1 Channel OptimisationAuthor: Tim KirvarDRAFT WORK IN PROGRESS

2 References[1] WiMAX Statistics Definition & Use Cases WMX-ICD-014 R01.00.05 Jan 24, 2007 [2] WiMAX Information Model EMS Version R02.00.01.04[3] Wimax ICD MS-BS Layer 2 Messages and Procedures WMX-ICD-002 R01.00.15[4] Wimax ICD MS-BS Layer 1 WMX-ICD-001 R01.00.13[5] WiMax System Architecture Document WMX-SAD-001 R01.00.15[6] Part 16: Air Interface for Fixed Broadband Wireless Access Systems”, IEEEStd802.16-2004[7] “Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access SystemsAmendment 2: Physical and Medium Access Control Layers for Combined Fixed andMobile Operation in Licensed Bands and Corrigendum 1”, IEEE Std 802.16e-2005,IEEE Std 802.16-2004/Cor 1-2005.[8] “Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, Corrigendum 2 (Draft 2), January 30, 2007; http://compass.mot.com/doc/225497999/802.16_corrigendum_2_draft_2[9] WiMAX Base Station Software Architecture. WMX-BTS-AD-001 May 17, 2007

3 IntroductionTO DO BASED ON CONTENT- NEEDS TO BE DONE RETROSPECTIVELY

4 Fast Feedback Optimisation

4.1 IntroductionFast feedback enables the MS to send CINR information to the BS which enables the BS to determine the modulation and coding rate of downlink transmissions. It is sent by the MS to the BS periodically using the Channel Quality Indication Channel (CQICH).

In the uplink portion of the frame, the CQICH (a.k.a. Fast Feedback) region consists of a number of single-slot bursts, each burst originating from a separate MSS. The CQICH bursts are allocated within the CQICH region using vertical rastering method (for more details see 3.6.2 of [4]). Each burst is numbered with an offset which defines the location of the burst. The CQICH Alloc IE, sent to the MS, defines in which slot each MSS can transmit its fast feedback information.

Fast Feedback operation is described by four different procedures: 1) BS-Initiated Fast Feedback Procedure: Describes the initial allocation of a fast-

feedback channel to a MS when initiated by the BS.2) MS-Initiated Fast-Feedback Procedure: Similar to BS-Initiated Fast Feedback

Procedure but is triggered by the MS.

3) BS-Initiated HARQ Fast Feedback Procedure: Uses the HARQ allocation to extend an existing fast-feedback channel allocation.

4) Fast-Feedback Reporting Procedure Describes the periodic reporting of CINR in the assigned fast-feedback channel.

Procedures 1-3 are the used to set up the fast feedback procedure. The fast feedback measurements are actually sent in procedure 4.

For a MS to send fast feedback it must support it. NOTE: Add info relating to how mobile sends its fast feedback capability: Bit#1 (Enhanced Fast-feedback) must be set to 1 in the “Uplink control channel support” SBC-RSP TLV. The MS support CINR measurements on the preamble. Bit #0 (Physical CINR measurement from the preamble) must be set to 1 in the “OFDMA MS CINR measurement capability” SBC-RSP TLV.

4.2 BS-Initiated Fast Feedback ProcedureThis procedure assigns a fast-feedback channel to a MS and defines the type of CINR measurement reported and the duration and periodicity of the feedback. This procedure is discussed in sections 8.4.5.4.10.4 and 8.4.5.4.10.5 in the 802.16 spec

The BS-Initiated Fast Feedback Procedure starts when downlink unicast data is to be sent to an MS.

The BS sends in the CQICH Allocation IE in the compressed UL-MAP message. In this IE, the basic CID of the MS is used to allocate the fast feedback channel. Along with the CID the following information is sent:

1) Allocation index: Index to the fast feedback channel region marked by UIUC 0. An offset value 0 indicates the first slot in the fast feedback region.

2) Period: The number of frames that each fast feedback channel is sent. If the period is p the the number of frames is 2^p. The BS configuration parameter wmanIfBsCQICHMaxPeriod is used to configure this parameter.

3) Frame Offset: The frame of next available fast-feedback channel.4) Duration: The number of frames that the fast feedback channel has been allocated to the

MS. BS configuration parameter wmanIfBsCQICHDuration5) C/N measurement type : The CQICH Allocation IE fields defines how the C/N

measurements are to be made. The values are set according to the CM parameter wmanIfBsCINRMeasurementType. See 16.1.3 of [3] for details.

