Multicarrier modulation with data dependent frequency-domain redundancy
AssigneeTexas Instruments Incorporated
InventorArthur J. Redfern
Life of this patent
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Abstract
A modem (10) for transmitting a discrete multitone modulated (DMT) signal over a communications channel (H) is disclosed. In the encoding of an input bitstream, unloaded subchannels in the DMT spectrum are assigned signal values so that a trailing portion of each block or frame of the resulting datastream are forced to a known value, for example zero. The known-valued trailing portion of each block provides the effect of a cyclic prefix, without necessitating the prepending of an actual cyclic prefix and incurring the corresponding data rate loss; alternatively, the effect of a cyclic prefix can be augmented by the forcing of the trailing portion of the blocks to known values.
Claims43
A method of transmitting discrete multitone modulated signals to a receiver over a communications facility, comprising the steps of:
- determining bit loading for each of a plurality of subchannels for a communications session with the receiver;
- then identifying loaded and unloaded subchannels of the plurality of subchannels;
- deriving a transformation matrix, responsive to the identifying step, and according to a block length and a selected number of fixed-value samples;
- receiving a block of an input signal;
- modulating the received block of the input signal, using the transformation matrix, to produce a time-domain signal having a trailing portion comprised of the selected number of fixed-value samples;
- and
- transmitting, over the communications facility, an analog signal corresponding to the time-domain signal.
An apparatus for modulating and transmitting a discrete multitone signal to a receiver over a communications facility, comprising:
- analog front end circuitry for coupling to the communications facility, for receiving a digital datastream and for transmitting a corresponding analog signal over the communications facility;
- a host interface, for coupling to a host source of data to be transmitted;
- and
- digital signal processing circuitry, coupled to the host interface and to the analog front end circuitry, for receiving data from the host source and for producing a digital datastream corresponding to this data and forwarding the digital datastream to the analog front end circuitry for transmission, the digital signal processing circuitry programmed to perform a sequence of operations comprising:
- determining bit loading for each of a plurality of subchannels for a communications session with the receiver;
- then identifying loaded and unloaded subchannels of the plurality of subchannels;
- deriving a transformation matrix, responsive to the identifying step, and according to a block length and a selected number of fixed-value samples;
- receiving a block of an input signal;
- and
- modulating the received block of the input signal, using the transformation matrix, to produce the digital datastream in the form of a time-domain signal having a trailing portion comprised of the selected number of fixed-value samples.
A method of communicating a discrete multitone modulated signals from a transmitter to a receiver, comprising the steps of:
- operating the transmitter to communicate, to the receiver, information corresponding to a plurality of subchannels available for being unloaded, and information corresponding to a trailing sequence length;
- then operating the receiver to select subchannels to be unloaded, and to communicate information identifying the selected subchannels to the transmitter;
- then operating the transmitter to communicate the discrete multitone modulated signals, by repeatedly performing a sequence of operations comprising:
- deriving a transformation matrix, responsive to the selected subchannels communicated by the receiver, and according to a block length and to the trailing sequence length;
- receiving a block of an input signal;
- modulating the received block of the input signal, using the transformation matrix, to produce a time-domain signal having a trailing portion comprised of the selected number of fixed-value samples;
- and
- transmitting, to the receiver, an analog signal corresponding to the time-domain signal.
Dependencies are inferred from the claim text.