Transmission apparatus and method

Abstract

A burst signal generator generates a burst signal that is a variable length portion whose length changes in accordance with fluctuations in data input at a predetermined period. An OFDM modulator generates an OFDM signal (including a guard interval portion and an effective symbol portion) that is a fixed length portion containing data corresponding to n (n is a positive integer) times or 1/n of the predetermined period. A frame includes the variable length portion and the fixed length portion. This makes a transmission signal actually have a frame period almost equal to the period of a signal synchronized with the clock of a player, including the fluctuations.

1 . A transmission apparatus comprising:
 an input unit configured to input data at a predetermined period;   a transmission signal generator configured to generate a transmission signal formed from a frame including a variable length portion whose length changes in accordance with fluctuations in the predetermined period of the data input by said input unit, and a fixed length portion containing data corresponding to n (n is a positive integer) times or 1/n of the predetermined period; and   a transmitter configured to transmit the transmission signal generated by said transmission signal generator.   
   
   
       2 . The apparatus according to  claim 1 , wherein said input unit inputs the data at a first period based on a first clock,
 the apparatus further comprises a clock signal generator configured to generate a signal having the second period by reclocking the first period by a second clock, and   said transmission signal generator generates the transmission signal formed from the frame including the variable length portion whose length changes in accordance with fluctuations in the second period of the data input by said input unit, and the fixed length portion containing data corresponding to n (n is a positive integer) times or 1/n of the first period.   
   
   
       3 . The apparatus according to  claim 1 , wherein the variable length portion contains no signal including significant data in transmission of the data input at the predetermined period. 
   
   
       4 . The apparatus according to  claim 1 , wherein the data contained in the fixed length portion is data modulated by orthogonal frequency division multiplexing. 
   
   
       5 . The apparatus according to  claim 4 , wherein the variable length portion is arranged adjacent to one of an effective symbol and a guard interval of the data contained in the fixed length portion. 
   
   
       6 . A method of causing a transmission apparatus to transmit data, comprising the steps of:
 inputting data at a predetermined period;   generating a transmission signal formed from a frame including a variable length portion whose length changes in accordance with fluctuations in the predetermined period of the data input in the inputting step, and a fixed length portion containing data corresponding to n (n is a positive integer) times or 1/n of the predetermined period; and   transmitting the transmission signal generated in the generating step.   
   
   
       7 . A program for causing a computer to function as a transmission apparatus of  claim 1 . 
   
   
       8 . A computer-readable storage medium which stores a program for causing a computer to function as a transmission apparatus of  claim 1 . 
   
   
       9 . A transmission apparatus comprising:
 a decoder configured to receive and decode medium data and a first synchronizing signal based on a first clock signal;   a data frame generator configured to generate a data frame in every period based on the first synchronizing signal decoded by said decoder;   a modulator configured to modulate the data frame generated by said data frame generator to generate symbol data;   a clock signal generator configured to generate a second clock signal independently of the first clock signal;   a timing signal generator configured to generate a second synchronizing signal by reclocking the first synchronizing signal decoded by said decoder using the second clock signal generated by said clock signal generator, and to generate an output enable signal which rises after elapse of a predetermined time from a leading edge of the generated second synchronizing signal, and falls after elapse of a time length of the symbol data generated by said modulator;   a D/A converter configured to D/A-convert the symbol data generated by said modulator to generate an intermediate frequency signal when the output enable signal generated by said timing signal generator is at H level;   a burst signal generator configured to generate a burst signal having a frequency equal to a carrier frequency by dividing a frequency of the second clock signal generated by said clock signal generator and filtering the second clock signal;   a transmission frequency converter configured to generate a carrier frequency signal by converting the intermediate frequency signal generated by said D/A converter into the carrier frequency using the burst signal generated by said burst signal generator; and   a switching unit configured to output the carrier frequency signal generated by said transmission frequency converter to a transmission path when the output enable signal generated by said timing signal generator is at H level, and to output the burst signal generated by said burst signal generator to the transmission path when the output enable signal is at L level.   
   
   
       10 . The apparatus according to  claim 9 , wherein the predetermined time has a length equal to a time necessary from output of the medium data from said decoder to input to said D/A converter. 
   
