Interference aspects of adaptive modems over slow Rayleigh fading channels

Abstract

Adaptive modulation can achieve channel capacity gains by adapting the number of bits per transmission symbol on a burst-by-burst basis, in harmony with channel quality fluctuations. This is demonstrated in the paper for target bit error rates of 1 and 0.01%, respectively, in comparison to conventional fixed modems. However, the achievable gains depend strongly on the prevalant interference levels and hence interference cancellation is invoked on the basis of adjusting the demodulation decision boundaries after estimating the interfering channel's magnitude and phase. Using the modem-mode switching levels of Table X and with the aid of interference cancellation, target BER's of 1 and 0.01% can be maintained over slow-fading channels for a wide range of channel Signal-to-noise ratios (SNR) and Signal-tointerference ratios (SIR), as seen in Figs. 20 and 21, respectively.

Burst-by-burst adaptive turbo-coded radial basis function-assisted decision feedback equalization

“…Due to lack of space these issues are beyond the scope of this contribution and we have assumed zero-delay perfect AQAM mode signaling. For a deeper discussion on this topic the reader is referred to [4], while the associated co-channel interference aspects were treated in [34].…”

Adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications

“…Steele and Webb [97] proposed adaptive modulation for exploiting the time-variant Shannonian channel capacity of fading narrow-band channels, which stimulated further research by Sampei et al [98], Goldsmith et al [99], Pearce et al [100], Lau and McLeod [101], and Torrance et al [102], [103]. The associated principles can also be invoked in the context of parallel modems, as has been demonstrated by Kalet [17], Czylwik et al [104], and by Chow et al [105].…”

“…Unlike adaptive serial systems, which employ the same set of parameters for all data symbols in a transmission packet [102], [103], adaptive OFDM systems have to react to the frequency-selective nature of the channel, by adapting the modem parameters across the subcarriers. The resulting signaling overhead could become significantly higher than that for serial modems, and can be prohibitive, for example, for subcarrier-by-subcarrier modulation mode adaptation.…”

Dynamic channel allocation techniques using adaptive modulation and adaptive antennas

“…Hence, its throughput is almost as high, as that of say the 16-QAM mode, while maintaining almost as high a robustness, as BPSK. The effects of co-channel interference on AQAM modems were detailed in [18], while the practical engineering aspects its latency-and buffering requirements, as well as the impact of various Doppler frequencies were studied in [19]. As a means of mitigating the effects of latency, frequency hopping was shown to be a powerful countermeasure.…”