4.3 BS-Initiated HARQ Fast Feedback Procedure [3]This procedure assigns a fast-feedback channel to a MS during a DL HARQ allocation.While this approach can be used to initially assign a fast-feedback channel to a MS, it isnot used in this way since the HARQ DL MAP IE it does not allow the BS to specify thespecific CINR reporting type/permutation (as specified in the BS-Initiated Fast Feedback Procedure). Instead, this procedure is used right before an existing fast-feedback allocation expires to extend the allocation. This procedure is discussed in sections 8.4.5.3.21 in the 802.16 spec.

This procedure is not supported in WMX1.0 since there is no method to specify the typeof CQICH the MS reports. It may be supported in a future release once ambiguities areremoved in the standard.

The procedure is logically similar to the BS-Initiated Fast Feedback Procedure apart from the fact that the Allocation offset, Period (p), Frame Offset, and Duration are obtained from HARQ DL MAP_IE.

4.4 MS-Initiated Fast-Feedback Procedure [3]This procedure allows the MS to request a fast-feedback allocation. This procedureshould not be needed since the BS will initiate Fast-feedback using either the BS-InitiatedFast Feedback Procedure or BS-Initiated HARQ Fast Feedback Procedure whenthere are DL SDUs to send to the MS. The trigger event for this procedure is not defined in the 802.16 spec. One possible scenario is when the MS needs clarification of a fast-feedback allocation.

The procedure is started by the MS obtaining UL allocation and sending the CQICH allocation request header. The BS decodes the UL allocation and checks if MS has been assigned a Fast-feedback channel. If MS has already been assigned a fast-feedback channel, the BS-Initiated Fast Feedback Procedure is completed again. If MS has not already been assigned a fast-feedback channel, The BS ignores the request and the procedure is completed.

In effect this procedure will not initiate fast feedback.

4.5 Fast-Feedback Reporting ProcedureFollowing the allocation of a fast feedback channel to an MS, this procedure takes care of the allocation of uplink resources so that the MS can send the CINR measurements. The BS sends the Fast-Feedback Channel IE in the Compressed UL-MAP to the target MS. This IE contains the region which the MS can use to send the CINR measurement The following frame the MS sends the CINR measurement. This procedure is repeated every 2^p frames where p is the value wmanIfBsCQICHMaxPeriod.

If the BS in unable to decode the first fast feedback channel, the BS assumes that the MS did not receive the CQICH Allocation IE and resends the CQICH Allocation IE. If the number of resends (Fast-Feedback_Alloc_Retries) is exhausted, all DL SDUs for MS are discarded and an alarm is raised 16.1.7 of [3].

Question: Which alarm is made and is there a stat pegged? Does the procedure simply restart after an alarm when a new DL SDU arrives for the MS?

4.6 CM Parameters

4.7 wmanIfBsCQICHMaxLengthMaximum number of fast-feedback channel in a single frame. The maximum number of MSS allowed to be concurrently assigned a fast-feedback is wmanIfBsCQICHMaxLength times wmanIfBsCQICHMaxPeriod. Range: 1-64Default: 8

4.7.1 wmanIfBsCQICHMaxPeriodExponent indicating the number of frames between fast-feedback channelassignments to an individual MSS. Actual period = 2^ wmanIfBsCQICHMaxPeriod.Range: 0-3Default: 3

4.7.2 wmanIfBsCQICHDurationDuration exponent of fast-feedback channel assignment. Actual duration =10* 2^ wmanIfBsCQICHDuration frames. Range: 0-7, 0 means stop periodic feedback, 7 means continuous feedback.Default: 6

4.7.3 wmanIfBsCINRMeasurementTypeThis configuration parameter describes the type of CINR measurement toreport. Defined in the CQICH Allocation IE.Range: 1-3Default: 11 (Frequency Reuse factor = 1) : Uses all preamble subcarriers (except guard and DC) to calculate CINR. The unmodulated subcarriers should be considered noise and interference for the CINR estimate. Use with 1x3x1(PUSC1/1 ) or 1x3x3(PUSC1/1) reuse.2 (Frequency Reuse factor = 3): The unmodulated subcarriers should be ignored. Use with 1x3x1 (PUSC1/3) reuse. Should apply to the PUSC reuse on the data portion of the frame.3: Physical CINR from PUSC zone using pilots

4.7.4 wmanIfBsDefaultCINRAveParamDefault averaging parameter for physical CINR measurements for CQICH inmultiples of 1/16. Range 0-15 Default 4

4.8 Performance Management StatisticsNone defined although various RF statistics have been deferred. No specific fast feedback statistics have been identified.

