JPH1188228A - Receiver at spread code system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To consist of an analog circuit of a small dynamic range and to unnecessitate inverse spread processing even at a digital signal processor by multiplying a demodulation signal making the reciprocal number of a signal obtained by quadrature-modulating spread code a carrier frequency to a received signal. SOLUTION: An antenna 10 receivers a transmitted signal. A demodulating signal generating circuit 62 quadrature-demodulates the spread code assigned to a communication channel, generates the reciprocal number of this quadrature- modulated complex signal and generated the I signal 40 and the Q signal 42 of demodulating signals obtained by multiplying a local oscillation frequency signal to the reciprocal number. Then multipliers 44 and 46 multiply the I signal 40 and the Q signal 42 being these demodulating signals to the received signal 43 to generate the I signal 48 and the Q signal 50 in the frequency band of a base band. Namely, the I signal 40 and the Q signal 42 being the demodulating signals are multiplied to the received signal 43 to simultaneously execute quadrature detection and the demodulation of spread code by a high frequency circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus in a code spreading system, and more particularly to a receiving apparatus in which a circuit for processing a received signal in a high frequency band is reduced as much as possible.

[0002]

2. Description of the Related Art Code division multiple access (CDMA) which is one of spread spectrum communications.
s) is attracting attention as a communication method capable of generating more channels in a limited frequency in mobile phone communication, high-speed data communication, and the like. This CDMA
In a communication system, communication between two communication units is
This is performed by spreading the transmission signal on the frequency band of the communication channel with a unique spreading code. As a result, the communicated signal is in the same frequency band as the other communicated signals and is separated only by a unique spreading code. That is, the receiving side despreads the transmitted signal with a spreading code, so that the original transmission signal is extracted from the communication channel. Further, the transmission signal further spread by the spreading code is transmitted after being digitally modulated such as four-phase phase shift keying. By performing digital modulation such as four-phase shift keying,
It is possible to make the frequency band of a transmission wave as narrow as possible and reduce interference with other transmission waves on the same communication channel.

As described above, the code spreading process and the four-phase phase shift keying are all performed by digital signals. In recent years, these processes are generally performed by a digital signal processor. I have.

FIG. 7 is a diagram showing an example of a receiving apparatus in the conventional code spreading system. In this conventional example, a communication signal received by a receiving antenna 10 is passed through a bandpass filter 2 to extract a signal in a frequency band of a communication channel, and is amplified by a low noise amplifier 3. Then, by multiplying the signal Lo1 having a local frequency f _L to the signal amplified by the multiplier 4, the carrier frequency f _R
Drop to an intermediate frequency f _M from. As a result of the multiplication, the frequencies are f _R −f _L and f _R + f _L , and further pass through the band-pass filter 5 to generate the signal 6 having the intermediate frequency f _M = f _R −f _L.

After that, the second local frequency Lo2, π / 2,
The shifted signals are multiplied by the multipliers 7 and 8 to perform quadrature detection (quadrature demodulation). That is, a signal having a second local frequency Lo2 shifted by π / 2 is multiplied by a signal having the second local frequency Lo2 shifted by π / 2 to a signal of the I component and the signal of the Q component at the intermediate frequency. Is generated. Each signal passes through a low-pass filter, is converted into a digital signal by AD converters 56 and 58, and is input to a digital signal processor 70. In the digital signal processor 70, the code-spread baseband signal is despread (code-correlated) by a spreading code, and is returned to the original digital signal.

[0006]

However, in the above-mentioned conventional example, the despreading process using the spreading code is performed by the digital signal processor 70 at the final stage, so that the circuit up to the digital signal processor 70 is performed. In this case, it is necessary to process a signal in a dynamic range including signals of other channels in the same frequency band. In particular, as the number of channels is increased and the degree of multiplexing is increased, the required dynamic range is increased and the signal bandwidth is also increased. Therefore, it is necessary to sufficiently widen the dynamic range of the analog circuit from the receiving antenna 1 to the digital signal processor 70, and a large SN ratio is required.

Furthermore, high-speed digital processing is required for despreading processing (code correlation) using a spreading code. In particular, the higher the degree of multiplexing, the higher the demand for this high-speed digital processing, resulting in an increase in the power consumption of the digital signal processor 70. This point is inconsistent with the demand for saving power consumption in portable communication terminals and the like, and the operation speed of the digital signal processor cannot be made sufficiently high.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a code spreading communication system which does not need to widen the dynamic range of an analog circuit.

It is another object of the present invention to provide a code spread communication receiving method which does not use digital processing for despreading processing (code correlation) using a spreading code.

