JP7673366B2 - COMMUNICATION DEVICE AND COMMUNICATION METHOD - Google Patents

Description

The present invention relates to a communication device and a communication method that can improve frequency utilization efficiency.

In recent years, the demand for wireless communication has been steadily increasing, and the shortage of frequency resources has become serious. Various technologies have been proposed to improve spectrum utilization efficiency. One of them is In-Band Full-Duplex (IBFD). A base station (BS) performs bidirectional communication with multiple user equipment (UE). In conventional Half-Duplex (HD), uplinks and downlinks with each UE must be assigned to different time slots (or different frequency resources), but IBFD has been expected to be a promising technology that can ideally double spectrum utilization efficiency by allowing the BS to simultaneously transmit and receive in the same frequency band. In addition, IBFD has many advantages over conventional HD, such as solving the hidden terminal problem and reducing traffic congestion.

However, IBFD has not yet been put to practical use because the strong interference (Self-Interference, SI) that the transmission signal causes to the received signal (desired signal) significantly deteriorates the reception quality of the desired signal. To solve this problem, various self-interference cancellation techniques have been proposed, such as antenna cancellation (see Non-Patent Document 1), analog circuit cancellation (see Non-Patent Document 2), and digital circuit cancellation (see Non-Patent Document 3).

J. Il Choi,M, Jain, K. Srinivasan, P. Levis, and S. Katti, “Achieving single channel, full duplex wireless communication,” Proceedings of the Sixteenth Annual International Conference on Mobile Computing and Net-working (MobiCom 10), pp. 1-12, Sep. 2010. D. Bharadia, E. McMilin, and S. Katti, “Full duplex radios,” SIGCOMM Com-put. Commun. Rev., Vol. 43, No. 4, pp. 375-386, Aug. 2013. E. Ahmed and A. M. Eltawil, “All-digital self-interference cancellation technique for full-duplex systems,” IEEE Transactions on Wireless Communications, Vol. 14, No. 7, pp. 3519-3532, Jul. 2015.

The technique described in Non-Patent Document 1 uses three antennas, and the distance between the two transmitting antennas is large, making it difficult to put into practical use. The technique described in Non-Patent Document 2 uses a circulator to implement analog self-interference cancellation, but the hardware scale of the circulator is large. The technique described in Non-Patent Document 3 uses two identical receiving circuits to implement digital self-interference cancellation, which increases the hardware scale. These techniques attempt to cancel the self-interference component by directly subtracting the time waveform of the self-interference signal component from the time waveform of the mixed received signal of the self-interference signal and the desired signal. It has been reported that some of these techniques can achieve sufficient cancellation performance under certain environments, but due to the complexity of the implementation, the increase in hardware scale, and the extremely limited environment in which they can be implemented, each technique alone cannot be said to be sufficiently practical.

Therefore, the object of the present invention is to provide a communication device and a communication method that can cancel the self-interference signal remaining after applying these conventional self-interference cancellation techniques in the digital domain, thereby making it possible to double the frequency utilization efficiency.

The present invention relates to a communication device that simultaneously receives data from a first user terminal and transmits data to a second user terminal in the same frequency band using single carrier transmission ,
A transmitter and an antenna for transmitting a training signal consisting of known data during training;
a transmission timing adjustment unit that adjusts the transmission timing of a transmission signal;
a receiving unit including an antenna and a training signal detection unit for receiving a received signal including a self-interference signal based on data transmission and a desired signal based on data reception ;
an offset calculation unit that calculates a transmission timing offset , which is a time difference between a reception sampling timing of a reception signal and a transmission sampling timing of a transmission signal sampled at a time when an eye pattern of a self-interference signal is most open based on a training signal or at a time within a predetermined timing offset;
A separation unit that separates a self-interference signal and a desired signal,
the transmission timing adjustment unit adjusts the transmission timing of the transmission signal based on the transmission timing offset to substantially match the transmission sampling timing with the reception sampling timing , and controls so that sampling of the reception signal is performed at the time when the eye pattern of the self-interference signal is most open or within a predetermined timing offset;
The separator subtracts the self-interference signal component on a complex plane from the signal obtained as a result of the sampling to generate a residual complex signal;
The communication device is adapted to obtain a demodulated result of a desired signal by demodulating the residual complex signal.

