CN105530215A - 8PSK soft differential decoding method based on CORDIC - Google Patents
8PSK soft differential decoding method based on CORDIC Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
- H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
- H04L27/2271—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses only the demodulated signals
- H04L27/2273—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses only the demodulated signals associated with quadrature demodulation, e.g. Costas loop
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Abstract
The invention relates to a receiving end phase differential decoding method of an 8PSK single carrier modulation system, belonging to the field of signal processing of wireless communication receivers. The invention provides a novel differential decoding method, which not only overcomes phase ambiguity, but also meets the requirements of subsequent error correction decoding on soft information, can fully exert the error correction decoding performance and reduce the demodulation threshold requirement. The method provided by the invention firstly utilizes a CORDIC algorithm to calculate IQ information phase after symbol synchronization to obtain a standard phase of a transmitting end, and then adopts the phase angle subtraction of the standard phase and a subsequent symbol to obtain phase information after soft differential decoding. The information has no phase ambiguity, the phase soft information is reserved, and the phase angle error diffusion is avoided. The novel method utilizes the CORDIC algorithm to combine with 8PSK differential phase characteristics to carry out soft differential decoding on the phase angle demodulated by a receiving end, so that the accuracy of phase soft information can be obviously improved, and the receiving performance is improved. The algorithm has small complexity and is easy to realize.
Description
Technical field
The present invention is applicable to the 8PSK single-carrier modulated system receiving end signal process of wireless communication field.The present invention's application receiving end adopts that carrier wave is blind synchronously exists in the 8PSK single carrier continuous communiction system of phase fuzzy problem, solve the problem of hard differential decoding loss soft decision information, the diffusion of traditional soft differential decoding phase angle error, the basis of this technology is cordic algorithm design and phase difference process.
Background technology
In high-speed microwave, satellite communication link, wireless channel all belongs to the channel of power and frequency limited, in order to save power or save bandwidth, raising throughput etc., needs to adopt better modulation /demodulation and coding and decoding mode.In satellite before or microwave telecommunication system, the normal mode of 8PSK+TCM that adopts realizes high speed radio transmission.Along with the development of coding and decoding and large scale integrated circuit, the mode of 8PSK+LDPC becomes easy realization, and the mode of the relative 8PSK+TCM of performance has a certain upgrade, and for wireless channel saves power or frequency resource, obtains a wide range of applications.The fuzzy general employing hard decision differential decoding of the blind locking phase of 8PSK, but in order at utmost play coding and decoding performance, LDPC decoding needs soft decision information, the two is contradiction, need to find a kind of method, both solved phase fuzzy problem, the soft decision information of decoding can be provided again.
Due to the relatively high availability of frequency spectrum and good interference free performance, 8PSK is modulated in satellite communication and mobile communication system, obtains a wide range of applications.Because 8 constellation point of 8PSK are all on unit circle, so the peak-to-average force ratio that transmits after modulation is lower, power amplifier is required that relative qam mode is lower, the requirement to power amplifier can be reduced, reduce radio-frequency power consumption etc.Under the prerequisite that character rate is constant, the message transmission rate adopting 8PSK technology to reach is 3 times of GMSK, is 2 times of QPSK.The feature of 8PSK modulation is that 8 vector end-points are evenly distributed on unit circumference, and its mathematic(al) representation is:
（1）
Modulation block diagram is as Fig. 1.
Data after error correction coding give Joint Mapping module, first transmission sequence is carried out 3 bit groupings by 8PSK modulation, according to the relation that 3 bit informations and phase place change, the Gray's rule realizing bit information and phase angle change maps, the phase angle simultaneously mapped is variable quantity, achieve differential coding, mapping relations are as table 1.
After completing mapping, generate IQ modulation signal according to angle, give DAC converter after completing the process such as molding filtration and be converted to analog baseband signal, launch after rf modulations, amplification.
