Joint Detection and Decoding of High-Order Modulation Schemes for CDMA and OFDM Wireless Communications

Wireless communications call for high data rate, power and bandwidth efficient transmissions. High-order modulation schemes are suitable candidates for this purpose as the potential to reduce the symbol period is often limited by the multipath-induced intersymbol interference. In order to reduce the power consumption, and at the same time, to estimate time-variant wireless channels, we propose low-complexity, joint detection and decoding schemes for high-order modulation signals in this dissertation. We start with the iterative demodulation and decoding of high-order CPM signals for mobile communications. A low complexity, pilot symbol-assisted coherent modulation scheme is proposed that can significantly improve the bit error rate performance by efficiently exploiting the inherent memory structure of the CPM modulation. A noncoherent scheme based on multiple symbol differential detection is also proposed and the performances of the two schemes are simulated and compared. Second, two iterative demodulation and decoding schemes are proposed for quadrature amplitude modulated signals in flat fading channels. Both of them make use of the iterative channel estimation based on the data signal reconstructed from decoder output. The difference is that one of them has a threshold controller that only allows the data reconstructed with high reliability values to be used for iterative channel estimation, while the other one directly uses all reconstructed data. As the second scheme has much lower complexity with a performance similar to the best of the first one, we further apply it to the space-time coded CDMA Rake receiver in frequency-selective multipath channels. We will compare it to the pilot-aided demodulation scheme that uses a dedicated pilot signal for channel estimation. In the third part of the dissertation, we design anti-jamming multicarrier communication systems. Two types of jamming signals are considered - the partial-band tone jamming and the partial-time pulse jamming. We propose various iterative schemes to detect, estimate, and cancel the jamming signal in both AWGN and fading channels. Simulation results demonstrate that the proposed systems can provide reliable communications over a wide range of jamming-to-signal power ratios. Last, we study the problem of maximizing the throughput of a cellular multicarrier communication network with transmit or receive diversity. The total throughput of the network is maximized subject to power constraints on each mobile. We first extend the distributed water-pouring power control algorithm from single transmit and receive antenna to multiple transmit and receive antennas. Both equal power diversity and selective diversity are considered. We also propose a centralized power control algorithm based on the active set strategy and the gradient projection method. The performances of the two algorithms are assessed with simulation and compared with the equal power allocation algorithm

Orthogonal multicarrier modulation for high-rates mobile and wireless communications

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN037085 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Wavelet-based multi-carrier code division multiple access systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Time-Frequency Jammer excision for Multi-carrier spread spectrum using adaptive filtering

The development of new wireless technologies, the improvement of existing ones and thereduction on the wireless devices prices is increasing the number of users, the demand forbandwidth and the demand for higher data rates. The spread of the technology howeverbring some drawbacks. One is the increasing interference level that can degrades the wirelesscommunications. Many different techniques are used to minimize the interference and theeffect of the channel (multipath, Doppler etc) in a wireless channel. This thesis considers thefrequency and time processing of a jammer affected multi-carrier spread spectrum (MC-SS)system. A linear chirp is used as a spreading sequence. Such a sequence not only providesa constant envelope, but also allows the estimation of the channel parameters using a lineartime-invariant model. Hence time-delays and Doppler frequency shifts can be representedby effective time shifts. The discrete evolutionary transform (DET) time-frequency repre-sentation is used for estimating the channel characteristics and for detecting jammers. Oncethe jammers are detected, the original spreading function corresponding to the jammed fre-quency is adapted to minimize the jammer effects. The bit detection is then performed usinga least mean square (LMS) adaptive filter and it is done in both time- and frequency-domain.To illustrate the performance of the method, simulations with different signal to noise ratios,different jammer to signal ratios and different Doppler shifts were performed. The resultsindicate that the method is capable of excising the jammers providing a good bit error ratein low Doppler situations

