JP3875079B2 - Orthogonal frequency division multiplexing system and transmitter / receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an orthogonal frequency division multiplexing system using a large number of orthogonal subcarriers.
[0002]
[Prior art]
In Europe and Canada, development of high-quality digital sound broadcasting (DSB) for mobiles is underway. This audio broadcasting system employs an Orthogonal Frequency Division Multiplexing (OFDM) system that has good transmission characteristics even in a multipath transmission path. In this OFDM communication system, an information data sequence is transmitted using a number of subcarriers orthogonal to each other. In this case, since the length of one symbol can be increased, ghost interference can be reduced. Furthermore, providing a guard interval makes it more resistant to frequency selective fading. In addition to time interleaving, frequency interleaving is also possible, and the error correction effect can be used effectively. Furthermore, the spectrum of each subcarrier can be densely arranged, and the frequency utilization efficiency can be increased. Furthermore, since information to each subcarrier can be arbitrarily assigned, it is possible to perform flexible information transmission such as not using subcarriers that are expected to interfere.
[0003]
[Problems to be solved by the invention]
By the way, when a high-speed transmission system is realized, there arises a problem that required reception power increases as the bandwidth becomes wider. Therefore, the transmission power can be reduced by applying the transmission power control conventionally used in the CDMA communication system to the OFDM communication system. By performing transmission power control, it is possible to set the transmission power based on many terminals located at the cell edge, so it is possible to reduce excessive transmission power conventionally consumed by many terminals around the base station become able to. Furthermore, when the OFDM signal undergoes fading in the OFDM communication system, the average received signal power fluctuates. However, transmission power control can compensate for fluctuations in the average received signal power due to fading. . As a result, transmission quality is improved, and good transmission quality can be achieved with low transmission power.
[0004]
However, when transmission power control is applied to the OFDM communication system, fluctuations in the average reception power level are compensated, but it is not possible to compensate for fluctuations in the reception power level for each subcarrier caused by the influence of frequency selective fading. . Here, the influence of frequency selective fading in the OFDM communication system will be described. FIG. 13 is an example of the transmitted OFDM signal in the OFDM communication system. This OFDM signal is composed of a number of subcarriers, and each subcarrier is transmitted with equal transmission power. When such an OFDM signal propagates through a multipath environment, the received power between subcarriers varies due to the influence of frequency selective fading. In this case, the fluctuation characteristics vary depending on the propagation path environment. For example, an OFDM signal subjected to frequency selective fading in the propagation path has a variation in received power between subcarriers as shown in FIG. As a result, a predetermined transmission quality cannot be satisfied in a subcarrier having a low reception power level.
[0005]
Therefore, in order to prevent the received power from fluctuating for each subcarrier, a method for controlling the transmission power for each subcarrier has been proposed (Research Reports SSE2000-71, RCS2000-60 (2000 -07) 2 other authors, Tomoaki Yoshinori, “Characteristics of multi-level transmission power control application in OFDM subcarrier adaptive modulation system”). This method aims to apply transmission power control to the OFDM communication system, and is composed of transmission power control for the entire received signal level and transmission power control for the level corresponding to the number of modulation levels of each subcarrier. Transmission power control is performed. In this multi-level transmission power control, the transmission power is controlled for each subcarrier so that the subcarriers to which each modulation multi-level number is assigned satisfy the required BER, and there is a possibility that higher transmission power may be consumed. Power efficiency is improved by not assigning transmission power to subcarriers with low power levels.
[0006]
However, in order to effectively perform transmission power control for each subcarrier according to the state of the propagation path, information on transmission power control for each subcarrier based on reception power measured on the reception side is notified to the transmission side. There is a need. For this reason, in order to perform transmission power control for each subcarrier, a large amount of control information is required on the transmission side or reception side, and the amount of processing and storage amount for transmission power control increases. Further, since the processing amount and storage amount of the transmission power control depend on the number of subcarriers, the processing amount and storage amount further increase as the number of subcarriers increases, and there is a problem that the realization becomes difficult. .
