Search

With the rapid growth of cloud computing services, there is an increasing need to expand applications across data centers. In these paradigms, common information exchange between two data centers can be assisted via one or more substrate nodes, which correspond to bidirectional relaying communication. In this paper, we investigate the performance of time division broadcast TDBC protocol in bidirectional cloud networks in the presence of channel estimation errors CEEs. The tight asymptotic expressions for individual and system outage probabilities are first presented in closed-form. It is shown that CEE causes outage probability to remain fixed even if the channel is noiseless. Then, the symbol error rate performance for TDBC protocol with M-ary Phase Shift Keying and M-ary quadrature amplitude modulation signals is analyzed. Simulation results validate the accuracy of our analytical results. Furthermore, comparison of signal-to-noise ratio gap ratio shows that TDBC protocol is less sensitive to the effect of CEE than analog network coding protocol. Copyright © 2014 John Wiley & Sons, Ltd.

In cognitive radio (CR) networks, unlicensed secondary users need to conduct spectrum sensing to gain access to a licensed spectrum band. And cooperation among CR users will solve the problems caused by multipath fading and shadowing. In this paper, we propose a multi-threshold method at local nodes to cope with noises of great uncertainty. Functions of distance between bodies of evidence are used at fusion centre to make synthetic judgment. To guarantee security which is an essential component for basic network functions, we will take selfish nodes into account which try to occupy channels exclusively. The proposed technique has shown better performance than conventional algorithms without increase the system overhead.

One of the critical middleware services for sensor networks is the time synchronization, which provides supports to different applications. Synchronization protocols used for Internet and LANs are not appropriate in the sensor networks for the high-density and limited energy resource. This paper describes two-hop time synchronization (TTS) that aims at reducing the synchronization overhead and providing more accurate network-wide synchronization. The synchronization message exchanges are minimized by making full use of sensors’ broadcast domain and enlarging the common node synchronization range in multi-hop scenarios. By halving synchronization hops, the TTS achieves high multi-hop synchronization precision. The proposed protocol contains single-hop synchronization model, multi-hop synchronization algorithm, and a power control scheme. We prove that the extension of single-hop TTS to network-wide synchronization is NP-complete. The complexity and convergence time of multi-hop TTS are analyzed in detail. We simulate TTS on MATLAB and show that it requires minimal overhead and convergence time compared with other protocols. We also implement TTS on common sensors and its multi-hop synchronization error is less than that of receiver-receiver synchronization (R-RS).

This paper presents a simple single-carrier (SC) distributed space-time block coded transmission scheme for asynchronous cooperative communications over frequency-selective channels. The cyclic prefix (CP) at the source node and relay nodes is used to combat inter-symbol interference from multi-path fading and the timing errors from the relay nodes. In this scheme, the relay nodes only implement very simple operations on their received signals to construct distributed space-time block code, and decoding, DFT and IDFT operations are only needed at the destination node. The low complexity SC zero-forcing frequency domain equalization (ZF-FDE) is applied at the destination node to recover the transmitted signals. The analysis and simulation results demonstrate that this simple SC scheme can achieve order-two spatial diversity gain for amplify-and-forward based cooperative communication over frequency-selective channels in the presence of asynchronization between relay nodes.

In this paper, we propose a novel cooperative transmission strategy with broadcasting and cellular communication in a hybrid network system. With the help of cellular base station (CBS), two cooperative schemes are analysed to improve hybrid network performance, which does not affect the original broadcasting signal. We investigate two cooperative schemes based on the different channel quality information (CQI) in this paper. For users whose CQI is less than the defined low threshold, e.g., the users near the edge of the broadcast cell, we deploy cooperative diversity transmission. Meanwhile, cooperative multiplexing transmission is exploited for users whose CQI is greater than the defined high threshold, such as those near the broadcasting base station (BBS). Furthermore, we propose a new quasi-orthogonal coding scheme with nested structure applying to the cooperative diversity scheme, which can be easily employed in two or three CBS cooperative scenarios. Our simulation results validate the effectivenes...