4G Wireless Video Communications

8

Cross-Layer Optimized Video Delivery over 4G Wireless Networks

8.1 Why Cross-Layer Design?

As we discussed in Chapter 2, a networking system can be designed by using the methodology of layering architecture such as Open Systems Interconnection (OSI) or TCP/IP, where each layer focuses on solving different design issues. For example, physical layer (PHY) minimizes bit errors during transmissions, medium access layer (MAC) deals with channel access, network layer handles routing issues, and transport layer manages issues of congestion control.

However, the original design goal of current layering network architecture is to support simple delay-insensitive and loss-intolerant data services with little QoS consideration, which cannot support delay-sensitive, bandwidth-intense and loss-tolerant multimedia services. Therefore, how to accommodate multimedia services into future broadband wireless network design becomes a very challenging problem.

Cross-layer design methodology provides a new concept, in which the interactions among different protocol layers are utilized to achieve the best end-to-end service performance. For example, the end-to-end delay in a multi-hop multimedia network can be represented by three components: 1) transmission delay, influenced by channel conditions, modulation and channel coding scheme, number of allowed packet retransmission, and source coding rate; 2) queuing delay, determined by the source rate, transmission rate, and the selected routing path; and ...