CN105530215B - 8PSK soft differential decoding method based on CORDIC - Google Patents

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 patent provides a new 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 patent firstly utilizes a CORDIC algorithm to calculate IQ information phase after symbol synchronization, obtains a standard phase of a transmitting end, and then subtracts the phase angle of the standard phase and a phase angle of a next 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

A kind of soft differential decoding methods of 8PSK based on CORDIC

Technical field

The 8PSK single-carrier modulated system receiving end signals that the present invention is suitable for wireless communication field are handled.Application of the present invention Receiving end is synchronized using carrier wave is blind in the 8PSK single carrier continuous communiction systems there are phase fuzzy problem, solves hard differential decoding The basis of the problem of losing soft decision information, the diffusion of traditional soft differential decoding phase angle error, the technology is cordic algorithm design With phase difference processing.

Background technology

In high-speed microwave, satellite communication link, wireless channel belongs to power and the channel of frequency limited, in order to save Power or saving bandwidth, raising handling capacity etc., need to use better modulation /demodulation and coding and decoding mode.In satellite before Or in microwave telecommunication system, high speed radio transmission is realized frequently with the mode of 8PSK+TCM.With coding and decoding and large-scale integrated The mode of the development of circuit, 8PSK+LDPC becomes easy realization, and mode of the performance with respect to 8PSK+TCM has a certain upgrade, and is Wireless channel saves power or frequency resource, has been widely used.Fuzzy general use of the blind locking phases of 8PSK is sentenced firmly Certainly differential decoding, but in order to utmostly play compiling code performance, it is contradiction that LDPC decodings, which need soft decision information, the two, , it needs to find a kind of method, not only solves phase fuzzy problem, but also the soft decision information of decoding can be provided.

Since the relatively high availability of frequency spectrum and good interference free performance, 8PSK are modulated at satellite communication and movement In communication system, have been widely used.Since 8 constellation points of 8PSK are on unit circle, so modulated transmitting Signal peak-to-average power is relatively low, requires opposite qam mode lower power amplifier, can reduce the requirement to power amplifier, reduce radio frequency work( Consumption etc..Under the premise of character rate is constant, using 8PSK technologies attainable message transmission rate be 3 times of GMSK, be 2 times of QPSK.The characteristics of 8PSK is modulated is that 8 vector end-points are evenly distributed on unit circumference, and mathematic(al) representation is：

（1）

Modulate block diagram such as Fig. 1.

Data after Error Correction of Coding give Joint Mapping module, and 8PSK modulation will send sequence and carry out 3 bit groupings first, According to the relationship of 3 bit informations and phase change, Gray's rule mapping of bit information and phase angle change is realized, while mapping Phase angle is variable quantity, realizes differential encoding, mapping relations such as table 1.

After completing mapping, IQ modulated signals are generated according to angle, DAC converters turn are given after completing the processing such as molding filtration It is changed to analog baseband signal, is emitted after radio-frequency modulations, amplification.

1 incoming symbol of table 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, carrier synchronization, sign synchronization, decoding phase information generation etc. are mainly completed.Using blind same In the system of step, carrier synchronization carries out phase demodulation frequently with cordic algorithm, and decoding angle information is generated frequently with cordic algorithm Generate symbol angle.Exemplary block diagram such as Fig. 2.

Cordic algorithm, that is, Coordinate Rotation Digital computational methods（Coordinate Rotation Digital Computer）It is to be put forward for the first time by Volder nineteen fifty-nine.It is initially for calculating trigonometric function, later due to its algorithm Simply, hardware is easily achieved etc. a variety of advantages, and is widely used in the operation of many kinds of function（Including triangle letter Number, hyperbolic functions, evolution, exponential function, logarithmic function, multiplying, division arithmetic etc.）, in communication system modulation /demodulation Etc., it suffers from and is widely applied.

