Wireless LAN Technology: Current State and Future Trends Zahed Iqbal Helsinki University of Technology Telecommunications Software and Multimedia Laboratory [email protected] Abstract In this paper, a comprehensive overview of the current state and future trends of Wireless Local Area Network (WLAN) has been presented. This document stud- ies and compares two most competing commercialy potential WLAN technologies, namely IEEE 802.11 and ETSI HiperLAN. This study also addresses the challenges of their coexistance and convengences towards a global standards. KEYWORDS: Wireless Local Area Network (WLAN), IEEE 802.11, ETSI, HiperLAN 1 Introduction Wireless Local Area Network (WLAN) is a flexible data communication system that can either replace or extend a wired LAN to provide added functionality. Using Radio Fre- quency (RF) technology, or Infrared (IR) WLANs transmit and receive data over the air, through wall, ceilings, and even cement structures, without wired cabling. A WLAN pro- vides all the features and benefits of traditional LAN technologies like Ethernet and Token Ring, but without the limitations of being connected by a cable. This provides greatly increased freedom and flexibility. [8] Wireless Local Area Networks have been used increasingly in many critical applications over the past few years, particularly since 1997 when the first IEEE802.11 WLAN standard was issued followed by its European competitor standard High Performance LAN (Hiper- LAN). In certain locations, the use of WLANs could save millions of dollars in cost and deployment time when compared to permanent wired networks. In other locations, WLAN services are complimentary to existing wired LANs adding the advantage of user mobility. Currently there exists an enormous number of Wireless LAN standards from different stan- dardization organs and they are competing to each other to a certain degree capable enough to create a puzzling situation when to chose a wireless data communication solution. The main problem is that there is not one unique standard like Ethernet with a guaranteed com- patibility between all standards and devices, but many proprietary standards pushed by 1 Ad Hoc Mobile Wireless Networks – Research Seminar on Telecommunications Software, Autumn 2002 HUT TML – Course T-110.557 – Publication ISBN 951-22-6309-2 ISSN 1456-7628 TML-C8 http://www.tml.hut.fi/Studies/T-110.557/2002/papers/ each independent organs and incompatible between themselves. So many standards brings some good aspect like lower product price but at the same time it introduces some chal- lenges concerning lack of compatibility and interoperability. The motivation of this paper is to identify the characteristics of those different standards and compare them. Over all, this paper gives an overview of the current state of two wireless LAN standard, namely in the IEEE 802.11 and the HiperLAN, compare them and discusses the future trends of WLAN, as well as presents the challenges of their coexistence or convergence towards a global standard. 1.1 Background Over the past ten years or so an alternative to wired LAN structures has evolved in the form of the Wireless LAN. The first generation Wireless LAN products, operating in unlicensed 900-928 MHz Industrial Scientific and Medical (ISM) band, with low range and through- put offering (500 Kbps), subjected to interference came to market with few success in some applications. But they enjoyed reputation of being inexpensive due to break through devel- opment in semiconductor technologies, on the other hand the band become crowded with other products with in short period of time leaving no room for further development. The second generation in 2.40-2.483 GHz ISM band WLAN products boosted by the de- velopment of semiconductor technology was developed by a huge number of manufactures. Using Spread spectrum technology and modern modulation schemes this generation prod- ucts were able to provide data rate up to 2 Mbps, but again the band become crowded since most widely used product in 2.4 GHz is microwave oven which caused interference. Third generation product assembled with more complex modulation in 2.4 GHz band al- lows 11 Mbps data rate. In June 1997, the IEEE finalized the initial standard for wireless LANs: IEEE 802.11. First fourth generation standard, HiperLAN, came as specification from European Telecommunication Standard Institute (ETSI) Broadband Radio Access Network (BRAN) in 1996 operating at 5 GHz band. Unlike the lower frequency bands used in prior generations of WLAN products, the 5 GHz bands do not have a large "in- degenous population" of potential interferors like microwave ovens or industrial heating system as was true in 900 MHz and 2.4 GHz [8]. In late 1999, IEEE published two supple- ments to the 802.11: 802.11b and 802.11a following the predecessor success and interest from the industry [2]. ETSIs next generation HiperLAN family, HiperLAN/2, proposed