synchronization(編輯修改稿)
2025-08-13 17:35 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 Nonlineartransformationbased method ? Square PLL 18 Inphase orthogonal loop— Costas Loop 2. Inphase orthogonal loop —Costas Loop Contains inphase branch and orthogonal branch. All parts except LF and VCO are similar with a “phase detector”. 19 ? ? ? ?? ? ? ? ? ? ? ? ? ?? ? ? ?? ? ? ?11L e t s c o s111c o s sin sin sin 2221Af te r L P F sin212(cc c e e c eeeeet f t tf t t t f t f t tr t f tW he n r t f t?? ? ? ? ? ??????? ? ? ? ???（ ） upper branch is the phase difference between generat ed carrier and the original carrier is small ，? ? ? ? ? ?? ? ? ? ? ?2222)11c o s221( 3 ) ( )4e1 e dr t f t f tr t r t f t v t????? ? ? lower branchInphase orthogonal loop— Costas Loop ? ? ? ?c21 .Co st a s lo o p wo r k s o n in st e a d o f 2 so wh e n f is la r g eCo st a s lo o p is e a si e r to r e a liz e2 .T h e o u tp u t o f in p h a se lo o p r is th e s ig n a l fccffttAdvantages of Costas loop ： ， ，20 Performance 3. Performance of carrier synchronization technique 1) Phase error: steadystate phase error, random phase error 2) Synchronization build time and hold time 21 Symbol Synchronization ? In a digital munication system, the output of the receiving filter must be sampled periodically at the symbol rate and at the precise sampling time instance. ? To perform this periodic sampling, we need a clock signal at the receiver ? The process of extracting such a clock signal is called symbol synchronization or timing recovery ? One method is for the transmitter to simultaneously transmit the clock frequency along with the information signal. The receive can simply employ a narrowband filter or PLL to extract it. This method requires extra power and bandwidth and hence, but frequently used in telephone transmission systems. ? Another method is to extract the clock signal from the received data signal by using some kind of nonlinear transformation. 22 EarlyLate Gate Synchronization ? Basic Idea: exploit the symmetry properties of the output signal of matched filter or correlator ? Due to the symmetry, the values of the correlation function at the early samples and the late samples are equal. ? Thus, the proper sampling time is the midpoint between and 23 24 Nonlineartransformationbased method 1. Nonlineartransformationbased method Some transformations can add synchronous signal with f=1/T to the original signal. For example, we can transform the signal to returntozero waveform. After narrowband filtering and phase shifting, we can generate the clock signal used for synchronization. 25 Digital PLL (DPLL) 2. DPLL 26 Digital PLL (DPLL) 27 Performance 3. Performance of symbol synchronization system —DPLL 1). Phase error 2). Synchronization build time 3). Synchronization hold time 4). Synchronous bandwidth 28 Frame Synchronization ? Recall that carrier and symbol synchronization nee
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