Low-complex-degree timing recovery method for TDS-OFDM system

Abstract

The invention provides a low-complexity timing recovery method in a TDS-OFDM system, belonging to the technical field of digital information processing. The method comprises the steps as follows: intermediate frequency signals are received and sampled by fixed frequency; quasi-baseband complex data is gained by carrying out down transformation on the intermediate frequency sampled signals; the quasi-baseband complex data is re-sampled by an interpolation filter on the basis of decimal delay and sampled enabling signals returned by a loop numerically controlled oscillator; PN correlation is carried out on the re-sampled data to gain the correlation value of the local sequence and the receiving sequence. A simplification error detector extracts timing error information based on the gained correlation value; the timing error information, with noise components filtrated by a loop lowpass filter, is corrected by negative timing error and then input into the numerical control oscillator, and further the decimal delay and enabling signal required by the interpolation filter and a sampler are generated, thus forming a closed loop. The method has the advantages of low complexity, easy realization of hardware circuit and strong compatibility.

Description

technical field [0001] The invention belongs to the technical field of electric communication, and further relates to a method for realizing a low-complexity timing recovery loop in the technical field of digital information processing. technical background [0002] Due to the inconsistency of the transceiver crystal frequency and other reasons, the digital receiver receives the A / D sampling signal and has the influence of timing frequency error and timing phase error, which must be eliminated through the sampling clock synchronization loop. The traditional time-domain timing recovery loop based on interpolation includes several main units such as interpolation filter, timing error detector, loop low-pass filter and digitally controlled oscillator. Wherein, the timing error detector extracts timing error information, typically such as the Gardner algorithm, which utilizes the zero-crossing characteristic of the interpolated data. The Gardner timing error detection algorithm...

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Problems solved by technology

However, the Gardner algorithm also has its own defects, that is, it requires enough zero-crossing points of the signal. For multi-carrier data or high-order QAM modulation data, the algorithm is difficult to work or has poor performance.

Time-domain synchronous OFDM (TDS-OFDM) is the core technology adopted in China's digital terrestrial television standard (GB20600-2006). It uses a combination of PN sequence and OFDM symbol sequence for transmission. Classical algorithms such as Gardner cannot be directly applied.

[0003] According to the relevant characteristics of the frame header structure, Tsinghua University proposed a "Time Domain Synchronous OFDM Receiver Timing Recovery Method and System" (application number: 200410003485.6), and the specific implementation of the technical solution of the patent application is relatively complicated , since the received data is complex data containing multipath, frequency offset and noise, the algorithm includes the realization of the absolute value of the complex

In order to avoid the related square root operation, its square can be used instead of the absolute value, however, the estimation accuracy or range is reduced to a certain extent

If you use the general table lookup method based on the square value, you must know the general range of the input complex number, otherwise it will easily cause overflow

In the timing recovery loop based on PN correlation, the input of the timing error detector is the correlation value, which fluctuates greatly, resulting in excessive resources occupied by the table length and more clocks required for table lookup, which reduces the throughput rate. Obtaining the absolute value of precision is a very worthwhile consideration for hardware implementation

[0004] On the other hand, the above system does not consider the problem of commercial crystal oscillators, because the actual crystal oscillator frequency may be lower than the rated sampling rate, resulting in negative timing errors, such as -10ppm

For the negative timing error in engineering, although it can be implemented by adding interpolation filters and dual-port RAM, it will undoubtedly increase the complexity of loop implementation and control

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