In an OFDMA-based cellular system, a frame of a downlink signal includes a common slot and traffic slots. The common slot includes a synchronization preamble and a cell search preamble. The synchronization preamble has a structure for synchronizing time and frequency, and the cell search preamble has a cell search structure. The traffic slot includes pilot symbols provided on the time and frequency axes. A cyclic prefix is used to estimate initial symbol synchronization, and the initial symbol synchronization and the synchronization preamble are used to synchronize the frame. The synchronization frame and the cell search preamble are used to estimate time and frequency synchronization. The cell search preamble is used to search cells. When the initial synchronization is performed, the cyclic prefix is used to track the frequency, the synchronization preamble is used to track symbol synchronization, and the cell search preamble is used to track fine frequency synchronization.

Method and apparatus for embodying and synchronizing downlink signal in mobile communication system and method for searching cell using the same

A method of monitoring an element in wireless communication system is provided. An operational noise measurement is obtained by measuring a noise value outside of a bandwidth of a first device, but within a bandwidth of a second, subsequent device. The operational noise measurement is alternatively obtained by tuning an input band of the element to shift the input band partially or completely outside of a bandwidth of a first device to create an open band or by suppressing an input of the antenna and measuring noise within the open bandwidth of the element of the wireless communication network. A stored parameter is retrieved and compared to the measured operational noise. Alternatively, a leakage signal of the element may be received at a signal receiver and compared to a reference. The reference is a function of components of the wireless communication system in a leakage path of the leakage signal.

Gain measurement and monitoring for wireless communication systems

Techniques for generating preamble sequences for OFDM and OFDMA communication systems based on CAZAC sequences (120) with desired properties of constant amplitudes (CA) and zero autocorrelation (ZAC). Such preamble sequences may be used for synchronization and identification of individual transmitters. For example the OFDMA symbol is constructed using a CAZAC sequence in the frequency-domain (160) and the resulting time-domain waveform is a near-CAZAC sequence (170).

Transmission and reception of reference preamble signals in ofdma or ofdm communication systems

Eyeglass and eyeglass components

In a digital receiver for receiving COFDM modulated television signals or the like, consecutive samples are compared with a detection threshold and the number of samples having amplitudes greater than the threshold is determined. This is compared with a further threshold and, if the number of such samples exceeds the further threshold, affected samples are blanked to zero. Similarly, an automatic gain control loop is disabled when the samples are blanked. A demodulator forms the difference in phase of pilot carriers from symbol to symbol. If the variance of the phase differences exceeds an averaged value, this indicates the presence of impulsive noise and is used to inhibit signal correction techniques within the demodulator. Noise energy is thus reduced and propagation of effects resulting from impulsive noise from symbol to symbol is substantially reduced.

Method of and apparatus for detecting impulsive noise, method of operating a demodulator, demodulator and radio receiver

An impulse noise reducer detects impulse noise in an audio signal by detecting and smoothing the high-frequency amplitude of the audio signal, attenuating the non-smoothed amplitude according to the smoothed amplitude, and comparing the attenuated amplitude with a threshold. Impulse noise is discriminated from high-frequency audio components because the latter tend to occur in longer-lasting bursts and are therefore attenuated more strongly. The impulse noise reducer is simplified because it does not have to perform intermediate-frequency signal processing, and its sensitivity is not affected by adjacent-channel signals because these signals are substantially absent from the audio signal. The impulse noise reducer can be implemented by digital signal processing, and is suitable for use in a medium-wave AM audio broadcast receiver.

Impulse noise reducer detecting impulse noise from an audio signal

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 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

An audio signal noise reduction system comprises a noise detecting circuit 11 for detecting a noise from an audio signal and outputting a detection signal indicating a start time and an end time of a noise period of the noise, an LPF 12 for extracting a low frequency component of the audio signal, an HPF 14 for extracting intermediate and high frequency components of the audio signal, a polynomial interpolation circuit 13 for polynomial-interpolating the noise period of the low frequency component being extracted, a mute circuit 15 for muting an output level of the noise period of the intermediate and high frequency components being extracted, and a signal synthesizing circuit 16 for synthesizing the low frequency component whose noise period is polynomial-interpolated and the intermediate and high frequency components the level of whose noise period is suppressed to thus output the audio signal

Audio signal noise reduction system

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.

Ishida Masayuki

Papers

Impulse noise reducer detecting impulse noise from an audio signal

Frequency searching method and digital audio broadcast receiver

Digital audio broadcast receiver and tuning method thereof

Audio signal noise reduction system

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