Beamforming for Cooperative Non-Orthogonal Multiple Access with Full-Duplex Amplify-and-Forward Relaying

In this paper, a novel communication scheme that combines beamforming, energy harvesting, and cooperative non-orthogonal multiple access (NOMA) system is introduced. In the proposed scheme, NOMA is first combined with beamforming to serve more than one user in each beamforming vector. Later, simultaneous wireless information and power transfer (SWIPT) technique is exploited to encourage the strong user to relay the weak user's information messages in full-duplex (FD) manner. However, one major drawback of FD communications is the self-interference (SI) signal due to signal leakage from terminal's output to the input. Three different cases are adopted. In the first case, the SI signal is assumed to be fully cancelled at the strong user using SI cancellation techniques. In the second case, SI is only cancelled at the information decoding circuits, while being harvested in the energy harvester to provide extra energy. The third case investigates the impact of imperfect SI cancellation on system performance is investigated. It is proved that introducing SWIPT doesn't only motivate users to collaborate, but also mitigates the impact of the SI signal. In addition, the problem of total sum rate maximisation is formulated and solved locally by means of two-step difference of convex functions (DC)-based procedure. Furthermore, the outage probability of both weak and strong user is derived and provided in closed-form expressions. Numerical simulations are presented to illustrate the sum rate gain of the proposed scheme if compared with existing schemes, and to verify the derived formulas.

In full duplex (FD), which improves frequency efficiency and achieves flexible resource assignment between the uplink and downlink, self-interference (SI) from a transmitter should be suppressed by using antenna isolation, an analog SI canceler, and digital SI canceler (DSIC) to a level such that the data or control channel satisfies the required block error rate (BLER). This paper proposes an alternately iterative DSIC (AI-DSIC) structure for orthogonal frequency division multiplexing (OFDM) using FD. We first present the required SI suppression level considering SI, quantization noise of an analog-to-digital converter, and nonlinear distortions of a power amplifier and RF receiver circuitries for a direct conversion transceiver using FD. Then, we propose an AI-DSIC structure that iterates alternately the generation of the SI estimate, the downlink symbol estimate, and removal of each from the received signal in the downlink including SI. We investigate the average BLER performance of the AI-DSIC for OFDM using FD based on link-level simulations under the condition that the derived required signal-to-SI ratio is satisfied.

This paper investigates the performance of coop- erative non-orthogonal multiple access (C-NOMA) in cellulardownlink systems. The system model consists of a base station(BS) that needs to serve multiple users within a region of service.A subset of the users, especially those located close to thecell edge, undergo severe fading and suffer from poor channelquality and low achievable rates. To overcome this problem, C-NOMA is proposed as the system design methodology, in whichusers that have the capability of full-duplex (FD) communicationcan assist the transmissions between the BS and users withpoor channel quality through device-to-device (D2D) communi-cations. To harness both the multiplexing gain from NOMA andthe diversity gain from FD-D2D communications, we formulateand solve a novel optimization problem that jointly deter-mines D2D user pairing and power allocation. The formulatedproblem is a mixed-integer non-linear program (MINLP) withprohibitively high complexity. To overcome this issue, a two-steppolicy is proposed to solve the problem in polynomial time. Oursimulation results show that with reasonable assumptions, theproposed scheme always outperforms some existing schemesin the literature, and that, under undesirable conditions, e.g.,poor D2D channel conditions or imperfect self-interference (SI)cancellation, the proposed scheme is reduced to conventionalNOMA.

We investigate an amplify-and-forward (AF) full-duplex (FD) relay system, where the FD incurred self-interference (SI), through partial cancelation at relay, is treated as a useful source at destination to enhance degree of freedom in signal detection, while reducing the signal processing cost of SI cancelation. An independent component analysis (ICA) based equalization structure is employed at destination to separate and detect the desired signal from the residual SI in a semi-blind way. The mode of SI cancelation at relay is chosen adaptively based on the threshold of signal-to-interference ratio (SIR) at relay. The proposed FD relay system not only features reduced signal processing cost of SI cancelation, but also achieves much higher energy efficiency (EE) than conventional FD relay systems where SI is canceled as much as possible. Also, the proposed system enables full resource utilization via consecutive data transmission at all time and the same frequency, leading to much higher throughput and EE than the conventional time-splitting and power-splitting based SI recycling approaches that occupy partial resources. Last but not least, the proposed system demonstrates a bit error rate (BER) performance that is robust against a wide range of SI and close to the ideal case with perfect channel state information (CSI) and perfect SI cancelation, while requiring no training sequence for estimation of any channel involved.

The full-duplex (FD) cooperative nonorthogonal multiple access (NOMA) achieves a superior throughput over the conventional half-duplex (HD) cooperative NOMA, wherein the strong users (SUs) with good channel conditions can act as an FD relay node for the weak users with poor channel conditions. However, the energy efficiency (EE) of a cooperative NOMA may be degraded due to the additional power consumption incurred at the SUs. We are, therefore, motivated to investigate the EE maximization problem of an FD cooperative NOMA system. More importantly, we investigate the “signal-to-inference-noise ratio gap reversal” problem of cooperative NOMA systems, which imposes successive interference cancellation (SIC) performance degradation at the SUs. This problem has not been documented in the existing cooperative NOMA literature. A low-complexity algorithm is proposed for maximizing the system's EE while guaranteeing a successful SIC operation. Our numerical results show that the proposed algorithm achieves both a higher EE and throughput over the existing HD cooperative NOMA and nonadaptive FD cooperative NOMA. More importantly, the proposed scheme guarantees a successful SIC operation at the SUs.