   
       11 . A transmission apparatus comprising:
 a decoder configured to receive and decode medium data and a first synchronizing signal based on a first clock signal;   a data frame generator configured to generate a data frame in every period based on the first synchronizing signal decoded by said decoder;   a modulator configured to modulate the data frame generated by said data frame generator to generate symbol data;   a clock signal generator configured to generate a second clock signal independently of the first clock signal;   a burst signal generator configured to generate a burst signal having a frequency equal to a carrier frequency by dividing a frequency of the second clock signal generated by said clock signal generator and filtering the second clock signal;   a timing signal generator configured to generate a second synchronizing signal by reclocking the first synchronizing signal decoded by said decoder using the second clock signal generated by said clock signal generator, and to generate an output enable signal which falls after elapse of a predetermined time from a leading edge of the generated second synchronizing signal, and rises after elapse of a predetermined burst signal time length;   an adjustment data adding unit configured to add, to the symbol data generated by said modulator, adjustment data having a length corresponding to a fluctuation in a period of the second synchronizing signal generated by said timing signal generator;   a D/A converter configured to D/A-convert the symbol data to which the adjustment data is added by said adjustment data adding unit to generate an intermediate frequency signal when the output enable signal generated by said timing signal generator is at H level;   a transmission frequency converter configured to generate a carrier frequency signal by converting the intermediate frequency signal generated by said D/A converter into the carrier frequency using the burst signal generated by said burst signal generator; and   a switching unit configured to output the carrier frequency signal generated by said transmission frequency converter to a transmission path when the output enable signal generated by said timing signal generator is at H level, and to output the burst signal generated by said burst signal generator to the transmission path when the output enable signal is at L level.   
   
   
       12 . The apparatus according to  claim 11 , wherein the burst signal time length is obtained by subtracting a time length of the burst signal generated by said burst signal generator from a time necessary from output of the medium data from said decoder to input to said D/A converter. 
   
   
       13 . A transmission method comprising the steps of:
 receiving and decoding medium data and a first synchronizing signal based on a first clock signal;   generating a data frame in every period based on the decoded first synchronizing signal;   modulating the generated data frame to generate symbol data;   generating a second clock signal independently of the first clock signal;   generating a second synchronizing signal by reclocking the first synchronizing signal decoded in the decoding step using the second clock signal generated in the step of generating the second clock signal, and generating an output enable signal which rises after elapse of a predetermined time from a leading edge of the generated second synchronizing signal, and falls after elapse of a time length of the symbol data generated in the modulating step;   D/A-converting the symbol data generated in the modulating step to generate an intermediate frequency signal when the generated output enable signal is at H level;   generating a burst signal having a frequency equal to a carrier frequency by dividing a frequency of the second clock signal generated in the step of generating the second clock signal and filtering the second clock signal;   generating a carrier frequency signal by converting the intermediate frequency signal generated in the D/A-converting step into the carrier frequency using the burst signal generated in the step of generating the burst signal; and   outputting the carrier frequency signal generated in the step of generating the carrier frequency signal to a transmission path when the output enable signal generated in the step of generating the second synchronizing signal and the output enable signal is at H level, and outputting the burst signal generated in the step of generating the burst signal to the transmission path when the output enable signal is at L level.   
   
   
       14 . A transmission method comprising the steps of:
 receiving and decoding medium data and a first synchronizing signal based on a first clock signal;   generating a data frame in every period based on the decoded first synchronizing signal;   modulating the generated data frame to generate symbol data;   generating a second clock signal independently of the first clock signal;   generating a burst signal having a frequency equal to a carrier frequency by dividing a frequency of the generated second clock signal and filtering the second clock signal;   generating a second synchronizing signal by reclocking the first synchronizing signal decoded in the decoding step using the second clock signal generated in the step of generating the second clock signal, and generating an output enable signal which falls after elapse of a predetermined time from a leading edge of the generated second synchronizing signal, and rises after elapse of a predetermined burst signal time length;   adding, to the symbol data generated in the modulating step, adjustment data having a length corresponding to a fluctuation in a period of the second synchronizing signal generated in the step of generating the second synchronizing signal and the output enable signal;   D/A-converting the symbol data to which the adjustment data is added in the adding step to generate an intermediate frequency signal when the output enable signal generated in the step of generating the second synchronizing signal and the output enable signal is at H level;   generating a carrier frequency signal by converting the generated intermediate frequency signal into the carrier frequency using the burst signal generated in the step of generating the burst signal, and   outputting the carrier frequency signal generated in the step of generating the carrier frequency signal to a transmission path when the output enable signal generated in the step of generating the second synchronizing signal and the output enable signal is at H level, and outputting the burst signal generated in the step of generating the burst signal to the transmission path when the output enable signal is at L level.   
   
