8 Half Rate Feature Description, Raphaël De Beys, Version 2.0, 26 June 2001.

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2.5. Abis, Ater and A Interfaces configuration

2.5.1. A bis Interface (BTS to BSC)

In order to be able to use Half Rate the most efficiently, we recommend 32kbps TRX Signalling on the Abis at least for each TRX where Half Rate is activated. Indeed, for 1 TRX configured with 8 Dual Rate Time Slots, we can afford only 11 Half Rate stable with 16 kbps TRX Signalling calls instead of 16 Half Rate stable calls with 32 kbps TRX Signalling. But, given that 32 kbps TRX Signalling allows also to profit at maximum from Dynamic SDCCH and that we have the place on our Abis Interfaces, it's more efficient to put 32 kbps TRX Signalling for all the TRX's of the involved Site.

We need to modify the channel type to TCHD (Dual Rate) so that each pair of bits corresponding to a timeslot on the air interface is used dynamically for either one FR Traffic Channel (16kbps) or two HR Traffic Channel (2 x 8kbps).

2.5.2. A & A ter Interfaces (BSC to MSC)

The Nokia BSC and TCSM2 must be reconfigured to support Half Rate. To do so, all TC-PCM's must be reconfigured from EFR-FR support to EFR-DR support. This Circuit Mode supporting FR-EFR-HR is called "C".

The A and Ater interface transmission requirement is as for normal network expansion, extra transmission capacity will be required to handle the increased traffic capacity of the Half Rate BSS.

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3. Interactions with other features

3.1. Tandem Free Operation and Noise Suppression

We cannot implement on the same BSC Half Rate together with EFR enhanced by Noise Suppression/Tandem Free Operation because the A Interface Circuit pooling Feature is restricted in the Releases SR8 and SR9 of our Siemens MSC's9.

Moreover, we cannot implement at the same time Half Rate with Noise Suppression/Tandem Free Operation because the only circuit pool (n°2) supporting this in our BSC is not available in our Siemens MSC's. Nokia doesn't support any other circuit pool affording Half Rate simultaneously with Noise Suppression/Tandem Free Operation.

3.2. Directed Retry

A Directed retry handover is initiated in the SDCCH signalling phase, so possible channel rate change prohibitions stated by either the BSC or the MSC have no effect here. The following principles are observed in TCH allocation for internal Directed retry handover (No external Directed Retry available):

9 For more informations about how the A Interface Circuit Pool feature should work, please refer to Half Rate Feature Description, Raphaël De Beys, Version 2.0, 26 June 2001.

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3.3. Queuing and Preemption

3.3.1. Queuing

When the BTS has been configured with TCHs of the channel rate which is required in the resource request and which the A interface circuit pool supports, queuing of the TCH resource request is possible.

When both types of TCH resources are available in the BTS, the queuing procedure itself is not dependent on the requested channel type. The place of the resource request in the queue is determined merely by the priority-based queuing requirements set to the BTS and to the call. A released TCH is allocated for the first queuing TCH request which has the channel rate requirement that matches with the channel rate of the TCH. Nevertheless, other possible conditions, for example, channel quality requirements, must be fulfilled. For the queued calls, there are no rate change to the freed TCH Type.

3.3.2. Pre-emption

The TCH channel rate requirement of the resource request makes the candidate selection procedure for forced handover and forced release (Pre-emption) more complicated, especially in the case that the BTS contains dual rate resources and a full rate TCH is requested.

The following three cases are possible in that case: the MS of lowest priority is found among the FR mobiles, the MS of lowest priority is found from a half occupied dual rate RTSL, the MS of lowest priority is found from a dual rate RTSL which has also the other half occupied.

The MSs of the first two cases can be accepted for candidates but the last case is exceptional, especially when the forced release is requested.

3.4. DL & UL Power Control

There are no specialities in power control with Half Rate. For instance, for 2 HR Calls in the same TSL belonging to two different MS (at different distance from the BTS), Power control work normally for both HR calls.

3.5. GPRS

Permanent type Half Rate Time Slots are not used for GPRS traffic. Thus it's recommended not to configure permanent Half Rate Time Slots in TRX's that are planned to be capable of GPRS. That's another reason why we will implement only Dual Rate Resources.

