DSS Part-2

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When it comes to deploying 5G, spectrum is a key differentiator for operators. And while 24 GHz millimeter wave (mmWave) spectrum is being auctioned specifically for 5G, mid-band spectrum will be critical for operators to get widespread 5G coverage across their markets. 

That’s why a technology called DSS (dynamic spectrum sharing) is so compelling. This technology, which is part of the 3GPP Release 15, allows operators to dynamically allocate some of their existing 4G LTE spectrum to 5G and use existing radios to deliver 5G services by deploying a software upgrade.

DSS allows 4G and 5G to exist simultaneously on the same band while adjusting the bandwidth allocated to each generation dependent on demand. This is clearly ideal for low-band rollout, as it will allow operators to continue to use valuable spectrum for LTE, while adding 5G (NR) capacity as demand grows. But whether it will be enough to address the looming issue of huge data demand on 5G (NR) networks remains to be seen.

Let’s put it this way: Without DSS, an operator that has 20 MHz of mid-band spectrum would have to split that spectrum in two. In other words, operators would have to allocate 10 MHz of spectrum to 4G LTE and cram all their LTE users into that 10 MHz of spectrum. 

Then the remaining 10 MHz of spectrum could be used for 5G, even though initially there will only be a minimal number of 5G users. With DSS, an operator doesn’t have to split that mid-band spectrum or have dedicated spectrum for either LTE or 5G. Instead, operators can share that 20 MHz of spectrum between the two technologies.

DSS in the time and frequency domains, allows one to have full bandwidth for LTE and for 5G from the control channel point of view while the data channel resources are shared dynamically between the two radios. DSS requires fast coordination between LTE and 5G packet schedulers.

For NR downlink transmission, either semi-static or dynamic spectrum sharing mode can be applied from network perspective. For the semi-static mode, the spectrum sharing strategy will keep the same in the second-level time duration. For the dynamic spectrum sharing, the strategy can be changed with a smaller time domain granularity with RRC and/or DCI configuration.

NR UE can support the semi-static spectrum sharing between LTE network and NR network via the following approaches.
  • NR UE can support BWP switching via RRC signaling, timer, or DCI signaling to implement the semi-static spectrum sharing. When the traffic load in LTE decreases and that in NR network increases,the LTE network can share the spectrum to the NR network by reducing the number of LTE aggregated carriers or switching off the LTE network,and the NR network can enlarge the NR bandwidth by BWP switching and vice versa.
  • NR UE can support RB-level RateMatchPattern configuration to achieve FDMed multiplexing between LTE and NR, where the resources corresponding toRateMatchPattern could be used for LTE network.
  • Carrier-level spectrum sharing can also be achieved only by network scheduling without BWP switchingorRB-level RateMatchPattern. When the LTE carrier is on, NR networks can schedule NR UEs within some portions of system BW and other remaining bandwidth can be used by the LTE networks.
In the next section, we will learn more about DSS and its basic and advance level stuff. So keep reading……. And Stay tune……………
Pinal Dobariya………..

3GPP TS 38.331
3GPP TS 38.221
3GPP TS 36.331
RP-191042, Enhancements for dynamic spectrum sharing in Rel-16, Ericsson, RAN #84, 3-6 June 2019


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