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In this paper, we investigate the secrecy performance of a full-duplex (FD) non-orthogonal multiple access (NOMA) relay system under the presence of multiple non-colluding eavesdroppers over Rayleigh fading channels. Furthermore, to improve legitimate link's capacity, the partial relay selection (PRS) scheme is applied to choose the best relay. To evaluate the secrecy performance, we derive the closed-form expressions of the secure outage probability (SOP) of each user, the overall SOP and the sum effective secrecy throughput (EST) of the considered FD-NOMA relay system. We compare the SOP of the FD-NOMA relay system with that of the half-duplex (HD)-NOMA system and the SOPs of FD-NOMA relay system in the cases that PRS and multiple-relay (MR) schemes are employed at multiple relays. Monte-Carlo simulations verify the correctness of all derived mathematical expressions. Numerical results show that thanks to utilizing FD relays and PRS scheme, the considered FD-NOMA relay system has superior secrecy performance than other systems. Furthermore, increasing the number of FD relays, enhancing their self-interference cancellation capability, and selecting a suitable transmission power help to reduce the SOP of the considered FD-NOMA relay system. Meanwhile, the EST rapidly increases with the equivocation rate of the eavesdropping channel then gradually reaches the saturated maximum value.

In this paper, we investigate the performance of a full-duplex (FD) relay system where multi-antennas are exploited at source and destination. Unlike previous works, the impacts of imperfect channel state information (I-CSI), transceiver hardware noise (THN), and residual self-interference (RSI) are taken into account. We mathematically derive the exact closed-form expressions of the outage probability (OP), symbol error rate (SER), and ergodic capacity (EC) of the FD relay system with I-CSI, THN, and RSI over Nakagami- $m$ fading channels. From the derived expressions, the performance of the considered system under the effects of three negative factors (I-CSI, THN, and RSI) is compared with that system in the case of all ideal factors (perfect channel state information (P-CSI), perfect transceiver hardware (P-TH) and perfect self-interference cancellation (P-SIC)), two ideal factors (P-CSI and P-TH, P-CSI and P-SIC, P-TH and P-SIC), or one ideal factor (P-CSI or P-TH or P-SIC). Numerical results show a strong impact of three negative factors on the OP, SER, and EC of the considered FD relay system, especially when the data transmission rate of the system and signal-to-noise ratio (SNR) are high. In particular, OP, SER, and EC go to the floors in the high SNR regime due to the three negative factors. Therefore, when I-CSI, THNs, and RSI exist in the FD relay system, we should use suitable source and relay transmission power to obtain excellent performance while saving energy consumption. Moreover, when two of the three negative factors are large enough, the remaining factor’s impact becomes weaker and may be neglected in certain circumstances.

This article investigates performance of an advanced scheme of index modulation for orthogonal frequency division multiplexing (IM-OFDM), called the repeated index modulation-OFDM with coordinate interleaving (RIM-OFDM-CI), which achieves higher transmission reliability than the conventional IM-OFDM with coordinate interleaving (IM-OFDM-CI). We first derive the approximated expressions for the symbol error probability (SEP) of RIM-OFDM-CI. The obtained SEP provides an insight into the impact of system parameters on the error performance, which allows for selection of an optimum constellation rotation angle to minimize SEP. Two enhanced detectors, namely, the log likelihood ratio (LLR) and greedy detector for RIM-OFDM-CI are proposed. The proposed detectors not only achieve nearly same performance as the maximum likelihood detector but also significantly reduce detection complexity of the RIM-OFDM-CI system. Simulation results are reported to validate advantages of the proposed RIM-OFDM-CI and low-complexity detectors against benchmarks.

In this paper, we analyze the performance of an in-band full-duplex (IBFD) decode-and-forward (DF) two-way relay (TWR) system whose two terminal nodes exchange information via a relay node over the same frequency and time slot. Unlike the previous works on full-duplex two-way relay systems, we investigate the system performance under the impacts of both hardware impairments and imperfect self-interference cancellation (SIC) at all full-duplex nodes. Specifically, we derive the exact expression of outage probability based on the signal to interference plus noise and distortion ratio (SINDR), thereby determine the throughput and the symbol error probability (SEP) of the considered system. The numerical results show a strong impact of transceiver impairments on the system performance, making it saturate at even a low level of residual self-interference. In order to tackle with the impact of hardware impairments, we derive an optimal power allocation factor for the relay node to minimize the outage performance. Finally, the numerical results are validated by Monte Carlo simulations.

Although the theory of nonorthogonal multiple access (NOMA) has been widely investigated, so far, there is a lack of applying beamforming into NOMA systems. In this article, we propose a multiple-input and multiple-output (MIMO)-NOMA system, where all users in the whole system are divided into multiple clusters to reduce the inner interference. Next, the superpositioned signals at base station are beamed to the relays, and then, the relays communicate with the users through superposition coding in the power domain. We derive the exact expressions of the outage probability of each user and the ergodic capacity (EC) of each cluster in both cases, i.e., perfect successive interference cancellation (SIC) and imperfect SIC, taking into account the Nakagami- $m$ fading channels and imperfect channel state information (CSI). We also compare the outage performance and the EC of our proposed MIMO-NOMA relay system with an orthogonal multiple access (OMA) relay system. Monte Carlo simulations are used validate the derived mathematical expressions. Numerical results show that the outage performance and the EC of each user and the whole system are reduced remarkably due to the imperfect CSI but get better as the fading severity is less. Moreover, the EC of our proposed MIMO-NOMA relay system is higher than that of the OMA relay system.

