Chapter 25: What’s the Point (to Point)

It seems like the longer I wait to write these, the further I get behind with all the news in the broadband industry. Between AT&T trying to relive its glory days of a total monopoly of the wireless telecommunications market and the government finally figuring out that CenturyLink was smarter than they were, it’s been interesting times. It is hilarious to watch CenturyLink completely corrupt the concept behind the RUS and then surprise the industry with a massive takeover move. If Cox and Comcast hadn’t thrown it in the face of the RUS, the RUS would still be feeding money through the various shell companies CenturyLink used to hide their activities. I wonder how many more proposals from CenturyLink subsidiaries are stilling pending on the desks of the RUS and what they plan to do about them. It’s been strangely quiet over there.

The growth of CenturyLink was partially funded on government ineptitude. I applaud CenturyLink for figuring out the best way to play by the rules (if it really was legal), no matter how much the taxpayer got screwed and how unethical it appears to be. If it was legal, they won and heads should roll. Can you imagine being a fly on the wall when CenturyLink announced they were buying Qwest after growing like crazy partially on the $1.7 Billion dollars they weasled out of the FCC under questionable pretenses. Of course, using the local companies CenturyLink hid behind in rural areas must have made it hard for the RUS to figure it out since nobody there must be capable of looking at a corporate filing. Somebody at that division should either be fired for incompetence or outright stupidity but probably according to government union employee rules, neither is a valid reason for termination. Of course, if they couldn’t figure out Bernie Madoff or that drug cartels moved $350 billion dollars through CityBank over several years (for which nobody has been prosecuted nor will be), why should we expect the government to watch out for a measly $1.7 billion dollars of taxpayers’ money? As Comcast and Cox adroitly pointed out in their letter, private industry isn’t going to invest or compete in areas where the federal government is propping up their competitors. Of course, Hughes and WildBlue also come to mind against the WISP community but at least they are training the next generation of inexperienced users that have more than one option of what not to buy. But then again, Ford could use the same argument when Obama paid off his union cronies by giving them billions of dollars and the majority of the stock in GM. Jimmy Hoffa would be proud since he never owned a President as completely as the United Auto Workers do now with Obama.

But let’s not dwell on the continuing story of government incompetence and corruption and move back into the realm of real wireless projects. After all, that’s what these articles started out as. I’m in this industry because almost every project has something unique and challenging. 

My latest product is a simple Point-To-Point link (PTP). I’m currently working on a project between 2 buildings that needs a leased tower location as the relay point. The tower is located about 10 miles from the taller building and less than a mile from the shorter building. Bandwidth needs to be at least 40Mbps or more and it’s fairly rural so 5.8GHz unlicensed isn’t going to be an issue in terms of interference. The only challenge is that the longer range link is going to require that the antennas are at least 250’ in the air.

There is nothing special about this project and many of you have done similar installations. Normally you calculate the link path, which in this case would be work great with a pair of 2’ 30dBm parabolic antennas. However, the crimp in this equation is that we get charged on the tower based on antenna size. The base charge is roughly $300 for but each additional foot of diameter of antenna costs roughly an additional $100. If the base is a 1’ antenna, then a 2’ parabolic dish antenna costs $400 per month, a 3’ parabolic dish antenna $500 and so forth.

I’m sure you can see where we are going with this. It’s our building on the other side of the 10 mile link to the tower so it’s possible to put up the Seti array if we wanted to on the building as long as the link path antenna gain equals or exceeds 60dBi. I calculated that a pair of 2’ parabolic dish is sufficient for the link but if we use a 1’ flat panel on the tower and a 4’ dish on the building, we can save $100 per month. Since we are using redundant links, meaning 2 antennas, that actual savings is $200 per month. The calculated antenna gain with the 2’ dish was 60dBi for both antennas. It so happens that Ubiquiti manufacturers a 25dBi flat panel radio/antenna that is 14” across with a 25dBi gain. On the other side we can use a 34dBi gain antenna which comes close enough to our link budget for government work.

So, what is the drawback to this idea? Well, considering we are using a lower gain, less directional flat panel antenna 250’ in the air that means the noise figure on the tower is going to be higher than it would be for the 2’ parabolic. That also means that the S/N ratio is going become more of a factor and has to be considered. Assuming you don’t think the noise figure is going up significantly, then there are no issues. On the other hand, the tower climber will hug you since he only has to deal with 5lbs of equipment instead of 60lbs.

I mentioned the redundancy to the link so let’s discuss that. Since the radio costs are so cheap compared to downtime, we can afford to put 2 of the antennas on the tower. Yes, that adds another $100 per month but compared to the cost of downtime and tower climbing costs, it’s relatively cheap insurance. That also means that we have to mount two 4’ antennas on a building for the other side of the link. Running the numbers again shows that we could cut down the gain on the antennas and use a second flat panel on the building side and still get close to the same performance or a slightly. Since the secondary link is only there for backup purposes and the radio on the primary link can be replaced in 30 minutes or less, then if the secondary link has a slightly slow modulation rate such as MCS(12) instead of MCS(15) rates, then it’s not a big problem. That also means that the backup radio can be another flat panel instead of the 4’ dish since it only has to operate a short time while the radio is replaced on the back of the dish. That reduces the cost and the size of the roof mount on the building size also.

On the tower side, we have now limited the wind load to two 14” flat panels for redundancy. Redundancy can be handled many ways. The easiest is to power up both radios and use something like OSFP, STP, or RSTP to maintain redundant links. Another alternative it is to use something like an IP based power switch from Digital Loggers http://www.digital-loggers.com/lpc.html which can be programmed to power off one radio and power on another radio if there is a failure. I have used both methods in different projects. In this case, because towers are more susceptible to lightning hits, I’m more inclined to go the power switch route. The power switch basically turns off the power to the radio, thus disconnecting it from the power lines in case of an indirect hit. A direct hit to the tower probably fries both radios, regardless of whether it’s powered up or not. I can attest from personal experience that unpowered radios will get fried also when that happens. Although 8 unpowered radios were fried, 1 unpowered radio survived so you take your chances. A good strategy and this was the only thing I can attest this to, was that the unpowered radio was also several feet below all the other radios. I’m covering both bases with this install. This will also be the strategy on the tower with the two flat panel radios.

I mentioned early on that the tower was a relay point for the link which really means 4 radios. If we were using 2 more radios for the link, then we are adding to the wind load and thus the costs of the monthly rental fee. However, what if we can reduce the size of the radios so that their footprint doesn’t add to the cost? Since the second link is only ¾ of a mile, then we can use a very small footprint, Ubiquiti NS5M, which literally at 3” wide, is thinner than tower legs themselves. That means that it adds no cross section and even if there is a small charge, it probably will be very minimal. Again, we are going to use 2 radios for redundancy and these will get mounted towards the bottom where they pretty much become invisible against the legs.

PTP links don’t need to be symmetrical. Antenna gain takes into account both sides, not just one. If you are paying for tower footprint by the square footage, it makes sense to reduce the antenna size as much as possible. Obviously there may be some additional costs on the other side but usually Esmits minor compared to tower rental costs.

Chapter 22 - Is Law Enforcement the Red–Headed Step Child of the Broadband Movement?

When Wireless Broadband was on everyone’s lips 8 years ago, we all thought we would be able to use our laptops everywhere. About the same time that Earthlink and Metro-Fi realized you can’t make “Free” pay off for their investors, 3G started moving in to fill the void. Then YouTube came along, pushed 3G to the ground and said, “I spit in the face of your puny bandwidth (insert Austrian Accent Here).” 3G then said, “Oh yea, my big brother, 4G, is coming and he will take care of you. You will be sorry.” YouTube said, “BTW, meet my cousins, Hulu and NetFlix”. 4G took one look at these guys and said, “I’ll fight you guys but you have to have one hand tied behind your back, both legs tied together, and we are only going to fight for 10 minutes. After that I win and you have to go home”.

