Effects of High Peak Power and its analysis of OFDM signals

Effects of High Peak Power and its analysis of OFDM signals

Abstract:

One of the major drawbacks of any Multi-Carrier Modulation (MCM) system, which is often an obstacle to its use, is the fact that the signal has a non-constant envelope, that is, it exhibits peaks whose power strongly exceeds the mean power. The power analysis depends on the number of iterations performed, which also increases the complexity of the transmitter. In this paper, several replicas of the OFDM symbol of a given data frame is formed and the one with the minimum peak power is chosen for transmission where significant gains can be achieved. Simulation results shows the performance analysis of the reliable reduction of peak power which is of viable importance for the practical implementation of OFDM schemes.

Introduction:

Orthogonal Frequency Division Multiplexing (OFDM) technique has been proposed to combat the effects of multipath fading channels, by multiplexing a serial data stream into a large number of subcarriers. This results in a flat fading on each subcarrier and avoids complicated channel equalization. Combined with channel coding and a proper modulation in each subcarrier, such an OFDM scheme can provide bandwidth and power efficient transmission of high quality over severe frequency selective fading channels. Due to the large number of subcarriers, the OFDM signal owns a large dynamic signal range with a very large Peak­to­Average Power Ratio (PAPR). When considering a system with a transmitting power amplifier, the non­linear distortions and peak amplitude limiting introduced by the High Power Amplifier (HPA) will produce intermodulation between the different carriers and introduce additional interference into the system. This additional interference leads to an increase in the Bit Error Rate (BER) of the system. One way to avoid such nonlinear distortion and keep a low BER is by forcing the amplifier to work in its linear region. Unfortunately such solution is not power efficient and thus not suitable for wireless communication systems. A better solution is then to try to prevent the occurrence of such nonlinear distortion by reducing the peak power of the transmitted signal with some manipulations of the OFDM signal itself.


for more info visit.
http://www.enjineer.com/forum