[USRP-users] MIMO bug?

Dan Sego bubbadoradar at gmail.com
Mon Dec 29 12:09:13 EST 2014


Good morning to the list.

I have 2 N200 r4 units with WBX daughter cards operating with the following
Win32; Microsoft Visual C++ version 10.0; Boost_105400;
UHD_003.008.000-release. One unit has an internal GPSDO.

In MIMO operation (via the MIMO cable). The slave unit experiences an
unexplained 25 dB of attenuation relative to the master. This change does
not follow the hardware: that is it tracks the slave.

I am using US HDTV as probing signal: tuning to 575 MHz with fc32 formatted
data sampled as 12.5 MCSPS per unit. The code operated successfully
performing data capture to file (though does have the windows prompt upon
completion to terminate). An example run screen capture is pasted below:
the collection operation involves continuous sampling saving
contiguous packets (28) and skipping 50 for a approximate burst sampling
rate of 25 Hz.

Win32; Microsoft Visual C++ version 10.0; Boost_105400;
UHD_003.008.000-release

-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes
-- Creating WSA UDP transport for 192.168.10.3:49156
-- Creating WSA UDP transport for 192.168.10.3:49158
-- Creating WSA UDP transport for 192.168.10.3:49157
-- Creating WSA UDP transport for 192.168.10.3:49159
-- Detecting internal GPSDO.... Found an internal GPSDO
-- Creating WSA UDP transport for 192.168.10.2:49156
-- Creating WSA UDP transport for 192.168.10.2:49158
-- Creating WSA UDP transport for 192.168.10.2:49157
-- Creating WSA UDP transport for 192.168.10.2:49159
-- Setting references to the internal GPSDO
-- Initializing time to the internal GPSDO
Using Devices: Multi USRP:
  Device: USRP2 / N-Series Device
  Mboard 0: N200r4
  Mboard 1: N200r4
  RX Channel: 0
    RX DSP: 0
    RX Dboard: A
    RX Subdev: WBXv3 RX+GDB
  RX Channel: 1
    RX DSP: 0
    RX Dboard: A
    RX Subdev: WBXv3 RX+GDB
  TX Channel: 0
    TX DSP: 0
    TX Dboard: A
    TX Subdev: WBXv3 TX+GDB
  TX Channel: 1
    TX DSP: 0
    TX Dboard: A
    TX Subdev: WBXv3 TX+GDB

Actual RX Rate Master: 12.500000 Msps...

Actual RX Rate Slave: 12.500000 Msps...

Actual Gain Master: 10.000000 dB...

Actual Gain Slave: 10.000000 dB...

GPS lock status: locked
GPS epoch time: 1419183071 seconds
-- Successfully tuned to 575.000000 MHz
-- 
-- Successfully tuned to 575.000000 MHz
-- 
Checking LO Lock Master LO: locked...
Checking LO Lock Slave LO: locked...
Checking MIMO Lock MIMO: locked...

sample time first packet2.3000003

full seconds2.3000003


sample time first packet2.34068534

full seconds2.34068534


Done!


I have measured the channel signals of the units individually
and configured for MIMO. Examples of the individual measurements (power
spectra and mean noise power and total signal power are summarized in slide
1 attached. All runs were made at 10 dB of gain. Both units were
individually exercised from 0 to 30 dB of gain to have side-by-side
responses (indeed one unit is 5 dB less sensitive which track over gain and
both have distinctive and repeatable gain responses using identical log
periodic antennas and matched length coax).

Slide 2 has the MIMO results in both possible configurations.

Has anyone encountered this? Any suggestions?

 regards, Dan Sego
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