In the meantime, the Big Land Barons who wanted to expand their holdings went to the Lords of the FCC and whispered in their ears, “Our lands aren’t big enough and we have rocks and trees in our way. If you kick out the squatters that are on some of your prime land, we will buy it from you and enrich your coffers.” So it was that the Lords of the FCC created The Great Plan. They took The Great Plan to the Council of Kings and said, “We need you to pass a law to kick out the old squatters. We will tell them they are doing the right thing for the country and then resell their land for a fat purse. We will then give some of the land to new squatters for free who will also develop the land and make our Kingdom better.”

When the Sheriffs heard of The Great Plan, they said unto the Lords of the FCC, “We have worked our lands to death and need new lands. The Bandits are smarter, faster, and meaner. We need new lands all across the Kingdom and in every village so Sheriffs are closer and can work together to stop the bandits.” In the Great Plan, the Lords of the FCC decided to appease the Council of Kings and not ask them to use the coin from the Great Sale to pay for the Huts and Barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle. Oh no, they were more clever than that. The thought they could fool the Big Land Barons into paying for the not only the land, but for the huts and barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle (I’m a huge Arlo Guthrie fan). The Lords of the FCC said unto the Sheriffs, “we will grant you new lands in order for you to protect the peasants from the bandits.” Thus, the Lords of the FCC were happy with their new plan and went forth to preach it. And so it was written, and so it was done.

To the peasants, the Lords of the FCC preached, “We are confiscating ill-gotten lands given away by the former Lords of the FCC in order to give you better services and enhance your cities and huts”. Prosperity will grow across thy land and all will be connected to the Great Message.” And the peasants and other squatters did not object for it was not their land being confiscated.

The FCC executed The Great Plan. They confiscated the lands and sold them off to the new Land Barons. The new Land Barons offered the Lords of the FCC a great amount of coin, thus ensuring that the Lesser Land Barons weren’t going to be able to buy the new prime land. At the same time, the FCC told the Sheriff’s, “We have decided that your land is too valuable to just give to you so we are going to sell it to the Big Land Barons. However, we are going to make the Big Land Barons build you houses and barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle.”

When the Land Barons read the scrolls written by the Lords of the FCC on how to use the new lands designated for the Sheriffs, they went to the Lords of the FCC and said, “We do not want that land. It is too costly and cumbersome to build the houses and barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle.” They then paid the Lords of the FCC a great amount of coin for the land they had already bought. The Lords of the FCC quickly left the Great Hall so as to not have to explain to the Sheriffs why their plan had failed and the Sheriffs still had no new land.

After that, many Sheriffs sent many riders to the Lords of the FCC requesting the new land. The Lords of the FCC spent long seasons pontificating on what to do about the land they confiscated for the Sheriffs. After a very long time, they came up with The Little Plan. The Lords of the FCC decided in the Little Plan that they would grant the land directly to the Sheriffs. They said, “We will give you the lands, but we will tell you what you may build on the land. You may only build huts and barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle as to our specification.” The Sheriffs said, “We have no coin to build huts and barns and lookout towers with 360 degree coverage and an 8” spyglass mounted in the middle. Where is the coin from the Land Barons for sale of the other Land?” The Lords of the FCC said, “It has been confiscated by the Council of Kings and redistributed to friends of the Great Messiah and the Council of Kings. There is no coin for you. You have to find your coin from somewhere else to follow the Llittle Plan.” And that my dear friend, brings us to today.

Basically State and Municipal Law Enforcement sort of got left out in the cold when it came to the new 700MHz frequencies. It’s not that they didn’t eventually get the bandwidth they needed; they were told that they must deploy the most expensive technology available to actually use it. Instead of using the money from the auction to build out this infrastructure, each municipality must fund their own infrastructure. Of course, considering that 3 different agencies in the Justice Department haven’t been able to build a simple radio together after wasting hundreds of millions of dollars with no end or product in sight, it’s probably too much to ask them to build a nationwide wireless system. This edict was also given at a time when government budgets are getting hammered from top to bottom. Since public safety has no money to deploy even two tin cans and a kite string, I don’t think we will be seeing high-speed bandwidth for mobile public safety in the near future in most major cities.

We started discussing a project last month where I needed to move 1Gbps or more of bandwidth 20 miles for a county wide system. There is new wideband equipment being released as we speak and I haven’t finished my homework so I’m going to table that phase of the project for a while. Since the project has several components, I thought we might jump over to the third tier, the last mile, since it directly ties into public safety.

As many of you live in areas where your vegetation grows over 8’ and doesn’t make you look like a porcupine when you bump into it, I thought tackling a project like that would be a good idea. Living in the desert has made me oblivious to the fact that there are cities across the country where houses are surrounded by trees that could double as space elevators and should have lights on top to warn airplanes away. Throw in vegetation that comes with its own zip codes, and there are places where the term Non-Line-of-Sight (NLOS) takes on a whole new meaning. Every cell tower that I saw in the area was so tall I figured I was coming down with magic beans if I ever had to climb one. I also learned that approaching someone getting out of a truck that came with a factory gun rack was probably not the best idea.

However, as high as all the cellular towers were around the county, there is no chance that 80% of the houses are ever going to see one from their front window. That means we are left to figure out how to get through the trees. In Chapter 17, we talked about how 900MHz can punch through vegetation, houses, and really mean neighbors. Since that article was written, some of the data I’m reading on current 900MHz deployments is pretty promising. However, deploying 900MHz can be kind of like trying to give a cat a bath, you get a trip to the emergency room and the cat just gets really ticked.

A quick review of 902-928MHz band means that we only have 26MHz of bandwidth to work with. By comparison, 5.8GHz has about 100MHz of spectrum to work with and 2.4GHz has approximately 60MHz. In practical application, a 5.8GHz system can deploy 4-5 APs with non-overlapping 20Mhz channels and a 2.4GHz tower can have 3 non-overlapping 20MHz channels. The 902-928MHz band is a little tighter so we only have room for one channel if we are using a standard 20MHz wide channel.

That means we need a different strategy. Assume that our coverage area is 360 degrees. Most wireless products in 902-928MHz band use down-converted WiFi chipsets. That means the throughput will be the same as 802.11a and 802.11g radios with the same channel widths. Motorola uses an FSK scheme instead of an OFDM modulation scheme that trades off a lower throughput for a better s/n ratio.

Both systems have a bandwidth rate in Mbps that is numerically about ½ the spectrum size. For example, Motorola uses an 8MHz channel and has a maximum capacity of 3.3Mbps total aggregate. WiFi down-converted systems with a 10MHz wide channel will have an aggregate throughput of about 5Mbps. Some Wifi systems have a little higher throughput but all of this assumes a connection at the highest level modulation rate. The other side of this equation is the whereas Motorola will work with a s/n ratio of 3dB, a WiFi system needs a minimum of 10dB.

802.11N 2x2 MIMO has a different formula. Not only is the efficiency of the protocol better than 802.11a/g, the processors are typically faster, more efficient, and have better sensitivity ratings than older a/g chipsets. From there, throw in the fact you are transmitting two signals in the frequency spectrum. The end result is such that the rule of thumb of throughput is approximately quadruple the channel frequency width. A 10MHz channel width should have a theoretical throughput of about 40Mbps.

The lack of channel bandwidth in the 900Mhz band is one reason that it never caught on very well. The other reason is that the noise floor is significantly higher in the 900MHz band than it is for other unlicensed bands. Because of the NLOS nature of the band, it’s heavily used for SCADA, baby monitors, cordless phones, ham operators, and many other things. In any major city or suburb, you probably have noise levels in the 50-60dBi range which makes it very difficult for most WiFi based chipset radios to operate.

