JP2020043526A - Communication system and terminal - Google Patents

Abstract

To provide a communication system and a terminal capable of improving deterioration of error rate due to the fact that a signal of other channel becomes noise for a signal of a specific channel, in a communication system for multiplexing signals.SOLUTION: In a communication system using CDMA, a receiver 130 has an unwanted wave removal part 200 for removing unwanted waves from signals received from transmitters 100, 112-116, and a demodulation section 138, the unwanted wave removal part has a first frequency conversion part for converting an input signal into a signal of frequency equal to a positive integer times of symbol rate, a diffusion part for holding the output signal value from the first frequency conversion part at a prescribed time interval in one symbol period, and then reading and outputting the signal values, thus held, repeatedly at an interval shorter than the prescribed time interval in the holding order, a lowpass filter and a bandpass filter for passing the output from the diffusion part, and a second frequency conversion part for converting the signal after passing into a signal having the carrier frequency of the input signal. With such an arrangement, error rate can be improved.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a communication system and a terminal device that can improve an error rate in communication.

  2. Description of the Related Art In a communication system that enables communication by a mobile phone, a smartphone, or the like (hereinafter, referred to as a mobile terminal device), various multiplexing methods are used in order to effectively use a limited frequency band in a large number of mobile terminal devices. Have been. As typical examples, FDMA (frequency division multiple access), TDMA (time division multiple access) and CDMA (code division multiple access) are known.

  Referring to FIG. 1, in a wireless communication system employing CDMA as a multiplexing scheme, a transmitter performs spreading code processing, and a receiver performs despreading code processing. Although FIG. 1 shows four transmitters and one receiver, an actual wireless communication system includes more transmitters and receivers. Communication between the transmitter and the receiver is performed via a known wireless communication base station (not shown).

  The first transmitter 900 includes a first transmitter body including a high-frequency generator 902, a primary modulator 904, a secondary modulator 906, and a spreading code generator 908, and an antenna 910. The second to fourth transmitters 912 to 916 have the same configuration as the first transmitter 900. The high frequency generator 902 generates a high frequency used as a carrier. The primary modulator 904 performs primary modulation on the high frequency input from the high frequency generator 902 using input data (digital data). For the primary modulation, a known modulation method is used, for example, ASK (amplitude shift keying), FSK (frequency shift keying), PSK (phase shift keying), QAM (quadrature amplitude modulation), or the like. You. The secondary modulator 906 receives the signal S1 after the primary modulation, performs secondary modulation on the signal S1 using the spreading code input from the spreading code generator 908, and outputs the result as a signal S2. Specifically, the signal S1 is multiplied by the spreading code and output. The signal S2 after the secondary modulation is transmitted from the antenna 910 as a signal of CH1. Similarly, the signals after the secondary modulation are transmitted from the second transmitter 912 to the fourth transmitter 916 as signals of CH2 to CH4. Note that different transmitters use different spreading codes, but the carrier has the same frequency band.

  FIG. 2A shows the signal S1 after the primary modulation in each of the first to fourth transmitters 900 to 916. The spread code generator 908 spreads the signal S1 after the primary modulation over a wider frequency range (the frequency band is widened), and the energy does not change, resulting in a signal S2 having a small intensity (see FIG. 2B). ). Here, it is assumed that a signal to be detected by a receiver 930 described later is a signal (CH2) transmitted from the second transmitter 912.

  Referring to FIG. 1 again, receiver 930 includes antenna 932 and a receiver main body including despreader 934, BPF (bandpass filter) 936, demodulator 938, and despread code generator 940. . The antenna 932 receives a wireless signal. Despreader 934 performs a despreading process on received signal S3 using the despread code output from despread code generator 940. Specifically, the signal S3 is multiplied by the despread code and output. The BPF 936 is a band-pass filter that allows a signal in a predetermined frequency range (predetermined band) of the input signal S4 to pass, attenuates other signals, and outputs the signal S5. The demodulator 938 performs a demodulation process on the input signal S5 in a method according to the modulation method adopted in the primary modulator 904. As a result, predetermined data (digital data before primary modulation in first transmitter 900) is output from demodulator 938.

  Note that the mobile terminal device has a transmission function and a reception function, and the first to fourth transmitters 900 to 916 show the transmission functions of the corresponding mobile terminal devices, respectively. It can be said that this indicates the receiving function of the corresponding portable terminal device.

  FIGS. 2C to 2E show waveforms of the signals S3 to S5 assuming that the signal to be detected by the receiver 930 is the signal (CH2) from the second transmitter, as described above. The received signal S3 is a signal on which a spread spectrum signal transmitted from CH1 to CH4 is superimposed (see (c) of FIG. 2). In contrast, in signal S4 after being despread using a despreading code corresponding to the spreading code used in second transmitter 912, the signal of CH2 used by second transmitter 912 is Returning to the previous state, the other signals remain spread (see FIG. 2 (d)).

  This is due to the properties of the used spreading code and despreading code. A PN (Pseudorandom Noise) sequence is used as the spreading code, and the despreading code is the same as the spreading code. When the same spreading code is applied twice (multiplied twice), the original signal is restored. On the other hand, the signal remains spread even if two different spreading codes are applied once each. Therefore, in (d) of FIG. 2, only the signal of CH2 returns to the original state, and the signals of CH1, CH3, and CH4 remain spread. The despreading code generator 940 stores a plurality of despreading codes corresponding to each of CH1 to CH4, and transmits the second despreading code to the receiver 930 via the control channel in advance from the second transmitter 912. By transmitting the information of the spreading code used in the transmitter 912, the despreading code generator 940 can output the despreading code to be used for detecting the signal from the second transmitter 912. .

  Thereafter, the signal S4 passes through the BPF 936 in FIG. 1 to generate a signal S5 from which signals outside the predetermined band have been removed (see FIG. 2E). The demodulator 938 performs a demodulation process on the signal S5 by a method according to the modulation method adopted in the primary modulator 904. As a result, the data transmitted by the first transmitter 900 is output from the demodulator 938.

