It is most difficult for any wireless communication product to achieve bit synchronization. In consideration of digital signal being a string of consecutive code sequence and the existence of noise and inter-symbol interference, in order to get a more reliable decision and reduce bit error rate of a system, the related demodulated baseband signal should be voted at a optimal sampling time of each code element period (i.e. when a eye pattern opens to its limit) to recover an orderly and regular signal code flow. Because of a signal transmission delay, such a time is often unknown and needs to be obtained by timed recovery of bit synchronization. Therefore the timed recovery of bit synchronization is crucial for decoding accuracy.
A most frequently used bit synchronization technology is Maximum Likelihood Estimate, which is a synchronization technology based on Fast Fourier Transform (FFT) algorithm, and is called Late/Early Gate bit synchronization technology. Theoretically, the Maximum Likelihood Estimate could be optimized, but the calculation is the most complicated, and is not suitable for digitization. The FFT algorithm is mainly used in communication system of OFDM (orthogonal frequency division multiplexing), which must process a received signal with some non-linear operations to obtain a desired timing line spectrum. For example, in a conventional non-data-aided timing recovery system, after non-linear processing is applied to the received signals, clock signals are extracted via a narrow band bandpass filter or a PLL (phase locked loop). Such a method is also called Tone filtering with complicated calculation. Currently the Late/Early Gate technology is mainly applied to communication systems with PSK (phase shift keying) and QPSK (quadrature phase shift keying) modulation.
The DMR is a new standard for professional digital communication newly released by ETSI (European Telecommunication Standards Institute). Considering that no DMR product has been released in China, this invention, aiming at a research and development of DMR products, provides a DMR bit synchronization technology that facilitates realization of digitization and reduces calculation.
USPTO Backgrounds
USPTO Backgrounds