156 results about "Qam constellations" patented technology

In transmitter apparatus for a digital television (DTV) broadcasting system, internet-protocol (IP) packets of digital television information are subjected to multilevel concatenated Bose-Chaudhuri-Hocquenghem (BCH) coding and low-density parity-check convolutional coding (LDPCCC) before being bit-interleaved and mapped to quadrature-amplitude-modulation (QAM) constellations. The QAM constellations are used in coded orthogonal frequency-division modulation (COFDM) of plural carrier waves up-converted to a radio-frequency broadcast television channel. In receiver apparatus for the DTV broadcasting system the results of de-mapping QAM constellations recovered from demodulating the COFDM carrier waves are de-interleaved, and the constituent LDPCCC codewords are decoded to recover constituent BCH codewords of the multilevel BCH coding. The constituent BCH codewords are decoded to correct remnant bit errors in them. Then, IP packets of digital television information are reconstituted from the systematic data bits in those BCH codewords.

A Viterbi decoding system interprets bits in received QAM constellations as many-valued parameters rather than binary valued parameters. It performs the Viterbi algorithm using these many-valued parameters to provide results superior to hard decision decoding. Rather than applying a hard 0-1 function to the QAM data, the system uses a non-stepped linear or curved transfer function to assign values to the bits. In another aspect, a system differentiates between data bits based on their estimated reliability, giving more emphasis to decoding reliable bits than unreliable bits using any of a variety of techniques. By differentiating between god and bad bits and de-emphasizing or ignoring unreliable bits, the system can provide a significant reduction in uncorrectable errors and packet loss.

A method and apparatus to adaptively puncture bits within QAM modulated data symbols transmitted in a communication system in order to effect a signaling channel. The method and apparatus utilize inherent characteristics of a particular mapping scheme for the QAM constellation to selectively puncture particular bits within a data symbol with signaling information and predetermined binary values to selectively increase the log-likelihood ratio gains of those particular bits punctured with the signaling information. The log-likelihood ratios are used to obtain the signaling information and, thus, increasing the gain of the log-likelihood ratios affords greater reliability for the signaling information without increasing the required system resources.

A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate. The method comprises the following steps: (1) generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; (2) selecting a passband or a baseband mode; and (3) generating an analog output signal in the passband or baseband mode. The step of selecting the passband or the baseband mode depends on the complexity of QAM constellation. If QAM constellation includes less than 64 QAM plant points, the passband mode is selected, and if QAM constellation includes more than 64 QAM plant points, the baseband mode is selected. If the QAM constellation includes less than 64 QAM plant points, initially selecting the passband mode until a D/A conversion speed reaches a maximum passband conversion speed, and until an output symbol rate reaches a maximum passband symbol output rate, and subsequently switching to the baseband mode in order to double the maximum passband conversion speed and to double the maximum passband symbol output rate.

According to one embodiment of the invention, a 16-QAM optical modulator has a Mach-Zehnder modulator (MZM) coupled to a drive circuit that drives the MZM based on two electrical binary signals. The output of the MZM corresponds to an intermediary constellation consisting of four constellation points arranged on a straight line in the corresponding in-phase/quadrature-phase (I-Q) plane. Two of these constellation points correspond to a zero phase, and the remaining two constellation points correspond to a phase of π radian. The 16-QAM optical modulator further has a phase shifter that modulates the output of the MZM based on two additional electrical binary signals. The resulting optical output signal corresponds to a star 16-QAM constellation, which is produced by incremental rotation of the intermediary constellation.

In a coding system for asymmetric digital subscriber line (ADSL) communications, a method of encoding a sequence of information bits is provided comprising the steps of dividing the information bits into encoding bits and parallel bits; encoding the encoding bits to produce encoded bits; mapping the encoded bits and the parallel bits into first and second pulse amplitude modulation (PAM) signals; and generating a quadrature amplitude modulation (QAM) signal from these first and second PAM signals. This method overcomes the decoder complexity that would otherwise be required due to the large QAM constellations involved for ADSL communications.

