Selectivity improvement solutions proposal for UmTRX

Jean-Samuel Najnudel - BJT PARTNERS SARL jsn at bjtpartners.com
Fri Mar 16 00:19:05 UTC 2012


Hi Robin,

Thank you very much for your help. This could be very convenient. Thanks a
lot.

Best regards.

Jean-Samuel.
:-)


On Fri, Mar 16, 2012 at 12:08 AM, Robin Coxe <coxe at close-haul.com> wrote:

> **
> Hittite is located in Massachusetts about 40 km from Boston. Let me know
> if I can help with sourcing components or requesting samples.
>
> -Robin
> ------------------------------
> *From: * Andrey Sviyazov <andreysviyaz at gmail.com>
> *Date: *Fri, 16 Mar 2012 02:54:51 +0400
> *To: *Jean-Samuel Najnudel - BJT PARTNERS SARL<jsn at bjtpartners.com>
> *Cc: *Alexander Chemeris<alexander.chemeris at gmail.com>; <
> gsm-internal at lists.fairwaves.ru>; Robin Coxe<coxe at close-haul.com>;
> Project Mayotte<project-mayotte at sysmocom.de>
> *Subject: *Re: Selectivity improvement solutions proposal for UmTRX
>
> Hi Jean-Samuel!
>
> About  ADL5802, you can't use it as Down and Up converter simultaneously.
> Also I'm afraid that we can't yet receiving 2 GSM carriers simultaneously.
> So lets done single channel first but 2 or more keep in mind for
> experiments.
>
> I try to find better components too.
> ADI mixers have internal IF AMP and it is not good in this case.
> Components of Hittite are known for me as a very good through my main job.
> I'd like to recommend to use any of the next:
> for GSM900
> 1/ HMC830LP6GE + HMC483MS8GE + TB0130A.  (20.6+4.69+3=$28.29)
> 2/ HMC830LP6GE + HMC686LP4E + TB0448A. (20.6+9.67+3=$32.97)
> for DCS1800
> 1/ HMC830LP6GE + HMC485MS8GE + TB0130A .  (20.6+4.69+3=$28.29)
> 2/ HMC830LP6GE + HMC687LP4E + TB0448A. (20.6+9.67+3=$32.97)
> By the way, LMS lower limit 0.3GHz as per datasheet.
>
> About GSM 05.05 specs I still can't understand blocker requirements:
> MS spectrum with RBW=200kHz have -65dBc level at 600-1200kHz offset,
> therefore blocker MS with -26dBm will be jammer for wanted MS with level
> less then -91dBm and noise level of receiver's heterodyne isn't matter in
> this case.
> I really can't understand why CW levels -26dBm and -16dBm blocking tests
> required.
> May be it just universal test of heterodyne quality?
>
> I think we should be reasonable people, and therefore we should use
> parameters which really necessary for us.
> So, ADRF6601 parameters seems to be quite enough even if it pass only mBS
> requirements.
> On the other hand, BOM difference between ADRF and HMC's around $20-25
> only and it isn't much for normal BS.
> In short, it seems that we should do three options front-end mezzanines:
> 1/ without channel preselector for picoBS or nanoBS upto 0.5W/ch.
> 2/ preselector ADRF based for microBS upto 2W/ch.
> 3/ preselector HMC based for normal BS with 10-20W/ch TMB.
>
> Please find attached pictures that my simple calculations for RX chain.
> Also, please let me know real PA parameters which you decide to use
> for TMB.
>
> Best regards,
> Andrey Sviyazov.
>
>
>
> 15 марта 2012 г. 4:42 пользователь Jean-Samuel Najnudel - BJT PARTNERS
> SARL <jsn at bjtpartners.com> написал:
>
>> Hi Andrey,
>>
>> Thank you for your e-mail.
>>
>> Yes, you are all right.
>>
>> It think your calculations are good. I just did not knew how hard was the
>> GSM macro BTS spec.
>>
>> I browsed a bit the web and found the GSM 05.05 specs which confirm what
>> you say. I also found some similar information and calculations in an
>> academic paper which confirm your figures.
>> http://www.uta.edu/rfmems/Conferences/2001_SPIE_MicroMEMS/4592-20.pdf(page 5 and 6)
>>
>> Anyway, I tried to look at other components than the ADRF6601.
>>
>> I found a quite low phase noise VCO/PLL from Hittite which seems to be
>> able to let us probably pass the macro BTS spec or at least the micro BTS
>> spec.
>> http://www.hittite.com/products/view.html/view/HMC830LP6GE
>>
>> For the mixer, we may use a separate component like the ADL5801.
