Full-duplex Orthogonal Frequency Division Multiplexing Research Articles

Iterative phase noise suppression for full-duplex communication systems

Oscillator phase noise is one of the bottlenecks that limits the self-interference (SI) cancellation capability of full-duplex systems. In this paper, we propose a method for the suppression of common phase error (CPE) and intercarrier interference (ICI) induced by the phase noise in full-duplex orthogonal frequency division multiplexing (OFDM) systems. First, we regard the effect of CPE as a portion of the SI channel and perform estimation, reconstruction and elimination in the time domain. Then, the ICI signal is estimated and suppressed in the frequency domain. Additionally, by analysing the performance of proposed algorithm, we further develop an iterative mechanism to reduce the parameter estimation error and improve SI cancellation capability. Simulation results show that the proposed method has a significant SI cancellation capability improvement over the traditional SI cancellation schemes.

Robust hybrid beamforming designs for full-duplex OFDM millimeter wave systems with imperfect channel estimates

In this paper, robust hybrid beamforming designs are developed for full-duplex millimeter wave multiple-input multiple-output orthogonal frequency division multiplexing (OFDM) systems. A zero-space projection based method is proposed to attenuate the self-interference. The imperfect channel estimations are considered to design the robust full digital beamformers. Then, the hybrid processors are solved via an alternating algorithm. The simulation results show that the proposed design prevails the existing designs.

Hybrid wideband multipath self-interference cancellation with an LMS pre-adaptive filter for in-band full-duplex OFDM signal transmission.

A wideband multipath self-interference cancellation (SIC) system employing both dual-drive Mach-Zehnder modulator-based analog SIC and least mean square (LMS) algorithm-based pre-adaptive filter digital SIC is proposed and demonstrated for the cancellation of multipath self-interference (SI) and facilitation of in-band full-duplex (IBFD) orthogonal frequency-division multiplexing (OFDM) signal transmission. The multipath effect is an unavoidable challenge in SIC due to the dynamic and unpredictable properties in each path, as well as the need for separate matching components for compensating for each path. In this Letter, an LMS algorithm-based adaptive filter is used as a pre-equalizer to adapt and generate the matching signal to the closest approximate of the multipath SI signal. The adaptation is based on the minimization of the error signal generated from the matching signal and multipath SI signal in the LMS algorithm. With the introduction of the LMS adaptive filter to the analog SIC, an additional 9 dB cancellation improvement is obtained, resulting in a total of 32 dB cancellation depth over a cancellation bandwidth of 2.7 GHz at a center frequency of 1.65 GHz. To the best of our knowledge, the achieved performance is by far the widest cancellation bandwidth in a multipath SIC system, which is essential in a large bandwidth and high data rate transmission system. With the help of the proposed LMS adaptive filter digital SIC assisted analog SIC located at the remote node, power-efficient IBFD transmission of an OFDM signal through a 25 km fiber is experimentally demonstrated with a 6 dB bit error rate and 8% error vector magnitude improvements.

Secure full duplex OFDM wireless communication based on phase relay between the legitimate nodes

This study proposes a scheme to realise secure orthogonal frequency-division multiplexing (OFDM) wireless communication between two full duplex nodes—node A and node B. If node A wants to send secret messages to node B, node A and node B transmit the training signal to each other to acquire channel state information (CSI) in the first time frame. Node A acquires the phases of the received signal from node B (no need to decode). In the second time frame, node A then sends secret messages to node B with the phases of the modulated signal being added to the random phases of the signal from node B in the previous time frame, i.e node A relaying the phases of the signal from node B. Node B can recover the secret messages from node A, but eavesdroppers cannot because they do not know the CSI of the main channel. The secrecy capacity is irrelevant to the CSI of the eavesdropper channel, which is a big advantage over other schemes. The scheme can guarantee secrecy capacity to be positive in all circumstances and work well for single-input single-output systems. A computation efficient algorithm is presented to optimally allocate power over sub-carriers for secrecy capacity maximisation.

Analysis of Self-Interference Cancellation Under Phase Noise, CFO, and IQ Imbalance in GFDM Full-Duplex Transceivers

This article investigates a full-duplex base station using a generalized frequency division multiplexing (GFDM) transceiver with the radio frequency (RF) impairments including phase noise, carrier frequency offset (CFO) and in-phase (I) and quadrature (Q) imbalance. To fully focus on the RF impairment issue, we study the simple configuration of single uplink user and single downlink user. They both are half-duplex wireless. In the uplink, we study analog and digital self-interference (SI) cancellation and propose a complementary SI suppression method. Desired signal and residual SI powers and signal-to-interference ratio (SIR) are derived in closed form. Similarly, in the downlink, we derive desired signal power, co-channel interference signal power caused by the uplink user and SIR. The RF impairments degrade the efficiency of SI cancellation and affect GFDM more negatively than full-duplex orthogonal frequency division multiplexing (OFDM). Hence, we propose full-duplex GFDM receiver filters for maximizing the SIR for both uplink and downlink transmissions. Finally, the uplink and downlink rates and the uplink-downlink rate region are derived. Significantly, the optimal-filter based GFDM outperforms full-duplex OFDM by 25 dB higher SIR and an uplink rate increase of 500%.