   
       15 . A program for causing a computer to function as a transmission apparatus of  claim 9 . 
   
   
       16 . A computer-readable storage medium which stores a program for causing a computer to function as a transmission apparatus of  claim 9 . 
   
   
       17 . A transmission method executed by a transmission apparatus for transmitting a transmission frame including a variable length portion and a fixed length portion, the method comprising the steps of:
 generating, from data input from an external device, a playback synchronizing signal having a period corresponding to a sampling period of the input data;   generating a clock signal having a period corresponding to the sampling period of the data input from the external device;   detecting a phase difference generated between the playback synchronizing signal and the clock signal upon switching an operation mode;   generating the transmission frame in which a length of the variable length portion is changed in accordance with the detected phase difference; and   transmitting the generated transmission frame to a reception apparatus in synchronism with the period of the clock signal.   
   
   
       18 . The method according to  claim 17 , wherein in the detecting step, the phase difference between the playback synchronizing signal and the clock signal is detected, the phase difference being generated upon switching a first operation mode to transmit a transmission frame including the variable length portion and a data frame of a fixed length portion generated based on data generated in the transmission apparatus to a second operation mode to transmit a transmission frame including the variable length portion and a data frame of a fixed length portion generated based on the data input from the external device. 
   
   
       19 . The method according to  claim 17 , wherein the operation mode switches when the external device for inputting data changes. 
   
   
       20 . The method according to  claim 17 , wherein in the step of generating the transmission frame, the length of the variable length portion changes within a predetermined range. 
   
   
       21 . A transmission apparatus for transmitting a transmission frame including a variable length portion and a fixed length portion, comprising:
 a unit configured to generate, from data input from an external device, a playback synchronizing signal having a period corresponding to a sampling period of the input data;   a unit configured to generate a clock signal having a period corresponding to the sampling period of the data input from the external device;   a unit configured to detect a phase difference generated between the playback synchronizing signal and the clock signal upon switching an operation mode;   a unit configured to generate the transmission frame in which a length of the variable length portion is changed in accordance with the detected phase difference; and   a unit configured to transmit the generated transmission frame to a reception apparatus in synchronism with the period of the clock signal.   
   
   
       22 . A program for causing a computer to execute a transmission method of  claim 17 . 
   
   
       23 . A computer-readable storage medium which stores a program for causing a computer to execute a transmission method of  claim 17 . 
   
   
       24 . A transmission apparatus capable of operating while switching between a first operation mode to transmit a transmission frame generated from data input from an external device and a second operation mode to transmit a transmission frame generated from data generated in the transmission apparatus, comprising:
 a decoder configured to decode multi-channel audio data input from the external device and including playback synchronization data to generate data frame and a playback synchronizing signal;   a transmission data generator configured to generate one of null data and command data associated with system setup;   a data selector configured to output the audio data generated by said decoder in the first operation mode, and to output the data generated by said transmission data generator in the second operation mode;   a clock selector configured to control to output the playback synchronizing signal generated by said decoder in the first operation mode and not to output a signal in the second operation mode;   a clock signal generator configured to generate a clock signal having a period corresponding to a period of the playback synchronizing signal;   an output unit configured to output phase difference information between the playback synchronizing signal generated by said decoder and the clock signal generated by said clock signal generator in the first operation mode, and to output predetermined phase difference information in the second operation mode;   an adjustment time determination unit configured to generate adjustment time information based on an output from said output unit;   a data frame generator configured to generate a data frame based on an output from said data selector and the adjustment time information generated by said adjustment time determination unit;   an OFDM symbol generator configured to generate an OFDM symbol from the data frame generated by said data frame generator;   a burst signal generator configured to generate a burst signal;   a transmission frame generator configured to generate a transmission frame including the burst signal, the OFDM symbol, and a frame adjustment signal having a length corresponding to the adjustment time information; and   a transmitter configured to transmit the transmission frame in synchronism with the period of the clock signal generated by said clock signal generator.