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    • Christopher Chidi ECE 4007 – Section L05: Professor Keezer Group: WaitLess Wireless Network Technology: Embedded Serial to Wi-Fi Modules
    • Introduction Wireless technology has become prevalent in modern society as it presents a solution to the dilemma of making life easier by breaking down the networking barriers of distance and mobility. In a study of the benefits of wireless LAN conducted in 2001[1], 87% of survey respondents credited WLAN to an increase in their quality of life due to the flexibility and mobility of wireless internet connectivity; moreover, WLAN has been attributed to a 22% productivity increase for end- users. The appeal of wireless networking has resulted in the vast expansion of WLAN infrastructure with millions of public, private, and commercial wireless access points dispersed around the globe [2]. Consequentially, the pervasive availability of wireless network access enables the potential for remote data transfer with a variety of electronic devices by means of embedded serial to Wi-Fi modules. For instance, security and surveillance systems employ serial to Wi-Fi modules to stream surveillance video from remotely mounted security cameras to wired network systems [1]. The following review provides an analysis of the features and cost effectiveness of Wi-Fi modules while highlighting the commercial applications of these devices. Commercial Applications of Wi-Fi Modules Application in Industry An increasingly popular application for Wi-Fi modules is in industrial monitoring systems. Emerson Process Management is among several instrumentation vendors developing wireless transmitters for industrial applications. The Rosemount 3051S Wireless Series of Instrumentation features WirelessHART and 802.11 Wi-Fi capabilities for their pressure, level, and flow transmitters [3]. Some of the advantages of the wireless transmitters include: the ability to install transmitters in distant or low accessibility areas, the elimination of the need for cable and conduit which reduces material and labor cost, and the capability of bidirectional interaction between the transmitter and network enabling the execution of preventative diagnostics and maintenance from a centralized location. The wireless output of the transmitters operates on either the 2.4 GHz frequency band with DSSS modulation or 900 MHz with FHSS modulation. The networking system does require the allocation of several transceivers / receivers, located several hundred feet apart, to route signals between the transmitters and hardwired gateways. Although the instrumentation associated with the Rosemount Wireless Field Networks are relatively expensive compared to their hardwire counterparts; as aforementioned, a significant amount of project costs are saved when eliminating the material cost of cable and conduit as well as the labor cost of cable mounting. 2
    • Chevron, for example, saved two-thirds of its quoted hardwire installation costs, or $60,000, in a recent installation of Rosemount wireless pressure transmitters for a steam injection service [4]. Comparison of Available Consumer Wi-Fi Modules As of early 2007, embedded serial to Wi-Fi modules have become readily available in public consumer markets. Each brand boasts similar features such as low power consumption and onboard wireless encryption or firewall security. The following section will investigate two embedded serial to Wi-Fi modules currently available on the market: the WiFly RN-111B 802.11b Wi-Fi “SuperModule” [5] and the Secure Socket iWiFi module [6]. The key feature of the WiFly device is its ultra low power module with 40 mA RX and 120 mA TX current usage, which can be supplied on as low as a 2-3V low power battery source. In addition, the module supports a low power programmable sleep function which reduces power consumption to approximately 12µA. The WiFly module is compatible with the IEEE 802.11b standard and interacts with serial devices by means of a RS232 serial port in conjunction with UART. Data transfer speeds range from 1200 bps up to 921 kbps. Other features include a real-time clock, WEP128 and WPA / WPA2 encryption, 500 KB of flash memory, 6 I/O pins, and 8 sensor inputs. The typical retail price of this Wi-Fi module is $69.95 [7]. The developers of the iWiFi module also boast low power consumption with a 190 mA RX and a 260 mA TX current usage supplied on a 3.3V power source. The Wi-Fi module supports a power save mode which reduces power consumption to approximately 8 mA. The iWiFi is compliant with IEEE 802.11b and 802.11g standards, and the module interacts with serial devices through a custom AT+i Serial Data Format or SerialNet mode. Data transfer speeds can reach up to 3 Mbps in serial mode. Other features of the iWiFi module include a random number generator, capability to send and receive textual or binary email with MIME attachments, retrieval of time data from a Network Time Server, WEP and WPA / WPA2 encryption, 10 TCP/UDP sockets, and two listening sockets. The retail price for the iWiFi module is $59.00; however, the antenna and cable are not included [8]. Despite the fact that the Secure Socket iWiFi module is $10.95 cheaper than the WiFly RN-111b, one must be cognizant of the significantly larger power consumption of the iWiFi module which translates to greater long term energy costs. Nevertheless, each device possesses its own set of advantages and disadvantages which may prove valuable for certain applications. Underlying Technology Technical Function 3
