Wireless in Ohio.
In March 1998 the department at Trumbull County, Ohio, faced a dilemma. Its goal was to implement a wide area network, connecting the county buildings, city of Warren buildings, and the sheriff's department. The total number of locations was 30, most sites being within two miles from the central location, with the furthest remote site being 12 miles from the central site. In addition, the county wanted to establish an Internet connection at T-1 speed.
A panel of IS experts, headed up by Linda Sypert and Ray Chambers of Trumbull County's data processing department, was charged with finding the most cost-effective and reliable means of implementing the network. The members ruled out a fiber network due to economics and logistics issues in obtaining fights-of-way. Leasing T-1 lines also proved exorbitantly expensive. What the panel finally concluded was that the only viable way of achieving its objective was to build the network infrastructure on wireless LAN technology--specifically, spread-spectrum Ethernet radio. The added bonus was that the total project cost of installing a wireless WAN was substantially lower than the county had anticipated.
The county contacted Winncom Technologies, Inc. of Cleveland. Winncom is a worldwide distributor and integrator of wireless network products and systems for data and voice. Following a preliminary meeting with the county's IS specialists and their consultants, Winncom's engineers went to work on designing one of the most sophisticated wireless WANs in the state of Ohio.
The first order of business was to come up with a detailed implementation plan. Although most spread-spectrum LAN products are designed for quick and easy deployment, their installation in a WAN environment is not a trivial task. In designing and installing a reliable outdoor wireless network, a system integrator must follow these important steps:
1. Define the objective--i.e., type of data to be carried by the network, desired throughput, and network topology.
2. Conduct a detailed site survey. A proper site survey consists of the following elements:
* RF line of site (also known as Freznel zone) availability
* Path distance to each remote location
* Antenna elevation, location, and mounting method
* Location of radio equipment
* Cable lengths
* Level and sources of RF interference.
3. Determine the type and quantity of equipment to be used, including radios, antennas, cable, surge protectors, etc.
The first decision facing an integrator in designing a wireless network is what type of radio to use. Spread-spectrum radios are generally divided into two categories--direct sequence (DS) and frequency hopping (FH). Although the debate over the advantages and disadvantages of FH vs. DS modulation is still going, there are fairly simple rules to follow in selecting the right device for a specific application. In general, DS provides higher data throughput over longer distances in environments with low-to-moderate amounts of RF interference. FH is better suited for high-interference areas, such as downtown or where radio co-location is required to achieve a desired aggregate throughput. Due to RF channel spacing, the maximum number of co-located DS radios is three. Using FH devices, up to 12 radios can be co-located without experiencing a significant degradation in performance. Proper antenna selection and placement are critical, regardless of the radio type used.
For Trumbull County, the engineers chose two different FH Ethernet bridges. The main selection criteria included a downtown location, path distance, and co-location requirement. The multipoint short-range bridge was selected for distances less than two miles. For longer-distance backbone applications, a point-to-point radio was specified. Both radios exceed T-1 speeds in Ethernet applications. The two radios at the central site were set up in a redundant "hot-standby" mode, ensuring against single-point system failure. A separate point-to-point link to a local ISP, half a mile away from the administration building, took care of Internet connectivity at a blazing 1.6 Mbps throughput.
The antenna type is even more important than the type of radio used. It is critical to identify harmful in-band interference by using a spectrum analyzer and to select an antenna to minimize or eliminate the effects of such interference. Using the wrong antenna may render the link useless. In the city of Warren, a frequency scan showed a source of interference in the 2.4 GHz band. The interference was coming from a wireless cable tower approximately 10 miles from the proposed central location. Although the engineers concluded that the interference did not present a significant problem for a FH radio, the team decided to change polarization of antennas to avoid potential degradation in wireless network performance. At the central and repeater sites, a combination of omnidirectional and directional antennas was used to achieve the necessary coverage and maximum RF channel separation. The omnidirectional antenna of choice was Winncom's 13.5 dBi horizontal polarity Omni. It is a unique antenna, highly suitable for challenging applications due to its high gain and horizontal polarization. The directional antennas were 24 dBi parabolic grids. The grid is an inexpensive antenna with excellent long-range stability. Distances in excess of 60 miles have been achieved with this antenna in point-to-point applications.
Initially, the project was divided into several phases. At the present time two phases have been completed with absolute success. Total installation time was five days. Compare this number to six months for leased lines and five years for a fiber network! Despite a high concentration of radios in the center of the city, the network is performing flawlessly with plenty of spare capacity for future expansion--a tribute to proper planning and execution. Implementing the wireless WAN is saving the county tens of thousands of dollars annually.
Circle 273 for more information from Winncomm
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|Title Annotation:||Technology Information; OH; Winncom Technologies' wireless WAN for Trumbull County,|
|Date:||Jan 1, 1999|
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