>>
>> Please let me know what you think about these chips. Please do not
>> hesitate to let us know some other suggestions if you know or if you can
>> find some other components that would have better performances.
>>
>> Actually, even if the specs are not easy to pass, I still feel quite
>> optimistic as it was possible to pass these specs 15 years old components.
>> Anyway, if the macro BTS specs are really too hard to pass, we may focus on
>> the micro BTS spec. This would already be great to convince the market you
>> may be interested in and the performances would be good enough for most
>> practical situations in my deployment in Mayotte.
>>
>> Best regards.
>>
>> Jean-Samuel.
>> :-)
>>
>>
>>
>> 2012/3/14 Andrey Sviyazov <andreysviyaz at gmail.com>
>>
>>> Hi all!
>>>
>>> I am again about far-near problem.
>>>
>>> If we have heterodyne noise -135dBc/Hz at 600kHz offset (ADRF6601), then
>>> for blocking signal at the same offset and at 200kHz RBW we get additional
>>> noise level 135-53=72dBc relative to blocking signal level.
>>> To keep "normal GSM900 BS" sensitivity -104dBm we must keep additional
>>> noise as low as -107dBm, therefore blocking signal maximum level must less
>>> then -107+73=-39dBm.
>>> But in GSM-05.05 (sec 5.1) I saw blocking characteristics requirements
>>> for normal BTS must be -26 dBm at 0.6-0.8 MHz offset and -16 dBm at 0.8-1.6
>>> MHz offset.
>>> So, I do not know how and who can meet those requirements and I am
>>> really hope that there are fundamental mistakes in my calculations.
>>> Correct me please.
>>>
>>> Best regards,
>>> Andrey Sviyazov.
>>>
>>>
>>>
>>> 16 января 2012 г. 19:22 пользователь Jean-Samuel Najnudel - BJT PARTNERS
>>> SARL <jsn at bjtpartners.com> написал:
>>>
>>> Hi Alexander,
>>>>
>>>> These last days, I tried to find a solution for the selectivity
>>>> improvement.
>>>>
>>>> I have 5 solutions to propose. 1st and 2nd are inboard solutions. 3rd,
>>>> 4th and 5th uses an external board. Some seems to be much better than
>>>> others.
>>>>
>>>> 1/ We could use an IF frequency above 375 MHz to be able to connect the
>>>> IF signal dirtectly to the LMS, without any upconvertion back to RF
>>>> frequency. This would save some components.
>>>> We could use the ADRF6601 (PLL/VCO + mixer) and the TB0448A IF SAW
>>>> filter.
>>>> The ADRF6601 is single chip PLL/VCO and mixer. This would be quite
>>>> convenient.
>>>> The TB0448A is cheap (< 3 USD), narrow band (good selectivity) and 400
>>>> MHz center frequency (> 375 MHz LMS lower limit).
>>>>
>>>> Cost of this solution would be about 60 USD and selectivity would be
>>>> really good.
>>>> The main disadvantage of this solution is the filter would restrict the
>>>> signal to a single GSM carrier. This would avoid us to get both GSM
>>>> carriers on each LMS. We would not be able to get true diversity. We would
>>>> only be able to get switched diversity.
>>>>
>>>> After the LNA, RF SAW filter and the RF switches, we can split the
>>>> signal between the current RX path to LMS RX LNA 3 and a new alternate RX
>>>> path (ADRF6601 => TB0448A => LMS RX LNA 1).
>>>> Depending of our need for selectivity, we would be able to select 1 of
>>>> these 2 RX path (direct RX path to LMS RX LNA 3 or IF filter RX path to LMS
>>>> RX LNA1).
>>>>
>>>> This would allow to use the board either as a normal wideband SDR board
>>>> or with a very selective filter.
>>>>
>>>>
>>>> 2/ A very nice option would be to use a variant of the 1st solution
>>>> with a wider bandwidth SAW IF filter. For example, if we use a 400 to 600
>>>> KHz bandwidth IF filter, we would also get a very good selectivity and we
>>>> would also be able to sample both GSM carriers on each LMS. This would
>>>> allow a good selectivity and full diversity.
>>>>
>>>> The problem is we would need a 400 to 600 KHz SAW IF filter, with good
>>>> selectivity, reasonable price and an IF center frequency above 375 MHz. I
