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"What's the frequency, Kenneth?" Interpreting your engineering screen. Part one.

Posted by WiWavelength , in Author: Andrew J. Shepherd 23 April 2013 · 24,110 views

band class 1 band 25 carrier channel EARFCN
"What's the frequency, Kenneth?" Interpreting your engineering screen. Part one. by Andrew J. Shepherd
Sprint 4G Rollout Updates

Friday, April 26, 2013 - 6:29 AM MDT

A significant piece of S4GRU's educational mission is helping our readers understand what goes on behind the scenes and underneath the hood in the operation of a wireless network.  This often requires getting readers to access internal engineering (or debug) screens on their handsets to view numbers and metrics, such as PN offset, Ec/Io, cell identity, etc., as we track the progress of Sprint's Network Vision deployment around the country.  So, S4GRU staff thought it long overdue to publish a tutorial on what all of those engineering screen numbers and metrics actually mean.  And in this first part of what will hopefully be a long running series, we will examine frequencies, namely center frequencies.

First, let us kick things off with CDMA2000 (e.g. CDMA1X/EV-DO).

CDMA2000 is divided into band classes.  Those band classes basically represent spectrum bands of operation.  Some common CDMA2000 band classes familiar to Sprint users include:  band class 0 (Cellular 850 MHz), band class 1 (PCS 1900 MHz), band class 10 (SMR 800 MHz), and band class 15 (AWS 2100+1700 MHz).

Then, each band class is further divided into carrier channels.  These carrier channel numbers represent the actual RF locations -- center frequencies -- of the carrier channels that we use for voice and data services.

To illustrate, see the EV-DO engineering screenshot below, specifically the "Channel Number" and "Band Class" fields:

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Taking into account the band class and carrier channel number, we can use the following formulas to calculate both uplink and downlink center frequencies:

uplink center frequency (MHz) = 1850 + (0.05 × carrier channel)
downlink center frequency (MHz) = 1930 + (0.05 × carrier channel)


In other words, the spacing in between potential carrier channel assignments in band class 1 is 0.05 MHz (or 50 kHz).  And the band class 1 range of carrier channel numbers extends from 0-1199.

So, using our formulas, the band class 1 carrier channel 100 in the included screenshot has an uplink center frequency of 1855 MHz, a downlink center frequency of 1935 MHz.  This FDD paired set of center frequencies falls toward the lower end of the PCS A block 30 MHz license, which is 1850-1865 MHz x 1930-1945 MHz.

Next, we can shift over to the 3GPP (e.g. LTE) side, which does things a bit differently.  

3GPP sets forth bands, instead of band classes, but otherwise, the functions of bands and band classes are the same.  In the US, common 3GPP bands for LTE include:  band 4 (AWS 2100+1700 MHz), band 13 (Upper 700 MHz), and band 17 (Lower 700 MHz).  But we are most interested in band 25 (PCS 1900 MHz + G block), the band in which Sprint is initially deploying LTE.

As with carrier channel numbers in CDMA2000 band classes, 3GPP bands are subdivided into Evolved Absolute Radio Frequency Channel Numbers (EARFCNs).  And like carrier channel numbers, EARFCNs indicate center frequencies.  However, EARFCNs do so separately for uplink and downlink, as LTE allows for different pairings of uplink and downlink via carrier aggregation.

Now, see the LTE engineering screenshot below for its "Band," "UL channel," and "DL channel" fields:

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Per band 25, we can enter the "UL/DL channels" (i.e. EARFCNs) into the following formulas to determine again both uplink and downlink center frequencies:

uplink center frequency (MHz) = 1850 + [0.1 × (uplink EARFCN - 26040)]
downlink center frequency (MHz) = 1930 + [0.1 × (downlink EARFCN - 8040)]


In this case, spacing between EARFCNs is 0.1 MHz (or 100 kHz).  Additionally, the uplink EARFCN range is 26040-26689, the downlink EARFCN range 8040-8689, both for band 25.

And in the end, EARFCN 26665 in the included screenshot has an uplink center frequency of 1912.5 MHz, while EARFCN 8665 has a downlink center frequency of 1992.5 MHz.  This is an FDD paired set of center frequencies, not a carrier aggregated set, and it resides exactly in the middle of the PCS G block 10 MHz license, which is 1910-1915 MHz x 1990-1995 MHz.

In part two, we will take a similar look at center frequencies in the PCS 1900 MHz band's lower frequency cousins, SMR 800 MHz and Cellular 850 MHz.  So, stay tuned.

Sources:  3GPP, 3GPP2




Great write up!
Damn, I love this site! Thanks, AJ!
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WiWavelength
Apr 26 2013 11:47 AM
For anyone who is curious but not familiar with my title reference...



And the song itself has an interesting backstory.

AJ
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jnredman524
Apr 26 2013 11:48 AM
Nice!! As an added bonus, I now have the R.E.M. song stuck in my head!
Another interesting fact, R.E.M. are from Athens, GA. The first place with Sprint LTE. I can attest to that!
Richard said "Withdrawl is disgust is not the same as apathy".
http://en.wikipedia.org/wiki/What's_the_Frequency,_Kenneth

Bonus points if you can tell the difference in the final verse of the chorus at the end of the song in the album version. :)

http://en.wikipedia.org/wiki/What's_the_Frequency,_KennethBonus points if you can tell the difference in the final verse of the chorus at the end of the song in the album version. :)

I'm going to keep it PG-13, it's the F word.
What about Band Class 18? I'm in a Shentel area. HTC ONEPosted ImagePosted Image

What about Band Class 18? I'm in a Shentel area. HTC ONE


How can that be? It must be an error in the HTC One, because it doesn't support CDMA Band Class 18, and no one in the US that we know of has even begun to release CDMA on said band class. Only LTE has been going on 700 MHz spectrum so far.

