Research Into The Algorithm Of Power Control In OFDM Systems With Array Technique

Orthogonal frequency division multiplexing(OFDM)is mainly designed to combat the effect of multipath by dividing the wide-band frequency selective fading channel into many narrow-band flat subchannels. Suppression co-channel interference(CCI)is the key of increasing the capacity of multi-user systems. Power control algorithms can decrease transmitter power and control CCI effectively in multi-user OFDM systems.The previous studies on algorithms of power control are mainly proposed for single-input single-output(SISO)systems. In this thesis the algorithm of power control with adaptive beamforming of array technique is studied for the single-input multi-output(SIMO)system, which has several antennas in the receiver. Multi-antenna receiving systems supply another freedom: the space beamforming. The expression of optimum space weight vector is deduced and given according to linearly constrained minimum variance(LCMV)based on the Lagrange algorithm. In the condition of satisfying signal interference noise ratio(SINR)limits of all base stations, an iterative algorithm of transmitter power combined with the algorithm of optimum space weight vector is deduced and given for every sub-carrier. Both theoretical analyses and simulation results indicate that: the total transmitter power of the SIMO-OFDM system is obviously less than that of the SISO-OFDM system at the same SINR.Information theory shows that the multi-input multi-output(MIMO)technique can significantly increase the spectrum efficiency of wireless channels. And combined with OFDM technique, higher spectrum efficiency of wide-band channels is obtained in MIMO-OFDM systems, so higher data transmission rate can be realized. In single-user MIMO-OFDM systems, the water-filling power allocation algorithm can obtain higher capacity than the average power allocation algorithm. In multi-user MIMO-OFDM systems, the technique of power control combined water-filling power allocation algorithm is deserved to investigate in order to obtain higher total capacity of systems. Relative issues are analyzed and discussed, and some base theories are prepared for future work.