Liqin Ding

Bit Error Probability of Spatial Modulation over Measured Indoor Channels

The Spatial Modulation (SM) transmission scheme boosts the spectral efficiency and achieves the multiplexing gain by activating a single transmit antenna in each time slot. Radio wave propagation characteristics determined by the environment is a decisive factor for the SM system. In this paper, we investigate the performance of the SM scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios. Firstly, a MIMO channel sounder is established. Based on the sounder, 15150 complex 4×4 MIMO channel matrices are measured inside a typical teaching building under both Line of Sight (LOS) and None Line of Sight (NLOS) scenarios. Secondly, by comparing the SM system over the measured channel and commonly-used channel models, we prove that both the Independently and Identically Distribute (i.i.d.) Rayleigh and the Spatial Correlation (SC) channel model are oversimplified, and that only practical experiences can yield definitive answers to the achievable real-world system performance. Thirdly, the Average Bit Error Probability (ABEP) performance of the SM system is studied based on the measured data under a variety of system configurations. The study of different receive antenna array settings (4×4, 4×2 and 4×1 MIMO setups) approves the significance of combining scheme at the receiver. SM systems employing different signal constellations (Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM)) are also investigated and some interesting results are revealed. Lastly, performance assessment of SM against State-Of-The-Art (SOTA) MIMO schemes (Space-Time Block Code (STBC) and Vertical Bell Labs Layered Space-Time (V-BLAST) code) is conducted. Results show that for a 4×4 MIMO, the low-complexity SM scheme outperforms both STBC and V-BLAST.

Performance of spatial modulation with constant transmitted power under LOS and NLOS scenarios

Previous work shows that Average Bit Error Probability (ABEP) of SM systems under Non Line of Sight (NLOS) scenario is lower than that under Line of Sight (LOS) scenario because of a lower spatial correlation with a given Signal to Noise Ratio (SNR). However, when transmit power is constrained as a constant, the SNR under LOS scenario is larger than that under NLOS scenario benefiting from the strong LOS ray. Spatial correlation and SNR are two contradictory factors which both impact the performance of SM systems. In order to analyze performances of SM systems with a constant power under LOS and NLOS indoor scenarios, 15150 complex MIMO channel matrices are measured in a typical building of Shenzhen Graduate School, Harbin Institute of Technology. Based on measured data and motivated by the Minimum Distance Lower Bound (MDLB) approach, Euclid distances between received symbols of SM systems, as a monotonic function of ABEP, is analyzed. It is found that the effect of the SNR is much more important than the spatial correlation in the indoor environment so that SM system under LOS scenario shows a better performance than NLOS when the transmitting power is a constant. Furthermore, it is observed that bottlenecks of ABEP under LOS and NLOS scenarios are different. Under the LOS scenario, the bottleneck of ABEP is the antenna index error. On the contrary, under the NLOS scenario, the bottleneck of ABEP is the joint error. Using two extreme cases, such phenomena is analytically explained in the paper.

On the Error Probability of Spatial Modulation over Keyhole MIMO Channels

The keyhole effect causes a dramatic performance degradation to Multiple-Input Multiple-Output (MIMO) systems. The main contribution of this letter is the analytical performance evaluation of Spatial Modulation MIMO (SM-MIMO) systems over the keyhole channel. The closed-form Pairwise Error Probability (PEP) is derived with accuracy verified by simulations. Based on the PEP, the achievable diversity gain is extracted and shown to be no more than 1 under any configuration. In addition, a tight Average Bit Error Probability (ABEP) upper bound is given. Numerical results demonstrate that compared to independent fading scenarios, the keyhole channel causes a significant performance degradation to the SM-MIMO system. It is shown that SM-MIMO schemes outperforms Space-Time Block Code (STBC) and V-BLAST schemes over the keyhole channel. Therefore, among multiple antenna transmission schemes, SM-MIMO schemes are better choices for systems that may experience the keyhole effect. However, owing to the inherent unfitness of the keyhole channel for multiple antenna transmission, SM-MIMO schemes are still inferior to SISO/SIMO schemes.

Polarization Shift Keying (PolarSK): System Scheme and Performance Analysis

The single-radio-frequency (RF) multiple-input-multiple-output (MIMO) system has been proposed to pursue a high spectral efficiency while keeping a low hardware cost and complexity. Recently, the available degrees of freedom (DoF) in the polarization domain has been exploited to reduce the size of the transmit antenna array and provide 1 bit per channel use (bpcu) multiplexing gain for the single-RF MIMO system. Nevertheless, the polarization domain resource still has the potential to provide a higher multiplexing gain in the polarized single-RF MIMO system. In this paper, we propose a generalized polarization shift keying (PolarSK) modulation scheme that uses polarization states in the dual-polarized transmit antenna as an information-bearing unit to increase the overall spectral efficiency. At the receiver, the optimum maximum likelihood (ML) detector is employed to investigate the ultimate performance limit of the PolarSK. A closed-form union upper bound on the average bit error probability (ABEP) of the PolarSK with the optimum ML receiver is derived. Inspired by the analytic ABEP, a constellation diagram optimization algorithm is proposed. To reduce the computational complexity of the receiver, a linear successive interference cancellation (SIC) detection algorithm and a sphere-decoding (SD) detection algorithm are introduced. Through numerical results, performances of the proposed PolarSK in terms of ABEP and computational complexity are analyzed. Furthermore, the PolarSK is analyzed over measured indoor channels. Numerical and measurement results show that the PolarSK scheme outperforms the state-of-the-art dual-polarized/unipolarized SM schemes.

