On the maximum achievable rates in the decode-forward diamond channel

We study the fundamental capacity trade-off between full-duplex and half-duplex transmission modes in a two- hop communication system with a fixed infrastructure-based amplify-and-forward relay. First, we derive closed-form expressions for the average end-to-end capacity in the relay link. We show that it may be better to tolerate some loop interference with the full-duplex mode than to consume channel resources by allocating two orthogonal channels with the half-duplex mode. Furthermore, we evaluate the maximum loop interference power levels that still allow the full-duplex mode to achieve the same capacity as the half-duplex mode. Our results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.

This paper investigates a X-duplex decode-and-forward relay system in the presence of direct link from the source to destination. X-duplex relays can adaptively switch between half-duplex mode and full-duplex mode according to the instantaneous channel conditions. Unlike previous work on X-duplex relay, we treat the direct link as an additional information path and propose a new transmission scheme based on dirty paper coding (DPC). By using DPC as the precoding scheme at the source, the messages can be divided into two parts which are sent from the source to destination through the relay link and direct link, respectively. In addition, the destination performs successive interference cancellation as the decoding strategy. The optimal transmit powers at the source and relay by maximizing the end-to-end achievable rate are obtained. The numerical results show that the new transmission scheme achieves a better performance over the reference scheme.

In this paper, we analyze the performance of underlay communication between full-duplex capable device-to-device (D2D) nodes transmitting in the cellular band. The D2D nodes use peak interference type of power control to restrict the overall interference at the cellular base station below a statistically determined interference temperature limit (ITL), thereby ensuring its quality of service for uplink cellular users. From the derived analytical expressions, sum-throughput optimal strategies are evolved to choose between full-duplex and half-duplex modes of operation for the D2D nodes. Since both D2D nodes transmit simultaneously in full-duplex mode, the ITL needs to be apportioned between the D2D terminals. A closed-form expression is presented for the optimum ITL apportioning that maximizes D2D sum-throughput. It is shown that switching to half-duplex mode is advantageous when the target rate is above a certain critical target-rate, for which an expression is derived. Computer simulations are presented that demonstrate accuracy of the derived expressions.

Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.

Multi-antenna relay assisted NOMA network with multiple imperfect factors

The diamond channel is a dual-hop communication system composed of a source, and a destination connected through two noninterfering relays. Operating in the half-duplex mode, relays are not capable of simultaneous transmission and reception of signals. This paper studies coding and scheduling schemes achieving within constant gap from the maximum achievable rate possible assuming the scheduling is fixed for all messages and known to all nodes prior to transmission. It is shown that under constant power constraints, a simple transmission scheme for relays is within 0.71 bits of the optimum rate. It is also demonstrated that the proposed scheme can attain the optimum rate, when channels satisfy a certain property. Furthermore, it is proved that under average power constraints, the same scheme can be used to achieve within 3.6 bits of the optimum rate.

This paper has investigated a downlink non-orthogonal multiple access (NOMA) cooperative scheme with user-assisted relaying, where near users are viewed as decode-and-forward (DF) relays operating full/half-duplex mode to assist multiple far users. Especially, the impact for the randomness of users location on the system performance has also been studied. Further, to overcome the zero diversity gain inherent to full-duplex (FD) operation, the direct link between a base station (BS) and each far user is exploited. The comprehensive performance analysis is conducted through the closed-form expressions in terms of outage probability, the diversity gain, system throughput, and ergodic sum rate. With respect to outage behavior, throughput, and ergodic sum rate, FD-based NOMA outperforms half-duplex (HD) NOMA in the lower signal-to-noise ratio (SNR) region. However, with the negative influence brought by residual loop-interference (LI), the advantage of FD NOMA scheme is not pronounced enough in the high SNR regime. Therefore, according to different SNR levels, we further propose a hybrid relaying scheme that switches opportunistically between the FD and HD modes. Afterward, the mode switching threshold is characterized such that the outage probability of each user is minimized. The simulation results confirm the correctness of our analysis and offer a significant guideline for system design in practice.

In this paper we investigate the effect of interference caused by in-band full-duplex radios in device-to-device communication (D2D). While using full-duplex radios in D2D, both users transmit, compared to half-duplex D2D in which one user transmits. This is going to cause more interference in underlay D2D communication since D2D link operates on the same radio resource blocks as cellular users. We consider uplink radio resource reuse of cellular users by D2D communication, and try to maximize the number of possible D2D links constrained to the interference on the cellular user. The number of D2D pairs that can be active in the full-duplex mode is smaller than in the half-duplex mode due to more interference from transmissions of both D2D nodes. We compare the total rate of half-duplex and full-duplex modes and evaluate the benefits of full-duplex radios.

This article studies the energy efficiency (EE) of a three-node decode-and-forward (DF) relay channel, where the relay operates in full-duplex (FD) or half-duplex (HD) mode. In particular, for the FD mode, both the residual self-interference (RSI) and the extra circuit power consumption introduced by the self-interference cancellation (SIC) at the relay node are considered and modeled as linear functions over the relay transmission power. Under this setup, the EE maximization problems for the considered FD and HD modes subject to the total transmission power and spectral efficiency (SE) constraints are formulated as max–min problems, whose optimal power allocation is computed by fractional programming. Next, the EEs for the FD, HD, and direct transmission (DT) modes are compared under different channel conditions, and a hybrid mode selection scheme, i.e., selecting the one with the maximum EE among the above three modes, is proposed. Besides, we also prove that both the EE and the SE monotonically increase with the total transmission power under a given condition. Finally, numerical results show that the maximum EE of the FD relaying exceeds those of the HD and DT ones when the required SE is relatively high. Furthermore, the proposed hybrid mode selection scheme can provide up to 192.4% higher EE compared with the DT mode.