4.9 MSS CINR Measurements (section of 3.17.2 of[4])The MSS measures CINR of the serving sector for handover purposes as well as for CQICH where DL CINR is periodically reported to the BS.The WiMAX Profile defines six CINR measurement types, as specified in 802.16 clause 8.4.5.4.12:1. Physical CINR measurement from the preamble for frequency reuse factor = 12. Physical CINR measurement from the preamble for frequency reuse factor = 33. Physical CINR measurement for a permutation zone from pilot subcarriers4. Effective CINR measurement for a permutation zone from pilot subcarriers5. Major Group indication for a PUSC zone (required for MSS)6. MIMO permutation feedback cycle (only applicable to MIMO)

For CQICH, CINR averaging is defined in the 802.16e spec (clause 8.4.11.3 in 802.16e-2005 and Corrigendum 2 [8]) using a recursive filter approach:

CINRavg(k) = CINR(0) for k=0 (i.e. first measurement)

CINRavg(k) = 10log[ (1-(1-α)n+1)10 CINR(k)/10 + (1-α)n+110 CINRavg(k-1)/10] for k > 0    where

k is the current CINR measurement samplen is the number of consecutive frames in which no measurement is madeα = DCD TLV “default RSSI and CINR Averaging parameter” which is set to wmanIfBsDefaultCINRAveParam

NOTE: Note that this equation is from Corrigendum 2 which doesn’t appear in the IEEE active standards and is a draft. See [8] for the equation in standard. Effectively the averaging restricts the effect of past measurements depending on the time of the last measurement. Based on the default averaging value of ¼, a frame with no measurement will set n = 1. The multiplier for the last average will be (1-1/4)^2 = 9/16 and the multiplier for current frame will be (1-9/16) = 7/16. It can be seen that the past average values have very little affect on the average after 7 frames of no measurment ~ 10% weighting of past frames. This goes down to 1% after 14 frames of no measurements. It is not clear what affects how many frames do not have measurments.

QUESTION: How often are measurements made? What affects the frequency of measurements?

4.10Optimisation Opportunities

4.10.1 Fast feedback channel dimensioningThe number of fast feedback channels that can be simultaneously allocated is based on the number of fast feedback channels per frame, wmanIfBsCQICHMaxLength and the period of reporting controlled by wmanIfBsCQICHMaxPeriod. Based on the default values, 64 fast feedback channels are available (8 channels per frame and each channel is allocated every 8 frames). The duration of allocation will be 640 frames or 3.2 seconds.The MS will send feedback every 8 frames or every 40ms.

There appears to be a trade off between the amount of space allocated in the UL for CQICH (fast feedback channel) and the number of users that can be supported in the fast feedback channel.

QUESTION: What are the implications of all Fast Feedback channels being used in terms of latency to other Mobiles as they need to wait for a fast feedback channel being allocated?

QUESTION: Is there a statistic that monitors the utilisation of the fast feedback channel which can be used?

QUESTION: The Channel Measurement Report Procedure see 17.1 in [3] can be used to obtain tx power and CINR for the mobile incases where the MS does not support open loop power control and fast feedback channel. Can this procedure be used as a back up when the CQICH channels are fully used?

4.10.1.1 Data to collectNo statistic or alarm has been identified that could indicated issues with the dimensioning of the fast feedback channel.

To determine the performance of the fast feedback channel the channel utilisation should be determined. This can be a statistic that logs the peak utilisation of the fast feedback within a given time duration.

In addition a statistic that logs the number of DL data allocations that have been denied or delayed as a result of in sufficient fast feedback channels shall be collected.

For DL allocations that have been delayed a statistic that is able to quantify the delay would be helpful to determine the effect of the lack of resources.

The configuration parameters in 4.6 should also be collected.

5 Idle mode and paging

5.1 Introduction (section 14.7.4 of [5])Idle mode for a MSS is the period of time in which the MSS receives only intermittent downlink transmission from the system and yet retains its ability to move throughout the system while retaining its IP address.

A MSS may choose to enter idle mode during periods of data inactivity to conserve its battery resources. Likewise, a serving BTS may choose to sequester an inactive MSS to idle mode in order to conserve its air-interface resources.

