A channel allocation mechanism for cognitive radios (CRs) is proposed to enable maximum throughput and minimum forced termination probability for CR users (CUs) that are not capable of spectrum handover (SH). SH is an optimal collision-avoidance scheme used by CUs to evacuate from time-slots that will be used by primary users (PUs) based on time-slot assignment (TA) information obtained in advance. The proposed scheme has extensive applicability for CR-networks where SH is not possible owing to PU TA information not being obtainable in advance, which is very common. For CR-networks without SH capability, the proposed scheme enables remarkable throughput performance, equivalent to the level of when SH is used.Introduction: Owing to the rapidly increasing popularity of mobile devices, techniques that can maximise wireless channel utilisation are needed. In this Letter, an optimal cognitive radio (CR) channel allocation scheme is proposed. The objective of the proposed scheme is to minimise forced termination probability (P F ) and maximise throughput (r) of CR users (CUs). The channel is assumed to be time division multiple access (TDMA) based where primary users (PUs) have priority to access the M time-slots of the TDMA frame. The CUs can access the empty time-slots of the PUs, where each time-slot that a PU can use is divided into N CU sub-time-slots. Therefore, assuming that no PUs are using the TDMA frame, a total of NM time-slots can be used by CUs. When a PU accesses a time-slot, it will pre-empt the CUs that have been using that time-slot, which results in forced termination of CUs. When channel utilisation of the PUs is high, there will be very few vacant time-slots for CUs to access and therefore forced termination of CUs will occur unavoidably. Fig. 1 illustrates the PU and CU timeslots of a TDMA frame.

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