Wireless Sensor Networks Utilizing The Ieee 802.15.4 Standard In An Ecet Curriculum

Recently our Electrical Engineering Technology Baccalaureate Program at Penn State Erie, The Behrend College, was expanded to the Electrical and Computer Engineering Technology (ECET) Baccalaureate Program with options in both Electrical Engineering Technology (EET) and Computer Engineering Technology (CMPET). Based upon the TAC of ABET criteria for accrediting engineering technology programs, the ECET program must satisfy the criteria for both EET and CMPET programs. Thus networking concepts need to be included in both program options. In this paper, several laboratory applications utilizing low-rate wireless personal area network (LRPAN) technology are presented. This material can be included within one of several typical courses in EET curriculums (such as a communications or microcontroller course) as well as a networking course within CMPET curriculums. The device used for the laboratory applications is the MaxStream XBee wireless module, since it is compatible with the IEEE 802.15.4 standard. It uses a radio transceiver operating in the Industrial, Scientific, and Medical (ISM) RF band at frequencies from 2.400GHz to 2.484GHz. The standard device has a maximum outdoor line-of-sight range of 300 feet and a maximum data throughput of 250kbps with a UART interface. The device is intended to be used in conjunction with the internal RS-232 port found in most microcontrollers and computers for applications in wireless sensor networks and remote data collection. Several laboratory projects utilizing the MaxStream XBee wireless module are presented. The first lab is designed to introduce this module to the students. The objectives include interfacing the module to the computer serial port, using HyperTerminal to communicate with the module, configuring the module through AT commands, and verifying functionality of the module through file transfer. The second lab is designed to introduce remote data acquisition. Students will design a terminal program utilizing LabVIEW, integrate a temperature sensor, and perform remote data collection. The third lab will introduce students to personal area networking (PAN). The objective is the establishment of a wireless sensor network. It will utilize a star network configuration with temperature sensors and the development of LabVIEW software for remotely collecting temperature data and performing statistical analysis on the data. There are several primary objectives for the presentation of these applications within this paper. First, it presents suitable networking material to be included in one or more courses within the EET option of an ECET program as required by ABET. It can also be utilized in a typical networking course within CMPET curriculums. Second, it provides a resource to aid instructors interested in introducing wireless RF technology within their courses. Wireless Personal Area Networks P ge 13405.2 The IEEE 802.11 Working Group 1 defined wireless local area networks (WLANs) as a complement to the IEEE 802 wired local area networks (LANs). These networks were created for high-speed data communications. Wireless personal area networks (WPANs) were designed to function in a personal operating space, which extends up to 10m in all directions. Data rates are not greater than 250Kbps. WPANs were designed to carry data over short distances and involve little or no infrastructure. This enables devices utilizing WPAN technology to be small, power efficient, and inexpensive. The IEEE 802.15 Working Group 2 defined three classes of WPANs that are distinguished by categories that include data rate, battery drain, and quality of service (QoS). High-data rate WPANs (IEEE Standard 802.15.3) are used for multimedia applications that require very high QoS. Medium-data rate WPANs (IEEE Standard 802.15.1 – Bluetooth) are meant as cable replacements for consumer electronic devices such as mobile phones and PDAs. Low-data rate WPANs (LRWPANs – IEEE Standard 802.15.4) are designed for applications that include such areas as wireless sensors, home automation, automotive sensing, precision agriculture, etc. Wireless Sensor Networks Wireless sensor networks (WSNs) focus on enabling communication to sensors and actuators without the use of wires. The development of WSNs is primarily the result of three areas. First, there is a need to reduce the cost of sensor installation, which includes materials, labor, and testing. Then, cables require the usage of connectors that can get disconnected or break due to the need to access adjacent devices. Lastly, there is the desire to gather more frequent data on a large number of systems to improve industrial operations. WSNs provide flexible environments without the need for connectors and with improved operator safety. Some important characteristics for the design and implementation of WSNs are mentioned below. 