Playback experience driven cross layer optimisation of APP, transport and MAC layer for video clients over long-term evolution system

In the traditional communication system, information of application (APP) layer, transport layer, and media access control (MAC) layer has not been fully interacted. To solve the problem, the authors propose a joint optimisation framework, which consists of the APP layer, transport layer, and MAC layer, to improve the video clients' playback experience and system throughput. First, a client requirement aware autonomous packet drop strategy, based on packet importance, channel condition, and playback status, is developed to decrease the network load and the probability of rebuffering events. Furthermore, TCP state aware downlink and uplink resource allocation schemes are proposed to achieve smooth video transmission and steady acknowledgment (ACK) feedback, respectively. For the downlink scheme, the maximum transmission capacity required for each client is calculated based on feedback ACK information from the transport layer to avoid allocating excessive resource to the client, whose ACK feedback is blocked due to bad uplink channel condition. For the uplink scheme, information of retransmission timeout and TCP congestion window are utilised to indicate ACK scheduling priority. The simulation results show that their algorithm can significantly improve the system throughput and the clients' playback continuity with the acceptable video quality.