Table 1 incoming symbol and phase modulation variation relation
| Incoming symbol | 111 | 110 | 100 | 101 | 001 | 011 | 010 | 000 |
| Phase modulation changes | 0° | 45° | 90° | 135° | 180° | -45° | -90° | -135° |
In 8PSK demodulation, mainly complete carrier synchronization, sign synchronization, the generation of decoding phase information etc.In the blind synchronous system of employing, carrier synchronization often adopts cordic algorithm to carry out phase demodulation, and decoding angle information generates the normal cordic algorithm that adopts and generates symbol angle.Exemplary block diagram is as Fig. 2.
Cordic algorithm and Coordinate Rotation Digital computational methods (CoordinateRotationDigitalComputer) are proposed first by Volder nineteen fifty-nine.At first for calculating trigonometric function, simple afterwards due to its algorithm, hardware is easy to realize etc. multiple advantage, and is widely used in the computing of many kinds of function (comprising trigonometric function, hyperbolic functions, evolution, exponential function, logarithmic function, multiplying, division arithmetic etc.), in communication system modulation /demodulation etc., all have a wide range of applications.
The basic representation of cordic algorithm is as follows:
（2）
（3）
Formula (2) represents the iterative manner of cordic algorithm, the result of formula (3) representative vector rotary mode, finally obtains the polar coordinates information of rectangular coordinate data, i.e. angle and amplitude.In 8PSK demodulation, cordic algorithm is widely used, and usual carrier synchronization, differential decoding, Soft Inform ation generate all can apply this algorithm.
At 8PSK receiving terminal, owing to adopting carrier wave synchronously blind, after I/Q signal carrier synchronization and Symbol Timing complete, there is phase ambiguity in 8PSK symbol.Phase ambiguity is FAQs in PSK, QAM modulation system, and the general differential coding and decoding that adopts overcomes.In such as 8PSK differential coding system, input data information is phase accumulator increment, and phase-accumulated result is for sending constellation point phase place, and front and back constellation point phase changing capacity represents input data information.The form that before and after receiving terminal adopts, phase angle subtracts each other, namely the declinate of acquisition is reduced to transmitting terminal input data information.
Hard differential decoding realizes simple, after CORDIC CMOS macro cell phase information, adopts 3 bit symbol information after phase place judgement to carry out decoding, only needs 3 bit subtraction devices to realize.But soft-decision quantitative information loses, and there is the problem that subsequent error correction decoding performance can not give full play to.
Traditional soft difference realizes slightly complicated, and before CORDIC CMOS macro cell phase information, former and later two symbol I/Q data are carried out conjugation and taken advantage of, and obtain new IQ two paths of data, and the IQ information after then conjugation being taken advantage of asks for phase angle, obtains differential phase.Or carry out front and back phase angle additive operation after CORDIC CMOS macro cell phase information, obtain difference phase angle.Two kinds of traditional methods overcome the problem that hard difference can not obtain Soft decision decoding information, but the problem of phase angle error diffusion when all there is low signal-to-noise ratio, reduce the accuracy of follow-up coding soft decision information.
The explanation of traditional soft difference error code diffusion is carried out for Fig. 3.B1, B2 are standard point position, are respectively 22.5 ° and 67.5 °.What before supposing, symbol sent is B1 point, and following symbol input 110, according to mapping ruler shown in table 1, rear symbol sends phase place increases by 45 ° on B1 point, transmission be B2 point, according to judgment rule, angle after differential received is best with 45 °, and correct scope is between 22.5 ° and 67.5 °.Affect by Gaussian noise, the B1 point of reception may at M11, also may at M12, or other positions, and the B2 point of reception may at M21, also may at M22, or other positions.If B1 acceptance point is at M11 point, B2 acceptance point is at M22 point, and differentiated angle may be greater than 67.5 °; If B1 acceptance point is at M12 point, B2 acceptance point is at M21 point, and differentiated angle may be less than 22.5 °.Obviously when signal to noise ratio is lower, there is phase angle error diffusion, the accuracy that coding soft decision information below generates can be reduced.
Summary of the invention
Hard differential decoding realizes simple, but subsequent error correction decoding can not use soft decision information; Traditional soft differential decoding can provide Soft Inform ation for subsequent error correction decoding, but there is the problem of phase angle error diffusion; Newly-designed soft differential decoding solves two kinds of differential decoding Problems existing above, both overcomes phase ambiguity, and does not have again phase angle error to spread, and met the requirement of subsequent error correction decoding to Soft Inform ation.
