Design and implementation of a frequency-aware wireless video communication system

In an orthogonal frequency division multiplexing (OFDM) communication system, data bits carried by each subcarrier are not delivered at an equal error probability due to the effect of multipath fading. The effect can be exploited to provide unequal error protections (UEP) to wireless data by carefully mapping bits into subcarriers. Previous works have shown that this frequency-aware approach can improve the throughput of wireless data delivery significantly over conventional frequency-oblivious approaches. We are inspired to explore the frequency-aware approach to improve the quality of wireless streaming, where video frames are naturally not of equal importance. In this work, we present FAVICS, a Frequency-Aware Video Communication System. In particular, we propose three techniques in FAVICS to harvest the frequency-diversity gain. First, FAVICS employs a searching algorithm to identify and provide reliable subcarrier information from a receiver to the transmitter. It effectively reduces the channel feedback overhead and decreases the network latency. Second, FAVICS uses a series of special bit manipulations at the MAC layer to counter the effects that alter the bits-to-subcarrier mapping at the PHY layer. In this way, FAVICS does not require any modifications to wireless PHY and can benefit existing wireless systems immediately. Third, FAVICS adopts a greedy algorithm to jointly deal with channel dynamics and frequency diversity, and thus can further improve the system performance. We prototype an end-to-end system on a software defined radio (SDR) platform that can stream video real-time over wireless medium. Our extensive experiments across a range of wireless scenarios demonstrate that FAVICS can improve the PSNR of video streaming by 5~10 dB.