WO2013166750A1 - M-ary digital pulse period modulation and demodulation method for use in optical communication system - Google Patents

Abstract

An M-ary digital pulse period modulation and demodulation method for use in an optical communication system, which relates to an M-ary digital pulse period modulation and demodulation method. It is intended to improve the data transmission rate of an optical communication system. The modulation method is that: the M-ary system data of an optical communication system are modulated into a binary pulse using an MDPCM method; and the modulation method is realized by changing the period of the binary pulse corresponding to each code element in the M-ary system data. The demodulation method is that: demodulated data are obtained from the modulated binary pulse according to a demodulation formula. The present invention is applicable to an optical communication system.

Description

 Multi-digit digital pulse period modulation and demodulation method for use in an optical communication system

 The present invention relates to a multi-ary digital pulse period modulation and demodulation method.

 Background technique

 At present, the optical communication field mainly uses Intensity Modulated/Direct Detection (TOP/DD) technology, and there are mainly three types of modulation methods based on M/DD technology: 00K, On-Off-Keying, Pulse Position Modulation (PPM) and Digital Pulse Interval Modulation (DPM) modulation.

 The key-critical mode realizes the transmission of information by controlling the light-emitting diode (LED) in the optical communication. When the LED is off, it indicates that the data is "0"; when the LED is lit, it indicates that the data is transmitted "1"; The method has simple circuit requirements, does not require symbol synchronization, and has high bandwidth utilization. It is currently the modulation technology that supports the highest utilization of IM/DD bandwidth.

 Pulse position modulation divides the transmitted waveform into equal proportions into small time slots. The positions of the small time slots are different, and the information represented is different. The advantage of pulse position modulation is that it improves the energy utilization efficiency, but it requires high bandwidth and requires slot synchronization and symbol synchronization at the receiving end, which also increases the difficulty of the circuit.

 Digital pulse interval modulation is a non-isochronous pulse interval modulation method based on the improvement of pulse position modulation. The same small time slot as pulse position modulation is used, but the symbol length is changed, and different symbol lengths are represented. Different information; digital pulse interval modulation has higher energy utilization than open-key modulation; compared with pulse position modulation, no need for slot synchronization and symbol synchronization at the receiving end, which reduces the complexity of the circuit. degree. However, digital pulse interval modulation also has a high bandwidth requirement.

 For the actual optical communication system, since the switching speed of the LED of the light-emitting element is limited, it often becomes a bottleneck of the transmission speed, and the communication efficiency of the optical communication link is limited. Typically, it is only a few tens of MHz, how to improve the bandwidth when the bandwidth is limited. The data transmission rate of existing optical communication systems has become the target for studying new modulation and demodulation methods.

 Summary of the invention

 SUMMARY OF THE INVENTION The present invention is directed to improving the data transmission rate of an optical communication system, thereby providing a multi-digital digital pulse period modulation and demodulation method for use in an optical communication system.

 A multi-digit digital pulse period modulation and demodulation method for use in an optical communication system, a modulation method: modulating a f-ary system data of an optical communication system into a binary pulse by using a MDPCM method;

The modulation method is to change the period of the binary pulse corresponding to each symbol in the system data of the f-ary system. Implemented; the cycle is based on the formula:

T (n) = t _BS + (n + \) - obtained by t _slot ; where: w is the symbol in the system data of f-ary, " = 0,1,...,M-1; ^ The duration of the MDPCM modulated fundamental waveform, t _itoi is the time resolved interval between the modulated pulse periods of two adjacent symbols; is a positive integer greater than two.

Demodulation method: The modulated binary pulse is based on the formula:

 Obtain the demodulated data; where Γχ is to demodulate the received binary pulse cycle time, [□] represents the rounding function, when “< 0 or “> Μ -1, it means “empty symbol, does not mean any information.

The relationship between the time-resolved interval t^ between the modulation pulse periods of each symbol in the binary system data and the basic waveform duration ^, satisfies the following equation:

The duration of the MDPCM modulation basic symbol t _BS is:

^BS 0.555

 Where is the bandwidth of the optical communication system.

The time resolution interval t ^ between the modulation pulse periods of MDPCM adjacent symbols is:

 Where Γ is the time interval error of modulating two adjacent symbols.

 Advantageous Effects: The present invention is an MDPCM modulation method. The present invention distinguishes different information according to different transmission symbol periods, improves bandwidth utilization, and can greatly increase information transmission rate under the same bandwidth.

