A new decoding strategy of belief propagation (BP) for low-density parity-check codes is presented by serially concatenating the traditional simultaneous decoding (also known as flooding) and the informed dynamic decoding (IDD) (e.g. node-wise residual belief propagation (NW RBP) or informed variable-to-check (IVC) RBP). The frame error rates (FER) and bit error rates (BER) of the concatenated BP decoder outperform that of the non-concatenated single decoder. In addition, as the signal-to-noise ratio (SNR) increases, the average number of decoding iterations required for the concatenated BP decoder decreases, and tends to merge with that of the first sub-decoder in the high SNR region. Moreover, since the IDD strategies concerned in this paper require extra effort for the residual computation, and the sequential updating of IDD is much more time consuming than the simultaneous updating of flooding. Therefore, compared with using a single IDD, serially concatenating flooding and IDD reduces both the approximate decoding complexity and the decoding latency because the concatenated decoder is still dominated by the sub-decoder flooding.

Cooperative communication has great potential to enhance the performance of wireless networks by exploiting relay nodes' spatial diversity. Relay assignment plays a vital role in making the most of this potential. However, most previous studies investigate relay assignment in a rather static manner which may lead to the under-utilisation of relay nodes, especially in the scenarios where source nodes' demands are time varying. Hence, in this study, the authors consider the relay assignment problem for cooperative networks using auction model with access flexibility, i.e. providing sufficient flexibility for source nodes to access relay nodes in time domain. They divide relay nodes' access time into multiple smaller access units and permit each source node to bid for a bundle of desired access units in the auction. This model is formulated as a combinational auction whose winner determination problem is NP hard. They thus present an auction mechanism with an elaborated greed strategy which not only achieves adorable properties such as truthfulness, individual rationality and computational efficiency, but also guarantees near-optimal social welfare. Finally, they conduct extensive evaluations to verify the performance of their mechanism.

Due to the broadcast nature of the radio propagation, requirements of high data rates and low probability of detection (LPD) form a well-known trade-off problem in covert wireless communication. Frequency hopping (FH) is a communication technology that is able to efficiently solve this problem by randomly switching its transmission channels. However, it is extremely complex to design an FH sequence (FHS) in a coloured noise scenario where different channels have different noise levels. To address this issue, in this paper, we propose a novel probabilistic FHS based on spectrum sensing. The FHS achieves the LPD among typical FHS under the constraint on a prescribed bit error rate. The authors present two algorithms that are used to generate the FHS and we analyse their computational complexity. To evaluate the performance of the sequence, we derive an expression for the probability of detection (PD). Simulation results show that the system bit error rate and the PD of the proposed FHS are low, and can be flexibly adjusted according to various practical requirements.

Idle nodes are used in cooperative communication to achieve performance gains. Energy harvesting (EH) technology makes cooperative communication less dependent on batteries. In this study, the performance of EH amplify-and-forward relaying is analysed by considering the throughput for Rician fading channels and non-ideal relaying nodes, compared with previous works that focused on Rayleigh fading channels with ideal relaying nodes. The authors consider discrete time EH protocol and continuous time EH protocol. In addition, they derive the analytical expressions for the average throughput. Numerical results are presented to show the good performance of the system in Rician fading channels and the satisfactory performance while using the non-ideal relaying node by examining various system parameters using the analytical expressions.

This study proposes a finely quality of service (QoS)-guaranteed algorithm to jointly optimise the throughput and energy efficiency in MU-multiple-input multiple-output systems. The latency requirements of real-time services are guaranteed by user scheduling in the first stage. The energy efficiency and system throughput are jointly optimised while the required transmission rate is finely guaranteed in the second stage. Simulation results show that the algorithm can achieve a good balance between the energy efficiency and throughput, and is superior to the existing schemes in terms of QoS guarantee.

In this study, the authors propose a new two-stage decoding scheme for low-density parity-check codes to lower the error-floor, which consists of the conventional belief propagation (BP) decoding algorithm as the first-stage decoding and the re-decodings with manipulated log-likelihood ratios (LLRs) of variable nodes as the second-stage decoding. In the first-stage decoding, an early stopping criterion is proposed for early detection of decoding failure and the candidate set of the variable nodes are determined, which can be partly included in the small trapping sets. In the second-stage decoding, the scores of the variable nodes in the candidate set are computed by the proposed unreliable path search algorithm and the variable nodes are sorted in ascending order by their scores for the re-decoding trials. Each re-decoding trial is performed by BP decoding algorithm with manipulated LLR of a selected variable node in the candidate set one at a time with the second early stopping criterion. The parallel unreliable path search algorithm is also proposed for practical application of the proposed algorithm. Numerical results show that the proposed early stopping criteria and the proposed decoding algorithms for the second-stage decoding can correct most of the unsuccessfully decoded codewords by the first-stage decoding in the error-floor region.

