Baoyu Zheng

An Adaptive Cooperation Diversity Scheme With Best-Relay Selection in Cognitive Radio Networks

In this correspondence, an adaptive cooperation diversity scheme with best-relay selection is proposed for multiple-relay cognitive radio networks to improve the performance of secondary transmissions while ensuring the quality of service (QoS) of primary transmissions. Exact closed-form expressions of the outage probability of secondary transmissions, referred to as secondary outage probability, are derived under the constraint of satisfying a required outage probability of primary transmissions (primary outage probability) for both the traditional non-cooperation and the proposed adaptive cooperation schemes over Rayleigh fading channels. Numerical and simulation results show that, with a guaranteed primary outage probability, a floor of the secondary outage probability occurs in high signal-to-noise ratio (SNR) regions. Moreover, the outage probability floor of the adaptive cooperation scheme is lower than that of the non-cooperation scenario, which illustrates the advantage of the proposed scheme. In addition, we generalize the traditional definition of the diversity gain, which can not be applied directly in cognitive radio networks since mutual interference between the primary and secondary users should be considered. We derive the generalized diversity gain and show that, with a guaranteed primary outage probability, the full diversity order is achieved using the proposed adaptive cooperation scheme.

Cooperative relay techniques for cognitive radio systems: Spectrum sensing and secondary user transmissions

Cognitive radio is a promising technology that enables an unlicensed user (also known as a cognitive user) to identify the white space of a licensed spectrum band (called a spectrum hole) and utilize the detected spectrum hole for its data transmissions. To design a reliable and efficient cognitive radio system, there are two fundamental issues: to devise an accurate and robust spectrum sensing algorithm to detect spectrum holes as accurately as possible; and to design a secondary user transmission mechanism for the cognitive user to utilize the detected spectrum holes as efficiently as possible. This article investigates and shows that cooperative relay technology can significantly benefit the abovementioned two issues, spectrum sensing and secondary transmissions. We summarize existing research about the application of cooperative relays for spectrum sensing (referred to as the cooperative sensing) and address the related potential challenges. We discuss the use of cooperative relays for the secondary transmissions with a primary users quality-of-service (QoS) constraint, for which a diversity-multiplexing trade-off is developed. In addition, this article shows a trade-off design of cognitive transmissions with cooperative relays by jointly considering the spectrum sensing and secondary transmissions in cognitive radio networks.

A Selective-Relay Based Cooperative Spectrum Sensing Scheme without Dedicated Reporting Channels in Cognitive Radio Networks

Typically, each cooperative spectrum sensing process requires two phases: the primary users signal detection phase, in which all cognitive users attempt to detect the presence of the primary user within a certain observation window (called signal detection overhead); and the initial detection result reporting phase, in which the cognitive users forward their detection results to a fusion center. To avoid interfering with the primary user in the reporting phase, previous research assumed that there is a common control channel (also known as dedicated reporting channel) between the cognitive users and fusion center, which, however, requires extra channel resources and introduces an additional complexity due to the dedicated channel resource management. In this paper, we propose a selective-relay based cooperative spectrum sensing scheme, which is able to control and reduce the interference from cognitive reporting users to primary user without the dedicated channel. We analyze the interference impact on the primary user and show that the interference induced by the reporting users is controllable and can be reduced to satisfy a given outage probability requirement of the primary transmissions. In addition, we investigate the receiver operating characteristics (ROC) of the traditional cooperative sensing scheme (with dedicated reporting channel) and the proposed scheme (without dedicated reporting channel) by jointly considering the signal detection and reporting phases. It is proven that, given a target detection probability, a unique optimal signal detection overhead exists to minimize an asymptotic overall false alarm probability in high SNR regions. We illustrate that, compared to the traditional scheme, the selective-relay based cooperative sensing scheme can save the dedicated channel resources without sacrificing ROC performance. Numerical results also show that, under a guaranteed overall detection probability, an overall false alarm probability can be minimized through an optimization of the signal detection overhead.

Outage Probability Analysis of Cognitive Transmissions: Impact of Spectrum Sensing Overhead

In cognitive radio networks, a cognitive source node requires two essential phases to complete a cognitive transmission process: the phase of spectrum sensing with a certain time duration (also referred to as spectrum sensing overhead) to detect a spectrum hole and the phase of data transmission through the detected spectrum hole. In this paper, we focus on the outage probability analysis of cognitive transmissions by considering the two phases jointly to examine the impact of spectrum sensing overhead on system performance. A closed-form expression of an overall outage probability that accounts for both the probability of no spectrum hole detected and the probability of a channel outage is derived for cognitive transmissions over Rayleigh fading channels. We further conduct an asymptotic outage analysis in high signal-to-noise ratio regions and obtain an optimal spectrum sensing overhead solution to minimize the asymptotic outage probability. Besides, numerical results show that a minimized overall outage probability can be achieved through a tradeoff in determining the time durations for the spectrum hole detection and data transmission phases. In this paper, we also investigate the use of cognitive relay to improve the outage performance of cognitive transmissions. We show that a significant improvement is achieved by the proposed cognitive relay scheme in terms of the overall outage probability.

