Systems and methods for automatic level control
Systems and methods for automatic level control (ALC) are provided. In one embodiment, a system comprises a multi-threshold programmable ALC controller; and at least one signal path that includes: a digital step attenuator to receive an analog communications signal and attenuate the communications signal in response to an attenuation adjustment signal from the ALC controller; and an analog-to-digital converter configured to receive the communications signal as attenuated by the digital step attenuator, wherein the ALC controller receives complex IQ samples of the attenuated communication signal; wherein the ALC controller comprises a plurality of clip detectors that function in parallel, wherein each of the clip detectors are programmed with a respective amplitude and time threshold, wherein based on which of the plurality of clip detectors determine that the complex IQ samples exceed their respective amplitude and time threshold, the ALC controller generates the attenuation adjustment signal to the digital step attenuator.
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 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 communications signal as attenuated by the digital step attenuator, wherein the multi-threshold programmable ALC controller receives complex IQ samples of the attenuated communication signal;
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 complex IQ 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 IQ processor function configured to calculate a peak sample from the complex IQ 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 IQ processor function further calculates 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 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 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 10 , wherein the ALC state machine determines which of the plurality of clip detectors triggers an ALC adjustment and drives the digital step attenuator a number of steps as a function of the determination.
12. The system of claim 10 , wherein the at least one signal path comprises a plurality of signal paths;
wherein the multi-threshold programmable ALC controller comprises a plurality of ALC state machines each associated with a corresponding digital step attenuator, wherein each of the plurality of ALC state machines communicate with their corresponding digital step attenuator through a common bus;
wherein access to the bus is controlled by a gate keeper coupled to each of the ALC state machines, wherein the gate keeper controls access to the bus base on a dynamic priority list, wherein the gate keeper dynamically updates the dynamic priority lists such that the ALC state machine which has communicated a most recent ALC adjustment to its corresponding digital step attenuator is assigned to a lowest priority position on the dynamic priority list.
13. The system of claim 1 , wherein the multi-threshold programmable ALC controller further comprises a headroom detector, wherein the multi-threshold programmable ALC controller drives the digital step attenuator to decrease attenuation based at least in part on a determination that none of the plurality of clip detectors exceed their respective amplitude and time threshold.
14. 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).
15. 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).
16. The system of claim 1 , further comprising:
a bus that communicatively couples the multi-threshold programmable ALC controller to each of the digital step attenuators; and
a gate keeper that controls access to the bus from the multi-threshold programmable ALC controller based on a dynamic priority list that indicates which of the digital step attenuators most recently received an attenuation adjustment signal.
17. The system of claim 16 , wherein the gate keeper adjusts the dynamic priority list to assign a lowest priority to a digital step attenuator that most recently received the attenuation adjustment signal.
18. The system of claim 16 , wherein the multi-threshold programmable ALC controller comprises a plurality of ALC state machines each associated with a corresponding digital step attenuator, wherein each of the plurality of ALC state machines communicate with their corresponding digital step attenuator through the bus;
wherein the gate keeper is coupled to each of the ALC state machines and access to the bus is controlled by the gate keeper.
19. A method for automatic level control (ALC) system for communications signals, the method comprising
monitoring an output from a programmable attenuation manager that comprises a plurality of clip detectors and a headroom detector, wherein each of the plurality of clip detectors are programmed with a respective amplitude and time threshold,
wherein the output indicates when one of the plurality of clip detectors has detected a communications signal that has exceeded the respective amplitude and time threshold and generated an ALC adjustment signal;
when the output includes the ALC adjustment signal, determining which of the plurality of clip detectors of the programmable attenuation manager generated the ALC adjustment signal;
adjusting at least one of a plurality of attenuation states of an ALC state machine to increase attenuation based on which of the clip detectors of the programmable attenuation manager generated the ALC adjustment signal; and
driving a digital step attenuator to increase attenuation of the communications signal in response to the adjusted plurality of attenuation states.
20. The method of claim 19 , further comprising:
wherein the output further indicates when the headroom detector has detected that headroom is available; and
adjusting at least one of the plurality of attenuation states of the ALC state machine to decrease attenuation of the communications signal when the output indicates that headroom is available.