Improving QoE for Skype video call in Mobile Broadband Network

In this paper, we introduce an app-radio cross-layer framework for improving Quality of user Experience (QoE) of Over-The-Top (OTT) Internet applications in Mobile Broadband Networks, e.g. WiMAX, 3G, LTE, etc. We apply methods similar to the well-known network layer techniques: Explicit Congestion Notification (ECN) and Differentiated Services (DiffServ) to application layer and wireless link layer. We focus on UDP based delay-sensitive real-time video call applications such as Skype, and propose to exchange cross-layer information, e.g. congestion, packet priority, etc., through API (application programming interface) based control signals instead of the existing ECN and DiffServ fields in IP data packet header. We built a prototype system with Microsoft Windows XP OS and Intel Mobile WiMAX network adapter, and use POLQA Mean Opinion Score (MOS) to measure the audio QoE for the video call. Empirical results show that immediate congestion indication effectively speeds up Skype response to bandwidth variation, and intra-flow prioritization further reduces the delay of audio packets. Both significantly improve the audio MOS of a video call.