 DRAWINGS

1 is a schematic diagram showing the waveform of the modulation method of the present invention; FIG. 2 is a schematic diagram showing the structure of the optical communication system of the present invention; and FIG. 3 is a schematic diagram of the principle of the pulse triggering error. detailed description

 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the present embodiment will be described with reference to FIG. 1 for a multi-digit digital pulse period modulation and demodulation method in an optical communication system, and a modulation method: a method for using MDPCM of a system data of an optical communication system Modulated into binary pulses;

 The modulation method is implemented by changing a period of a binary pulse corresponding to each symbol in the f-ary system data; the period is according to a formula:

T(n) = t _BS + (n + \)-t _slot obtained; where: w is the symbol in the system data of f-ary, "=0,1,...,M-1; ^ The duration of the MDPCM modulated fundamental waveform, t _itoi is the time resolved interval between the modulated pulse periods of two adjacent symbols; is a positive integer greater than two.

Demodulation method: The modulated binary pulse is based on the formula:

 Obtain the demodulated data; where Γχ is to demodulate the received binary pulse cycle time, [□] represents the rounding function, when “<0 or ”-1, it means “empty symbol, does not mean any information.

 Principle: MDPCM modulation (M-ray Digital Pulse-Cycle Modulation) is a non-isochronous pulse time modulation method for multi-ary transmission systems, which belongs to the category of pulse period modulation. The information is transmitted by encoding the original data onto the transmitted symbol period. The period in which the symbol is transmitted is variable and is determined by the information carried in the symbol. In order to ensure a high transmission rate, the difference in cycle time corresponding to adjacent data is small. Then, according to the period, the waveform of the symbol transmission is accurately constructed.

 MDPCM modulation is a binary pulse that modulates different periods of different numbers. In MDPCM modulation, all symbols of information in f-ary are represented as ", = 0, 1, ..., M-1, then symbols The corresponding modulation signal period is:

T(n) = t _BS + (n + l) - t _{slot (1)} where is the MDPCM modulated fundamental waveform duration, and t, _nt is the time-resolved interval between the modulated pulse periods of each symbol after MDPCM modulation. In MDPCM modulation, the relationship between t and ^ satisfies the following formula:

When demodulating at the receiving end, it can be obtained from equation (1), ie:

 Where Γχ is the demodulated pulse cycle time, [□] indicates the rounding function. When <0 or Μ-1, it means “empty symbol, does not represent any information.

According to equation (1), it can be concluded that the MDPCM modulated signal waveform is as shown in FIG. The MDPCM waveform consists of two parts, the basic waveform part and the information waveform part. The basic waveform portion is a fixed portion of the MDPCM modulated waveform, consisting of a "10" pulse of duration ^, where "1" level duration t _ff , " ₀ " level duration ^. The information waveform part is the change part of the MDPCM modulation waveform, the duration is ^), by "+ 1 time resolution interval

^ Composition.

 Figure 1, MDPCM modulated signal expression is:

₍₄₎ 其中， ^≤^< + (« + 1^^， 每个码元的周期是指当前码元的上升沿到下一个 码元的上升沿之间的时间间隔， 由于每个码元波形在结束时均需要恢复到零电平， 因此该 调制方式属于归零码范畴。 «

₍₄₎ where ^ ≤ ^ < + (« + 1^^, the period of each symbol refers to the time interval between the rising edge of the current symbol and the rising edge of the next symbol, due to each symbol The waveform needs to be restored to zero level at the end, so the modulation method belongs to the return-to-zero code category.

 In equation (4), ^, ^, and values are involved. The following is a detailed analysis of the relationship between ^, ^ and ^^ values and system performance.

The choice method of t _H and ^: From equation (1), min{r(«)} = J(-l) = t _ss , which is the minimum period time of the waveform in this modulation mode, according to the reciprocal relationship between time and frequency. , ^ corresponds to the bandwidth of the highest bandwidth of the modulation mode. It is known from the Nyquist bandwidth that if a binary symbol is transmitted per second, the minimum bandwidth required is = /2 Ηζ. Due to the limitations of the actual filter, the system bandwidth is generally 1.4 times wider than the minimum bandwidth of the Nyquist. When the bandwidth is determined, the value of ^ and ^ should satisfy: \.\B

 1

 >.

^L "ll^ (5) again = +t _r , then the duration of the MDPCM modulation basic symbol ^ satisfies:

How to determine 0.555 (6):

 It is known from equation (4) that it is the time resolution interval for distinguishing the waveforms of each symbol in MDPCM modulation, and its value will be determined.

Data transmission efficiency of MDPCM modulation. The system block diagram of optical communication is shown in Figure 2.

