Abstract:
A CDMA (Code Division Multiple Access) modulation and demodulation method and a communication system using the same which simultaneously transmits a pilot signal and a data signal through the same channel, thereby being capable of not only greatly the complexity of its transceiver, but also achieving an improvement in performance where a large number of multipaths are used. The method includes the steps of (a) generating a pilot signal and a transmission data signal; (b) spreading the pilot signal and the transmission data signal, by multiplying the pilot signal by an inphase pseudo noise sequence and by multiplying the transmission data by a quadrature pseudo noise sequence, respectively; (c) generating an inphase signal and a quadrature signal, by multiplying the spread pilot signal by an inphase walsh data sequence and by multiplying the spread transmission data by a quadrature walsh data sequence, respectively; (d) modulating the inphase signal and the quadrature signal, by multiplying the inphase signal and the quadrature signal by carrier signals; and (e) transmitting a composite signal created by adding the modulated inphase signal to the modulated quadrature signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a CDMA (Code Division Multiple Access) modulation and demodulating method and a communication system using the same, and more particularly relates to a CDMA modulation and demodulation method and a communication system using the same which simultaneously transmits a pilot signal and a data signal through the same channel. 
     2. Description of the Prior Art 
     FIG. 1 shows a block diagram of a CDMA QPSK modulator in accordance with a conventional techniques. 
     Multipliers 101A and 101B multiply the inphase data signal d I  (t) and the quadrature data signal d Q  (t) by the walsh code Wd(t). Then, adders 102A and 102B add each signal from multipliers 101A and 101B to the pilot signal Wp(t). Multipliers 103A and 104A multiply the inphase data signal from the adder 102A by the inphase pseudo noise sequence and carrier signal cos(ωct+φ), which generates an inphase signal. Multipliers 103B and 104B multiply the quadrature data signal from the adder by the quadrature pseudo noise sequence and the carrier signal sin(ωct+φ), which generates a quadrature signal. The carrier signal multiplied by the quadrature signal has a 90° phase difference from the carrier signal multiplied by the inphase signal. The adder 105 adds the inphase signal to the quadrature signal and generates transmission signal. Here, the QPSK modulation and demodulation method is used as a signal modulation and demodulation method. 
     FIG. 2 shows a block diagram of a CDMA QPSK demodulator in accordance with a conventional technique. 
     The demodulator consists of a pilot signal detecting part and a data signal recovering part. 
     The transmitted signal is received by the antenna (not shown in FIG. 2). The multiplier 201A multiplies the received signal from the antenna by cos (ωct+φ) and then undergoes low pass filtering by the LPF (Low Pass Filter) 202A, which generates a baseband inphase signal. Also, the multiplier 201B multiplies the received signal by sin(ωct+φ) and then undergoes low pass filtering by LPF (Low Pass Filter) 202B, which generates baseband quadrature signal. 
     Multipliers 203A and 203C multiply the inphase signal I(t) by the inphase and the quadrature pseudo noise sequence P I  (t) and P Q  (t), which generate despreading inphase signals. Multipliers 203B and 203D multiply the quadrature signal by the inphase and the negative quadrature pseudo noise sequence P I  (t) and P Q  (t), which generates despreading quadrature signals. The adder 204A adds the despread inphase signals. The adder 204B adds the despread quadrature signals. The multipliers 205A and 205B multiplies result values from the adders 204A and 204B by the pilot walsh sequence Wp(t). Then, the integration circuits 206A and 206B integrate the resulting values from the multipliers 205A and 205B, which generates phase difference compensation signals. The squaring circuits 207A and 207B squares the resulting value from the integration circuits 206A and 206B. Pilot signal is recovered by combining the resulting values from the squaring circuits 207A and 207B. 
