COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI

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1 Daffodil International University Institutional Repository DIU Journal of Science and Technology Volume 11, Issue 1, January COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI Khan, Md. Abbas Ali Downloaded from Copyright Daffodil International University Library

2 DAFFODIL INTERNATIONAL UNIVERSITY JOURNAL OF SCIENCE AND TECHNOLOGY, VOLUME 11, ISSUE 1, JANUARY COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI Md. Abbas Ali Khan, Md. Alamgir Kabir Department of Information & Communication Technology, KTH Royal Institute of Technology, Sweden dobila2005@gmail.com Abstract: Bluetooth (IEE ), ZigBee (IEEE ) and Wi-Fi (IEEE ) are three emerging wireless technology in the area of short range wireless communication. Bluetooth is intended to support a list of application such as data, audio, graphics and even video. For example, device can include cordless keyboard, mouse, and hands free headset and standard phones. The primary purpose of ZigBee is to monitor and control networks wirelessly. Wi-Fi is amid at computer to computer connection wirelessly instead of traditional cable network. In this paper, it is being to represent a comparative study of these wireless protocols, evaluating their main characteristics and performance in terms of some metric such as co-existence, data rate, power consumption, network size, cost, distance coverage and security. For application engineers this paper will help him to select an appropriate protocol. Keywords: Bluetooth, Wi-Fi, ZigBee, 2.4 Communications, , , Introduction Bluetooth is also known as the IEEE standard based on wireless radio system that enables of electronics devices to communicate each other. It was originally developed by Ericsson, later on 1998 it is being developed by a company consortium called Bluetooth Special Interest Group or simply SIG (Ericsson, Intel, Toshiba, Nokia and IBM). On 2008, at 10th anniversary Bluetooth SIG welcomes its 10000th members [1]. Bluetooth is a wireless protocol designed for short-range, low power and cheap devices to replace cables for cell phones, PDA, Hands-free Audio as well as computer peripherals such as mice, keyboards, joysticks, and printers. Since Bluetooth was developed for mobile phone industry, so it is very common in mobile phones. ZigBee over IEEE is low data rate WPAN (LR-WPAN) design specially to replace the proliferation of individual remote controls. ZigBee is anticipated Date of submission : Date of acceptance : to be able to eliminate electric cabling in houses so allowing choice of wireless light switches. It was designed to satisfy the market need for costefficient standard based wireless network that support low data rate, low power consumption, security and reliability. Its mode for simple sending command such as tuning on a TV or small bit of data, such as weather a door is locked. ZigBee tends to use far less power than other short range networking technologies. The battery life of ZigBee device can often be measured in years, rather than hours in the case of Wi-Fi or days with Bluetooth. Also ZigBee devices to automatically connect with and transmit data one another with having to go through a central gateway like a router. ZigBee Alliance, an industry working group developed application software of IEEE wireless standard. Wi-Fi, wireless networking technology that uses radio frequency to allow high-speed data transfer over short distances. It includes IEEE a/b/g standard for WLAN support technologies have its origins in a 1985 ruling by Federal Communications Commission that released ISM band for unlicensed use. At the early beginning the movement of this technology remained fragmented due to lack of compatibility among the devices from different manufacturer. In 1997 IEEE approved a common standard formed by industry leaders. After two years, a group of major companies formed the Wireless Ethernet Compatibility Alliance (WECA), and named the new technology Wi-Fi. Wi-Fi allows local area networks (LANs) to operate without cables and wiring, making it a popular choice for home as well as business networks. Wi-Fi also provides facility of wireless broadband internet access for most of the modern devices, such as laptop, mobile phones, PDAs, and electronic gaming consoles. Any Wi-Fi enabled devices are able to connect

