srsRAN + LimeSDR Carrier Aggregation?

Hi All,

I’ve been setting up srsRAN with a LimeSDR for LTE network simulation purposes.

Following @andrewback 's great notes on the LibreCellular site (https://librecellular.org/).

Using the native lime API version of srsRAN (GitHub - myriadrf/srsRAN at native_lime_20.10.1)

I’ve got MIMO working well, with 150MBps down and 50MBps up, as measured by iperf.

I’m now looking to get carrier aggregation working but may have misunderstood the hardware and am wondering if it’s not actually possible.

LimeSDR USB has 2 x Tx and 2 x Rx channels. With each TX/RX pair sharing a LO.

I was therefore hoping to configure intra-band aggregation with 2 x 20Mhz channels next to each other. Thereby allowing the tx / rx lo’s to be sat at the midpoint with the 40Mhz fitting within the 61.44MHz bandwidth limit.

Everything seems to start ok and my UE can see the network, but upon attempting to associate I end up with lots and lots of events from srsenb and an unhappy UE.

After stopping srsenb LimeSuite confirms that both RX and TX frequencies are correct and the LO’s are set as I would expect between the two channels.

Here’s the sort of thing I see from srsRAN when using 2 x 5Mhz channels (EARFCN 2850 and 2900):

RACH:  tti=3651, cc=1, pci=4, preamble=39, offset=5, temp_crnti=0x46

               -----------------DL----------------|-------------------------UL-------------------------
rat  pci rnti  cqi  ri  mcs  brate   ok  nok  (%) | pusch  pucch  phr  mcs  brate   ok  nok  (%)    bsr
lte    4   46   15   0    6   9.1k    4    0   0% |  27.0   31.8   33   13    91k    6    0   0%    0.0
RACH:  tti=4301, cc=1, pci=4, preamble=47, offset=7, temp_crnti=0x47
RRCReestablishmentReject for rnti=0x47. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x47.
RACH:  tti=4441, cc=1, pci=4, preamble=1, offset=5, temp_crnti=0x48
lte    4   46   14   0    9   2.9k   11   12  52% |  18.1   29.6   34   22    29k    7    4  36%    0.0
lte    4   48   15   0    3   5.4k   11    0   0% |  28.1   30.2   33   18    83k   10    0   0%    0.0
RACH:  tti=5021, cc=1, pci=4, preamble=24, offset=7, temp_crnti=0x49
RRCReestablishmentReject for rnti=0x49. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x49.
RACH:  tti=5131, cc=1, pci=4, preamble=14, offset=7, temp_crnti=0x4a
RACH:  tti=5681, cc=1, pci=4, preamble=42, offset=7, temp_crnti=0x4b
RRCReestablishmentReject for rnti=0x4b. Cause: Unhandled Reestablishment due to ReconfigFailure
lte    4   46  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   48   15   0   15   1.6k    4   12  75% |   5.5   30.3    0   22   4.1k    1    4  80%    0.0
lte    4   4a   15   0   11   5.3k   13   12  48% |  20.7   28.7   33   19    49k   11    4  26%    0.0
lte    4   4b  n/a   0    0      0    0    0   0% |  26.9    n/a    0    0    727    1    0   0%    0.0
Disconnecting rnti=0x4b.
RACH:  tti=5821, cc=1, pci=4, preamble=51, offset=5, temp_crnti=0x4c
RACH:  tti=6381, cc=1, pci=4, preamble=40, offset=7, temp_crnti=0x4d
RRCReestablishmentReject for rnti=0x4d. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x4d.
RACH:  tti=6511, cc=1, pci=4, preamble=36, offset=5, temp_crnti=0x4e
lte    4   46   14   0    0      0    0    3 100% |   n/a    1.3    0    0      0    0    0   0%    0.0
lte    4   48  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4a  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4c   13   0    8   3.6k   14   15  51% |  21.1   28.6   33   19    32k   11    4  26%    0.0
lte    4   4e   12   0    4   4.0k    5    0   0% |  27.8   30.5   33   16    56k    7    0   0%    0.0
RACH:  tti=7091, cc=1, pci=4, preamble=10, offset=7, temp_crnti=0x4f
RRCReestablishmentReject for rnti=0x4f. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x4f.
RACH:  tti=7221, cc=1, pci=4, preamble=31, offset=5, temp_crnti=0x50
lte    4   46  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   48  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4a  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4c  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4e   15   0   12   2.4k    9   12  57% |  14.1   30.3   34   22    17k    4    4  50%    0.0
lte    4   50   15   0   10   6.3k   13   12  48% |  21.0   30.6   33   18    57k   11    4  26%    0.0
RACH:  tti=7891, cc=0, pci=1, preamble=36, offset=7, temp_crnti=0x51
RRCReestablishmentReject for rnti=0x51. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x51.
RACH:  tti=8011, cc=0, pci=1, preamble=45, offset=7, temp_crnti=0x52
lte    4   46  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   48  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4a  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   4c   12   0    0      0    0    3 100% |   n/a    5.0    0    0      0    0    0   0%    0.0
lte    4   4e  n/a   0    0      0    0    0   0% |   n/a    n/a    0    0      0    0    0   0%    0.0
lte    4   50    5   0    0      0    0    0   0% |   n/a   -0.3    0    0      0    0    0   0%    0.0
lte    1   52   15   0    8   4.5k   15   12  44% |  18.2   28.9   33   18    40k   10    4  28%    0.0
RACH:  tti=8821, cc=0, pci=1, preamble=17, offset=9, temp_crnti=0x53
RRCReestablishmentReject for rnti=0x53. Cause: Unhandled Reestablishment due to ReconfigFailure
Disconnecting rnti=0x53.
RACH:  tti=8941, cc=0, pci=1, preamble=11, offset=7, temp_crnti=0x54
RACH:  tti=9741, cc=0, pci=1, preamble=16, offset=7, temp_crnti=0x55
RRCReestablishmentReject for rnti=0x55. Cause: Unhandled Reestablishment due to ReconfigFailure

I’m a lowly embedded engineer rather than an RF guy so any pointers appreciated…am I merrily wandering down a dead end track?

Thanks,

Phil

I’m afraid I can’t help, as I’ve not attempted to get CA up and running.

Tagging @Zack in case he can spot anything obvious.

Failing which you might want to try posting to the srsRAN mailing list. The native LMS API implementation is not supported, but you could try using SoapySDR also just to be on an officially supported stack.

Thanks for the speedy reply…hopefully it wasn’t just my shameless name dropping that got your attention :smiling_face:.

I subsequently found a ticket in the main srsRAN repo that asked a similar question. One of the srsRAN devs appeared to believe that the LimeSDR wouldn’t be capable of it.

The example given would match mine, all be it with 20Mhz channels rather than the 5Mhz I selected (although I tried 20Mhz with the same outcome).

It would be good to know if it the LimeSDR should theoretically support it RF wise, with the two channels next to each other as I was planning?

If it should be possible, all be it with limitations the mainline repo + soapy was going to be my next port of call.