The demodulator shestnadtsetirichnoe quadrature amplitude manipulation

 

The invention relates to radio engineering. The technical result consists in the evaluation of the demodulator of the probability of error in each of the four partial digital communication channels. The essence of the invention lies in the fact that the input signal shestnadtsetirichnoe quadrature amplitude-shift keying (QAM-16) coherently demodulated and receive at the output of the demodulator tetrad demodulated symbols {A; B; C; D}, form the first and second signals of the four-phase modulation (FM-4), increase in time To received noise signal and summed with the input signal, QAM-16, and measuring the frequency of the pulsed flow mismatches for each of the four partial channels, get the probability of errors in digital symbols {A; B; C; D} at the output of the demodulator. 2 C.p. f-crystals, 3 ill.

The invention relates to electrical engineering and can be used for demodulation of shestnadtsetirichnoe quadrature amplitude-shift keying (QAM-16).

Known demodulator quadrature amplitude manipulation, containing two phase detector, two lowpass filter, two multiplier-driven generator and an adder. The outputs of multiplier products Soetoro, the first input which is the input device (see and.with 1758899, MKI 5 H 04 L 27/38, publ. in BI 32, 30.08.92 - [1]).

The known device has four outputs, each of which the consumer receives digital information streams (also referred to as subchannels or partial channels).

The disadvantage of this demodulator is the inability to assess the probability of error for each of the four partial digital communication channels, as in the known demodulator lack of the necessary technical means.

Also known demodulator signals shestnadtsetirichnoe quadrature amplitude manipulation, containing two phase detector (PD), two regeneration unit (computing device), two modulators, two myCitadel, the adder, a filter and a voltage controlled oscillator (VCO). The first input of the first FD is an input device, and a second input connected to the output of the VCO, the input connected to the filter output, the input connected to the output of the adder. The outputs of the first PD is connected to the inputs of the first regeneration unit, the outputs of which are connected with inputs of the first modulator. The outputs of the second PD is connected to the inputs of the second regeneration unit, outputs the cat is, The KI 5 H 04 L 27/34, publ. in BI 16, 30.08.94 - [2]).

The disadvantage of this demodulator is the inability to assess the probability of error for each of the four partial digital communication channels, as in the known demodulator lack of the necessary technical means.

Known technical solutions closest to the technical nature of the claimed device (prototype) is the demodulator shestnadtsetirichnoe quadrature amplitude manipulation, containing the first and second phase detectors, the first crucial device, the first and second myCitadel, the first four modulator, the first and second multiplier products, the first and second limiters, filter and a voltage controlled oscillator, and the first input of the first phase detector connected to the input device and to the first input of the first myCitadel, a second input connected to the output of the first four of the modulator first input connected to the output of the generator, voltage-controlled and the second and third inputs respectively with the first and second outputs of the first casting device, the first and second inputs which are connected respectively with the first and the detector and the generator output, voltage-controlled input connected to the output of the filter. Input filter connected to the output of the second myCitadel, the first and second inputs which are connected respectively to the outputs of the first and second multiplier products, the first inputs of which are connected respectively to the outputs of the first and second limiters, the input of the first limiter connected to the second input of the second multiplier and a second output of the second phase detector. The input of the second limiter connected to the second input of the first multiplier and the first output of the second phase detector, a first input connected to the output of the first myCitadel, the first, second, third and fourth outputs of the first deciding device are respectively the first, second, third and fourth outputs of the device (see patent RU 2013018, IPC 5 H 04 L 27/22, publ. in BI 9, 15.05.94 - [3]).

As described above device, the prototype has four outputs on which the consumer receives four partial channel information.

The drawback of the prototype is the inability to assess the probability of error for each of the four partial transmission channels of information.

In transmission systems of discrete messages, the probability of error in each of AK and the quality of the received messages (see Radio communication system, Ed. by C. C. Kalmykov. M. : Radio and communication, 1990, S. 62-63 - [4]). In this regard, the task of measuring the probability of error in the partial channels is important.

Trivial by measuring the probability of error is an estimate of the number of corrupted symbols in some famous synchronously (concentrated or distributed).

