CN1852279A

CN1852279A - 4FSK soft demodulating method

Info

Publication number: CN1852279A
Application number: CN 200610020632
Authority: CN
Inventors: 程郁凡; 裴亚丽; 李少谦
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2006-03-31
Filing date: 2006-03-31
Publication date: 2006-10-25
Anticipated expiration: 2026-03-31
Also published as: CN100471189C

Abstract

Belonging to technical area of wireless communication, the method is suitable to communication system with severe interference on channel. The method converts energy values a, b, c, d obtained from four modulated frequency points at current time to follows: setting up a1=a+b,b1=c+d, c1=a+c,d1=b+d; based on formula (b1-a1)/sqrt((a1)2+(b1)2), (d1-c1)/sqrt((c1)2+(d1)2) or (b1-a1)/max(a1, b1), (d1-c1)/max(c1, d1) to calculate high and low output value of 4FSK soft modulation. Then, using quantizing conversion in multiple scales obtains quantized output value of 4FSK soft modulation in multiple scales at current time. The invention is adapted to soft decision decoding mode of viterbi. Under channel with high gauss noise, comparing with performance of traditional demodulation with combining viterbi-decoding technique, the performance of disclosed method is higher than one order of magnitude. The invention raises reliability of performance of wireless communication system.

Description

A kind of 4FSK soft demodulating method

Technical field

A kind of 4FSK soft demodulating method belongs to wireless communication technology field, is specially adapted to disturb on the channel more serious communication system.

Background technology

The most basic wireless communication system as shown in Figure 1, transmitting terminal comprises coded portion and modulating part, receiving terminal comprise the demodulation part and decoding part.Now, a kind of 4FSK communication system is arranged, as shown in Figure 2, the transmitting terminal coded portion often uses the convolutional encoding mode, and what corresponding receiving terminal decoding part was used is the Viterbi decoding mode; The transmitting terminal modulating part is used the 4FSK modulation system, and the 4FSK demodulation mode is used in corresponding receiving terminal demodulation part.

4FSK is a kind of more common modulation demodulation system, and full name is the modulation of quaternary frequency shift keying.Its basic principle is, at transmitting terminal 0 after encoded, per two of 1 code element carried out sequential packet, will obtain altogether four kinds of code element packet results-00,01,10,11; Adopt different transmission frequency to modulate respectively to different code element packet, 00 set of symbols is corresponding to carrier frequency f ₁, 01 set of symbols is corresponding to carrier frequency f ₂, 10 set of symbols are corresponding to carrier frequency f ₃, 11 set of symbols are corresponding to carrier frequency f ₄Corresponding, what receiving terminal received be and time dependent frequency spectrum; Separate timing, by relatively four of current times may information frequency (f ₁, f ₂, f ₃And f ₄) go up the size of energy, find out the wherein information frequency of energy maximum, just can know that according to modulation scheme current modulation intelligence is 00,01,10 or 11, the code element of output correspondence gets final product.

The hard decision mode is adopted in existing 4FSK demodulation, can be called hard demodulation mode, and its basic technical scheme main points are as above-mentioned 4FSK demodulation basic principle, and the result of its output is exactly a modulation intelligence.The hard demodulation of 4FSK exists two drawbacks: 1, adopt the mode of hard decision, the result is either-or, and the output of decision device so inevitably can produce erroneous judgement, reduces the reliability of system; 2, as the optimal decoding algorithm-Viterbi decoding of convolutional encoding, its Soft decision decoding mode performance is better than the Hard decision decoding mode, and the hard demodulation mode of 4FSK has determined the Viterbi decoding algorithm of back can only adopt Hard decision decoding, and the reliability of system has corresponding reduction again like this.

Because the Soft decision decoding mode performance of Viterbi is better than hard decision, therefore in order to adapt to the actual communication systems needs, it is very necessary designing a kind of soft demodulation mode of 4FSK that goes for the Viterbi soft-decision.

Summary of the invention

The invention provides a kind of 4FSK soft demodulating method, it can adapt with Viterbi Soft decision decoding mode, makes to have adopted the performance in wireless communication systems of such demodulation mode and decoded mode more reliable.The purpose of the soft demodulation of 4FSK is exactly and the Viterbi soft-decision combines, and quantizes integer for Viterbi decoding provides multi-system, carries out Soft decision decoding.

Technical solution of the present invention is:

A kind of 4FSK soft demodulating method is characterized in that, it divides following step:

Step 1 received signal is obtained four energy values of modulating frequency of current time.Because the output of 4FSK demodulation can be following four kinds of possibilities: 00,01,10,11, so establish current time: the modulating frequency of 00 correspondence is f ₁, and f ₁The energy of frequency is a; The modulating frequency of 01 correspondence is f ₂, and f ₂The energy of frequency is b; The modulating frequency of 10 correspondences is f ₃, and f ₃The energy of frequency is c; The modulating frequency of 11 correspondences is f ₄, and f ₄The energy of frequency is d.

Step 2 is separately considered the height bit of modulation intelligence, is done following conversion.

