The study introduces the novel message authentication schemes for the smart meter system, where the symmetric cryptography-based physical layer-assisted message authentication (PLAA) scheme and the public key infrastructure- based PLAA scheme are introduced. The proposed schemes integrate the conventional message authentication schemes and the physical layer authentication mechanisms by taking advantage of temporal and spatial uniqueness in physical layer channel responses, aiming to achieve fast authentication while minimising the packet transmission overhead. The authors also verify their claims through extensive analysis and simulation via comparing with proposed PLAA scheme with traditional upper layer authentication schemes. The proposed novel schemes yield the lower time delay for authenticating each message, which can satisfy the requirement of the real-time control over the smart grid.

Multiple secondary users can cooperate to increase the reliability of spectrum sensing in cognitive radio (CR) networks. However, the total transmission power grows approximately linearly with the number of cooperative secondary users. This study proposes a new approach to optimise the trade-off between sensing reliability and power efficiency in cooperative CR networks over fading channels. The authors assume K cooperative secondary users each collect N samples during the sensing time. The proposed approach is based on dividing the spectrum sensing into two phases. In the first phase, the authors use only n ₁ of N samples (n ₁ ≤ N), to check the channels state, then k of K cooperative secondary users (k ≤ K), which are in deeply faded channels are discarded. The authors call this n ₁ a check point of the sensing time. The spectrum sensing with relatively less-faded channels are continued during the second phase. Therefore there is a check point at which the sensing time can be optimised in order to maximise the probability of detection and the power efficiency. Several experiments are carried out to test the performance of the proposed approach in terms of probability of detection and power efficiency. The obtained results show that the proposed approach enhances the probability of detection and shortens the optimal sensing time. Moreover, it improves the overall power efficiency.

The author presents the design and analysis of low-complexity symbol timing error detectors (TEDs) for timing synchronisation in quasi-orthogonal space–time block code (QOSTBC) receivers. The estimators operate on data symbols and approximate decision variables, producing timing error measurements which are shown to be robust to channel fading. In evaluating the detector S-curve for the general form of the estimator, the author shows that the result is independent of the constellation rotation angle employed by the code. The expressions for the estimation error variance and TED signal-to-noise ratio are also obtained, with the analysis carried out under the assumptions of perfect data and channel knowledge at the receiver. Through system simulations, the effects of decision errors on the detector characteristics are examined, and the overall system performance is evaluated, where the proposed TEDs are incorporated into the receiver timing loop. Receivers with perfect channel knowledge and pilot-based channel estimation are considered. Symbol error rate results show timing synchronisation loss of less than 0.5 dB for a receiver with perfect channel information. In addition, it is shown that the receiver is able to track the timing variations two orders of magnitude faster than required by the present-day hardware oscillators.

Reducing energy consumption for data transmissions and prolonging network lifetime are crucial in the design of energy-efficient routing protocols. The proportion of successful data transmissions is significant for the reduction of data transmission and traffic load energy consumption, although the energy remaining in node is important for prolonging network lifetime. In this study, the authors propose an energy-efficient cross-layer design for the network layer and medium access control (MAC) layer that reduces energy consumption and prolongs network lifetime. In the network layer, a minimum transmission energy consumption (MTEC) routing protocol is proposed for selecting the MTEC path for data transmission, based on the proportion of successful data transmissions, the number of channel events, the remaining node energy of nodes and the traffic load of nodes. The authors design an adaptive contention window (ACW) for the MAC layer that provides nodes with high successful transmission rates with greater opportunity for contending for a channel to save energy. They used simulations to compare the proposed cross-layer design (MTEC with ACW) with related protocols, including dynamic source routing, traffic-size aware and the Varaprasad routing protocol. The simulation results showed that the proposed cross-layer design (MTEC with ACW) provided better packet delivery rate and throughput than existing protocols. MTEC with ACW also exhibited lower-energy consumption during data transmission and a higher network lifetime than existing protocols.

In this study, the authors investigate the expected complexity of increasing radii algorithm (IRA) in an independent and identified distributed Rayleigh fading multiple-input–multiple-output channel with additive Gaussian noise and then present its upper bound result. IRA employs several radii to yield significant complexity reduction over sphere decoding, whereas performing a near-maximum-likelihood detection. In contrast to the previous expected complexity presented by Gowaikar and Hassibi (2007), where the radius schedule was hypothetically fixed for analytic convenience, a new analytical result is obtained by considering the usage of multiple radius schedules. The authors analysis reflects the effect of the random variation in the radius schedule and thus provides a more reliable complexity estimation. The numerical results support their arguments, and the analytical results show good agreement with the simulation results.