     Multipliers 211A and 211B multiply the baseband inphase signal and the baseband quadrature signal by the walsh data sequence Wd(t). Multipliers 212A and 212C multiply the resulting value from the multiplier 211A by the inphase pseudo noise sequence P I  (t) and the negative quadrature pseudo noise sequence -P Q  (t). Multipliers 212B and 212D multiply result value from the multiplier 211B by the inphase pseudo noise sequence P I  (t) and the quadrature pseudo noise sequence P Q  (t). Integration circuits 213A through 213D integrate the resulting values from the multipliers 212A through 212D. Multipliers 214A and 214D each multiply the resulting values from the integration circuits 213A and 213D by Acosφ. Multipliers 214B and 214C each multiply the resulting values from the integration circuits 213B and 213C by Asinφ. An adder 215A adds the resulting value from the multiplier 214A to the resulting value from the multiplier 214B. which recovers the inphase data signal. An adder 215B adds result from the multiplier 214C to result from the multiplier 214D, which recovers the quadrature data signal. 
     A general DS/CDMA communication system needs a pilot signal for the establishment and tracking of synchronization. Using the pilot signal, it is easy to implement receiver because of easy extraction of the phase difference compensation signal. However, it needs electric power and radio channel for transmitting the pilot signal, which reduces a accommodation capacity of the communication system. 
     To overcome these problems, in the conventional system, the pilot signal is used only in the forward channel transmission from the base station to the mobile station, and not in the backward channel transmission from the mobile station to the base station. This does not cause a reduction in the accommodation capacity. However, there is a problem in performance and a difficult implementation of the receiver. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a modulation and demodulation method and a communication system using the same, which transmits both data signal and pilot signal on a radio channel, thereby improving performance and complexity of the receiver without a high power consumption and a capacity reduction. 
     According to the first aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) modulation method for modulating a transmission signal in a CDMA communication system, including the steps of: 
     (a) generating a pilot signal and a transmission data signal; (b) spreading the pilot signal and the transmission data signal, by multiplying the pilot signal by an inphase pseudo noise sequence and by multiplying the transmission data by a quadrature pseudo noise sequence, respectively; (c) generating an inphase signal and a quadrature signal, by multiplying the spread pilot signal by an inphase walsh data sequence and by multiplying the spread transmission data by a quadrature walsh data sequence, respectively; (d) modulating the inphase signal and the quadrature signal, by multiplying the inphase signal and the quadrature signal by carrier signals; and (e) transmitting a composite signal created by adding the modulated inphase signal to the modulated quadrature signal. 
     According to the second aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) demodulation method for demodulating a transmitted signal in a CDMA communication system, including the steps of: 
     (a) receiving a signal compounded by an inphase signal and a quadrature signal; (b) demodulating the transmitted signal; (c) establishing and tracking synchronization of the demodulated transmitted signal; (d) recovering a pilot signal and a phase difference compensation signal using the demodulated transmitted signal and the signal performed of synchronization establishment and tracking; and (e) recovering the transmission data using the demodulated transmitted signal, the signal established and tracked of synchronization, the recovered pilot signal and the recovered phase difference compensation signal. 
     According to the third aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) modulation and demodulation method for modulating and demodulating a transmission signal in a CDMA communication system, including the steps of: 
     (a) generating a pilot signal and a transmission data signal; (b) spreading the pilot signal and the transmission data signal, by multiplying the pilot signal by an inphase pseudo noise sequence and by multiplying the transmission data by a quadrature pseudo noise sequence, respectively; (c) generating an inphase signal and a quadrature signal, by multiplying the spread pilot signal by an inphase walsh data sequence and by multiplying the spread transmission data by a quadrature walsh data sequence, respectively; (d) modulating the inphase signal and the quadrature signal, by multiplying the inphase signal and the quadrature signal by carrier signals; (e) transmitting a composite signal created by adding the modulated inphase signal to the modulated quadrature signal; (f) receiving a small compounded by an inphase signal and a quadrature signal; (g) demodulating the transmitted signal; (h) establishing and tracking synchronization of the demodulated transmitted signal; (i) recovering a pilot signal and a phase difference compensation signal using the demodulated transmitted signal and the signal performed of synchronization establishment and tracking; and (j) recovering the transmission data using the demodulated transmitted signal, the signal established and tracked of synchronization, the recovered pilot signal and the recovered phase difference compensation signal. 