3 2 with internet, when they are within the range of wireless hot spots. Demanding the popularity of Wi-Fi, hot spots have become common, with many public places such as airports, hotels, bookstores, and coffee shops offering Wi-Fi access. For Bluetooth and Wi-Fi Ferro and potorti compared their main features and behaviors in terms of various metrics included capacity, network topology, security, quality of service support, and power consumption[12]. The power management of is easier then that For Bluetooth and ZigBee, Baker studied their strengths and weaknesses for industrial applications and claimed that Zigbee over can meet a wider variety of real industrial needs than Bluetooth due to its long term battery operation, greater useful range, flexibility in a number of dimensions and reliability of the mesh network architecture [13]. 2. Bluetooth Bluetooth operates on 2.4 unlicensed ISM (Industrial, Scientific and Medical) band at a data rate of 720 Kbps. Other wireless technology (e. g. Wi-Fi and ZigBee) and equipment (e.g. microwave oven) also shares the same frequency band. In order to avoid interference, the Bluetooth specification employs Frequency Hopping Spread Spectrum (FHSS) techniques which divide the frequency band into a number of channels. As we can see in Table 1.1 there are 79 physical channels each are 1, those Bluetooth may use for its hopping algorithm. Frequency hopping occurs by jumping from one physical means each physical channel is occupied for duration of 62µs. Network range of a Bluetooth device depends on its output power level. Not all of the Bluetooth devices have the equal signal not they can over same distance. Most of the Bluetooth devices have liberty to choose their output power. Bluetooth radio specification classifies the Bluetooth devices into their classes based on their output power. The Bluetooth power classes are given below: [2] Class 1: In this class the maximum output power is 100mW (+20dBm) and the minimum output power is 1mW (0dBm). For class 1 power control is obligatory, ranging from 4dBm to 20dBm. This mode provides maximum distance coverage of 100m (328 feet.). Class 2: Maximum output is 2.5mW (4dBm) and COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI minimum is 0.25mW (-6dBm). In class 2 mode communication range is 10 meters and power control is not mandatory. Class 3: Lowest power class, lmw (0dBm). With 0dBm power, the communication range may be up to 10 meters (30 feet). Table 2.1 International Bluetooth Frequency allocations RF Area Frequency Channels Range U.S., most of Europe, and most of other countries. Japan Spain France F=2402+k, k=0,..,78 F=2473+k, k=0,..,22 F=2449+k, k=0,.., 22 f=2454+k, k=0,..,22 As we know wireless networks do not really share any physical media, such as a common cable, it uses other way to join in a network. When tow Bluetooth devices come within a range of each other can set up an ad-hoc network. Two connectivity topologies are defined in Bluetooth: the Piconet and Scatternet. A Piconet is a Wireless Personal Area Network (WPAN) formed by a device called master in the piconet and one or more Bluetooth devices act as slaves. A frequency hopping channel based on the address of the master defines each piconet. The devices those are participating on the communication only, with their master in a point-to-point manner and may only communicate when granted permission from master. Master can communicate either in pointto-point or point-to-multipoint. Also besides in an active mode, a slave can go sniff, hold or park mode to reduce power consumption. In a piconet there could have at most eight devices, one act as master and rest of them serves as slaves. With the use of park mode, there could be more than seven slaves in a piconet [3]. A Scatternet ia a collection of operational piconets overlapping in time and space. Two piconet can be connected to

4 DAFFODIL INTERNATIONAL UNIVERSITY JOURNAL OF SCIENCE AND TECHNOLOGY, VOLUME 11, ISSUE 1, JANUARY form a scatternet. A device in a scatternet could be a slave of several piconects but master only one of them. The advantages of scatternet are to allow many devices to share same physical area and the maximum utilization of the bandwidth. Figure 2.1: Bluetooth Piconet Figure 2.2: Bluetooth Scatternet 2.1 Bluetooth Protocol Versions Bluetooth version 1.2, on November 5, 2003 Bluetooth SIG released version 1.2 of Bluetooth specification. This is the first successful version of Bluetooth. Version 1.2 did not come with any new functionality; the goal of this version was to improve performance of version. Enhance enquiry feature of version 1.2 provides 100% reliable and faster device discovery than version 1.1. It also introduced adaptive frequency hopping (AFH) technique which supports better coexistence with other 2.4 technology such as Wi-Fi, ZigBee. Bluetooth Version ERD are most successful version. It has backward compatibility with version 1.2 and more capable of recovering error from version 1.2. It also introduces enhanced data rate which used