5G + 4G Dual Connectivity Related Question : Component carriers overlap in bandwidth

[ilchisingh]

1. I have a fundamental question that relates to Dual Connectivity i.e. N-DC refers to the dual connection of 4G wireless access network and 5G NR.

2. Let’s say that we are using Band-X in 4G and another similar band in 5G and are attempting to communicate with both RATs to take advantage of EN-DC.

3. The question is what will happen if there is overlap in terms of the “spectrum occupied”.

4. Let’s say that the 4G component has been assigned spectrum in Band 3 from 1830 MHz through to 1850 MHz (i.e. a chunk of 20 MHz Bandwidth).

5. Let’s say that the 5G component has been assigned spectrum in Band n3 from 1820.45 MHz through to 1830.45 MHz (i.e. a chunk of 10 MHz Bandwidth).

6. In such a scenario, there is an overlap of 450 KHz between these two components i.e. the assigned 5G-NR band component eats into the 4g spectrum component by 450 KHz.

7. Will such a deployment work in light of the designated configuration based on existing product implementations? There are bound to be issues in decoding such transmissions at the UE because of the overlap in the spectrum. The reason, I am asking this question was because an argument (however erroneous) can be made that the 5G transmissions would potentially be orthogonal to the 4G transmissions (even if they have an SCS of 15 kHz or 30 kHz). I did not agree that the orthogonality provided by the OFDM structure of the waveforms would protect them against each other (i.e. from the UE perspective in the sense that the UE can successfully decode the two transmissions). I would be very grateful if you could enlighten me with your perspective.

8. If the answer is in the negative, from an R&D implementation, perspective – what changes would one need to implement to make such a configuration (i.e. characterized by overlapping assigned spectrums) workable in realistic network implementations?

9. It would also be immensely helpful if you could further substantiate your arguments with references from the relevant 3GPP specifications (or other relevant specifications) or draw my attention to any specific specifications or publications which can further clarify my doubt?

[auto_art]

1. I have a fundamental question that relates to Dual Connectivity i.e. N-DC refers to the dual connection of 4G wireless access network and 5G NR.

2. Let’s say that we are using Band-X in 4G and another similar band in 5G and are attempting to communicate with both RATs to take advantage of EN-DC.

3. The question is what will happen if there is overlap in terms of the “spectrum occupied”.

4. Let’s say that the 4G component has been assigned spectrum in Band 3 from 1830 MHz through to 1850 MHz (i.e. a chunk of 20 MHz Bandwidth).

5. Let’s say that the 5G component has been assigned spectrum in Band n3 from 1820.45 MHz through to 1830.45 MHz (i.e. a chunk of 10 MHz Bandwidth).

6. In such a scenario, there is an overlap of 450 KHz between these two components i.e. the assigned 5G-NR band component eats into the 4g spectrum component by 450 KHz.

7. Will such a deployment work in light of the designated configuration based on existing product implementations? There are bound to be issues in decoding such transmissions at the UE because of the overlap in the spectrum. The reason, I am asking this question was because an argument (however erroneous) can be made that the 5G transmissions would potentially be orthogonal to the 4G transmissions (even if they have an SCS of 15 kHz or 30 kHz). I did not agree that the orthogonality provided by the OFDM structure of the waveforms would protect them against each other (i.e. from the UE perspective in the sense that the UE can successfully decode the two transmissions). I would be very grateful if you could enlighten me with your perspective.

8. If the answer is in the negative, from an R&D implementation, perspective – what changes would one need to implement to make such a configuration (i.e. characterized by overlapping assigned spectrums) workable in realistic network implementations?

9. It would also be immensely helpful if you could further substantiate your arguments with references from the relevant 3GPP specifications (or other relevant specifications) or draw my attention to any specific specifications or publications which can further clarify my doubt?

The simplistic answer to this any overlap of band is an interference doesn't matter what spread spectrum you use, Now depending on how strong the interferer is it may or may not effect performance.

if you look at the frequency plane. there is guard band on both ends of spectrum so this scenario could be find for a wide band like 20 MHZ that spares 1 MHZ on each side as GB. If some of the RB experiences interference eNb don't assign those resources to users if it is not that busy. eNB uses uses sounding references signals for this.

any overlap should be taken care during RF planning etc. I have not seen such scenario practically commercially.

[Nyquist]

Hi.
Related to your point number 8.

As far as I know and see:
Sometimes due to a malfunction or design fail, a filter is needed (please talk to vendor of malfunction system)
In case all is OK and it is a band assignation issue, you should do a 4G Refarming in order to free the overlapping portion and to ensure that 5G NR is the only user of their assigned band. Vendors should have the Refarming Process well documentated.

Sorry for not provide more detailed information. I have only a global view on this issue

Hope this can help.

Nyquist

[ilchisingh]

Aloha

Thank you for your response.

From a physical layer perspective, can you focus on the topic of the "orthogonality" i.e. orthogonality will not save the two transmissions from interfering with each other, will they? This is a view that I read in another forum but it does not make sense to me i.e. I do understand from the perspective of the UE being able to decode the combined transmissions (i.e. the Dual Connectivity based transmission), orthogonality will not save the transmission from interfering with each other (given the overlap). I would be very grateful for any inputs analysing the issue from a PHY layer decoding perspective (taking the UE's view from the perspective of decoding the downlink Dual-connective transmissions)?

I look forward to discussing this matter with all those who have a technical interest in the matter.

I hope that more people can share these kind of interesting questions on this forum as I truly believe that it will become a more interesting and lively platform.

Cheers
Ilchi