3-4 ‚ Power Consumption: Some applications may require the usage of batteries. Thus, energy conservation is needed. A common solution is the usage of power cycling, in which the duty cycle of operation for the device is lowered. ‚ Range: RF power outputs ranging from 0dBm to 20dBm are typical for these devices. Due to the limited power, this reduces the maximum transmission distance between the transmitter and receiver. This requires the usage of multi-hop network protocols that are enabled through routing algorithms. ‚ Frequency Bands: RF spectrums are regulated by governments. However, there are special unlicensed frequency bands available for usage of devices that operate within a set of rules that govern the RF output in terms of time, frequency, and amplitude. The usage of these unlicensed frequency bands is free of charge. The frequency bands are shown in Table 1. In the U.S., the Federal Communications Commission 5 (FCC) regulates the RF spectrum. In Europe, the European Telecommunications Standards Institute (ETSI) coordinates regulatory efforts. Other countries have their own regulatory agencies, but many of them P ge 13405.3 accept either the FCC or ETSI as proof of compliance. ‚ Network Topology: Due to the limited transmit power which reduces the maximum transmission range, multihop networks are needed. In multihop networks, the message source and destination addresses are not necessarily within range, and communication may occur through intermediate devices that relay messages. This happens with devices that are configured as peer-to-peer. ‚ Self-organization: To enable ease of installation, WSNs need to be self-organizing. Thus, each sensor device can participate in the network automatically without the need for special addressing or association. This is a feature of ad hoc networks, which are collections of transceivers that create a network without the aid of any fixed infrastructure. These networks use routing protocols to transfer data from a source to a destination that may include intermediary devices. IEEE Standard 802.15.4 The objective of the IEEE Standard 802.15.4 is to enable low range, cost, power, and data rate wireless connectivity among inexpensive devices. There are several unique features of the standard. 3-4 ‚ Duty Cycle: The battery provides the energy for the communications. In order to minimize battery cost and maximize battery life, the energy must be taken at a low-rate. The standard allows devices to operate at duty cycles less than 1%. ‚ Modulation: For low cost implementation, only data communication is specified. Also, the protocol only supports half-duplex operation. The types of modulation supported along with the bit rates are shown in Table 1. Table 1. Frequency Bands and Modulation Parameters Freq Band # of Channels Bit Rate Modulation 868.0 – 868.6MHz 1 20Kbps Binary phase shift keying (BPSK) 100Kbps Offset quadrature phase shift keying (OQPSK) 250KBps Parallel sequence spread spectrum (PSSS) 902 – 928MHz 10 40Kbps Binary phase shift keying (BPSK) 250Kbps Offset quadrature phase shift keying (OQPSK) 250Kbps Parallel sequence spread spectrum (PSSS) 2.40 – 2.4835GHz 16 250Kbps Offset quadrature phase shift keying (OQPSK) ‚ Direct Sequence Spread Spectrum: Direct sequence spread spectrum (DSSS) is one way to increase the bandwidth of the transmit signal, while simultaneously reducing the power P ge 13405.4 spectral density. DSSS is achieved by applying a predetermined pseudo-random digital sequence to phase modulate the carrier. The signal is recovered in the receiver by using a replica of the pseudo-random digital sequence. The replica signal is generated in the receiver by a technique that maintains coherence with the transmitted signal. ‚ Transmit Power and Receiver Sensitivity: Devices that are compliant with the standard must be capable of transmitting at -3dBm, which is within the capability of low cost system-on-achip (SoC) implementations. For the 868MHz and 915MHz bands, the receiver sensitivity level is at -92dBm. For the 2.4GHz band, the sensitivity is at -85dBm. These sensitivity levels enable the use of simple receiver designs to achieve compliance with the standard. ‚ Network Components: Each network contains one network coordinator, called the PAN coordinator. It defines the structure and operating mode of the network. Other devices join the network by being granted permission from the PAN coordinator. Each network also contains at least one network device. The device can be defined as either a full function device (FFD) or a reduced function device (RFD). The FFD implements the complete protocol set and can function as a coordinator. The coordinator provides services to other devices of the network, such as acting as a proxy for devices outside the range of the PAN coordinator. The RFD implements only a portion of the protocol set. ‚ Network Topology: The network consists of one of two basic topologies: peer-to-peer network or star network. The star network has an FFD that functions as the PAN coordinator, which acts as a hub, and additional FFD or RFD devices that act as data t