JP6869596B2 - Communication system and terminal equipment - Google Patents

Description

The present invention relates to a communication system and a terminal device capable of improving an error rate in communication.

In communication systems that enable communication by mobile phones, smartphones, etc. (hereinafter referred to as mobile terminal devices), various multiplexing methods are used in order to effectively use the limited frequency band in a large number of mobile terminal devices. Has been done. As typical ones, FDMA (frequency division multiple access), TDMA (time division multiple access) and CDMA (code division multiple access) are known.

With reference to FIG. 1, in a wireless communication system that employs CDMA as the multiplexing method, diffusion code processing is executed at the transmitter and despreading code processing is executed at the receiver. 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 main body including a high frequency generator 902, a primary modulator 904, a secondary modulator 906, and a diffusion code generator 908, and an antenna 910. The second transmitter 912 to the fourth transmitter 916 are also configured in the same manner as the first transmitter 900. The high frequency generation unit 902 generates a high frequency used as a carrier wave. The primary modulator 904 primary-modulates the high frequency input from the high-frequency generator 902 using the input data (digital data). A known modulation method is used for the primary modulation, for example, ASK (amplitude shift key modulation), FSK (frequency shift key modulation), PSK (phase shift key modulation), QAM (quadrature phase amplitude modulation), or the like is used. To. The secondary modulator 906 receives the signal S1 after the primary modulation, secondarily modulates the signal S1 using the diffusion code input from the diffusion code generator 908, and outputs the signal S2 as the signal S2. Specifically, the signal S1 is multiplied by the diffusion code and output. The signal S2 after the secondary modulation is transmitted from the antenna 910 as a signal of CH1. Similarly, the signal after the secondary modulation is also transmitted from the second transmitters 912 to the fourth transmitter 916 as the signals of CH2 to CH4. In each transmitter, different diffusion codes are used, but the frequency band of the carrier wave is the same.

FIG. 2A shows the signal S1 after the primary modulation in each of the first transmitter 900 to the fourth transmitter 916. By the diffusion code generator 908, the signal S1 after the primary modulation is diffused over a wider frequency range (the frequency band is widened), and the energy does not change, so that the signal S2 has a low intensity (see (b) in FIG. 2). ). Here, it is assumed that the signal to be detected by the receiver 930, which will be described later, is the signal (CH2) transmitted from the second transmitter 912.

With reference to FIG. 1 again, the receiver 930 includes an antenna 932 and a receiver body including a despreader 934, a BPF (bandpass filter) 936, a demodulator 938 and a despread code generator 940. .. Antenna 932 receives the radio signal. The despreader 934 uses the despread code output from the despread code generator 940 to execute the despread process on the received signal S3. Specifically, the signal S3 is multiplied by the reverse diffusion code and output. The BPF 936 is a bandpass filter, passes a signal in a predetermined frequency range (predetermined band) of the input signal S4, attenuates the other signals, and outputs the signal S5. The demodulator 938 executes demodulation processing on the input signal S5 by a method corresponding to the modulation method adopted in the primary modulator 904. As a result, predetermined data (digital data before the primary modulation in the first transmitter 900) is output from the demodulator 938.

The mobile terminal device has a transmission function and a reception function, and the first transmitter 900 to the fourth transmitter 916 show the transmission function of the corresponding mobile terminal device, and the receiver 930 , It can be said that it shows the reception function of the corresponding mobile terminal device.

As described above, the waveforms of the signals S3 to S5 are shown in FIGS. 2 (c) to 2 (e), assuming that the signal to be detected by the receiver 930 is the signal (CH2) from the second transmitter. The received signal S3 is a signal on which the band-spread signals transmitted from CH1 to CH4 are superimposed (see (c) of FIG. 2). On the other hand, in the signal S4 after being despread using the backspread code corresponding to the spread code used in the second transmitter 912, the signal of CH2 used by the second transmitter 912 is spread. It returns to the previous state, and the other signals remain diffused (see (d) in FIG. 2).

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

After that, when the signal S4 passes through the BPF 936 of FIG. 1, the signal S5 from which the signal outside the predetermined band is removed is generated (see (e) of FIG. 2). The demodulator 938 executes demodulation processing on the signal S5 by a method corresponding 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.

Japanese Unexamined Patent Publication No. 2000-341149

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 by backdiffusion on the receiving side, increasing the number of channels is the opposite. Unnecessary wave (hereinafter, also referred to as noise) level of other channels due to diffusion will increase. Therefore, there is a problem that the ratio of the desired wave to the unnecessary wave (hereinafter, also referred to as the SN ratio) deteriorates. For example, as shown in FIG. 2 (e), the diffused signals of CH1, CH3, and CH4 become noise (intensity N) with respect to the signal of CH2 (intensity S). As the number of channels increases, the noise intensity increases, whereas the signal intensity of CH2 does not change, so that the SN ratio decreases (deteriorates). Therefore, in a communication system using CDMA, there is a limit to the number of channels that can be used in order to maintain the SN ratio above a predetermined value.

