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noise power

Noise equivalent power

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Signal-to-noise ratio Required incidence at 1 infrared radiation power 。 That is to say, projection to micro Bolometer On infrared radiation The output voltage generated by the power is exactly equal to that of the microbolometer itself Noise voltage , this Radiant power be called Noise equivalent power 。

Chinese name: noise power
Foreign name: Noise Equivalent Power
Referred to as: NEP。

Also known as: Noise equivalent power
Classification: Sound power
Unit: W

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definition

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Noise The equivalent power is called NEP for short.

Noise equivalent power (NEP) is also called noise equivalence power 。

The noise power is the total energy of the noise source radiating sound in space in unit time.

Spectral density

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Noise power spectral density estimation method

With CP segment Sampling point Estimate:

Assumptions:

1 Do not consider channel residue signal Impact of;

2 Single antenna;

3 single path channel

4 channels in one OFDM Keep unchanged within the block length, that is Slow fading Channel.

This includes:

h1=h2,a1=a2,

E((h1*a1+n1-h2*a2-n2)^2)

=E((n1-n2)^2)

=E(n1^2+n2^2)-2E(n1*n2)

=2σ^2

Actual considerations

When applied to Gbit systems, the following situations need to be considered:

1 Considering the influence of channel residual signal Sampling point When making estimates^[1] , on the back end of the CP sampling , try to eliminate the influence of residual signals;

2 Consider the case of multiple antennas^[1] , Gbit system antenna is configured as 4 * 4 antenna;

3 Consideration multipath The situation of;

Gbit platform

In the Gbit platform, the noise power spectral density The calculation method is as follows:

var =h_pow*pow(10,-Eb_N0/10)*Nr/M

Including:

H_power: channel gain=∑ i=1... path_number {10 ^ 0.1 * (path_avg_power [i])}

Nr: Number of receiving antennas

M: Modulation order (2: QPSK ,4： 16QAM ）

Eb/N0: Signal-to-noise ratio

After the var is calculated in the Gbit platform, it is used when adding noise Noise power spectrum The density is var/FFT_notes, which is because IFFT and FFT are not calculated on the Gbit platform normalization , that is, when IFFT is calculated, the coefficient is 1/FFT_notes, while when FFT is calculated, the coefficient is 1, so the actually transmitted signal bit energy is attenuation It is 1/FFT_notes under normal conditions. In this way, the noise power calculated must also be attenuated by FFT_notes times to ensure the correct signal-to-noise ratio (refer to Gbit program).

simulation result

Also consider the channel Slow fading Under^[2] , take 10 time domains on each receiving antenna Sampling point ，

CP：(S118,S119,…,S127)

OFDM :(S1142,S1143,…,S1151)

Calculate as follows:

Get noise power spectral density For:

Use the noise power spectral density in the above formula and actually added var /FFT_notes

The following simulation results are obtained:

Eb/N0（dB）
zero	seven point four nine nine
ten	twenty-three point seven zero six
twenty	seventy-four point eight seven six
thirty	two hundred and thirty-five point nine two zero
forty	seven hundred and thirty-eight point seven six four
fifty	two thousand two hundred and ninety-six point zero one nine

Result analysis:

Noise estimated at 1.0dB power spectral density Compared with the actual added Noise power spectrum The density is 7.499 times higher, and the reason is unknown;

2. Estimated Eb/N0 for every 10dB increase Signal-to-noise ratio The above multiples will increase by 3.1 times, and the reason is unknown.

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