Packet detection in time/frequency hopped wireless communication systems
Systems and methods for packet detection for frequency hopping networks. Multiple receiver chains are set to different frequencies to check for packets at the different frequencies, at least until receipt of a preamble sequence in a packet is received. After detection of a packet at least some of the receiver chains are used to process received signals according to a frequency hopping pattern.
1. A method for detecting packets in a radio frequency (RF) communication network using orthogonal frequency division multiplexing (OFDM) in a frequency hopping manner, comprising:
setting a first RF receiver to receive signals in a first frequency sub-band;
setting a second RF receiver to simultaneously receive signals in a second frequency sub-band;
checking received signals in the first frequency sub-band to determine if a first known sequence has been received;
checking received signals in the second frequency sub-band to determine if a second known sequence has been received;
determining if a packet has been received based on receipt of the first known sequence or receipt of the second known sequence; and
selecting signals from the first RF receiver and the second RF receiver based on a hopping pattern determined according to a time frequency code after determining that a packet has been received, the time frequency code indicating usage of the first frequency sub-band and the second frequency sub-band over time for transmission of OFDM symbols.
2. The method of claim 1 wherein the first known sequence and the second known sequence are the same.
3. The method of claim 1 wherein each of the first known sequence and the second known sequence comprise a preamble sequence.
4. The method of claim 1 wherein setting the first RF receiver to receive signals in the first frequency sub-band comprises providing a mixing signal having a first frequency to a mixer in the first RF receiver and setting the second RF receiver to receive signals in the second frequency sub-band comprises providing a mixing signal having a second frequency to a mixer in the second RF receiver.
5. The method of claim 1 wherein determining if a packet has been received based on receipt of the first known sequence or receipt of the second known sequence comprises determining if either the first known sequence or the second known sequence has been received, waiting a period of time based on the hopping pattern, and determining if either the first known sequence or the second known sequence is again received approximate the conclusion of the period of time.
6. The method of claim 1 further comprising setting the first RF receiver to frequency sub-bands based on the time frequency code after determining a packet has been received.
7. The method of claim 1 further comprising performing automatic gain control and channel estimation if a packet is determined to be received.
8. A method of detecting receipt of a preamble sequence in a radio frequency (RF) communication network using logical channels defined by time frequency codes, the time frequency codes indicating usage of frequency sub-bands over time for transmission of orthogonal frequency division multiplexing (OFDM) symbols, comprising:
setting each of N RF receiver chains each simultaneously to one of N different frequency sub-bands, wherein N is greater than one;
checking signals received by the N RF receiver chains for a preamble sequence;
determining that a packet has been received if any of the signals received by the N RF receiver chains comprise the preamble sequence; and
selecting signals from the N RF receiver chains based on a hopping pattern determined according to the time frequency code after determining that a packet has been received.
9. The method of claim 8 wherein the communication network uses N logical channels defined by time frequency codes.
10. The method of claim 9 further comprising setting the N RF receiver chains to the same frequency sub-band after determining that a packet has been received.
11. The method of claim 10 further comprising performing maximum ratio combining on received information after setting the N RF receiver chains to the same frequency sub-band.
12. The method of claim 11 further comprising repeatedly setting the N RF receiver chains to frequencies in accordance with a time frequency code.
13. A radio frequency (RF) receiver for receiving orthogonal frequency division multiplexing (OFDM) symbols on a frequency hopping communication channel defined by a time frequency code, comprising:
a plurality of mixers, each of the plurality of mixers coupled to an antenna receiving a radio frequency signal and each of the plurality of mixers simultaneously receiving a mixing signal of a different frequency;
a plurality of correlation circuits, each of the correlation circuits coupled to a separate mixer and each of the correlation circuits configured to determine if a received signal comprises a known sequence, wherein each correlation circuit includes both auto-correlation circuitry and cross-correlation circuitry;
a logic circuitry that combines the correlation results based on a frequency hopping pattern defined by a time frequency code after determination by any of the correlation circuits that the received signal comprises the known sequence; and
processing circuitry coupled to the mixers, the processing circuitry including a Fast Fourier Transform (FFT) block.
14. The receiver of claim 13 wherein the logic circuitry couples the mixing signals of different frequencies to different mixers based on the correlation results of the logic circuitry.
15. The receiver of claim 14 wherein the processing circuitry further comprises a maximum ratio combining (MRC) block.
16. The receiver of claim 13 wherein each mixer is part of a different RF receiver chain, and the logic circuitry couples the different RF receiver chains to the processing circuitry based on the state of the logic circuitry.