This paper proposes a dynamic bound restriction iterative algorithm (DBRIA) framework, which can make iterative algorithms converge quickly. We apply this framework to realize computationally efficient iteration-based suboptimal bit and power allocation in OFDM systems. The implementation methods for three classes of suboptimal allocation algorithms are analyzed; margin-based, water-filling-based, and Lagrange-multiplier-based. We extend the water-filling-based power allocation algorithm to implement the bit allocation as well. Additional techniques for further reducing the computational complexity for all three allocation methods are also discussed. Simulation results show that both the maximum and the average computational complexity of all three allocation algorithms are reduced dramatically by applying the DBRIA and the additional techniques. For the water-filling-based algorithm, the allocation performance is also improved.

We point out that the model in (3) of [1] is not accurate enough to characterize the energy captured by realistic ultra-wideband (UWB) receivers and hence the average bit error rate (ABER) evaluated by using the framework in [1] can be remarkably far from the actual ABER of realistic UWB receivers. We also show that good performance can be achieved by using the framework in [1] if models tailored for realistic receivers are employed instead of the original model in (3) of [1].

This paper proposes a new optimal bit and power direct allocation algorithm. Based on the analysis of the regularity of the Greedy allocation result, we propose and prove a necessary and sufficient condition for the Greedy allocation result. According to this condition, a bit and power allocation algorithm aiming to allocate the total bits or total power at a time to all subchannels is proposed. The impact of SNR Gap on the allocation result and the technique to eliminate its impact are analyzed. Though iterations are needed to obtain the ideal allocation result, the computational complexity is lower than that of existing optimal algorithms in the literature, even lower than that of some suboptimal algorithms.

Based on the concept of multi-hop relaying, a cooperative macro-diversity system is suggested. In the Rayleigh-lognormal composite fading environment, the performances of a hexagonal macro-diversity cellular system are investigated. The maximum ratio combining (MRC) is considered for the uplink analysis of outage probability and bit error rate (BER) for differential phase shift keying (DPSK). Numerical results show that the performances of the new system outperform those of the conventional single-hop macro-diversity system. The multi-hop relaying can enhance the robustness of performance, and it is helpful to improve the reliability of the radio link.