Cognitive Radio and multimedia communications

Multimedia applications have grown greatly following the increase of smartphones and the proliferation of new services hugely demanding in terms of quality of service (QoS) and bandwidth. This recent trend has lead to increasing demands for spectrum and bandwidth and thus a pressing need for new paradigms to overcome the scarcity of spectrum resources. The cognitive radio (CR) has emerged as new solution which aims to increase the spectral efficiency by leveraging the spectrum holes [1].

Most of recent communication systems have integrated the use of multimedia contents for sake of interactivity, portability and information exchange flexibility. CR networks have a great potential to become a promising foundation for reliable and safe multimedia transmissions under lossy and delay constrained conditions. 

Multimedia packets are conveyed on the idle sub-channels as long as the licensed users are far away from the unlicensed network. The secondary transmission has to dynamically adapt to the changing conditions of CR contexts. Moreover, the dynamics of the CR network due to its complex topology further complicates the study of such communication systems [2].

Explicitly, cognitive radio contexts are distinguished by the multitude of factors leading to packet loss issues. This is a critical point for the multimedia transmission which is among the most affected by the problem of packet erasures due to its stringent QoS constraints and delay requirements. In particular, during the sensing phase the fact that there exists a failure in detecting the presence of a primary activity constitutes a missed detection because the sub-channel will be sensed as being idle. The primary transmission could be disrupted accordingly. After the beginning of transmitting the secondary packets, once the primary user captures its own sub-channel, the secondary transmission may encounter a short period of interference before switching to another vacant sub-channel; so that some packets will be corrupted and delay generated from spectrum hand-off activities may cause some packets miss the deadline. Besides, the operation of heterogeneous primary and secondary devices simultaneously in the same frequency band is source of collisions which may impede the success of secondary transmissions. Apart from that, a frequency channel is also a propagation media, where usually a communication signal may be attenuated because of fading.

Obviously, characterizing reliability in CR networks [3] is one of the major bottlenecks in the performance evaluation of multimedia traffic transmissions in unlicensed usage situations. For future research, this is a challenging direction that opened up new horizons for this research area.

BIBLIOGRAPHY

[1] H. Kushwaha, Y. Xing, R. Chandramouli, and H. Heffes, "Reliable multimedia transmission over cognitive radio networks using fountain codes," Proceeding of IEEE, vol. 96, pp. 155-165, January 2008.

[2] A. Chaoub, E. Ibn Elhaj, and J. El Abbadi, "Multimedia traffic transmission over TDMA shared cognitive radio networks with poissonian primary traffic," in Proceedings of the International Conference on Multimedia Computing and Systems. IEEE, April 2011, pp. 378-383.

[3] A.S. Kamil and I. Khider, "Open research issues in cognitive radio," in Proceedings of the 16th Telecommunications forum TELFOR, November 2008, pp. 25-27.