[0007]
Therefore, an object of the present invention is to provide an orthogonal frequency division multiplexing system and a transmission / reception apparatus that can reduce the amount of control information and the amount of transmission power control and the amount of storage.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an orthogonal frequency division multiplexing system according to the present invention receives an orthogonal frequency division multiplexing signal transmitted at a fixed transmission power from a transmission side at the reception side, and receives the received orthogonal frequency division multiplexing. Depending on the received power values of a plurality of subcarriers constituting the signal, the blocks are composed of several subcarriers, and the subcarrier number at a specific position in the block and the received power in each of the blocks The difference information between the value and the specified reception power is notified to the transmission side, and the transmission side that has received the subcarrier number and the difference information, a plurality of subcarriers constituting an orthogonal frequency division multiplexed signal, The block is divided into blocks based on the subcarrier number, and the subcarrier transmission of the block is transmitted based on the difference information. So as to control the power.
[0009]
In the orthogonal frequency division multiplexing system of the present invention, subcarriers in which the difference in received power between subcarriers falls within a predetermined threshold may be combined into the blocks.
Further, in the orthogonal frequency division multiplexing system of the present invention, when the plurality of subcarriers are divided into the blocks, a block having the minimum number of subcarriers included in the divided blocks is obtained, The block length may be the block length of the obtained block.
[0010]
Furthermore, in the orthogonal frequency division multiplexing system of the present invention described above, the number of subcarriers to be divided into blocks is obtained by referring to a table of cumulative values of probability distributions where the number of subcarriers with respect to the number of subcarriers exists. May be.
Furthermore, in the orthogonal frequency division multiplexing system of the present invention, for a block whose received power does not reach a predetermined minimum received power value on the receiving side, the transmitting power of the block is set based on the difference information on the transmitting side. You may make it distribute to another block.
[0011]
Next, the transmission / reception apparatus of the present invention capable of achieving the above object is a transmission / reception apparatus capable of transmitting / receiving an orthogonal frequency division multiplexed signal, and constitutes an orthogonal frequency division multiplexed signal transmitted with a fixed transmission power. According to the received power values of a plurality of subcarriers, dividing means for combining the blocks into a number of subcarriers, subcarrier numbers at specific positions in the blocks divided by the dividing means, Control means for obtaining difference information between the received power value and the prescribed received power in each of the divided blocks, and the control information comprising the subcarrier number and the difference information is obtained as a control basis of the control means. In this case, transmission is performed at predetermined intervals.
[0012]
Further, in the transmission / reception apparatus according to the present invention, subcarriers in which a difference in received power between subcarriers falls within a predetermined threshold may be grouped into the blocks.
Furthermore, in the transmission / reception apparatus of the present invention, when the plurality of subcarriers are divided into a plurality of blocks, a block having the minimum number of subcarriers included in the divided blocks is obtained, and the block lengths of all the blocks are determined. May be the block length of the obtained block.
[0013]
Furthermore, in the transmission / reception apparatus of the present invention, the number of subcarriers to be divided into blocks may be obtained by referring to a table of cumulative values of probability distributions in which the number of subcarriers is present relative to the number of subcarriers. .
Furthermore, in the transmission / reception apparatus according to the present invention, for a block whose reception power does not reach a predetermined minimum reception power value, the control means creates control information for distributing the transmission power of the block to other blocks. You may make it do.
[0014]
According to the present invention as described above, subcarriers are grouped into blocks according to received power, and transmission power control is performed for each block. As described above, since transmission power control is performed for each block in which several subcarriers are combined, the amount of control information can be reduced, and the processing amount and storage amount of transmission power control can be reduced. become able to. Such transmission power control processing is performed every time a pilot signal is transmitted from the transmission side with a fixed transmission power.
In addition, as described above, the reason why blocking is performed is that adjacent subcarriers have high frequency correlation, and fluctuations in received power due to the effect of frequency selective fading on subcarriers within a certain correlation bandwidth may be regarded as almost equal. Because it can. Therefore, the block configuration becomes adaptive to a specific change in the propagation path, and efficient transmission power control can be performed. Therefore, the orthogonal frequency division multiplexing system of the present invention can enable high speed transmission and high quality transmission.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A configuration example of an orthogonal frequency division multiplexing system according to an exemplary embodiment of the present invention is shown in FIG. However, although FIG. 1 shows the base station 1 and one mobile station 2, there are many mobile stations, and only the mobile station 2 is shown. The mobile station 2 corresponds to the transmission / reception apparatus according to the embodiment of the present invention.