On the one hand, the appropriate device type cyclic or human synchronizer) is much more difficult of the demodulator. On the other hand, in some cases, the predetermined singlecompany in the signal may be absent (for example, if the signal is QAM-16 when the transmission is sealed by other signals). Thus, the main task is to measure the probability of mistakes in the demodulator and it is for anyone (including those that do not contain known singaporelocalnews) traffic signal. The term "traffic signal" means a useful information signal (as opposed to special technological test signals).

The technical result-evaluation in the demodulator of the probability of error in each of the four partial digital communication channels directly on the graph is chased QAM-16, and receives the output of the demodulator tetrad demodulated symbols {A; B; C; D}.

2. Using the restored signal carrier frequency and two numeric characters {C; D} of Fallot demodulated symbols {A; B; C; D} form at the output of the first four of the modulator signal of the four-phase modulation (FM-4).

3. Subtract from the input signal QAM-16 generated signal of the FM-4 and obtained by subtracting the signal process in the schema of the Costas to generate the control voltage for the oscillator, voltage-controlled (VCO), the output of which receives the signal recovered carrier frequency.

4. Using the restored signal carrier frequency and two numeric characters {;} of Fallot demodulated symbols {A; B; C; D} form at the output of the second four-way second modulator signal FM-4.

5. Subtract the second signal of the FM-4 from the difference signals of the input signal QAM-16 and the first signal of the FM-4. Thus, the result of performing this procedure on signal, receives the signal noise component present in the input signal. This signal (noise) on the principal constraints cannot be used to reduce the probability of errors at the output of the demodulator, but it can be used for the evaluation of this verojatnost gerente demodulated signal QAM-16, mixed with amplified To noise signal, and then receive the output of the second casting device tetrad demodulated symbols {to;to;to; Dto}.

8. Compare the values of the symbols a and ato; And Into; C and Cto; D and Dtoand form a stream of pulses discrepancies between these pairs of characters.

9. Measuring the frequency of the pulsed flow mismatches for each of the four partial channels, get the probability of errors in digital symbols {A,B,C,D} at the output of the demodulator.

Thus, for the evaluation of the error probability at the output of the demodulator, a phase detector, which coherently demodulated input signal is QAM-16, additional noisy signal of the input noise components with normalized level K.

The technical result is achieved in that the demodulator shestnadtsetirichnoe quadrature amplitude manipulation includes first and second phase detectors, the first crucial device, the first and second myCitadel, the first four modulator, the first and second multiplier products, the first and second limiters, filter and a voltage controlled oscillator, and the second input of which is connected to the output of the first four of the modulator, first input connected to the output of the generator, voltage-controlled, and the second and third inputs respectively from the first and second outputs of the first casting device, the first and second inputs which are connected respectively with the first and second outputs of the first phase detector, a second input connected to the second input of the second phase detector and the output of the generator, voltage-controlled, the input connected to the output of the filter. Input filter connected to the output of the second myCitadel, the first and second inputs which are connected respectively to the outputs of the first and second multiplier products, the first inputs of which are connected respectively to the outputs of the first and second limiters, the input of the first limiter connected to the second input of the second multiplier and a second output of the second phase detector. The input of the second limiter connected to the second input of the first multiplier and the first output of the second phase detector, a first input connected to the output of the first myCitadel, the first, second, third and fourth outputs of the first deciding device are respectively the first, second, third and fourth outputs of the device.

According to the invention it contains dopey four modulator, the first, second, third, and fourth XOR, and the first and second inputs of the third vicites connected respectively to the outputs of the first vicites and second four-position modulator, the first, second and third inputs of which are connected respectively with the output of the generator, voltage-controlled, third and fourth outputs of the first casting device, the first, second, third and fourth outputs of which are connected respectively to the first inputs of the first, second, third, and fourth XOR, the outputs of which are respectively the fifth, sixth, seventh and eighth outputs of the device, and the second inputs are connected respectively with the first, the second, third and fourth outputs of the second casting device, the first and second inputs which are connected respectively with the first and second outputs of the third phase detector, a second input connected to the output of the generator, voltage-controlled, and the first input with the output of the adder, a first input connected to the first input of the first myCitadel, and the second input with the amplifier output, the input connected to the output of the third myCitadel.

