Radar detection and dynamic frequency selection for wireless local area networks

• US 6,697,013 B2
• Filed: 12/31/2001
• Issued: 02/24/2004
• Est. Priority Date: 12/06/2001
• Status: Expired due to Term

• Current Assignee: The Connectivity Patent Trust
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: McFarland, William, Dhamdhere, Deepak, Zeng, Chaohuang
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US10/039,451
• Publication Number:
  US 20030107512A1
• Time in Patent Office: 785 Days
• Field of Search: 342/159, 342/162, 370/332, 370/333, 455/63.1, 455/296, 455/403, 455/436
• US Class Current: 342/159
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals
• CPC Class Codes: H04K 2203/18 for wireless local area networks or WLAN
• CPC Class Codes: H04K 3/226 Selection of non-jammed channel for communication spectrum sharing arrangements H04W16/14; selection of wireless resources by user or terminal H04W72/02
• CPC Class Codes: H04K 3/822 by detecting the presence of a surveillance, interception or detection
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A system for detecting and avoiding interference with radar signals in wireless network devices is described. The receiver circuit of the device receives incoming 5 GHz traffic. Such traffic could comprise both WLAN traffic as well as radar signals from radar systems. The incoming packets are treated as an input event, and are screened to be examined as radar pulses. Radar pulses are identified using the length of the detected event. The radar pulses are examined using frequency domain analysis, and the packet train is examined to find gaps between radar pulses. The periodic nature of the packet is determined using frequency domain and time domain analysis to calculate the period of the pulse train. Particular intervals within the pulse train are analyzed using threshold numbers of periodic pulses within the interval and threshold power levels for the pulses. The calculated period information is used to identify the radar source and screen non-radar traffic.

Claims

1. A method of detecting radar signals in a wireless network device comprising the steps of:

receiving a plurality of signal pulses as detected events;

time stamping the events upon reception to produce a time stamp for an event of the detected events;

eliminating any detected events that correspond to network traffic;

determining whether any non-eliminated events of the individual detected events correspond to radar signals by examining at least one of;

a pulse repetition frequency, a pulse period, or a number of pulses in a pre-defined time period, wherein determining a period of the event comprises performing a time domain analysis of the non-eliminated events;

determining a first time interval between a first pulse and second pulse of the event;

assuming that the first time interval represents the period of the event; and

comparing the first time interval with a second time interval between the second pulse and a third pulse of the event to determine whether the first and second time intervals match to within an error factor associated with the time stamp for each detected event.

2. The method of claim 1 further comprising the steps of:

assuming a pulse repetition frequency to create an assumed frequency;

multiplying a time interval between the pulses by the assumed frequency to create a result; and

determining if the result is within a pre-defined margin of being an integer value.

3. The method of claim 2 in which an initial assumed frequency is obtained by inverting the time interval between the pulses.

4. The method of claim 2 in which a plurality of assumed frequencies is created by assuming different pulse repetition frequencies.

5. The method of claim 3 further comprising the steps of:

initially selecting widely spaced frequencies and wide margins;

determining when a positive result is found; and

subsequently selecting finely spaced frequencies and margins to confirm the presence of a radar signal.

6. A device coupled to one or more remote terminals over a wireless network, comprising:

a receiver circuit for receiving network data traffic as an input signal from the one or more remote terminals;

a media access control circuit coupled to the receiver circuit, and configured to detect an error contained in the network data traffic received by the receiving circuit, and to classify the error based on a pre-defined error type;

a radar detection circuit coupled to the media access control circuit and configured to receive the input signal if the error contained in the input signal is of a first error type, the radar detection circuit comprising,

a first process receiving a plurality of signal pulses as detected events, wherein each pulse is considered an event, and the events appear as a first event burst followed by one or more subsequent event bursts,

a second process eliminating any detected events that correspond to network traffic, and

a third process determining whether any non-eliminated events of the individual detected events correspond to radar signals by examining at least one of;

a pulse repetition frequency, a pulse period, or a number of pulses in a pre-defined time period,

a time stamp circuit assigning a time stamp to each event that is above a pre-defined power threshold;

an event analysis circuit defining a threshold number of events within a time interval, above which the events are considered to be radar events, wherein the period of the event bursts is determined by a time domain analysis process performed on the event bursts as detected by the event analysis circuit to determine a pulse burst period, and wherein the time domain analysis process determines a first time interval between a first pulse burst and second pulse burst;

assumes that the first time interval represents the period of the event; and

compares the first time interval with a second time interval between the second pulse burst and a third pulse burst of the event to determine whether the first and second time intervals match to within an error factor associated with the time stamp.

7. The device of claim 6 further comprising:

a fourth process assuming a pulse repetition frequency to create an assumed frequency;

a fifth process multiplying a time interval between the pulses by the assumed frequency to create a result; and

a sixth process determining if the result is within a pre-defined margin of being an integer value.

8. The device of claim 7 in which a plurality of assumed frequencies is created by assuming different pulse repetition frequencies.

9. The device of claim 8 further comprising:

a seventh process for initially selecting widely spaced frequencies and wide margins are used;

an eighth process determining when a positive result is found; and

a ninth process for subsequently selecting finely spaced frequencies and narrow margins to confirm the presence of a radar signal.

10. A method of identifying radar signals in a network device coupled to one or more remote terminals over a wireless network, comprising the steps of:

receiving an input signal comprising a plurality of pulses as detected events;

determining whether the detected events correspond to expected network traffic;

assigning a time stamp to each event of the detected events that is above a pre-defined power threshold;

determining a first time interval between a first event and second event;

assuming that the first time interval represents the period of the events; and

comparing the first time interval with a second time interval between the second event and a third event to determine whether the first and second time intervals match to within an error factor associated with the time stamp.

11. The method of claim 10 further comprising the step of defining a period of the events to correspond to a time interval between successive pulses that matches the first or the second time intervals.

12. The method of claim 11 further comprising the steps of:

defining periodic time intervals;

defining a threshold number of pulses within each time interval; and

defining a threshold power level for the pulses within the time interval.

13. The method of claim 12 further comprising the step of determining whether the number of pulses above the threshold power level within a time interval meets or exceeds the threshold number of pulses.

14. The method of claim 13 further comprising the step of determining whether the number of pulses above the threshold power level within two or more time intervals meets or exceeds a threshold number of pulses, if the number of pulses within one interval does not meet the threshold number of pulses for a single interval.

15. The method of claim 11 wherein the detected event represents an input signal exhibiting physical errors beyond a pre-defined tolerance.

16. The method of claim 10 further comprising the step of matching the period of the event to known radar sources.

17. The method of claim 10 further comprising the step of switching an input channel of the network device to a different frequency band to avoid interference with the input signal.

18. The method of claim 10 further comprising the step of reducing network traffic for the network device using one of:

a beacon signal transmitted to one or more remote terminals coupled to the network device causing the one or more terminals to suspend transmission to the network device, and a jamming signal operable to lengthen a contention period of time for prioritizing network traffic from the one or more remote terminals.

19. The method of claim 10 wherein the network device comprises an access point station coupled to a 5 GHz radio network, and wherein the network utilizes one of:

802.11 network protocol and HIPERLAN network protocol.