As mentionned on §2.2.4 in the calculation of the Free FR TCH(%) for the threshold parameters (FRL, FRU, HRL, HRU), a default or dedicated GPRS Time Slots is not counted as a working nor available FR Resource.

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3.6. Measurement Reporting

For a TCHF, the reporting period has a length of 104 TDMA frames (480ms) as for a TCHF and is defined in terms of TDMA frame numbers (FN) as follows10:

For RXLEV_FULL and RXQUAL_FULL, the full set of TDMA frames is 100 (i.e. 104-4 idle) frames for a full rate TCH but 52 frames for a Half Rate TCH.

For RXLEV_SUB and RXQUAL_SUB, the subset of TDMA frames is for Half Rate 12 as for Full Rate.

3.7. Uplink DTX

The Uplink DTX feature works with Half Rate. The only change is in the uplink DTX indicator of the System information type 6. This indicator included in the Cell Options IE of the System Information Type 6 message has different interpretations when the message is sent on a FR TCH SACCH or an HR TCH SACCH11.

On the SDCCH and on the Half Rate traffic Channel TCH/H in signalling only mode DTX is not allowed. In these cases and on TCH/F in signalling only mode when DTX is not use, the same L2 fill frame shall be transmitted in case there is nothing else to transmit.

In case of Half Rate Speech channel TCH/H, if an SID frame or a speech frame is replaced by an FACCH frame, the RXQUAL measurement on these frames shall be excluded from the RXQUAL_SUB Report. In case of Half Rate Traffic Channel TCH/H in signalling only mode, -SUB values are set equal to -FULL values in the SACCH message, since DTX is not allowed in this case.

10 GSM Specifications 05.08 version 7.4.0 Release 1998,pp.2611 See §4.2.1 Half Rate Feature Description, Raphaël De Beys, Version 2.0, 26 June 2001.

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3.8. Frequency hopping

Synthesised (RF) Hopping works fine with Half Rate without any problems.

Baseband Hopping works fine given that all the TRX's implemented in our network are Hardware Half Rate Compatible. The parameter HRS that defines this Hardware Half Rate compatibility is put by default Yes. When the Cell is in Baseband Hopping, it's imperative to check that all the TRX's (even those where Half Rate is not activated) have HRS set to Yes.

3.9. Dynamic SDCCH

As 32 kbps Telecom Signalling will be recommended with Half Rate, it allows to use optimally the feature SDCCH: indeed, with 32 kbps TRX Signalling, up to 16 dynamic SDCCH or 8 static SDCCH + 8 dynamic SDCCH can be configured per TRX.

3.10. Tandem Prevention Feature

If a MSC detects that for Mobile-To-Mobile Call (MMC) both parties use Half Rate, then the call is forced to Full Rate for the terminating party (MTC12-leg of the call). This MMC Half Rate Tandem Prevention for the MTC party is by default active in our complete network (SR8). We cannot switch this behaviour off.

This feature is only implemented for both parties being located in the same MSC because if both parties are located in different MSC's, the Half Rate Tandem cannot be detected. The ISUP standards do not foresee to transfer the channel rate signalling (Half Rate or Full Rate) from the calling Mobile to the second MSC. A Siemens feasibility study is started to investigate the necessary changes to implement this functionality.

This MTC Tandem Prevention is a default behaviour non administrable. Don't confuse this with the feature flag FRHRTANP that manages the tandem prevention mechanism for the MOC13-part.

In summary, we have in our network the following behaviour:

IF

There is a Mobile-to-Mobile Call

AND

The calling MS is in Half Rate,

THEN

The MTC-part of the call will be forced to Full Rate

ONLY IF

Both Parties are located in the same MSC's

12 MTC: Mobile Terminating Call13 MOC: Mobile Originating Call

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4. Impact on the Speech Quality

4.1. General Results

Audio Listening Tests have been conducted to assess the subjective Speech Quality performance of the Half Rate Codec. 40 people have participated to the tests: 10 from the E&O Department (technical people) and 30 from the Customer Service & Marketing Department (non-technical people). The ITU-T P.800 recommendation suggests to use the Comparison Category Rating (CCR) Method. With this method, the listeners use the following scale which is called CMOS (Comparative Mean Opinion Score) :

