Thursday, August 15, 2013

SIGCOMM2013: Bringing Cross-Layer MIMO to Today's Wireless LANs

Presenter: Swarun Kumar
Co-authors: Diego Cifuentes, Shyamnath Gollakota, and Dina Katabi

Major recent advances in cross-layer MIMO don't work on today's Wi-Fi cards, because chip manufacturers hesitate to make investments in new hardware that hasn't been fully tested on real networks.

OpenRF brings MIMO techniques to today's Wi-Fi cards. OpenRF's data plane needs to be able to apply PHY techniques to commodity cards and its control plane needs to self-configure to dynamism in the network. OpenRF handles these challenges by using two transmit queues and by handling some scheduling locally.

OpenRF was implemented on Intel 5300 Wi-Fi cards. OpenRF demonstrated an average gain of 1.6x in TCP throughput over 802.11 in a large-scale experiment, as well as clear improvements in video quality in real applications.

Q: How would you carry the same techniques to cellular networks?
A: This is a lot more natural for cellular networks because they already have some notion of scheduling.

Q: What if Alice and Bob move? How do you locate them?
A: The location of Alice and Bob really doesn't matter. These access points can track the channels as they change at the clients.

Q: You seem to use the same matching as OpenFlow for your flow tables. Wouldn't just the MAC address be sufficient? Why do you have to look at flows?
A: Sometimes you might care about different flows (for example long-lived flows but not bursty traffic).

Q: As you add more antennas you can move towards a wire abstraction. Have you thought about how this would affect your techniques?
A: Our techniques work even better with more antennas (ex: 3), so this would work.

Q: Today's mobile networks have a coordination mechanism. To what extent do we need centralized control?
A: The centralized controller is important for dealing with interference. You need to coordinate interference between access points.