The explosive growth of connected devices and the increasing number of broadband users have led to an unprecedented growth in traffic demand. To this effect, the next generation wireless systems are envisioned to meet this growth and offer a potential data rate of 10 Gbps or more. In this context, an attractive solution to the current spectrum crunch issue is to exploit the visible light spectrum for the realization of high-speed commutation systems. However, this requires solutions to certain challenges relating to visible light communications (VLC), such as the stringent requirements of VLC-based intensity modulation and direct detection (IM/DD), which require signals to be real and unipolar. The present work proposes a novel power-domain multiplexing based optical asymmetric modulation (OAM) scheme for indoor VLC systems, which is particularly adapted to transmit high-order modulation signals using linear real and unipolar constellations that fit into the restrictions of IM/DD systems. It is shown that the proposed scheme provides improved system performance that outperforms alternative modulation schemes, at no extra complexity.

In-phase/quadrature-phase Imbalance (IQI) is considered a major performance-limiting impairment in direct-conversion transceivers. Its effects become even more pronounced at higher carrier frequencies such as the millimeter-wave frequency bands considered for 5G systems. In this work, we quantify the effects of IQI on the performance of different modulations under multipath fading channels. This is realized by developing a comprehensive framework for the symbol error rate (SER) analysis of coherent phase shift keying (PSK), noncoherent differential phase shift keying (DPSK) and noncoherent frequency shift keying (FSK) under IQI effects. In this context, the moment generating function of the signal-to-interference-plus-noise-ratio is first derived for single-carrier systems suffering from transmitter (TX) IQI only, receiver (RX) IQI only and joint TX/RX IQI. Capitalizing on this, we derive analytic expressions for the SER of the different modulation schemes considered. These expressions are corroborated with simulation results and they provide insights into the dependence of IQI on the system parameters. We further demonstrate that, while in some cases, IQI can cause a slight degradation of the SER performance and, hence, it can be neglected, in other cases it should be compensated in order to achieve a reliable communication link.

Non-orthogonal multiple access (NOMA) has been recently proposed as a viable technology that has the potential to improve the spectral efficiency of fifth generation (5G) wireless networks and beyond. However, in practical communication scenarios, transceiver architectures inevitably suffer from radio-frequency (RF) front-end related impairments that can lead to non-negligible degradation of the overall system performance. In this context, in-phase/quadrature-phase imbalance (IQI) constitutes a major impairment in direct-conversion transceivers. Based on this, the present contribution quantifies the effects of IQI on the performance of NOMA based systems under multipath fading conditions. This is realized by first deriving novel analytic expressions for the signal-to-interference-plus-noise ratio and the outage probability of NOMA systems subject to IQI at the transmitter and/or the receiver sites. Capitalizing on these results, we demonstrate that the effects of IQI differ considerably between the different NOMA users and depending on the considered system's parameters.

Visible light communication (VLC) systems are expected to provide remarkably high speed indoor communications and effective ubiquitous connectivity. However, the key limitation of such systems is the narrow modulation bandwidth of the light sources. Based on this, non-orthogonal multiple access (NOMA) has been recently proposed as an effective method that can enhance considerably the spectral efficiency of indoor downlink VLC systems. In this context, the present work is devoted to the evaluation of the bit-error-rate (BER) performance of NOMA-based VLC systems. Specifically, a novel closed-form expression is first derived for the BER of the considered set up, by also taking into account the realistically incurred cancellation errors and interference terms. The validity of the derived expressions is verified through extensive comparisons with respective results from Monte Carlo simulations, while their algebraic representation is relatively simple, which renders them convenient to handle both analytically and numerically. This leads to meaningful insights on the behavior and performance gains achieved, thanks to the adoption of NOMA, which are particularly useful in future design and deployment of VLC systems.

Coherent detection requires exact knowledge of the channel state information, which is often a challenging task in demanding practical applications. Based on this, non-coherent detection of differentially modulated signals can be considered as an alternative method. The present paper investigates the effects of in-phase/quadrature-phase imbalance (IQI), which are known to degrade the performance of wireless communication systems. Specifically, we evaluate the effects of IQI on the bit error rate (BER) performance of differential quadrature phase shift keying (dQPSK) for ideal receiver (RX) with transmitter (TX) IQI, ideal TX with RX IQI and joint TX/RX IQI. Explicit analytic expressions are derived for the BER of both single-carrier and multi-carrier systems suffering from IQI at the TX and/or RX. Extensive Monte-Carlo simulation as well as offered analytic results show that realistic TX/RX IQI values can degrade the corresponding BER by over 30%. Likewise, it is shown that the detrimental effects of IQI are more considerable on DQPSK than on QPSK.

Visible light communication (VLC) has been proposed as a promising and efficient solution to indoor ubiquitous broadband connectivity. In this paper, non-orthogonal multiple access, which has been recently introduced as an effective scheme for fifth generation (5G) wireless networks, is considered in the context of VLC systems under different channel uncertainty models. To this end, we first derive a novel closed-form expression for the bit-error-rate (BER) under perfect channel state information (CSI). Capitalizing on this, we then quantify the effect of noisy and outdated CSI by deriving a simple and accurate approximation for the former and a tight upper bound for the latter. The offered results are corroborated by respective results from extensive Monte Carlo simulations and assist in developing useful insights on the effect of imperfect CSI knowledge on the overall system performance. Furthermore, it was shown that while noisy CSI leads to slight degradation in the BER performance, outdated CSI can cause considerable performance degradation, if the order of the users' channel gains change due to the involved mobility.

We present a new multiple input multiple output (MIMO) technique, based on Walsh Hadamard Transform (WHT) precoding, to improve the robustness of space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems. The WHT is applied to the data symbols prior the Alamouti encoder at the transmitter and to the output of the Alamouti decoder at the receiver. The computational complexity of the proposed system is evaluated in terms of complex additions and multiplications where the numerical results show that the proposed system has a lower complexity as compared to other precoded OFDM systems. Moreover, the proposed system is highly robust to the channel time and frequency selectivity as compared to conventional SFBC, space time block coded (STBC) and other precoded OFDM systems.

High speed transmission of information suffers inevitably by intersymbol interference (ISI) induced by multipath propagation over frequency selective channels. ISI has been a major obstacle preventing the successful implementation of physical layer network coding (PLNC) systems in these environments. Another major obstacle is the high computational complexity of existing algorithms dealing with ISI, which is a determining factor in the design of relay nodes. In this paper, we propose a novel and computationally efficient decision feedback equalizer structure that is utilized at the end node and in conjunction with a simple amplify and forward (AF) technique employed at the relay. We derive the optimal equations for the decision feedback equalizer (DFE) coefficients and evaluate the end-to-end bit error rate performance in frequency selective channels, and provide both analytical and numerical simulation results that demonstrate the feasibility of the proposed approach under realistic channel conditions. The obtained results show that E2E performance is dominated by the channel with most severe frequency selectivity.

Novel analytic solutions are derived for integrals that involve the generalized Marcum Q-function, exponential functions and arbitrary powers. Simple closed-form expressions are also derived for specific cases of the generic integrals. The offered expressions are both convenient and versatile, which is particularly useful in applications relating to natural sciences and engineering, including wireless communications and signal processing. To this end, they are employed in the derivation of the average probability of detection in energy detection of unknown signals over multipath fading channels as well as of the channel capacity with fixed rate and channel inversion in the case of correlated multipath fading and switched diversity.

Energy harvesting has been recognized as a key technique for improving the performance of energy constrained networks. In this paper, the application of wireless information and power transfer, an emerging concept of energy harvesting, to wireless cooperative networks is considered. Particularly the focus is on a cooperative network in which a source communicates with a destination with the help of relays and the relays are randomly deployed according to homogeneous Poisson point process. According to the available channel state information, three different strategies to use the available relays are studied, and their impact on the outage probability and diversity gain is characterized by applying stochastic geometry. Particularly the developed analytical results demonstrate that the use of energy harvesting relays does not degrade the achievable diversity gain of cooperative protocols, but has a deteriorating effect on the outage performance. Simulation results are provided to confirm the accuracy of the developed analytical results and facilitate a better performance comparison.

In this paper, a new receiver structure is proposed for uplink interleaved division multiple access (IDMA) on multipath fading channels. In a conventional IDMA rake detector, jointly removing inter symbol interference (ISI) and multiple access interference (MAI) is achieved by exchanging extrinsic log-likelihood ratio (LLR) chips between an elementary signal estimator (ESE) and a posteriori probability decoders (DEC)s in a turbo-like manner. The same exchanging principle takes place between a centralized decision feedback equalizer (CDFE) and the DECs in CDFE-IDMA systems. However, the proposed IDMA receiver can be considered a mixture between the two mentioned receivers as it employs an adaptive DFE for each user to remove the ISI effects while MAI is eliminated by a parallel interference canceller (PIC). The PIC utilizes the same ESE principles in removing MAI effects from received symbols which is more efficient than cross-over filters in a CDFE-IDMA system. Moreover, the ISI abstraction in DFE is more active in removing ISI than ESE. Simulation results demonstrate the superiority of DFE-IDMA over the other systems' performances found in the literature for both optimal and adaptive algorithms (AA).

A new cost efficient automated planning and optimization method is proposed for OFDMA future-generation cellular networks targeting throughput maximization. The mathematical formulation is a non-linear multi-objective optimization problem subject to minimum interference, cost and similar resource constraints at each cell within a defined heterogeneous traffic environment. The fundamental objective is to maximize the individual cell throughput without deteriorating it over other cells, which results in a throughput equilibrium maximization over multiple cells. This implicitly implies traffic and co-channel interference congestion avoidance across the network whilst maintaining both cost efficiency and quality of service (QoS) policies. Optimal solution existence is subject to the network size, traffic and computational complexity constraints which converges to a throughput equilibrium or alternatively to the well known Nash Equilibrium (NE).

In this paper, the application of wireless information and power transfer to cooperative networks is investigated, where the relays in the network are randomly located and based on the decode-forward strategy. For the scenario with one source-destination pair, three different strategies for using the available relays are studied, and their impact on the outage probability and diversity gain is characterized by applying stochastic geometry. By using the assumptions that the path loss exponent is two and that the relay-destination distances are much larger than the source-relay distances, closed form analytical results can be developed to demonstrate that the use of energy harvesting relays can achieve the same diversity gain as the case with conventional self-powered relays. For the scenario with multiple sources, the relays can be viewed as a type of scarce resource, where the sources compete with each other to get help from the relays. Such a competition is modeled as a coalition formation game, and two distributed game theoretic algorithms are developed based on different payoff functions. Simulation results are provided to confirm the accuracy of the developed analytical results and facilitate a better performance comparison.

In this work, a new low complexity linear precoded orthogonal frequency division multiplexing (LP-OFDM) system, called Haar-OFDM (H-OFDM), is proposed. The proposed system employs a fast precoder, denoted as inverse D-precoder (IDP), which is derived by merging the operations of the fast Haar precoder (FHP) and inverse fast Fourier transform (IFFT) as one transform. Interestingly, the number of arithmetic operations required by the H-OFDM system are noticeably smaller than the conventional OFDM. Furthermore, extensive simulation results demonstrate that the H-OFDM system is robust against the frequency-selectivity of the channel.

Throughput maximization is generally the major objective when allocating resources in orthogonal frequency division multiple access (OFDMA)networks. Traditionally, dynamic allocation methods were developed to exploit multi-user diversity in these networks. These techniques achieved significant gain in throughput by adopting relaxed convex models to define system upper bound capacity. Frequency diversity, on the other hand, is only considered to a certain extent in order to meet user service constraints. The vast majority of existing research relies on these techniques. Separately, research considering combining frequency diversity and multi-user diversity in full has been scarce. The results of our research in this paper show that using this dual diversity combining can substantially maximize system capacity and resource efficiency, and minimize outage probability whilst users' quality of service (QoS) demands are maintained.

In this letter, a Sum-Product algorithm (SPA) utilizing soft distances is shown to be more resilient to impulsive noise than conventional likelihood-based SPAs, when the noise distribution is unknown. An efficient version of the soft distance SPA is also developed but with half the storage requirements and running time.

In this work, a new technique for mitigating the impulsive noise impact on the orthogonal frequency division multiplexing (OFDM) system is proposed, and its performance is compared with a previously published technique (referred to as time-domain interleaving (TDI) technique). In the TDI technique, the samples contaminated by impulsive noise are spread in timedomain over N OFDM symbols by using an interleaver after the inverse fast Fourier transform (IFFT) process. Accordingly, the effect of the impulsive noise burst will be averaged over N OFDM symbols, which reduces the impact on the bit error rate (BER) considerably. However, to achieve the same goal, the proposed system is using an additional orthogonal transform in form of an IFFT at the output of the interleaver. In general, the two techniques have shown a superior improvement in BER performance compared to that of the standard OFDM system, which suffers from error floors at high values of signal to noise ratio (SNR). However, for quadrature phase shift keying (QPSK) modulation with low signal to impulsive noise ratio (SIR), the proposed technique outperforms the TDI technique for different impulsive noise distributions. For high modulation order 16 and 64 quadrature amplitude modulation (QAM) in severe impulsive noise channels, the proposed technique demonstrates more robustness than the TDI, which suffers from error floors for the considered values of SIR and impulsive noise distributions.

Due to the nonlinear characteristics of the high power amplifier (HPA), the employment of orthogonal frequency division multiplexing (OFDM) based modulation schemes results in significant amplitude and phase signal distortion due to the high peak-to-average power ratio (PAPR) nature of the OFDM. To overcome this problem, PAPR reduction methods are commonly applied at the transmitter. Among the plenitude of methods available, partial transmit sequences (PTS) and selected mapping (SLM) are the most powerful schemes. The computational complexity for these schemes is considered as the main disadvantage. In this paper, we propose a low-complexity scheme based on iterative PTS (IPTS) that employs two inverse fast Fourier transforms (IFFT) and two circulant transform matrices. Numerical results demonstrate that the proposed scheme using a partition vector for IPTS with an odd number of ones can achieve both a reduction in PAPR of approximately 2 dB and an improvement of 1.4 dB in terms of signal-to-noise ratio (SNR) to achieve a bit error rate (BER) of 10-4. A further simplification can be achieved by omitting one of the circulant transform matrices in order to improve the computational complexity reduction ratio (CCRR) by 30% and reduce the number of side information bits by 1-bit compared with the IPTS, however, at the cost of a small reduction in PAPR and BER performance.

In this work, an elegant interleaving process is used not only to mitigate the impact of bursty impulsive noise on the performance of orthogonal frequency division multiplexing (OFDM) systems but also to break bursty multipath fading channel errors. While, conventional OFDM systems implement the interleaving process in the frequency domain, the system proposed here uses a block interleaver of size N2samples in the time domain. As a result, time diversity has been exploited through the use of the interleaver by spreading the samples contaminated by impulsive noise over the impulse-free OFDM symbols and breaking the correlated behaviour of the multipath fading channel. Nevertheless, the results, given in this work, have shown that the performance of the proposed system depends on the kind of equalization process used. A serious degradation in the performance is noticed when zero forcing (ZF) equalizer is utilized. However, a simple and low complexity solution to improve the ZF equalizer performance is also proposed. On the other hand, utilizing a minimum mean square error (MMSE) equalizer demonstrates better performance than the ZF equalizer. The simulation results have confirmed the validity of the proposed system over different scenarios of the channels considered in this work.

In this paper, a new network planning framework is proposed for orthogonal frequency-division multiple access (OFDMA) cellular systems based on co-channel interference and traffic congestion avoidance. The network planning is formulated as a non-linear multi-objective optimization problem subject to minimum interference and related resource constraints at each cell under heterogeneous traffic. The multi-objective problem is represented by the throughput maximization of each single cell without penalizing the remaining cells, which results in a throughput equilibrium over the whole network. The fundamental objective is to maximize the throughput balance and, hence, traffic and co-channel interference congestions are avoided across the network. In order to maximize the equilibrium, the optimization problem is decomposed into a positioning problem and a resource allocation problem, which are solved by parallel heuristics and convex optimization. Additionally, a novel rotated polarization assignment method is proposed to minimize further the effect of the co-channel interference.

In this paper, we develop a general transmission scheme for bi-directional communications by using eigenmode sharing, where existing two-way relaying protocols can be viewed as a special case of the proposed transmission scheme. In addition, the proposed bi-directional scheme can also be applied to more challenging scenarios with more than one source pair. Asymptotical behavior of the outage probability achieved by the proposed transmission protocol is studied in order to obtain insightful understandings for the fundamental limits of the proposed scheme. Our developed results show that the proposed bi-directional transmission scheme can realize larger system throughput than time sharing based approaches, and serving more than one pair at the same time is more beneficial than simple two-way relaying in terms of multiplexing gains.

This paper presents an efficient technique to eliminate the inter-layer interference (ILI) inherent in hierarchical modulation (HM) schemes operating over nonlinear satellite channels. The HM considered in this work is used in conjunction with an orthogonal frequency division multiplexing (OFDM) system. The proposed technique is based on an enhanced version of the selective mapping (SLM) scheme used for peak-to-average power ratio (PAPR) reduction. The enhanced SLM is constructed by using a new metric, which is more informative than the conventional PAPR metric. Simulation results confirmed that a noticeable bit error rate (BER) and interference reductions can be achieved by using the proposed technique.

Two adaptive receivers for jointly detecting active users in an interleave division multiple access (IDMA) system are considered for highly dispersive underwater acoustic channels (UACs) using a continuous pilot approach. A direct adaptive interference cancellation (IC) IDMA receiver is proposed and compared with the standard Rake-IDMA receiver that performs adaptive semi-blind channel estimation developed by the authors. Both iterative decoding receivers incorporate a phase locked loop (PLL) and are optimized based on the minimum mean square error (MMSE) criterion. The theoretical basis of both receivers is presented along with experimental results obtained by processing data from actual underwater communication experiments. The transmission results of 3 active users at a data rate of 441.3 b/s per user within 4 kHz bandwidth demonstrate that the IC-IDMA receiver has better performance and significantly mitigates the bit errors associated with Rake-based IDMA receiver.

In this paper, a novel actuation system for Wireless Capsule Endoscopes (WCE) based on magnetic levitation is proposed. This study focuses on the design of a multi-input, multi-output (MIMO), controller to maintain a desired position and orientation of the capsule relative to the movable electromagnet frame so that it can navigate the intestine by moving this frame and/or the patient. Tracking algorithms for the linear controller based on pole placement, entire eigenstructure assignment (EEA), and linear quadratic regulator (LQR) techniques are designed and simulated using Matlab/Simulink. Simulation results suggest that the LQR controller can be used for capsule actuation.

In this paper, a time varying Doppler-shift compensation scheme for wideband orthogonal frequency division multiplexing (OFDM) suitable for shallow water communications is proposed. This scheme accommodates a channel model having velocity that accelerate and de-accelerate during a packet of multiple OFDM frames. Furthermore, it assumes that the Doppler-shift varies linearly during the symbol time. To deal with this variation, the time expansion/compression is measured within a fraction of the sample period and then compensated using sample-by-sample interpolation. The Doppler-shift and its residual are frequently estimated during the symbol time to mitigate the inter-carrier interference (ICI) by estimating the first order moment of the cyclic prefix correlation. Additionally, in this technique, the fractional deviation of the sub-carrier spacing, which is considered to be the source of ICI, is estimated by exploiting the fractional part of the normalized sampling frequency offset. The proposed algorithm performance is investigated with real data obtained from an experiment that took place in the North Sea in 2009. In addition, results show that the technique is robust and more pragmatic than existing cyclic prefix (CP)-based algorithms.

This paper presents a robust timing recovery scheme for orthogonal space-time block coding (OSTBC) multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed system, the symbol timing is achieved either by minimizing the power difference between adjacent subcarriers in one STC block or between subcarriers with similar indices in consecutive STC blocks. The proposed technique is totally blind because it does not require any prior information about the channel state or the transmitted data. The early-late gate (ELG) configuration is utilized to realize the proposed timing recovery scheme efficiently. Monte Carlo simulations are used to assess the performance of the two realizations of the proposed system over fading channels with different frequency-selectivity conditions. Simulation results demonstrated the superiority of the proposed technique to provide accurate symbol timing even in severe frequency-selective fading channels which remarkably outperforms other timing metrics.

In this study, new mathematical formulations and algorithms for joint scheduling and hybrid resource allocation are derived and investigated for a multi-user downlink orthogonal frequency division multiple access system. A three-sectored multi-cellular heterogeneous traffic environment is considered where users are randomly distributed and categorised under different priority levels. Traffic consists of time delay-sensitive and time delay-insensitive services. Three practical scheduling and resource allocation methods are proposed to address the balance between throughput, outage probability and resource efficiency under varying channel conditions. The proposed methods are based on the Lagrangian duality framework, and are formulated as mixed integer programming problems constrained by the total power of the base station and users' data rate while maintaining the quality of service for each user. Both dynamic and fixed resource allocation approaches are included in the main problem formulation. The complexity of the resource allocation problem is minimised by approximating the well-known water level. Simulation results show that the total system throughput is penalised for the method that aims to minimise the outage probability of the highest priority level. This is because of the severe channel conditions experienced by some users, whereas the alternatively proposed methods maintain system efficiency under a similar amount of constrained resources and required traffic.

In this work, we propose a new decoding algorithm to correct closed-chains error patterns in hard-input hard-output (HIHO) turbo product codes (TPCs). The proposed technique is based on correlating the horizontal and vertical component codes to estimate the location of the erroneous bits in the closed-chain of errors, then erasure decoding is used to correct the identified bit errors. Simulation results demonstrated that, for particular codes, a noticeable coding gain improvement of about 1.5 dB can be achieved when compared to the standard sequential HIHO decoding and about 0.8 dB when compared to the non-sequential HIHO decoding. The computational complexity of the proposed decoder can be substantially reduced at moderate and high signal-to-noise ratios by stopping the iterative process when it is not more beneficial to perform further iterations.

This paper introduces a new multicarrier system that uses a low computational complexity transform developed by Boussakta to combine the Walsh-Hadamard Transform (WHT) and Discrete Fourier Transform (DFT) into a single orthogonal transform or as a transition from one transform domain to another. The proposed transform is used in a new orthogonal frequency division multiplexing (T-OFDM) system, across fixed and mobile multipath channel models. Use of the proposed transform with OFDM has been found to achieve high diversity gain by spreading each subcarrier with all the others. Consequently, severe distortion arising from channel fading on the subcarrier power is minimised. Simulation results confirm that the proposed T-OFDM system outperforms the conventional OFDM system when utilizing the minimum mean square error (MMSE) equalizer. The main, merits of such a transform are low computational complexity, no bandwidth expansion, the same average transmitted power, and a high ability to mitigate the influence of multipath channel dispersion.

In this work, an efficient interleaving process is proposed for orthogonal frequency division multiplexing (OFDM) systems over impulsive noise channels. Unlike the conventional OFDM systems where the interleaving process is implemented before the inverse discrete Fourier transform (IDFT), the proposed scheme is based on performing the interleaving process post the IDFT. The aim of this process is to average the effect of the impulsive noise burst over a large number of OFDM symbols, which can reduce its impact on the bit error rate (BER) significantly. For the system and channel models considered in the work, simulation results have confirmed that the proposed system can effectively reduce the BER degradation due to the impulsive noise to about 1 dB as compared to the impulsive noise-free case.

We propose a cross-layer strategy that jointly optimizes user scheduling and resource allocation for adaptive modulation and coding (AMC) based orthogonal frequency multiple access (OFDMA). The objective of this paper is to maximize the system throughput as a function of the bit error rate (BER) and the spectral efficiency based on selected modulation and coding schemes (MCSs). The proposed optimal user scheduling and resource allocation (OSRA) strategy arranges the users in distinct queues according to their priorities and selects users in an optimal manner that guarantees fair services for users among different priority levels. Moreover, it allocates the available resources optimally over the utilized sub-channels. The transmitter of the investigated AMC-OFDMA system at the assigned base station (BS) divides the transmitted OFDMA frame into sub-channels depending on the number of the considered priority levels. Simulation results show that the performance of the investigated AMC-OFDMA system based on the proposed OSRA strategy outperforms the conventional approaches.

In this paper, a new joint scheduling and hybrid resource allocation method is derived and investigated for a multi-user downlink Orthogonal Frequency Division Multiple Access (OFDMA) system that provides Time Delay-Sensitive services (TDS) and Time Delay-Insensitive services (TDI). A three sectored multi-cellular heterogeneous traffic environment is considered where users are randomly distributed and categorised under different priority levels. The method is proposed to address the balance between throughput, outage probability, and user priorities under varying channel conditions. The proposed method is based on the Lagrangian duality framework, and have been formulated as a Mixed Integer Non Linear Problem (MINLP) constrained by the total power of the Base Station BS and users' data rate while maintaining the Quality of Service (QoS) for each user. The hybrid resource allocation includes dynamic and fixed allocations in the main problem formulation. Simulation results show that the outage probability gaps between the priority levels are reasonably balanced. This is due to the optimality conditions which restrict the resource allocation domain for each priority level to avoid sever penalisation of one priority level over the others.

This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions. Monte Carlo simulation is used to assess the two realizations of the proposed system. The system performance is evaluated by means of mean squared error (MSE) over additive white Gaussian noise (AWGN) and frequency selective mobile radio channels. The simulation results demonstrate that the MSE of the proposed system is well below the MSE of other well-established estimators reported in the literature.

In this paper, we propose a bit and power allocation strategy for adaptive modulation and coding (AMC) based spatial multiplexing multi-input-multi-output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. This strategy aims to maximize the average system throughput by allocating the available resources optimally among the utilized bands depending on the corresponding channel conditions and the total transmission power constraints. The average system throughput is represented as a trade-off criterion between the spectral efficiency and bit error rate (BER). The considered AMC technique utilizes distinct modulation and coding scheme (MCS) options rather than adopting fixed or uncoded approaches. The transmitter divides the OFDMA frame at each transmit antenna into bands depending on the number of active users in an assigned base station (BS). The simulation results show superior performance of the MIMO-AMC-OFDMA system, which adopts the proposed strategy, over other conventional schemes.

In this paper, a new planning method is proposed for the next generation wireless networks that are based on Orthogonal Frequency Division Multiple Access (OFDMA). As a consequence of the wide variety service demands in terms of data rate and Quality of Service (QoS), the traffic pattern is considered to be heterogeneous. Therefore, the complexity of obtaining Base Stations (BSs) positions increases with the randomness of the traffic distribution. In addition to this challenge, the capacity of each BS is limited due to power and bandwidth constraints, propagation losses, Gaussian antenna pattern, and the Co-Channel Interference (CCI), which in turn increase the complexity measures for an efficient network design. According to Nash Equilibrium, combined efficient systems must perform equally to achieve certain performance. This implies that the traffic of a cellular system should be equally distributed over all the BSs to achieve the highest network performance. Hence, we formulate the planning problem as a non-linear multi-objective optimization problem. The optimum solution should not dominate the throughput of one BS over the others and this is referred to as Pareto optimal. However, loading all cells equally may not be possible in certain traffic distributions. Therefore, the proposed method tends to approach the optimal solution by tackling the problems of BS positioning and resource allocation simultaneously. We adopt a hybrid approach, i.e. Pareto-Metaheuristic (PMH) that achieves a balanced throughput over all cells as well as minimizing the number of the installed BSs targeting a certain service outage probability. Simulation results show that, in addition to maximizing the individual cell throughput, the network throughput variation decreases as the number of iteration increases.

This study presents an iterative carrier frequency offset estimator for orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator is based on the efficient Viterbi-and-Viterbi (VAV) algorithm. The proposed estimator is blind and can be used with non-constant modulus subcarrier modulations such as quadrature amplitude modulation (QAM). The performance of the proposed estimator is assessed theoretically and via Monte Carlo simulations over various channel models and compared to the performance of other well established blind techniques in addition to the Cramèr–Rao lower bound. The comparison results demonstrate that the proposed estimator outperforms other well-established blind estimators by more than 12 dB at moderate and high signal-to-noise ratios (SNRs).

This study presents a new blind carrier frequency offset (CFO) estimation technique for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems employing space–time coding (STC). CFO estimation is crucial for OFDM systems to avoid the performance degradation because of the inter-carrier interference that results when the CFO is not estimated and compensated accurately. Based on the assumptions that the data symbols are selected from a constant modulus constellation and the channel is varying slowly over time, a new blind CFO estimator is proposed by minimising the power difference between all subcarriers in two consecutive STC blocks. Therefore the proposed system exploits all subcarriers in time and frequency domain, which provides a remarkable performance improvement over other techniques reported in the literature. The complexity of the proposed estimator is substantially reduced by approximating the cost function by a sinusoid that can be minimised using direct closed-form computations within one OFDM symbol period. Monte Carlo simulations are used to assess the performance of the proposed system by means of mean squared error (MSE) in both static and time-varying frequency-selective fading channels. The simulation results demonstrate that the proposed estimator can eliminate the MSE error floors that usually appear at moderate and high signal-to-noise ratios for the estimators that work only in frequency domain.

Precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback are mainly based on the notion of delay-free feedback channels. In this paper, we take into account the time varying nature of the channel, and consider the feedback delay problem. In order to reduce performance degradation of spatial multiplexing systems in the presence of feedback delay, we propose the use of a Kalman filter linear predictor at the receiver to provide the transmitter with the predicted channel state information, and hence, mitigate the effect of feedback delay. The performance of this method is assessed using computer simulation, and the obtained results for the proposed channel prediction scheme demonstrate improved bit error rate performance for time varying Rayleigh fading channels.

Fourth generation (4G) mobile access is drawing particular attention as it promises to deliver high data rates and reliable coverage for broadband wireless access. In this paper, Orthogonal Frequency Division Multiplexing Access (OFDMA) and Multi-Carrier Code Division Multiplexing Access (MC-CDMA) are investigated to highlight their strengths and weaknesses as candidates for 4G wireless access. Using a multi-cell environment, MC-CDMA and OFDMA coverage is dimensioned based on the value of the Signal to Interference plus Noise Ratio (SINR). The results show that OFDMA system offers cell coverage of 92.5% and a maximum actual throughput of 24.2 Mbps/cell (fade margin 10 dB). Using the same assumptions for MC-CDMA, the results show better coverage only with complete orthogonal spreading codes which can guarantee 97% of user coverage and actual throughput of 28.8 Mbps. These measurements decrease as the orthogonality between the spreading codes is reduced. In the case of 94% orthogonality the MC-CDMA system achieved 89.3% coverage and 21.9 Mbps throughput while with a 60% orthogonality 47% coverage and 5.8 Mbps throughput was achieved.

In this paper, we consider the effect of impulsive noise on the performance of multicarrier code division multiple access (MC-CDMA) systems and analyze the performance by examining the MC-CDMA system model in time domain. We have discovered that conventional Walsh-code based MC-CDMA is less robust to the presence of impulsive noise than the corresponding direct sequence (DS) CDMA and multicarrier modulation based (MCM) systems. Furthermore, it is demonstrated that the performance of MC-CDMA depends strongly on the selection of the utilized spreading codes. A modified MC-CDMA structure, called MC-SI-CDMA, is proposed and investigated in impulsive noise that employs subcarrier interleaving (SI) to reduce the cross- correlation between the time-domain MC-CDMA waveforms and the impulsive noise. Computer simulation results conducted to support our analysis indicate that the proposed MC-SI- CDMA system in impulsive noise can provide a performance improvement of 2.5 dB at a bit error rate (BER) level of 10-3compared with the DS-CDMA system.

We propose a novel iterative decoder for block turbo codes (BTCs). The proposed decoder combines soft-input/softoutput (SISO) and hard-input/hard-output (HIHO) constituent decoders in order to obtain better error performance and reduce the computational complexity compared to classical BTC decoders. We show that the new decoder, called 'hybrid decoder', offers a better complexity/performance tradeoff than a classical BTC decoder.

In this letter, we propose a new decoding algorithm to improve the bit error rate performance of the hard-input hard-output (HIHO) turbo product codes (TPC) with hard iterative decoding. The proposed algorithm iteratively, but not sequentially, decodes the received TPC blocks based on the reliability of the constituent codes. Simulation results confirm a noticeable coding gain improvement using the proposed decoding process with respect to standard HIHO TPC decoding. An efficient implementation of the new technique offers a negligible additional complexity when the channel-bit error probability is less than 10-2.

Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side information bits for each data block, which results in some data rate loss. These bits must generally be channel-encoded because they are particularly critical to the error performance of the system. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output provided that the number of subcarriers is large enough.

Selected mapping (SLM) is a technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. SLM requires the transmission of several side information bits for each data block, which results in some data rate loss. These bits must be channel-encoded because they are particularly critical to the error performance of the system. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of several OFDM systems using either QPSK or 16-QAM modulation, we show that the proposed method performs very well in terms of bit error rate at the receiver output provided that the number of subcarriers is large enough.

Precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback have been extensively studied to reduce the feedback information based on the notion of delay-free feedback channel. In order to reduce performance degradation of precoded spatial multiplexing MIMO systems due to delay in the feedback channel, in this paper, we take into account the time varying nature of the channel, and consider the feedback delay problem. We propose the use of a linear predictor at the receiver to provide the precoder at the transmitter with predicted channel state information, and hence, mitigate the effect of feedback delay. The predictor is implemented using Kalman filter. The performance of this method is evaluated using computer simulation, and the achieved results demonstrate improved bit error rate performance in frequency selective Rayleigh fading channels.

Making distance measurements with RSS can be challenging in indoor environments. The effect of multipath and shadowing introduces ambiguity into the readings, leading to a range of distances that can be inferred from a single measurement. This contribution highlights the frequency dependancy of these effects. Lower and upper bounding constraints are introduced to achieve an practical operational range and mitigate the possibility of ambiguous RSS measurements. In the results section we verify our theoretical limits with practical based experimental results. We also highlight the gains in RMSE when our thresholding approach is transferred to a localisation scheme.

In wireless sensor networks, the use of energy efficient infrastructure such as clustering may be used to lengthen the network lifetime and prevent network connectivity degradation. In such systems, the performance of the clustering scheme is generally influenced by the cluster head selection method and the number of clusters. This paper presents a dynamic clustering method with multi-objectives that automatically determines the optimum number of clusters in the network. The algorithm, which is based on binary Particle Swarm Optimization (PSO), eliminates the need to set the number of clusters a priori. In addition, a multi-objective approach is utilized in the cluster head selection algorithm in order to select the best set of cluster heads. Simulation results demonstrate that the proposed protocol can achieve an optimal number of clusters, as well as prolong the network lifetime and increase the data delivery at the base station when compared to other well known clustering algorithms.

A novel hybrid multiuser detection scheme that jointly uses linear and nonlinear interference suppression techniques is developed for high-speed direct-sequence code-division multiple-access communications in multipath frequency-selective fading channels. The detector detects signals in a symbol-by-symbol style. Conventional decorrelating detectors suffer from the noise enhancement problem, which becomes more serious for dispersive multipath channels. The proposed detector uses interference cancellation technology to reduce the rank of the expanded signal subspace and hence it preserves the advantages of the expanded decorrelating detector in terms of complete multiple access interference and intersymbol interference suppression and meanwhile avoids its disadvantage in terms of noise enhancement. Computer simulation shows clear superiority of the new detector to other existing methods.

Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.

In this paper, the performance of a downlink synchronous MC-CDMA system with joint frequency-time domain spreading over time-variant frequency-selective Rayleigh fading channels is investigated. We propose an adaptive two dimensional MMSE (minimum mean square error) receiver, which works in decision-directed model after the initial training period. Due to the time variability, a subcarrier phase tracker, which comprises a bank of phase locked-loops (PLLs), is employed in the proposed receiver to track the fading phase variability. Furthermore, a simplified phase tracker structure is proposed to reduce the complexity of system. The theoretical bit error rate (BER) is derived and simulation results indicate that the proposed receiver can achieve good frequency diversity and subcarrier synchronisation, compared to the conventional MCCDMA structures.

Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.

Implementing positioning systems for indoor environments is notoriously difficult. The vast array of interacting parameters such as furniture, room shape and materials mean that the simulation of such an environment is of limited value. We present in this paper results from an empirical investigation as to the attainable accuracy of a Radio Frequency (RF) positioning system based on received signal strength (RSS). Methods to improve confidence, such as frequency averaging and bi-directional ranging, are explored. Finally we present and evaluate a novel method for calibrating the channel propagation exponent with no prior knowledge of the sensor network layout or room shape.

Clustering in wireless sensor networks (WSNs) is one of the techniques that can expand the lifetime of the whole network through data aggregation at the cluster head. This paper presents performance comparison between particle swarm optimization (PSO) and genetic algorithms (GA) with a new cost function that has the objective of simultaneously minimizing the intra-cluster distance and optimizing the energy consumption of the network. Furthermore, a comparison is made with the well known cluster-based protocols developed for WSNs, LEACH (low-energy adaptive clustering hierarchy) and LEACH-C, the later being an improved version of LEACH, as well as the traditional K-means clustering algorithm. Simulation results demonstrate that the proposed protocol using PSO algorithm has higher efficiency and can achieve better network lifetime and data delivery at the base station over its comparatives.

Wireless sensor networks (WSNs) are mainly characterized by their limited and non-replenishable energy supply. Hence, the need for energy efficient infrastructure is becoming increasingly more important since it impacts upon the network operational lifetime. Sensor node clustering is one of the techniques that can expand the lifespan of the whole network through data aggregation at the cluster head. In this paper, we present an energy-aware clustering for wireless sensor networks using particle swarm optimization (PSO) algorithm which is implemented at the base station. We define a new cost function, with the objective of simultaneously minimizing the intra-cluster distance and optimizing the energy consumption of the network. The performance of our protocol is compared with the well known cluster-based protocol developed for WSNs, LEACH (low-energy adaptive clustering hierarchy) and LEACH-C, the later being an improved version of LEACH. Simulation results demonstrate that our proposed protocol can achieve better network lifetime and data delivery at the base station over its comparatives.

The process of WIMAX radio network design and deployment is greatly affected by the nature of the customer premises equipment and the intended access service, which may be fixed, nomadic or indoor. This paper advances network design methodologies, traditionally used for fixed access, in the scope of hybrid fixed outdoor / indoor-nomadic networks. With the main objective being performance, time-to-market and cost optimisation, a dual layer outdoor / indoor coverage deployment is proposed which allows for co-existence and performance balancing of different customer profiles. By comparing to purely outdoor or indoor deployments, this approach provides benefits, both in terms of equipment reduction and spectrum usage and optimises the deployment costs, especially in the initial phases of the network. This approach is applicable both for OFDM and future OFDMA systems.

Mobile ad hoc networks in road transport applications exhibit special characteristics, mainly due to their dynamic chain behaviour. In this paper, we introduce a node decision algorithm in both the routing and packet priority mechanism, based on the node's driving direction with respect to the next hope towards packet destination. In the routing algorithm, a router direction index (RDI) parameter is introduced to enhance the performance of AODV in updating its routing table, as well as to assist the destination nodes to choose route requests from different paths in inter-vehicular ad hoc network scenarios. A packet transmission priority is set according to the driving direction of both transmitter and receiver of the packet. Simulation results of the proposed algorithm for 200 vehicles travelling at speeds between 60 ~ 120 km/h on a 2-directional highway demonstrate a performance increase in the packet delivery ratio, and decrease in the packet end to end delay and routing overhead for the proposed algorithm

In this paper, iterative detection is applied in the receiver for downlink of both direct sequence (DS) and multi-carrier (MC) code division multiple access (CDMA) systems in the flat Rayleigh fading channels. A joint iterative detection and phase recovery scheme is proposed. Unlike the conventional bit-interleaved coded modulation with iterative decoding (BICM-ID) structure, the proposed receiver feeds the extrinsic information from soft-input soft-output (SISO) decoder back to update both the adaptive minimum mean squared error (MMSE) correlator and phase locked-loop (PLL) instead of de-mapper. We also investigate how the second-order PLL benefits from the iterative process over the time-varying flat Rayleigh fading channel. Simulation results illustrate that the iterative process significantly improves the performance of the adaptive detector by suppressing multiple access interference (MAI). Additionally, the tracking capability of PLL is enhanced by reducing the equivalent noise power.

In adaptive time division duplex (ATDD) wireless systems, severe co-channel interference conditions can occur if the movable downlink/uplink (UL) TDD boundary is not synchronised among all frames in base stations. To reduce interference outage and to improve a system's spectral efficiency, a new single frequency cell (SFC) network architecture is proposed, which allows for distributed boundary synchronisation (DBS) via inter-sector signalling. SFC-DBS dynamically synchronises TDD boundaries among neighbouring sectors for each frame, thus avoiding sector-to-sector interference, while preserving the ATDD radio resource assignment efficiency. Analysis shows that SFC-DBS achieves an additional 6–11 dB in the average UL signal-to-interference ratio, compared with existing channel assignment schemes, which corresponds to 25–50 % capacity gain subject to traffic asymmetry in different sectors. More importantly, the proposed SFC scheme does not incur any further cost in the frequency planning, whereas the DBS scheme requires only minor system modifications. Compared with interference cancellation via antenna arrays and beamforming, SFC-DBS achieves similar performance, albeit without the cost for complex radio transceivers and multiple antenna elements.

This paper introduces a new technique for combining constellation shaping and bit-interleaved turbo-coded modulation (BITCM) over additive white Gaussian noise channel. The proposed scheme consists of serial concatenation of a binary turbo code, short-length binary shaping code, and mapping function using Gray labeling. The corresponding receiver is made up of four blocks (demapper, shaping decoder, and two constituent RSC decoders) exchanging extrinsic information in order to optimize error performance. A BITCM scheme employing 16-PAM constellation to achieve a rate of 3 bits/dim is considered as an example. It is shown that, by careful selection of the shaping code parameters, shaping gains almost equal to 0.8 dB can be obtained at a little cost in terms of system complexity.

In this paper, the performance of a computationally efficient adaptive MMSE receiver is investigated for asynchronous MC-CDMA systems over multipath fading channels. According to Wiener filter and LMS algorithm theories, we prove that the proposed computationally efficient MMSE receiver has the same BER and convergence performance as that of the conventional MMSE receiver, assuming the sampling rate per symbol is equal to the number of subcarriers. When the sampling rate per symbol is increased, the proposed receiver can outperform the conventional MMSE receiver without sacrificing the convergence speed. The theoretical analysis is verified by the results through Monte-Carlo simulation

This paper presents an iterative (turbo) channel estimation and turbo equalization when orthogonal frequency division multiplexing (OFDM) has been concatenated to space-time block code (STBC) over time-varying multipath Rayleigh fading channels. Based on the Kalman filter channel estimator, softinput- soft-output (SISO) minimum mean square error (MMSE) equalizer and a maximum posterior probability (MAP) decoder, the channel estimate can be improved for each iteration by using soft information feedback from the decoder. Computer simulations show good estimation and tracking by the Kalman filter with only a few training (pilot) symbols even when signals experience deep fading. It is observed from simulations that the overall system performance can be improved by 4dB after 14 iterations compared to non-iterative channel estimation and equalization. The proposed method is shown to obtain fast channel estimation and low complexity turbo equalization which are requirements in time-varying fading channels.

Adaptive time division duplex (ATDD) systems have the ability to efficiently utilize the radio spectrum and achieve higher capacity, when the traffic conditions are time-varying within a cell or diverse among different cells. However, severe co-channel interference conditions can occur when the movable TDD boundary is not synchronized amongst all frames in the base stations, compromising the spectral efficiency and the system's robust operation. To reduce the interference outage probability, a distributed boundary synchronization (DBS) scheme is proposed that dynamically synchronizes the TDD boundaries amongst neighbouring sectors, thus avoiding sector-to-sector interference, whilst preserving the ATDD efficiency. Results show that DBS achieves an 8 dB improvement in the uplink SIR for the same interference outage, and a 27.5-60% increase in terms of capacity, subject to traffic asymmetry conditions. More importantly the proposed DBS scheme requires only simple modifications in the system

We investigate the association between constellation shaping and bit-interleaved coded modulation with iterative decoding (BICM-ID). To this end, we consider a technique which consists of inserting shaping block codes between mapping and channel coding functions in order to achieve constellation shaping. By assuming the example of a 2-bit/s/Hz 16-QAM BICM-ID, it is demonstrated using computer simulations that this technique can improve the performance of BICM-ID schemes by a few tenths of decibels.

In time division duplex (TDD) fixed broadband wireless access networks, co-channel interference that arises from the correlation of downlink and uplink signals in different sectors may considerably degrade the spectral efficiency. To overcome the complexity and costs of complete frame-TDD boundary synchronization in the network, a combined channel assignment (CA) and antenna array (AA) approach is proposed to mitigate interference. First a rotated-interleaved CA (RICA) scheme is applied, which exploits sector antenna directivity to reject the majority of interferers by receiving them through the antenna side and back lobes. Combined with RICA, an AA system is used in the base station side to further reduce intersector interference during both transmission and reception phases. For the worst-case interference scenario an unsynchronized TDD scheme, the proposed methodology achieves a 51.5% improvement in the average channel capacity while it considerably improves the uplink availability. An advantage of this approach is that it considers only low-complexity AA system configurations, thereby optimizing the corresponding cost

A linear transmitter precoding technique based on partial equalization receiver (TP-PER) is proposed for time-duplex division (TDD) downlink multi-carrier code-division multiple-access (MC-CDMA) systems to pre-suppress multiple access interference (MAI) in frequency selective Rayleigh fading channels. Given that the channel state information (CSI) is known to the transmitter and the channel is slowly varying, the proposed transmitter precoding algorithm can outperform conventional precoding schemes, such as transmitter precoding with equal gain combining (TP-EGC), transmitter precoding with maximum ratio combining (TP-MRC), and the linear equalization receiver. Numerical results show that the proposed algorithm achieves optimal performance by using an appropriate partial equalization factor that depends on the system specification

An improved resource allocation scheme is proposed in this paper which uses genetic algorithms (GAs) in conjunction with the recently developed plane cover multiple-access (PCMA) scheme in order to maximize the attainable capacity of packet-based wireless cellular networks. The studied problem has been proven to be in the class of nondeterministic polynomial (NP)-hard problem, therefore, the powerful search capability of the GA is a key factor in improving the performance of cellular resource allocation. Computer simulation results suggest that the proposed approach outperforms the "uniform" and the "greedy" algorithm-based "min " methods in terms of the number of serviced users.

We present a new and simple method for combining constellation shaping and bit-interleaved coded modulation over Gaussian channels. By considering the example of a 3-bit/dim turbo coding scheme using a 16-PAM constellation, it is shown that this technique can provide shaping gains of 0.7 dB, and that error performance within 1.6 dB of the continuous-input channel capacity limit is achieved.

In multiple input multiple output systems (MIMO), the increase in the number of channel parameters, renders less reliable conventional training based schemes. For a reasonable performance, conventional training based methods require a larger number of training symbols which reduces system bandwidth efficiency. In this paper, a semiblind channel estimation and tracking technique is proposed for concatenated turbo codes (TC) with space-time and frequency block codes (STFBC) over time-varying Rayleigh fading channels. The paper describes an effective approach to reduce the number of training symbols to half by implementing the Kalman filter (KF) with the constant modulus algorithm (CMA). Computer simulations show good estimation and tracking by the Kalman filter and CMA with only few training symbols (less than 7% of bandwidth efficiency loss) even when signals experience deep fades. The proposed method is shown to obtain fast channel estimation and tracking which is a requirement in fast fading channels.

A space-time nonlinear receiver for a DS-CDMA synchronous channel is proposed for jointly mitigating impulsive noise and multiple access interference. The proposed scheme combines linear decorrelators and antenna arrays with nonlinear front ends based on the affinity matched myriad nonlinear filter. This myriad (log Cauchy) filter is incorporated to combat the impulsive noise and prevent it from entering the system. The proposed detector also incorporates a structure for estimating the impulsive noise parameter in order to update a filter parameter called the nonlinearity parameter. Monte Carlo simulation results of the proposed space-time receiver are presented to justify the relative merits of nonlinear signal processing in the space-time domain.

We consider frequency channel assignment (CA) and antenna polarization assignment (PA) schemes jointly in the scope of non line-of-sight fixed wireless networks. First, we introduce a new, more accurate method to characterize CA and PA schemes. Following this approach, we propose a new rotated-interleaved CA scheme that outperforms existing CA schemes and a new interleaved-interleaved PA methodology that is more efficient than basic strip-by-strip PA when applied on top of most CA schemes for re-use factor F/sub R/ = 1. An investigation on the total capacity gains of the CA and PA schemes showed that each CA scheme performs differently when combined with different PA schemes and for different re-use factors and only a joint consideration can highlight the best CA-PA combination. In a further step, instead of simply combining CA, PA schemes, we introduce a methodology to design new PA patterns that are optimized (oPA) on the distinct features of each CA scheme. Our results demonstrate that the oPA strategy achieves higher performance than other PA methodologies for F/sub R/ = 1, 2.

An asynchronous multicarrier code division multiple access (MC-CDMA) scheme over frequency selective multipath Rayleigh fading channels for the reverse link of a mobile communication system is investigated when the delay spread is in excess of a symbol interval. An architecture of a centralized decision feedback equalizer (CDFE) based on the minimum mean-square-error (MMSE) criterion is suggested to reduce both inter-symbol-interference (ISI) and multiple access interference (MAI) due to the multi-path propagation, and the MAI due to the effect of the reverse asynchronous reception mode at the base station. The receiver architecture is for multi-user detection (MUD) consisting of a multiple-layer feed-forward filter (ML-FFF) and a centralized feed back filter (CFBF). Results indicate that an enhancement in capacity and good interference resistance are obtained by the proposed multi-user detection scheme over the structure without CFBF (NCDFE), which only uses ML-FFF and FBF. Additionally, it is demonstrated that the structure performs multi-path energy Rake combining.

An Adaptive minimum bit error rate (MBER) based linear multiuser detection scheme is proposed for an asynchronous multicarrier code-division multiple-access (MC-CDMA) system in frequency selective Rayleigh fading channels. In general, a MC-CDMA system employs the minimum mean square error (MMSE) receiver due to its good performance and amenability to adaptive implementation. However, the MSE cost function is nut optimal in terms of the bit error probability performance of the system. The proposed multiuser detector (MUD) that directly minimizes the BER can significantly improve the performance by employing an adaptive stochastic gradient algorithm based on the estimation of kernel density function in order to adjust the weights in the receiver. Simulation results demonstrate a clear performance improvement by using the proposed multiuser detection scheme.