Conventionally, the bit error rate (BER (Bit Error Rate)) is improved by removing unnecessary waves other than the transmission signal. The purpose is to remove noise superimposed on the signal output from the transmitter by the communication path as an unnecessary wave. As described above, regarding CDMA, there is a problem that signals used on other channels can always be noise with respect to signals on a predetermined channel to be detected, that is, the multiplexing method (CDMA) adopted. It has never been considered to improve the problems caused by itself. Further, the conventional method for improving the bit error rate is not aimed at improving the problem caused by the adopted multiplexing method (CDMA) itself.

For example, when CH1 to CH4 are used, if CH2 is the desired wave, the other channels are unnecessary waves (see (d) and (e) in FIG. 2). When received in CH2 alone, even if the signal strength is to be BER = 1x10 ^-5 if sufficient, and becomes BER = 1x10 ^-3 to signals of other channels interfere. In reality, the error rate is further deteriorated by an external unnecessary wave or the like. However, the conventional unnecessary wave removal, because it is the purpose of removing foreign undesired wave as described above, a limit be close to BER = 1x10 ^-3, can not lead to BER = 1x10 ^-5.

Further, in the conventional FDMA, each channel is arranged on the frequency axis so that the frequency bandwidths of the respective channels do not interfere with each other (so that the frequency bands of the respective channels do not overlap). Therefore, if the number of channels is increased, there is a problem that it is necessary to reduce the amount of data of each channel. This causes interference due to the overlapping bandwidths of each channel, and signals of other channels interfere with the desired wave before the bit error rate deteriorates due to the influence of unnecessary waves such as noise. This is because the input signal itself is input with the error rate deteriorated. It would be nice if this problem in FDMA could be improved.

Further, in OFDM (Orthogonal Frequency Division Multiplexing) belonging to multi-carrier modulation, data is transmitted from a transmitter on a plurality of carriers (subcarriers, hereinafter also referred to as subchannels) orthogonal to each other, and a plurality of data are transmitted in a receiver. Collects data transmitted by subcarriers. Each subcarrier is modulated at a low symbol rate by a known method such as QAM. That is, in OFDM, not a single wideband signal with high-speed modulation, but a large number of narrow-bandwidth signals with slow modulation (low modulation rate) are denser (narrower frequency intervals) than FDMA. ) To improve 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, so that usually, the overlap occurs on the frequency axis. Despite being densely arranged, it has the advantage that the subcarriers do not interfere with each other. In FIG. 12, the spectrum of the subcarrier SC2 is shown by a thick solid line. Subcarriers SC1 and SC3 to SC5 also have similar spectra, although their frequencies are shifted. Each subcarrier can be efficiently separated by the Fast Fourier Transform (FFT). In such OFDM, the number of subcarriers within the bandwidth is further increased in order to increase the data rate without changing the bandwidth, but each subcarrier must be orthogonal and low data. 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 specified, if the number of subcarriers is increased, the power of each subcarrier must be reduced, which causes deterioration of the error rate. Therefore, it is preferable if the problem that it is difficult to increase the number of subcarriers (the number of subchannels) can be solved.

Therefore, the present invention improves the deterioration of the error rate due to unnecessary waves of signals of other channels with respect to signals of a specific channel (including subchannels) in a communication method for multiplexing signals. It is an object of the present invention to provide a communication system and a terminal device capable of performing the above.

The communication system according to the first aspect of the present invention is a communication system including a plurality of transmitters communicating based on a predetermined multiplexing method and at least one receiver, and the transmission of each of the plurality of transmitters. At least part of the frequency band overlaps with each other. The receiver has an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulating unit that demodulates output signals from the unnecessary wave removing unit. The unnecessary wave removing unit corresponds to the first frequency conversion unit and one symbol, which converts the input signal into a signal having a frequency f of f = n / ΔT, where the symbol period is ΔT and n is a positive integer. After holding the signal value of the output signal from the first frequency converter at the timing of the predetermined time interval, the held signal values are held in the order in which M is a positive integer, which is 1 / of the symbol period. A diffuser that is M and is repeatedly read and output at intervals shorter than a predetermined time interval, a low-pass filter unit to which a signal output from the diffuser is input, and a band path to which the output signal of the low-pass filter unit is input. It has a filter unit and a second frequency conversion unit that converts the output signal of the band path filter unit into a signal having a carrier frequency of an input signal to the first frequency conversion unit and outputs the signal.

As a result, in a communication method for multiplexing signals, it is possible to improve the deterioration of the error rate due to the spread of signals of other channels over a wide band with respect to the signals of a specific channel.