According to the present invention, it is possible to cancel the residual self-interference caused by conventional self-interference cancellation technology with a small circuit scale, and to increase the frequency utilization efficiency. Note that the effects described here are not necessarily limited, and may be any of the effects described in this invention. Furthermore, the contents of this invention should not be interpreted as being limited by the effects exemplified in the following description.

FIG. 1 is a block diagram showing an example of a communication system to which the present invention can be applied. 2A and 2B are schematic diagrams illustrating the time and frequency domain operation of the two communication methods. FIG. 3 is a block diagram for explaining self-interference. FIG. 4 is a block diagram showing the configuration of a base station according to an embodiment of the present invention. 5A and 5B are schematic diagrams showing a waveform diagram and a complex plane used to explain the influence of a self-interference signal. 6A and 6B are schematic diagrams showing a waveform diagram and a complex plane used to explain one embodiment of the present invention. FIG. 7 is a schematic diagram for explaining separation of a self-interference signal and a desired signal in an embodiment of the present invention. 8A and 8B are waveform diagrams showing the in-phase and quadrature components, respectively, of a signal transmitted from a base station BS to a user terminal UE2. 9A, 9B, and 9C are waveform diagrams showing the in-phase and quadrature components of a self-interference signal received at the base station BS itself from a base station BS that transmits the signal to a user terminal UE2, as well as schematic line diagrams showing these signals on a complex plane. 10A, 10B, and 10C are waveform diagrams showing the in-phase and quadrature components of a desired signal received at the base station BS from a user terminal UE1 to the base station BS, and are schematic diagrams showing these signals on a complex plane. Figures 11A, 11B, and 11C are waveform diagrams showing the in-phase and quadrature components of a signal obtained by adding together a self-interference signal and a desired signal when the self-interference signal and the desired signal are received at exactly the same timing at a base station BS, i.e., when the reception timing offset of the self-interference signal and the desired signal is 0 (τ = 0), as well as schematic line diagrams showing these signals on a complex plane. FIG. 12 is a schematic diagram for explaining a superposition constellation formed by a self-interference signal and a desired signal. FIG. 13 is a schematic diagram for explaining the process of removing a self-interference signal and separating a desired signal. FIG. 14 is a graph for explaining the simulation results (BER characteristics) of the present invention.

One embodiment of the present invention will be described below. Note that the embodiment described below is a preferred specific example of the present invention, and various technically preferable limitations are included, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

IBFD will be described with reference to FIG. 1. A base station BS (Base Station) performs bidirectional communication with each of user devices UE1 and UE2. In reality, the base station BS is designed to perform wireless communication with many more user terminals. Communication from the user device UE1 or UE2 to the base station BS is called the uplink, and communication from the base station BS to the user device UE1 or UE2 is called the downlink. In conventional HD, as shown in FIG. 2A, it is necessary to assign uplinks and downlinks with each UE to different time slots TS (or different frequency resources). For example, in FIG. 2A, uplink communication from the user device UE1 to the base station BS is performed in TS1, uplink communication from the user device UE2 to the base station BS is performed in TS2, downlink communication from the base station BS to the user device UE1 is performed in TS3, and downlink communication from the base station BS to the user device UE2 is performed in TS4. Therefore, a total of four time slots TS are used. In contrast, as shown in FIG. 2B, in IBFD, the base station BS simultaneously transmits and receives in the same frequency band, ideally doubling the spectrum utilization efficiency. For example, in FIG. 2B, in TS1, uplink communication from the user equipment UE1 to the base station BS and downlink communication from the base station BS to the user equipment UE2 are simultaneously performed, and in TS2, uplink communication from the user equipment UE2 to the base station BS and downlink communication from the base station BS to the user equipment UE1 are simultaneously performed. Therefore, ideally, only two time slots TS are required in total, resulting in a maximum doubling of spectrum utilization efficiency. In addition, IBFD has many advantages over conventional HD, such as solving the hidden terminal problem and reducing traffic congestion.

