Direct sequence spread spectrum signal receiving device and method
View Patent ↗A direct-sequence spread spectrum signal receiving device may comprise a receiver unit, a chip sequence generating unit, a correlation unit, and comparison unit. The receiver unit may extract a chip stream from a radio-frequency signal, said chip stream containing a first chip sequence. The chip sequence generating unit may generate a plurality of trial chip sequences on the basis of a first trial chip sequence and on the basis of a plurality of index rotations. The correlation unit may determine a plurality of correlation values on the basis of said plurality of trial chip sequences and on the basis of said first chip sequence, each of said correlation values indicating a degree of correlation between a respective one of said trial chip sequences and said first chip sequence. The comparison unit may determine whether a maximum one of said correlation values exceeds a defined threshold value.
1. A direct-sequence spread spectrum signal receiving device, comprising:
a receiver unit arranged to extract, in a first detection phase, a chip stream from a radio-frequency signal, said chip stream comprising a first chip sequence having a length of one symbol;
a chip sequence generating unit arranged to generate, in said first detection phase, a plurality of trial chip sequences on the basis of a first trial chip sequence representing a first trial symbol and on the basis of a plurality of index rotations, each trial chip sequence being index-rotated relative to said first trial chip sequence by one of said index rotations;
a correlation unit arranged to determine, in said first detection phase, a plurality of first correlation values on the basis of said plurality of trial chip sequences and on the basis of said first chip sequence, each of said first correlation values indicating a degree of correlation between a respective one of said trial chip sequences and said first chip sequence; and
a comparison unit arranged to determine, in said first detection phase, whether a maximum one of said first correlation values exceeds a defined threshold value;
wherein said receiving unit is further arranged to initiate a second detection phase in response to said maximum correlation value exceeding said threshold value,
wherein said correlation unit is further arranged to determine, in said second detection phase, a plurality of second correlation values on the basis of said plurality of trial chip sequences and on the basis of a second chip sequence contained in said chip stream, said second chip sequence having a length of one symbol, each of said second correlation values indicating a degree of correlation between a respective one of said trial chip sequences and said second chip sequence,
wherein said comparison unit is further arranged to determine, in said second detection phase, whether a maximum one of said second correlation values exceeds said defined threshold value.
2. The receiving device of claim 1 , wherein said chip sequence generating unit comprises:
an encoding unit arranged to generate, in said first detection phase, said first trial chip sequence by applying a spreading code to said first trial symbol.
3. The receiving device of claim 1 , wherein said first trial symbol is part of a preamble of a data packet.
4. The receiving device of claim 1 , further comprising:
an antenna unit comprising one or more antennas for receiving said radio-frequency signal; and
an antenna control unit arranged to select another operating mode of said antenna unit in response to said maximum correlation value being below said threshold value.
5. The receiving device of claim 4 , wherein said antenna unit has at least two different operating modes, each of said operating modes being characterized by a set of active antennas, an orientation of said antennas, or a combination thereof.
6. The receiving device of claim 4 , wherein said selecting another operating mode comprises deactivating one and activating another one of said antennas.
7. The receiving device of claim 1 , further comprising:
a power control unit arranged to set said receiving device into a sleep mode in response to said maximum correlation value being below said threshold value.
8. The receiving device of claim 1 , wherein said first chip sequence and said second chip sequence are subsequent chip sequences or partly overlapping chip sequences.
9. The receiving device of claim 1 , further arranged to initiate a decoding phase in response to said maximum second correlation value exceeding said threshold value.
10. The receiving device of claim 9 , wherein:
said chip sequence generating unit is arranged to generate, in said decoding phase, a plurality of third trial chip sequences representing a plurality of trial symbols;
said correlation unit is arranged to determine, in said decoding phase, a plurality of third correlation values on the basis of said plurality of trial chip sequences and on the basis of a third chip sequence contained in said chip stream, said third chip sequence having a length of one symbol, each of said third correlation values indicating a degree of correlation between a respective one of said third trial chip sequences and said third chip sequence; and
said comparison unit is arranged to determine, among said plurality of trial symbols, the trial symbol associated with the highest one of said third correlation values.
11. The receiving device of claim 10 , arranged to repeat said decoding phase at a symbol rate of said chip stream.
12. The receiving device of claim 1 , arranged to operate in accordance with a ZigBee protocol.
13. A method comprising:
selecting a first set of at least one antenna as an active antenna;
correlating a first chip sequence against each of a plurality of first trial chip sequences to produce a set of first correlation values, wherein each of the first trial chip sequences is a rotated version of a defined symbol value;
when none of the first correlation values exceeds a first defined threshold value, selecting a second set of at least one antenna as the active antenna;
when at least one of the first correlation values exceeds the first defined threshold value, providing a second chip sequence based on the first chip sequence and correlating the second chip sequence against each of a plurality of second trial chip sequences to produce a set of second correlation values;
when none of the second correlation values exceeds a second defined threshold value, selecting the second set of at least one antenna as the active antenna;
when at least one of the second correlation values exceeds the second defined threshold value, determining whether the second chip sequence contains a preamble;
when the second chip sequence is determined to contain the preamble, determining whether the second chip sequence contains a lower level preamble of a data packet of a protocol of a lower level;
when the second chip sequence is determined to contain the lower level preamble, decoding the data packet of the protocol of the lower level.
14. The method of claim 13 further comprising:
prior to the correlating the first chip sequence against each of the plurality of the first trial chip sequences, waiting a first period of greater than one symbol period to obtain the first chip sequence.
15. The method of claim 14 further comprising:
following the correlating the first chip sequence against each of the plurality of the first trial chip sequences, waiting a second period of less than one symbol period to obtain the second chip sequence.
16. The method of claim 13 further comprising:
in response to the decoding the data packet of the protocol of the lower level, switching off a receiver that received a direct sequence spread spectrum (DSSS) signal from which the first chip sequence was obtained.
17. A non-transitory computer program product, comprising code portions for executing steps of a method as claimed in claim 13 when run on a programmable apparatus.