The communication system according to the second aspect of the present invention is a communication system including a plurality of transmitters communicating based on a predetermined multiplexing method and at least one receiver, and the transmission of each of the plurality of transmitters. At least part of the frequency band overlaps with each other. The receiver has an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulating unit that demodulates output signals from the unnecessary wave removing unit. The unnecessary wave removing unit corresponds to the first frequency conversion unit and one symbol, which converts the input signal into a signal having a frequency f of f = n / ΔT and outputs it with the symbol period as ΔT and n as a positive integer. After holding the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval, the held signal value is randomly read and output in units of one wavelength of frequency f without duplication. The first frequency conversion unit converts the diffuser, the low-pass filter unit to which the signal output from the diffuser is input, the band-pass filter unit to which the output signal of the low-pass filter unit is input, and the output signal of the band-pass filter unit. It has a second frequency conversion unit that converts the input signal to the signal into a signal having a carrier frequency and outputs the signal.

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

The terminal device according to the third aspect of the present invention is a terminal device used in a communication system including a plurality of transmitters that communicate based on a predetermined multiplexing method, and each transmission frequency band of the plurality of transmitters. At least some of them overlap each other. The terminal device has an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulating unit that demodulates output signals from the unnecessary wave removing unit. The unnecessary wave removing unit corresponds to the first frequency conversion unit and one symbol, which converts the input signal into a signal having a frequency f of f = n / ΔT, where the symbol period is ΔT and n is a positive integer. After holding the signal value of the output signal from the first frequency converter at the timing of the predetermined time interval, the held signal values are held in the order in which M is a positive integer, which is 1 / of the symbol period. A diffuser that is M and is repeatedly read and output at intervals shorter than a predetermined time interval, a low-pass filter unit to which a signal output from the diffuser is input, and a band path to which the output signal of the low-pass filter unit is input. It has a filter unit and a second frequency conversion unit that converts the output signal of the band path filter unit into a signal having a carrier frequency of an input signal to the first frequency conversion unit and outputs the signal.

The terminal device according to the fourth aspect of the present invention is a terminal device used in a communication system including a plurality of transmitters that communicate based on a predetermined multiplexing method, and each transmission frequency band of the plurality of transmitters. At least some of them overlap each other. The terminal device has an unnecessary wave removing unit that removes unnecessary waves from modulated signals received from a plurality of transmitters, and a demodulating unit that demodulates output signals from the unnecessary wave removing unit. The unnecessary wave removing unit corresponds to the first frequency conversion unit and one symbol, which converts the input signal into a signal having a frequency f of f = n / ΔT and outputs it with the symbol period as ΔT and n as a positive integer. After holding the signal value of the output signal from the first frequency conversion unit at the timing of the predetermined time interval, the held signal value is randomly read and output in units of one wavelength of frequency f without duplication. The first frequency conversion unit converts the diffuser, the low-pass filter unit to which the signal output from the diffuser is input, the band-pass filter unit to which the output signal of the low-pass filter unit is input, and the output signal of the band-pass filter unit. It has a second frequency conversion unit that converts the input signal to the signal into a signal having a carrier frequency and outputs the signal.

Preferably, the spreading unit includes an A / D conversion unit that samples an output signal from the first frequency conversion unit at a predetermined frequency to generate and output digital data, and a first storage unit and a second storage unit. Digital data from the first switch unit that alternately stores the digital data output from the A / D conversion unit in the first storage unit and the second storage unit for each symbol, and the digital data from the first storage unit and the second storage unit. The second switch section, which repeatedly reads and outputs 1 / M of the symbol cycle and at a time interval shorter than the predetermined time interval, and the digital data output from the second switch section, are analog signals in the order in which they are stored. Includes a D / A conversion unit that converts to and outputs.

More preferably, the diffusion unit divides and holds the signal value for one symbol in the unit corresponding to one wavelength of the frequency f, and repeatedly reads the held signal value in the unit corresponding to one wavelength of the frequency f. , Read randomly without duplication in each reading.

More preferably, the diffusion unit transfers the output signals from the first sample hold unit and the second sample hold unit, which hold the values of the input signals at a predetermined timing, and the first frequency conversion unit for a predetermined time for each symbol. At the timing of the interval, the values held in the first switch section and the first sample hold section and the second sample hold section, which are alternately held by the first sample hold section and the second sample hold section, are held. In order, it includes a second switch unit which is 1 / M of the symbol cycle and is repeatedly read and output at a time interval shorter than a predetermined time interval.

According to the present invention, in a communication method for multiplexing signals, it is possible to improve the deterioration of the error rate due to the spread of signals of other channels over a wide band with respect to the signals of a specific channel. Therefore, the number of channels can be increased as compared with the conventional case 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.

