Jun-Bo Wang

Tight Bounds on Channel Capacity for Dimmable Visible Light Communications

In this paper, the upper and lower bounds for the channel capacity of dimmable visible light communications(VLC) systems are investigated. Because the information is modulated into the instantaneous optical intensity, the transmitted optical intensity is represented by a nonnegative input that is corrupted by an additive white Gaussian noise. Considering the illumination support in a VLC system, the transmitted optical intensity signal must satisfy the illumination constraint, i.e., the average transmitted optical intensity is constrained by a target illumination intensity, which is determined by the nominal optical intensity of the light source devices and dimming target. An upper bound on the channel capacity is derived based on the signal space geometry via a sphere packing argument. A lower bound on the channel capacity is derived by maximizing the mutual information between the channel input and output. Both the upper and lower bounds are presented in closed forms. Furthermore, a closed-form optimal intensity distribution of the transmitted optical signal is obtained. The numerical results show that the presented bounds are very tight at the application zone of dimmable VLC links.

Performance Analysis of Multi-Antenna Hybrid Satellite-Terrestrial Relay Networks in the Presence of Interference

The integration of cooperative transmission into satellite networks is regarded as an effective strategy to increase the energy efficiency as well as the coverage of satellite communications. This paper investigates the performance of an amplify-and-forward (AF) hybrid satellite-terrestrial relay network (HSTRN), where the links of the two hops undergo Shadowed-Rician and Rayleigh fading distributions, respectively. By assuming that a single antenna relay is used to assist the signal transmission between the multi-antenna satellite and multi-antenna mobile terminal, and multiple interferers corrupt both the relay and destination, we first obtain the equivalent end-to-end signal-to-interference-plus-noise ratio (SINR) of the system. Then, an approximate yet very accurate closed-form expression for the ergodic capacity of the HSTRN is derived. The analytical lower bound expressions are also obtained to efficiently evaluate the outage probability (OP) and average symbol error rate (ASER) of the system. Furthermore, the asymptotic OP and ASER expressions are developed at high signal-to-noise ratio (SNR) to reveal the achievable diversity order and array gain of the considered HSTRN. Finally, simulation results are provided to validate of the analytical results, and show the impact of various parameters on the system performance.

Outage Analysis for Relay-Aided Free-Space Optical Communications Over Turbulence Channels With Nonzero Boresight Pointing Errors

Free-space optical (FSO) communications has recently received significant attention and commercial interest for a variety of applications. In this paper, the outage probabilities for both the parallel and serial relay-aided FSO communications are analyzed. Initially, a new aggregated channel fading model is established, which considers atmospheric attenuation, M-distributed atmospheric turbulence, and nonzero boresight pointing errors. After that, the statistical characteristic of the aggregated channel is analyzed. Under the aggregated channel model, closed-form expressions of the outage probabilities for both the parallel and serial relay-aided FSO communications are derived, respectively. Numerical results show that the derived theoretical expressions are quite accurate and can provide sufficient precision for evaluating the outage performance, which is helpful to the design of future FSO communication systems.

Ant-Colony-Optimization-Based Scheduling Algorithm for Uplink CDMA Nonreal-Time Data

Scheduling plays an important role in determining the overall performance of code-division multiple-access (CDMA) systems. This paper is focused on the uplink scheduling of CDMA nonreal-time data. In practical CDMA systems, data can only be transmitted with a few fixed transmission rates. Moreover, to guarantee receiving accuracy, the actual received signal-power-to-interference-plus-noise-power ratio (SINR) is expected to be no less than the target SINR value. Using Heaviside unit step functions, the relationship between the actual SINR value and the actual available maximum transmission rate is described in the proposed system model. Based on the proposed system model, an integer optimization problem is formulated to simultaneously maximize the throughput and the scheduling efficiency. Particularly, an ant-colony-optimization (ACO)-based scheduling algorithm is proposed to solve the proposed optimization problem. The computational complexity analysis indicates that the proposed ACO-based scheduling algorithm is computationally efficient in terms of both running time and storage space. In addition, the numerical results show that the proposed optimization problem is more efficient at guiding the development of scheduling algorithms for uplink CDMA nonreal-time data. Moreover, the proposed ACO-based scheduling algorithm performs quite well in terms of quality, running time, and stability.

