Coordinated multi-point (CoMP) – joint processing (JP) is a technique which improves the cell edge user data rate and spectral efficiency. The practical requirements for CoMP-JP in terms of capacity and latency constraints should be solved by considering backhaul network. The possibility of deploying CoMP-JP in practical cellular systems strongly depends on the backhaul network capabilities. The authors propose a selective clustering scheme which is able to selectively form clusters in order to decrease the traffic load of the backhaul network for CoMP-JP. In addition, the authors propose a new frequency reuse scheme for downlink CoMP-JP. The authors are able to decrease intra-cell and inter-cell interference with our proposed frequency reuse scheme. Therefore the authors increase the spectral efficiency and SINR (signal to interference and noise ratio) performance of the system.

The authors investigate the performance of multiple-input–multiple-output multicarrier direct sequence code division multiple access system operating over arbitrarily and equally correlated η–µ fading channels in terms of average bit error probability and average symbol error probability. Closed form expressions for average error probability using moment generating function-based approach are derived and expressed in terms of Lauricella's multivariate hypergeometric functions. Furthermore, based on numerical results, they observe that the performance of the system improves when the number of multipath clusters increases as well as the number of subcarriers (frequency diversity). Similarly, substantial enhancement in system performance is observed due to the effect of spatial diversity. Finally, they verify the results via Monte Carlo simulation-based method to support the accuracy of the analytical approach and also compare with already published ones.

An orthogonal frequency-division multiplexing (OFDM) system with non-uniformly spaced pilots, such as worldwide interoperability for microwave access, voids virtually all discrete Fourier transform (DFT)-based interpolation methods for channel estimation, because they all require pilots to be uniformly spaced. Therefore, we propose two iterative algorithms to solve this problem. In the proposed algorithms, the inverse discrete Fourier transform and DFT are iteratively used to smooth the channel frequency response estimated by linear interpolation (LI) or other means. To be complete, we also propose a method to truncate the channel impulse response for the proposed algorithms. The simulation results show that the proposed approach has much lower mean square error in a long delay channel than the LI method has, and it also outperforms a decision-directed approach at high speed and/or lower signal-to-noise ratio environments. Overall, the proposed approach is a promising approach for channels with long delay spread in an OFDM system with non-uniformly spaced pilots.

In this study, the authors propose an improved frequency-domain fractionally spaced (FDFS) minimum mean square error (MMSE) receiver for zero-padded multi-carrier code division multiple access (MC-CDMA) systems when the guard interval is not enough to avoid the inter-symbol interference (ISI) caused by the multipath channel. The proposed novel iterative FDFS-based receivers firstly reconstruct the received symbol to reduce the ISI and then followed by the FDFS-based equalisers to minimise the effect of ISI and inter-carrier interference (ICI) caused by carrier frequency offset (CFO) and Doppler shifts. A few iterations are performed to achieve the expected bit error rate (BER) performance. To reduce the receiver complexity, the novel simplified diagonal FDFS-based receivers with a fixed noise variance are developed with slight performance degradation. The proposed iterative receivers have never been studied in the existing literature. Simulation results show that the proposed iterative FDFS-based receivers can significantly improve the BER performance of the conventional FDFS-MMSE receiver in severe multiple interferences environments caused by multipath, CFO and Doppler shift.

In this study, the authors present a novel low backhaul load cooperative transmission framework for the two-cell multiple-input–single-output systems. In this framework, the neighbouring two base stations (BSs) take turns to transmit data in two consecutive slots. In each slot, only one BS is active, transmitting the preprocessed data symbols of both its own serving user and the cooperative user in neighbouring cell, and sharing its preprocessed data symbols to the other cooperative BS for next transmission. Linear constellation spreading is utilised for preprocessing which helps the system to exploit the macro-diversity without reducing the multiplexing gain. Besides, zero-forcing beamforming is applied in each transmission slot so as to cancel the multiuser interference. In this way, the inter-cell links become beneficial rather than detrimental. Pairwise error probability analysis demonstrates that the multi-cell spatial diversity gain can be achieved for each data stream. Both theoretical analysis and simulation results confirm that the proposed scheme outperforms the existing relevant strategies with less channel estimation overhead. It is shown that because of the higher diversity order it achieved, the proposed scheme can significantly improve the error performance in a distributed manner while maintaining the same multiplexing gain.

