JP3962031B2 - Multi-carrier communication system, receiving apparatus and transmitting apparatus used in the same system - Google Patents

Description

  The present invention relates to a multi-carrier communication system that performs communication using an orthogonal frequency division multiplexing (OFDM) system that uses a plurality of orthogonal subcarriers, and particularly relates to a communication that has a standby state for communication.

  Conventionally, for example, Patent Document 1 discloses a technique for performing reception only for a part of subcarriers in OFDM communication in order to reduce power consumption during standby. In the prior art described in Patent Document 1, a bandpass filter is used in order to receive and demodulate only signals from some subcarriers.

Also, an OFDM receiver that receives a narrowband signal by reducing the number of carriers and lowering the sampling frequency is known in communication during standby (for example, Patent Document 2).
JP 2001-274767 A JP 2003-218833 A

  The prior art described in Patent Document 1 requires a high-performance band-pass filter to obtain a desired subcarrier signal, so that there is a problem that the circuit scale and power consumption overhead increase. In addition, the prior art of Patent Document 2 requires a circuit for preparing a plurality of sampling clocks and increases interference components from subcarriers other than the subcarrier to which the control signal is assigned, resulting in a decrease in transmission efficiency. There is a problem.

  The present invention has been made in view of such circumstances, and can be used for a multi-carrier communication system and system capable of simplifying demodulation processing during standby without increasing processing overhead and realizing low power consumption. An object of the present invention is to provide a receiving apparatus and a transmitting apparatus to be used.

  A multicarrier communication system according to one embodiment of the present invention is a multicarrier that performs communication using an orthogonal frequency division multiplexing (OFDM) scheme that uses a plurality of orthogonal subcarriers between a transmission device and a reception device. In the communication system, the transmission apparatus transmits k * (N / n) -th subcarriers (where k = 0, 1,..., N−1), and N is the entire control signal necessary for the communication standby operation. N is a power of 2 representing the number of subcarriers, and n is a power of 2 representing the number of subcarriers to which a control signal necessary for standby operation is assigned, and a value smaller than N). And assigning the subcarrier as an OFDM signal to the receiving apparatus, the receiving apparatus receiving the OFDM signal, and transmitting the control signal. Which is a multi-carrier communication system operating waiting by demodulating.

  According to the present invention, there is provided a multicarrier communication system capable of simplifying demodulation processing during standby without increasing processing overhead and realizing low power consumption, and a receiving apparatus and a transmitting apparatus used in the system. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of a multicarrier communication system according to an embodiment of the present invention. Here, the base station 101 transmits data to the terminals 102 and 105. It is assumed that the terminal 102 is performing data communication and the terminal 105 is waiting. Since the base station 101 and the terminal 102 are performing data communication, a lot of data is transmitted / received, and the base station 101 and the terminal 105 transmit / receive control signals such as a paging information signal, a synchronization signal, and a position information signal. However, it is assumed that the amount of information is less than the information during data communication. Note that the signal 103 from the base station 101 to the terminal 102 and the signal 104 from the base station 101 to the terminal 105 are communication systems using multicarriers, specifically, orthogonal frequency division multiplexing using a plurality of orthogonal subcarriers ( It shall be transmitted according to an OFDM (Orthogonal Frequency Division Multiplex) communication system.

  2A and 2B are diagrams showing an example of using subcarriers in multi-carrier communication. FIG. 2A is a diagram showing data communication, and FIG. 2B is a diagram showing standby. In this example, the number of subcarriers N = 16 and the number of control signal subcarriers n = 4.

  In the transmission signal 103 during data communication, data is transmitted using all 16 subcarriers. The control signal and the data signal may be allocated to any subcarrier, but during data communication, for example, if the control signal is allocated to a subcarrier having good frequency characteristics, it is preferable because transmission efficiency can be improved. Further, during data communication, it is not always necessary to use all 16 subcarriers.

