Novel pilot-free adaptive modulation for wireless OFDM systems

Orthogonal frequency division multiplexing (OFDM) is the contemporary technology adopted for digital audio/video broadcasting as well as wireless local-area and metropolitan-area networks. Since the wireless multimedia services often have different quality-of-service requirements and their performance is sensitive to the channel conditions, the conventional fixed OFDM modulation scheme might not be a satisfactory solution nowadays. In this paper, we introduce a novel pilot-free adaptive modulation scheme, which is bandwidth-efficient and allows variable data rates, for the future robust OFDM systems. We design a number of modulation modes in a combination of different constellation sizes and different polynomial cancellation coding methods (PCC) to combat the crucial intercarrier interference problem. Instead of estimating the channel quality based on the overhead pilot symbols, we propose to directly estimate the signal-to-noise ratio (SNR) without using any pilot. Besides, our scheme offers more modulation modes than some other existing adaptive modulation methods which are simply based on different constellation sizes. According to the Monte Carlo simulations, the empirical results show that our adaptive modulation scheme, in most channel conditions (SNR≥15 dB), not only can satisfy the predetermined bit error rate (BER) requirement (BER≤10^-4) but also can dynamically enhance the throughputs in the rather clean environments with high SNR values.