Application And Study Of Key Techniques Of Embedded Wireless Multimedia Terminal

With the rapid development of the multimedia technology and high-speed wireless network technology, wireless-based multimedia communication which mainly carries services of video、audio and data has become the theme of the new age and has been concerned by more and more people. Wireless-based multimedia terminal equipment is an indispensable part of wireless-based multimedia communication system. Its demand for the miniaturization drives it to the direction of the development of embedded system inevitably. At the same time, because of its powerful function and broad application prospects, embedded wireless multimedia terminal will become a research hotspot and has great practical value and significance in nowadays as well as the coming decades.In this paper, the key technologies which includes Embedded technology, Audio Echo Cancellation technology and Multimedia Data Transmission techonology of embedded wireless multimedia terminal have been studied.And Multimedia Data Transmission techonology includes WiFi access, Audio and Video Synchronization, RTP / RTCP and Network Congestion Control. The chief task of this paper is that embedded wireless multimedia doorbell system has been designed and implemented and the key technologies have been applied in this system. The main contents and achievements can be concluded as below:1、The structure characteristics and device drivers, as well as process/multi-threaded application programming of embedded linux operating system are introduced.2、The structure of Audio Echo Canceller which includes an Adaptive Filter and a Double Talk Detecter(DTD) is studied. A Fast Iterative Adjust Normalized Least Mean Square (FIANLMS) method is applied for the adaptive filter algorithm and an audio echo path mismatch based method for double talk detection algorithm. Matlab simulation has been used for analyzing the effects of the audio echo canceller which includes the two algorithms. The simulation results demonstrate that the Echo Return Loss Enhance(ERLE) of FIANLMS achieves 17dB higher and the Misalignment of FIANLMS achieves 10dB lower than those of Normalized Least Mean Square(NLMS). The DTD algorithm detects very correctly in both Double Talk(DT) and echo-path change. The ERLE achieves 25dB higher using DTD than without using it when DT happens and the canceller converges all the same.3、Two types of Audio and Video Synchronization algorithms are studied and the timestamp synchronization algorithm will be applied in the terminal system. RTP/RTCP in case of unicast is introduced. And Adaptive Network Congestion Control algorithm based on RTP/RTCP is also studied. A novel Adaptive Congestion Control algorithm based on AIMD (Additive Increase/Multiplicative-Decrease), which mainly targeted to congestion happened when the network congestion has been recovering is proposed.4、Solution of embedded wireless video doorbell system is proposed. A CPU that is assembled Micro-Controller and Digital Signal Processor and Hardware-based Video Encode/Decode Module ([MC + DSP + VHM]) is used for the hardware solution and embedded linux operating system for the software solution. The software of indoor unit and outdoor unit of system are designed and implemented. The system software flow as well as the working principle are presented.5、Audio Echo Cancellation, WiFi module, Audio and Video Synchronization, RTP / RTCP protocol, and Adaptive Network Congestion Control are designed and implemented in the embedded wireless video doorbell system. The test results of this system as well as the effectiveness of these modules applied in the system show good by the Mean Objection Score (MOS) evaluation method.