## What is a Site Survey?

A site survey is an in-depth examination and analysis of a proposed wireless LAN site. The purpose of a site survey is to determine the number of access points needed, the types of antennas needed, and the best placement for those access points and antennas.

Although the goal of a site survey is simple, the means of arriving at that goal are not. Some of the steps involve taking measurements, but most involve experience, trial and error, and a little guesswork rather than numbers and figures.

### When to Perform a Site Survey

Intel recommends that you perform a site survey prior to installing a wireless LAN. Site surveys are especially important at these three times:

- Before installing a new site - Evaluate the placement of the access points and antennas throughout the proposed site.
- Before changing an existing site - When modifying or extending an existing network structure, re-evaluate the placement of the access points and antennas. If you need a different level of coverage in some areas, you may need to move, replace, or supplement access points and antennas.
- After physical changes to the site - Remodeling may introduce new sources of interference, such as motors and metal structures within the coverage area of the access point, even if it does not directly effect the sites where the access points are located.

### Elements of an Effective Site Survey

An effective site survey requires four elements. Failure to commit the appropriate time, money, and energy to accomplish a proper site survey in advance may result in greater expenditures of money and time later, when problems arise that require repeated adjustments to the wireless configuration. The four elements of an effective site survey are:

1. Examine the network usage problems the wireless LAN solves.
   How many clients need a wireless LAN connection? What areas of the site require wireless LAN connectivity? How many hours each day is wireless LAN connectivity required? Which locations are likely to generate the largest amount of data traffic? Where is future network expansion most likely?
2. Study blueprints of the proposed wireless LAN site.
   A site blueprint provides a map of the site as well as the location of objects such as walls, partitions, and anything else that could effect the performance of a wireless LAN. Examining the site blueprint prior to conducting the physical walk-through helps you identify areas where wireless equipment is likely to perform well and areas where it is not. Many obstructions are not readily visible and, in some cases, a room originally built for a specific purpose, such as a radiology lab, might have been converted into something completely different, such as a conference room. The blueprint may also show areas proposed for future building expansion.
   To prepare for the next step of the site survey, mark possible wireless device locations on the blueprint and refer to the marked blueprint during the physical walk-through and inventory.
3. Conduct a physical walk-through and inventory.
   The primary purpose of the physical walk-through is to document any items or materials near a proposed device location that may interfere with reception or transmission and effect network performance. Document stock and inventory levels, current environmental conditions and any materials that may interfere with wireless LAN transmissions.
4. Measure the radio frequency (RF) transmissions.
   Intel® PRO/Wireless LAN Site Survey provides the means to measure the signal strength, the transmission rate and the number of successfully transmitted packets. This step in the site survey involves mounting access points and antennas in the proposed locations and measuring the RF signal strength, transmission rate and packet throughput.

## Network Usage Requirements

When designing a site, consider all of the possible uses for the wireless network. Important factors include mobility, performance, security, redundancy, and system interface requirements.

#### Mobility Requirements

Determine whether the customers are in motion continually, such as in a warehouse or hospital, or whether the customers work from different fixed locations throughout the site.

#### Performance Requirements

Consider whether the people using wireless devices need higher data rates for time-bound transmissions, such as audio and video, or whether the system most often handles burst or typical knowledge worker data traffic. If computers require higher data rates, put access points closer together, because the higher transmission rates can only be obtained near the access points.

The number of computers per access point varies with the customer applications and other system factors. Typically, an access point readily accommodates 10 to 30 computers. Areas with a high density of computers, such as conference rooms, may require additional access points.

#### Security Requirements

Because wireless LANs use unsecured radio waves to transmit data, security is an important consideration for network administrators designing wireless networks. Network administrators should consider whether encryption such as Wired Equivalent Privacy (WEP) is necessary to protect sensitive data transmitted over wireless networks or if the customer can afford a lower degree of security.

#### Redundancy Requirements

It is recommended that you design your wireless system so that each access point has redundancy from another access point. This provides not only for redundancy, but improved overall system performance.

#### System Interface Requirements

Consider the degree to which the wireless LAN (WLAN) will interact with the conventional wired LAN. Some legacy systems, such as older mainframe networks, may not support WLANs without additional hardware or software.

Roaming from one access point located on one IP subnet to an access point located on another IP subnet causes loss of IP connectivity, unless special arrangements are made.

## Channel Selection Considerations

The exact number of available channels is dependent on local regulation. To avoid inter-channel interference between access points, configure your access points to local clear channels or their equivalents in other countries. Arrange your access points to avoid having same channel units adjacent to one another.

You cannot adhere to this recommendation in some situations, such as in a building with several access points on multiple, adjacent floors, where the access points transmit through many floor structures. Adjacent access points operate properly when they use the same channels. Each access point "hears" the other, and takes its turn transmitting. This situation may cause a reduction in data throughput if it occurs in a very active area, so design your channel layout accordingly.

## Preparing for an Intel® Wireless LAN Site Survey

Installing an Intel® PRO/Wireless LAN begins with conducting a site survey. A site survey involves using the Site Survey Utility to determine the physical requirements for a site-specific Intel PRO/Wireless LAN. A site survey analyzes the installation environment and provides recommendations for equipment and placement.

Use the Site Survey Utility to determine the placement of access points and antennas, as well as the number of devices necessary to provide optimal service. The facility can be a warehouse, manufacturing plant, office building or retail store.

In the installation of an Intel PRO/Wireless LAN, complete radio coverage could require optional antennas.

## Inspecting the Survey Area

During the planning stages of the site survey, a network administrator or equivalent visits the proposed radio coverage site. As a standard practice in the site survey consultation, the network administrator gathers facility drawings and completes a Site Survey Requirements document and a site survey questionnaire. The network administrator documents the wiring used within the facility (Category 5 for 10 Mbps Ethernet or 10/100 switched Ethernet, fiber optic cabling, etc.) and assesses its applicability to Intel PRO/Wireless LAN components.