     According to the fourth aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) transmitter comprising: 
     a generator for generating a pilot signal and a data signal; a first multiplier for spreading the pilot signal by multiplying the pilot signal by an inphase pseudo noise sequence; a second multiplier for spreading a data signal by multiplying the data signal by a quadrature pseudo noise sequence, a third multiplier for multiplying an input signal from the first multiplier by an inphase walsh data sequence, which generates an inphase signal; a fourth multiplier for multiplying an input signal from the second multiplier by a quadrature walsh data sequence, which generates quadrature signal; a modulator for modulating the inphase signal and the quadrature signal; and a transmitting part for transmitting transmission data, after generating the transmission data signal by adding the modulated inphase signal to the modulated quadrature signal. 
     According to the fifth aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) receiver comprising: 
     a receiving part for receiving a transmitted signal; demodulator for demodulating the transmitted signal; a low pass filter for converting the transmitted signal to a baseband inphase signal and a baseband quadrature signal; a synchronization establishing and tracking part for of the baseband inphase signal and the baseband quadrature signal, a pilot signal and phase difference compensation signal detecting part for detecting a pilot signal and a phase difference compensation signal using the baseband inphase signal and the baseband quadrature signal; and a data signal detecting part for recovering a data signal using the baseband inphase signal, the baseband quadrature signal, the pilot signal and the phase difference compensation signal. 
     According to the sixth aspect of the present invention, this object is accomplished by providing a CDMA (Code Division Multiple Access) communication system comprising: 
     a transmitter comprising: 
     a generator for generating a pilot signal and a data signal; a first multiplier for spreading the pilot signal by multiplying the pilot signal by an inphase pseudo noise sequence; a second multiplier for spreading a data signal by multiplying the data signal by a quadrature pseudo noise sequence; a third multiplier for multiplying an input signal from the first multiplier by an inphase walsh data sequence, which generates an inphase signal, a fourth multiplier for multiplying an input signal from the second multiplier by a quadrature walsh data sequence, which generates quadrature signal; a modulator for modulating the inphase signal and the quadrature signal; and a transmitting part for transmitting transmission data, after generating the transmission data signal by adding the modulated inphase signal to the modulated quadrature signal, and 
     a receiver comprising: 
     receiving part for receiving a transmitted signal demodulator for demodulating the transmitted signal; a low pass filter for converting the transmitted signal to a baseband inphase signal and a baseband quadrature signal, a synchronization establishing and tracking part for establishing and tracking synchronization of the baseband inphase signal, and the baseband quadrature signal, a pilot signal and phase difference compensation signal detecting part for detecting a pilot signal and a phase difference compensation signal using the baseband inphase signal and the baseband quadrature signal; and a data signal detecting part for recovering a data signal using the baseband inphase signal, the baseband quadrature signal, the pilot signal and the phase difference compensation signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and aspects of the invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings in which: 
     FIG. 1 is a block diagram of a CDMA QPSK modulator in accordance with a conventional technique; 
     FIG. 2 is a block diagram of a CDMA QPSK demodulator in accordance with a conventional technique; 
     FIG. 3 is a block diagram of a CDMA QPSK modulator in accordance with the present invention; 
     FIG. 4 is a block diagram of a CDMA QPSK demodulator in accordance with the present invention; 
     FIG. 5 is a detail diagram of the pilot signal detecting part and the phase compensation signal detecting part of FIG. 4; 
     FIG. 6 is a detail diagram of the synchronization establishing and tracking part of FIG. 4; 
     FIG. 7 is a detail diagram of the data signal demodulating part in accordance with the present invention; 
     FIG. 8 is a flowchart illustrating a CDMA modulating method reducing interference in accordance with the present invention, and 
     FIG. 9 is a flowchart illustrating a CDMA demodulating method reducing interference in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be described with reference to the accompanying FIGS. 3 through 9. 
