Prepared By: Pandian. M  

Introduction:

In BSNL CDMA technology is used for WLL coverage. Previously IS95 WLL, CORdect WLL services were available. Presently MSC based WLL services have been launched.

This is mainly used for providing Tarnag services in rural areas, where basic services could not be given due to want of cable pair, and to clear the available waiting list and so to lay the pavement for met on demand condition.

Optimization:

The monitoring and optimization on the network will proceed gradually with the development of the network, and cannot be completed at a single attempt. In order to make full use of the existing network devices, resources and capacity, maximize the average Quality of Service of the network, and improve the benefits, we must optimize the network continuously.

When the system is to be optimized:

• When a new BTS is installed
• Additional BTS are added to the network
• When subscriber base is increased
• During environmental changes (Addition of new Buildings in the town)
• When the traffic pattern changes
• Subscriber complaint

 Objectives of the Optimization:

• To optimize the network topology structure, and balance the traffic.
• To optimize the settings of wireless parameters, ensure the overall performance of the network, and provide the best Quality of Service.
• To meet the coverage and capacity objectives of the network planning as far as possible.
• To resolve the main unresolved problems in the existing network.
• To reduce complaints from the users.

Description:

Before doing any attempt of optimization, do the following:

• Analyze the problem
• Site inspection
• Verify the configuration and Antenna locations with the basic data.
• Check of VSWR and Trans Power
• Have detailed coverage test

 Performance parameters for CDMA Network

• Dropped Call
• Blocked Call
• FER ( Frame Erasure rate)
• Ec /Io
• Delay and Delay spread

Causes of call drop and other call failures:

• Poor RF Coverage
• Pilot Pollution
• Missing Neighbor PN
• Search window settings in BSS System
• GPS failure

 How tested:

Proper coverage test should be carried out periodically and as and when a BTS is added to the system. The following are essential for carrying out the Drive Test or Coverage Test. During test the coverage requirements should be taken as -75 db in Car, -85 db in Building, -95 db in outdoor with Pencil Antenna. The expected Ec/Io value should be between -3 to -10 for better performance.

Equipments required for testing:

• Laptop with CDMA test software and License Key
• GPS receiver with Data Cable and out built Antenna.
• Test Telephone; FWT or Hand held with data cable to connect to Laptop
• Campus
• 800 M PN Scanner
• PCMCIA card in the laptop for additional serial ports.

Software available for RF coverage test or Drive test

1. Agilent RF tester ( Receiver Based)
2. CNT1 CDMA Network tester (ZTE make- Phone Based and Receiver Based)
3. CNA1 CDMA Network Analyzer (ZTE make)

Note: Phone based is useful to make Calls during test and Handovers can be verified.

Software available for Planning.

• ZXPOS CNS1 – CDMA Network Simulation Module

 Possible Solutions after completing the Drive Test and Analyzing;

• Antenna azimuth adjustments can be very helpful to improve dominant coverage, reduce overlap, and increase the percentage of area coverage in a CDMA system.
• Antenna orientation = Individual azimuth adjustment of each sector.
• Antenna down tilt can improve coverage in well designed systems.
• Cell sites that are too tall may not allow down tilted antennas to control overshooting coverage. Even above the antenna's upper half power point coverage, power is very strong.
• Cell sites that are too short to differentiate the edge of the cell's coverage from the horizon may be too short to be down tilted. Any down tilt just reduces coverage.

 The following are to be considered before doing Antenna Down tilt:

• Cell antenna height and cell site terrain elevation
• Terrain topology in the sector coverage area
• Distance to the neighbor cell in the sector face
•  Antenna pattern.

 The parameters to be adjusted in the BSS / MSC

• Definition of Active Set, Candidate set and Neighbor set (PN off sets of the sectors)
• Search window dimensioning.
• T_add , threshold values for the pilot to be picked up by a MS or FWT.
• Pilot power adjustments
• Allocation of traffic channel and power assigned to traffic channel

 Case 1.

 Sample test sheet to be done during a Drive Test:

 Here at the range of 12 to 15 KM, the receive level without Patch panel antenna are ok and call status are alright. But the serving area and Pilot received are different. The serving area is Salem SDCA and the Pilot received is from Omalur SDCA.

Antenna at 210’ at Omalur BTS is radiating beyond 12 KM also; but we need this is to be available upto 10 to 10.5 Km range. The mechanical tilt assigned to this antenna at Omalur BTS was 3’; But actually this is without tilt. Once the required tilt is provided the problem has been solved.

(Site inspection and check up of actual value with the available)

 Case 2.

 The coverage test report taken from the CNA1 software at Moolanur BTS of Erode SSA.

Right from Elugamvalasu to Ellapalayam, the expected signal from 120 PN antenna from Moolanur BTS was not received properly. Here the distance from the BTS is 15 KM.

The Antenna at Moolanur was at 220’ with mechanical tilt 1’.

The same is adjusted to 210, and the tilt is removed and the problem solved.