Mitsubishi Denki Kabushiki Kaisha

Mitsubishi Electric Corporation

Tadatoshi Ohkubo

Kenichi Taura

Masahiro Tsujishita

Masayuki Ishida

Yoshiharu Ohsuga

Masakazu Morita

A digital broadcast receiving apparatus has two systems as a receiving system: a first receiving demodulation section including a first tunerand the like; and a second receiving demodulation section including a second tunerand the like. A controllerestablishes either a first receiving mode or second receiving mode. In the first receiving mode, both the receiving systems receive the broadcasting waves of the same station to be viewed according to the signals from a vehicle speed detecting sectionand receiving level detecting sectionsand. In the second receiving mode, one of the two receiving systems receives the broadcasting wave of the station to be viewed, and the other of them receives the broadcasting wave of another station.

Digital broadcast receiving apparatus

A digital audio broadcast receiver detects frame synchronization signals, measures the pulse widths of and intervals between the detected frame synchronization signals, and stores this information in a memory, together with a history of counts of frame synchronization signals, and stores this information in a memory, together with a history of counts of frame synchronization signals of certain widths detected at certain intervals. This information is retained in the memory until frame synchronization is acquired, as determined from the stored count values, enabling frame synchronization to be acquired quickly despite the false detection of frame synchronization signals due to noise.

Digital audio broadcast receiver acquiring frame synchronization quickly in the presence of noise

A digital audio broadcast receiver is tuned by performing a sliding correlation on data demodulated from a phase reference symbol, correlating the demodulated data with known data at negative carrier numbers and, separately, with known data at positive numbers, thus obtaining a lower correlation coefficient and an upper correlation coefficient. The peak sum of these two correlation coefficients, as found in the sliding correlation, is recognized as valid if the two correlation coefficients do not differ greatly in magnitude, and do not differ greatly in phase angle. The tuning is adjusted only according to sliding shifts corresponding to valid peak sums, thereby avoiding frequency control errors.

Digital audio broadcast receiver and tuning method thereof

A digital broadcast receiver receiving a multi-carrier signal controls the timing of a sampling window, used in demodulation of the multi-carrier signal, according to a channel impulse response waveform obtained by processing of a synchronization signal occurring in the multi-carrier signal. The values in the channel impulse response waveform are multiplied by corresponding weighting coefficients, the resulting products are added to obtain a weighted sum, and the timing of the sampling window is adjusted according the weighted sum. Under a wide variety of reception conditions, this control scheme avoids inter-symbol interference, and leaves adequate timing margins to accommodate new signal components that may appear.

Digital broadcast receiver using weighted sum of channel impulse response data to adjust sampling window

A digital audio broadcasting receiver comprises a phase error detector for detecting a phase error from data from a differential demodulator, an average value processing unit for determining the average value of phase errors, a memory for storing the phase errors of the carriers outputted from the phase error detector, and a phase error correcting unit which excludes a phase error whose sign is opposite to that of the average value among the phase errors stored in the memory, and determined the average value of phase errors again, thereby making it possible to obtain a phase error signal which is less affected by leakage from other carriers.

Digital audio broadcasting receiver

To control the oscillation frequency of a local oscillator, a digital broadcast receiver demodulates a phase-reference symbol contained in an orthogonal frequency-division multiplexed broadcast signal to obtain an array of complex values, selects several sets of values from the array, multiplies each selected value by the complex conjugate of a value offset by N positions in the array (where N is a fixed integer that may be equal to zero), averages the results in each set, takes differences between the average values, or between sums of these average values, thereby obtains two difference values, and calculates a frequency offset from the difference values. Each set of values is taken from positions at which the known reference-symbol values satisfy certain conditions in relation to the known values at adjacent positions.

Digital broadcast receiver

When an edge detecting unit detects a falling edge of a digital audio broadcasting (DAB) signal, a time instant of a timer, which has a periodic characteristic, is stored via a calculating unit into a memory. If there is one piece of data continued a number of times, when an output value of a timer becomes a value of this data offset by a frame time period, the calculating unit resets the timer. Subsequently, when the value of the timer becomes equal to the period length T, the calculating unit resets the timer and at the same time, outputs an L level to an output terminal only during a preselected time period after the timer is set to 0. Accordingly, even when another signal is mixed into a frame synchronizing signal of a DAB signal, the synchronizing signal timing is detected without increasing the time required to detect a frame header.

