In wireless communication networks, performance goals are often conflicting with each other. For example, in point-to-point multi-input-multi-output (MIMO) links, spectrum efficiency and reliability are in a tradeoff relation; in ad-hoc wireless networks, we need to sacrifice throughput to decrease packet delay. In this dissertation, we investigate problems on the diversity-multiplexing tradeoff (DMT) in cellular wireless communication networks and problems on the throughput-delay tradeoff in ad-hoc wireless networks.
We first consider two topics on the DMT in cellular uplinks (or multiple-access channels, MACs): (1) the diversity-multiplexing-delay tradeoff (DMDT) in a random-access scenario and (2) an explicit construction of space-time coding scheme achieving the DMT. For the random-access scenario, we propose an incremental-redundancy automatic repeat request (IR-ARQ) scheme. We prove that our scheme successfully exploits both ARQ diversity and joint-decoding advantage, and achieves a better DMT than other existing protocols, such as Tsatsanis et al.'s network-assisted diversity multiple-access (NDMA) and Gallager tree algorithm. Next, we propose a lattice-space time (LAST) coding/decoding scheme in MACs and prove that it achieves the optimal DMT in MACs. Although our result is established using a random coding argument, it is important to note that the proposed scheme is explicit in a sense that it lends itself to a structured encoder and an efficient decoder which does not require exhaustive search.
Next, we formulate and analyze the DMT in delay-constrained cellular downlinks (or broadcast channels, BCs). We show that dirty-paper precoding achieves the optimal DMT in BCs. Furthermore, we analyze the DMTs for a few suboptimal precoding schemes. In particular, we find that vector precoding schemes such as vector perturbation of Peel et al. and LLL lattice reduction achieve the optimal DMT of a type of BCs, in which a BS has a larger number of antennas than the number of users each with a single antenna.
Besides the DMTs in cellular wireless networks, we also analyze the throughput-delay scaling in ad-hoc wireless networks in which Ozgur et al.'s hierarchical cooperation is allowed. We propose a hierarchical multihop scheme for these networks, and prove that the throughput-delay relation of the proposed scheme is, for any small ϵ > 0, D(n) = Θ (nϵT(n)) up to T(n) = Θ (n1–ϵ), where T(n) is the aggregate throughput and D(n) is the packet delay in such a network with n nodes. Thus our result successfully extends the throughput-delay result of El Gamal et al.'s where they proved the same throughput-delay relation using a multi-hop scheme, only up to T(n) = Θ(n1/2 ).
|Commitee:||El Gamal, Hesham, Koksal, Emre, Schniter, Phil.|
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Broadcast channel, Diversity multiplexing tradeoff, Lattice coding, Lattice decoding, Multiple access channel, Throughput delay tradeoff|
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