It is a block diagram which shows the structure of the conventional wireless communication system. It is a graph which shows the signal in the transmitter and the receiver of FIG. It is a block diagram which shows the structure of the wireless communication system which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the unnecessary wave removing part of FIG. It is a graph which shows the baseband signal, the modulated signal, and the signal after conversion by the 1st frequency conversion circuit. It is a graph which shows the modulated signal and the signal after multiplication. It is a graph which shows the signal in the receiver of FIG. It is a graph which shows the random data reading from the memory which concerns on the 1st modification. It is a block diagram which shows the unnecessary wave removing part which concerns on 2nd modification. It is a block diagram which shows the structure of the wireless communication system which concerns on 2nd Embodiment of this invention. It is a graph which shows the signal in the receiver of FIG. It is a graph which shows the subcarrier in OFDM.

In the following embodiments, the same parts are given the same reference number. Their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

(First Embodiment)
With reference to FIG. 3, the 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 the multiplexing method. Although FIG. 3 shows four transmitters and one receiver, it may actually have more transmitters and receivers. Further, communication between the transmitter and the receiver is performed directly via a known wireless communication base station (not shown) or without a base station. The transmitter and receiver can also be considered as a mobile terminal device. The mobile terminal device has a transmission function and a reception function, the first transmitter 100 to the fourth transmitter 116 show the transmission function of the corresponding mobile terminal device, and the receiver 130 is a receiver 130. It can be said that it shows the reception function of the corresponding mobile terminal device.

The first transmitter 100 is configured in the same manner as the first transmitter 900 shown in FIG. That is, the first transmitter 100 includes a first transmitter main body including a high frequency generator 102, a primary modulator 104, a secondary modulator 106, and a diffusion code generator 108, and an antenna 110. The second transmitter 112 to the fourth transmitter 116 are configured in the same manner as the first transmitter 100. The high frequency generation unit 102 generates a high frequency used as a carrier wave. The primary modulator 104 primary-modulates the high frequency input from the high-frequency generator 102 using the 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 inputs the signal S1 after the primary modulation, secondary-modulates the signal S1 using the diffusion code input from the diffusion code generator 108, and outputs the signal S2 as a signal S2. As a result, the signal S1 after the first-order modulation (for example, see (a) of FIG. 2) becomes a signal S2 whose frequency is diffused and the intensity is low (for example, see (b) of FIG. 2). 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 also transmitted from the second transmitter 112 to the fourth transmitter 116 as the signals of CH2 to CH4. The spreading codes used in each transmitter are different from each other.

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 unwanted wave removing unit 200. The antenna 132 receives the radio signal. The received signal S3 is a signal on which the band-spread signals transmitted from CH1 to CH4 are superimposed (see, for example, FIG. 2C). The despreading device 134 executes the despreading process on the received signal S3 by using the despreading code output from the despreading code generator 140. Specifically, the signal S3 is multiplied by the reverse diffusion code and output as the 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 diffusion, and the other signals remain diffused. Yes (see, for example, (d) in FIG. 2). The BPF 136 is a bandpass filter, passes a signal in a predetermined frequency range (predetermined band) among the input signals S4, attenuates the other signals, and outputs the signal S5 (for example, (for example, (for example) in FIG. 2). e) See).

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

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

The signal S5 (including unnecessary waves) after the primary modulation output from the BPF 136 is input to the first frequency conversion circuit 202. The first frequency conversion circuit 202 has a local oscillation circuit, and the input signal S5 has a frequency f (n is a positive integer) n times (n is a positive integer) a frequency (symbol rate) having a symbol period of one period (the symbol period is ΔT). , F = n / ΔT). FIG. 5 shows a signal (excluding unnecessary waves) after the modulation target data (symbol) indicated by the “baseband” is first-order modulated by each of the ASK, FSK, and PSK modulation methods. For example, when n = 2, when the signal (carrier frequency is arbitrary) shown in FIG. 5 (c) is input to the first frequency conversion circuit 202, the first frequency conversion circuit 202 has a symbol rate (1). The signal shown in FIG. 5 (d) having a frequency (2 / ΔT) twice that of / ΔT) is output. The signal of (a) or (b) of FIG. 5 is also converted in the same manner.

The A / D converter 204 samples the output (analog signal) of the first frequency conversion circuit 202 according to the clock output from the PLL oscillation circuit 222 and digitally encodes it. The PLL oscillator 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 the reference clock of the 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. 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, alternately reads data (corresponding to one symbol) from the first memory 206 and the second memory 208, 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 designated by the control circuit 228. The second bus selector switch 212 uses the D / A converter 214 and the other that is not in the writing state while the first bus selector switch 210 writes data to either the first memory 206 or the second memory 208. Connect and input data to D / A converter 214. At this time, the second bus selector switch 212 has a speed of M times (M is a positive integer) of the frequency whose symbol period is one in the signal S5 (input signal to the first frequency conversion circuit 202) after the primary modulation. Then, the stored data for one symbol is repeatedly read cyclically (circularly) 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 operating 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 digital signal. The D / A conversion of the D / A converter 214 is performed at the timing of the clock output from the DDS226.