Synchronizing signal detecting apparatus

To control the oscillation frequency of a local oscillator, a digital broadcast receiver demodulates a phase-reference symbol contained in an orthogonal frequency-division multiplexed broadcast signal, modifies the resulting frequency-domain data by multiplication with complex conjugates of known data encoded in the phase-reference signal, under different assumed frequency offsets, converts the modified data to time-domain data, and thereby detects a first frequency error equal to a multiple of the subcarrier spacing and a second frequency error not exceeding the subcarrier spacing. Differential phase error is also detected. The oscillation frequency is adjusted to correct the first frequency error and differential phase error; then the second frequency error is used to correct for ambiguity in the differential phase error.

A digital audio broadcast receiver searches for a receivable digital audio broadcast signal by first searching for a signal, having at least a predetermined power level, in which frame synchronization symbols can be detected. This stage of the search is made by searching a known frequency grid, or by scanning in steps approximately equal to the bandwidth of the digital audio broadcast signal. After frame synchronization symbols have been detected, the receiver attempts to find the center frequency of the received signal, changing the receiving frequency in steps less than the bandwidth of the digital audio broadcast signal, if necessary. A prompt indication that a receivable digital audio broadcast signal has been found is given when frame synchronization symbols are detected, or when the center frequency is found.

Frequency searching method and digital audio broadcast receiver

A digital broadcasting receiver reduces the amount of operations in timing synchronization processing while reducing circuit scale and power consumption. Selective data extraction thins out and band-limits input data from demodulation data of phase reference symbols subjected to known modulation as synchronizing signal to reduce the number of data, so that the amount of required operations in phase correcting, IDFT and peak detecting can be reduced.

Digital broadcasting receiver

To control the oscillation frequency of a local oscillator, a digital broadcast receiver demodulates a phase-reference symbol contained in an orthogonal frequency-division multiplexed broadcast signal. The resulting frequency-domain data are modified by multiplication with complex conjugates of the known data encoded in the phase-reference signal, under different assumed frequency offsets between the frequency-domain data and known data. The results are converted to time-domain data, yielding one time series for each assumed frequency offset. One value is taken from each time series, these values are compared, and the oscillation frequency is adjusted according to the comparison results. A digital broadcast receiver for receiving a PSK-OFDM signal, having a local oscillator with a controllable oscillation frequency, a mixer for down-converting said PSK-OFDM signal to an intermediate-frequency signal by mixing said PSK-OFDM signal with a signal generated by said local oscillator, and demodulating circuits for obtaining an array of frequency-domain data from said intermediate-frequency signal, said array of frequency-domain data representing subcarrier phase information of said PSK-OFDM signal. The digital broadcast receiver further including a phase modifying means, an inverse-fast-Fourier-transform means, a peak detecting means, and a frequency-deviation detector. The digital broadcast receiver can also include a data selecting means in addition to the elements previously described.

Digital Broadcast receiver and method of tuning control

It is an object to correct a frequency deviation at the time of reception of a digital signal in which each carrier is subjected to phase modulation and orthogonal frequency division multiplexing (OFDM). A vector of fixed pattern symbols for reference of received carriers is multiplied by a vector of conjugate complex numbers of the defined values for each element. In the result, elements separated by the same numbers forward and backward from an element at a particular carrier frequency are multiplied together and the results are added. The same processing is applied to cases in which the elements of the vectors are mutually shifted by a plurality of elements from a certain correspondence and synchronization control to the broadcasting frequency is provided on the basis of a value which maximizes the absolute value in the results of the addition and the correspondence at that time.

A digital receiver uses a local oscillator to down-convert an orthogonal frequency-division multiplexed signal that has been modulated by differential phase-shift keying, and performs further processing to obtain a differentially demodulated array of phase values. According to a first aspect of the invention, the digital receiver detects a carrier offset, applies a corresponding phase correction to the values in the array, then shifts the entire array by an amount corresponding to the carrier offset. As a result, the local oscillator need be tuned only in a frequency range equal to the subcarrier spacing. According to a second aspect of the invention, the local oscillator is tuned within a range equal to the subcarrier spacing multiplied by a certain integer, the array is shifted by a multiple of this integer, and the phase correction is eliminated.

Method and digital receiver for receiving orthogonal frequency-division

A digital sound broadcasting receiver and method receives a radio wave from a digital sound broadcasting station, demodulates the radio wave into baseband signals at a tuner, subjects the signals to demodulation, performs error detection and error correction at signal processors to obtain digital data, and inputs the digital data into an audio circuit to obtain audio or data output. A CRC error rate detector 13 for a fast information channel (FIC) for APC pseudo lock releasing action on demodulating the signals is arranged to determine, based on the possibility of an error rate of an error-detecting code (CRC) of the FIC, whether an APC pseudo lock state occurs, and to control releasing action for the APC pseudo lock state.

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Tokyo, Japan

Tadatoshi Ohkubo