Adaptive subcarrier bandwidth and power in OFDM‐based cognitive radio systems for high mobility applications

OFDM‐based cognitive radio systems are spectrally flexible and efficient, but they are vulnerable to intercarrier interference (ICI), especially in high mobility environments. High mobility of the terminal causes large Doppler frequency spread resulting in serious ICI. Such ICI severely degrades the system performance, which is ignored in the existing resource allocation of OFDM‐based cognitive radio systems. In this paper, an adaptive subcarrier bandwidth along with power allocation problem in OFDM‐based cognitive radio systems for high mobility applications is investigated. This adaptive subcarrier bandwidth method should choose the suitable subcarrier bandwidth not only to balance the tradeoff between ICI and intersymbol interference but also to be large enough to tolerate an amount of Doppler frequency spread but less than the coherence bandwidth. The power budget and interference to primary users caused by cognitive radio users are imposed for primary users' protection. With these constraints, a joint optimization algorithm of subcarrier bandwidth and power allocation is proposed to maximize the bandwidth efficiency of OFDM‐based cognitive radio systems in such conditions. Numerical simulation results show that the proposed algorithm could maximize the system bandwidth efficiency and balance this tradeoff while satisfying the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

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WiMAX系统基于CID的压缩机制研究

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Crostalk in WDM SCM Systems due to SRS

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Performance of an OFDM Based Downlink Multiple Access System for Indoor Wireless Communications

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OVPN软管模型的分层路由及时延优化算法研究

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CORD: Optical packet-switched network testbed

We are implementing and investigating CORD, a 2.5 Gbit/s/λ WDM packet-switched network testbed. CORD features: (i) contention resolution optics (CRO), which consist of optical switches and delay lines to perform all-optical packet contention resolution; (ii) multichannel subcarrier multiplexed (MSCM) signaling to transmit an 80 Mbit/s control channel and 2.5 Gbit/s payload data on the same wavelength; (iii) networkwide distributed slot synchronization technique with maximum slot jitter of ± 6.5 ns; (iv) novel ultrafast signaling synchronization using delay-line phase alignment for data recovery within 4 bits; and (v) pilot-tone payload data synchronization for clock recovery within 16 ns.

In this article, we describe the CORD network testbed and discuss the performance and scaling potential of the technologies developed for CORD.     

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