A Gaussian multiple-input single-output (MISO) fading channel is considered. We assume that the transmitter, in addition to the statistics of all channel gains, is aware instantaneously of a noisy version of the channel to the legitimate receiver. On the other hand, the legitimate receiver is aware instantaneously of its channel to the transmitter, whereas the eavesdropper instantaneously knows all channel gains. We evaluate an achievable rate using a Gaussian input without indexing an auxiliary random variable. A sufficient condition for beamforming to be optimal is provided. When the number of transmit antennas is large, beamforming also turns out to be optimal. In this case, the maximum achievable rate can be expressed in a simple closed form and scales with the logarithm of the number of transmit antennas. Furthermore, in the case when a noisy estimate of the eavesdropper’s channel is also available at the transmitter, we introduce the SNR difference and the SNR ratio criterions and derive the related optimal transmission strategies and the corresponding achievable rates.

The severe interference in full-duplex (FD) cellular network largely degrade the system performance, especially for cell edge users. In this paper, hybrid full/half duplex cellular network which is composed of a mixture of FD and half duplex (HD) base-stations (BSs) is focused. In order to relieve the received inter-cell interference, frequency reuse (FR) is applied. The adopted FR schemes include traditional full FR and two kinds of fractional FR (FFR) named Strict FFR (StFFR) and Soft FFR (SoFFR). Stochastic geometry is adopted to evaluate the system performance. Tractable results of the ergodic rate and coverage probability for different FR schemes are obtained. Through the numerical results, we can observe that full FR and StFFR schemes can improve the user coverage probability at the expense of system spectrum efficiency (SE). SoFFR can improve both the coverage probability and the system SE. The numerical results also show that if the residual Self-interference is not very strong, operating all the BSs in FD mode can achieve the best performance, otherwise, it is better to operate all the BSs in HD mode.

This paper studies the impact of channel error on the achievable rate of symmetrical K-user multiple-input multiple-output linear interference alignment (IA) networks. The upper and lower bounds of the achievable sum rate are derived analytically with the assumption of orthonormal transmit precoders and receive filters designed from imperfect channel state information (CSI) over both the uncorrelated and correlated channels. For uncorrelated channels, quite tight lower and upper bounds are obtained. The impact of channel error on the degrees of freedom (DoF) and the DoF persistence conditions are also investigated. Results show that the DoF of IA networks persists only if the channel error decreases in an order higher than the signal-to-noise ratio. For correlated channel, the lower and upper bounds for one realization of IA are derived. The derived upper bound can be used to characterize the achievable rate approximately. Simulation results indicate that the achievable rate of IA network is influenced significantly by CSI uncertainty. The obtained analytical bounds provide an intuitive way to show the impact of channel error on the achievable rate and thus can help practical systems deign.

We consider the problem of optimizing the allocation of available energy across training and data symbols under linear precoding in multiuser downlink systems with imperfect channel state information (CSI). Our figure of merit is the sum rate across all users. This paper derives a lower bound on achievable rate under linear precoding and extends existing precoder designs to the case of imperfect CSI. Optimality and separability results for the energy allocation and precoder design problems that were found previously for sum-MSE minimization are extended to the problem of sum-rate maximization when channels are modelled using uncorrelated Rayleigh block fading with equal variances of the fading coefficients. Simulation results suggest significant improvements in achievable rate under the proposed algorithm.

In this paper, we re-examine the relay channel under the decode-forward (DF) strategy. Contrary to the established belief that block Markov coding is always the rate-optimal DF strategy, under certain channel conditions (a link regime), independent signaling between the source and relay achieves the same transmission rate without requiring coherent channel phase information. Further, this independent signaling regime allows the relay to conserve power. As such, we design a composite DF relaying strategy that achieves the same rate as block Markov DF but with less required relay power. The finding is attractive from the link adaptation perspective to adapt relay coding and relay power according to the link state. We examine this link adaptation in fading under both perfect channel state information (CSI) and practical CSI, in which nodes have perfect receive and long-term transmit CSI, and derive the corresponding relay power savings in both cases. We also derive the outage probability of the composite relaying scheme which adapts the signaling to the link regime. Through simulation, we expose a novel trade-off for relay placement showing that the relay conserves the most power when closer to the destination but achieves the most rate gain when closer to the source.

Full-duplex (FD) radio has been introduced for bidirectional communications on the same temporal and spectral resources so as to maximize spectral efficiency. In this paper, motivated by the recent advances in FD radios, we provide a foundation for downlink hybrid-duplex heterogeneous networks (HDHNs), composed of multi-tier networks with a mixture of access points (APs) operating either in FD mode or half-duplex (HD) mode. Specifically, we characterize the network interference from FD-mode cells, and derive the HDHN throughput by accounting for AP spatial density, self-interference cancellation (IC) capability, and transmission power of APs and users. By quantifying the HDHN throughput, we present the effect of network parameters and the self-IC capability on the HDHN throughput, which shows the superiority of FD mode for larger AP densities (i.e., larger network interference and shorter communication distance) or higher self-IC capability.