     FIG. 3 shows a block diagram of a CDMA QPSK modulator in accordance with the present invention. 
     A pilot signal is multiplied by the inphase pseudo noise sequence P 1 , the inphase walsh data sequence W I  and the carrier signal cos(ω c  t) by using multipliers 301A, 302A and 303A, which becomes the spread modulated pilot signal. A data signal is multiplied by a quadrature pseudo noise sequence P Q , quadrature walsh data sequence W Q  and a carrier signal -sin(ω c  t) by using multiplies 301B, 302B and 303B, which becomes the spread modulated data signal. The adder 304 combines a spread modulated pilot signal with the spread modulated data signal and generates a transmission signal s(t). In the present embodiment, QPSK modulation method is used as a modulation method. 
     The input value of the pilot channel is a constant binary data value 1, and the input value of the data channel is any binary data value 0 or 1. 
     The above described modulation process can be expressed by the following equation. 
     
         s(t)=P.sub.I (t)W.sub.I (t)cos(w.sub.c t+φ)-d(t)P.sub.Q (t)W.sub.Q (t)sin(w.sub.c t+φ) 
    
     Where, s(t) designated a transmission signal, P I  (t) an inphase pseudo noise sequence, P Q  (t) a quadrature pseudo noise sequence, W I  (t) an inphase walsh data sequence, and W 0  (t) a quadrature inphase walsh data sequence. 
     Pseudo sequences P I  and P Q  have a constant period and a similar frequency distribution to white noise in the constant period. They are generated by a general pseudo noise generator. The pseudo sequences P I  and P Q  must have minimum cross-correlation values. 
     Walsh data sequences W I  and W Q  are selected in a plurality of walsh data sequences. The walsh data I1 having a length of 2 is described as ##EQU1## The walsh data I1 having a length of 2 can be obtained from the matrix as follows: ##EQU2## 
     Here, I.sub.π&#39; --1 has a reverse value of I.sub.π --1. 
     FIG. 4 shows a block diagram of CDMA QPSK demodulator in accordance with the present invention. The CDMA QPSK demodulator shown in FIG. 4 demodulates the transmission signal s(t) modulated by the modulator as shown in FIG. 3. 
     The pilot signal is demodulated by an asynchronous method. Multipliers 401A and 401B multiply the modulated input signal s(t) by carriers cos(ω c  t+φ) and -sin(ω c  t+φ). The LPF (Low Pass Filter) 402A and 402B convert the signal from the multipliers to the baseband inphase signal I(t) and the baseband quadrature signal Q(t). In other words, the transmitted signal undergoes baseband filtering after being multiplied by carrier and becomes the inphase signal I(t) and the quadrature signal Q(t) as follows: 
     
         I(t)=[P.sub.I (t)W.sub.I (t)cos(φ)-d(t)P.sub.Q (t)W.sub.Q (t)sin(φ)] 
    
     
         Q(t)=[P.sub.I (t)W.sub.I (t)sin(φ)+d(t)P.sub.Q (t)W.sub.Q (t)cos(φ)] 
    
     The pilot signal and the phase difference compensation signal detecting part 404 detects pilot signal p(t) and the phase difference compensation signal Acosφ and Asinφ by using the inphase signal I(t) and the quadrature signal Q(t) fed from the LPF 402A. The synchronization establishing and tracking part 403 establishes and tracks synchronization of the spreading code using the inphase signal I(t), the quadrature signal Q(t) and the pilot signal p(t). The data signal detecting part 405 recovers the data signal by using the inphase signal I(t), the quadrature signal Q(t) and the phase difference compensation signal. 