The DDS226 is a known signal generator with variable frequency and phase, consisting of a phase accumulator, a phase-amplitude converter, and a D / A converter. The oscillation frequency of the DDS 226 is controlled by the 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 having the symbol cycle as one cycle (the cycle is the symbol cycle). 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.

With such a high frequency clock, the D / A converter 214 repeatedly reads the data of the first memory 206 and the second memory 208, so that the frequency of the output signal from the D / A converter 214 is set to the input signal S5. It is possible to multiply the input signal S5 by M / N while maintaining the bandwidth of. 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, and the output clock of the PLL oscillator circuit 222 is 20 kHz (the number of samples in the symbol period is 10 and N = 10). ), Assuming that the output clock of the DDS226 is 30 kHz (M = 30), the frequency of the output from the D / A converter 214 can be set to 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 the bandwidth is maintained as before the multiplication.

The synchronization correction circuit 224 is for synchronizing the oscillation output of the PLL oscillation circuit 222 and the DDS226 with the reference clock of the received signal. For example, the oscillation phase of the DDS226 is slightly moved 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 0. 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 synchronizing in this way, the sign of one symbol is discriminated, and the writing and reading of the signal to the first memory 206 and the second memory 208 are multiplied in a phase-shifted state due to a phase shift. Can be prevented.

The reference clock of the received signal is the same as the clock used when the carrier wave is modulated by the baseband signal in the transmitter, and modulation of several bits is performed based on the rising edge or falling edge of this clock. ..

The analog signal output from the D / A converter 214 is input to the LPF216, the high frequency component is attenuated, and the smoothed signal is output from the LPF216. The output of LPF216 is input to BPF218, limited to a predetermined band, and output from BPF218. The output of 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 to the frequency before multiplication, and outputs the signal S7.

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

The data read 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, and the converted signal waveform is input. It is converted to the multiplication frequency of the signal. 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 (M> N) of the reference clock, thereby causing a phase shift. It is possible to output a waveform in units of one symbol that is not multiplied. The spectrum of the modulated wave whose phase is aligned and multiplied 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, so that they are diffused 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 the alternate long and short dash line. The circuit 222 and the DDS 226 form a diffuser.

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 is H = fc / fb = 1000/100 = 10 times. The noise in the occupied band is also multiplied and spreads to 125 kHz. Here, since the power density of the multiplied and uniformly diffused noise and the interfering wave decreases, when such a multiplied wave is passed through the BPF 218, the level of the unnecessary wave included in the output signal (signal S7) is increased. Can be lowered. Therefore, noise and interfering waves can be eliminated by converting this signal to the frequency before multiplication by the second frequency conversion circuit 220.

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 signals of CH1, CH3 and CH4 are compared with the signal of CH2 which is the detection signal. Is included as an unwanted wave, but after passing through the LPF216 of the unwanted wave removing unit 200, the unwanted wave (signals of CH1, CH3, and CH4) has a wide frequency range as shown in FIG. 7 (b). It is diffused and the signal strength is reduced. Therefore, if the signal outside the frequency range of CH2 is removed by BPF218, as shown in FIG. 7 (c), the unnecessary wave intensity N ₁ is higher than _{the unnecessary wave intensity N 0 in} FIG. 7 (a). (N ₁ <N ₀ ), but the signal strength S 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 front of the second frequency conversion circuit 220, but the present invention is not limited to this. The BPF 218 may be arranged after the second frequency conversion circuit 220 as long as it can remove the diffused unnecessary waves. 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 of FIG. 3 is not limited to the configuration shown in FIG. Similar to the second embodiment or the third embodiment of Patent Document 1, unnecessary waves are also removed by the configuration changed in FIG. 4 to a configuration in which reading from the first memory 206 and the second memory 208 is performed at random. be able to. Here, random means that the data corresponding to one symbol is set as one set and the storage addresses are randomly specified without duplication.

It will be specifically shown with reference to FIG. Similar 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 ΔT is the symbol period). FIG. 8A shows the waveform included in the signal after frequency conversion when one symbol is represented by four wavelengths (that is, when the frequency is converted to four times the symbol rate). There is. The actual signal is a superposition of signals obtained by converting the amplitudes of the desired wave (solid line) and the unnecessary wave (broken line) of FIG. 8 (a) into predetermined values. The analog signal is sampled and stored in memory. Data is read from the memory in units of one wavelength without duplication.