Simultaneous bidirectional transmission and recep- tion of signals on a single channel in a full duplex (FD) system is gaining increased attention from both academia and industry. Recent advances in radio transceiver design have been able to minimize the self interference (SI) to a great extent making realization of a FD transceiver possible. For FD deployment in a multi-cell environment, minimizing SI is not sufficient due to the presence of a complex array of network-wide interference. This paper investigates the critical deployment challenges for a dense urban FD multi- cell network and provides solutions for successful deployment of FD cellular networks. Extensive simulation results show that the proposed user selection and power control algorithms are able to increase the FD performance gain by more than 80% when compared to the traditional half duplex (HD) counterpart.

The advent and advancement of full-duplex (FD) technology in radio transceivers is expected to lead to full-duplex enabled multi-cell (FD-MC) networks in next generation wireless communication systems. Additional interferences between FD nodes and devices are the main challenges for the deployment of such networks. As in an early deployment scenario where the base stations (BS) operate in FD mode while the user equipments (UE) remain in the half-duplex (HD) mode, the self-interference (SI) within the FD-BS, the mutual interference (MI) between the FD-BS's and between the HD-UE's paired for FD scheduling are the major issues that could jeopardize the capitalization of FD system gains if they are not well addressed. In this paper, we present a system architecture for multi-stage cancellation of SI and joint cancellation of MI and residual SI in an FD-MC network. Multiple orthogonal pilots and their derived forms are utilized for channel estimation during a common training period. System-level delay calibration necessary for SI and MI channel estimation and cancellation is also provided.

In-band Wireless Full Duplex communication systems are capable of transmimng and receiving in the same band by canceling the self-interference (SI) power originated during the transmission. However, several issues may degrade its performance, including the nature of wireless SI channel. In this work we study the distribution of the residual SI power of an in-band full-duplex analog post-mixer canceler, which represents the amount of uncanceled SI. The impact of the fading channel is evaluated on the distribution of the residual SI power. The results achieved confirm that the type of fading channel strongly impacts the distribution of the residual SI power. This is a first step to understand the stochastic properties of the residual SI power, which is an important feature when digital-domain cancellation is jointly adopted with analog-domain cancellation to account with the effects of the propagation channel.

In this paper, we consider a shared-antenna full-duplex massive MU-MIMO system and prove that the self-interference (SI) at the base station (BS) can be suppressed, though the direct-path SI exists and the signal/SI channel is imperfectly estimated. The BS is assumed to employ zero-forcing (ZF) or maximal-ratio transmission/maximal-ratio combining (MRT/MRC) method to linearly process signals. We propose a precoded SI channel training scheme by employing orthogonal sequences and downlink precoding, so the SI channel can be estimated like the signal channel with a much lower dimension. Based on the channel estimation, we further analyze the SI suppression by combining the SI removal and the large-scale antenna linear processing (LALP) method. Numerical results show that an additional 36 dB SI can be suppressed by combining the SI removal and the LALP suppression. We derive the tight closed-form lower bounds of the achievable rates for the combined suppression. Finally, we maximize the system spectral efficiency and energy efficiency based on the simulation and closed-form approximations.

This paper is concerned with wireless relay networks that employ K full-duplex (FD) decode-and-forward relays to help a source to communicate with a destination. Each FD relay is equipped with multiple antennas, some for receiving and some for transmitting. The paper considers joint relay-antenna selection schemes that are based on the instantaneous channel conditions for two cases of antenna configurations, namely fixed antenna configuration (FAC) and adaptive antenna configuration (AAC). Under FAC, the transmit and receive antennas at each relay are fixed, whereas in the case of AAC an antenna at a relay can be configured to be either a transmit or a receive antenna.In addition to equal power allocation between the source and selected relay, a power scaling approach to counteract the effect of residual self-interference is also examined. Closed-form expressions of the outage probability and average capacity are obtained and provide important insights on the system performance. The accuracy of the obtained expressions are corroborated by simulation results. In particular, it is shown that under FAC and without power scaling, the diversity order approaches K as the self-interference (SI) level gets smaller, while it approaches zero whenever the SI level is nonzero and the SNR increases without bound. Under FAC and with power scaling, the diversity order approaches K for any SI level. For the case of AAC and without power scaling, the diversity order approaches 2K for small SI level. When power scaling is applied in AAC, the diversity order approaches 2K at any SI level.

