This is merely a historical archive of years 2008-2021, before the migration to mailman3.
A maintained and still updated list archive can be found at https://lists.osmocom.org/hyperkitty/list/UmTRX@lists.osmocom.org/.
Alexander Chemeris alexander.chemeris at gmail.comHi Srdjan, If I understand correctly, I/Q imbalance calibration precision depends on the sampling rate. What sampling rate do you use to achieve <-60dBc image level? On Mon, Oct 29, 2012 at 5:19 PM, Srdjan Milenkovic <s.milenkovic at limemicro.com> wrote: > Hi Alexander, > > It is IQ imbalance indeed. It has to be corrected in BB. I believe you have > access to the document: > > "LMS6002D Improving transceiver performance using digital techniques > -1.0r1.pdf" > > It may be useful. Also, we recommend to implement RX DC auto cancellation as > explained in section 3.3 of the same document. This should solve RX LO > leakage issue. > > We usually measure < -60dBc unwanted image level when IQ imbalance is > corrected. > > Regards, Srdjan > > > On 29/10/2012 12:33, Alexander Chemeris wrote: >> >> Hi Srdjan, >> >> Have you seen a question at the end of this e-mail, regarding the LMS >> calibration? >> To me it looks like a result of the I/Q imbalance which we should >> compensate at the baseband level. Is that correct? >> >> On Thu, Oct 25, 2012 at 10:16 PM, Thomas Tsou <ttsou at vt.edu> wrote: >>> >>> Hi all, >>> >>> I spent some time yesterday testing UmTRX with MCBTS. Aside from some >>> trivial fixes (inverted sample rate), the code ran fine with no >>> issues. The default bandwidth of the LPF was insufficient, so that was >>> widened. I tested with 9 handsets between 3 and 7 carriers on a Core2 >>> Duo (P7570) laptop. >>> >>> git://github.com/ttsou/openbts-multi-arfcn.git umtrx >>> >>> Configuration is through sqlite database, which is unchanged from >>> mainline; just set the number of ARFCN (7 max) and C1 channels. >>> Because of the bandwidth involved, be sure to increase the maximum >>> buffer sizes for UHD. The uhd_usrp_probe utility will warn if the >>> target size cannot be set. >>> >>> >>> http://files.ettus.com/uhd_docs/manual/html/transport.html#linux-specific-notes >>> >>> Design >>> ===== >>> There are three resampling stages. >>> >>> 1. Outer resampler converts from the device rate to a multiple of the >>> 400 kHz channel spacing. >>> 2. Channelizer demultiplexes input stream to M channels >>> 3. Inner resampler converts from 400 kHz to a multiple of the GSM symbol >>> rate. >>> >>> UmTRX rates: >>> >>> Channelizer Rate Device Rate Decimation >>> >>> 1.6 Msps 1.625 Msps 8 >>> 3.2 Msps 3.250 Msps 4 >>> >>> Options >>> ====== >>> >>> To broadcast dummy bursts on all carriers for spectrum testing, >>> uncomment the following preprocessor declaration in radioParams.h. >>> >>> #define ENABLE_ALL_CHANS >>> >>> With dummy bursts on all carriers: >>> >>> http://filebox.vt.edu/users/ttsou/http/7carrier_umtrx.PNG >>> >>> Calibration >>> ======== >>> >>> Calibration remains a concern. With single carrier, the carrier >>> leakage and and IQ imbalance appear as in-band distortion. For MCBTS, >>> OpenBTS offsets C0 on to the lowest carrier. This makes the carrier >>> and image quite visible, as shown in the following uncalibrated >>> capture. I checked with a swept tone to verify that this issue was not >>> a result of baseband DSP. The USRP also shows similar effects. >>> >>> http://filebox.vt.edu/users/ttsou/http/carrier_image.PNG >>> >>> Any idea how much carrier and image suppression we should expect with >>> calibration on UmTRXv2? >>> >>> Thomas >> >> >> > -- Regards, Alexander Chemeris. CEO, Fairwaves LLC / ООО УмРадио http://fairwaves.ru