Symbol TIMING estimation

13
PRESENTED BY: Sarbjeet Singh (NITTTR-chandigarh)

Transcript of Symbol TIMING estimation

Page 1: Symbol TIMING estimation

PRESENTED BY:Sarbjeet Singh

(NITTTR-chandigarh)

Page 2: Symbol TIMING estimation

In a digital communication system, the output of the demodulator must be sampled periodically at the symbol rate, at the precise sampling time instants,

tm = mT + τ

Where,T is the symbol intervalτ is a nominal time delay that accounts for the propagationtime of the signal from the transmitter to the receiver.

Page 3: Symbol TIMING estimation

To perform periodic sampling we require a clock signal at the receiver.

The process of extracting such a clock signal at the receiver is called symbol synchronization or timing recovery.

Page 4: Symbol TIMING estimation

Timing recovery is the most critical functions that is performed at the receiver of a synchronous digital communication system.

The receiver must know the frequency (1/ T) at which the outputs of the matched filters or correlators are sampled,

And where the samples to be taken within each symbol interval.

Page 5: Symbol TIMING estimation

The choice of sampling instant within the symbol interval of duration T is called the timing phase.

Symbol synchronization can be accomplished in several ways.

Page 6: Symbol TIMING estimation

In communication systems, the transmitter and receiver clocks are synchronized to a master clock, which provides a very precise timing signal.

In this case, the receiver must estimate and compensate for the relative time delay between the transmitted and received signals.

Page 7: Symbol TIMING estimation

APPLICATION

Page 8: Symbol TIMING estimation

In this method of achieving symbol synchronization the transmitter simultaneously transmit the clock frequency 1/ T or a multiple of 1/ T along with the information signal.

The receiver may simply employ a narrowband filter tuned to the transmitted clock frequency and, thus, extract the clock signal for sampling.

Page 9: Symbol TIMING estimation

ADVANTAGE

This approach has the advantage of being simple to implement.

Page 10: Symbol TIMING estimation

1. The transmitter must allocate some of its available power to the transmission of the clock signal.

2. Some small fraction of the available channel bandwidth must be allocated for the transmission of the clock signal.

Page 11: Symbol TIMING estimation

This method is used in telephone transmission systems that employ large bandwidths to transmit the signals of many users.

Here the transmission of a clock signal is shared in the demodulation of the signals among many users.

Page 12: Symbol TIMING estimation

MERIT

Page 13: Symbol TIMING estimation