PSK modulation and has two variants: (π/4-dqpsk and 8DPSK. The gross air data rate for EDR is 2Mbps using (π/4-dqpsk and 3Mbps using 8DPSK. Bluetooth Version2.1+EDR, architecture of Bluetooth 2.1 and 2.0 is almost same, 2.1 includes Secure Simple Paring. The primary goal of Secure Simple Paring is to make the pairing procedure simper and faster. Secondary goal are to improve security of Bluetooth wireless technology. Secure Simple Pairing offers two types of security: protection form passive eavesdropping and protection against man-in-the middle (MITH) attacks (active eavesdropping) [4]. Bluetooth version 2.1 also consumes less power than Bluetooth version 2.0. Bluetooth version HS, in April 2009, Bluetooth Special Interest Group announced the release of new Bluetooth high speed specification, version 3.0+HS (High Speed). It includes protocol adaptation layer (PAL) so data rate can be increased by 15 times that of a standard Bluetooth link. Increased bandwidth enables consumer to synchronize music libraries between PC and music player or phone, downloading photos to a printer or PC, sending video form camcorder to PC or to a Television. Bluetooth 3.0+HS, it supports data rate approximately 24Mbps [5]. It has also backward compatibility with the previous versions. 1.8 Bluetooth version 4.0, on July, 2010, the Bluetooth SIG announced core specifications of Bluetooth version 4.0 with hallmark feature, Bluetooth low energy (BTLE). BTLE operates on two different modes of chips (single mode chips and dual mode chips). Single mode chips support only Bluetooth low energy. Dual mode chips support Bluetooth low energy as well as interoperability with classic Bluetooth devices. Bluetooth low energy wireless technology consumes only a fraction of power compare to classic Bluetooth radios. It can run more than a year by a single coin cell battery without recharging. It supports very short data packet minimum is 8 octets and maximum is 27 octets that are transmitted with 1 Mbps speed. Bluetooth low energy provides a greater amount of intelligence in the controller which permits a host to sleep for longer period of time and be awoken up the controller only when the host needs to perform some action [6]. 3. ZigBee The aim of ZigBee techonology is to create a low duty cycle sensor network (<1%). A device can connected newly with in 30 ms. A sleeping slave changing to active and transferring data by accessing a channel need around 15 ms respectively. The advantages of ZigBee over Bluetooth and Wi-Fi is to rapidly attach information, detach, and goes to sleep mode, that

5 4 makes ZigBee faster and consume less power than other wireless networks. State of Operation of ZigBee are active (transmit/receive) and sleep mode specially designed to accommodate battery powered devices. Any ZigBee-compliant radio can switch automatically to sleep mode when it s not transmitting and remain asleep mode until it needs to communicate again. In ZigBee the MAC defines two modes operation, beacon and non-beacon modes to enable the to-and-fro data traffic. Beacon mode is used when the coordinator runs on batteries and thus offers maximum power savings, whereas non beacon mode looks for favors when the coordinator is mains-powered. Beacon mode is timing dependent, where a beacon frame is transmitted periodically and provides 16 equal width tine slots for contention free channel assess in each time slot. Any device wishing to communicate during the contention access period (CAP) between two beacons shall complete with other devices using a slotted CSMA-CD mechanism. Starting of a super frame is defined by the beacon which is normally the interval between the beacons, and is used as a way for the device on the network to synchronize with each other. There are two parts, the active part where data can transfer and the inactive part the device can sleep. Beacon is transmitted in the first slot of each superframe. ZigBee network consists of different traffic types with their own characteristics such as periodic data is wireless sensor or control used by beaconing system whereby the sensor activates, checks for beacon, exchange data and goes to sleep. An automatic meter reading application represents the periodic type traffic. Intermittent data define by either application or external stimulus such as a wireless light switch. Data can be handled using a beaconless system. The device needs to connect to the network only when communication is required, saving energy. Frequency range of ZigBee Protocol uses spread spectrum technique and use 2.4 band, which is unlicensed in most countries as the ISM (Industrial, Scientific and Medical) band. A total of 27 channels [7], numbered 0 to 26, are COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI available across the frequency bands. 