Transforming tomorrow, today

Wireless Site Surveys

Krishan Mistry, Head of Mobility Solutions

A radio frequency (RF) site survey is the first step in the deployment of a Wireless Network and the most important one to ensure desired operation. A site survey is a task-by-task process, by which the surveyor studies the facility to understand the RF behaviour, discovers RF coverage areas, checks for RF interference and determines the appropriate placement of Wireless devices. We use this site survey as the basis for the RF design and will guarantee the functionality and underwrite any project where an onsite RF survey is conducted by its personnel.

An onsite RF survey provides detailed information that addresses coverage, interference sources, equipment placement, power considerations and wiring requirements. The site survey documentation serves as a guide for network design, for the installation and verification of the Wireless communication infrastructure.

There are two major categories of conducting an onsite RF survey which include:

  1. Physical Site Survey: An examination of the physical environment in which the WLAN will operate, this is inclusive of the physical premises and the location for the antenna placement or cable runs. The primary objective is to ensure that the location can accommodate a WLAN.
  1. RF Manual Site Survey: The RF survey is the process where the current RF activity and utilisation is examined in the physical space, where the WLAN must operate.  Additionally, it involves evaluating how the new WLAN will function within the environment.

The actual process of performing a wireless site survey involves many stages. The manual site survey requires the traditional method of a WLAN engineer conducting both a physical and RF survey onsite, where WLAN coverage is required. The engineer will place one or more APs at strategic locations and will walk throughout the intended service area, using an advanced surveying tool to test signal strength, signal to noise ratio, channel interference and data rate. Manual surveys are the most accurate form of surveying for WLAN coverage, as AP locations are based actual RF information in the intended coverage area. As a result, guesswork and theorised analysis is removed from the RF planning.

In a Wireless network, many issues can arise which can prevent the radio frequency (RF) signal from reaching all parts of the facility. Examples of RF issues include multipath distortion, hidden node problems, and near/far issues. By conducting a site survey, the regions where these issues occur can be identitifed. A site survey helps define the contours of RF coverage in a particular facility. It also helps us to discover regions where multipath distortion can occur, areas where RF interference is high and helps to find solutions to eliminate such issues. A site survey that determines the RF coverage area in a facility also helps to define the number of Wireless devices that are required to meet its business requirements.

When conducting an RF wireless site survey, there are three main areas of focus, to ensure a reliable and scalable wireless network is provisioned:

  1. Survey for Coverage: Provide blanket coverage throughout the desired areas with a minimum signal strength or data rate.
  2. Survey for Capacity: To ensure the wireless network provides sufficient bandwidth for the anticipated number of users and in particular, to provide scope for high density of users.
  3. Application Support: Ensure that the wireless network supports all predicted applications that the client wishes to use on the wireless network, including Wireless VoIP, radio frequency identification (RFID) and data applications.

Application Support

Data Applications

The requirement to support laptop and handheld devices for TCP and UDP data transfer. Typically, an Access Point will support up to 50 users per radio (only includes 802.11n/ac).

Wireless VoIP

The requirement to support voice calls over the wireless network using WiFi enabled phones.  This requires a higher quality wireless coverage using the signal to noise ratio (SNR), to gauge the performance and capacity of the wireless network.  The SNR value is the received signal strength minus the surrounding noise level from neighbouring APs.

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For a voice ready infrastructure, it is important to understand the voice handsets that will be deployed, as each handset has a different RF requirement. As a benchmark, a minimum of 25 SNR is required to support a good quality voice call with minimum latency and low jitter rate. An important parameter in VoWLAN planning is call capacity, the number of simultaneous VoWLAN calls that can be supported in an area. This value can vary, depending upon the RF environment, the VoWLAN handset features, and the WLAN system features. For example, the VoWLAN maximum capacity for a Cisco Unified IP Phone 7925 using a WLAN that provides optimised WLAN services, the capacity is expected to be 14 simultaneous VoWLAN calls per 2.4 GHz channel and 20 simultaneous VoWLAN calls per 5 GHz channel. These capacity values are based on assuming no other competing high priority WLAN traffic and normal background noise.

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