Wireless Surveys
BIAS Technology are also fully skilled in the installation, commissioning and support of Wireless data networks (WLan), our engineers are Cisco trained. We are fully equipped and resourced to conduct site surveys for new and enhancing existing wireless networks.
Background to RF Networks
The Wireless Advantage
When a computer system has to share information around several terminals, it is interconnected by means of a network. This usually consists of Ethernet cabling being installed.
However, some situations are not well suited to having cable running between parts of the computer system. Wireless Ethernet, or Radio Frequency (RF) networking, removes the need for installing physical cabling to each computer. Instead, RF communication is used.
This allows the computers to be completely mobile while retaining network connections.
Wireless Network Devices
A device known as an Access Point (AP) is attached to the wired Ethernet network, and acts as a radio transceiver. The AP is effectively a bridge between the wired and wireless sections of the network.
Each computer contains a wireless network card, which communicates to the AP's, and therefore to the rest of the computer system.
Purpose of Survey
Because the AP's use license-free radio, they are limited in their radio power output. This means that the communication range of the AP's is limited, typically to a few tens of metres.
In order to cover the surveyed area, several AP's may be required. The survey assesses where best to locate the AP's, to give maximum performance and cost effectiveness.
One further problem is the attenuation (i.e. signal fall-off). Although affected little by freespace, it is reflected by metal but greatly absorbed by organic materials. Therefore the materials contained within the survey area have a great affect on the signal.
The survey performs a test of how the wireless network responds in the real survey environment, and aids in deciding where to locate the AP's.
Survey Pre-requisites
Typical Conditions
Because RF propagation is affected greatly by the materials in the survey area, the survey area must be in a state of highest (or at least typical) usage. If the site is unusually empty of materials, then the survey may not be representative.
RF coverage is not guaranteed in the event that the layout of the site changes in any way, after the survey has been conducted. The installation of additional racking, partitioning or walls are examples of that which constitutes a site change.
It is recommended that a second survey be conducted in such circumstances, to re-appraise the site.
Coverage Areas
It is unlikely that the whole of the site will require RF coverage. In order to minimise the number of AP's that are required, those areas not requiring coverage will be disregarded.
Survey Method
Procedure
The site survey is based around approximating the survey area to a grid of sample points. These points are ideally separated by 4m vertically, and 4m horizontally. In the case of an obstruction, the sample point is shifted to accommodate it.
The Access Point is installed in a test location (on an AP test mast), as chosen by the survey engineer, and each point on the grid is subjected to a signal strength test. This consists of the engineer walking to that grid point and performing a test between a hand-held RF Data Terminal and a laptop PC, across the wireless link.
Once the Access Point reaches the limit of its range, and all grid points within range have been sampled, the Access Point is moved to a new location and the test performed again.
This process is repeated until several Access Point locations have been tried, and complete coverage to the desired bandwidth is found.
Pictures of test AP mast.
The data is collected and logged on the Laptop computer for analysis reporting.
Unprocessed Survey Data
Each test at a particular grid sample point depending upon the support access point can
return the following statistics:
- Signal/Noise ratio
- Signal strength
- Noise
- Bandwidth
- Data Processing
In the case of maps that show coverage from multiple Access Point locations, the raw data is first combined to remove overlapping samples. In the event of multiple readings being performed at one grid location, all but the maximum SNR are ignored.
As the survey is conducted the engineer is provided with a plan view of the Radio signal strength, therefore allowing him to adjust the location of the AP to ensure all required areas are covered.
Wireless “Heatmap”
Single Room Survey Results
Full Survey Results
If you would like to discuss this more then please contact our technical department on:
01202 620955
Or Email us at enquires@biastechnology.com
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