A method and a device for transmitting and receiving data are provided. The method comprises the following steps: A: data to be transmitted are interleaved after being divided, randomized and conducted forward error correction coding on the transmitting terminal. B: QAM maps the interleaved data into corresponding QAM constellation points according to the sub-channel bit and energy distribution parameter. C: after the QAM mapping treatment, the data are generated into frequency field data frame, which are then conducted IFFT transformation and generated into OFDM signals. D: insert cyclic prefix into the OFDM signals, which are then generated into baseband analog signals after digital to analog conversion; the baseband analog signals are transmitted to the receiving terminal in the service sub-channel of the logging cable. By adopting the method and device of the invention, data transmission rate in present logging cable is greatly improved, which in turn meets requirements of the large data amount transmission of under-well instruments.

A method and apparatus is disclosed to map a sequence of data to Quadrature Amplitude Modulation (QAM) constellation symbols. The method and apparatus encodes only a portion of the sequence of data and leaves a remaining portion of the sequence of data unencoded. The encoded portion of the sequence of data and the remaining unencoded portion of the sequence of data are then mapped into modulation symbols of the QAM constellation. The encoded portion of the sequence of data selects subsets of the QAM constellation, and the remaining unencoded portion of the sequence of data determines a specific modulation symbol within each subset of the QAM constellation.

The invention discloses a trellis code modulated (TCM) code modulation method, and is to solve the problem of poor entirety of the prior TCM codes. The invention comprises the following steps. Firstly, a square QAM planisphere with the modulation order number larger than 4 is used as a constellation mapping scheme so that after the codes on a way I and a way Q of the constellation mapping scheme are mapped, and bit blocks are arranged repeatedly on a periodic basis on the ways I and Q, and corresponding uncoded bit blocks are different after each repeated arrangement on a periodic basis. Constellation indices including coded bit blocks and uncoded bit blocks are acquired according to original bit message block. Signaling points in the constellation mapping scheme according to the constellation indices are determined as the final emissive TCM signals. As the coded bit blocks are repeatedly arranged on a periodic basis, and corresponding uncoded bit blocks are different from each other, mappings of symbols for parallel paths on the way Q of the constellation mapping scheme are uniform, and the entirety of TCM codes can be improved.

In one aspect, the present invention greatly simplifies soft modulation calculations, in part by exploiting certain properties of Gray-mapped QAM constellations used in modulating symbols of interest. In at least one embodiment, the simplified processing includes performing the soft modulation separately for the real and imaginary parts of each symbol of interest, by using the Gray mapping to decompose each of the real and imaginary parts into binary soft modulations for each bit, and then using a computationally-efficient table lookup to calculate the binary soft modulation. Here, the look-up table comprises pre-computed bit contributions to the complex soft symbol value to be formed for the symbol of interest.

In transmitter apparatus for a digital television broadcasting system, internet-protocol (IP) packets of digital television information are subjected to multilevel coding (MLC) before being Gray-mapped to quadrature-amplitude-modulation (QAM) constellations. The constituent codes of the MLC comprise respective low-density parity-check (LDPC) inner coding. Preferably, the LDPC inner coding is LDPC convolutional coding. The QAM constellations are used in coded orthogonal frequency-division modulation (COFDM) of plural carrier waves up-converted to a radio-frequency broadcast television channel. In receiver apparatus for the digital television broadcasting system the results of de-mapping QAM constellations recovered from demodulating the COFDM carrier waves are de-interleaved, and the LDPC constituent codes of the MLC are independently decoded in parallel with decoding results time-interleaved to recover the IP packets of digital television information.

