While attending conferences and seminars, I have been approached by several attendees inquiring about doing a proper survey. Many who believe they are performing surveys correctly are still not even getting close to a proper design.
As I mentioned in a previous blog post, the applications that will be used on the wireless network are very important to have before you start your design. Surveying for a data only hot spot is simple and requires little to no ability at all, but if you are looking at having location services and/or VoIP on your wireless network then you must know what you are doing in order to provide proper coverage to your customer.
Let's start with the basics of setting up for your survey:
1) What devices (type of VoIP phones and or/location tags) are you going to be using?
2) What is the expected customer experience?
Before you begin a survey, the actual devices to be used on the wireless network would be a great thing to know about. Each device is designed slightly different and you could get a VoIP phone with a single antenna with no diversity, or you may have one with a higher output and diversity. Without the specs on the phone, you are taking a risk of designing a network that your customer will experience problems with while using their devices.
You should always ask the customer what they see as an end result of getting a wireless network. Let them tell you what they expect their experience to be. Don't go in with a cookie cutter approach and tell them what you intend to do and what their network will do when you finish. If the customer has pictured a certain experience in their mind, ask them to share that though with you so that you can set out to provide that experience if its possible.
Lets look at the actual survey now.
Based on the customer's vision, you now have to survey the facility with the limitations of their wireless devices in mind. If their VoIP phones will only transmit at 30mW then you do not want to go in and survey with your access point set to full power. This will spell out problems for the voice network and the customer's experience isn't going to be good.
It is always good to set your network's transmit power at or below the power of the devices on the network. Since the VoIP phone is the most crucial and lower power than laptops, use the phone as a measuring tool to set your survey transmit power. This way you are not designing a network that transmits more powerful than the devices on it.
How to survey correctly
If you are using a survey software like Air Magnet or Ekahau, then you have tools in the software that allows you to adhere to standards during the survey. For example.. Above we spoke of surveying for a VoIP network so you need to know what the minimum cell edge requirements are for the VoIP phone you will be using. If the minimum signal requirement is -67dB then you can set the software to display a gray area for all locations surveyed that do not meet that requirement. If you do not use this tool, then you will have no idea where the edge of the cell needs to stop because the software will continue to pain the floor map in colorful schemes until you reach -100dB signal and disassociate from the survey access point (average default setting to disassociate;may vary). If you want to really see the device requirements met on your floor plan, you will use this option to display the boundary as you survey. Then...
You can display the footprint of the first access point's coverage and make a great determination as to where the next one will need to be. Survey the next access point with the required 20% average overlap of cells and then combine the two footprints to see how much area you have surveyed and how much you have left. Continue this until you have all of the required areas surveyed properly and then combine the total coverage into a single drawing and look for gray areas on the floor. If none exist, then you are off to a great start.
Surveying has a lot more involved in it than what I have posted, but I have provided the basics here. I look forward to seeing your experiences in your comments and input.
Brett Hill, CWNE #147
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