DBPSK调制方式是利用前后相邻码元的载波相对相位变化传递数字信息的，所以又称为相对相移键控。假设 △q为当前码元与前一码元的载波相位差，可定义一种数字信息与△q 之间的关系为：
DBPSK modulation transmits digital information using the relative phase alterations of the carriers of previous-and-next neighboring code-elements, therefore is also called relative phase shift keying. Assume Δq is the phase difference of carrier between the current and the previous code-elements, and the relation between a digital information and Δq can be defined as:
于是可以将一组二进制的数字信息与其对应的DBPSK信号载波关系示例如下：
Thereby, the relation between an array of binary digital information and their corresponding DBPSK signal carriers can be demonstrated as the following:
同时数字信息与△q之间的关系也可定义为
Meanwhile, the relation between digital information and Δq can also be defined as
由此示例可知，对于相同的基带数字信息序列，由于初始相位不同，2DPSK信号的相位并不直接代表基带信号，而前后码元相对相位的差才唯一决定信息符号。
From this demonstration it can be told that, for identical sequences of baseband digital information, due to the difference of their initial phases, the phase of 2DPSK signal does not directly represent baseband signal; rather, it is the relative phase difference between previous and next code-elements that uniquely determines information symbols.
2DPSK信号的产生方法：先对二进制数字基带信号进行差分编码，即把表示数字信息的序列的绝对码变换成相对码（差分码），然后再根据相对码绝对调相，从而产生二进制差分相移键控信号。2DPSK信号调制器原理框图如图２－4所示。
Method to generate 2DPSK signal: First, apply differential encoding to the binary digital baseband signal, namely convert the absolute codes representing digital information sequence into relative codes (differential codes). Then, generate binary differential phase shift keying signal by absolute phase modulation on the relative codes. The block diagram of the principle of 2DPSK signal modulator is shown in Fig. 2-4.
差分码可取传号差分码或空号差分码。其中，传号差分码的编码规则为
Differential code may take marking differential code or vacant differential code. Where the encoding rule of the former is
（1）
式中：为模２加；为的前一码元，最初的可任意设定。
Where: is module-2 plus; bn-1 is the previous code-element to bn; the initial value of bn-1 can be set at random.
式（1）称为差分编码（码变换），即把绝对码变换为相对码
Formula (1) is called differential encoding (codes conversion) through which to convert absolute codes into relative codes.
2.DBPSK信号的解调原理及组成结构
2. Demodulation principle and composition of DBPSK signal
DBPSK信号有两种解调方法，其中之一是相干解调（极性比较法）加码反变换法。其解调原理是：对DBPSK信号进行相干解调，恢复出相对码，再经过码反变换器变换为绝对码，从而恢复出发送的二进制数字信息。在解调过程中，由于载波相位模糊性的影响，使得解调出的相对码也可能是“1”和“0”倒置，但经差分译性带来的问题。DBPSK相干解调的原理框图可由图6所示。
DBPSK signal can be demodulated in two ways. One is coherent demodulation (polarity comparison method) plus code inverse transformation method, whose demodulation principle is: Apply coherent demodulation to DBPSK signal to regain relative codes to be converted into absolute codes through code inverse transformer, so that the emitted binary digital information is regained. During the demodulation process, vagueness of carrier’s phase may lead the demodulated relative codes to be the inverse of “1” or “0”, yet an issue brought about from differential. The block diagram of the principle of DBPSK coherent demodulation is shown in Fig. 6.
上图中的码反变换器的基本原理为：
Where the fundamental principle of the code inverse transformer is:
an = bn⊕bn-1
式中：⊕为模2加，bn为解调后得到相对码元序列，bn-1 为bn的前一个码元，an为所要求的绝对码元。
Where: is module-2 plus; bn is the sequence of relative code-elements after demodulation; bn-1 is the previous code-element to bn; an is to be determined as the absolute code-element.
DBPSK信号的另一种解调方法是差分相干解调（相位比较法），其原理框图可由图2-7所示。用这种解调的方法时不需要专门的相干载波，只需由收到的DBPSK信号延时一个码元间隔Ts，然后与DBPSK信号本身相乘。相乘起着相位比较的作用，相乘的结果反映了前后码元的相位差，经低通滤波器后在抽样判决，即可直接恢复出原始数字信息，故解调器中不需要码反变换器。
Another demodulation method for DBPSK signal is differential coherent demodulation (phase comparison method), whose principle can be demonstrated as the block diagram in Fig. 2-7. No specific coherent carrier is in need for this demodulation method; the only requirement is to delay the received DBPSK signal by a code-element interval Ts, before multiplying the DBPSK signal itself. The multiplication serves a function as phase comparison. The product reflects the phase difference between the previous and next code-elements. The original digital information can directly be regained through a low-pass filter before sampling and arbitration, thus no code inverse transformer is required in demodulator.
由于这种方法用模块更好实现，并且解调的效果也很好，所以在运用Simulink模块实现DBPSK解调器时，采用后一种差分相干解调的方法
This method can be better implemented using module with more effective demodulation, so the latter differential coherent demodulation method is adopted when Simulink Module is applied to implement the DBPSK demodulator.
3.
构建DPSK调制与解调电路，并用示波器观察调制与解调前后的信号波形。
Construct DPSK modulation and demodulation circuits and observe the signals’ waveforms before and after modulation and demodulation using an oscilloscope.
第一条是原始的基带信号，第二条为2DPSK信号的波形，第3条为解调后的波形。可以看出第一条和第3条的波形相同，说明了仿真正确。
The first strip is the original baseband signal; the second is the waveform of 2DBSK signal; the third is the waveform after demodulation. It can be seen the first and the third are the same in waveform, thereby the simulation is correct.
图4-15可知，解调后的码元序列与发送的码元序列向比较延时了进两个码元时间，以致后面的两个码元无法在示波器中显示出来。但解调后所得到的码元序列与发送码元序列相比有发生码元的失真，从而得出用Simulink模块所设计的DBPSK解调器符合要求，同时DBPSK的调制波形也和发送码元相吻合，证明整个模型工作正常，满足设计的要求。
From Fig. 4-15 it can be seen that, the sequence of demodulated code-elements delays by approximately two code-element intervals as compared with the emitted sequence of code-elements, such that, the following two code-elements cannot be shown in oscilloscope. But a distortion has occurred to the code-elements in the regained sequence after demodulation compared to the emitted code-elements sequence, thereby it is concluded that the DBPSK demodulator designed by Simulink Module meets the demand, meanwhile the modulation waveform of DBPSK also matches that of the emitted code-elements, which proves that the entire module works in a normal state and meets the designing requirement.
