The communication system includes a hybrid fiber/coax distribution network. A head end provides for downstream transmission of telephony and control data in a first frequency bandwidth over the hybrid fiber/coax distribution network and reception of upstream telephony and control data in a second frequency bandwidth over the hybrid fiber/coax distribution network. The head end includes a head end multicarrier modem for modulating downstream telephony information on a plurality of orthogonal carriers in the first frequency bandwidth and demodulating upstream telephony information modulated on a plurality of orthogonal carriers in the second frequency bandwidth. The system includes service units, operatively connected to the hybrid fiber/coax distribution network for upstream transmission of telephony and control data and for receipt of the downstream control data and telephony. Also provided is a method and apparatus for performing a Fast Fourier Transform (FFT).

Communication system with multicarrier telephony transport

A method and apparatus for pilot-symbol aided channel estimation in a wireless digital communication system which transmits packets of N OFDM data blocks, each data block comprising a set of K orthogonal carrier frequencies. At the transmitter, pilot symbols are inserted into each data packet at known positions so as to occupy predetermined positions in the time-frequency space. At the receiver, the received signal is subject to a two-dimensional inverse Fourier transform, two-dimensional filtering and a two-dimensional Fourier transform to recover the pilot symbols so as to estimate the channel response.

Pilot-aided channel estimation for OFDM in wireless systems

In this patent, we present MultiCode Direct Sequence Spread Spectrum (MC-DSSS) which is a modulation scheme that assigns up to N DSSS codes to an individual user where N is the number of chips per DSSS code. When viewed as DSSS, MC-DSSS requires up to N correlators (or equivalently up to N Matched Filters) at the receiver with a complexity of the order of N2 operations. In addition, a non ideal communication channel can cause InterCode Interference (ICI), i.e., interference between the N DSSS codes. In this patent, we introduce new DSSS codes, which we refer to as the "MC" codes. Such codes allow the information in a MC-DSSS signal to be decoded in a sequence of low complexity parallel operations which reduce the ICI. In addition to low complexity decoding and reduced ICI. MC-DSSS using the MC codes has the following advantages: (1) it does not require the stringent synchronization DSSS requires, (2) it does not require the stringent carrier recovery DSSS requires and (3) it is spectrally efficient.

Multicode direct sequence spread spectrum

A multicarrier frequency hopping spread spectrum communications system wherein a transmitting station assigns encoded data symbols to particular ones of a predetermined series of fixed carrier frequencies, the frequency assignments being periodically mixed according to a frequency hopping code, and the encoded data symbols are combined with their assigned carrier frequencies in accordance with an inverse Fourier transform so as to multiplex the encoded data symbols by orthogonal frequency division modulation. A receiving station performs demultiplexing and de-mixing of such multiplexed signals in accordance with the inverse of the multiplexing and mixing performed at the transmitter. The system thereby provides frequency hopping operation without requiring a rapidly tunable and accurately phase controlled oscillator at each of the transmit/receive stations.

Multicarrier frequency hopping communications system

A few high power tones (1506, 1508) used for synchronization and/or other purposes are transmitted in a FDM system (400) during a period of time into a region, e.g., sector (SECTOR 1-Y) of a cell (Cell 1-N), e.g., a symbol transmission time period. During normal data transmission symbol periods, signals are transmitted using at least 10 tones, e.g., per symbol time. Less than 5 high power signals (1506, 1508) are transmitted in a symbol time with at least 80% the maximum total transmitter power used for transmitting into said region being allocated to the high power signals where the maximum total transmitter power is determined from a period of time which may includes one or more data and/or high power tone (1506, 1508) transmission periods. When the high power tones (1506, 1508) are transmitted at most 20% of transmitter power used for transmitting into the region is available for transmitting other tones with the power normally being distributed among multiple tones. Often some tones, which would be transmitted in a symbol time go unused during transmission of the high power signals (1506, 1508).

Beacon signaling in a wireless system

A coherent demodulation device, for the demodulation of a digital signal of the type constituted by digital elements distributed in the time-frequency space and transmitted in the form of symbols constituted by a multiplex of N orthogonal carrier frequencies modulated by a set of the digital elements and broadcast simultaneously, the digital signal comprising reference elements, having a value and a position, in the time-frequency space, that are known to the demodulation device, comprising means for the estimation, by Fourier transform, of the frequency response of the transmission channel at any instant, carrying out the transformation of the received samples, corresponding to reference elements, from the frequency domain to the temporal domain, the multiplication in the temporal domain of the transformed samples by a rectangular temporal window (f n) and the reverse transformation, after the multiplication, of the obtained samples from the temporal domain into the frequency domain, the estimation means comprising means for the thresholding of the samples in the temporal domain, providing for the systematic elimination of the samples below a certain threshold.

