GSM Concentric Cells Concept

Concentric-Dual Band

Cells

Introduction

Definition

Why Dual Band Cells?

Propagation Overview

Fading Effect

Path loss and Link Budget Calculations

Alcatel/Motorola Parameters and features

Prepared By - Faraz Husain Concentric - Dual Band Cells

IntroductionDefinition

• Enables a single Network Operator with licenses in two or more frequency bands to support the use of Multiband mobiles in all bands of the licenses

• The use of Layers to provide highcapacity with contiguouscoverage. The Outer Zonemaintains contiguous coverageand the Inner Zone provideshigher capacity. The layersappear as being concentric dueto Inner Zone having a reducedcoverage area when comparedwith the Outer Zone.


Definition (cont.)

The idea is to split the cell area of anormal cell into an inner and an outerzone by operating a certain number ofcarriers (inner zone carriers) at a lowertransmission power (Fig). Mobilestations situated in the outer zonecommunicate on the outer carriers.The mobiles which are closer to thebase station preferably communicateon the inner carriers but they can usethe outer carriers if needed.

With this feature the operator may configure non-BCCH carriers within a cell to have a smaller coverage area. The carriers equipped within a cell may be grouped into two zones:

• Zone 0: Also referred to as the "outer zone", is reserved for carriers that may broadcastat the maximum transmit level defined for the cell.• Zone 1: Also referred to as the "inner zone", may be defined with non-BCCH carrierstransmitting lower power than the BCCH carrier, or having a tighter reuse patternthat reduces the useful coverage area of the carrier.


Definition (Cont.)

Concentric Cells can be implemented using one of the three different algorithms (this is vendor dependent):

Power Based Concentric Cells: Inner zone carriers transmit less power than outer ones and the transitions between zones are based on absolute level thresholds.

Interference Based Concentric Cells: Inner and outer zone carriers transmit all the same power within and the transitions between zones are based on some interference conditions. These interference conditions are protection margins against potential interfering neighbours.

Dual Band Cells: Support for the management of the cells operating in different bands by different single band BTS’s or by the same dual band BTS. This is further divided into two kinds

Coincident Multiband

Single BCCH for Dual Band cells

Since we’re using Dual Band Concentric Cells in our network, we’ll be concentrating more on them for the rest of the workshop!


Why Dual Band Cells?

Increasing Capacity

Improving Grade of Service

Relieving Congestion

Advanced Network Management Techniques Efficient management of traffic required to exploit capacity gain

potential of concentric cells

Goals Maximize handled capacity

Avoid congestion

Maintain good call quality

Avoid unnecessary handovers

Improved Multi-layer Network Best system performance through optimal choice over

Call originations

Traffic movement between concentric cell layers

Generalized handover situations


Let us see how DCS is different from GSM!


Propagation OverviewFading Effect

Serving

Site

Distant

Site

Higher pathloss at

1800 MHz

Half wavelength l at 1800 MHz

Fading rate twice as fast as 900MHz

1800 radio wave

•Reduced interference fromdistant site at 1800MHz

•More aggressive reuse pattern can be achieved

•Diversity systems become more

important especially for slow

moving mobiles


Propagation OverviewFading Effect

The wavelength of a radio signal determines many of its propagation characteristics

• Antenna elements size are typically in the order of 1/4 to ½ wavelength

• Objects bigger than a wavelength can reflect or obstruct RF energy

• RF energy can penetrate into a building or vehicle if they have apertures a wavelength in size, or larger


Propagation OverviewAntennas

Different Antenna Types

• Different antenna for each Band

• Dual antennas with four ports

• Dual Antennas with 2 ports (900 and 1800 are multiplexed )


•Extra Duplexers will be needed to split 1800 signal from 900 signal

•Duplexers will be with different polarization to maintain diversity

2 Ports Antennas


Propagation Overview (cont.)

Path Losses in 900 vs. 1800

• A little physics

– Diffraction loss and Penetration loss higher in 1800 MHz band

– 6dB minimal theoretical difference

• Path loss difference - on-street

– Path loss at 1800MHz is typically 6 - 12 dB higher

– Most probable difference in urban environment: 8 dB

– Difference is nearly distance-independent (fixed), in typical urban cells (

i.e. constant offset in “ loss per length unit ” )

– Actual difference depends on site configuration like antenna height and

antenna characteristics

– Cell radius at 1800 MHz typically 25 - 50% less compared to 900 MHz




• Path loss difference - in-building– Additional attenuation at 1800MHz when penetrating into buildings

– High dependency of penetration loss on building structure, window size, floor height, angle of incident waves and floor level

– Difference can be compensated with a higher ERP at the 1800 band

• Empirical measurement results– Building penetration loss at 900MHz:

5dB to 25dB

– Average additional path loss at 1800MHz:

7dB, 4dB standard deviation




Receiv

e l

evel

(dB

)

Log (Distance)

LOS dominates Non-LOS dominates

~ 150m - 300m

GSM 900

GSM 1800

>8 dB

6 - 8 dB

in typical urban cells:

• difference is nearly distance-independent

prerequisite:

• same ERP on both bands

• equal antenna pattern




Optimisation process:

• Comparing predictions of appropriate GSM900 and GSM1800 cells for in-building coverage level

(e.g. -68 dBm at 900Mhz / -61 dBm at 1800MHz)

• Adjusting GSM1800 antenna tilts to obtain similar footprint compared to the appropriate GSM900 cell

– Good overlapping needed to achieve efficient traffic relief on GSM900

– Supports introduction of new multi-band features like coincident multi-band handover or single BCCH

• Same coverage conditions (except fairly fixed offset) can be achieved easily with dual band antennas

• Reducing Combining stages in the DCS cells to reduce the losses and use air combining instead.



Link Budget & Path Loss

Free Space Path Loss



Link Budget Calculations


After having studied in detail the propagation

difference between GSM 900 and DCS 1800,

let us switch back to our original discussion of

Implementing the DCS in a Live network.

Lets look at some BSC and Cell Level

Parameters and then we’ll move forward to

their details.


Database Parameters

BSC Level Parameters

freq_types_allowed

mb_preference

early_classmark_sending

early_classmark_delay

phase2_classmark_allowed

MOTOROLA ------------ ALCATEL

EN_INTERBAND_NEIGH

PREFERRED_BAND

GSM_PHASE

EN_SEND_CM3

EN_LOAD_OUTER

MSC:

Ensure phase2 signalling is enabled between BSCs and/or MSCs (Phase 1 = Legacy MS, Phase 2 introduced around 1999 supporting features like AMR and DCS)


Database Parameters (cont)

BSC Level Parameters – Description

freq_types_allowed

Numeric value Text string

1 pgsm

2 egsm

3 pgsm,egsm

4 dcs1800

5 pgsm, dcs1800

6 egsm, dcs1800

7 pgsm, egsm, dcs1800

8 pcs1900

9 pgsm, pcs1900

10 egsm, pcs1900

11 pgsm, egsm, pcs1900

12 dcs1800, pcs1900

13 pgsm, dcs1800, pcs1900

14 egsm, dcs1800, pcs1900

15 pgsm, egsm, dcs1800, pcs1900

MOTOROLA

mb_preference

The mb_preference parameter enables or disables the Multiband Inter-cell Handover feature.

Valid Range

0 = Disabled

1 = Enabled




To have a working Dual-Band capability, the MSC needs to have the capability to handle Classmark 3 IE (info element)

CM3 info is sent by multiband MS and contains info about multiband capabilities and power classes of the mobile in different bands

This info is present in the MSC for the duration of the call

In case a multiband handover needs to take place, the serving BSC needs to transmit this info to the target BSC to inform the target BSS of the capabilities of the MS

CM3 is important message but is only sent by the MS when requested by the MSC

However, it is possible to send an early CM3 spontaneously using some BSS level parameters.

