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GSM/EDGE RAN - BR line

Feature descriptionBR10.0

FD10550: Different level thresholds for RACH access and HO access

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FD10550: Different level thresholds for RACH accessand HO access

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Das System entspricht den Anforderungen der EN 60950 / IEC 60950. Angeschlossene Geräte müssen die zutreffenden Sicherheitsbestimmungen erfüllen.

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Table of ContentsThis document has 13 pages.

Reason for update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1 Introduction to the feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.1 In general. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.2 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1 Software requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Hardware requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1 Functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Functional split . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.3 Functional details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 System impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5 User interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115.1 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Activating and configuring the feature . . . . . . . . . . . . . . . . . . . . . . . . . . 126.1 Setting the thresholds for RACH access and handover access . . . . . . 12

7 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13A – Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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List of TablesTable 1 Parameters for different level thresholds for RACH access and handover

access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

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Reason for update

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Reason for update

Issue history

Details

Issue number

Date of issue Reason for update

01 07/2008 First issue for new release

02 11/2008 Minor editorial changes

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Reason for update

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Introduction to the feature

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1 Introduction to the feature

1.1 In generalThis feature provides two different thresholds for discrimination between valid access bursts and noise (no burst, empty timeslot) at the receiving BTS: one for access bursts on the random access channel (RACH) and the other one for access bursts on a traffic channel (TCH/FACCH), mainly occuring as initial access to the target BTS in case of an inter-cell handover.

Up to now there was only one common threshold for both use cases causing a tradeoff between these cases. This feature allows to handle signal-noise discrimination for RACH access bursts and TCH access bursts received by the BTS separately and inde-pendently.

The thresholds can be configured by the network operator via O&M parameters.

1.2 BenefitsWith this feature it is now possible to set up optimal threshold values for discrimination of access bursts on RACH and on TCHs as well (with only one threshold for both cases before, it was necessary to find a compromise for the threshold value). Thus phantom RACH access bursts can be avoided efficiently while TCH access bursts (e.g. to access the target cell / BTS in case of inter-cell handover) are accepted even in case of low receive power level. As a consequence the RACH load in the BTS and the rejection of inter-cell handovers (or even call drops) can be kept low simultaneously.

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Requirements

2 Requirements

2.1 Software requirementsThis feature does not require any new or additional software.

2.2 Hardware requirementsThe BTSs belong to the present BTS familiy (comprising BS-240/241, BS-240/241II, BS-240XS, BS-240XL, BS-240XL II, BS-288, BS-40/41, BS-40 II, BS-82 II eMicro).

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Functional description

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3 Functional description

3.1 Functional overviewIn the BTS a threshold for the received power level is used to discriminate between a received valid access burst and received noise. If the received power level exceeds the threshold, the received signal is treated as a valid burst, otherwise the timeslot is declared empty. Access bursts can be sent by an MS and received by the BTS on dif-ferent channels:

– On the random access channel (RACH).This situation occurs when the MS requests radio resources from the BTS.

– On a traffic channel (TCH/FACCH).This situation occurs when the MS accesses the target cell / BTS in case of an inter-cell handover or when a listener of a VGCS call becomes the talker.

For each of the two cases an own threshold attribute is provided allowing separate and independent signal-noise discrimination.

3.2 Functional splitThe different level thresholds for RACH access and handover access functionality is executed by the BTS exclusively.

The BSC administers the database for the parameters of the feature.

3.3 Functional detailsThe BTS does not know if and when an MS will send an access burst to the BTS. The BTS gets this information just in time when it receives and detects the access burst on the relevant channel. Therefor it is necessary to discriminate actual bursts from noise which is done via thresholds.

The following effects of the thresholds are desired for the two principle use cases:

• Signal-noise discrimination regarding access bursts on RACH:A high dBm value for the RACH threshold efficiently prevents from phantom RACH access bursts even in networks with high RACH interference figures and allows only sufficient signal levels which guarantees a certain QoS level in uplink direction. All RACH signals lower than the specified value are related with empty timeslots.

