On multiple access and capacity in frequency-selective channels

Abstract

Investigates the problem of improving communication rates for frequency-selective multi-access channels (MACs). In this context, multi-pulse methods offer a new opportunity to revisit MAC approaches that are aware of and exploit channel characteristics. For the single-link case, multi-pulse methods such as OFDM split the channel into a set of orthogonal subchannels, or dimensions, and enable the use of Shannon's water-filling technique to achieve capacity. This paper proposes MAC approaches based on water-filling for high-speed ad-hoc wireless networks. The basic framework divides time into uniform slots; during each interval, the active links must share the subchannels, with each link defined by its set of per-subchannel SNRs. Using this framework, pragmatic protocols are proposed that balance overall capacity and per-link quality of service. They are based on adaptively allocating slots and subchannels using knowledge of the links.