Chapter 4: Radio Interface: Physical Layer

Overview

GPRS uses the same underlying radio interface principles as GSM. The notions of time slot, frame, multiframe , hyperframe, and logical channels, described in Chapter 1, also apply to GPRS. All the participants involved in the standardization process, operators, handsets, and network vendors have taken care to minimize the impacts on the GSM radio interface. Although the main principles are upheld, new options have been introduced at the physical link layer (PLL) level during the specification phase of the GPRS standard, such as new logical channels, a new multiframe, and new coding schemes. New power control algorithms are specified for uplink and downlink to reduce the level of interference caused by the transmitters. A link adaptation mechanism is used to change the coding scheme according to the radio conditions in order to find the best trade-off between error protection and achieved throughput. We provided an overview of these additions in Section 3.3.1. Section 4.1 describes them in greater detail.

At the RF physical layer level, the main characteristic is the possibility of managing multislot configurations for GPRS MSs, in order to provide high-rate packet-switched services. New RF requirements have been introduced on the transmitter and on the receiver path . The details of the RF requirements are described in Section 4.2.

At the end of the chapter, case studies are given to show implementation constraints or issues concerning the GPRS system design.