• Signal-noise discrimination regarding access bursts on TCH/FACCH:A low dBm value for the TCH/FACCH threshold ensures a high uplink sensitivity of the BTS for incoming handover messages on the TCH/FACCH and for ASCI uplink access bursts. This supports a low handover failure rate and also keeps the rejection of ASCI uplink requests on a low level.

The description above shows that the threshold requirements for RACH access bursts and TCH access bursts are different and that only separate threshold attributes allow to set up optimum thresholds for each case. Thus phantom RACH access bursts can be avoided efficiently while TCH access bursts are accepted even in case of low receive power level.

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System impacts

4 System impactsThe different level thresholds for RACH access and handover access feature is related to inter-cell handovers, radio channel allocation and VGCS calls (Voice Group Call Service, one kind of ASCI calls). The functional range of these areas are neither reduced nor extended, but drops of calls or access failures are decreased.

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User interface

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5 User interfaceThe different level thresholds for RACH access and handover access feature can be configured by network operators.

The parameter administration can be done via LMT (for BSC or BTSE), Radio Com-mander or O&M ToolSet.

5.1 ParametersTable 1 shows the parameters implemented for the different level thresholds for RACH access and handover access feature.

The FACHBT is introduced in BR10.0, RACHBT already existed in BR9.0 but its usage is restricted for BR10.0 (RACHBT in BR9.0 comprised also the use case handover access and ASCI uplink access, now shifted to the FACHBT attribute).

Short name Long name Description Default Range

Parameters of the BTS Managed Object

FACHBT fachBusyThreshold Threshold for the received signal level (RXLEV) during handover access and ASCI uplink access. An access burst signal is assumed as valid (not noise), if the receive level exceeds this threshold.

109 [dBm] 0 ... 127 [dBm]

( step size: 1 dBm)

RACHBT rachBusyThreshold Threshold for the received signal level (RXLEV) during RACH access. An access burst signal is assumed as valid (not noise), if the receive level exceeds this threshold.

109 [dBm] 0 ... 127 [dBm]

( step size: 1 dBm)

Table 1 Parameters for different level thresholds for RACH access and handover access

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Activating and configuring the feature

6 Activating and configuring the featureThis chapter provides the procedure to configure the different level thresholds for RACH access and handover access feature.

6.1 Setting the thresholds for RACH access and handover accessTwo different thresholds are provided for discrimination between valid access bursts and noise (no burst, empty timeslot) at the receiving BTS: one for access bursts on the random access channel (RACH) and the other one for access bursts on a traffic channel (TCH/FACCH).

g If the RACHBT values for BTSs have already been set in BR 9.0 and a BTSM software update to BR10.0 is performed afterwards, the FACHBT values (not provided for BR9.0) are automatically set to the current RACHBT values.

1 Set the threshold parameters

• BSC1: b SET BTS

• eBSC: b SET BTS

Set the following attributes:

– FACHBT (“fachBusyThreshold”)This attribute determines the threshold for the received signal level (RXLEV) during handover access and ASCI uplink access. An access burst signal is assumed as valid (not noise), if the receive level exceeds this threshold.

– RACHBT (“rachBusyThreshold”)This attribute determines the threshold for the received signal level (RXLEV) during handover access and ASCI uplink access. An access burst signal is assumed as valid (not noise), if the receive level exceeds this threshold.

END

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Abbreviations

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7 Abbreviations

A – ZASCI advanced speech call item

BSC base station controller

BTS base transceiver station

DL downlink

FACCH fast associated control channel

HO handover

LMT local maintenance terminal

MMI man machine interface

MOC managed object class

MS mobile station

O&M operation and maintenance

RACH random access channel

TCH traffic channel

UL uplink

VGCS voice group call service

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