3 Much Better

2 Better

1 Slightly Better

0 About the Same

1 Slightly Worse

2 Worse

3 Much Worse

Several background noise conditions were examined: Low Car Noise Medium Babble Noise High Street Noise Clean: Noiseless Speech ( @ 45 dB SNR)

Global Scores (in clean speech and all noise conditions, in tandem and non-tandem conditions):

Global Scores

7%

18%

37%

22%

15%

1% 0%2%

15%

28%

33%

18%

4%

0%0%

5%

10%

15%

20%

25%

30%

35%

40%

-3 -2 -1 0 1 2 3

CMOS

Non Technical

Technical

Poly. (Technical)

Poly. (Non Technical)

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On the global score, we can see that technical people is bit more optimistic than non-technical people.

The majority of the people estimate Half Rate about the same or slightly worse than Enhanced Full Rate but a part estimate also Half Rate slightly better and even more. This contradictory fact shows the difficulty to differentiate both except in tandem conditions. This confirms also the results of the drive-tests during which we didn't notice a big difference in voice quality on Half Rate compared to Enhanced Full Rate. In the most cases the customer will not hear the difference with EFR. You hear a difference only if you concentrate on the voice quality and compare with another call in EFR, which is clearly not the case for most of our customers.

4.2. Tandem & Non-Tandem Results

As we will see on the following charts, there is a big difference in the speech quality impact between the tandem conditions (Half Rate-to-Half Rate Call) and the non-tandem conditions (Half Rate-to-fixed Call or vice-versa).

General Scores in Tandem and Non-Tandem Conditions

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The Performance of the Half Rate Codec is well degraded (worse and even much worse) in tandem conditions. The statistical chance to have a Half Rate-to-Half Rate Call depends:

-On the Tandem Prevention Feature14 implemented in our Siemens MSC

- On the Implementation Scale: if Half Rate is implemented on a large scale, the statistical chance of tandem conditions could be non negligible; if Half Rate is only implemented for Events and Capacity Extensions, thus only on Hot Spots during a temporary period of time, the statistical chance of tandem conditions should be negligible.

14 See §4.7 Tandem Prevention Feature

Scores in Tandem Conditions

17%

30%

34%

13%

6%

0% 0%

7%

20% 20%

10%

3%

0%

40%

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

-3 -2 -1 0 1 2 3

CMOS

Non Technical

Technical

Poly. (Technical)


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4.3. MOS Impact evaluation

For the moment, it's not possible to evaluate the impacts of Half Rate on the speech quality in the Life Network with CellAD or with TEMS. So, in order to have an idea about in our Network, we will make some assumptions:

We will take the results of the Audio-Tests and will separate Tandem & Non-Tandem Conditions.

We assume that 28% (~16/17 * 30%) of the Half Rate Traffic are HR-to-HR Calls given that:

- The Mobile-to-Mobile (MTM) Proportion in our Network is around 30%- There are 17 MSC's in our Life Network so that 16/17 of the MTM Half Rate Traffic are in Tandem

Conditions.

We consider the Reference of the CMOS "0" as the MOS Error Pattern n°1 of EFR in tandem or non-tandem conditions. According to the specifications GSM 06.08, this Error Pattern n°1 corresponds to a mobile well inside the cell with a C/I = 10 dB and a GBER (Average Gross Bit Error Rate) = 5%.

We have made a linear regression of the MOS between the Reference and the maximum allowed MOS (= 4.61) which corresponds to Direct Speech without GSM.

With these assumptions, the results are the following:

Assuming 100% of Half Rate Traffic, 74% of the Calls should have a Good Mean Opinion Score >= 3.5.

Half Rate Tandem Conditions28%

CMOS MOS 3 0,0% 4,612 0,8% 4,221 7,0% 3,840 14,8% 3,45-1 30,5% 3,06-2 32,5% 2,68-3 14,5% 2,29

Total 100%

Half Rate Non Tandem Conditions72%

CMOS MOS3 0,0% 4,612 1,8% 4,451 19,5% 4,280 29,3% 4,12-1 37,0% 3,96-2 10,8% 3,79-3 1,5% 3,63

Total 100%

0,000%

20,000%

40,000%

60,000%

80,000%

100,000%

Good: MOS >=3,5

73,774%

Acceptable:2,5<=MOS<3,5

21,953%

Poor: 1,5<=MOS<2,5

4,094%

HR

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4.4. Results in Clean and Noisy environments

In the following charts, we have presented the Scores in Clean Conditions and in Noisy Environments. The performance of the Half Rate Codec is about as good as the performance of the Enhanced Full Rate Codec for Error Free Condition. We can see that the level of background noise seems to be the major factor limiting the quality of Half Rate, the performance is worse than with EFR.

