How to Conduct a Wireless Site Survey Part 3

Meetings

In part 1 I talked about what equipment you will need to do a site survey; in part 2 I helped you visualize what the airwaves would look like while walking through the area to be surveyed. Having the equipment and an idea of what you are looking for is a great start; we need to push on however into specific skill sets.

The next thing that we need to do is to get the Survey Requirements, especially if it is a new installation. We need to meet with the end users of the system and determine what they need, and what they want. They may not necessarily realize that they need security, but they probably know that they want to push graphics through the air which means to us engineers, high speed.

If you are re-surveying a live pre-existing space for specific metrics such as throughput, errors, noise, or rogues, you will need to get detailed information about what the end user is experiencing. Latency, loss off data, and other tangible events are where you should start.

You will need blueprints of the facility (if available), otherwise you will need to make your own maps. Square footage, room size, ceiling heights, and obstructions need to be taken into consideration.

TIP: Take detailed and accurate notes at all of your discussions. As systems evolve sometimes expectations do as well.

You are surveying for the middle links in a network, so logically you will need to know both endpoints:
* Where data is sent from (laptops, hand held scanners, etc.)
* Where data is going to (Internet, across the office, to a printer, mainframe, etc.)

Many professionals fail to scope for capacity. A single access point could probably cover an area the size of a grammar-school gymnasium but if there are a couple of hundred people in seated in the room, the system will choke big time. How many users in each AP's zone is a crucial metric to know. A good rule of thumb may be no more than 20 per AP.

As long as I brought up the topic of a high density of people in a small area, how would you service them? In the 802.11g world you have (realistically) only 3 channels to choose from--we said 20 per AP... that's 60 people running OK. What about the other 140 people?

You would have to have a high density of Access Points, closely mounted, all running minimum power and the most attenuation you could get on their antennas. You would want the coverage of each AP zone to be very small. Very small. Not pretty but doable.

Knowing what the end user needs and wants is the basis of what you will accomplish in your survey. For example if you determine that most of the clients have 802.11g NICs with a few 802.11b units, you may want to explain how converting 802.11g wall to wall is a better investment, especially if they are going to be sending graphics.

To recap this installment provides direction on :
* End user requirements on a new install, or report on pre-existing problems
* Type of equipment they are using
* Accurate detailed notes and Maps.

Survey Views

How to Conduct a Wireless Survey Part 2

Visualizing Radio Waves

To give you time to assemble your survey kit, I thought that the next logical stop on our journey would be your understanding of how RF works in your environment. To do this, I’m going to have you visualize how it would look if you could see the radio waves. You will have a mental picture that will always be with you.

Every beginning RF class teaches that radio waves radiate of a dipole antenna in nice neat concentric circles progressively getting larger and weaker as they move away from the antenna; picture this: you standing at the edge of a perfectly calm lake and tossing in a rock. Visualize what the waves look like. This is what radio waves look like (only a great deal smaller); what radio transmission would look like outdoors in a parking lot or empty field.

Is that your environment though? Not hardly. There are all kinds of things in our world that scatter and deflect radio transmissions. What would it look like if we returned to our calm lake but tossed a rock under the legs of a pier? You would see the initial circle, but as it encountered the legs of the pier, some of the waves would get bounced back and dispersed, some would wrap around. You would see a disturbed radiation pattern of waves. This is a bit truer to our environment.

Now picture a city street with tall buildings. I just placed an Access Point at the intersection of two streets. Do you think that the radiation pattern will be circular? Well perhaps right around the Access Point there will be concentric circles, but if you looked at the pattern from above and could see how far the waves radiated, you would notice that they extend farther than they would in open air due to the buildings “herding” the waves down the corridors. The radiation pattern would look perhaps like an “H” or “t”. Can you visualize that? This is how waves might move down a hallway in an office.

Mentally skip a stone across the water. Waves can skip across the air (sometimes that’s why we can hear radio stations far away from where they are transmitted from). Waves can bounce off of hard surfaces. They can be absorbed; in a warehouse with fairly equal coverage throughout a few pallets of peat moss can render a “hole” in the coverage around those skids. There is another effect called “radio shadow” where behind an obstruction the coverage falters the similarly to the way light casts a shadow on an obstruction.