JP 2000-341149 A

  In a method such as CDMA in which a plurality of channels are used in the same band by code division and a signal of a desired channel (hereinafter also referred to as a desired wave) is selected on the receiving side by despreading, if the number of channels is increased, the inverse Unnecessary wave (hereinafter, also referred to as noise) levels of other channels due to diffusion increase. Therefore, there is a problem that the ratio between the desired wave and the unnecessary wave (hereinafter, also referred to as SN ratio) is deteriorated. For example, as shown in FIG. 2 (e), for the CH2 signal (strength S), the other spread signals of CH1, CH3 and CH4 become noise (strength N). If the number of channels increases, the noise intensity increases, but the signal intensity of CH2 does not change, so that the SN ratio decreases (deteriorates). Therefore, in a communication system using CDMA, the number of usable channels is limited in order to maintain the SN ratio at or above a predetermined value.

  Conventionally, the bit error rate (BER (Bit Error Rate)) has been improved by removing unnecessary waves other than the transmission signal. It aims at removing noise superimposed on a signal output from a transmitter by a communication path as an unnecessary wave. As described above, with respect to CDMA, a problem that a signal used in another channel can always become noise with respect to a signal of a predetermined channel to be detected, that is, an adopted multiplexing method (CDMA). Remedying the problems caused by itself has not been considered before. Further, the conventional method for improving the bit error rate does not aim at improving the problem caused by the employed multiplexing method (CDMA) itself.

For example, when CH1 to CH4 are used, if CH2 is a desired wave, other channels become unnecessary waves (see (d) and (e) of FIG. 2). When the signal is received by CH2 alone, it is assumed that BER = 1 × 10 ⁻³ because the signal of another channel interferes even if BER = 1 × 10 ⁻⁵ if the signal strength is sufficient. Actually, the error rate further deteriorates due to extraneous unnecessary waves. However, since the conventional unnecessary wave removal aims at removing an extraneous unnecessary wave as described above, the limit is to approach BER = 1 × 10 ⁻³ and cannot reach BER = 1 × 10 ⁻⁵ .

  Further, in the conventional FDMA, each channel is arranged on the frequency axis so that the frequency bandwidth of each channel does not interfere (so that the frequency bands of each channel do not overlap). Therefore, when the number of channels is increased, it is necessary to reduce the data amount of each channel. This is because interference occurs when the bandwidth of each channel overlaps, and before the bit error rate deteriorates due to the influence of unnecessary waves such as noise, the signal of another channel interferes with the desired wave. This is because the input signal itself is input with the error rate deteriorated. It would be desirable if this problem in FDMA could be ameliorated.

  In OFDM (orthogonal frequency division multiplexing) belonging to multicarrier modulation, data is transmitted from a transmitter on a plurality of mutually orthogonal carrier waves (subcarriers; hereinafter, also referred to as subchannels) and transmitted to a receiver by a plurality of carriers. Aggregate data transmitted by subcarriers. Each subcarrier is modulated at a low symbol rate by a known method such as QAM. That is, in OFDM, rather than a single wide-bandwidth signal subjected to high-speed modulation, a large number of narrow-bandwidth signals subjected to slow modulation (low modulation rate) are denser (narrower frequency spacing) than FDMA. ) Improves the frequency utilization rate. Each subcarrier is orthogonal, and as shown in FIG. 12, at the position of the center frequency of each subcarrier, the signal strength of the other subcarriers becomes zero. Despite being densely arranged, there is an advantage that the subcarriers do not interfere with each other. In FIG. 12, the spectrum of subcarrier SC2 is indicated by a thick solid line. The subcarriers SC1 and SC3 to SC5 have the same spectrum, though the frequency is shifted. Each subcarrier can be efficiently separated by a fast Fourier transform (FFT). In such OFDM, in order to increase the data rate without changing the bandwidth, the number of subcarriers within the bandwidth is further increased. However, each subcarrier needs to be orthogonal and low data rate is required. Because of the rate, the overall data rate does not increase in direct proportion to the number of subcarriers. Further, when the total power in the band is stipulated, if the number of subcarriers is increased, the power of each subcarrier must be reduced, which causes deterioration of an error rate. Therefore, it is preferable to solve the problem that it is difficult to increase the number of subcarriers (the number of subchannels).

  Therefore, the present invention is to improve the error rate degradation due to unnecessary signals of other channels for signals of a specific channel (including sub-channels) in a communication system for multiplexing signals. It is an object of the present invention to provide a communication system and a terminal device that can perform the communication.

  A communication system according to a first aspect of the present invention is a communication system including a plurality of transmitters for performing communication based on a predetermined multiplexing method and at least one receiver, wherein each of the plurality of transmitters At least some of the frequency bands overlap each other. The receiver includes an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulation unit that demodulates an output signal from the unnecessary wave removing unit. The spurious wave removing unit converts the input signal into a signal of a frequency f of f = n / ΔT, where n is a positive integer and a symbol period is ΔT, and a first frequency converting unit that corresponds to one symbol. After the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval is held during the predetermined period, M is set to a positive integer, and the held signal values are stored in the holding order in the order of 1 / s of the symbol period. A spreading section that is M and is repeatedly read and output at a time interval shorter than a predetermined time interval, a low-pass filter section to which a signal output from the spreading section is input, and a band-pass to which an output signal of the low-pass filter section is input A first frequency conversion unit that converts an output signal of the band-pass filter unit into a signal of a carrier frequency of an input signal to the first frequency conversion unit and outputs the signal;

  As a result, in a communication system that multiplexes signals, it is possible to improve deterioration of an error rate due to spreading of signals of other channels in a wide band with respect to signals of a specific channel.

