Advanced Scheduling Schemes in 4G Systems

The deterministic factor for 4G wireless technologies is to successfully deliver high value services such as voice, video, real-time data with well defined Quality of Service (QoS), which has strict prerequisite of throughput, delay, latency and jitter. This requirement should be achieved with minimum use of limited shared resources. This constraint leads to the development and implementation of scheduling policy which along with adaptive physical layer design completely exploit the frequency, temporal and spatial dimensions of the resource space of multi-user system to achieve the best system-level performance. The basic goal for scheduling is to allocate the users with the network resources in a channel aware way primarily as a function of time and frequency to satisfy individual user’s service request delivery (QoS guarantee) and overall system performance optimization. Advanced scheduling schemes consider cross-layer optimization principle, where to fully optimize wireless broadband networks; both the challenges from the physical medium and the QoS-demands from the applications are to be taken into account. Cross-layer optimization needs to be accomplished by the design philosophy of jointly optimizing the physical, media access control, and link layer, while leveraging the standard IP network architecture. Cross-layer design approaches are critical for efficient utilization of the scarce radio resources with QoS provisioning in 4G wireless networks and beyond. The scheduler, in a sense, becomes the focal point for achieving any cross-layer optimization, given that the system design allows for this. The scheduler uses information from the physical layer up to the application layer to make decisions and perform optimization. This is a fundamental advantage over a system where the intelligence is distributed throughout the all entities of the network. In this chapter, the authors present an overview of the basic scheduling schemes as well as investigate advanced scheduling schemes particularly in OFDMA and packet scheduling schemes in all-IP based 4G systems. Game theoretic approach of distributed scheduling, which is of particular importance in wireless ad hoc networks, will also be discussed. 4G wireless networks are mostly MIMO based which introduces another degree of freedom for optimization, i.e. spatial dimension, for which scheduling in MIMO systems is very much complicated and computation intensive. MIMO resource allocation and scheduling is also covered in this chapter. The key research challenges in 4G wireless networks like LTE, WiMAX and the future research direction for scheduling problems in 4G networks are also presented in this chapter.