Systems and methods for automatic level control
Systems and methods for automatic level control (ALC) are provided. In one embodiment, an ALC system for communications signals comprises: a multi-threshold programmable ALC controller; and at least one signal path that includes: a digital step attenuator configured to receive an analog communications signal and attenuate the analog communications signal in response to an attenuation adjustment signal from the ALC controller; and an analog-to-digital converter configured to receive the analog communications signal as attenuated by the digital step attenuator and generate samples of the attenuated analog communications signal, wherein the ALC controller receives the samples. The ALC controller comprises a plurality of clip detectors that function in parallel. Each of the clip detectors are programmed with a respective amplitude and time threshold. Based on which of the plurality of clip detectors determine that the samples exceed their respective amplitude and time threshold, the ALC controller generates the attenuation adjustment signal.
1. An automatic level control (ALC) system for communications signals, the system comprising:
a multi-threshold programmable ALC controller; and
at least one signal path that includes:
a digital step attenuator configured to receive an analog communications signal and attenuate the analog communications signal in response to an attenuation adjustment signal from the multi-threshold programmable ALC controller; and
an analog-to-digital converter configured to receive the analog communications signal as attenuated by the digital step attenuator and generate samples of the attenuated analog communications signal, wherein the multi-threshold programmable ALC controller receives the samples;
wherein the multi-threshold programmable ALC controller comprises a plurality of clip detectors that function in parallel, wherein each of the plurality of clip detectors are programmed with a respective amplitude and time threshold, wherein based on which of the plurality of clip detectors determine that the samples exceed their respective amplitude and time threshold, the multi-threshold programmable ALC controller generates the attenuation adjustment signal to the digital step attenuator.
2. The system of claim 1 , the at least one signal path further comprising a 1-bit step attenuator in series with the digital step attenuator prior to the analog-to-digital converter, wherein the 1-bit step attenuator is configured to attenuate the communications signal in response to the attenuation adjustment signal from the multi-threshold programmable ALC controller.
3. The system of claim 1 , wherein the multi-threshold programmable ALC controller comprises:
a processor; and
a programmable attenuation manager that includes the plurality of clip detectors, wherein the programmable attenuation manager configures the respective amplitude and time threshold for each of the plurality of clip detectors based on input from the processor.
4. The system of claim 3 , wherein the respective amplitude and time threshold for each of the plurality of clip detectors are defined based on a Complementary Cumulative Distribution Function (CCDF) analysis.
5. The system of claim 3 , the multi-threshold programmable ALC controller further comprising:
at least one processor function configured to calculate a peak sample from the samples of the attenuated communication signal, wherein the peak sample is evaluated by one or more of the plurality of clip detectors to determine when their respective amplitude and time threshold is exceeded.
6. The system of claim 5 , wherein the at least one processor function further calculate a Received Signal Strength Indicator (RSSI) value, wherein at least one of the plurality of clip detectors evaluates the RSSI value to determine when their respective amplitude and time threshold is exceeded.
7. The system of claim 5 , wherein the analog communications signal comprises a communications signal for a single band;
wherein the samples of the attenuated communication signal comprise complex IQ samples and the peak sample is calculated from the complex IQ samples as a function of I 2 +Q 2 .
8. The system of claim 5 , wherein the analog communications signal comprises a communications signal comprising a first signal band x and a second signal band y; and
wherein the samples of the attenuated communication signal comprise complex IQ samples and the peak sample is calculated from the complex IQ samples as a function of I (x+y) 2 +Q (x+y) 2 .
9. The system of claim 3 , wherein the each of the plurality of clip detectors of the programmable attenuation manager comprise at least a level detector and a counter, wherein the counter determines when an input to the respective clip detectors exceeds an amplitude level for at least a defined number of samples, wherein the amplitude level and the define number of sampled are determined from the amplitude and time threshold.
10. The system of claim 3 , wherein the multi-threshold programmable ALC controller further comprises:
an ALC state machine coupled to the programmable attenuation manager, wherein one or more states of the ALC state machine are adjusted based on outputs from the plurality of clip detectors of the programmable attenuation manager, wherein the attenuation adjustment signal to the digital step attenuator is generated by the ALC state machine as a function of the one or more states of the ALC state machine.
11. The system of claim 1 , wherein the multi-threshold programmable ALC controller is implemented within a radio point of a Centralized cellular radio access network (C-RAN).
12. The system of claim 1 , wherein the multi-threshold programmable ALC controller is implemented within a remote antenna unit of a distributed antenna system (DAS).
13. A method for automatic level control (ALC) system for communications signals, the method comprising:
attenuating an analog communications signal in response to an attenuation adjustment signal;
generate samples of the attenuated analog communications signal;
receiving the samples at a multi-threshold programmable ALC controller, wherein the multi-threshold programmable ALC controller comprises a plurality of clip detectors that function in parallel, wherein each of the plurality of clip detectors are programmed with a respective amplitude and time threshold;
based on which of the plurality of clip detectors determine that the samples exceed their respective amplitude and time threshold, generating the attenuation adjustment signal.
14. The method of claim 13 , wherein attenuating the analog communications signal is performed by a digital step attenuator coupled to the multi-threshold programmable ALC controller.
15. The method of claim 13 , wherein the samples of the attenuated analog communications signal comprise complex IQ signals.
16. The method of claim 13 , further comprising:
calculating a peak sample from the samples of the attenuated communication signal, wherein the peak sample is evaluated by one or more of the plurality of clip detectors to determine when their respective amplitude and time threshold is exceeded.
17. The method of claim 16 , wherein the analog communications signal comprises a communications signal for a single band;
wherein the samples of the attenuated communication signal comprise complex IQ samples and the peak sample is calculated from the complex IQ samples as a function of I 2 +Q 2 .
18. The method of claim 16 , wherein the analog communications signal comprises a communications signal comprising a first signal band x and a second signal band y; and
wherein the samples of the attenuated communication signal comprise complex IQ samples and the peak sample is calculated from the complex IQ samples as a function of I (x+y) 2 +Q (x+y) 2 .
19. The method of claim 13 , wherein the multi-threshold programmable ALC controller further comprises an ALC state machine coupled to the programmable attenuation manager, the method further comprising:
adjusting one or more states of the ALC state machine based on outputs from the plurality of clip detectors of the programmable attenuation manager, wherein the attenuation adjustment signal is generated by the ALC state machine as a function of the one or more states of the ALC state machine.
20. The method of claim 13 , wherein the each of the plurality of clip detectors comprise at least a level detector and a counter, the method further comprising:
determining when an input to the respective clip detectors exceeds an amplitude level for at least a defined number of samples, wherein the amplitude level and the define number of sampled are determined from the amplitude and time threshold.