The third problem with the 900MHz band is that laying out a network design for a large area is significantly more difficult. In 5.8GHz, the antenna beam patterns are pretty well defined, the signal can’t penetrate lace curtains, and it has limited reflection characteristics compared to the 900MHz. For those reasons, it’s relatively easy to define optimal tower locations. 2.4GHz sort of falls in between but the noise figures for 2.4GHz will still be lower than 900MHz at ground level. At the tower locations, I can imagine it’s a toss-up as to which frequency band will have a higher noise level between 900MHz and 2.4GHz depending on the population density around the tower. 900MHz on the other hand, bounces around like a Superball in bathroom, needs a Fresnel zone the size of Delaware, and just feels a little tickle when busting through a brick wall.

Verizon is probably about halfway to deploying their 700MHz LTE system across the country. The difference between them and us is years of experience in 800MHz and software that costs more than my last car. In addition, the antennas they use can be remotely adjusted on the fly in micro increments to fine-tune coverage zones. Since I haven’t heard anything about WISP operators learning to levitate, that means lifts or tower climbs, both of which are significantly more difficult and time consuming than moving a mouse.

With these issues, why would anyone want to use 900MHz band? Well, that is because we really don’t have much of an option. It’s our only option through Sherwood Forest and we need to figure out how to make that work. Let’s first define the environment as being rural which reduces the variables and takes the noise figure off the table. Then let’s assume we are covering about 2 miles in every direction and we have trees all around. Throw in the decision to limit users to a maximum download speed of 4Mbps and upload of 1Mbps for Round 1 and the system design gets a little easier.

The first issue is the AP configuration. Since 802.11n 2x2 MIMO is pretty much standard in the WiFi industry today, the use of it in 900MHz is unique. The Ubiquiti Rocket M900 with a dual-polarity 13dBi 120 degree sector antenna makes an attractive option. Assuming a 20MHz wide channel, the AP should be able to support a theoretical maximum of 60-100+Mbps of aggregate bandwidth. However, we have to put 3 of them on the tower to cover 360 degrees and I guarantee we aren’t the only squatter on that land. That means that we are going to have to limit the channel size to 5Mbps to avoid overlapping channels and minimize interference. It also means that the maximum theoretical throughput is about 20Mbps and from my testing, I would assume 10Mbps per AP.

If we use the 10-1 client/bandwidth formula, then we should be able to support 20 users per AP with a 4Mbps down and 1Mbps up scheme. That’s also 60Mbps of total capacity per tower. Those aren’t bad numbers if you are charging $40 per month per client. If you are using Water Tanks for example, where you can isolate the antennas from each other, you may have the option of using 10MHz channels. There are also antenna shields from sales@rfarmor.net that promise that you can use 10MHz channels and radios on the same tower and they won’t interfere with each other. However, this could also be accomplished with GPS synchronization with close to similar results if the Rockets every support this feature. I’m a fan of as much isolation as possible with multiple APs on the same tower regardless of synchronization so they are in my budget list.

This is where we tie all this together. 900MHz in rural areas is also a great poor man’s Public Safety System. With the right RF engineering and other design features, the same system could deploy 2-10Mbps or more to a police vehicle. Fast handoff hasn’t been resolved yet but I’m working on a couple solutions as I’ve mentioned in other articles. A system like this should cost about 1/20^th to 1/100^th the cost of an equivalent LTE system. I’m not suggesting that this type of system be deployed in any cities or suburban areas that have high noise issues in that band or that plan on deploying a 900MHz smart grid system, but since over 90% of this country is still rural, this capability can be added for at a cost of under $3000 per AP with each AP covering 4-36 sq miles. The cost for the cars is less than $400 without fast handoff or redundancy. Compare that with a typical LTE or WiMax deployment that the police clearly have no money for, and it’s a pretty good alternative for small towns and rural counties.

900MHz is both magical and a pain to work with. It opens up new opportunities in rural areas where wired fears to tread for financial reasons. At the same time, it’s also a little more expensive than traditional 5.8GHz PTP systems but a lot less expensive than most street level 2.4GHz muni systems. However, when compared to 3G speeds, 5GB caps, spotty coverage, or even worse, no coverage, it’s still a far better option. The application of 802.11n 2x2 MIMO technology now makes it a more viable technology for rural areas.

Chapter 19 – Catch a Wave-Guide and You are Sitting on Top of the World

The Beach Boys are going to hate me for this but I’ve been waiting for years to use that line. I also wanted to title it, “Look Ma, no mesh” but I should have used that one several articles ago. It’s not that I have anything against mesh as there is an application for almost every technology. At this point in the industry and the economy, however, it’s time to get past a word very few non-technical people understand and the excessive associated cost of it. Anyway, this article is about wave-guide antennas so let’s get back to that.

Vivato was a wave-guide based antenna. I have had Securawave wave-guide antennas installed for about 7 years. I became a believer when I connected a car at 2 miles and my laptop inside a Jack-in-the-Box at 1 mile. The horizontal polarity was a huge advantage since most wireless APs were vertical polarity. Securawave is no longer in business so I’m hoarding the last few units I have to support units I have in the field. Not that solid aluminum blocks have a tendency to fail as I suspect they will last longer than the buildings they are mounted to (they just don’t make them like this anymore), but in case of physical damage. I don’t need dual-polarity and 2x2 MIMO yet in these areas because Qwest hasn’t figured out how to get more then 3Mbps over the so-called HD Internet services and I’m not ready to mortgage my house for their other service offerings. Of course it’s hard to dial the phone when your eyes are tearing up from laughter when they advertise their new 40Mbps service. 18 months ago they couldn’t even keep a 640Kbps DSL line running properly in the middle of Phoenix less than 1 mile from Sky Harbor Airport.

Historically, wave guide antennas were expensive to make which is probably why it didn’t have more popularity. Ubiquiti seems to be bringing it back with its new omni-directional dual-polarity antennas. We know that dual-polarity has better penetrating and range capability than single polarity. So the idea of extending that into an omni-directional antenna seems like a great idea. Since there isn’t any other 2x2 MIMO omni-directional dual-polarity antennas that I know about, this is really cool from a technical, design, and financial standpoint. It’s also how we are going to keep Guerilla WiFi cost-effective and make it better.

The new Ubiquiti omni-directional antenna isn’t a true wave-guide antenna. Since it needs both polarities, half the antenna is basically two 180 degree vertical polarity sector antennas back to back with dual 180 degree wave guide antennas. Since it’s not out yet, I haven’t tested the unit but the pre-spec guess is it’s around 12-13dbi. That means the effective LOS range with dual polarity is going to be about 30% farther than an omni with 15dBi of gain for a couple of reasons. However, real world performance is going to be significantly better since dual-polarity will definitely penetrate vegetation better, reduce noise off-polarity, and reduce fading. If the client is using a dual-polarity indoor radio, then not only will range be better, noise will be significantly reduced even further. I smell a huge performance improvement in the air for Guerilla WiFi.

Let’s go back to Chapter 1 of Tales where we designed a $10K per square mile system. In that design, we used a 15dBi omni-directional antenna with a single polarity omni-directional. This design was using a single stream 802.11 b/g/n design. With the new dual-polarity omni-directional antenna, we still use a single radio for our AP but we have doubled the throughput with a 2x2 MIMO stream. In addition, we have doubled the throughput of every hop and added an additional hop. Even at the 4rd hop we are still delivering up to 10Mbps. Keep in mind that at a 10-1 oversell rate, that means that you can sell twenty clients 5Mbps at the end of the chain. Although pricing hasn’t been released, I’m pretty sure this antenna with a Rocket M2 radio will still cost less than $300. Double the performance of the original Guerilla WiFi at no additional cost and it’s better than triple coupon day at my local grocery.

