Nuo Huang

Totally distributed energy-efficient transmission design in MIMO interference channels

In this paper, we consider the problem of maximizing the energy efficiency (EE) for multiple-input-multiple-output (MIMO) interference channels (ICs), subject to the per-link power constraint. To avoid extensive information exchange among all links, the optimization problem is formulated as a noncooperative game, where each link maximizes its own EE. We show that this game always admits a Nash equilibrium (NE) and the sufficient condition for the uniqueness of the NE is derived for the case of large enough maximum transmit power constraint. To reach the NE of this game, we develop a totally distributed EE algorithm, in which each link updates its own transmit covariance matrix in a completely distributed and asynchronous way. Some players may update their solutions more frequently than others or even use the outdated interference information. The sufficient conditions that guarantee the global convergence of the proposed algorithm to the NE of the game have been given as well. We also study the impact of the circuit power consumption on the sum EE performance of the proposed algorithm in the case when the links are separated sufficiently far away. Moreover, the tradeoff between the sum EE and the sum spectral efficiency (SE) is investigated with the proposed algorithm under two special cases: 1) low transmit power constraint regime; and 2) high transmit power constraint regime. Finally, extensive simulations are conducted to evaluate the impact of various system parameters on the system performance.

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.

Downlink Resource Allocation and Power Control for Device-to-Device Communication Underlaying Cellular Networks

This letter investigates the resource allocation and power control for both device-to-device (D2D) pairs and cellular users (CUs) in D2D communication underlaying single-cell cellular networks, where multiple D2D pairs can share the same resources with CUs. Our goal is to maximize the sum rate of D2D pairs subject to the rate requirements for all CUs and power requirements for both D2D pairs and the base station. We first give the optimal conditions for the resource allocation of D2D pairs and power control of CUs and then propose an iterative resource allocation and power control algorithm. Numerical results show that the proposed algorithm achieves higher sum rate of D2D pairs than the existing schemes.

Receiver Design for PAM-DMT in Indoor Optical Wireless Links

In the conventional receiver for pulse-amplitude-modulated discrete multitone (PAM-DMT), the real parts of the subcarriers are distorted by the clipping noise and ignored in detection. In this letter, the signal analysis shows that the real parts of the subcarriers also contain the information of the transmitted signal. An iterative receiver is then proposed to improve the transmission performance of PAM-DMT by exploiting both the real and imaginary parts of the subcarriers. Simulation results show that the proposed iterative receiver can significantly improve the transmission performance of PAM-DMT systems.

Iterative Receiver for Flip-OFDM in Optical Wireless Communication

To guarantee nonnegative signals in optical wireless communication systems, flipped orthogonal frequency division multiplexing (Flip-OFDM) transmits the positive and negative parts of the signal over two consecutive OFDM subframes (positive subframe and negative subfame, respectively). The conventional receiver for Flip-OFDM recovers the data by subtracting the negative subframe from the positive one. However, the signal analysis shows that the signals in the two subframes contain the information of the transmitted data and can be used together to decode the data. An iterative receiver is then proposed to improve the transmission performance of Flip-OFDM by exploiting the signals in both subframes. Simulation results show that the proposed iterative receiver provides significant signal-to-noise ratio gain over the conventional receiver. Moreover, the iterative receiver also outperforms the existing advanced receiver.

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.

Pilot Allocation and Power Control in D2D Underlay Massive MIMO Systems

In this letter, we propose pilot reuse among device-to-device (D2D) users (DUs) in a D2D underlay massive MIMO system to shorten pilot overhead. First, we derive a lower bound on the average signal-to-interference-plus-noise ratio of DUs. Then, a revised graph coloring-based pilot allocation (RGCPA) algorithm is proposed to mitigate the pilot contamination. Finally, a power control problem to minimize D2D links’ data transmit power is formulated and an iterative scheme is adopted to solve the problem. The simulation results show that pilot overhead can be shortened greatly by pilot reuse, and the effect of pilot contamination can be almost cancelled using the proposed RGCPA algorithm. In addition, the power control scheme converges rapidly.

Sum Rate Maximization for VLC Systems With Simultaneous Wireless Information and Power Transfer

This letter investigates the sum rate maximization problem in a downlink visible light communication system with simultaneous wireless information and power transfer. To solve this nonconvex sum rate maximization problem, we first transform it into an equivalent convex problem. Then, we provide the optimal condition and propose a low-complexity iterative algorithm, which yields the optimal solution. Numerical results show that the proposed algorithm can achieve good performance.

Pricing-based distributed power control for weighted sum energy-efficiency maximization in ad hoc networks

We consider the problem of maximizing the weighted sum energy efficiency (WS-EE) in ad hoc networks. To solve this problem in a distributed manner, one novel distributed adaptive-pricing algorithm is developed based on limited information exchange among the nodes. Specifically, each node updates its current interference information and broadcasts it to the other nodes. Having collected all this information, each node can adjust its transmit power accordingly with simple arithmetical operations. Then iterate these two steps. This algorithm is strictly proven to be convergent and can attain the KKT optimality conditions of the problem. Moreover, an alternative centralized algorithm based on gradient projection method is proposed to serve as the performance benchmark. Simulation results show that the proposed distributed algorithm converges rapidly. Furthermore, this distributed algorithm performs as well as the centralized one and significantly outperforms the existing algorithm in terms of the WS-EE.