Knowing how radio waves move is an important first step in conducting a site survey. With a bit of experience you should be able to walk into an environment and have an understanding of how the RF is working or what you need to do to enable a wireless environment.

I will revisit the topic later as we advance in our study. We will look at radiation patterns of various antennas.

How to Conduct a Wireless Site Survey Part 1

How to Begin

There are a lot of articles written about how to do a wireless site survey, but from what I’ve seen they don’t give the real story as far as how to organize, and conceptualize the survey. I will take a modular approach to teaching this discipline which is a heterogeneous mix of physics, experience, and creativity.

Before you begin site survey you will need a survey kit. These kits vary in complexity and price but the most basic kit will have the following items:

Maps: Map of area to be surveyed.
* A large blueprint is useful for fine details
* You will need several 8’x10’ clipboard maps for notes related to finding at specific locales (a single map can be photocopied—copies can be handed out to people who work in the airspace that have specific problems or concerns).
* Softcopy is necessary for most survey software packages, reports

Laptop PC with Survey Software
* You will need a survey console. There are many survey tools out there these days at this writing the defacto standard is AirMagnet.
* Several wireless NIC cards that operate in the radio bands that you are surveying (each card views elements such as signal-to-noise, roaming, signal strength a bit differently. Many survey products load proprietary firmware drivers for each specific card so that it has more precise control of the card.

Digital Camera, notebook, 100’ tape measure.
* You will need to take accurate notes for future reference.

This is the very least you will need to conduct a wireless site survey.

There are several commercial survey kits on the market that have components such as Access Points, and different types of Antennas (to play ‘what ifs’), and other tools to help aid the surveyor. If you have the budget for one of these kits (that often come in travel ready flight-cases), they are recommended; they will give you additional options, views, and abilities for conducting a survey.

Don't think however that you need to spend tens of thousands in surveying equipment in order to to an accurate and meaningful wireless survey. The most vital piece of equipment is your intellect.

Wireless Survey Questionnaire #1 New Installation:

Instructions: Interview End User to obtain as many answers as you can, then investigate the rest.

1. What is the approximate Square Footage of the environment that you want to provide wireless coverage for?
2. How high are the ceilings?
3. Are there any immediate concerns about the environment that you are about to outfit with wireless (for example: Outdoor environment, area with lots of metal obstructions)?
4. Is your facility in a populated area, or out in the country?
5. Are there neighboring businesses within 100 yards of your environment? If so how many?
6. Approximately How many uses will access the wireless network at any given time?
7. What type of devices will use the network (for example laptop computers, or hand held scanners)?
8. Do you know what type Wireless Network you want to install (for example: 802.11g, 802.11n)?
9. Will there be a mixed environment of different types of equipment with varying capabilities?
10. Do you know what type of Data you will be sending across the Wireless Link (for example: Graphics, or Bar Codes)?
    

Site Survey Pricing

Survey Menu: ala cart / Smorg.


Pricing.
You will probably will want to make at least $50 an hour for your trouble. In a large installation, the end users will want MANY deliverables for the amount of time an accurate survey will take. In a small shop you might need to provide a solid network, and summary report.

You might want to consider price packaging your services, especially on smaller surveys. For example you could offer a survey with an air audit, and recommendations for $200 if you think that you can get the job done in four hours or less (this is doable in a store-front business).
A warehouse may take three eight hour days, you might want to consider block pricing your time in a flat rate structure such as $500-800 per day, or perhaps a flat rate for a two or three day survey.

As far as incidentals go, you have “zoning” or travel charges, consumables (such as batteries-what you will use specifically for each particular survey). Some Analysts group reports into packages and bulk price them some charge per items, and some have in inclusive deals.

As far as reporting goes here are some options:
* Signal Strength
* Noise
* S/N
* Rogues/Neighbor AP maps.
* Throughput
* Channel Map
* Packet Traces