Praneeth Jayasinghe

Linear Precoder-Decoder Design of MIMO Device-to-Device Communication Underlaying Cellular Communication

This paper proposes linear precoder-decoder schemes for a multiple-input multiple-output (MIMO) underlay device-to-device (D2D) communication system by considering two D2D modes: two-way relaying based D2D and direct D2D. The D2D communication takes place in the same spectrum as the cellular communication. In the two-way relaying based D2D mode, the relay uses physical layer network coding (PNC). The precoder-decoder design is based on minimizing mean square errors (MSE), which is useful to mitigate interference and to improve the performance of both D2D and cellular communications. Distributed and centralized algorithms are proposed considering bi-directional communication in both D2D and cellular communications. In the direct D2D mode, a similar MSE procedure is adopted, and exact solutions are derived for precoder-decoder matrices. In the numerical results, the optimality and convergence properties of the proposed algorithms are analyzed. Additionally, the system performances are investigated with interference thresholds and maximum available power at the nodes. Two transmit mode selection schemes are considered as dynamic and static selection schemes. Finally, these selection schemes are investigated over an XY grid by varying the position of a given device. The results reveal that the PNC two-way relaying based D2D mode extends the coverage area of D2D communication.

Secure Beamforming Design for Physical Layer Network Coding Based MIMO Two-Way Relaying

In this letter, we propose a secure beamforming scheme for physical layer network coding (PNC)-based multiple-input multiple-output (MIMO) two-way relaying system. The relay node performs PNC mapping. An eavesdropper is attempting to intercept the user information. The channel state information (CSI) of the user-to-eavesdropper channel is imperfect at the user nodes. A robust optimization problem is formulated to design beamforming vectors at the user nodes and relay. The problem is non-convex, and an algorithm is proposed to solve that. In the numerical analysis, we discuss the convergence of the proposed algorithm and the impact of the CSI error on the performance.

Vehicle-to-vehicle radio channel characterization in urban environment at 2.3 GHz and 5.25 GHz

In this paper, we present the channel measurement results of vehicle-to-vehicle (V2V) measurement campaign carried out in Oulu city center, Finland. The measurements were conducted with EB Propsound CSTM at 2.3 GHz and 5.25 GHz center frequencies. The antennas were installed on the roof of the vehicles and the measurements were performed for single-input multiple-output (SIMO) antenna configuration. The campaign results are presented in the form of path loss, delay spread (DS), maximum excess delay, the standard deviation of slow fading (SF) and K-factor. Furthermore, we propose the method for calculating correlation distance for large scale parameters in V2V channel and present the results for correlation distances of SF, DS and K-factor. The correlation distances less than 11 meters were observed.

Bi-directional signaling for dynamic TDD with decentralized beamforming

This paper introduces a novel bi-directional signaling scheme for decentralized beamformer design to maximize the weighted sum rate (WSR) of multi-cell multi-user multiple-input multiple-output dynamic time division duplexing (TDD) system. In particular, the base stations are assumed to be either in uplink or downlink state based on the instantaneous traffic demand. The WSR maximization problem is solved via the corresponding weighted sum mean-squared error (MSE) minimization problem. An iterative algorithm is proposed with the bi-directional signaling embedded into the TDD frame structure. A detailed signaling architecture is proposed to facilitate channel estimation, exchanging the user beamformers and the user MSE weight matrices among the coordinating nodes. The proposed coordinated system is compared with the uncoordinated system while taking into account the overhead originated from bi-directional signaling. Finally, a periodic beamformer re-initialization strategy is introduced, which enhances the beamformer convergence rate and the system performance in a time-correlated fading environment. The proposed coordinated system provides significant performance gain in an interference limited environment.

MIMO physical layer network coding based underlay device-to-device communication

We propose a multiple-input multiple-output (MIMO) two-way relaying based underlay device-to-device (D2D) communication system, in which relay uses physical layer network coding (PNC). Both cellular and D2D communication take place in the same spectrum. D2D communication is based on PNC, and a joint transceiver design is required to facilitate PNC mapping with MIMO channels. A joint precoder-decoder scheme is also considered in the cellular communication to mitigate interference, and improve the error performance. Mean square errors at nodes are considered as the objective function, and interference threshold limits and power constraints are also used in joint precoder-decoder design problems. These turn out to be non-convex optimization problems, and we propose two algorithms in both phases of D2D and cellular communication. Distributed optimization methods are used in the proposed algorithms. We analyze the convergence of proposed algorithms, and the system performances are investigated with different D2D pair locations, interference constraint thresholds, and maximum available power at nodes.

