Wireless communications, as one of the most popular technologies in the past several decades, has undergone evolutional changes and brought forth its magic power in improving the human life. Currently, the 3^rd Generation Partnership Project Long Term Evolution (3GPP LTE) is considered as a prominent path to the next generation of cellular systems. The key objective is to develop a framework towards a high-data-rate, low-latency, and packet-optimized radio access technology. To this end, single carrier frequency division multiple access (SC-FDMA) has been recently accepted as the uplink multiple access scheme in the 3GPP LTE for its lower peak-to-average power ratio (PAPR), when compared with orthogonal frequency division multiple access (OFDMA)....[ Read more ]

Wireless communications, as one of the most popular technologies in the past several decades, has undergone evolutional changes and brought forth its magic power in improving the human life. Currently, the 3^rd Generation Partnership Project Long Term Evolution (3GPP LTE) is considered as a prominent path to the next generation of cellular systems. The key objective is to develop a framework towards a high-data-rate, low-latency, and packet-optimized radio access technology. To this end, single carrier frequency division multiple access (SC-FDMA) has been recently accepted as the uplink multiple access scheme in the 3GPP LTE for its lower peak-to-average power ratio (PAPR), when compared with orthogonal frequency division multiple access (OFDMA).

In the first part of the thesis, we show that carrier frequency offsets (CFOs) in SC-FDMA systems destroy the sub-band orthogonality. This results in multiuser interference (MUI) and leads to the system performance degradation. We then propose a combined minimum mean square error frequency-domain equalization (MMSE-FDE) and interference cancellation scheme to mitigate the effect of CFOs for SC-FDMA systems. In this scheme, joint FDLE (linear FDE) with CFO compensation (JFC) is utilized to obtain an initial estimation of the transmitting sequence. To further eliminate the MUI, we combine JFC with parallel interference cancellation (JFC-PIC) in an iterative signal processing procedure. In each iteration, estimations of the desired symbols fed back from the previous iteration stage are used to regenerate the MUI component for PIC. The remaining MUI can be further suppressed in the FDLE block whose coefficients are updated by only considering the mean square error (MSE) in the previous iteration stage. Both SINR analysis and simulation results show that the proposed scheme can achieve significant performance improvement over the conventional CFO compensation schemes.

Although it is generally known that SC-FDMA signal has lower PAPR than OFDMA because of its inherent single carrier structure, which benefits the mobile terminal in terms of transmit power efficiency and manufacturing cost in the uplink communications. However, the peak-power-average ratio (PAPR) is still a problem, especially for the localized subcarrier allocation (SC-LFDMA). Block coding is a promising approach that can reduce the peak power. However, to construct the codewords is a nondeterministic polynomial-time hard (NP-hard) problem, for which there is no known algorithm that can find the optimal solution within polynomial-time. In the second part of the thesis, we will first formulate the PAPR reduction by block coding as a combinatorial problem, and then propose a semidefinite relaxation approach that can relax the problem which can then be solved in polynomial time. We consider the problem for different modulation schemes, where different relaxation techniques are applied. To avoid an increase of the relative mean transmit power, we shall consider an additional constraint. It is shown that the proposed scheme can efficiently reduce the peak power. Also we will show that there is a tradeoff between the transmit power increase and the peak power reduction, where less stringent power constraint corresponds to better PAPR reduction.