INTRODUCTION

GSM Core Systems Engineering

11/30/98 printed

Concentric CellsVersion 0.2

Test PlanNov. 30, 98

Introduction3Functionality Description4Zone definition4Power based algorithm4Power based handover in to zone 15Power based handover in to zone 05Interference based algorithm5interference based handover into zone16Guard timer6interference based handover into zone06Interfering neighbors definition7Application8Feature Benefits and Limitations8Handovers Behavior8Subzones9Power Control9Impacted Features10Impacted Commissioning Issues10Compatibility11Advantages11Disadvantages11Test plan12Feature Test12Testing Items12Environment Description12Real System Test12Environment Description12Appendix14Study of Concentric Cells Traffic Distribution14Pathloss Evaluation For Interference Based Algorithm14MS_POWER_FACTER14

Introduction

Concentric Cell is an optional feature of Motorola BSS system after GSR3 software version. It provides cell resource partitioning using the concept of the concentric cell structure, to allow for tighter re-use patterns than normal frequency plan in super re-used underlay in each cell. So that, frequency resource can be saved, better performance or more traffic could be achieved.

The feature uses only BCCHs for interference estimation or measurement to move traffic between the conventional macrocell underlay and super re-use layer.

Figure Concentric Cell layouts

It is an elegant and simple technique in which the size of cells on the super re-use layer is self governed by interference. However, the use of a single BCCH means that the macrocell is a critical dependency for all call set-ups and inter-site handovers and is thus susceptible to congestion.

Functionality Description

Zone definition

We can set two zones in a cell. One is inner zone, which have a smaller coverage area, focus on near site traffic absorb. Another is outer zone, have normal cell coverage, and focus on dealing with all the traffic which inner zone could not handle. Inner zone can only consist of non-BCCH carrier; Outer zone always contains the BCCH carrier and all SDCCH channels. A Mobile Station is always setting up in outer zone and can be assigned to inner zone if meet specified criteria (by intra handover or directly TCH assignment in inner zone). We also use Zone 0 representing for outer zone and Zone 1 representing for inner zone.

There is a parameter, outer_zone_usage_level, which is the percentage of TCH congestion in outer zone, and is a precondition before allowing handovers to inner zone. The parameter is defined by the command

chg_element outer_zone_usage_level In database description, we can give each RTF a definition as either outer zone RTF or inner zone RTF. The command is:

equip site_no. RTF

enter cell zone: 0/1enter trx power reduction:43 to 1dBm (0-21) GSM900

39 to 3dBm (0-21) DCS1800

Parameter trx power reduction is only prompted if cell zone=1, it must be greater than or equal to max_tx_bts if inner_zone_alg=1.

Parameter max_tx_bts is an add_cell parameter, defines BTS maximum transmit power

Parameter inner_zone_alg is used to define zone algorithm, described later.

Parameter trx power reduction is named as trx_pwr_red later.

The command below can be used for the RTF modification also:

modify_value cell_zone rtf There are two algorithms to make traffic handover between zones in a cell, power bases algorithm and interference based algorithm. With the chg_cell_element, we can decide which algorithm should be used in a certain cell. The command is:

chg_cell_element inner_zone_alg :0 no concentric cell

1 power based algorithm

2 interference based algorithm

inner_zone_alg=0

No prompted parameters

inner_zone_alg=1

Prompts for ms_txpwr_max_inner, zone_ho_hyst, rxlev_dl_zone, and rxlev_ul_zone

inner_zone_alg=2

prompts for neighbor_report_timer

The selection can be only made per cell basis, parameters above will be explained later.

