Rateless codes for cognitive radio in a virtual unlicensed spectrum

In this paper we investigate the use of rateless codes by secondary users equipped with cognitive radio in a virtual unlicensed spectrum. Assuming a Poisson model for the arrival of primary users, we analyze the goodput and the throughput of secondary users. Rateless codes are used for transmitting the secondary data through parallel subchannels available in a spectrum. They can compensate for the packet loss in secondary transmission due to appearance of primary users. We calculate the overall frame error probability at the secondary receiver and use it for calculating the throughput and goodput. Numerical results indicate that LT codes as a class of rateless codes provide reliable transmissions with high throughput and small redundancy. Except for very small Poisson arrival rates, the throughput is much higher than the case without erasure coding. Therefore, in real-time multimedia transmission that retransmitting lost information packets is not possible, the use of rateless codes is very beneficial.