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Zigbee is synonymous with the IEEE 802.15.4 protocol. According to the agreement of the technology is a short distance, low-power wireless communication technology. The name comes from the bee character dance, as bees (bee) is flying by and the "buzz" (zig) shake the wings of the "dance" to transfer pollen with peers where the position information in such a way that bees rely on constitute a group communication network. Its characteristics are close, low-complexity, self-organizing, low power, low data rate, low cost. Mainly suitable for automatic control and remote control, can be embedded in various devices. In short, ZigBee is a cheap, low-power short-range wireless network communication technology group.
Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) QoS measurement of Zigbee home automation network using various modulation schemes Gurjit Kaur Faculty ECE Deptt. Rayat Polytechnic College Distt. SBS Nagar, Punjab email@example.com Kiran Ahuja Faculty ECE Deptt DAVIET Distt. Jalandhar, Punjab firstname.lastname@example.org ABSTRACT Increased demands on implementation of wireless sensor networks in automation praxis resulted in relatively new wireless standard – Zigbee. The IEEE 802.15.4 standard specifies the multiple PHYs for 868, 915 and 2400 MHz three frequency bands. In this paper we presents the performance analysis of different modulation schemes at different frequency range like ASK, BPSK and QPSK at 868, 915 & 2400 MHz based on their effect on the quality of service parameter by using CBR application in Zigbee home automation network using static IEEE 802.15.4. The QoS parameters such as average end-to-end delay, jitter, and throughput are investigated as the performance metrics. The results show that even though ASK at 868 MHz gives the highest throughput of 100% which is highest amongst all five modulation schemes but still overall ASK at 915 MHz is the best suited modulation schemes for CBR application of Zigbee home automation since it produced lowest jitter value of 0.03s and lowest average end-to-end delay value of 3.30s which are both favorable conditions for better performance of CBR application of Zigbee home automation network. Keywords ASK, QPSK, BPSK, HOME AUTOMATION, CBR. 1. INTRODUCTION The rapid progress of wireless communication and embedded micro-sensing MEMS technologies has made wireless sensor networks (WSNs) possible. A WSN consists of many inexpensive wireless sensors capable of collecting, storing, processing environmental information, and communicating with neighbouring nodes. Applications of WSNs include wildlife monitoring, object tracking, and dynamic path finding [1,2]. Recently, many WSN platforms have been developed, such as MICA and Dust Network. For interoperability among different systems, standards such as Zigbee/IEEE 802.15.4 [ 3] protocols have been developed. Zigbee/IEEE 802.15.4 specifies a global standard on physical, MAC, and network layers for WSNs requiring high reliability, low cost, low power, scalability, and low data rate. To meet these challenges, IEEE 802.15.4  low rate wireless personal area network (LR-WPAN) standard has been introduced. The goal of the IEEE 802.15.4 standard is to provide a highly reliable protocol for wireless connectivity among inexpensive, fixed and portable devices . These devices can form a sensor network or a Wireless Personal Area Network (WPAN). Thus it suits wireless sensor network applications where a large number of tiny smart sensors having the low power, low range, and low bandwidth are deployed in an ad hoc manner for the purpose of automation. Zigbee is a relatively new technology for short-range wireless networking, which has low-power consumption, low latency, and low cost. It is able to provide a transfer rate of up to 256 Kbps at 2.4 GHz within 10 m. It has a maximum power consumption of 30mW when transmitting short-range data which allows a single battery to power one Zigbee device from months up to years. ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1589 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) This paper provides the performance analysis of different modulation schemes like ASK, BPSK and QPSK at 868, 915 and 2400 MHz by measuring quality of service parameters such as average end-to-end delay, jitter and throughput on the Zigbee home automation using static IEEE 802.15.4 star topology. The rest of the paper is organized as follows. Section 2 discusses related works for performance evaluation of IEEE 802.15.4 topology in various simulation environments. The overview of Zigbee and IEEE 802.15.4 frequency range is discussed briefly in Section 3. Simulation set up has been discussed in Section 4. Simulation results have been discussed in Section 5. Finally, we conclude our work in Section 6. 