Mumbai university > Comp > SEM 8 > Mobile Communication

Marks: 5M

Year: Revised 2012

• In CDMA, the power of multiple users at a receiver determines the noise floor after decorrelation. If the power of each user within a cell is not controlled such that they do not appear equal at the base station receiver then the near-far problem occurs.

• The near far problem is undesirable effect in CDMA systems. It occurs when many mobile users share the same channel. In general strongest mobile signal will capture the demodulator at the base station. In CDMA strongest signal level raise the noise floor at the base station demodulators for the weaker signals thus decreasing the probability that weaker signals will be received.

• To combat the near-far problem, power control is used in most CDMA implementations. Power control is provided by each base station in a cellular system and assures that each mobile in base station coverage area provides the same signal level to the base station. This solves the nearby subscribers overpowering the base station receiver and drowning out the away the signals of faraway subscribers.

• Despite of use of power control within each cell, out0of-cell mobiles provide interference which is not under the control of receiving base station.