Abstract
In digital communication systems, different clock frequencies of transmitter and receiver usually are translated into cycle slips. Receivers and transmitters may experience different sampling frequencies due to manufacturing imperfection, Doppler effect introduced by channel or having error in estimation of symbol rate. Timing synchronization in presence of cycle slip for a burst sequence of received information leads to severe degradation in system’s performance. Therefore, the necessity of prior detection and elimination of cycle slip is obvious. Accordingly, the main idea introduced in this paper is to employ the Gardner detector (GaD) not only to recover a fixed timing offset, but also its output is processed such that timing drifts can be estimated and corrected. By deriving a two-step algorithm, first the cycle slips arising from symbol rate offset is eliminated, and then symbol’s timing offset is synchronized in an iterative manner. GaD structure is used in a feedforward structure with the additional benefit that convergence and stability problems, which are typical challenges of the systems with feedback, are avoided. The proposed algorithm is able to compensate considerable symbol rate offsets at the receiver side. Results in terms of BER confirm the algorithm’s proficiency.
Highlights
Timing recovery as a process of sampling at the right time are critical in digital communication receivers
Simulations are carried out with BPSK- and QPSK-modulated signals which are shaped by a square root raised cosine filter with roll-off factor of 0.5 in transmitter, and they are passed through AWGN channel
In order to implement the matched filtering in digital domain, the received signal is sampled with the rate of 10 samples per symbol and a sample rate conversion (SRC) is used at the output of matched filter for conversion of the sample rate to 2 samples per symbol
Summary
Timing recovery as a process of sampling at the right time are critical in digital communication receivers. While the good tracking performance of feedback schemes is not deniable, they require, in counterpart, relatively long acquisition time that makes them unsuitable for burst transmission schemes In this sense, a feedforward structure based on extracting timing delay estimation from the statistics of received samples, and adjusting the time by interpolation is more suitable. Simulation results shows that the performance of the proposed algorithm is very close to the theoretical lower bound (which is derived with the assumption of the perfect synchronization) even when there is a considerable symbol rate offset. The general structure of this paper is as follows: the problem of timing offset and CS are formulated, the proposed algorithm to eliminate CS is derived . The final section is about the conclusion of the introduced algorithm
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