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This dissertation, Cyclic Prefix in OFDM Systems by Zhiqiang, Chen, 陳志強, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Cyclic Prefix in OFDM systems Submitted by Chen ZhiQiang for the degree of Doctor of Philosophy at The University of Hong Kong in July 2007 Orthogonal frequency division multiplexing (OFDM) is an efficient multiplexing technology in wireless communications. A guard time, usually in the form of cyclic prefix (CP), is inserted between OFDM symbols to eliminate both the inter-symbol interference (ISI) and the inter-channel interference (ICI). The traditional one size fits all CP insertion method sets the CP length longer than the channel maximum excess delay. In contrast, one novel CP insertion method is proposed in this thesis which not only depends on the channel delay profile but also the signal-to-noise ratio (SNR). The numerical results show that the newly proposed CP length outperforms the traditional length in both bandwidth efficiency and power efficiency. Because the insertion of CP requires additional bandwidth to accommodate the redundancy, many algorithms have been proposed to decrease the CP length at the expense of the transceiver's complexity. The novel method of CP insertion, however, proposes to decrease the CP length without any increase in complexity. The scheme without CP insertion is also proposed for the system working at low SNR regime. Numerical results show that in such a system the scheme without CP insertion yields a significant bandwidth efficiency increase with a penalty of a trivial power efficiency decrease. While hybrid OFDM systems, which are the combinations of OFDM and other technologies such as code division multiple access (CDMA) and multiple-input multiple- output (MIMO) have been the subject of considerable research, the CP insertions in these systems have not been studied sufficiently. These issues are therefore intensively investigated in this thesis. Firstly, the CP insertion in the point-to-point multi-carrier CDMA (MC CDMA) system, which is the major form of the combination of OFDM and CDMA, is examined. The simulation results show that the optimum CP length decreases with the increase of the spreading gain. Secondly, for the MC CDMA cellular system, a novel CP insertion method based on maximizing the system effective data rate is proposed. It is concluded from the analytical numerical results that the insertion of CP has achieved no benefit and can be discarded. Thirdly, the pairwise error probability (PEP) performance is analyzed and derived for the space time coding OFDM (STC- OFDM) system with insufficient CP. Particularly, the bit error rate (BER) performance is derived for the Alamouti coding OFDM (Alamouti-OFDM) system. Both the analytical numerical results and the Monte Carlo simulation results show that the optimum CP length decreases as the number of receive antennae increases. Finally, the frame error rate (FER) performance is evaluated for the single-input multiple-output OFDM (SIMO- OFDM) system and MIMO-OFDM system. The simulation results reveal that the insertion of CP can be abandoned while the number of receive antennae is large. In all these situations the schemes without CP insertion require no increase in complexity. DOI: 10.5353/th_b3955833 Subjects: Interference (Sound)Orthogonal frequency division multiplexing

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