Dave Mast

Wireless Site Survey Network General

Overview

The site survey is an assessment of coverage signal for each access point within a specific building. Confirmed by the customer 100% coverage to a specific signal that ensures employees do not have problems by sending packets through the wireless network. Each structure of the building will have a design that determines the characteristics of the signal. The most often causes problems with the decline of wireless signals include water, metal, construction of contour lines and devices that emit electro-magnetic interference. Some access points can send a pattern of coverage extends from 100 to 170 feet, while some will emit a signal 50 feet with the same characteristics.

The structural building design has a lot to do with it.

The following is a summary of the process of site inspection:

1) Discuss / N ratio and data rate Customer

2) Collection of Maps

3) Buildings Survey Noting signal coverage

4) Document Access Point location

So what is an acceptable signal? Signal to noise separation of about 20 to 25 dBm at 54 Mbps is a minimum with most designs. The site survey software for measuring a continuous signal of 75 dBm and 95 dBm Noise (75/95) would be sufficient for employees online and send packets with the same level of service and cable customers. As the signal weakens, it becomes more difficult to distinguish between a signal of 80 dBm and 95 dBm Noise (80/95). There is less separation between the signal and the noise by the signal difficult to detect. It seems inconsistent more is a weaker signal however, the key measurements of the noise signal and the signal is a negative number and therefore a higher value Bass is a larger number. Talk to customer specific client adapter 802.11a/b/g standard wireless data speeds that will implement and study it. Implementing the 802.11a standard does not require a separate study if implemented and monitored on a dual-band 802.11g. Some companies with higher bandwidth demands the band will improve cellular coverage to a separate survey 802.11a. It is not as cost effective with additional access points deployed by cellular coverage. Set point access with 802.11a/b/g protocol selected, transmit power and data rate. Set the type of data and transmission power of the client adapter to a maximum during the survey.

The study of the site of a building is walking on a laptop in a car driven configured with a wireless client adapter Cisco and the Cisco Aironet Desktop Utility (ADU). The software is a utility available with the Cisco client adapters. The Cisco access point is placed at a specific point in the roof or above the ceiling tile, wall, desk or cubicle and measurements of the signal coverage is observed. The access point moves until there is coverage optimal cell. ADU Select active mode to examine the data of speed, link status and errors while surveying. Cellular coverage can be transferred to a plane Visio drawing with the placement of specific access and limits the signal. The access point is moved around until the entire building is assigned. The signal intensity minimum must be recorded per cell coverage. Be as specific as you can describe where access points should be applied. Some customers have floor plans that makes the study of the site much easier to document coverage. Scan each plant as a Visio drawing indicating the specific location of access points and channel assignment.

The map will have some overlap in coverage is not a concern. You must assign a channel that does not overlap with cells neighbors and employees have no problem with channel interference. As mentioned the 802.11b and 802.11g wireless standards use the frequency band 2.4 GHz can cause interference but there are 3 non-overlapping channels (1, 6 and 11) that can be assigned. For example, if your building has a main floor with 17 rooms and each point of access to rooms housing 3 using the following channel assignments:

AP1 Channel 1 1-3 Rooms

AP2 Channel 6 Rooms 4-6

Channel 11 Rooms 7-9 AP3

AP4 Channel 1 Rooms from 10 to 12

AP5 Channel 6 rooms from 13 to 15

Rooms from AP6 Channel 11 16 to 17

In some cases you may be the sign of saturation between AP2 and AP5 with specific forms of building design. Decreased transmission power of 100 mW to 20 mW in access points or both to confirm the signal strength is still acceptable in the rooms. If the reduced power transmission setting does not allow such coverage, the shift position of the access point, apply an additional access point at reduced power or an external antenna. Site surveys take some trial and error knowing that signal coverage may occur. You know after doing some preliminary tests on a specific building to cover what to expect. Walking around with your laptop to start and get some understanding of the signal patterns. Saturation signal can often occur outside the building in which the security risk with the pirates on the street. The site survey should confirm no sign invaded by minimizing access point transmitter power.

multi-story buildings will have some access points that send signals through several floors. You can use access points unless of course access points that cover the floors or decrease the transmit power and assign non-overlapping channels as discussed. The problem with the sign of saturation is a concern in an access point covers some of one story and not all of a room on another floor. You want space access points, with adequate signal coverage and minimum overlay. Again, the building could allow an access point to cover one floor or 2 floors with an output signal as required in all parties. If there is a third floor can be implemented on that floor. The first and second floor have an access point on the first floor. Implement on the second floor would make the signal overlap. That's not a problem with non-overlapping channels, however fast roaming customers should be associated with the nearest access point. After access points in the second and third floors might make some customers on the third floor to select an access point to use the second floor and lower performance.

The client sends a beacon and select the nearest access point with the best signal, fewer customers and match the security settings. A negotiation between access point and client adapter is produced and sent the data to the highest level of support available. The coverage map with positioning access points should be specific as possible during the study that describes the placement of access points. Implement all access points and connectivity test. With all the access points transmit the potential for interference and the design can be modified before implementation. Signal out of overshoot can be tested to confirm the signal remains within the limits of the wall and there is no access from the street. Spectrum analyzers can be made during the site inspection or after to examine the frequency of interference and possible sources. Defining a security test plan is a good idea after deploying access points.

Take survey notes mounting issues where AC power outlets is not available, the distance between the wiring closets and wiring distance between the access point and switch. Cisco is out of wireless bridges available buildings with line of sight. There is a survey involving with the implementation bridges that considers the loss of route of transmission signals and how environmental issues such as wind and rain affect the data transmitted.

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Shaun Hummel is the author of several technical books and has a web site focused on solutions for information technology job search and certifications.

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About the Author

Shaun Hummel, CCNP, is a Senior Network Engineer with 11 years experience in enterprise network planning, design, and implementation. He has worked for various private and public companies in Canada and the United States improving infrastructure, security, and management. He has written Network Planning and Design Guide, Cisco Wireless Network Design Guide and Network Assessment Guide. www.networkjobsolutions.com

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