  A communication system according to a second aspect of the present invention is a communication system including a plurality of transmitters for performing communication based on a predetermined multiplexing method and at least one receiver, wherein each transmission of the plurality of transmitters is performed. At least some of the frequency bands overlap each other. The receiver includes an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulation unit that demodulates an output signal from the unnecessary wave removing unit. The spurious wave removing unit converts the input signal into a signal of a frequency f of f = n / ΔT, where n is a positive integer and a symbol period is ΔT, and a first frequency converting unit that corresponds to one symbol. After the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval is held during the predetermined period, the held signal value is read out and output in units of one wavelength of the frequency f at random without overlapping. A spreading unit; a low-pass filter unit to which a signal output from the spreading unit is input; a band-pass filter unit to which an output signal of the low-pass filter unit is input; And a second frequency conversion unit that converts the input signal to a carrier frequency signal and outputs the signal.

  Preferably, in the communication system, CDMA, FDMA, or a non-orthogonal multi-carrier scheme using a plurality of non-orthogonal subcarriers is used as a multiplexing scheme. When CDMA is used, each of the plurality of transmitters transmits a signal to which a different spreading code is applied, and the receiver receives a despreading code corresponding to the spreading code used by the transmitter to be communicated. The signal obtained by applying the signal is input to the unnecessary wave removing unit.

  A terminal device according to a third aspect of the present invention is a terminal device used in a communication system including a plurality of transmitters that perform communication based on a predetermined multiplexing method, and includes a transmission frequency band of each of the plurality of transmitters. At least partially overlap each other. The terminal device includes an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulation unit that demodulates an output signal from the unnecessary wave removing unit. The spurious wave removing unit converts the input signal into a signal of a frequency f of f = n / ΔT, where n is a positive integer and a symbol period is ΔT, and a first frequency converting unit that corresponds to one symbol. After the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval is held during the predetermined period, M is set to a positive integer, and the held signal values are stored in the holding order in the order of 1 / s of the symbol period. A spreading section that is M and is repeatedly read and output at a time interval shorter than a predetermined time interval, a low-pass filter section to which a signal output from the spreading section is input, and a band-pass to which an output signal of the low-pass filter section is input A first frequency conversion unit that converts an output signal of the band-pass filter unit into a signal of a carrier frequency of an input signal to the first frequency conversion unit and outputs the signal;

  A terminal device according to a fourth aspect of the present invention is a terminal device used in a communication system including a plurality of transmitters that perform communication based on a predetermined multiplexing method, and includes a transmission frequency band for each of the plurality of transmitters. At least partially overlap each other. The terminal device includes an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulation unit that demodulates an output signal from the unnecessary wave removing unit. The spurious wave removing unit converts the input signal into a signal of a frequency f of f = n / ΔT, where n is a positive integer and a symbol period is ΔT, and a first frequency converting unit that corresponds to one symbol. After the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval is held during the predetermined period, the held signal value is read out and output in units of one wavelength of the frequency f at random without overlapping. A spreading unit; a low-pass filter unit to which a signal output from the spreading unit is input; a band-pass filter unit to which an output signal of the low-pass filter unit is input; And a second frequency conversion unit that converts the input signal to a carrier frequency signal and outputs the signal.

  Preferably, the spreader samples an output signal from the first frequency converter at a predetermined frequency, generates and outputs digital data, an A / D converter, a first storage unit and a second storage unit, Digital data output from the A / D converter is stored in the first storage unit and the second storage unit alternately for each symbol in the first storage unit and the second storage unit, and the digital data is stored in the first storage unit and the second storage unit. In a stored order that is 1 / M of the symbol period and is repeatedly read and output at a time interval shorter than a predetermined time interval, and that the digital data output from the second switch unit is converted into an analog signal. And a D / A conversion unit for converting the data into an output.

  More preferably, the spreading unit divides and holds the signal value of one symbol in units corresponding to one wavelength of frequency f, and repeatedly reads the held signal value in units corresponding to one wavelength of frequency f. In each reading, reading is performed at random without duplication.

  More preferably, the spreading section includes a first sample hold section and a second sample hold section for holding a value of the input signal at a predetermined timing, and an output signal from the first frequency conversion section for each symbol for a predetermined time. At the timing of the interval, the first switch unit and the value held in the first sample and hold unit and the second sample and hold unit, which are alternately held in the first and second sample and hold units, are held. And a second switch unit that repeatedly reads out and outputs at a time interval that is 1 / M of the symbol period and shorter than a predetermined time interval.

  ADVANTAGE OF THE INVENTION According to this invention, in the communication system which multiplexes a signal, it can improve the deterioration of the error rate by the signal of other channels spreading to the wideband with respect to the signal of a specific channel. Therefore, the number of channels can be increased more than before without changing the communication method and the bandwidth of each channel, and the communication band allocated to the communication service can be used more effectively.

FIG. 11 is a block diagram illustrating a configuration of a conventional wireless communication system. 2 is a graph showing signals at the transmitter and the receiver of FIG. FIG. 1 is a block diagram illustrating a configuration of a wireless communication system according to a first embodiment of the present invention. FIG. 4 is a block diagram illustrating a configuration of an unnecessary wave removing unit in FIG. 3. 5 is a graph illustrating a baseband signal, a modulation signal, and a signal after conversion by a first frequency conversion circuit. 6 is a graph showing a modulated signal and a signal after multiplication. 4 is a graph showing a signal in the receiver of FIG. 15 is a graph showing random data reading from a memory according to a first modification. It is a block diagram showing an unnecessary wave removal part concerning a 2nd modification. FIG. 9 is a block diagram illustrating a configuration of a wireless communication system according to a second embodiment of the present invention. 11 is a graph showing a signal in the receiver of FIG. 4 is a graph showing subcarriers in OFDM.

  In the following embodiments, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

(First Embodiment)
Referring to FIG. 3, a wireless communication system according to the first embodiment of the present invention includes a first transmitter 100, a second transmitter 112, a third transmitter 114, a fourth transmitter 116, and a receiver 130. It has. In this wireless communication system, CDMA is adopted as a multiplexing method. Although FIG. 3 shows four transmitters and one receiver, actually, more transmitters and receivers may be provided. Communication between the transmitter and the receiver is performed via a known wireless communication base station (not shown) or directly without passing through the base station. Note that the transmitter and the receiver can be considered as a portable terminal device. The mobile terminal device has a transmission function and a reception function. The first to fourth transmitters 100 to 116 indicate the transmission functions of the corresponding mobile terminal devices, respectively. It can be said that this indicates the receiving function of the corresponding portable terminal device.

