Zhiqing Wei

An effective approach to 5G: Wireless network virtualization

Nowadays, the explosively growing demands for mobile service bring both challenges and opportunities to wireless networks, giving birth to fifth generation (5G) mobile networks. The features and requirements of different services are diverse in 5G. The management and coordination among heterogeneous networks, applications, and user demands need the 5G network to be open and flexible to ensure that network resources are allocated with high efficiency. To fulfill these requirements, wireless network virtualization is used to integrate heterogeneous wireless networks and coordinate network resources. In this article we propose a model of wireless network virtualization consisting of three planes: the data plane, the cognitive plane, and the control plane. A novel control signaling scheme has also been designed to support the proposed model. From the implementation perspective of network virtualization, a hierarchical control scheme based on cell-clustering has been used with dynamically optimized efficiency of resource utilization. Two use cases have been analyzed to demonstrate how the schemes work under the proposed model to improve resource efficiency and the user experience.

On the construction of Radio Environment Maps for Cognitive Radio Networks

The Radio Environment Map (REM) provides an effective approach to Dynamic Spectrum Access (DSA) in Cognitive Radio Networks (CRNs). Previous results on REM construction show that there exists a tradeoff between the number of measurements (sensors) and REM accuracy. In this paper, we analyze this tradeoff and determine that the REM error is a decreasing and convex function of the number of measurements (sensors). The concept of geographic entropy is introduced to quantify this relationship. And the influence of sensor deployment on REM accuracy is examined using information theory techniques. The results obtained in this paper are applicable not only for the REM, but also for wireless sensor network deployment.

Connectivity of two nodes in cognitive radio ad hoc networks

This paper analyzes the connectivity of cognitive radio networks. The connectivity of cognitive network which is more consistent with reality is redefined in our article and the closed-form formula of relation between connectivity and density of PUs, density of SUs, and transmission radius of SU is given. Specifically, the impact of correlation of adjacent nodes for connectivity of cognitive radio ad hoc network is illustrated. On the basis of Random geometric graph and probability theory, a novel method that divides connectivity of cognitive radio ad hoc network into topological connectivity and physical connectivity is proposed to derive the close-form formula. We prove theoretically that once the density of secondary users is large enough and the transmission radius is appropriate, the probability of cognitive network connectivity tends to a stable non-zero value under the condition that density of primary users is small.

Security management based on trust determination in cognitive radio networks

Security has played a major role in cognitive radio networks. Numerous researches have mainly focused on attacking detection based on source localization and detection probability. However, few of them took the penalty of attackers into consideration and neglected how to implement effective punitive measures against attackers. To address this issue, this article proposes a novel penalty mechanism based on cognitive trust value. The main feature of this mechanism has been realized by six functions: authentication, interactive, configuration, trust value collection, storage and update, and punishment. Data fusion center (FC) and cluster heads (CHs) have been put forward as a hierarchical architecture to manage trust value of cognitive users. Misbehaving users would be punished by FC by declining their trust value; thus, guaranteeing network security via distinguishing attack users is of great necessity. Simulation results verify the rationality and effectiveness of our proposed mechanism.

Three regions for space-time spectrum sensing and access in cognitive radio networks

In this paper, spectrum holes in space-time dimensions are exploited to improve the spectrum utilization of cognitive radio networks (CRNs). To achieve this goal, we design the architecture of three regions, which are separately known as the black region, the gray region, and the white region. Temporal spectrum holes exist in the gray region, where secondary users (SUs) can opportunistically access the licensed spectrum with interweave spectrum sharing. In the white region, SUs can exploit spatial spectrum opportunities and transmit at any time by taking advantage of their long distances from the primary users (PUs), without causing severe interference to PUs. Moreover, the existence condition of the transition zone between the gray region and the white region is theoretically analyzed, where power control should be implemented in SUs. Closed-form bounds of three regions are obtained, which can be used in space-time spectrum sensing and access in CRNs. Finally, we provide numerical results to evaluate the relations among the key parameters in the three regions.

