The direct effect of the pilot positions to the channel estimation performance gives an opportunity for minimising the estimation errors in multicarrier transmission technologies. To this end, harmony search (HS) algorithm is proposed for optimising the pilot distribution pattern in order to increase the performance of least squares estimator employed in orthogonal frequency division multiplexing-interleave division multiple access (OFDM-IDMA) system. Besides, the upper bound of mean square error (MSE) utilised as the fitness function of HS algorithm is obtained by using Gershgorin disc theorem to get rid of matrix inversion process required in MSE calculation. In the simulations, the authors’ proposed HS-based pilot optimisation technique proves to be an effective way of pilot design for OFDM-IDMA system by providing a clear performance superiority over the other considered pilot placement strategies.

Received signal strength (RSS) in wireless networks is widely adopted for indoor positioning purpose because of its low cost and open access properties. However due to the sophisticated propagation of radio signals, the RSS shows a significant variation during pedestrian walking, which introduces critical errors in deterministic indoor positioning. To solve this problem, the authors present a novel method to improve the indoor pedestrian positioning accuracy by modelling fingerprinting and information on the movement into a hidden Markov models (HMMs). They divide the whole continuous positioning process into specified-size sub-processes, which could efficiently reduce the accumulative and resonance error caused by iterative estimation. They use an accelerometer sensor to provide the information on the movement distance to calculate the transition probability of the HMMs. In their experiments, they demonstrate that, compared with the deterministic pattern matching algorithm, the proposed method greatly improves the positioning accuracy and shows robust environmental adaptability.

The weighted K-nearest neighbour (WKNN) algorithm is widely applied to fingerprint positioning. However, the node position estimated by the WKNN algorithm is not optimal in a noisy environment. To obtain the optimised node location estimate, the authors propose an optimal WKNN (OWKNN) algorithm for wireless sensor network (WSN) fingerprint localisation in a noisy environment. The proposed OWKNN algorithm is composed of an adaptive Kalman filter (AKF) and a memetic algorithm (MA). First, the AKF is utilised to reduce the measurement noise of the received signal strength indication (RSSI) between the nodes in the WSN. Then, the MA is employed to optimise the calibration point weight for estimating the position of a target node in the WSN according to the filtered RSSI and a calibrated radio map. Finally, an optimal node location estimate is achieved based on the optimised weight. The extensive experimental results reveal that the localisation accuracy of the proposed algorithm is at least ∼50% higher than those of the state-of-the-art fingerprint localisation algorithms regardless of the placement of the target node, number of beacon nodes, and size of the calibration cell.

In this study, the authors focus on segment characteristic analysis and joint optimisation of modulation and coding scheme (MCS) selection, resource block (RB) assignment and the block error ratio (BLER) determination and segment adaptation scheme to satisfy dynamic adaptive streaming over HTTP (DASH) clients over wireless networks. First, the authors define a utility function as the continuous playback time that the packets scheduled with the allocated resource can support. Then, the authors formulate the MCS selection, RB assignment and BLER determination into a mathematical model. The relationship among the above three factors can be explored instead of performing MCS selection and RB assignment with the fixed BLER. By decomposing the original problem into some sub-problems, the authors can get a solution to the original problem with low complexity. At the client level, the authors develop an adaptive segment request strategy based on the playback information, the segments' characteristics and the estimated transmission rate. To decrease the influence of the inaccurate estimations, an adaptive guard time interval based on the real playback information and transmission information of the previous segments is introduced. Simulation results show that the proposed algorithm can efficiently improve playback continuity and video quality over the existing algorithms.

Location-aware services enable location intelligence which provides many benefits such as personalisation of communications, consumer analytics, locating a fireman in a burning building or classifying daily activities in the home among numerous other services. Active localisation technology is where a person carries a device such as a phone or beacon which communicates with a nearby wireless access point, whereas passive localisation is where a person does not carry any electronic device but their presence in a room causes a nearby monitoring device to detect them. This is the holy grail of tracking people as they do not need to carry tracking devices. A hybrid tracking approach is where both active and passive tracking techniques can be used to complement each other in tracking individuals indoors. This study provides an overview of an indoor location framework which allows the plugging in of multiple active tracking solutions such as Bluetooth beacons in addition to facilitating passive localisation techniques to provide a flexible hybrid indoor tracking solution for pinpointing individuals in locations and accordingly classify their activities. The authors demonstrate the practicalities of such a technique when used to classify everyday activities of daily life within a typical home environment.

