ABSTRACT
Contents 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 6.2 HSDPA Physical Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 6.3 HSDPA MAC Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
6.3.1 Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 6.3.2 Scheduling and Priority Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 6.3.3 HARQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 6.3.4 Transport Format and Resource Combination (TFRC) . . . . . 213 6.3.5 MAC-hs Protocol Data Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
6.4 HSDPA Packet Scheduling Algorithms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 6.4.1 Fast Scheduling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
6.4.1.1 Maximum C/I Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . 216 6.4.1.2 Proportional Fair Scheduling. . . . . . . . . . . . . . . . . . . . . . . 217 6.4.1.3 Fast Fair Throughput Scheduling . . . . . . . . . . . . . . . . . . 217
6.4.2 Slow Scheduling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 6.4.2.1 The Round Robin Scheduler . . . . . . . . . . . . . . . . . . . . . . . 218 6.4.2.2 The Average C/I Scheduler . . . . . . . . . . . . . . . . . . . . . . . . 218 6.4.2.3 The Fair Throughput Scheduler . . . . . . . . . . . . . . . . . . . 218
6.4.3 Delay Differentiated Packet Scheduling Schemes . . . . . . . . . . 219
6.4.3.1 Channel-Dependent Earliest Due Deadline . . . . . . . 219 6.4.3.2 Exponential Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 6.4.3.3 Modified Largest Weighted Delay First . . . . . . . . . . . . 220
6.4.4 Scheduling with Inter-class Prioritization for End-User Multiplexed Diverse Flows . . . . . . . . . . . . . . . . . . . . . . . 220 6.4.4.1 The Largest Average Weighted Delay
First (L-AWDF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 6.5 Buffer Management-Based Scheduling Approaches . . . . . . . . . . . . . . . 221
6.5.1 Integrated Scheduling and Buffer Management for HSDPA Multimedia Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 6.5.1.1 Time-Space Priority Buffer Management . . . . . . . . . . 224 6.5.1.2 Buffer Management with Dynamic Inter-Class
Prioritization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
6.1 Introduction Providing high-speed data has always been an important goal of the wireless community. The 3rd Generation Partnership Project (3GPP) has introduced the High-Speed Downlink Packet Access (HSDPA) as a step forward in this direction. HSDPA evolved from WCDMA (Wideband Code Division Multiple Access) utilizing a number of existing technologies. Several techniques have been employed to compensate for the changing link conditions. The main theme is based on link adaptation by modifying the transmission parameters of the system to adapt to the instantaneous transmission conditions. Among many, HSDPA employs fixed spreading factor, adaptive modulation and coding (AMC), fast scheduling, and physical layer retransmission by applying Hybrid Automatic Repeat Request (HARQ) to provide high-speed downlink packet access by means of High-Speed Downlink Shared Channel (HS-DSCH). All this implies that substantial changes have been made to the Node B to enhance Release 99 WCDMA with packet scheduling embedded in a new MAC sub-layer known as the MAC-hs (Medium Access Control) (MAC-high speed). Because this necessitates data buffering at the air interface, which poses a bottleneck to end-to-end communication, buffer management in the Node B MAC-hs is essential and critical for Quality-of-Service (QoS) provision.