In FIG. 1, a base station 1 includes an OFDM modulator 10, an OFDM demodulator 17, and a control unit 16 that performs transmission power control. This OFDM demodulator 17 has a configuration in which the received power measurement unit 22 of the OFDM demodulator 20 in the mobile station 2 described later is omitted. The transmission data is applied to the encoder 11 in the OFDM modulator 10, subjected to encoding such as error correction encoding and compression encoding, and is symbol-modulated in the symbol modulator 12. In the symbol modulator 12, BPSK, QPSK, or 16QAM, depending on the transmission speed and the required transmission quality, 64QAM Etc. are modulated. A modulation symbol output from the symbol modulator 12 is converted into a modulation symbol having a parallel number corresponding to the number of subcarriers in a serial-parallel conversion unit (S / P conversion unit) 13. As a result, the symbol rate of the modulation symbol output from the S / P converter 13 is reduced to 1 / number of subcarriers.
[0016]
The transmission power control of the parallel modulation symbol, which is the number of subcarriers output from the S / P conversion unit 13, is performed for each block described later by the transmission power control unit 14 using a transmission power control signal from the control unit 16. Become. This block is composed of several subcarriers. The parallel modulation symbols having the number of subcarriers subjected to transmission power control in the transmission power control unit 14 are subjected to inverse Fourier transform in an inverse fast Fourier transform unit (IFFT) 15 to be an OFDM signal. The IFFT 15 may be an inverse discrete Fourier transform unit (IDFT). This OFDM signal is transmitted from the base station 1 on a carrier wave having a predetermined frequency.
[0017]
The mobile station 2 that can receive the OFDM signal includes an OFDM demodulator 20, an OFDM modulator 27, and a control unit 26. The OFDM modulator 27 is configured such that the transmission power control unit 14 of the OFDM modulator 10 in the base station 1 is omitted. The OFDM signal received by the mobile station 2 is subjected to Fourier transform in a fast Fourier transform unit (FFT) 21 and decomposed for each subcarrier. The FFT 21 may be a discrete Fourier transform unit (DFT). The received power of each subcarrier output in parallel from the FFT unit 21 is measured by the received power measuring unit 22, and the received power value of each subcarrier is supplied to the control unit 26. The subcarriers output in parallel from the FFT unit 21 are supplied to the parallel-serial conversion unit (P / S conversion unit) 23 via the reception power measurement unit 22, and the modulation symbols of the subcarriers that are paralleled are serial. Are converted into modulation symbols. The modulation symbol of the subcarrier output from the P / S conversion unit 23 is demodulated by the symbol demodulation unit 25 into demodulated data. In the symbol demodulator 25, BPSK, QPSK or 16QAM applied on the transmission side 64QAM Demodulation is performed in accordance with such modulation. The demodulated data output from the symbol demodulator 25 is subjected to error correction, decompression processing, and the like in the decoder 24, decoded into received data, and output.
[0018]
The control unit 26 divides the data into blocks composed of several subcarriers according to the reception power value of each subcarrier supplied from the reception power measurement unit 22. Then, control information including the subcarrier number of the first subcarrier of the divided block and transmission power control information for controlling the transmission power so that the reception power of the block becomes the prescribed reception power is sent to the OFDM modulator 27. Supply. In this case, the last subcarrier number may be used instead of the first subcarrier number. In the OFDM modulator 27, control information is periodically transmitted from the mobile station 2 to the base station 1.
In order to measure the reception power of the subcarrier in the mobile station 2, the base station 1 periodically transmits an OFDM-modulated pilot signal for which transmission power control is not performed. The mobile station 2 obtains control information by measuring the reception power of the pilot signal. In this way, the channel for transmission power control in the base station 1 is a communication channel set for each mobile station. Since this transmission power control is performed according to the control information transmitted from the mobile station, different transmission power control is performed for each mobile station.