Think about that for a moment. If we only had one egress point for our network, our base network was limited to 3 hops with the same capacity at the end. This single antenna, which allows us to change from a single stream 802.11b/g/n radio to a 2x2 AP, doubles that throughput, thus extending our single AP model out even further and doubling bandwidth down the chain. Our egress point can also use multiple radios which can triple the throughput to 3 times that for $300-$600 more without even getting into out next topic, GPS Synchronization. So for less than $11K per square mile, the system now supports 180-300Mbps, depending on the clients. So if your town is 20 square mile and this whole system cost $250K to put in, then it’s a no-brainer simply for cameras, security, mobile access, and department efficiency. Of course, if it goes through federal funding, has government engineers add in the fact that it has to support mesh (pointless in this and most designs but adds significant costs), throws in ridiculous temperature requirements like -30C for Phoenix or 80 degrees centigrade when -75 degrees centigrade would work fine, and requires copious amounts of paperwork to tell 14 different government agencies that you are paying wages equal to union scale even though you pay your guys more than that, then it’s going to cost $1,000,000 (my English teachers just had heart attacks over that sentence). If you can sense my frustration with federal rules that require union contractor shops to do work that is clearly better suited to IT companies, then you are very astute. This is why projects involving the government cost so much and take so long.

If this is a for profit network, $250,000 to cover 20 square miles with this level of bandwidth is pretty impressive. It’s fairly easy and cheap to add 100Mbps backhaul to each square mile for a total of 2GBps for the entire system. Realistically, I would guess that you would get about 500Mbps before the price starts going up for full-duplex links. Keep in mind that we are back to the core idea of an inexpensive municipal deployment.

Using numbers from previous articles, let’s assume 800 potential clients per square mile. If we get 10% of that base at $30 per month, that’s $48,000 per month. With this type of system, only a very small percentage of clients are going to need truck rolls. Total revenue on this network is almost $600K per year. If users have to get client radios, then they start at $30 for 802.11n 1x1 Vertical Polarity CPE’s. For about $80, you can include a window mount and get 2x2 MIMO. In most environments, I would be surprised if truck rolls needed to be done on more than 10% of the clients. Even if you add in the cost of the client radios, this system should be cash flow positive at 800 clients and should pay for itself at 2400 clients within 12 months. This just covers residential and doesn’t even get into business revenue. The numbers are now speaking to me so it’s time to kick the venture capital market back into high gear.

Also consider this, the 16 AP per square mile strategy now covers a higher percentage of deployments, especially profit oriented ones. If you live in the middle of high-density city, then you would want more APs per square mile for density or you fall back on the super AP concept described in previous articles. Since WiFi is far more unpredictable that PTP RF modeling, there is nothing wrong with installing 16 AP’s and then site surveying to see if there are coverage gaps than hinder more revenue.

Cell phone companies don’t cover every square inch of every house on the planet. It’s not cost effective. They deploy with the best models they have and then decide if it’s profitable after field testing to fix poor signal areas. WiFi should be deployed the same way. Put up 16 AP’s, field test, check the areas with poor coverage, and then decide if it’s worth another $300 in equipment to cover that area. If an area has higher usage, add in a triple radio AP upgrade for a few hundred dollars more. If an area really just needs more signal gain, look at adding a beam-forming AP just for a specific direction. There are many options but all of them would be based on sound profitability principals. There is nothing wrong with walking away from 2 customers that might cost $3000 to add additional infrastructure to cover.

I have 2 “Peeves of week” I have to get off my chest. The second is 99.999% uptime. I was asked to design a system where I have to guarantee the CPE’s have 99.999% uptime. Since the wireless industry has new equipment out every few months, very little of what I would deploy today has enough history for me to put my reputation behind that request. I’m not talking about PTP full-duplex $10K and put links but $50-$400 CPE’s. First off, anything less than 802.11N is too old and too slow for this type of video application. Second, anything that’s 802.11N hasn’t been around long enough to know how it’s going to run 3 years from now. It’s kind of a catch-22 situation. That means using cameras with built-in recorders that are going to cost three times as much or more than using lower priced cameras with CPE’s. Unfortunately there is no product history out there than guarantees that. The reality is that all the radios I work with rarely, if ever, just simply go offline if installed correctly. That doesn’t mean that they aren’t going to down for planned firmware upgrades or other system changes. However, the 99.999% uptime request didn’t stipulate whether planned maintenance was included.

I’ve already mentioned my first pet peeve, municipal bids that ask for mesh when every AP connected has a directional antenna. To everyone who keeps adding this expensive request into these bids, it’s a waste of money taxpayers’ money and costs the city a lot more to support in the long run. When you add a directional antenna to an AP or CPE, it’s a PTP or PTMP design, regardless of what firmware is on there. There is no mesh because the radio can’t connect to anything it’s not pointed at. By adding the mesh requirement, you are either getting the most expensive product out there or White Box APs with custom open-source mesh firmware that is cheaper. I’m not saying there isn’t a place for mesh, but don’t eliminate other options like WDS. It’s not your money you are spending; it’s ours, the taxpayers. Let the industry and a wireless engineer decide what the best product for the design is. It shouldn’t be the salesperson that took you out to lunch last week and has shiny brochures. If mesh is appropriate and the best fit, let the companies bidding on the project put that down. If WDS will work just as well or a PTMP design is better, they will bid that. So can anyone guessed what crossed my desk again this week? I know I’m beating my head against the wall on this since arguing with government is like trying to tell a 3 year old that candy isn’t good for them.

So we have come full circle on Guerilla WiFi from $10K per square mile to $50K per square mile and now back to $10K per square mile with double the performance. If this doesn’t kick the industry back into high gear, I’m not sure what will. Next we will cover GPS sync and how that affects deployments strategies.

Chapter 18 - Demystifying Beam-Forming

Based on some of the emails I’m getting, the biggest complaint is not enough details and without them, it’s difficult to implement the idea. Fair enough, I’m definitely guilty of that. In my defense, please understand that I want to have a personal life. Not that I have one now, as most WISP’s can attest, but if I had to put down every single detail on every single project or idea, I would be writing from here to Kingdom come. Except for the 6 guys on the planet like me that think they ought to make a movie out of every article in EETimes (I think a lower noise figure on a 741 OP-Amp makes a compelling plot line), most of you would be cancelling your Ambien prescriptions. The reality is that the details only matter to technical people and those are called White Papers. I’ve written a couple but I can’t sit still long enough to finish dinner, let alone do a 20 page technical document. My wife says that if I had put as much time into my homework as I have these articles, I would have my Master Degree by now. Of course, if University of Phoenix gave me real life credit for standing in a man-lift hanging antennas 80 feet in the air, I could get my Doctorate without ever attending class.

Let’s get back to the really cool stuff like beam-forming. We covered 900MHz and both the positive and negative aspects. Let’s move on to the category of what’s old is now new again, beam-forming. Vivato pioneered the idea several years ago but the financial model, coupled with irresponsible pre-marketing, didn’t really work in the real world. However, they did get the FCC to change the rules which is going to be a very good thing moving forward. The difference is how the different implementations of beam-forming are implemented and the effect in the real world, technically and financially.

Long before Vivato, the Super Scanner antenna from Antenna specialist tried to get an antenna to function in both a directional and omni-directional mode with the turn of a knob. Some of the manufacturers such as Wavion and Netronics sort of copied this model by using a ring of vertical omni-directional antennas. They can get up to 12dBi of antenna gain off of 7-9dBi antennas. Currently these units are limited to 802.11b/g bands and vertical polarity.