  On the other hand, for the signal 104 to be transmitted to the terminal 105 in the standby state, at least one (all in the present embodiment) of the control signals necessary for the communication standby operation is selected as the k * (N / n) th subcarrier. It shall be assigned to a subcarrier. However, k = 0, 1,..., N−1, and N is a power of 2 representing the total number of subcarriers (here, 16). In addition, n is a power of 2 that represents the number of subcarriers to which a control signal necessary for the operation in standby is assigned, and is a value smaller than N (here, 4).

  According to FIG. 2B, control signals are assigned to the subcarriers f0, f4, f8, and f12 during standby. The terminal 105 performs demodulation processing on these four subcarriers.

  Specifically, the base station 101 performs a transmission operation as follows. That is, the terminal 105 that has transitioned to the standby state is detected, the control signal necessary for the standby operation of the terminal 105 is assigned to the k * (N / n) th subcarrier as described above, and the other subcarriers are assigned. Assigns a null signal. In this way, the subcarriers to which the control signal and the null signal are assigned are transmitted to the terminal 103. On the other hand, a control signal is assigned to any one of the 0th to (N-1) th subcarriers and transmitted to the terminal 102 in data communication. The terminal 105 that has received the subcarrier from the base station 101 can perform a standby operation while demodulating the subcarrier to which the control signal is assigned.

  In this way, if the control signal necessary for the communication standby operation is limitedly assigned to the k * (N / n) -th subcarrier, interference from other subcarriers can be suppressed more than when all subcarriers are used. In addition, the amount of demodulation processing in the terminal 105 can be reduced. Therefore, it is possible to reduce power consumption when the terminal 105 is on standby.

  FIG. 3 is a block diagram showing a receiving system according to an embodiment of the present invention. According to FIG. 2, an OFDM multicarrier communication system is assumed in which the number of subcarriers N = 16 and the number of control signal subcarriers n = 4.

  A signal received by the antenna is converted into a baseband frequency signal by the RF unit 301. After the baseband frequency signal is converted into a digital signal by the A / D converter 302, the GI (guard interval) added on the transmitter side is removed by the GI remover 303 and the S / P (serial The parallel conversion unit 304 converts the signal into 16 parallel signals.

  These 16 parallel signals are processed in the dividing unit 305 in accordance with the mode signal 311. When the mode signal 311 represents the data communication mode, the dividing unit 305 outputs the 16 input signals as they are, and when the mode signal 311 represents the standby mode, the dividing unit 305 obtains the following expression, that is, ((( n * 0 + k) + (n * 1 + k) +... + (n * (N / n-1) + k)) is selected and added to output n output signals.

  However, k = 0, 1,..., N−1, and N is a power of 2 that represents the total number of subcarriers (here, 16). n is a power of 2 representing the number of subcarriers to which a control signal necessary for standby is allocated, and is a value smaller than N (here, 4).

  At the time of data communication, the 16 signals output from the dividing unit 305 are subjected to discrete Fourier transform by the 16-signal FFT unit 307 to be converted into frequency component signals. On the other hand, at the time of standby, a discrete Fourier transform is performed on the four control signals output from the dividing unit 305 by the four-signal FFT unit 306, and converted into frequency component signals. These FFT units 306 and 307 are preferably composed of fast Fourier transformers.

  The switch 308 selects either the 16-signal FFT unit 307 or the 4-signal FFT unit 306 according to the mode signal 311 indicating whether the terminal is in the data communication mode or the standby mode. A P / S (parallel / serial) conversion unit 309 converts the parallel signal output from the 16-signal FFT unit 306 or the 4-signal FFT unit 307 into a serial signal, and the demodulation processing unit 310 performs demodulation for each subcarrier.

  FIG. 4 is a circuit diagram illustrating a configuration example of the dividing unit. The signal processing circuit 400 corresponding to the dividing unit 305 includes adders 401 to 404 that perform signal addition in accordance with the mode signal 311. In the standby mode, since n = 4 and N = 16 in this example, the signal processing circuit 400 outputs four signals (S0 + S4 + S8 + S12), (S1 + S5 + S9 + S13), (S2 + S6 + S10 + S14), and (S3 + S7 + S11 + S15). Note that Sk is a serial / parallel converted signal, and k = 0 to 15. At the time of data communication, the input signals S0 to S15 are output as they are.