16 channels are available in the 2450 band, 10 in the 915 band, and 1 in the 868 band. Table 2.2 International ZigBee Frequency allocations Area Frequency Data Rate Almost All Countries range (Global) Europe North America RF Channels kbps 20 kbps 40 kbps The channel width is 2 and 5 channel spacing. For each PHY supported, a compliant device shall support all channels allowed by regulations for the region in which the device operates. The transmission distance is expected to range from 10 to 70+ miters, depending on the power output and environmental characteristics [9]. And up to 1500m for ZigBee pro (2007 stack profile 2). The output power of the radios is normally 0 dbm refereed to 1 mille Watt (mw). The upper limit on power is defined by the regularity commission of each country. Modulation scheme in the 2.4 band, ZigBee uses DSSS (Direct Sequence Spread Spectrum) with offset quadrature phase-shift keying (O- QPSK) where the symbol rate is Both the 868 and 900 band also use DSSS (Direct Sequence Spread Spectrum) with BPSK (Binary Phase-shift Keying) modulation and the symbol rate should be sequentially 20 and 40. ZigBee provides self-organized, multi-hop, and reliable mesh networking with low power. In a LR- WPAN (Low range wireless personal area network) network two different device can participate [7] a Full Function Device (FFD) and a Reduced Function Device (RFD). However, a network shall include at least one FFD [7], operating as the PAN coordinator. An IEEE networks requires at least one full function device as a network coordinator, but end point devices may be reduced functionality devices to reduce system cost. Several connectivity topologies are supported by ZigBee

6 DAFFODIL INTERNATIONAL UNIVERSITY JOURNAL OF SCIENCE AND TECHNOLOGY, VOLUME 11, ISSUE 1, JANUARY including star, peer-to-peer, mesh and cluster tree. 4. Wi-Fi IEEE standard was the first standard describing the operation of wireless LANs. This standard contained all of the available transmission technologies including DSSS, FHSS and operating 2.4 ISM (unlicensed) band at data rates of 1 Mbps and 2Mbps. Infrared at 1 Mbps operating at a wavelength between 850 and 950 nm. IEEE a standard operates 5 band, OFDM modulation technique with 54 Mbps data rate. IEEE b standard supports up to 11 Mbps and it uses the 2.4 frequency with DSSS spreading technique. IEEE g standard has OFDM technique in the 2.4 band with 54 Mbps data rate. There are 14 RF channels (13 in Europe and 1 in Japan) with 22 bandwidth. The DS and BSSs allow IEEE to make wireless network arbitrary size and complexity. ESS appears as a single logical LAN to the logical link control level (LLC). A portal is used to integrate IEEE architecture with a traditional wired LAN. The MAC layer is subject to provide reliable data delivery, medium access control and security for IEEE local area network (LAN). The IEEE MAC layers uses physical such as b and a, the tasks to perform career sensing, transmitting and receiving MAC frame [8]. 5. Comparison There are a lot of technical differences and similarities present among Bluetooth, ZigBee and Wi-Fi. The main difference includes data rate, power consumption, network size, cost, distance coverage and security. In Table 1.3 is summarized the main differences among the three protocols. RF Channel and Coexistence of these three wireless networks use universal 2.4 ISM band and spread spectrum technology. Bluetooth uses frequency hopping spread spectrum (FHSS) and splits 2.4 band into 79 RF channels and each of them 1 bandwidth. ZigBee uses direct sequence spread spectrum (DSSS) and operates in three different radio frequencies depending upon geographical areas such as 868 band (in Europe), 915 (in North America) and 2.4 band (Worldwide). In ZigBee 2.4 ISM band is divided into 16 RF channel with 2 bandwidth, centered at 5 each other and there is 2 gap between two consecutive channels. Wi-Fi, the IEEE family is a set of standard such as a, b, and g and so on. Both b and g operates in 2.4 band uses direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM) respectively. On the other hand a uses OFDM and operates in 5 bandwidth b and 14 RF channels (11 in North America, 13 in Europe and 1 in Japan) each are spaced 5 apart with 22 in bandwidth, but most of them are over-laps each other. There are only 3 non-overlapping channels (typically 1, 6 and 11) a provides up to 23 non overlapping channels. Since Bluetooth, ZigBee and Wi-Fi uses 2.4 band so there must have frequency interference (collide) to minimize interference among them different technical strategy and suggestion have been made. Bluetooth 1.1 introduced adaptive