"What's the frequency, Kenneth?" Interpreting your engineering screen. Part one.
Entry posted by WiWavelength
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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:
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:
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
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