The next kind of design was done by SkyPilot where they simply rotated connection to one of 8 integrated sector antennas at any one time. This gave them up to 44dBm of EIRP in the 4.9-6.0 GHz bands. Ruckus, Netgear (with Ruckus helping), Cisco, and others are now integrating the antennas on circuit boards but at a lower gain. There will be several antennas cut into the boards or some other internal antenna hardware to add vertical and/or dual-polarity to the board that provide directional coverage. These designs are achieving up to 10dBi in gain with the bigger advantage being the noise reduction from other directions. They use the model of picking the 2 best signal antennas to receive the signal simultaneously since doubling antenna capture area provides up to a 3dB increase.

Vivato is still the technical King here in this realm though, although they weren’t covering 360 degrees. Vivato achieved 24dBi of gain in a 100 degree pattern in 2.4GHz. The catch is they did it for $8,000-$15,000, which meant I could either buy a new van for my company or 2 APs. That sort of limited the market for the product to the point that they are no longer in business, which is also what happens when you don’t listen to your vendors trying to sell the equipment. However, that 24dBi of gain is a huge advantage for reaching underpowered smartphones. Since Ubiquiti has now announced that they are releasing a beam-forming product over the next 2-4 months, the question is, does that have value for a municipal design?

Getting back to today, Wavion’s newest product, the WBS-2400 is probably the closest to the Ubiquiti beam-forming radio. It’s also very similar to Altai A8-Ei product with multiple radios, sectored antennas, and one enclosure. Both products tighten up the beam and assign a single radio per antenna. Unfortunately, both these products are still b/g.

Going back to the formula that distance doubles for every 6dBi of gain, if a 2.4GHz beam-forming AP has 21dBi of gain, or what I’m guessing the new Ubiquiti units are going to be, that almost quadruples the range of most omni-directional AP’s. Throw in the fact that noise will be reduced by at least -20dB, and the s/n ratio goes berserk. The effective range increase, and this is only my best estimate in the worst scenarios, is probably a factor of 8-16 in open air environments. This means hitting a smartphone at 3000-4000 feet or more is possible.

Here is where it gets interesting though. Based on past experience, I’m guessing the Ubiquiti beam-forming AP will be less than $300. That is 10 times less than other beam-forming products, none of which support 802.11N 2x2 MIMO. Heck, it’s less than I paid for a baseball bat last season.

We were all trained to think in terms of APs needing to cover 360 degrees for municipal deployments. Every product out there is designed for that. The end result of this is when the density reaches a certain level, the self-interference is basically self-defeating. I’ve seen proposals that suggest 60 APs per square mile for example. Central management systems can dynamically adjust power output between APs to reduce the interference and can simultaneously adjust power output on a per packet basis to reduce the interference even further. However, all this costs which effectively drives the price up to $150,000 per square mile or more for this level of performance. However, what in the playbook says that every AP has to have omni-directional coverage?

Throughout this series, we’ve been driving towards a low-cost, high-capacity design that can be commercially deployed. The original idea was trying to develop an inexpensive Super AP. I’ve gone from $200 to $2000 and was working on an idea that would have driven the cost to a retail level of $4000. It supported 1Gbps per AP and 700+ simultaneous clients, but still it got away from my original idea which was to lower the bar on the per mile cost, which it didn’t accomplish. It basically comes down to the following, are you trying to compete with cable which can deliver up to 50Mbps or delivering Internet to people who have to suffer with dial-up, or worse, DSL delivered by Qwest in Arizona (okay, bad joke).

Beam-forming lets us start with a new playbook. The first thing you do in a playbook is define your assets (okay, I never played organized football so I’m making this part up.). Using the Ubiquiti beam-forming product (2.4GHz version), we know roughly that we will have about 21dBi of gain, 90 degree coverage zone, 16 degree beam pattern, GPS synchronization, and 2x2 dual-polarity 802.11N MIMO. Since we can now hit a phone at 2500 feet without much of a problem in open air, the design mentality changes. Even with 21dBm of gain, we still aren’t going to penetrate several buildings. However, we probably bought ourselves another house or two. By changing the angle of transmission, ala cell towers, and to be fair to Vivato’s deployment design in Spokane, tops of buildings aiming down, and all of a sudden we are hitting several houses down the street. Throw in 2x2 MIMO dual-polarity, and the connection distance goes way up.

Because of the price point, I’m guessing Ubiquiti’s product uses the same type of design as SkyPilot in terms of switching between multiple feed points on the antenna. The difference is that each feed generates a different angle of radiation versus being a completely separate physical antenna. Ruckus hits multiple feeds also with circuit board based antennas.

Although the tops of buildings aren’t ideal for sector antennas due to amount of AP’s that are going to get picked up, if you aim it towards the horizon, angle it down 60 degrees or more, you still get coverage down the street and pretty impressive building coverage. At that angle, you are reducing attenuation from outer wall penetration and even taking the route of shooting through the roof. This doesn’t work all that well in areas with trees, but if the buildings are made out of concrete, brick, or stucco, then this might be the best option. There are a lot of cities where the street lights are decorative and there is no way to install an AP down at ground level, so secondary options are a must. Beam-forming makes this design more useable by effectively reducing the beam pattern down way down.

This model might work in a different way also. Think in terms of 3 dimensions instead of 2. Larger buildings or apartments in downtown areas might be 10 floors or more. Placing these antennas on the side of one building several stories up and aiming into another building let’s you build a vertical WiFi Although attenuation has been a killer, 21dB of gain makes up for a lot of wall and window attenuation. In addition, dual polarity will improve penetration even further. If you pick up 30 customers in a building at $20 per month, 3-4 antennas pointing into the building get paid for in a couple of months. I would have also said it’s significantly cheaper than AP’s in the building until I saw another product that I’m testing (to be discussed later). However, when you add in the savings on pulling cable, it’s a no-brainer.

Irregular areas with streets curving all over the place are another option for this type of design. Intermixed homes and small business areas with mostly 1-2 story homes and 2-5 story buildings work well for this design. Outdoor coverage is universal with indoor coverage hitting around 80% or more with careful planning. Keep in mind I’m assuming everyone wants to give you free vertical assets to enhance the system.

Bringing us back to earth gives us most of the real-world deployments, street lights. This is where the GPS synchronization really kicks in and is now the direct comparison to Wavion or Ruckus. Placement of four of these radios on a pole to cover 360 degrees provides the absolute farthest range of any AP on the market. This is only possible with GPS synchronization to keep them from interfering with each other. It effectively provides twenty four 16 degree beams shooting out in 360 degree pattern. The cost of this super AP will be about $1500 which isn’t a lot less than Wavion or other beam-forming 360 degree APs. It does have significantly longer range through, by a factor of 9dBi and dual-polarity which is worth another 3dB in my field testing. With the IPad supporting 802.11n and the Beam-Forming antenna supporting dual-polarity, this would be a potent combination for off-loading some bandwidth.

If we duplicate this design with Altai or Ruckus, the cost is now over $10K per AP. There are other manufacturers such as Motorola that use sector antennas but then the antenna gain drops back to 12dBi or less and their beam patterns are 120 degrees. The best way to reduce noise is to decrease the beam pattern which it also doesn’t do. Effectively we get a 9dBi increase and 20+dB of noise reduction for a cumulative 29dBm improvement in s/n ratio. Regardless of what wireless philosophy you follow, that’s huge.

Here is one of my philosophies though, “If you spend too much, all you have lost is a little money. If you spend too little, you could lose everything.” Guerilla WiFi is based on the concept of being the most cost-effective way to deploy and what I feel is the only way to make municipal wireless a self-sustaining profitable model. That doesn’t mean it’s the best way in every situation. I’m describing equipment that isn’t even out on the market yet and isn’t field tested. Wavion, Ruckus, Altai, Bel-Air, Motorola, FireTide, Cisco, Enterasys, and a host of other vendors are proven products that have been deployed and tested. I do think these vendors are making it difficult to meet the financial needs of a profitable municipality model which is where Guerilla WiFi comes in, but the products are solid. This models works for me and others who are willing to spend the time to work through early firmware issues and fine-tune the models during deployment. It’s kind of like the difference between Linux and Windows. Since Ubiquiti uses a common firmware platform across all of their outdoor products and has made great strides towards stability and features, I expect the new products to use the same firmware base which means , the firmware. However, there is still a long way to go towards a turn-key municipal deployment without a lot of engineering intervention. Based on the cost/performance ratio, I believe it’s worth it. But realistically I spend a lot of time testing and adjusting. Most customers are going to expect a more turn-key solution. However, if it’s your money, then this solution provides the best chance of financial success.

