KR960001041B1 - Multiple access circuit in the direct spread spectrum - Google Patents

Abstract

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Description

Direct Spread Communication Multiple Access Circuits

1 shows a multiple access circuit of a conventional direct spread communication method.

2 illustrates a multiple access circuit of a direct spread communication method according to the present invention.

The present invention relates to a direct spread communication method, and more particularly, to a multiple access circuit of a direct sequence spread communication method.

In the general direct sequential spreading communication method, modulation and demodulation are performed by using the same PN code and the same carrier frequency in the communication between the main transmitter / receiver and the carrier / receive period. In this case, when implementing the receiver, not only the carrier wave but also the synchronization tracking of the spreading code is required at the same time. In the case of multiple communication, the near / far effect becomes serious.

1 is a block diagram illustrating a conventional multiple access method of a direct spread communication method.

In FIG. 1, the transmitting unit includes a mixer 10 for mixing data and spreading codes from the spreading code generator 20, and a mixer 40 for mixing with the spread signal and the carrier generated by the carrier generator 30. Consists of.

The receiver includes a mixer 60 for mixing the received signal with a spread code from the spread code generator 50, a band pass filter 70 for band filtering the signal from the mixer 60, and the band pass filter 70. And a mixer 90 for outputting the recovered data by mixing the signal from the carrier generator 80 with the output signal.

The operation according to the above configuration is as follows.

At the transmitter, the user data is spread by the mixer 10 using the given spreading code and the signal is mixed in the mixer 40 with the carrier generated in the carrier raw wing 30 again. Since the receiver receives signals from several users, it extracts the data from a specific user and performs despreading by exactly synchronizing with the PN code used by the user. Therefore, in the receiver, when the PN code used for spreading in the transmitter and the PN code used for backspreading are the same, the signal passing through the mixer 60 shows an output through the band pass filter 70, but the PN code used in the spreading. If the PN codes used in reverse spreading are different, only a very weak signal is output. Therefore, if a PN code unique to each user is used, multiple access is possible.

However, when implementing a code division multiple communication receiver, not only carrier synchronization but also synchronization tracking of spreading codes is required at the same time. In addition, the perspective problem (NEAR / FAR EFFECT) in multiple communication has become serious. That is, when communicating between one master and multiple slaves, if power control is not performed well, communication between remote slaves and masters becomes impossible due to interference by nearby slaves. Occurs.

An object of the present invention is to provide a multiple access circuit of the asynchronous direct spread communication method by assigning different spreading codes and identification frequencies to each user in the direct spread communication method.

In order to achieve the above object, the multiple access circuit of the direct spread communication method of the present invention allocates and spreads a different code to each user, modulates the spread signal using an intermediate frequency and a different identification frequency, and modulates the signal. A transmitter for modulating a carrier wave; First means for removing carrier and identification frequency from the signal from the transmitter, and second means for outputting a data signal modulated by the spreading code from the signal of the first means, and digitalizing the output signal of the second means. And a receiving unit comprising bit spreading and tracking, a spreading code output with bit synchronization, and third means for demodulating the digitalized signal.

Referring to the accompanying drawings, a multiple access circuit of a direct spread communication method according to the present invention will be described.

2 is a block diagram illustrating a multiple access circuit of a direct spread communication method according to the present invention.

In FIG. 2, the transmitter 92 mixes the input data DATA using spread PN code data, and an identification frequency to the spread signal from the mixer 101. f _ID ) and a mixer 103 for mixing the signal from the intermediate frequency (f _IF ) generator 102, the signal from the mixer 103 and a carrier frequency (f _C ) generator ( And a mixer 105 for mixing and transmitting the signals from the 104.

The receiver 94 mixes the signal from the mixer 105 with the signal from the carrier frequency f _C and the identification frequency f _ID generator 106 from the mixer 107. A band pass filter (BPF) 108 for band-passing the signal of the amplifier, an amplifier 109 for amplifying the signal from the band pass filter 108, and a signal of the amplifier 109. A square circuit (() ² )) 110 that squares, a band pass filter 111 that band-passes the output signal of the square circuit 110, and 1 / N that divides the signal from the band pass filter 111. Pass through N frequency division circuit (1 / N) 112, Loop Filter (LF) 114, Voltage Controlled Oscillator (VCO) 115, 1 / N frequency division circuit 116 Phase comparator (PC) 113, which compares the phase of one signal with the signal from the frequency division circuit 112, outputs the output signal of the voltage controlled oscillator 115 to 1; 1/2 dividing circuit (1/2) 117 for dividing / 2, a mixer 118 for mixing the output signal of the amplifier 109 and the output signal of the 1/2 dividing circuit 117, and the mixer ( Low pass filter (LPF) 119 for low pass filtering the output signal of 118, amplifier 120 for amplifying the output signal of the low pass filter 119, analog output of the amplifier 120 Bits that cause the output signal of the analog digital conversion circuit 121, the PN code generator 122, and the analog digital conversion circuit 121 to convert the signal into a digital signal to be synchronized with the PN code generator 122. Bit Synchronization / Tracking 123 and a PN code from the PN code generator 122 to a demodulator circuit 124 that demodulates the output signal of the analog digital conversion circuit 121. Consists of.

The operation according to the above configuration is as follows.

The transmitter 92 spreads the user data DATA to the PN code generator PN 100, modulates the spread data as a result of the intermediate frequency and the identification frequency generator 102, and modulates the carrier data to the carrier generator 104. Output

The receiver 94 may firstly demodulate the output signals of the carrier and the identification frequency generator 106 and filter the result with a band filter 108 having a bandwidth of BW around the intermediate frequency to remove the carrier and the identification frequency. .

