Carrier and Symbol Synchronization

Hardware Software Co-design Final ProjectR91943045 楊進發R91943050 楊雅嵐R91943068 陳宴毅

Outline

IntroductionClock error & Frequency errorCarrier Recovery & Sampling RecoveryImplementResultConclusionReference

Introduction

Wireless communication has received much attention from researchers working on personal communication systems in recent years.

We have observed that in a digital communication system, the output of the demodulator must be sampled periodically, once per symbol interval, in order to recover the transmitted information.

Introduction (cont’)

Since the propagation delay from the transmitter to the receiver is generally unknown at the receiver, symbol timing must be derived from the received signal in order to synchronously sample the output of the demodulator.

The propagation delay in the transmitted signal also results in a carrier offset, which must be estimated at the receiver if the detector is phase-coherent.

Frequency error

Caused by mismatch of carrier and Doppler shift

ΔωT

ω0+ Δω

ω0

Clock error

Caused by clock signal mismatch and Doppler shift

→ Correct sampling clock--> Incorrect sampling clock

Carrier Frequency Recovery

Carrier recovery is to synchronize the locally generated carrier with the carrier contained in the received input.

This can eliminate crosstalk between I and Q channel data, thus increasing output SNR.

Carrier Frequency Recovery (cont’)

• QPSK Decision-Directed Costas Loop

Timing Recovery

To find the correct timing for sample-and-hold or integrate-and-dump devices in the receiver.

Timing Recovery (cont’)

Sample-Derivative Timing Recovery Loop

Implement

QPSK Transceiver Signal

Implement (cont’)

Carrier frequency offset and timing offset

Implement (cont’)

Carrier frequency recovery

Implement (cont’)

Sampling Recovery

Result

․QPSK Transceiver Signal

Result (cont’)

Carrier frequency offset and timing offset

Result (cont’)

Carrier frequency recovery

Result (cont’)

Sampling Recovery

Conclusion

Carrier recovery and timing synchronization are two topics that have been thoroughly investigated over the past three decades.

Symbol synchronization is required in every digital communication system which transmits information synchronously.

Reference

Jen-Shi Wu, Ming-Luen Liou, His-Pin Ma and Tzi-Dar Chiueh, “A 2.6V 44MHz all-digital QPSK direct-sequence spread-spectrum transceiver IC,” IEEE J. Solid-State Circuits, vol. 32,No. 10, Oct. 1997.

John G. Proakis, Digital Communications, McGraw Hill.

R. L. Peterson, Introduction to Spread Spectrum Communications, Prentice Hall, 1995.

Baseband Communication VLSI Lab.