This study presents an orthogonal design of space-time block code (STBC) that is single symbol decodable and enables full diversity and full rate transmission in a quasi-static channel environment. In the proposed scheme, full diversity is achieved by use of constellation rotation and co-ordination interpolation as is the case for the co-ordinate interleaved orthogonal design, whereas the transmission matrix of the proposed code consists of orthogonal columns with all non-zero elements, alleviating the concern about high peak-to-average power ratio. In particular, the proposed code offers lower complexity of channel estimation, and exhibits lower symbol error rate than the conventional quasi-orthogonal STBC when an maximum-likelihood decision-directed channel estimator is assumed. The advantages of the proposed code over the conventional codes are demonstrated through computer simulations. In addition, the selection of the angle of rotation for the proposed design is also presented, regarding the impact of channel estimation error.

To suppress co-channel interference in polarisation-enabled wireless communication systems, this work aims to provide an interference suppression scheme by exploiting polarisation domain, besides the state-of-the-art temporal, frequency, spatial and code domains. System models, algorithms, characteristics and applications of polarisation filtering (PF) for co-channel interference suppressions for polarisation-enabled (e.g. orthogonal dually polarised antennas) wireless communications are investigated. Specifically, four system models for PF using subspace analysis are established and discussed. The four proposed system models are categorised based on different statistic characteristics of the target signal and that of the interfering signal: both the target signal and interference are temporal deterministic, the target signal is deterministic whereas interference is temporal random, the target signal is random whereas interference is deterministic and both the target signal and interference are random, respectively. Based on the statistic characteristics and subspace theory, the detailed PF implementation for each model is analysed and the closed-form filtering operator is given. It is also shown that the PF implementation for each model can be attained by using one of the zero-forcing matched subspace processing, decorrelating matched subspace processing or Wiener subspace processing. Furthermore, relationship among these four models indicates that, under certain conditions, the implementation of the other three models can be fulfilled by using the implementation of the first model. Numerical and simulation results show the effectiveness of the proposed scheme.

In IEEE 802.16e networks, with the popularisation of multimedia services, multicast and unicast services can coexist in one mobile subscriber station (MSS). The mobile devices are generally powered by battery, which is limited in energy. Thus, power saving is an important issue to be considered for extending the lifetime of the MSSs. The authors have proposed a multicast services-based scheduling (MSBS) algorithm that improves the energy efficiency of both unicast and multicast services, while satisfying the quality of service requirements of the MSSs in 802.16e wireless networks. MSBS schedules the packets in such a way that each packet is transmitted before its deadline and the energy consumed by the MSSs is reduced by minimising the number of state transitions by the MSSs. The simulation results show that MSBS can produce significant overall energy-saving and prolonged lifetime as compared to other scheduling schemes in 802.16e wireless networks.

This study addresses the problem of carrier frequency offset (CFO) tracking in co-operative space-frequency block-coded orthogonal frequency division multiplexing (OFDM) systems with multiple CFOs. Considering that the inserted pilot tones are decayed by data subcarriers in the presence of multiple CFOs, a novel recursive residual CFO tracking (R-RCFOTr) algorithm is proposed. This method first removes CFO-induced inter-carrier interference from data subcarriers, and then updates the residual CFO (RCFO) estimation of each OFDM block recursively. When used in conjunction with a multiple CFOs estimator, the proposed R-RCFOTr can effectively mitigate the impacts from the multiple RCFOs with affordable complexity. Finally, simulation results are provided to validate the effectiveness of our proposed R-RCFOTr algorithm, which has performance close to that of perfect CFO estimation at moderate and high signal-to-noise ratio, and significantly outperforms conventional CFO tracking algorithm for large CFOs.

Goppa codes have some of the largest minimum distances possible for linear codes. The authors use some binary Goppa codes in which four new binary codes are obtained with parameters better than any codes known to date. The authors also present the necessary conditions for a code obtained by shortening a longer code which will have a greater minimum distance than the original code.