First bit is the energy of ' 0 ': 00 correspondence, i.e. a

The energy of 01 correspondence, i.e. b

First bit is the energy of ' 1 ': 10 correspondences, i.e. c

The energy of 11 correspondences, i.e. d

Second bit is the energy of ' 0 ': 00 correspondence, i.e. a

The energy of 10 correspondences, i.e. c

Second bit is the energy of ' 1 ': 01 correspondence, i.e. b

The energy of 11 correspondences, i.e. d

Make a '=a+b, b '=c+d, c '=a+c, d '=b+d.

Step 3 is calculated the high low level output valve of the soft demodulation of 4FSK.

Calculate: (b '-a ')/sqrt ((a ') ²+ (b ') ²) as the high-order output valve of the soft demodulation of 4FSK, (d '-c ')/sqrt ((c ') ²+ (d ') ²) as the low level output valve of the soft demodulation of 4FSK;

Or,

Calculate: (b '-a ')/max (a ', b ') is as the high-order output valve of the soft demodulation of 4FSK, and (d '-c ')/max (c ', d ') is as the low level output valve of the soft demodulation of 4FSK.

Step 4 multi-system quantizes conversion.The high and low position output valve of the soft demodulation of 4FSK of step 3 gained is changed, and by quantizing the quantification integer that code conversion becomes multi-system, the multi-system that promptly obtains the soft demodulation of current time 4FSK quantizes output valve.

Step 5 repeated execution of steps 1 is to step 4, and the multi-system that can obtain next soft demodulation of 4FSK constantly quantizes output valve; Execution in step 1 is to step 4 repeatedly, and the multi-system that can obtain all soft demodulation of 4FSK constantly quantizes output valve.

Need to prove, two kinds of computing formula in the step 3 when calculating high and low output valve of the soft demodulation of 4FSK, have all also been carried out from normalization signal in demodulation, be equivalent to like this signal before the quantization encoding is compressed, to improve the signal to noise ratio of small-signal; And output valve is an absolute value less than 1 floating number, converts the quantification integer of multi-system to by step 4 quantization encoding, and the multi-system that just obtains the soft demodulation of 4FSK quantizes output valve.This multi-system quantification output valve is imported into carries out the Viterbi Soft decision decoding in the viterbi decoder.Because the output of 4FSK soft demodulating method is that multi-system quantizes integer, rather than the concrete modulation intelligence of the hard demodulation method output of 4FSK, so this method is called the 4FSK soft demodulating method.

As can be seen from Figure 3, under the Gaussian noise channel, the method for the present invention of employing is higher one more than the order of magnitude in conjunction with the performance of Viterbi decoding technology than traditional demodulation in conjunction with the performance of Viterbi decoding technology.

In the present invention, with respect to conventional method, on hardware is realized, increased adder, in two kinds of methods that step 3 adopts, method one has been used the computing of evolution, and what method two adopted is the MAX computing, this on hardware is realized also than being easier to.Though will be a bit larger tham traditional demodulation in method of the present invention in the complexity that realizes, the raising of the systematic function that brings thus but is worth, because this complexity of increase, can realize fully with the level of Modern DSP processor.

Description of drawings

Fig. 1 is the most basic wireless communication system architecture block diagram.

Fig. 2 is the wireless communication system architecture block diagram that adopts the 4FSK modulation demodulation system.

Fig. 3 is the simulation result comparison diagram of a kind of 4FSK soft demodulating method of the present invention and the hard demodulation method of existing 4FSK: the simulated conditions of employing is the white Gaussian noise channel.

Fig. 4 is the schematic flow sheet of a kind of 4FSK soft demodulating method of the present invention.

Claims

1, a kind of 4FSK soft demodulating method is characterized in that, it divides following step:

Step 1 received signal is obtained four energy values of modulating frequency of current time

Because the output of 4FSK demodulation can be following four kinds of possibilities: 00,01,10,11, so establish current time: the modulating frequency of 00 correspondence is f ₁, and f ₁The energy of frequency is a; The modulating frequency of 01 correspondence is f ₂, and f ₂The energy of frequency is b; The modulating frequency of 10 correspondences is f ₃, and f ₃The energy of frequency is c; The modulating frequency of 11 correspondences is f ₄, and f ₄The energy of frequency is d;

Step 2 is separately considered the height bit of modulation intelligence, is done following conversion

First bit is the energy of ' 0 ': 00 correspondence, i.e. a

The energy of 01 correspondence, i.e. b

First bit is the energy of ' 1 ': 10 correspondences, i.e. c

The energy of 11 correspondences, i.e. d

Second bit is the energy of ' 0 ': 00 correspondence, i.e. a

The energy of 10 correspondences, i.e. c

Second bit is the energy of ' 1 ': 01 correspondence, i.e. b

The energy of 11 correspondences, i.e. d

Make a '=a+b, b '=c+d, c '=a+c, d '=b+d;

Step 3 is calculated the high low level output valve of the soft demodulation of 4FSK

Or,

Calculate: (b '-a ')/max (a ', b ') is as the high-order output valve of the soft demodulation of 4FSK, and (d '-c ')/max (c ', d ') is as the low level output valve of the soft demodulation of 4FSK;

Step 4 multi-system quantizes conversion

The high and low position output valve of the soft demodulation of 4FSK of step 3 gained is changed, and by quantizing the quantification integer that code conversion becomes multi-system, the multi-system that promptly obtains the soft demodulation of current time 4FSK quantizes output valve;