Performance analysis for free-space optical communications using parallel all-optical relays over composite channels

In the last 2 years, all-optical relaying techniques for free-space optical (FSO) communications have drawn considerable attention. In this study, the outage performance of an FSO communication system with parallel all-optical relays is investigated. A composite channel is established, which includes atmospheric loss, pointing error and atmospheric turbulence. To show the impact of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. After that, the theoretical expressions of the outage probabilities for different scenarios are derived. Numerical results show that the derived expressions are quite accurate to evaluate the system performance. Moreover, the derived results demonstrate that the systems with semi-blind CSI relaying can provide comparable performance to systems with full CSI relaying, and also indicate that the performance over strong turbulence channels with clear weather outperforms that over weak turbulence channels with light fog.

Optimal training sequences for indoor wireless optical communications

Since indoor wireless optical communication (WOC) systems can offer several potential advantages over their radio frequency counterparts, there has been a growing interest in indoor WOC systems. Influenced by the complicated optical propagation environment, there exist multipath propagation phenomena. In order to eliminate the effect of multipath propagation, much attention should be concentrated on the channel estimation in indoor WOC systems. This paper investigates optimal training sequences (TSs) for estimating a channel impulse response in indoor WOC systems. Based on the Cramer–Rao bound (CRB) theorem, an explicit form of search criterion is found. Optimum TSs are obtained and tabulated by computer search for different channel responses and TS lengths. Measured by mean square error (MSE) performance, channel estimation errors are also investigated. Simulation results show that the MSE of the channel estimator at the receiver can be reduced significantly by using the optimized TS set. Moreover, the longer the TS, the better the MSE performance that can be obtained when the channel order is fixed.

Network planning for distributed antenna-based high-speed railway mobile communications

Network planning in wireless communication systems, which has strong impacts on the system performance, is a complex and challenging issue. This paper investigates the network planning problem under high-speed railway communication scenarios. A system model is characterised in terms of distributed antenna technology. An optimisation problem is formulated to optimise the total system cost with transmission rate, handoff time and antenna number constraints. Because the optimisation problem is NP-hard, a particle swarm optimisation PSO-based network planning strategy is proposed to tackle it. The complexity analysis demonstrates the effectiveness of the proposed PSO-based network planning scheme in terms of running time and memory space. Finally, the simulation results substantiate that the proposed method can consistently offer a better performance gain in comparison with the uniform network planning scheme. Copyright

Downlink System Capacity Analysis in Distributed Antenna Systems

This paper focuses on the downlink system capacity in distributed antenna systems (DAS). Due to the complexity of actual wireless environments, a composite channel model is established which takes into account three factors, i.e., path loss, lognormal shadowing and Rayleigh fading. Based on the channel model, the probability density function (PDF) of the output signal-to-noise ratio (SNR) is derived. To facilitate the analysis, the distribution of the output SNR is approximated by a lognormal distribution. After that, by making use of selective diversity (SD) scheme for distributed antennas, an approximate analytical expression of the capacity for a mobile station (MS) over a given position is derived. Furthermore, considering the distribution of MSs in the system, a closed-form expression of the system capacity is obtained. Numerical results show that the closed-form expression can evaluate the system capacity performance of DAS very accurately.

Capacity analysis for pulse amplitude modulated visible light communications with dimming control

This paper focuses on the capacity-approaching, nonuniform signaling for the pulse amplitude modulated (PAM) visible light communications under the non-negativity, peak power, and dimmable average power constraints. The input distribution is characterized by three parameters, i.e., the intensities, the probabilities, and the number of mass points in the PAM constellation. In the open literature, no analytical expression can be used to obtain the capacity-achieving input distribution. In this paper, a computationally simple but capacity-approaching input distribution is alternatively derived by determining the three aforementioned parameters. The resulting input distribution can serve as a useful tool not to approach the channel capacity but to guide the practical system design. Numerical results substantiate that the derived input distribution is a capacity-approaching distribution and can offer a better performance gain in comparison with the commonly employed uniform input distribution.

Ergodic capacity and outage capacity analysis for multiple-input single-output free-space optical communications over composite channels

Abstract. Free-space optical (FSO) communications have attracted significant attention recently. The ergodic capacity and outage capacity of a multiple-input single-output FSO communication system are investigated. Initially, a composite channel model including distance-dependant atmospheric loss, pointing error, and atmospheric turbulence is derived. To show different weather conditions, both the weak and strong atmospheric turbulence conditions are taken into account. Moreover, the statistical characteristics of two composite channels (i.e., weak turbulence composite channels and strong turbulence composite channels) are provided. Furthermore, approximated expressions of the ergodic capacity and closed-form expressions of the outage capacity are derived under the two composite channels, respectively. Numerical results finally substantiate that the derived theoretical expressions can provide a very good approximation to the simulation results.