Broadband radio LANs and the evolution of wireless beyond 3G

IBM Journal of Research and Development, Mar/May 2003 by Chevillat, Pierre R, Schott, Wolfgang

The wireless communication landscape will continue to develop at a rapid pace over the next few years. New systems and standards are on the horizon which enable broadband wireless communication in the office, at home, and "on the move. " They will finally bring the information services provided by the Internet and the World Wide Web to mobile users, together with a variety of new multimedia entertainment services. In this paper we give an overview of key developments in wireless communication systems. The emerging third-generation (3G) cellular systems and the growing importance of wireless local- and personal-area networks are discussed. The physical and medium-access control (MAC) layers are described for the new broadband wireless local area networks (LANs), which enable "hot-spot" data and multimedia services in airports, hotel lobbies, and a variety of other "public" places. We present an outlook toward a future fourth-generation wireless communication system. It can be integrated with the Internet protocol (IP) backbone network and can provide quality-of-service (QoS) support for multimedia applications. It supports dynamic scheduling, link adaptation, and frequency selection as well as full mobility. We conclude by describing some of the underlying technology developments driving the wireless evolution.

1. Introduction

Cellular radio technology has transformed voice communication and messaging in a spectacular way. However, the low data rates of a few kb/s have so far prevented mobile users from enjoying the full benefits of Internet and World Wide Web services, but this is changing rapidly. The emerging third-generation (3G) mobile cellular systems (UMTS, IMT-2000) are designed for data rates up to 2 Mb/s [1]. In Japan and Europe, where additional capacity for voice communication and multimedia-enriched message services is urgently needed, deployment of 3G has already begun. Third-generation systems will have a hierarchical cell structure with suburban macrocells, urban microcells, "hot-spot" picocells, and possibly also a satellite overlay. Seamless coverage, ubiquitous roaming, and operation at vehicular speeds up to 200 km/h (120 mph) will be supported in macrocells and microcells for data rates up to 64 kb/s (cf. Figure 1). A richer variety of wireless services, at least for slower-moving platforms, will become available with the deployment of 384-kb/s data services which will finally bring many of the Internet and Web services to the mobile user. In particular, multimedia services such as MPEG audio and video streaming are expected to unlock new revenue streams for the cellular operators. However, cellular networks will have to compete with new wireless broadcasting networks based on the digital audio broadcast (DAB) and digital video broadcast (DVB) standards. In addition, the 3G standard defines a high-speed 2-Mb/s mode for stationary hot-spot services.

A second wave of radio technology has recently begun to penetrate our offices and homes. Indeed, very shor-range wireless systems, in particular IEEE 802.11b radio LANs [2] and "Bluetooth" [3], may soon rival cellular systems in ubiquity. Bluetooth is a system that enables the coexistence of a small number of low-cost radio links for voice or data communication within a range of up to 10 meters, allowing wireless access to a plethora of devices and appliances and a variety of new personal area network (PAN) scenarios. Bluetooth was standardized in IEEE 802.15.1 and operates at 1 mW in the worldwide license-free 2.4-GHz industrial, scientific, and medical (ISM) frequency band. It uses frequency hopping to transmit data at a rate of 1 Mb/s-sufficient for three 64-kb/s voice links or for asynchronous data up to 723 kb/s.

IEEE 802.11b radio LANs have recently achieved spectacular market growth. They typically operate at 100 mW in the same license-free 2.4-GHz ISM band, supporting asynchronous data up to 11 Mb/s. The 802.11 MAC allows two modes of operation, either using an access point (base station) that is typically connected to a wired backbone network, or operating in ad hoc networking mode without a base station. In addition to their traditional use in office environments, 802.11b systems are rapidly penetrating the home networking market, where wireless operation is particularly attractive for connecting entertainment devices. In addition, 80211b base stations increasingly serve as access points for delivering Internet access in airports, hotel lobbies, and other "public" places. Integrating such 802.11b hot spots into the emerging 3G networks may prove to be more cost-efficient than deploying the 2-Mb/s data service defined in the 3G standard. Indeed, as we describe later in this paper, wireless LANs will play a key role in the further evolution of wireless communications.

The evolution of 2.4-GHz wireless LANs and PANs toward higher data rates and richer functionality is underway: IEEE 802.11g has drafted a higher-speed wireless LAN for data rates of up to 55 Mb/s. It is backward-compatible with 802.11b, which uses complementary code keying (CCK) for 11 Mb/s. For higher data rates, orthogonal frequency-division multiplexing (OFDM) and, as an option, packet binary convolutional coding (PBCC) are employed [4]. IEEE 802.11e is working on an enhanced MAC with QoS provisions, and 802.11i on enhanced security functionality. Similarly, 802.15.3 is pursuing a high-speed wireless PAN for data rates as high as 55 Mb/s using trellis-coded modulation [5]. The MAC supports ad hoc networking and QoS provisions. Concerns about the coexistence of the various systems operating in the 2.4-GHz band are addressed by yet another group. Nevertheless, the 2.4-GHz ISM band has a bandwidth of only about 80 MHz and is also shared by a number of industrial, scientific, and medical users. More bandwidth for short-range radio transmission is available at higher frequencies, notably between 5.1 and 5.8 GHz.