The formula for bits/sec/Hz is quite simple. Take bits/sec and divide by Hz.
So for example, if a Rocket Ti is capable of 75 Mbps actual throughput in a 20 MHz channel, that’s a spectral efficiency of 75/20 = 3.75 bits/sec/Hz. If you want to calculate based on physical layer throughput, it’s more like 5 or 6. Similarly, if a Cambium PMP450 does 100 Mbps in a 20 MHz channel at 8X modulation (256 QAM), that’s a spectral efficiency of 5. I don’t know what spectral efficiency is for something like a Mimosa B5, they claim 1 Gbps actual payload throughput, I’m guessing that’s in 160 MHz of spectrum, so that would be 6.25? The Wikipedia article divides by 3 for 802.11 and by 1 for LTE, based on the formula “multiply by the frequency reuse factor”. The problem is not the formula but the numbers plugged into the formula. Garbage in, garbage out. Where did the number 3 come from? Just because it’s on Wikipedia doesn’t mean somebody didn’t pull that number out of their ass. In a WISP equipment context, I think we usually talk in terms of just bits/sec/Hz. Frequency reuse, whether due to GPS sync or MU-MIMO or beamforming or whatever, that’s a separate factor to tout, and mostly a cellular concept. I don’t see why someone chose to arbitrarily divide the spectral efficiency of WiFi by 3. As far as SISO vs MIMO, the table says the numbers for 802.11n are for SISO, but I think they may actually be for 2x2 MIMO. From: Josh Reynolds via Af Sent: Sunday, October 26, 2014 10:14 PM To: [email protected] Subject: Re: [AFMUG] questions about filters Then post the correct formula, IYHO, so it can be fixed. Josh Reynolds, Chief Information Officer SPITwSPOTS, www.spitwspots.com On 10/26/2014 06:20 PM, Ken Hohhof via Af wrote: That doesn’t address my complaints about the USE of those formulas. Do you agree that WiFi bits/sec/Hz should be divided by 3 but LTE should not, because of assumptions about frequency reuse? In the context of a WISP application which may use GPS sync? How about assuming one spatial stream for WiFi but 8 for LTE? And what about treating LTE Advanced like a current technology but 802.11ac as a future technology? And 802.11n is capable of more than 1.2 bits/sec/Hz. If the formula disagrees with reality, it’s the formula (or the numbers plugged into the formula) that must change, not reality. It’s not like a Looney Toons cartoon where the character falls to the ground once you point out they can’t walk on air. From: Josh Reynolds via Af Sent: Sunday, October 26, 2014 8:59 PM To: [email protected] Subject: Re: [AFMUG] questions about filters The formulas are at the top of the chart. Josh Reynolds, Chief Information Officer SPITwSPOTS, www.spitwspots.com On 10/26/2014 05:31 PM, Ken Hohhof via Af wrote: I think those numbers are flawed. Especially dividing the 802.11n numbers by 3 due to “frequency reuse” factor. And using SISO for 802.11n but 8x8 MIMO for LTE. Not to mention using 802.11n and not 802.11ac. Saying 802.11n is only good for 1.2 bits/sec/Hz is saying it can only do 24 Mbps in a 20 MHz channel. Hogwash. From: Josh Reynolds via Af Sent: Sunday, October 26, 2014 5:49 PM To: [email protected] Subject: Re: [AFMUG] questions about filters Well... http://en.wikipedia.org/wiki/Spectral_efficiency 802.11n has a spectral efficiency of around 1.2. LTE advanced has a spectral efficiency of _30_. If we could get some fairly cheap radio chipsets with even a 10-15 in spectral efficiency at this point, we would probably all be incredibly happy. Doing that would likely cause us to (A) Not be compatible with 802.11 (fine by me), and (B) would require mass market adoption. Josh Reynolds, Chief Information Officer SPITwSPOTS, www.spitwspots.com On 10/26/2014 02:40 PM, Mike Hammett via Af wrote: That's what I was hoping for but I was told to sit down. ----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com ----- Original Message ----- From: "Bill Prince via Af" mailto:[email protected] To: [email protected] Sent: Sunday, October 26, 2014 12:36:58 PM Subject: Re: [AFMUG] questions about filters Perhaps some innovation in improving efficiency? Maybe takes someone thinking outside of the current box(es). bp On 10/26/2014 9:55 AM, Chuck McCown via Af wrote: I was just going to mention that. Make a clean signal and you don’t have to filter so much. Anyone remember what a Class A amplifier is? (45% efficient at best) Cavity filters? I would think that in this day and age, you ought to be able to go DSP direct to antenna up to a 5 volt p-p signal. Or if you had to use a PA, inject a pre-distortion component. The cable TV guys have been dealing with these issues for decades. And then there is the issue with physical size of filters. A nice filter, with decent response and low insertion loss is large. SAW filters are about as small as you can get but they are higher loss than, for example, a waveguide filter however they are maybe 1% of the volume. You want a small radio that consumes very little power, then ... it will be more noisy than a large radio that consumes more power. That said, modern tech is unbelievable in performance and it just keeps getting better. Perhaps Chuck will get to come to AnimalFarm this year and show us something fun. From: Chuck Macenski via Af Sent: Sunday, October 26, 2014 10:24 AM To: [email protected] Subject: Re: [AFMUG] questions about filters Hi again, Another factor that causes expense is the linearity of the final stage output amplifiers...these puppies are linear for most modern radios and more linearity = more cost and higher power consumption. I will stop now... Chuck On Sun, Oct 26, 2014 at 10:47 AM, Chuck Macenski < [email protected] > wrote: Hi, There are many questions (explicit and implicit) in your question. Focusing on the tx side only (since we are talking about band edge), the filters you are talking about are electromechanical. Do a wikipedia search on SAW filters and you will get a sense for what you are dealing with. There are many other factors involved in meeting band edge requirements and other filtering that is or can be performed, but, the expense is often in the electromechanical components. Chuck On Sun, Oct 26, 2014 at 1:45 AM, That One Guy via Af < [email protected] > wrote: with the changes in the 5ghz rules, it may force innovation in filtering technology to bring cost down, assuming the innovators arent stuck in a mindset of the only thing that would work is what there is. How do filters works? Are there electronically adjustable filters? Where does the cost come from on filters? It is not new technology, so recovery of R&D on a new tech has long since past, what is it that drives the cost up? Is it primarily a matter of it being something needed, so its more valuable, or is it something in the physical properties of the filters that drives up the cost? Can you filter electronically a transmitter using something along the same lines of noise cancelling headphones
