KR20010104994A - Synchronization method of reference signal of transceiver for optical repeater in mobile communication - Google Patents

Abstract

The present invention relates to a method of synchronizing a reference signal used in a transmitting and receiving end of a mobile communication optical repeater. The repeater consists of a transmitter and a receiver, each of which requires a reference oscillator that is the reference of the system. Since the performance of the reference oscillator greatly affects the whole system, it should be excellent in phase noise and frequency stability. Also, since CDMA mobile communication uses QPSK modulation, the phase information of the received signal is important. Transmitting and receiving signals are modulated or demodulated by each reference frequency. If the reference frequency of the transmitter and the receiver are not synchronized, it is difficult to obtain accurate information due to the phase error. Currently, the base station receives a very stable 10MHz signal from the GPS satellite at the transmitting and receiving stages to synchronize frequencies. In addition, repeaters use OCXO (Oven Compensated Crystal Oscillator), which has excellent frequency stability. However, both methods are expensive and bulky.

In order to obtain accurate information, the optical repeater must also synchronize the transceiver reference signal. An optical repeater is a wired relay method that carries an RF signal to light generated from a laser diode, transmits it through an optical fiber, and then converts the light into RF through a photodiode to transmit the signal. Therefore, if the 10MHz transmitter reference frequency is sent to the receiver as it is through the optical fiber to be used as the reference signal of the receiver, the frequency can be synchronized at the lowest cost. However, in the optical repeater, a conversion module that converts a radio wave into light and a light wave into a radio wave is used. Since the frequency band is not wide, it is possible to simultaneously convert a 10 MHz reference signal and an information signal of 800 MHz band (Cellular) or 1800 MHz band (PCS) at the same time. In this case, the loss is large. Therefore, the 10MHz reference signal is raised to 800MHz or 1800MHz, and then transmitted along with the information signal through the optical fiber, and the bandpass filter is used to separate the reference signal and the information signal. The separated signal is lowered to 10MHz using a prescaler, and then a phase locked loop (PLL) is formed by using a voltage-controlled crystal oscillator (VCXO) in a 10MHz band with excellent phase noise, thereby restoring a 10MHz reference signal having excellent phase noise characteristics. do. By using the restored reference signal as the reference frequency of the receiver, if the local oscillator of the receiver is implemented, an accurate signal can be detected. Using this synchronization method, a high performance receiver reference signal synchronized with the reference frequency of the transmitter can be obtained.

Description

Synchronization method of reference signal of transceiver for optical repeater in mobile communication}

The technical field of the present invention is the frequency synchronization technology of the transmission and reception reference signal used in the mobile communication repeater. Currently, the base station uses a method of synchronizing frequencies by receiving 10 MHz signals from the GPS to the transmitting and receiving ends, and repeaters use OCXO (Oven compensated crystal oscillator) with excellent frequency stability. However, both methods are expensive and bulky.

The present invention is to solve the disadvantages of the conventional transmission and reception reference signal synchronization method used in the optical repeater to provide a simple and inexpensive new performance synchronization method.

1 is a transmission and reception reference signal synchronization method for an optical repeater

2 is a transmitter PLL module

3 is a receiver PLL module

4A shows frequency characteristics of a local oscillation frequency of a system using a prescaler output signal (A of FIG. 3).

Fig. 4b shows the phase noise characteristics of the local oscillation frequency of the system using the prescaler output signal (A in Fig. 3).

5A shows frequency characteristics of a local oscillation frequency of a system using a VCXO output signal (B of FIG. 3).

5B is a phase noise characteristic of a local oscillation frequency of a system using a VCXO output signal (B of FIG. 3).

1 shows a method of synchronizing a transceiver reference signal for an optical repeater according to the present invention. The configuration of Figure 1 is a) a step of raising the 10MHz reference signal to the 800MHz band (Cellular) or 1800MHz band (PCS) using the PLL to the optical module (Fig. 2), and b) 800MHz band (Cellular) through the optical fiber ) Or separating the 1800 MHz band (PCS) reference signal using a band pass filter and then lowering it to 10 MHz using a prescaler, and c) configuring the PLL using a VCXO that has excellent phase noise characteristics for the received 10 MHz signal. Obtaining a reference signal (FIG. 3).

4 is a characteristic of an output signal when a PLL for an RF LO for a PCS system is configured using a reference signal (A of FIG. 3) having a signal separated by a bandpass filter reduced to 10 MHz using a prescaler.

5 is a characteristic of an output signal when a PLL for an RF LO for a PCS system is configured with an output (B in FIG. 3) as a reference frequency when a PLL is configured using a VCXO.

In the present invention, the 10MHz reference signal of the transmitting end is raised to 800MHz band (Cellular) or 1800MHz band (PCS), and then sent to the receiving end through the optical fiber, and then lowered to 10MHz again to be used as the reference frequency of the receiving end, so that the synchronization system is simple and the price is low. It is cheaper. In addition, the present invention can improve the phase noise characteristics of the reference frequency by configuring the PLL using the VCXO. When the RF local oscillation frequency of the system was implemented using the reference frequency using the actual VCX0 (FIG. 5b), it was confirmed that 8dBc / Hz was improved at an offset of 1 KHz than when the VCXO was not used (FIG. 4B).

Claims (1)

In the reference signal synchronization system of the transceiver of the optical repeater, the 10MHz reference signal is raised to 800MHz band (Cellular) or 1800MHz band (PCS) using a PLL and input to the optical module (Fig. 2) and the 800MHz band passed through the optical fiber. (Cellular) or 1800MHz band (PCS) reference signal is separated by using a band pass filter, and then reduced to 10MHz using a prescaler, and the received 10MHz signal using a VCXO with excellent phase noise characteristics to form a PLL Method of configuring a reference signal synchronization system for an optical repeater comprising the step of obtaining a signal (Fig. 3)