Packet configuring method and packet receiver

Abstract

A packet receiver is provided that accurately estimates a frequency offset and a channel impulse response even when a transmitted packet is detected with an erroneous timing in a communication mode (typified by the LAN (local Area Network)) where packets are asynchronously transmitted, and thus provides a training sequence which can demodulate the received packet. The training sequence 101 is formed of K sequences 100 - 1 to 100 -K serially connected, each formed of the same N symbols. Even in a channel where a inter-symbol interference occurs when such a training sequence is used, a received signal shifted by the time corresponding to N-symbols becomes the signal which is different by a phase difference caused by a frequency offset between the transmitter and the receiver. Thus, even if the head of a packet is detected with an erroneous timing, the frequency offset can be estimated.

What is claimed is: 
     
       1. A method of configuring packets packet transmission in a transmitter, said packets each including a training portion and a data portion, the method comprising: said transmitter forming said training portion by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 2 1 or more), wherein at least two neighboring sequences of said K sequences are used for frequency-offset estimation, wherein an auto-correlation function for said sequence of N symbols is in an impulse state; and
 said transmitter transmitting said packets. 
 
     
     
       2. A packet receiver that receives packets, each packet including a training portion and a data portion used to initialize said packet receiver, said training portion being formed by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 2 or more), the packet receiver comprising:
 a frequency-offset estimation means for estimating a frequency offset based on a phase difference between two neighboring sequences of K sequences of a received packet, each of said K sequences being formed of N symbols;   a frequency-offset compensation means for compensating a frequency offset contained in said received packet based on said frequency offset estimation; and   a channel impulse response estimation means for estimating an impulse response of a channel based on an output for which the frequency offset is compensated.   
     
     
       3. The packet receiver defined in  claim 2 , wherein:
 an auto-correlation function of said N symbol sequences is in an impulse state; and   said channel impulse response estimation means comprises means for estimating a channel impulse response based on a sequence for which the auto-correlation function is in an impulse state, and a received training sequence.   
     
     
       4. The packet receiver defined in  claim 2 , wherein said frequency offset estimation means comprises:
 a delay circuit for delaying said received packet by a transmission period of time of a sequence of N-symbol sequences;   a phase difference detection circuit for detecting a phase difference between an output of said delay circuit and said received packet;   an integrator for integrating a detection output of said phase difference detection circuit over a transmission period of time of a sequence of M symbols (where M is an integer of 2 or more); and   a divider circuit for dividing an output of said integrator by a product of N and M.   
     
     
       5. The packet receiver defined in  claim 2 , wherein said impulse response estimation means outputs a channel impulse response estimation value after inputting a pulse representing that said frequency offset estimation means has completed frequency offset estimation. 
     
     
       6. A packet receiver for receiving packets, each of said packets including a training portion and a data portion used to initially set a receiver, said training portion being formed by serially connecting K sequences (where K is an integer of 2 or more), each of K sequences being formed of N symbols (where N is an integer of 2 or more), said packet receiver comprising:
 a frequency offset estimation means for detecting a phase difference between a sequence received prior to NT (where T is a continuous time of one symbol) and a currently received sequence, and for estimating a frequency offset based on said phase difference;   a frequency offset compensation means for compensating said frequency offset by rotating the phase of a received signal in the frequency offset compensation direction based on a frequency offset estimation value; and   a channel impulse estimation means for estimating an impulse response of a channel based on an output from an output for which the frequency offset is compensated.   
     
     
       7. The packet receiver defined in  claim 6 , wherein an auto-correlation function of said N symbol sequences is in an impulse state; and wherein said channel impulse response estimation means comprises means for estimating a channel impulse response based on a sequence in which the auto-correlation function is in an impulse state, and a received training sequence. 
     
     
       8. The packet receiver defined in  claim 6 , wherein said impulse response estimation means outputs a channel impulse response estimation value after inputting a pulse representing that said frequency offset estimation means has completed frequency offset estimation. 
     
     
       9. A packet receiving method for receiving packets, each of said packets including a training portion and a data portion to initially set a receiver, said training portion being formed by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 2 or more), said method comprising:
 estimating a frequency offset based on a phase difference between two neighboring sequences of K sequences of a received packet, each of K sequences being formed of N symbols;   compensating a frequency offset contained in said received packet based on a frequency offset estimation value; and   estimating an impulse response of a channel based on a received packet of which the frequency offset is compensated.   
     
     
       10. The packet receiving method defined in  claim 9 , wherein said step of estimating an impulse response of said channel comprises estimating a channel impulse response by placing an auto-correlation function of said sequence of N symbols in an impulse state, and detecting a peak value of an autocorrelation value between a received signal and said sequence of N symbols. 
     
     
       11. The packet receiving method defined in  claim 9 , wherein said step of estimating an impulse response of said channel comprises the step of outputting a channel impulse response estimation value after frequency offset estimation has been completed. 
     
     
       12. A method of packet transmission in a transmitter, said packets each including a training portion and a data portion, the method comprising: said transmitter forming said training portion by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbol(s) (where N is an integer of 1 or more), wherein at least two neighboring sequences of said K sequences are used for frequency-offset estimation; and
 said transmitter transmitting said packets.    
     
     
       13. A packet transmitter comprising:
 a packet configuring unit, each packet including a training portion and a data portion, that forms said training portion by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 1 or more), wherein at least two neighboring sequences of said K sequences are used for frequency-offset estimation; and   a transmitting unit that transmits each said packet.    
     
     
       14. A packet receiver comprising:
 a receiving unit that receives a packet;   a packet estimating unit, each packet including a training portion and a data portion, said training portion being formed by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 1 or more), said packet estimating unit estimating frequency offset by using at least two neighboring sequences of said K sequences.    
     
     
       15. A method of receiving a packet with a packet receiver, the method comprising:
 the packet receiver receiving a packet;   the packet receiver estimating the packet, each packet including a training portion and a data portion and formed that said training portion by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 1 or more), the estimating step estimating frequency offset by using at least two neighboring sequences of said K sequences.    
     
     
       16. A communication system comprising:
 a packet transmitter;   a packet receiver;   wherein said packet receiver comprises:   a receiving unit that receives a packet;   a packet estimating unit, each packet including a training portion and a data portion, said training portion being formed by serially connecting K sequences (where K is an integer of 2 or more), each of said K sequences being formed of N symbols (where N is an integer of 1 or more), said packet estimating unit estimating frequency offset by using at least two neighboring sequences of said K sequences.    
     
     
       17. The method according to claim 1, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.  
     
     
       18. The method according to claim 12, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.  
     
     
       19. The packet transmitter according to claim 13, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.  
     
     
       20. The packet receiver according to claim 14, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.  
     
     
       21. The method according to claim 15, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.  
     
     
       22. The communication system according to claim 16, wherein the frequency offset is estimated based on a phase difference between neighboring sequences of the training portion.