A practical complex BKZ reduction algorithm for near-optimal MIMO SIC detection

The Block Korkine-Zolotareff (BKZ) reduction can trade off between performance and complexity by adjusting the size of the local reduction blocks, and therefore, offers the opportunity to approach the optimal performance achieved by the KZ reduction at a lower cost, when adopted by the lattice reduction (LR) aided successive interference cancellation (SIC) receiver for multiple-input multiple-output (MIMO) systems. In this paper, a novel complex-domain BKZ (CBKZ) reduction algorithm is developed by employing an on-demand complex-domain Schnorr-Euchner (SE) enumeration strategy for local shortest lattice vector searching, and a tailored unimodular transform scheme for basis updating. The sorted-QR decomposition coupled with size reduction is employed for pre-processing, rather than the widely adopted Lenstra-Lenstra-Lovász (LLL) reduction. Simulation results show that the proposed CBKZ reduction achieves close-to-optimal performance by using relatively small block sizes, and at the same time, causes only a small proportion of the overall computations required by its competitors: the complex LLL (CLLL) reduction and CLLL-deep reduction. In addition, a unified mathematical framework is provided to encompass the traditional SIC detection with ordering, the LR-aided SIC detection, and the integer-forcing (IF) SIC detection, under the same umbrella.

Performance analysis of FeICIC and adaptive spectrum allocation in heterogeneous networks

Cellular heterogeneous networks (HetNets) with densely deployed small cells can effectively boost network capacity. The co-channel interference and the prominent energy consumption are two crucial issues in HetNets which need to be addressed. Taking the traffic variations into account, in this paper, the performances of HetNets with joint further-enhanced inter-cell interference coordination (FeICIC) and adaptive spectrum allocation (ASA) for downlink communications are analytically analyzed for the first time. An analytical framework to evaluate performance gains via a stochastic geometric approach for two-tier HetNets is proposed. The overall signal to interference plus noise ratio (SINR) coverage and energy efficiency (EE) are derived and validated by Monte Carlo simulations. Numerical results confirm the effectiveness of the joint FeICIC and ASA scheme in terms of improving the SINR coverage and EE. Especially, the gains increase significantly with the growth of the pico cell density. The results indicate that joint FeICIC and ASA is a promising scheme for the next generation cellular networks.

Coverage and Association Bias Analysis for Backhaul Constrained HetNets with eICIC and CRE

Heterogeneous networks (HetNets) are envisioned as a key solution to address the ever increasing capacity demand in wireless networks. With the deployment of enhanced radio access technologies, the non-ideal backhaul will become a potential network bottleneck. However, the impact of backhaul capacities (BCs) on the network coverage and offloading are not well understood. To address these issues, using tools from stochastic geometry, we propose a tractable framework for analyzing the impact of BCs on the network coverage and the optimal offloading bias in HetNets with cell range expansion (CRE) and time domain enhanced inter-cell interference coordination (eICIC) techniques. Conditioned on guaranteeing the minimum quality of service (QoS) of serving users, the coverage probability is derived as a function of offloading bias and BC parameters. We show how non-ideal backhaul alters the network coverage and the optimal bias. Compared with the perfect backhaul case, the optimal coverage and the optimal bias exhibit different behaviors in the case of limited BC.

Research on three-dimensional omnidirectional wireless power transfer system for subsea operation

In this paper, a three-dimensional omnidirectional underwater wireless power transfer (OUWPT) system is proposed. The transmitting coil is consisted of three mutually orthogonal loops with different feeding phases. The output power and transmission efficiency of the system are studied when the transmitting loops are using the simplest feeding phase differences and the optimal feeding phase differences. The simulation results show that the output power and transmission efficiency are greatly improved by around 5 times and 10% when using the optimal feeding phase differences compared to the conventional system.

Complex Minkowski Reduction and a Relaxation for Near-Optimal MIMO Linear Equalization

First, this letter presents a Minkowski reduction algorithm working directly on complex lattices. Then, a relaxation is proposed to Minkowski criterion by restricting the search of basis vectors within sublattices whose dimensions are determined by an integer parameter

Spatial characterization of indoor MIMO radio channel at both 6.05GHz and 2.45GHz based on measurement

\beta