| In recent years, driven by emerging technologies, Ultra Wideband (UWB) techniques have become hot research subjects, especially following the approval of the UWB technology by the FCC (Federal Communications Commission) in February 2002. And it also results in an increasing research in UWB applications. UWB impulse radio technique makes full use of ultra-short duration pulses, which yields ultra-wideband signals characterized by extremely wide frequency band and extremely low power spectral densities. UWB has many benefits, including high data rate, low transmit power, low probability of intercept, exceptional multipath immunity, low interference and accurate position localization (UWB allows up to a few centimeters ranging accuracy ranging).Whether in the military field or in the civilian field, its application is becoming wider and wider. If we accomplish wireless localization using UWB on cargo tracking, patients monitoring or searching and rescuing of urgent accident locale, we can get twice the result with half the effort.Influenced by the multipath and NLOS (Non-Line of Sight), the traditional positioning technologies such as GPS (Global Positioning System) and positioning in the mobile communication system have low positioning precision in the indoor environment. But the UWB transmission technologies have many advantages, it makes a figure among many categories of wireless location technology. Therefore, ranging and positioning based on UWB have immense advantages over these conventional methods.In this thesis, after introducing the basic principles of UWB systems, we mainly finish three tasks just described as follows:Firstly, based on the integrative analysis of former papers, the main ranging and positioning technologies used in UWB wireless communications are concluded . Respective advantages and disadvantages are listed. The RSS method's position accuracy is depended on the channel parameters and the distance between the two nodes. Therefore, it doesn't fully exploite the unique characteristic of a UWB signal, namely the very large bandwidth. An AOA-based positioning technique uses antenna arrays, which increases the system cost. The TOA method can be improved by increasing the SNR or the effective signal bandwidth.Secondly, we choose TOA as research object. Though the ranging method by using the signal cross-correlation can get much high accuracy, it needs very high sampling rates. It increases the complexity and difficulty of systems. So, energy detection (ED) based ranging becomes a feasible alternative because of its simplicity and lower sampling rates.A new two-step energy detection ranging algorithm based on simple adaptive threshold is proposed. In the proposed method, the first step is to obtain the rough TOA and the second is to improve the ranging accuracy by using energy detection based on adaptive threshold again for the rough TOA. Adaptive threshold is near to the optimal threshold in different SNR. And it is difficulty to estimate the SNR.Theoretics and simulation results shows that it can improve the ranging accuracy.The last part mainly introduces two typical localization algorithms of UWB.One is the recursive Taylor series, the other one is non-recursive Chan method. Though Taylor series has large computing capacity, it is suitable for all kinds of channels and can get high positioning accuracy. Chan method is simple to compute. But once there dose not exist line of sight, the positioning accuracy is low. So, a cooperative location method based on Chan and Taylor algorithms is proposed. We choose CM3 sub-channels of non-standward IEEE802.15.3a as the dense multipath channel simulation model. And the results show that the cooperative location method can significantly improve the location accuracy under non-line of sight. |
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