Self-Interference Cancellation for Full-Duplex Massive MIMO OFDM With Single RF Chain

In this letter, the digital self-intereference (SI) canellation in a single radio frequency (RF) chain massive multi-input multi-output (MIMO) full-duplex (FD) orthogonal frequency division multiplexing (OFDM) system with phase noise is studied. To compsenate the phase noise, which introduces SI channel estimation error and thus degrades the SI cancellation performance, a weighted linear SI channel estimator is derived to minimize the residual SI power in each OFDM symbol. The digital SI cancellation ability of the proposed method, which is defined as the ratio of the SI power before and after the SI cancellation, is anlyzed. Simulation results show that the proposed optimal linear SI channel estimator significantly outperforms the conventional least square (LS) etimator in terms of the SI cancellation ability for the cases with strong SI and low oscillator quality.

Sum-MSE Gain of DFT-Based Channel Estimator Over Frequency-Domain LS One in Full-Duplex OFDM Systems

In this paper, we make an investigation on the sum-mean-square-error (Sum-MSE) performance gain in full-duplex orthogonal frequency-division multiplexing (OFDM) systems in the presence of colored interference-plus-noise (IPN). This gain is defined as the ratio of Sum-MSE of frequency-domain least-square (LS) channel estimator to that of DFT-based LS one. The closed-form formula of the gain is derived. And, its simple upper and lower bounds are given using inequalities of matrix eigenvalues. The exact value of Sum-MSE gain depends heavily on the correlation factor of the IPN covariance matrix. More importantly, we also find that the Sum-MSE performance gain grows from 1 to $N/L$ as the correlation factor gradually decreases from 1 to 0, where $N$ and $L$ denote the number of total subcarrier and the length of cyclic prefix, respectively. Also, via theoretical analysis, the exact Sum-MSE gain degenerates into 1 and $N/L$ in two extreme scenarios: fully-correlated and white, respectively. The former 1 means there is no performance gain, while the latter $N/L$ corresponds to the maximum Sum-MSE performance gain achievable. Numerical simulation further validates the above results. Additionally, the derived lower bound is shown to be closer to the exact value of Sum-MSE gain compared to the upper bound.

Multicarrier Relay Selection for Full-Duplex Relay-Assisted OFDM D2D Systems

In this paper, we propose a full-duplex orthogonal frequency-division multiplexing (OFDM) device-to-device (D2D) system in two-hop networks, where multiple full-duplex decode-and-forward (DF) relays assist the transmission from D2D user equipment (DUE) transmitter to DUE receiver. By such a transmission mechanism, the signal transmitted by the DUE transmitter does not need to go through a base station (BS). Meanwhile, due to the adoption of underlay D2D communication protocol, power control mechanisms are thereby necessary to be applied to mitigate the interference to conventional cellular communications. Based on these considerations, we analyze the outage performance of the proposed system, and derive the exact expressions of outage probabilities when bulk and per-subcarrier relay selection criteria are applied. Furthermore, closed-form expressions of outage probabilities are also obtained for special cases when the instantaneous channel state information (CSI) between BS and cellular user equipments (CUEs) is not accessible, so that a static power control mechanism is applied. Subsequently, we also investigate the outage performance optimization problem by coordinating transmit power among DUE transmitter and relays, and provide a suboptimal solution, which is capable of improving the outage performance. All analysis is substantiated by numerical results provided by Monte Carlo simulations. The analytical and numerical results demonstrated in this paper can provide an insight into the full-duplex relay-assisted OFDM D2D systems, and serve as a guideline for its implementation in next generation networks.

Adaptive Self-Interference Cancellation for Full Duplex Radio: Analytical Model and Experimental Validation

Recent experimental results show that full-duplex (FD) communication is feasible provided that the residual self-interference after cancellation is close to the noise floor. In this paper, we present a low-complexity active self-interference cancellation technique for FD orthogonal frequency division multiplexing (OFDM) systems, which accounts for the inherent cyclostationarity of the OFDM signal in order to effectively cancel the self-interference. The method here proposed estimates the self-interference cancellation path by using a time-averaged mean-square error criterion, combined with a filtered least mean squares adaptive algorithm. Then, its performance is experimentally validated using a self-developed FD radio testbed implemented with off-the-shelf components. When combined with passive cancellation, applying the proposed technique provides enough self-interference suppression as to reach close (less than 2 dB) to the receiver noise floor.