The basic representation of cordic algorithm is as follows：

（2）

（3）

Formula（2）Represent the iterative manner of cordic algorithm, formula（3）Representative vector rotary mode as a result, final obtain Obtained the polar coordinates information of rectangular co-ordinate data, i.e. angle and amplitude.In 8PSK demodulation, cordic algorithm is widely used, and is led to Normal carrier synchronization, differential decoding, Soft Inform ation generation can all apply the algorithm.

In 8PSK receiving terminals, due to using the blind synchronization of carrier wave, after the completion of I/Q signal carrier synchronization and Symbol Timing, 8PSK symbols Number there are phase ambiguities.Phase ambiguity is FAQs in PSK, QAM modulation system, generally using differential coding and decoding progress gram Clothes.Such as in 8PSK differential encoding systems, input data information is phase accumulator increment, and phase-accumulated result is to send constellation Point phase, front and back constellation point phase changing capacity represent input data information.Receiving terminal uses the form that front and back phase angle subtracts each other, and obtains The declinate obtained is reduced to transmitting terminal input data information.

Hard differential decoding is realized simply, after CORDIC modules generate phase information, 3 bit symbols after being adjudicated using phase Information is into row decoding, it is only necessary to which 3 bit subtraction devices can be realized.But soft-decision quantitative information loses, there are subsequent error corrections to translate The problem of code performance cannot give full play to.

Traditional soft difference realize it is slightly complicated, before CORDIC modules generate phase information, former and later two symbol I/Q datas into Row conjugation multiplies, and obtains new IQ two paths of data, and the IQ information after then multiplying conjugation seeks phase angle, obtains differential phase.Or It is to carry out front and back phase angle additive operation after CORDIC modules generate phase information, obtains difference phase angle.Traditional two methods gram What phase angle error was spread when having taken the problem of hard difference cannot obtain Soft decision decoding information, but all there is low signal-to-noise ratio asks Topic, reduces the accuracy of follow-up coding soft decision information.

The explanation of traditional soft difference error code diffusion is carried out by taking Fig. 3 as an example.B1, B2 be standard point position, respectively 22.5 ° and 67.5°.Assuming that preceding symbol transmission is B1 points, following symbol input 110, according to mapping ruler shown in table 1, rear symbol sends phase Position increases by 45 ° on B1 points, and transmission is B2 points, according to judgment rule, angle after differential received with 45 ° be it is best, correctly Range is between 22.5 ° and 67.5 °.It is influenced by Gaussian noise, the B1 points of reception may be in M11, it is also possible in M12, Huo Zheqi His position, the B2 points of reception may be in M21, it is also possible in M22 or other positions.If B1 receiving points connect in M11 points, B2 Sink is likely larger than 67.5 ° in M22 points, differentiated angle；If B1 receiving points, in M12 points, B2 receiving points are poor in M21 points Angle after point is likely less than 22.5 °.Obviously when noise is relatively low, there are phase angle error diffusion, can reduce decode below it is soft The accuracy that discriminative information generates.

Invention content

Hard differential decoding is realized simply, but subsequent error correction decoding cannot use soft decision information；Traditional soft differential decoding It can be decoded for subsequent error correction and Soft Inform ation is provided, but there are problems that phase angle error diffusion；Newly-designed soft differential decoding solution Certainly two kinds of front differential decoding there are the problem of, not only overcome phase ambiguity, but also spread without phase angle error, meet subsequent error correction Decode the requirement to Soft Inform ation.

This patent utilizes cordic algorithm combination 8PSK differential phase characteristics, and the phase angle after being demodulated to receiving terminal carries out soft difference Divide decoding, overall algorithm block diagram as shown in Figure 4.

CORDIC modules are designed first.CORDIC module designs be phase place pattern, phase [- π, π) be quantified as N, Ranging from [- 2^N-1, 2^N-1-1).CORDIC module designs can refer to disclosed in the integrated circuits companies such as XILINX, ALTERA CORDIC module I P core introductions can directly invoke ready-made IP kernel and realize if realized in FPGA.

I/Q signal is inputted into CORDIC modules, finds out phase information.

