Joint Transmit and Receive Beamforming Design for a Full Duplex UAV Sensing Network

Unmanned aerial vehicles (UAVs) have recently been envisaged as an enabling technology of 5G. UAVs act as an intermediate relay node to facilitate uninterrupted, high quality communication between information sources and their destination. However, UAV energy management has been a major issue of consideration due to limited power supply, affecting flight duration. Thus, we introduce in this paper a unified energy management framework by resorting to wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT) and self-interference (SI) energy harvesting (EH) schemes, in cooperative relay communications. In our new technique, UAVs are deployed as relays equipped with a decode and forward protocol and EH capability operating in a full-duplex (FD) mode. The UAV assists information transmission between a terrestrial base station and a user. The UAV's transmission capability is powered exclusively by the energy harvested from WPT, radio frequency signal transmitted from the source via time-switching SWIPT protocol and SI exploitation. We improve the overall system throughput by the use of FD based UAV-assisted cooperative system. In this proposed system, we formulate two optimization problems to minimize end-to-end outage probability, subject to UAV's power profile and trajectory for a DF relay scheme, respectively. The KKT conditions have been used to obtain closed-form solutions for the two formulated problems. Numerical simulation results validate all the theoretical results. We demonstrate that the performance of our proposed unified EH scheme outperforms that of existing techniques in the literature.

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.

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%.

In this paper, a promising spectrum sensing technique is proposed using Neyman Pearson (NP) based energy detection scheme for cognitive radio (CR) systems, where the secondary user is running in full duplex (FD) mode under residual self-interference (SI). First, NP based likelihood ratio test is carried out in additive white Gaussian noise (AWGN) environment and the closed form expressions for performance metrics are derived analytically. Next, minimum mean square error based estimator correlator for spectrum sensing under AWGN scenario is proposed, where PU signal having uncertain/arbitrary covariance structure is considered affirming a more realistic scenario in a heterogeneous network. Finally, the proposed detection scheme is extended to a practical Rayleigh fading scenario in FD CR under residual SI, where closed form analytical expressions for performance metrics are also derived. The simulated and analytical results are found in good compliance with each other.

In this paper, we propose a secure unmanned aerial vehicle (UAV) mobile edge computing (MEC) system where multiple ground users offload large computing tasks to a nearby legitimate UAV in the presence of multiple eavesdropping UAVs with imperfect locations. To enhance security, jamming signals are transmitted from both the full-duplex legitimate UAV and non-offloading ground users. For this system, we design a low-complexity iterative algorithm to maximize the minimum secrecy capacity subject to latency, minimum offloading and total power constraints. Specifically, we jointly optimize the UAV location, users' transmit power, UAV jamming power, offloading ratio, UAV computing capacity, and offloading user association. Numerical results show that our proposed algorithm significantly outperforms baseline strategies over a wide range of UAV self-interference (SI) efficiencies, locations and packet sizes of ground users. Furthermore, we show that there exists a fundamental tradeoff between the security and latency of UAV-enabled MEC systems which depends on the UAV SI efficiency and total UAV power constraints.

This paper investigates a new scenario of spectrum sharing between unmanned\naerial vehicle (UAV) and terrestrial wireless communication, in which a\ncognitive/secondary UAV transmitter communicates with a ground secondary\nreceiver (SR), in the presence of a number of primary terrestrial communication\nlinks that operate over the same frequency band. We exploit the UAV's mobility\nin three-dimensional (3D) space to improve its cognitive communication\nperformance while controlling the co-channel interference at the primary\nreceivers (PRs), such that the received interference power at each PR is below\na prescribed threshold termed as interference temperature (IT). First, we\nconsider the quasi-stationary UAV scenario, where the UAV is placed at a static\nlocation during each communication period of interest. In this case, we jointly\noptimize the UAV's 3D placement and power control to maximize the SR's\nachievable rate, subject to the UAV's altitude and transmit power constraints,\nas well as a set of IT constraints at the PRs to protect their communications.\nNext, we consider the mobile UAV scenario, in which the UAV is dispatched to\nfly from an initial location to a final location within a given task period. We\npropose an efficient algorithm to maximize the SR's average achievable rate\nover this period by jointly optimizing the UAV's 3D trajectory and power\ncontrol, subject to the additional constraints on UAV's maximum flying speed\nand initial/final locations. Finally, numerical results are provided to\nevaluate the performance of the proposed designs for different scenarios, as\ncompared to various benchmark schemes. It is shown that in the quasi-stationary\nscenario the UAV should be placed at its minimum altitude while in the mobile\nscenario the UAV should adjust its altitude along with horizontal trajectory,\nso as to maximize the SR's achievable rate in both scenarios.\n

The IEEE 802.16 standard defines two main duplexing modes: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). The FDD can be divided further into Full-FDD (F-FDD) and Half-FDD (H-FDD). F-FDD requires full duplexing support from subscriber stations and works with two frequency bands. TDD operates a single frequency band, but it does not need full-duplexing support. H-FDD is a combination of these: it works with two frequency bands and does not require full-duplexing support. The cost of this is a more complicated scheduling and added overhead. Still, H-FDD might be the only possible duplexing mode in some occasions. In this paper, these duplexing modes are compared and the H-FDD specific features, such as group balancing, are presented. The simulation results show that H-FDD does not quite match the performance of F-FDD or TDD. In the downlink direction, F-FDD and TDD have similar performance but in the uplink direction F-FDD can benefit from subchannelization gain with fewer bursts per frame.

