Cognitive networks: A new access scheme which introduces a Darwinian approach

In this paper we present a new approach for cognitive radio. In the usual approach the secondary network is in charge of monitoring the channel to determine whether or not the primary network is active in the area. If it is not, the secondary network is allowed to use the spectrum. In the new access scheme we propose, the primary network encompasses the techniques which allow it to capture the bandwidth even if the secondary network is transmitting in the area. The access scheme of the primary network preempts the secondary network activity. We present an access scheme which preempts the IEEE 802.11 decentralized scheme. This protocol is a generalized Carrier Sense Multiple Access scheme using active signaling. Instead of only sensing the carrier, this algorithm also transmits bursts of signal which may be sensed by the other nodes. If so, they give up the selection process. We show that this scheme preempts the IEEE 802.11 decentralized access scheme if the bursts transmitted by the node in the primary network are made up of special sequences which alternate between bursts of signal and periods of sensing. These sequences called (d, k) sequences [1] encompass a minimum number d and a maximum number of k successive zeros during which the node senses the channel to find other possible concurrent transmissions. In practice we use d = 0 and k depends on the duration of the IEEE 802.11 interframe space and the duration of a signaling burst. We compute the number of (0, k) sequences with respect to the length n of the sequence. We also show that (d, k) sequences (with 2d >; k) can be used if, by mistake, during the signaling phase one burst is not detected. We evaluate the number of such sequences.