This will enable a multiband MS to spontaneously send CM3 info within some specific time during Call initializing procedure and ALSO enables the MSs to handover a call to target BSC (external Handover) by sending CM3 info in Handover Request Message

MSC Requirements







MOTOROLA

early_classmark_sending

The early_classmark_sending parameter specifies the following:

• Whether the BSS suppresses the early sending of the Classmark Update message to the MSC.• Whether an MS is allowed to send an early Classmark Change message.Valid Range0 = Disabled across both the A-interface and the Air-interface1 = Enabled on A-interface, disabled on Air-interface2 = Disabled on A-interface, enabled on Air-interface3 = Enabled across both the A-interface and the Air-interface

By Air Interface, Motorola means CM3 sending during Call Setup and by A-Interface, it means CM3 sending during External Handover

When early_classmark_sending is set to 2, the BSS does not forward classmark update messages to the MSC. This means that the MSC does not obtain any information about the MS capabilities. However, the MSC can still make solicited requests for classmark updates by sending a Classmark Request message to the BSS. If this is not done, the frequency capabilities of the MS are based on the target cell frequency when multiband handovers are being performed. Therefore, after an external handover, neighbours are reported by the BSS to the MS as follows:

Handover from GSM900 to GSM900 - only the GSM900 neighboursHandover from GSM900 to GSM1800 - only the GSM1800 neighboursHandover from GSM1800 to GSM900 - only the GSM900 neighboursHandover from GSM1800 to GSM1800 - only the GSM1800 neighbours.

External multiband capabilities will be limited, and subsequent handovers to GSM1800 cells are therefore not possible.




early_classmark_delay

The early_classmark_delay timer specifies how long the BSS delays sending the Classmark Update message to the MSC during Early Classmark sending.

Valid Range

0 to 100000 milliseconds

phase2_classmark_allowed

The phase2_classmark_allowed parameter defines the format of the classmark parameter sent to the MSC based on GSM phases.

Valid Range

0 = Formatted for Phase 1

1 = Formatted for Phase 2

2 = Formatted for Phase 2 with Multiband

MOTOROLA




EN_INTERBAND_NEIGH (EN_INTERBAND_HO)

This flag enables / disables the multiband operation by filtering the sending of SYSTEM INFORMATION TYPE 2ter/5ter.

PREFERRED_BAND

Frequency band to which the multiband MS are preferentially directed.

Valid Range

0 = None

1 = GSM

2 = DCS

GSM_PHASE

This flag indicates the GSM Phase used by the BSC to format messages towards the MSC.

Valid Range

0 = GSM Phase 1

1 = GSM Phase 2

ALCATEL


EN_SEND_CM3This flag enables/disables sending of "Classmark

3" IE to the MSC.

Valid Range

0 = Disabled

1 = Enabled

ALCATEL






EN_LOAD_OUTER (Load computation in outer zone)

Flag to enable/disable the load computation on the outer zone of a Concentric/multiband cell instead of the load computation on the whole cell.

Valid Range

0 = Disabled

1 = Enabled

When enabled, the values of the parameters FREElevel_1 to FREElevel_4 need to be updated to number of TRX considered in the load computation. EN_LOAD_BALANCE & EN_LOAD_OUTER should not be both "Enabled".

ALCATEL


Lets take a break. I’d advise we all take

some deep breaths….How about a

joke?!?!??!


Lets head back to the Workshop!

Now we’ll discuss the Cell Level Parameters

that are most commonly used in relation to

Dual band cells.



Cell Level Parameters

frequency_type

interband_ho_allowed

Inner_zone_alg

Thresholds:

Rxlev_dl_zone

Rxlev_ul_zone

Zone_ho_hyst

Dual_band_offset

Secondary_freq_type

Optional:

band_preference

band_preference_mode

multiband_reporting

Ms_txpwr_max_inner

Bts_txpwr_max_inner

Ho_pwr_level_inner

Outer_zone_usage_level

Pbgt_mode

sdcch_tch_assign_delay

MOTOROLA ------------ ALCATEL

•EN_BETTER_ZONE_HO

•CELL_TYPE

•FREQUENCY_RANGE

•EN_MULTIBAND_PBGT_HO

•EN_Bi-BAND_MS

Thresholds:

•RXLEV_DL_ZONE•RXLEV_UL_ZONE•ZONE_HO_HYST_UL•ZONE_HO_HYST_DL•Ping_pong_Margin

•Optional:

•EN_PREFERRED_BAND_HO

•PREFERRED_BAND

•EN_BETTER_ZONE_HO

•BS_TXPWR_MAX_INNER

•MS_TXPWR_MAX_INNER

•MULTIBAND_REPORTING


Let us first discuss the parameters that

ENABLE the Dual-Band capability in both

vendors. Then we’ll discuss one by one the

Call Assignment and Inter-Zone

Handovers in Motorola and Alcatel



Cell Level Parameters -- MOTOROLA

frequency_typeThe frequency_type parameter specifies the frequency type of a cell.

Valid Range

1 = PGSM

2 = EGSM

3 = DCS 1800

4 = PCS 1900

BEWARE!!!!intra_cell_handover_allowed This database parameter you’ll see every now and once which you’ll confuse with enabling of Inter

Zone Handovers. This parameter has nothing to do with Inter Zone handovers. However, if a Zone attempt to Inner Zone fails due to some reason and you really need to make a handover, you cant initiate an emergency (Quality, Interference) Handover if intra_cell_handover_allwd is disabled




interband_ho_allowed

Changes or sets the allowable frequencies which a cell may handover to.

This parameter must include, at a minimum, the frequency type for the cell. For example, if the cell has a frequency_type of pgsm, then the interband_ho_allowed parameter must include pgsm as a possible destination frequency band for handovers

Valid Range : 1 to 11

1 = PGSM

2 = EGSM

3 = PGSM and EGSM

4 = DCS1800

5 = PGSM and DCS1800

6 = EGSM and DCS1800

7 = PGSM, EGSM and DCS1800

8 = PCS1900

9 = PGSM and PCS1900

10 = EGSM and PCS1900

11 = PGSM, EGSM and PCS1900




Inner_zone_algThe inner_zone_alg parameter specifies the use algorithm and the associated parameters for the inner zone of the cell.

Valid Range

0 = Disable inner zone

1 = Power based use algorithm.

The system displays prompts for:

ms_txpwr_max_inner

Zone_ho_hyst

Rxlev_ul_zone

Rxlev_dl_zone

2 = Interference based use algorithm.

The system prompts for:

neighbor_report_timer

3 = Dual Band Cell use

The system prompts for:

Secondary_freq_type

Bts_txpwr_max_inner

ms_txpwr_max_inner

Ho_pwr_level_inner

Zone_ho_hyst

Rxlev_ul_zone

Rxlev_dl_zone

Dual_band_offset




Every MS reports 6 best neighbors in measurement reports when in dedicated mode.

However, in a multiband environment, to ensure that each band gets its share of MS selecting the target band’s cell, it is possible that we reserve some positions of neighbors in the measurement report for a particular band

This is done using the parameter multiband_reporting

Valid Range:

0 = Normal reporting of 6 strongest neighbors

1 = Report One strongest neighbour cell, in each of the frequency bands in the neighbour cell list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting Cells in the band of the serving Cell.

2 = Report the two strongest cells, in each of the frequency bands in the neighbour cell list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting Cells in the band of the serving Cell

3 = Report the three strongest cell, in each of the frequency bands in the neighbour cell list, excluding the frequency band of the serving cell. The remaining positions in the measurement report shall be used for reporting Cells in the band of the serving Cell

multiband_reporting



Cell Level Parameters -- ALCATEL

CELL_TYPE

Combination of CELL_DIMENSION_TYPE, CELL_LAYER_TYPE, CELL_PARTITION_TYPE, CELL_RANGE. Used for cell default parameter template.

Valid values

CELL_DIMENSION_TYPE Single (0), Concentric (1)

CELL_LAYER_TYPE Umbrella (2), Micro (3), Umbrella, Concentric (4), Mini (5)

CELL_PARTITION_TYPE Mini Concentric (8), Micro Concentric (9), Indoor (10), Indoor, Concentric(11)

CELL_RANGE Extended Inner (6), Extended Outer (7)

EN_BETTER_ZONE_HO

This flag enables/disables the detection of "too high level in outer zone" handover cause (cause 13).