Power based algorithm

When power based handover algorithm is selected, we should set the zone parameter like:

Zone0 outer zone:

Maximum downlink transmit power is BCCH level ( Max_tx_bts defined in add_cell command)

Maximum uplink transmit power is max_tx_ms, defined in add_cell command

Non_BCCH carrier can use APC-DL (downlink adaptive power control )

Zone1 inner zone:

Maximum downlink transmit power is trx_pwr_red Maximum uplink transmit power is ms_txpwr_max_inner, the maximum power a Mobile Station (MS) can use in the inner zone, defined in chg_element command Each carrier can have a different trx_pwr_red value, giving multiple sub-zones inside zone 1

Power based handover in to zone 1

When both conditions below are true, traffic will handover from outer zone to inner zone:

RXLEV_DL > rxlev_dl_zone + zone_ho_hyst + (BS_TXPWER BS_TXPWER_MAX_INNER)

And

RXLEV_UL > rxlev_ul_zone + zone_ho_hyst + (MS_TXPWER ms_txpwer_max_inner)

RXLEV_DL and RXLEV_UL is current downlink and uplink receive level

BS_TXPWR and MS_TXPWR is current BTS or MS transmit power in outer zone

BS_TXPWR_MAX_INNER is BTS TRX maximum power capability menus trx_pwr_red

Parameter rxlev_ul_zone and rxlev_dl_zone is minimum receive level in inner zone, modified by chg_element command.

Parameter zone_ho_hyst is inner zone handover margin, modified by chg_element command.

Parameter ms_txpwr_max_inner is defined for all sub-zones in inner zone, modified by chg_element command.

The expressions above are evaluated for each inner zone carrier; carrier with highest priority is the carrier with lowest maximum downlink transmit level (BS_TXPWER_MAX_INNER). Inside inner zone, different sub zone may also use this criterion to handover to inner carriers of the zone 1.

Power based handover in to zone 0

When either of conditions below is true, traffic will handover from inner zone to outer zone:

RXLEV_DL < rxlev_dl_zone AND BS_TXPWER = BS_TXPWER_MAX_INNER

Or

RXLEV_UL < rxlev_ul_zone AND MS_TXPWER = ms_txpwer_max_inner

RXLEV_DL and RXLEV_UL is current downlink and uplink receive level

BS_TXPWR and MS_TXPWR is current BTS or MS transmit power in inner zone

BS_TXPWR_MAX_INNER is BTS TRX maximum power capability menus trx_pwr_red

Parameter rxlev_ul_zone and rxlev_dl_zone is minimum receive level in inner zone, modified by chg_element command.

Parameter ms_txpwr_max_inner is defined for all sub-zones in inner zone, modified by chg_element command.

Interference based algorithm

We can also select interference based algorithm in a concentric cell. In this case, handovers between inner zone and outer zone are based on interference that traffics suffered. When traffic is near cell site, normally the interference level it suffered is lower, traffic can be handover to the inner zone, when traffic is leaving cell site, interference level become higher, a handover to outer zone is needed. The coverage area of inner zone is defined by the interference levels from neighboring cells using the same or adjacent frequencies. The inner zone carrier maximum output power should be the same as its outer zone.

interference based handover into zone1

A handover from outer zone to inner zone will be initialed if both conditions below are true for all interfering neighbors:

Uplink:

PBGT(n) + MS_PWR_FACTOR + INNER_ZONE_THRESHOLD(n) + INNER_ZONE_MARGIN(n)==0

Where :

PBGT(n) = (MS_TXPWR_MAX RXLEV_DL PWR_C_D) - (MS_TXPWR_MAX(n) RXLEV_NCELL(n)), means SEVER_PATHLOSS NEIGHBOR(N)_PATHLOSS.

MS_TXPWR_MAX means maximum MS transmit power allowed in serving cell, we use max_tx_ms find in add_cell command.

MS_TXPWR_MAX(n) is maximum MS transmit power allowed in concerned neighbor cell, it is defined in add_neighbor command or a default value defined in add_cell command.

RXLEV_NCELL(n) is measured value, concerned neighbor cells downlink strength.

RXLEV_DL is downlink receive level.

PWR_C_D is downlink power difference caused by power control

MS_PWR_FACTOR = RXLEV_UL + (ORDERED LEVEL USED LEVEL) l_rxlev_ul_p RXLEV_UL is serving cells uplink receive level

ORDERED LEVEL USED LEVEL is to take into account the fact that there is a delay in implementing power control.