Another difference is that the phase detector coderre both inputs of multiplier products are connected to the first input of PD, the second input is connected with the second input of the first multiplier and the input of the phase shifter 90owhose output is connected to the second input of the second multiplier, the outputs of the first and second multiplier products are connected with inputs respectively of the first and second low-pass filter, which are the first and second outputs FD.

Another difference is that the solver (PN) contains the first, second, third and fourth limit switches and the first and second myCitadel. The first input of RU is connected to the input of the first limiter and the first input of the first myCitadel, the output of which is connected to the input of the third limiter whose output is the second output of the RU. The output of the first limiter connected to the second input of the first vicites and is the fourth release of RU. Second input of the PN is connected to the input of the second limiter and the first input of the second myCitadel, the output of which is connected to the input of the fourth limiter whose output is the first output of the RU. The output of the second limiter connected to the second input of the second vicites and is the third release of RU.

In Fig.1 shows a functional diagram of the demodulator QAM-16.

In Fig.2 shows a functional diagram of the phase detector is ora not given circuit, are not significant in this case: circuit and clock synchronization.

The demodulator shestnadtsetirichnoe quadrature amplitude manipulation (Fig. 1) contains a first phase detector (PD) 1, the second PD 2 and the third FD 3, the first solver (PY) 4 and the second PN 5, the first four modulator (DEPOSITS) 6 and second 7 ENTERPRISE, the first, second and third myCitadel 8, 9 and 10, an adder 11, an amplifier 12, the first and second multiplier products 13 and 14, the first and second restrictors 15 and 16, a filter 17, a voltage controlled oscillator (VCO) 18, first, second, the third and fourth XOR 19, 20, 21 and 22.

The transmission ratios of the first vicites 8 on the first input of +1, the second1/2; transfer coefficients of the second vicites 9 to the first input of -1, the second +1; transfer coefficients of the third vicites 10 according to the first input of +1, the second input -1.

Each phase detector 1, 2 and 3 (Fig.2) includes first and second multiplier products 23 and 24, the first and second low pass filters (LPF) 26 and 27 and the phase shifter 90o25. The first inputs of both multiplier products 23 and 24 are connected to the first input FD 1, 2 and 3, a second input connected to the second input of the first multiplier 23 and the input of phase shifter on ogiela 23 and 24 are connected to the inputs of respectively the first and second low-pass filter 26 and 27, which are the first and second outputs FD 1, 2 and 3.

Each solver (PY) 4 and 5 includes first, second, third and fourth stops 28, 29, 30 and 31 and the first and second myCitadel 32 and 33. The first entrance RU 4 and 5 connected to the input of the first limiter 28 and the first input of the first vicites 32, the output of which is connected to the input of the third limiter 30 whose output is the second output PN 4 and 5. The output of the first limiter 28 is connected with the second input of the first vicites 32 and is the fourth release of RU 4 and 5. The second entrance RU 4 and 5 connected to the input of the second limiter 29 and the first input of the second vicites 33, the output of which is connected to the input of the fourth limiter 31 whose output is the first output PN 4 and 5. The output of the second limiter 29 is connected with the second input of the second vicites 33 and the third output PN 4 and 5.

The demodulator operates as follows.

At the demodulator input signal QAM-16, which in the Cartesian basis can be represented as:where0- carrier frequency signal QAM-16; a, b, C, D is selected from the set {+1;-1} information symbols; N(t) is additive noise.

Convert the expression (1) to �r/969.gif">0t; (3) S2= Ccos0t+Dsin0t (4) analysis of the expressions (3) and (4) shows that each of them describes the signal of the four-phase manipulation FM-4, and the information signals are the sets {A, At} and {C; D}, respectively.

