Mumbai university > Comp > SEM 8 > Mobile Communication

Marks: 10M

Year: Revised 2012

• The mobile station and the base station receiver measure the received power and use the measurements to maintain a power level for adequate performance.

• The mobile station unit measurement is part of the open loop power control and the base station measurement is a part of closed loop power control.

• A proper power control on both uplink and downlink has several advantages:

  • System capacity is improved or optimized.

  • Mobile battery life is extended.

  • Radio path impairments are properly compensated

  • Quality of service at various bit rates can be maintained.

• The reverse link uses a combination of open loop ans closed loop power control to command the mobile station to make power adjustments.

• In the Closed Loop mode the mobile transmitter power is controlled by a signal from the base station site. Each base station demodulator measures the received SNR for that mobile station and sends a power command either to increase or decrease mobile station power. The measure command react cycle is performed at a rate of 800 times per second for each mobile station in IS-95.

• The power adjustment command is combined with the mobile’s open loop estimate and the result is used to adjust the transmitter gain. This solves the near-far interference problem. Reduces interference to other mobiles using the same CDMA radio channel, helps to overcome fading and conserves battery power in portable and mobile units.

• On the uplink the objective of the mobile station is to produce nominal received power signal at the base station regardless of the mobile’s position. If the mobile’s signal arrives at the base station with a lower power level than the required power level. Its error rate performance will be high while if the mobile’s signal is too high, it will interfere with other users with same CDMA radio channel.

• A combination of open loop and closed loop power control is used at forward link to keep SNR at the mobile almost constant. Forward link power control mitigates the corner problem. Forward link power control minimizes interference to mobiles on the same base station as well as mobiles in other base stations. Using downlink power control the base station transmits the minimum required power hence minimizes the interference to mobiles in the surroundings base station.

• The Open Loop power control is the finer power control over the closed loop power control. It adjusts the target signal to interference ratio in the base station according to the needs of the individual radio links and aims at a constant quality which is defined as a certain target bit error rate (BER) or frame error ratio (FER).