Overcoming the Antennas-Per-Node Throughput Limit in MIMO LANs
Today, the number of concurrent packets in a MIMO LAN is limited by the number of antennas on the AP. This paper shows how to overcome this limit. It presents a new design where multiple client-AP pairs can communicate concurrently, on the same 802.11 channel. We demonstrate both analytically and experimentally that our design almost doubles the throughput of a MIMO LAN. The key idea underlying our approach is Interference Alignment and Cancellation (IAC), a novel technique for decoding concurrent sender-receiver pairs in MIMO LANs. It exploits two basic properties of MIMO LANs. First, MIMO transmitters can control the alignment of their signals at a receiver. Second, APs are typically connected to a backend Ethernet, which they can use for coordination. Hence, in IAC, transmitters align their signals such that the first AP can decode at least one of the concurrent packets. Once a packet is decoded, it is sent over the Ethernet to the second AP, which subtracts it from its received signal to decode a second packet, which it sends to the third AP to decode the next packet, and so on. We implement our technique in 2x2 MIMO GNU Radios, and demonstrate via wireless experiments that IAC increases the average throughput of a MIMO LAN by 1.5x on the downlink and 2x on the uplink.