For a while I have been of the opinion that antennas and particularly antenna gain is something that in my opinion is often overlooked when considering different Wi-Fi access points.
Cambium have kindly given me a cnPilot E700 access point for review and this access point is a perfect example of why I think antennas are so important.
Firstly a quick overview of the E700 access point. This is an IP67 rated access point designed for outdoor use. It has a 4x4 antenna array and has a 802.11ac Wave 2 chipset. It boasts some other cool features as well like LTE filtering (you can read more about this here). This is currently the flagship outdoor AP in the cnPilot range. But what particularly stood out to me when I first saw the product launch a few months ago was the 8dBi antennas for both the 2.4 and 5Ghz frequencies. In my experience most APs in the marketplace today typically have antennas that range between 3 to 5dBi. Due to how dBi is calculated an 8dBi antennas is actually two times more powerful than a 5dBi antenna (more detailed explanation on how this is calculated).
Let's discuss the impact of having multiple antennas and the impact of having larger gain antennas.
The E700 is has a 4x4 antenna array. Most client devices typically have 1 or 2 antennas and some higher end client devices have 3. Does this mean we'll never get the benefit of the extra antennas on the E700? No, there are a number of technologies that we can make use of to improve performance even when an AP has more antennas than a connecting client.
- Multi-user, multi-in multi-out (MU-MIMO) - This allows an access point to use its extra antennas to talk to multiple clients both independently and simultaneously. This technology must be supported on both the client and AP.
- Space Time Block Coding - This technology can be used when there are more transmit antennas than receive antennas, it adds signal redundancy to improve the signal-to-noise ratio.
- Maximum Ratio Combining - This technology can be used when there are more receive antennas than transmit antennas and helps to improve the received signal strength.
The antenna and its size is critical, it's effectively the ear and the mouth of the access point. Transmitting to a client device at distance isn't really a problem in most enterprise access points (even with lower gain antennas), you can simply turn up the power. But remember Wi-Fi is very much a two way conversation and that signal has to be received back at the access point for communications to exist. As we normally can't turn up the power on client devices the only option is to use to use an antenna with sufficient receive gain (like the one on the E700) and then communications can exist even at extended distances.
It's important to note that the Antenna Gain also affects how the RF propagates, higher gain antennas are great at pushing the signal in a horizontal direction (as long as the access point is mounted properly!) but it's not quite as effective for pushing RF waves above and below the access point. So it makes sense to use a higher gain antenna in an outdoor access point like the E700 as everyone is typically going to be at a similar height.
To help prove my point I've conducted a simple experiment. I've set up an E700 access point next to an E410 access point. Here is a quick comparison of how the 2 APs compare.
| Â | E700 | E410 |
| Manufacturer | Cambium | Cambium |
| Chipset | ac Wave 2 | ac Wave 2 |
| Antennas | 4x4 | 2x2 |
| Antenna Gain 2.4Ghz | 8dBi | 4.55dBi |
| Antenna Gain 5Ghz | 8dBi | 4.25dBi |
Admittedly the test has been carried out in my home and not in a test environment. So there may be interference from neighbouring access points (one example of how this test is not perfect) but I have tried to conduct the experiment as fairly as possible. I've set both APs to transmit at the same power level, use the same frequency, channel widths etc. Using a 802.11ac client with a single antenna I've measured both upload and download speed (using iperf) over varying distances. Here are the results:
Before I go any further, I want to take a quick moment to say that I haven't picked the E410 because its a bad performing access point, quite the opposite, the E410 is in my experience a very good access point. I've picked the E410 as it is a good benchmark of how an enterprise access point should perform. The takeaway here should be on how well the E700 has performed.
OK back to the results, as you can see from the above the E700 and E410 are quite evenly matched at position 1 (the closest distance) both delivering around 200 Mbps download and 100 Mbps upload. But at soon as I started to move further and further away the E700 comes into its own and it delivers significantly better performance in both the download and upload iperf tests.
There are already a few Outdoor 4x4 802.11ac Wave 2 access points on the market, most of them marketed for high density deployments (having a high number of simultaneous client connections) and there's no doubt that the E700 will also cope with a high numbers of concurrent users. But to the best of my knowledge these other high density access points lack the larger gain antennas required to transmit over larger distances.
I really have been impressed with the coverage and overall performance of the E700, it's an extremely well designed product. I'm very please that going forward I can now offer an access point to my customers that is capable of both high capacity and excellent coverage. Take notice everyone else, this is how it is done!
Nice work Cambium!