Hi Experts.
Is it possible to use different frequency bands for Uplink and Downlink in LTE?
For example DL: 1800 / UL: 900?
What can be the unexpected deteoritation or expected achievement?
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For FDD it is possible to use different BW.
In MIB you can see DL BW and in SIB 2 UL BW.
No.
EARFCN is defined frequency for both DL and UL in a pair.
For each DL EARFCN there is UL EARFCN fixed.
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If we have valid license, such not fixed DL_UL Combination?
Even though you have valid license how commercial UE will decide UL frequency, as UE is 3GPP compliances?
Correct.
The number of bands allocated for use has increased as the pressure increases on spectrum.
It has not been possible for all LTE band allocations to be the same across the globe because of the different regulatory positions in different countries. It has not been possible to gain global allocations.
In some cases bands appear to overlap. This is because of the different levels of availability around the globe, where various countries have allocated the frequencies differently now and historically.
This means that roaming with LTE may have some limitations as not all handsets or UEs will be able to access the same frequencies.
As far as I know there is no any restriction depend on the band and license assignment per country per operator ? Are there any band combo restriction according to the 3gPP?
If yes could you please share ?
May we can say, there shouldn’t be far away DL_UL from each others due to syncronization issues?
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Please share if you came across n this combo.
Tested in your network.
Not tested yet, still on progress for brainstorm.
If we tested surely I will share. 
Theoretically it’s possible, but vendors have developed the hardware to support the fixed DL/UL combination as per ITU standards.
Operators only need to define DL frequency.
The logic is to avoid interference with another ISPs frequency
Yes, uplink is always fixed for a downlink in case of duplex band.
E.g. in 2100 band, if Downlink is 2150, Uplink will be 1960.
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Is it possible to configure different bandwidth for DL and UL?
Yes, that is possible.
36.101 section 5.7.3
Thanks!
Last question: are there any feature name for different UL_DL band combination?
DL 1800 UL 900 or vice versa.
In case of supplementary Uplink and Downlink.
This technique is called frequency UL frequency decoupling. In spite of I had not seen this to any integrated site a similar behaviour can be experienced on carrier aggregation.
Let me explain it better: In cases where the PCELL is on 850 MHz, for example and SCell is on either 1800, 1900 and 2100 MHz. The final behaviour will be similar to the concept of frequency decoupling since the UL will be on 900 MHz and the majority of DL will be on 1800, 1900 and 2100 MHz.
BR, Pierre
In FDD, the UL and DL config symmetrically, thus not possible to use different band for UL/DL.
There is a defined band that works in this way, it is known as AWS, or rather BAND 4. Its UL is at 1700 and its DL at 2100.
Combinations of this type are already standardized to avoid conflicts both at the HW level and at the level of operators or different services that can use said frequencies.
There are other combinations of AWS, such as Band 66, which is called AWS Extended.
Band 4
Uplink Frequency: 1710-1755 MHz
Downlink Frequency: 2110-2155 MHz
Band 66
Uplink Frequency: 1710 - 1780 MHz
Downlink Frequency: 2110 - 2200 MHz