     FIG. 5 shows a detail diagram of the pilot signal detecting part and the phase compensation signal detecting part of FIG. 4. 
     Multipliers 501A and 502A multiply the inphase signal I(t) by both the pseudo noise sequence P I  (t) and walsh data sequence W I  (t). Multipliers 501B and 502B multiply the quadrature signal Q(t) by both the pseudo noise sequence P I  (t) and walsh data sequence W I  (t). The integration circuits 503A and 503B integrate the resulting value from the multipliers 502A and 502B and detect the phase difference compensation signal Acosφ and Asinφ. The phase difference compensation signal Acosφ and Asinφ is used for compensating the phase difference in the data signal detecting part 405. Each output signal from the integration circuits 503A and 503B are combined after squared by square circuit 504A and 504B such that a pilot signal can be recovered. 
     FIG. 6 shows a detail diagram of the synchronization establishing and tracking part of FIG. 4. 
     The synchronization establishing and tracking part 403 coincides order of the pseudo noise sequence generated by the demodulator with that of the order of the pseudo noise sequence generated by the modulator. 
     The synchronization establishment is performed by comparing the value of the pilot signal with the threshold value, and by operating the state machine. The state machine shifts the comparing result between the pilot signal and the threshold value. If the establishment of synchronization is determined, the tracking circuit tracks the generation order of the pseudo noise sequence in the modulator. 
     Multipliers 601A and 601B multiply the inphase signal I(t) and the quadrature signal Q(t) by the pseudo noise sequence whose clock is 1/2 clock prior to the present pseudo noise sequence. Multipliers 602A and 602B multiply the inphase signal I(t) and the quadrature signal Q(t) by the walsh data sequence whose clock is 1/2 clock prior to the present walsh data sequence. Integration circuits 603A and 603B integrate the resulting values from the multipliers 602A and 602B. The squaring circuits 604A and 604B square result values from the integration circuits 603A and 603B. The adder 605A adds the resulting values from the squaring circuits 604A and 604B, which generates signal E(t). 
     Multipliers 601C and 601D multiply the inphase signal I(t) and the quadrature signal Q(t) by the pseudo noise sequence whose clock is 1/2 clock later than the present pseudo noise sequence. Multipliers 602C and 602D multiply the inphase signal I(t) and the quadrature signal Q(t) by the walsh data sequence whose clock is 1/2 clock later than the present walsh data sequence. Integration circuits 603A and 603D integrate the resulting values from the multipliers 602C and 602D. Squaring circuits 604C and 604D square the resulting values from the integration circuits 603C and 603D. Adder 605B adds the resulting values from the squaring circuits 604C and 604D, which generates signal L(t). 
     Tracking is performed by reducing or by expanding one clock of the clock generator using the difference between the signal E(t) and the signal L(t). In other words, if the amplitude of the signal E(t) is the same as that of the signal L(t), the same clock as the present clock is generated, if the amplitude of the signal E(t) is larger than that of the signal L(t), a faster clock than the present clock is generated, and if the amplitude of the signal E(t) is smaller than that of the signal L(t), a slower clock than the present clock is generated. The clock adjusted in this method is used as a clock of the pseudo noise sequence generator of the walsh data sequence generator in the demodulator. 
     FIG. 7 is a detail diagram of the data signal demodulating part in accordance with the present invention. 
     The inphase signal I(t) is multiplied by the inphase pseudo noise sequence P I  (t) and the inphase walsh data W I  (t), which generates signal A(t). The quadrature signal Q(t) is multiplied by the inphase pseudo noise sequence P I  (t) and the inphase walsh data W I  (t), which generates signal B(t). The inphase signal I(t) is multiplied by the quadrature pseudo noise sequence P 0  (t) and the quadrature walsh data W Q  (t), which generates signal C(t). The quadrature signal Q(t) is multiplied by the quadrature pseudo noise sequence P Q  (t) and the quadrature walsh data W Q  (t) which generates signal D(t). Adders 703A through 703D add the signals and generate signals A(t)30 D(t), A(t)-D(t), B(t)+C(t) and B(t)-C(t). 