Device for the coherent demodulation of time-frequency interlaced digital data, with estimation of the frequency response of the transmission channel and threshold, and corresponding transmitter

A method for the time synchronisation of a multi-carrier signal receiver consisting of a series of symbols that each comprise a plurality of carrier frequencies each modulated by a modulation coefficient. The position of some of said carrier frequencies in the time-frequency space is known to the receiver, and said frequencies are reference carrier frequencies with a reference coefficient whose value is known to said receiver. The method includes a fine synchronisation step, wherein the signal transmission channel impulse response hn is estimated (773) on the basis of reference coefficients belonging to at least two received symbols; and the start of the operative portion of each of the symbols is determined (75), and/or a receiver clock is controlled, by analysing the estimate of said impulse response hn.

Multi-carrier symbol synchronisation

of EP0499560The field of the invention is that of the coherent demodulation of a digital signal of the type consisting of digital elements distributed in time-frequency space and emitted in the form of symbols consisting of a multiplex of N orthogonal carrier frequencies modulated by a string of the said digital elements and broadcast simultaneously, and comprising reference elements, of known value and known position within the said time-frequency space of the said demodulating device. The invention relates to a device for coherent demodulation comprising means of estimation, by Fourier transformation, of the frequency response of the transmission channel at any instant, carrying out the transformation (14) of the received samples corresponding to reference elements from the frequency domain into the time domain, the multiplication (15), in the time domain, of the said transformed samples by a rectangular time window (fn) and the inverse transformation (16), after the said multiplication, of the samples obtained from the time domain into the frequency domain, the said means of estimation comprising means (17) of thresholding the said samples in the said time domain, ensuring the systematic elimination of the samples below a certain threshold.

Channel estimation system and method for COFDM transmission system

Decoding apparatus provides the maximum likelihood decoding of a sequence of samples of the type implementing a Viterbi type of decision algorithm that defines an initial decoding trellis. Sub-sampling apparatus sub-samples the initial trellis by a ratio p to preserve nodes corresponding to one sample out of p consecutive samples. This sub-sampling apparatus associates a p order antecedent node to each preserved node. Trace-back apparatus traces an optimal path back in the sub-sampled trellis by associating the p order antecedent node for each preserved node. The trace back apparatus designates at least the last two nodes of the optimal path. Over-sampling apparatus over-samples the designation of the last two nodes of the optimal path. The factor p is an integer greater than 1 selected so that there is a single path between a node and its p order antecedent in the initial trellis. Hence the bit rate is increased by a factor p, without loss of information.

Method of maximum likelihood decoding with sub-sampled decoding trellis, and corresponding decoding device

L'invention concerne notamment un procede de synchronisation temporelle d'un recepteur d'un signal multiporteuse constitue d'une suite de symboles formes chacun d'une pluralite de frequences porteuses modulees chacune par un coefficient de modulation, certaines desdites frequences porteuses, de position dans l'espace temps-frequence connue dudit recepteur, etant des frequences porteuses de reference, portant un coefficient de reference de valeur connue dudit recepteur, procede comprenant une phase de synchronisation fine comprenant les etapes suivantes: - estimation (773) de la reponse impulsionnelle h|^n canal de transmission dudit signal, a partir de coefficients de reference appartenant a au moins deux symboles recus; determination (75) du debut de la partie utile de chacun desdits symboles et/ou asservissement d'une horloge du recepteur, par analyse de ladite estimation de la reponse impulsionnelle h|^n .

Jean-Francois Helard

Papers

Device for the coherent demodulation of time-frequency interlaced digital data, with estimation of the frequency response of the transmission channel and threshold, and corresponding transmitter

Multi-carrier symbol synchronisation

Channel estimation system and method for COFDM transmission system

Method of maximum likelihood decoding with sub-sampled decoding trellis, and corresponding decoding device

Procede et dispositif de synchronisation temporelle d'un recepteur d'un signal multiporteuse