[0019]
Next, specific processing of transmission power control in the orthogonal frequency division multiplexing system shown in FIG. 1 will be described in detail with reference to FIGS.
FIG. 2 shows an OFDM signal that is a pilot signal in a control channel in which the transmission power transmitted from the base station 1 is a fixed value. It is assumed that the subcarriers of this OFDM signal are composed of subcarriers of subcarrier SC1 to subcarrier SC23, for example. SC1 to SC23 are subcarrier numbers, respectively. When an OFDM signal composed of subcarriers of subcarrier SC1 to subcarrier SC23 is affected by frequency selective fading in a propagation path in a multipath environment, for example, the envelope of the subcarrier varies as shown in FIG. It becomes like this. That is, the level of each subcarrier in the OFDM signal received by the mobile station 2 varies.
[0020]
Then, the received power values of the subcarriers SC1 to SC23 measured by the received power measuring unit 22 in the mobile station 2 are indicated by the length of the spectrum with an arrow attached to the end shown in FIG. This received power value is represented as {E1, E2,..., En}. However, E1 is the received power value of the subcarrier SC1, E2 is the received power value of the subcarrier SC2, and En is the received power value of the last subcarrier (in the figure, subcarrier SC23, that is, n = 23). . In this case, adjacent subcarriers have high frequency correlation, and variations in received power due to the influence of frequency selective fading on subcarriers within a certain correlation bandwidth can be regarded as substantially equal. Therefore, using this, next, subcarrier SC1 to subcarrier SC23 are divided into blocks made up of several subcarriers in control unit 26. When the control unit 26 divides the data into blocks, continuous subcarriers that fall within ± ΔE of the reception power value of the first subcarrier are defined as one block. That is, | Eh−Ei | <ΔE is calculated, and consecutive subcarriers corresponding to the received power value Ei satisfying the given expression are set as subcarriers of the block. However, Eh is a received power value corresponding to the head subcarrier of the block. In addition, subcarriers of received power that are less than the threshold value Emin of the minimum received power are grouped into one block.
[0021]
In this case, decreasing the threshold value ΔE increases the number of blocks, and increasing the threshold value ΔE decreases the number of blocks. In this way, it can be divided into arbitrary numbers of blocks. However, the threshold ΔE that provides the number of blocks that can be considered to have almost the same variation in received power due to the influence of frequency selective fading. The value is determined in advance. In this case, the range in which the BER (Bit Error Rate) is substantially equivalent can be regarded as the reception power fluctuation due to the influence of frequency selective fading being substantially equivalent. When the subcarrier of the OFDM signal affected by the frequency selective fading shown in FIG. 3 is divided into blocks using the threshold value ΔE determined in this way, the result is as shown in FIG. That is, the first block B1 includes subcarriers SC1 to SC5, the second block B2 includes subcarriers SC6 to SC8, the third block B3 includes subcarriers SC9 to SC11, and the fourth block B4 includes subcarriers. The fifth block B5 is composed of subcarriers SC15 and SC16, the sixth block B6 is composed of subcarriers SC17 and SC18, and the seventh lock B7 is composed of subcarriers SC19 and SC20. The eighth block B8 is composed of subcarriers SC21 to SC23. In this way, the block length is divided according to the intensity of fluctuation.
[0022]
Thus, by making the control unit 26 block, each block can be configured by subcarriers that fall within the threshold value ΔE. Instead of this blocking, the control unit 26 may block as shown in FIG. In the blocking shown in FIG. 5, the number of subcarriers included in one block is divided into blocks with a fixed value. In this case, the number of subcarriers included in one block is the number of subcarriers of the block having the smallest number of subcarriers when the block is formed on the condition that it falls within the threshold ΔE as shown in FIG. In the case shown in FIG. 4, the fifth block B5 to the seventh block B7 are made up of two subcarriers, so that each block B5 to B11 is made up of two subcarriers as shown in FIG. .