The expression (2) is in good agreement with the principle of the so-called superposition signal QAM-16 (see Polezhaev C. A., Wiesel A. A. high-Speed phase modulators and demodulators for digital transmission systems microwave range. Foreign electronics, 1980, 3 - [5]), when the signal is QAM-16 is formed by summing the two signals of the FM-4, one of which is weakened relative to another 6 dB (this corresponds to a factor1/2in the expression (2)).

On the second inputs (inputs reference oscillations) all FD comes from the VCO output signal types:
Sop= cos(0t+), (5)
wherephase mismatch.

In accordance with this principle blocks 23-27, at the first output of the first PD 1 (Fig.2) to generate a signal

and on the second output of the first FD 1 will be formed Susie noise process N(t)
The multiplier products 13 and 14, the stops 15 and 16 and the second myCitadel 9 form the famous diagram of the Costas to form at the output of the second vicites 9 for signal FM-4 control voltage for recovering the carrier frequency in the loop phase-locked loop (PLL).

In the capture state_0 and, in accordance with expressions (6), (7) and logic PN 4 (Fig.3), at its first and fourth outputs will form the transmitted symbols D, C, B, a, respectively (in accordance with the principle of blocks 28-31).

Then the output of the first ENTERPRISE 6 is formed a signal of the form S2(see the expression (4)) and respectively output the first vicites 8 will form the signal S8type:
S8= SI-(1/2)S2. (8)
Substituting in the expression (8) expression (2), we get:
S8=S1+N(t). (9)
Since the output of the second ENTERPRISE 7 is formed, the signal S1of the form (3), the output of the third vicites 10 is formed, the signal S10type:
S10=S8-S1,
S10=N(t).

After that, the signal N(t) allocated thus from the input mixture (1) signal with noise passing through the amplifier 12 with a coefficient of USIM mixture, coming to the first input of the third FD 3.

Selected so the noise from the input mixture signal and noise) cannot be in any way (for example, by subtracting N(t) from SI) used to improve immunity demodulation signals in PD 1-PY 4. This is because the actual procedure of receiving the implementation of the noise N(t) on each interval of the duration of the symbol signal QAM-16 is realized only in the assumption that no errors on the outputs PN 4 (boundaries of such assumptions is theory of potential noise immunity A. Kotelnikov).

Thus, isolated from the input noise N(t) in any way cannot be used to reduce the probability of errors at the output of the demodulator, but it can be used to assess the probability of this error (i.e., signal quality).

Evaluation of the probability of bit error occurs by performing the following operations on the signal.

As you know, when demodulation independent and equiprobable symbols signal QAM-16, the error probability per symbol is calculated using a function
Pwith=f(RI),
where Rc- the probability of bit errors;
RI- input signal-to-noise ratio.

When 232D/chr/8776.gif">(1/4)Pc,
where P is the probability of error in a bit, i.e., the probability of error in each of the four partial channels.

The exact analytical expression of the function f for signals QAM-16 is quite complicated, so in practice usually are widely known graphical representations of functions (see, for example, Peer K. Wireless digital communication. M.: Radio and communication, 2000 - S. 248, Fig. 4.8.3 - [6]).

Known from the literature (for example [6]) dependencies
P = (1/4)Pc= (1/4)f(RI)
you can find the following characteristic value of the probability of error in each partial channel:
P=10-4when RI= 13,2 dB.

At the output of the adder 11 signal-to-noise ratio is less than the input signal-to-noise ratio.

Signal-to-noise ratio R11at the output of the adder 11 is found from the following formula:



where SCam- the input signal is QAM-16.

From the last expression it follows that the third FD 3 demodulates the signal QAM-16 in terms of the signal-to-noise ratio, 10lg(1+K), dB smaller than the first PD 1. In particular, when K = 1 the decrease of the ratio signal/noise is 6 dB.

The first to fourth elements IL is b>to; C and Cto; D and Dto). If RIis large enough, the probability of error at the output of the first RU 4 can be neglected and assumed that all pulses mismatch on the fifth-eighth outputs of the device are caused by the deterioration of the signal-to-noise ratio on the value 10lg(1+K) dB.