A transmit processor that includes a transmit frequency domain equalizer (TX FEQ) that pre-compensates packets in the frequency domain to flatten transmit filter response to improve spectral mask and reduce PER. The TX FEQ taps may be selected so that the average power at output equals the average power applied to the input. The TX FEQ may be designed to yield 64 QAM packets with no quantization distortion at the input of an Inverse Fast Fourier Transform (IFFT) processor. The 64 QAM constellation map points and TX FEQ gain values are selected to avoid exceeding the bit resolution of the IFFT processor. The tones may be bound together into zones to reduce implementation complexity by reducing the number of TX FEQ taps.

This disclosure describes a simple spreading technique that improves performance for communication over fading channels with QPSK or BPSK modulation. The technique may comprise combining two symbols at the transmitter by applying a 2×2 transform, resulting in a 4-PAM or 16-QAM constellation. The receiver may utilize a 2-dimensional soft de-mapper to provide inputs to a soft-input decoder. This scheme can offer significant performance gains over fading channels with minimal additional complexity. This technique is most beneficial on systems with a weak code or no code at all. One application of this technique is for coded OFDM systems that experience frequency-selective fading. An example of such a system is the MBOA draft specification for UWB wireless communications.

A Viterbi decoding system interprets bits in received QAM constellations as many-valued parameters rather than binary valued parameters. It performs the Viterbi algorithm using these many-valued parameters to provide results superior to hard decision decoding. Rather than applying a hard 0-1 function to the QAM data, the system uses a non-stepped linear or curved transfer function to assign values to the bits. This results in performance superior to pure hard decision decoding and approaches that of soft decision decoding; moreover, it is applicable in many situations where soft decision decoding cannot be used.

A transmitter may map, using a selected modulation constellation, each of C′ bit sequences to a respective one of C′ symbols, where C′ is a number greater than one. The transmitter may process the C′ symbols to generate C′ inter-carrier correlated virtual subcarrier values. The transmitter may decimate the C′ virtual subcarrier values down to C physical subcarrier values, C being a number less than C′. The transmitter may transmit the C physical subcarrier values on C orthogonal frequency division multiplexed (OFDM) subcarriers. The modulation constellation may be an N-QAM constellation, where N is an integer. The processing may comprise filtering the C′ symbols using an array of C′ filter tap coefficients. The filtering may comprise cyclic filtering. The filtering may comprise multiplication by a circulant matrix populated with the C′ filter tap coefficients.

Turbo-coded data are transmitted using quadrature amplitude modulation (QAM) of COFDM carrier waves in digital television (DTV) broadcast systems. The QAM symbol constellations map the parity bits of the turbo coded data so as to be de-mapped with higher confidence levels than the data bits, facilitating turbo decoding. A preferred DTV receiver delays the first transmissions of time-slices of a service selected for iterative-diversity reception to concur with second transmissions of those time-slices. The complex coordinates of QAM constellations in the delayed first transmission and the second transmission of the same time-slice are combined by a maximal-ratio QAM combiner after COFDM demodulation, but before de-mapping QAM constellations and turbo decoding. In a less-preferred DTV receiver, QAM constellations in the delayed first transmission of each time-slice and in the second transmission of the same time-slice are de-mapped separately. A maximal-ratio code combiner then combines de-mapping results before turbo decoding.

Three channel coding schemes for multi-carrier HSDPA packet data transmission are disclosed. The first scheme includes: dividing data into N groups (S210); performing CRC attachment, code block segmentation, channel coding and rate matching on each group of data respectively (S220); scrambling and interleaving the N groups of data unitedly, and then dividing the data into N groups again to perform QAM constellation rearrangement and then map to physical channels of respective carriers for transmission. The second scheme includes: dividing data to be sent into groups (S510); and sending each group of data via a physical channel of a carrier after coding it according to single-carrier HSDPA (S520). The third scheme includes: sending N carrier channels as a whole to a physical layer to perform processing from CRC attachment to QAM constellation rearrangement (S710); dividing the processed data into groups and mapping them to respective carrier channels for transmission (S720).