In this study, the authors design a multi-user ultra-wideband system for indoor wireless communication. The proposed system is useful in multipath radio reception as the full multipath diversity gain is achieved. The system has multiple transmitters and receivers. They use polyphase spreading waveforms which feature low levels of mutual interference and enable each of the channel impulse responses to be measured free from distortion continuously with each data symbol transmission. A key feature of the proposed system is that transmitted waveforms are used which produce outputs from the receiver cross correlators, which are zero on both sides of the main correlation peak, for each radio path. This zero response lasts for a duration in excess of the expected delay spread of the radio channel enabling full Rake processing of the multipath signal. The effects of the low levels of mutual interference are reduced further by using time and frequency hopping, forward error correction and soft decision decoding.

This study proposes a method to handle unrecoverable data using a formula called Bézier curve. The proposed method suggests the possibility to approximate the damaged data, which have been processed by the error correction scheme. The proposed method works on the real-time distributed system which retransmission is considered as unsuitable solution to manage the overall networked system. By using the Bézier curve, the transmitted unrecoverable data are reconstructed again by using the functional approximation. This method provides a smoothing effect on damaged data that usually are normalised on real-time transmission of PROFIBUS. Three differences Bézier curve methods are compared in PROFIBUS data, four-points (FP) method, two-points two-degrees method and four-degrees (FD) method. Simulation results show that all three Bézier curve methods can approximate data in PROFIBUS. FD has higher computation complexity compared with others. However, FD compensates with its data size which is only half of FP method.

Inter destination video synchronisation (IDVS) is a key technology in emerging interactive multimedia applications. It is essential to ensure the synchronous experiences of users in such applications. However, one inevitable barrier for IDVS is the packet transfer delay differences (PTDDs) among different destinations. Existing researches have tried to eliminate the side effects of PTDD passively and schedule the video packets in a ‘back-to-back’ fashion. In this paper, the authors propose to proactively leverage such differences to design a transmission scheme that enhances video quality while ensuring the synchronous arrival of packets. Based on the network measurements from a real multimedia conferencing system and the Planetlab, they find that the PTDD is between the ranges of 100–250 ms. Motivated by this observation, they propose a scheme named asynchronous departure for synchronous arrival (ADSA), which inserts intervals between consecutive packets according to the synchronisation reference. To prove the superiority of ADSA, they carry out analysis based on Gilbert loss model and continuous time Markov chain. They conduct performance evaluation through emulations in Exata and experimental results show that ADSA improves the video peak signal-to-noise ratio by up to 9.1 and 6.9 dB compared with existing latest and earliest schemes, respectively.

The sensing field on three-dimensional (3D) terrains that is supposed to be fully covered by deployed nodes may not be covered because of random aerial deployment. Non-uniform coverage has a negative impact upon that their lifetime and performance get short and worse, respectively. Mobile sensor networks (MSNs) are introduced to improve a coverage problem from sensor malfunction by an obstacle or the terrestrial environment. Providing coverage in a mountainous terrain has become critical issues in MSNs. This work proposes a 3D coverage method that can consider a physical feature, such as slope, in a mountainous terrain, that is, a 3D spiral model that allows mobile sensors to move freely in spiral lines devised using the height and radius of a concaved terrain. In the proposed model, the reasonable number of sensors to be deployed and the designated sensing points achieve full coverage. This paper focuses on full coverage for which the spiral model challenges the reasonability in the number of sensors. The experimental results show that the proposed method provides improved performance in terms of coverage ratios and expected coverage time; in addition, this has higher accuracy in lower power cost and better expansibility.

Statistical quality of service (QoS) provisioning is a performance metric that determine the user satisfaction as the main purpose of future wireless networks. Effective capacity (EC) is a valuable quantity which helps analysing delay QoS performance as the most popular QoS metric. In this study, the authors concentrate on characterising the delay QoS performance via the EC of uplink transmission mode of individual users in multiuser centralised networks in which the user's transmitted signals may interfere with each other. To reduce the computational complexity of finding EC, the authors first propose closed form expressions for the EC of each user, with or without considering the inter-symbol interference (ISI). Then, two general algorithms are presented to clarify the relation of EC and QoS guarantee performance of a system in which the way of analysing QoS guarantee performance is explained step-by-step. By the use of these algorithms and the obtained closed form EC functions, the authors investigate the statistical delay QoS performance of individual users and the effects of channel conditions and ISI on their performance. The numerical results validate our analytical outcomes in deriving closed form equations and evaluate the offered schemes in characterising delay QoS performance.

In all-optical orthogonal frequency division multiplexing (AO-OFDM) systems, symbol time misalignment (STM) and subcarrier frequency offset (ScFO) result in intercarrier-interference and intersymbol interference, leading to degradation of bit error rate (BER) performance. In this study, an analytical study of the impacts of STM and ScFO on AO-OFDM system performance is conducted. In the presence of STM and ScFO, AO-OFDM system performance is evaluated with the number of subcarriers (N _SC), cyclic prefix requirements and receiver bandwidth (BW_RX ). For AO-OFDM system without CP, results show that the STM gives higher BER than the ScFO. To keep the BER below 10 ^{− 3} in AO-OFDM systems with on-off keying-modulated three optical subcarriers and homodyne detection with BW_RX = 30 GHz, the maximum acceptable relative deviations for the STM and the ScFO are 11 and 14%, respectively.