  The first transmitter 100 has the same configuration as the first transmitter 900 shown in FIG. That is, the first transmitter 100 includes the first transmitter main body including the high-frequency generator 102, the primary modulator 104, the secondary modulator 106, and the spread code generator 108, and the antenna 110. The second transmitter 112 to the fourth transmitter 116 have the same configuration as the first transmitter 100. The high frequency generator 102 generates a high frequency used as a carrier. The primary modulator 104 performs primary modulation on the high frequency input from the high frequency generator 102 using input data (digital data). A known modulation method such as ASK, FSK, PSK, or QAM is used for the primary modulation. The secondary modulator 106 receives the signal S1 after the primary modulation, performs secondary modulation on the signal S1 using the spreading code input from the spreading code generator 108, and outputs the signal S2. As a result, the signal S1 after the primary modulation (see, for example, FIG. 2A) is spread in frequency and becomes a signal S2 having a small intensity (see, for example, FIG. 2B). The signal S2 after the secondary modulation is transmitted from the antenna 110 as a signal of CH1. Similarly, the signals after the secondary modulation are transmitted from the second transmitter 112 to the fourth transmitter 116 as signals of CH2 to CH4. Different spreading codes are used in each transmitter.

  The receiver 130 includes an antenna 132 and a receiver main body including a despreader 134, a BPF 136, a demodulator 138, a despread code generator 140, and an unnecessary wave removing unit 200. The antenna 132 receives a radio signal. The reception signal S3 is a signal on which a band-spread signal transmitted from CH1 to CH4 is superimposed (for example, see FIG. 2C). Despreader 134 performs a despreading process on received signal S3 using the despread code output from despread code generator 140. Specifically, the signal S3 is multiplied by the despread code and output as a signal S4. Assuming that the detection target of the receiver 130 is the signal of CH2, in the signal S4, the signal of CH2 used by the second transmitter 112 returns to the state before spreading, and the other signals remain spread. (For example, see FIG. 2D). The BPF 136 is a band-pass filter that allows a signal in a predetermined frequency range (predetermined band) of the input signal S4 to pass, attenuates other signals, and outputs the signal as a signal S5 (for example, as illustrated in FIG. e)).

  The unnecessary wave removing unit 200 removes unnecessary waves from the input signal and outputs a signal S7. The unnecessary wave removing section 200 is disclosed, for example, in Patent Document 1 as a first embodiment. The demodulator 138 performs a demodulation process on the signal S7 output from the unnecessary wave removing unit 200 by a method according to the modulation method adopted by the primary modulator 104. As a result, predetermined data (for example, data transmitted by the first transmitter 100) is output from the demodulator 138.

  Referring to FIG. 4, unnecessary wave removing section 200 includes first frequency conversion circuit 202, A / D converter 204, first memory 206, second memory 208, first bus selector switch 210, and second bus selector switch. 212, a D / A converter 214, an LPF (low-pass filter) 216, a BPF 218, a second frequency conversion circuit 220, a PLL oscillation circuit 222, a synchronization correction circuit 224, a DDS (Direct Digital Synthesizer) 226, and a control circuit 228. I have.

  The first frequency conversion circuit 202 receives the signal S5 (including an unnecessary wave) after the primary modulation output from the BPF 136. The first frequency conversion circuit 202 has a local oscillation circuit, and converts the input signal S5 into a frequency f (n is a positive integer) n times (n is a positive integer) a frequency (symbol rate) having one symbol period as a symbol period. , F = n / ΔT). FIG. 5 shows a signal (not including an unnecessary wave) after the data to be modulated (symbol) indicated by “baseband” is primarily modulated by each of the ASK, FSK, and PSK modulation schemes. For example, if n = 2 and the signal shown in FIG. 5C (the carrier frequency is arbitrary) is input to the first frequency conversion circuit 202, the first frequency conversion circuit 202 sets the symbol rate (1 5D having a frequency (2 / ΔT) that is twice as high as (/ ΔT). The signal of FIG. 5A or 5B is similarly converted.

  The A / D converter 204 samples and digitally encodes the output (analog signal) of the first frequency conversion circuit 202 in accordance with the clock output from the PLL oscillation circuit 222. The PLL oscillation circuit 222 supplies the A / D converter 204 with a clock whose frequency is N times (N is a positive integer) the input clock (clock synchronized with a reference clock of a receiver described later).

  The first bus selector switch 210 is controlled by the control circuit 228, and outputs the output (conversion data) of the A / D converter 204 to the first memory 206 and the second memory 208 alternately for each symbol. The first memory 206 and the second memory 208 are, for example, RAMs (Random Access Memory) and have a capacity sufficient to store conversion data for one symbol. Note that the first memory 206 and the second memory 208 may be configured by different memory elements or may be configured as different areas on one memory element. The second bus selector switch 212 is controlled by the control circuit 228, reads data (corresponding to one symbol) from the first memory 206 and the second memory 208 alternately, and inputs the read data to the D / A converter 214. . The addresses of the first memory 206 and the second memory 208 accessed by the first bus selector switch 210 and the second bus selector switch 212 are specified by the control circuit 228. While the first bus selector switch 210 writes data to one of the first memory 206 and the second memory 208, the second bus selector switch 212 connects the other which is not in the write state to the D / A converter 214. Connection and input data to the D / A converter 214. At this time, the second bus selector switch 212 operates at a speed that is M times (M is a positive integer) the frequency of one cycle of the symbol cycle in the signal S5 (the input signal to the first frequency conversion circuit 202) after the primary modulation. The reading of the stored data for one symbol is cyclically (cyclically) repeated from the head data. At this time, M is set to a value larger than N, and the data output speed (frequency) to the D / A converter 214 is set to a value larger than the operation clock frequency of the A / D converter 204.

