Designing medium access control protocols for multiple-input-multiple-output wireless networks

CarrierSenseMultipleAccesswithCollisionAvoidance(CSMA/CA)andtherequestto-send(RTS)/clear-to-send(CTS)controlpacketexchangemechanismbasedmedium access control (MAC) protocols, such as the IEEE 802.11 MAC protocol, are extremely successful in single-hop environments. Unfortunately, in multi-hop environments, they suffer from unfair access to the channel due to a side effect of carrier sense and do not perfectly address the hidden node problem and thus degrade network performance. Fortunately, Multiple-Input-Multiple-Output (MIMO) technologies, which employ multiple antennas on both the transmitter and the receiver, provide capabilities to mitigate interference from neighboring nodes, to mitigate fading, and to increase the capacity of a link. We claim that designing MAC protocols jointly with flexible MIMO physical layer technologies can address the problems of conventional MACs and higher layer protocols for multi-hop wireless networks. To show this, we first propose a MAC protocol, Mitigating Interference using Multiple Antennas MAC (MIMA-MAC), which mitigates interference from neighboring nodes by using MIMO in its spatial multiplexing mode. We show that the MIMA-MAC can address the problems caused by neighboring interference and can also increase the utilization of network resources. We further enhance the MIMAMAC and propose the Mitigating Interference using Multiple Antennas with Antenna Selection diversity MAC (MIMA/AS-MAC), which fully utilizes multiple antennas by employing antenna selection diversity together with spatial multiplexing to mitigate fading as well as to suppress interference from neighboring nodes. For a multi-hop network, we show that the MIMA-MAC can improve TCP performance by mitigating neighboring interference. We further enhance the MIMA/AS-MAC and propose the TCP enhanced MIMA/AS-MAC, which increases the efficiency of small packet transmission. Finally, we explore ways of designing cross-layer MAC protocols that can address the problems of a system using reactive ad hoc routing protocols by controlling transmission modes based on the type of packets and channel conditions.