Youyun Xu

A practical HARQ scheme with network coding for LTE-A broadcasting system

In order to improve broadcasting efficiency in LTE-A system, a novel HARQ scheme with network coding (NC) technology is presented in this paper. The implementation level of XORing NC is selected based on LTE system, and an XORing NC Combined (XNCC) strategy is developed to perform combined retransmission. The main idea of proposed scheme is to retransmit lost packets for multiple receivers simultaneously utilizing NC technology. Moreover, we extend the proposed scheme to relay broadcasting system. The simulation results illustrate that compared with traditional retransmission scheme, the average number of transmissions of the proposed NC-HARQ scheme can be sharply decreased, and the coding gains can be attributed to the potential advantage of NC technology.

A High Efficiency Algorithm of Power and Bit Allocation for OFDMA Systems

In this paper, we propose a high efficiency algorithm of power and bit allocation for orthogonal frequency division multiple access (OFDMA) system, in which the allocation procedure is divided into three parts: linear water-filling power allocation, bit allocation and power and bit adjustment. It can quickly achieve the power and bit allocation on the users sub-carrier level with a good fairness performance. Simulation results show that the proposed algorithm can obviously decrease the operation complexity and slightly descended system throughput contrast to other algorithms. It is a promising algorithm to be used in a practical system for radio resource allocation.

Outage probability analysis of opportunistic cooperative multicast based on coded cooperation

Cooperative communication has been proposed to improve the performance affected by multi-path propagation in the wireless network. Then, coded cooperation is emerging as a promising technology to improve the outage performances. Combining the coded cooperation with opportunistic relaying scheme can minimize the outage probability. In this paper, we propose a multicast cooperation strategy based on opportunistic relay selection with coded cooperation. The outage performance analysis of this strategy is obtained in this work. Furthermore, through numerical results, we analyze the average outage probability of different number of relay and cooperative ratio.

Efficient cooperative spectrum sensing with minimum sensing error in cognitive radio networks

Spectrum sensing is one of the most important components of cognitive radio technology. Due to fading or shadowing effects of the channel, a cognitive radio (CR) may fail to sense the presence of the primary user (PU). Cooperative spectrum sensing is a good solution to this problem. In this paper, we focus on the optimization of cooperative spectrum sensing in which multiple CRs efficiently cooperate to achieve superior detection accuracy with minimum sensing error. We derive the optimal randomized rule for different decision threshold. Then, the optimal final decision threshold is derived according to minimum sensing error (MSE) rule. By simulations, our proposed strategy shows better performance on ameliorating the final probability of false alarm and the probability of detection simultaneously.

A novel spectrum-aware routing protocol for multi-hop cognitive radio ad hoc networks

Cognitive radio (CR) technology is a new communication paradigm that can be a solution to the spectrum scarcity problem. The new spectrum usage pattern necessitates corresponding routing protocols to exploit the available spectrum opportunistically. In this paper, we propose a novel Spectrum-Aware Routing Protocol (SARP) for multi-hop cognitive radio ad hoc networks. SARP integrates channel choice with route discovery to cope with dynamic spectrum by considering the actions of PUs. In addition, a local route maintenance and recovery mechanism is presented to deal with sudden appearance of PUs. Rerouting probability and channel usage ratio are introduced to evaluate the performance of this routing protocol. Simulation results show that the proposed scheme reduces rerouting probability obviously and increases channel usage ratio of SUs significantly.

Throughput maximization for cognitive radio networks with time-domain combining cooperative spectrum sensing

To improve the sensing performance, cooperation among cognitive users can be utilized to collect space diversity. In this paper, we propose a novel time-domain cooperative spectrum sensing framework, in which the time consumed by reporting for one cognitive user is also utilized for other cognitive users sensing. For time varying channels, the novel time-domain combining cooperative spectrum sensing is derived. We focus on the optimal sensing settings to maximize the throughput of the secondary network under the constraint that the primary users are sufficiently protected. Some simple algorithms are also derived to calculate the optimal solutions. Simulation results show that fundamental improvement of the achievable throughput can be obtained by optimal sensing settings. In addition, the novel time-domain cooperative spectrum sensing scheme shows a much larger throughput than cooperative sensing based on general frame structure.

A Resource Scheduling Scheme Utilizing Grey Space Spectrums for OFDM Based Cognitive Radio Systems

In this paper, we proposed a resource scheduling scheme for OFDM based Cognitive Radio(CR) systems. The available spectrum resources detected by certain sensing method are separate into white space and grey space. Different from other researches which aim at only allocating white space spectrums to cognitive users, our discussion present a proper solution to make use of grey space spectrums. When the white space spectrums are not sufficient for all users, the grey space will be deployed for the non real-time services while a simple subcarrier selection method is adopted in order to limit the interference to the primary user and meet the BER need for transmission. This scheme gives a method to utilize grey space spectrum appropriately and the simulation result reveals that our proposed scheme could increase the throughput of system and improve the QoS guarantee of non-real-time services.

Asymmetric network coding for two-way OFDM relay system with power allocation

Asymmetric data transmission commonly exists in two-way orthogonal frequency division multiplexing (OFDM) relay system. In this paper, we propose a novel asymmetric network coding scheme for two-way OFDM relay system with power allocation to improve the throughput and bit error rate (BER) performance. In the multiple access channel (MAC) phase, the relay receives asymmetric data from two terminals, respectively. The Max-Min power allocation is used to improve the system BER performance during the MAC phase. In the broadcast (BC) phase, a novel asymmetric network coding scheme based on the thought of adaptive modulation (AM) is proposed. The stronger link can reliably transmit more data by using higher-order modulation. The weaker link can adaptively reduce the modulation order with the help of bit-inserting zero approach and well-designed signal constellation and bit labeling, hence, improve the transmission reliability. Simulation results validate that the proposed scheme outperforms the symbol-inserting zeros scheme in BER and throughput.

A Novel Cooperative Routing Strategy for Wireless Broadcast Communication

In wireless communication, it is enough to transmit the same information only once to reach a group of users due to the broadcast nature of wireless media. However, some users may fail to receive as a result of channel fading and etc. Cooperative communication can make use of space diversity to enhance communication quality. In this paper, we proposed a novel cooperative routing strategy for wireless broadcast communication to improve the system throughput with slight packet loss.

Delay performance evaluation for supporting heterogeneous traffic in cognitive radio sensor networks

Traditional wireless sensor networks (WSNs) working in the license-free band, suffering from heavy interference as the license-free spectrum becomes increasingly crowded. Designing a WSN based on cognitive radios could be a promising approach in the near future to provide data transmissions with strict QoS requirements. In this paper, the heterogeneous traffic including real-time and best effort traffic is considered in a cluster-based cognitive radio sensor network (CRSN). Using the reservation-based policy, satisfactory to the latency requirements of CBR traffic can be achieved and adequate time can be reserved for serving the BE traffic simultaneously. We analyze the delay performance of the real-time traffic, and verify the analytical results using computer simulations. The results show that satisfactory to the latency requirements of CBR traffic can be achieved and adequate time can be reserved for serving the BE traffic at the same time. And the radio resources can be utilized efficiently.