Scores in Noisy Conditions

3%

9%

42%

32%

14%

0% 0%0%

5%

38%

48%

8%

3%0%

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

-3 -2 -1 0 1 2 3

CMOS

Non technical

Technical

Poly. (Technical)

Poly. (Non technical)

Scores in Clean Conditions

1%

15%

38%

18%

25%

2%0%0%

3%

33%

37%

27%

0% 0%0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

-3 -2 -1 0 1 2 3

CMOS

Non Technical

Technical

Poly. (Technical)


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5. New Parameters and Recommended Values

In order to explain more explicitly the choice of the recommended values for FRL & FRU, HRL & HRU used in the Channel Rate allocation based on Cell Load, we have showed the results of the FOA's. Two different threshold values have been used Lower Limit = 20% & Upper Limit = 30% compared to Lower Limit = 10% & Upper Limit = 20%. From the quality point of view, the 2 nd type of parameters Lower Limit = 10% & Upper Limit = 20% is recommended to activate because there are less Half Rate Traffic and that we can have the same kind of TCH_Load_Peak which depends on the number of Dual Rate TRX's activated. However, as the threshold parameters determine the dynamic of the Half Rate Allocation, it 's be better to set the Lower Limit = 20% and Upper Limit = 30% when Events are concerned. Indeed, the increase of traffic during Events is often very quick. By putting the Lower Limit to 20%, you have more Dual Rate resources free15 when the Half Rate threshold has been reached so that you can better overcome quick increase of traffic.

15 Full Rate Calls are allocated on dedicated FR Resources preferably to Dual Rate Resources when both kinds of resources are available.

Load

0%20%40%60%80%

100%120%140%160%

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TCH_Load_peak

Halfrate seizures (%)

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%HR-seizures

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%HR-seizures

FRL= 10% & FRU= 20%

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5.1. Transceiver (TRX) Parameters

Half Rate Support

HRS = Y or NWith this parameter you define whether the TRX hardware supports half rate. But All the TRX's of our Network supports Half Rate.Default Value: YRecommended Value: this parameter is put on "Yes" by default but it must be checked that on the TRX's where Half Rate is implemented the parameter HRS is set on "Yes". When the Cell is in Baseband Hopping, it's imperative to check that all the TRX's of the cell (even those where Half Rate is not activated) have HRS set to Yes.

5.2. Base Transceiver Station (BTS) Parameters

Limit for FR TCH Resources Lower

FRL = decimal numberWith this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are allocated until the number of free full rate resources is reduced below the threshold given in the parameter. The half rate resources are then allocated.Values Range from 0% to 100%.Default value is 100%.Recommended Value: 100% for normal area, 20% for Events.

Limit for FR TCH Resources Upper

FRU = decimal numberWith this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are again allocated when the number of the free full rate resources increases above the threshold given by the parameter.Values range from 0% to 100%.Default value is 0%.Recommended Value: 0% for normal area, 30% for Events.

TCH Rate Intra Cell HO

TRIH = decimal numberWith this parameter you control the TCH channel rate determination in TCH allocation and the TCH speech codec to be allocated during internal intra-cell handover.Values range from 0 to 4.Default value is 0.Recommended Value: 0 (No extra-constraints, constraints given by the BSS-level parameter HRI are followed).

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5.3. Base Station Controller (BSC) Parameters

BTS Load Lower Dependent TCH Rate

HRL= decimal numberThe parameter controls the TCH channel rate determination on the BSC level according to the cell load in traffic channel allocation. With this parameter you define the lower limit for the percentage of free full rate resources. Full rate TCHs are allocated until the number of free full rate resources is reduced below the value of the parameter. The half rate resources are then allocated.Values range from 0% to 100%.Default value is 100%.Recommended Value: 10%.

