Radio Receiver Specifications
Receiver Specifications :
- Receiver sensitivity
- Receiver selectivity
- Receiver Dynamic Range
Receiver sensitivity
The Minimum Detectable Signal(MDS) power, P
i(min) at which a receiver can detect a signal,
while providing an adequate SNR
o(min) at analog receiver output or BER at
digital receiver output, for demodulation is called
receiver sensitivity.
The maximum BER dictates the minimum output SNR(SNR
o(min)) necessary
for satisfactory reproduction of the desired signal.
The relation between SNR and BER is given as,
|
SNRo(min)(dB) = (Eb/No)dB + (R/B)dB
|
(1) |
R - Bit rate
B - Channel Bandwidth
E
b - Energy per bit
SNR at the input,SNR
in is determined by input signal power(P
in) and noise
floor(
NFloor).
SNRin(dB)=Pin(dBm) -NFloor(dBm)
NFloor = -174dBm/Hz + 10 log(B)
|
(1) |
After determining the minimum SNR required at the output of receiver from top level
simulation, and knowing the SNR at the input, NF of the receiver can be determined.
NFRx(dB) = SNRin(dB)- SNRo(min)(dB)
= Pin(dB) + 174 (dBm/Hz) - 10 log(B) -
(Eb/No)dB + (R/B)dB
|
(1) |
In a Receiver chain with n-cascaded stages, the Noise Figure of
Receiver(NF
Rx) is given by Friss Formula as
 |
(1) |
If P
in = P
i(min), then sensitivity is given as,
|
Pi(min)(dBm)- 174 dBm/Hz + 10 log(B) + NFRx(dB) + SNRo(min)(dB)
|
(1) |
From the above equation, we can observe that sensitivity depends on Bandwidth,
Noise Figure and SNR(or BER) at the output of receiver. Bandwidth is determined
by communication standard(DECT, GSM,CDMA, etc.,) where we are going to employ
our receiver. After knowing the sensitivity, based on the communication
standard, NF
Rx of the receiver can be calculated using Friss formula.
Then Nioise Figure for each block in the cascaded chain can be distributed.
Receiver Selectivity
The ability of a receiver to extract the desired signal in the presence
of strong adjacent frequency interferers and channel blockers.
Selectivity is determined by SSB phase noise, synthesizer spurs, IF
selectivity, IF BW and co-channel rejection.
- Selectivity of the adjacent and alternate channels.
- Selectivity of interferences to Inter modulation of Third order.
- Blocking Interferences Selectivity.
- Selectivity is critical for good intermodulation performance.
Note :