Parameter l_rxlev_ul_p is uplink receive level power control boxs lower threshold, defined in add_cell command.

INNER_ZONE_THRESHOLD(n) and INNER_ZONE_MARGIN(n) is defined in add_neighbor command, know as the threshold for inner zone handover and the margin for inner zone handover

Negative result of PBGT(n), means good path with lower pathloss to serving cell, mobile is good candidate for inner zone if further test is success. The further test(MS_PWR_FACTOR and inner_zone_margin(n)) performed to prevent mobile from experiencing or causing interference. Measurement and calculated PBGT(n) value used differently for UL and DL for handover into each zone.

With interference based algorithm, Inter cell handovers and TCH assignment can go straight into inner zone regardless the guard timer which was mentioned later, if both:

RXLEV_DL > direct_inner_zone_threshold

outer_zone_usage_level exceeded

Guard timer

In case of interference based handover to inner zone, the algorithm is based on mobiles measurements and calculations. To get the measurement report, a mobile has to first take some time to decode the neighbors BCCH signal. There is a guard timer to ensure the MS has stayed in outer zone long enough to decode neighbors signal.

Parameter neighbor_report_timer, can be modified by chg_element command, value between 0-255 SACCH multiframeIf all defined interference neighbors are decoded before this guard timers expiration, this timer is ignored. Or, MS has to wait for the guard timers expiration, then the handover to inner zone may be initiated if all other conditions are fulfilled.

interference based handover into zone0A handover from inner zone to outer zone will be initialed if either condition below is true:

Uplink

PBGT(n) + MS_PWR_FACTOR + INNER_ZONE_THRESHOLD(n) > 0

Downlink

RXLEV_DL + PWR_C_D (RXLEV_NCELL(n) + INNER_ZONE_THRESHOLD(n)) < 0

Parameters and items are the same like those defined earlier

Interfering neighbors definition

As interference based algorithm is taking the neighbors with co-channel or adjacent channel into account, we should give serving cell knowledge, which neighbor should be considered as an interfering source and which one should not. We use add_neighbor command to achieve this. Below is a part of command reference of add_neighbor when we choose interference based concentric cell algorithm. For adding interference neighbors, input yes to Does this neighbor have a carrier with an interfering frequency?

Application

Concentric Cells has been added to the list of BSS restricted features. If this feature is not enabled, all functionality related to the Concentric Cells feature will be disabled.

The BSS supports selection of the inner zone by either the Power Based Algorithm or the Interference Based Algorithm on a per cell basis. The timeslots on the carriers in the inner zone must only be configured as Traffic Channels, all SDCCHs must be configured on the carriers in the outer zone. The BSS always selects an outer zone channel for an Immediate Assignment, even if a traffic channel is allocated for the purpose. If there are no resources available in the outer zone, the BSS sends an Immediate Assignment Reject. And BSS maintains the existing maximum of two timeslots of SDCCHs per carrier for carriers in the outer zone, regardless of the preferred number of SDCCHs specified in the database.

Feature Benefits and Limitations

The concentric cell can be quickly deployed without the need for site acquisition, extra spectrum, new handsets or hardware, requires only minor changes to site configurationBut this feature depends upon bulk of cells traffic being located close to the cell site to achieve maximum benefit, so we need to evaluate the cell sites traffic distribution verifying if the feature is a suitable selection. The capacity gain can be difficult to predict, and Maximum gain in practice is less than 30%. Please refer to the appendix on concentric cell traffic distribution study.

Handovers Behavior

The parameter outer_zone_usage_level is the percentage of TCH congestion in outer zone, it is a precondition before handover to inner zone is allowed. We can set it as 0 to enable the handovers no matter the outer one busy or not.

