ACCEPTED FROM OPEN CALL BLUETOOTH AND WI-FI WIRELESS PROTOCOLS: A SURVEY AND A COMPARISON ERINA FERRO AND FRANCESCO POTORTI`, INSTITUTE OF THE NATIONAL RESEARCH COUNCIL (ISTI—CNR) ABSTRACT ging. Another advantage lies in the way new wireless users can dynamically join or leave the Bluetooth and IEEE 802.11 (Wi-Fi) are two network, move among different environments, communication protocol standards that define a create ad hoc networks for a limited time, and physical layer and a MAC layer for wireless then leave. Wireless networks are simple to communications within a short range (from a deploy, and in some cases cost less than wired few meters up to 100 m) with low power con- LANs. Nevertheless, the technological chal- sumption (from less than 1 mW up to 100 mW). lenges involved in wireless networks are not triv- Bluetooth is oriented to connecting close devices, ial, leading to disadvantages with respect to serving as a substitute for cables, while Wi-Fi is cabled networks, such as lower reliability due to oriented toward computer-to-computer connec- interference, higher power consumption, data tions, as an extension of or substitution for security threats due to the inherent broadcast cabled LANs. In this article we offer an overview properties of the radio medium, worries about of these popular wireless communication stan- user safety due to continued exposition to radio Bluetooth and IEEE dards, comparing their main features and behav- frequency, and lower data rates. iors in terms of various metrics, including Currently the wireless scene is held by two 802.11 (Wi-Fi) are capacity, network topology, security, quality of standards: the Bluetooth and IEEE 802.11 pro- service support, and power consumption. tocols, which define the physical layer and medi- protocol standards um access control (MAC) for wireless communications over a short action range (from that define a physical INTRODUCTION a few up to several hundred meters) and with Wireless communications is a fast-growing tech- low power consumption (from less than 1 mW layer and a MAC nology that enables people to access networks up to hundreds of milliwatts). Bluetooth is main- and services without cables. Deployment can be ly oriented toward connections between closely layer for wireless envisaged in various scenarios: different devices connected devices as a substitute for data trans- belonging to a single user, such as a mobile tele- fer cables; IEEE 802.11 is devoted to connec- communications phone, a portable computer, and a personal digi- tions among computers, as an extension to or tal assistant (PDA), that need to interact in substitute for cabled LANs. The standards cover within a short range order to share documents; a user who receives different techniques at the physical layer: infrared email on a PDA; a shopping mall where cus- communications, which are rarely used in com- with low power tomers display special offers on their PDAs; car mercial products and are not treated in this drivers loading maps and other tourist informa- work, and different radio signal multiplexing consumption. The tion while driving on a motorway. All of these techniques: frequency hopping spread spectrum scenarios have become reality from a technologi- (FHSS), used by Bluetooth devices, direct authors offer an cal point of view, and successful experiments are sequence spread spectrum (DSSS), complemen- being carried out around the world. tary code keying (CCK), and orthogonal fre- overview of these The wireless approach shows many advan- quency-division multiplexing (OFDM), used in tages but also has some disadvantages with IEEE 802.11 commercial devices. wireless standards, respect to cabled networks. Mobility is clearly Both Bluetooth and IEEE 802.11 systems are one of the major advantages of wireless with evolving toward more powerful multiplexing comparing their respect to cabled devices, which require plug- technologies: ultra wideband (UWM) and multi- ple-input multiple-output (MIMO), respectively. main features and The material presented here is widely avail- Work funded by the Italian Ministry of Instruction, Uni- able in the literature; therefore, the main pur- behaviors versity and Research (MIUR) within the framework of the pose of this article is not to contribute to Infrastructure Software for Mobile Ad Hoc Networks (IS- research in the area of wireless standards, but to MANET) project and by the Satellite Communications present a comparison of the major characteris- Network of Excellence (SatNEx) in the VI Research tics of the two main protocols for short-range Framework Program of the European Commission. terrestrial communications. 