Differentiating channel access probability based on only traffic priority can ensure QoS statistically in enhanced distributed channel access (EDCA) of IEEE 802.11e. However, it may seriously affect the overall performance in presence of degraded channel condition among distant stations. In this paper, we propose a novel channel access scheme which exploits the benefit of cooperative communication in order to mitigate the adverse effect of bad channel condition while maintaining deterministically prioritized channel access for high priority traffic. Unlike EDCA, in our proposed scheme whenever a station with degraded channel condition wins the channel contention, our scheme searches for a prospective helper node to assist the sender in transmission. Eventually by exchanging sequence of busy tones and a special frame, it selects an optimal helper which has data with equal or higher priority as well as supports significantly higher data rate for cooperative transmission. Simulation results demonstrate that our proposed protocol enhances the QoS of the network while improving the overall performance of EDCA.