SDR - Multi Cells on One SDR
The purpose of this tutorial is to show you how to configure (map) multiple cells to single sdr card. This kind of mapping is possible as long as following condition is met.
- The center frequency of every cell should be within the frequency and bandwidth range of each sdr card support. (Both SDR50 and SDR100 support upto 6 Ghz frequency in terms of center frequency)
- The bandwidth aggregation of all cells should be accommodated by the each sdr card(SDR50 support upto 50 Mhz and SDR100 support upto 100 Mhz in terms of bandwidth)
- In case of FDD, both Uplink and Downlink frequency and Bandwidth of all cells should be accommodated by each SDR card
However, you should take into considerations a few possible limitations as below. This tutorial will be updated as we confirm further on following items. So for now, I would not recommend you to try any of the following cases.
- This feature is supported only on Callbox and is not supported on UEsim
- LTE + NR mapping on the same sdr card is still under test. Theoretically this should be possible, but some tricky issues were identified during the test.
- It is not easy to find LTE and NR that can map onto single sdr card due to the limited bandwidth supported by sdr card. The frequency separation between LTE and NR should be less than 50 Mhz (SDR50) or 100 Mhz(SDR 100)
- For LTE TDD + NR TDD, it is not confirmed whether we can use different DL and UL configuration for each cell
- It is not confirmed whether LTE FDD and NR TDD can be mapped onto the same sdr card.
- It is not confirmed whether different subcarrier spacing between LTE and NR can be used.
Table of Contents
- SDR - Multi Cells on One SDR
Test Setup
Test setup for this tutorial is as shown below. This is just for low layer testing, you may not need any complicated IP layer setup.
- SIM Card used in this tutorial is the one delivered with the system as it is.
- If you want to change the configuration, The tutorial Configuration Guide would help
Key Configuration Parameters
Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.
Test 1 : 2 LTE on One SDR
In this test, three cells are configured on Callbox which is LTE + LTE + NR. The two LTE cells are mapped to the same sdr card and the NR cell is mapped to another sdr card. Overall structure of the setting is illustrated as below.
If you are using commercial phones for the test, this is all. You can use one UE trying to connect to each of the cell at a time. or you may use three different UEs and let each of them to get access to each of the cell.
In my case, I used Amarisoft UEsim and configured the three UEs in it and configured as shown below. You would notice two things as below
- Each of the cells in cell_groups is mapped to different rf_port meaning that they are mapped to different sdr. This is because UEsim does not support multicell mapping on a single sdr card as mentioned before.
- I set different values for cell_index for each UEs in ue_list. This makes each UE to camp onto different cells.
Configuration
The configuration shown here is common configuration for all the subtests belonging to Test 1 and I will not show this configuration repeatedly for every subtest.
I have used enb-multicell-onesdr.cfg which is copied and modified from gnb-nsacfg
I am using the default mme, ims config as shown below.
I have used ue-3ue-3sdr.cfg which is copied and modified from ue-nr-nsa.cfg
In enb-multicell-onesdr.cfg, it is configured as follows. In this test, two LTE FDD and one NR TDD are used. So TDD is set to 0 (meaning FDD) and NR_TDD is set to 1 (meaning TDD). LTE bandwidth is set to 10Mhz (N_RB_DL 50) and NR bandwidth is set to 40 Mhz (NR_BANDWIDTH 40). And both LTE and NR are set to 2x2 MIMO (N_ANTENNA_DL 2)
Two SDR cards are used in this test. dev0 is mapped to sdr0 and dev1 is mapped to sdr1.
Two RF ports are configured. rf_port0 will be used for LTE cell and rf_port1 will be used for NR. Both RF is set to default configuration without any change.
In cell_list configuration (LTE cell configuration), the first cell is mapped to the first rf port (rf_port: 0).
The second cell is also mapped to the first rf port (rf_port: 0).
In nr_cell_list configuration (NR cell configuration), the NR cell is mapped to the second rf port(rf_port: 1).
In ue-3ue-3sdr.cfg, it is configured as follows. This test uses 3 cells (2 LTE cell and 1 NR cell), so N_CELL is set to 3.
UEsim does not support the multicell on one card, so we need 3 sdr card for the test. In this test, dev0 is mapped to sdr0, dev1 is mapped to sdr1 and dev2 is mapped to sdr2.
In cell configuration, you see each of the three cells are mapped to different rf ports. The first LTE cell is mapped to the first rf port(rf_port: 0), the second LTE cell is mapped to the second rf port(rf_portL 1) and the NR cell is mapped to the third rf port(rf_port: 2).
Now we will map each of the 3 UEs to each of 3 cells.
The first UE is mapped to the first cell (cell_index: 0)
The second UE is mapped to the second cell (cell_index: 1)
The third UE is mapped to the third cell (cell_index: 2)
Perform the Test
Check if all three cells show up and their configuration is as you want. You can check the basic configuration with 'cell phy' and 'cell' command, but you cannot check on sdr and rf port mapping with command line command. You may get some additional information with rf_info command, but this one does not show the detailed mapping either.
If you are using UEsim for test, check on UEsim and see if all cells are active and detected all three cells. The UEsim should detect all the cells even before you do 'power_on'.
Check on cell information on UEsim and see if it matches as you intended. Here you see all three cells (2 LTE cells and one NR cell) are detected.
Now power_on all the UEs (power_on *)
On Callbox, check if all the cells got connected. Make it sure that you see all cell IDs in CL column.
You can check if all the UE got connected and assigned with IP addresses. You should see all three UEs are attached and assigned with IP address.
You can confirm on UEside as well and see if all UEs are properly registered.
Log Analysis
Nothing much you need to check on the log. Just make it sure that you see all RRC (or RRC + NAS) that you need to see for initial attach. You can confirm on this with 'Cell' colum and 'UE ID' column.