  The D / A converter 214 converts a digital signal (data read from the first memory 206 and the second memory 208) input from the second bus selector switch 212 into an analog signal and outputs the analog signal. The D / A conversion of the D / A converter 214 is performed at the timing of the clock output from the DDS 226.

  The DDS 226 is a known signal generator having a variable frequency and phase, which includes a phase accumulator, a phase-amplitude converter, and a D / A converter. The oscillation frequency of the DDS 226 is controlled by phase data input from the synchronization correction circuit 224 and the control circuit 228. At this time, the oscillation frequency of the DDS 226 is set to a frequency equal to or higher than the output clock of the PLL oscillation circuit 222, and is M times the frequency with one symbol period (the period is the symbol period). 1 / M). That is, the D / A conversion by the D / A converter 214 is executed at the same speed as the data reading by the second bus selector switch 212.

  The D / A converter 214 repeatedly reads the data of the first memory 206 and the second memory 208 with such a high frequency clock, and thereby the frequency of the output signal from the D / A converter 214 can be determined by the input signal S5. Can be made M / N times the input signal S5 while maintaining the bandwidth of the input signal S5. For example, the frequency of the modulation output of one symbol of the input signal S5 is 2 kHz, the carrier frequency fb of the input signal S5 is 2 kHz, the output clock of the PLL oscillation circuit 222 is 20 kHz (the number of samplings in the symbol period is 10, and N = 10 ), If the output clock of the DDS 226 is 30 kHz (M = 30), the frequency of the output from the D / A converter 214 can be 3 kHz (= 1 kHz × M / N). By doing so, since no phase shift occurs between the waveform data, only the carrier frequency is multiplied while maintaining the same bandwidth as before the multiplication.

  The synchronization correction circuit 224 is for synchronizing the oscillation output of the PLL oscillation circuit 222 and the DDS 226 with the reference clock of the received signal. For example, the oscillation phase of the DDS 226 is moved slightly back and forth, and the phase is moved back and forth. The level change of the generated signal is taken out, and the phase is controlled so that the displacement becomes zero. Therefore, as shown in FIG. 4, the output of the D / A converter 214 is input to the synchronization correction circuit 224 via the LPF 216 and the BPF 218. By taking synchronization in this manner, the code of one symbol is discriminated, and the writing and reading of the signal to and from the first memory 206 and the second memory 208 are phase-shifted, and are multiplied in a state where the phase is shifted. Can be prevented.

  The reference clock of the received signal is the same as the clock used when modulating the carrier with the baseband signal in the transmitter, and modulates several bits based on the rising or falling of this clock. .

  The analog signal output from the D / A converter 214 is input to the LPF 216, and a high-frequency component is attenuated and a smoothed signal is output from the LPF 216. The output of the LPF 216 is input to the BPF 218, and is output from the BPF 218 after being limited to a predetermined band. The output of the BPF 218 is input to the second frequency conversion circuit 220. The second frequency conversion circuit 220 includes a local oscillation circuit, converts the output of the BPF 218 into a frequency before multiplication, and outputs the converted signal as a signal S7.

  As described above, the control circuit 228 controls the switching of the first bus selector switch 210 and the second bus selector switch 212, generates the address data of the first memory 206 and the second memory 208, writes the data to the address or Control of reading, setting of the local oscillation frequency of the second frequency conversion circuit 220, setting of the frequency of the DDS 226, and the like are performed.

  The reading of data from the first memory 206 and the second memory 208 and the D / A conversion of the read data by the D / A converter 214 are performed at the clock frequency of the DDS 226. It is converted to the frequency of the signal multiplication. At this time, the synchronization correction circuit 224 synchronizes so that the frequency of the PLL oscillation circuit 222 becomes N times the reference clock and the frequency of the DDS 226 becomes M times the reference clock (M> N), so that the phase shift is reduced. Can output a multiplied waveform of one symbol unit. The spectrum of the modulated wave multiplied with the phases aligned in this way moves from the spectrum at the time of input shown in FIG. 6A to the high frequency side as shown in FIG. 6B. At this time, unnecessary waves such as noise and interference waves included in the input signal are multiplied in a state where the phases are not aligned, and thus are spread over a wide frequency range. In FIG. 4, the A / D converter 204, the first bus selector switch 210, the first memory 206, the second memory 208, the second bus selector switch 212, the D / A converter 214, and the PLL oscillation surrounded by a chain line. The circuit 222 and the DDS 226 constitute a diffusion unit.

  For example, if the frequency of the input signal is fb = 100 kHz, the occupied bandwidth is 12.5 kHz, and the frequency after multiplication is fc = 1000 kHz, the multiplication factor H becomes H = fc / fb = 1000/100 = 10 times. The noise in the occupied band is also multiplied and spread to 125 kHz. Here, since the power density of noise and interference waves that have been multiplied and spread uniformly decreases, when such a multiplied wave is passed through the BPF 218, the level of an unnecessary wave included in the output signal (signal S7) is reduced. Can be reduced. Therefore, by converting this signal to the frequency before multiplication by the second frequency conversion circuit 220, it is possible to eliminate noise and interference waves.

As described above, in the signal S5 output from the BPF 136 and input to the unnecessary wave removing unit 200, as shown in FIG. 7A, the signal of CH1, CH3 and CH4 is compared with the signal of CH2 which is the detection signal. Are included as unnecessary waves, but after passing through the LPF 216 of the unnecessary wave removing unit 200, the unnecessary waves (CH1, CH3, and CH4 signals) are spread over a wide frequency range as shown in FIG. 7B. The signal is spread and the signal strength is reduced. Thus, BPF218, by removing the frequency range of the signals of CH2, as shown in FIG. 7 (c), the intensity _{N 1} of the unnecessary waves, than the intensity _{N 0} of the unnecessary wave (a) of FIG. 7 Is smaller (N ₁ <N ₀ ), but the signal strength of CH2 does not change, so that the SN ratio can be improved and the bit error rate can be improved.