 MDPCM transmits information by changing the period of the transmitted symbols, so measuring the accuracy of the waveform period at the receiving end is the key to correctly recovering the original code. It can be analyzed from Fig. 2 that the period measurement error of the MDPCM modulation waveform mainly comes from the occurrence of MDPCM modulation waveform, electro-optical conversion, photoelectric conversion, and demodulation end to MDPCM demodulation. By classifying these errors, digital modulation and digital demodulation can be used to express the time interval error TIE (Time Interval Error) as:

TIE = Shi _{[TE docki + TE triggerl + TE} counterl + TE trigger2 + TE trigger3 + TE dock2 + TE trigger4 + TE counter2]

(7) The system random error of equation (7) uses the most unfavorable case absolute value synthesis method, where:

^TE ^: transmitting periodic pulse generator circuit of the modulator as clock accuracy error, usually within ^10-5;

^TEtri,: The pulse trigger error when the transmitter modulation circuit generates the MDPCM modulation waveform;

^TE : ±1 count error of the periodic pulse generator of the transmitting end modulation circuit;

^{TEtri 2} : Electro-optic conversion jitter error of the transmitting circuit of the transmitting end;

^TE : photoelectric conversion jitter error of the receiving terminal receiving circuit;

^TE ^ 2, the accuracy error of the receiving end clock pulse measurement period of the demodulating circuit, typically less than ^10-5;

^{TEtri 4} : Pulse trigger error when the receiving modulation circuit recovers the MDPCM waveform;

TE _counter2 : ±1 count error of the modulation pulse of the receiving circuit.

^3⁄4. M, ^3⁄4. When the circuit is employed accuracy oscillator ^10-5 or higher, and _t, 1, TE, ₇ 2 of The ±1 error is negligible.

The pulse trigger error includes the rising edge trigger error r3⁄4 _ff and the falling edge trigger error Γ. As shown in Figure 3, for a given decision threshold, the pulse trigger error is caused by noise and distortion in the input signal due to temperature change, linearity. The voltage level changes and the trigger level drift introduced by component aging, as well as the energy effect of the rapidly rising signal.

In the pulse trigger error, TE _trig is the pulse trigger error when the transmitter modulation circuit generates the MDPCM modulation waveform, which is negligible compared with the transmitter ±1 count error ^ _∞ „„^. Similarly, 7¾ _"4 and the receiving end _¾ ^ ± 1 count error. ₂ can be neglected compared.

 Therefore, equation (7) can be approximated as:

a — ^counterl ^{τ 1} ^trigg r! ^{τ 1} ^triggeri ^{τ 1} ^counterA” ( g ) For electro-optic photoelectric conversion error 7E _{g 2} TE _trigger3 In visible light communication systems, three typical sources of receiver jitter are LEDs and LED switching fluctuations caused by the drive circuit, multipath effects caused by the path of the transmitting and receiving ends, and jitter caused by receiver noise. According to the analysis of Fig. 3, the multipath effect caused by the path of the transmitting and receiving ends, when the transmitter and the receiver are stationary, the optical multipath effect reaching the receiver can only cause the jitter of the falling edge of the receiver, and the demodulation of the MDPCM is only Measuring the period duration of the symbol is not sensitive to the jitter of the falling edge, so the cause 2 can be ignored. It can be set that the maximum value of the photoelectric and electro-optic conversion trigger error is r^ _ffmax, then 7 _gger2 + _{trigger3 <} 2 _LH (8) can be written as:

TIE-土[ E _{2TE Lffmax} + TE _counter2 ] ( 9 ) The formula for selecting t ^ from equation (9) is: t _slot >WIE

 (10)c

Claims

claims 1. Multi-ary digital pulse period modulation and demodulation method used in optical communication systems. Its characteristics are: Modulation method: Modulate the f-ary system data of the optical communication system into binary pulses using the MDPCM method; The modulation method is achieved by changing the period of the binary pulse corresponding to each symbol in the f-ary system data; The period is based on the formula: T (n) = t _BS + (n + \) - t _slot , obtained; where: w is the code element in the system data in base f, " = 0,1,...,M— 1; ^ is the duration of the basic waveform in MDPCM modulation, t^ is the time resolution interval between the modulation pulse periods of two adjacent symbols; is a positive integer greater than 2; Demodulation method: Modulate the binary pulse according to the formula: n = -l],

Obtain the demodulated data; where Γχ is the binary pulse cycle time received by demodulation, and [□] represents the rounding function. 2. The multi-ary digital pulse period modulation and demodulation method used in optical communication systems according to claim 1, characterized in that the difference between the modulation pulse periods of adjacent symbols in the f-ary system data is The relationship between the time resolution interval t^ and the basic waveform duration^ satisfies the following formula: lot < ^BS. 3. The multi-ary digital pulse period modulation and demodulation method used in optical communication systems according to claim 1, characterized in that the value of the duration of the MDPCM modulation basic waveform is: ° 0.55Β In the formula, is the bandwidth of the optical communication system. 4. The multi-ary digital pulse period modulation and demodulation method used in optical communication systems according to claim 1, characterized in that the value of the time resolution interval t between the modulation pulse periods of adjacent symbols is: t, _ot > 2 \TIE\, where Γ is the time interval error of modulating two adjacent symbols.