Implements an automatic gain controller (AGC).

Notes

x[n] -->X---------------------------------------------------------------------+--> y[n]
        ^                                                                     |
        |                                                                     |
    +--------+      +------+                     -1  +--------+   +-------+   |
    | exp(.) |<--+--| z^-1 |<--@<---X<--------@<-----| log(.) |<--|  |.|  |<--+
    +--------+   |  +------+   ^   alpha    log(R)   +--------+   +-------+
                 |             |  or beta
                 +-------------+

x[n] = Input signal
y[n] = Output signal
alpha = Attack rate
beta = Decay rate
R = Reference magnitude
@ = Adder
X = Multiplier

References

• Michael Rice, Digital Communications: A Discrete-Time Approach, Section 9.5.

• Qasim Chaudhari, How Automatic Gain Control (AGC) Works.

Examples

Create an example received signal with two bursty signals surrounded by noise.

In [1]: x = np.exp(1j * 2 * np.pi * np.arange(5000) / 100); \
   ...: x[0:1000] *= 0; \
   ...: x[1000:2000] *= 10; \
   ...: x[2000:3000] *= 0; \
   ...: x[3000:4000] *= 0.1; \
   ...: x[4000:5000] *= 0
   ...: 

In [2]: x += 0.001 * (np.random.randn(x.size) + 1j * np.random.randn(x.size))

In [3]: plt.figure(); \
   ...: sdr.plot.time_domain(x); \
   ...: plt.title("Input signal");
   ...: 

Create an AGC with an attack rate of \(\alpha = 0.5\) and a decay rate of \(\beta = 0.01\). Notice that over time the noise is amplified (according to the decay rate). Also notice that when the signal of interest appears the AGC gain is quickly decreased (according to the attack rate).

In [4]: agc = sdr.AGC(0.5, 0.01)

In [5]: y = agc(x)

In [6]: plt.figure(); \
   ...: sdr.plot.time_domain(y); \
   ...: plt.ylim(-1.5, 1.5); \
   ...: plt.title("Output signal");
   ...: 

Constructors¶

AGC(attack: float, decay: float, reference: float = 1.0, ...)

Creates an automatic gain controller (AGC).

Special methods¶

__call__(x: ArrayLike) → NDArray[complex128]

Performs automatic gain control on the input signal.

Streaming mode only¶

reset(gain: float = 1.0)

Resets the AGC gain. Only useful when using streaming mode.

property streaming : bool

Indicates whether the AGC is in streaming mode.

property gain : float

The current linear gain.

Properties¶

property attack : float

(Settable) The attack rate \(\alpha\).

property decay : float

(Settable) The decay rate \(\beta\).

property reference : float

(Settable) The desired output magnitude.