A receiver is synchronised to a signal by studying which among the previously calculated responses to known synchronisation errors corresponds to the response of a real, received signal. A sample sequence decimated from an oversampled signal is compared to model sequences which correspond to decimation at a different distance from the optimum decimation point, and in further processing the employed decimation point is used according to how far from optimum the best correlated model sequence is situated. From the phase angles of the samples, there is calculated an average phase angle change per symbol, and on the basis of that and the known symbol rate, the frequency error in the reception is determined. For each sample of the data burst, there is calculated an individual phase correction by multiplying the individually defined average phase shift per symbol by the distance from a given symbol corresponding to a phase reference value, and by adding the result to said phase reference value. Bursts are received in groups, and timing and frequency errors are predicted on the basis of the trends indicated by preceding groups in order to receive the next group. A unit formed of several groups is used for measuring and predicting the change in the doppler frequency.
A time error compensation arrangement (TCOMP) that compensates for a time error (.epsilon., .DELTA.k) between a transmitter sample clock in a multi-carrier transmitter and a receiver sample clock (CLK) in a multi-carrier receiver (RX1, RX2) includes a digital time correction filter (FILTER, FILTER'), operative in time domain, to compensate for a linearly increasing contribution (.DELTA.k) in the time error (.epsilon., .DELTA.k) and rotation means (ROTOR), operative in frequency domain, to compensate for a second, remaining contribution (.epsilon.) in said time error (.epsilon., .DELTA.k).
A digital communications signal processing apparatus applied to digital radar signal processing and a method therefor are provided. The digital signal processing apparatus in which windowing, Doppler filtering and half phase filtering algorithms are successively performed, includes a storage portion for storing half phase filter coefficients, a first processor for processing windowing and half phase filtering according to a window weighting function using the coefficients stored in the storage portion, and a second processor for receiving an input signal and an output signal of the first processor and processing Doppler filtering.
The invention relates to a system for transmitting packets from interactive terminals to a head station. The terminals intended for consumers are provided with local oscillators which are not very accurate and use carriers having frequency errors which are relatively large with respect to the theoretical reference value (Fp). The invention provides an improvement of the reception of signals having such a frequency shift at the receiver end. To this end, the invention provides a method of estimating the frequency error .DELTA.f, which consists of rapidly obtaining the maximum value of a discrete error function denoted Z(.DELTA.f) for a given accuracy (Acc) by computing the function Z(.DELTA.f) for a minimal number of points.
A receiving apparatus and method for a synchronizing process in the digital communication system is disclosed. A receiving apparatus includes: a A/D converting unit for performing an over-sampling process and outputting over-sampled points; a sample classifying unit for classifying the over-sampled points; a integration unit for integrating classified symbol values; a symbol synchronizing unit for selecting a point of symbol synchronization; a frequency estimating unit for estimating a frequency error; and a digital demodulating unit for demodulating values outputted from the symbol synchronizing unit and the frequency estimating unit to a signal. The present invention can simplify a configuration of the apparatus and reduce an amount of parameter-control. Moreover, the present invention can be used in a burst mode of a digital communication system.
This invention provides a method for bit detection of the GFSK signals at the receiver end. The bit detection is done digitally after the carrier is removed. It employs differential detection incorporated with decision feedback, which uses previous one (so-called on-bit differential detection), or two (so-called two-bit differential detection) bits as correcting information. In addition, synchronization for bit timing and frequency offset resulted from clocks between the transmitter and receiver are also performed with or without preamble as prior information. If preamble is available, the bit timing and frequency-offset bias are estimated from the preamble, which is the case of this present invention. If preamble is not available, this information is estimated directly from the unknown received signals. Once the information about the bit timing and frequency offset is obtained, it is used for the following bit detection.