Bi-directional signaling strategies for dynamic TDD networks

This paper investigates several bi-directional signaling strategies to facilitate decentralized beamformer design in a dynamic time division duplexing (TDD) system. A small-cell network with multi-antenna base stations and user terminals is considered, where the cells are operating either in uplink or downlink mode depending on the instantaneous traffic demand. Decentralized beamformer design is proposed to maximize the weighted sum rate of the network subjected to individual power constraints at BSs and user terminals. The weighted sum mean-squared error (MSE) minimization framework is used to decouple the optimization problem across the nodes, which enables decentralized iterative solution. Iterative algorithms are proposed with the different bi-directional signaling schemes embedded into the TDD frame structure. A detailed signaling flow of exchanging beamformer and channel information is described for each bi-directional signaling strategy. The proposed strategies are compared with the uncoordinated system while taking into account the signaling overhead.

Performance Analysis of Optimal Beamforming in Fixed-Gain AF MIMO Relaying over Asymmetric Fading Channels

This paper analyzes the performance of an optimal single stream beamforming scheme for a multiple-input multiple-output (MIMO) relay network with dual-hop fixed-gain amplify-and-forward (AF) relaying. The source-relay and relay-destination channels undergo Rayleigh and Rician fading respectively. Different Rician fading scenarios are considered for relay-destination channel, depending on the rank of the Rician channel matrix. The channel state information is only available at the destination, and the destination computes the optimal transmit and receive beamforming vectors to maximize the instantaneous signal-to-noise ratio (SNR). The optimal transmit beamforming vector is sent back to the transmitter via a dedicated feedback link. We derive new analytical expressions for the cumulative distribution function, probability density function, and moments to statistically characterize the properties of the instantaneous SNR. These statistical properties are used to analyze the system performance in terms of the outage probability, average bit error rate, and the ergodic capacity. The performance analysis investigates the effects of the Rician factor, rank of the line-of-sight component, and number of antennas at the nodes on the system performance. The results reveal that the optimal single stream beamforming system provides better performance than an orthogonal space-time block coded based AF MIMO system.

Physical layer security for relay assisted MIMO D2D communication

This paper presents a secure beamforming design to prevent eavesdropping on multiple-input multiple-output (MIMO) device-to-device (D2D) communication. The devices communicate via a trusted relay which performs physical layer network coding (PNC), and multiple eavesdroppers are trying to intercept the device information. The beamforming design is based on minimizing mean square error of the D2D communication while employing signal-to-interference-plus-noise ratio (SINR) threshold constraints to prevent possible eavesdropping. The channel state information of the device-to-eavesdropper and relay-to-eavesdropper channels is imperfect at the devices and relay. The channel estimation errors are assumed with Gaussian Markov uncertainty model. Consequently, robust optimization problems are formulated considering the multiple access and broadcasting stages of the D2D communication. These problems are non-convex, and two algorithms are proposed to solve them. In the numerical analysis, we discuss the convergence of the proposed algorithms, impact of the number of eavesdroppers on the performance, and the SINR distributions at eavesdroppers.

Bi-directional Beamformer Training for Dynamic TDD Networks

In dynamic time-division-duplexing networks, the available resources per cell can be freely allocated to either uplink (UL) or downlink (DL) depending on the instantaneous traffic demand. Hence, complicated UL–DL and DL–UL interference scenarios arise due to simultaneous UL and DL data transmission in adjacent cells. In this paper, decentralized iterative beamformer designs are obtained for several traffic aware network optimization objectives such that only minimal information exchange is required among the coordinated base stations (BS) and user equipment (UE). Bi-directional forward–backward training via spatially precoded over-the-air pilot signaling is used to facilitate coordinated beamforming. This allows BSs and UEs to iteratively optimize their respective transmitters/receivers based on only locally measured reverse link pilot measurements. Novel bi-directional beamformer training strategies and methods for direct estimation (DE) of the stream specific beamformers are developed for each intermediate beamformer update in a limited and noisy pilot environment. The proposed signaling and DE schemes allow for non-orthogonal and overlapping pilots, which considerably reduces the resource coordination effort. Also, the decontamination ability of the proposed strategies are analyzed with limited pilot resources. The numerical examples illustrate the superior system performance of the proposed training and estimation framework in comparison to both the traditional stream-specific channel estimation method and an uncoordinated system.

Traffic aware pilot de-contamination for multi-cell MIMO systems

Traffic aware precoder/decoder design in multi-cell multi-user multiple-input multiple-output systems is considered with the objective of weighted queue minimization, where the original non-convex optimization problem is solved via successive convex approximation. Centralized pilot reuse algorithms for mitigating the pilot contamination are investigated to reflect the traffic aware optimization objective. Distinctive feature of the proposed pilot reuse algorithms is to utilize the user buffer state information jointly with the traditional large scale fading values when allocating the limited pilot resources among the served users. Numerical examples compare the performance of the proposed pilot reuse algorithms for varying number of available pilots and different traffic arrival models. The results demonstrate that significant performance gains are available when the pilot allocation strategy is designed to reflect closely the overall system optimization objective.