[0023]
Next, after dividing into blocks as shown in FIG. 4, the control unit 26 creates transmission power control information for controlling transmission power so that each block can receive with substantially the same reception power. This transmission power control information defines a prescribed value Eth of received power as shown in FIG. 6, and obtains the difference between this prescribed value Eth and the minimum value of the received power value of the subcarrier in each block as the transmission power control information. . For example, in the example shown in FIG. 6, the transmission power control information of the first block B1 is the difference EB1 between the reception power of the minimum subcarrier SC5 in the first block B1 and the specified value Eth. When transmission power control is performed in the base station 1 by this transmission power control information EB1, the transmission power of the first block B1 is reduced by an amount corresponding to the transmission power control information EB1. This is because the received power of the subcarrier SC5 exceeds the specified value Eth. Also, the transmission power control information of the second block B2 is the difference EB2 between the reception power of the minimum subcarrier SC8 in the second block B2 and the specified value Eth. When transmission power control is performed in the base station 1 by this transmission power control information EB2, the transmission power of the second block B2 is increased by an amount corresponding to the transmission power control information EB2. This is because the received power of the subcarrier SC8 is less than the specified value Eth.
[0024]
Similarly, the transmission power control information of the third block B3 is EB3, and when the transmission power control is performed in the base station 1 by this transmission power control information EB3, the transmission power of the third block B3 is the transmission power control information EB3. It is increased by the amount corresponding to. Further, the transmission power control information of the fourth block B4 is EB4. When transmission power control is performed in the base station 1 by this transmission power control information EB4, the transmission power of the fourth block B4 corresponds to the transmission power control information EB4. Increased by what you do. Further, since the fifth block B5 is a block of subcarriers SC15 and SC16 that does not satisfy the threshold value Emin of the minimum reception power, transmission power control information EB5 that does not transmit the subcarriers SC15 and SC16 of the fifth block B5 Is done. This is because the threshold Emin is a level in the vicinity of the background noise level on the receiving side in the mobile station 2, and thus the received power of the subcarriers SC15 and SC16 of the fifth block B5 cannot be accurately measured, This is because when the transmission power is controlled, the fifth block B5 consumes a high transmission power, and the transmission power of other blocks is relatively lowered.
[0025]
Furthermore, the transmission power control information of the sixth block B6 is EB6, and when transmission power control is performed at the base station 1 by this transmission power control information EB6, the transmission power of the sixth block B6 is transmitted to the transmission power control information EB6. Increased by the corresponding amount. Furthermore, the transmission power control information of the seventh block B7 is EB7. When the transmission power control is performed in the base station 1 by this transmission power control information EB7, the transmission power of the seventh block B7 is changed to the transmission power control information EB7. Increased by the corresponding amount. Furthermore, the transmission power control information of the eighth block B8 is EB8, and when the transmission power control is performed in the base station 1 by this transmission power control information EB8, the transmission power of the eighth block B8 is changed to the transmission power control information EB8. It is reduced by a corresponding amount.
[0026]
Control information including transmission power control information in each block and number information of the first subcarrier of each divided block is supplied from the control unit 26 to the OFDM modulator 27. In the OFDM modulator 27, as shown in FIG. 8, control information is periodically inserted into communication data and transmitted from the mobile station 2 to the base station 1. The period for sending the control information is a period in which the frequency selective fading characteristic in the propagation path does not change much.
[0027]
The base station 1 receives the control information transmitted from the mobile station 2, and the OFDM demodulator 17 demodulates the control information and supplies it to the control unit 16. The communication data is demodulated by the OFDM demodulator 17 and output as received data. The demodulated control information is supplied to the control unit 16 and stored in a built-in control information management table 16a. Since the control information is periodically sent, the control information on the control information management table 16a is updated every time it is received. For this reason, even if the influence of frequency selective fading in the propagation path changes, the control information following the change is stored in the control information management table 16a. The control information management table 16a stores control information of mobile stations located in the base station 1.
