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Zhan G.,Institute of Communications Engineering
2011 International Conference on Management Science and Industrial Engineering, MSIE 2011 | Year: 2011

Spectrum sensing is one of core technologies in cognitive radio. It can adapt to complicated electric-magnetic environments. By detecting environments in real time and extracting interference characteristic in frequency spectrum, it can use flexible spectrum assign strategy for adaptive communications. Spectrum sensing technology is discussed in this article. Then the realization scheme is proposed and applied in frequency-hopping communication systems. Computer simulations show that it can exactly provide spectrum occupation in real time for frequency-hopping communication systems. ©2011 IEEE. Source


Zhong W.,Institute of Communications Engineering
Proceedings - 2013 Wireless and Optical Communications Conference, WOCC 2013 | Year: 2013

In this paper, we study the optimal spectrum access in cognitive relay networks where multiple secondary users can access the unutilized idle spectrum of the primary users and conduct bidirectional communication. The spectrum access problem in the considered system model is defined as joint relay selection and discrete power control. Our goal is to maximize network utility function which takes the sum rate and the power consumption into account. We propose a decentralized synchronous update algorithm to obtain the optimal solution rather than the high complicated exhaustive search algorithm. In our proposed algorithm, we design a new objective function which consists of the network utility function and the penalty functions. Our designed objective function can guarantee the feasibility of the solution without knowing the infeasible strategy profiles in advance under mild conditions. It is proved that our proposed algorithm can converge to the optimal solution in finite steps. Simulation results verify our theoretic analysis. © 2013 IEEE. Source


Tao Z.,Institute of Communications Engineering | Xiong-Wei Z.,PLA University of Science and Technology
Przeglad Elektrotechniczny | Year: 2011

Based on research of frame distortion estimation, an extraction priority assignment method is proposed for the MGS bit-stream. Firstly, extraction priority is derived from rate distortion optimization method. Then, frame distortion estimation is performed from estimation of coefficients dropping distortion and drift distortion. At last, depending on quality layer concept, extraction priorities are assigned efficiently. Experimental results show that the proposed method outperforms the priority assignment method and bit-stream extraction of H.264/SVC. Source


Zhu T.,Institute of Communications Engineering | Zhang X.-W.,PLA University of Science and Technology
Przeglad Elektrotechniczny | Year: 2011

This paper presents a rate control scheme for spatial scalability of H.264/SVC. At first, an adaptive method is proposed to decide the initial quantization parameter. Then, based on the transform coefficients distribution of spatial scalability, a new natural logarithm domain rate-distortion model is derived from the inspiration of the Cauchy-Density-Based model. Next, with above method and model, a rate control scheme is developed to match the characteristic of spatial scalability. The excellent performance of the proposed scheme is demonstrated by experimental results. Source


Zhang D.,Institute of Communications Engineering | Xu Y.,Shanghai JiaoTong University
IEEE Transactions on Vehicular Technology | Year: 2014

The average symbol-error-rate (SER) performances for the three-phase two-way relaying (TWR) protocols are analyzed and compared in Rayleigh fading channels, where the terminals and relay are interfered with by a finite number of cochannel interferers. The relay is assumed to operate in the decode-and-forward (DF) mode. Three TWR protocols where the terminals adopt different combining methods on the received signals from a relay link and a direct link are considered, and the tight approximate expressions of average SERs for these protocols are theoretically derived. Based on the analytic results, the SER performances of the three TWR protocols are compared in the interference-limited scenario. The results show that the TWR protocol where the terminals employ selection combining on the received signals from the relay and direct links can achieve good tradeoff between the average SER performance and computational complexity at the terminals. Moreover, we show that the three-phase TWR protocol outperforms the two-phase TWR protocol significantly in SER performance. © 1967-2012 IEEE. Source

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