Automatic gain control and low power start-of-packet detection for a wireless LAN receiver

• US 7,151,759 B1
• Filed: 03/08/2002
• Issued: 12/19/2006
• Est. Priority Date: 03/19/2001
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Systems Wireless Networking (Australia) Pty Limited (Cisco Systems, Inc.)
• Inventors: Hart, Brian, Ryan, Philip J., Adams, Andrew R., Zyner, Grzegorz B., Parker, Uri, O'Sullivan, John D.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Boakye, Alexander O.
• Application Number:
  US10/095,668
• Time in Patent Office: 1,747 Days
• Field of Search: 370/252, 370/328, 370/318, 370/320, 370/321, 370/342, 370/335, 370/324, 370/332, 455/234.1, 455/226.2, 455/67.11, 455/67.13
• US Class Current: 370/332
• CPC Class Codes: H03G 3/3078 Circuits generating control signals for digitally modulated signals

Abstract

A digital AGC system for burst operation, particularly suited for receiving packets in a wireless local area network. One embodiment includes a log detector that provides a signal strength measure, called the received signal strength indication (RSSI) over a wide dynamic range. The AGC system includes estimating the power in a received signal by averaging the log of the signal power. The Start of Packet detection avoids using the radio receiver'"'"'s main analog to digital converters to preserve power.

Claims

1. A method comprising:

measuring the received signal strength (RSSI) over a relatively wide dynamic range of the signal received in a radio receiver for packetized data;

filtering the measured RSSI by a first filtering operation to produce a filtered RSSI;

detecting a start event by when a function of the filtered RSSI is greater than a first threshold; and

filtering the measured RSSI by a second filtering operation to produce a quiescent level, the second filtering operation having a longer response than the first filtering operation, such that the output of the second filter indicates the quiescent level even when the output of the first filter rises due to the RSSI rising,

such that the start event is indicative of the radio receiver receiving a packet.

2. A method as recited in claim 1, wherein the detecting of a start event is by when the difference between the filtered RSSI and the quiescent RSSI is greater than the first threshold.

3. A method as recited in claim 1, wherein the detecting of a start event is selectable to be from the set of criteria that includes when the filtered RSSI is greater than the first threshold and when the difference between the filtered RSSI and the quiescent RSSI is greater than a second threshold.

4. A method as recited in claim 1, further comprising:

locating the peak of the difference between the filtered RSSI and the quiescent RSSI, the peak position in time indicative of when the start of packet (SOP) occurs.

5. A method as recited in claim 1, wherein the radio receiver includes a first bandpass filter in the received signal path, the method further comprising:

determining the RSSI by filtering the signal received by the radio receiver by a second bandpass filter having a passband included in and narrower than that of the first bandpass filter to produce a narrowly filtered received signal, and using the narrowly filtered received signal to measure the RSSI,

such that the contribution to the RSSI of out-of-channel interferers is reduced by reducing the contributions from signals outside the passband of the first bandpass filter.

6. A method as recited in claim 1, wherein the radio is for operation in the 5 GHz band and wherein the start event is detected within no more than 4 μ

s.

7. A method as recited in claim 1, wherein the radio receiver includes a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, and wherein the receiver has one or more adjustable gains, the method further comprising:

prior to the start event,

adjusting the gains of the radio receiver to a default gain level; and

,

after the start event,

using received signal samples from ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event.

8. A method as recited in claim 7, further comprising:

after the start event and before obtaining the fine measure,

determining a measure of the average signal strength from the measured RSSI;

adjusting the gains of the radio receiver according the determined average signal strength measure.

9. A method as recited in claim 7, wherein each packet includes a preamble having a preamble time duration, and wherein the gain adjusting is completed by at most one half of a preamble time duration after the start event.

10. A method as recited in claim 9, wherein the radio receiver conforms to a standard and wherein the gain adjusting is completed by the time allowed for automatic gain control (AGC) by the standard.

11. A method as recited in claim 10, wherein the standard is the IEEE 802.11a standard.

12. A method as recited in claim 9, wherein the gain adjusting is completed within 8 μ

s of the start event.

13. A method as recited in claim 7, further comprising:

detecting an abnormal condition by running a set of one or more reasonability tests on a function of the signal received by the radio receiver to determine when the received signal does not resemble a normal packet.

14. A method as recited in claim 13, wherein the set of set reasonability tests includes determining when the fine measure falls below a power threshold.

15. A method as recited in claim 13, wherein the set of set reasonability tests includes after the start event determining when the RSSI level has increased markedly.

16. A method as recited in claim 15, wherein the determining when the RSSI level has increased markedly is by comparing the difference between the filtered RSSI and the quiescent RSSI to an RSSI threshold.

17. A method as recited in claim 15, wherein the abnormal condition by the RSSI level increasing markedly resets a new start event.

18. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

with the gains at the default gain level detecting a start event by using the measured RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein the ADCs have an on-state and a low-power standby state, and wherein the ADCs are in the standby state during the detecting of the start event and are switched to the on-state prior to using the ADCs for obtaining the fine measure.

19. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

with the gains at the default gain level detecting a start event by using the measured RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein the default gain level used in the default gain adjusting step is selected from a group of default gains to allow for different receiver characteristics.

20. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

with the gains at the default gain level, detecting a start event by using the measured RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein the method further comprises;

after the start event and before obtaining the fine measure,

determining a measure of the average signal strength from the measured RSSI; and

adjusting the gains of the radio receiver to a coarse gain level according to the determined average signal strength measure,

wherein the coarse gain adjusting is according to a loadable coarse gain mapping that maps the average signal strength measure to a coarse gain level adjustment.

21. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

with the gains at the default gain level, detecting a start event by using the measured RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein the fine gain adjusting is according to a loadable fine gain mapping that maps the fine average signal strength measure to a fine gain level adjustment.

22. A method as recited in claim 21, wherein obtaining the fine measure includes determining the amplitude of the signal samples and averaging a function of the amplitudes.

23. A method as recited in claim 22, wherein obtaining the fine measure includes converting the average to an approximate logarithmic scale in order to reduce the number of bits required to represent the dynamic range of the average.

24. A method as recited in claim 21, wherein the fine gain mapping is set to match one or more of the characteristics of the radio receiver.

25. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

filtering the measured RSSI by a first filtering operation to produce a filtered RSSI,

with the gains at the default gain level detecting a start event by using the filtered RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time including using the filtered RSSI;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein each packet includes a preamble having a preamble time duration, and wherein the gain adjusting is completed by at most one half of a preamble time duration after the start event.

26. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

filtering the measured RSSI by a first filtering operation to produce a filtered RSSI,

with the gains at the default gain level detecting a start event by using the filtered RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time including using the filtered RSSI;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

wherein the gain adjusting is completed within 8 μ

s of the start event.

27. A method for adjusting the gains of a radio receiver for packetized data, the radio receiver having one or more adjustable gains and including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the method comprising:

adjusting the gains to a default gain level;

measuring the received signal strength (RSSI) over a relatively wide dynamic range;

filtering the measured RSSI by a first filtering operation to produce a filtered RSSI,

with the gains at the default gain level, detecting a start event by using the filtered RSSI, the start event indicative of the radio receiving a packet;

determining an estimate of the start of packet (SOP) time including using the filtered RSSI;

using the received signal samples from the ADCs, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver to a fine gain level according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event,

further comprising;

detecting an abnormal condition by running a set of one or more reasonability tests on a function of the signal received by the radio receiver to determine when the received signal does not resemble a normal packet.

28. A method as recited in claim 27, wherein the set of set reasonability tests includes determining when the fine measure falls below a power threshold.

29. A method as recited in claim 27, wherein the set of set reasonability tests includes after the start event determining when the RSSI level has increased markedly.

30. A method as recited in claim 29, wherein the determining when the RSSI level has increased markedly is by comparing the difference between the filtered RSSI and the quiescent RSSI to an RSSI threshold.

31. A method as recited in claim 29, wherein the abnormal condition by the RSSI level increasing markedly resets a new start event.

32. A method comprising:

measuring the received signal strength (RSSI) over a relatively wide dynamic range of the signal received in a radio receiver for packetized data, the receiver including a first set of one or more analog-to-digital converters (ADCs) to convert one or more analog received signals to samples of the received signals, the ADCs having a low power standby state and an on-state;

filtering the measured RSSI by a first filtering operation to produce a filtered RSSI;

detecting a start event by comparing a quantity determined by the filtered RSSI to a first threshold,

wherein the ADCs are in the standby state for at least some of the steps of RSSI measuring, filtering, detecting, and peak locating, such that the power consumption of the radio receiver remains low by the ADCs being in the standby mode, and such that the start event is indicative of the radio receiving a packet.

33. A method as recited in claim 32, wherein the ADCs are switched off in the standby state.

34. A method as recited in claim 32, further comprising

filtering the measured RSSI by a second filtering operation to produce a quiescent RSSI, the second filtering operation having a longer response than the first filtering operation, such that the output of the second filter indicates the quiescent level even when the output of the first filtering operation rises due to the RSSI rising.

35. A method as recited in claim 34, wherein the quantity compared to the first threshold is also determined by the quiescent RSSI, the start event detecting being by comparing the difference between the filtered RSSI and the quiescent RSSI to the first threshold.

36. A method as recited in claim 35, wherein the first threshold is determined by a specification of an allowable error rate to signal strength for a type of signal, the specification specified by a standard.

37. A method as recited in claim 36, wherein the standard is the IEEE 802.11a standard.

38. A method as recited in claim 34, wherein the start event detecting is by comparing the filtered RSSI to the first threshold.

39. A method as recited in claim 38, wherein the first threshold is determined by a specification of an allowable error rate to signal strength for a type of signal, the specification specified by a standard.

40. A method as recited in claim 39, wherein the standard is the IEEE 802.11a standard.

41. A method as recited in claim 34, wherein the detecting of a start event is selectable to be from the set of criteria that includes when the filtered RSSI is greater than the first threshold and when the difference between the filtered RSSI and the quiescent RSSI is greater than a second threshold.

42. A method as recited in claim 34, wherein the first and second filtering operations are moving average filtering operations performed on samples of the RSSI.

43. A method as recited in claim 42, wherein the samples of the RSSI are obtained using an ADC having one or more of a lower resolution and a lower rate than the ADCs of the first set of ADCs.

44. A method as recited in claim 42, wherein the samples of the RSSI are obtained using one of the ADCs of the first set of ADCs, the one ADC being an ADC having a number of stages, and having a standby mode during which some of the stages are turned off so that a lower resolution output is obtained.

45. A method as recited in claim 44, wherein the lower resolution output obtained at a lower sampling rate than in the non-standby mode.

46. A method as recited in claim 34, wherein the first and second filtering operations are IIR filtering operations performed on samples of the RSSI.

47. A method as recited in claim 34, wherein the radio includes a first bandpass filter in the received signal path, the method further comprising:

determining the RSSI by filtering the received signal by a second bandpass filter having a passband included in and narrower than that of the first bandpass filter to produce a narrowly filtered received signal, such that the narrowly filtered received signal is used to measure the RSSI,

such that the contribution to the RSSI of out-of-channel interferers is reduced by reducing the contributions from signals outside the passband of the first bandpass filter.

48. A method as recited in claim 34, further comprising:

locating the peak of the difference between the filtered RSSI and the quiescent RSSI, the peak position in time indicative of when the start of packet (SOP) occurs.

49. A method as recited in claim 34, wherein the radio is for operation in the 5 GHz band and wherein the start event is detected within no more than 4 μ

s.

50. A method as recited in claim 34, wherein the radio receiver has one or more adjustable gains, the method further comprising:

before the start event detecting,

adjusting the gains of the radio receiver to a default gain level; and

after the start event,

switching the ADCs to the on-state such that the ADCs provide signal samples;

using the signal samples, obtaining a fine measure of the average signal strength; and

adjusting the gains of the radio receiver according the fine measure of the average signal strength,

such that the receiver gains are set to receive the remainder of the packet indicated by the start event.

51. A method as recited in claim 50, wherein obtaining the fine measure includes determining the amplitude of the signal samples and averaging a function of the amplitudes.

52. A method as recited in claim 51, wherein obtaining the fine measure includes converting the average to an approximate logarithmic scale in order to reduce the number of bits required to represent the dynamic range of the average.

53. A method as recited in claim 50, wherein each packet includes a preamble having a preamble time duration, and wherein the gain adjusting is completed by at most one half of a preamble time duration after the start event.

54. A method as recited in claim 50, wherein the radio receiver conforms to a standard and wherein the gain adjusting is completed by the time allowed for automatic gain control (AGC) by the standard.

55. A method as recited in claim 54, wherein the standard is the IEEE 802.11a standard.

56. A method as recited in claim 50, wherein the gain adjusting is completed within 8 μ

s of the start event.

57. A method as recited in claim 50, further comprising:

before switching the ADCs to the on-state,

determining a measure of the average signal strength from the measured RSSI; and

adjusting the gains of the radio receiver to a coarse gain level according to the determined average signal strength measure.

58. A method as recited in claim 50, further comprising:

detecting an abnormal condition by running a set of one or more reasonability tests on a function of the signal received by the radio receiver to determine when the received signal does not resemble a normal packet.

59. A method as recited in claim 58, wherein the set of set reasonability tests includes determining when the fine measure falls below a power threshold.

60. A method as recited in claim 58, wherein the set of set reasonability tests includes after the start event determining when the RSSI level has increased markedly.

61. A method as recited in claim 60, wherein the determining when the RSSI level has increased markedly is by comparing the difference between the filtered RSSI and the quiescent RSSI to an RSSI threshold.

62. A method as recited in claim 60, wherein the abnormal condition by the RSSI level increasing markedly resets a new start event.

63. An apparatus comprising:

a signal strength detector, the detector measuring the received signal strength (RSSI) of signals received in a radio receiver receiving packetized data, the radio receiver having one or more adjustable gains, the detector measuring over a relatively high dynamic range of the received signal;

a first set of one or more analog-to-digital converters (ADCs) connected to the radio receiver, the one or more ADCs converting one or more analog received signals and providing samples of the received signals;

a start event detector coupled to the signal strength detector output to detect a start event indicative of the radio receiving a packet;

a signal strength averager coupled to the output of the ADCs, the signal strength averager providing a fine measure of the average signal strength;

a gain adjustment mapper coupled to the output of the signal strength averager and having an output connected to the radio receiver, the gain adjustment mapper providing an output for adjusting the gains of the radio receiver to a fine gain level according to the provided fine measure of the average signal strength; and

a controller coupled to the start event detector, to the signal strength averager, and to the fine gain adjustment mapper, to control in sequence the start event detecting, the signal strength averager, and the gain adjustment mapper to set the gain to a fine gain level after the start event,

such after the fine gain setting, the receiver gains are set to receive the remainder of any packet indicated by the start event.

64. An apparatus as recited in claim 63, wherein the start event detector includes

a first filter and a second filter each coupled to the signal strength detector and each having an input coupled to the signal strength detector output, the first filter having a first impulse response and producing a filtered RSSI output, the second filter having an impulse response longer than the first impulse response and providing a quiescent RSSI, such that the output of the second filter indicates the quiescent level even when the output of the first filter rises due to the RSSI rising;

and

a comparator to compare a quantity determined by the filtered RSSI to a first threshold.

65. An apparatus as recited in claim 64, wherein the comparator in the start event detector compares the difference between the filtered RSSI and the quiescent RSSI to the first threshold to detect the start event.

66. An apparatus as recited in claim 64, wherein the comparator in the start event detector compares the filtered RSSI and the quiescent RSSI to the first threshold to detect the start event.

67. An apparatus as recited in claim 64, wherein the start event detector includes a control input from the controller to select how the start event detector detects from the set of criteria that includes when the filtered RSSI is greater than the first threshold and when the difference between the filtered RSSI and the quiescent RSSI is greater than a second threshold.

68. An apparatus as recited in claim 64, wherein each packet includes a preamble having a preamble time duration, and wherein the gain adjusting is completed by at most one half of a preamble time duration after the start event.

69. An apparatus as recited in claim 64, wherein the radio receiver conforms to a standard and wherein the gain adjusting is completed within the time allowed for automatic gain control (AGC) by the standard.

70. An apparatus as recited in claim 69, wherein the standard is the IEEE 802.11a standard.

71. An apparatus as recited in claim 64, wherein the gain adjusting is completed within 8 μ

s of the start event.

72. An apparatus as recited in claim 71, wherein the start event detector, the signal strength averager, the gain adjustment mapper, and the controller are parts of a monolithic integrated circuit.

73. An apparatus as recited in claim 72, wherein the integrated circuit includes the ADCs.

74. An apparatus as recited in claim 64, further comprising:

an abnormal condition detector coupled to the radio receiver and to the controller, the abnormal condition detector detecting an abnormal condition when the received signal does not resemble a normal packet.

75. An apparatus as recited in claim 74, wherein the abnormal condition detector includes a first comparator coupled to the signal strength averager to determine when the fine measure falls below a settable power threshold.