Recent works have demonstrated the feasibility and potential of full-duplex (FD) wireless systems to double the spectral efficiency of half-duplex (HD) systems. Self-interference (SI) cancellation is the key to FD communication and the residual SI is the major factor determining the performance of an FD radio. This paper presents a novel frequency domain based approach, for the reconstruction of SI signal in digital domain. Unlike the existing time domain reconstruction approach, which requires convolution, the proposed approach is simple and uses FFT processing for SI signal reconstruction. By means of computational complexity evaluation, it is shown that the proposed reconstruction approach offers 61% reduction in the floating point operations required to reconstruct SI signal. Furthermore, via detailed simulations on the performance of digital SI cancellation under fading channels, it is demonstrated that the SI suppression achieved with the proposed approach is not only comparable to existing approach, but with frequency domain SI channel estimates, it can offer 5-7 dB better cancellation under highly frequency selective fading conditions, suggesting its suitability for long range transmission.

Self-interference (SI) cancellation is one of the most important techniques for full duplex wireless communication. As an indispensable component, the active analog canceller (AC) needs to mitigate the analog SI to ensure it meets the analog-to-digital converter (ADC) sampling requirement. However, the active AC cancellation performance is often restricted by the nonideal electronic components, e.g., the tunable attenuator, the phase shifter and associated circuits, which introduce nonlinear distortions to the residual SI signal that enters the receive chain, as the transmit power increases. This paper presents a full duplex architecture with AC nonlinearity modeling and suppression by including an extra feedback loop right after the power amplifier and an AC nonlinear distortion modeling and cancellation process followed by SI channel estimation and digital SI cancellation. By analyzing the feedback signal feeding the AC and the residual signal after AC cancellation, the AC nonlinear distortion can be estimated and subsequently suppressed by subtracting its estimates from the received samples. The distortion-suppressed signal is then processed by the refined digital SI cancellation with channel estimation and mitigation to further improve the cancellation performance. Experiments are performed on 20-MHz Long Term Evolution-advanced signals to demonstrate the effectiveness of the proposed full duplex architecture with signal power ranging from -5 dBm to 23 dBm at the PA output while from -23 dBm to 5 dBm at the receiver front end.

Mitigating self-interference (SI) is vital for advancing simultaneous transmit and receive (STAR) systems. The noise and linearity of the canceller impose limitations on SI power handling. This article proposes a novel dual-path SI cancelling scheme for high-power SI handling. The proposed approach breaks self-interference cancellation (SIC) tradeoffs between operating frequency, SI power handling, and canceller noise/distortion by using a frequency-translated (FT) SI canceller and an auxiliary FT noise-cancelling (NC) path that cancels the noise/distortion from the primary canceller. This approach can work well for both full-duplex (FD) and frequency-division duplex (FDD) schemes. The 65-nm CMOS implementation achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 45-dB SIC for 12-dBm receiver (RX) SI peak power (9-dBm avg.) with only 4-dB noise figure (NF) degradation and 207-mW power consumption at 600 MHz. The SIC approach enables a blocker-1 dB with respect to SI of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 16 dBm (8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> higher than prior work) while operating from 0.5 to 1.3 GHz. Therefore, this implementation can support watt-level SI power handling with transmitter (TX)–RX isolation <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 15 dB. This is demonstrated through measurements that show 30-dBm TX power handling with 22-dB initial isolation from the circulator.

Over the last decade, infrastructure relays have been employed by wireless standards, such as WiMAX and LTE, for coverage and performance enhancement. However, due to their Half-Duplex (HD) nature, these relays incur spectral losses and increase the end-to-end delay. In contrast, in-band Full-Duplex (FD) relays can effectively cope with these issues through simultaneous reception and forwarding, provided that the looped-back Self-Interference (SI) is sufficiently suppressed. Driven by the possible performance gain of FD relaying over traditional HD relay systems; in this work, we present the first implementation of IEEE 802.11a/g compliant FD relay system in GNU Radio framework. Given the Open Source nature of this real-time signal processing software, the implementation is completely transparent and can be studied in all details and modified if needed. For a holistic evaluation of our relay system, we implemented both Amplify and Forward (AF) and Decode and Forward (DF), the two widely adopted relaying strategies. We assess the performance of these relaying strategies both analytically and in simulation experiments. Our results demonstrate and underline the potential gains of full-duplex relays in-terms of spectral efficiency and end-to-end physical layer latency over traditional half-duplex relay systems.

Residual self-interference (SI) cancellation in the digital baseband is an important problem in full-duplex (FD) communication systems. In this paper, we propose a new technique for estimating the SI and communication channels in a FD communication system, which is inspired from superimposed signaling. In our proposed technique, we add a constant real number to each constellation point of a conventional modulation constellation to yield asymmetric shifted modulation constellations with respect to the origin. We show mathematically that such constellations can be used for bandwidth efficient channel estimation without ambiguity. We propose an expectation maximization (EM) estimator for use with the asymmetric shifted modulation constellations. We derive a closed-form lower bound for the mean square error (MSE) of the channel estimation error, which allows us to find the minimum shift energy needed for accurate channel estimation in a given FD communication system. The simulation results show that the proposed technique outperforms the data-aided channel estimation method, under the condition that the pilots use the same extra energy as the shift, both in terms of MSE of channel estimation error and bit error rate. The proposed technique is also robust to an increasing power of the SI signal.