On the other hand, IBFD has not yet been put to practical use because the strong self-interference signal (shown by the dashed line) that the transmission signal itself gives to the received signal (desired signal) as shown in Figure 3 significantly deteriorates the reception quality of the desired signal. The present invention solves this problem.

In contrast to conventional self-interference cancellation techniques that directly subtract the self-interference signal component from the mixed received signal as a time waveform, this invention proposes a "signal separation and reception technology using superimposed modulation characteristics" in which the BS receiver adjusts the timing of the transmitted signal (i.e., the self-interference signal) on the received signal (i.e., the desired signal) and modulates it, and then uses the modulation characteristics of the superimposed signal to extract only the received signal.

Figure 4 shows an example of a transceiver configuration in a BS that introduces the "superimposed modulation feature-based signal separation reception technology" proposed by the present invention. A transmitter 1, a high-frequency transmitter 2, and a transmitter antenna 3 are provided, as well as a receiver 11, a high-frequency receiver 12, and a receiver antenna 13. The time for training is set in advance. Training may be performed during an initial setting period, or may be performed during reception. Adjustment values obtained by training are stored, for example, in a non-volatile memory (not shown).

The transmitter 1 is provided with switches 4 and 5 that can be switched between transmission and reception and training. In the transmission and reception state, the transmission timing of the data signal 6 selected by the switches 4 and 5 is adjusted in the transmission timing adjustment unit 8, and the data signal 6 is then transmitted through the transmission radio frequency unit 2 and the transmission antenna 3. In training, the transmission timing of the training signal 7 selected by the switches 4 and 5 is adjusted in the transmission timing adjustment unit 8, and the training signal 7 from the transmission timing adjustment unit 8 is transmitted through the transmission radio frequency unit 2 and the transmission antenna 3. The training signal 7 is a signal that has been modulated in the same way as the transmission signal, and is known data.

The received signal received by the receiving antenna 13 is processed by the receiving high frequency section 2 and supplied to the receiving section 11. The transmitting section 11 is provided with switches 14 and 15 that are switched between transmission and reception and training. In the transmission and reception state, the received signal selected by the switches 14 and 15 is supplied to the separating section 16. The separating section 16 has the function of removing the self-interference signal and separating and outputting the desired signal.

During training, the detection unit 17 detects a training signal from the received signal selected by the switch 15. The detected training signal is supplied to the offset calculation unit 18. The offset calculation unit 18 calculates the offset of the transmission timing. The offset of the transmission timing is the time difference between the sampling timing of the received signal and the sampling timing of the transmitted signal. Generally, in pulse communication, it is preferable that the sampling timing for data judgment is the time when the eye pattern is most open (the central time). When the sampling timing of the received signal and the transmitted signal are the same, the effect of the transmitted signal (self-interference signal) on the received signal (desired signal) can be easily removed or reduced by processing by the separation unit 16, which separates the self-interference signal and the desired signal, as described later.

The offset obtained by the offset calculation unit 18 is supplied to the transmission timing adjustment unit 8 of the transmitter 1, and the transmission timing adjustment unit 8 adjusts the timing of the transmission signal so that the offset is eliminated. The transmission timing adjustment unit 8 adjusts the timing of sending the transmission signal taking into account circuit delays and the like. The self-interference signal and the desired signal are separated by the separation unit 16, which separates them, and the desired signal is extracted. When training is completed, the switches 4 and 5 are switched and transmission and reception operations are performed. Since the data signal 6 to be transmitted is transmitted via the transmission timing adjustment unit 8, the sampling timing of the received signal and the self-interference signal are considered to be consistent, and the separation unit 16 performs good separation processing of the desired signal and the self-interference signal.