This paper proposes a novel spread spectrum and sub-carrier index modulation (SS-SIM) scheme, which is integrated to orthogonal frequency division multiplexing (OFDM) framework to enhance the diversity over the conventional IM schemes. Particularly, the resulting scheme, called SS-SIMOFDM, jointly employs both spread spectrum and sub-carrier index modulations to form a precoding vector which is then used to spread an M-ary complex symbol across all active sub-carriers. As a result, the proposed scheme enables a novel transmission of three signal domains: SS and sub-carrier indices, and a single M-ary symbol. For practical implementations, two reduced-complexity near-optimal detectors are proposed, which have complexities less depending on the M-ary modulation size. Then, the bit error probability and its upper bound are analyzed to gain an insight into the diversity gain, which is shown to be strongly affected by the order of sub-carrier indices. Based on this observation, we propose two novel sub-carrier index mapping methods, which significantly increase the diversity gain of SSSIM-OFDM. Finally, simulation results show that our scheme achieves better error performance than the benchmarks at the cost of lower spectral efficiency compared to classical OFDM and OFDM-IM, which can carry multiple M-ary symbols.

In this paper, we analyze the performance of vehicle-to-vehicle (V2V) communication system, which employs full-duplex (FD) and energy harvesting (EH) techniques at source and relay nodes from power beacon (PB) through radio frequency. Unlike previous systemswhere all nodes located at fixed locations, we investigate the case that three nodes (source, relay,and destination) are moving vehicles. Therefore, the channels between them follow double (cascade) Rayleigh fading distributions. Furthermore, the source and relay nodes can harvest the energy from PB for data transmission when they move on the road. We derive the exact expressions of the outage probability (OP) and symbol error probability (SEP) of the proposed system and then intensively study the impacts of various parameters such as the number transmission antennas of PB, the time duration for EH, the distances between nodes, and the residual self-interference (RSI) at the FD relay node on the system performance. Monte-Carlo simulations validate all theory analysis. Numerical results show that system performance is strongly impacted by the number of transmission antennas of the power beacon, the EH duration, the RSI, and the distances between nodes. Moreover, for a given transmission of power beacon and the SIC capability of the FD relay node, there exist optimal EH duration and optimal distance from the source to relay, which provide the best system performance.

In this paper, a design of 3-stacked GaN highelectron-mobility transistor radio-frequency power amplifier employing an independently biased technique is presented to meet stringent requirements of next-generation wireless communication systems. The ability of independently adjusting operation conditions for each transistor of the proposed amplifier makes it possible to operate not only for high efficiency, high linearity but also for both improved efficiency and linearity. Efficiency can be optimized through varying drain bias voltages. Linearity, however, can be optimized independently through varying gate bias voltages. Importantly, both efficiency and linearity can be optimized simultaneously by making a compromise between drain and gate bias voltages. In contrast to conventional methods, the proposed configuration still ensures a compact size for design of the power amplifier. This can be feasible because the proposed solution is introduced in the device level using a MMIC technology. These superior advantages make the proposed PA a promising candidate for using in transceiver of the next-generation wireless communications systems.

Transmit antenna selection (TAS) is an effective solution to enhance the performance of a multiple-input multiple-output (MIMO) system, especially when combined with spatial modulation (SM), and full duplex (FD) technique. However, there still lacks a comprehensive understanding on the system behavior of such a system. In this article, we consider a point-to-point bidirectional FD-SM-MIMO system using channel gain based TAS under the impact of imperfect successive interference cancellation and develop an analytical solution for analyzing its performance. In particular, we derive the exact closed-form expressions of the outage probability (OP) and the symbol error probability (SEP) for the FD-SM-MIMO system with TAS. The analytical solution can also be used for evaluating the performance of the half-duplex SM-MIMO (HD-SM-MIMO) systems with and without TAS. The OP, SEP, and system throughput of the FD-SM-MIMO system with TAS are evaluated against the case without using TAS and the HD-SM-MIMO system to demonstrate the benefits of using TAS and impact of the residual self-interference. All analysis results are validated by the Monte Carlo simulation ones to confirm the correctness of the derived mathematical expressions.

In this paper, we propose a full-duplex (FD) relaying system with multi-input multi-output (MIMO) with simultaneous wireless information and power transfer (SWIPT), where the communication from source to destination is assisted by a full-duplex decode-and-forward (DF) relay. The time switching (TS) protocol is used at the relay to harvest the energy of radio-frequency (RF) signals transmitted from the source. To improve both system performance and the amount of harvested energy, multiple antennas are used at source and destination. Transmit antenna selection (TAS) is employed at the source with an assumption that the feedback of channel state information (CSI) is outdated. Meanwhile, both selection combining (SC) and maximal ratio combining (MRC) techniques are applied at the destination. The closed-form expressions of the outage probability (OP), optimal throughput, and symbol error probability (SEP) are derived subject to the outdated CSI over Rayleigh fading channels. We also make a comparison between the performance of the proposed MIMO-FD relaying system with SWIPT and that of MIMO half-duplex (HD) relaying systems with and without SWIPT. The validity of derived mathematical expressions is verified by Monte-Carlo simulations. Numerical results show that the TAS/MRC scheme gives better system performance than the TAS/SC scheme. Moreover, higher energy harvesting time is needed to maximize the throughput than to minimize the OP.