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

8 (c) and 8 (d) are desired waves and unnecessary waves extracted from (b) of FIG. 8, respectively. As is clear from this, the desired wave contained in the data read from the memory is the same as that in (a) of FIG. 8, but the unnecessary wave contained in the data read from the memory has a phase at the joint of each wavelength. Is shifted, and the waveform is modulated within one symbol. Therefore, similarly to the above, the desired wave is maintained, the unnecessary wave is diffused over a wide area, and the unnecessary wave can be removed by passing the BPF 218 (see FIG. 4).

(Second modification)
The unnecessary wave removing unit 200 of FIG. 3 may be as shown in FIG. 9 provided with a sampling hold circuit, as in the fourth embodiment of Patent Document 1. With reference to FIG. 9, the unnecessary wave removing unit 240 includes a first frequency conversion circuit 242, a sample hold unit 244, a first sample hold group 246, a second sample hold group 248, and a first multi-channel analog switch (first multi-channel analog switch). It includes a CH analog SW) 250, a second multi-channel analog switch (second multi-CH analog SW) 252, a control circuit 254, an LPF256, a BPF258, a second frequency conversion circuit 260, and a synchronization correction circuit 264.

The first frequency conversion circuit 242, LPF256, BPF258, the second frequency conversion circuit 260, and the synchronization correction circuit 264 are the first frequency conversion circuit 202, LPF216, BPF218, the second frequency conversion circuit 220, and the synchronization correction circuit 224 in FIG. 4, respectively. And perform the same function. The local oscillation frequency of the second frequency conversion circuit 260 is set by the control circuit 254. The control circuit 254 has a function corresponding to the PLL oscillation circuit 222 and the DDS226 of FIG. 4, and controls each part 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 an input signal at a timing controlled from the outside. By sequentially operating a plurality of S / H circuits, it is possible to sample and hold as many input signals as there are S / H circuits. The plurality of S / H circuits are divided into a first sample hold group 246 and a second sample 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 a 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, and the output signal of the first frequency conversion circuit 242 is sequentially transferred to the S / H circuit of the sample hold unit 244. Enter and memorize. The timing for switching the first multi-channel analog switch 250 and the timing for storing data in each S / H circuit of the sample hold unit 244 are determined by the 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 alternately performed in symbol units. That is, when the storage in the plurality of S / H circuits constituting the first sample hold group 246 is completed, the storage in the plurality of S / H circuits constituting the second sample hold group 248 is started, and the second sample 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 receives an external control and outputs one of a plurality of input signals. Each S / H circuit of the second multi-channel analog switch 252 and the sample hold unit 244 is controlled by the control circuit 254, and the data stored in each S / H circuit of the sample hold unit 244 is sequentially read out to the LPF256. input. The timing for switching the second multi-channel analog switch 252 and the timing for reading data from each S / H circuit of the sample hold unit 244 are determined by the oscillation signal generated by the DDS function of the control circuit 254. Reads from the S / H circuits constituting the first sample hold group 246 and the second sample hold group 248 are alternately performed. That is, the reading is executed for the group in which the storage operation is not executed. At this time, the reading speed from each of the first sample hold group 246 and the second sample hold group 248 is set to one cycle of the symbol cycle in the signal S5 (input signal to the first frequency conversion circuit 242) after the primary modulation. It is performed at M times the frequency (M is an integer of 2 or more), and the data read from each group is cyclically repeated from the head data. The control circuit 254 is generated 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 for the synchronization correction circuit 224, the PLL oscillation circuit 222, and the DDS 226 of FIG. The phase of the oscillation signal and the phase of the oscillation signal generated by the DDS function are synchronized.

Thereby, the desired wave can be maintained and the unnecessary wave can be diffused in the same manner as described above with reference to FIG. In FIG. 9, the first multi-channel analog switch 250, the sample hold unit 244, and the second multi-channel analog switch 252 surrounded by the two-point chain line function as a diffusion unit under the control of the control circuit 254. Therefore, in the signal S7 after the output from the second multi-channel analog switch 252 has passed through the LPF256, BPF258, and the second frequency conversion circuit 260, the unwanted wave can be reduced while maintaining the desired wave.

(Second Embodiment)
In the above, 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 that employs FDMA as the multiplexing method as shown in FIG. 10 may be used.