BTS Load Upper Dependent TCH Rate

HRU = decimal numberThe parameter controls the TCH channel rate determination on the BSC level according to the cell load in traffic channel allocation. With this parameter you define the upper limit for the percentage of free full rate resources. Full rate TCHs are allocated when the number of free full rate resources exceeds the value of the parameter.Values range from 0% to 100%.Default value is 0%.Recommended Value: 20%.

HR TCH Alarm Limit

ALHRT = decimal numberWith this parameter you define the alarm limit for available half rate traffic channels. The parameter is used by radio network recovery.Values range from 0% to 100%.Default value is 30%.Recommended Value: 30% = the same as for FR TCH Alarm Limit

TCH Rate Internal HO

HRI = decimal numberWith this parameter you define the traffic channel allocation during BSS internal or external handovers.Values range from 1 to 5.Default value: 1.Recommended Value: 5 which corresponds to the "Best Candidate in Handover" and after, the same TCH type is taken as used in the source cell (if possible).

In Chapter 11 Instructions, we can see an overview about the recommended values of the parameters.

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6. New Counters

6.1. Traffic Counters

1. TCH_HALF_REQ_SUCC_UNSUCC : Number of HR TCH requests (both successful and unsuccessful). This counter is updated when the channel rate of the TCH requested is uniquely determined to be HR only (The type of the TCH may be limited either by an assignment request or an HO request from the A interface, or it may be due to BSC restricting the selection of the channel type in TCH allocation).

2. TCH_REQ_HALF_PREFERRED: Number of TCH requests with HR preferred (both successful and unsuccessful). The preferred channel rate can be defined either by assignment request or HO request received from the A interface or by features which are activated on the BSC for controlling the selection of the channel type in TCH allocation. In the latter case, the preferred channel type can be quite the opposite to the one initially set by the MSC.

3. TCH_REQ_FULL_PREFERRED: Number of TCH requests with FR preferred (both successful and unsuccessful). The preferred channel rate can be defined either by assignment request or HO request received from the A interface or by features which are activated on the BSC for controlling the selection of the channel type in TCH allocation. In the latter case, the preferred channel type can be quite the opposite to the one initially set by the MSC.

4. TCH_HALF_SUCC_SEIZ: Number of successful Half Rate TCH Seizures.

5. TCH_HALF_SEIZ_SPEECH_VER1: Number of successful Half Rate TCH seizures when

speech version 1 is used.

6. TCH_HALF_SEIZ_SPEECH_VER2: HR version 2 not implemented in our Network.

7. TCH_HALF_SEIZ_SPEECH_VER3: HR version 3 not implemented in our Network.

8. TCH_HALF_SEIZ_NORM_ASS: Number of the successful Half Rate TCH seizures for a normal assignment (TCH request for a call attempt).

9. TCH_HALF_SEIZ_INT_HO_CH_RATE: Number of the successful Half Rate TCH seizures for internal HO when the channel rate changed from FR to HR.

10. TCH_FULL_SEIZ_INT_HO_CH_RATE: Number of the successful Half Rate TCH seizures for internal HO when the channel rate changed from HR to FR.

11. TCH_REJ_REQ_DUE_LACK_HR: Number of the TCH requests rejected due to lack of resources. This counter is updated when no TCH's are available when requested from the RRM either in a call or HO attempt and either HR or preferred HR TCH was requested.

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12. TCH_REJ_REQ_DUE_LACK_FR: Number of the TCH requests rejected due to lack of resources. This counter is updated when no TCH's are available when requested from the RRM either in a call or HO attempt and either FR or preferred FR TCH was requested.

13. TCH_HALF_REJ_DUE_FR_TRAF: Number of rejected Half Rate TCH resource requests due to FR traffic, whether queuing occurred or not. This counter is updated when no HR TCH is available in a situation where a FR call is being maintained in a DR TSL and at the same time there is a permanent FR type TSL free.

14. TCH_REJ_DUE_TO_REQ_CH_A_IF_CRC: Number of the requests for TCH rejected due to mismatch between the types of the requested channel and the A interface circuit, whether queuing occurred or not.

15. TCH_SUCC_HALF_SEIZ_FAST_CALL: Number of the successful HR TCH's seizures for a FACCH Call setup, which is not active in our network.