For all inter cell handout, the source traffics are all from the outer zone of the source cell. With power based algorithm, inter cell handovers always into outer zone, If there are no resources available in the outer zone, the handover request is denied. If additional neighbours have been provided in the candidate list, the BSS proceeds to the next qualified candidate. Normal intra cell handovers move traffic to new channel in the same zone. All immediate assignment in outer zone only (SDCCH in outer zone).

When an intra-cell handover is initiated due to interference and intra-cell handovers are allowed, the BSS attempts to move the Mobile Station to another channel within the same zone of the cell. If the Mobile Station is on a channel in Zone 1 using the Power Based Algorithm and these inner zone carriers have different maximum downlink transmit levels, the Mobile Station is only moved to a carrier which its maximum transmit level is greater than or equal to the current carrier. If there is no suitable resource available in the same zone and the call is in the inner zone, the BSS then attempts to allocate a resource from the outer zone. A call served by the outer zone is not moved to the inner zone. If no available resource can be found, the handover request is denied.

The BSS may determine that a call is qualified to handover to an inner zone channel, prior to initiation of the Assignment procedure in one of three ways:

If the Power Based Algorithm is used and the defined conditions for handover into the inner zone have been met.

If the Interference Based Algorithm is used and the defined conditions for handover into the inner zone have been met.

If the Interference Based Algorithm is used and the receive level as reported by the Mobile Station exceeds the database parameter direct_inner_zone_threshold. This mechanism allows the BSS to assign the Mobile Station an inner zone resource prior to receipt of neighbour cell reports from the Mobile Station, so that the guard timer is no longer considered in this case. This direct assignment can be disabled by setting the threshold to the maximum value in the database.

When the BSS detects that the call is qualified to be moved to an inner zone prior to initiation of the assignment procedure, an inner zone channel is chosen for the assignment procedure if an inner zone resource is available and the outer_zone_usage_level condition is satisfied. Otherwise, the Mobile Station will be assigned a resource in the outer zone.

intra_cell_handover_allowed parameter has nothing to do with inter-zone handovers. The BSS does not consider if the intra_cell_handover_allowed flag is set or not when initiating inter-zone handovers. Inter-zone handovers can be enabled or disabled separately, using new database parameters introduced by this concentric cell feature. If a inter-zone handover attempt to the inner zone fails due to inner zone congestion, and the call qualifies for an interference handover, the call will not perform a intra-cell handover due to interference if the intra_cell_handover_allowed flag is disabled.

Subzones

With power based algorithm, more than 1 subzones can be existing in the inner zone. If we define inner zone carriers to have different maximum downlink transmit power levels, there are different sub-zones. For every inter-zone handover from outer zone to inter zone, BSS evaluates each carrier in the inner zone for the handin conditions. All qualified carriers in the inner zone then are sorted by a order of their maximum downlink transmit levels, the one with lowest maximum downlink transmit level has the highest priority to serve the coming call.

If the sub-zone configuration exist in inner zone, the BSS may initiate an intra-zone handover when it detects that a Mobile Station could be better served by a other sub-zone (a different carrier in that inner zone). The decision to initiate an intra-zone handover is based on the same equations used to determine the need for inter-zone handovers. For example, in Figure below, a Mobile Station is on a channel in Zone 1 - carrier A, the BSS initiates a handover into Zone 1 - carrier B if the Mobile Station is qualified using the criteria defined for an inner zone handover. If a Mobile Station is on a channel in Zone 1 - carrier B, the BSS initiates a handover into Zone 1 - carrier A if the Mobile Station is qualified using the criteria defined for an outer zone handover.

Figure Power based Concentric Cells example

Power Control

The power control algorithm is the same mechanism when the concentric cell feature is implemented. However, for interference based algorithm, there is an additional condition to be fulfilled before downlink power control in the inner zone.