Normalized phase is generated using high 3 bit of phase information, is denoted as, carry out storage delay, the generation of normalized phase The mode tabled look-up may be used 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 bit is with no symbol Number [000,001,010,011,100,101,110,111] finds the value of corresponding normalized phase.

The phase information for being continued to seek latter one symbol using pipelined cordic module, is denoted as。

Finally find out, that is, the phase information after soft differential decoding is obtained, is provided this information to follow-up Soft decision information generation module spreads without phase ambiguity and angular error, remains more true Soft Inform ation.

The benefit brought to newly-designed soft differential decoding equally by taking Fig. 3 as an example illustrates.Assuming that B1 receiving points are in M11 Point, B2 receiving points are in M22 points.Normalized phase is extended to after sentencing phase information firmly according to M11 points using new method, it is corresponding to be B1 point normal places, after M22 points and B1 difference, phase is not more than 67.5 °, between 22.5 ° and 67.5 ° of normal range (NR)；It is false If B1 receiving points are extended to mark in M21 points, using new method in M12 points, B2 receiving points after sentencing phase information firmly according to M12 points Quasi- phase, corresponding is B1 point normal places, and after M21 points and B1 difference, phase will not be less than 22.5 °, in 22.5 ° of normal range (NR) And between 67.5 °.According to the above analysis, new method solves phase angle error diffusion problem after difference.

Description of the drawings

Fig. 1 8PSK typical case's transmitting terminal block diagrams

Fig. 2 8PSK typical receptions end block diagram

Fig. 3 constellation point phase angle schematic diagrames

The soft differential decoding new methods of Fig. 4 realize block diagram

Fig. 5 8PSK receiving terminal planispheres

Fig. 6 LDPC decoding performance compares figures

Specific implementation

In order to make the purpose , technical scheme and advantage of the present invention be clearer, in conjunction with the following drawings and embodiment, right The soft differential decoding methods of the 8PSK based on CORDIC of the present invention are further elaborated.It should be appreciated that described herein Specific examples are only used to explain the present invention, is not intended to limit the present invention.

Assuming that incoming symbol and phase modulation relationship such as table 1, receiving end carries out the planisphere after the blind synchronization of carrier wave, sign synchronization Such as Fig. 5, start offset phase is π/8.

1) first design CORDIC modules, phase [- π, π) be quantified as 16, ranging from [- 32768,32767).

2) I/Q signal after sign synchronization is sent into CORDIC modules, seeks phase information。

3) it is tabled look-up according to high 3 bit of phase information, obtains normalized phase information, be denoted as.8 standard information are deposited Storage is [4096,12288,20480,28672, -28672, -20480, -12288, -4096].High 3 bit is with unsigned number [000,001,010,011,100,101,110,111] value of corresponding normalized phase is found.

4) CORDIC modules are pipeline operation mode, seek out the phase of next I/Q signal, are denoted as。

5) it finds out, that is, the phase information after soft differential decoding is obtained, which does not have phase ambiguity, and Remain more true Soft Inform ation.The information can be obtained into better performance, LDPC decodings for soft-decision error-correcting decoding Performance map is as shown in Figure 6.

Claims (1)

1. a kind of soft differential decoding methods of 8PSK based on CORDIC, which is characterized in that it utilizes cordic algorithm combination 8PSK Differential phase characteristic, the phase angle after being demodulated to receiving terminal carry out soft differential decoding, realize that steps are as follows：

1）Design CORDIC modules, by phase [- π, π) be quantified as N, ranging from [- 2^N-1, 2^N-1-1)；

2）8 normalized phases of 8PSK are quantified 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], it is 8 to constitute an address depth, number According to the look-up table LUT_P that bit wide is N；

3）I/Q signal after sign synchronization is sent into CORDIC modules, seeks phase information, phase information symbolIt indicates；

4）Intercept phase informationHigh 3 bit table look-up as address, that is, look into LUT_P tables, obtain normalized phase information, note For；

5）CORDIC modules are pipeline operation mode, seek out the phase information of next I/Q signal, are denoted as；

6）It finds out, obtain the phase information after soft differential decoding.