357 results about "Multipath channels" patented technology

Wireless communications for frequency-selective fading channels is realized by employing a system including orthogonal frequency division multiplexing (OFDM) in combination with an at least two antenna transmit diversity arrangement. Specifically, OFDM converts a multipath channel into a plurality of narrowband subchannels each having flat fading. Then, the signals on the same frequency subchannels of the at least two antennas are grouped together. Considering a first frequency subchannel, during a first OFDM time interval, a first signal and a second signal are transmitted on the first frequency subchannel from a first antenna (0) and from a second antenna (1), respectively. During a second OFDM time interval, a reverse sign (−) complex conjugate of the second signal and a complex conjugate of the first signal are transmitted from the first antenna and the second antenna, respectively. In a specific embodiment of the invention, reduced complexity in the implementation is realized by a reverse order complex conjugate and a reverse order, reverse sign (−) complex conjugate and judicious selection of the processed data signals in order to transmit the appropriate ones of the signals during the first and second OFDM intervals. Again, if the channel remains constant over the two OFDM intervals, diversity combination is realized for each frequency subchannel. In another embodiment of the invention, antenna-group hopping is employed in conjunction with pairing in time of the OFDM frequency subchannel signals to realize increased transmit diversity without rate loss.

Disclosed is a digital broadcasting transmission/reception system having an improved reception performance and a signal-processing method thereof. A digital broadcasting transmitter comprises a TS stream generator for inputting robust and normal packets having stuff bytes in predetermined positions and generating dual TS stream by inserting the robust packets between the normal packets; a randomizer for randomizing the dual TS stream; a stuff byte exchanger for replacing the stuff bytes of a randomized data streams from the randomizer to a predetermined known data; and an encoder for encoding a data streams to which the known data is inserted. Accordingly, the present invention detects the known data from a signal received from a reception side and uses the detected known data for synchronization and equalization, so that the digital broadcasting reception performance can be improved at poor multipath channels.

A single frame format is employed by a millimeter wave communication system for single-carrier and OFDM signaling. A Golay-coded sequence in the start frame delimiter (SFD) field identifies the data transmission as single carrier or OFDM. Complementary Golay codes are employed in a channel estimation field to allow a perfect estimate of the multipath channel to be made. Marker codes generated from Golay codes are inserted periodically between slots for tracking and/or for reacquiring timing, frequency, and multipath channel estimates. The length of the marker codes may be adapted relative to the multipath delay spread.

A method and system is described for more optimally managing the usage of a wideband space-time multipath channel. The wideband space-time multipath channel is decomposed into a plurality of orthogonal sub-channels, where the orthogonal sub-channels having the best signaling characteristics are used for transmitting one or more signal streams. For purposes of decomposing the wideband space-time multipath channel into a plurality of orthogonal sub-channels, channel estimates are determined for each signal propagation path. A closed-form singular value decomposition of the channel corresponding to each receive antenna before coherent combining is utilized to obtain an orthogonal decomposition of the overall effective space-time channel after coherent combining. By using the overall effective space-time channel after coherent combining rather than before coherent combining, the complexity and correspondingly the resources required for obtaining the orthogonal sub-channels is significantly reduced. The method and system further provide for transmit power to be allocated between the selected sub-channels in order to minimize the effective bit-error rate for a fixed average throughput or to maximize average throughput for a fixed minimum effective bit-error rate.

A digital broadcasting transmission and/or reception system having an improved reception performance and a signal-processing method thereof. A digital broadcasting transmitter comprises a TRS encoder for to TRS-encode an MPEG-2 transmission stream having null data for inserting an SRS data and a TRS parity at predetermined positions, randomizer to input and randomize data stream from the TRS encoder, a SRS exchanger to replace the null data for inserting the SRS data to the known data, and an encoder for encoding a data streams to which the Known data is inserted. Accordingly, the present invention detects the known data from a signal received from a reception side and uses the detected known data for synchronization and equalization and further uses the TRS parity for correcting error of the received signal, so that the digital broadcasting reception performance can be improved at poor multipath channels.