In this case, the interval fi between two adjacent users' identification frequencies is much smaller than BW, so when looking at the result of the band pass filter 108, the desired signal is spread around the intermediate frequency f _IF , and the other user signals f is diffused around _IF ± nf _i . Here, nfi means the identification frequency f _{ID, n} of the nth user. The signals are then amplified through the amplifier 109. The signal amplified by the amplifier 109 is input to the square circuit 110 to remove the baseband signal components, and through the band pass filter 111, the band filtering is performed around twice the frequency of the intermediate frequency f _IF . Do this. This signal is divided into 1 / N through the 1 / N frequency distribution circuit 112. On the other hand, the voltage controlled oscillator 115 is a voltage controlled oscillator with a frequency twice as intermediate frequency f _IF as its frequency, and its output is frequency-divided at 1 / N through the 1 / N frequency divider circuit 116. . The output signals of the 1 / N frequency distribution circuits 112 and 116 are phase compared in the phase comparator 113.

The phase difference component from the phase comparator 113 drives the voltage controlled oscillator 115 through the loop filter 114. Through this process, the output signal of the voltage controlled oscillator 115 is well controlled by the phase locked loop (PLL) consisting of the voltage controlled oscillator 115, the phase comparator 113, and the loop filter 114. By setting, the signal corresponding to twice the input signal f _IF component is synchronously tracked. The output signal of the voltage controlled oscillator 115 has a frequency lowered to 1/2 in the 1/2 frequency divider 117.

The output signals of the amplifier 109 and the half frequency distribution circuit 117 are synchronously demodulated in the mixer 118. The synchronous demodulated signal becomes a distorted PN baseband signal through the low pass filter 119. The output signal of the low pass filter 119 becomes a relatively normalized PN base signal through an amplifier 120 including a limiter. The standardized PN base signal is converted into a digital signal through the analog digital converter 121. By using the output signal of the analog digital converter 121 and the PN code generated by the PN code generator 122, the PN code of the PN code generator 122 is initially synchronized with the output signal of the analog digital converter 121. The output of the PN code generator 122 is adjusted using the bit sync / tracking circuit 123 to make this fit. In this way, when the PN synchronization is matched, the demodulator 124 despreads and demodulates the PN baseband signal with the PN code from the PN code generator 122. In the circuit of FIG. 2, the circuit after the band pass filter 108 will use the same circuit regardless of the user except for the PN generator 122. In addition, the band pass filter 111 may not be used.

A signal that is first modulated by a synchronous demodulation and a PN code by synchronizing the intermediate frequency f _IF reproduced by the receiver 94 using the identification frequency f _IF in synchronization with the intermediate frequency of the input signal. After the base bend signal (base band) is extracted, the PN code generator performs initial synchronization and synchronization tracking using the signal. Then, demodulation is performed using the PN code output and the PN baseband signal that are bit-synchronized to obtain desired data. Here, as described above, if f _i is the difference frequency between the identification frequencies of two adjacent users, the nth user and the identification frequency f _{IF, n} become nf. That is, f _{IF, n} = nfi, fi = f _{ID, n} -f _{ID, n-1} ). If the band spread by the spreading code is BW, fi <BW, so that multiple users can simultaneously use a number of users within a given spreading band (BW), and not only the identification frequency per user but also the PN code By doing so, the identification frequency can greatly reduce mutual interference between neighboring users and can reduce perspective problems. Accordingly, the system of the present invention enables multiple accesses in an asynchronous direct spread communication scheme.

Claims (5)

A transmitter for allocating and spreading different codes to each user, modulating the spread signal using an intermediate frequency and a different identification frequency, and modulating the modulated signal into a carrier wave; First means for removing the carrier and the identification frequency by inputting an output signal from the transmitter, and second means for outputting a data signal modulated by the code spread from the signal of the first means and the second means. Direct access spread spectrum multiplexing comprising: a receiver having digitalized output signals, bit synchronization and tracking, bit-synchronized spreading code output and third means for demodulating the digitalized signal; Circuit. The band pass of claim 1, wherein the first means inputs an output signal from the transmitter and inputs and mixes the carrier frequency and the identification frequency and band-pass filters the output signals of the first mixer and the first mixer. A multiple access circuit of direct sequential spread spectrum, characterized in that it consists of a filter. 3. The method of claim 2, wherein the second means comprises: a first circuit for amplifying the output signal of the band pass filter circuit, a square circuit for squaring the output signal of the first amplifier circuit, and a predetermined number of output signals of the square circuit; A first frequency divider circuit for dividing the frequency into a plurality of frequencies; 2 for dividing the frequency of the output signal of the voltage control oscillation circuit and the loop filter for filtering the phase difference component of the phase comparison circuit and the phase comparison circuit and comparing the phase of the output signal of the frequency division circuit and driving the voltage controlled oscillation circuit. A second mixer which synchronously demodulates the output signal of the divider circuit, the second divider circuit and the output signal of the second amplifier circuit, and a low pass filter that low pass filters the output of the second mixer. Passing the low-pass circuit and a second circuit of a sequential multiple-access spread-spectrum directly, it characterized in that an amplifier circuit consisting of a circuit for amplifying an output signal. 4. The multiple access circuit of claim 3, wherein the second means further comprises a band pass circuit between the square circuit and the first divider circuit. 4. The bit synchronization and tracking arc of claim 3, wherein the third means inputs an analog digital conversion circuit for converting the output signal of the second amplification circuit into a digital new circuit, and an output signal of the analog digital conversion circuit. And a spreading code generator for bit synchronization and tracking with a tracking circuit, and a demodulator for demodulating the output digital signal of the analog digital conversion circuit using the synchronized spreading code. Circuit.