Frequency-Domain Cross-Layer Diversity Techniques – Efficient Ways of Coping with Lost Packets in Broadband Wireless Systems

The design of broadband wireless communications presents considerable challenges. The propagation conditions can be very hostile (e.g., highly dispersive channels and/or deep fading or shadowing effects). This is especially true for systems operating in mm-wave conditions, where one must rely in LoS and/or reflected rays. Moreover, these systems are expected to have power and spectral efficiencies, together with high QoS requirements. There are also implementation complexity constraints, especially at the mobile terminals. Prefix-assisted block transmission techniques combined with frequency-domain detection are known to be suitable for high rate transmission over severely time-dispersive channels. The most popular modulations based on this concept are OFDM (Orthogonal Frequency-Division Multiplexing) and SC-FDE (Single-Carrier with Frequency-Domain Equalization). However, the severe propagation conditions in multiuser wireless systems make it likely that a non-negligible fraction of the transmitted packets will be lost, either due to deep fading/shadowing effects or due to collisions in the MAC (Medium Access Control) phase. The traditional approach to cope with lost packets is to drop them and ask for its retransmission. However, even packets with a large number of bit errors have useful information on the transmitted blocks that can be employed to improve the detection performance. To take advantage of this, we need to employ a cross-layer approach combining PHY, MAC and LLC layer aspects to cope with lost packets. In this talk we show how we can design powerful cross-layer network diversity techniques specially designed for broadband wireless systems employing block transmission techniques combined with frequency domain detection. Speaker(s): Rui Dinis Room: EV003.309, Concordia University, 1515 Ste. Catherine West, MONTREAL, Quebec, Canada, H3G 1M8