receive GSM signals using USRP 2920

[MHantera]

Hello every one 

I'm working on cognitive radio project on the GSM band 890 MHZ–915MHZ uplink 935–960 downlink and I use energy detection technique for spectrum measurement so I'm questioning for the minimum power the usrp can detect note that the power of signals for downlink (-60dbm -100dbm ) and for uplink (-70 dbm to -90 dbm)

Mohamed Hantera

[Doug-W]

Hi Mohamed,

The USRP's receiver senstivity (i.e. minimum detectable signal) is dependent upon a variety of factors including carrier frequency, modulation, error correction coding, data rate, error rate, and receiver noise bandwidth. Using higher throughput data rates such as 320kb/s versus 32kb/s will negatively affect the sensitivity. Error correction techniques such as Hamming code versus reed-solomon codes for example will also affect the performance and so on. In essence, the only universal measurement that is not dependent on the aforemtentioned factors is the receiver noise figure. The receiver's sensitivity can be derived with the preceding info, and noise figure which, per the specifications, is between 5 to 7 dB for the USRP-2920.

Regards

Doug W.

[MHantera]

Thanks a lot for your reply, but I have another question how could I calculate the power of the signal I receive ?? When I calculate it using power block as attached it gives me false results   

[ErikL]

The USRP does not provide back a calibrated power level in engineering units. It varies both in frequency and gain. Relative power level can be observed using more traditional methods as you describe above.

[Doug-W]

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@ErikL wrote:
The USRP does not provide back a calibrated power level in engineering units. It varies both in frequency and gain. Relative power level can be observed using more traditional methods as you describe above.

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I also wanted to add that when you calculate the power in the specified bandwidth, you should be multiplying each bin or 'magnitude' value by the 'df' value (if !=1 Hz) then call the add array elements function.

[petroldevil]

what do you mean by relative power? relative to what exactly?

[MHantera]

Thanks alot for this important note

[ErikL]

Signal increases 10dB, signal power increases 10dB. The bottom line is that anything using antennas is relative. You can get into the general ballpark but calibrated engineering units are not so useful. It's like RSSI in a phone. It can vary substantially across devices, antennas, and rf architectures.

[Abusala7]

Ok but why are we always reading around -70 dbm in the GSM band reagrdless whether the channel we are tuning on is busy or empty ??

[Anthony_F]

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@Abusala7 wrote:

...why are we always reading around -70 dbm ...reagrdless whether the channel ...is busy or empty ??

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Can you post a picture? Is this the same project that MHantera is working on?