This study analyses the delay-limited throughput performance of an uplink cellular relay network utilising hybrid automatic repeat request (HARQ) protocol in which one mobile station (MS) communicates with one base station (BS) with the aid of one amplify-and-forward relay station (RS). The authors’ analysis allows for a practical fading scenario where MS → RS and RS → BS channels undergo independent Rayleigh and Rician fading, respectively. Delay-limited throughput expressions for two HARQ protocols are derived, respectively, namely Repetition Time Diversity and Incremental Redundancy. Furthermore, the impact of different parameters on the achievable throughput, such as the maximum HARQ round number L, line-of-sight signal K, information rate R etc., is analysed. The authors’ analysis unveils that, for the presumed dual-hop cooperation model with the specified tolerable delay requirement and given channel condition, there exists an optimal information rate R* that achieves the maximum delay-limited throughput for the two HARQ protocols. Moreover, it is disclosed that, both HARQ protocols with the adaptive optimised information rate outperform the counterpart with the fixed information rate in low and moderate SNR regions, suggesting that an adaptive transmission scheme should be employed to achieve a better throughput performance.

Beyond 3G mobile networks will be data service centric. User equipment (UE) stays in the Connected State relatively long while supporting data services, so efficient power-saving mechanisms for the Connected State are becoming more significant in order to prolong battery life of a handset. Discontinuous reception (DRX) has been a dominant approach for power saving in the Idle State and Connected State. In this study, a novel counter-driven adaptive DRX (CDA-DRX) scheme is proposed and analysed. The CDA-DRX scheme is intended to present a generic and easy-to-implement algorithm to adaptively and autonomously adjust DRX cycle to keep up with changing user activity level. The scheme distinguishes itself from all other researches by minimising signalling overhead and easily balancing packet delivery latency and power consumption. Numerical analysis and system simulation showed that this scheme produces a better tuned DRX operation than the ones proposed in literature or suggested in the standards.

Channel estimation for single-input–multiple-output systems over doubly selective channel using superimposed training and discrete prolate spheroidal basis expansion model is considered. To remove the interference from unknown data, a two-step interference cancellation scheme is proposed, where in the first step, a first-order statistics-based estimator with cyclic mean removal before transmission is proposed. In this step, only interference components corresponding to cyclic mean of data sequence are removed, which avoids the conflict between total interference elimination and symbol recovery. In the second step, a low complexity iterative interference cancellation scheme is proposed to further improve estimation performance with detected symbols at the receiver's end. Simulation results show that the proposed iterative scheme has the symbol error rate (SER) performance slightly inferior to that of the partially-data-dependent approach but with less computational complexity and outperforms the data-dependent scheme in terms of SER as well as mean-square error over doubly selective channels.

Channel polarisation results are extended to the case of communications over parallel channels, where the channel state information is known to both the encoder and decoder. Given a set of parallel binary-input discrete memoryless channels (B-DMCs), by performing the channel polarising transformation over independent copies of these component channels, we obtain a second set of synthesised binary-input channels. Similar to the single-channel case, we prove that as the size of the transformation goes infinity, some of the resulting channels tend to completely noised, and the others tend to noise-free, where the fraction of the latter approaches the average symmetric capacity of the underlying component channels. For finite-length polar coding over parallel channels, performance is found to be relied heavily on the specific channel-mapping scheme. To avoid exhaustive searching, an empirically good scheme that is called equal-capacity partition channel mapping is proposed and numerical results show that the proposed scheme significantly outperforms random mapping. Further, utilising the above results, a polar coding method for arbitrary code length is proposed, which has potential applications in practical systems.

In recent years, the scheduling scheme of exploiting multiuser diversity gain has attracted much attention for the purpose of efficient spectrum utilisation. The authors consider the problem of analysing the quality of service in the scheduler extracting multiuser diversity gain. The authors use not only the channel state information but also the queue information in determining the optimal user to be scheduled. Through queuing analysis, the guaranteed rate, the average delay and the delay-bound violation probability can be calculated.

In this study, two relativity-based access strategies are proposed for frequency hopping system with cognitive ability (C-FH). Sensing module is added in the receiver to perform real-time measurement of channel states. The first access strategy is studied in consideration of partial relative FH pattern. The spectrum band is divided into several groups and each C-FH user can only jump over the channel group authorised by the active user. In the second access strategy, the C-FH user will adaptively choose an active user as the scheduler to apply for access. The application users may be rejected because of lack of resources or accepted to access the available channels in order of arranged sequence. The chosen scheduler will accept applications according to number of available channels and the spectrum resource will be shared in condition of being temporally correlated. With relativity-based strategies, FH patterns of users have the minimum Hamming correlation, even to zero. Markov chains are built to model the access processes. The performance analysis and the simulation results show that the relativity-based access strategy brings lower collision probability, higher bandwidth utilisation and higher normalised average throughput.

The bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in mobile multi-hop relaying (MMR) system is severely degraded by the effect of Doppler shift and the severity of this degradation increases with the number of hops traversed by the OFDM signal. In this study, the authors propose a method to mitigate the effect of Doppler shift in MMR system (such as the IEEE 802.16j system) using directional antennas. It is shown that the effect of the resulting inter-carrier interference (ICI) because of the phase noise generated by the Doppler shift over multi-hop relaying channels, can be reduced by employing directional antennas at both the mobile and relay stations. Consequently, the BER performance of MMR system is significantly enhanced. Analysis and simulation results show that the BER enhancements using the proposed approach are strongly related to the orientation and beamwidth of the directional antenna employed. As the antenna beamwidth is reduced, the BER enhancement increases for both the perpendicular and parallel antenna orientations, and comparing these two orientations, the parallel orientation case provides slightly better BER enhancements.

A combined analytical and simulation framework is presented for study of the link-layer protocol that is currently used to control the operation of Gb/s infrared links in optical-wireless-based personal communication systems. The analytical and simulation methods are utilised to evaluate protocol efficiency and demonstrate that protocol performance is strongly affected by physical layer parameters including the bit-error-rate and the link turnaround time. The networking parameters, such as the protocol window and frame size, that optimise the protocol operation against any given physical layer arrangement are also determined.

Direct-conversion-based wireless communication systems suffer from I/Q imbalances in the front-end analog processing. In this study, the authors investigate the impact of frequency-independent (FI) I/Q imbalance on the channel reciprocity of time-division-duplexing (TDD) multiple-input multiple-output (MIMO) systems over frequency flat-fading channels. Moreover, in order to compensate the channel non-reciprocity caused by FI I/Q imbalance, the authors propose two pre-compensation algorithms with and without I/Q imbalance parameters. The performance of the TDD MIMO system under study is evaluated in terms of downlink capacity and bit-error rate. Simulation results show that the proposed algorithms can effectively mitigate the negative effect of FI I/Q imbalance on the channel reciprocity.

This study presents an efficient location tracking algorithm to reduce the computational complexity of the conventional Kalman filtering algorithm. In the proposed location estimation and tracking approach, using the inherent message-passing nature of factor graphs, the data information is passed efficiently between the variable nodes and the factor nodes by taking weights based on the message reliability, thus simplifying implementation of the Bayesian filtering approach for location tracking. Numerical simulations and experimental results show that the proposed location tracking scheme not only can achieve the location accuracy close to that of the Kalman filtering scheme, but also has lower computational complexity with decoupling approach.

In uplink orthogonal frequency division multiple access (OFDMA) systems with carrier frequency offsets (CFOs), there always be a dilemma that high performance and low complexity cannot be obtained simultaneously. In this study, in order to achieve better trade-off between performance and complexity, the authors propose a grouped minimum mean squared error (G-MMSE)-based multi-stage interference cancellation (MIC) scheme. The first stage of the proposed scheme is a G-MMSE detector, where the signal is detected group by group using banks of partial MMSE filters. The signal group can be either user based or subcarrier based. Multiple novel interference cancellation (IC) units are serially concatenated with the G-MMSE detector. Reusing the filters in the G-MMSE detector significantly reduces the computational complexity in the subsequent IC units as shown by the complexity analysis. The performance of the proposed G-MMSE-MIC schemes are evaluated by theoretical analysis and simulation. The results show that the proposed schemes outperform other existing schemes with considerably low complexity.