With the explosive growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast etc. have been considered. In this paper, we propose a technique for distributed multimedia transmission over the secondary user network, which makes use of opportunistic spectrum access with the help of cognitive radios. We use digital fountain codes to distribute the multimedia content over unused spectrum and also to compensate for the loss incurred due to primary user interference. Primary user traffic is modelled as a Poisson process. We develop the techniques to select appropriate channels and study the trade-offs between link reliability, spectral efficiency and coding overhead. Simulation results are presented for the secondary spectrum access model.

With the advent of cognitive radios, secondary usage of spectrum on opportunistic basis, in the licensed band, is becoming practical. In this type of opportunistic spectrum access, secondary users may loose access due to the sudden arrival of a primary user who owns the spectrum. In order to ensure the link reliability and to compensate for the loss, some spectrally efficient mechanisms are required. In this paper we consider the spectrum pooling model for secondary spectrum access for delay-constrained applications. Along with this we study the application of Luby Transform (LT) codes to compensate the secondary user for the loss incurred due to primary user interference. We study the trade-offs between spectral efficiency, link reliability and overhead due to LT coding. Primary user traffic model is used to parametrize the trade- offs. Simulation results are presented for the secondary spectrum access model.