12 1536-1284/05/$20.00 © 2005 IEEE IEEE Wireless Communications • February 2005 The original idea 7 Application Applications/profiles behind Bluetooth 6 Presentation Other technology was con- 5 Session TCS SDP LLC RFCOMM ceived in 1994, 4 Transport Logical Link C when Ericsson 3 Network Adaptation Protocol Audio (L2CAP) Control Mobile Communica- Logical link control (LLC) Link manager Data tions began to study 2 link Medium access control (MAC) Baseband a low-power- consumption system 1 Physical Physical (PHY) Physical radio for substituting the ISO OSI IEEE 802 IEEE 802.15.1 layers standards Bluetooth WPAN cables in the short- n Figure 1. The Bluetooth stack. (Reproduced from the IEEE 802.15.1 standard, page 22.) range area of its mobile phones and A SURVEY OF mitter and receiver, but in return are able to tra- relevant accessories. verse common obstacles, such as walls, even at BLUETOOTH AND IEEE 802.11 low emission power. Among the many proposed applications for this technology are high-speed BLUETOOTH low-range low-power communications, making it Bluetooth [1] is a standard for wireless commu- a natural candidate for WPANs. The WPAN nications based on a radio system designed for working group at IEEE is considering adopting short-range cheap communications devices suit- UWB for the physical layer of the 802.15.3a able to substitute for cables for printers, faxes, standard, capable of rates in the hundreds of joysticks, mice, keyboards, and so on. The megabits per second range. devices can also be used for communications between portable computers, act as bridges Basic Operation — When a Bluetooth device is between other networks, or serve as nodes of ad powered on, it may try to operate as one of the hoc networks. This range of applications is slave devices of an already running master device. known as wireless personal area network It then starts listening for a master’s inquiry for (WPAN). new devices and responds to it. The inquiry phase lets the master know the address of the History, Current Status, and Prospective Developments slave; this phase is not necessary for very simple — The original idea behind Bluetooth technolo- paired devices that are granted to know each gy was conceived in 1994, when Ericsson Mobile other’s address. Once a master knows the address Communications began to study a low-power- of a slave, it may open a connection toward it, consumption system to substitute for the cables provided the slave is listening for paging requests. in the short-range area of its mobile phones and If this is the case, the slave responds to the mas- relevant accessories. In 1998 Ericsson, Nokia, ter’s page request and the two devices synchro- IBM, Toshiba, and Intel formed the Bluetooth nize over the frequency hopping sequence, which Special Interest Group (SIG). Subsequently, is unique to each piconet and decided by the 1999 was the year of the first release of the master. Bluetooth predefines several types of Bluetooth protocol; the next year, four other connection, each with a different combination of companies joined the SIG group: 3COM, Agere available bandwidth, error protection, and quality (Lucent Technologies), Microsoft, and Motoro- of service. Once a connection is established, the la. In that year, the first Bluetooth headset, from devices can optionally authenticate each other Ericsson, appeared on the market. and then communicate. Devices not engaged in Bluetooth is currently at version 1.2. Since transmissions can enter one of several power- March 2002, the IEEE 802.15 working group has and bandwidth-saving modes or tear down the adopted the work done on Bluetooth (without connection. Master and slave can switch roles, any major changes) and made it an IEEE stan- which may be necessary when a device wants to dard, 802.15.1 (Fig. 1). participate in more than one piconet. The future of Bluetooth may be based on UWB [2]. UWB systems use very high-speed, Protocol Overview — Bluetooth defines not only a precisely timed impulses for transmitting infor- radio interface, but a whole communication mation over a very wide spectrum; this is very stack that allows devices to find each other and different from most other transmission schemes, advertise the services they offer. In Fig. 1 the which modulate a sine wave. UWB pulses link manager layer handles the type of link con- require precise synchronization between trans- figuration, authentication, security, quality of IEEE Wireless Communications • February 2005 13 A Bluetooth device may operate in either master or slave mode; a maximum of eight devices — seven active slaves plus one master — working together form a Piconet (Fig. 2), which is the simplest configuration of a Bluetooth net- work. Piconets may be connected together, thus forming a scatternet. A scatternet (Fig. 3) is a topology over which a multihop wireless network can be built. A wire- less network is said to be multihop when two nodes can communicate with each other even if Master there is no direct connection between them by using other nodes as relays. Two piconets can Active slave communicate by means of a common node belonging to both of them. A node can be a Parked slave master in one piconet at most and a slave in sev- eral others.