[0028]
In the control unit 16, when performing transmission power control of the communication channel, the control information of the mobile station corresponding to the set communication channel is read from the control information management table 16a. Next, the subcarrier is divided into blocks based on the first subcarrier number of the block in the control information. Further, based on the transmission power control information in each divided block in the control information, transmission power control of the block is performed. In this case, the total transmission power of each block is always equal. That is, when the transmission power control information is changed, the transmission power in each block is changed according to the control information, but the total transmission power of each block is the sum of the transmission power before the change. Is equal to
[0029]
Here, FIG. 7 shows an example of the transmission power of each block of the OFDM signal whose transmission power is controlled by the transmission power control unit 14 in the base station 1 based on the transmission power control information shown in FIG. As shown in FIG. 6, in the first block B1 and the eighth block B8, the reception power exceeds the specified value Eth, so the transmission power is reduced. In addition, as described above, the fifth block B5 is less than the threshold value Emin of the minimum reception power, so that high transmission power is consumed when transmission power control is performed, and transmission power of other blocks is reduced. Therefore, the transmission power of the fifth block B5 is set to zero. Thereby, the transmission power of the fifth block B5 is distributed to other blocks. In this case, a subcarrier that is not transmitted is a carrier hole, and no modulation symbol is transmitted on that subcarrier. The remaining blocks B2, B3, B4, B6, and B7 are controlled so that the transmission power increases according to the transmission power control information EB2, EB3, EB4, EB6, and EB7 shown in FIG.
[0030]
As described above, in the orthogonal frequency division multiplexing system of the present invention, continuous subcarriers in which the received power falls within a predetermined range are grouped into blocks, and transmission power control is performed for each block. As described above, since transmission power control is performed for each block in which several subcarriers are combined, the storage amount of the control information management table 16a for storing control information can be reduced, and transmission power control can be performed. The amount of processing can be reduced. In addition, since the fluctuation of the received power due to the influence of frequency selective fading is made into a block so that it can be regarded as almost equal, the block configuration is changed to adapt to the change of the propagation path, Efficient transmission power control can be performed. For this reason, the orthogonal frequency division multiplexing system of the present invention can enable high-speed transmission and high-quality transmission.
[0031]
By the way, the subcarriers may be grouped as a block as follows. Assume that the OFDM signal received by the mobile station 2 is received with an envelope as shown in FIG. The number n of subcarriers in this case is 60, for example. Then, when the received power subcarriers within the range of the threshold ΔE are grouped into blocks as shown in FIG. 4, the number of subcarriers in the first block B1 is 10, as shown in FIG. Assume that the number of subcarriers in B2 is 10, the number of subcarriers in the third block B3 is 5, the number of subcarriers in the fourth block B4 is 15, and the number of subcarriers in the fifth block B5 is 20. When the cumulative value of the probability distribution in which the number of carriers with respect to the number of carriers in this case is obtained, the chart shown in FIG. 10 is obtained.
[0032]
That is, the third block B3 is the only block in which the number of carriers is 5, and in this case (number of blocks / total number of blocks) is 1/5. Accordingly, the cumulative value of 5 or less carriers is also 1/5. Further, the blocks with the number of carriers of 10 are the first block B1 and the second block B2, and in this case (number of blocks / total number of blocks) is 2/5. Therefore, the cumulative value when the number of carriers is 10 or less is 1/5 + 2/5 = 3/5. Further, the block having the carrier number of 15 is only the fourth block B4. In this case, (number of blocks / total number of blocks) is 1/5. Therefore, the cumulative value of 15 or less carriers is 1/5 + 2/5 + 1/5 = 4/5. Furthermore, the block in which the number of carriers is 20 is only the fifth block B5, and (number of blocks / total number of blocks) in this case is 1/5. Therefore, the cumulative value when the number of carriers is 20 or less is 1/5 + 2/5 + 1/5 + 1/5 = 5/5. When the cumulative value is expressed as a percentage value and the number of carriers (number of SCs) is displayed as a graph on the horizontal axis, the graph shown in FIG. 11 is obtained. For example, when the number of carriers with a cumulative value of about 54% is obtained from this graph, the number of subcarriers is approximately 9. Therefore, 60 subcarriers are grouped into blocks every 9 subcarriers. As described above, the number of subcarriers obtained from the cumulative value of the probability distribution may be a block. In this case, the number of subcarriers in each block is a fixed value.