  In FIG. 4, the BPF 218 is arranged in a stage preceding the second frequency conversion circuit 220, but is not limited to this. Since the BPF 218 only needs to be able to remove the undesired spread wave, it may be arranged at the subsequent stage of the second frequency conversion circuit 220. In that case, the signal output from the BPF 218 may be input to the demodulator 138.

(First Modification)
The unnecessary wave removing unit 200 in FIG. 3 is not limited to the configuration shown in FIG. As in the second or third embodiment of Patent Document 1, unnecessary waves are also removed by a configuration in which reading from the first memory 206 and the second memory 208 is changed to a random configuration in FIG. be able to. Here, "random" means that data corresponding to one symbol is set as one set and its storage address is randomly specified without duplication.

  This is specifically shown with reference to FIG. Similarly to the above, a signal including an unnecessary wave and a desired wave is input to the unnecessary wave removing unit, and the first frequency conversion circuit 202 converts the input signal into a signal having a frequency that is an integral multiple of the symbol rate. (F = n / ΔT where symbol period is ΔT). FIG. 8A shows a waveform included in the frequency-converted signal when one symbol is represented by four wavelengths (that is, when one symbol is converted to a frequency four times the symbol rate). I have. The actual signal is obtained by superimposing signals obtained by converting the respective amplitudes of the desired wave (solid line) and unnecessary wave (dashed line) of FIG. 8A to a predetermined value. The analog signal is sampled and stored in a memory. Data reading from the memory is performed without random overlap in units of one wavelength.

  For example, FIG. 8B shows a case where data is read in the order of the period t2, the period t4, the period t1, and the period t3 shown in FIG. 8A. The actually read data is digital data of a signal obtained by superimposing signals obtained by converting respective amplitudes of a solid line (desired wave) and a broken line (unwanted wave) shown in FIG. 8B into predetermined values.

  (C) and (d) of FIG. 8 are obtained by extracting a desired wave and an unnecessary wave from (b) of FIG. 8, respectively. As is clear from this, the desired wave included in the data read from the memory is the same as that shown in FIG. 8A, but the unnecessary wave included in the data read from the memory has a phase difference at the joint of each wavelength. Are shifted, and the waveform is modulated within one symbol. Therefore, as described above, the desired wave is maintained, and the unnecessary wave is spread over a wide area, and the unnecessary wave can be removed by passing through the BPF 218 (see FIG. 4).

(Second Modification)
The unnecessary wave removing unit 200 in FIG. 3 may be the one having a sampling and holding circuit as shown in FIG. 9 similarly to the fourth embodiment of Patent Document 1. Referring to FIG. 9, unnecessary wave removing section 240 includes a first frequency conversion circuit 242, a sample and hold section 244, a first sample and hold group 246, a second sample and hold group 248, a first multi-channel analog switch (first multi-channel analog switch). CH analog SW) 250, second multi-channel analog switch (second multi-channel analog SW) 252, control circuit 254, LPF 256, BPF 258, second frequency conversion circuit 260, and synchronization correction circuit 264.

  The first frequency conversion circuit 242, LPF 256, BPF 258, second frequency conversion circuit 260, and synchronization correction circuit 264 are respectively the first frequency conversion circuit 202, LPF 216, BPF 218, second frequency conversion circuit 220, and synchronization correction circuit 224 of FIG. And performs a similar function. The setting of the local oscillation frequency of the second frequency conversion circuit 260 is performed by the control circuit 254. The control circuit 254 has a function corresponding to the PLL oscillation circuit 222 and the DDS 226 in FIG. 4, and controls each unit as described later.

  The sample hold unit 244 includes a plurality of sampling hold circuits (hereinafter, also referred to as S / H circuits) in parallel. Each S / H circuit samples and holds the input signal at a timing under external control. By sequentially operating a plurality of S / H circuits, input signals can be sampled and held by the number of S / H circuits. The plurality of S / H circuits are divided into a first sample and hold group 246 and a second sample and hold group 248 including the same number of S / H circuits.

  The first multi-channel analog switch 250 is a switch that receives an external control and outputs an input signal to any of the plurality of S / H circuits. Each S / H circuit of the first multi-channel analog switch 250 and the sample / hold unit 244 is controlled by the control circuit 254 to sequentially output the output signal of the first frequency conversion circuit 242 to the S / H circuit of the sample / hold unit 244. Enter and store. The timing of switching the first multi-channel analog switch 250 and the timing of storing data in each S / H circuit of the sample and hold section 244 are determined by an oscillation signal generated by the function of the PLL oscillation circuit of the control circuit 254. . The storage in the S / H circuits constituting the first sample-hold group 246 and the second sample-hold group 248 is performed alternately in symbol units. That is, when the storage in the plurality of S / H circuits forming the first sample and hold group 246 is completed, the storage in the plurality of S / H circuits forming the second sample and hold group 248 is started, and the second sample and hold is started. When the storage in the plurality of S / H circuits constituting the group 248 is completed, the storage in the plurality of S / H circuits constituting the first sample hold group 246 is started.

  The second multi-channel analog switch 252 is a switch that outputs one of a plurality of input signals under external control. The S / H circuits of the second multi-channel analog switch 252 and the sample and hold unit 244 are controlled by the control circuit 254 to sequentially read data stored in each of the S / H circuits of the sample and hold unit 244, and send the data to the LPF 256. input. The timing of switching the second multi-channel analog switch 252 and the timing of reading data from each S / H circuit of the sample and hold unit 244 are determined by an oscillation signal generated by the DDS function of the control circuit 254. Reading from the S / H circuits constituting the first sample and hold group 246 and the second sample and hold group 248 is performed alternately. That is, reading is performed for the group in which the storage operation has not been performed. At this time, the reading speed from each of the first sample and hold group 246 and the second sample and hold group 248 is one symbol period in the signal S5 after primary modulation (input signal to the first frequency conversion circuit 242). Reading is performed at M times the frequency (M is an integer of 2 or more), and data reading from each group is cyclically repeated from the first data. Note that the control circuit 254 generates the signal by the function of the PLL oscillation circuit using the signal input from the synchronization correction circuit 264 in the same manner as described above with respect to the synchronization correction circuit 224, the PLL oscillation circuit 222, and the DDS 226 in FIG. The phase of the oscillation signal is synchronized with the phase of the oscillation signal generated by the DDS function.

