Cooperation and resource allocation in relay and multicarrier systems

Abstract

In modern wireless communications, various techniques have been developed in order to exploit the dynamics existing in wireless communications. Diversity has been recognized as one of the key techniques, which has the potential to significantly increase the capacity and reliability of
wireless communication systems. Relay communication with possible cooperation among some nodes is capable of achieving spacial diversity by forming a virtual antenna array for receiving and/or transmission. Dynamic resource allocation is capable of taking the advantages of the timevarying characteristics of wireless channels and wireless systems themselves, generating promising increase of energy- and spectrum-efficiency. This thesis focuses on the cooperation and resource allocation in relay and multicarrier systems, via which we motivate to design the low-complexity algorithms that are capable of achieving the spectrum-efficiency and reliability as high as possible.

First, we investigate and compare the error performance of a two-hop communication links (THCL) system with multiple relays, when distributed and cooperative relay processing schemes are respectively employed. Our main objectives include to find some general and relatively simple ways for error performance estimation, and to demonstrate the trade-off of using cooperative relay processing. The error performance of the THCL employing various relay processing schemes is investigated, with the emphasis on the cost of cooperation among relays. In order to analyze the error performance of the THCL systems novel approximation approaches, including two Nakagami approximation methods and one Gamma approximation method, are proposed. With the aid of these approximation approaches, a range of closed-form formulas for the error rate of the THCL systems are derived. Our studies show that cooperation among relays may consume a significant portion of system energy, which should not be ignored in design of cooperative systems.

Second, resource allocation, including both power- and subcarrier-allocation, is investigated in the context of the single-cell downlink orthogonal frequency division multiple-access (OFDMA)and multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) systems. Our resource allocation is motivated to maximize the system reliability without making a trade-off with the attainable spectrum-efficiency of the system, while demanding the complexity as low as possible. For the sake of achieving low-complexity in implementation, we carry out power- and subcarrierallocation separately in two stages, which has been proved without much performance loss. On this topic, we propose a range of subcarrier-allocation algorithms and study their performance with the OFDMA and MC DS-CDMA systems. In general, our proposed algorithms are designed either to avoid assigning users as many as possible the worst subchannels, or to assign users the best possible subchannels. Our studies show that all the proposed algorithms belong to the family of low-complexity subcarrier-allocation algorithms, and they outperform all the other reference suboptimal algorithms considered, in terms of both the error and spectrum-efficiency performance.
Furthermore, some of our proposed subcarrier-allocation algorithms are capable of achieving the performance close to that achieved by the optimum subcarrier-allocation algorithm.

Finally, based on our subcarrier-allocation algorithms, we investigate the resource allocation in multicell downlink OFDMA and MC DS-CDMA systems, with the emphasis on the mitigation of intercell interference (InterCI). Specifically, we extend the subcarrier-allocation algorithms
proposed in the single-cell systems to the multicell scenarios, in which each base station (BS) independently
carries out the subcarrier-allocation. After the subcarrier-allocation, then minimum BS cooperation is introduced to efficiently mitigate the InterCI. In the multicell downlink OFDMA systems, two novel InterCI mitigation algorithms are proposed, both of which are motivated to set up the space time block coding (STBC) aided cooperative transmissions to the users with poor signal-to-interference ratio (SIR). Our studies show that both the proposed algorithms can significantly increase the spectrum-efficiency of the multicell downlink OFDMA systems. In the multicell MC DS-CDMA systems, after the subcarrier-allocation, we propose two low-complexity code-allocation algorithms, which only require the BSs to share the large-scale fading, including
the propagation pathloss and shadowing effect. Our studies show that both the code-allocation algorithms are highly efficient, and they are capable of achieving significantly better error and spectrumefficiency performance than the random code-allocation (i.e., the case without code-allocation).

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Identifiers

ORCID for Lie-Liang Yang: orcid.org/0000-0002-2032-9327

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