in 1999 operating at same band with its predecessor, is still under development, the goal is to provide high-speed (raw bit rate 54Mbps) communications access to different broadband core networks and moving terminals [8]. It is expected that 802.11b will compete with HiperLAN/1 and 802.11a will compete with HiperLAN/2 in near fut! ure. 1.2 Wireless LAN Topologies The infrastructure mode and the ad-hoc mode are two most common topologies that are supported by Wireless LAN. In HiperLAN terminology they are referred as "centralized mode" and "direct mode", but the basic idea and how they work are same. The infrastruc- 2 Ad Hoc Mobile Wireless Networks – Research Seminar on Telecommunications Software, Autumn 2002 HUT TML – Course T-110.557 – Publication ISBN 951-22-6309-2 ISSN 1456-7628 TML-C8 http://www.tml.hut.fi/Studies/T-110.557/2002/papers/ ture mode is some times called Basic Service Set (BSS), which rely on an Access Point (AP) that acts as a controller in each radio cell or channel. If station A want to commu- nicate with station B, it goes through the AP. This mode of operation is mainly used is suitable for business applications, both indoors and outdoors, where an area much larger than a radio cell has to be covered. The access point performs several tasks, like connecting to wired network, bridging function to connect multiple WLAN cells or channels. Ad-hoc modes are known as "peer-to-peer" mode in some literature. In this mode mobile nodes can form network among themselves without the help of any fixed or wireless in- frastructure like AP. It is principally used to quickly and easily build a network where no infrastructure is available. A good example of the use of this mode could be in military, or convention center to share file or some information sharing between users. Another mode sometime referred in IEEE 802.11 standard is Extended Service Support (ESS), where multiple BSS are joined together to use the same channel to boost the aggre- gate throughput. Basically this mode is a set of BSS working together. 1.3 Outline of the paper Chapter one starts with the general introduction of wireless local area network; it’s back- ground and problem statement. The network topologies, its use and benefits are also dis- cussed in chapter one. Chapter two tells about the different WLAN technologies and standard in brief, mainly IEEE 802.11 family standards and HiperLAN, considering the fact that they are commer- cially potential competitor to each other. Chapter three deals with the WLAN layer architecture - this is related to the OSI lower layers (PHY, MAC). In physical layer level, different modulation techniques used by both of the technologies are discussed; their strength and shortcomings are also taken in con- sideration when comparing them. The medium access control mechanism of competing standards have been presented and compared. In Chapter four, the future trends in wireless area networking is presented, why the current technologies are not adequate to meet the future requirements, how they can be addressed using the new upcoming standards etc. Chapter five concludes this paper with findings and recommendations; a coexistence of standards is also outlined. 2 Wireless LAN Standards Variants An introduction to the wireless LAN standards, currently available from IEEE and ETSI has been presented in this chapter. 3 Ad Hoc Mobile Wireless Networks – Research Seminar on Telecommunications Software, Autumn 2002 HUT TML – Course T-110.557 – Publication ISBN 951-22-6309-2 ISSN 1456-7628 TML-C8 http://www.tml.hut.fi/Studies/T-110.557/2002/papers/ 2.1 IEEE 802.11 Standard family 802.11 The 802.11 standard for WLAN operates at data rates up to 2 Mbps in the 2.4-GHz ISM band. The goal of this standard was to serve the same purpose as IEEE 802.3 for wired Ethernet to define an open standard for wireless networks so that the consumers no longer was tied to a single vendor with proprietary technologies [10]. This standard describes the specification of one Medium Access Control (MAC) layer and three physical layers: Fre- quency Hopping, Direct Sequence and diffuse infrared. The MAC has two main standards of operation, a distributed mode (CSMA/CA), and a coordinated mode (polling mode. 802.11 of course uses MAC level retransmissions, and also RTS/CTS and fragmentation. The physical layers and MAC layer will be discussed in next chapter in details. This standard includes an optional but quite complex power management features, which supports two separate modes: Active mode and Power save mode. Power management features define functionality relating to how stations can enter into a power mode and the functionality relating to when another station desires to communicate with it during power saving state, but the standard does not define when to enter or leave low power operating state, that is the reason why power management features are considered as complex.