If a call is active on a channel in the inner zone right now, the BSS performs an additional check prior to ordering a power decrement. When the BSS power control algorithm determines that the downlink power should be decreased, a check will be performed to verify that the power decrement will not cause the MS to subsequently require a handover to the outer zone. The power control decrement is only allowed if all the interfering neighbors fulfill:

RXLEV_DL POWER DECREMENT RXLEV_NCELL(n) > INNER_ZONE_THRESHOLD(n)

If the inner zone downlink power is not the highest which allowed in the inner zone, and there is interference to the call, the downlink power should increase. The downlink power should increase a minimum POWER INCREMENT value, so that the equation below can be fulfilled for all the interfering neighbors.

RXLEV_DL + POWER INCREMENT RXLEV_NCELL(n) > INNER_ZONE_THRESHOLD(n)

Impacted Features

If parameter option_emergency_preempt sets to 1 (on), the BSS selects a call from the outer zone to be pre-empted for the emergency call pre-emption procedure.

The traffic channel flow control, congestion relief, and dynamic reconfiguration features use the traffic channel's usage in the outer zone ONLY to determine if the cell is congested. Congestion relief procedures only initiate handovers for calls in the outer zone. To avoid barring of access classes effects before using the inner zone resources, the outer_zone_usage_level should be set to a lower value than both the normal_overload_threshold and the critical_overload_threshold used by the flow control feature.

When the full power feature is used in a concentric cell and the power based algorithm has been selected for it, each inner zone carrier is set to transmit at the defined per carrier maximum power level. The BSS sets the transmit power level to max_tx_bts for all outer zone carriers

When concentric cells feature is enabled both with the frequency hopping operation. Usually, there will be three frequency groups existing in the system. First group is BCCH group, same as before; second is hopping outer zone frequency group, like normal hopping TCH carrier; third group is non-hopping inner zone frequency group, to give the system a more aggressive reused frequency group.

When BCCH carrier unit broken, the BSS should select a carrier to replace the BCCH. Firstly, it Selects an unused (redundant) carrier unit within the same redundancy group. When this is not available, select an inner zone carrier with the lowest maximum transmit power level If the power-based algorithm is used. If more than one carrier are set to the lowest maximum transmit level, select the carrier with the least number of active channels. If the interference based algorithm is used, select an inner zone carrier with the least number of active channels. When there is no inner zone carrier available, the system will use carrier in outer zone. The selected carrier is taken out of service and the associated carrier unit will be used to replace the BCCH carrier.

Impacted Commissioning Issues

DRCU calibration may be impacted when power based algorithm is using in system, as the inner zone RTF is intentionally set to be lower max power level than outer zones. This may affect the DRCUs output power in the same cell. The way to avoid mistakes on this is adjust all RTFs to same maximum output power level before any calibrations are taken.

There are no further demand on installation and commissioning job, combining, antenna type and down tilt, cable things can all be done like normal cell. However, for power based algorithm, we could use a separated micro antenna for the inner zone only, and may give the micro antenna a lower mounting location like a micro cell. There is a rule for interference based algorithm that the inner zone carriers should have the same maximum output power as outer zone carriers. Anyhow, we can give the inner zone carriers a lower maximum output power setting but we should not do that. We should avoid the case that a weak concentric cells outer zone handover its traffic to the inner zone which is not interfered by others, but does not have coverage there. So, we could not do the similar micro antenna selection like power based algorithm.

Compatibility

This feature is supported for BSS GSR3 software releases onwards on all configurations.

Advantages

The Concentric cells feature is one of a number of capacity enhancement features. Concentric cells are complementary to Microcellular operation, frequency hopping operation, the congestion relief features, dual band operation and EGSM etc.

Power based concentric cell is suitable used along with micro system together. It will be much easier to form a micro layer with this features help.A hopping cell usually has two frequency groups (BCCH do not hopping), one is BCCH, and another is TCH frequency group in the cell. But when the hopping system is combine with concentric cell, it may need some changes. For example, a combined system may have BCCH frequency layer, hopping frequency layer and non-hopping inner zone frequency layer. As normal SFH frequency re-use pattern is nearly 6~9 cell re-use, and concentric inner zone could be 3~6 cell re-use pattern. Theoretically, there should be some capacity gain or quality gain than a mere SFH system.

