Study On General Demodulation Testing Algorithms For Wide-band Multi-standards Wireless Communication Signals

Nowadays, the digital modulation modes, coding schemes and transmission protocols of wideband wireless communication become more and more sophisticated to achieve high-speed, reliable mobile multimedia transmission; At the same time, with the extensive application of spread spectrum communication technology, the signal transmission bandwidth becomes increasingly wide, and the transmission power is also further reduced to improve security and the performance of anti-interference. The wireless communication signal, which is characterized by its wide band, high symbol rate, abruptness and transient, is consequently difficult to be tested and analyzed. Therefore, it is a great challenge to implement panoramic observation and real-time analysis for wide-band wireless communication signal in multi-domain.Considering the existing wideband wireless communication testing problems, based on digital communication principle and software radio technology, this dissertation devotes to the real-time multi-domain analysis theory of wide-band wireless communications. Some key technologies are thoroughly studied and critical algorithms researched in depth. The main contribution and corresponding achievements of the dissertation are as follows:1. Based on the three-step processing procedure of"trigger-capture-analysis", an innovative real-time multi-domain signal analysis architecture for wide-band wireless communications is proposed. A novel digital detector is introduced into this architecture. With this universal open architecture, full analysis band, user defined real-time multi-domain analysis and high-precision dynamic parameters measurement can be realized at fast speed by reloading different processing algorithms into hardware on-line.2. A novel joint real-time multi-domain capture algorithm is presented based on some existing real-time trigger algorithms and the forgoing signal analysis architecture. Differing with the original real-time trigger algorithms which detect the signal's characteristics variation in a single analysis domain independently, the new capture algorithm, which is combined with cyclic variable delay storage mechanism, detects and identifies the signal's characteristics variation along with time in multi-domain simultaneously. The drawbacks of the original real-time trigger algorithms, such as error trigger and missing trigger, are improved. Finally, the accuracy and efficiency of the proposed algorithms are proved by the experimental results.3. For real-time multi-domain analysis of wide-band wireless communications, a novel general-purpose joint demodulation scheme oriented to measurement is put forward, and the signal processing mechanism and corresponding algorithms are studied. This joint demodulation scheme consists of 2 portions, the demodulation preprocessing portion and the specified demodulation processing portion. At the preprocessing stage, the large carrier frequency offset pre-amendment, the equivalent sample rate adjustment and the constant compensation for signal processing channel are firstly executed within the RTBW; and then the signal is accurately demodulated by utilizing the appropriate algorithm and processing flow which match the signal's modulation mode at the specified demodulation processing stage. Compared to the fixed demodulation algorithms adopted by usual receivers, the general joint demodulation scheme is more flexible and applicable.4. A novel blind carrier frequency offset estimation algorithm on the basis of Discrete Fourier Transform (DFT) is presented and theoretically deduced. The proposed algorithm utilizes the results of real-time spectrum analysis to estimate and compensate the large carrier frequency offset within RTBW. The frequency offset estimation error and random jitter are effectively suppressed by introducing spectrum moving average and track-hold processing into this new algorithm. Compared to the current algorithms, the presented algorithm can counteract the large carrier frequency offset within RTBW very quickly without any prior information, avoiding the losing lock of subsequent carrier synchronization loop, and improve the performance of the whole carrier carrier synchronization in the demodulation analysis. Moreover, the system costs are significantly reduced owing to the sharing of FFT (Fast Fourier Transform) engine by both the proposed algorithm and the real-time spectrum analysis.5. Presents a novel arbitrary ratio resampling algorithm based on polyphase filtering to tune the equivalent sampling rate of input measured signal to integer multiple of the symbol rate. The polyphase filter is generated by sectional fitting the impulse function of prototype filter with low-order polynomials in accordance with equivalent sampling rate to symbol rate ratio, combined with resample control mechanism in Gardner timing synchronization algorithm, and implemented via Farrow filter structure. The experimental results show that the out-of-band spectrum suppression of proposed algorithm is better than what the conventional Lagrange interpolator does.6. Aiming at efficient real-time multi-domain analysis of M-QAM and M-PSK communication signal, a specified joint demodulation algorithm is presented. The preprocessed signal is successively processed by the improved Gardner timing synchronization algorithm, the reformed duel-mode carrier recovery algorithm and the dual-mode blind adaptive equalization algorithm to achieve exact demodulation. All the proposed algorithms are theoretically derived and testified their validity by simulation.7. For real-time multi-domain analysis of OQPSK communication signal, the preprocessed signal is now processed in turn by the quadricorrelator and the feed-forward phase-timing joint estimation algorithm based on ML (Maximum Likelihood estimation) approach to realize accurate demodulation at fast speed. All the proposed algorithms are theoretically derived and verified by simulation too. In comparison with the current OQPSK demodulation algorithms, the carrier phase offset and timing error are extracted concurrently, eliminating the synchronous property degradation which is due to carrier phase error.Based on the proposed real-time multi-domain signal analysis architecture and all above algorithms, a real-time multi-domain analysis system for high-order QAM signal is constructed. A 256QAM communication signal is experimentally applied to the system, and then analyzed and test. The results have proved the flexibility, feasibility and high efficiency of the proposed architecture and algorithms.