Doctor of Philosophy

dissertationWireless communications pervade all avenues of modern life. The rapid expansion of wireless services has increased the need for transmission schemes that are more spectrally efficient. Dynamic spectrum access (DSA) systems attempt to address this need by building a network where the spectrum is used opportunistically by all users based on local and regional measurements of its availability. One of the principal requirements in DSA systems is to initialize and maintain a control channel to link the nodes together. This should be done even before a complete spectral usage map is available. Additionally, with more users accessing the spectrum, it is important to maintain a stable link in the presence of significant interference in emergency first-responders, rescue, and defense applications. In this thesis, a new multicarrier spread spectrum (MC-SS) technique based on filter banks is presented. The new technique is called filter bank multicarrier spread spectrum (FB-MC-SS). A detailed theory of the underlying properties of this signal are given, with emphasis on the properties that lend themselves to synchronization at the receiver. Proposed algorithms for synchronization, channel estimation, and detection are implemented on a software-defined radio platform to complete an FB-MC-SS transceiver and to prove the practicality of the technique. FB-MC-SS is shown through physical experimentation to be significantly more robust to partial band interference compared to direct sequence spread spectrum. With a higher power interfering signal occupying 90% of its band, FB-MC-SS maintains a low bit error rate. Under the same interference conditions, DS-SS fails completely. This experimentation leads to a theoretical analysis that shows in a frequency selective channel with additive white noise, the FB-MC-SS system has performance that equals that obtained by a DS-SS system employing an optimal rake receiver. This thesis contains a detailed chapter on implementation and design, including lessons learned while prototyping the system. This is to assist future system designers to quickly gain proficiency in further development of this technology

Robust multicarrier spread spectrum technique for data transmission over partially jammed channels

Journal ArticleMulticarrier spread spectrum (MC-SS) is an altemative to the conventional spread spectrum (SS) techniques that behaves significantly better when the system is subject to narrow- or partial-band interference. However; successful implementation of the optimum detector requires knowledge of noise and interference valiance in each subcarrier band. In this correspondence, we propose a suboptimal detector for MC-SS that keeps the sign GCant gain of MC-SS over the conventional SS, with a relatively low loss compared to the optimum MC-SS detector. Theoretical analysis and computer simulations that corroborate the theory are presented

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions

On the theoretical aspects of multi-carrier spread spectrum systems.

by Tsan-Fai Ho.Thesis (M.Phil.)--Chinese University of Hong Kong, 1996.Includes bibliographical references (leaves 64-68).Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Review on spread spectrum communications --- p.1Chapter 1.2 --- The spread spectrum techniques --- p.2Chapter 1.2.1 --- Direct Sequence (DS) Systems --- p.2Chapter 1.2.2 --- Frequency Hopping (FH) Systems --- p.2Chapter 1.2.3 --- Time Hopping (TH) Systems --- p.4Chapter 1.2.4 --- Hybrid Systems --- p.4Chapter 1.3 --- Existing Applications of the spread spectrum systems --- p.5Chapter 1.4 --- Organization of the thesis --- p.6Chapter 2 --- The Concept of Duality --- p.7Chapter 2.1 --- Multi-Carrier Systems - An Overview --- p.7Chapter 2.2 --- Orthogonal Frequency Division Multiplexing --- p.8Chapter 2.2.1 --- Bandwidth Efficiency --- p.9Chapter 2.2.2 --- Spectral Efficiency --- p.10Chapter 2.2.3 --- Effects of fading --- p.11Chapter 2.3 --- Applications of OFDM in multiple access --- p.13Chapter 2.3.1 --- ST-CDMA --- p.13Chapter 2.3.2 --- MC-DS-CDMA --- p.14Chapter 2.3.3 --- OFDM-CDMA --- p.15Chapter 2.4 --- Duality - Time-Frequency Interrelation --- p.16Chapter 3 --- Performance of Multi-Carrier CDMA System --- p.17Chapter 3.1 --- System Model --- p.17Chapter 3.2 --- Performance Analysis --- p.20Chapter 3.2.1 --- Gaussian Channel --- p.20Chapter 3.2.2 --- Fading Channel --- p.24Chapter 3.3 --- Performance with Pulse Shape --- p.33Chapter 3.4 --- Appendix --- p.34Chapter 4 --- Signal Design Criteria for MC-CDMA System --- p.36Chapter 4.1 --- Existence of Signal Distortion --- p.37Chapter 4.2 --- Measures of the Signal Envelope Fluctuation --- p.38Chapter 4.3 --- Complementary Sequences --- p.41Chapter 4.4 --- Crest Factors --- p.42Chapter 4.4.1 --- Time-limited Pulse --- p.43Chapter 4.4.2 --- Ideally Band-Limited Pulses --- p.43Chapter 4.4.3 --- Shaped Pulses --- p.45Chapter 4.5 --- Spectrally Efficient Complementary (SEC) Sequences --- p.48Chapter 4.6 --- Construction of Spectrally Efficient Complementary(SEC) Sequences --- p.50Chapter 4.7 --- Generalized Multiphase Spectrally Efficient Complementary Sequences --- p.55Chapter 5 --- Summary and Future Extensions --- p.58Chapter 5.1 --- Summary of the Results --- p.58Chapter 5.2 --- Topics for Future Research --- p.59AppendixChapter A --- Exhaustive search of MPSEC sequences --- p.61Chapter B --- Papers derived from this thesis --- p.63Bibliography --- p.6