16. TCH_ENDED_DUE_TRANSC_HR_RATE1: Number of the Radio TCH transactions ended due to transcoder failure when speech HR version1 is in use.

17. TCH_ENDED_DUE_TRANSC_HR_RATE2: HR version 2 not implemented in our Network.

18. TCH_ENDED_DUE_TRANSC_HR_RATE3: HR version 3 not implemented in our Network.

19. TCH_HALF_TR_FAIL: Total Number of the HR TCH transaction failures.

20. TCH_TRUNK_REFUSED_HR_REG: Number of trunk reservation function invocations that request allocation being refused when HR or preferred HR TCH has been requested. Trunk Reservation is not used in our network.

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6.2. Resource Availability Counters

1. AVE_IDLE_H_TCH_1: Average Number of the Idle HR TCH's per interference band (band1). This counter is updated:

- When an HR TCH is seized while the other half is already busy- When an HR TCH is released and the other half is still busy- When one half of the DR Channel is seized- When one half of the DR Channel is released while the other half is free.

2. Peak_AVE_IDLE_HTCH_1: Peak of the Average Number of the Idle HR TCH's per interference band (band1).

3. AVE_IDLE_H_TCH_2: Average Number of the Idle HR TCH's per interference band (band2). The update is similar as for the counter AVE_IDLE_H_TCH_1 but in the band 2.





8. Peak_AVE_IDLE_HTCH_4: Peak of the Average Number of the Idle HR TCH's per interference band (band4)

9. AVE_IDLE_H_TCH_5 Average Number of the Idle HR TCH's per interference band (band5). The update is similar as for the counter AVE_IDLE_H_TCH_1 but in the band 5.


11. AVE_TCH_AVAIL_HALF: Average Number of the HR TCH's available, i.e. permanent HR or one half of DR Channel.

12. AVE_AVAIL_FULL_TCH: Average Number of available Full Rate TCH's, i.e. permanent FR or DR Channel.

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13. PEAK_AVE_AVAIL_FULL_TCH: Peak of the Average Number of available Full Rate TCH's.

14. TCH_HR_RADIO_CONGESTION_TIME: Total Duration of the congestion on the HR TCH's within a measurement period (10ms).

15. AVE_TCH_BUSY_HALF: Average Number of busy Half Rate TCH's, i.e. permanent HR or one half of DR Channel.

16. TCH_PEAK_BUSY_FULL: Peak Number of busy Full Rate TCH's, i.e. permanent FR or DR Channel completely used.

17. TCH_PEAK_BUSY_HALF: Peak Number of busy Half Rate TCH's, , i.e. permanent HR or one half of DR Channel.

7. New Alarms

ALARM N° 7054: "TRX DOES NOT SUPPORT HALF RATE (TCH/H) CONFIGURATION"

There has been an attempt to configure the half rate channel (TCH/H) to the FU (Frame Unit) which does not support half rate channels. This alarm affects the provided service.

ALARM N° 7717: "WORKING HALF RATE TCH RATIO BELOW THRESHOLD"

The radio network configuration and failure management has detected that the ratio between the number of half rate traffic channels in normal working state (UNLOCKED-WORKING) and the number of unlocked half rate traffic channels is below the defined threshold.

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8. Feature Benefits

The Half Rate feature has clearly proven during the FOA's his major benefit: Dynamic Increase of Capacity.

For Events, thanks to the Half Rate Feature, we could improve the Customer Satisfaction by:

Decreasing the % CSDC and the number of TCH Blocking Increasing the Capacity (with all the TRX's configured in Dual Rate, we have had up to 195% TCH Load Peak

during the Rock-Werchter Festival 2001).

For Temporary Capacity (For instance during Summer Holidays at the Coast):

Half Rate is used only when needed, i.e. when the cell load requires it. The major KPI's (ACDC, CSDC, HO Success Rate) remain stable.

For Extra Capacity:

To reduce the investments before adding extra cabinets. To reduce the % CSDC and % TCH Blocking

For sites where the full configuration is no more sufficient. For a short period each day (i.e. traffic jams, …)

For TRX-Efficiency:

By replacing an add TRX by the activation of an Half Rate TRX, or in other terms, by removing some TRX's and activate Half Rate on some TRX's.

