WiFi Data Systems: What to Watch Out For (Part 5 of 5)

Using wireless modems is an appealing way to build a data network because it's convenient. Long cable runs aren't necessary, which tends to keep the labor costs down. Modems are inexpensive and can be obtained easily. Expansion of the network can be as simple as buying another modem box and locating it where it's needed.

However, despite all the advantages, there are a few land mines that one can hit when deploying a wireless network. In fairness, it should be noted that the problems listed below are rare and very few networks will have these issues. But, such problems have been known to arise and it's worthwhile to keep them in mind. Especially, if a network develops a problem that needs troubleshooting after it's been deployed.

LICENSED AND UNLICENSED USAGE

First, I should clarify something about the legal aspects of anything that uses radio waves. In a broad sense, radio (or wireless) devices fall into two classes; those that require the user to obtain a license from the Federal Communication Commission (FCC), and those that don't.

The FCC issues licenses to users for their radio communications equipment. This includes everyone from police and fire departments to radio and television stations. Without a license, those organizations can't use their radio equipment. However, when WiFi and wireless computer networks began to be deployed in increasing numbers, it became obvious that trying to issue licenses to everyone who wanted a local network just wouldn't be practical. There were just too many users.

So, the Commission set up various bands that users could access with unlicensed devices. They also put the burden on manufacturers to insure that the equipment they were making for use in these bands met the certain technical specifications. All products that are made to be used in these bands must comply with Part 15 of the FCC rules.

The good news here is that when you purchase a new wireless modem for your computer network, you don't have to worry about getting a license to use it. All you have to do is plug it in and let it work.

Except there is one downside to this: the possibility of interference.

INTERFERENCE FROM OUTSIDE SOURCES

The bands used for wireless data communications for unlicensed users are the 2.4 GHz and 5.8 GHz bands. Because of the proliferating usage of radio frequency based systems today, it is possible for some non-WiFi devices, such as cordless phones, to create a problem for a wireless network.

In essence, there are two main criteria that Part 15 of the FCC rules lays down. First, any unlicensed device used in these bands must not cause interference with a licensed device. Second, any unlicensed device must accept interference that is caused to it.

In the first instance, if your wireless network is causing interference to a licensed users, then you have no choice but to correct the problem immediately or, worst case, shut down your network. The user with the license has the priority and the right to the usage of the band in question.

In the second case, if a user has a device that is causing you trouble and that user has a valid FCC license, then, bluntly put, you are probably out of luck. You can't force a licensed user to stop using their devices or equipment. Again, this is because the user with the license has the priority.

There are other technical issues that also need to be taken into account when one of these situations arise, but those are generally ones that you may hit with outside interference. That is, when something other than a wireless LAN interferes with another wireless LAN.

INTERFERENCE FROM INSIDE SOURCES

Under certain conditions, it is possible for a data network to interfere with another data network. This is extremely rare, but as anyone who has worked with radio equipment will testify, almost anything is possible.

If you have an existing wireless network deployed and you want to add another network, you might experience this issue. Even with all of the modern software and sophisticated modulation techniques, it can still happen. Many times the instruction books provided with wireless modems will discuss this and will suggest some ways to keep the two networks from colliding with each other. Difficult cases may require you to obtain the help of a competent radio engineer to overcome the problem.

A more difficult challenge is when your network is interfering with another user in your area, say a next-door business or neighbor. You'll have to then work with them to fix the problem. However, because of the low power levels used in wireless networks, it's unlikely you'll ever have to deal with this issue.

Some users, in an effort to cover more area, will attach a different antenna to the wireless modem than the one that came with it. Some cordless phone system users will try this too. But, the FCC publication "OET Bulletin No. 63" explains the need of using the proper antenna as follows:

"...Part 15 transmitters must have permanently attached antennas, or detachable antennas with unique connectors. A "unique connector" is one that is not of a standard type found in electronic supply stores.

It is recognized that suppliers of Part 15 transmitters often want their customers to be able to replace an antenna if it should break. With this in mind, Part 15 allows transmitters to be designed so that the user can replace a broken antenna. When this is done, the replacement antenna must be electrically identical to the antenna that was used to obtain FCC authorization for the transmitter."

So, if you want to try to make your system cover more territory, it's better to use a "booster" or get another modem. Changing an antenna could create more problems for you than you want.

PROBLEMS WITH THE PHYSICAL ENVIRONMENT

Part 4 of this series discussed the problems that can happen due to the building that you're in. Things like large steel beams used in the framework or large quantities of concrete in walls or slabs dividing sections of a building can block signals from covering all the areas that need to be served. Again, a good radio engineer is the best person to help solve problems caused by the structure that the network is deployed into.

HACKERS, INVADERS AND SPOOFERS

Also in Part 4 of this series, we discussed the security issues involved in over-the-air networks as opposed to wired networks. This is a real problem and needs to be considered if you're going to go wireless. Don't assume you'll be alright and that you won't need to protect the network. Use the proper recommended security techniques.

FINAL THOUGHTS

I hope that this Wi-Fi Series have been helpful in understanding radio, wireless, radio frequency information and the use of over-the-air data transmissions. The main goal of this series was to make it clear that the hardware and software requirements are very complex. Sometimes it may seem like magic, but it's really not. It takes a lot of work on part of both the hardware and software engineers to make our data modems work as well as they do. Even so, future developments will probably be even more astounding than what we have today. That's the beauty of living in a high technology world. 

Click here to revisit any of the the posts you may have missed in this series:

Part 1 - WiFi: What Does the Name Mean and How Does it Work? 

Part 2 - The History of Wireless Technology: Wireless or Radio? 

Part 3 - WiFi Radios and Modulation Techniques 

Part 4 - WiFi RF and Data Security Issues

Paul Black is a freelance writer and broadcast engineer in Northern California. He holds a Certified Professional Broadcast Engineer certification from the Society of Broadcast Engineers and an FCC Lifetime General Class Operator License. He is a licensed amateur radio operator (call sign N6BBZ) and has worked for several broadcast companies, including Bonneville Broadcasting, RKO General Broadcasting, and CBS Television. Visit his website at www.paulblackcopy.com.