LMS6002D support of LTE

Srdjan Milenkovic s.milenkovic at limemicro.com
Sun Oct 14 11:50:02 UTC 2012


Hi Alexander,
Remaining questions are addressed below.

Dr Srdjan Milenkovic On 13/10/2012 21:47, Alexander Chemeris wrote:
> Hi Srdjan,
>
> We're looking into re-purposing UmTRX for LTE and there a few things 
> which we need to understand better.
>
> 1. Is it possible to support 15MHz and 20MHz LTE channel bandwidths? 
> To achieve this we at least need to sample at 23.04Msps and 30.72Msps 
> respectively. LMS6002D datasheet specifies the maximum I/Q samplerate 
> of 14Msps, which is not enough. But at the same time, datasheet claims 
> that ADC and DAC are specified up to 50Msps. How does this fits together?
>
> 2. Do you have any experience what maximum output power we could 
> achieve with LMS and proper amplifiers, while still staying in the 
> bounds of the LTE Standard? What would be the limiting factor for the 
> further power increase?
The limiting factor here would be absolute specs on ACPR, out of band 
spurs ... i.e. TX spectrum mask, expressed in dBm not in dBc. For 
example, you may meet <= -45dBc ACPR but on the other hand you can not 
inject noise into adjacent channel more than xdBm. LMS device is OK for 
20-25dBm modulated output power. We can probably push it more however 
this is  not tested so far.

>
> 3. Is there any issues using TDD mode in LMS6002D? We've been using 
> onnly FDD mode so far and it would be great to know what issues could 
> we expect when switching to TDD mode.
TDD mode should be just fine. We measured around 20us TX<->RX switching 
time. We will probably need to reconfigure VCO supplies on UmTRX board 
to simplify switching control while keeping switching time at 20us. Lat 
us know when you are ready for such experiment.

>
> -- 
> Regards,
> Alexander Chemeris.
> CEO, Fairwaves LLC / ООО УмРадио
> http://fairwaves.ru

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