Valid Range

0 = Disabled

1 = Enabled




FREQUENCY_RANGE

This parameter indicates the frequency range of the cell.

Valid Range: Coded over 8 bits

0: PGSM (GSM 900), 1: DCS 1800, 2: EGSM, 3: DCS 1900, 4: PGSM-DCS1800, 5: EGSM-DCS1800, 6: GSM 850, 7..255: for future use. The parameter shall be coded over 8 bits as a provision for future frequency bands support.




EN_MULTIBAND_PBGT_HO

This flag enables/disables the power budget handovers Cause 12 and the traffic handovers Cause 23 between cells belonging to different frequency bands.

Valid Range

0 = Disabled

1 = Enabled

EN_Bi-BAND_MS

This flag enables/disables the incoming handovers of bi-band MSs from the preferred band

Valid Range

0 = Disabled

1 = Enabled

.




EN_PREFERRED_BAND_HO:

This flag enables/disables the detection of handover cause 21 (high level in neighbour cell in the preferred band).

HO Cause 21 : high level in neighbour cell in the preferred band

Traffic load is taken into account for serving and target cell. Mostly used in parallel to capturing towards preferred band and discussion would be OOS (here S=Scope) of this workshop.


Concentric Cells – Implementation

After listing all the relevant parameters for Concentric cells, lets

switch our discussion to Channel Allocation Rules for

TCH Assignment

Handovers

It should be clear to you that TCH Assignments to DCS or Inner zone are always

made using the same thresholds as used for Inter-Zone (IntraCell) Handovers.

Think of TCH assignment to Inner zone as a sort of Directed Retry to Inner

Zone. We all know about Directed Retry now…don’t we? :P


Concentric Cells

Database ParametersTCH Assignment --- Motorola

The BSS always selects an outer zone channel for an Immediate Assignment. If there are no resources available in the outer zone, the BSS sends an Immediate Assignment Reject. (WE Cannot AVOID SD Blocking!)

In order to decide to assign the call to Outer zone or Inner Zone, following parameters are checked:

Band_preference

Band_preference_mode

Inner_zone_alg

If band_preference = DCS and band_preference_mode is programmed so that SD to TCH assignment is towards Inner Zone, the decision is taken by the same algorithms used for Outer to Inner Zone Handovers.

outer_zone usage_level: allows the operator to specify the level of traffic channel congestion which must be reached in the outer zone prior to the use of the inner zone resources. If the operator chooses to use inner zone resources whenever a MS is qualified, regardless of outer usage, the database parameter outer_zone_usage_level can be set to 0.

Valid Range: 0 to 100 (Indicating the percentage of outer zone TCH usage)


Concentric Cells


Band_preference: In Motorola BSS, after having set interband_ho_allowed = 1, it may be useful to utilize our DCS resources once the immediate assignment is completed. A preference for a particular BAND is set by the parameter band_preference. parameter displays the frequency bands that the cell prefers to use for handovers and specifies the destination frequency band for inter-cell handovers.

Valid range

1 (PGSM),

2 (EGSM),

4 (DCS1800),

8 (PCS1900)

16 (GSM850)

Band_preference_mode: parameter specifies the method the system uses to program a Multiband MS with the preferred frequency band for a given cell in the BSS. This parameter plays role for both Inner Zone Assignment of the calls (From SD to TCH) and the Handover of the call to Inner zone.


Concentric Cells


VALID Ranges:

Band_preference_mode = 0 The BSS attempts to hand a Multiband MS over to the strongest neighbour that the MS reported when a

handover is required for normal radio resource reasons.

