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

Superimposed training-based channel estimation and data detection for OFDM amplify-and-forward cooperative systems under high mobility

In this paper, joint channel estimation and data detection in orthogonal frequency division multiplexing (OFDM) amplify-and-forward (AF) cooperative systems under high mobility is investigated. Unlike previous works on cooperative systems in which a number of subcarriers are solely occupied by pilots, partial data-dependent superimposed training (PDDST) is considered here, thus preserving the spectral efficiency. First, a closed-form channel estimator is developed based on the least squares (LS) method with Tikhonov regularization and a corresponding data detection algorithm is proposed using the linear minimum mean square error (LMMSE) criterion. In the derived channel estimator, the unknown data is treated as part of the noise and the resulting data detection may not meet the required performance. To address this issue, an iterative method based on the variational inference approach is derived to improve performance. Simulation results show that the data detection performance of the proposed iterative algorithm initialized by the LMMSE data detector is close to the ideal case with perfect channel state information. © 2006 IEEE.published_or_final_versio

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

Efficient channel estimation algorithms for cooperative multiple-input multiple-output (MIMO) wireless communication networks

Multiple-input multiple-output (MIMO) relay communication systems have been identified to be one of the promising solutions to high rate wireless communications. In optimizing the MIMO relay networks, the knowledge of channel state information (CSI) is essential. This thesis develops novel channel estimation algorithms for MIMO relay communication networks, considering the amplify-and-forward relaying scheme. The proposed algorithms outperform existing schemes in estimating the CSI of each hop in MIMO relay networks

Channel Estimation in Half and Full Duplex Relays

abstract: Both two-way relays (TWR) and full-duplex (FD) radios are spectrally efficient, and their integration shows great potential to further improve the spectral efficiency, which offers a solution to the fifth generation wireless systems. High quality channel state information (CSI) are the key components for the implementation and the performance of the FD TWR system, making channel estimation in FD TWRs crucial. The impact of channel estimation on spectral efficiency in half-duplex multiple-input-multiple-output (MIMO) TWR systems is investigated. The trade-off between training and data energy is proposed. In the case that two sources are symmetric in power and number of antennas, a closed-form for the optimal ratio of data energy to total energy is derived. It can be shown that the achievable rate is a monotonically increasing function of the data length. The asymmetric case is discussed as well. Efficient and accurate training schemes for FD TWRs are essential for profiting from the inherent spectrally efficient structures of both FD and TWRs. A novel one-block training scheme with a maximum likelihood (ML) estimator is proposed to estimate the channels between the nodes and the residual self-interference (RSI) channel simultaneously. Baseline training schemes are also considered to compare with the one-block scheme. The Cramer-Rao bounds (CRBs) of the training schemes are derived and analyzed by using the asymptotic properties of Toeplitz matrices. The benefit of estimating the RSI channel is shown analytically in terms of Fisher information. To obtain fundamental and analytic results of how the RSI affects the spectral efficiency, one-way FD relay systems are studied. Optimal training design and ML channel estimation are proposed to estimate the RSI channel. The CRBs are derived and analyzed in closed-form so that the optimal training sequence can be found via minimizing the CRB. Extensions of the training scheme to frequency-selective channels and multiple relays are also presented. Simultaneously sensing and transmission in an FD cognitive radio system with MIMO is considered. The trade-off between the transmission rate and the detection accuracy is characterized by the sum-rate of the primary and the secondary users. Different beamforming and combining schemes are proposed and compared.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Adaptive relay techniques for OFDM-based cooperative communication systems

Cooperative communication has been considered as a cost-effective manner to exploit the spatial diversity, improve the quality-of-service and extend transmission coverage. However, there are many challenges faced by cooperative systems which use relays to forward signals to the destination, such as the accumulation of multipath channels, complex resource allocation with the bidirectional asymmetric traffic and reduction of transmission efficiency caused by additional relay overhead. In this thesis, we aim to address the above challenges of cooperative communications, and design the efficient relay systems. Starting with the channel accumulation problem in the amplify-and-forward relay system, we proposed two adaptive schemes for single/multiple-relay networks respectively. These schemes exploit an adaptive guard interval (GI) technique to cover the accumulated delay spread and enhance the transmission efficiency by limiting the overhead. The proposed GI scheme can be implemented without any extra control signal. Extending the adaptive GI scheme to multiple-relay systems, we propose a relay selection strategy which achieves the trade-off between the transmission reliability and overhead by considering both the channel gain and the accumulated delay spread. We then consider resource allocation problem in the two-way decode-and-forward relay system with asymmetric traffic loads. Two allocation algorithms are respectively investigated for time-division and frequency-division relay systems to maximize the end-to-end capacity of the two-way system under a capacity ratio constraint. For the frequency-division systems, a balanced end-to-end capacity is defined as the objective function which combines the requirements of maximizing the end-to-end capacity and achieving the capacity ratio. A suboptimal algorithm is proposed for the frequency-division systems which separates subcarrier allocation and time/power allocation. It can achieve the similar performance with the optimal one with reduced complexity. In order to further enhance the transmission reliability and maintaining low processing delay, we propose an equalize-and-forward (EF) relay scheme. The EF relay equalizes the channel between source and relay to eliminate the channel accumulation without signal regeneration. To reduce the processing time, an efficient parallel structure is applied in the EF relay. Numerical results show that the EF relay exhibits low outage probability at the same data rate as compared to AF and DF schemes