The aim of this study was to investigate the value of fractal dimension in separating normal and cancerous images, and to examine the relationship between fractal dimension and traditional texture analysis features. Forty-four normal images and 58 cancer images from sections of the colon were analyzed. A "leave-one-out" analysis approach was used to classify the samples into each group. With fractal analysis there was a highly significant difference between groups (p < 0.0001). Correlation and entropy features showed greater differences between the groups (p < 0.0001). Nevertheless, the addition of fractal analysis to the feature analysis improved the sensitivity from 90% to 95% and specificity from 86% to 93%.

Abstract-Recently, a robust version of the linear decorrelating detector (LDD) based on the Huber's M-estimation technique has been proposed. In this paper, we first demonstrate the use of a three-layer recurrent neural network (RNN) to implement the LDD without requiring matrix inversion. The key idea is based on minimizing an appropriate computational energy function iteratively. Second, it will be shown that the M-decorrelating detector (MDD) can be implemented by simply incorporating sigmoidal neurons in the first layer of the RNN. A proof of the redundancy of the matrix inversion process is provided and the computational saving in realistic network is highlighted. Third, we illustrate how further performance gain could be achieved for the subspace-based blind MDD by using robust estimates of the signal subspace components in the initial stage. The impulsive noise is modeled using non-Gaussian alpha-stable distributions, which do not include a Gaussian component but facilitate the use of the recently proposed geometric signal-to-noise ratio (G-SNR). The characteristics and performance of the proposed neural-network detectors are investigated by computer simulation.

We propose a multistage joint adaptive array (AA) and spatial interference cancellation (IC) structure for a direct sequence code division multiple access (DS/CDMA) system. The structure utilizes both space and time processing to improve the performance of the base station receiver under the influence of multiple access interference (MAI) and in the absence of power control. The AA comprises a bank of temporal matched filters followed by a beamformer. IC is then used to remove the detected strong user from the received array input. This stage can be repeated for recover and remove more users. Computer simulation shows that, in the absence of power control, the proposed algorithm efficiently detects the weak user information at MAI levels of 30 dB where the conventional space-time structure fails.

Power control is a well-established technique in the design and operation of cellular radio systems. It can be use to reduce the co-channel interference, near-far effect. This leads to improved capacity and longer battery life. Two main approaches have been adopted for power control, centralised and distributed. Centralised power control requires knowledge of the information of all link gains between base stations and mobiles in real time, which is difficult to implement in the large system. In this paper, we consider distributed power control algorithms which are only based on local information with a cell. We adopt the method of projection onto convex sets (POCS) as an iterative approach to obtain the minimum protection ratio. Numerical results show that the POCS-method achieves much faster convergence and improved outage probability than other conventional methods.

Multiuser communications channels based on code division multiple access (CDMA) technique exhibit non-Gaussian statistics due to the presence of highly structured multiple access interference (MAI) and impulsive ambient noise. Linear adaptive interference suppression techniques are attractive for mitigating MAI under Gaussian noise. However, the Gaussian noise hypothesis has been found inadequate in many wireless channels characterized by impulsive disturbance. Linear finite impulse response (FIR) filters adapted with linear algorithms are limited by their structural formulation as a simple linear combiner with a hyperplanar decision boundary, which are extremely vulnerable to impulsive interference. This raises the issues of devising robust reception algorithms accounting at the design stage the non-Gaussian behavior of the interference. We propose a multiuser receiver that involves an adaptive nonlinear preprocessing front-end based on a multilayer perceptron neural network, which acts as a mechanism to reduce the influence of impulsive noise followed by a postprocessing stage using linear adaptive filters for MAI suppression. Theoretical arguments supported by promising simulation results suggest that the proposed receiver, which combines the relative merits of both nonlinear and linear signal processing, presents an effective approach for joint suppression of MAI and non-Gaussian ambient noise.

An automated knowledge-based vision system for skeletal growth estimation in children is reported in this paper. Images were obtained from hand radiographs of 32 male and 25 female children of age 1-16 yr. Phalanx bones were automatically localized and segmented using hierarchical inferences and active shape models, respectively. A number of shape descriptors were obtained from the segmented bone contour to quantify skeletal growth. From these descriptors, a feature vector was selected for a regression model and a Bayesian estimator. The estimation accuracy was 84% for females and 82% for males. This level of accuracy is comparable to that of expert pediatric radiologists, which suggests that the proposed approach has a potential application in pediatric medicine.

The development of an automated algorithm for the categorization of normal and cancerous colon mucosa is reported. Six features based on texture analysis were studied. They were derived using the co-occurrence matrix and were angular second moment, entropy, contrast, inverse difference moment, dissimilarity, and correlation. Optical density was also studied. Forty-four normal images and 58 cancerous images from sections of the colon were analyzed. These two groups were split equally into two subgroups: one set was used for supervised training and the other to test the classification algorithm. A stepwise selection procedure showed that correlation and entropy were the features that discriminated most strongly between normal and cancerous tissue (P < 0.0001). A parametric linear-discriminate function was used to determine the classification rule. For the training set, a sensitivity and specificity of 93.1% and 81.8%, respectively, were achieved, with an overall accuracy of 88.2%. These results were confirmed with the test set, with a sensitivity and specificity of 93.1% and 86.4%, respectively, and an overall accuracy of 90.2%.

This paper presents the development and performance of blind algorithms for a spatial diversity scheme to enable reliable data telemetry over a long range underwater acoustic channel. A number of Bussgang based stochastic gradient algorithms were tested for this multipath channel with additive white and coloured shipping noise. Both simulation and real experimental tests have shown that a significant improvement is obtained by utilising the spatial diversity of the long range channel and the ability of the combiner to perform joint equalisation and carrier phase tracking.

A robust contour detection algorithm is presented for noisy images characterised by close objects. The proposed approach uses an adaptive multi-scale edge tracking scheme based on active shape models and the wavelet transform. This adaptive method effectively adjusts the appropriate Gaussian function bandwidth according to the noise level so that close object edges can be detected before they are merged by excessive smoothing. This gives an improved performance over a single scale approach, where an incorrect Gaussian function bandwidth can lead to erroneous edge detection. The results obtained show an adaptive multi-scale scheme is robust regardless of the image signal to noise ratio.

This paper describes a parallel architecture that has been developed to perform real-time synthetic aperture sonar imaging as part of the Acoustical Imaging Development (ACID) project. The project has successfully developed a synthetic aperture sonar system for producing high resolution images of the sea floor and that has been tested during a series of sea trials in May 1993 off the south coast of France. This paper describes the synthetic aperture processing system developed by the University of Newcastle upon Tyne and its use of transputer modules and associated devices in order to obtain real-time imaging performance, the software structure of the processing system and the load balancing techniques that have been developed in order to provide efficient processing. The use of a parallel distributed architecture has also allowed a processing system that can readily be extended to deliver greater computational power in the future. Images produced by the synthetic aperture processor from data collected from around the Toulon coastal region are presented. These images highlight the improvement in azimuth resolution that can be obtained from synthetic aperture processing over conventional sidescan sonars.