December 15, 2016

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


December 1, 2016

WiFi RF and Data Security Issues (Part 4 of 5)

The use of radio-frequency (RF) devices for wireless transmission of data is an appealing way to set up local networks (LAN). RF-based routers have become relatively inexpensive, easily available from many suppliers, and simple to implement.

In places like private homes, small business locations and even larger areas, such as malls and hotels, wireless networks have become about as common as telephones. Retailers, especially those that operate large brick-and-mortar stores (ie supermarkets or department stores) frequently set up these networks. Consumers who walk into a store are urged to sign-on and thereby get special prices or get help navigating through the store. 



In the last decade or so, many businesses that exist in an office environment, like insurance companies, have implemented wireless LANs, both for their employees and also for use by visitors. However, there are some potential problems for both the operator of the network and the users of the network.

RF SIGNAL BLOCKAGE ISSUES

Unfortunately, radio waves can't go through all materials. Metallic items used in most commercial construction, like metal wall studs, window frames and HVAC ducts, can act as signal shields. These items can also deflect signals around in ways that make I hard for mobile devices, like laptops and smartphones, to receive the signals. This can result in some areas being inaccessible to any over-the-air connection.



Not only does this make it hard for the mobile devices to receive the signal from the LAN, it can make it equally hard for the LAN to "hear" the mobile device. Data sent from the mobile device, either doesn't get through or it requires so many retries due to dropped packets that the response time is slowed down dramatically. The result is frustration on the part of the users.

SCRAMBLED DATA / INTERFERENCE

Two of the more frustrating experiences users suffer are problems with data being scrambled and other services that use the wireless bands creating interference (almost always unintentionally).

As previously mentioned, it can take many retries to send or receive the information. Besides slowing down response time, the data can get badly corrupted. This can result in problems like missing or garbled text, images and graphics not loading, and other unwanted effects.

Interference to a LAN signal these days is rare, thanks to modern modulation methods and encoding/encryption techniques. But it does happen occasionally. Wireless LANs typically use the unlicensed sections of the Industrial, Scientific and Medical bands (also called ISM bands for short). Many other services use these bands also.

Because the Federal Communication Commission does not issue licenses to users to operate in these bands, there is no protection to any individual user against invasion from unwanted signals.

HACK ATTACKS

By far the largest drawback, and the most dangerous one, is the ability of "wide open" networks to be invaded by hackers. Attacks of this type are very common. Criminal hackers can extract everything from documents to credit card and banking information stored on mobiles. The rise of identity theft is due in part to this kind of activity.



SOLUTIONS

Wireless data LANs that operate in the ISM bands must use a fixed power level. It's not possible to increase the actual transmitted power. Federal Communications Commission (FCC) rules prohibit changing this. Increasing the power to improve coverage is not an option.

However, much work and research has been done by the hardware manufacturers in the area of antenna technology. If you look at a modern router, you'll probably see at least two, or as many as eight, antennas attached to it. This helps a great deal with coverage. Routers from the major makers, such as Linksys or Netgear, now have much longer ranges and larger areas of coverage than those of just a few years ago.

In some environments, areas to be covered and materials used in the construction mean that one single router can't cover the entire area. It is possible to deploy another router, but many times a wireless range extender device will provide signal where it's needed.These devices are simple to install and relatively inexpensive compared to the cost of a router. They are used extensively in both commercial and residential locations. 

Proper placement of both the router and any range extenders can help a lot in improving coverage. Avoiding putting these devices near large metallic objects, or anywhere a large number of electrical cables are installed, can help to insure that signal quality is the best it can be.

By creating proper hardware placement, the number of dropouts and the need for continuous retries to get data delivered successfully can be reduced to a much more tolerable level. This can also help alleviate interference from other users in the band. 

The problem of hackers invading a LAN, particularly one that is open and not secured, will always be with us. In an employee-usage environment, like in an office, or in a home where the LAN is used by only one family, proper security methods typically eliminate attempts by hackers to compromise the network. If visitors need access, they can be given a temporary password that will allow use of the wireless LAN for a limited time.

From the user standpoint, another way to insure that a mobile device can communicate securely in an open-network environment is to set up a Virtual Private Network (VPN). This creates a tunnel from the user to the website or server that is being accessed and is encrypted to keep data from being interrupted. There are many companies that offer this service for a monthly fee.

Now the concern is; what are the pros and cons of deploying a wireless network in any given environment? Our next, and final post in this series, will define some of these and point out the good, the bad and the ugly sides of wireless LANs.




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




October 21, 2016

WiFi Radios and Modulation Techniques (Part 3 of 5)

As mentioned in our History of Wireless Technology post, getting data sent over the air without wires isn't as easy as it is when you have a wired, or cabled, connection system. 

