**6. Conclusion**

36 Ultra Wideband – Current Status and Future Trends

**Figure 23.** DLL transient performance (symbol number vs. natural frequency)

**Figure 24.** BER for the proposed DLL (� � ��� �(�) � �������)

In this chapter, we use TDT algorithms for carrying out low-complexity high-performance timing synchronization, which constitutes a major challenge in realizing the UWB communications. TDT technique is based on correlating the received signal with "dirty template" extracted from the received waveforms. This template is called dirty; because it is distorted by the unknown channel and by the ambient noise. TDT allows enhancing received energy capture and reducing receiver structure complexity. The described technique can be applied to UWB systems even in the presence of time hopping TH codes, Inter-Frame Interference (IFI) and rich multipath environment, where Inter-Symbol Interference (ISI) is absent.

TDT synchronization system consists of three main blocks: signal detection, timing acquisition and tracking. Each block of them is explained in a separated section of this chapter. In signal detection section: the dirty template detector is derived by applying the Neyman-Pearson theory. Then, Monte Carlo simulations are performed to find the probabilities of false alarm (���) and detection (��). The results of simulation analysis show that the detection performance of the dirty template approach is improved by increasing the signal-to-noise ratio (SNR) or data-aided (DA) number. After detecting the UWB signal, the symbol-level timing offset estimation relies on searching the best statistics �.

Next section presents the timing acquisition in both DA and NDA modes. Then, we improve the timing estimator by adding a suitable window filter to the structure of the crosscorrelation. Both the theoretical analysis and Matlab simulation results show the performance of the proposed TDT estimator, and confirm that DA mode has the high performance and fast timing, compared to NDA mode, but that is at the price of bandwidth efficiency.

Timing Synchronisation for IR-UWB Communication Systems 39

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In tracking section, we demonstrate tracking system design taking into consideration the relative motion between Transmitter and receiver. We combine DLL with TDT, which enables to enhance the received energy capture and to improve tracking performance. Simulation results illustrated that increasing natural frequency parameter ߱ helps to reduce transient error effect, but in the price of noise handling ability.
