Wavelet-based multi-carrier code division multiple access systems

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Channel estimation, synchronisation and contention resolution in wireless communication networks

In the past decade, the number of wireless communications users is increasing at an unprecedented rate. However, limited radio resources must accommodate the increasing number of users. Hence, the efficient use of radio spectrum is a critical issue that needs to be addressed. In order to improve the spectral efficiency for the wireless communication networks, we investigate two promising technologies, the relaying and the multiple access schemes. In the physical (PHY) layer of the open systems interconnect (OSI) model, the relaying schemes are capable to improve the transmission reliability and expand transmission coverage via cooperative communications by using relay nodes. Hence, the two-way relay network (TWRN), a cooperative communications network, is investigated in the first part of the thesis. In the media access control (MAC) layer of the OSI model, the multiple access schemes are able to schedule multiple transmissions by efficiently allocating limited radio resources. As a result, the contention-based multiple access schemes for contention resolution are explored in the second part of the thesis. In the first part of the thesis, the channel estimation for the two-way relay networks (TWRNs) is investigated. Firstly, the channel estimation issue is considered under the assumption of the perfect synchronisation. Then, the channel estimation is conducted, by relaxing the assumption of perfect synchronisation. Another challenge facing the wireless communication systems is the contention and interference due to multiple transmissions from multiple nodes, sharing the common communication medium. To improve the spectral efficiency in the media access control layer, a self-adaptive backoff (SAB) algorithm is proposed to resolve contention in the contention-based multiple access networks

Channel estimation, synchronisation and contention resolution in wireless communication networks

In the past decade, the number of wireless communications users is increasing at an unprecedented rate. However, limited radio resources must accommodate the increasing number of users. Hence, the efficient use of radio spectrum is a critical issue that needs to be addressed. In order to improve the spectral efficiency for the wireless communication networks, we investigate two promising technologies, the relaying and the multiple access schemes. In the physical (PHY) layer of the open systems interconnect (OSI) model, the relaying schemes are capable to improve the transmission reliability and expand transmission coverage via cooperative communications by using relay nodes. Hence, the two-way relay network (TWRN), a cooperative communications network, is investigated in the first part of the thesis. In the media access control (MAC) layer of the OSI model, the multiple access schemes are able to schedule multiple transmissions by efficiently allocating limited radio resources. As a result, the contention-based multiple access schemes for contention resolution are explored in the second part of the thesis. In the first part of the thesis, the channel estimation for the two-way relay networks (TWRNs) is investigated. Firstly, the channel estimation issue is considered under the assumption of the perfect synchronisation. Then, the channel estimation is conducted, by relaxing the assumption of perfect synchronisation. Another challenge facing the wireless communication systems is the contention and interference due to multiple transmissions from multiple nodes, sharing the common communication medium. To improve the spectral efficiency in the media access control layer, a self-adaptive backoff (SAB) algorithm is proposed to resolve contention in the contention-based multiple access networks

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

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Communication and Jamming BDA of OFDMA communication systems using the software defined radio platform WARP

The aim of this research is to demonstrate and evaluate the ability to eavesdrop and interfere with orthogonal frequency division multiple access-down link (OFDMA-DL) signal features utilising Wireless Open Access Research Platform (WARP) boards. The OFDMA-DL waveforms have been developed with 64 sub carriers and have guards and pilots as comparable to the 802.11a WiFi standard. An eavesdropper/interferer (ExJx) is used to estimate signal features, remotely gaining intelligence without alerting the communication system. This research also demonstrates how estimated signal features can be used to interfere with an established communication system. Methods used to perform the signal feature estimation exploit the cyclostationary nature of the OFDMA-DL waveform, with higher order cumulants utilised to classify modulation schemes. To assess the ability of the ExJx system to eavesdrop (Ex), Communication Battle Damage Assessment (CBDA) techniques are used. To assess the ability of the ExJx system to interfere (Jx), Jamming Battle Damage Assessment (JBDA) techniques are used

Multiuser MIMO-OFDM for Next-Generation Wireless Systems

This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems