ePMP eDetect feature

One of the biggest tasks on a wireless AP is finding clean channels.  Once you find those clean channels, making sure you stay on a clean channel is the next task. ePMP has a feature under tools called eDetect. One of the things this can do is give you an idea of how many devices are on a given frequency.

The ePMP AP you see above is on a 20mhz channel, which is why many home routers and other devices are showing up.  If this was on a cleaner frequency it would look like the following.

While eDetect is not a replacement for spectrum analysis, it can give you a pretty good idea of what’s using a particular frequency.  Please note, you see the most things on 20MHZ channels because that is what most home routers are set to. If you would like to read up on eDetect in more detail go here: https://community.cambiumnetworks.com/t5/ePMP-Configuration-Management/ePMP-Tools-eDetect-Explained/td-p/42997

The changing WISP RF landscape

Recently, there have been some discussions on Facebook about waining support for 2.4GHZ .  KP Performance recently published a Future of 5GHZ and beyond blog post. So why all this focus on 5GHZ and why are people forgetting about 2.4?

To answer this question, we need to update our thinking on the trends in networks, not just wireless networks.  Customers are demanding more and more speed. Network backbones and delivery nodes have to be updated to keep up with this demand. For anything but 802.11 wifi,2.4GHZ can’t keep up with the bandwidth needs.

One of the significant limitations of many 2.4 radios is they use frequency-hopping spread spectrum (FHSS) and/or direct-sequence spread spectrum (DSSS) modulation. Due to 2.4GHZ being older, the chipsets have evolved around these modulation methods because of age.  When you compare 2.4GHZ to 5GHZ radios running OFDM, you start to see a significant difference.  In a nutshell, OFDM allows for higher throughput. If you want to read all about the differences in the protocols here ya go: http://www.answers.com/Q/Difference_between_ofdm_dsss_fhss

Secondly, is the amount of spectrum available.  More spectrum means more channels to use, which translates into a high chance of mitigating interference. This interference can be self-induced or from external sources. To use an analogy, the more rooms a building has, the more simultaneous conversations can happen without noise in 2.4GHZ we only have 3 non-overlapping channels at 20mhz. Remember the part about more and more customers wanting more bandwidth? In the wireless world, one of the ways to increase capacity on your APs is to increase the channel width. Once you increase 2.4 to 30 or 40 MHz, you do not have much room to deal with noise because your available channels have shrunk.

One of the biggest arguments in support of using 2.4GHZ for a WISP environment is the physics.  Lower frequencies penetrate trees and foliage better. As with anything, there is a tradeoff.  As the signal is absorbed, so is the available “air time” for transmission of data.  As the signal travels through stuff, the radios on both sides have to reduce their modulation rates to deal with the loss of signal.  Lower modulation rates mean lower throughput for customers.  This might be fine for customers who have no other choice.  This thinking is not a long term play.

With LTE especially, the traditional thinking is being uprooted.  Multiple streams to the customer as well as various paths for the signal due to antenna stacking are allowing radios to penetrate this same foliage just as well as a 2.4 signal, but delivering more bandwidth. These systems are becoming more and more carrier class.  As the internet evolves and becomes more and more critical, ISPs are having to step up their services.  The FCC  says the definition of broadband is at least 25 meg download. A 2.4 radio just can’t keep up in a WISP environment.  I am seeing 10 meg becoming the minimum customers want. Can you get by with smaller packages? Yes, but how long can you maintain that as the customer demand grows?

So what is the answer? Cell sizes are shrinking.  This is helping 2.4 hold on.  The less expensive radios can be deployed to less dense areas and still provide decent speeds to customers.  This same trend allows 5GHZ cells to be deployed as well. With less things to go through, 5GHZ can perform in modern networks at higher modulation rates.  Antenna manufacturers are also spending R&D to get the most out of their 5GHZ antennas. More money in the pipeline means stronger products. My clients are typically deploying 3.65 and 5GHZ on their towers.  LTE is changing RF WISP design and taking the place of 2.4 and 900.

PTP 550 continuation

In a previous post, I mentioned a 5-mile link using Cambium PTP550s and why frequency matters. Today we enabled the second radio and have some results from that.  First, let us talk about some of the parameters.

As you can see from our frequency scan we have a very noisy frequency.  Without DFS we have very few open channels.  Due to this, the results you will see later are not optimal.  The limiting factor is the noise on the band.

After much channel selection, this is what we ended up with. As you can see we are just running a 40mhz and a 20mhz channel.  This is because the band is so noisy.

As a result of the frequency, this is what we have ended up with for quality and capacity. The second radio is less than optimal, but it is passing solid data.

So what do speed tests look like across the link?

Single Radio Speedtest

Using channel bonding

Some of you may still be asking, it should be more. If you have noticed the noisy frequency band has been the greatest factor on this link.  In the quality and capacity screenshot, you will notice the 2nd radio only has a 45% capacity.  This is due to channel selection. If we could get better channels this would improve the link.

Wo what is the answer? Better backhaul antennas are upgrade number 1.  Currently, we are using UBNT 2 foot dishes, which were chosen due to the gain needed on this link. Secondly, when DFS is certified for these radios we will have more channels available.  The frequency scan shows the DFS channels are less noisy in this area, which will increase throughput.

Just for giggles, we had the tech on-site run a speedtest.  This was through a wireless router with a 100 meg ethernet port plugged into the local router.

 

Frequency does matter

Recently we installed a PTP 550 link for a client.  This is a connectorized version with 2-foot dishes on it for a four-mile link.  Overkill you say, but the idea is the dishes make up the gain and not transmitter power.  A much cleaner signal can be achieved which falls within the FCC guidelines for total EIRP.

So let’s get to it.  Our first image is out path.  This link had clear line of sight from a 150-foot foot water tower to a 240-foot tower.

Google Earth Path

The 240 Foot tower

150 Foot water tower

After getting out of the cold we let things burn in for a few days. This is what an initial spectrum analysis looked like.

Radio Frequency set on 5820 mhz

Radio Frequency set on 5200mhz

As you can see the RSSI was within 2 DB, which isn’t terrible.  However, due to interference, the MCS rates are markedly different, which is what results in the big differences in speed.  Please note this is only with one radio enabled and on a 20mhz channel.  We fully expect bigger speeds once we up channel sizes and enable the second radio.