In this study, two novel decoding algorithms for cooperative beamforming (CBF) systems are proposed. In decode-and-forward-based CBF, multiple relay nodes decode the packets transmitted from the source node and forward them to the destination node. However, decoding errors at the relay nodes cause erroneous retransmission of packets, which degrades the signal decoding performance at the destination node. To solve this problem, the optimal decoding strategy is derived; this strategy takes the potential errors in forwarded signals into account in the computation of the likelihood ratio of coded bits. Furthermore, to reduce the required computational complexity, a suboptimal decoding algorithm, which assumes that only one of the multiple relayed signals potentially contains errors in each time slot, is also proposed. In simulation results, it is observed that the proposed decoding algorithms for CBF provide performance improvements in terms of the achievable packet error rates with respect to the conventional schemes.

The effect of spectrum sensing errors on the performance of bit loading algorithms in cognitive radio systems based on orthogonal frequency division multiplexing is studied in terms of throughput and average bit error rate. Different spectrum sensing parameters and data transmission parameters are examined to evaluate the performance degradation. Numerical results show that the sensing errors cause significant performance degradation and that, when the signal-to-noise ratio is high, the inter-carrier interferences caused by carrier frequency offset are dominant in the performance degradation.

This study investigates the performance of multicarrier delay diversity modulation (MDDM) systems with both cyclic delay diversity and space–time Trellis code (STTC) techniques and compares its performance with conventional MDDM systems. Deploying STTCs can allow cost efficient and flexible system deployment compared with classical MDDM systems with multiple cyclic delays. In this study, the authors’ propose MDDM systems with both cyclic delay and STTCs. The MDDM system is modelled for two and four transmit antennas. In this study, they compare the performance of the proposed MDDM systems with quadrature phase shift keying (QPSK), 8 phase shift keying (8PSK) and 16 quadrature amplitude modulation (16QAM) STTCs and compare its results with conventional MDDM systems. The noise variance of the received signals at the MDDM receiver is mathematically derived. The minimum mean square error technique for channel estimation is applied to the proposed MDDM systems. Simulation results demonstrate that the proposed MDDM systems enhance the performance of classical MDDM systems and give large coding gains compared with the classical case.

Power consumption and costs of analogue front-end (AFE) chains are often not negligible for large-scale antenna array systems. A low-complexity hardware architecture is to use a number of AFE chains that are less than the number of antennas. Beamforming for this low-complexity hardware architecture involves both digital and analogue beamforming, which is termed hybrid analogue/digital beamforming. In this study, minimising the transmit power subject to signal-to-interference-plus-noise ratio (SINR) constraints and maximising the minimal SINR under the constraint of the transmit power, are investigated, respectively, for hybrid analogue/digital beamforming. Properties on the feasibility and optimality of the two problems are derived. Numerical algorithms based on semi-definite positive relaxation are proposed in an attempt to solve the two optimisation problems. The performance of the proposed algorithms is evaluated under the Gaussian and 60 GHz channel models. It is shown that the performance of hybrid analogue/digital beamforming is highly related to the correlation of the channel coefficients of subcarriers. Additionally, for different extents of the users’ spatial separability, some heuristics ways of designing analogue beamforming are shown to be able to approach to at least the local optimums under the 60 GHz channel model.

