Online source rate control is designed for video streaming over HSPA and LTE-style Variable BitRate (VBR) downlink channels. The problem is formulated as the adaptive adjustment of the operational mode of a video encoder based on the buffer overflow probability (BOP) feedback received from the Radio Link Control (RLC) layer at base station. This allows us to maximize the attainable visual quality, while keeping the transmitter buffer overflow probability below a desired threshold as well as maintaining as low a video delay as possible. We derive an online measurement based BOP estimation model for the RLC buffer, which is capable of operating without any prior knowledge of the channel variations and of the video characteristics. Based on this estimation model, an online adaptive rate control algorithm is proposed in order to seamlessly adapt the bit stream to the characteristics of VBR channels. Our experiments are conducted in multiuser scenarios using VBR video encoding combined with adaptive modulation and coding (AMC) in the transceiver. The results demonstrate that the proposed source rate control regime supports near-instantaneous, yet smooth bit stream adaptability, which makes it useful for HSPA and LTE-style systems for the sake of accommodating unknown video traffic characteristics and dynamically fluctuating propagation conditions
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