Band_preference_mode = 1

Attempt handover to strongest preferred band neighbour on SDCCH - TCH assignment

This is where SD_TCH_ASSIG_BAND_DELAY is used just in case one wants a delay before Preferred band neighbors are reported for Inner Zone Assignments

If unable to handover to preferred band TCH, cancel band preference bias for the lifetime of the current connection

Multiband handovers due to normal radio reasons may still occur

The algorithm used for Assignment to Inner Zone is actually the one used for Handover to Inner Zone (will be discussed later in the Handover part)

Band_preference_mode = 2 Do not invoke band changes on SDCCH - TCH assignment Go to strongest preferred band neighbour when normal radio reason (or congestion relief) handover required Preferred band neighbours take priority in the neighbour list

Band_preference_mode:


Concentric Cells


Band_preference_mode = 3 This value combines the functions of values 1 and 2.

• This would mean to prioritise preferred band at SDCCH-TCH assignment AND when radio reason handovers are required

Band_preference_mode = 4 Do not invoke band changes on SDCCH - TCH assignment As soon as possible after TCH assignment, attempt to handover to a preferred band channel For normal radio reason handover, also prioritise preferred band neighbours

Band_preference_mode = 5 This value combines the functions of values 1, 2, and 4. Attempt to hand to preferred band at SDCCH - TCH assignment As soon as possible after TCH assignment, attempt to handover to a preferred band channel For normal radio reason handover, also prioritise preferred band neighbours

Band_preference_mode = 6 This value functions identically to value 5, except it is only triggered when the cell is congested.


Concentric Cells



Concentric Cells

Database ParametersHANDOVERS --- Motorola

The inner zone use algorithm must adjust for values being from two different frequency bands and convert the primary band receive levels to an estimated value for the secondary band. This is done using the dual band offset parameter.

RXLEVINNER = RXLEVOUTER + dual_band_offset

This offset is applied to both uplink and downlink receive levels

The calculated receive level inner value is then used in the dual band inner zone algorithm for both uplink and downlink

RXLEV_DLINNER > rxlev_dl_zone + zone_ho_hyst + (bts_txpwr - bts_txpwr_max_inner)RXLEV_ULINNER > rxlev_ul_zone + zone_ho_hyst + (ms_txpwr - min(ms_txpwr_max_inner,P)

Within this algorithm are database parameters that are set per cell after theinner_zone_alg = 3 (dual band use)rxlev_dl/ul_zone = <*> *= Range 0 to 63zone_ho_hysteresis = <*> *= Range as defined for max_tx_bts (0 to 21)bts_txpwr_max_inner = <*> *= Range -63 to 63ms_txpwr_max_inner = <*> *= Range as defined for max_tx_ms (5 to 39 PGSM andEGSM 0 to 36 DCS 1800)P = maximum capability of the mobile in the inner zone frequency band.


Concentric Cells

Database ParametersTCH Assignment --- Alcatel

All SDCCH channels are in the outer zone.

The BSC can allocate a TCH in the inner zone or in the outer zone.

Cause 13 is checked to determine the MS location (Outer to Inner Zone Handover)

Zone Assignment:

The 900 SDCCH is always allocated to the MS (SDCCH channels are on the 900 TRX).

Then according to the MS location (outer zone or inner zone), a TCH is allocated in the 900 band (outer zone) or in the 1800 band (inner zone).

To determine the location of the mobile, cause 13 (outer zone to inner zone HO) is checked.

If the cell is congested, it is possible to allocate the TCH in a neighboring cell (Directed Retry or Forced Directed Retry).

Then, according to the location of the mobile, the value of the parameter EN_BETTER_ZONE_HO, the serving BSC of the serving and the neighboring cells the TCH is allocated in :

The 900 band if the two cells belong to two different BSC,

the 900 band if the two cells belong to the same BSC and EN_BETTER_ZONE_HO =disable for the neighboring cell

The 900 band if the two cells belong to the same BSC,EN_BETTER_ZONE_HO = enable for the neighboring cell and the MS is located in the outer zone of the neighboring cell,

The 1800 band if the two cells belong to the same BSC, EN_BETTER_ZONE_HO = enable for the neighboring cell and the MS is located in the inner zone of the neighboring cell.