Next, an example of a signal transmitted from the base station BS to the user device UE2 is observed. As an example, an 8-bit information bit sequence (0,1,1,0,0,1,1,0) is transmitted by QPSK (Quadrature Phase Shift Keying) modulation. Here, as an example, consider QPSK in which a 2-bit information bit sequence (1,1) is mapped to a complex symbol (1+j), a 2-bit information bit sequence (0,1) is mapped to a complex symbol (-1+j), a 2-bit information bit sequence (0,0) is mapped to a complex symbol (-1-j), and a 2-bit information bit sequence (1,0) is mapped to a complex symbol (1-j). If the coefficient by which the transmitted signal is attenuated or amplified before being received is A, the QPSK modulated received symbol is four complex symbols, (-A+jA, A-jA, -A+jA, A-jA), in the example of FIG. 5. Also, in Fig. 5, the desired signal transmitted by the user equipment UE1 to the base station BS is also modulated by QPSK, but it is not clear which symbol is being transmitted, and all the locations indicated by x in Fig. 5B are candidates for the desired signal. The signal transmitted by the base station BS to the user equipment UE2 is s ₁ (t-τ) (τ represents the time difference between the sampling timing of the desired signal and the self-interference signal SI), and the desired signal received by the base station BS from the user terminal UE1 is r ₁ (t). At this time, the self-interference signal SI is expressed as hs ₁ (t-τ). Here, h is a channel coefficient, and in the example of Fig. 5, h=A.

Fig. 5A shows the in-phase and quadrature components of a signal hs ₁ (t-τ) transmitted from a base station BS to a user terminal UE2. In Fig. 5A, the horizontal axis represents time, measured in units of sample time. The vertical axis represents signal strength. The sampling timing of the desired signal is also shown by a dashed line. Sampling at the time when the eye pattern of the received signal is most open (the central time) provides optimal reception performance during data determination. However, there is an offset between this timing and the sampling timing of the desired signal.

Unlike the present invention, if the timing of sending the transmission signal is not adjusted, the signal to be sent is also sampled at the timing of sampling the desired signal, and as shown in FIG. 5B, the distribution of the desired signal on the complex plane becomes random, making it impossible to demodulate. In other words, it becomes unclear where in the four quadrants of the complex plane the desired signal is located, and the desired signal cannot be QPSK demodulated.

In the present invention, the timing of the transmission signal is adjusted so that the time (center time) when the eye pattern of the transmission signal is most open is perfectly matched or within an acceptable timing deviation, as shown in FIG. 6A. Therefore, as shown in FIG. 6B, in the case of a single carrier, for example, the mixed signal of the self-interference signal and the desired signal is in a state in which the received signal (desired signal) is superposition coded (superposition coded) on the transmission signal (self-interference signal). The constellation (modulated complex signal) of the received signal (desired signal) is received with a bias added by the self-interference signal. Therefore, as shown in FIG. 7, the desired signal can be demodulated by subtracting the self-interference signal component on the complex plane in the manner of demodulation of superposition coding and directly demodulating the residual complex signal component.

Further, the processing of the present invention will be described in more detail. As described above, an example of a signal that the base station BS transmits to the user equipment UE2, for example, a 4-bit information bit string (0,0,1,1) by QPSK modulation is observed. The signal that the base station BS transmits to the user equipment UE2 is s ₁ (t-τ) (τ represents the time difference between the sampling timing of the desired signal and the self-interference signal SI), and the desired signal from the user terminal UE1 that the base station BS receives is r ₁ (t). At this time, the self-interference signal SI is expressed as hs ₁ (t-τ).