With reference to FIG. 10, the wireless communication system according to the 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. I have. Although FIG. 10 shows four transmitters and one receiver, it may actually have more transmitters and receivers. Further, communication between the transmitter and the receiver is performed directly via a known wireless communication base station (not shown) or without a 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 in the same manner as the first transmitter 300. The high frequency generation unit 302 generates a high frequency used as a carrier wave. The modulator 304 modulates the high frequency input from the high frequency generation unit 302 by using the input data (digital data). For modulation, a known modulation method such as ASK, FSK, PSK, or QAM is used. The modulated signal is transmitted from the antenna 306. Similarly, the modulated signal is also transmitted from the second transmitters 312 to the fourth transmitter 316. Transmission frequencies CH1 to CH4 assigned to each transmitter are different from each other. That is, as will be 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 unwanted wave removing unit 200. The antenna 332 receives the radio signal. The received 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 on which the signals of CH1 to CH4 are superimposed. For convenience, CH1 to CH4 are shown with the same signal strength, but the signal strengths are actually different. The frequency converter 334 converts the input high frequency signal into an intermediate frequency signal. The BPF 336 is a bandpass filter, passes a signal in a predetermined frequency range (predetermined band) among the input signals, attenuates the other signals, and outputs the 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 the signal S7. The unnecessary wave removing unit 200 is the same as that shown in FIG. The demodulator 338 executes demodulation processing on the signal S7 output from the unnecessary wave removing unit 200 by a method corresponding to the modulation method adopted in the modulator 304. As a result, predetermined data (data from the transmitter) is output from the demodulator 338.

Assuming that the detection target of the receiver 330 is the signal of CH2, the output signal S6 (see FIG. 4) of the LPF216 in the unnecessary wave removing unit 200 is an unnecessary wave (CH1) as shown in (c) of FIG. 11, for example. , CH3 and CH4 signals) 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 is as shown in FIG. 11 (d). Since the signal strength of CH2 does not change while it is smaller than the strength of the unnecessary wave in a), the SN ratio can be improved and the bit error rate can be improved.

In this embodiment as well, as in the first embodiment, the unwanted wave removing unit 200 can be the one of the above-mentioned first modification or second modification.

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

For example, the above-mentioned unnecessary wave removing unit can be applied to a communication system that employs a multi-carrier modulation method that uses a plurality of subcarriers (subchannels) as the multiplexing method. The multi-carrier modulation method includes, for example, the above-mentioned OFDM with reference to FIG. OFDM requires subcarriers to be orthogonal to each other. If the number of subcarriers is increased in order to increase the data rate in the same band, that is, if the interval between the subcarriers SC1 to SC5 shown in FIG. 12 is further narrowed, the orthogonality between the subcarriers is broken. At the position of the center frequency of each subcarrier, the signal strength of the other subcarriers does not become zero, and each subcarrier cannot be separated accurately. Even in such a case (subcarriers are non-orthogonal), the signals of other subcarriers contained in each subcarrier can be removed or reduced as unnecessary waves by using the unnecessary wave removing unit described above. it can. That is, the unnecessary wave removing unit can improve the error rate in the communication system adopting the non-orthogonal multi-carrier system using non-orthogonal subcarriers, and can increase the number of subcarriers (number of subchannels).

Further, the configuration of the unnecessary wave removing portion is not limited to the above-mentioned configuration (FIGS. 4, 9, etc.). In addition to the first frequency conversion circuit, LPF, BPF, low-pass filter, and second frequency conversion circuit, the signal value of the output signal from the first frequency conversion circuit at the timing of a predetermined time interval in the period corresponding to one symbol. After holding, M is a positive integer, and the held signal values are repeatedly read out in the held order at 1 / M of the symbol period and at time intervals shorter than the predetermined time interval, and output to the LPF. Anything that has it will do.

Although the present invention has been described above by explaining the embodiments, the above-described embodiments are examples, and the present invention is not limited to the above-described embodiments. The scope of the present invention is indicated by each claim of the scope of claims, taking into consideration the description of the detailed description of the invention, and all changes within the meaning and scope equivalent to the wording described therein. Including.

100, 300, 900 First transmitter 102, 302, 902 High frequency generator 104, 904 Primary modulator 106, 906 Secondary modulator 108, 908 Diffuse code generator 110, 132, 306, 332, 910, 932 Antenna 112 , 312, 912 2nd transmitter 114, 314, 914 3rd transmitter 116, 316, 916 4th transmitter 130, 330, 930 Receiver 134, 934 Reverse diffuser 136, 218, 258, 336, 936 BPF
138, 338, 938 Demodulator 140, 940 Reverse spread code generator 200, 240 Unnecessary wave remover 202, 242 First frequency conversion circuit 204 A / D converter 206 First memory 208 Second memory 210 First bus selector switch 212 2nd bus selector switch 214 D / A converter 216, 256 LPF
220, 260 Second frequency conversion circuit 222 PLL oscillation circuit 224, 264 Synchronous correction circuit 226 DDS
228, 254 Control circuit 244 Sample hold unit 246 1st sample hold group 248 2nd sample hold group 250 1st multi-channel analog switch 252 2nd multi-channel analog switch 304 Modulator 334 Frequency converter

Claims (5)