This patent utilizes cordic algorithm in conjunction with 8PSK differential phase characteristic, and carry out soft differential decoding to the phase angle after receiving terminal demodulation, overall algorithm block diagram as shown in Figure 4.
First CORDIC module is designed.CORDIC modular design is phase rotating pattern, and phase place [-π, π) be quantified as N position, scope is [-2
n-1, 2
n-1-1).CORDIC modular design can be introduced with reference to CORDIC module I P core disclosed in the integrated circuit companies such as XILINX, ALTERA, if realized in FPGA, then directly can call ready-made IP kernel and realize.。
I/Q signal is inputted CORDIC module, obtain phase information.
Adopt high 3 bits of phase information to generate normalized phase, be designated as
, carry out storage time delay, the generation of normalized phase can adopt the mode of tabling look-up to obtain.8 standard information are stored as [2
n/ 16,2
n/ 16+2
n/ 8,2
n/ 16+2*2
n/ 8,2
n/ 16+3*2
n/ 8 ,-(2
n/ 16+3*2
n/ 8) ,-(2
n/ 16+2*2
n/ 8) ,-(2
n/ 16+2
n/ 8) ,-2
n/ 16].High 3 bits find the value of corresponding normalized phase with unsigned number [000,001,010,011,100,101,110,111].
Utilize pipelined cordic module to continue to ask for the phase information of a symbol next, be designated as
.
Finally obtain
, namely obtain the phase information after soft differential decoding, this information be supplied to follow-up soft decision information generation module, there is no phase ambiguity and angular error diffusion, remain comparatively real Soft Inform ation.
For Fig. 3, the benefit that newly-designed soft differential decoding brings is described equally.Suppose that B1 acceptance point is at M11 point, B2 acceptance point is at M22 point.Adopt new method, after firmly sentencing phase information according to M11 point, expand to normalized phase, correspondence be B1 point normal place, after M22 point and B1 difference, phase place can not be greater than 67.5 °, between normal range (NR) 22.5 ° and 67.5 °; Suppose that B1 acceptance point is at M12 point, B2 acceptance point, at M21 point, adopts new method, after firmly sentencing phase information according to M12 point, expand to normalized phase, corresponding is B1 point normal place, after M21 point and B1 difference, phase place can not be less than 22.5 °, between normal range (NR) 22.5 ° and 67.5 °.According to above analysis, new method solves phase angle error diffusion problem after difference.
Accompanying drawing explanation
Figure 18 PSK typical case transmitting terminal block diagram
Figure 28 PSK typical reception end block diagram
Fig. 3 constellation point phase angle schematic diagram
Fig. 4 is soft, and differential decoding new method realizes block diagram
Figure 58 PSK receiving terminal planisphere
Fig. 6 LDPC decoding performance contrast figure
Concrete enforcement
In order to make object of the present invention, technical scheme and advantage clearly understand, in conjunction with the following drawings and embodiment, the soft differential decoding method of the 8PSK based on CORDIC of the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.
Suppose that incoming symbol and phase modulation relation are as table 1, receiving end carries out the planisphere after blind synchronous, the sign synchronization of carrier wave as Fig. 5, and start offset phase place is π/8.
1) first design CORDIC module, phase place [-π, π) be quantified as 16, scope be [-32768,32767).
2) I/Q signal after sign synchronization sends into CORDIC module, asks for phase information
.
3) table look-up according to high 3 bits of phase information, obtain normalized phase information, be designated as
.8 standard information are stored as [4096,12288,20480,28672 ,-28672 ,-20480 ,-12288 ,-4096].High 3 bits find the value of corresponding normalized phase with unsigned number [000,001,010,011,100,101,110,111].
4) CORDIC module is pipeline operation mode, seeks out the phase place of next I/Q signal, is designated as
.