As a combination of spatial modulation (SM) system and massive multiple-input multiple-output (MIMO) system, massive SM aided MIMO (SM-MIMO) system is recently proposed. In broadband scenarios, single-carrier (SC) modulation is introduced to massive SM-MIMO system, thus massive SC-SM MIMO system is proposed for uplink multi-user transmission over frequency-selective fading channels. In this study, the uplink spectral efficiency (SE) of multi-cell massive SC-SM MIMO system is analysed, meanwhile the pilot contamination effect is taken into consideration. A tight SE lower bound of multi-cell massive SC-SM MIMO system is proposed with maximum ratio (MR) combining, which also takes into account the imperfect channel estimation, transmit antenna correlation and path loss. The tightness of the authors' proposed closed-form SE lower bound is shown via simulation results. The optimal pilot reuse factor can be determined with different system configurations by simulations, and the pilot reuse factor that is larger than one is more suitable for less TAs and user equipments.

We developed an improved algorithm for an indoor positioning system based on an image sensor. By using the algorithm that tilts the image sensor when it is placed at room corners, the authors reduced the positioning error at the corners and increased the effective positioning area. When in room corners, the image sensor is placed at an appropriate angle that allows the reception of light from all three light-emitting diodes (LEDs). The unknown sensor position is calculated from the geometrical relations among the LED images created on the tilted image sensor plane. According to the obtained experimental results, signal–to-noise ratio of the received signal can be improved when the image sensor tilts at certain angle at the corner. It was found that the effective range of the tilt angle of the image sensor is estimated to be within the range of 30°–60° at the corners. The root mean-square of the positioning error obtained with the developed algorithm is 0.6 mm when the image sensor is located within the effective positioning area. The effective positioning area was increased by 15.3% at the corner areas when the image sensor was tilted by the optimal angle.

Device to device (D2D) communications are emerging as an essential part of technological solutions to boost data rates in the next generation networks. Cognitive radio (CR) opportunistically utilises spectrum to boost spectral efficiency. CR-assisted D2D networks will bring the benefits of both D2D as well as CR together in futuristic cellular networks. This study proposes to opportunistically use TV spectrum white spaces. A joint user selection, mode assignment, and power allocation in CR-assisted D2D networks can definitely yield higher data rates. The proposed study maximises data rate together with users' selection fulfilling various users' power, base station's transmit power, quality of service, and interference related thresholds. This problem is mixed integer non-linear programming and considered non-deterministic polynomial time (NP)-complete. Due to the discrete variables in the problem, finding an optimal solution with the help of an exhaustive search algorithm (ESA) becomes very challenging. The problem gets exponentially complex with the increasing number of user pairs. Thus, the need of another method becomes imperative that yields near optimal solution. Mesh adaptive direct search (MADS) algorithm is considered for solution in the CR-assisted D2D network resource management problem. Simulation results using MADS yield near optimal solution confirming the suitability of MADS for CR-assisted D2D networks.

In recent years, high-speed railways (HSRs) are being developed rapidly all over the world because of their convenience, safety, comfort, and other advantages. However, the reliability and security of HSR wireless communication systems have faced severe challenges, such as the Doppler effect, complicated wireless channel model, frequent handovers and so on. The International Union of Railways is pushing the evolution of the global system for mobile communications for railway (GSM-R) internationally. In this study, a high-speed based adaptive beamforming handover scheme is proposed to improve the handover performance for HSR wireless communication systems. When the high-speed train enters the overlapping region, the serving evolved NodeB (eNodeB) and target eNodeB are using beamforming with different gain factors to improve the received signal quality. In addition, this scheme can dynamically adjust the handover hysteresis margins of the reference signal receiving power (RSRP) and the reference signal receiving quality (RSRQ) based on the speed and position. Simulation results have demonstrated that the proposed handover scheme can improve the handover performance by increasing the handover trigger probability and success probability effectively.

The authors address the problem of channel estimation and data detection in a large multiple-input multiple-output (MIMO) systems in Rayleigh fading environment. A method of channel estimation and data detection is proposed in large MIMO systems. The channel matrix is decomposed in channel matrices; where and are the number of antennas at the destination and source, respectively. The pilot signals are clubbed with data symbols encoded in orthogonal space-time block codes (OSTBC), and then by using the properties of null matrix, channel estimation is performed. A decoder of OSTBC data is derived by assuming the perfect channel state information (CSI) at the destination; then perfect CSI is replaced by estimated CSI in the decision metric. The expression for the moment generating function (MGF) of the received signal-to-noise ratio at the destination node is derived for the proposed scheme. Using the MGF expressions, they obtain the analytical symbol error rate for the proposed channel estimation-based decoders for general OSTBCs with M-ary phase-shift keying modulation symbols.

