Symbol Synchronizer

The symbolic time synchronization algorithm is based on the phased lock loop (PLL) algorithm, which consists of four components:

With OQPSK modulation, the components of the common-mode and quadrature signals are first aligned (as with QPSK modulation) using a status buffer to accumulate the last half of the symbol of the previous input. After the initial alignment, the rest of the synchronization process is the same as with QPSK modulation.

The block diagram shows an example of a synchronizer. In the PLL picture, symbol synchronization works with , the received reference signal after consistent filtering. The PLL character synchronizer outputs a character signal after correcting the clock mismatch between the transmitter and receiver.

The symbolic time synchronizer supports data-free and decision-based synchronization error detector types. This table shows time estimation expressions for different types of synchronization error detector.

Synchronization error detection methods without using data (Gardner (non-data-aided) and Early-Late (non-data-aided)) use the received samples without knowledge of the transmitted signal or the channel evaluation results. Synchronization error detection methods without using data are used to estimate the synchronization error of signals with modulation schemes in which the constellation points are aligned with the axis of common-mode or quadrature synchronization. Examples of signals suitable for these methods include QPSK modulated zero-phase shift signals, which have points in and BPSK-modulated signals with zero phase shift.

Method Early-Late (non-data-aided) similar to the method Gardner (non-data-aided), but the method Gardner (non-data-aided) It works better in systems with a high signal-to-noise ratio, as it has less intrinsic noise than the method Early-Late (non-data-aided).

Methods of synchronization error detection with decision making (Zero-Crossing (decision-directed) and Mueller-Muller (decision-directed)) use the function sign to evaluate the common-mode and quadrature components of the accepted samples, which leads to less computational complexity than that of non-decision methods.

Because decision-oriented methods (Zero-Crossing (decision-directed) and Mueller-Muller (decision-directed)), estimate the synchronization error based on the sign of the common-mode and quadrature components of the signals transmitted to the synchronizer, they are not recommended for constellations in which there are points with zero common-mode or quadrature component.

Common - mode and quadrature the components of the input signals coming to the synchronization error detector, where — estimated synchronization error. Coefficients of the Miller-Muller method and — these are estimates and . Time estimates are made by applying the function sign They belong to common-mode and quadrature components and are used only in methods of detecting synchronization errors with decision making.

The time delay is estimated based on fixed samples of the matched filter, which are asynchronous with the frequency of character transmission. Since the resulting samples do not match the boundaries of the symbols, an interpolator is used to "move" them. Since the time delay is unknown, the interpolator must be adaptive. Moreover, since the interpolator is a linear combination of available samples, it can be considered as a filter output.

A piecewise parabolic interpolator with a Farrow structure and a coefficient is used as an interpolator. (see [1]).

The interpolation control provides the interpolator with a base point index and a fractional interval. The base point index is the reference index closest to the interpolator. The fractional interval is the ratio of the time between the interpolator and its base point index to the interpolation interval.

Interpolation is performed for each sample, and a gating signal is used to determine the output of the interpolator. The synchronizer uses modulo-1 counter interpolation control to provide gating and fractional spacing for use with the interpolator.

The synchronizer uses a proportional integration (PI) contour filter. Proportional gain and the integration gain factor calculated as follows:

and

.

Intermediate member It is defined as follows:

,

where