In this paper we consider an overlay cognitive network in which to guarantee a Quality of Service (QoS) for the primary users, a maximum probability of collision is enforced to secondary service. When collision, caused by imperfect spectrum sensing, happens, it results in increasing error rate in both primary and secondary systems. While such degradation in primary service conforms with QoS requirements of that service, this may not be acceptable from secondary user perspective. Such degradation can be dealt with in secondary service either by employing channel coding techniques at the expense of effective rate reduction or increasing the sensing time to reduce the collision probability. This results in the reduction of the data transmission time which also results in the reduction of effective data rate for secondary users. In this paper, we compare these two cases and show that using rate-compatible Low-Density Parity-Check codes, the effective data rate for the coded case can be significantly more than that of the case without channel coding while exhibiting a considerably better performance.