A MSS exits idle mode and returns to active mode upon either outbound or inbound data activity for the MSS or when it becomes necessary to re-authenticate.

While in idle mode, an MSS is under the administration of a paging controller (PC). The PC, through the use of its Location Register database (LR), is responsible for tracking the location of idle mode MSSs and for paging an MSS when it is required to re-enter the system and become active.

A PC conducts its administration of idle mode MSSs while those MSSs reside in an area of coverage represented by a group of BTSs the PC manages, called a paging group. The coverage of paging groups overlap such that some BTSs function in more than a single paging group. As an idle MSS moves from a cell in one paging group to a non-overlapping cell in another paging group, the PC will transfer its administration of theidle mode MSS to the PC that manages the moved-to paging group (if the PC doesn’t manage both).

Figure 1 Paging Group Overlap

When the MS determines that it wants to enter idle mode, it deletes its service flows and requests uplink resources to send a DREG-REQ message. This message contains the request to enter idle mode along with Idle Mode Retain Information which states which information the network can retain for when the mobile re-enters the network. In addition, the paging request cycle is sent which is the desired paging cycle that the MS wishes to use. On receiving the DREG-REQ the BS requests to the CAPC that the MS enters idle mode. Following positive confirmation from the CAPC, the BS commands the MS to enter idle mode by sending the DREG-CMD message using the MS’s basic CID with the paging parameters to use. The BS will allocate the paging group (if it is configured with multiple paging groups) which has parameters as close to the omes requested by the MS. If the paging request fails, the mobile will reset its MAC and re-enter the network.

The BS may determine that it needs to force an MS to enter idle mode (section 12.2 in [3]). This decision is based on the number of active MSs and is triggered when the number of active MSSs exceeds a configurable high water mark threshold wmanIfBsInitIdleModeHighThreshold. An MS is deemed an idle mode candidate if it has had no activity on all of its CIDs for wmanIfBsDeregEligibleIdleTimer. An MS with active connection for VOIP bearer traffic is excluded from the candidate list. The BS initiates the idle mode procedure for each MS where

the MS with the longest time of inactivity is put into idle mode first. MSs are put into idle mode until the number of active MSs fall below wmanIfBsInitIdleModeLowThreshold.

NOTE: What is the implication of setting wmanIfBsInitIdleModeHighThreshold? Currently it is set to the maximum value. What is the impact on the BS if the 255 active users are on active and what is there to gain when they are in idle mode?

For each MS to be put into idle mode, the BS initially deletes all service flows for the MS. The BS requests to the CAPC that the MS enters idle mode. Following positive confirmation from the CAPC, the BS commands the MS to enter idle mode by sending the DREG-CMD message using the MS’s basic CID with the paging information to use.

5.2 Paging InformationThe BS sends the following paging information to the MS: Using this information the MS can determine when to monitor the downlink for pages. The MS monitors frames in the MS Paging Listening Interval, staring in frame N and ending in frame N+ Paging Interval Length where

N modulo PAGING_CYCLE = PAGING OFFSET Paging Interval Length is set to configuration parameter wmanIfBsPagingIntervalLength. PAGING_CYCLE - set to BS configuration parameter wmanPagingCycle PAGING OFFSET - set to configuration parameter wmanPagingOffset

Figure 2 Paging Timings

Paging-group-ID - set to configuration parameter wmanIfPagingGroupId

The MS decodes all DL allocation sent on the Idle mode multicast CID orBroadcast CID (e.g. MOB_NBR-ADV or MOB_PAG-ADV)In the first frame of the MS Paging Listening Interval the BS may sends a MOB_PAG-ADV, if SDUs are pending for any of the MSs in the paging group and the MS’s connection accepts paging (Note that the allocation for this message is done by sending a DL Allocation IE which

states the CID (broadcast in this case) and the region that the MS shall decode). The MOB_PAG-ADV message contains the paging group IDs and the MAC addresses that the pages are for. For each MAC, the page may command the MS to “Perform Ranging to establish location and acknowledge message” or to Enter Network using an action code. In addition a vendor specific TLV is sent which tells the mobile if further MOB_PAG-ADV should be read in the paging listening interval. This TLV also specifies if the MOB_NBR-ADV is sent immediately after the paging interval.QUESTION: The action code may also be No action required. Why have this option?