[0033]
Next, FIG. 12 shows a flowchart of transmission power control processing in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
When the transmission power control process shown in FIG. 12 is started and the base station transmits a pilot signal through the control channel (step S1), the mobile station receives the pilot signal (step S10). Next, the received power of all subcarriers of the OFDM signal in the pilot signal received in step S11 is measured. In step S12, by utilizing the fact that adjacent subcarriers have high frequency correlation, and fluctuations in received power due to the influence of frequency selective fading in subcarriers within a certain correlation bandwidth can be regarded as being substantially equal. Is blocked. That is, subcarriers are blocked by grouping consecutive subcarriers that do not exceed the set threshold value ΔE into blocks. Further, the number of blocks divided in step S13 is detected, and the head subcarrier number in each block is determined. Here, the block length may be fixed to the block length with the smallest number of subcarriers grouped into blocks, and the blocks may be re-blocked. Furthermore, referring to the graph of the number of subcarriers with respect to the cumulative value as shown in FIG. 11, the number of subcarriers having a desired cumulative value may be obtained and re-blocked into blocks of the obtained number of subcarriers.
[0034]
Next, in step S14, the difference between the reception power value of the subcarrier with the minimum reception power in each block and the specified reception power is calculated and set as the transmission power control value. Then, control information including the calculated transmission power control value and the head subcarrier number determined in step S13 is notified to the base station (step S15). Upon receiving this notification, the base station controls the transmission power of each block based on the control information notified in step S2. That is, subcarriers are grouped into several subcarriers up to immediately before the first subcarrier number in the control information, and the subcarrier transmission power in each of the blocked blocks is changed to the corresponding subcarriers in the control information. Control is performed according to the transmission power control information of the block. Thereby, even when subjected to frequency selective fading, it is possible to control so that the reception power of the subcarriers of the OFDM signal received at the mobile station becomes substantially constant.
[0035]
In the mobile station 2 of the present invention described above, a transmission power control unit is provided in the OFDM modulator 27 as in the base station 1, and the transmission power of the OFDM signal is based on the control information obtained by the control unit 26. Control may be performed. In this case, the subcarriers are blocked based on the head subcarrier number in the control information, and the transmission power of the subcarriers in the block is controlled according to the transmission power control value corresponding to the block.
Note that the period of transmission of an OFDM-modulated pilot signal transmitted from the base station 1 and not subjected to transmission power control is a period that can sufficiently follow fluctuations in received power caused by frequency selective fading or the like in the propagation path. Has been.
[0036]
【The invention's effect】
As described above, according to the present invention, subcarriers are grouped into blocks according to received power, and transmission power control is performed for each block. As described above, since transmission power control is performed for each block in which several subcarriers are combined, the amount of control information can be reduced, and the processing amount and storage amount of transmission power control can be reduced. become able to. Such transmission power control processing is performed every time a pilot signal is transmitted from the transmission side with a fixed transmission power.
In addition, as described above, the reason why blocking is performed is that adjacent subcarriers have high frequency correlation, and fluctuations in received power due to the effect of frequency selective fading on subcarriers within a certain correlation bandwidth may be regarded as almost equal. Because it can. Therefore, the block configuration becomes adaptive to a specific change in the propagation path, and efficient transmission power control can be performed. Therefore, the orthogonal frequency division multiplexing system of the present invention can enable high speed transmission and high quality transmission.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of an orthogonal frequency division multiplexing system according to an embodiment of the present invention.
FIG. 2 is a diagram showing a pilot signal in a control channel transmitted from a base station in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 3 is a diagram showing an OFDM signal affected by selective fading in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention;
FIG. 4 is a diagram for describing received OFDM signals in blocks in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 5 is a diagram for explaining another example of collecting received OFDM signals into blocks in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention;
FIG. 6 is a diagram for explaining transmission power control information of a block in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 7 is a diagram showing an OFDM signal transmitted under transmission power control in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 8 is a diagram showing a mode of sending control information in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 9 is a diagram showing the number of subcarriers obtained by blocking an OFDM signal affected by selective fading in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
10 is a chart showing a cumulative value of a probability distribution in which the number of carriers with respect to the number of carriers in the example shown in FIG. 9 exists.
