16 quadrature amplitude modulation (QAM) demodulation synchronization method

A carrier synchronization, in-phase quadrature technology, applied in the field of communication, can solve the problems of 90° phase ambiguity, large application limitation, low precision, etc., to achieve the effect of improving tracking accuracy and speed, easy FPGA implementation, and improving system performance

Inactive Publication Date: 2015-08-05
NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
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  • Abstract
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  • Application Information

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Problems solved by technology

However, since 16QAM is a non-constant envelope signal, if the traditional QPSK Costas ring is used in the carrier recovery process, it is easy to cause defects such as low precision and slow tracking speed.
In addition, the FPGA tool software with DSP Builder as the core to develop QAM modem is simple and easy, but its stability and portability are poor, and its application is limited.
Due to the 90° phase ambiguity problem in 16QAM, if the carrier generated during carrier recovery is not the same frequency and phase as the carrier during modulation, decoding errors will occur

Method used

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  • 16 quadrature amplitude modulation (QAM) demodulation synchronization method
  • 16 quadrature amplitude modulation (QAM) demodulation synchronization method
  • 16 quadrature amplitude modulation (QAM) demodulation synchronization method

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Embodiment Construction

[0048] The complete modulation and demodulation process of the 16QAM signal is described below in conjunction with the accompanying drawings, and verified by FPGA hardware.

[0049] 1. Modulation principle

[0050] 1. Differential coding

[0051] Considering the phase ambiguity problem of 16QAM, the transmission signal adopts partial differential coding, that is, only the first two bits of 4-bit parallel data are differentially coded. Compared with full differential coding, this coding method reduces the number of bits of differential coding, thus reducing error diffusion and having better bit error performance.

[0052] In partial differential encoding, the first two bits a 1 a 2 Specifies the quadrant of the signal and differentially encodes it; the remaining two bits b 1 b 2 It is used to specify the configuration of signal vectors in each quadrant, and make the configuration exhibit π / 2 rotational symmetry, such as figure 1 shown.

[0053] encoding rules:

[0054] ...

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Abstract

The invention provides a 16 quadrature amplitude modulation (QAM) demodulation synchronization method. The method comprises a first step of adding a power detection technology on a traditional costas loop of quadrature phase shift keying (QPSK) so as to finish carrier recovery; a second step of performing matched filtering on each same-phase orthogonal component signal, so as to reduce noise effect and prepare for bit synchronization; a third step of performing bit timing recovery on same-phase orthogonal signals through an "early-late gate"; a fourth step of setting a threshold, and performing sampling judgment and 4-2 level conversion on each of two paths of signal to obtain parallel signals; and a fifth step of performing differential decoding and parallel-serial conversion on the parallel signals, then recovering and obtaining original signals. According to the introduced novel carrier synchronization technology, the carrier recovery is finished by using a phase-locked loop; on the basis of the traditional costas loop, the power detection technology is added, so that the linear output of a phase discriminator is guaranteed, the tracking precision and speed are improved, and the novel carrier synchronization technology passes field programmable gate array (FPGA) hardware verification.

Description

technical field [0001] The invention relates to the communication field, in particular to a 16QAM demodulation synchronization method. Background technique [0002] In the multi-ary keying system, phase keying has advantages in terms of bandwidth and power occupation, that is, the bandwidth occupation is small, and the bit signal-to-noise ratio requirement is low. MPSK (Multiple Phase Shift Keying) and MDPSK (Multiple Differential Phase Shift Keying) have the characteristics of constant envelope and high power efficiency, but they have high side lobes and large spectrum leakage, which is easy to cause spectrum expansion, and with the increase of M , the distance between adjacent phases gradually decreases, the noise margin decreases accordingly, and the bit error rate is difficult to guarantee. Quadrature Amplitude Modulation (QAM, Quadrature Amplitude Modulation) is a modulation technique that performs amplitude modulation on two quadrature carriers often used in modern co...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H04L7/033H04L27/34
Inventor 李畅樊涛王旭东
Owner NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
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