     The integration circuit 704A integrates the signal B(t)+C(t) from the adder 703B. The integration circuit 704B integrates the signal A(t)-D(t) from the adder 703D. The integration circuit 704C integrates the signal A(t)+D(t) from the adder 705C. The integration circuit 704D integrates the signal B(t)-C(t) from the adders 703A. And the integration circuit 704B integrates the signal A(t)-D(t) from the adder 703D. 
     Multipliers 705A and 705D multiply the output signal from integration circuits 704A and 704D by Asinφ. Multipliers 705B and 705C multiply the output signal from integration circuits 704B and 704C by Acosφ. 
     An adder 706A adds the output signal from the multiplier 705A to the output signal from the multiplier 705B, which generates the signal J(t). An adder 706B adds the output signal from the multiplier 705C to the output signal from the multiplier 705D, which generates the signal K(t). 
     The comparator 707 compares the signal J(t), with the signal K(t) and outputs the compared result. In other words, if the signal J(t) is larger than the signal K(t), the transmitted data value is determined as 1. If the signal J(t) is less than the signal K(t), the transmitted data value is determined as 1. 
     In the present embodiment, the transmitted data is detected by assuming the transmitted data in advance, by calculating the assumed data in the above described method, and by comparing the calculated values. 
     Hence, the above described process can be expressed by the following equation. ##EQU3## 
     FIG. 8 shows a flowchart illustrating a CDMA modulating method reducing interference in accordance with the present invention. 
     The data generator generates the pilot signal p(t) and the transmission data d(t) at step 71. The multipliers 301A and 301B spread the pilot signal p(t) and the transmission data d(t) using the pseudo noise sequences at step 72. In other words, the multiplier 301A multiplies the pilot signal p(t) by the inphase pseudo noise sequence P I  (t), and the multiplier 301B multiplies the transmission data d(t) by the quadrature pseudo noise sequence P Q  (t). The multipliers 302A and 302B discriminate channels using the walsh data sequences at step 73. The multiplier 302A multiplies the spread signal from the multiplier 301A by the inphase walsh data sequence, and the multiplier 302B multiplies the spread signal from the multiplier 301B by the quadrature walsh data sequence. The multipliers 303A and 303B QPSK modulate the pilot signal p(t) and the transmission data d(t) at step 74. In other words, the multiplier 303A multiplies the signal from the multiplier 302A by the carrier cosφct, and the multiplier 303B multiplies the signal from the multiplier 302B by carrier cosωct. The adder 304 adds the inphase signal I(t) from the multiplier 303A to the quadrature signal Q(t), generates the transmission signal s(t) and transmits the transmission signal s(t) through the antenna (not shown in FIG. 3) at step 75. 
     FIG. 9 shows a flowchart illustrating a CDMA demodulating method reducing interference in accordance with the present invention. 
     The transmitted signal is received through the antenna (not shown in FIG. 4) at step 81, and then QPSK demodulated at step 82. In other words, the multipliers 401A and 401B multiply the received signal s(t) by cos(ωct+φ) and -sin(ωct+φ). The provided signals from the multipliers 401A and 401B undergo low pass filtering by the LPF 402A and 402B. The LPF 402A and 402B output the baseband inphase signal I(t) and the baseband quadrature signal Q(t). The inphase signal I(t) and the quadrature signal Q(t) undergo establishment of synchronization and tracking in the same method as described above with reference to FIG. 6 such that the pilot signal p(t) is recovered at step 83. At step 84, the phase difference compensation signals are extracted in the same method as described above with reference to FIG. 7. At step 85, the transmitted data is recovered in the same method as described above with reference to FIG. 7. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.