Research On Transmission Technology Of Emergency Multimedia Communication In A Wireless Network

With the improvement of living standards, people’s sense of security is alsoincreasing, and the multimedia emergency communications in wireless network has madea significant contribution to protecting and enhancing the quality of life. However, sincethe multimedia emergency communications requires high real-time, continuity and acertain degree of reliability, it puts a high demand on transmission performance ofwireless network and data processing ability of communication terminal. According tothe characteristics of3G network and requirements of multimedia emergencycommunications, the thesis makes some researches from two aspects of the transmissionprotocol and the communication terminal system.Aiming at the characteristics of video data transmission in3G network, this thesisprovides a hybrid TCP/UDP protocol and the corresponding golden section congestioncontrol mechanism. The hybrid TCP/UDP protocol makes use of the respectiveadvantages of TCP and UDP protocol, with the UDP protocol to transmit data and theTCP protocol to transmit control information, so that it has both the transmission speedand a certain degree of transmission reliability. According to the characteristics of videodata, it sets a TTL(time to live) for each packet which has been sent out, and no longertransmits or retransmits the data packets that beyond the TTL in the hybrid TCP/UDPprotocol; but for the I-frames, P-frames and B-frames in these data packets, it sets updifferent reliability levels, and these packets won’t be acknowledged if they are receivedcorrectly, they require retransmission only when I-frame is lost or the packet loss rate ofP-frame and B-frame exceeds a certain limit. Aiming at the defects of TCP congestioncontrol, the golden section congestion control mechanism cancels the slow-start threshold,resets the slow-start initial value, uses the golden section point to segment the data speedand implements these different acceleration and deceleration operations according to thesegments. The fast retransmission mechanism of golden section congestion control startsthe corresponding deceleration operation at the first received requests for retransmissioncontrol information packet, to make the network state more quickly and smoothly; thefast recovery mechanism uses golden section point to segment and renew the reasonabletransmission speed according to segment, to make itself adapt to the real-time changes of3G network. The experimental results show that, compared with the TCP protocol, it takes less transmission time and gains more stable transmission to use the hybridTCP/UDP protocol and golden section congestion control mechanism to transmit videodata, without losing the I-frame data.The multimedia data processing has a greatly improved demand for computingability of embedded terminal, with the proposal of the latest video compression standardH.264. In order to ensure the transmission of multimedia data without the effect ofreal-time video codec processing, this thesis introduce a dual-core embedded processingsystem based on ARM9(S3C2440) and DSP(Blackfin533), which is connected throughSPI interface. In this system, the ARM-side works in the master mode and is responsiblefor boot loader DSP-side and the transmission of multimedia data while the DSP-side isresponsible for the real-time video data codec processing. And they control the datatransmission by clock signal and enable signal. In this thesis, it designs the systemconnection mode and the device and put them in actual application.By studying these above two aspects, it improves the overall performance ofreal-time multimedia emergency communication in wireless network.