JP4468160B2 - Subcarrier adaptive control method and apparatus, and radio apparatus - Google Patents

Description

  The present invention relates to a multicarrier wireless communication system that transmits information in parallel using a plurality of subcarriers, and in particular, subcarrier adaptation that adaptively controls a modulation scheme or a coding rate and transmission power for each subcarrier. The present invention relates to a control method, an apparatus thereof, and a radio apparatus.

  When performing high-speed transmission in mobile communication, the influence of delayed waves due to multipath cannot be ignored, and transmission characteristics deteriorate due to frequency selective fading. As one of the frequency selective fading countermeasure techniques, a multicarrier transmission system that performs parallel transmission of information using a plurality of low-speed subcarriers orthogonal to each other is known. In the multicarrier transmission method, the occupied bandwidth of each subcarrier is sufficiently narrow so that it is not easily affected by frequency selective fading, and the spectrum is densely arranged because each subcarrier is orthogonal on the frequency axis. And high frequency utilization efficiency can be obtained.

  Also, an adaptive modulation and coding (AMC) technique that adaptively selects a modulation scheme or coding rate in accordance with a propagation path condition has been studied. In AMC, QPSK (Quadrature Phase Shift Keying, Quadri-Phase Shift Keying) or the like, which is a low-speed modulation method, is applied when the propagation path condition is poor, while high speed is applied when the propagation path condition is good. 64QAM (Quadrature Amplitude Modulation) or the like is applied. As for the coding rate, a low coding rate is applied when the propagation path condition is bad, and a high coding rate is applied when the propagation path condition is good. As a result, by selecting an optimal combination of modulation scheme and coding rate according to the propagation path condition, it is possible to improve transmission throughput as a result.

  When the AMC described above is applied to a multi-carrier transmission scheme, it is common to employ the same modulation scheme and coding rate for all subcarriers. At this time, the modulation scheme and coding rate are the average received signal level or average SINR (Signal to Interference and Noise power Ratio; received signal power vs. interference power + noise power) affected by the subcarrier whose propagation path condition is worst. Therefore, when the channel conditions of some subcarriers are extremely bad due to frequency selective fading, the transmission capacity that can be sent by other subcarriers with good channel conditions is It is not used to the fullest. For this reason, a subcarrier adaptive modulation technique that applies AMC in units of subcarriers has been studied. In subcarrier adaptive modulation technology, AMC is applied independently for each subcarrier according to the propagation path condition, thereby greatly improving transmission throughput compared to the case where AMC is applied to all subcarriers collectively. can do.

  Furthermore, in addition to the subcarrier adaptive modulation technology, transmission power control (TPC) is performed in units of subcarriers to reduce the interference power to other cells, resulting in transmission throughput as a whole system. A technique for improving the above is known (see, for example, Patent Document 1). In the technique disclosed in Patent Document 1, only subcarriers that can obtain a transmission rate of a certain value or more are used for communication, and transmission is not performed on unused subcarriers. In addition, a technique is known in which surplus power generated by the generation of a frequency band (carrier hole) of the unused subcarrier is allocated to another subcarrier (see, for example, Patent Document 2).

FIGS. 6, 7, and 8 are conceptual diagrams for explaining the conventional subcarrier adaptive modulation and transmission power control procedures described above.
A SINR threshold value (SINR threshold value) necessary to achieve a required transmission quality is set in advance for a combination of selectable modulation schemes and coding rates. In the example shown in FIGS. 6, 7, and 8, the SINR threshold is set for each of the four combinations of “64QAM + 1/2 coding”, “16QAM + 1/2 coding”, “QPSK + 1/2 coding”, and “BPSK + 1/2 coding”. Value is set.

  First, as shown in FIG. 6, on the transmission side, the SINR of each subcarrier is estimated on the assumption that equal transmission power is allocated to all subcarriers. Next, the SINR estimated for each subcarrier (estimated SINR) is compared with the required SINR threshold value of each modulation method, and the modulation method having the maximum multi-level number that the estimated SINR does not fall below the SINR threshold value is selected. As a result, the subcarriers # 12, # 13, and # 50 are unused subcarriers because the estimated SINR has not reached any SINR threshold value. This generates a carrier hole.

