neighbor cell optimization HUAWEI CDMA2000 NETWORK

OBJECTIVE

Optimize the network on the basis of analysis collection PSMM trace data. These data it is possible to receive, I use a command SET PSMMTRACE of the controller.

This command is used to start or stop the neighbor cell optimization data collection task of the CDMA2000 1X system.

After the data collection task is started, a specified number of calls are traced and specified messages such as PSMM, PPSMM, EPSMM, or CFSRPT reported by these calls are collected, saved as a text file, and then sent to the network Huawei optimization analyzing tool for the neighbor cell optimization analysis.

This tool is a paid product and does not extend freely. Therefore for the analysis of the information containing in a file we have developed the special program. This program will transform a binary file to a usual text file which is convenient for analyzing.

File: PSMMTRACE3.dat

Date: 2008-5-24 14:55:42.225

Version: BSC6600-OMCV100R003ENGC03B118

EcIo: 12 Subscribers: 50 BTSID: 04 Chanel: 0200

CH:200 CID:42 S:76 CID:40 S:88

CH:200 CID:41 S:75 CID:1a1 S:88

CH:200 CID:10 S:95 CID:a1 S:86

CH:200 CID:50 S:100 CID:42 S:20

CH:200 CID:40 S:77 CID:41 S:11

CH:200 CID:50 S:93 CID:10 S:88

CH:200 CID:50 S:95 CID:10 S:24

CH:200 CID:41 S:74 CID:60 S:88

CH:200 CID:40 S:74 CID:41 S:24

CH:200 CID:40 S:73 CID:41 S:24

CH:200 CID:40 S:74 CID:1a2 S:86

CH:200 CID:41 S:77 CID:210 S:20 CID:200 S:88

CH:200 CID:41 S:71

CH:200 CID:42 S:74 CID:40 S:84

CH:200 CID:40 S:76 CID:1a1 S:20 CID:41 S:86

CH:200 CID:40 S:83 CID:41 S:14 CID:1a2 S:88

CH:200 CID:41 S:92 CID:21 S:22 CID:51 S:87

CH:200 CID:40 S:75 CID:1a1 S:24 CID:1a2 S:88

CH:200 CID:41 S:85 CID:210 S:13 CID:42 S:88

CH:200 CID:a1 S:77

CH:200 CID:42 S:87 CID:210 S:13 CID:41 S:23 CID:52 S:88

CH:200 CID:a0 S:88 CID:a2 S:24 CID:40 S:23 CID:1a2 S:88

On all questions of use of this program write to cdmatest@yandex.ru

INTRODUCTION

Soft handoff – add to active set

Soft handoff is a complex process.

Mobile station supports handoff as it moves from one area to another. Along the way, it transfers its communication from one base station to another. There are different handoff scenarios in different states of the mobile station.

Soft handoff occurs when the mobile begins to communicate with the second base station without breaking its communication path with the current serving base station. In general, this is known as the “make before-break” approach. During the soft handoff, the mobile can communicate with more than two base stations simultaneously. IS-2000.5-0 defines the maximum number of simultaneous links to be six, which implies that the mobile can talk to six base stations at the same time. Each base station has its unique pilot. The pilot provides the mobile stations with a timing reference and the information for the mobile stations to acquire the communication with the network. The pilots of the base stations that the mobile is actively communicating over the traffic channel constitute the mobile’s active set. The mobile generally initiates soft handoffs. During a call, when the mobile is in the mobile station control on the traffic channel state , it will continuously scan for better pilots. Better pilot refers to the pilot that has a stronger signal strength than the add threshold (T_ADD). If better pilots are found, then the mobile reports them to the base station. Thus, the mobile assist the base station in soft handoff. This is characterized as the Mobile Assisted Handoff (MAHO) approach.

In order to achieve soft handoff, the participating base stations must support the same frequency. The mobile transmits on the same frame offset on all communication links. In other words, soft handoff can only be used between CDMA channels having identical frequency assignments.

As mentioned earlier, the mobile maintains the links with multiple base stations during soft handoff. The mobile stores the values for add threshold and drop threshold (T_DROP) for adding or dropping a base station during soft handoff. These thresholds are supplied to the mobile at call initiation.

The mobile maintains a list, called the active set, of the base stations involved in soft handoff. It maintains a list of candidates, called candidate set, whose measured signal strength are above the add threshold. The mobile assists in soft handoff by reporting both lists to the system whenever a new candidate appears in the candidate set or the signal strength of an existing base station in the active set falls below the drop threshold. The system can add base stations from the candidate set to soft handoff or drop base stations during soft handoff.

Pilot sets are groups of pilots. Pilots are stored in different groups to assist the mobile in soft handoff. Each mobile maintains its own pilot sets when it is on the traffic channel. This set can be changed dynamically during a call by transitioning pilots among different sets:

§ Active Set: Pilots (based stations) with which mobile is in soft handoff. This active set can have up to six pilots.

§ Candidate Set: Pilots not currently in the active set, but are candidates for handoffs. These pilots have been received by the mobile with signal strength above the add threshold.

§ Neighbor Set: Pilots that are not currently in active or the candidate sets but are likely candidates for handoffs.

§ Remaining Set: All possible pilots in the current system excluding pilots in neighbor set, the candidate set and the active set.

A soft handoff scenario for a mobile station moving from BS1 to BS2.

Figure depicts the trigger for adding and dropping a pilot. In this scenario, mobile starts moving from base station 1 (BS1) towards base station 2 (BS2). As it moves closer to BS2, the signal strength of BS2 becomes stronger. Once the signal strength of this pilot reaches the T_ADD threshold, this pilot can be added to the active set.

At the same time, the signal strength of BS1 drops as the mobile moves away from BS1. Once the signal strength drops below the T_DROP threshold, this event triggers the T_TDROP timer to be set. If the signal strength goes above the T_DROP threshold before the T_TDROP timer

expires, the pilot will not be dropped. Only if the signal strength is below the T_DROP threshold for at least the duration of the T_TDROP timer, the pilot will be dropped from the active set.

1. As the mobile continuously scans for better pilots, it detects the pilot for base station BS2. When the signal strength of the pilot from BS2 rises above the add threshold, it then becomes a candidate for soft handoff. The mobile sends a Pilot Strength Measurement Message (PSMM) to base station BS1. The PSMM includes both the signal strength of the current serving pilots (active set) and potential candidates (candidate set).

2. Upon receiving the PSMM through BS1, the network decides to add BS2 to soft handoff. After allocating internal resources in BS2 for the call, the network sends a Handoff Direction Message to the mobile through base station BS1. The Handoff Direction Message includes information about the set of traffic channels, which includes BS1 and BS2. The BSC starts “multicasting” the forward direction frames.

3. The mobile tunes to BS2 and sends a Handoff Completion Message to the network through BS1 and BS2. At this point, BS2 is added to soft handoff. The BSC starts “selection” of frames in the reverse direction. The mobile starts “combining” frames in the forward direction.

Message sequence diagram showing pilot being added to the active set during soft handoff

OTA-R-FCH-pilot strength measurement message for MS to return the pilot strength to BS, including pilots in both active and candidate set.