On receiving a page, the MS will re-enter the network using the initial ranging procedure (with a few exceptions see 12.4.3 for details).

Location area update is performed when a) The mobile reselects a call which is not in the paging group of the MSb) The Idle Mode Timer expires.c) Mobile receives a “Perform Ranging to establish location and acknowledge

message” command in the MOB_PAG-ADV message sent during the paging interval.

The location are update procedure begins with the initial ranging procedure with the following exceptions: The MS sends a RNG-REQ Idle Mode TLV List which states that the ranging purpose is for location area update (Ranging Purpose Indication = 0x02). This TLV contains the MS paging controller ID.On receiving the RNG-REQ message, the BS sends the RNG-RSP message containing the RNG-RSP Idle Mode Location Update TLV List. This TLV list will contain Paging Information TLV if the new paging group has different paging information (paging cycle, paging offset, paging group id, paging interval length) compared to the old paging group. The RNG-RSP also contains the Paging Controller ID TLV if the paging controller ID is different in this BS compared to the Paging Controller ID in the RNG-REQ.

QUESTION: How does cell reselection work while in idle mode? MOB_NBR-ADV message is used to give insight into available Neighbor BSs for cell reselection consideration. Serving BS may schedule scanning intervals or sleep-intervals to conduct cell reselection activity. Couldn’t find anything in standards relating to how this is done...

5.3 Timers and Counters

5.3.1 T45 (table 342 of [7])Time the MS waits for DREG-CMD after sending a DREG-REQ. Value used: 100ms. maximum value 500ms.

5.3.2 DREG Request Retry CountNumber of retries of DREG-REQs message (i.e. the number of T45 timeouts allowed before idle mode entry fails). Value used 3.

5.3.3 Management Resource Holding TimerTime the BS maintain connection information with the MS after the BS send DREG-CMD to the MS. Controlled by wmanIfBsMRHTimer.

5.3.4 Idle Mode TimerMS timed interval to conduct Location Update. Set timer to MS Idle Mode Timeout capabilities setting. Timer recycles on successful Idle Mode Location Update. Default 4096 sec.

5.4 CM parameters

5.4.1 wmanPagingCycleNumber of frames between the beginning of MS listening intervals. Determines the frame in which the paging message is transmitted to a specific paging group.Range: 0 to 65535, step size 1, unit = framesDefault: 100 frames (0.5 seconds)

5.4.2 wmanPagingOffsetSpecifies the frame within the cycle in which the listening interval begins and paging message is transmitted. Must be smaller than PAGING CYCLE valueRange: 0-255Default: None specified

5.4.3 wmanIfBSPagingGroupIdID number of the paging group assigned to the BS. Range: 0-65535

5.4.4 wmanIfPagingControllerIdLogical network identifier for the CAPC retaining MS context information while MS in Idle Mode.

5.4.5 wmanIfBsNbrAdvMinIntervalPagGrpThe minimum number of frames between transmission of MOB_NBR-ADV messages for an individual paging group. If wmanPagingCycle is greater or equal to wmanIfBsNbrAdvMinIntervalPagGrp, then MOB_NBR_ADV sent every PAGING_CYCLE frames. If wmanPagingCycle is less than wmanIfBsNbrAdvMinIntervalPagGrp, then MOB_NBR_ADV messages are every Ceiling (wmanIfBsNbrAdvMinIntervalPagGrp/wmanPagingCycle) PAGING_CYCLE frames.

5.4.6 wmanIfBsReqDurationWaiting value for the DREG-REQ message re-transmission

5.4.7 wmanIfBsPagingIntervalLengthDuration of paging listening interval that the BS can page idle MS on.Range: (2-5) frames.

5.4.8 wmanIfBsIdleModeSystemTimerMax time interval at BS to receive Idle Mode Location Update from MS. Paging Controller will discard MS context when this timer expires IM rule: wmanIfBsIdleModeSystemTimer should be greater than wmanIfBsIdleModeTimeout

5.4.9 wmanIfBsIdleModeTimeoutMax time interval at MS to send Idle Mode Location Update to BS.

5.4.10 wmanIfBsMRHTimerManagement Resource Holding (MRH) timer that defines how long the BS will retain MS connection information with the MS after the BS send DREG-CMD to the MS.

