Implementation of an effective video transmission scheme over ad hoc networks

Real-time video transmission over ad hoc networks faces many challenges including low bandwidth, long end-to-end delay, high packet loss rate, frequently changing topology and limited-powered mobile nodes. This paper presents an effective real-time video transmission scheme and improves implementation of DSR (Dynamic Source Routing) protocol. We set up a test-bed by using DSR routing in the IP layer, and an application transmitting video stream over UDP protocol. We get a continuous JPEG image stream from a ZC0301p web camera and split each image into small blocks according to the MCU (Minimum Coding Unit) borderline. The strong point of splitting JPEG image is that IP layer fragmentation can be avoided so we can determine which part of data in the frame gets lost to do loss recovery at the receiver. By using JPEG image stream, the video encoding complexity is reduced, which can save computing power of mobile nodes compared with MPEG and other Multiple Description Coding (MDC) methods. We also improve implementation of DSR to make it suitable to transfer real-time multimedia data. First different priorities are given to different traffic classes in DSR routing. Second the route maintenance scheme is modified to decrease overhead and link failure misjudgments. We carry out two experiments both indoors and outdoors using six mobile nodes. The first is to transmit continuous JPEG images using our former DSR implementation according to DSR draft. The second is that we split JPEG images into blocks and then transmit them using improved DSR implementation. Results show the latter gives better video stream fluency and higher image quality.