frequency hopping (AFH) algorithm which dynamically allows Bluetooth to avoid channels occupied by DSSS system like zigbee and Wi-fi. AFH has intelligence to identify channel as bad, good and unknown. Bluetooth master periodically listen on bad channel to verify if the interference has disappeared; if so then the channel marked as good channel and removed from the look up table. Collision between two Bluetooth piconet is also minimal due to hopping nature of Bluetooth. Probability of interference between two Bluetooth piconet is 1/79. ZigBee faces serious interference problem in the presence of Wi-Fi (IEEE802.11b/g) networks. Musaloiu-E et al discovered that there is up to 52% of packet loss in multi hop sensor network due to interference of Wi-Fi network. They proposed an algorithm which is very effective to detect and avoid interference from networks, also able to successfully reduce packet loss from 52% to less than 1% [10]. If ZigBee uses a channel that overlaps with a heavily used Wi-Fi channel then up to 20% of packets will be retransmitted due to packet collisions. To avoid interference between and Schneider Electric s Innovation Department proposed two installation procedures [11]. Distance of Wi-Fi

7 6 interferers to ZigBee nodes should be at least 2 m. Frequency offset between both networks should be at least 30. According to their test setup daintree Networks says IEEE g networks have less impact on ZigBee than IEEE b networks due to less time spent on air. Network Size in a Bluetooth piconet, there can be at most 8 active devices (1 master and 7 slaves) but at park mode there could be more than 8 devices. In a ZigBee star network there could be more than devices and for a structured Wi-Fi BSS there may have 2007 devices. But all of these three protocols support complex networking such as scatternet of Bluetooth, cluster tree or mesh networking ZigBee and extended service set in Wi-Fi. Network joining time in a Bluetooth piconet, new slave joining time is 3 seconds, typically 20 seconds and a sleeping slave changes to active in 3 seconds and channel access time of an active slave is 2 milliseconds. On the other hand in ZigBee new device joining time is typically 30 milliseconds, sleeping slave changes to active in 15 milliseconds and active channel access time is typically 15 milliseconds. For Wi-Fi, a device takes 3 seconds to join in a network. Communication Range and Output Power of Bluetooth, Zigbee and Wi-Fi are harmonizing technologies. Bluetooth, Wi-Fi and ZigBee are short range wireless communication technology using the same frequency (ISM) band but ZigBee and Wi-Fi both are use same modulation scheme. Bluetooth and ZigBee are intended for WPAN communication while Wi-Fi is oriented to WLAN. Bluetooth refers to user s mobility and replacement of cable in a small scale application, ZigBee is more oriented toward remote control, sensing and automation. The transmission distance of ZigBee is from 10 to 70+ meters depending upon the output power and environmental characteristics where as Bluetooth and Wi-Fi is from 10 to 100 meters and 100 meters respectively. The distance of Bluetooth depends upon the power classes. The output power of the radios of ZigBee is normally 0 dbm refereed to 1 milli Watt (mw) and the maximum power output maintains the regulatory commission of each country. For Bluetooth maximum output power is 100mW (+20dBm) and the minimum output power is 1mW (0dBm). In the Wi-Fi the nominal output power is 20 COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI dbm means 100 mw. Data Rate and Power Consumption of Bluetooth represent 720 Kbps data rate and the peak data rate is 1Mbps where as Bluetooth Hs supports data rate approximately 24Mbps, works with large packet devices, higher data rate and higher power consumption than ZigBee. In contrast ZigBee represents 250 kbps data rate and the symbol rate is It has low data rate, low power consumption and works with small packet devices. And for Wi-Fi the data rate is 54 Mbps, higher data rate, higher power consumption than Bluetooth and ZigBee, largely used to provide high speed to the internet access or local area network. Figure 2.3: Comparison of the normalized energy consumption of each protocol. Wi-Fi provides higher throughput and covers a great distance and need higher power consumption on the other hand ZigBee and Bluetooth provide lower throughput and need low power consumption. Security of any wireless standard is included encryption, key management, and authentication method. Bluetooth uses the E0 stream cipher and CRC-16 where as ZigBee security based on 128-bit Advanced Encryption standard (AES) for encryption with counter mode (CTR) and 32-bit Message Integrity code (MIC) to assure message freshness. In Wi-Fi used RC4 stream cipher for encryption and CRC-32 is used for integrity. Any Wired Equivalent privacy (WEP) uses a