>>>> was not able to find such a filter.
>>>>
>>>>
>>>> 3/ As suggested a few days ago, we may use the external selectivity
>>>> improvement board design I sent you. Instead of the Triquint 856378 IF SAW
>>>> filter, we could use the TAISAW TB0448A narrow band filter. This TAISAW
>>>> filter is really much cheaper than the Triquint. This would save a lot of
>>>> budget. However, we would still need 4 mixer and 2 PLL/VCO for each LMS RX
>>>> path. This external board would cost approximately 100 USD (excluding PCB
>>>> and assembly). We would need 2 of these boards for each UmTRX board. This
>>>> would make 200 USD per UmTRX. Including PCB and assembly, toatl cost would
>>>> be around 300 USD. This is not compeltely unrealistic but it seems still
>>>> quite expensive.
>>>>
>>>>
>>>> 4/ Another solution would be to build a single carrier version of the
>>>> 3rd solution design. We would need only 1 RF path (PLL/VCO + mixer) with
>>>> only 1 narrow band filter per LMS RX path. This would not need any splitter
>>>> or combiner. Design would be quite simple and cost would be about 2 times
>>>> lower. However, as we will have only 1 carrier on each antenna, we would
>>>> not be able to get diversity at all.
>>>>
>>>> This solution would finally not have many advantages compared to 1st
>>>> solution. It would cost more and would not allow any kind of diversity.
>>>>
>>>>
>>>> 5/ Last solution would be to build an external diversity improvement
>>>> board, as 4th solution, but with a wider band IF SAW filter.
>>>>
>>>> We could use the following RF path:
>>>> LNA => RF SAW filter => mixer => IF SAW filter => mixer => RF SAW
>>>> filter.
>>>> Dual mixer could be the ADL5802 connected to the ADF4350 PLL/VCO.
>>>>
>>>> We could use the TB0218A IF SAW filter. This filter is quite affordable
>>>> (< 10 USD). Selectivity is good and bandwidth is wide enough to select 2
>>>> GSM carriers (separated by 400 KHz).
>>>>
>>>> Cost of such external diversity improvement board would be quite
>>>> reasonable.
>>>> This would be a very nice solution to select 2 GSM carriers. Connected
>>>> to the UmTRX, this selectivity improvement board would allow to get both
>>>> switched or true diversity.
>>>>
>>>> As TB0218A center frequency is 140 MHz, we would not be able to connect
>>>> directly the IF signal to the LMS. We would need to up convert the signal
>>>> back to the RF frequency.
>>>> As IF down converted signal is upconverted back to the original RF
>>>> frequency, it would be possible to use this selectivity improvement board
>>>> with any kind of existing OpenBTS (UmTRX, USRP, SSRP...) or OpenBSC
>>>> (Sysmocom BTS, IP.access nanoBTS...) hardware to improve the Rx
>>>> selectivity. This would offer a wider potential market than an inboard
>>>> solution.
>>>>
>>>>
>>>> Considering all these solution, I believe 1st and 5th solutions seems
>>>> to be the best choices. 2nd solution would also be really nice but I was
>>>> not able to find the appropriate IF SAW filter.
>>>> Please let me know your opinion regarding each of these two solutions.
>>>>
>>>> By the way, the TB0448A and TB0218A SAW filters looks really good but I
>>>> am not 100% sure the GSM carrier spectrum distortion due to the pass band
>>>> ripple of the SAW filter is acceptable.
>>>> Center part of the GSM carrier (f +/- 100 KHz) is fine but side parts
>>>> of the GSM carrier (bellow f - 100 KHz and above f + 100 KHz) may be cut a
>>>> bit by the SAW filter.
>>>>
>>>> Could you also please check the TB0448A and TB0218A datasheets to
>>>> double check if the usable bandwidth is wide enough ? Especially, do you
>>>> think cutting a bit the side parts of the GSM carrier may cause problem ?
>>>>
>>>> Anyway, please let me know your point of view regarding these
>>>> selectivity improvement solutions.
>>>>
>>>> Best regards.
>>>>
>>>> Jean-Samuel.
>>>> :-)
>>>>
>>>>
>>>
>>
>
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