Select several trial installation areas. The site survey team analyzes each proposed installation area to document radio transmission constraints and to develop preliminary access point placement alternatives to be tested during the actual site survey. Document the findings from the initial site inspection in a Site Survey Request Form and use that form as the outline of the site survey.

Consider the following variables in the site survey requirements definition:

- RF systems already in use
- Availability of lifts for mounting access points
- Location of host system(s).
- Available AC power
- Interfering metal fire breaks and wall structures
- Availability of customer technical personnel to answer questions during the survey
- Doorways and passages effecting RF propagation

The completion of the RF Site Survey Requirements document is a coordinated effort between the network administrator and the customer management team.

This document does not identify potential installation constraints within the customer site, nor does it recommend access point and antenna placement location. The document represents a preliminary overview of the customer site used as a baseline for refining site survey requirements.

#### Assessing Environmental Radio Coverage

The network administrator selects trial component installation areas away from transformers, heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and other industrial equipment. Areas with excessive moisture, heat and dust are inappropriate for staging a wireless network.

Signal loss can occur when metal, concrete, walls or floors block access point transmission areas. Access point antennas are trial-mounted in open areas or added to an existing access point to boost the Intel PRO/Wireless LAN coverage area.

The positioning of an access point depends on the floor plan of the site. The network administrator makes access point and antenna placement recommendations based on the following installation site variables:

- Outdoor or indoor installation site
- Large or small proposed radio coverage area
- Wide or narrow proposed coverage area
- Number of additional devices operating in the proposed coverage area
- Open coverage area or area with documented obstructions

#### General Guidelines

Site surveys for wireless devices require experimentation with different antenna coverage at various angles. Placing a directional antenna in a vertical position can often minimize multi-path problems.

| NOTE: Do not locate access points near corners, against walls, against metal walls or inside metal conduits.

#### Preventing Channel Interference in a 2.4 GHz environment

Intel PRO/Wireless LAN access points require careful survey area testing to ensure radio transmissions do not overlap.

Intel PRO/Wireless LAN access points supporting different coverage areas in close proximity to one another should be configured using direct sequence channels as far apart as possible, such as channels 1, 6, and 11.

#### Supplying Power from Site Electric Circuits

Intel PRO/Wireless LAN access points draw power from wall outlets. Access point performance is subject to degradation due to inherent or random electrical problems or site-specific disturbances.

Access point electrical installation alternatives are listed below in order from most to least preferred for an installation area.

1. Isolated ground circuit with an online, uninterruptible power supply (UPS) that also acts as a filter and surge suppressor.
2. Isolated ground circuit with a surge suppressor.
3. Dedicated circuit with a UPS.
4. Dedicated circuit with a surge suppressor.
5. Non-dedicated circuit with a UPS.
6. Non-dedicated circuit with a surge suppressor.

| CAUTION: When using a Network Controller Unit, items one through four are recommended. The use of nondedicated circuits for configurations five and six could cause data loss and serious transmission problems. By its nature, a nondedicated circuit contains open receptacles. The load and type of use of open receptacles in a nondedicated circuit cannot be predicted after installation.

If you must use a non-dedicated circuit, Intel recommends that the circuit not support any of the following:

- Hard-wired devices.
- Devices with components intended or known to produce heat such as space heaters, laser printers, heat guns and soldering irons.
- A single device drawing more than 20% of the rated value of the circuit.
- Devices drawing more than 60% of the rated circuit value.

| NOTE: Ensure that each access point has power available 24 hours per day. It is recommended access point power never be provided from an Energy Management System (EMS).

## Recommended Procedure for Performing a Site Survey

Using the Site Survey Utility to perform a site survey involves selecting possible locations for the access points from a review of the floor plan layout, based on estimated of the range of an access point within the site. Range estimates are based on previous experience, physical test and measurement or calculation from the rated hardware specifications.

Proposed locations are validated by temporarily installing one access point and using the Site Survey Utility to test the actual range and coverage area of that access point in that location. Adjust the position of the access point as required until you validate the coverage area.

After you validate the first proposed access point position, annotate it on the floor plan layout, move the access point to the next adjacent location, and test the access point coverage from that location. Repeat this procedure of testing, adjusting positions, and relocating the access point until the entire proposed coverage area and all of the proposed locations have been validated.

It is recommended that you accomplish the site survey using the continuous Internet Control Message Protocol ( ICMP ) "ping" test with a block size of 1024 bytes.

#### Helpful Hints and Tips

- Floor to floor interaction between access points is usually not a problem, unless the floor is wood. If interaction can occur, ensure that the channel selections are appropriate for vertically adjacent access points. Floor to floor interaction can be a good thing, as it provides for redundancy.
- Close all office and room doors before beginning the survey. This puts more material between the transmitter and receiver, allowing you to assess reception at its lowest everyday level.
- Conference rooms may have a high density of computers, so ensure adequate access points for satisfactory throughput. Consider redundancy for these areas.
- In high security areas where access may be limited, such as boardrooms and labs, consider placing access points adjacent or straddling the area, rather than directly in the area. When maintenance is required on the access points, access to the restricted area is not required.
- Cafeteria areas can be a high usage and demand area, as informal employee meetings are often conducted there.
- Computer to access point ratios are typically maintained at a maximum of approximately 20-to-1, depending on the type of applications and data.
- Areas with multiple conference rooms in close proximity are often given additional access points to provide redundancy and ensure adequate throughput.

Copyright© 2002 Intel Corporation. Legal Information