Hailin Xiao

Aggregate Interference Modeling in Cognitive Radio Networks with Power and Contention Control

In this paper, we present interference models for cognitive radio (CR) networks employing various interference management mechanisms including power control, contention control or hybrid power/contention control schemes. For the first case, a power control scheme is proposed to govern the transmission power of a CR node. For the second one, a contention control scheme at the media access control (MAC) layer, based on carrier sense multiple access with collision avoidance (CSMA/CA), is proposed to coordinate the operation of CR nodes with transmission requests. The probability density functions (PDFs) of the interference received at a primary receiver from a CR network are first derived numerically for these two cases. For the hybrid case, where power and contention controls are jointly adopted by a CR node to govern its transmission, the interference is analyzed and compared with that of the first two schemes by simulations. Then, the interference PDFs under the first two control schemes are fitted by log-normal PDFs to reduce computation complexity. Moreover, the effect of a hidden primary receiver on the interference experienced at the receiver is investigated. It is demonstrated that both power and contention controls are effective approaches to alleviate the interference caused by CR networks. Some in-depth analysis of the impact of key parameters on the interference of CR networks is given as well.

Novel Partial Selection Schemes for AF Relaying in Nakagami-

New partial relay selection schemes for cooperative diversity based on amplify-and-forward (AF) relaying are proposed in Nakagami-m fading channels. Their performances are compared with the conventional partial selection scheme. Numerical results show that the new schemes have performance gains of up to 5 dB over the conventional scheme. In some cases, their performances are indistinguishable from the full selection scheme, but they have much simpler structures. Numerical results also show that it is more important to choose the idle user for the hop with a small average signal-to-noise ratio (SNR) or an m parameter in partial selection. Based on this observation, a new adaptive partial selection scheme based on the average SNR, and the m parameter is derived. A complexity analysis also shows that the new schemes reduce the complexity in some cases.

m

In this paper, throughput improvement of device-to-device (D2D)-aided underlaying cellular networks is analyzed. The D2D devices are assumed to be capable of operating at the full duplex (FD) mode to enable the concurrent transmission and reception with a single frequency band. We analyze the impact of activating D2D users on the throughput of FD-based D2D (FD-D2D) aided underlaying network by considering non-ideal self-interference cancellation at the FD devices. Despite of an extra interference imposed on the cellular users (CUs) by the active D2D links, which may erode the signal-to-interference ratio of the former significantly, the FD-D2D mode is still shown to exhibit its superiority in terms of the throughput improvement. Furthermore, in order to avoid a severe FD-D2D-induced interference imposed on the CUs, a new mechanism called “dynamic cellular link protection (DCLP),” which prohibits the transmissions of FD-D2D users when they are located inside the pre-set guard areas, is proposed. Numerical results show that the proposed DCLP mechanism is capable of substantially improving the throughput of the underlaying cellular networks without seriously eroding the capacity of the conventional cellular links.

Fading Channels

Space-time block codes (STBCs) are known to orthogonalize the multiple input multiple out (MIMO) wireless channels. In this paper, we study the capacity of STBCs over Weibull MIMO channels under three adaptive transmission techniques: optimal power and rate adaptation, optimal rate adaptation with constant transmit power and channel inversion with fixed rate, and obtain closed-form expressions for the corresponding capacity. This capacity provides an upper bound on spectral efficiency using these techniques and avoids Monte Carlo simulations. Moreover, we also examine the effects of the fading severity on the concerned quantities. The figures show that our theoretical results of channel capacity line up exactly with the simulations.

Throughput Improvement in Cellular Networks via Full-Duplex Based Device-to-Device Communications

A general formula for the cross polarization discrimination (XPD) of multiple input multiple output antennas at mobile station is provided, taken the influence of mobile antenna inclination into account. A statistical distribution indoor model for both vertically polarized and horizontally polarized incident waves that are uniform in elevation and in azimuth is also proposed. By using the formula jointly with this statistical model, the effect of some parameters on XPD is analyzed numerically. The obtained XPD values vary from approximately 5 dB to less than 11 dB. These values are consistent with the measurement, which are typically used in system specifications. For antennas inclination, deviation angle has little effect on the XPD, but clear differences exist between antennas.

