THESIS
2008
xvii, 145 leaves : ill. ; 30 cm
Abstract
The scarcity of bandwidth has always been the bane of high-speed wireless transmissions whose demand has been tremendously increasing over the years. In order to tackle this challenge, either the current resources should be more efficiently utilized, or new radio resources should be sought for. This thesis is built upon these two philosophies and aims to provide new insights and design principles for wireless multiuser transmissions over the physical, link and medium-access control layers....[
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The scarcity of bandwidth has always been the bane of high-speed wireless transmissions whose demand has been tremendously increasing over the years. In order to tackle this challenge, either the current resources should be more efficiently utilized, or new radio resources should be sought for. This thesis is built upon these two philosophies and aims to provide new insights and design principles for wireless multiuser transmissions over the physical, link and medium-access control layers.
Initial efforts are put on the multiuser resource allocation problem over the multiple-input-multiple-output (MIMO) channels using multiple antennas. The downlink is of interest since most data loading of many multimedia services goes there. Specifically, two emerging multiplexing schemes, namely, orthogonal frequency division multiple access (OFDMA) and multi-carrier code division multiple access (MC-CDMA), are evaluated. Their capacity limit and relationship with the number of antennas, fading channel condition, fairness among users and delay concern are investigated and compared through the proposed sum-rate-optimal joint power and sub-channel allocation algorithms. The multi-cell scenario, essentially an interference channel, is also studied.
Then, new radio resources are investigated and the rest of the thesis focuses on a new paradigm of communications with user cooperation. Conventional MIMO point-to-point transmission exploits efficiently the spatial-domain resources, but it is never meant to be a solution for small devices, nor does it represent the full picture of the potential values in the wireless medium. User cooperation further takes advantage of the broadcasting nature of wireless transmissions and exploits the signal copies received by multiple users. In this thesis, there are three main results corresponding to the downlink, uplink and two-way cooperative communications. The first one tackles a fundamental bottleneck of cooperative transmissions for the downlink, the spectral loss due to splitting a timeslot into two halves for half-duplex relaying. System dynamics are exploited and resource allocation is investigated under the proposed new cooperation framework. The second one provides a new interpretation for coded cooperation in the uplink. A generalized cooperative concatenated coding framework is proposed. Unlike conventional schemes that focus only on cooperative spatial diversity, a novel joint-user coding technique is devised which can also enhance the code structure while requiring only limited degree of cooperation. Other practical issues such as erroneous inter-user channels and variable cooperation group are also taken into consideration. The third one studies the roles of binary and analog network coding on two-way relay-assisted wireless communications with equal-rate applications. The binary and analog versions are often associated with a three-step and two-step frameworks, respectively. While there is an increasing interest in the latter one, we demonstrate that the three-step framework may actually offer more potential benefits. A simple but efficient protocol is proposed which outperforms the schemes in the literature, and the outage regions of the schemes are theoretically characterized.
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