2011 17th Asia-Pacific Conference on Communications (APCC) 2nd – 5th October 2011 | Sutera Harbour Resort, Kota Kinabalu, Sabah, Malaysia
A Comparative Study of Short Range Wireless Sensor Network on High Density Networks Mahdi Zareei1*, Azar Zarei2, Rahmat Budiarto3, Mohd. Adib Omar4 1, 3, 4
School of Computer Sciences, Universiti Sains Malaysia, Penang, Malaysia 2 1
Jahad Daneshgahi University, Hamedan, Iran
*
[email protected], (3rahmat, 4adib)@cs.usm.my
Abstract—ZigBee, Wibree, Z-Wave, and RuBee are four protocol standards for short range wireless communications with low power consumption. From an application point of view, ZigBee is designed for reliable wirelessly networked monitoring and control networks, RuBee is proposed for high security applications and use in harsh environment, Wibree considered for sports and healthcare while Z-Wave is planned for residential control systems. In this paper, after an overview of the mentioned four short-range wireless protocols, we attempt to make a preliminary comparison of them and then specifically study their radio frequency, data coding, security etc. At last we have compared different protocols capabilities in high density network. Keywords-Wireless Sensor Netwrok; ZigBee; RuBee; Wibree; Z-Wave;
I.
INTRODUCTION
Wireless sensor networks (WSNs) are compact-size, low power, inexpensive devices which are capable of measuring local environmental conditions or other parameters and forward such information to a sink for proper processing. WSNs have a wide range of applications such as environmental monitoring [1], biomedical research [2], human imaging and tracking [3], and habit monitoring [4]. Recently, WSNs receive significant attention from industry, academia and standard development organization. There are several protocols for wireless sensor networks available. The characteristics of these solutions (e.g. data rate, power use, frequency band, networking capabilities) vary making the selection for a specific application difficult. Due to increasing the demand of using wireless sensor networks, study on the high density network must have taken more into consideration. Because of the crowd dispersal, large number of the sensors and the high rate of data transition, there are some factors that should be considered more in high density network, such as the economic vision and the security of the system as it is transferring lots of data. Due to support the coverage area, having a high data rang is advisable, also Low power consumption and having a long life battery are important factors in WSN. This work focuses the comparison of different wireless protocols along with its capability to implementing on high density network. The remainder of the paper is organized as follows: Section II briefly introduces the wireless protocols including ZigBee, RuBee, Wibree, and Z-Wave. Next, we analyze and compare the short distance wireless communication protocols in Section III. Finally, we conclude our paper in chapter IV.
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II.
WIRELESS SENSOR NETWORK APPLICATIONS
This section introduced ZigBee, RuBee, Wibree, and ZWave protocols which correspond to WPAN networks. The information discussed in this section is widely available in the literature. Hence, the major goal of this paper is not to contribute to research in the area of wireless standards, but to present a comparison of the six main short-range wireless networks. A. ZigBee ZigBee is short range wireless technology based on the IEEE 802.15.4 standard for WPAN (Wireless Personal Area Network) which implements low-cost, low-data-rate wireless network with long battery life. It is useful for setting up WPANs of service enabled devices. Also, ZigBee allows the enable nodes to talk together, regardless of manufacturer. The ZigBee standard was developed by the ZigBee Alliance [5], which is an association of companies collaborating together to enable reliable, cost-effective, lowpower, wirelessly networked monitoring and control products based on an open global standard, which has hundreds of member companies, from the semiconductor industry and software developers to original equipment manufacturers (OEMs) and installers. The ZigBee Alliance was formed in 2002 and it is open to everyone who wants to join, as it is a nonprofit organization. The ZigBee standard has adopted IEEE 802.15.4 as its Physical Layer (PHY) and Medium Access Control (MAC) protocols [6, 7] (Figure 1). B. RuBee RuBee is a bidirectional, on-demand, peer-to-peer network protocol that uses long wavelength transceiver mode under 450 kHz [8]. This protocol can support network with thousands of tags within area range of 3 to 15 meters, also battery life can extend up to 10 years. Companies such as IBM, Sony, Metro, Panasonic, Motorola and NCR supported the RuBee for its ability to work in harsh environment such as near steal or water and around corners, where ZigBee or RFID is not applicable. On 11 February 2009, the IEEE Standards Association approved P1902.1 project-Standard based on RuBee protocol [9]. P1902.1 standard also have a “real-time, tag searchable” protocol for RuBee tags, using IP like addresses and subnet addresses linked to asset taxonomies which will allow tags to have unique “.tag” URLs associated with them and tag data may be viewed as a stand-alone, web server from anywhere in