In this study, the ergodic secrecy capacity and the corresponding outage probability of two-hop amplify-and-forward relaying system in the presence of a passive eavesdropper are analysed. In order to improve the security, in this study, zero-forcing (ZF) scheme is implemented at different locations in the system. The effect of the ZF-based scheme on the system security is considered for three different scenarios, based on where the ZF scheme is applied, namely, (i) ZF receivers at the relay and destination nodes, (ii) ZF precoders at the source and relay nodes, and (iii) ZF precoders/receivers at the relay nodes. For each scenario, explicit analytical expressions for the ergodic secrecy capacity and secrecy outage probability are derived. Monte Carlo simulations are also provided to validate the analysis. Results show that increasing the number of source, relay and/or destination nodes can be favourable or unfavourable to the system security and the significance of this enhancement/degradation depends on the particular scenario deployed. In addition, the system security improves with increasing the source and/or relay power.

The physical layer security in the up-link of the wireless communication systems is often modelled as the multiple access wiretap channel (MAC-WT), and recently it has received a lot attention. In this paper, the MAC-WT has been re-visited by considering the situation that the legitimate receiver feeds his received channel output back to the transmitters via two noiseless channels, respectively. This model is called the MAC-WT with noiseless feedback. Inner and outer bounds on the secrecy capacity region of this feedback model are provided. To be specific, we first present a decode-and-forward (DF) inner bound on the secrecy capacity region of this feedback model, and this bound is constructed by allowing each transmitter to decode the other one's transmitted message from the feedback, and then each transmitter uses the decoded message to re-encode his own messages, i.e. this DF inner bound allows the independent transmitters to co-operate with each other. Then, we provide a hybrid inner bound which is strictly larger than the DF inner bound, and it is constructed by using the feedback as a tool not only to allow the independent transmitters to co-operate with each other but also to generate two secret keys, respectively, shared between the legitimate receiver and the two transmitters. Finally, we give a sato-type outer bound on the secrecy capacity region of this feedback model. The results of this paper are further explained via a Gaussian example, and from this example, we see that the noiseless feedback helps to enhance the achievable secrecy rate region of the Gaussian MAC-WT without feedback.

This paper studies cooperative transmission for securing a two-hop network where the eavesdropper can wiretap the relay channels. With outdated channel state information (CSI), we propose an opportunistic relaying with destination-based jamming scheme, where one relay is chosen to forward the confidential signal and the destination sends jamming signal to confuse the eavesdropper. To reveal the capability of the proposed scheme in improving the system secrecy, we investigate the two common performance metrics under different assumptions on the eavesdropper CSI. First, lower bound on the ergodic secrecy capacity (ESC) is derived assuming perfect knowledge of the eavesdropper channel gains. We, then, extend our results to the scenario where only the legitimate channel gain is known. Here, lower bound on the secrecy outage probability (SOP) is obtained. To further improve the utility of the destination, under total power constraint, a power allocation between data signal and jamming noise is considered. Both the analysis and simulation results indicate that the system performance is significantly improved in terms of both ESC and SOP when the jamming power at the destination is adjusted according to the selected relay position. We verify that, with outdated CSI, the secrecy performance of opportunistic relaying is severely degraded.

The energy harvesting paradigm enables the design of new wireless powered cellular networks (WPCNs) for the Internet-of-Things (IoT). In a WPCN, if the harvested energy is larger than the consumed energy, an IoT device may utilise the surplus harvested energy to extend the battery lifetime or to enhance the performance. Otherwise, a power saving mechanism is utilised as in traditional wireless cellular networks. In long-term evolution (LTE) systems, the discontinuous reception (DRX) mechanism has been adopted to save the power consumption of user equipments (UEs). However, the wakeup delay increases as the amount of the saved energy increases, and the optimisation for the DRX mechanism is required. In this study, the authors propose a novel energy harvesting DRX (EH-DRX) mechanism to minimise the wakeup delay in WPCNs. In the authors' proposed EH-DRX mechanism, an IoT device utilises the harvested energy to minimise the wakeup delay. Then they provide an optimisation algorithm to allocate the DRX parameters by utilising the harvesting capability of IoT devices. The optimisation algorithm is based on the analytical model for the proposed EH-DRX mechanism. Analysis and simulations indicate that the proposed EH-DRX mechanism reduces the wakeup delay compared to the traditional DRX mechanisms.

