Performance Analysis of a Combined Adaptive OFDM Transmission Scheme for Broadband Power Line Communications

Adaptive modulation can approach the channel capacity by adapting the number of bits per transmission symbol to channel quality variations. This paper proposes a fixed threshold adaptive modulation scheme for orthogonal frequency division multiplexing (OFDM) used in power line communications. This adaptive OFDM is combined with an adaptive power control scheme in order to combat with multipath fading and increase total data transmission rate. In this paper, it is assumed that duplex data transmission is performed and channel characteristics are easily estimated and shared between transmitter and receiver. According to the channel estimation, the transmitter selects the modulation mode among BPSK, QPSK, 16QAM, 64QAM and 256QAM, and determines the transmission power for each OFDM subcarrier. A reallocation algorithm is also proposed to optimize allocations of both modulation modes and subcarrier transmission power. Simulation results show that better performances are confirmed for targeted bit error rates of 1.0times10^-2 and 1.0times10^-3 as compared to conventional modulation schemes