With this AP design, $1500 per AP is getting pretty pricey. However, it will also combine with our next article, the 360 degree dual-polarity 2x2 MIMO AP for under what I’m guessing is going to be $300. I’ll try not to wait 3 weeks to make this happen.

One other note that I want to mention is that Mike Ford is no longer at Ubiquiti. Mike was a central figure that seemed to have his hands in everything from testing to customer support. Over the last 3 years, he has become a friend that always went the extra mile to make sure I had the resources I needed for my clients. He was also instrumental in some of my decisions on my deployments. Although I don’t know his future plans, I am very sorry to see him go.

Chapter 17 - Who needs White Space?

It’s time to step up our game. There is no problem generating massive bandwidth from an AP location. We have proven that fact. What we haven’t figured out yet is how to leap tall trees in a single bound or walk through brick walls. If you are willing to add in another 20Mhz of super-powerful, wall-penetrating, obstruction busting, tree smashing signal, then we have solved the problem.

You are thinking I’m going to jump on the White Space bandwagon. I’m sure I will someday but there’s a lot of work that has to happen before that option is available. However, the infrastructure we have designed is pretty flexible and inexpensive. When White Space becomes feasible and cheap (my favorite word), we can add it. In the meantime, we have two other options. I think I will save the best for last though.

White Space is touted for 2 reasons, extended range and building penetration. It also has one big disadvantage. In major cities, there may not be a lot of channels available according to Spectrum Bridge, for White Space to operate. In addition, limited power output from clients is still going to limit high-bandwidth range back to the AP. I also see the 6MHz channels being an issue with bonding being the same problem as trying to run 40MHz outdoors.

Before we jump into this though, let me make note that Ubiquiti just released a stack of new products that are game changers in WiFi, indoor and outdoor, Video Surveillance, and cellular service. These technologies cover everything from Beam-Forming to GPS sync to dual-polarity omni’s. I’ve had to hold back due to NDA’s but we will now start covering how these technologies can be integrated into our Guerilla WiFi design to take the systems to a whole new level. Most of these products are several weeks away from shipping so we have time to develop our system. I do a have a pair of the 900MHz M series 802.11N 2x2 MIMO AP’s in my hands and that is the topic of this article.

Option one is 900MHz. Yes, it’s crowded, noisy, and seriously overused. So is a Japanese subway but people still use it because it’s the best option. Until now though, the best WISPs systems limited users to about 3Mbps under ideal conditions with APs limited to about 7Mbps. There really wasn’t a lot of development in that frequency band due to the interference and reduced band size as compared to all the other unlicensed options.

900MHz has close to the broadcast properties as White Space except for the vastly higher interference. In a municipal system with 16 AP’s per square mile, AP’s are within 600’ so range of everybody. Unfortunately, 2.4GHz can’t penetrate obstructions very well. Brick or Stucco buildings that will suck the life out of 2.4GHz are merely a few dB of loss to a 900MHz signal. At that range, trees effectively disappear. Junior’s frequency hopping baby monitor and the SCADA transmitter hanging on your water meter is now more of a problem than obstructions. In 900Mhz, with 802.11N 2x2 MIMO now being applied, bandwidth isn’t the issue any longer. The biggest problem is interference.

Everything has a threshold though and you just have to find it. With parents, it’s how low your grades can go before you become the prisoner of the bedroom Alcatraz and your friends start filing missing person’s reports. With RF, it’s the difference between the signal and the noise and how efficiently we use the bandwidth. Now toss in a very narrow band, 26MHz, and the total bandwidth throughput from any AP is going to be limited. Oh, yea, did I mention that we only have to go 600 feet?

802.11N isn’t just for 2.4GHz and 5.8GHz. It just hadn’t been applied before in the 900MHz band. Ubiquiti just released several new 900MHz products with 802.11N 2x2 MIMO protocol. Using a 5MHz channel will allow up to 4 APs to operate on one pole, which each one providing up to 20Mbps. However, using buildings and some shielding, might allow up to 4 channels of 10-20MHz in more remote areas to allow up to 300Mbps. I’m sort of guessing here but when I get one of the base station sector antennas in, I will do some testing to determine what would be needed for isolation.

Keep in mind through all of this that we are still dealing with an AP/sector antenna combination that cost less than $500. If budget is an issue and the city thinks that a several 4’ antennas on a pole aren’t their idea of aesthetically pleasing, then look at using 4 of the Nanostation M900 Loco’s. They are very small, and although rated at a 60 degree beam pattern, they can easily cover 90 degrees with a small drop off in antenna gain. In fact, the beam pattern for these radios is way over 90 degrees at 7.5dBi of gain.

The only problem here is that you need one of these radios in or on the house since there is no portable device that can support 900MHz. That starts getting expensive at $200 for the radio and another $50-$150 for an indoor WiFi device for wireless coverage. However, the problem of building penetration is completely solved.

If I haven’t mentioned it before, we only have to go 600’ from an AP location if we have 16 poles per square mile. Realistically though, if we have 16 APs per square mile, I would probably only use a maximum of 4 AP locations with the 900MHz radios for budget reasons. That means we might have to go 1300’. Of course, we are using a proprietary polling scheme and a dual-polarity signal to go that far. If the noise floor starts at -65, the signal level needs to be at -55 or better. At 1300’, even with obstructions, our signal level should easily exceed that.

Trilliant and other Smart Grid companies are releasing MOAB (Mother of All Bombs) 900MHz radios that are up to 1W for residential installations. If you think that a few towers can cause interference, try fighting tens of thousands of radios dropped into the middle of your coverage zones. Motorola 900MHz WISPS from here to Canada are getting hammered and there isn’t a lot they could do about it. There are going to be cities where running 900MHz WiFi may not be feasible. Don’t panic yet, we will take our 2.4GHz game up a notch also.

There are two advantages to the Ubiquiti 900MHz radios to fight interference. One is the dual-polarity MIMO design. In the city though, most radios are using antennas with such low gain, polarity isn’t going to make a lot of difference. However, the M900 product line came out simultaneously with the ability to frequency hop. That means you have 4, 5MHz channels to jump around with at 300ms rates to avoid noise try and punch a signal through. If the Smart Grid density is too high, then even that isn’t going to matter but right now it’s the best option available.

The second advantage is AirMax. AirMax will simply ignore other packets in the band and also eliminate the hidden node problem. Although interference is interference, AirMax AP’s won’t slow down acknowledging other APs in the band.

Ahh, but what works for city folk works even better for country folk. The dreaded trees of death for 2.4GHz and 5.8GHz are merely pin pricks to 900MHz. Toss in the dual-polarity 2x2 MIMO design and now signal will punch through the forests like Ray Lewis through an NFL helmet. Expand out the channel to 10 or even 20MHz, and throughput for a single AP could go as high as 80Mbps.

On the muni-wireless issue, we can assume that designating 4 AP sites per square mile will add about $1000 or about $4000 per square mile. It also adds 320Mbps of total capacity per square mile. Add in the CPE Capex of $200 per client, assume 25 clients need this radio to avoid a truck roll, and you have an additional $5000. If you truck roll, add another $3750 in the Capex column for those of you keeping track.