  FIG. 5 is a circuit diagram showing a configuration example of a fast Fourier transform (FFT) unit. This fast Fourier transform unit is related to an implementation example of the above-described 4-signal FFT unit 306 and 16-signal FFT unit 307, and here is assumed to be composed of an FFT circuit 501 using butterfly computation. The FFT circuit 501 has a configuration in which a part of the 16-signal FFT unit 307 is shared as the 4-signal FFT unit 306, thereby reducing the circuit scale of the entire FFT circuit 501.

  Specifically, the FFT circuit 501 is composed of one 16-signal FFT having two 8-signal FFTs 502 and 503. The 8-signal FFT 502 is composed of two 4-signal FFTs 504 and 505, and the 8-signal FFT 503 is composed of two 4-signal FFTs 506 and 507. Switches 508 and 509 are connected to the 4-signal FFT 507.

  When the mode signal 311 is in the data communication mode, the switch 508 connects the input terminal of the four-signal FFT 507 to the terminal on the four-signal side based on the 16 signals from the dividing unit 305 (signal processing circuit 400), and the mode signal 311 is on standby. In the mode, the input terminal of the 4-signal FFT 507 is connected to the terminal on the 4-signal side from the dividing unit 305 (signal processing circuit 400).

  On the other hand, the switch 509 corresponds to the switch 308 in FIG. 3, and when the mode signal 311 is in the data communication mode, the output terminal of the 4-signal FFT 507 is connected to the output terminal on the 16 signal side, and the mode signal 311 is in the standby mode. In this case, the output terminal of the 4-signal FFT 507 is connected to the output terminal on the 4-signal side.

  In the FFT circuit 501 configured as described above, when the mode signal 311 is in the data communication mode, the entire circuit operates as a 16-signal FFT, and FFT processing using all 16 signals is performed, while the mode signal 311 is in the standby mode. In this case, only the 4-signal FFT 507, which is a part of the 16-signal FFT circuit, operates, and an FFT process using only 4 signals is performed. At this time, for other FFT circuits 504, 505, and 506 that are not used, the power consumption of the FFT circuit 501 can be easily reduced by stopping the supply of the clock signal and power.

  As described above, according to the embodiments of the present invention, a multi-carrier communication system and system that can simplify demodulation processing during standby without increasing processing overhead and achieve low power consumption. A receiving device and a transmitting device to be used can be provided.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  The present invention can be applied to a wide variety of communication systems such as an OFDM communication system, for example, a cellular communication system such as a mobile phone and a hot spot communication system such as a wireless LAN.

1 is a schematic diagram of a multicarrier communication system according to an embodiment of the present invention. It is a figure which shows the example of use of the subcarrier in multicarrier communication, Comprising: The figure (a) is a figure which shows the time of data communication, The figure (b) shows the time of standby The block diagram which shows the receiving system which concerns on one Embodiment of this invention Circuit diagram showing a configuration example of the dividing unit It is a circuit diagram which shows the structural example of a fast Fourier transform (FFT) part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Base station, 102, 105 ... Terminal, 103, 104 ... Signal, 301 ... RF part, 302 ... A / D conversion part, 303 ... Guard interval (GI) removal part, 304 ... Serial parallel (S / P) Conversion unit, 305 ... Dividing unit, 306 ... 16 point FFT, 307 ... 4 point FFT, 308 ... Switch, 309 ... P / S converter, 310 ... Demodulator, 311 ... Mode signal

Claims (7)

