Multicarrier digital transmission system using an OQAM transmultiplexer
View Patent ↗An emitter converts a serial input data stream into a set of parallel substreams. An OQAM modulator ( 120 ) receives and supplies each substream to an input of a synthesis filter bank ( 130 ). Synchronization input(s) of the filter bank receive an OQAM signal that carries a data sequence. This sequence contains frame, superframe and hyperframe synchronization patterns, and specifies the number of bits allocated to each subchannel. A receiver ( 200 ) includes an analysis filter bank ( 210 ) that decomposes the multicarrier signal into a set of elementary signals for each subchannel. A synchronizing processing block ( 270 ) receives output(s) of the filter bank for synchronization subchannel(s). The block ( 270 ) includes a first cascade of blocks that control receiver sampling times, and a second cascade of blocks that extract synchronization patterns and subchannel bit assignment data. Other filter bank outputs are each coupled to a cascade subchannel equalizer ( 220 ) followed by a data extractor ( 230 ) and a parallel-to-serial converter ( 240 ).
1. A multicarrier digital transmission system for communicating bits of digital data over set of different frequencies in a transmission channel's frequency band, each frequency constituting a subchannel of the transmission channel's frequency band, the multicarrier digital transmission system comprising:
a. an emitter ( 100 ) for receiving a digital input data stream d(n) and for emitting therefrom a digital multicarrier signal Se(n), the emitter ( 100 ) including:
i. a serial/parallel converter ( 110 ), which operates responsive to a synchronization and service data signal scdatar, for splitting the digital input data stream d(n) into a number of substreams of digital data di, each of the digital substreams di being assigned to at least one used subchannel of the transmission channel's frequency band;
ii. an OQAM modulator ( 120 ) for receiving the digital substreams di produced by the serial/parallel converter ( 110 ), and for producing from the digital substreams di, responsive to the synchronization and service data signal scdatar, a set of N sequences of OQAM modulated quantized signal samples xi;
iii. synchro+data unit ( 150 ) for generating, responsive to service data scdatae, a transmitted synchronization and service data signal xis that is assigned to at least one synchronization subchannel of the transmission channel's frequency band; and
iv. a synthesis filter bank ( 130 ) having inputs for receiving:
A. from the OQAM modulator ( 120 ) the set of N sequences of quantized signal samples xi, and
B. from the synchro+data unit ( 150 ) the transmitted synchronization and service data signal xis; and
for producing, from the received set of N sequences of quantized signal samples xi and from the received transmitted synchronization and service data signal xis, the multicarrier output digital signal Se(n); and
b. a receiver ( 200 ) for receiving an input signal Sr(n) and for producing therefrom an output data stream d′(n), the receiver including:
i. an analysis filter bank ( 210 ) for receiving the input signal Sr(n), and for producing:
A. from used subchannels of the input signal Sr(n) a set of sequences xir equal to the number of used subchannels; and
B. from the at least one synchronization subchannel of the input signal Sr(n) a received synchronization and service data signal xisr;
ii. a subchannel equalizer ( 220 ) for receiving the sequences xir produced by the analysis filter bank ( 210 ) and, for producing from the received sequence xir an output signal vi, wherein the subchannel equalizer ( 220 ) in producing the output signal vi adjusts both the amplitude and phase of the received sequence xir by processing the received sequence xir through a cascade of;
A. an amplitude equalizer ( 221 );
B. a phase and residual amplitude equalizer ( 222 ); and
C. a fine equalizer ( 223 );
iii. a data extractor ( 230 ) which receives the signal vi from the subchannel equalizer ( 220 ) and, responsive to the service data scdatae, produces a binary representation dir of the received signal vi by quantizing real and imaginary parts thereof;
iv. a parallel-to-serial converter ( 240 ) for receiving the binary representations dir from the data extractor ( 230 ) and for producing therefrom the output data stream d′(n);
iv. a synchro processor ( 270 ) for receiving from the analysis filter bank ( 210 ) the received synchronization and service data signal xisr and for detecting therein at least the synchronization and service data signal scdatar to which the serial/parallel converter ( 110 ) and the OQAM modulator ( 120 ) respond; and
vi. a capacity +bit assign ( 250 ) which receives from the phase and residual amplitude equalizer ( 222 ) of the subchannel equalizer ( 220 ) an error signal eip and from the data extractor ( 230 ) an error signal ei, and from the error signals eip and ei:
A. for every used subchannel estimates a reference amplitude ra which the capacity+bit assign ( 250 ) transmits to the subchannel equalizers ( 220 ); and
B. decides a number of bits to be assigned to every used subchannel which the capacity+bit assign ( 250 ) transmits via the service data scdatae both to data extractor ( 230 ) and to the synchro+data unit ( 150 ).
2. The multicarrier digital transmission system of claim 1 wherein a synchronization and service data signal transmitted via at least one synchronization subchannel contains a superframe synchronization pattern and a hyperframe synchronization pattern.
3. The multicarrier digital transmission system of claim 1 , wherein the emitter ( 100 ) transmits the synchronization and service data signal xis envelope modulation.
4. The multicarrier digital transmission system of claim 1 , wherein:
a. the received synchronization and service data signal xisr has an envelope; and
b. the receiver ( 200 ) uses the envelope of the received synchronization and service data signal xisr for producing signals:
i. for controlling the receiver sampling times; and
ii. for performing frame synchronization including the synchronization and service data signal scdatar.
5. The multicarrier digital transmission system of claim 1 , wherein each superframe the serial/parallel converter ( 110 ) and the OQAM modulator ( 120 ) of the emitter ( 100 ) introduce a short fixed pattern reference signal into each used subchannel.
6. The multicarrier digital transmission system of claim 1 , wherein the receiver ( 200 ) updates the phase and residual amplitude equalizer ( 222 ) of the subchannel equalizer ( 220 ) at a superframe rate using a short fixed pattern reference signal present in each used subchannel.
7. The multicarrier digital transmission system of claim 1 , wherein the fine equalizer ( 223 ) of the subchannel equalizer ( 220 ) is a decision directed equalizer.
8. The multicarrier digital transmission system of claim 1 , wherein:
a. data specifying bit assignment in used subchannels are transmitted each hyperframe; and
b. the number of bits carried by each used subchannel are confirmed or modified each hyperframe.
9. The multicarrier digital transmission system of claim 1 , wherein:
a. the same substream di is fed to at least two used subchannels; and
b. outputs from subchannel equalizers ( 220 ) corresponding to the at least two used subchannels are combined for producing the output signal vi.
10. The multicarrier digital transmission system of claim 9 wherein:
i. a weighted summation combines outputs from the subchannel equalizers ( 220 );
ii. coefficients for the weighted summation are inverses of estimated total distortion powers for the used subchannels which receive the same substream di; and
iii. data are obtained from the summed outputs using the sign of the weighted summation.
11. The multicarrier digital transmission system of claim wherein coefficients in the filter banks ( 130 ) and ( 210 ) are selected so a prototype filter response satisfies both:
a. the first Nyquist criterion; and
b. the second Nyquist criterion.