Next, as shown in FIG. 7, transmission power is not allocated in the carrier hole because transmission is not performed. For subcarriers other than carrier holes, the transmission power is limited to the minimum necessary transmission power according to the required SINR threshold value of the selected modulation scheme.
Next, as shown in FIG. 8, the surplus power generated by the carrier hole is allocated to the other subcarriers # 24, # 26, # 46, and # 58.
JP 2003-304214 A JP 2003-32218 A

However, the above-described conventional technology has the following problems.
According to the prior art, first, the subcarrier used by AMC and its modulation scheme and coding rate are selected based on the estimated SINR of each subcarrier, and then TPC is applied to the selection result. However, the range in which TPC can be applied is limited by the application result of AMC, and there is a problem that optimization is not necessarily performed in terms of both transmission throughput and transmission power.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a subcarrier adaptive control method, an apparatus thereof, and a radio apparatus that can optimize both transmission throughput and transmission power. It is to provide.

  In order to solve the above problems, the subcarrier adaptive control method according to the present invention adaptively selects one to be used for each subcarrier from among a plurality of modulation schemes or coding rates, and for each subcarrier. A subcarrier adaptive control method that adaptively changes transmission power, and based on a propagation path estimation result of each subcarrier, required transmission power per unit bit of each combination of subcarrier and modulation scheme or coding rate And a process of selecting a combination of a subcarrier and a modulation scheme or a coding rate in ascending order of required transmission power per unit bit.

  In the subcarrier adaptive control method according to the present invention, a process of calculating a required total transmission power related to a combination of the selected subcarrier and a modulation scheme or a coding rate, and the calculated required total transmission power is a predetermined limit. The method further includes a step of canceling a new selection of the combination of the subcarrier and the modulation scheme or the coding rate when the range is exceeded.

  In the subcarrier adaptive control method according to the present invention, the process of calculating the total number of transmittable bits related to the combination of the selected subcarrier and the modulation scheme or coding rate, and the calculated total number of transmittable bits are predetermined. The method further includes a step of canceling a new selection of the combination of the subcarrier and the modulation scheme or the coding rate when the number is reached.

  In the subcarrier adaptive control method according to the present invention, the process of calculating the selected number of subcarriers, and when the calculated number of subcarriers reaches a predetermined number, the subcarrier and the modulation scheme or coding rate are calculated. And a process of canceling a new selection of the combination.

  The subcarrier adaptive control method according to the present invention is characterized in that no transmission power exceeding a predetermined value is assigned to each subcarrier.

  The subcarrier adaptive control apparatus according to the present invention adaptively selects one to be used for each subcarrier from a plurality of modulation schemes or coding rates, and adaptively changes transmission power for each subcarrier. A carrier adaptive control apparatus, comprising: means for obtaining a required transmission power per unit bit of each combination of a subcarrier and a modulation scheme or a coding rate based on a propagation path estimation result of each subcarrier; And a means for selecting a combination of subcarriers and modulation schemes or coding rates in ascending order of required transmission power.

  The subcarrier adaptive control apparatus according to the present invention includes means for calculating a required total transmission power related to a combination of the selected subcarrier and a modulation scheme or a coding rate, and the calculated required total transmission power is a predetermined value. When the limit range is exceeded, new selection of a combination of the subcarrier and the modulation scheme or coding rate is stopped.

  The subcarrier adaptive control apparatus according to the present invention comprises means for calculating the total number of transmittable bits related to the combination of the selected subcarrier and the modulation scheme or coding rate, and the calculated total number of transmittable bits is When the predetermined number is reached, a new selection of a combination of the subcarrier and the modulation scheme or coding rate is stopped.

  The subcarrier adaptive control apparatus according to the present invention further comprises means for calculating the selected number of subcarriers, and when the calculated number of subcarriers reaches a predetermined number, the subcarrier and modulation scheme or coding rate. The new selection of the combination with is canceled.

  The subcarrier adaptive control apparatus according to the present invention is characterized in that no transmission power exceeding a predetermined value is assigned to each subcarrier.

  A radio apparatus according to the present invention, in a radio apparatus of a multicarrier radio communication system that transmits information in parallel using a plurality of subcarriers, the subcarrier adaptive control apparatus according to any one of claims 6 to 10, According to the modulation scheme and coding rate of each subcarrier determined by the subcarrier adaptive control apparatus, the adaptive modulator that encodes and modulates transmission data, and the transmission data after encoding and modulation of each subcarrier, A transmission power controller for allocating transmission power of each subcarrier determined by the subcarrier adaptive control apparatus.

  According to the present invention, the combination of the subcarrier and the modulation scheme or coding rate is selected in order from the combination with the smallest required transmission power per unit bit, so that the efficiency can be improved while maximizing the total number of transmittable bits. Thus, transmission power can be allocated. This makes it possible to optimize both transmission throughput and transmission power.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing a procedure of a subcarrier adaptive control method according to an embodiment of the present invention. FIG. 2 is a diagram showing a combination table of subcarriers and MC levels according to the embodiment.

