Packet detection, symbol timing, and coarse frequency estimation in an OFDM communications system
First Claim
1. A system for the detection of data packets from a baseband signal where said baseband signal includes data packets which are encoded with symbols which use orthogonal frequency division multiplexing (OFDM), said packets include a short preamble part and a data part, said short preamble part being formed from a plurality of short symbols, each said short symbol comprising a pattern of L said samples, said detection of said data packets comprising:
- said baseband signal coupled to a first delay line having a delay equal to the time required to receive said L samples, said delay line having an output;
a conjugator coupled to said delay line output, said conjugator inverting the sign of imaginary part of said delay line output;
a first multiplier having an output, said first multiplier output substantially equal to said baseband signal multiplied by said conjugator output;
a first summer having an output equal the sum of L previous said first multiplier output values;
a magnitude having an output which has a value equal to the magnitude of the output of said first summer;
a second multiplier having a real output, said second multiplier generating said output substantially equal to said baseband signal multiplied by the conjugate of baseband signal;
a second summer having an output equal to the to sum of twice said L previous said second multiplier output values;
a third multiplier having an output equal to said second summer output multiplied by a first baseline, said output forming a threshold value;
said packet detect output asserted when said magnitude output exceeds said threshold value.
3 Assignments
0 Petitions
Accused Products
Abstract
A integrated system for generation of packet detection, symbol timing, and coarse frequency offset for an orthogonal frequency division multiplexed (OFDM) receiver having a stream of input symbols applied comprises a first multiplier performing a multiplication on a delayed and conjugated stream of input symbols multiplied by the input symbol stream. The output of the first multiplier is summed over a symbol length. A second multiplier has an output formed from multiplying the delayed symbol stream by its conjugate, thereby providing a signal strength term Pn. The output of the second multiplier is summed over two symbol periods, and multiplied by a known threshold to form a threshold value. When the magnitude of cn term rises above the known threshold, this generates a packet detect output, and when the magnitude of Cn terms thereafter falls below the known threshold, this generates a symbol timing output.
40 Citations
34 Claims
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1. A system for the detection of data packets from a baseband signal where said baseband signal includes data packets which are encoded with symbols which use orthogonal frequency division multiplexing (OFDM), said packets include a short preamble part and a data part, said short preamble part being formed from a plurality of short symbols, each said short symbol comprising a pattern of L said samples, said detection of said data packets comprising:
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said baseband signal coupled to a first delay line having a delay equal to the time required to receive said L samples, said delay line having an output; a conjugator coupled to said delay line output, said conjugator inverting the sign of imaginary part of said delay line output; a first multiplier having an output, said first multiplier output substantially equal to said baseband signal multiplied by said conjugator output; a first summer having an output equal the sum of L previous said first multiplier output values; a magnitude having an output which has a value equal to the magnitude of the output of said first summer; a second multiplier having a real output, said second multiplier generating said output substantially equal to said baseband signal multiplied by the conjugate of baseband signal; a second summer having an output equal to the to sum of twice said L previous said second multiplier output values; a third multiplier having an output equal to said second summer output multiplied by a first baseline, said output forming a threshold value; said packet detect output asserted when said magnitude output exceeds said threshold value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for the detection of symbol timing from a baseband signal where said baseband signal includes data packets which are encoded with symbols which use orthogonal frequency division multiplexing (OFDM), said packets include a short preamble part and a data part, said short preamble part being formed from a plurality of short symbols, each said short symbol comprising a pattern of L said samples, said detection of said data packets comprising:
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said baseband signal coupled to a first delay line having a delay equal to the time required to receive said L samples, said delay line having an output; a conjugator coupled to said delay line output, said conjugator inverting the sign of imaginary part of said delay line output; a first multiplier having an output, said first multiplier generating an output from multiplying said baseband signal and said conjugator output; a first summer having an output equal the sum of L previous said first multiplier output values; a magnitude having an output which has a value equal to the magnitude of the output of said first summer; a second multiplier having a real output, said second multiplier forming said real output by multiplying said baseband signal with the conjugate of said baseband signal; a second summer having an output equal to the to sum of twice said L previous said second correlator output values; a a third multiplier having an output equal to said second summer output multiplied by a first baseline, said output forming a threshold value; said symbol timing output asserted when said magnitude square output falls below said threshold value. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A system for the estimation of coarse frequency offset from a baseband signal where said baseband signal includes data packets which are encoded with symbols which use orthogonal frequency division multiplexing (OFDM), said packets include a short preamble part and a data part, said short preamble part being formed from a plurality of short symbols, each said short symbol comprising a pattern of L said samples, said detection of said data packets comprising:
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said baseband signal coupled to a first delay line having a delay equal to the time required to receive said L samples, said delay line having an output; a conjugator coupled to said delay line output, said conjugator inverting the sign of imaginary part of said delay line output; a multiplier having an output, said first multiplier output formed from the multiplication of said baseband signal and said conjugator output; an averager coupled to said multiplier and producing an average of the output of said multiplier; a phase finder for converting a complex value into an angle, said phase finder receiving as an input the output of said averager. - View Dependent Claims (21, 22, 23, 24)
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25. A system for the detection of symbol timing and packet detection from a baseband signal where said baseband signal includes data packets which are encoded with symbols which use orthogonal frequency division multiplexing (OFDM), said packets include a short preamble part and a data part, said short preamble part being formed from a plurality of short symbols, each said short symbol comprising a pattern of L said samples, said detection of said data packets comprising:
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said baseband signal coupled to a first delay line having a delay equal to the time required to receive said L symbols, said delay line having an output; a conjugator coupled to said delay line output, said conjugator inverting the imaginary part of said delay line output; a first multiplier having an output, said first multiplier generating an output by multiplying said baseband signal and said conjugator output; a first summer having an output equal the sum of L previous said first correlator output values; a magnitude having an output which has a value equal to the magnitude of the output of said first summer; a second multiplier having a real output, said second multiplier output formed from multiplying said baseband signal and the conjugate of said baseband signal; a second summer having an output equal to the to sum of twice said L previous said second multiplier output values; a third multiplier having an output equal to said second summer output multiplied by a first baseline, said output forming a threshold value; said packet detect output asserted when said magnitude square output rises above said threshold value; said symbol timing output asserted when said magnitude square output falls below said threshold value. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34)
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Specification