Figure 2. Wibree protocol stack
Figure1. ZigBee protocol stack the world. Each RuBee tag, if properly enabled, can be discovered and monitored over the Internet using popular search engines (e.g., Google) or via Visible Asset's ".tag" Tag Name Server [10]. C. Wibree Wibree is a digital radio technology with ultra-low power consumption, low-cost intended to become open standard for application and devices within short range (10 meters). On October 3rd, 2006, Nokia introduced Wibree technology as an open industry initiative extending local connectivity to small devices, which is supported by a group of leading companies such as Broadcom, CSR, Epson, Nordic and so on [11]. As of June, 2007 Wibree is known as Bluetooth ultra-low power, in 2008 renamed Bluetooth low energy [12]. Nokia’s Wibree solution has two implementation alternatives: Stand-Alone Chip and Bluetooth-Wibree DualMode Chip. The stand-alone chip is well suited for applications where only small quantities of data are transferred such as for watches and sports sensors [13] and the BluetoothWibree dual-mode chip is designed for use in Bluetooth devices [11] (Figure 2). Therefore, for minor incremental cost, Wibree functionality can be integrated with Bluetooth by utilizing key Bluetooth components and the existing Bluetooth RF. Link layer specification in Wibree provides simple device discovery, reliable point-to-multipoint data transfer and ultralow power idle mode operation with advanced power-save and encryption functionalities. D. Z-Wave Z-Wave is a wireless networking protocol developed by ZenSys (now a division of Sigma Designs) and promoted by the Z-Wave Alliance for a 908.42MHz or 868.42MHz frequency operation [14]. This is a low-power wireless technology designed specifically for automation in residential and light commercial environments. It is largely impervious to interference from common household wireless electronics,
such as Wi-Fi routers, cordless telephones and Bluetooth devices that work in the same frequency range. Z-Wave protocol defines a two way radio system (Figure 3) which operates at 908MHz. Therefore, it uses a data rate of just 9.6Kbps originally and is extended later to 40Kbps. It focuses on these small amounts of data applications such as lighting and appliance control, HVAC, access control, intruder and fire detection etc. Z-Wave is currently supported by over 160 manufacturers worldwide and appears in a broad range of consumer products in the U.S. and Europe [15]. III.
COMPARATIVE STUDY
Table 1 summarizes the main differences among the six protocols. In general, all these protocols intended for short range communication (about 10m), however, ZigBee and ZWave can reach more distance in some applications. A. Technical Aspectsd 1) Radio frequency and channel coding ZigBee and Wibree protocols operate in the 2.4 GHz band, which is unlicensed in most countries and known as the industrial, scientific, and medical (ISM) band. Also, ZigBee uses direct sequence spread spectrum (DSSS) with 16 channels and 2 MHz bandwidth [10], however, Wibree defines 40 channels with 2 MHz channel spacing and the signal bandwidth is 1 MHz. and use FHSS [7]. The RuBee standard specifies a single fixed frequency of 131.072 kHz with Biphase Mark Coding [16]. While Z-Wave operates at 908MHz (U.S.) and 860MHz (Europe) in unlicensed ISM bands on only one channel and use Manchester channel encoding [14]. 2) Data rate and data range ZigBee is limited at 20 Kbps, allows an increased range until a maximum of 75 meters. RuBee that runs at speeds of 300 to 9,600 Baud can achieve a read range of 30 meters. Wibree Supported communication rates of up to 1 Mbps and communication range is 5-10 meters (Figure 4). Meanwhile, Z-Wave uses a data rate of just 9.6 Kbps originally and is extended later to 40 Kbps with a range of approximately 30 meters depending on environment.
TABLE 1. COMPARISON OF RFID, ZIGBEE, RUBEE, WIBREE, Z-
3) Modulation & Access mode There are three modulation types for ZigBee: binary phase shift keying (BPSK), amplitude shift keying (ASK) and offset quadrature phase shift keying (O-QPSK) [7]. In BPSK and OQPSK, the digital data are in the phase of the signal. In ASK, in contrast, the digital data are in the amplitude of the signal [7]. ZigBee also implements a simple method to allow multiple devices to use the same frequency channel for their communication medium. The channel access mechanism used is Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) [7]. RuBee standard specifies a single fixed frequency of 131.072 kHz with either amplitude or binary phase shift modulation and biphase mark coding [17]. Wibree modulation will be GMSK (Gaussian minimum shift keying—a small change from the Bluetooth case). For co-existence of multiple devices, connection setup channel access method is CSMA and for data delivery FDMA. For jamming avoidance FDMA is used [18]. Z-Wave using frequency shift keying (FSK) modulation [14]. ZigBee supports 64-bit and 16-bit addressing, whereas ZWave supports only 8-bit addressing. Therefore, in a single ZWave network, there can be up to 232 nodes, over 65000 for a ZigBee star network [7] and Wibree devices use 48-bit addresses [19]. The maximum number of devices belonging to the network’s building cell is 8 (7 slaves plus one master) For a UWB piconet and Wibree piconets, while RuBee use an 8 nibble address (32 bit) [16].