FIG. 8A shows the in-phase component of the self-interference signal hs ₁ (t-τ) received by the base station BS itself, which is a signal transmitted from the base station BS to the user terminal UE2, and FIG. 8B shows the quadrature component of this signal. The horizontal axis shows time, with the unit being sample time. The vertical axis shows the signal strength. Since an example of a signal in which a 4-bit information bit string (0,0,1,1) is QPSK modulated and transmitted is observed, the QPSK modulated transmission symbol is two complex symbols of (-1-j,1+j). Here, if the channel coefficient h=A ₁ , the in-phase component and quadrature component of the received self-interference signal are (-A ₁ ,A ₁ ) (-A ₁ ,A ₁ ), respectively, and are indicated by arrows in FIG. 8A and FIG. 8B. The power has a constant value at the sampling point. In the case of the self-interference signal in this case, the magnitude is A ₁ . In FIGS. 8A and 8B, the power at the sampling points is constant, which is a feature of convolving the impulse response of a Nyquist filter on the transmitting side.

Figure 9C shows the signal simultaneously in the time domain and in the complex plane. The time domain waveforms (Figures 9A and 9B) are the same as those in Figures 8A and 8B. The horizontal axis of the complex plane is the in-phase component (I axis), and the vertical axis is the quadrature component (Q axis).

10A, 10B, and 10C show an example of a signal (desired signal) transmitted from a user terminal UE1 to a base station BS. The transmission information bit sequence is assumed to be (0, 1, 1, 1), in which case, the in-phase and quadrature components of the desired signal after QPSK modulation are (-1, 1) (1, 1). If the channel coefficient is A ₂ , the in-phase and quadrature components of the desired signal received at the base station BS are (-A ₂ , A ₂ ) (A ₂ , A ₂ ), which are respectively indicated by arrows in FIG. 10A and FIG. 10B. FIG. 10C shows the received desired signal on a complex plane. The horizontal axis of the complex plane is the in-phase component (I axis), and the vertical axis is the quadrature component (Q axis). The power has a constant value at the sampling point. In the case of this self-interference signal, the magnitude is A ₂ . Since the desired signal has a smaller power than the self-interference signal, the amplitude _A2 is smaller than _A1 in FIGS. 10A, 10B, and 10C.

In the present invention, the time difference τ between the sampling timing of the desired signal and the self-interference signal SI is set to 0, so that the time waveform of the self-interference signal (Figures 9A and 9B) and the time waveform of the desired signal (Figures 10A and 10B) are added together when the signals are aligned at a certain time.

Figures 11A and 11B show the in-phase and quadrature components of the time waveforms resulting from the addition, and Figure 11C shows a plot on the complex plane. Since the addition is performed at τ=0, the information signals match where they exist. The amplitude of the signal waveforms where the information signals exist is constant. Therefore, there are four possible amplitudes for the in-phase and quadrature components where the information signals exist in the added waveforms: ( _A1 + _A2 ), ( _A1 - _A2 ), ( _-A1 + _A2 ), and ( _-A1 - _A2 ).

Since there are four possibilities for the in-phase and quadrature components, there are 16 possible locations (candidates) on the IQ plane. In Figure 11C, the white dots indicate two of the 16 candidates. The black dots indicate where the self-interference signal exists.

A new constellation obtained by adding up the constellations on the IQ plane in this way is called a superposition constellation. All the possibilities are shown in FIG. 12. In FIG. 12, black dots represent self-interference signals, and x represents the desired signal. In this way, in order to extract the desired signal after obtaining the superposition constellation, the self-interference component can be removed on the IQ plane based on the method of superposition coding. This process is shown in FIG. 13. First, the received signal is assumed to be all self-interference signals, and QPSK demodulation is performed. The resulting bit string is QPSK demodulated again, and a replica signal is generated by multiplying it by the amplitude component _A1 of the estimated self-interference signal component. This generated replica signal of the self-interference signal is subtracted from the composite signal of the originally received desired signal and the self-interference signal, leaving only the desired signal. This residual component is QPSK demodulated to obtain the received bit string of the desired signal.

Fig. 14 shows an example of the results of a communication quality evaluation by computer simulation when the present invention is applied to a single carrier. The vertical axis of Fig. 14 is BER (bit error rate), and the horizontal axis is E _B /N _O (communication quality). The lower the BER is, the better it is, and the further to the right the E _B /N _O is, the better it is.

