TABLE OF CONTENTS Jijun Luo
In the 3rd Generation Partnership Project (3GPP) WCDMA (wideband code division multiple access)/HSPA (high-speed packet access) standards, the radio link control sublayer [1] is defined on top of the medium access control (MAC) sublayer and under other higher sublayers such as RRC (radio resource control) and PDCP (packet data convergence protocol) [2]. Its main function is to guarantee reliable data transmission by means of segmentation, ARQ (automatic retransmission request), in-sequence delivery, etc. The radio link control (RLC) layer has three functional modes: the TM (transparent mode), UM (unacknowledge mode), and AM (acknowledge mode), enabling services with different speed and reliability for the upper layer. In this chapter, we mainly study the AM mode of RLC for the unicast traffic on the downlink user plane. The AM mode incorporates the ARQ functionality, so it is by far the most important operation mode for reliable data transfer.
In the traditional WCDMA context, the responsibility of providing ARQ lies solely on the RLC layer because the MAC layer assumes no retransmission functionality. Moreover, the RLC layer and MAC layer are separated by the Iub interface [2] between the radio network controller (RNC) and the base station (BS). Such separation determines that the RLC layer transmission is much slower than the MAC layer, which resides on the BS and communicates directly to the air interface.
The RLC layer functions (in AM mode) mainly include the following:
Segmentation, concatenation, and reassembly: RLC service data units (SDUs) that...
