Adaptive modulation for powerline communication

Abstract

This report presents the effects of adaptive modulation on powerline communications performance. In this project, the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme is used in powerline communications. OFDM is used since a larger amount of data could be carried by different subcarrier frequency which is orthogonal to each other and they would not be interference to others. The adaptive OFDM modulation scheme is divided into two parts, the bit allocation and power allocation. This is a way to due with multipath fading in the powerline channel and maintains a lower error rate with a reasonable data transmission rate. In this report, the channel characteristics are estimated using Least Square approaches base on Block-type and Comb-type pilot scheme and transmitter as well as receiver are both obtained that information. Base on the channel estimation, the transmitter selects the modulation mode between BPSK, QPSK, 16QAM, 64QAM, 256QAM, 1024QAM or nothing to be sent in the corresponding subcarrier. Meanwhile, the transmission power of each subcarrier is reallocated in order to achieve higher modulation scheme and optimize transmission power on that subcarrier. The simulation results show that a better performance obtained, in bit rate and bit error rate, while the bit allocation and power allocation scheme are used in the system rather that the same modulation mode apply to all subcarrier. If only BPSK modulation apply to all subcarrier, a better bit error rate but a poor transmission rate obtained. On the other way, it results a better transmission rate but poor bit error rate if only 256QAM or 1024QAM modulation apply to all subcarrier. Thus, adaptive modulation uses to strike a balance between transmission rate and bit error rate.