Encryption is primarily used to ensure the confidentiality of information transmitted over an insecure wireless channel. However, an encrypted signal may be received with some errors due to noise and interference in the wireless channel. To alleviate these errors in the received encrypted signal, Zibideh and Matalgah proposed two different versions of key-based coded permutation cipher (KBCPC) aimed to improve the error performance and security of the transmission in the wireless channel. These two versions were designed based on the modified data encryption standard (M-DES) and provide different levels of security. This study presents a divide-and-conquer attack on both M-DES and KBCPC by exploiting the function that extends the length of output. Their analysis shows that these two ciphers can only provide 56-bit level of security instead of the claimed 136-bit and 173.67-bit level of security for different versions. The authors' analysis is further verified through experiments. More importantly, their attack can be easily adapted to other schemes with a different encryption design but the same coding technique used in M-DES or KBCPC.

Due to its tree-like topology, the point-to-point (P2P) indoor power line communication (PLC) channel exhibits a similar broadcasting property as the wireless propagation channel shows. However, after relay nodes are introduced, the relay-assisted PLC (RaPLC) channel shows some notable differences compared with its wireless counterpart. A lot of results about the relay-assisted wireless channel can be found in the literature, but the work of modelling RaPLC channel has rarely been discussed in detail. As the first attempt to fill this gap, we apply the ABCD method to compute the channel transfer function (CTF) of the RaPLC channel. It has been clarified that, in general, the CTF of RaPLC channel cannot be obtained as a cascade of two independent P2P PLC sub-channels located on two sides of the relay node. Also, it is shown that the challenge of generating CTF of the RaPLC channel can be transformed into a group of equivalent P2P PLC channel modelling tasks. Under the time-division duplexing constraint, the relay node changes its working mode from the receiving phase to the transmitting phase, which shows that the RaPLC channel is abruptly time-varying in nature. Following the hybrid bottom-up approach, a statistical channel model with a simple six-segment indoor power grid topology has been developed for simulation. Practical measurements and numerical examples verify our results.

Due to the broadcasting property of visible light communication (VLC) channels, VLC systems are under the threat of eavesdropping and malicious attack. In this study, the authors present an uncoordinated chaotic channel scrambling scheme to enhance the physical layer security for a multiple-input, multiple-output based VLC system. With the authors design, the legitimate receiver can self-descramble the data with the location information shared between the transceivers, and the eavesdroppers cannot retrieve the information without the secret key. The authors firstly embed the location information into the chaotic channel scrambling matrix, and then apply the non-negative orthogonal factorisation method to improve both the reliability and the security. Notably, with the aid of the shared location information, the received data can be self-descrambled and thus the uncoordinated channel scrambling could be realised. The theoretical security performances including the information leakage and the secrecy capacity are analysed and the simulation results demonstrate that the proposed scheme achieves higher security and more reliable performances compared with the counterpart schemes.

A multi-level construction of polar-coded single carrier frequency division multiple access (SC-FDMA) with multiple input multiple output (MIMO) antennas scheme is proposed and its bit error rate performance over frequency selective Rayleigh fading channels has been evaluated. The existence of a parallel split in the design of multi-level construction of polar code has enabled the authors to effectively extend the proposed scheme in coded cooperative scenarios. As in coded cooperation communication, the relay plays a crucial role in the design of communication system; therefore, an efficient selection criterion for reinforcing the bad channels has been adopted at the relay node. Moreover, the joint successive cancellation decoding is employed at the destination node. To check the efficacy in the performance of the proposed coded cooperative scheme, the authors have also upgraded the traditional nested polar-coded cooperative scheme in the context of SC-FDMA with MIMO antennas as a useful benchmark. Monte Carlo simulated results revealed that the proposed coded cooperative scheme have triumphed the conventional nested polar coded cooperative scheme based on SC-FDMA system by gain of 0.5 dB under identical conditions. Moreover, the proposed cooperative schemes outperform their corresponding non-cooperative counterpart schemes by the gain of 1 dB under identical conditions.

A multi-channel medium access control (MAC) is proposed for dense wireless ad-hoc networks, called MSR-MMAC, which aims to enhance throughput by introducing multi-slot reservation into multiple channels environment. Based on the integration of carrier sense multiple access with collision avoidance and time division multiple access, MSR-MMAC alternately implements contention-based channel access and multiple reservation-based data transmission on a certain frequency channel. Besides, the authors build an enhanced Markov model to analyse the throughput performance of the proposed MSR-MMAC protocol, which is further validated by extensive simulations using ns-2. Simulation results show that the proposed MSR-MMAC protocol reduces the average collision probability and improves throughput significantly.