Key Issues in Radio Interface Design

Summary of a Project within PCC

Mikael Sternad et. al.

The first annual PCC Workshop, Upplands Väsby, Nov. 2-3 1998.

Outline:

The strategic research program PCC organizes and supports research and graduate education within mobile communications and data communication at several main Swedish universities. Graduate projects ("work packages") are organized and coordinated into projects. The present paper is an overview over one of these projects, "Key Issues in Radio Interface Design", presented at the first annual PCC Workshop, in November 1998.

Extended Abstract:

This project aims at investigating key issues in radio interface design for practical frequency-selective fading channels. It is focused on the new opportunities and challenges that arise when considering broadband radio systems, with an emphasis on packet data transmission.

The purpose of such a radio interface is to carry packets to or from wireless users. The destination of packets may be one single user but especially in the downlink it may also be several users (broadcasting). The most important aspects related to the radio interface are

• high spectrum efficiency (as high number of bps/Hz as possible),
• high power efficiency (low transmitter power is important at least in wireless terminals),
• low delay (some packets are likely to have a maximum transmission delay of 10 ms),
• low complexity of algorithms (again, especially in wireless terminals) and
• adaptivity, for different requirements and channel conditions.

Some of the particular issues we investigate are:

• Efficient codes for data transmission (Turbo codes),
• new ways of optimizing the downlink transmission in CDMA systems,
• synchronization at low SNR's,
• channel modelling for improved antenna array receivers,
• multiuser detectors for CDMA and array receivers and
• adaptive methods for modulation, coding and protocols in packet radio systems.

Our aim is to master these key issues, and thereby provide input to a discussion of possible future system designs which we expect to emerge within PCC in the coming years. Our input takes the form of both possibilities and constraints. Possibilities, in the form of novel transmission schemes, receiver algorithms and novel ways of modelling and understanding the radio interface. Constraints, in the form of limits of performance in various situations.

There are presently seven workpackages (WP's) within this project. Their purpose, motivation and present status are outlined briefly below. The project has been running since 1997, with Uppsala University joining in 1998. Thus, much of the work is still at a preliminary stage, and the results presented at the PCC conference describe our pilot studies and initial research results.

To coordinate the project as a whole, we held a kickoff meeting in November 1997 and organized a workshop on April 7-8 1998. This workshop was organized jointly with participants in the NUTEK Telecommunications program. Several main advisors and researchers have been active in helping and supporting the work of all the graduate students, in a process of cross-reviewing the work packages. A joint graduate course on Digital Communications was held by Arne Svensson (CTH), Göran Lindell (LTH) and Tommy Öberg (UU).