Disadvantages

Traffic Distribution impacts the feature a lot. The concentric feature is impacted by the traffic distribution in the cell. If more traffic is near the cell site, the feature is powerful, but if there is not enough traffic near cell site, the use of this feature may cause worse effecting.

Roughly, an example system with BCCH carrier 4*3 reuse, and TCH carrier 3*3 reuse (BFH hopping may used, or 1*3 SFH with 1/3 loading), have 5/4/4 cell structure, needs 42 channels. If we change the system to concentric cell structure, with 42 channels, BCCH carrier 4*3 reuse, outer zone carrier 3*3 reuse and inner zone carriers 2*3 reuse, we could build a 5/5/5 cell with 3 carriers in outer zone, 2 carriers in inner zone. If all traffic is in outer zone, the effective cell configuration covering traffic is 3/3/3, much less than the original 5/4/4 configuration. Only when the traffic in inner zone covering area is more than about 40% of the total traffic in the cell, this concentric cell is bringing gains.

The pictures above show two cells receive level distribution example, the first cells traffic distribution is good for implementing concentric cell, and the second cell is not.

A interference based concentric cell can hardly reuse the inner zone frequency in micro system when the inner zone carriers have the same transmit power as outer zone carrier do. If we have micro layer and interference based concentric cell together in a same system in this case, we have to give three different frequency layers to cope with the needs.

Test plan

This test plan is first trying to verify that the feature works as described in the function descriptions. Then a real implementation case may be lunched to evaluate the effecting of the features using in a living system.

Feature Test

Testing Items

If inter cell handovers and inter zone handovers are as described in the function descriptions

If we can use different power in inner and outer zone when interference based algorithm is applied.

If the BCCH carrier unit out of service, an inner zone carrier unit will take over the function.

Environment Description

In a laboratory testing system, should have two cells at least, one of the cells should have 3 carriers.

Enable a concentric cell structure for this cell, the inner zone have one carrier with lower transmit power than outer zone:

chg_cell_element inner_zone_alg 2 prompts for neighbor_report_timer, give it 6.

Then, use command:

equip site_no. RTF

enter cell zone: 0/1enter trx power reduction:43 to 1dBm (0-21) GSM900

39 to 3dBm (0-21) DCS1800

Or :

modify_value cell_zone 1 rtf

to set the inner carrier RTF and its maximum output power.

We will find if we can use interference based algorithm in the cell that has lower maximum output power in inner zone.

We select a neighbor cell as the concentric cells interfering neighbor, doesnt matter if there is a real co-channel or adjacent channel used in the neighbor. When the system is running, we can test the inter zone handovers, and inter cell handovers.

Lock the BCCH dri, see if the inner zone carrier unit takes over the BCCH function.

When the laboratory testing is successful, we can think about testing the feature in a real system, to find the gains it brings to us.

Real System Test

Environment Description

After the successful test in a laboratory environment, we know the feature works well as described in the function specification. Now, we will study what the function can bring to us in a real running system.

Now that the SFH feature is used in most Motorolas network in China, we give this test under the SFH environment. As concentric cells inner zone frequency re-use pattern is more aggressive than 1x3 SFH TCH group (38% loading for example), with using of concentric cells, we can have a looser frequency reuse in the hopping outer zone TCH group, it means lower loading factor in outer zones hopping carriers. This may result in a less interference to each other in the outer zone hopping frequency layer than before, and therefor improves successful call rate and reduce drop call rate etc.

A SFH system (a small system or several continuous sites in a system), with 6/6/6 site configuration. BCCH group uses 4x3 frequency reuse pattern, out of hopping group; the hopping TCH groups use 1x3 frequency reuse pattern with 38% loading. The total channels needed are

12+5x3/(5/13)=51channels. 10.2M bandwidth is used.