A communication system including a plurality of transmitters and at least one receiver that communicate based on a predetermined multiplexing method.
At least a part of each transmission frequency band of the plurality of transmitters overlaps with each other.
The receiver
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
It has a demodulation unit that demodulates the output signal from the unnecessary wave removal unit.
The unnecessary wave removing part is
A first frequency converter that converts an input signal into a signal with a frequency f of f = n / ΔT and outputs it, where the symbol period is ΔT 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 a predetermined time interval, M is a positive integer, and the held signal values are held in the order of holding. , A diffuser that repeatedly reads and outputs at 1 / M of the symbol period and at a time interval shorter than a predetermined time interval, and
A low-pass filter unit to which a signal output from the diffusion unit is input, and a low-pass filter unit.
The bandpass filter unit to which the output signal of the lowpass filter unit is input and the bandpass filter unit
Wherein the output signal of the band-pass filter section, have a second frequency converter for converting the signal of the carrier frequency of the input signal to the first frequency converter,
A communication system in which CDMA or a non-orthogonal multi-carrier method using a plurality of non-orthogonal subcarriers is used as the multiplexing method . A communication system including a plurality of transmitters and at least one receiver that communicate based on a predetermined multiplexing method.
At least a part of each transmission frequency band of the plurality of transmitters overlaps with each other.
The receiver
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
It has a demodulation unit that demodulates the output signal from the unnecessary wave removal unit.
The unnecessary wave removing part is
A first frequency converter that converts an input signal into a signal with a frequency f of f = n / ΔT and outputs it, where the symbol period is ΔT and n is a positive integer.
After holding the signal value of the output signal from the first frequency conversion unit at the timing of a predetermined time interval in the period corresponding to one symbol, the held signal value is randomly overlapped in one wavelength unit of the frequency f. A diffuser that reads and outputs without doing
A low-pass filter unit to which a signal output from the diffusion unit is input, and a low-pass filter unit.
The bandpass filter unit to which the output signal of the lowpass filter unit is input and the bandpass filter unit
Wherein the output signal of the band-pass filter section, have a second frequency converter for converting the signal of the carrier frequency of the input signal to the first frequency converter,
A communication system in which CDMA or a non-orthogonal multi-carrier method using a plurality of non-orthogonal subcarriers is used as the multiplexing method . CDMA A is used as the multiplexing method , and
Each of the previous SL plurality of transmitter transmits a signal of applying mutually different spreading codes,
Claim 1 or 2 in which the receiver inputs a signal obtained by applying a reverse spreading code corresponding to the spreading code used in the transmitter to be communicated to the received signal to the unnecessary wave removing unit. The communication system described in. A terminal device used in a communication system including a plurality of transmitters that communicate based on a predetermined multiplexing method.
At least a part of each transmission frequency band of the plurality of transmitters overlaps with each other.
The terminal device is
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
It has a demodulation unit that demodulates the output signal from the unnecessary wave removal unit.
The unnecessary wave removing part is
A first frequency converter that converts an input signal into a signal with a frequency f of f = n / ΔT and outputs it, where the symbol period is ΔT 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 a predetermined time interval, M is a positive integer, and the held signal values are held in the order in which they are held. , A diffuser that is 1 / M of the symbol period and is repeatedly read and output at time intervals shorter than a predetermined time interval, and
A low-pass filter unit to which a signal output from the diffusion unit is input, and a low-pass filter unit.
The bandpass filter unit to which the output signal of the lowpass filter unit is input and the bandpass filter unit
Wherein the output signal of the band-pass filter section, have a second frequency converter for converting the signal of the carrier frequency of the input signal to the first frequency converter,
A terminal device in which CDMA or a non-orthogonal multi-carrier system using a plurality of non-orthogonal subcarriers is used as the multiplexing method. A terminal device used in a communication system including a plurality of transmitters that communicate based on a predetermined multiplexing method.
At least a part of each transmission frequency band of the plurality of transmitters overlaps with each other.
The terminal device is
An unnecessary wave removing unit that removes unnecessary waves from the modulated signals received from the plurality of transmitters,
It has a demodulation unit that demodulates the output signal from the unnecessary wave removal unit.
The unnecessary wave removing part is
A first frequency converter that converts an input signal into a signal with a frequency f of f = n / ΔT and outputs it, where the symbol period is ΔT and n is a positive integer.
After holding the signal value of the output signal from the first frequency conversion unit at the timing of a predetermined time interval in the period corresponding to one symbol, the held signal value is randomly overlapped in one wavelength unit of the frequency f. A diffuser that reads and outputs without doing
A low-pass filter unit to which a signal output from the diffusion unit is input, and a low-pass filter unit.
The bandpass filter unit to which the output signal of the lowpass filter unit is input and the bandpass filter unit
Wherein the output signal of the band-pass filter section, have a second frequency converter for converting the signal of the carrier frequency of the input signal to the first frequency converter,
A terminal device in which CDMA or a non-orthogonal multi-carrier method using a plurality of non-orthogonal subcarriers is used as the multiplexing method.

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