In the universal mobile telephony system (UMTS) the frequency division duplex (FDD) and time division duplex (TDD) modes have adjacent carriers at 1920 MHz. This creates adjacent channel interference (ACI) between the two different air interfaces. Since different duplexing modes are used, the implications for each system are different, with respect to capacity and coverage: these implications are investigated in the paper. The separation distance of the TDD and FDD base station and the load in each system are varied and a symmetrical speech service in both systems is considered, with non-ideal power control assumed. It is found that for an FDD cell radius of 1000 m, a TDD cell radius of 50 m and 10% maximal tolerable outage, the effects of ACI on capacity can be compensated by dynamically increasing the required power at each BS, without affecting the coverage.

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.

This paper studies the performance of the analog multi-tap (MT) canceller, where the tap coefficients are calculated based on the estimated self-interference (SI) channel state information (CSI). In this paper, both the time-invariant and the time-varying SI channels scenarios are investigated, considering the dynamic range of the analog-to-digital converter (ADC) and the linearity of the receiver chain. Closed-form expressions are first developed to calculate the residual SI power after the MT cancellation, characterizing the joint effects of the imperfect SI CSI, reconstruction errors on the estimated SI CSI, and the variation of the SI channels. Then, the achievable rate of the full-duplex transceivers is derived as a function of the residual SI power after the MT cancellation, dynamic range of the ADC, and the linearity of the receiver chain. Theoretical and simulated results show that with imperfect SI CSI, deploying more taps may harm the amount of analog SI cancellation. The sensitivity of the canceller to the doppler frequency shift reduces the amount of analog SI cancellation, and thus brings rate gain loss even with a doppler negligible in conventional communications.

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.

As one of the promising approaches to increase the network capacity, Full-duplex (FD) communications have recently gained a remarkable attention. FD communication enables wireless nodes to simultaneously send and receive data through the same frequency band. Thanks to the recent achievements in the self-interference (SI) cancellation, this type of communication is expected to be potentially utilized in cellular systems, especially in small cell networks. In this paper, we integrate the FD communications into femtocell networks where femtocell users (FUs) share the same spectrum with macro users (MUs). In particular, aiming to maximize the number of admitted FUs in the network and satisfying the target rate for FUs, we jointly study the problem of sub-channel allocation, duplexing-mode selection, and power control for FUs in both uplink (UL) and downlink (DL) transmissions. Moreover, we address the power control problem for macro-tier where the main goal is to minimize the transmission power of prioritized MUs while guaranteeing a target rate for them. To jointly address these problems for both tiers, we propose a distributed algorithm in which FBSs and admitted FUs choose whether to operate in half-duplex (HD) or FD mode so as to meet their target rate. The convergence and performance of the proposed algorithm are evaluated through simulation where it is demonstrated that the average admission ratio of FUs in our proposed distributed scheme surpasses the existing traditional HD approaches.

Multi-antenna unmanned aerial vehicle (UAV) networks can improve throughput by spatial multiplexing and UAVs dominant line-of-sight (LOS) connections, which will intensify interference and exacerbate user fluctuation. This paper proposes user-centric interference cooperation in multi-antenna UAV networks, where multi-antenna beamforming and joint transmission are performed among cooperative UAVs, and derives a semi-closed expression of the ergodic rate using stochastic geometry. Specifically, a dynamic UAV group with adjustable radius <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${R}$</tex-math></inline-formula> is organized for each user that forms a 3D conical region to guarantee seamless service, which provides spatial multiplexing freedom via cooperative multi-antenna beamforming to achieve interference mitigation. In addition, both signal power and inter-cluster interference power are approximated by Gamma distributions with appropriate parameters experiencing generic Nakagami-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading in air-to-ground (AtG) channel. Furthermore, zero-forcing (ZF) beamforming is adopted with equal power allocation among beams, which is across the distributed set of UAVs within the cluster and considering different antenna loading. Numerical results show that the average ergodic rate can achieve 86.01% gain compared to the uncoordinated single-cell multi-antenna UAV network when UAV density is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${100\mathrm{/km^{2}}}$</tex-math></inline-formula> and UAV group radius <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${R}$</tex-math></inline-formula> is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${20\mathrm{m}}$</tex-math></inline-formula>. The optimal network parameters are investigated to maximize ergodic rate, thus providing guidelines for practical network configuration. For instance, when UAV density is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$50\mathrm{/km^{2}}$</tex-math></inline-formula> and loading factor is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K/M=2/16$</tex-math></inline-formula>, the optimal deployment altitude for UAVs is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ h=20m$</tex-math></inline-formula>, which can achieve a rate gain of 144% compared to the case of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$h=0\mathrm{m}$</tex-math></inline-formula>.

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.

Energy optimization for full-duplex wireless-powered IoT networks using rotary-wing UAV with multiple antennas