Concentric Cells


Cause 13 (too high level on UL/DL in outer zone)

Better condition Intra-cell Handover

Maybe Triggered from OUTER Zone of a concentric Cell TOWARDS inners zone of the same cell


Concentric Cells



RXLEV_UL_ZONE: Uplink level threshold for inner to outer zone handover.

Valid Range:

0 to 63 (0 = -110dBm, 63 = -47dBm)

RXLEV_DL_ZONE: Downlink level threshold for inner to outer zone handover.

Valid Range:

0 to 63 (0 = -110dBm, 63 = -47dBm)


Concentric Cells


ZONE_HO_HYST_UL

UL static hysteresis for interzone HO from outer to inner – In case of multi-band cell, should take into account the difference of propagation between GSM and DCS (difference in Propagation between two bands is countered in Motorola by dual_band_offset)

Valid Range

-40 to 40 dB

ZONE_HO_HYST_DL

DL static hysteresis for interzone HO from outer to inner – In case of multi-band cell, should take into account the difference of propagation between GSM and DCS and the difference of BTS transmission power in the two bands

Valid Range

-40 to 40 dB



Concentric Cells


PING_PONG_MARGIN(0,call_ref)

Its a penalty put on cause 13 if :

The immediately precedent zone on which the call has been is the inner zone of the serving cell and less than T_HCP seconds have elapsed since the last handover. In this case PING_PONG_MARGIN(0,call_ref) = PING_PONG_HCP.

If the call was not precedently on the serving cell’s inner zone (case of intercell or intrazone handover), or if the timer T_HCP has expired, then PING_PONG_MARGIN(0,call_ref) = 0

PING_PONG_HCP

Valid Range:

0 to 127 dB

T_HCP

Time during which PING_PONG_HCP is applied after handover.

Valid Range:

0 to 240 Seconds



Concentric Cells

Database ParametersHANDOVERS

And now Dual Band Handovers…….!


Concentric Cells


During add_cell command, when inner_zone_alg = 3 (dual band), a series of parameters are given as inputs which will now follow along with their descriptions

Secondary_freq_type:

If for example, frequency_type= DCS1800, the secondary_freq_type has to be any of the other types.

Valid range

1 (PGSM),

2 (EGSM),

4 (DCS1800),

8 (PCS1900)

DUAL_BAND_OFFSET:

The inner_zone_alg has to consider other factors in order to handover multiband MSs between different frequency bands. The factors are:

Due to different level of combining the loss of power between the radio unit and the top of the antenna may not be consistent across all radio units within the cell. The power difference is calculated by subtracting the secondary band power loss from the primary band power loss.

Due to the radio frequency propagation being weaker at 1800 MHz than at 900 MHz, propagation loss over the air interface has got to be taken into consideration.

These factors are accounted for in the database parameter dual_band_offset


Concentric Cells


The inner zone use algorithm must adjust for values being from two different frequency bands and convert the primary band receive levels to an estimated value for the secondary band. This is done using the dual band offset parameter.

RXLEVINNER = RXLEVOUTER + dual_band_offset

This offset is applied to both uplink and downlink receive levels

The calculated receive level inner value is then used in the dual band inner zone algorithm for both uplink and downlink

RXLEV_DLINNER > rxlev_dl_zone + zone_ho_hyst + (bts_txpwr - bts_txpwr_max_inner)RXLEV_ULINNER > rxlev_ul_zone + zone_ho_hyst + (ms_txpwr - min(ms_txpwr_max_inner,P)

Within this algorithm are database parameters that are set per cell after theinner_zone_alg = 3 (dual band use)rxlev_dl/ul_zone = <*> *= Range 0 to 63zone_ho_hysteresis = <*> *= Range as defined for max_tx_bts (0 to 21)bts_txpwr_max_inner = <*> *= Range -63 to 63ms_txpwr_max_inner = <*> *= Range as defined for max_tx_ms (5 to 39 PGSM andEGSM 0 to 36 DCS 1800)P = maximum capability of the mobile in the inner zone frequency band.


Concentric Cells


rxlev_dl_zone parameter specifies the downlink receive level threshold that must be crossed for a handover to take place between the outer zone and the inner zone.