5) obtain
, namely obtain the phase information after soft differential decoding, this information does not have phase ambiguity, and remains comparatively real Soft Inform ation.This information is used for soft-decision error-correcting decoding and can obtains better performance, LDPC decoding performance contrast figure as shown in Figure 6.
Claims (4)
1. based on the soft differential decoding method of 8PSK of CORDIC, it is characterized in that, it utilizes cordic algorithm in conjunction with 8PSK differential phase characteristic, and carry out soft differential decoding to the phase angle after receiving terminal demodulation, overall algorithm block diagram as shown in Figure 4.
2., based on the soft differential decoding new method of 8PSK of CORDIC, it is characterized in that, typical performing step is as follows:
First CORDIC module is designed, and phase place [-π, π) be quantified as N position, scope is [-2
n-1, 2
n-1-1);
I/Q signal after sign synchronization sends into CORDIC module, asks for phase information
;
High 3 bits according to phase information are tabled look-up, and obtain normalized phase information, are designated as
;
CORDIC module is pipeline operation mode, seeks out the phase place of next I/Q signal, is designated as
;
Obtain
, namely obtain the phase information after soft differential decoding, this information does not have phase ambiguity, and remains comparatively real Soft Inform ation.
3., by step 3) according to claim 2, it is characterized in that, ask for the normalized phase mode of current receiving symbol, 8 standard information are stored as [2
n/ 16,2
n/ 16+2
n/ 8,2
n/ 16+2*2
n/ 8,2
n/ 16+3*2
n/ 8,
-(2
n/ 16+3*2
n/ 8) ,-(2
n/ 16+2*2
n/ 8) ,-(2
n/ 16+2
n/ 8) ,-2
n/ 16], high 3 bits find the value of corresponding normalized phase with unsigned number [000,001,010,011,100,101,110,111].
4. by step 5) according to claim 2, it is characterized in that, the standard value being deducted a upper I/Q signal phase place by the phase value of next I/Q signal obtains phase difference value, and this phase difference value represents the Soft Inform ation of the input data information of transmitting terminal.
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| CN110611631A (en) * | 2019-09-25 | 2019-12-24 | 电子科技大学 | DBPSK demodulator with low time delay and low overhead |
| CN111865848A (en) * | 2020-06-16 | 2020-10-30 | 武汉邮电科学研究院有限公司 | Signal modulation format identification method and system |
| CN112491766A (en) * | 2020-12-24 | 2021-03-12 | 深圳市鼎阳科技股份有限公司 | Digital modulation method and device, and storage medium |
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| US20120128092A1 (en) * | 2010-11-22 | 2012-05-24 | Jie-Wei Lai | Digital signal processing circuit for generating output signal according to non-overlapping clock signals and input bit streams and related wireless communication transmitters |
| CN103166635A (en) * | 2011-12-15 | 2013-06-19 | 英特尔移动通信有限责任公司 | Method and faculty to measure and compensate dco frequency distortions using a dpll |
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| US20120128092A1 (en) * | 2010-11-22 | 2012-05-24 | Jie-Wei Lai | Digital signal processing circuit for generating output signal according to non-overlapping clock signals and input bit streams and related wireless communication transmitters |
| CN102332935A (en) * | 2011-09-21 | 2012-01-25 | 北京华力创通科技股份有限公司 | Carrier compensation system and carrier compensation method |
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| CN110611631A (en) * | 2019-09-25 | 2019-12-24 | 电子科技大学 | DBPSK demodulator with low time delay and low overhead |
| CN111865848A (en) * | 2020-06-16 | 2020-10-30 | 武汉邮电科学研究院有限公司 | Signal modulation format identification method and system |
| CN111865848B (en) * | 2020-06-16 | 2023-03-24 | 武汉邮电科学研究院有限公司 | Signal modulation format identification method and system |
| CN112491766A (en) * | 2020-12-24 | 2021-03-12 | 深圳市鼎阳科技股份有限公司 | Digital modulation method and device, and storage medium |
| CN112491766B (en) * | 2020-12-24 | 2022-12-13 | 深圳市鼎阳科技股份有限公司 | Digital modulation method and device and storage medium |
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