We have all these ideas out there so I thought we would tidy them up before continuing on some new ones. Let’s start with what’s really old is sometimes new again. Various ideas have been coming to me as I have been writing these articles and I thought I would share a few of them.
For those of you who are too young to have missed the Golden era of Ham and CB radio era, I have some bad news for you. Many of the “new” ideas that WiFi AP manufacturers have come up with are the same as CB radio antenna systems from 35 years ago. It’s really funny to see how these ideas are implemented and then manufacturers claim “unique” designs. I had this concept on my roof when I was 15.
The best one is the Wavion design. The directional/omni-directional design concept is actually similar to an antenna called a SuperScanner which used 3 vertical elements in a triangular format. By using a switch inside, you basically decided which one of the antennas is the driven element which makes the 2 vertical elements behind it the reflectors (look up Yagi antenna design). Obviously it’s done electronically within the radio with the Wavion, but it’s interesting to see it being deployed in WiFi.
One of the projects I sort of mentioned in Chapter 10 got me thinking about some other ideas and what’s going to push municipal WiFi deployments even faster. I talked in Chapter 11 about using multiple vendors to complete a project since almost nobody makes a fully universal product line. Motorola is getting there with their new licensed PTP radios but they have made some decisions on the mesh AP side that limit my consideration of them in some of my designs. They have the most wide-ranging product line however but I’m seeing more vendors expanding their product lines.
In Chapter 10 I also mentioned wanting to test a couple ideas in Phoenix that might make the Florida project more cost effective. The costs started going through the roof because each AP needed a pole and electricity. The question that popped in my mind went back to an old design I put into Stratosphere with dual 802.11b radios. I didn’t have 5GHz backhaul yet so we used WDS on the 2.4GHz side and we backhauled 4 APs. I also didn’t have omni-directional antennas since I was shooting straight down a hall. Throw in two more random thoughts and an idea starts forming.
What works better, a 15dBi omni or a 16dBi 120 degree sector antenna? In terms of pure range, the sector antenna obviously beats the omni antenna for a couple reasons (this is where spending hours surfing the different on-line catalogs starts having value). However, we need 360 degree of coverage which means 3 antennas, 3 radios. There are some radios like the Motorola AP7181 which uses a single 2.4GHz and a single 5.8GHz radio that uses an amplifier to feed 3 dual-polarity sector antennas.
Now let’s introduce my favorite car analogy. What accelerates faster to 60mph, 3 Ford Ranger trucks carrying 1000 lbs of dirt or one Ford F-250 carrying 3000lbs of dirt? My money is on the Ford Rangers. Don’t fall asleep on my yet, there really is a sane idea forming here.
In TriadLand, we covered using a single 2.4GHz radio for AP and backhaul for cost reasons. Everybody and their Mom are also using 5.8GHz for backhaul. Most manufacturers are using two 5.8GHz radios to prevent the 1/n problem but even the big boys like Motorola and SkyPilot still use a single 5.8GHz radio. However, one trip to Florida showed me that there needed to be another option to get through the Amazon forest that grows along the street. There is the serious question of whether we could get 5.8GHz to reliably shoot down the street without doing pole gymnastics by adding horizontal arms that move out towards the center of the street. That would add even more to the cost.
I was forced to come up with ways to reduce the cost of the deployment in South Florida because of the pole costs. Before I came up with my mobile idea and gave up on the idea of not using 2.4GHz everywhere, I looked at extending the range of the APs even further but still had no way to get 5.8GHz through the trees. Although it’s on my testing schedule, the end result of this idea was using a three 2.4GHz 802.11n 2x2 MIMO radio combination with three 120 degree dual-polarity sector antennas. The 2.4GHz radios would also handle backhaul down the road. I still avoid the 1/n problem since most hops are 180 degrees apart in relation to surrounding APs. Yes, this is what Motorola and BelAir do so it’s not a unique idea. However, the 16dBi antenna are dual polarity which although the same as Motorola, use 3 radios to feed them. In addition, this idea would also have 4dBi antenna gain (I’m estimating here) which gets added to the client side of the link budget equation.