8 DAFFODIL INTERNATIONAL UNIVERSITY JOURNAL OF SCIENCE AND TECHNOLOGY, VOLUME 11, ISSUE 1, JANUARY single encryption key for all devices and packets but WEP is not safe, it can be broken in about one minute. Wi-Fi protected Access (WAP) was designed in order to replace WEP because of its weakness. WAP is used as master key for its cryptographic and security purposes. The IEE standard developed Wi-Fi protected Access2 (WAP2), i. e. IEEE i beyond WEP and decided to use Advanced Encryption standard (AES) for encryption which works in a counter mode (CTR). Also WAP2 uses a 128-bit key for all purpose (encryption and integrity), of which cipher block Chaining message authentication code (CBC-MAC) is employed. Table 2.3 Comparison among Bluetooth, ZigBee & Wi-Fi Standard Bluetooth ZigBee Wi-Fi IEEE a/b/g Specification Frequency Band / , 5 Max Data Rate 3 Mbps 250 kbps 54 Mbps Packet Length 1024 Bytes, 8-27 Bytes (BTLE) 22 Bytes 1024 Bytes Distance 10 m m 100 m Coverage Battery life Regular charging 1+ year Hourly charging Nominal TX 0-10 dbm (-25) dbm Power dbm Number of RF 79 1, 10, 16 14, 23 Channel Bandwidth Modulation Scheme GFSK Coexistence Mechanism AFH BPSK (+ASK, O-QPSK Dynamic Frequency Selection BPSK, QPSK, COFDM, CCK, M- QAM Dynamic Frequency Selection, Transmit power control Basic Cell Piconet Star BSS Extended Cell Scatternet Cluster Tree and Mesh ESS Max Number of Nodes Encryption 8 > E0 Stream Cipher AES Block Cipher (CTR, RC4 stream cipher (WEP), AES block counter cipher mode) Authentication Shared Secret CBC- MAC WPA2 ( i) (CCMP) Data 16-bit 16 bit 32-bit CRC protection CRC CRC Protocol High Low Medium Complexity Cost Medium Low High 6. Conclusion The goal of this paper is to focus the comparison among three (Bluetooth, ZigBee and Wi-Fi) short range wireless networks. A comparative study concerning data rate, power consumption, power output, communication range, coexistence and frequency range. The differences among these wireless standards depend on the design of architectural manufacturing. Though these three wireless technology using the same radio frequency (ISM) band but they contain different characteristics from the point of technological uses and design as well. And the suitability of network protocol is greatly influenced by practical applications. Acronyms BTLE (Bluetooth low energy), ASK (Amplitude Shift keying), GFSK (Gaussian frequency shift keying), BPSK/QPSK (Binary/quardrature phase shift keying), O-QPSK (Offset-QPSK), OFDM (Orthogonal frequency division multiplexing), COFDM (Coded OFDM), M-QAM (M-ary quadrature amplitude modulation), CCK (Complementary code keying), AFH (Adaptive frequency Hopping), FHSS/DSSS (Frequency hopping/direct sequence spread spectrum ), BSS/ESS (Basic/extended service set), AES (Advanced encryption standard), WEP (Wired Equivalent privacy), WPA (Wi-Fi protected access), CBC-MAC (Cipher block chaining message authentication code), CRC (Cyclic redundancy check). References [1] Bluetooth SIG, History of Bluetooth Technology HYPERLINK" History_of_the_SIG.aspx" SIG/pages/History_of_the_SIG.aspx, Accessed October 12, 2010 [2] Stallings, W., Wireless communications and networks, 2nd ed., Prentice Hall of India, New Delhi, 2006, p. 471.

9 8 [3] Stallings, W., Wireless Communications and Networks, 2nd ed., Pretice Hall of India, New Delhi, 2006, p [4] Bluetooth Specification Version EDR [vol 0], July 26, 2007 or [5] Bluetooth Specification Version HS [Vol 0], April 21, 2009 or [6] Bluetooth Specification Version 4.0 [Vol 0], June 30, [7] Aiello, R. Wireless Medium Access control (MAC) and physical Layer (PHY) Specifications for low-rate wirless personal Area Networks (WPANs), September 8, [8] Anonymous, The protocol stack and physical layer Protocol-Stack-and-Physical Layer, Accessed November 12, [9] Wireless Center, Point Coordination Function (PCF), http// COMPARISON AMONG SHORT RANGE WIRELESS NETWORKS: BLUETOOTH, ZIGBEE, & WI-FI.html, April [10] Musaloiu-E., R. and Terzis, A. (2008), Minimising the effect of Wi-Fi interference in wireless sensor networks, Int. J. Sendor Networks, Vol. 3, No. 1, pp [11] Gilles Thonet, Patrick Allard-Jacquin, and Pierre Colle. ZigBee - Wi-Fi Coexistence. Schneider Electric White Paper, April.2008 [12] E. Ferro and F. Potori, Bluetooth and Wi-Fi protocols: A survey and comparison, IEEE wireless commum., Vol. 12, no. 1, PP 12-26, Feb.2005 [13] Baker, N. ZigBee and Bluetooth: strengths and weaknesses for industrial applications, IEE Computing & Control Engineering, Vol. 16, no. 2, pp 20-25, April/May arnumber= &isnumber=31235