First, processing in the preparation stage will be described.
First, MC (Modulation and Coding) levels (M), which are combinations of applicable modulation schemes and coding rates, are defined. In the present embodiment, SINR is used as an index representing the propagation path condition of the subcarrier, and the required SINR threshold value of each MC level is set in proportion to the minimum inter-code distance of each modulation scheme. Also, the number of transmittable bits for each MC level is tabulated.

Next, a combination C _ij with the MC level (hereinafter simply referred to as a combination C _ij ) is defined for each subcarrier. Here, i is a subcarrier number (= 1 to N), and j is an MC level number (= 1 to M). As a result, a subcarrier / MC level combination table (hereinafter simply referred to as a combination table) shown in FIG. 2 is created.

Further, a limit value of the total transmission power is set. This limit value may be the maximum transmission power value of the transmitter, or may be any value less than or equal to the maximum transmission power value.
The above processing is performed in the preparation stage.

Next, the subcarrier adaptive control procedure will be described with reference to FIG.
When this control is activated, the processing of FIG. 1 is started.
In FIG. 1, first, the propagation path condition of each subcarrier is estimated. Specifically, the power fluctuation amount, interference power, and noise power due to distance attenuation and multipath fading of each subcarrier are calculated (step S1). Next, a required transmission power value for achieving each required SINR and a required transmission power value per unit bit are calculated for each combination C _ij in the set table according to the estimated propagation path state (step S2). .

Next, the required transmission power values per unit bit for each combination C _ij are respectively compared, and one combination C _ij that is the minimum value is selected (step S3). Here, when there is a combination C _ij having the same value, only one is selected by a predetermined method. For example, the smaller MC level number is selected. Alternatively, the smaller subcarrier number is selected. In step S3, the selection is not yet confirmed.

Next, the required total transmission power is calculated for one combination C _ij whose selection has not been confirmed and a combination C _ij whose selection has already been confirmed in step S6 described later (step S4). In this total transmission power calculation process, the required total transmission power is calculated by summing the required transmission power of each combination C _ij to be calculated.

Next, the required total transmission power is compared with the limit value of the total transmission power, and if the required total transmission power is within the limit, the combination C _ij selected in step S3 is added to the selection confirmation list (step S6). . The combination C _ij described in the selection confirmation list is a target for calculating the total required transmission power in step S4. Also, the combination C _{ij ′} of the subcarrier #i and the MC level j ′ (j ′ <j) is added to the exclusion list (if the combination C _{ij ′} already exists in the selection confirmation list, the combination C _{ij ′} Is removed from the selection confirmation list and added to the exclusion list).

On the other hand, if the required total transmission power is not within the limit, the combination C _ij selected in step S3 is added to the exclusion list (step S7).

Next, it is determined whether or not a combination C _ij that is not described in either the selection confirmation list or the exclusion list remains in the combination C _ij in the set table, and if it remains, the process returns to step S3. On the other hand, if it does not remain, the processing in FIG. 1 is terminated. In the step S3, from among the combinations C _ij in the set table, and selection of a combination C _ij that are not listed in any of the selection decision list and the exclusion list.

As a result, the combination C _ij described in the selection confirmation list represents a subcarrier to be transmitted, a modulation scheme and a coding rate applied to the subcarrier.

If no combination C _ij is described in the selection confirmation list, it means that no subcarrier to be transmitted has been found.

According to the above-described embodiment, since the required transmission power value per unit bit is selected in order from the combination C _ij , transmission power can be efficiently allocated while maximizing the total number of transmittable bits. . This makes it possible to optimize both transmission throughput and transmission power.

FIG. 3 is a conceptual diagram for explaining the effect of this embodiment.
The example of FIG. 3 corresponds to FIG. 6, FIG. 7, and FIG. In FIG. 3, in the conventional technique, subcarrier # 14 that performs transmission by “BPSK + 1/2 coding” (see FIG. 8) is unused (carrier hole) according to the present embodiment. Further, according to the present invention, subcarrier # 23 that performs transmission by “16QAM + 1/2 coding” (see FIG. 8) performs transmission by “64QAM + 1/2 coding” according to the present invention. This is because “64QAM + 1/2 coding” by SINR of subcarrier # 23 is prioritized because the required transmission power value per unit bit is smaller than “16QAM + 1/2 coding” by SINR of subcarrier # 14. It is.

  As described above, according to the present embodiment, the applicable range of TPC is not limited by the application result of AMC, so that the transmission throughput can be maximized and the transmission power can be optimally allocated at the same time.