The asymptotic throughput and connectivity of cognitive radio networks with directional transmission

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area have been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is θ (1√(n log n). In this paper, we show that by exploiting directional spectrum opportunities in secondary network, the throughput of secondary network can be improved. If the beamwidth of secondary transmitter (TX)s main lobe is σ = o(1/ log n), SUs can achieve a per-node throughput of θ (1√(n log n) for directional transmission and omni reception (DTOR), which is θ (log n) times higher than the throughput without directional transmission. On the contrary, if θ = ω (1/ log n), the throughput gain of SUs is 2π/δ for DTOR compared with the throughput without directional antennas. Similarly, we have derived the throughput for other cases of directional transmission. The connectivity is another critical metric to evaluate the performance of random ad hoc networks. The relation between the number of SUs n and the number of PUs m is assumed to be n = mβ. We show that with the HDP-VDP routing scheme, which is widely employed in the analysis of throughput scaling laws of ad hoc networks, the connectivity of a single SU can be guaranteed when β > 1, and the connectivity of a single secondary path can be guaranteed when β > 2. While circumventing routing can improve the connectivity of cognitive radio ad hoc network, we verify that the connectivity of a single SU as well as a single secondary path can be guaranteed when β > 1. Thus, to achieve the connectivity of secondary networks, the density of SUs should be (asymptotically) bigger than that of PUs.

Joint power allocation and relay selection for multi-hop cognitive network with ARQ

In this paper, we investigate the power saving issue in cognitive radio (CR) multi-hop relay network. Due to the dynamic property of the wireless channel, the quality of service (QoS) guarantee for multi-hop transmission is quite challenging. To deal with these problems, automatic repeat-request (ARQ) protocol in an end-to-end manner is incorporated. For multi-hop transmission evaluation purpose, the end-to-end packet delivery probability is put forward as a QoS indicator in this paper. Besides, by underlay spectrum sharing, each relay is possessed of a power budget (i.e., maximum transmit power) to protect primary user from suffering intolerable interference. This paper addresses the power saving problem under each relays power budget constraint, which means the end-to-end QoS constraints can be satisfied with the minimum total power consumption for relays along the optimal path. Motivated by this, we propose a joint Lagrange dual method based power allocation and exhaustive search based relay selection algorithm to obtain the solution. Numerical simulations are presented to validate the theoretical analysis. The results show that the proposed algorithm achieves a good performance in power saving.

A game-theoretic approach for bandwidth allocation and pricing in heterogeneous wireless networks

In this paper, a distributed two-level Stackelberg game for bandwidth allocation and pricing in heterogeneous wireless networks is proposed. The proposed Stackelberg game consists of two competition game levels, namely, a user level game and a network level game. Networks are the Stackelberg leaders which play the network level game and decide price to maximize the revenue of networks. The multi-mode users are the Stackelberg followers which play the user level game and decide bandwidth allocation to maximize the utility of users. In the user level game, the notion of Match-Degree is introduced to take into account the suitability of networks to various traffics. Then the existence of Stackelberg equilibrium (SE) is verified for this Stackelberg game. To obtain the SE, an iterative algorithm is constructed. Simulation results show that our proposed game not only can significantly increase the utility of users compared with traditional bandwidth allocation schemes, but also can set suitable network price by considering network competition and user behavior.

Three Regions for Space–Time Spectrum Sensing and Access in Cognitive Radio Networks

In order to improve the spectrum utilization in cognitive radio networks, the spectrum holes in space-time-frequency multiple dimensions should be exploited accurately and efficiently. Therefore, a novel three region scheme, which includes the black region, grey region and white region, has been designed and proposed with one primary transmitter at the center, taking into account key interference factors from secondary users (SUs) and the miss detection and false alarm probabilities in spectrum sensing. Between the black region where only primary users (PUs) have exclusive right to use the spectrum and the white region where SUs can utilize the same spectrum without causing severe interference to PUs, the grey region has been designed, which has temporal spectrum access opportunities in time dimension once neglected by existing works. Moreover, the condition of the existence of a transition zone between grey region and white region is analyzed with theoretical results, where power control should be applied to SUs. The closed-form bounds of three regions are obtained, which can be used in the space-time spectrum sensing and access in cognitive radio networks.

Throughput scaling laws of cognitive radio networks with directional transmission

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area has been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is equation. In this paper, we show that by exploiting directional spectrum opportunities in secondary networks, the SU throughput can be improved. If the main lobe of the SU antenna pattern can be as narrow as possible, then the SUs can achieve a per-node throughput of equation which is Θ(log n) times higher than the the throughput without directional transmission. If we consider practical constraints and assume the minimum angle of the main lobe is δth, then the SU throughput gain is equation compared with the throughput without directional transmission. We also explore the statistics of directional spectrum holes in this paper.