5.4.11 wmanIfBsDregCommandRetryCountNumber of retries on DREG-CMD Message

5.4.12 wmanIfBsT46Time the BS waits for DREGREQ in case of unsolicited Idle Mode initiation from BS. wmanIfPagingRetryCount Scope: per BS and/or per CAPC Total number of paging retries on paging transmission that the BS will send to a MS.

5.4.13 wmanIfBsInitIdleModeHighThresholdThe number of active MSs in a BS that forces the BS to start initiating idle mode with MSs in the BS. Range: 1-255 Default: 255IM rule: wmanIfBsInitIdleModeHighThreshold should be greater than wmanIfBsInitIdleModeLowThreshold

5.4.14 wmanIfBsInitIdleModeLowThresholdThe number of active MSs in a BS that forces the BS to stop initiating idle mode with MSs in the BS.

5.4.15 wmanIfBsderegEligibleIdleTimerThe amount of time that an MS has no activity on any of its connections before it qualifies to be forced into idle mode.Range 1-36,000 seconds (10 hours) 0 (disabled)Default: 3600 (1 hour)

5.5 Performance management information(section 3.7 of [2])

Name Description Scope

apDlPagingSlotsUsed Total number of Downlink slots used for Broadcast paging. MMS computes

APSector

this value by assuming a fixed MCS for Idle mode Multicast CID (Question is the MCS based on wmanIfBsBroadcastCodingRate?):

apDropPageAp Number of times a page was dropped by the AP because the paging queue is full. Quesiton: Appears to be a queue length of 1025 is this per sector as it specifies as per MAC in [9]

APSectorPaging Group

apDelayedPages Number of times a page didn’t fit into the current paging cycle. NOTE: A single paging message might be counted more than once if it misses more than one paging cycle. Question: What is the capacity of a paging cycle in terms of number of messages sent?

APSectorPaging Group

capcInitPagesSent Total initial pages sent. CAPCLogical PayloadPaging Group

capcPageRetrySent Total retried pages sent. CAPCLogical PayloadPaging Group

apPageCycles (section 9.37.1.5.0.7 of [9])

Number of messages per paging group per sector. This is a 32 bit counter that counts the number of MOB_PAG-ADV messages sent by theMAC during the paging/listening intervals.

APSectorPaging Group

apLocUpdError (section 9.37.1.5.0.16 of [9])

This is a 32 bit counter that counts the number of RNG-RSP messages sent by the MAC withthe Location Update Error indicated

AP Sector

apIdleEntryMssError (section 9.37.1.5.0.17 of [9])

This is a 32 bit counter that counts the number of DREG-REQ messages sent by the MAC andis not responded by the MSS during network initiated Idle Mode entry.

AP Sector

apLocUpdSucc (section 9.37.1.5.0.21 of [9])

This is a 32 bit counter that counts the number of RNG-RSP messages sent by the MAC with the Location Update success.

AP Sector

apLocUpdPgChg Number of Location Updates received due to change in Paging Groups. This is a 32 bit counter that counts the number of RNG_RSP messages sent by the MAC with Location Update Response and the paging group is different from the previous paging group(defined in MS context leased from CAPC).

APSector

apPwrDn Number of Power Down Location Update requests received.

AP Sector

capcIdleModeRlsReq Number of received requests to release the MSS from idle mode.

CAPCLogical Payload

Paging Group

5.6 Paging Group Association Rules [2]

1 Paging controller (pCAPC/payload card) is associated with 1 or more paging groups2. Border paging groups can be defined for paging controllers residing in another Management Domain (EMS)3. 1 BTS can be associated with 1 to 4 paging groups on any CAPC in the Management Domain or Border Area4. Each paging group is associated with 1 paging controller (pCAPC/payload card)

5.7 Optimisation OpportunitiesDetermining the optimum location areas is a trade off between amount of paging traffic and the number of location area updates generated. Large location areas require fewer location area updates but require the paging information to be sent on multiple sectors. Conversely small location areas will result in frequent location area updates. This problem is well known in mobile wireless technologies and is tackled in numerous ways therein. The optimisation algorithm makes use of several statistics which can measure the effect of both paging load and location area update load. The best solution paging area solution is the one that minimizes both paging traffic and location area updates and additionally ensures no system resource is fully consumed due to paging.