2. RELATED WORK According to our best knowledge, there exist only few articles  that analyze mathematically or simulate the performance of IEEE 802.15.4. The performance of IEEE 802.15.4 in a star network with 100 nodes was analyzed in . The paper contained a compact mathematical analysis of average power consumption and transmission failure rate. The analysis was complemented with real measurements of steady state powers and transient energy, and switch times from a standard compliant evaluation board. A special contribution was bit error rate measurements with two evaluation boards connected through a set of calibrated attenuators. The operational analysis considered mainly the effect of path loss and packet size on energy consumption. J. Zheng and M.J. Lee  implemented the IEEE 802.15.4 standard on NS2 simulator and provided the comprehensive performance evaluation on 802.15.4. The literature comprehensively defined the 802.15.4 protocol as well as simulations on various aspects of the standard. It mainly confined to performance of IEEE 802.15.4 MAC. The authors provided performance evaluations of IEEE 802.15.4 MAC in beacon-enabled mode for a star topology . The performance evaluation study revealed some of the key throughput-energy-delay tradeoff inherent in IEEE 802.15.4 MAC. The performance of IEEE 802.15.4 was analyzed for medical sensor body area networking . The analysis considered quite extensively a very low data rate star network with 10 body implanted sensors transmitting data 1 to 40 times per hour. The analysis focused on the effect of crystal tolerance, frame size, and the usage of IEEE 802.15.4 Guaranteed Time Slots (GTS) on a node lifetime. For analyzing the standard performance in WSN applications, further analysis with larger and more complex network topologies and other IEEE 802.15.4 MAC parameters would be required. The authors presented a novel mechanism intended to provide Quality of Service (QoS) for IEEE 802.15.4 based Wireless Body Sensor Networks (WBSN) used for pervasive healthcare applications . The mechanism was implemented and validated on the Aquis Grain WBSN platform. The performance simulations of IEEE 802.15.4 in a star network were presented . The network consisted of 49 nodes configured to IEEE 802.15.4 beacon-enabled mode. The evaluation considered latency and energy with different amounts of background traffic. Also, the performance of IEEE 802.15.4 GTS and beacon tracking were simulated. Still, the applicability of the results for WSN applications was insufficient, since larger network sizes with cluster tree network topologies were required. 3. ZIGBEE WIRELESS NETWORK Zigbee is a group of protocols which is developed based on IEEE802.15.4 wireless communication standard.[13,14] The goal of the standard is to meet the requirements for wireless home control, industrial automatic control and remote control. It can be built in most of instruments and also support geographical position. IEEE802.15.4 is a low rate wireless Personal Area Network standard developed by IEEE. It defines the two lower layers Physical layer and MAC layer. High level application, test and marketing promote are charged by Zigbee alliance. Zigbee alliance was established in October, 2002. It consists of Holland Philips semiconductor company, US Motorola, UK Invensys and Japanese Mitsubishi electric company and more. At present, the number of members is over 175, which includes world leading semiconductor manufacturers, technology providers, OEMs and end-users . A complete Zigbee protocol set is made of high level application specification, application support sub-layer, network layer, MAC layer and physical layer. To minimize the effects of interference, 802.15.4 uses direct sequence spread spectrum. The standard defines two PHY layers suitable for three different frequency bands, ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1590 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) 868 MHz (Europe), 915 MHz (USA) and 2.4 GHz (Worldwide) . The two physical data package are of the same format but of difference in work frequency, modulation technique, PN-code length and transmission rate. 2.4GHz physical layer could offer 250kb/s transmission rate by using high order modulation technique, which is helpful to gain higher handling capacity, shorter transmission delay and work circle. Thus it can save more energy. Table I: Frequency bands and data rates Physical Frequency Channels Bit rate Modulation layer Band (Kbits/s) 868/915 868-870 0 20 BPSK MHz MHz 902-928 1-10 40 BPSK MHz 2.4 GHz 2.4-2.4835 11-26 250 O-QPSK GHz The stack above the network layer is defined by Zigbee alliance, it includes network layer and application layer standard. The network layer supports three topologies: star, cluster tree, mesh topology. Additionally it defines the Security Service Provider (SSP) that handles encryption and access control lists (ACL) to ensure secure communication. The complete Zigbee stack architecture is shown in Figure.1 Figure 1: Zigbee architecture  Zigbee networks use three device types : The network coordinator maintains overall network knowledge. It is the most sophisticated of the three types and requires the most memory and computing power. The full function device (FFD) supports all 802.15.4 functions and features specified by the standard. It can function as a network coordinator, Additional memory and computing power make it ideal for network router functions. The reduced function device (RFD) carries limited (as specified by the standard) functionality to lower cost and complexity. 