Valid Range: 0 to 63 (0 = -110 dBm)

rxlev_ul_zone parameter specifies the uplink receive level threshold that must be crossed for a handover to take place between the outer zone and the inner zone.

Valid Range: 0 to 63 (0 = -110 dBm)

Zone_ho_hyst parameter specifies the margin for the inner zone handover hysteresis.Valid Range: -63 to 63

Bts_txpwr_max_inner parameter specifies the maximum transmit power BTS inner zone for Dual Band cells.

Valid range -1 to 21 for PGSM, EGSM, and DCS1800. 1 step = 2dBm-1 = 44 dBm, 0 = 42dBm, 21 = 0 dBm

Ms_txpwr_max_inner parameter specifies the maximum power an MS can use in the inner zone of a concentric cell.

Valid range: Depends on the system:5 to 39 dBm (odd values only) PGSM/EGSM0 to 30 dBm (even values only) DCS18000 to 30 dBm (even values only) PCS1900



Concentric Cells


Dual Band Inner Zone Use Algorithms

The algos below show what conditions must exist in order to handover a call from Inner to Outer Zone

BTS Power Control on

rxlev_dl < rxlev_dl_zone and bts_txpwr = bts_txpwr_max_inner

Or if Power Control is off

rxlev_dl < rxlev_dl_zone

MS Power Control

rxlev_ul < rxlev_ul_zone & ms_txpwr = min(ms_txpwr_max_inner,P)

Or if MS_PC is off

rxlev_ul < rxlev_ul_zone

pbgt(n) > ho_margin if neighbour qualifies inter-cell handover

If no neighbour qualifies handover MS to outer zone


Concentric Cells

Database Parameters

HANDOVERS & PC --- Motorola

A network where Power Control is enabled, the power budget equation determines the need for an inter-cell handover by essentially comparing the serving cell BCCH signal strength to the neighbour cell BCCH signal strength.

This means the signal strength in a dual band cell must come from the primary zone.

When the call is in the secondary zone, the signal strength reported by the mobile cannot be used in the power budget equation, because

frequencies in the secondary band have a different propagation than frequencies in the primary band.

In a Power Control enabled network, the serving cell will always have the signal strength between the PC window whereas the neighbour would report a much better level of its BCCH (Full Power)


Concentric Cells


Pbgt_mode

If pdgt_mode = 0If the mobile is assigned to a resource on the secondary band, the mobile will use theserving channel measurements and then subtract the dual_band_offset. This estimatedvalue is then inserted into the power budget equation.

If the pbgt_mode = 1The serving cell BCCH is included in the ba_sacch neighbour cell list of the serving cell.The mobile will then report the serving cell signal strength for the primary band, which canbe used in the calculation of power budget for neighbours with the same frequency band.The actual number of neighbour frequencies that can be reported on is reduced by one,also the number of true neighbours that the MS can report on is reduced from six to five. Ifpbgt_mode = 1 then the server is auto equipped as a neighbour.

To solve this problem, we have been provided with a smart parameter by Motorola!


Concentric Cells

Database ParametersHANDOVERS --- Alcatel

Cause 10, 11: UL or DL level too low in the inner zone

Emergency HO

Intracell handovers from inner to outer zone

• cause 10: too low level on the uplink in inner zone

• cause 11: too low level on the downlink in inner zone

Cause 10:

AV_RXLEV_UL_HO < RXLEV_UL_ZONE

and MS_TXPWR = min (P, MS_TXPWR_MAX_INNER)

Cause 11:

AV_RXLEV_DL_HO < RXLEV_DL_ZONE

and BS_TXPWR = BS_TXPWR_MAX_INNER


Further Reading

Motorola SYS12 (Directed Retry, Congestion Relief, Power and Interference

based Concentric Cells)

BSS Command Reference GSR 7

Alcatel RFT B9 (Cause 13,10,11,21,23 Handovers and their descriptions)

Concentric Cells – Alcatel Official Document

Telecom Parameter Dictionary – Alcatel

Documents

GSM Concentric Cells Concept