Timing Acquisition Research Of IR-UWB

The coming information era promotes communication toward two ways. One is bringing the bandwidth from narrowband to wideband. With the bandwidth increasing, the channel capacity is improved, which consequently increases the maximum data rate to satisfy the demands for higher speed, longer distance and better communication quality; The other is from analog to digital. The development of material technology, integrated circuit and digital signal processing technology pave the way for the communication technology to step forward to digital age. In particular, the emergence of software defined radio concept is able to provide a uniform platform for various wireless communication systems utilizing programmable hardware modules.The impulse radio-based ultra wideband technology (IR-UWB) has the potential to fulfill the development trends mentioned above. It adopts ultra-short pulses to transmit information with duration of the order of nanoseconds. The extremely short pulses occupy the bandwidth of the order of several GHz and have a huge capacity to serve for high data rate. Meanwhile, only simple digital implementation is required as IR-UWB directly transmits pulse in baseband, eliminating the needs of carrier modulation and RF power amplifier, and almost all modules can be implemented in digital devices except for an ultra wideband antenna. IR-UWB, on the other side, has some critical problems to be solved. In particular, the design of fast and efficient synchronization, or acquisition scheme becomes more challenging due to ultra-short pulse, extremely low power, and dense multi-path channels. Traditional synchronization techniques result in prohibitively long acquisition time and a suboptimum performance. How to design a suitable algorithm for efficient synchronization is a key research point. In this dissertation, three algorithms are gradually proposed in view of mean acquisition time, implementation complexity to give inspirations to these challenges mentioned above.A novel acquisition algorithm based on adaptive templates is firstly proposed in this dissertation using detection theory, which takes acquisition time, implementation complexity and channel characteristics into account. Firstly two adaptive templates are generated using multi-path characteristics, and correlate with the received signal. The correlation results are compared to proceed the next iteration: the search region decreases gradually after each iteration is executed. The search region decreases to a certain small cell rapidly after a few iterations. Finally traditional serial search algorithm is applied to acquire the timing parameter. Mean acquisition time is analyzed and compared to other algorithms; and the mean detection probability is deduced to evaluate the algorithm performance. Both mean acquisition time and detection probability are analyzed utilizing signal flow graph. The theoretical deduction and simulation results show the proposed algorithm greatly reduces the acquisition time and effectively improves the detection probability.In order to resolve the synchronization of IR-UWB in the waveform distortion environment, a data-aided PPM-UWB acquisition algorithm using estimation theory is afterward proposed. Firstly the cross correlation function of PPM is deduced, which is found to be relative to three factors. The difference value of the cross-correlation function is constructed according to relative table between cross correlation and information symbol, then a simple training pattern is designed to expedited the synchronization. To remove the noise impact, we propose two noise suppression methods. We also prove that the two acquisition algorithms are mean square sense consistent.Traditional digital implementation of IR-UWB receiver adopts analog-to-digital converter with high sampling frequency which leads to high receiver manufacturing cost. From this point of view, a low sampling frequency based acquisition algorithm is finally proposed in this dissertation using sampling theory. Firstly the classical shannon sample theorem and innovative sample theorem are compared and some physical interpretations are given, then the reconstruction error is evaluated. Secondly the innovative sample theorem is applied to IR-UWB to propose a practical digital synchronization and receiver design method. A novel symbol synchronization algorithm under low data rate IR-UWB communication environment is also proposed, which translates the joint channel and timing estimation problem into a harmonic retrieval problem and utilizes subspace method to acquire the timing parameters. This proposed algorithm has practical meanings under certain affordable BER condition.