Classified by function: carrier synchronization, bit synchronization, group synchronization, network synchronization

Synchronization method: external synchronization method, self-synchronization

Square transformation method and square loop method: modulated signal - square law component - 2fc narrow-band filter - two-way frequency division - carrier output --- 2f narrow-band filter is often replaced by phase-locked loop, and the two-way frequency dividing circuit has different starting points for frequency division. Certainty, the inverted Π phenomenon may occur.

In-phase orthogonal ring method (costas ring): Compared with the square ring, the Costas ring has a lower operating frequency and is easy to implement. And the Costas ring can directly obtain the demodulation output. Costas ring uses multiplication instead of squarer

MPSK carrier extraction: - M square law device - Mfc bandpass filter - loop filter - frequency divider -, the M square ring will have a phase ambiguity of 360°/M

Although the double sideband signal (DSB, etc., 2PSK VSB) that suppresses the carrier contains a carrier component, it is difficult to separate. VSB has no carrier component and cannot be extracted by direct method.

Insert an additional low-power single-frequency signal with a fixed frequency relationship to the carrier into the modulated signal

Correlation encoding of baseband signals prior to modulation

Waveform transformation-filtering method: the unipolar signal becomes zeroed and then narrow-band filtered to extract the component.

Envelope detection-filtering method: a method for extracting bit synchronization information from band-limited PSK signals

Phase locking method: The phase detector compares the received symbol with the local bit synchronization signal. If the two are inconsistent, the phase detector generates an error signal to adjust the phase of the bit synchronization signal.

Supplement: The narrowband filter can be a simple single-tuned loop or a crystal filter or a phase-locked loop. The phase-locked loop is the phase-locked loop method. Divided into two categories: analog phase locking method and bit synchronization loop (quantization synchronizer)

Phase locked loop = signal controller - controller - frequency divider (counter function) - phase comparator (phase comparison between received pulse and bit synchronization signal)

Phase error θc360°/n Tc=T (symbol period)/n

Synchronization establishment time ts=nT

Synchronization hold time tc

Synchronization bandwidth=2T0/2n or F0/2n

Continuous insertion method: concentrated insertion method, looking for special code groups (requirements: an autocorrelation function with sharp unimodal characteristics; easy to distinguish from information codes; appropriate code length, such as: all 0, all 1, 10 alternating Barker code, telephone base group frame synchronization code 0011011)

Interval insertion method: dispersed forms are evenly inserted into the information code stream. Features: No information time slots are occupied, and the transmission efficiency of each frame is high, but the synchronization acquisition time is longer.

Missing synchronization probability P1

False synchronization probability P2

Capture state: (before synchronization is established) The decision threshold increases, m decreases, and the false synchronization probability P2 decreases.

Maintenance state: (after synchronization is established) The decision threshold decreases, m increases, and the probability of missed synchronization P1 decreases.

In the PCM 30/32 system, the frame synchronization capture time is: the time to return to the synchronization state due to out-of-synchronization detection.

When the cross-correlation coefficient between s1 and s2 = -1, the s1 and s2 waveforms are called the best waveforms, also called anti-correlated signals.

Cross-correlation coefficient = 0, no correlation, bit error rate =

Cross-correlation=1 Bit error rate=0.5

The energies of s1 and s2 are not equal pe=