[0010]

In order to achieve the above object, the present invention relates to a code spread communication type receiving apparatus, comprising: a receiving means for receiving a transmitted signal; and a spread code assigned to a communication channel. Quadrature-modulates, generates a reciprocal of the quadrature-modulated complex signal, generates a demodulated signal multiplied by a local frequency signal, and multiplies the demodulated signal by a transmission signal received by the receiving unit. And a first multiplier for performing despreading and quadrature demodulation.

That is, quadrature demodulation and despreading can be performed simultaneously by multiplying the above-mentioned demodulated signal by the high-frequency received signal. Therefore, in the subsequent analog circuit, only a low-frequency signal is processed, and the dynamic range can be narrowed. Further, since the despreading process is performed by the analog circuit, the load on the digital processing device at the subsequent stage is reduced.

Further, according to the present invention, in the above-mentioned invention, the demodulated signal generating means includes a spread code generating section for generating a spread code which is phase-synchronized with the transmitting side, A parallel-to-parallel conversion unit for converting a complex number consisting of the I component and Q component of the converted symbol point into a reciprocal, and a reciprocal I component and Q component for the reciprocal, A second multiplier for multiplying the local frequency signal out of phase.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, such embodiments do not limit the technical scope of the present invention.

FIG. 1 is a diagram showing a receiving apparatus in a code spreading system according to an embodiment of the present invention. The receiving antenna 10 receives a signal obtained by orthogonally modulating a signal obtained by code-spreading transmission data with a spreading code to obtain a phase shift keying wave. The reception signal received by the reception antenna 10 is subjected to removal of signals outside the frequency band used by the band-pass filter 12 and amplified by the low-noise amplifier 14. Thus, its output signal 43 is substantially the same as the received phase shift keying wave.

The demodulated signals 40 and 42 generated by the demodulated signal generation circuit 62 by the multipliers 44 and 46 are output from the signal 43.
, The baseband I signal 4 that has been quadrature detected in the high frequency circuit and despread in code spreading
8 and Q signals 50 are generated. These I signals 48
The Q signal 50 passes through low-pass filters 52 and 54 in order to remove a high-frequency signal generated by the multiplication, and is converted into a digital signal by AD converters 56 and 58. Then, phase synthesis and parallel-serial conversion are performed by the digital signal processor 60, and final transmission data is generated.

In the demodulation signal generating circuit 62, the spreading code generating circuit 16 generates a spreading code signal 17 which is a spreading code assigned between the transmitting and receiving stations and which has the same phase as the transmitting side spreading code signal. The spread code generation circuit 16 generates the spread code signal 17 having the same phase as that of the transmitting side by a normal method such as detecting the phase when the received signal becomes the strongest when the phase of the spread code signal is changed. Generate.

Further, in the modulation signal generation circuit 62, for example, a 2-bit example of the spread code is converted into four symbol points by the serial-parallel conversion circuit 18, and the I component 18I and the Q component 18Q of the coordinates of the symbol point are converted. Is output. This process is performed in the same manner as the process of the quadrature modulation.

Then, a reciprocal conversion circuit 19 generates a reciprocal of a complex number composed of the I component 18I and the Q component 18Q. Reciprocal I component signal 20 and Q component signal 22
Pass through the low-pass filters 24 and 26. The low-pass filters 24 and 26 are, for example, RRCOS (Root Rai).
It is composed of a Nyquest Filter such as sed Cosine) or RCOS (Raised Cosine), and removes high frequency components of a signal moving between four symbol points as a result of serial-parallel conversion. In other words, signal noise of a frequency other than the cycle of moving the symbol point is removed. These low-pass filters 24 and 26 may be provided on the input side of the reciprocal conversion circuit 19.

Signal 2 passed through the low-pass filter
Multipliers 8 and 30 are multiplied by carrier frequency signals Lo generated by local oscillation circuit 36 in multipliers 32 and 34. The π / 2 shift circuit 3 is added to the I component signal 28 and the Q component signal 30.
The I signal 40 and the Q signal 42 are generated by multiplying the local oscillation frequency signal whose phase is shifted by π / 2 by 8. The local oscillation frequency signal Lo has the same frequency as the carrier signal of the received signal 43, and is multiplied by the local oscillation frequency signal Lo, so that the I signal 40 and the Q signal 42 in the same frequency band as the carrier signal are obtained. Generated.

Then, the I signal 40 and the Q signal 42, which are the demodulated signals, are received by the
To generate an I signal 48 and a Q signal 50 in the baseband frequency band. That is, the demodulated signals 40 and 42
Is multiplied by the received signal 43, the quadrature detection and the demodulation of the code spread are simultaneously performed in the high frequency circuit.

As described above, the reciprocals of the coordinate values 18I and 18Q after the conversion of the spread code into the symbol points
, A despreading process is performed. Assuming that the received signal 43 is s (t), the received signal s (t) is expressed as s (t) = | H (D (a + ib)) e ^iwt |. Here, H is the transmission filter characteristic, D is transmission data, a + ib is a complex number representing the coordinates of a constellation (symbol point) after serial-to-parallel conversion of the spreading code, and e ^iwt is a carrier signal.