Think about a standard two-way radio. The correct name for this kind of radio is a "transceiver". It both transmits and receives, therefore it's called a "transceiver". 

It's probably safe to say that most people know at least something about how a radio like this works. If you've ever watched a television show that feature police, fire, or other people that use two-way radios, like airline pilots, you've seen these radios in use. When you want to talk, you pick up the microphone and push the button on the microphone. When you're done talking, you let up on the button. The person you're talking to will then reply to you and you can hear them.




Unfortunately, for data communications, trying to use radios in this manner won't work. This doesn't begin to allow data to be sent and received with the speed, accuracy and reliability that is needed.

SPEED AND BANDWIDTH NEEDS

Radios used for data have to be fast, with lots of bandwidth, and be reasonably immune to natural and man-made noise and interference. They also have to be able to accept data streams in various protocols and translate the digital data (the ones and zeros, if you will) into something that can be impressed upon a radio signal. Following that, the signal has to be of a high enough quality that it can be received and turned back into the original data (again, the ones and zeros).

The proper word for putting any information onto a radio wave is called "modulation". We don't have time here to delve deeply into all the math and theory involved to explain the way digital data is modulated into a radio wave. However, we will look at the main method used for LANs, WANs, mobile cellular phones and data communication in general.

The modulation technique that's almost always used is a method called "spread spectrum". It's got an interesting history. Spread spectrum was developed for use in military communications. The idea was to keep the enemy from being able to intercept and decode secret communications, yet also make it hard for the enemy to jam radio signals. 

The original spreading technique was called "frequency hopper", or it's more modern term, Frequency Hopping Spread Spectrum (FHSS). It worked by actually changing the frequencies as it was transmitting the signals. Every few milliseconds, the transmitter would hop to a new frequency. So, even if you could tune into one of the frequencies in use, it wasn't long before it was gone. Then, on the other end, the receiver had to be able to follow the transmitter when it changed. This took a lot of careful timing and delicate control, but it did work. It kept the enemy from being able to intercept the communications.


Frequency Hopping Spread Spectrum (FHSS)

The first patent for this type of modulation was issued in 1942 to music composer George Antheil and Hollywood actress Hedy Lamarr. The two were introduced at a party where they originally bonded over the women's magazine articles Antheil wrote about endocrinology and ways to increase Lamarr's bust size to make her more attractive in Hollywood. But it was during these scientific discussions that they turned their conversations over to the war and how the Germans were struggling with their torpedoes missing their targets. This is rather a fascinating story as told in a previous blog post, Beauty, Brains and Secret Communication, or if you're a podcast listener, check out the You Must Remember This episode featuring Hedy Lamarr.




For many years, the frequency hopping communication system was classified as "SECRET" by the United States government. The Army Signal Corps was the only organization that used it or knew all of the details on how it worked. As time passed, however, researchers in the private sector began discovering how spread spectrum functioned. When the scientists and engineers outside of the military figured out the secret, it wasn't really a secret anymore. Finally, after the patent expired in 1962, it was declassified and available for use by the civilian sector.

MORE THAN ONE WAY TO HIDE THE SIGNAL

In addition to the original Frequency Hopping Spread Spectrum (FHSS), the other spread spectrum system is the Direct Sequence Spread Spectrum, or DSSS for short. This works differently, as it doesn't "hop". DSSS takes the digital signal and combines it with the radio signal in such a way that the signal is spread out over a large number of adjacent frequencies, at the same time.
Direct Sequence Spread Spectrum (DSSS)

There are several ways to do this, but one of the more common spreading methods is called Code Division Multiple Access, or CDMA. Almost all mobile phones used in the United States operate using this method. Among its many advantages, it allows a high level of security for phone calls to help eliminate eavesdropping on phone conversations. It also allows several mobile cell phone calls to exist in the same general frequency band at the same time. By allowing that, more mobiles can be used by more people without the problem of running out of available channels, which was a common issue in the early days of mobile cell phones.

It also helps in allowing what is called "duplex" communications. This means that you don't have to push a button to talk, like you do with the two-way radios as described in those previously mentioned tv shows about police and firemen. This makes a mobile cell phone call sound and function almost the same as a regular landline telephone call.

THE NEW AGE OF DATA COMMUNICATIONS

With the development of the capabilities described above, mobile phones and data communications entered a new era. Now, there are ways to create radio-based systems that emulate a cabled system. The age of the wireless router came about as a result of these advancements in radio-frequency systems. However, despite all of the wonderful capabilities we now have, there are still some pitfalls, land mines and other difficulties that a radio/wireless data communication system is subject to. In our next installment, we'll explore some of the what-not-to-do's.

If you'd like to read more on all of this, plus more that we didn't cover here, I recommend reading "Wireless Communications and Networks", by Dr. William Stallings. It's very easy to read and makes all of the theories very understandable.




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