Rui Guan

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.

Channel capacity and receiver deployment optimization for multi-input multi-output visible light communications

Multi-input multi-output (MIMO) technique is attractive for visible light communication (VLC), which exploits the high signal-to-noise ratio (SNR) of a single channel to overcome the capacity limitation due to the small modulation bandwidth of the light emitting diode. This paper establishes a MIMO VLC system under the non-negativity, peak power and dimmable average power constraints. Assume that perfect channel state information at the transmitter is known, the MIMO channel is changed to parallel, non-interfering sub-channels by using the singular value decomposition (SVD). Based on the SVD, the lower bound on the channel capacity for MIMO VLC is derived by employing entropy power inequality and variational method. Moreover, by maximizing the derived lower bound on the capacity under the given constraints, the receiver deployment optimization problem is formulated. The problem is solved by employing the principle of particle swarm optimization. Numerical results verify the derived capacity bound and the proposed deployment optimization scheme.

PSO-based LED deployment optimization for visible light communications

The LED deployment optimization is a key technology for indoor visible light communications (VLC). This paper investigates the LED deployment problem in terms of the average outage area rate for on-off keying (OOK) modulated VLC. Based on the VLC channel model, the average outage area rate is derived on the conditions of the non-uniformity distribution of a receiver. Furthermore, an optimization problem is formulated to minimize the average outage area rate to obtain the best LED deployment. Employing the particle swarm optimization (PSO), two LED deployment schemes, i,e., single-LED-based deployment scheme and array-LED-based deployment scheme, are proposed to tackle it. The simulation results are compared using both the proposed schemes and the conventional random scheme. It is shown that the PSO-based LED deployment schemes outperform the random scheme.

Free-space optical communications using all-optical relays over weak turbulence channels with pointing errors

In this paper, the outage performance of a free-space optical (FSO) communication system with parallel all-optical relays is investigated by employing the photon counting methodology. Initially, a composite channel model is considered which includes atmospheric loss, pointing error and weak atmospheric turbulence. To show the impacts of the channel state information (CSI) on system performance, either full CSI or semi-blind CSI at the relay nodes is considered. Based on the channel model, the approximate expressions of the outage probability for both full CSI relaying and semi-blind CSI relaying are derived, respectively. Numerical results substantiate that the derived expressions can provide sufficient precision for evaluating the outage performance of FSO communication systems. Moreover, for the scenario we considered, semi-blind CSI relaying can provide nearly identical performance to its full CSI counterpart.

Novel spectral efficient OFDM for optical wireless communication

This paper presents an enhanced hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (OFDM) scheme referred to as EHACO-OFDM. The scheme uses asymmetrically clipped optical OFDM (ACO-OFDM) on the odd subcarriers, pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) on the imaginary parts of even subcarriers, and direct-current-biased optical OFDM (DCO-OFDM) on the real parts of even ones. Since the entire available bandwidth is utilized for data modulation, this scheme can achieve higher spectral efficiency than HACO-OFDM and ACO-OFDM. Moreover, as a smaller DC bias is introduced in our scheme, it is more power efficient than asymmetrically clipped DC-biased optical OFDM (ADO-OFDM) and DCO-OFDM. Simulation results show that EHACO-OFDM performs much better than ADO-OFDM and HACO-OFDM at high bit rates.

Enhanced hybrid asymmetrically clipped orthogonal frequency division multiplexing for optical wireless communications

Abstract. This paper presents an enhanced hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (EHACO-OFDM) scheme, which benefits from the simultaneous transmission of ACO-OFDM, pulse-amplitude-modulated discrete multitone modulation, and direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM). Since the entire available bandwidth is utilized for data modulation, this scheme can achieve higher spectral efficiency than HACO-OFDM and ACO-OFDM. Moreover, as a smaller DC bias is introduced in our scheme, it is more power efficient than asymmetrically clipped DC-biased optical OFDM (ADO-OFDM) and DCO-OFDM. A modified receiver is also designed for this system, taking advantage of an iterative algorithm and a pairwise averaging. It has been shown by simulation that our three-path simultaneous transmission scheme can surpass the existing mixed OFDM-based schemes at high data rates. In addition, compared with the noniterative receiver, the modified receiver exhibits significant gains.

Energy Minimization in Machine-to-Machine Systems with Energy Harvesting

In this paper, we investigate the sum energy minimization problem in an uplink machine-to- machine (M2M) system with energy harvesting. To solve this nonconvex sum energy minimization problem, we first transform it into an equivalent convex problem and provide the optimal condition of the original problem. Then, we propose a low- complexity iterative scheme, which yields the optimal solution. The complexity of the proposed scheme is also analyzed. Numerical results show that the proposed scheme can achieve good performance.

Energy efficient resource allocation for machine-to-machine communications with NOMA and energy harvesting

The vast amount of the machine type communication devices (MTCDs) in machine-to-machine (M2M) communications and their limited energy budget are the crucial challenges to transmission scheme design. This paper proposes an energy-efficient power control and time scheduling scheme in M2M communications with non-orthogonal multiple access (NOMA) and energy harvesting. User equipment (UEs) are configured as gateways for MTCDs. Our aim is to minimize the total energy consumption of both MTCDs and UEs, on condition that the throughput constraints for both MTCDs and UEs as well as the minimal required harvested energy constraints for MTCDs are satisfied. We obtain the optimal conditions for the total energy minimization problem. Numerical results show that the proposed algorithm achieves the optimal energy consumption.