9. Feature Drawbacks

The speech quality is slightly worse with Half Rate than with Enhanced Full Rate in noisy conditions. In tandem conditions (Half Rate to Half Rate Calls), the speech quality with Half Rate is worse and even much worse than with Enhanced Full Rate.

As no Circuit Pools support all the Codecs together with noise Suppression and Tandem Free Operation and that the A-Interface Circuit Pool doesn't work correctly, Half Rate cannot be implemented on the same BSC with Full Rate enhanced by Noise Suppression/Tandem Free Operation.

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10. Instructions

10.1. Activation of Half Rate on BSC & Transcoder Level

10.1.1. New PRFILEWe recommend to check if the new PRFILE with the Half Rate Feature included is present on the BSC.

10.1.2. TCSM2, Ater and A Interfaces ConfigurationWe recommend to reconfigure all the TCSM2's16 related to the involved BSC from EFR-FR support to EFR-DR support (i.e. in Circuit Mode "C"). The reconfiguration of 1 TCSM2 takes around 1 hour and has no subscriber impact if done carefully and well planned.

10.1.3. Activation of Acoustic Echo Cancellation (AEC) for Half Rate Because of the TCSM2 reconfiguration, we must reactivate AEC on the TCSM2.

10.2. Activation of Half Rate on TRX Level

The activation of 1 TRX (Channel definition only) in Dual Rate is very quick and takes around 1 minute. However, when we have also to change the TRX Signalling from 16kbps to 32 kbps, it takes around 10' per TRX with Customer Impact.

10.2.1. 32 kbps TRX SignallingAs mentioned in §2.5.1, we recommend 32kbps TRX Signalling on the Abis at least for each TRX where Half Rate is activated.

10.2.2. Dual Rate Traffic Channel Definition We recommend to define all the Traffic Channels of the involved TRX's as Dual Rate.

10.2.3. Number of TRX's to activate in Half RateThis depends on the usage and the needs. See specification about "Half Rate for Events and Capacity extensions".

10.2.4. Which TRX to activate in Half Rate ?We recommend to activate the TRX's in Dual Rate where all the Timeslots are Traffic Channels (TCH) in order to use the capacity most efficiently given the price we pay for Half Rate activation. That's a first reason why we don't recommend to activate Half Rate on the BCCH TRX. A second reason is the following: the GPRS Timeslots are configured on the BCCH TRX and GPRS Traffic cannot be transported on a half-occupied Dual Rate Timeslot (but well on a completely free Dual Rate Timeslot). But for very big events, it can be useful to activate Half Rate on all the TRX's (even the BCCH TRX) and it's allowed as specified in the Recommendation "Half Rate for Events and Capacity extensions".

16 TCSM2: Transcoder Submultiplexer of 2nd generation

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10.3. Recommended Parameters

Parameter Symbol Parameter Name Parameter Type Non Event Area Event AreaHRS Half Rate Support TRX Parameter Yes (Default Value) Yes (Default Value)

HRI TCH Rate Internal HO BSC Parameter 5 (Best Candidate) 5 (Best Candidate)

TRIH TCH Rate Intra Cell HO BTS Parameter 0 (Default Value) 0 (Default Value)

ALHRT HR TCH Alarm Limit BSC Parameter 30% (Default Value) 30% (Default Value)

FRL Limit for FR TCH Resources Lower

BTS Parameter 100% (Default Value)17 20%

FRU Limit for FR TCH Resources Upper

BTS Parameter 0% (Default Value) 30%

HRL BTS Load Lower Dependent TCH Rate

BSC Parameter 10%18 10%

HRU BTS Load Upper Dependent TCH Rate

BSC Parameter 20% 20%

17 We can prohibit the effect of either parameter by setting the lower limit of the parameter higher than the upper limit.18 We can overwrite the BSS level values of the upper and lower limits by determining new values to the corresponding BTS-specific limits.

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11. References

1. Nokia Electronic Documentation NED BSC S9 - Functional Descriptions - Voice Coding - Half Rate in BSC (ETSI).

2. Nokia Electronic Documentation NED TCSM2 S9 - Functional Descriptionsof TCSM2.

Documents

HR Feature