Adaptive OFDM over Frequency Selective and Fast Fading Channel using Blockwise Bit Loading Algorithm

Effect of spectrum sensing errors on the performance of bit loading for orthogonal‐frequency‐division‐multiplexing‐based cognitive radio systems

“…This leads to bit allocation, which assigns different numbers of bits to different subcarriers in the N C chosen subcarriers based on the transmitting ability of each subcarrier such that the overall data rate satisfies the required constant. There have been several iterative bit loading algorithms proposed in [3,4,18]. In these applications, the bit allocation satisfies the equation…”

“…As a result, the reception performance may highly fluctuate across the subcarriers and vary from symbol to symbol as well. If the same modulation scheme is used in all the subcarriers, the overall error probability is dominated by those subcarriers with the lowest signal-to-noise ratio (SNR), leading to an overall poor performance [3]. Bit loading is an excellent solution to this performance unbalancing problem.…”

Performance Comparison of Uncoded OFDM & Uncoded Adaptive OFDM System Over AWGN Channel

“…Based on the instantaneous SNR the best mode will be selected for next transmission frame. This task is done by the mode selector block [1].The channel estimation and mode selection are done at the receiver side and the information is sent to the transmitter using a feedback channel [4]. In this model the adaptation is done frame by frame.…”

Adaptive Modulation Using Neuro-Fuzzy (N-F) Controller for OFDM System

“…Prasad Babu proposed adaptive modulated system using fuzzy logic interface which performed better than fixed modulation systems. The channel performance may be highly fluctuating across the sub carriers and varies from symbol to symbol [3]. If the same fixed transmission scheme is used for all OFDM sub carriers, the error probability is Manuscript received February 9, 2013; revised June 26, 2013.…”