The importance of a Wireless LAN survey

With our experience in performing installations of wireless LAN networks, a survey is the most crucial stage of the implementation.

There are a number of survey techniques that are used to determine how a Wireless Network is ideally designed. Most use heat map pictures overlaid onto site plans that indicate the signal strength, with a key showing what the colours indicate. The wireless surveys can be achieved in a number of ways.

1. Passive Survey

A passive survey is where a physical survey is performed with one or more access points in operation, and signal test readings are taken with special site survey and planning software (Airmagnet & Ekahau are the industry leaders in this field). Positions for AP's are placed to determine to viability of such location according to the layout of wireless access points across the coverage floor to meet end user requirements. A survey report can be generated that provides details such as AP locations, Signal Strength charts in heat map format, photographs of AP mount locations, detailed analysis of interference, and descriptions of cable installations.

2. Active Survey

This is also a physical survey which is performed after a wireless network has been just deployed, or to the health check an existing network. This is called an "Active Survey" which measures signal coverage, throughput tests SSID and VLAN per AP allocation and behaviour of data packets. This is usually performed after an install has occurred to ensure the wireless network is performing as per the scope of the requirements. This type of survey can also be performed when an established wireless network is experiencing issues that may occur over time, which may be contributed by internal changes within the network (e.g. Config changes, higher number of concurrent users), or due to exterior reasons outside the network (e.g. additional interference from new networks, new non network devices outputting signal).

3. Predictive Survey

This is where the site plans are inserted into a program that simulates the walls and floors. Sometimes a site visit is not even required. This is NOT recommended as survey tool. A program cannot take into consideration the thickness, density, material type, interference etc of the interior space of a property, and is therefore less than useful for the design of a Wireless LAN, as it can be providing very wrong information which may lead to an inferior network, which can potentially cost more in time, funds, and resource to correct.

For a new install the survey aspect of an installation determines how many access points are required to provide coverage in the most economical layout. This takes into consideration the internal layout of the interior space, which can be divided up by partitions for different rooms, what those partitions are made of, furniture, aesthetic considerations, bleed of radio signal through floors, interference from other networks, interference from non IP networks, etc etc, the list goes on.

If a survey is not performed, then all the negative factors mentioned may cause the effect of a poor wireless network, so issues such as dark spots for coverage, lack of throughput due to interference, not enough Access Points to cater for concurrent users, and too many Access Points (causing self-interference) are issues that come to mind. This in turn may mean remedial work to resolve these issues post survey, which will cost more in resource and possibly hardware. If you are performing work for a client, worse than monetary loss is reputational damage to yourself and your company.

For any queries regarding a Survey, please feel free to discuss with us. Our Technical Sales department can be reached on 01202 612400.

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