Channel Bandwidths

I have a question on channel bandwidths that were selected for the original LTE Rel-8 spec. There are several channel bandwiths supported in Rel-8 and Rel-9: 1.4, 3, 5, 10, 15 and 20 MHz. I am familiar with the fact that the FCC and other regulatory bodies around the world often allocated licensed spectrum in 5 MHz blocks, when possible. So, the 5, 10, 15, 20 appear to be quite understandable. However, why were the 1.4 and 3 MHz channel bandwidths designated? The ligical answer is compatibility with existing mobile cellular standards/deployments at the time (3G era). But I have no clue what they bandwidths were used for in legacy networks. I know Qualcomm’s CDMA used 1 25 MHz channels. China’s TD-SCDMA deployed in China Telecom networks used 1.6 MHz channels.

If anyone can answer my question: what were 1.25 MHz and 1.6 MHz channels originally used for in mobile cellular networks, I would be grateful!

Channel Bandwidths

Can be for IoT or MTC.

My question is what was 1.4 MHz and 3 MHz spectrum originally earmarked for regarding mobile cellular bands. These allocations had to have been made long before IoT and MTC existed… befire the Internet was global. I do realize today 1.4 MHz is significant with LTE-M.

When the 3GPP was developing OFDMA for LTE (pre-4G), prior to 2010, they included these channel bandwidths to make it easier for mobile operators to upgrade to LTE that would eventually become 4G LTE-Advanced. I just dont know why?? cdma-2000 was widespread back the, but it used 1.25 MHz channels. Was 1.4 MHz needed by mobile operators that deployed cdma2000 because the extra channel size was needed for an additional guardband?

I have never been able to find any documenation that explained why these bandwidths already exusted in the first place. This was long before the thought of Cellulat-IoT was even conceived. This has to go back to 2G or even 1G. But even AMPS used 30 kHz frequency channel sizes. Nothing I can think of fits 1.4 MHz and 3 MHz channels. The 3GPP doesnt provide any background in the 36 series specs for 4G LTE. I realize there are thousands of pages and I havent read them all, but nithing where they define these channel bandwidths. It seems like they conjured it up from thin air. But that is obviously not the case. 3GPP have a legitimate reason for doing that. My background doesnt go back far enough to understand it.

Hey, thanks for jumping in. There has to be an answer somewhere for this great mystery.

1.4 MHz and 3 MHz are quite useful for RF Sharing situations.

Imagine you have a 5 MHz spectrum allocation in 900 MHz and you would like to offer both 2G and 4G services within this 5 MHz allocation.

By configuring a 3 MHz for LTE Band 8 carrier - you can also fit 10 GSM900 Channels within the same 5 MHz spectrum. And thus you offer perfectly valid 2G and 4G services simultaneously using just 5 MHz spectrum.

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Michael, this is exactly the kind of information I was looking for. You gave an excellent example of a 3 MHz, in a 5 MHz band with LTE and 2G. Would you by any chance have an example of 1.4 MHz?

Many thanks for thus info. I have been trying to find the reason behind this for a long time. I cannot begin to tell you how much I appreciate you taking the time to respond to my post.

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Well suppose the situation is the same; 5 MHz spectrum allocation available. Need to offer both 2G and 4G. It will be difficult to make a GSM radio plan for a dense urban area using just 10 channels (2 MHz of spectrum).

For this situation, a cell using 1.4 MHz for LTE will make 3.6 MHz available for GSM, which is 18 GSM Channels. This makes it easier to design a usable GSM radio plan for dense urban area - at the cost of LTE bandwidth.

Normally, the LTE spectrum is placed in the middle of the block - with GSM channels below and above it. This way the cells of your network can be defined with either 1.4 or 3 MHz LTE allocation - but all of them still operate on exactly same carrier frequency (EARFCN).

My apologies for not responding much sooner. I have been so busy with work projects I neglected to check back on this post. I do want you to know I appreciate you willingness to share another example with me. You two responses have been most helpful.


I have one more follow up to all the good information I received from you on why the 3GPP supported 1.4 and 3 MHz carrier bandwidths. There must be some scenarios from the 1.25 MHz carriers for MNOs like Verizon and Sprint migrating from CDMAone and CDMA2000 to LTE.

Did the 3GPP ever release a Technical Report (TR) on this subject, as the often do to provide recommendations and guidance for options?