Multiple Input Multiple Output (MIMO) offers significant advantages in terms of rate and reliability. We consider sharing the MIMO increased rate in Wireless Mesh Networks (WMNs) links. Such sharing allows nodes in a WMN to concurrently meet more demanding communication requirements such as high data rates, increased transmission range, power savings and low dropping rates. In this paper, we propose the Rate Splitting MIMO-based Mac Protocol (RSMP) which is a distributed Mac protocol where pairs of nodes can locally cooperate with other nodes in their vicinities to reserve the required rate through effective selection on transmit antennas. Nodes can then use any preferable MIMO coding technique that best suit their communication requirements. RSMP is evaluated using OPNET interfaced with Matlab. OPNET is used to model the details of the Mac protocol while Matlab is used to compute the MIMO channel capacity and interference. Simulation results are obtained and compared to those of 802.11n MIMO-based DCF MAC protocol. We show that our proposed RSMP scheme outperforms MIMO DCF MAC in medium access delay and throughput. We also show that nodes can always attain their requested rate and that RSMP can be applied to satisfy multiple QoS requirements.