11 is a graph showing a cumulative value of a probability distribution in which the number of carriers with respect to the number of carriers shown in FIG. 10 exists.
FIG. 12 is a flowchart of transmission power control processing in the orthogonal frequency division multiplexing system according to the exemplary embodiment of the present invention.
FIG. 13 is a diagram illustrating an OFDM signal transmitted from a base station in a conventional orthogonal frequency division multiplexing system.
FIG. 14 shows an OFDM signal affected by selective fading in an orthogonal frequency division multiplexing system.
[Explanation of symbols]
1 base station, 2 mobile station, 10 OFDM modulator, 11 encoder, 12 symbol modulator, 13 S / P conversion unit, 14 transmission power control unit, 15 IFFT unit, 16 control unit, 16a control information management table, 17 OFDM demodulator, 20 OFDM demodulator, 21 FFT unit, 22 received power measurement unit, 23 P / S conversion unit, 24 decoder, 25 symbol demodulation unit, 26 control unit, 27 OFDM modulator

Claims (10)

An orthogonal frequency division multiplex signal transmitted at a fixed transmission power from the transmission side is received at the reception side,
In accordance with the received power values of a plurality of subcarriers constituting the received orthogonal frequency division multiplex signal, the blocks are composed of several subcarriers,
Notifying the transmitting side of the subcarrier number at a specific position in the block and the difference information between the received power value and the specified received power in each of the blocks,
The transmitting side that has received the subcarrier number and the difference information divides a plurality of subcarriers constituting an orthogonal frequency division multiplexed signal into blocks based on the subcarrier number, and An orthogonal frequency division multiplex system characterized in that the transmission power of subcarriers of the block is controlled based on this. 2. The orthogonal frequency division multiplexing system according to claim 1, wherein subcarriers in which a difference in received power between subcarriers falls within a predetermined threshold are grouped into the blocks. When the plurality of subcarriers are divided into the blocks, a block having the minimum number of subcarriers included in the divided blocks is obtained, and the block lengths of all the blocks are set as the block lengths of the obtained blocks. The orthogonal frequency division multiplexing system according to claim 1, wherein the orthogonal frequency division multiplexing system is configured. 2. The orthogonal frequency division according to claim 1, wherein the number of subcarriers to be divided into blocks is obtained by referring to a table of cumulative values of probability distributions for the number of subcarriers with respect to the number of subcarriers. Multiple system. For blocks where the reception power at the reception side does not reach a predetermined minimum reception power value, the transmission power of the block is distributed to other blocks based on the difference information at the transmission side. The orthogonal frequency division multiplexing system according to claim 1. A transmission / reception apparatus capable of transmitting / receiving orthogonal frequency division multiplexed signals,
Dividing means for grouping the blocks into a plurality of subcarriers according to the received power values of a plurality of subcarriers constituting an orthogonal frequency division multiplexed signal transmitted with a fixed transmission power;
Control means for obtaining a subcarrier number at a specific position in each block divided by the dividing means and difference information between the received power value and the prescribed received power in each divided block;
A transmission / reception apparatus, wherein control information including the subcarrier number and the difference information is transmitted at predetermined intervals under the control of the control means. 7. The transmission / reception apparatus according to claim 6, wherein subcarriers in which a difference in received power between subcarriers falls within a predetermined threshold are grouped into the blocks. When the plurality of subcarriers are divided into a plurality of blocks, a block having the minimum number of subcarriers included in the divided blocks is obtained, and the block lengths of all the blocks are determined as the block lengths of the obtained blocks. The transmission / reception apparatus according to claim 6, wherein: 7. The transmission / reception apparatus according to claim 6, wherein the number of subcarriers to be divided into blocks is obtained by referring to a table of cumulative values of probability distributions in which the number of subcarriers with respect to the number of subcarriers exists. For a block whose received power does not reach a predetermined minimum received power value, the control means creates control information in which the transmission power of the block is distributed to other blocks. The transmitting / receiving apparatus according to claim 6.

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