摘要:
A method for demodulating a carrier wave that is modulated using a digital symbol sequence and that is transmitted over a noise-impacted channel, the ideal edge shapes of possible transitions between two symbols being known and stored in memory as reference edges, and a received edge being scanned and digitalized using a scanning frequency that is a multiple of the frequency of the symbol sequence. In particular, for detecting a received and scanned edge, all scanning values are used for calculating Euclidean distances from at least two reference edges, and the reference edge associated with the lowest Euclidean distance is selected. A Viterbi algorithm is applied to a sequence of estimated edges (rather than to an estimated symbol sequence) and the specific Euclidean distances between the edge received in one symbol period and the reference edges are considered as the costs of one trellis branch of the Viterbi algorithm.
摘要:
In a method for demodulation of multistage-modulated data, correspondence variables (decision variables) are determined from the comparison of the received signal with stored signals, and these correspondence variables are converted into a posteriori symbol probabilities. The received signal represents a symbol which in turn represents a data group. The a posteriori symbol probabilities are now accounted for in turn such that one individual probability information item is produced for each bit of a data group, which information indicates the probability of a relevant bit being +1. Reliability values are determined from these bit-specific probabilities, and these reliability values are output, together with the bits, as soft bits.
摘要:
FM Signals are demodulated on an entirely digital basis by converting the digitalized signal into a pair of signals which are substantially Hilbert transforms of each other. This requires at least one pair of nonrecursive filters having lower signal sample rates at the output than at the input. Each signal is delayed by one output sample interval, so that cross products of the delayed and undelayed Hilbert transforms can be formed, and the difference between them obtained. Finally, an arc-sine table is used to remove sine-function distortion. A single multiplier-accumulator provided with extra registers can perform all of the necessary arithmetical operations at the speeds required.
摘要:
Multi-phase/multi-level modulation data signals recorded on tape after conversion from original digital data are first converted to complex digital signals in an analog-to-digital converter in which the sampling rate is set by a pulse generator frequency controlled by the received signals through a control loop which develops a frequency control voltage (A). The complex digital signals have their real and imaginary parts separately filtered by filters of variable propagation time, but of constant bandwidth to produce complex signals to which the nearest permissible output complex signal (reference signal) is selected by a decision circuit (17), for final conversion to binary signals by a decoder (19) and a shift register (20). Timing shift correction is based on comparison of the received signals and reference signals of the decision stage to produce a control signal (.phi.) which further processed by addition to its previous value to produce a timing correction signal (A) which is applied both to the pulse generator for the sampling frequency of the analog-to-digital converter and to control the propagation time of digital non-recursive filters (14, 15). The timing correction signal (A) control of the filter propagation time makes possible a rapid timing shift correction that overcomes tape jitter effects. It is not necessary to stabilize the received carrier frequency because the tap recording preserves the relation between the sampling/keying frequency and the carrier frequency.
摘要:
The influence of a DC offset with a carrier-frequency offset at the same time is reduced in that the values of the assumed or determined DC offset and of the assumed or determined carrier-frequency offset are included in the determination of reliability information for one sub-carrier in the multicarrier system, and the reliability information is corrected in this way. A factor M, where M
摘要:
For compensation of the effects of multi-path reception, a cascade distortion corrector composed of distortion corrector blocks successively connected in series is provided for a digital FM demodulator that needs non-recursive filtering. Each distortion corrector block produces an increase of the phase rotation and of the propagation time as well as a reduction of the reflection factor of the input signal. The cascade distortion corrector leads to a significant reduction of the hardware expense compared to the previously used transversal type filter structures. Sufficient compensation of the multi-path reception effects can be obtained by connecting five or six distortion corrector blocks one after the other.