In a multi-carrier communication system that performs communication in an orthogonal frequency division multiplexing (OFDM) method using a plurality of orthogonal subcarriers between a transmission device and a reception device,
In the transmitter, the control signal necessary for the communication standby operation is k * (N / n) -th subcarrier (where k = 0, 1,..., N−1, where N is the total number of subcarriers. And n is a power of 2 that represents the number of subcarriers to which a control signal necessary for operation in standby is assigned, and is assigned to at least one subcarrier. Transmitting the subcarrier as an OFDM signal to the receiving device;
The receiving device includes receiving means for receiving the OFDM signal;
Conversion means for converting the OFDM signal into N input signals (where N is a power of 2 representing the total number of subcarriers);
Mode signal generating means for generating a mode signal representing either the data communication mode or the standby mode;
When the mode signal represents the data communication mode, N output signals based on the N input signals are output. When the mode signal represents the standby mode, the following expression is obtained from the N input signals. That is, ((n * 0 + k) + (n * 1 + k) +... + (N * (N / n−1) + k, where k = 0, 1,..., N−1, 2 is a power of 2 representing the number of subcarriers, and n is a power of 2 representing the number of subcarriers to which a control signal required for standby is assigned, and is selected and added according to a value smaller than N) A signal output means for outputting n output signals;
Fourier transform means having a first Fourier transform unit corresponding to the first number of signals and a second Fourier transform unit corresponding to a second number of signals smaller than the first number of signals;
When the mode signal represents the data communication mode, the N output signals are connected to the first Fourier transform unit, and when the mode signal represents the standby mode, the n output signals are transmitted to the first Fourier transform unit. A multi-carrier communication system comprising: a switch connected to two Fourier transform units; and a standby operation by demodulating the control signal.   The multicarrier communication system according to claim 1, wherein the control signal is assigned to any one of 0th to (N-1) th subcarriers during data communication. In a receiving apparatus used in a multicarrier communication system that performs communication by an orthogonal frequency division multiplexing (OFDM) method using a plurality of orthogonal subcarriers,
Receiving means for receiving a signal transmitted using the plurality of subcarriers;
Conversion means for converting the signal into N input signals (where N is a power of 2 representing the total number of subcarriers);
Mode signal generating means for generating a mode signal representing either the data communication mode or the standby mode;
When the mode signal represents the data communication mode, N output signals based on the N input signals are output. When the mode signal represents the standby mode, the following expression is obtained from the N input signals. That is, ((n * 0 + k) + (n * 1 + k) +... + (N * (N / n−1) + k, where k = 0, 1,..., N−1, 2 is a power of 2 representing the number of subcarriers, and n is a power of 2 representing the number of subcarriers to which a control signal required for standby is assigned, and is selected and added according to a value smaller than N) A signal output means for outputting n output signals;
Fourier transform means having a first Fourier transform unit corresponding to the first number of signals and a second Fourier transform unit corresponding to a second number of signals smaller than the first number of signals;
When the mode signal represents the data communication mode, the N output signals are connected to the first Fourier transform unit, and when the mode signal represents the standby mode, the n output signals are transmitted to the first Fourier transform unit. And a switch connected to two Fourier transform units.   The receiving apparatus according to claim 3, further comprising a control unit that stops supply of a clock and power to the first Fourier transform unit when the mode signal represents a standby mode.   The receiving apparatus according to claim 3, wherein a part of the first Fourier transform unit is shared as the second Fourier transform unit. In a transmission device used in a multi-carrier communication system that performs communication by an orthogonal frequency division multiplexing (OFDM) method using a plurality of orthogonal subcarriers,
Detecting means for detecting a receiving device that has transitioned to a standby state;
The control signal necessary for the standby operation of the receiver is k * (N / n) th subcarrier (where k = 0, 1,..., N−1, where N represents the total number of subcarriers. N is a power of 2 that represents the number of subcarriers to which a control signal necessary for operation in standby is assigned and is smaller than N), and is assigned to at least one subcarrier. Means for assigning a null signal to the carrier;
A transmission apparatus comprising: transmission means for transmitting a subcarrier to which the control signal and a null signal are assigned to the reception apparatus as an OFDM signal.   The transmission apparatus according to claim 6, wherein the control signal is allocated to any one of 0 to (N−1) -th subcarriers for a reception apparatus in a data communication state.

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