Random access heterogeneous MIMO networks

Abstract

This paper presents the design and implementation of 802.11n+ , a fully distributed random access protocol for MIMO networks. 802.11n+ allows nodes that differ in the number of antennas to contend not just for time, but also for the degrees of freedom provided by multiple antennas. We show that even when the medium is already occupied by some nodes, nodes with more antennas can transmit concurrently without harming the ongoing transmissions. Furthermore, such nodes can contend for the medium in a fully distributed way. Our testbed evaluation shows that even for a small network with three competing node pairs, the resulting system about doubles the average network throughput. It also maintains the random access nature of today's 802.11n networks.

Concurrent channel access and estimation for scalable multiuser MIMO networking

“…A full design of concurrent RTS however is beyond the scope of this paper and left as future work. (b) Frequency and time synchronization: MIMO/CON does not have more stringent requirement on frequency and time synchronization over existing MU-MIMO systems such as the system described in [15]. Synchronization techniques in previous literature [21][15] can be employed in MIMO/CON.…”

“…MIMO/CON is closely related to and built on prior work on practical MU-MIMO systems [22] [15]. For backward compatibility reasons, we share the same goal of realizing MU-MIMO throughput gains with widely used WiFi-like CSMA.…”

“…Existing MU-MIMO systems (e.g., [22], [15]) stagger data transmissions in order to allow random access yet avoid preamble collisions which could impede CSI estimation. Staggered transissions, however, result in efficiency loss that increases with the number of senders.…”

“…A noisy preamble under such interference prohibits accurate CSI estimation and results in poor MIMO performance. Prior work [22] [15] resolves this issue by ensuring that preambles from different senders are not overlapped in time. The AP can then estimate the CSI vectors by sequentially projecting the received signal onto interference-free subspaces.…”

Grouping Based Proportional Fair User Schedule Algorithm in MU-CoMP

“…On the other hand, by using user pairing scheme, only two users are dispatched in the same schedule slot, thus the system resources are not made full use. It has been proved in [4] that the multiplexing of the same time frequency resource block by multiple users will significantly increase the system performance, when the count of transmitting antennas is less than that of the receiving antennas.…”