Power Security
Figure 3. Z-Wave protocol stack
Network
Technical Aspect
WAVE AND UWB PROTOCOLS ZigBee
RuBee
Z-wave Zensys Corp.
Standard
IEEE 802.15.4
Frequency (Hertz) Data rate (kb/s) Data Range Modulation Type
2.4G/915 M 20-250 75 m BPSK QPSK
131K
2.4G
9.6 15 m
1000 10 m
908M/86 0M 9.6 100 m
BPSK
GMSK
FSK
Chanel Coding
DSSS
Biphase Mark Coding
FHSS
Manches ter NRZ
Access Mode
CSMA/C A
N/A
CSMA FDMA
N/A
Network (nodes)
64000
8
8
232
size
IEEE P1902.1
Wibree Bluetoot h (IEEE 802.15.1 )
Network Topology
Mesh, ad hoc , star
peer-topeer
Encryption
AES 128
AES
Data protection
16-bit CRC 15mW
Power consumption
Ad hoc , point to point, star AES 128
Mesh (TDES)
N/A
24-bit CRC
N/A
40 nW RF600 mG magnetic
15 mA
1mW
piconets (these piconets are limited to 8 devices), where a master device controls multiple slaves [20]. C. Security: Encryption and data protection For securing of the network, ZigBee uses the National Institute of Standards and Technology (NIST) Advanced Encryption Standard (AES). This protocol AES-128, is a block cipher that encrypts and decrypts packets in a manner that is very difficult to crack. It’s one of the best-known and well-respected standards [21]. ZigBee also uses Direct Sequence Spread Spectrum (DSSS) to spread the packets into symbols and reassemble them at the other end, verifying that the data were decoded correctly through use of a 16-bit CRC [21]. This protocol uses a 16-bit CRC on each packet, called a Frame Checksum (FCS). This ensure that the data bits are correct [21].
B. Network size and Topology All the protocols have a provision for more complex network structures built from the respective basic cells: the peer-to-peer for UWB and RuBee, cluster tree or mesh networks for ZigBee. Similar to ZigBee, Z-Wave supports mesh networking, broadcasting, and multicasting. Wibree does not support mesh networking so it operates primarily in ad hoc Figure 4. Comparing data rate vs. data range
According to Stevens [22], because RuuBee tags have a CPU static memory (SRAM), high content mask m ROM, a date and time (clock) therefore it can use optionall advance bit swap keys/data algorithms, to rewrite a secure woord once every 10 minutes. This can guarantee RuBee taags from reverse engineering or cloning tags’ pedigree. Besiddes bit swapping is very hard with EEPROM, due to long write times, high power M RuBee consumption, and limited read/write life. Moreover, tags use Real-Time AES-128 encryption. RuBee R Real-Time Range Management makes eavesdroppingg difficult. Also, RuBee tags have a clock they can optionally use single keys or (One Time Pads) OTP [23]. Wibree is a PAN radio intended for applications and devices with low-power constraints. Thus, the security and privacy mechanisms have been scrutinized with this in mind [24]. Session confidentiality is provided byy AES encryption, used in counter mode. One AES block per packet is used to e sessions initiate keys for a keyed checksum that for encrypted replaces a CRC checksum deployed in plaain-text link-layer PDUs [19]. Wibree also supports plain-texxt communication (24 bit CRC ) [25]. However, Z-Wave relays on the Triplee Data Encryption Standard (TDES) [26]. The Data Encryption Standard (DES) is considered insecure for many applicationss due to small key size (56 bits). Triple DES uses DES three times to improve security. DES is superseded by the Advanced Encryption Standard (AES). D.
Consuming only a fractionn of the power, enabling small, inexpensive implementations as a well as easy integration with Bluetooth solutions, makes Wibree W as a new solution for a short range, very mobile com mmunication to transfer medium amount of data. In order to minimize the power consumption low duty w an efficient radio and cycle operation combined with streamlined protocol. Typiccal stand-alone Wibree chip operations – for example sportts watch communicating with a heart rate monitor – demand duuty cycles of less that 1%. When transmitting, the chip’s powerr consumption will be less than 15 mA (around 10 to 25% thatt of a Bluetooth chip), dropping to around 30 μA in standby moode, and 900 nA in sleep mode. It has been discussed, due to shhort range (
