Preamble sequence sending and receiving method and apparatus, and system

A preamble sequence sending method, comprising:

• generating, by a transmit end, a frequency offset estimation sequence, wherein the frequency offset estimation sequence comprises N subsequences each with a length of M, wherein N is a positive integer greater than or equal to 2, and M is a positive integer;
• generating, by the transmit end, a prefix and a suffix based on the frequency offset estimation sequence;
• adding, by the transmit end, the prefix and the suffix before and after the frequency offset estimation sequence, respectively, to form a preamble sequence, wherein the prefix and the suffix are used for canceling multipath interference, wherein each subsequence comprised in the frequency offset estimation sequence is rotated by a phase of θ relative to a previous subsequence adjacent to the subsequence, and −π≦θ≦π;
• and
• adding, by the transmit end, the preamble sequence to a data packet and sending the data packet to a receive end,
• wherein the generating, by the transmit end, a prefix and a suffix based on the frequency offset estimation sequence comprises:
• replicating, by the transmit end, a last L1 element values comprised in the first subsequence of the frequency offset estimation sequence, and separately rotating the replicated L1 element values by a phase of −θ to generate the prefix;
• and
• replicating, by the transmit end, a first L2 element values comprised in the last subsequence of the frequency offset estimation sequence, and separately rotating the replicated L2 element values by the phase of θ to generate the suffix;
• wherein L1 and L2 are set by the transmit end according to a channel multipath feature, and L1 and L2 are integers not greater than M.

A preamble sequence receiving method, comprising:

• receiving, by a receive end, a data packet;
• extracting, by the receive end, a preamble sequence from the data packet, wherein the preamble sequence comprises a prefix, a frequency offset estimation sequence, and a suffix in order, the prefix and the suffix are used for canceling multipath interference, the frequency offset estimation sequence comprises N subsequences each with a length of M, wherein N is a positive integer greater than or equal to 2, and M is a positive integer, wherein each subsequence comprised in the frequency offset estimation sequence is rotated by a phase of θ relative to a previous subsequence adjacent to the subsequence, and −π≦θ≦π;
• finding, by the receive end, the frequency offset estimation sequence in the preamble sequence according to a length of the prefix;
• delaying, by the receive end, each subsequence comprised in the frequency offset estimation sequence by a length of K subsequences to obtain a new sequence, wherein K is a positive integer less than N;
• performing, by the receive end, conjugation on the new sequence to obtain a processed sequence;
• multiplying, by the receive end, an element value in a subsequence in the processed sequence by a corresponding element value in a subsequence in the frequency offset estimation sequence to obtain (N−K)*M complex numbers;
• calculating, by the receive end, a sum of the (N−K)*M complex numbers;
• obtaining, by the receive end, a phase of the sum to obtain a phase value;
• and
• dividing, by the receive end, the phase value by M to obtain a frequency offset estimation value.

A preamble sequence sending apparatus, comprising:

• a first generation unit, configured to generate a frequency offset estimation sequence, wherein the frequency offset estimation sequence comprises N subsequences each with a length of M, wherein N is a positive integer greater than or equal to 2, and M is a positive integer, wherein each subsequence comprised in the frequency offset estimation sequence is rotated by a phase of θ relative to a previous subsequence adjacent to the subsequence, and −π≦θ≦π;
• a second generation unit, configured to generate a prefix and a suffix based on the frequency offset estimation sequence;
• an adding unit, configured to add the prefix and the suffix before and after the frequency offset estimation sequence, respectively, to form a preamble sequence, wherein the prefix and the suffix are used for canceling multipath interference;
• and
• a sending unit, configured to add the preamble sequence to a data packet and send the data packet to a receive end,
• wherein the first generation unit is configured to:
• generate a bit stream;
• modulate the bit stream to a preset data modulation format, wherein the modulated bit stream is used as a basic subsequence, and a length of the basic subsequence is M;
• replicate the basic subsequence to obtain a long sequence comprising N basic subsequences;
• and
• rotate each subsequence comprised in the long sequence by the phase of θ relative to the previous subsequence adjacent to the subsequence, to obtain the frequency offset estimation sequence.

A preamble sequence sending apparatus, comprising:

• a first generation unit, configured to generate a frequency offset estimation sequence, wherein the frequency offset estimation sequence comprises N subsequences each with a length of M, wherein N is a positive integer greater than or equal to 2, and M is a positive integer, wherein each subsequence comprised in the frequency offset estimation sequence is rotated by a phase of θ relative to a previous subsequence adjacent to the subsequence, and −π≦θ≦π;
• a second generation unit, configured to generate a prefix and a suffix based on the frequency offset estimation sequence;
• an adding unit, configured to add the prefix and the suffix before and after the frequency offset estimation sequence, respectively, to form a preamble sequence, wherein the prefix and the suffix are used for canceling multipath interference;
• and
• a sending unit, configured to add the preamble sequence to a data packet and send the data packet to a receive end,
• wherein the second generation unit is configured to:
• replicate a last L1 element values comprised in the first subsequence of the frequency offset estimation sequence, and separately rotate the replicated L1 element values by a phase of −θ to generate the prefix;
• and
• replicate a first L2 element values comprised in the last subsequence of the frequency offset estimation sequence, and separately rotate the replicated L2 element values by the phase of θ to generate the suffix;
• wherein L1 and L2 are set by the second generation unit according to a channel multipath feature, and L1 and L2 are integers not greater than M.

A preamble sequence receiving apparatus, comprising:

• a receiving unit, configured to receive a data packet;
• an extraction unit, configured to extract a preamble sequence from the data packet, wherein the preamble sequence comprises a prefix, a frequency offset estimation sequence, and a suffix in order, the prefix and the suffix are used for canceling multipath interference, the frequency offset estimation sequence comprises N subsequences each with a length of M, wherein N is a positive integer greater than or equal to 2, and M is a positive integer, wherein each subsequence comprised in the frequency offset estimation sequence is rotated by a phase of θ relative to a previous subsequence adjacent to the subsequence, and −π≦θ≦π;
• a positioning unit, configured to find the frequency offset estimation sequence in the preamble sequence according to a length of the prefix;
• and
• a frequency offset estimation unit, configured to:
• delay each subsequence comprised in the frequency offset estimation sequence by a length of K subsequences to obtain a new sequence, wherein K is a positive integer less than N;
• perform conjugation on the new sequence to obtain a processing sequence;
• multiply an element value in a subsequence in the processed sequence by a corresponding element value in a subsequence in the frequency offset estimation sequence to obtain (N−K)*M complex numbers;
• calculate a sum of the (N−K)*M complex numbers;
• obtain a phase of the sum to obtain a phase value;
• and
• divide the phase value by M to obtain a frequency offset estimation value.