Therefore, the demodulated signals 40 and 42 are I (t)
Then, I (t) = {1 / H (a + ib)} e ^iwt . Accordingly, the demodulated signal I is output by the multipliers 44 and 46.
As a result of multiplying the received signal s (t) by (t), the recovered data D is as follows: D = Hlpf (s (t) I (t)). Note that Hlpf is a low-pass filter 52, 54.
Is the characteristic value.

The reciprocal of a complex number is easily generated by the following equation.

1 / c = c ^* / | c | ² As described above, in the above embodiment, the code-spread received signal having a wide frequency band and including signals of other channels is transmitted from the receiving antenna to the band. It only passes through the pass filter 12 and the amplifier 14. Then, the low-pass filters 52 and 54, the AD converters 56 and 58, and the digital signal processor 60 only need to process the signal of the data reception rate, and the signals of the other channels are attenuated by code despreading. Since they have been removed, there is no need to increase the dynamic range of those circuits. Also, the SN characteristics do not need to be so high. Further, in the digital signal processor 60,
Since it is not necessary to perform the despreading process of code spreading, high speed operation is not required for the digital signal processor 60, and power consumption can be suppressed.

FIG. 2 is a diagram showing another example of the demodulated signal generation circuit 62 in the above-mentioned receiving apparatus. In the figure, the same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals. FIG.
In the example, the spreading code generation unit 16 generates a part of the high frequency spreading code among the final spreading codes used for multiplexing. For example, when the spread code is composed of A × B obtained by multiplying a high-frequency code A and a low-frequency code B, the spread code generation unit 16 generates only the high-frequency code A. The generated spread code signal 17 is converted by a serial / parallel conversion circuit 18 into a parallel signal of an I component signal 18I and a Q component signal 18Q. Then, in the reciprocal conversion circuit 19, the coordinate values 20 and 22 of the reciprocal of the complex number are generated as digital values. The low-pass filters 24 and 26 are constituted by digital filters composed of the above-mentioned RRCOS,
Signals 28 and 30 are generated from the digital signals in DA conversion circuits 25 and 27, respectively.

Each of the RRCOS filters 25 and 27 has a half-Nyquist characteristic, and together with the half-Nyquist characteristic of the RRCOS filter provided on the transmission side, generates noise other than the symbol period moving between symbol points. Remove. Further, the code correlation for the remaining code signal B of the spread code is determined by the DSP 60 shown in FIG.
It takes place within. Because of the low frequency, the processing of the code correlation is relatively easy.

FIG. 3 is a diagram showing an example of a configuration on the transmitting side of the above-mentioned receiving apparatus. In order to understand the configuration on the receiving side, a configuration example on the transmitting side will be described. FIG. 3 shows an example of the transmitting side using a filter similar to the digital filter shown in FIG.

First, a spreading code 81 unique to a transmission channel is added to an EOR gate 82 for data 80 to be transmitted.
, The code spreading is performed. This code-spread bit string data 83 is used for quadrature modulation.
A serial-parallel conversion circuit 84, an orthogonal conversion unit 90, a filter 91,
92 and DA conversion circuits 93 and 94, for example, 2
It is converted to bit data four parallel data u _s, the u _c. These data u _s, the u _c, any of the local signal Lo3 having an intermediate frequency [pi / 2 shifted signals multiplied by the multipliers 85 and 86, and the I and Q signals respectively generated. The I signal and the Q signal are combined by the combiner 87, and the local signal Lo4 is multiplied by the multiplier 88 to further increase the carrier frequency, and transmitted from the transmission antenna 89.

As described above, on the transmission side, code spreading modulation is performed on transmission data by a spreading code, and quadrature modulation, which is digital modulation, is performed on the bit sequence. Moreover, the low-pass filters 91 and 92 have half-next characteristics equivalent to those of the filters 24 and 26 shown in FIG. 2, and remove noise other than the frequency of movement between symbol points after orthogonal transformation.

FIG. 4 is a configuration diagram of a receiving apparatus according to another embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals. In this example, the spread code generation circuit 16, the serial-parallel conversion circuit 18, the reciprocal number conversion circuit 19, and the low-pass filters 24 and 26 in the example of FIG. 1 are all realized in the digital signal processor 90. The function of these circuits is
This is realized by software by the digital signal processor 90.

Then, the generated I component signal 28 and Q component signal 30 are converted into digital / analog conversion circuits 91 and 9.
2 is generated as an analog signal. After that, multiplying the carrier frequency signal Lo by a signal shifted by π / 2 to generate demodulated signals 40 and 42 in the carrier frequency band and multiplying the demodulated signals 40 and 42 by the received signal 43 is the same as the circuit of FIG. is there.

