No description available.

No description available.

The use of coded modulations such as continuous phase modulation (CPM) can improve the power and bandwidth efficiency of digital communication links. The price paid for these gains is in increased receiver complexity. The power efficiency attainable with the highly redundant signal sets employed by coded modulations becomes limited by the ability of the receiver to achieve accurate carrier phase synchronisation. Power efficiency is assessed in terms of the bit error rate performance in white Gaussian noise. A new CPM detector called the partially coherent Viterbi algorithm (PCVA) is introduced which tries to preserve the power efficiency in the presence of mild phase perturbations. The detector employs the Viterbi algorithm with a new partially coherent decision metric. Carrier phase estimates are derived dynamically from the detector's own survivor paths. In the presence of phase jitter, the PCVA is superior to a Viterbi decision directed phase locked loop. The PCVA could be applied to the detection of modulation schemes other than CPM. An error analysis of the PCVA in the absence of phase jitter provides a new and more realistic way of assessing the relative merits of various CPM schemes. Unmerged error events have been found to occur when CPM is detected with carrier phase uncertainty. The carrier phase estimator pulls in the residual phase error in such cases. A reduced state Viterbi algorithm has been examined when using the partially coherent decision metric. Receiver complexity reduction is still possible even when the detector is not coherent. A method of acquiring the carrier frequency accurately from the received CPM signal is described. The other main research goal has been the development of a new low signal-to-noise ratio (SNR) error probability analysis for coherently detected CPM. CPM is designed for use on power limited channels, but the existing error probability analysis is only accurate at high SNR. The problem at low SNR is that several error events become significant, not just the one at minimum squared Euclidean distance. The new analysis considers many events and makes statistical allowance for their pairwise interaction. The probability of events intersecting and reclosing each other has not been analysed before. This work applies to maximum likelihood sequence detection on a memoryless channel in general. A new survey of CPM error performance is made and proves the existing minimum distance results to be often optimistic especially at low and intermediate signal-to-noise ratios. The new approximation is closer to the simulated error rates where these are available. The coherent error analysis involves some computation but it is still approximately three orders of magnitude faster than simulation.

No description available.

No description available.

No description available.

No description available.

The development of wireless communications has significantly changed people’s lifestyles in the last century. It can be shown that the use of multiple antennas, so called multiple-input multiple-output (MIMO) at both link ends can offer further improvement of spectral efficiency and link reliability of wireless systems, which has been studied in the past decade. With the maturity of theory, the practice ofMIMO technology has become feasible, though several problems still need to be solved especially at the receive end. The inadequate antenna spacing limited by the small dimension of the receive terminal causes the mutual coupling (MC) effect, which may degrade MIMO system performance. This thesis focuses on the performance improvement of compact MIMO terminals by introducing matching networks between the receive antenna array and the load terminations. The investigation spans from practical implementation to data analysis, and theoretical derivation to system performance optimisation. The contributions of this thesis are threefold. Firstly, three performance metrics signal correlation (SC), received power and capacity are well studied for compact MIMO terminals with matching networks. An overview of the existing methods to examine these metrics is presented. Especially for the received power, one proper approach is found and two methods are compared and unified analytically. The simulation results reveal that adding matching networks into compact MIMO terminals can significantly improve the system performance. However, SC and received power should be well balanced to achieve a good capacity performance. The second contribution describes the experimental measurement of the analytical SC and received power study of the first contribution. A set-up of two quarter-wavelength monopoles and a ground plane with various matching networks are measured and the system design is aided by two simulation tools SEMCAD and FEKO. The measured results agree well with the analytical prediction though discrepancies exist. The implementation confirms that relatively high total receive power and low SC of the compact array can be achieved by choosing proper load impedance in practice. It also indicates that the load impedance to optimise the received power is different from the one for MIMO capacity maximisation. Finally, inspired by the last finding of the second contribution, the optimal single-port matching (SPM) impedance for capacity maximisation in a two by two compact MIMO system is derived using an upper bound of the ergodic capacity for simplicity. A complete framework for MIMO systems with compact arrays at both link ends is deduced using Z-parameters for the analysis. A closed-form result for the optimal SPMimpedance in high signal-to-noise ratio (SNR) regime is given and proved to be the input impedance of the receive antennas. The optimal SPMnetworks outperform other matching networks for small antenna spacings with any SNR. Moreover, the system performance sensitivity of a two by two MIMO system with coupled half-wavelength dipoles and SPMnetworks is evaluated versus antenna spacing and dipole length. It shows that MIMO capacity is not sensitive to the optimal impedance mismatch with fixed antenna spacing and dipole lengths. However, the MIMO system is relatively sensitive to antenna structure mismatch with a precise optimal matching network. Overall, the optimal single-port match is a feasible technique to improve the performance of the compact MIMO systems.

Spatial modulation (SM) is a unique single-stream, multiple-input multiple-output (MIMO) transmission technique. Unlike traditional MIMO schemes, SM sends out signals through a single active antenna, and achieves multiplexing gains by encoding information bits into the index of the currently active antenna. In contrast to multi-stream MIMO systems, this particular characteristic offers great superiority in two main aspects. Firstly, SM completely avoids inter-channel interference. Secondly, SM requires a single radio-frequency chain, regardless of the number of antennas used, and therefore exhibits a significant energy saving. However, the property of a single active antenna challenges the channel estimation process for SM: the transmit antennas have to be activated sequentially for sending pilot signals. As a result, the time consumed in pilot transmission is proportional to the number of transmit antennas. However, this fact has so far been neglected in related research. Also, published research on SM has focused on point-to-point communications, and few have covered a network perspective. In this thesis, a comprehensive study is undertaken on SM systems in single-user, multi-user and multi-cell scenarios. As a unique three-dimensional modulation scheme, SM enables a trade-off between the size of the signal constellation diagram and the size of the spatial constellation diagram. In this thesis, an optimum transmit structure is proposed for SM to employ an adaptive scale of antennas against channel correlations. Unlike traditional antenna selection methods, this new approach is not sensitive to fast fading, due to the exploitation of statistical channel state information (CSI) instead of instant CSI. The proposed transmit structure is demonstrated to have a near-optimal performance against exhaustive search, while achieving very low computational complexity. In addition, three novel methods are developed to improve the channel estimation process for SM. A first method estimates the entire MIMO channel by sending pilot signals through only one of the transmit antennas, among which the channel correlation is exploited. In a similar way but focusing on the receiver, a second method can improve the estimation accuracy without increasing the pilot sequence length. A third method balances the transmission power between pilot and data to minimise the bit error rate. A framework of combined channel estimation is also proposed, in which the three methods are jointly applied. Furthermore, the antenna allocation in multi-user SM is studied, in order to explore multi-user diversity gains. A method that jointly manages transmit antennas and receive antennas for all co-channel users is proposed. The aim of this new method is to maximise the channel capacity for each user, and the fairness among users is taken into account. It is demonstrated that the proposed method significantly improves the performance of multi-user SM, especially when serving a large number of users. Finally, a novel cooperative scheme is proposed for SM in a multi-cell scenario. Based on the concept of coordinated multi-point transmission (CoMP), this scheme enables the coordinated users to swap the base station antennas pertaining to them. A three-tier cellular architecture is further developed to switch between CoMP and the cooperative scheme.

No description available.