Auction is a highly effective trading form for distributing resource among buyers in a market at competitive prices, and has been applied to many domains, e.g. spectrum allocation in wireless networks and the virtual machine allocation in cloud computing. Most of existing auction mechanisms based on McAfee double auction calculate the uniform clearing prices for winning buyers no matter what channel they acquired, which does not reflect the differences of buyers' personalised preferences for heterogeneous spectrums. Hence, in this paper, we propose a truthful double auction scheme, named TRUDA, which incorporates the marginal effect of buyer–seller pair into auction mechanism design and considers the case in which buyers are mutually exclusive. We show analytically that this auction mechanism guarantees the economic-robustness of the auction and has polynomial time complexity.

Radio frequency IDentification (RFID) applications in the Internet of Things usually use multiple readers to read multiple tags. In such a practice, reader collisions may critically affect the performance. To obtain better reading schedules for the readers in order to enhance the RFID performance, the authors introduce a new and efficient anti-collision algorithm – the SwitchTable algorithm – in this study. The authors build the new algorithm over the concepts of the four-colour theorem and also the switch tables to fix the loopholes in existing algorithms – mainly the practice of variable MaxColor and the broadcast of kick signals. The authors’ SwitchTable algorithm sets MaxColor to four according to the four-colour theorem, to avoid possible collisions and solve the problem of previous dynamic MaxColor change. It meanwhile uses a colour switch mechanism which works by switch tables and unicasting switch signals (not broadcasting kick signals) to remove the impact of sending kick signals and attain more efficient planned colour change. Extended simulation runs are carried out to evaluate the performance of various anti-collision algorithms, including DCS, ColorWave, ColorTable and the authors’ SwitchTable. The results show that, with the new features, the authors’ new algorithm produces constantly better transmission success ratios and throughput, particularly in more complex RFID networks.

In this study, zero-forcing matrix decomposition polynomial expansion update (ZF-MDPE-update) and zero-forcing successive over relaxation update (ZF-SOR-update) algorithms are proposed to update a zero-forcing detector quickly without requiring complicated matrix inversion recomputations when massive multiple-input multi-output systems channel estimates contain a small perturbation. To further accelerate the convergence rate and to maximise date throughput, a new method of calculating the optimal coefficients for the matrix polynomial that can significantly improve the accuracy of the initial input inverse matrix approximation is considered by the ZF-MDPE-update algorithm. On the other hand, the ZF-SOR-update algorithm with an optimal iterative initial solution and an optimal relaxation parameter is devised, which achieves excellent detection performance. Results demonstrate that when the ratio of base station (BS) antennas to user terminal (UT) antennas, , is small, the proposed update detection algorithms, with only a few operations, achieve a significant improvement in the average achievable rate of the UTs compared to the recently proposed update algorithm. Therefore, more UTs can be served in a cell with a fixed number of BS antennas. At the same time, the authors' algorithms are shown to facilitate easy memory transfer and are low cost.

Computational grid provides virtual powerful computer for solving any large-scale scientific, commercial, and engineering problems by aggregating and sharing heterogeneous resources. However, designing an effective resource allocation method is a complicated task. To undertake the task, several economic-based resource management models have been studied. Bargaining (or negotiation) is one of the most used and effective models even though it has several main defects such as high communication demand and the risk of losing a deal. Instead of repeating negotiation for every generated grid job (GJ), the novel contribution of threshold-based negotiation framework is to determine whether a new negotiation is needed or not, according to the current market conditions which depend on supply of resource providers and demand of consumers. In the proposed framework, agents request for renewing negotiation, provided that the amount of change in market conditions exceeds pre-defined threshold. Therefore, communication overhead and the risk of losing the deal are minimised by avoiding unnecessary negotiations.

The authors analyse a dual-hop mixed radio frequency/free space optical (RF/FSO) communication system comprising of single-input multiple-output (SIMO) RF hop and a single FSO hop. The RF source is connected to an optical destination through a decode-and-forward relay having RF/FSO capabilities. Each link in SIMO-RF hop is assumed to experience independent and identically distributed (i.i.d.) Nakagami-m fading. For FSO hop, a unified novel expression for the probability density function (PDF) of irradiance has been derived which unifies Gamma–Gamma and generalised-K () distributions with misalignment error. Moreover, we obtain a unified PDF of instantaneous signal-to-noise ratio (SNR) by unifying the heterodyne detection and intensity modulation/direct detection schemes. Utilising the unified PDF, we derive novel unified closed-form expressions for average symbol error probability (for different RF modulation techniques), outage probability, and ergodic capacity for the system under consideration. We have also analysed the considered system for high SNR conditions and have analytically obtained the unified diversity order of the same. The derived results clearly show the impact of misalignment error, severe atmospheric conditions, type of detection scheme, and number of RF links on the system performance. All the analytical results are validated through simulations.