How can that be? It must be an error in the HTC One, because it doesn't support CDMA Band Class 18, and no one in the US that we know of has even begun to release CDMA on said band class. Only LTE has been going on 700 MHz spectrum so far.

I have to go back to stock this afternoon to test something . I'll check then to see if it's any different. It shows up as channel 1 on my mom's GS3 right beside it.

Edit: It says Band Class 2 when I'm at my office
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WiWavelength
Apr 29 2013 07:01 AM
It is a known issue. The EV-DO engineering screen on the HTC One does not populate with valid data. The CDMA1X and LTE engineering screens, though, function normally.

AJ
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CriticalityEvent
May 02 2013 10:00 AM
Would the band number in the 1X Engineering screen always show as “CDMA PCS” as long as the band class was “1” (PCS 1900 MHz) in the EVDO Engineering screen? Would it change to something like “CDMA SMR” if the EVDO Engineering screen showed you were connected to band class 10? Since the HTC One’s EVDO Engineering screen is not accurate, could we use this as a work-around?

Do the channel numbers for CDMA2000 and/or UL/DL channels for LTE change as you switch cells (sectors?)? If so, does that mean each cell can only accommodate 1200 CDMA2000 connections and 649 LTE connections, or can two handsets share a channel through some kind of multiplexing?
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WiWavelength
May 04 2013 05:45 PM

Would the band number in the 1X Engineering screen always show as “CDMA PCS” as long as the band class was “1” (PCS 1900 MHz) in the EVDO Engineering screen? Would it change to something like “CDMA SMR” if the EVDO Engineering screen showed you were connected to band class 10? Since the HTC One’s EVDO Engineering screen is not accurate, could we use this as a work-around?


Well, a few comments...

The CDMA1X and EV-DO engineering screens are wholly separate because the two airlinks are wholly separate. For example, you can experience native service on band class 1 CDMA1X 1900 with simultaneous roaming service on band class 0 EV-DO 850 (and many other combinations.) So, idling on band class 10 CDMA1X 800 will not tell us anything about EV-DO. But do know that Sprint has no expressed plans for band class 10 EV-DO 800.

Do the channel numbers for CDMA2000 and/or UL/DL channels for LTE change as you switch cells (sectors?)? If so, does that mean each cell can only accommodate 1200 CDMA2000 connections and 649 LTE connections, or can two handsets share a channel through some kind of multiplexing?


You are misunderstanding the carrier channel assignments. They are like markings on a ruler, but they do not represent individual CDMA2000 carrier channels, which are 1.25 MHz FDD each. In other words, each CDMA2000 carrier channel is centered at a specific channel assignment -- center frequency -- but it covers 25 contiguous channel assignments. So, even if the entire PCS 1900 MHz band were CDMA2000, the absolute maximum number of carrier channels that could be deployed would be 48.

AJ
So it is a good thing my evolte is showing band class 0 on the evdo engineering screen which has better distance coverage and in building penetration?

J.
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WiWavelength
May 08 2013 09:43 AM

So it is a good thing my evolte is showing band class 0 on the evdo engineering screen which has better distance coverage and in building penetration?


A "good thing"? That depends on your perspective. What it does mean, though, is that you are roaming on some other operator's EV-DO 850. Where are you located? And what PRL are you running?

AJ

A "good thing"? That depends on your perspective. What it does mean, though, is that you are roaming on some other operator's EV-DO 850. Where are you located? And what PRL are you running?AJ


My prl is 25014. I'm for sure not roaming, in northern oc with LTE. Unless the phone shows band 0 on evdo when connected to LTE.
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WiWavelength
May 08 2013 11:12 AM

My prl is 25014. I'm for sure not roaming, in northern oc with LTE. Unless the phone shows band 0 on evdo when connected to LTE.


Well, two issues...

Actually, you could be EV-DO roaming, yet you have native CDMA1X signal. That is somewhat rare, but it happens.

In the EVO LTE, however, EV-DO and LTE share a transmit path, so only one can be active at a time. Thus, if you are connected to LTE, then you are not connected to EV-DO. And the band class 0 field is spurious.

AJ

Great stuff, really love these articles.

 

 

Amazing how many radios our devices are packed with. What's funny is how the screenshots depict a mobile locked to a WiFi signal in addition to camping on EVDO / LTE freqs. 

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WiWavelength
Jul 25 2013 11:49 AM

Great stuff, really love these articles.

 

 

Amazing how many radios our devices are packed with. What's funny is how the screenshots depict a mobile locked to a WiFi signal in addition to camping on EVDO / LTE freqs. 

 

Yes, in order to function additionally as mobile hotspots, smartphones have to maintain separate radio paths for WWAN and WLAN.

 

Also, thanks for the kind words.  And I am sorry that the intended continuation of this series is so long in coming.

 

My paid job in higher ed has kept me busier than expected this summer.  Plus, I have a major T-Mobile LTE focused article in the works soon to be published at a prominent tech web site.  So, the next installment in this series may have to wait until this fall sometime.

 

But I do really enjoy writing these engineering focused articles.  Thus, look for more in the future...

 

AJ

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AdmiralSirJohn
Jul 29 2013 06:32 AM

At the risk of sounding like a complete n00b... which, when it comes to Android, I am, how does one bring up the engineering screen on a HTC EVO 4G LTE?

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AdmiralSirJohn
Aug 11 2013 02:37 PM

Never mind, I found the dialer sequence for Field Test mode (which is essentially what the screenshots show above).