4. SIMULATION SETUP The main objective of this simulation study was to analyze the effect of different modulation schemes like ASK (Amplitude shift keying), BPSK (Binary phase shift keying) & QPSK (Quadrature phase shift keying) on the ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1591 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) performance of Zigbee home automation using static IEEE 802.15.4 star topology for varying parameters. The simulations have been carried out using QualNet version 5.0, software which provides scalable simulations of wireless networks. In the simulation model, a star topology with one PAN co-ordinator, one PDA (personal digital assistants), and 10 devices are uniformly deployed in an area of 1500m x1500m. PAN is static mains powered device placed at the centre of the simulation area. Only the uplink traffic i.e. devices to PAN co-ordinator are considered in the simulations which suits WSN application like automation industry where a large number of devices communicates to a single sink server for data delivery and processing. The transmission range of devices is one hop away from PAN Coordinator in star topology. The fact that BO (Beacon order) = SO (super frame order) assures that no inactive part of the super frame is present . A low value of this parameter implies a great probability of collisions of beacon frames as these would be transmitted very frequently by coordinators. Figure2: Simulation setup of Zigbee home automation network On the contrary, a high value of the BO (beacon order) introduces a significant delay in the time required to perform the MAC association procedure since channel duration which is a part of association procedure is proportional to BO (beacon order). In our simulation model, function for acknowledging the receipt of packets is disabled. It is due to the fact that overhead mechanism is too expensive for low data rate WSN application for which 802.15.4 is designed. Following QoS performance metrics were used to evaluate QoS parameters for IEEE 802.15.4 star topology using different modulation scheme: Jitter is often known as a measure of the variability over time of the packet latency across a network. A network with constant latency has no variation (or jitter). Packet jitter is expressed as an average of the deviation from the network mean latency. Jitter refers to a variation in packet delay, resulting in differing packet inter-arrival times or out-of-sequence packets or both Average End-to-End delay indicates the length of time taken for a packet to travel from the CBR (Constant Bit Rate) source to the destination. It represents the average data delay an application experiences during transmission of data. The end-to-end delay is the time taken for a data packet to reach the destination node. The delay for a packet is the time taken for it to reach the destination. And the average delay is calculated by taking the average of delays for every data packet transmitted. The parameter comes into play only when the data transmission has been successful. Packet Delay= (Receive Time at Destination) – ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1592 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) (Transmit Time at Source) Average Delay= (Sum of all Packet Delays)/( Total Number Of Received Pkts) (16) Throughput is the number of bits passed through a network in one second. It measures how fast data can pass through an entity (such as a point or a network). The throughput of a node is measured by first counting the total number of data packets successfully received at the node and computing the number of bits received, which is finally divided by the total simulation runtime. The throughput of the network is finally defined as the average of the throughput of all nodes involved in data transmission. Therefore, throughput can be stated as: Throughput of a Node = (Total Data Bits Received) / (Simulation Runtime) Similarly the throughput for the network can be defined as: Network Throughput = (Sum of Throughput of Nodes Involved in Data Trans.) / (Number of Nodes) (17) 5. PERFORMANCE ANALYSIS This section presents the simulation results to show the impact of various QOS metrics on different modulation scheme like ASK, BPSK & QPSK at different frequency range by using CBR application on Zigbee home automation network having static IEEE 802.15.4 star topology. Figure3: QualNet animation during simulation execution of Zigbee auto home The following table depicts comparison of modulation schemes at different frequency range based on CBR applications on the application layer. ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1593 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) Table II: Comparison of different modulation using CBR application in Zigbee home automation network Modulation Thruou- Avg. end Jitter schemes gput to end delay QPSK 95 3.32 0.43 (2.4GHz) BPSK 92 3.59 0.05 (915MHz) ASK 95 3.30 0.03 (915MHz) BPSK 94 7.90 0.67 (868Hz) ASK 100 10.07 0.98 (868MHz) Figure 4 shows the value of jitter for different modulation schemes. The ASK (amplitude shift keying), BPSK (binary phase shift keying) modulation technique at 915MHz frequency produced the lowest value of 0.03s and 0.05s, QPSK produced high value of 0.43s, and BPSK and ASK at 868 MHz frequency produced highest value of 0.67s and 0.98s respectively. So, in terms of jitter ASK at 915 MHz frequency performs better than other modulation scheme since low jitter corresponds to high efficiency. JITTER 1.2 1 JITTER(s) 0.8 0.6 0.4 0.2 JITTER 0 QPSK BPSK ASK BPSK ASK (2.4GHz) (915MHz) (915MHz) (868MHz) (868MHz) MODULATION SCHEME Figure 4: Impact of Jitter on various modulation scheme using CBR application of Zigbee auto home Figure 5 shows the performance of average end-to-end delay for different modulation scheme at different frequency ranges. The average end-to-end delay of a packet depends on delay at each hop comprising of queuing, channel access and transmission delays as well as route discovery latency. BPSK at 915 MHz produced average end-to-end delay value of 3.59s, QPSK and ASK at 915 MHz produced a significantly low value of 3.32s and 3.30s whereas BPSK and ASK at 868 MHz produced higher values of 7.90s and 10.07s respectively. So, in terms of average end-to-end delay ASK at 915 MHz frequency performs best since low average end-to-end delay would lead to faster performance. ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1594 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) Avg. end to end delay 12 Avg. end to end delay(s) 10 8 6 4 Avg. end to 2 end delay 0 QPSK BPSK ASK BPSK ASK (2.4GHz) (915MHz) (915MHz) (868MHz) (868MHz) MODULATION SCHEME Figure5: Impact of Average end to end delay on various modulation schemes using CBR application of Zigbee auto home Figure 6 presents the performance of throughput for different modulation techniques at different frequency range. According to our findings, BPSK at 915MHz produced a throughput value of 92%, BPSK at 868MHz 92%, QPSK, and ASK at 915MHz 95%, and ASK at 868MHz 100%. According to throughput results, ASK at 868 MHz performs best since it produces more output as compared to other modulation schemes. Throughput 102 THROUGHPUT(bits/s) 100 98 96 94 92 Throughput 90 88 QPSK (2.4GHz) BPSK ASK (915MHz) BPSK ASK (868MHz) (915MHz) (868MHz) MODULATION SCHEME Figure 6: Impact of throughput on various modulation scheme using CBR application of Zigbee auto home 6. CONCLUSION This paper has presented a preliminary performance study of the IEEE 802.15.4 wireless standard via simulation results. Results show the effects on QoS parameter by using different modulation schemes at different frequency range like ASK, BPSK and QPSK by using CBR application in Zigbee home automation network having static IEEE 802.15.4 star topology. Quality of service metrics (average end-to-end delay, throughput, jitter) are used to compare to different modulation schemes. The findings suggest that although ASK at 868 MHz produce a little higher throughput than all other modulation schemes which makes it a suitable choice for Zigbee home automation network but still ASK at 915MHz is the best suited protocol for CBR application of Zigbee home automation network because of the fact that ASK at 868 MHz throughput value is not significantly higher than ASK at 915MHz. Also, ASK at 915 MHz performs better overall and produce less jitter and average end to end delay as compared to all other modulation schemes. ISSN : 0975-5462 Vol. 3 No. 2 Feb 2011 1595 Gurjit Kaur et al. / International Journal of Engineering Science and Technology (IJEST) 7. REFERENCES  Y.-C. Tseng, S.-P. Kuo, H.-W. Lee, and C.-F. uang Location tracking in a wireless sensor network by mobile agents and its data fusion strategies. In Proc. of Int’l Sympon Information Processing in Sensor Networks (IPSN), volume 2634, pages 625-641, 2003.  Y.-C. Tseng, M.-S. Pan, and Y.-Y. Tsai. 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