FIG. 4 is a block configuration diagram illustrating an example of the transmission unit of the wireless device according to the present embodiment. FIG. 5 is a block configuration diagram illustrating an example of the receiving unit of the wireless device according to the present embodiment.
In the wireless transmission unit illustrated in FIG. 4, the propagation path estimation circuit 101 estimates the propagation path state for each subcarrier based on the received reception information. Specifically, the SINR of each subcarrier is calculated. Here, in the case of the time division duplex (TDD) method, the reception information is information of a received signal received by the receiving unit of the own radio apparatus, and is a frequency division duplex (FDD) method. In this case, the received signal information is received by the wireless device of the communication partner.

  The adaptive modulation / transmission power control unit 102 (subcarrier adaptive control apparatus) uses the propagation path information of each subcarrier calculated by the propagation path estimation circuit 101 to perform the subcarrier adaptive control method of the present embodiment described above. The transmission power allocated to each subcarrier and the modulation scheme and coding rate to be applied are determined simultaneously.

  The serial / parallel converter 103 parallelizes the input transmission data and outputs it to the adaptive modulator 104 provided corresponding to each subcarrier.

  The adaptive modulator 104 includes an encoder and a modulator. Adaptive modulator 104 encodes transmission data input from serial / parallel converter 103 according to the modulation scheme and coding rate of the subcarrier determined by adaptive modulation / transmission power control section 102, and further performs primary modulation.

  The transmission power controller 105 transmits the transmission power of each subcarrier determined by the adaptive modulation / transmission power control unit 102 for the transmission data after encoding and primary modulation of each subcarrier input from each adaptive modulator 104. Assign.

  The transmission data after the transmission power is assigned is subjected to IFFT by an inverse fast Fourier transform (IFFT) unit 106, and then a guard interval is added by a guard interval adding unit 107 and transmitted from an antenna 108.

  In the radio reception unit shown in FIG. 5, the received data received by the antenna 201 is subjected to FFT by a fast Fourier transform (FFT) unit 203 after the guard interval is removed by the guard interval removal unit 202, and each sub data is received. The signal is input to an adaptive demodulator 204 provided corresponding to the carrier.

Adaptive modulation determination section 205 determines the modulation scheme and coding rate of each subcarrier based on the received data.
The adaptive demodulator 204 includes a demodulator and a decoder. The adaptive demodulator 204 demodulates and further decodes the received data input from the FFT 203 according to the modulation scheme and coding rate of the subcarrier determined by the adaptive modulation determination unit 205. The demodulated and decoded received data is converted into serial data by the parallel / serial converter 206 and output.

  In the above embodiment, an example in which an Orthogonal Frequency Division Multiplexing (OFDM) system is applied as a multicarrier transmission system has been described. However, the present invention is applicable to various multicarrier transmission systems. is there.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, in the above-described embodiment, the set with the MC level is configured in units of subcarriers, but the set with the MC level may be configured in units of a plurality of subcarriers.

  In addition to the SINR described above, the received signal power, interference power, noise power, interference power + noise power, received signal power-to-interference power ratio (SIR), received signal power are used as indices representing the subcarrier propagation path conditions. A noise-to-noise ratio (SNR) or the like can be used.

  The required threshold value for each MC level is not only proportional to the minimum signal distance of the modulation method described above, but also proportional to the number of transmittable bits, and a measured value in an AWGN (Additive White Gaussian Noise) environment. Standards can be used.

In addition, it is possible to appropriately set constraint conditions for the above-described embodiments as necessary.
For example, in order to avoid the transmission power from concentrating on a specific subcarrier, the transmission power exceeding a predetermined value is not assigned to each subcarrier.

In addition, it is possible to appropriately set conditions for the control end conditions as necessary.
For example,
(1) When the total number of transmittable bits reaches a preset fixed number, selection of a new combination C _ij is stopped.
(2) When the number of subcarriers to be transmitted reaches a predetermined fixed number, selection of a new combination C _ij is stopped.
It is possible to provide any one or a plurality of limit end conditions among the limit end condition related to the total transmission power in the above-described embodiment, the limit end condition of (1), or the limit end condition of (2).

  The present invention can be applied to any kind of digital cellular system, digital mobile communication system, high-speed wireless access, subscriber wireless access, fixed microwave transmission, wireless LAN, personal area network, digital satellite communication, mobile satellite system, sensor network, etc. Applicable to digital radio systems.