In this study, the authors propose a distributed turbo coded (DTC) scheme utilising two best relays selected among multi-relays. In this scheme, the considered turbo encoder is a rate 1/3 parallel concatenated code composed of two recursive systematic convolutional codes. The systematic information sequence is transmitted directly to a destination, whereas the two parity sequences, one of which is interleaved, are transmitted through the two selected best relays. The authors derive a union bound for the frame error rate including an upper bounded closed form expression for the pairwise error probability of the DTC scheme with two ordered best relays (DTC-TBR) by utilising order of statistic, then the authors verify the analytical expression by simulations. Numerical results show that the proposed scheme outperforms the DTC scheme with a single best relay (DTC-SBR) because of the more selection gain of the DTC-TBR compared with those of DTC-SBR with the rise of number of relays.

In this study, a resource allocation scheme for energy-efficient communication in a cooperative orthogonal frequency division multiple (OFDM) network based on subcarrier pairing is proposed. Different from traditional cooperative OFDM networks, in the concerned network, one subcarrier pair can be forwarded by multiple relays, and the source is allowed to retransmit the signals sent in the first phase. The problem aimed at maximising the system energy efficiency (EE) under total power constraint and minimum spectral efficiency constraint is formulated into a mixed-integer nonlinear programming (MINLP) problem, which in general has intractable complexity because of its combinatorial nature. The authors simplify the optimising model as a typical fractional programming problem to solve the complex the MINLP problem. The simplified fractional programming problem is proved to be quasi-concave, thus Dinkelbach's method consisting of outer iterations and inner iterations can be used to find the optimal solution to the proposed MINLP problem.

In this study, the authors propose a signal detection technique of successive interference cancellation to reduce the effect of inter-symbol interference (ISI), which is caused by the time difference of arrivals among distributed nodes in an asynchronous wireless mesh network based on filtered multi-tone modulation. The proposed signal detection technique uses partial matrices of a transmission gain matrix to mitigate the ISI effect from the adjacent symbols. Under the assumption of perfect symbol time offset and channel estimation at each node, it is shown by simulation that the proposed technique can improve the bit error rate performance with lower complexity compared with the conventional technique.

This study evaluates the performance of a practical IEEE 802.15.4/4e/4g low-rate (LR) wireless personal area network (WPAN) with multiple physical (PHY) layers and multi-hop capabilities for smart utility networks, machine-to-machine networks and other advanced sensor networks. The proposal includes realistic design considerations addressing demands of practical applications, country-specific regulatory requirements and technical specification in international standards. A cross-layer open system interconnection model from the application, transport, network, medium access control, down to the multiple PHY layers is constructed based on the specification in IEEE 802.15.4 LR-WPAN and other layer-specific standards. Employing the cross-layer model, extensive computer simulations were conducted to investigate the performance of the LR-WPAN system in this application domain. As a result, the authors have successfully verified the simulated achievable average throughput in both PHY layer designs, multi-rate and multi-regional frequency shift keying (MR-FSK) and multi-rate and multi-regional orthogonal frequency division multiplexing (MR-OFDM) with the theoretical throughput by calculation. Secondly, in a multi-PHY environment with the presence of 30 interferer devices, throughput degradation of the victim system is observed within 30%. Furthermore, when interferer devices transmit frames with interval beyond 1 s, the degradation to the victim system becomes negligible. Thirdly, MR-FSK PHY has a simpler design with higher energy-efficiency, whereas MR-OFDM PHY is more complicated with more resilience to interference. They have found an interference tolerance capability difference of 15 dB between the MR-FSK and MR-OFDM systems. Fourthly, comparing with their single-hop counterparts, multi-hop systems have lower average throughput in MR-FSK by 25% and MR-OFDM by 10%. Finally, comparing with networks with periodical beacon transmissions, asynchronous networks have more inferior average throughput of 20% in MR-FSK and 3% in MR-OFDM, with the advantage of longer battery lifespan.

Spectrum handoff is one of key technologies of cognitive radio. A spectrum handoff strategy based on adaptive weights adjustment is proposed, considering the effect of secondary users’ (SUs) transmission power, fading factor, bandwidth and channel availability on the target channel selecting. According to the principle of multi-attribute simple additive weight algorithm (MA-SAW), the expected effect function of each channel is obtained by analysis. Making full use of the change of the various factors in cognitive wireless network, the LMS adaptive algorithm of dynamic weights is put forward. Finally, the dynamic weights are applied to MA-SAW, to determine target channel to switch. The simulation results show that the proposed algorithm can reduce the switching times of SUs, and improve the effective transmission rate.

