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 endusers. 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.
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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 RN111b, 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
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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.
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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%3
d%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 802.11b1999, 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.
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