It is a flowchart figure which shows the procedure of the subcarrier adaptive control method which concerns on one Embodiment of this invention. It is a figure which shows the combination table of the subcarrier and MC level which concern on the same embodiment. It is a conceptual diagram for demonstrating the effect by embodiment which concerns on this invention. It is a block block diagram which shows one Example of the transmission part of the radio | wireless apparatus which concerns on this invention. It is a block block diagram which shows one Example of the receiving part of the radio | wireless apparatus which concerns on this invention. It is a conceptual diagram for demonstrating the procedure of the conventional subcarrier adaptive modulation and transmission power control. It is a conceptual diagram for demonstrating the procedure of the conventional subcarrier adaptive modulation and transmission power control. It is a conceptual diagram for demonstrating the procedure of the conventional subcarrier adaptive modulation and transmission power control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Propagation path estimation circuit, 102 ... Adaptive modulation / transmission power controller, 103 ... Serial / parallel converter, 104 ... Adaptive modulator, 105 ... Transmission power controller, 106 ... Inverse fast Fourier transform (IFFT) converter, 107 DESCRIPTION OF SYMBOLS ... Guard interval addition part, 108, 201 ... Antenna, 202 ... Guard interval removal part, 203 ... Fast Fourier transform (FFT) device, 204 ... Adaptive demodulator, 205 ... Adaptive modulation determination part, 206 ... Parallel / serial converter.

Claims (11)

A subcarrier adaptive control method that adaptively selects one to be used for each subcarrier from a plurality of modulation schemes or coding rates, and adaptively changes transmission power for each subcarrier,
A process of obtaining a required transmission power per unit bit of each combination of a subcarrier and a modulation scheme or a coding rate based on a propagation path estimation result of each subcarrier;
A process of selecting a combination of subcarriers and modulation schemes or coding rates in ascending order of required transmission power per unit bit;
A subcarrier adaptive control method comprising: Calculating a required total transmission power related to a combination of the selected subcarrier and a modulation scheme or a coding rate;
A step of canceling a new selection of a combination of the subcarrier and a modulation scheme or a coding rate when the calculated required total transmission power exceeds a predetermined limit range;
The subcarrier adaptive control method according to claim 1, further comprising: Calculating a total number of transmittable bits according to a combination of the selected subcarrier and a modulation scheme or a coding rate;
When the calculated total number of transmittable bits reaches a predetermined number, a process of canceling a new selection of a combination of the subcarrier and a modulation scheme or a coding rate;
The subcarrier adaptive control method according to claim 1, further comprising: Calculating the selected number of subcarriers;
When the calculated number of subcarriers reaches a predetermined number, a process of canceling a new selection of a combination of the subcarrier and a modulation scheme or a coding rate;
The subcarrier adaptive control method according to claim 1, further comprising:   The subcarrier adaptive control method according to any one of claims 1 to 4, wherein no transmission power exceeding a predetermined value is assigned to each subcarrier. A subcarrier adaptive control apparatus that adaptively selects one to be used for each subcarrier from a plurality of modulation schemes or coding rates, and adaptively changes transmission power for each subcarrier,
Means for obtaining a required transmission power per unit bit of each combination of a subcarrier and a modulation scheme or a coding rate based on a propagation path estimation result of each subcarrier;
Means for selecting a combination of subcarriers and modulation schemes or coding rates in ascending order of required transmission power per unit bit;
A subcarrier adaptive control apparatus comprising: Means for calculating a required total transmission power related to a combination of the selected subcarrier and a modulation scheme or a coding rate;
The subcarrier according to claim 6, wherein when the calculated total required transmission power exceeds a predetermined limit range, a new selection of a combination of the subcarrier and a modulation scheme or a coding rate is stopped. Adaptive control device. Means for calculating the total number of transmittable bits related to the combination of the selected subcarrier and modulation scheme or coding rate;
The subcarrier according to claim 6, wherein when the calculated total number of transmittable bits reaches a predetermined number, a new selection of a combination of the subcarrier and a modulation scheme or a coding rate is stopped. Adaptive control device. Means for calculating the selected number of subcarriers;
The subcarrier adaptive control according to claim 6, wherein when the calculated number of subcarriers reaches a predetermined number, a new selection of a combination of the subcarrier and a modulation scheme or a coding rate is stopped. apparatus.   The subcarrier adaptive control apparatus according to any one of claims 6 to 9, wherein no transmission power exceeding a predetermined value is assigned to each subcarrier. In a wireless device of a multicarrier wireless communication system that transmits information in parallel using a plurality of subcarriers,
A subcarrier adaptive control apparatus according to any one of claims 6 to 10,
An adaptive modulator that encodes and modulates transmission data according to the modulation scheme and coding rate of each subcarrier determined by the subcarrier adaptive control apparatus;
A transmission power controller for allocating transmission power of each subcarrier determined by the subcarrier adaptive control apparatus to transmission data after encoding and modulation of each subcarrier;
A wireless device comprising:

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