Listening is a key skill for IT consultants, but I find myself more often trying to understand what the customer really expects when they say they need a 'site survey'.
A 'site survey' can mean quite a few different things and there isn't a standards body to formulate and finalize standard descriptions of site survey terms.
Active, passive, predictive, validation, simulated and budgetary are all words I've heard used to describe the type of site survey a customer wanted.
The first pieces of information I need to get are:
- Does the customer have an existing wireless deployment?
- Do they want their current RF coverage documented, then augmented?
- If augmentation is desired, existing access point power would need to be reduced to ~25mW before documenting the RF coverage
- Augmentation may not be the best solution due to the potentially vast differences in their current access point hardware and antennas vs. the features available in today's access points.
- Do they want to deploy a new wireless coverage design and disregard their current deployment?
- What does the customer intend to do with their wireless infrastructure?
- What types of client devices do they anticipate?
- What kinds of applications will be used?
- Is there the potential for high-density user counts?
- Is any level of real-time location tracking required?
Each deployment is different as a result of the building type, building layout, client use cases and customer budget. There are a great deal of questions that need answers before you can accurately define the type of site survey the customer needs.
Defining the different site survey terms is often problematic. Everyone seems to have their own idea of what an 'active' or a 'passive' site survey means. These are the terms I use to describe site surveys:
- Active (also known as AP-on-a-stick)
- Digital floor plans are obtained and scaled to a known distance.
- If the floor plans do not have a scale indicated, the scale of the drawings can be obtained by Google Earth measurements or by using a laser distance measurement tool when on site at the facility.
- The RF engineer brings in the actual access point the customer will purchase, powers the access point with a battery pack and documents the coverage of the access point in the actual installation location with the site survey software of choice. The access point installation locations can be surveyed one at a time and then merged, or multiple access points can be surveyed at a time (depending on the hardware resources available to the RF engineer)
- This type of survey will not give you accurate data on the RF noise floor that will be present once the final access point infrastructure is installed and operational, as there are a limited number of access points transmitting during the survey period.
- A Spectrum analysis should also be performed to determine if there are any major fixed sources of interference present in the facility.
- Passive (also known as validation)
- Digital floor plans are obtained and scaled to a known distance.
- If the floor plans do not have a scale indicated, the scale of the drawings can be obtained by Google Earth measurements or by using a laser distance measurement tool when on site at the facility.
- The RF engineer walks the facility with the survey laptop detecting one or more SSIDs in use at the customer site.
- The RF engineer may not have access to network credentials to authenticate the the customer's WLAN and would only document the RSSI/SNR detected by the site survey application.
- If the RF engineer has network credentials to associate/authenticate to the WLAN, additional testing of throughput/load/voice quality could be performed at the customers request.
- Spectrum analysis should also be performed to determine if there are any major fixed sources of interference present in the facility.
- Predictive
- Digital floor plans are obtained and scaled to a known distance.
- If the floor plans do not have a scale indicated, the scale of the drawings can be obtained by Google Earth measurements of the outside wall of the building, or by using known distances common to corporate facilities (doorways are typically 3 feet wide).
- RF obstacles are drawn in the RF simulation application
- A software model of the access point's RF coverage is used to place the access point at a given location in the floor plan drawing and predict what the coverage for that access point would be given the RF obstacles drawn by the RF engineer.
- Once the desired coverage level is achieved, a bill of materials can be generated
- NOTE: Predictive surveys are not 100% accurate and a post-deployment verification survey should be performed to ensure the desired coverage was achieved through the predictive survey process.
- Throughput/load test
- There are several methods to performing throughput testing (this list is just an example and is not all inclusive)
- The RF engineer would associate/authenticate the wireless client to the customer WLAN with credentials provided by the customer.
- The RF engineer would also need access to a wired port to do end-to-end testing from a wired client to a wireless client.
- Voice quality test
- There are several methods to test voice quality over a WLAN (this list is just an example and is not all inclusive)
Hopefully the more we all talk about the different types of site surveys and learn from one another about the words we use to describe them, we'll all encounter less RFPs/RFQs asking for validation surveys for wireless infrastructures that aren't installed in buildings that aren't built yet.