In long-term evoluation (LTE) femtocell networks, hysteresis is one of the main parameters which affects the performance of handover with a number of unnecessary handovers, including ping-pong, early, late and incorrect handovers. In this study, the authors propose a hybrid algorithm that aims to obtain the optimised unique hysteresis for an individual mobile user moving at various speeds during the inbound handover process. This algorithm is proposed for two-tier scenarios with macro and femto. The centralised function in this study evaluates the overall handover performance indicator. Then, the handover aggregate performance indicator (HAPI) is used to determine an optimal configuration. Based on the received reference signal-to-interference-plus-noise ratio, the distributed function residing on the user equipment (UE) is able to obtain an optimal unique hysteresis for the individual UE. Theoretical analysis with three indication boundaries is provided to evaluate the proposed algorithm. A system-level simulation is presented, and the proposed algorithm outperformed the existing approaches in terms of handover failure, call-drop and redundancy handover ratios and also achieved better overall system performance.

In this study, an efficient handover algorithm based on the received signal strength (RSS) prediction is presented for two-tier macro–femtocell networks in which, because of the fading effects of channel and short coverage range of femtocells, ping-pong handovers may take place. In the proposed approach, first each mobile station (MS) uses the recursive least square algorithm for predicting the RSS from the candidate base stations (BSs) including both femtocell and macrocell BSs. Then, according to the predicted RSS values, several future values of signal-to-interference plus noise ratio (SINR) are calculated. Afterwards, the candidate list of BSs is pruned according to the estimated future SINR values and the predicted RSS of each BS. Finally, the target BS which yields the highest throughput, is opted for handover. Through extensive simulations, the effects of speed of MSs and the density of femtocell BSs on the outage probability (OP), throughput and the ping-pong rate of MSs are studied. The results show that the proposed handover algorithm outperforms the previous ones and improves the throughput of MS while it reduces the OP and the number of ping-pong handovers.

Waiting time occupies an important position in user's quality-of-service (QoS) evaluation system. However, in conventional overlay cognitive radio networks (CRN), the secondary users are not permitted to transmit any personal information whenever the spectrum is occupied by primary users. It follows that the waiting time of users depends heavily on the primary spectrum occupancy, which, in turn, cannot guarantee the QoS of the secondary users. To remedy this, a game theoretical cooperative waiting-time reducing method (CWTRM) is proposed in a self-generated CRN to meet users’ waiting-time demands. The proposed scheme divides the users to temporary primary and secondary groups instead of introducing an extraneous secondary network. Specifically, waiting users are served as temporary secondary users. The cooperation between them and the temporary primary users is proceeded in each frame to make reuse of the unused time fractions, thereby reducing the global waiting time of the network. The optimal relay power, pricing and corresponding cooperating strategies are determined with the utilisation of Stackelberg game and Hungarian method. Finally, the superiority of the proposed CWTRM over non-cooperative schemes is validated through simulations.

This study derives several new and simple closed-form approximations for the average symbol error rate (ASER) and outage probability performance metrics of digital communication systems (with/without diversity receivers) impaired by additive white Gaussian noise and fading. These approximations utilise the coefficients of the Poincare series expansion for the probability density function (PDF) of signal-to-noise ratio (SNR) random variable in conjunction with Mellin transform of the conditional error probability and/or its auxiliary functions to generalise some of the known asymptotic ASER/outage probability expressions to a wider range of modulation schemes and different types of propagation environments (including κ–μ, η–μ and α–μ fading channels). A new class of asymptotic approximations for the ASER/outage probability is also derived (based on a normalised asymptotic PDF of SNR) that is considerably better than the conventional high-SNR approximation although both techniques need only the first non-zero term of the Maclaurin (if exists) or the Poincare series expansion of the channel PDF. The authors’ also investigate the utility/efficacy of Welch–Satterthwaite and Moschopoulos approximations for yielding accurate predictions of the ASER in the low-SNR regime for different fading environments. Closed-form approximations for the ergodic (average) channel capacities of different types of fading channels with/without diversity reception are also derived.

