A Survey of Communication Systems and Modulation Schemes for Spectrum Sensing by Cognitive Radio

The growth of wireless applications and spectral limitations are grave anxiety for the military service and for civilian communities. A particular spectrum task force set up by Federal Communications Commission discloses that in many bands spectrum access is a more important problem than physical scarcity of the spectrum. This is in part because present systems use a procedure draw up in the1920s where different frequency bands are allocated to users or service providers, and licenses are needed to operate with those bands. To avail unused spectrum more efficiently in dynamic environments, we desire a communication system that adapts to rapidly changing environmental conditions while ensuring that minimal or at least manageable interference is introduced to existing users. Such a technology is known as cognitive radio (CR) technology. Transform domain communication system (TDCS) and wavelet domain communication system (WDCS) have been reported to have interference avoiding capability under hostile environmental conditions. Conventionally, the Pseudo Random phase vectors in TDCS and WDCS were generated by a maximum length binary Pseudo Random sequence, which allows only a relatively small amount of users in the systems. This paper reports a method of Digital modulations schemes (FSK, PSK, CSK) and communications systems (TDCS,WDCS) for efficient utilization of the spectrum in Cognitive radio.