無線傳感器網(wǎng)絡(luò)的測(cè)距技術(shù)外文翻譯-其他專業(yè)(編輯修改稿)
2025-02-24 12:14 本頁面
【文章內(nèi)容簡介】 ristics of the DP blockage. It is possible to categorize the error based on the following ranging states [24] . In the presence of the DP, both () and () are met and the distance estimate is very accurate, yielding DP D P D Pd d z?? ? ?, （ ） where the random bias induced by the multipath, pdb is the bias corresponding to the propagation delay caused by NLOS conditions, and z is a zero mean additive measurement noise. It has been shown that mb is indeed a function of the bandwidth and the signal to noise ratio (SNR) [14] , while bpd is dependant on the medium of the the node experiences sudden blockage of the DP, Eq. () is not met and the DP is shadowed by some obstacle, burying its power under the dynamic range of the receiver. In this situation, the ranging estimate experiences a larger error pared to Eq. () . Emphasizing that ranging is achieved through the NDP ponent, the estimate is then given by ND P D P ND Pd d z?? ? ?, （ ） ND P m pd Bb b b? ? ? ?, （ ） where Bb is a deterministic additive bias representing the nature of the blockage. Unlike the multipath biases, but similar to the biases induced by the propagation delay, the dependence of Bb on the system bandwidth and SNR has its own limitations as reported in Ref. [14] . Formally, these ranging states can be defi ned as ? ?1 DPdd? ?? , （ ） ? ?2 DPdd? ?? , （ ） Figures and provide sample channel profiles of these two ranging situations [24] . The performance of TOA based ranging can be determined by the CramerRao lower bound (CRLB), which has been studied extensively for existing systems. The variance of TOA estimation 2TOA? is bounded by the CRLB [25] 22220 2181 12T O A wTwf f???? ???????, （ ） where T is the signal observation time, ? is the SNR, 0f is the frequency of operation, and w is the system bandwidth. In practice, TOA can be obtained by measuring the arrival time of a wideband narrow pulse, which can be obtained either by using spread spectrum technology or directly. Direct Spread Spectrum. One TOA estimation technique based on the direct spread spectrum (DSS) wideband signal has been used in GPS and other ranging systems for many years. In such a system, a signal coded by a known pseudorandom (PN) sequence is transmitted and a receiver cross correlates the received signal with a locally generated PN sequence using a sliding correlator or a matched filter. The distance between the transmitter and the receiver is determined from the arrival time of the first correlation peak. Because of the processing gain of the correlation at the receiver, DSS ranging systems perform much better than peting systems in suppressing interference from other radio systems operating in the same frequency band. In these band limited systems, super resolution techniques for TOA estimation have been applied successfully. Results have shown that these high resolution algorithms can provide improved accuracy [25] . Ultra Wideband Ranging. A promising alternative to DSS systems is ultra wideband (UWB) ranging [26] . According to Eq. () , it is clear that in multipath propagation environments, the performance of TOA estimation is inversely related to the system bandwidth. Increasin
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