Impacts of Phase Noise on Digital Self-Interference Cancellation in Full-Duplex Communications

In full-duplex (FD) radios, phase noise leads to random phase mismatch between the self-interference (SI) and the reconstructed cancellation signal, resulting in possible performance degradation during SI cancellation. To explicitly analyze its impacts on the digital SI cancellation, an orthogonal frequency division multiplexing (OFDM)-modulated FD radio is considered with phase noises at both the transmitter and receiver. The closed-form expressions for both the digital cancellation capability and its limit for the large interference-to-noise ratio (INR) case are derived in terms of the power of the common phase error, INR, desired signal-to-noise ratio (SNR), channel estimation error and transmission delay. Based on the obtained digital cancellation capability, the achievable rate region of a two-way FD OFDM system with phase noise is characterized. Then, with a limited SI cancellation capability, the maximum outer bound of the rate region is proved to exist for sufficiently large transmission power. Furthermore, a minimum transmission power is obtained to achieve β-portion of the cancellation capability limit and to ensure that the outer bound of the rate region is close to its maximum.

Compressed sensing-based time-domain channel estimator for full-duplex OFDM systems with IQ-imbalances

In full-duplex orthogonal frequency-division multiplexing (OFDM) systems with in-phase and quadrature (IQ) imbalances, a time-domain least squares (TD-LS) channel estimator is proposed for estimating both the source-to-destination (intended) and the destination-to-destination (self-interference) channels. To further improve the performance, an adaptive orthogonal matching pursuit (OMP) is proposed and its sparsity is estimated by a threshold method. Finally, the full-duplex interference is removed using serial interference cancellation and sphere decoding is used to complete the maximum likelihood detection. Simulation results demonstrate that in terms of both the mean square error (MSE) and the bit error rate (BER), the proposed adaptive OMP performs better than the TD-LS by exploiting the sparse property of the channel. Additionally, compared to the gradient projection, the proposed adaptive OMP is better in the low and medium signal-to-noise ratio (SNR) regions and marginally worse in the high SNR region.

Achievable Sum Rates of Half- and Full-Duplex Bidirectional OFDM Communication Links

While full-duplex (FD) transmission has the potential to double the system capacity, its substantial benefit can be offset by the self-interference (SI) and non-ideality of practical transceivers. In this paper, we investigate the achievable sum rates (ASRs) of half-duplex (HD) and FD transmissions with orthogonal frequency division multiplexing (OFDM), where the non-ideality is taken into consideration. Four transmission strategies are considered, namely HD with uniform power allocation (UPA), HD with non-UPA (NUPA), FD with UPA, and FD with NUPA. For each of the four transmission strategies, an optimization problem is formulated to maximize its ASR, and a (suboptimal/optimal) solution with low complexity is accordingly derived. Performance evaluations and comparisons are conducted for three typical channels, namely symmetric frequency-flat/selective and asymmetric frequency-selective channels. Results show that the proposed solutions for both HD and FD transmissions can achieve near optimal performances. For FD transmissions, the optimal solution can be obtained under typical conditions. In addition, several observations are made on the ASR performances of HD and FD transmissions.

Analog cancelation schemes for full-duplex MIMO OFDM systems

In this paper, we consider analog cancelation for full-duplex wireless multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in multipath self-interference channels, where a full-duplex node is equipped with multiple transmit and receive antennas. For analog cancelation in full-duplex MIMO systems, we propose baseband self-interference signal emulation approaches, where the baseband self-interference signals from all transmit antennas are emulated in the baseband at each receive antenna, and the emulated baseband self-interference signals are upconverted to obtain the emulated radio-frequency (RF) self-interference signals. Numerical results are presented to verify the self-interference suppression performance in MIMO multipath self-interference channels.

On Rate Region Analysis Of Half- and Full-Duplex OFDM Communication Links

The rate regions of half- and full-duplex links using the orthogonal frequency division multiplexing (OFDM) technique are analyzed after taking into account the non-ideality of practical transceivers. The non-ideality is quantified by a measure named error vector magnitude (EVM) level in practical systems. It is approximated as a Gaussian noise added to the original signal by the transmitter. The assumed full-duplex transceiver suppresses the self-interference via a three-stage process. The stages are antenna isolation, RF cancellation, and digital baseband cancellation. The self-interference caused by the EVM noise and the original signal are suppressed differently in the three-stage process. The optimal power allocation algorithms are developed to maximize the rates of the half- and full-duplex OFDM links under two different strategies. The first one aims at a low complexity design, where each node uniformly allocates the power over sub-carriers, whereas the second one adaptively allocates the power over sub-carriers to achieve the largest rate. Using the developed algorithms, the achieved rate regions under frequency-flat and frequency-selective environments are compared.