In this paper, the authors present a novel moment generating function-based technique to unify the performance evaluation of an average energy detector for detecting unknown deterministic signals over generalised fading environments (including the η-μ, κ-μ, α-μ, K, G and K_G generalised fading distributions) with diversity reception. Specifically, the authors exploit a known exponential-type integral representation for the generalised Marcum Q-function Q_v (a, b) that is valid for any ratio of a/b but for positive integer order v to greatly simplify the task of finding the statistical expectations over the fading signal-to-noise ratio random variables in the computation of the average detection probability metric. This new approach leads to a very compact and an elegant solution for many practical cases of interest including the independent but non-identically distributed fading statistics and/or arbitrarily correlated diversity branches in maximal-ratio combining, square-law combining and square-law selection diversity receivers. The authors’ numerical results also show that the performance of average energy detector is superior to the classical total energy detector with the increasing number of samples owing to the noise averaging effect. We have also demonstrated the versatility and utility of the proposed analytical framework to investigate the impact of dissimilar mean signal strengths, fading parameters, time-bandwidth product, diversity order and signal combining techniques on the receiver operating characteristics of diversity energy detectors in a myriad of fading environments that had heretofore resisted simple solutions.

This study proposes a delay-scheduler coupled throughput-fairness resource allocation algorithm for users of mixed traffic in a long-term evolution (LTE) wireless network. The design objective is to maintain quality of services (QoSs) for real-time (RT) traffic as well as to provide throughput fairness for non-RT (NRT) applications. Instead of classifying packets as RT and NRT types like other methods do, the authors’ scheme classifies packets as ‘urgent’ and ‘non-urgent’ for channel scheduling to optimise the tradeoff between RT, QoS and NRT throughput. The proposed scheme consists of two stages. In the first stage, the scheme determines the scheduling priorities of the ‘urgent’ packets to guarantee QoS for RT services. In the second stage, the authors’ approach aims at providing fairness of channel utilisation for the ‘non-urgent’ traffic flows including NRT flows and the RT flows which are below the delay bonds. From the simulation results, it is shown that the proposed algorithm can effectively improve the QoS for RT users and achieve throughput fairness for NRT users by comparison with other approaches in the downlink transmission of LTE wireless networks.

To the problem of information fusion estimation for large-scale sparse wireless sensor networks (WSNs), a novel algorithm, named the information weighted consensus-based distributed particle filter, is presented. The proposed filter can avoid the divergence of the consensus error introduced by the naive nodes in the large-scale sparse WSNs. This is achieved by embedding an information weighted local particle filter (LPF) and a weighted-average consensus filter as the underlying filter and the top filter, respectively in each sensor node. The information weighted LPF will enable the weighted-average consensus filter to be used in the information space to communicate the information matrix and information state in a distributed fashion. And the weighted-average consensus filter will guarantee that a weighted average consensus for all initial states can be reached with some consensus error, which will not be divergent. Moreover, at the same time, the cross correlation between each pair of networked nodes can be approximately computed, which will further inhibit the divergence among the local estimated states of the filters embedded in each node. Finally, some examples are presented to illustrate the reasonability of the theoretical derivation.

This study addresses the ill-conditioning problem of the memory polynomial (MP) model with application to the predistortion of highly non-linear power amplifiers with memory effects. A resource-efficient lattice-based MP structure built using the cascade of a MP generator and a lattice predictor is proposed to overcome the ill-conditioning of the MP's data matrix. The proposed model performances are benchmarked against those of the MP model as well as the orthogonal MP model. The experimental results demonstrate the suitability of the proposed predistorter as it achieves similar performance in the time and the frequency domains compared to the MP counterpart while alleviating its ill-conditioning problem.

Conventional hierarchical modulation (HM) only provides two levels of unequal error protection (UEP) for multimedia traffic transmission. An HM-based scheme is proposed that provides multiple levels of UEP by exploiting the structure of the Alamouti scheme. A typical Alamouti scheme operates based on the assumptions that the modulation scheme used for the transmission at each antenna is the same and that the power in each antenna is equal. In the proposed system, these two operating assumptions are relaxed, in that the modulation schemes as well as the transmission powers for the two antennas are varied in order to propose a multiple level UEP mechanism for multimedia traffic. The concept is applied to a recently proposed system which uses the Alamouti space–time block code (STBC) structure with HM and signal space diversity (SSD), and it is shown via theoretical and simulation results how the simple UEP mechanism can accommodate the simultaneous transmission of multiple classes of multimedia traffic.

Owing to the advancement of wireless communication technologies, the vehicular ad-hoc network (VANET) has experienced a rapid development in recent years. However, it is challenging to design a reliable and efficient medium access control (MAC) protocol for safety messages with strict quality of service demands, owing to unreliable wireless links and frequent changes of topology. On the other hand, cooperative communication can enhance the reliability of wireless links by exploiting the spatial diversity. The authors present here a cooperative clustering-based MAC (CCB-MAC) protocol for VANETs, in order to improve the transmission reliability of safety messages. In CCB-MAC, the selected helpers relay the safety message to the nodes that have failed in reception during the broadcast period. In addition, cooperation is conducted in idle slots, without interrupting the normal transmission. Both mathematical analysis and numerical results demonstrate that CCB-MAC increases the successful reception rate of safety messages significantly.

The authors propose a low complexity list successive cancellation (LCLSC) decoding algorithm, where the advantages of the successive cancellation (SC) decoding and the list successive cancellation (LSC) decoding are both considered. In the proposed decoding, SC decoding instead of LSC decoding is implemented when all information bits from bad subchannels are received reliably. While the reliability of each information bit is estimated by its likelihood ratio (LR), the bit channel quality is measured via its Bhattacharyya parameter. To achieve this goal, the authors introduce two thresholds: LR threshold and Bhattacharyya parameter threshold. Also, the methods to determine them are both elaborated. The numerical results suggest that the complexity of LCLSC decoding is much lower than LSC decoding and can be close to that of SC decoding, while the error performance is almost equal to that of LSC decoding. Especially, when the code rate is in low region, the advantage of our decoding is more obvious.

The authors investigate linear transceiver design in uplink (UL) coordinated multipoint transmission and reception (CoMP) multiple-input multiple-output (MIMO) systems with joint detections. A two-stage design algorithm is proposed by exploiting the technique of interference alignment, optimising the structure of the effective channel and employing power loading, with the goal to achieve high throughput and convergence performance. In contrast to conventional CoMP transceiver design, which is investigated under a predefined number of data streams transmitted by each user, the authors further investigate the selection of the number of data streams, called the configuration selection, and propose a corresponding low-complexity algorithm. By combining the proposed linear transceiver algorithm and low-complexity configuration selection algorithm, this work presents a new practical framework for linear transceiver design in UL CoMP MIMO systems. The simulation results confirm that the proposed algorithms achieve higher sum-rate performance than prior linear transceivers used in UL CoMP MIMO systems. Furthermore, the proposed transceiver offers comparable performance to existing IA-aided transceivers with significantly faster convergence.

This study studies dual-hop amplify-and-forward relaying system employing differential encoding and decoding over time-varying Rayleigh-fading channels. First, the convectional ‘two-symbol’ differential detection (CDD) is theoretically analysed in terms of the bit error rate. The obtained analysis clearly shows that performance of two-symbol differential detection severely degrades in fast-fading channels and reaches an irreducible error floor at high signal-to-noise ratio region. To overcome the error floor experienced with fast-fading, a practical suboptimal ‘multiple-symbol’ detection (MSD) is designed and its performance is theoretically analysed. The analyses of CDD and MSD are verified and illustrated with simulation results under different fading scenarios. Specifically, the obtained results show that the proposed MSD can significantly improve the system performance in fast-fading channels.