The optimisation algorithm should determine the paging groups that an access point should be a part of (an AP can have up to 4 paging groups)

The algorithm shall use 2 valueso Cost of sending a location area update: This value will be a function of the

system resource load due to a LAU and the probability of a cell reselection between two cells.

o Cost of sending a paging message to APs: This value will be a function of the system resource load due to a page and the probability of an MS being paged in a cell.

oThe algorithm shall try to determine the allocation of cells to paging area which minimizes the paging cost and the LAU cost. As seen in Figure 3 the cost of a paging group is the sum of the paging cost for each sector (node) and each LAU costs (edge) which is cut by the paging group boundary. There are two challenges:

1) How to calculate the LAU and the paging cost.2) Algorithm to find an optimum split (a MULTILEVEL GRAPH PARTITIONING

SCHEMES is used dealing with this in GSM which is used in IDGP no real details are known other that this. A similar approach can be used in wimax)

LAU cost

Paging Cost

Paging Group1

Paging Group2

Paging Group3

LAU cost

Paging Cost

Paging Group1

Paging Group2

Paging Group3

Figure 3 Location Area Division

5.7.1 Location Area CostThe relationship between two cells in terms of the number of cell reselections should be determined. Scaling this value with the cost of a location area update will provide the location area cost. The statistic apLocUpdSucc lists the number of successful Location Updates yet it does not list the MS’s previous cell. When the MS initiated location area update it sends the RNG-REQ Idle Mode TLV List. This TLV contains the paging controller ID specified in the DREG CMD when the MS entered idle mode1. Correlation of the controller ID and a subsequent Location are update may provide information on the mobility of the user.

One other statistic is per neighbour handover statistics. This statistic should correlate with idle mode mobility and could be used. In the absence of per neighbour statistics, the collection of MS and BS initiated handover events can be used to generate these statistics.

Idea: Paging group rotation: An AP has upto 4 paging groups. It is possible to set a cell to have a paging group that has only one cell and allocate MS to that paging group inorder to track the idle mode mobility The process will allocate a certain ratio of users to the paging group without causing adverse system loading. Any cell

1 Can this be used to determine where the cell is coming from? It appears that Paging controller id is related to paging group but how? What happens when the MS has changed paging groups, do subsequent location area updates cause the paging controller id to change to the last paging controller of the MS?

reselection will trigger a location update. Since the source and the destination is known, this information can be used to obtain an understanding of idle mode mobility without overloading system resources. Using this information the system can automatically optimise paging groups.

5.7.2 Paging CostPaging cost should reflect the impact of the cell’s traffic on paging load. Absence of this cost would lead to a paging group that covers all cells in the network. Similarly one can state that no traffic on a cell or more accurately no idle traffic on a cell will result in a zero paging cost. (It may be important to differentiate between mobile traffic and CPE traffic due to the way idle mode is handled). A method is required to determine the paging cost of a cell. In its simplest form the paging cost would be the number of pages a cell would receive if it were the only cell in the paging group (based on this definition the paging cost of a paging group is the #cells in paging group * sum(paging cost cells in paging group) as each page would be sent on all cells in the paging group..

The simplest method to state paging cost is to scale the traffic on a cell.

Question: What is the best way to determine the number of idle mobiles in a cell?

Note: Is it possible to calculate the total paging traffic per paging group in the network to quantify the minimum number of pages possible: For example a paging group that has 16 sectors will cause 16 pages on each sector per page. The statistics capcInitPagesSent and capcPageRetrySent are collected. Need to know how they are pegged

NOTE: It would be useful to know the number of times a paging group is paged and the number of times a mobile responded on a cell. This would determine the distribution of responded pages within a location area. This would effectively give us the probability mobile being paged. The BS will send a RNG-RSP with the RNG-RSP Idle Mode Network Re-entry TLV List as a response to a MS requesting to re-enter network following idle mode. However there doesn’t seem to be a way to differentiate between when an MS request to re-enter network due to page or due to wanting to send UL data. A better place to capture this maybe to determine the number of leases provided to a BS as a result of exit from idle.

NOTE: The CAPC lease statistics may be used to determine the number of mobiles entering idle mode on a cell. The lease of an MS will be taken by the CAPC on idle mode entry and the The ratio of idle mode entry per cell capcInitPagesSent

1) IDEA: Allocate paging groups to an AP to reflect the mobility if the user. Example. APs covering commuters roads will generally be in the same location area to reduce the location area updates. As the mobile approaches the place of work it is less likely to move. The functionality will change the users paging group to a paging group that covers a smaller geographical are after detecting that the user has not changed location for a certain period of time.

Paging group 1

Paging group 2

Paging group 3