  Thus, the desired wave can be maintained and the unnecessary wave can be spread, as described above with reference to FIG. In FIG. 9, the first multi-channel analog switch 250, the sample-and-hold unit 244, and the second multi-channel analog switch 252 surrounded by the two-dot chain line are controlled by the control circuit 254 to function as a diffusion unit. Therefore, in the signal S7 after the output from the second multi-channel analog switch 252 has passed through the LPF 256, the BPF 258, and the second frequency conversion circuit 260, unnecessary waves can be reduced while maintaining the desired waves.

(Second embodiment)
In the above description, the wireless communication system adopting CDMA as the multiplexing method has been described, but the present invention is not limited to this. A wireless communication system employing FDMA as a multiplexing method as shown in FIG. 10 may be used.

  Referring to FIG. 10, a wireless communication system according to a second embodiment of the present invention includes a first transmitter 300, a second transmitter 312, a third transmitter 314, a fourth transmitter 316, and a receiver 330. Have. Although FIG. 10 shows four transmitters and one receiver, actually, more transmitters and receivers may be provided. Communication between the transmitter and the receiver is performed via a known wireless communication base station (not shown) or directly without passing through the base station.

  The first transmitter 300 includes a high frequency generator 302, a modulator 304, and an antenna 306. The second transmitter 312 to the fourth transmitter 316 are configured similarly to the first transmitter 300. The high frequency generation unit 302 generates a high frequency used as a carrier. The modulator 304 modulates a high frequency input from the high frequency generation unit 302 using input data (digital data). A known modulation method such as ASK, FSK, PSK, or QAM is used for the modulation. The modulated signal is transmitted from antenna 306. Similarly, the modulated signal is transmitted from the second transmitter 312 to the fourth transmitter 316. Different transmission frequencies CH1 to CH4 are used for the respective transmitters. That is, as described later, the transmission frequency bands may overlap each other, but the center frequencies of the frequency bands are different from each other.

  The receiver 330 includes an antenna 332, a frequency converter 334, a BPF 336, a demodulator 338, and an unnecessary wave removing unit 200. The antenna 332 receives a radio signal. The reception signal S10 is a signal on which the signals of CH1 to CH4 are superimposed. FIG. 11A schematically shows that the received signal S10 is a signal in which the signals of CH1 to CH4 are superimposed. For the sake of convenience, CH1 to CH4 are shown with the same signal strength, but actually the signal strengths are different. The frequency converter 334 converts the input high-frequency signal into an intermediate frequency signal. The BPF 336 is a band-pass filter that allows a signal in a predetermined frequency range (a predetermined band) to pass therethrough, attenuates other signals, and outputs the signal as a signal S11 (for example, (b) in FIG. 11). )reference).

  The unnecessary wave removing unit 200 removes unnecessary waves from the input signal S11 and outputs a signal S7. The unnecessary wave removing unit 200 is the same as that shown in FIG. The demodulator 338 performs a demodulation process on the signal S7 output from the unnecessary wave removing unit 200 by a method according to the modulation method adopted by the modulator 304. As a result, predetermined data (data from the transmitter) is output from demodulator 338.

  Assuming that the detection target of the receiver 330 is a signal of CH2, the output signal S6 (see FIG. 4) of the LPF 216 in the unnecessary wave removing unit 200 is, for example, as shown in FIG. , CH3 and CH4) are spread over a wide frequency range, and the signal strength is reduced. Therefore, if the signal outside the frequency range of CH2 is removed by the BPF 218 (see FIG. 4) in the unnecessary wave removing unit 200, the intensity of the unnecessary wave becomes as shown in (d) of FIG. Since the signal strength of CH2 does not change while the strength of the unnecessary wave of a) becomes smaller, the SN ratio can be improved and the bit error rate can be improved.

  Note that, in the present embodiment, as in the first embodiment, the unnecessary wave removing unit 200 can be the one in the first modification or the second modification.

  The case where CDMA or FDMA is adopted as the multiplexing method of each channel signal in the wireless communication has been described above, but the present invention is not limited to this. A wireless communication system employing a multiplexing method other than these may be used. Further, the communication is not limited to wireless communication, and may be wired communication.

  For example, the unnecessary wave removing unit described above can be applied to a communication system that employs a multicarrier modulation scheme using a plurality of subcarriers (subchannels) as a multiplexing scheme. The multicarrier modulation scheme includes, for example, OFDM described above with reference to FIG. OFDM requires that subcarriers are orthogonal to each other. In the same band, if the number of subcarriers is increased to increase the data rate, that is, if the interval between the subcarriers SC1 to SC5 shown in FIG. 12 is further reduced, the orthogonality between the subcarriers breaks down. At the position of the center frequency of each subcarrier, the signal strength of the other subcarriers does not become zero, and it becomes impossible to separate each subcarrier accurately. Even in such a case (subcarriers are non-orthogonal), it is possible to remove or reduce signals of other subcarriers included in each subcarrier as unnecessary waves by using the above unnecessary wave removing unit. it can. That is, the unnecessary wave removing unit can improve an error rate in a communication system employing a non-orthogonal multicarrier scheme using non-orthogonal subcarriers, and can increase the number of subcarriers (the number of subchannels).