Disclosed is a digital broadcasting transmission/reception system having an improved reception performance and a signal-processing method thereof. A digital broadcasting transmitter comprises a randomizer for inputting dual TS stream consists of robust and normal packets having stuff bytes inserted in predetermined positions and randomizing the dual TS stream; a stuff byte exchanger for replacing the stuff byte of a randomized data stream from the randomizer to a predetermined known data; and an encoder for encoding a data streams to which the known data is inserted. Accordingly, the present invention detects the known data from a signal received from a reception side and uses the detected known data for synchronization and equalization, so that the digital broadcasting reception performance can be improved at poor multipath channels.

A method and apparatus for joint time and frequency synchronization for orthogonal frequency division multiplexing (OFDM) systems. A multitone pilot signal is sent in a designated OFDM symbol period. The receiver synchronizes to the pilot signal in a two-stage procedure. The first stage estimates the frequency offset coarsely with a frequency-domain correlation method and estimates the time offset with smoothed time-domain correlation. In a multipath channel, the smoothed time offset estimate is used to locate a cyclic prefix interval which captures the maximum total signal energy. The second stage improves the frequency estimate with a computationally efficient numerical optimization method.

A MIMO method based on distributed transmission sources for transmitting a downlink data stream between M transmitting antennas and a mobile terminal having P receiving antennas, M and P>1, channels from at least two transmitting antennas to one of receiving antennas have different multipath distributions, said method comprises transmitting corresponding M substreams to the mobile terminal by using the same spreading code; estimating the multipath channel matrix; and processing the signal according to the multipath channel matrix to restore the downlink data stream, the estimating including measuring the total number of actual multipath received components having different delays in the transmitted signals; constructing the multipath channel matrix by taking the number as the multipath number, so that if the signal transmitted by one of the transmitting antennas to the receiving antenna has no multipath component corresponding to one of the delays, the channel parameter corresponding to the transmitting antenna, the receiving antenna and the delay is set as 0, the transmitting comprises adjusting the gain of said M sub-data streams based on the average signal quality measurement of uplink signals from the mobile terminal to said M transmitting antennas, so that average path losses of respective downlink channels are substantially equal.

The specification and drawings present a new method, system, apparatus and software product for defining an adaptive preamble length of a preamble for a continuous connectivity transmission using a control channel, e.g., a UL (uplink) dedicated physical control channel (DPCCH), for transmitting the preamble. Such a preamble would reduce the accuracy requirement for the initial power setting after a transmission gap and also help the channel estimation and the synchronization of a data channel, e.g., an enhanced dedicated channel (E-DCH). The preamble length can be optimized and defined using a predetermined criterion depending on: a) a degree of fading of a multipath channel which is used for transmitting data on the data channel and/or b) a throughput relative to a nominal throughput in the data channel.

A precoding scheme for digital data transmission across multipath channels is described, which improves on existing methods of precoder stability. This precoding scheme uses radial reduction of unstable roots to stabilize the precoder. Furthermore, in a broadband access system in which the preceding scheme is used, all of the precoding and equalization is performed in the subscriber units. This eliminates the problems of equalization and training delays occuring at the base station, thus allowing rapid demodulation of data arriving at the base station for several disparate subscriber terminals units.

A method and apparatus for estimating channel tap delays of multipath components in a CDMA received signal. The search for the tap delays are split into two phases namely, a phase 1 and a phase 2 search. The phase 1 search is a coarse resolution quick search adapted to generate a rough estimate of the location of the tap delays. During this phase, the candidate codes are summed and the input signal correlated with the code sum creating an ambiguity in the code associated with the multipath. A finer resolution slower phase 2 search resolves the code ambiguity present in the initial rough estimates of the phase 1 search. Additional phase 2 correlations may be performed to implement a code-tracking loop.

Techniques to process a number of “received” symbol streams in a Multiple-Input Multiple-Output (MIMO) system with multipath channels such that improved performance may be achieved when using successive interference cancellation (SIC) processing. In an aspect, metrics indicative of the quality or “goodness” of a “detected” symbol stream are provided. These metrics consider the frequency selective response of the multipath channels used to transmit the symbol stream. For example, the metrics may relate to (1) an overall channel capacity for all transmission channels used for the symbol stream, or (2) an equivalent signal-to-interference noise ratio (SNR) of an Additive White Gaussian Noise (AWGN) channel modeling these transmission channels. In another aspect, techniques are provided to process the received symbol streams, using SIC processing, to recover a number of transmitted symbol streams. The particular order in which the symbol streams are recovered is determined based on the metrics determined for symbol streams detected at each SIC processing stage.