The circuit 93 shown by a broken line in FIG. 4 is desirably provided as an integrated circuit of a HEMT using a compound semiconductor and having excellent high-frequency characteristics. as a result,
The receiving circuit comprises two digital signal processors 9
0, 60 and the HEMT integrated circuit 93, so that miniaturization can be realized.

FIG. 5 is a vector diagram of a quadrature-modulated signal. The carrier frequency signal Lo provided in the demodulation circuit 62 has a fixed phase, but in the example of FIG. 5, the carrier frequency signal Lo whose phase shifts by π / 4 per unit time is used. It is a vector diagram.

The spreading code 17 has four symbol points B ₁₀ , B ₁₁ , B ₁₂ , B ₁₃ every two bits, and π / 4
The four shifted symbol points B ₂₀ , B ₂₁ , B ₂₂ , and B ₂₃ are alternately assigned. That is, DQPSK (Differen
FIG. 5 shows the trajectory of a quadrature modulation signal of the tial quadruture (phase shift keying) method. As shown in this figure, the spreading code is converted into a signal that moves between four symbol points. In addition, since the signal moves to another four symbol points shifted by π / 4 every unit time, the signal always moves the symbol point. By adopting such a method, it is possible to avoid the distortion of the amplifier circuit or the like without passing through the origin during the movement between the symbol points.

The trajectory of the orthogonal modulation signal shown in FIG. 5 moves eight symbol points at an acute angle. Therefore, it contains a high frequency component and is not preferable. Therefore, as described above, the RRCO
By passing through low-pass filters 24 and 26 such as S and RCOS, the high-frequency components are removed. FIG. 6 shows the locus of the quadrature modulated signal after passing through the low-pass filter. As shown in the figure, the locus has a smooth curve due to the removal of the high-frequency component. Therefore,
The frequency band of the demodulated wave can be narrowed.

[0036]

As described above, according to the present invention, a code-spread received signal is base-multiplied by multiplying a received signal by a demodulated signal having a carrier frequency equal to the reciprocal of a signal obtained by orthogonally modulating a spread code. It can be converted to a band signal. That is, despreading and quadrature detection are performed simultaneously at a stage before the high frequency circuit. Accordingly, only a part of the analog circuits of the receiving circuit handles received signals having a wide frequency band and a high S / N ratio, so that an analog circuit having a narrower dynamic range than before can be configured. Also, the digital signal processor does not need to perform the despreading process.

[Brief description of the drawings]

FIG. 1 is a diagram showing a receiving circuit in a code spreading system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating another example of the demodulated signal generation circuit in the receiving device.

FIG. 3 is a diagram illustrating a configuration example on a transmission side.

FIG. 4 is a configuration diagram of a receiving circuit according to another embodiment of the present invention.

FIG. 5 is a vector diagram of a quadrature-modulated signal.

FIG. 6 is a vector diagram showing a trajectory of a quadrature modulation signal after passing through a low-pass filter.

FIG. 7 is a diagram illustrating an example of a receiving circuit in a conventional code spreading method.

[Explanation of symbols]

 Reference Signs List 10 antenna 16 spreading code generator 18 serial-parallel converter 19 reciprocal converter 24, 26 low-pass filter Lo local frequency signal 32, 34 second multiplier 44, 46 first multiplier 62 demodulated signal generation circuit

Claims (5)

[Claims] 1. A receiving apparatus of a code spreading communication system, comprising: a receiving means for receiving a transmitted signal; and quadrature modulating a spreading code assigned to a communication channel, and generating a reciprocal of the quadrature modulated complex signal. A demodulated signal generating means for generating a demodulated signal multiplied by a local frequency signal, and a first multiplier for multiplying the transmission signal received by the receiving means by the demodulated signal to perform despreading and quadrature demodulation. A receiving device, characterized in that: 2. The demodulated signal generating means according to claim 1, wherein the demodulated signal generating means generates a spread code which is phase-synchronized with a transmitting side, and converts the spread code into a plurality of symbol points by performing serial-parallel conversion. A serial-to-parallel conversion unit; a reciprocal conversion unit that converts a reciprocal of a complex number composed of the I and Q components of the converted symbol point; and a phase shift of π / 2 between the reciprocal I component and the Q component. A second multiplier for multiplying the local frequency signal. 3. The receiving apparatus according to claim 2, wherein a low-pass filter having the same characteristics as a filter in the receiving apparatus is inserted on an input side or an output side of the reciprocal transform unit. 4. The receiving apparatus according to claim 1, wherein the local frequency signal has the same frequency as a carrier wave. 5. The receiving apparatus according to claim 1, wherein the spreading code is a part of a spreading code having a high frequency characteristic.