76. An apparatus as recited in claim 74, wherein the abnormal condition detector includes a second comparator coupled to the signal strength detector to determining when the RSSI level has increased markedly.

77. An apparatus as recited in claim 76, wherein the second comparator is coupled to the filter outputs and compares the difference between the filtered RSSI and the quiescent RSSI to an RSSI threshold.

78. An apparatus as recited in claim 63, wherein the ADCs are coupled to the controller and have an on-state and a low-power standby state, and wherein the ADCs are in the standby state during the detecting of the start event and are switched to the on-state prior to using the ADCs for obtaining the fine measure.

79. An apparatus as recited in claim 63, further comprising:

a coarse averager coupled to the controller, to the signal strength detector and to the gain adjustment mapper, the coarse averager providing a coarse measure of the average signal strength to the adjustment mapper based on the RSSI; and

wherein the gain adjustment mapper output is also for adjusting the gains of the radio receiver to a coarse gain level, the coarse gain level according to the provided coarse measure of the average signal strength, and

wherein the controller controls the gain adjustment mapper to adjust the gains to the default level prior to the start event and to adjust the gains to the coarse gain level after the start event and before the fine gain setting.

80. An apparatus as recited in claim 79, wherein the gain adjustment mapper includes a default gain memory to store one or more values for setting the default gain.

81. An apparatus as recited in claim 79, wherein the gain adjustment mapper includes a gain mapping memory storing:

a loadable coarse gain mapping that maps the average signal strength measure to a coarse gain level adjustment, and

a loadable fine gain mapping that maps the fine average signal strength measure to a fine gain level adjustment.

82. An apparatus as recited in claim 63, wherein the gain adjustment mapper includes a fine gain memory storing a loadable gain mapping that maps the fine average signal strength measure to a fine gain level adjustment.

83. An apparatus as recited in claim 82, wherein the signal strength averager includes a magnitude circuit determining the amplitude of the signal samples with an output coupled to an averaging circuit that provides an average of a function of the amplitudes.

84. An apparatus as recited in claim 83, wherein the signal strength averager further includes a log converter with an input coupled to the output of the averaging circuit, the log converter converting the average to an approximate logarithmic scale in order to reduce the number of bits required to represent the dynamic range of the average.

85. An apparatus as recited in claim 63, wherein the start event detector, the signal strength averager, the gain adjustment mapper, and the controller are parts of a monolithic integrated circuit.

86. An apparatus comprising:

a signal strength detector, the detector coupled to a radio receiver receiving packetized data, the detector measuring the received signal strength (RSSI) of signals received in the radio receiver, the radio receiver having one or more adjustable gains, the detector measuring over a relatively high dynamic range of the received signal;

a start event detector coupled to the signal strength detector output to detect a start event indicative of the radio receiving a packet;

a signal strength measurement circuit coupled to the radio receiver and providing a digital measure of the average signal strength; and

a mapping circuit coupled to the signal strength measurement circuit and to the radio, the mapping circuit including one or more memories storing one or more loadable mappings, the mapping circuit mapping signal measurements into appropriate gain settings and providing gain setting signals to the radio receiver for setting the gains of the radio receiver, the mapping circuit providing the gain setting signals after the start event,

such that the mapping from power measurement to gain settings can be changed to account for different radio receivers that have different characteristics, and to account for process and temperature variations.

87. An apparatus as recited in claim 86,

wherein the signal strength measurement circuit includes:

a coarse averager coupled to the signal strength detector, the coarse averager providing to the mapping circuit a digital coarse measure of the average signal strength based on the RSSI,

one or more analog to digital converters (ADCs) coupled to the radio receiver and providing samples of the received signal;

a fine averager coupled to the ADCs, the fine averager providing to the mapping circuit a digital fine measure of the average signal strength based on the samples of the received signal,

wherein the one or more loadable mappings include one or more loadable lookup tables that map the coarse measure to a coarse gain setting, and one or more loadable lookup tables that map the fine measure to a fine gain setting,

wherein the start event detector is operative after a default gain setting signal has been provided to the radio receiver to adjust the gains of the radio receiver to a settable default level, and

wherein the mapping circuit provides a fine gain setting signal based on the coarse measure to the radio receiver after the coarse gain setting signal has been provided,

such that after the fine gain setting, the receiver gains are set to receive the remainder of any packet indicated by the start event.