A channel parameter estimation method adapted to a wireless communication system is proposed. The wireless communication system includes a transmitter and a receiver. The proposed method includes following steps. The transmitter transmits a plurality of pilot signals to the receiver by using one of a plurality of preconfigured sparse random pilot patterns. The receiver receives the pilot signals, performs a channel parameter estimation on the pilot signals by using a compressive sensing algorithm to obtain a multipath channel number, and selects a pilot pattern for a next cycle among the preconfigured sparse random pilot patterns according to the multipath channel number and a current pilot number. Additionally, the receiver transmits feedback information associated with the selected pilot pattern to the transmitter.

A transmitting apparatus is disclosed. The transmitting apparatus includes a preamble symbol inserter configured to insert to a frame a preamble symbol including a signaling information, a guard interval inserter configured to insert guard intervals to both ends of the preamble symbol, and a transmitter configured to transmit a frame including the preamble symbol and the guard intervals, wherein one of the guard intervals which are inserted to both ends of the preamble symbol comprises a pseudo random noise (PN) sequence and another guard interval includes one between the PN sequence and a part of the signaling information. Accordingly, no separate algorithm to estimate size of FFT of the preamble symbol and the guard interval is necessary, robust signal detection and synchronization is enabled by the PN sequence inserted to the guard interval, and compensation of interference which is generated under multipath channel environment deems to be easier.

A symbol sequence contained in a received signal comprising a cyclic convolution of a Walsh code multiplexed signal and a channel impulse response of a multipath channel is detected using Walsh Hadamard domain equalization techniques. The method comprises converting the received signal and the channel impulse response of the multipath channel from the time domain to the WHT domain, and determining the symbol sequence based on equalizing the received signal in the WHT domain using WHT spectra of the channel impulse response to remove inter-symbol interference from the received signal due to cross-correlation between Walsh codes.

The invention discloses a method for phase and symbol synchronization, channel estimation and frequency domain equalization of an SC-FDE system, wherein a receiver in the method performs frame synchronization, fraction multiplication channel estimation and fraction multiplication frequency domain equalization on an over-sampling signal, and eliminates influences cause by carrier phases, multipath interferences and frame synchronization errors through the fraction multiplication channel estimation and the fraction multiplication frequency domain equalization so as to achieve the timing synchronization and the frequency domain equalization of a carrier phase and a symbol of a modulated signal. The method has the characteristics of strong anti-multipath capability, capability of estimating and equalizing a multipath channel with fraction multiplication symbol period intervals, no limitation to signal demodulation mode and signal demodulation and detection method and the like, and is especially suitable for single-carrier frequency domain equalization and synchronization of modulation (such as FQPSK modulation, SOQPSK modulation, CPM modulation and other efficient linear modulations) signals with efficient power and spectrum.

There is disclosed a system and method for sending low rate data on a packet basis in an 8-VSB standard data packet stream. The system of the invention comprises an 8-VSB signal transmitter that is capable of transmitting either standard full rate data packets or low rate data packets. A low rate data packet contains less data than is normally contained in a standard data full rate data packet. Each data byte in a low rate data packet contains information bearing bits and non-information bearing bits. The system is capable of assigning appropriate bit values to the non-information bearing bits in each data byte of a low rate data packet so that each low rate data packet will be properly encoded for transmission within an 8-VSB standard data packet stream. High definition television signals composed of low rate data packets possess increased resistance to noise and multipath channels.

An output signal of digital baseband processing section 41 is directly input, and receiver noise adding section 103 adds receiver noise simulating the SNR variation due to fading to the signal while keeping an entire signal level constant in single-path channel simulation, while in multipath channel simulation, instantaneous variation adding section 101 and short-term interval variation adding section 102 add only amplitude variations to respective signals of paths, and automatic gain control section 104 keeps a level of the path-combined signal constant, whereby it is possible to evaluate channel performance of digital baseband processing section 41 without waiting for development of radio circuit 53, i.e. without an AGC circuit and AFC circuit in reception system 50.