Based on those numbers with a $30 per month fee and a free install, it will take 17 months to recoup the Capex. Of course, we want to charge $100-$200 for an install to offset some of those costs. In areas where municipal staff thinks antennas are cool and interference is minimal, we could even use four 900MHz dual-polarity sector antennas with 13dBi of gain. That will provide over 6 times the coverage area which might reduce the AP locations from 4 to 2 but it will more than double the cost per AP, which is a wash. There will be scenarios where either option will be more appropriate.

Our second option is the new beam-forming radios. I’ll cover that in more detail in the future. Since the 2.4GHz versions of these units won’t be out for another 4 months or so, there is no hurry. However, they add another 4-6dBi of gain over a sector antenna and 8-9dB of antenna gain over any other beam-forming AP other than Vivato. Add in dual-polarity, which my field testing shows to be worth up to 3dBi more useable gain, and a 16 degree beam pattern to reduce noise (I’m extrapolating from the 5.8GHz beam-forming unit that was announced. The final specs may vary.) and that that’s enough gain to penetrate an extra wall or almost quadruple the coverage distance to a client. I’ll go into the difference between between all the beam-forming units on the market in our next article.

Now we have even more tools to play with for Guerilla WiFi. Theoretically, it wouldn’t be hard to build a 1Gbps AP to work across multiple frequencies with beam-forming and GPs for less than $4000. Taking this concept even further, it also wouldn’t be hard to create a load-balanced, business quality, multi-frequency design that could bond these frequencies together for very high-capacity throughput. There are other variations of this for backhaul, redundancy, and uptime. It’s possible, with a little networking work, to create a mission critical design capable of delivering tens or hundreds of MB’s to a CPE for less than $400 on the CPE side. This type of system could easily deliver 99.999% uptime using unlicensed frequencies, even with scheduled maintenance. And don’t get me started on 900MHz mobile options. The hits just keep on coming.

Chapter 8 – Half of Something is Better than Nothing, but Why Settle?

Our network is pretty inexpensive but suffers from first generation bandwidth problems of losing ½ the bandwidth capacity every hop. Patton wouldn’t settle for a partial victory and neither will we since we can do it for very little additional cost. It’s possible to virtually eliminate bandwidth loss per AP for up to $400 for the Gateway points ($100 for every direction it has to backhaul) $200 for midpoints and $100 for the end point. Keep in mind you don’t need to do this at every AP, just the links that have a higher load or to extend the network further. This is also something that can easily be added later as capacity increases.
We currently have the AP cost at about $200 and each AP can handle 30-50Mbps of traffic. However, 2 hops down from the gateway point or backhaul point, we are now down to about ½ of that. Go another hop and its ¼ of that using single radio WDS functionality. WDS has 3 other problems that we can’t get around with Ubiquiti’s Bullet 2M HP’s. The first is that we lose the client isolation function. The second is we lose a proprietary function that we will later cover called AirMax. The third is that we lose advance WPA encryption methods and we are limited to the evermore useless WEP. It’s easy to get around this though. Keep in mind the motto, “it’s not a problem if it can be fixed with money”.
Ubiquiti sells a little radio called a Nanostation Loco M5. It’s available in both 2.4GHz and 5.8GHz versions. We will focus on the 5.8GHz version since that limits the interference for our backhaul and as we discuss later, opens up new options for our network for PTMP. This little fellow only costs $70 and provides a 2x2 MIMO signal that can support up a total of around 100Mbps of total throughput with a 20MHz channel. I’m going a little conservative on throughput numbers since different types of IP traffic can test between 60-150Mbps. Put 2 of them on the pole with the Bullet M2 and your backhaul can now support all that bandwidth across several hops with a loss of about 1Mbps and about 2-3ms of latency added on each hop. However, you have just added another $200 per AP to do this with a switch. If you have two 5.8GHz radios on the pole along with the Bullet, you will need a switch.
The most cost effective switch I have found that is designed to handle reasonable temperatures is the Linksys SD205 unit. Although they are rated for 122 degrees, I have never seen one fail and I have had them in temperatures far in excess of 140 degrees for years. For around $25, they are the best little units for sealed outdoor installations and there is an SD-208 version if you need more ports. Compared to an industrial switch which starts at $250 (cheapest ones I have seen), the Linksys units are a steal. If you need a managed switch, then you are looking at industrial switches and the cost is going to start around $450.
The other good part of adding the Nanostation Loco M5 to our system is now if we have to add more AP’s in the middle of our network, we don’t have worry about the 1/n issue. We can also use WPA or AES security on the 2.4GHz network and 5.8GHz backhaul hops. This solves the wireless security issue. If we have to go around corners or Y off an AP, we can add up to 4 Nanostation Loco M5’s per pole if we use a 20MHz wide channel. Yes, I know that theoretically you can do 5 channels but that leaves no buffer between channels. With 4 channels, you get a 5MHz buffer which although not ideal, it’s not bad.
The drawback to the Nanostation Loco M5 is that to get maximum throughput or MCS (15) rates, you will be limited to 17dBm output with a 13dBm antenna or a total of 30dBm EIRP. If there are any tree obstructions or you need more power, the big brother, the Nanostation M5 has a 16dbi antenna and 21dBm of output for an extra $20. Keep in mind that these radios will go to a much higher power level if necessary but it comes at a reduction in throughput which we discussed in article 2. It does however, leave some room for increasing power if interference or obstructions start to cause issues later.
The Nanostation Loco M5 radios can also do one other thing. If we get back to the idea of a PTMP hybrid system, that means that users that are within the beam pattern of the Nanostation Loco M5’s can actually connect directly to the 5.8GHz backhaul. I suggest this stay reserved for truck rolls and trained technicians. 5.8GHz is a lot more sensitive to LOS which makes it more difficult for clients to install themselves. We are going to extend this concept further later also.
If the goal is that clients are going to install their own CPE’s, either indoors or out, it’s best if clients use a 2.4GHz product, preferably a Nanostation 2M or the upcoming Nanostation Loco 2M for indoor use with a window/wall mount. There is also some new indoor equipment from Ubiquiti, the WiFiStation, with directional and omni-directional antennas that support 802.11N and only cost around $30. The range is obviously lower but it also lowers the cost for clients.
Although our network also doesn’t support 2x2 MIMO on 2.4GHz yet, it is now supporting it on 5.8GHz so things are moving along. We have a couple options coming upon the 2.4GHz 2x2 MIMO solution coming up. There is also a way to customize the firmware on these units so that the CPE can be fixed only on your network with the proper settings and would allow you access to manage settings on the client side to optimize their connection quality. Imagine the client connecting to the system and then you get to remotely upgrade firmware on every client device simultaneously, monitor their connection quality, and manage the connection all way to the computer. That is the advantage to having all the radios from a single vendor. Tech support calls would go way down and staff wouldn’t have to fudge their way through 100 different products. Taking this a step further, if all the devices were Ubiquiti M series radios, you could also use the AirMax feature with polling for the clients. Of course, you sort of kiss off the legacy devices, or do you?

Chapter 3 - Share and Share Alike

Although this was the week that we were going to discuss putting APs on the poles, an incident occurred last week that I think is worth discussing before we go any farther. Always keep in mind that unlicensed bandwidth is a shared commodity. It’s also a good idea to have a relationship with your competitors or anyone in the area that is using unlicensed bandwidth. Sometimes that’s a little hard to do, but it’s definitely in your best interest to try.

Traffic lights and cameras are a perfect application for 4.9GHz or 5.8GHz radios where fiber isn’t installed. For example, we connected several traffic lights in Glendale, AZ a month before the city hosted the 2007 SuperBowl. The entire network consisted of 5.8GHz SkyPilot equipment with Pelco cameras. The system is used to monitor the intersections and also as the SCADA system for the traffic lights. This allows the city to manually adjust the traffic lights before and after events to optimize traffic flow. The city just recently closed on a bid that ADOT managed for the next phase. For some reason that I still can’t explain, they removed the compatibility clause with the existing system and simply went for low bid. Due to the cost of the SkyPilot equipment, it was obvious that low bid would not be SkyPilot or a compatible system but something else. This means the city will now be supporting multiple mesh networks along with the extra long term costs. He who controls the funding; writes the rules but apparently doesn’t have to support it.