For example, in IBFD, it is said that the desired BER cannot be obtained unless the self-interference signal is suppressed by about 110 dB. With the existing proposed self-interference signal suppression technology, it was difficult to achieve such performance. For example, it was only possible to suppress the self-interference signal by about 60 dB to 70 dB, which resulted in a high BER, as shown in the horizontal graph in Figure 14, and was not suitable for practical use.

The present invention can be used in combination with existing technology. For example, when the self-interference signal is 110 dB larger than the desired signal, by combining it with existing technology that can improve it by 70 dB, it is possible to achieve a BER as shown by the dashed line in Figure 14. This coincides with the BER during HD. Therefore, according to the present invention, it is expected that the requirements for conventional self-interference cancellation technology can be relaxed. However, it is not essential that the present invention be combined with existing self-interference cancellation technology, and it can be sufficiently effective even when used alone.

The above describes the embodiments of the present invention in detail, but the present invention is not limited to the above-mentioned embodiments, and various modifications based on the technical concept of the present invention are possible.

1: transmitting unit, 2: transmitting high frequency unit, 3: transmitting antenna, 6: data signal,
7... training signal, 8... transmission timing adjustment unit, 11... receiving unit,
12: high frequency receiving unit, 13: receiving antenna,
18: Transmission timing offset calculation unit

Claims (4)

A communication device that simultaneously receives data from a first user terminal and transmits data to a second user terminal in the same frequency band using single carrier transmission ,
A transmitter and an antenna for transmitting a training signal consisting of known data during training;
a transmission timing adjustment unit that adjusts the transmission timing of a transmission signal;
a receiving unit including an antenna and a training signal detection unit for receiving a received signal including a self-interference signal based on the data transmission and a desired signal based on the data reception ;
an offset calculation unit that calculates a transmission timing offset , which is a time difference between a reception sampling timing of the reception signal and a transmission sampling timing of a transmission signal that is sampled based on the training signal at a time when the eye pattern of the self-interference signal is most open or at a time within a predetermined timing offset ;
a separation unit that separates the self-interference signal and the desired signal,
the transmission timing adjustment unit adjusts the transmission timing of the transmission signal based on the transmission timing offset to substantially match the transmission sampling timing with the reception sampling timing , and is controlled so that sampling of the reception signal is performed at the time when the eye pattern of the self-interference signal is most open or within a predetermined timing offset;
The separation unit generates a residual complex signal by subtracting a component of the self-interference signal on a complex plane from the signal obtained as a result of the sampling,
A communication device configured to obtain a demodulated result of the desired signal by demodulating the residual complex signal. The communication device according to claim 1, wherein the self-interference signal is larger than the desired signal. The communication device according to claim 1, which is combined with an analog or digital self-interference signal cancellation device. A communication method in which data reception from a first user terminal and data transmission to a second user terminal are simultaneously performed in the same frequency band by single carrier transmission ,
During training, a training signal consisting of known data is transmitted;
A transmission timing adjustment unit adjusts the transmission timing of the transmission signal;
receiving a received signal including a self-interference signal based on the data transmission and a desired signal based on the data reception ;
an offset calculation unit calculates a transmission timing offset , which is a time difference between a reception sampling timing of the reception signal and a transmission sampling timing for sampling at a time when an eye pattern of the self-interference signal is most open or at a time within a predetermined timing offset based on the training signal ;
A separation unit separates the self-interference signal and the desired signal;
Based on the offset of the transmission timing , the transmission timing of the transmission signal is adjusted to approximately coincide with the transmission sampling timing, and the transmission timing adjustment unit is controlled so as to sample the reception signal at the time when the eye pattern of the self-interference signal is most open or within a predetermined timing offset;
The separating unit generates a residual complex signal by subtracting a component of the self-interference signal on a complex plane from the signal obtained as a result of the sampling;
A communication method comprising: demodulating the residual complex signal to obtain a demodulated result of the desired signal.

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