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Alexander Chemeris alexander.chemeris at gmail.comYes, I suppose that by default. Thanks for clarification anyway. On Tue, Oct 30, 2012 at 3:48 PM, Srdjan Milenkovic <s.milenkovic at limemicro.com> wrote: > Forgot to mention, < -60dBc image suppression has been achieved by > correcting both phase and gain imbalance. > > > On 30/10/2012 10:10, Alexander Chemeris wrote: >> >> Thank you. We will check how well we could compensate I/Q imbalance on >> UmTRX. >> >> On Mon, Oct 29, 2012 at 5:40 PM, Srdjan Milenkovic >> <s.milenkovic at limemicro.com> wrote: >>> >>> I am not sure calibration precision is affected by sample rate. >>> Theoretically, we are rotating I vector by alpha/2 and Q vector by >>> -alpha/2 >>> and that is done by multiplication. Hence, the resolution of quadrature >>> phase error (alpha) which we can correct is defined by the with of >>> multipliers. >>> >>> Any way, we clocked ADCs at 15.36MHz (30.72MS/s digital IQ interface) in >>> the >>> experiment I mentioned. >>> >>> >>> On 29/10/2012 13:26, Alexander Chemeris wrote: >>>> >>>> Hi 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