The present invention relates to a new parallel interference cancellation (PIC) configuration where the PIC is implemented after the rake reception and multipath combining. In the invention disclosed, the regenerated interference contributions (functions of signature sequence cross-correlations) for multiuser detection (MUD) in a multipath radio channel are explicitly filtered through the estimated multipath channels, and stored. These stored quantities already contain the effect of the channel, and only need updating according to the rate of change of channel dynamics, and not the symbol period. During each symbol period, interference is computed from each interfering user to each desired user using current estimates of symbol decisions and the aforementioned interference contributions. The precomputation of the interference contributions, which are valid for a sequence of symbols, allows for extremely low complexity baseband processing in the receiver.

Described is a method for compensation of an OFDM signal propagating through Doppler-distorted, time-varying multipath channels. The method is based on low-complexity post-FFT signal processing. Minimum mean square error combining of signals is performed for signals received at spatially-distributed receiver elements using adaptive channel estimation and phase tracking. Doppler shifts are modeled as a consequence of motion-induced time compression and dilation. The Doppler rate is assumed constant over one OFDM block but can vary between OFDM blocks. Thus a non-constant Doppler shift is accommodated by the method. Non-uniform Doppler compensation across subchannels is based on adaptive estimation and prediction of the Doppler rate. A single adaptively estimated parameter is used to track the phases of all the carriers and channel estimates are updated on a block by block basis.

The present invention relates to an apparatus and method for estimating down link wide-band interference power and noise power in a mobile communications system. By using filters that are matched to the multipath channels of a number of base stations the received powers from the base stations may be differentiated and calculated. The impulse responses of the multipath channels are estimated and the filters are matched such that the impulse response of each filter is the complex conjugate of the time reverse of the estimated impulse response of one of the multipath channels. White noise is modelled as a signal that has passed a single-ray channel. The received noise power is estimated by means of the output signals from the matched filters and the total received signal.

A maximum likelihood sequence estimator (MLSE) equalizer device being included in an MLSE sub-receiver includes a feedforward circuit responsive to input data for processing the same to generate feedforward circuit output, said input data being generated from transmitted data being transmitted by wireless transmission, in accordance with an embodiment of the present invention. The MLSE equalizer device further includes a feedback circuit responsive to said input data for processing the same to generate feedback circuit output. The MLSE equalizer device further includes an equalizer training module responsive to said feedforward circuit output and said feedback circuit output for training said MLSE equalizer device by minimizing the difference between said feedforward circuit output and said feedback circuit output, said MLSE equalizer device being trained to generate equalized data, said MLSE sub-receiver for decoding said equalized data to generate decoded transmitted data by mitigating the effects of multi-path communication channel due to wireless transmission of said transmitted data.

The invention provides an OFDM carrier frequency offset estimation method for packet transmission, which comprises the following steps: 1) performing IFFT conversion on frequency domain symbols to obtain time domain training symbols of two same repetition modules; 2) adding cyclic prefixes with the length of L on the front of the time domain training symbols to form integral OFDM symbols, and obtaining received OFDM signals carrying frequency offset epsilon through a multipath channel; 3) rotating phases with pi epsilon by N/2 spaced received sample values in the received OFDM signals to obtain fine frequency offset estimation epsilon [fine]; 4) performing fine frequency offset compensation on the received OFDM signals to obtain OFDM signals after the compensation; 5) performing FFT conversion on training symbol parts of the compensated OFDM symbols after the cyclic prefixes are removed so as to obtain receiving end modulation frequency domain symbols; 6) detecting peaks of cyclic shift of the receiving end frequency domain symbols and sending end frequency domain symbols to obtain coarse frequency offset estimation; and 7) performing coarse frequency offset compensation on the receiving end modulation frequency domain symbols in a receiving end frequency domain, and summing up the coarse frequency offset estimation and the fine frequency offset estimation to obtain the carrier frequency offset estimation.