We first should study the traffic distribution of the system, see if most of the sites have a suitable traffic model for inner zones traffic absorbing(about more than half of the cells traffic is in the inner zone area for most of the cells). If yes, we could change the sites to concentric cell system.

With the same bandwidth, we introduce concentric cell in the system. There will be three frequency layers in the new system, one is BCCH frequency group, one is the outer zone hopping TCH frequency group, and the last one is inner zone TCH frequency group. The sites are 6/6/6configuration, 4 carriers form outer zone and 2 carriers form inner zone(2x3 reuse)

zone 1: TCH (2x3)x2 => 12 channels

zone 0: BCCH 4x3 => 12 channels

TCH 1x3 with 51-12-12=27channels (for 3 cells) => cells loading factor is 33.3% (3/9).

With the successful setting of the system, we should then study the statistics to evaluate if the concentric cell structure brings the system better performance than before. The item below should be compared for several days average value (within only working days) before and after the changes, to give a more reasonable conclusion.

Erlang/total calls/drop call rate/TCH rf loss/SD rf loss/call setup successful rate/call successful rate etc.

Appendix

Study of Concentric Cells Traffic Distribution

The philosophy of concentric cell feature is if a call can be handled on the inner zone, then the inner zone is preferred. Assume that there is a concentric cell, and the traffic in the coverage area is A, study two case, one is all traffic A is in the inner zone, another is all the traffic A is in the outer zone. We can find from Erlang_B formula that the former case has less traffic blocking than the later one. So the conclusion is the inner zone traffic blocking probability is less than the outer zone.

We can model the behavior as follows:

Of the total traffic, A, in a cell, a certain proportion, r, can be handled by the inner zone. The traffic offered to the inner zone is therefore rA Erlangs. The proportion of this traffic redirected to the outer zone is PBi*rA Erlangs (PBi = Blocking probability on inner zone channels)

Then, total traffic offered to the outer zone is: (1-r)A+ PBi*rA Erlangs

This can be used with the Erlang B formula to obtain the outer zone blocking probability: PBoThe true blocking probability for the inner zone calls is then PBi * PBoPathloss Evaluation For Interference Based Algorithm

For interference based algorithm, the equation for PBGT(n) is:

PBGT(n) = (MS_TXPWR_MAX - RXLEV_DL - PWR_C_D) - (MS_TXPWR_MAX(n) - RXLEV_NCELL(n))

Think about MS_TXPWR_MAX and MS_TXPWR_MAX(n), they actually represent their own BTS output powers capability which can not be obtained from broadcasting information, so that MS_TXPWR_MAX - MS_TXPWR_MAX(n) is representing BTS_TXPWR_MAX - BTS_TXPWR_MAX(n). Put this idea into the PBGT(n) equation, we have:

PBGT(n) = SERVER_PATHLOSS NEIGHBOR(n)_PATHLOSSMS_POWER_FACTER

For interference based algorithm, A negative PBGT(n) value indicates that the path loss of the serving cell is less than the path loss of the neighbour cell, the mobile might be a good candidate to inner zone if other conditions are satisfied. As this algorithm is interference based, it is therefore able to prevent the Mobile Station from getting into a position where it can experience or cause interference. To avoid experiencing interference, a threshold INNER_ZONE_THRESHOLD(n) is introduced in for each interfering neighbor; to avoid causing interference, an additional factor is calculated to account for a Mobile Station which may be powered up above the defined power window.

MS_PWR_FACTOR = RXLEV_UL + (ORDERED_POWER_LEVEL - USED_POWER_LEVEL) - l_rxlev_ul_p

For a conservative behavior, the level is referenced to the bottom of the power box. This factor may be a quite big value when decision_alg_num=1 and poor quality is reported. To take into account the fact that there is a delay in implementing power control, we have the extra factor ORDERED_POWER_LEVEL - USED_POWER_LEVEL.

RXLEV

63

0

63

0

RXLEV

Inner zone coverage

Inner zone coverage

Good case

Bad case

>50%