The authors consider a subcarrier intensity-modulated relayed optical wireless communication system under the combined influence of path loss, atmospheric turbulence and pointing error impairments. The turbulence-induced fading is modelled by independent but not necessarily identically distributed (i.n.i.d.) Gamma–Gamma fading statistics where the relaying protocol followed by the system is decode and forward (DF). First, the statistics of instantaneous signal-to-noise ratio at the destination is derived, followed by the novel and exact closed-form expression for outage probability of the system. Then using the moment generating function-based approach, the authors evaluate error performance of the system in terms of average symbol error rate (SER) for M-ary phase shift keying modulation schemes. Further, as a special case for M = 2, that is, binary phase shift keying modulation scheme, the exact closed-form expression of average SER is derived in terms of mathematically tractable Meijer's G-function and extended generalised bivariate Meijer's G-function. Finally, at the end of the paper, various numerical examples are included to demonstrate the effect of different system parameters on the performance of the system and are verified by Monte-Carlo simulations.

The authors propose the construction of spatially coupled low-density parity-check (SC-LDPC) codes using a periodic time-variant quasi-cyclic (QC) algorithm. The QC-based approach is optimised to obtain memory efficiency in storing the parity-check matrix in the decoders. A hardware model of the parity-check storage units has been designed for a Xilinx field-programmable gate array (FPGA), to compare the logic and memory requirements for various approaches. It is shown that the proposed QC SC-LDPC code (with optimisation) can be stored with reasonable logic resources and without the need of block memory in the FPGA. In addition, a significant improvement in the processing speed is also achieved. This study also proposes a new QC algorithm for constructing spatially coupled repeat-accumulate (SC-RA) codes. The proposed construction reduces the implementation complexity of the encoder and subsequently saves significant computational resources required for storing and accessing the circulants in the decoder. The performance of the proposed code is also compared with the standard RA codes through simulations.

This study takes a new receiving approach to detect an ultra-wideband (UWB) signal in the presence of multiple access interference (MAI). A generalised normal-Laplace (GNL) distribution is exploited for designing a novel multiuser UWB receiver. To more accurately comply with real statistical behaviours of the MAI-plus-noise in time-hopping multiple access UWB systems, a modified parameter estimator, which is an adaptive method of moments estimation (aMME), is proposed. In the existing studies, the analysis about GNL model shows appropriate results for UWB simulations, while it requires heavy complexity to obtain the precise distribution because of no existence of a closed-form probability density function (PDF) expression. To practically evaluate the GNL PDF, the fast Fourier transform, which can significantly reduce the computational complexity is considered. The GNL using the aMME outperforms the conventional matched filter UWB receiver, the soft-limiting receiver, the Gaussian–Laplace mixture receiver, the p-order metric receiver and the previous GNL receivers, especially in high SNR ranges. Furthermore, the presented GNL receiving method is applied to each finger of the conventional Rake receiver for signal detection in IEEE UWB multipath channels. The proposed Rake receiver based on the GNL distribution performs better than the conventional Rake receiver in multipath fading channels.

In this study, a method is presented to construct column weight 3 (CW3) low-density parity-check (LDPC) codes using three-partite graphs. Let G_b be a bipartite graph and N_g be the set of all minimum length cycles in G_b . Using G_b and N_g , a three-partite graph denoted G(G_b , N_g ), or simply G_t , is formed. Let T be the set of length 3 cycles in G_t and T^a be the set of three element subsets of vertices in G_t such that each of these subsets form a subgraph with no edges in G_t and has precisely one element in each section of G_t . Furthermore, let H be the binary matrix in which the set of rows represent the set of vertices of G_t , the columns represent the elements of V:= T ∪ T^a , and h_ij = 1 if and only if the ith vertex of G_t belongs to the jth three element set in V. Then H is a CW3 binary matrix. Using the Tanner graph representing H , a recursive construction for CW3 LDPC codes is provided. Applying a simple restriction on T and T^a , codes free of length 4 cycles are generated. Euclidean and finite geometry codes are used as the base codes for generating new CW3 LDPC codes. Results are presented which show that these new codes perform well in an additive white Gaussian noise (AWGN) channel with the iterative sum-product decoding algorithm.