Capacity of Orthogonalized Weibull MIMO Channels Under Different Adaptive Transmission Techniques

In wireless distributed networks, multisource multirelay cooperative techniques can be used to exploit the spatial and temporal diversity gains to increase the performance or reduce the transmission energy consumption, which is very useful for intelligent transport system (ITS) networks. In this paper, we propose a power allocation method to optimize the hybrid decode-amplify-forward cooperative transmission for multisource multirelay ITS networks as a means to reduce the total power consumption while minimizing outage probability. Specifically, we derive closed-form outage probability expressions and present an energy-efficient relay selection method to form an optimal relay set. It is proven that the proposed methods can solve the joint power allocation and relay selection problem under outage probability constraint. Our performance analysis is supplemented by numerical simulation results to illustrate the significant energy savings of the proposed optimal power allocation and the relay selection methods.

The cross polarization discrimination OF MIMO antennas at mobile station

The device-to-device (D2D) communication has been regarded as an effective technique for complementing and enhancing the conventional cellular systems owing to its capability of substantially improving both the spectral and power efficiencies of wireless networks. However, the severe interference imposed on the conventional cellular users (CUs) by the geographically close-by D2D pairs may cause a significant performance erosion in the D2D-aided underlaying cellular networks (CNs). In this paper, performance analysis for the D2D-aided underlaying CNs in terms of throughput is provided. We first derive the closed-form expressions of the coverage probability for both the conventional cellular links and the D2D links, followed by giving out the approximated expressions of the ergodic data rate for both an individual cellular/D2D link and the whole underlaying network. Furthermore, the key parameters (e.g., the density of D2D users (DUs) or CUs, and the average geographical distance between a pair of D2D peers) significantly impacting the channel capacity are adaptively adjusted for maximizing the sum data rate of the proposed underlaying networks. In addition, both theoretical analysis and simulation results reveal the attainability of the maximal throughput by optimizing the critical parameters, such as the density of DUs, provided that the scale factor between the DUs and sum users (i.e., comprising both conventional CUs and DUs) can be effectively balanced subject to the constraints specified in the proposed scheme.

Power Allocation and Relay Selection for Multisource Multirelay Cooperative Vehicular Networks

This paper investigates the sum rate capacity of MIMO broadcast channels (MIMO-BCs) in cognitive radio networks. A suboptimal user-selection algorithm is proposed to achieve a large sum rate capacity with reduced complexity. This algorithm consists of two steps. First, zero-forcing beamforming is utilized as a downlink precoding technique that precancels inter-user interference. Second, singular value decomposition is applied to the channel matrices of all the secondary users and only consider the singular vectors corresponding to the maximum singular values. The proposed user-selection algorithm chooses singular vectors which are nearly orthogonal to each other and nearly orthogonal to the vector of primary users. With this algorithm, the sum rate capacity of MIMO-BCs in CR networks with interference power constraints and transmit power constraints is derived. We formulate the sum rate capacity as a multi-constraint optimization problem and develop an algorithm to solve the problem in its equivalent form. Finally, numerical simulations are conducted to corroborate our theoretical results in flat Rayleigh fading environments. It is shown that the proposed algorithms are capable of achieving a large sum rate capacity with a very low complexity.

Optimal Mode Selection With Uplink Data Rate Maximization for D2D-Aided Underlaying Cellular Networks

The cognitive radio multiple-input multiple-output Gaussian broadcast channels are studied where multiple antennas are available for both primary users and secondary users in a spectrum sharing environment, and the sum-rate capacity is also obtained under both the SUs’ transmit power constraint and interference power constraint at the primary receivers. The paper principally consists of two steps. First, a duality technique and dirty paper coding are adopted to simplify the channels. Second, we propose an iterative power allocation algorithm to obtain the maximum sum-rate capacity and examine the effects of the constraint parameters on the concerned quantities. Finally, numerical simulation results are presented to validate the proposed theoretical analysis.

On the Sum Rate Capacity of MIMO Broadcast Channels in Cognitive Radio Networks with Interference Power Constraints

In this paper, a novel spectrum sensing scheme, which is robust in the presence of impulsive noise, is proposed to meet the rigid requirements for sensing accuracy. An efficient least trimmed square algorithm incorporated with an adaptive signal trimming scheme is proposed to eliminate the set of signal samples contaminated by impulsive noise. Spectrum sensing based can be performed to the denoised data, thereupon. The studies on the theoretical and practical aspects of our proposed robust spectrum sensing scheme are presented. According to Monte Carlo simulation results, our new scheme effectively eliminates the impulsive noise, and offers more robustness compared with other existing methods.