    • Embedded serial to Wi-Fi modules function as device servers bridging serial devices to 802.11b/g wireless LANs. The Wi-Fi modules utilize RS232 serial ports in conjunction with UART to interact with serial machines. Some Wi-Fi modules such as the iWiFi employ custom serial protocols [6]. Furthermore, the modules are equipped with programmable processor chipsets with an OS that coordinates the data transfer between serial and IP protocols. The Wi-Fi modules connect to wireless access points by utilizing a built-in wireless adapter. IEEE Wireless LAN Standards IEEE 802.11 contains a set of standards that govern WLAN implementation on the 2.4, 3.6, and 5 GHz spectrum bands. The two standards particular to embedded serial to Wi-Fi modules are the 802.11b and 802.11g standards, which are amendments to the original 802.11 standard. IEEE 802.11b proposes a modulation technique that maintains a throughput of 4.5 Mbps and a net bit rate of 11 Mbps. The 802.11g standard employs a modulation method similar to the 802.11a standard, and maintains a throughput of 19 Mbps and a net bit rate of 54 Mbps. The similarities between the 802.11 b and g standards are that both define modulation on the 2.4 GHz band and devices implementing these standards are prone to interference by other electronics operating on the spectrum band. The notable difference between the two standards is the capability of faster data transfer speeds on 802.11g devices. Implementation of Embedded Serial to Wi-Fi Modules The typical embedded serial to Wi-Fi module is designed for relatively simple installation. The connections involve a DB9 pass through serial cable that links the module to a serial port terminal. For most modules, power is supplied by a 4 -12 VDC unregulated, 3.3V regulated, or in some cases 2-3 V low power battery sources. Initially, users must configure the module by connecting to a PC and utilizing the provided installation software prior to connecting the module to a serial M2M device. A potential difficulty associated with the installation of a Wi-Fi module involves configuring the module for passing through a wireless network security gateway such as the Georgia Tech LAWN system. However, users can counteract this problem with adequate programming during device configuration. 4
    • Works Cited: [1] K. K. Fong, “Wireless Technology and Trend,” presented at WTIA ITSD Seminar, Hong Kong, China, Sept. 2002. [2] K. Jones and L. Liu, “What Where Wi: An Analysis of Millions of Wi-Fi Access Points,” presented at the IEEE Int. Conf. on Portable Devices, Orlando, Florida, May 25-29, 2007. [3] Emerson Process Management. Rosemount 3051S Specification Sheet. [Online]. Available: http://www.emersonprocess.com/smartwireless/index.asp [4] J. Moon. (2009, January 8). Emerson’s Wireless Technology Helps Chevron Improve Oil Field Personnel Safety and Increase Production. Your Industry News [Online]. Available: http://www.yourindustrynews.com/news_item.php?newsID=20538 [5] Roving Networks. WiFly RN-111b Specification Sheet. [Online]. Available: http://www.rovingnetworks.com/rn-111.php [6] Connect One Ltd. Secure Socket iWiFi Specification Sheet. [Online]. Available: http://www.connectone.com/products.asp?did=73&pid=61 [7] SparkFun Electronics. WiFly RN-111b Vendor Catalog. [Online]. Available: http://www.sparkfun.com/commerce/product_info.php?products_id=8869 [8] Mouser Electronics. Secure Socket iWiFi Vendor Catalog. [Online]. Available: http://www.mouser.com/Search/ProductDetail.aspx?qs=y%2f2LRhZeS3Gyt4nJwwXnlQ %3d%3d [9] IEEE Standard for Information Technology - Telecommunications and information exchange between systems - Local and Metropolitan networks - Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher Speed Physical Layer (PHY) Extension in the 2.4 GHz band. IEEE Standard 802.11b-1999, 1999. [10] IEEE Standard for Information Technology - Telecommunications and Information Exchange Between Systems - Local and Metropolitan Area Networks - Specific Requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Further Higher Data Rate Extension in the 2.4 GHz Band. IEEE Standard 802.11g-2003, 2003. 5