Long- Term Evolution (LTE) is standardized by the 3rd Generation Partnership Project (3GPP) to meet the customers' need of high data-rate mobile communications in the next 10 years and beyond. A popular technique, orthogonal frequency division multiple access (OFDMA), is employed in the LTE down link. However, the high peak- to-average ratio (PAPR) of OFDMA transmit signals leads to low power efficiency that is particular undesirable for power-limited mobile handsets. Single-carrier frequency division multiple access (SC-FDMA) is employed in the LTE uplink due to its inherent low-PAPR property, simple frequency domain equalization (FDE) and flexible resource allocation. Working within the physical (PHY) layer, this thesis focuses on decision- feedback equalization (DFE) and channel estimation for SC-FDMA systems. In this thesis, DFE is investigated to improve the equalization performance of SC- FDMA. Hybrid-DFE and iterative block decision-feedback equalization (IB-DFE) are considered. It is shown that hybrid-DFE is liable to error propagation, especially in channel-coded systems. IB-DFE is robust to error propagation due to the feedback (FB) reliability information. Since the FB reliability is the key to optimize the performance of IB-DFE, but is generally unknown at the receiver, FB reliability estimation techniques are presented. Furthermore, several transform-based channel estimation techniques are presented. Various filter design algorithms for discrete Fourier transform (DFT) based channel estimation are presented and a novel uniform-weighted filter design is derived. Also, channel estimation techniques based on different transforms are provided and a novel pre-interleaved DFT (PI-DFT) scheme is presented. It is shown that SC-FDMA employing the PI-DFT based channel estimator gives a close error rate performance to the optimal linear minimum mean square error (LMMSE) channel estimator but with a much lower complexity. In addition, a novel windowed DFT-based noise variance estimator that remains unbiased up to an SNR of 50dB is presented. Finally, pilot design and channel estimation schemes for uplink block-spread code division multiple access (BS-CDMA) are presented. It is demonstrated that the recently proposed bandwidth-efficient BS-CDMA system is a member of the SC-FDMA family. From the viewpoint of CDMA systems, novel pilot design and placement schemes are proposed and a channel tracking algorithm is provided. It is shown that the performance of the proposed schemes remain robust at a Doppler frequency of 500Hz, while the pilot block scheme specified in the LTE uplink fails to work in such a rapidly time-varying channel.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:551318 |
| Date | January 2011 |
| Creators | Huang, Gillian |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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