In this study, the downlink spectral efficiency of multi-cell multi-user large-scale distributed antenna systems (DASs) with pilot contamination is studied in a composite correlated Rayleigh fading channel. Firstly, under a physical channel model, the equivalent channel model of large-scale DAS with pilot contamination is given. Secondly, based on the equivalent channel model, the closed-form expression is derived for the downlink achievable rate with maximum ratio transmission, and the ultimate rate is also given when the ratio of the total number of base station antennas to the number of users goes to infinity. Thirdly, the results are validated via numerical simulations. It is shown that the closed-form expression is very accurate, and the downlink achievable rate of the large-scale DAS is much larger than that of the co-located massive multiple-input multiple-output (MIMO) with the same antenna configuration.

This study addresses the pilot scheduling problem in multiuser multi-cell massive multiple-input–multiple-output (MIMO) systems, aiming at mitigating the inter-cell interference (pilot contamination), which constitutes a bottleneck of the system performance. First, the authors investigate the pilot reuse and scheduling problem in cellular systems with unlimited number of base station antennas, only considering the large fading coefficients. Three low-complexity pilot scheduling schemes are then proposed by maximising the system achievable sum rate, including the greedy algorithm, the tabu search (TS) algorithm and the greedy TS algorithm. Second, they investigate the pilot reuse problem among the inter-cell user terminals (UTs) under spatially correlated channels for massive MIMO transmission, trying to distinguish UTs sharing the same time-frequency resources from the spatial domain. A closed-form expression of the non-asymptotic downlink achievable rate is derived by exploiting the second-order channel statistical information. On the basis of the degree of the UTs’ covariance matrices overlap with each other, they further propose a spatial orthogonality-based greedy pilot scheduling algorithm. The proposed approaches can provide much better performance in the presence of pilot contamination. Theoretical analysis and numerical results both verify the effectiveness of the proposed algorithms.

Maximising the tag reading rate of a reader is one of the most important design objectives in radio frequency identification (RFID) systems as it is inversely proportional to the time required to completely read all the tags within the reader's radio field. To this end, numerous techniques have been independently suggested so far and they can be broadly categorised into pure advancements in the link-layer tag anti-collision protocols and pure advancements in the physical-layer RF signal reception model. This study shows by rigorous mathematical analysis and Monte-Carlo simulations that how those two independent approaches can be coupled to maximise the tag reading efficiency in an RFID system, considering a slotted Aloha-based dynamic link-layer anti-collision protocol at tags and a multi-packet reception capable RF reception model at the reader.

Low-density signature code division multiple access (LDS-CDMA) and low-density parity-check (LDPC) code can both be represented by a single sparse graph. In this study, the authors propose a joint sparse graph (JSG) over GF(q) which combines LDS-CDMA and non-binary LDPC codes, namely JSG-CDMA. On the JSG, multiple accessing and channel coding are well-linked together, in addition, joint detection and decoding are performed by message passing algorithm. Two schedules for message updating on the JSG, that is, flooding and serial schedules, are, respectively, presented. To predict the convergence behaviour of the joint detection and decoding, they depict the iterative structure of the JSG-CDMA receiver and analyse its extrinsic information transfer chart. Key factors of JSG-CDMA include message passing schedule, maximum iteration number and Galois field order. Simulation results show that JSG-CDMA performs much better than conventional CDMA, in addition, compared with LDS-CDMA and turbo structured LDS-CDMA, at a bit error rate of 3 × 10⁻⁴, JSG-CDMA brings about 1.9 and 1.1 dB gain, respectively.

A precoding scheme for physical layer security of multiple-input single-output (MISO) wiretap channel with spatial correlation is designed. Quality-of-service (QoS) of the link is defined in terms of upper bounds on average symbol error rate function at Bob (legitimate user) and Eve (illegitimate user). Specifically, two problems are considered. First, a precoder matrix is designed to minimise the average transmitted power subject to QoS requirements at Bob and Eve. Next, we propose two algorithms to minimize QoS of illegitimate party for a given reliability level, depending on whether main user link has no correlation or is fully correlated. Our result for uncorrelated case demonstrate that by increasing the allocated power, main user can increase secrecy level up to an optimum point above which both legitimate and illegitimate receivers experience adequate QoS in their links. In fully correlated case, the problem is identified as an instance of concave minimisation over a polytope, and optimum power allocation is obtained via the widely known vertex enumeration algorithm. In both cases, our simulations validate the analysis significantly. The results confirm that linear precoding is able to trade average power against minimum achievable Eve performance.

This study presents a low-complexity soft-interference cancellation equaliser (SICE) for the turbo detection of multiple-input–multiple-output systems operating in time dispersive channels. The SICE contains three time-invariant linear filters: a feedforward filter, a causal feedback filter and an anti-causal feedback filter. The feedforward filter is designed to suppress the intersymbol interference because of channel time dispersion and the multiplexing interference from multiple transmit antennas. The causal (or anti-causal) feedback filter is developed to remove the residual interference caused by the symbols transmitted before (or after) the symbol under detection. The filters are designed by analysing the statistical properties of soft decisions. The performance of the proposed SICE is verified through both extrinsic information transfer (EXIT) chart analysis and computer simulations. The EXIT chart analysis shows that, because of the inclusion of the anti-causal soft decision, the SICE performance approaches the ideal matched filter bound as the iteration progresses. Consequently, the proposed SICE achieves significant performance gains over conventional equalisers.