Daniel Halperin

Tool Release: Gathering 802.11n Traces with Channel State Information

By: 
Daniel Halperin, Wenjun Hu, Anmol Sheth, and David Wetherall
Appears in: 
CCR January 2011

We are pleased to announce the release of a tool that records detailed measurements of the wireless channel along with received 802.11 packet traces. It runs on a commodity 802.11n NIC, and records Channel State Information (CSI) based on the 802.11 standard. Unlike Receive Signal Strength Indicator (RSSI) values, which merely capture the total power received at the listener, the CSI contains information about the channel between sender and receiver at the level of individual data subcarriers, for each pair of transmit and receive antennas.

Predictable 802.11 Packet Delivery From Wireless Channel Measurements

By: 
Daniel Halperin, Wenjun Hu, Anmol Sheth, and David Wetherall
Appears in: 
CCR October 2010

RSSI is known to be a fickle indicator of whether a wireless link will work, for many reasons. This greatly complicates operation because it requires testing and adaptation to find the best rate, transmit power or other parameter that is tuned to boost performance. We show that, for the first time, wireless packet delivery can be accurately predicted for commodity 802.11 NICs from only the channel measurements that they provide. Our model uses 802.11n Channel State Information measurements as input to an OFDM receiver model we develop by using the concept of effective SNR.

802.11 with Multiple Antennas for Dummies

By: 
Daniel Halperin, Wenjun Hu, Anmol Sheth, and David Wetherall
Appears in: 
CCR January 2010

The use of multiple antennas and MIMO techniques based on them is the key feature of 802.11n equipment that sets it apart from earlier 802.11a/g equipment. It is responsible for superior performance, reliability and range. In this tutorial, we provide a brief introduction to multiple antenna techniques. We describe the two main classes of those techniques, spatial diversity and spatial multiplexing. To ground our discussion, we explain how they work in 802.11n NICs in practice.

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