The hint-aware protocol yielded up to 76% improvement over SampleRate alone, and averaged a 20% improvement, the researchers say.
To minimize access-point hops, the MIT team designed an association strategy based on whether the device is moving. If so, it is more likely to come across an access point with a stronger signal, so it should periodically seek other access points. How often it checks is determined by how fast the device is moving.
When the device stops moving, it should stop scanning, but start up again as soon as it registers that it is moving. It should also start scanning again if it is stationary but the strength of the associated access point drops below a given threshold.
The average throughput improvement using this scheme was 30%, the researchers say.
To reduce the number of access points connected to, the device must first be trained in the Wi-Fi environment. It then takes hints about direction and speed of movement to determine which access points to find the next one to connect to when the signal strength of the current one drops below a set threshold. The next access point chosen is the one that the device can remain connected to the longest, given its current speed and direction.
The number of handoffs was 40% lower when based on hints, the researchers say.
The sensor data is organized by a Sensor Hint Manager and sent to other mobile device and access points either via UDP packets or 802.11 Wi-Fi frames, depending on the network and the capabilities of each mobile device. Possible hints are: movement, true/false; walking, true/false; heading, degrees relative to true north; speed in miles per hour; environment, indoor/outdoor.
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