Then, by measuring the frequency of occurrence of pulses in the fifth-eighth outputs of the device, it is possible to indirectly estimate the probability of error respectively, the first and fourth outputs of the device.

Thus, by measuring Rnyou can find RIby inverse solution of the equation
Pn= (1/4f)(RI-10lg(1+K)),
where Rn- the frequency of appearance of pulses at the fifth and eighth outputs of the device, i.e. the probability of a discrepancy between the symbols a and ato(or In Intoor C and Ctoor D and Dto). Knowing RIusing the direct solution of the equation
P = (1/4f)(RI),
you can find the probability of error in each of the partial digital channels (on all four outputs of the demodulator QAM-16).

For example, let RIis the value more than 10 dB, unknown accurately and accordingly do not know the exact value of R. Let the gain of the amplifier 12 is selected so that at the output of amatadine signals a and Atois Rn= 510-2. Then the curve f(RI-3 dB) can be found that RI=10 dB, and accordingly the curve f(RIyou may find that P=510-5.

Thus, by forming a noise component from the input signal and, with it, the deterioration of the signal-to-noise ratio in the control phase detector, in the present demodulator is achieved technical result: the dimension of the probability of error in each of their four partial digital channels.

In the present demodulator measurement error probability is directly on grafikom (information) signal, which may not be pre-specified in the specifications singlecompany.


Claims

1. The demodulator shestnadtsetirichnoe quadrature amplitude manipulation, containing the first phase detector, the first input of which is connected to the input device and to the first input of the first myCitadel, a second input connected to the output of the first four of the modulator first input connected to the output of the generator, voltage-controlled, and the second and third whoudini respectively with the first and second outputs of the first phase detector, the second input of which is connected to the second input of the second phase detector and the output of the generator, voltage-controlled, the input connected to the filter output, the input connected to the output of the second myCitadel, the first and second inputs which are connected respectively to the outputs of the first and second multiplier products, the first inputs of which are connected respectively to the outputs of the first and second limiters, the input of the first limiter connected to the second input of the second multiplier and a second output of the second phase detector, the input of the second limiter connected to the second input of the first multiplier and the first output of the second phase detector, a first input connected to the output of the first myCitadel, the first, second, third and fourth outputs of the first deciding device are respectively the first, second, third and fourth outputs of the device, characterized in that it contains an additional third myCitadel, amplifier, adder, the third phase detector, the second solver, the second four-position modulator, the first, second, third, and fourth XOR, and the first and second inputs of the third vicites connected respectively to the outputs of Pervov is responsible with the generator output, voltage-controlled, third and fourth outputs of which are connected respectively to the first inputs of the first, second, third, and fourth XOR, the outputs of which are respectively the fifth, sixth, seventh and eighth outputs of the device, and the second inputs are connected respectively to the first, second, third and fourth outputs of the second casting device, the first and second inputs which are connected respectively with the first and second outputs of the third phase detector, a second input connected to the output of the generator, voltage-controlled, and the first input with the output of the adder, first input connected to the first input of the first myCitadel, and the second input with the amplifier output, the input connected to the output of the third myCitadel.

2. The demodulator under item 1, characterized in that each phase detector includes first and second multiplier products, the first and second low pass filters and Phaser 90oand the first inputs of both multiplier products are connected to the first input of the phase detector, the first input connected to the second input of the first multiplier and the input of the phase shifter 90owhose output is connected to the second input of the second perennou lower frequencies, which are the first and second outputs of the phase detector.

3. The demodulator under item 1, characterized in that each critical device includes first, second, third and fourth limit switches and the first and second myCitadel, and the first sign of a casting device is connected to the input of the first limiter and the first input of the first myCitadel, the output of which is connected to the input of the third limiter whose output is the second output of a casting device, the output of the first limiter connected to the second input of the first vicites and is the fourth release of a casting device, the second input of the casting device is connected to the input of the second limiter and the first input of the second myCitadel, the output of which is connected to the input of the fourth limiter, the output is the first output of a casting device, the output of the second limiter connected to the second input of the second vicites and is the third release of a casting device.

 

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