Joint physical-application layer security for wireless multimedia delivery

In recent years, there have been increasing demands for the security of wireless multimedia applications. Essentially, wireless networks, compared to traditional wired networks, are more likely to suffer from malicious attacks. Most current security methods consider physical layer and application layer security technologies independently and separately. Usually, physical layer information is dynamic in wireless networks, and application layer information is related to wireless multimedia delivery. Importantly, both of them have significant impact on security performance. In this work, we propose a joint framework involving both the physical and application layer security technologies. Specifically, by exploiting the security capacity and signal processing technologies at the physical layer and the authentication and watermarking strategies at the application layer, the available network resources can be utilized efficiently. In addition, scalable multimedia security services can be maximized within the given multimedia delivery deadlines. In particular, this joint scheme can be implemented easily with low communication overhead, which facilitates its deployment in large-scale wireless multimedia systems.

Outage analysis of opportunistic cooperation over rayleigh fading channels

Cooperation is emerging as a promising technology to combat the wireless fading and enhance the channel capacity. However,cooperative transmission can not be guaranteed to perform better always than direct transmission, since the statistics of both direct and relay channels are varied due to large scale fading. Therefore, we design an opportunistic criterion to automatically determine which transmission mode should be adopted depending on the channel quality from the source to the cooperative relay, as opposed to the deterministic cooperation regardless of relay channel conditions. According to the proposed criterion, we further present two opportunistic cooperation schemes, namely, the SDC (selection diversity combining) -based and the MRC (maximum ratio combining) -based opportunistic cooperation, and develop the closed-form expressions of outage probability for the proposed schemes over Rayleigh fading channels. For the purpose of comparison, we also analyze the outage probability for the known deterministic cooperation and coded cooperation. Numerical results show that our schemes outperform the traditional schemes in terms of outage probability, especially when the relay channel conditions worsen. In addition, we compare the MRC-based opportunistic cooperation with the SDC-based opportunistic cooperation, showing the superiority of the former scheme.

A Cooperative Sensing Based Cognitive Relay Transmission Scheme Without a Dedicated Sensing Relay Channel in Cognitive Radio Networks

In this correspondence, we investigate a selective relay spectrum sensing and best relay data transmission (SRSS-BRDT) scheme for multiple-relay cognitive radio networks. Specifically, in the spectrum sensing phase, only selected cognitive relays are utilized to transmit/forward their initial detection results (without a dedicated sensing relay channel) to a cognitive source for fusion, where the dedicated sensing channel refers to the channel transmitting initial spectrum sensing results from cognitive relays to the cognitive source. In the data transmission phase, only the best relay is selected to assist the cognitive source for its data transmissions. By jointly considering the two phases, we derive a closed-form expression of the outage probability for the SRSS-BRDT scheme over Rayleigh fading channels. We show that the SRSS-BRDT scheme outperforms the traditional cognitive transmission scheme (with a limited dedicated sensing channel) in terms of the outage probability performance. In addition, numerical results illustrate that the outage probability of the SRSS-BRDT scheme can be minimized through an optimal allocation of the time durations between the spectrum sensing and data transmission phases.

System Scheduling for Multi-Description Video Streaming Over Wireless Multi-Hop Networks

Providing real-time multimedia applications over wireless multi-hop networks is a challenging problem because the wireless channels are highly sensitive to delay, interference and topology changes. Multiple description coding (MDC), as a new emerging error-resilient technique, has been widely used recently in wireless video transmission. Its fundamental principle is to generate multiple correlated descriptions such that each description approximates the source information with a certain level of fidelity. Inevitably, MDC introduces many description streams which may influence each other and thus, reasonable system scheduling is needed to provide a satisfied video quality. The novelty of this work is to investigate the optimal distributed scheduling for multiple competing MDC streams in a resource-limited wireless multi-hop network. This is achieved by joint optimization of MDC, rate control and multipath routing. Two joint optimal algorithms, namely a distributed rate control and routing (DRCR) and a simplified DRCR algorithm, are proposed to solve this problem with constraints that arise from the multiple description streams among multiple users via multiple paths. Both algorithms are designed in a distributed manner that is amenable to on-line implementation for wireless networks. Theoretical analysis and simulation results are provided which demonstrate the effectiveness of our proposed joint schemes.

An opportunistic cooperation scheme and its BER analysis

The cooperative communication technology proposed in recent years enables network nodes to share their antennas to achieve diversity gain. In this paper, an efficient variation scheme on opportunistic cooperation is proposed by using an outage criterion, in which the cooperation mode will be adopted only when the channel from source to relay does not occur outage event. We derive a closed-form BER (bit error rate) expression for the proposed scheme over Rayleigh fading channels, showing that the full diversity is achieved by the new scheme. Also, the BER performance of the known coded cooperation is presented for the purpose of comparison with our scheme. Numerical results illustrate the superiority of the proposed scheme over the coded cooperation in terms of BER performance. It is pointed out that the corresponding BER advantage of the proposed scheme comes at the expense of increasing system overhead since the new scheme needs some feedback from relay to both source and destination.

Distributed Scheduling for Video Streaming over Multi-Channel Multi-Radio Multi-Hop Wireless Networks

An important issue of supporting multi-user video streaming over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resources while, at the same time, to meet each videos QoS (Quality of Service) requirement. In this work, we study the problem of video scheduling over multi-channel multiradio multi-hop networks with the goals of minimizing the video distortion. At first, we construct a general distortion model according to the networks transmission mechanism, as well as videos rate-distortion characteristics. Then, by joint considering the channel assignment, rate allocation and routing, we develop a fully distributed scheduling scheme to get an optimal QoS performance. Furthermore, the realization of the distributed scheduling scheme through cooperation among the channel, link and source is the highlight of this paper. Extensive simulation results are provided which demonstrate the effectiveness of our proposed scheme.