That led to another project to connect 13 traffic lights with 50 High-Definition cameras at resolutions up to 1600x1200 pixels. We settled on Axis cameras for this project. The ideal cameras, fixed and PTZ, would be 1080p, 24 frames per second, and H.264. The project came close with most of these specs, but there were some compromises. We either got PTZ and H.264 at 720p, or we got 1600x1200 at reduced frame rates with MPEG-4. Future intersections may get 1080p cameras. This was sufficient to meeting the system requirements for the application which was traffic light management, license plate recognition, video analytics, and future facial recognition software.

Either way, we needed a lot of bandwidth at the City Hall to make this work. There were no other antennas on City Hall. A quick site survey showed additional equipment in the area with fairly low signal levels. The AP chosen was Ubiquiti 802.11N Rockets with 90 degree, 20dBi dual-polarity sector antennas. The system has 4 APs and sector antennas on City Hall for 360 degree coverage. Each light depending on distance to City Hall gets either a Nanostation 5M (integrated antenna) or Rocket 5M (external flat panel sector antenna). We are also adding 2.4GHz 802.11N to all the intersections for future use. It only adds $200 to the cost of each intersection and has an 800’ range to a laptop.

The first AP was turned on about 6 months ago and covered one 3-way intersection with 3 cameras and a second client station for data backhaul to one of the City Parks. The park had maintenance staff and a camera for the skate area. The second AP was scheduled to be turned on this week to cover the next 90 degrees off City Hall. That was when we discovered that between the time we turned on the first base AP and then went back to turn on the second base AP a couple of months later, the IT department had a local WISP put a Motorola Canopy radio on the roof without notifying the traffic department. Even more fun, it was in the 5.8GHz band.

Our traffic system was designed to use all 100MHz of the 5.8GHz band and was designed with signal levels for each link between -50 and -65dBm. Since the general rule is at least 10dB headroom on the link path and the minimum signal for APs with an MCS15 link (130-144Mbps modulation rate), 2x2 MIMO is -75dBm, you try to design for your worst signal at the receiver to be -65dBm. At those signal levels with directional antennas on the client side at 2 miles or less, it’s fairly hard to interfere with this system.

As a courtesy to the vendor, I thought that giving them a call and asking if they could change the Canopy to 5.1-5.4GHz before I turned on any more APs would be the professional thing to do. Unfortunately, when you run into inexperienced WISP technical support staff who think that whatever product they use is significantly better than whatever product you use, there is a problem. The conversation started with me asking if there was any chance that they had other frequency options. The technician asked me what equipment I was using. I replied. He then made the comment, “Our equipment will stomp all over your equipment.” I quickly established that this wasn’t the person to which I needed to speak to resolve this issue.

Every wireless product handles interference in different ways. Better filtering, multiple polarity, diversity, beam-forming, better firmware and many other techniques are utilized to improve the quality of a connection. Obviously some equipment works better than others in high-interference environments. However, 802.11n doesn’t always play very well with 802.11 b/g or 802.11a radios. In addition, physics are physics. Throw in a 2x2 MIMO signal with very a high gain antenna and a total EIRP of 42dBi minimum on both polarities, and there is going to be interference. This is especially true if the competitor’s base station is 1000’ away and their system is based on a 30dBm EIRP signal level from the APs. Since the traffic system was designed with a very high level signal path with multi-polarity 2x2 MIMO, there wasn’t much concern that the local WISP was going to interfere with the traffic system. On the other hand, it was clear that the traffic system was going to cause some interference to the WISP operation. I was wondering if that was already the case.

The last thing I wanted to do was start a war between a city government and a local WISP. Since the WISP was already serving some of the registered voters, this was probably not a good idea. The ego in me wanted to turn the remaining two sector antennas directly at the WISP base station across the street, program the two radios with a channel width of 40MHz to cover most of the 5.8GHz band, turn on 802.11N mode only, start multicasting “Transformers 2” in UDP mode to my other laptop and phone, and crank the power to 48dBm EIRP. I felt there might be a lesson to teach on RF, signal-to-noise ratio, and how to be polite when other companies are trying to do the right thing. Instead, I called back and talked to upper level management to arrange a meeting to see what can be done. That’s when I found out as I had suspected, that the traffic system’s first AP possibly might already been causing some interference issues. Unfortunately that traffic system AP also serves the City Park and has been running for several months. As a courtesy, the best I could do was to turn the power down until we plan out a more cooperative strategy with the WISP.

Now we can come back to our design. The AP combo we are considering will have an EIRP of up to 36dBm and will be 802.11 b/g/n compatible in 2.4GHz. That is far more powerful than most indoor systems. There are ways to limit the interference and everyone sharing those bands should consider this. It’s good policy to always engineer for the least amount of power that you need. Also, you should consider using the least amount of bandwidth. If you don’t need a 40MHz channel, don’t use it. You gain 3dB on the receiver side with no more power if you use a 20MHz channel. Drop to 10MHz and you pick up 3dB more, etc… The tighter the channel, the better chance you have of getting a signal through.

There are many of you that may not even want b/g compatibility. If the system is only used where you control both the APs and the client radios, then you have some options. In that case, using 802.11N only is the best way to go. This results in fewer APs and better performance. It’s also possible in this same scenario to get as many as 100 users on an AP or as many as 300-400 on a single pole. If all the equipment is the same manufacturer, consider a 5-10MHz channel which will still deliver 12-25Mbps per AP. Running 2x2 MIMO doubles the throughput to 25-50Mbps in a 5MHz channel. This is probably more than most of us need for a link. With a 5MHz channel, there are 6 channels to work with in 2.4GHz instead of just 3.

Whatever gets installed will probably interfere with other existing systems. We have to be cognizant of the fact that nearby systems might be critical for hospitals, voice systems, video surveillance, office networks, etc. For example, a few years ago, we saw an outdoor AP in Scottsdale stadium take down a wireless voice system at a nearby hospital. Since we put our phone number in the SSID, they could contact us quickly. We adjusted our antennas and resolved the issue. Site surveys have to be done everywhere to understand the ramifications of the install in addition to understanding your own coverage zones.

Based on all this, if I saw a little Motorola Canopy radio on the roof and thought it was a good idea to possibly contact that vendor, what was the installer thinking when he saw all the Ubiquiti equipment along with a Motorola PTP600 radio? He obviously didn’t do any kind of site survey. The reality is that this is standard procedure for most companies.

Many companies that rent roof space for APs do it from some type of property management company. There is usually no bandwidth management on the roof. When someone finally overlaps frequencies, an avalanche of problems will start. For example, administrators may turn up power to overcome the interference if they have no other options which causes even more problems (this gets into noise and channel filtering). The responsible thing to do would be to notify all parties involved and see if there is a way to work together. Obviously this sentiment is not shared by everyone, or some field installers aren’t trained well enough to watch for this situation. Then again, they just may not have cared.

Unless I run into another tech support person who hasn’t been taught the concept of cooperation and I need to vent, we will get back on our project next article. I’m still working on some FCC equipment certification issues with the design. Not that we can’t do it but I want maximum performance and the equipment I need isn’t quite yet available. I’m also waiting for new products to test that may enhance the system. Anybody can build a system with unlimited budget. The fun is creating a carrier class dependable system on a shoestring budget; since, that’s what most cities have in their coffers these days. Any new products that have the potential to help preserve that coffer is going to get their attention. Next article, we get back to work.