  Further, the configuration of the unnecessary wave removing unit is not limited to the above-described configuration (FIG. 4, FIG. 9, etc.). In addition to the first frequency conversion circuit, the LPF, the BPF, the low-pass filter, and the second frequency conversion circuit, the signal value of the output signal from the first frequency conversion circuit at a predetermined time interval in a period corresponding to one symbol After holding, a function of repeatedly reading out the held signal values at a time interval that is 1 / M of the symbol period and shorter than a predetermined time interval, and outputs the signal value to the LPF, in the held order, where M is a positive integer. What is necessary is just to have.

  As described above, the present invention has been described by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment. The scope of the present invention is shown by each claim of the claims, in consideration of the description of the detailed description of the invention, and all changes within the meaning and range equivalent to the language described therein are described. Including.

100, 300, 900 First transmitter 102, 302, 902 High frequency generator 104, 904 Primary modulator 106, 906 Secondary modulator 108, 908 Spread code generator 110, 132, 306, 332, 910, 932 Antenna 112 , 312, 912 second transmitters 114, 314, 914 third transmitters 116, 316, 916 fourth transmitters 130, 330, 930 receivers 134, 934 despreaders 136, 218, 258, 336, 936 BPF
138, 338, 938 Demodulator 140, 940 Despreading code generator 200, 240 Unwanted wave removing unit 202, 242 First frequency conversion circuit 204 A / D converter 206 First memory 208 Second memory 210 First bus selector switch 212 Second bus selector switch 214 D / A converter 216, 256 LPF
220, 260 Second frequency conversion circuit 222 PLL oscillation circuit 224, 264 Synchronization correction circuit 226 DDS
228, 254 Control circuit 244 Sample hold unit 246 First sample hold group 248 Second sample hold group 250 First multi-channel analog switch 252 Second multi-channel analog switch 304 Modulator 334 Frequency converter

Claims (5)

A communication system including a plurality of transmitters for communicating based on a predetermined multiplexing method and at least one receiver,
At least a part of each transmission frequency band of the plurality of transmitters overlap each other,
The receiver,
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
A demodulation unit for demodulating an output signal from the unnecessary wave removing unit,
The unnecessary wave removing unit,
A first frequency conversion unit that converts the input signal into a signal having a frequency f of f = n / ΔT, where n is a positive integer and n is a positive integer;
In the period corresponding to one symbol, after holding the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval, M is a positive integer, and the held signal values are stored in the holding order. A spreading unit for repeatedly reading and outputting at a time interval that is 1 / M of the symbol period and shorter than a predetermined time interval;
A low-pass filter unit to which a signal output from the spreading unit is input;
A band-pass filter to which an output signal of the low-pass filter is input;
And a second frequency converter for converting an output signal of the band-pass filter into a signal having a carrier frequency of the input signal to the first frequency converter and outputting the signal. A communication system including a plurality of transmitters for communicating based on a predetermined multiplexing method and at least one receiver,
At least a part of each transmission frequency band of the plurality of transmitters overlap each other,
The receiver,
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
A demodulation unit for demodulating an output signal from the unnecessary wave removing unit,
The unnecessary wave removing unit,
A first frequency conversion unit that converts the input signal into a signal having a frequency f of f = n / ΔT, where n is a positive integer and n is a positive integer;
In a period corresponding to one symbol, after holding a signal value of the output signal from the first frequency conversion unit at a timing of a predetermined time interval, the held signal value is randomly overlapped in one wavelength unit of the frequency f. A diffusion unit for reading and outputting without performing
A low-pass filter unit to which a signal output from the spreading unit is input;
A band-pass filter to which an output signal of the low-pass filter is input;
A communication system comprising: a second frequency conversion unit that converts an output signal of the bandpass filter unit into a signal having a carrier frequency of the input signal to the first frequency conversion unit and outputs the signal. CDMA, FDMA, or a non-orthogonal multi-carrier scheme using a plurality of non-orthogonal subcarriers is used as the multiplexing scheme,
When CDMA is used,
Each of the plurality of transmitters transmits a signal to which a different spreading code is applied,
The said receiver inputs the signal obtained by applying the despreading code corresponding to the said spreading code used by the transmitter of a communication target to the received signal to the said unnecessary wave removal part. A communication system according to claim 1. A terminal device used in a communication system including a plurality of transmitters that perform communication based on a predetermined multiplexing method,
At least a part of each transmission frequency band of the plurality of transmitters overlap each other,
The terminal device,
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
A demodulation unit for demodulating an output signal from the unnecessary wave removing unit,
The unnecessary wave removing unit,
A first frequency conversion unit that converts the input signal into a signal having a frequency f of f = n / ΔT, where n is a positive integer and n is a positive integer;
In the period corresponding to one symbol, after holding the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval, M is a positive integer, and the held signal values are stored in the holding order. A spreading unit for repeatedly reading and outputting at a time interval that is 1 / M of the symbol period and shorter than a predetermined time interval;
A low-pass filter unit to which a signal output from the spreading unit is input;
A band-pass filter to which an output signal of the low-pass filter is input;
A second frequency conversion unit configured to convert an output signal of the band-pass filter unit into a signal of a carrier frequency of the input signal to the first frequency conversion unit and output the converted signal. A terminal device used in a communication system including a plurality of transmitters that perform communication based on a predetermined multiplexing method,
At least a part of each transmission frequency band of the plurality of transmitters overlap each other,
The terminal device,
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
A demodulation unit for demodulating an output signal from the unnecessary wave removing unit,
The unnecessary wave removing unit,
A first frequency conversion unit that converts the input signal into a signal having a frequency f of f = n / ΔT, where n is a positive integer and n is a positive integer;
In a period corresponding to one symbol, after holding a signal value of the output signal from the first frequency conversion unit at a timing of a predetermined time interval, the held signal value is randomly overlapped in one wavelength unit of the frequency f. A diffusion unit for reading and outputting without performing
A low-pass filter unit to which a signal output from the spreading unit is input;
A band-pass filter to which an output signal of the low-pass filter is input;
A second frequency conversion unit configured to convert an output signal of the band-pass filter unit into a signal of a carrier frequency of the input signal to the first frequency conversion unit and output the converted signal.

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