Since this wasn’t a public access system, bandwidth load wasn’t going to be a problem and the dual-polarity antennas would easily punch through the trees overhanging the street for backhaul. I lose one polarity to the car but that still meant 30-50Mbps to the vehicle which is more than enough. Although it’s a noisy band, I cut down the interference to an omni antenna by 1/3, triple the processor power of the AP, eliminate the 1/n problem, and increase the signal strength between APs and the car. Keep in mind that because of the trees, the noise is reduced from indoor AP’s to the street anyway. If noise continues to be a problem, which I doubt since I’m using dual-polarity, there are other techniques to add up to 6dBi on the path equation and reduce the noise even further. This is a rural environment, not Wall Street.
Another subject that came up was security with police departments. You radio guys are immediately jumping to 4.9GHz and the Police IT guys are thinking there is no way we transporting traffic over any system that has 2.4GHz radios or common infrastructure. I have news, there are so many holes in the NCIC through small towns and limited staff IT departments, that securing one hole in Florida doesn’t secure the hole in California. In one city, I found the traffic cameras that were being monitored on displays in the police dispatch room using public IP addresses and default passwords. I wrote an article in Mission Critical Magazine on security that also covered how our electrical Grid is still unsecured. Unless the justice department or FBI is doing audits at every single terminal and network attached to an NCIC database, you can be reasonably assured that a properly designed wireless system, whether it’s 2.4GHz or 4.9GHz, is going to be far more secure than the police network that is attached to the city infrastructure. Given that some IT people didn’t start their careers until later in life and don’t have a lot of experience, the security of wireless network really isn’t your worst problem.
If you have a choice between 2.4GHz and 4.9GHz, simply look at your budget and quadruple it for ¼ the performance for 4.9GHz over 2.4GHz. All of the cost and performance innovations are being done in 2.4GHz. Because 4.9GHz is a very limited market, the technologies are last generation and there isn’t a lot of financial motive to invest in it. For example, what works better in every environment except for the middle of a major city, 4.9GHz with 33dBm output and 7dBm omni with a 20MHz wide channel or 2.4GHz with 2x2 MIMO 802.11N with a 36dBm EIRP and 5MHz channel? In pure performance, it’s a wash. In terms of cost, the 2.4GHz system will be so much cheaper that there isn’t even a comparison. The 2.4GHz system can also be used with other departments much more cheaply. The only environment where a 4.9GHz system with mobility comes even close to a 2.4GHz system (meaning about 3 times more expensive), assuming you are willing to give up throughput to about ¼ the 2.4GHz system, is if there is little or no vegetation. But what about security?
With a 5MHz channel and dual-polarity in 2.4GHz, security is slightly enhanced, interference is greatly reduced, and range is doubled. VPN tunneling hardware or software from the client to the Firewall would encrypt all data. IPS/IDS would constantly be monitoring for hacking and irregular behavior. Police SSIDs don’t get broadcast while public IP’s are the honeypot and isolated from the police network. A user couldn’t even connect to the AP if done right, let alone try and get through the rest of the system.
But what about using a dual-frequency system like a 2.4GHz and 4.9GHz in the AP or backhaul? Same problem, older technology, and an even higher cost and common backhaul. How about a 2.4GHz AP with multiple SSIDs? In my mind, this is the best compromise the solution. The multiple SSIDs allow VLANs and different security options at the AP and the client. It doesn’t matter what the backhaul is since the traffic is on different subnets at that point anyway. The gateways and firewalls are also different. Traffic is prioritized so public safety has the highest priority over all other traffic.
Let’s get back to making some money. A while back I was approached by a company that wanted to design what they called an air fiber type of structure. They were using 4 redundant loops of 1Gbps radios around the city that could be tapped into with a PTP radio for their clients. This is pretty common within some cities as well as some of my designs. In their case though, this was their business plan. I bring this up to show how TriadLand can be adapted for more than just municipal wireless but in many cases you need the backhaul idea to really make it work. We touched upon the local data center concept and most WISPs utilize something along this line.
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