Abstract: The cognitive radios those are energy efficient which are operating in the television systems that means in the television white spaces where the vacant frequencies available compares with the other cognitive radio devices because of the interference constraint which is for whole frequency band rather than per signal carrier. In this paper we considered the Ratefair channel assignment protocol which is explained in the energy efficient frequency and power allocation for cognitive radios in television systems, taken from IEEE systems journal. In this protocol the users are allocated with the sub channels which are energy efficient based on their transmission rates. Users are arranged in the descending order based on the transmission rates. The user with higher transmission rate is assigned with the sub channel on which the user obtains a larger gain. But at the same time lower transmission rate user may also get larger gain on the same sub channel which is already allocated to the higher transmission rate. Because of the low transmission rate the user cannot acquire the sub channel on which the gain is large. Low transmission rate is may be due to larger separation distance between the cognitive base station or may be because of the more interference by the secondary users. In this paper we use two algorithms, one is recursive algorithm which is used to find the shortest distance and also the most reliable path by calculating the packet loss rate and another algorithm is Dynamic threshold algorithm which is used to reduce the interference of the secondary users. As a result transmission rate of users increases , delay decreases, data will be transmitted more reliably. Simulations are compared with the existing protocol and showed that the proposed method increases the transmission rate and decreases the delay in transmission and the channels are allocated which are more Energy Efficient than the existing.
Keywords: cognitive radio, channel assignment, TV white spaces, energy efficiency.