In last decades, the demand of wireless spectrum has

increased rapidly with the development of mobile communication

services. Recent studies recognize that traditional fi xed spectrum

assignment does not use spectrum effi ciently. Such a wasting

phenomenon could be amended after the present of cognitive

radio. Cognitive radio is a new type of technology that enables

secondary usage to unlicensed user. This paper presents an

Opportunistic Cognitive MAC Protocol (OC-MAC) for cognitive

radios to access unoccupied resource opportunistically and coex-

ist with wireless local area network (WLAN). By a primary traffi c

predication model and transmission etiquette, OC-MAC avoids

producing fatal damage to licensed users. Then a ns2 simulation

model is developed to evaluate its performance in scenarios with

coexisting WLAN and cognitive network.-In last decades, the demand of wireless spectrum has

increased rapidly with the development of mobile communication

services. Recent studies recognize that traditional fi xed spectrum

assignment　does　not　use　spectrum　effi ciently.　Such　a　wasting

phenomenon　could　be　amended　after　the　present　of　cognitive

radio. Cognitive radio is a new type of technology that enables

secondary　usage　to　unlicensed　user.　This　paper　presents　an

Opportunistic　Cognitive　MAC　Protocol　(OC-MAC)　for　cognitive

radios to access unoccupied resource opportunistically and coex-

ist with wireless local area network (WLAN). By a primary traffi c

predication　model　and　transmission　etiquette,　OC-MAC　avoids

producing fatal damage to licensed users. Then a ns2 simulation

model is developed to evaluate its performance in scenarios with

coexisting WLAN and cognitive network.