scholarly journals QPSK-Modulation Modem Invariant to the Rotation of the Signal Constellation Plane

2018 ◽  
Vol 14 (2) ◽  
pp. 149-156
Author(s):  
Andrey Sadchenko ◽  
Oleg Kushnirenko
Keyword(s):  
Phase Shift ◽  
Data Transfer ◽  
Binary Sequences ◽  
Frame Synchronization ◽  
Phase Ambiguity ◽  
Loop Filter ◽  
Signal Constellation ◽  
Reference Oscillator ◽  
Signal Demodulation ◽  
Periodic Autocorrelation Function

AbstractIn order to increase the efficiency of dedicated frequency channels, i.e. to increase the specific data transfer rate, multipositional quadrature phase shift keying (QPSK, aka 4-PSK) should be used. The problems with QPSK signal demodulation is a rotation of the signal constellation plane by an angle multiple of 90° and a slow response of the carrier oscillation recovery scheme. The study considers the existing methods for eliminating the phase ambiguity of the recovered carrier frequency in typical QPSK modems, and identifies the shortcoming of a low-speed response oscillation recovery circuit. The authors propose a QPSK demodulator circuit with a fast adjustment of the reference oscillator, which is due to the fact that no loop filter is used in the feedback and that a digital calculator of the required phase shift is used. An algorithm for the frame synchronization restoration with the simultaneous elimination of the phase ambiguity multiple of 90° was also developed using synthesized binary sequences with an ideal non-periodic autocorrelation function (NACF) at even shifts that do not have the rotary symmetry property. The phase ambiguity elimination algorithm proposed in the article can be used as an alternative to standard modems with differential coding.

scholarly journals Study of the corrective ability of sync codes for the matched processing decoder

2018 ◽  
pp. 17-23
Author(s):  
A. V. Sadchenko ◽  
O. A. Kushnirenko ◽  
A. G. Yurkevych ◽  
V. S. Sevastianov
Keyword(s):  
Communication Systems ◽  
Information Transfer ◽  
Noise Immunity ◽  
Side Lobe ◽  
Binary Sequences ◽  
Main Peak ◽  
Side Lobe Level ◽  
Frame Synchronization ◽  
Minimax Criterion ◽  
Periodic Autocorrelation Function

Increase of the operation reliability of the frame synchronization schemes of communication systems affected by interferences might be achieved by using sync sequences optimal according to the minimax criterion and having the best ratio of the maximum side-lobe level to the main peak of the non-periodic autocorrelation function. Obviously, the longer the minimax sequence, the higher its correction ability. However, with the increase in the length of the sync code, a conflict arises between the corrective ability and the speed of data transfer. This is caused by the decrease in the duration of the information section of the frame. At the same time, as the length of the code increases, the complexity of the technical implementation of the decoder synchronization scheme increases as well. This means that when developing an information transmission system, it is necessary to find a compromise between the complexity of the technical implementation of the decoder and the required noise immunity. To solve this problem, it is necessary to study the correcting ability of binary sync codes. The purpose of this work was to study the correcting ability of binary sequences with good non-periodic auto-correlation properties using a reception scheme with matched processing. This article discusses the possibility of using Barker sequences of lengths 7, 11, and 13 and M-sequences as corrective sync codes. The authors carry out an analysis of the correcting ability of the decoder model with matched processing for Barker codes of different lengths under the conditions of a one, two, and threefold error. Analytical expressions have been obtained to determine the decoding error probability of a binary minimax code depending on the length of the sync code. The dependence of the corrective ability of the code and the maximum level of the side lobe on the length of the sync code in the range from 4 to 128 with the best nonperiodic autocorrelation functions (NPAF) is obtained. It has been established that there are length ranges for minimax sequences within which their correction ability remains constant, that is, a sync code of shorter length has the same correction ability as a longer code. Thus, the research results allow us to optimize the complexity of the technical implementation of a sync signal decoder depending on the requirements for general noise immunity and information transfer rate in a communication system. The proposed approach can be successfully used to modify the existing synchronization schemes of communication systems with code division of channels.

Code-aided frame synchronization and phase ambiguity resolution

2006 ◽  
Vol 54 (7) ◽  
pp. 2747-2757 ◽  
Author(s):  
H. Wymeersch ◽  
H. Steendam ◽  
H. Bruneel ◽  
M. Moeneclaey
Keyword(s):  
Ambiguity Resolution ◽  
Frame Synchronization ◽  
Phase Ambiguity ◽  
Phase Ambiguity Resolution

scholarly journals 50 Gbit/s real-time test environment for integrated photonic DQPSK receivers

2014 ◽  
Vol 12 ◽  
pp. 117-121
Author(s):  
T. Föhn ◽  
C. Fischer ◽  
M. Berroth
Keyword(s):  
Phase Shift ◽  
Real Time ◽  
Test System ◽  
Error Rates ◽  
Binary Sequences ◽  
Phase Shift Keying ◽  
Time Operation ◽  
Quadrature Phase Shift Keying ◽  
Quadrature Phase ◽  
Shift Keying

Abstract. In this paper an FPGA-based test system for high-speed transmission experiments with integrated photonic receivers is presented. Pseudorandom binary sequences are generated inside the FPGA and encoded as either differential quadrature phase shift keying (DQPSK) or quadrature phase shift keying (QPSK) signals. The DQPSK encoder uses a 64-fold parallel-prefix-layers architecture for real-time operation which allows for a maximum internal encoder data rate of 64 Gbit/s. Two-fold parallel data streams of I and Q signals suitable for driving an optical IQ-modulator can be transmitted and received by four 12.5 Gbit/s transceivers. Integrated bit error testers are used to determine bit error rates in real-time.

scholarly journals High-speed algorithm for carrier frequency recovery and frame synchronization in QPSK-modulated modems

2018 ◽  
pp. 28-35
Author(s):  
A. V. Sadchenko ◽  
O. A. Kushnirenko ◽  
E. K. Koshelev ◽  
V. I. Bondar
Keyword(s):  
Carrier Frequency ◽  
Communication Systems ◽  
High Speed ◽  
Phase Shifter ◽  
Voltage Controlled Oscillator ◽  
Frame Synchronization ◽  
Phase Ambiguity ◽  
Circuit Realization ◽  
Simultaneous Formation ◽  
Carrier Frequency Recovery

When demodulating signals in communication systems with QPSK modulation operating in the pulsed mode, the following problems arise: rapid elimination of the reference oscillator phase ambiguity and ensuring reliable frame synchronization for a given noise immunity. In most QPSK modems, the carrier frequency recovery and synchronization recovery tasks are separated and solved with the help of different functional modules, which is not the optimal solution from the point of view of increasing the energy efficiency. In this paper, we propos a fast algorithm for frame synchronization and recovery of the carrier frequency of a QPSK modem using Barker sequences as synchronization signals in conjunction with the coordinated processing. The simulation of the combined circuit is performed, which allows to eliminate the phase ambiguity of the reference oscillation with the simultaneous formation of the frame synchronization signal for various combinations of binary sync codes of the length N = 7. To obtain a reference oscillation, a stable quartz oscillator is used. An external adjustable phase shifter block abruptly changes the phase of the oscillator, and the phase ambiguity, which is multiple of 90°, is eliminated by parallel analysis of all possible rotations of the signal constellation plane in the units, each of which contains a pair of filters matched to the signal distributed over in two quadratures. The timing for the proposed scheme does not depend on the initial phase difference between the received and the initial signal constellations, while the circuit realization of a non-tunable oscillator is much simpler than that for a voltage controlled oscillator.

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