We consider a fading version of the dirty-paper problem, as proposed by Grover and Sahai. In this formulation, the various signals involved are complex-valued, and the interference (known only to the transmitter) is multiplied by a random complex-valued coefficient, whose phase is known only to the receiver. We focus on a compound channel formulation, and seek to maximize the worst-case performance. We present an achievable strategy modeled on the lattice-based approach of Erez, Shamai and Zamir and propose heuristic methods to optimize its parameters. We also derive an upper bound on the maximum achievable transmission rates. Our bounds are shown to be tight in some settings, yielding a complete characterization of capacity. We also provide simulation results, indicating the practical effectiveness of our approaches.

We describe a new mechanism that extends the notion of current hybrid automatic repeat request (H-ARQ) schemes. Unlike other H-ARQ methods, if a retransmission for a packet is required, the retransmission jointly embeds the original information of the first packet as well as additional information from a second packet. In fading channels, this approach introduces diversity gain for the first packet without decreasing the overall code rate. This concept is demonstrated with an implementation based on low-density parity-check (LDPC) codes, and simulations show that this H-ARQ scheme provides a significant increase in coding gain for the first packet, and incurs negligible loss of coding gain for the second packet.

We analyze the impacts of multi-hop relaying on the quality of service of voice transmission in the downlink OFDMA communication system. It is shown that the system performance in terms of capacity and quality strongly depends on deployment and operating parameters such as the location of relays, traffic loads and the allowable packet error rate. The impact of relaying is less evident when the traffic load is light and the base station can effectively cover the whole cell. In the high traffic load region, multi-hop relaying is most effective in reducing the outage probability while increasing the cell throughput.

Voice over IP (VoIP) has become the fastest growing wireless alternative to conventional telephony service by way of ongoing deployment of WLAN hotspots and even powerful WiMAX coverage. Resulting from the wired/wireless combined best-effort based heterogeneous IP networks which provide more fluctuation in available bandwidth and end-to-end delay, the performance of VoIP quality, especially using the handheld wireless devices, has been greatly degraded due to frequent packet loss and longer delays. This paper proposes a real-time embedded packet train probing scheme for estimating end-to-end available bandwidth so as to accomplish effective congestion control. By trading acceptable delays with adaptive packetization of voice bitstreams, as well as adaptive insertion of forward error correction (FEC) packets, an optimized system driven QoS approach for VoIP can thus be achieved.

In a wireless network environment, common channel errors, due to multipath fading, shadowing and attenuation, may cause bit errors and packet loss quite different from the packet loss caused by network congestion. In congestion control, the packet loss information can serve as an index of network congestion for effective rate adjustment; therefore, wireless packet loss can mistakenly lead to dramatic performance degradation. The paper proposes a packet loss classification algorithm based on detecting the trend in relative one-way trip time (ROTT) when it falls in the ambiguous zone where the packet loss classification is not straightforward. We show that the proposed algorithm greatly benefits rate-based congestion control algorithms for multimedia over IP networks.

In wireless communication, noise and channel fluctuation often cause bit errors and subsequently the packet loss, which has different characteristic from the loss from network congestion. For most congestion control algorithms, the packet loss information serves as an index of network congestion and is used for effective rate adjustment; therefore wireless packet loss can mistakenly lead to dramatic performance degradation. We discuss the reasons leading to packet loss and propose a packet loss classification (PLC) algorithm that is based on trend detection of relative one-way trip time. With the assistance of PLC, not only can the wireless loss be separated from the congestion loss, the wireless packet error rate can be also estimated. With the combined information, the new adaptive congestion control algorithm is constructed so that a receiver can acquire an appropriate share of bandwidth. The transmitted data is protected by adaptive maximum distance separable erasure codes according to the wireless channel condition and end-to-end available bandwidth

We consider coded modulation with generalized selection combining (GSC) for bandwidth-efficient-coded modulation over Rayleigh fading channels. Our results show that reception diversity with generalized selection combining can conveniently trade off system complexity versus performance. We provide a number of new results by calculating the cutoff rate, and by deriving analytical upper bounds on symbol-interleaved trellis-coded modulation (TCM) and bit-interleaved-coded modulation (BICM) with GSC. All are verified by simulation. We show that our new bounds on TCM with GSC, which includes maximum ratio combining and selection combining as special cases, are tighter than the previously derived bounds. A new asymptotic analysis on the pairwise error probability, which can be used as a guideline for designing coded modulation over GSC channels, is also given. Finally, we show that BICM with iterative decoding (BICM-ID) can achieve significant coding gain over conventional coded modulation in a multiple-receiving-antenna channel.

We have suggested bit-interleaved coded modulation with soft decision iterative decoding (BICM-ID) for bandwidth-efficient transmission over Gaussian and fading channels. Unlike trellis coded modulation, BICM-ID has a small free Euclidean distance but large diversity order due to bit interleaving. With iterative decoding, soft bit decisions can be employed to significantly improve the conditional intersignal Euclidean distance. This leads to a large coding gain, comparable to that of turbo TCM, over both Gaussian and Rayleigh fading channels with much less system complexity. We address critical design issues to enhance the decoding performance and provide the analytical bounds on the performance with an ideal feedback assumption. We investigate the performance characteristics of BICM-ID through extensive simulations and show that at high signal to noise ratios, the performance of BICM-ID converges to the performance assuming error-free feedback.

We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of "turbo" coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10/sup -6/ can be achieved with 16-QAM, a four-state rate 1/2 code at E/sub b//N/sub 0/ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels.