JP6218305B2 - Wireless communication method and wireless communication device - Google Patents

Description

  The present invention relates to a wireless communication method and a wireless communication apparatus that perform multi-user transmission.

  As a standard of a high-speed wireless access system using the 5 GHz band, there is an IEEE 802.11a standard. This standard system uses an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, which is a technique for stabilizing characteristics in a multipath fading environment, and achieves a maximum throughput of 54 Mbps ( For example, refer nonpatent literature 1).

  IEEE802.11n is a MIMO (Multiple Input Multiple Output) communication technology that improves throughput by spatially multiplexing multiple data streams using multiple antennas using the same time and the same frequency channel. It is possible to realize a high-speed communication by using a technology using a frequency channel of 40 MHz by simultaneously using two frequency channels of 20 MHz used in the past (for example, non-patented). Reference 1).

  Furthermore, IEEE 802.11ac, whose standard is being developed, is faster than IEEE 802.11n by a multi-user MIMO communication technology that transmits a different data stream to each of a plurality of wireless stations at the same time and at the same time. It aims at realization of wireless communication (for example, see Non-Patent Document 2).

Here, multi-user MIMO communication will be specifically described with reference to the drawings. FIG. 8 is a diagram illustrating a conceptual diagram of multiuser-MIMO transmission. The wireless communication system shown in FIG. 8 includes a base station 100, and a terminal station 101-1 and a terminal station 101-2 that perform wireless packet communication with the base station 100. H ₁ and H ₂ indicate propagation channels. FIG. 9 is a time chart showing the operation of multi-user MIMO transmission. In FIG. 9, carrier sense (CS) is a frame for confirming whether other radio stations are communicating. A null data packet announcement (NDPA: Null Data Packet Announcement) is a frame that informs the transmission of a null data packet.

  A null data packet (NDP: Null Data Packet) is a frame composed of null data. A beamforming report (BR) is a frame for notifying propagation channel information estimated from NDP. A beamforming report poll (BRP) requests notification of propagation channel information. Data (Data1, Data2) is a frame composed of data to be transmitted to the terminal station 101-1 and the terminal station 101-2. A block ACK (BACK: Block Acknowledgment) is a frame for notifying whether a signal has been correctly received. A block ACK request (BACKR: Block Acknowledgment Request) is a frame for requesting a block ACK.

  Next, operations of the base station 100 and the terminal stations 101-1 and 101-2 shown in FIG. 8 will be described with reference to FIG. In the base station 100, when packet data (transmission target data) to be transmitted to the terminal stations 101-1 and 101-2 is generated, carrier sense (CS) is executed at random time intervals (step S1). Based on the carrier sense, it is determined whether the idle state in which the communication frequency band is not used or the busy state in which the communication frequency band is used. For example, it is assumed that an idle state in which a communication frequency band is not used is detected by carrier sense executed at time t1. In response to this, for example, the base station 100 generates and transmits NDPA in a period from time t3 to t4 when a certain time has elapsed from time t2 (step S2).

  Next, the base station 100 generates and transmits an NDP for estimating a propagation channel in a period from time t5 to t6 when a certain time has elapsed from time t4 (step S3). At this time, the base station 100 recognizes the destination terminal stations 101-1 and 10-2 of the transmission target data. Then, the same terminal stations 101-1 and 101-2 are designated as destinations, and a measurement signal is transmitted.

In response to reception of the measurement signal, the terminal station 101-1 and the terminal station 101-2 measure the propagation channel characteristics within the same period from time t5 to t6. Then, the terminal station 101-1 and the terminal station 101-2 generates a BR containing information calculated from the propagation channel characteristics or the propagation channel characteristics from the time t 6 in the period t 7.

  Next, the terminal station 101-1 transmits BR in a period from time t7 to t8 when a certain time has elapsed from time t6 (step S4). Subsequently, the base station 100 generates and transmits a BRP requesting propagation channel information to the terminal station 101-2 in a period from time t9 to t10 when a certain time has elapsed from time t8 (step S5). . Then, in response to the reception of the BRP, the terminal station 101-2 transmits BR in a period from time t11 to t12 when a certain time has elapsed from time t10 (step S6).

  Next, the base station 100 calculates a transmission weight and generates a transmission signal using the notified BR. Then, the base station 100 transmits the transmission target data during a period from time t13 to t14 when the specified time has elapsed from time t12 (step S7). Note that data transmitted in the period from time t13 to t14 is converted into a frame suitable for wireless communication, for example. When frame aggregation is applied, data transmitted in the period from time t13 to time t14 is a data unit in which a predetermined number of frames are connected.

  Next, in response to the end of data reception corresponding to time t14, the terminal station 101-1 transmits a BACK during a period from time t15 to t16 when a certain time has elapsed from time t14 (step S14). S8). The base station 100 receives the ACK and executes a predetermined process according to the reception of the ACK. Specifically, the base station 100 determines that data has been normally received on the receiving side, for example, by receiving BACK, and transitions to processing for next data transmission / reception. Further, when a timeout occurs without receiving the BACK, processing such as retransmission of the transmission target data is executed.

Next, the base station 100 generates and transmits a BACKR requesting a BACK to the terminal station 101-2 in a period from time t17 to t18 when a certain time has elapsed from time t16 (step S9). Subsequently, the terminal station 101-2 transmits a BACK during a period from time t19 to t20 when a certain time has elapsed from time t18 (step S10). The base station 100 receives the ACK and executes a predetermined process according to the reception of the ACK. Multi-user MIMO communication is performed by such an operation.

Masahiro Morikura, Shuji Kubota, “Revised Third Edition 802.11 High-Speed Wireless LAN Textbook”, Impress R & D, March 27, 2008 IEEE P802.11ac / D1.0 Draft STANDARD for Information Technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications Amendment 5: Enhancements for Very High Throughput for Operation in Bands below 6 GHz

  However, problems remain in packet-based communication used in wireless LAN systems in multi-user MIMO communication. In these wireless LAN systems, communication is performed using a packet called an Ethernet (registered trademark) frame having a variable data length in a wired section. The wireless LAN system employs adaptive modulation, and variably controls modulation modes of various transmission rates such as BPSK, QPSK, 16QAM, and 64QAM according to the situation. Also in multi-user MIMO communication, if the number of multiplexed signal sequences to be spatially changed is changed, the transmission rate is also variable. For these reasons, the time required for communication with a certain terminal station is proportional to the packet length and inversely proportional to the transmission rate. Therefore, the required time varies for each terminal.

  FIG. 10 is a diagram illustrating a frame configuration example of multi-user MIMO communication in the wireless LAN standard. A frame of multi-user MIMO communication includes a conventional preamble signal 102, a preamble signal 103, a data signal 104 addressed to each terminal station, and padding data 105. In FIG. 10, the horizontal axis represents time, the conventional preamble signal 102 is transmitted by SISO (Single Input Single Output) communication that does not use multiuser MIMO communication, and the signal after the conventional preamble signal 102 is multiuser MIMO communication. Sent by. The conventional preamble signal 102 includes a conventional short preamble / long preamble signal that performs timing synchronization, frequency synchronization, propagation channel estimation, and the like. Similarly, the preamble signal 103 is composed of a new standard short preamble / long preamble signal having a different configuration from that of the conventional preamble. The data signal 104 is a data signal after adaptive modulation and spatial multiplexing. Padding data 105 is a collection of random bits for aligning the data length of each terminal station.

  As shown in FIG. 10, in the frame configuration of multi-user transmission such as conventional multi-user MIMO communication, when the data signal addressed to each user is different, the data length of the multi-user set is made uniform so that a random bit is added to a short data frame. Is embedded as padding data. Therefore, there is a problem that communication to one user may cause interference of communication of the other user. In addition, padding data to be embedded has no problem because it is not related to communication.

The present invention has been made in view of such circumstances, and an object thereof is to provide a radio communication method and radio communication apparatus capable of performing multi-user transmission safely Joteki.

  The present invention is a wireless communication method for performing multi-user transmission for transmitting signals to a plurality of wireless stations, and includes a calculation step for calculating a bit length of each signal to be transmitted, and a longest bit length calculated by the calculation step. Bit addition that makes the bit length of each signal to be transmitted the same by duplicating and adding the bit string of the signal of the longest bit length of the portion longer than the short bit length signal to the short bit length signal And a step.

  The present invention is a wireless communication method using multiuser MIMO communication for transmitting signals to a plurality of wireless stations, a calculation step for calculating the number of symbols of each signal to be transmitted, and a maximum symbol calculated by the calculation step Signal addition to make the number of symbols of each signal to be transmitted the same by duplicating and adding the signal of the maximum number of symbols larger than the signal of the number of small symbols to the signal of the number of symbols smaller than the number And a step.

The present invention is characterized in that, in the signal adding step, when the signal is duplicated , modulation is performed so that a transmission rate is increased by changing a modulation method and a coding rate of the signal to be duplicated. .

The present invention is characterized in that, in the signal adding step, when the signal is duplicated, a transmission weight not performing interference suppression is multiplied .

  The present invention is a wireless communication apparatus that performs multi-user transmission for transmitting signals to a plurality of wireless stations, and includes a calculation unit that calculates a bit length of each signal to be transmitted, and a longest bit length calculated by the calculation unit. Bit addition that makes the bit length of each signal to be transmitted the same by duplicating and adding the bit string of the signal of the longest bit length of the portion longer than the short bit length signal to the short bit length signal Means.

  The present invention is a wireless communication apparatus using multi-user MIMO communication that transmits signals to a plurality of wireless stations, a calculation means for calculating the number of symbols of each signal to be transmitted, and a maximum symbol calculated by the calculation means Signal addition to make the number of symbols of each signal to be transmitted the same by duplicating and adding the signal of the maximum number of symbols larger than the signal of the number of small symbols to the signal of the number of symbols smaller than the number Means.

According to the present invention, the effect of being able to perform multi-user transmission safely Joteki is obtained.

It is a block diagram which shows the structure of the radio | wireless communication apparatus by 1st Embodiment of this invention. It is a figure which shows an example of a structure of an input signal. It is a figure which shows an example of a structure of an output signal. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 3rd Embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 4th Embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless communication apparatus by 5th Embodiment of this invention. It is a figure which shows the conceptual diagram of multiuser-MIMO transmission. It is a time chart which shows the operation | movement of multiuser-MIMO transmission. It is a figure which shows the example of a frame structure of the multiuser MIMO communication in a wireless LAN standard.

<First Embodiment>
Hereinafter, a wireless communication method and a wireless communication apparatus according to a first embodiment of the present invention will be described with reference to the drawings. Since the overall configuration and communication operation in the first embodiment are the same as those shown in FIGS. 8 and 9, detailed description thereof will be omitted. Further, the modulation scheme, coding rate, number of subcarriers, and number of spatial multiplexing of signals addressed to each terminal station are common. FIG. 1 is a block diagram showing the configuration of the wireless communication apparatus according to the first embodiment. In the description of the configuration of the wireless communication apparatus with reference to FIG. 1, known functions and configurations that are commonly possessed by a wireless communication apparatus that performs multi-user transmission, unless directly related to the description of the present invention. Description and illustration of the configuration are omitted. Here, description will be made assuming that the wireless communication apparatus is base station 100 shown in FIG.

  As shown in FIG. 1, the base station 100 calculates the bit length of each of the input signals (signals to be transmitted to the terminal stations 101 to A) of the terminal stations 101-1 to A (A is an arbitrary natural number). Based on the bit length calculated by the bit length calculation unit 106, the calculation unit 106 adds a duplicate signal to a signal that is not the longest bit based on the bit length calculated, and outputs an output signal addressed to the terminal stations 101-1 to A. Unit 107.

  The input signal is a bit signal addressed to each terminal station after encoding and interleaving, and the bit length of each signal is different. For example, when the number of terminal stations is 2 (when A is 2), the input signal is as shown in FIG. FIG. 2 is a diagram illustrating an example of the configuration of the input signal. The input signal is composed of an N1 bit (N1 is a natural number) signal addressed to the terminal station 101-1 and an N2 bit (N2 is a natural number) signal addressed to the terminal station 101-2. However, N2 <N1.

  The bit length calculation unit 106 calculates the bit length from the input bit signal for each terminal station, and outputs the bit length of each input signal to the duplicate signal addition unit 107. For example, when the signal shown in FIG. 2 is input, N1 and N2 are output to the duplicate signal adding unit 107.

  Based on the bit length of each input signal, the duplicate signal adding unit 107 has a short bit length with respect to the end of the input signal of the bit signal having a shorter bit length than the longest bit length bit signal. By duplicating and adding a bit string of a long part of the signal having the longest bit length than the signal, the bit length of each input signal is made the same as the output signal. For example, in the case of the input signal shown in FIG. 2, as shown in FIG. 3, a bit string longer than the short input signal of the terminal station 101-1 is added to the tail of the input signal of the terminal station 101-2. Output signal. FIG. 3 is a diagram illustrating an example of the configuration of the output signal. The output signal is a bit signal addressed to each terminal station output from the duplicate signal adding unit 107, and the bit length of each signal is the same.

  Thus, by duplicating and adding a bit signal addressed to a terminal station at the end of a short bit signal from among a plurality of bit signals, interference between terminal stations is reduced compared to adding a random bit signal. As a result, stable communication can be realized.

Second Embodiment
Next, a wireless communication method and a wireless communication apparatus according to the second embodiment of the present invention will be described. Since the overall configuration and communication operation in the second embodiment are the same as those shown in FIGS. 8 and 9, detailed description thereof will be omitted . FIG. 4 is a block diagram showing the configuration of the wireless communication apparatus according to the second embodiment. When the configuration of the wireless communication apparatus is described with reference to FIG. 2, known functions and configurations that are commonly possessed by a wireless communication apparatus that performs multi-user transmission, unless directly related to the description of the present invention. Description and illustration of the configuration are omitted. Here, description will be made assuming that the wireless communication apparatus is base station 100 shown in FIG.

As illustrated in FIG. 4, the base station 100 includes a modulation unit 108 that modulates input signals addressed to the terminal stations 101-1 to A, a symbol number calculation unit 109 that calculates the number of OFDM symbols of each OFDM signal , and the number of symbols. Based on the number of OFDM symbols calculated by the calculation unit 109, a duplication signal addition unit 110 that duplicates the OFDM symbol and adds it to other OFDM symbols to output an output signal addressed to the terminal stations 101-1 to A is provided. The input signal, Ru-bit signal der of each terminal station after coding and interleaving.

Modulator 108 distributes the input bit signal according to the number of subcarriers, and performs phase modulation such as BPSK or QPSK on each signal. The phase- modulated modulation symbol is output for each subcarrier. The modulation symbol output for each subcarrier is subjected to inverse Fourier transform for each terminal station 101-1 to A and output as an OFDM symbol.

Symbol number calculation section 109 calculates the number of OFDM symbols from the input OFDM signal for each terminal station.

Replica signal adding unit 110, based on the number of OFDM symbols for each terminal station to be input, to the end of the largest OFDM symbol number smaller number of OFDM symbols of the OFDM signal than the maximum number of OFDM symbols of the OFDM signal The OFDM symbols after the number of OFDM symbols smaller than the maximum number of OFDM symbols are duplicated, added so as to have the same number of OFDM symbols as the maximum number of OFDM symbols, and output. The output signal is an OFDM symbol addressed to each terminal station output from duplicate signal adding section 110, and the number of OFDM symbols in each signal is the same.

In this way, even if the modulation scheme, coding rate, number of subcarriers, and number of spatial multiplexing for each terminal station are different, it is addressed to other terminal stations at the end of the OFDM signal having a small number of OFDM symbols from among a plurality of OFDM signals. By duplicating and adding the OFDM symbol, the inter-terminal-station interference is reduced as compared with adding a random symbol, so that stable communication can be realized.

<Third Embodiment>
Next, a wireless communication method and wireless communication apparatus according to a third embodiment of the present invention are described. FIG. 5 is a block diagram showing a configuration of a wireless communication apparatus according to the third embodiment. In FIG. 5, the same parts as those of the apparatus shown in FIG. The apparatus shown in FIG. 5 is different from the apparatus shown in FIG. 4 in that the symbol number calculation unit 111 calculates the number of symbols from an input signal before being input to the modulation unit 108.

Symbol number calculation section 111 calculates the number of OFDM symbols from the input bit signal for each terminal station using equation (1).
Ln = Nn / (MKS) (1)
Here, Ln is the number of OFDM symbols of terminal station n. Nn is the bit length of the input signal addressed to the terminal station n. M is the bit length that can be transmitted by the modulation method, K is the number of subcarriers, and S is the number of spatial multiplexing.

Thus, changing the location of calculating the number of OFDM symbols, the last OFDM signal OFDM symbol number is small among the OFDM signals by other replicate OFDM symbol addressed to the terminal station adds a random symbol Stable communication can be realized by reducing interference between terminal stations as compared with the addition.

<Fourth embodiment>
Next, a wireless communication method and wireless communication apparatus according to a fourth embodiment of the present invention are described. In the fourth embodiment, efficient transmission can be performed by adjusting the modulation scheme of the OFDM signal to be replicated. FIG. 6 is a block diagram showing a configuration of a wireless communication apparatus according to the fourth embodiment. In FIG. 6, the same parts as those of the apparatus shown in FIG. The apparatus shown in FIG. 6 differs from the apparatus shown in FIG. 5 in that the symbol number calculation unit 112 outputs the calculation result to the modulation unit 113, and the modulation unit 113 modulates according to the number of symbols. Is a point.

  Symbol number calculation section 112 calculates the number of symbols using the equation (1) from the input bit signal for each terminal station, and outputs it to modulation section 113 and duplicate signal addition section 110. Based on the number of OFDM symbols input for each terminal station, the modulation unit 113 has the number of OFDM symbols longer than the number of short OFDM symbols at the end of the OFDM signal having the number of OFDM symbols smaller than the maximum number of OFDM symbols. Modulation is performed by changing the modulation scheme and coding rate of the signal copied from the OFDM signal. Specifically, the transmission rate is set to increase.

  In this way, efficient communication can be realized by adjusting the modulation scheme of the OFDM symbol to be copied.

<Fifth Embodiment>
Next, a wireless communication method and wireless communication apparatus according to a fifth embodiment of the present invention are described. In the fifth embodiment, efficient transmission can be performed by adjusting the transmission weight of the OFDM signal to be replicated. FIG. 7 is a block diagram showing a configuration of a wireless communication apparatus according to the fifth embodiment. 7, parts that are the same as the parts shown in FIG. 5 are given the same reference numerals, and explanation thereof is omitted. The apparatus shown in FIG. 7 differs from the apparatus shown in FIG. 5 in that a weight calculation unit 115 is newly provided and the symbol number calculation unit 114 outputs the calculation result to the weight calculation unit 115.

  Symbol number calculation section 114 calculates the number of symbols from the input bit signal for each terminal station using equation (1), and outputs it to duplicate signal addition section 110 and weight calculation section 115. The weight calculation unit 115 multiplies the terminal station to which the number of duplicated OFDM symbols is added by a transmission weight that does not perform interference suppression.

  In this way, efficient communication can be realized by adjusting the transmission weight of the OFDM symbol to be duplicated.

  When realizing multi-user transmission (multi-user MIMO or OFDMA) such as a conventional wireless LAN, random bits are embedded as padding data in a short data frame in order to make the data length of the multi-user group uniform. Even in multi-user transmission, communication to one user can cause interference with the communication of the other user. Also, padding data is inefficient because it is not related to communication. The wireless communication apparatus according to the above-described embodiment adds the last part of the other data frame (long data frame) of multi-user transmission to the last part of the short data frame. In addition, the modulation scheme and coding rate of the signal to be added are changed to be high. As a result, the communication of the other user is not interfered with the last portion, the quality of multi-user transmission is stabilized, and efficient communication can be realized.

  The wireless communication device in the above-described embodiment may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in the computer system. It may be realized using hardware such as PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array).

  As mentioned above, although embodiment of this invention has been described with reference to drawings, the said embodiment is only the illustration of this invention, and it is clear that this invention is not limited to the said embodiment. is there. Therefore, additions, omissions, substitutions, and other modifications of the components may be made without departing from the technical idea and scope of the present invention.

It is carried out multi-user transmission safely Joteki applicable to critical applications.

  DESCRIPTION OF SYMBOLS 100 ... Base station, 101-1, 101-2 ... Terminal station, 106 ... Bit length calculation part, 107, 110 ... Duplicate signal addition part, 108, 113 ... Modulation part, 109 , 111, 112, 114... Symbol number calculation unit, 115... Weight calculation unit

Claims (4)

A wireless communication method using multi-user MIMO communication for transmitting OFDM signals to a plurality of wireless stations,
A calculation step of calculating the number of OFDM symbols of each of the OFDM signals to be transmitted to the plurality of radio stations;
Among OFDM signals to calculate the number of OFDM symbols by the calculating step, the OFDM signal of the maximum OFDM symbol number L1 in OFDM signal to be transmitted to one radio station of the plurality of radio stations, a smaller maximum OFDM symbol number L1 OFDM signals of the OFDM symbol number L2 is a OFDM signal to be transmitted to the different radio station from said one radio station,
Wherein the OFDM signal of the OFDM symbol number L2, the is the OFDM signal larger portion of the OFDM symbol number L2 in OFDM signals up OFDM symbol number L1 (L2 + 1) -th from duplicate the OFDM symbol to L1 th And a signal addition step of making the number of OFDM symbols of each of the OFDM signals to be transmitted the same by adding to the end of the OFDM signal having the number of OFDM symbols L2. 2. The radio communication method according to claim 1, wherein, in the calculating step, the number of OFDM symbols of the OFDM signal is calculated from each bit signal addressed to each terminal station after encoding and interleaving by the following formula.

Here, Ln is the number of OFDM symbols of terminal station n. Nn is the bit length of the input signal addressed to the terminal station n. M is the bit length that can be transmitted by the modulation method, K is the number of subcarriers, and S is the number of spatial multiplexing.
A wireless communication device using multi-user MIMO communication for transmitting OFDM signals to a plurality of wireless stations,
Calculating means for calculating the number of OFDM symbols for each of the OFDM signals to be transmitted to the plurality of wireless stations;
Among OFDM signals to calculate the number of OFDM symbols by the calculation means, an OFDM signal of the maximum OFDM symbol number L1 in OFDM signal to be transmitted to one radio station of the plurality of radio stations, a smaller maximum OFDM symbol number L1 OFDM signals of the OFDM symbol number L2 is a OFDM signal to be transmitted to the different radio station from said one radio station,
Wherein the OFDM signal of the OFDM symbol number L2, the is the OFDM signal larger portion of the OFDM symbol number L2 in OFDM signals up OFDM symbol number L1 (L2 + 1) -th from duplicate the OFDM symbol to L1 th A radio communication apparatus comprising: a signal addition unit configured to add the number of OFDM symbols of each OFDM signal to be transmitted by adding the signal to the tail of the OFDM signal having the number of OFDM symbols L2. The radio communication apparatus according to claim 3, wherein the calculating means calculates the number of OFDM symbols of the OFDM signal from each bit signal addressed to each terminal station after encoding and interleaving by the following equation.

Here, Ln is the number of OFDM symbols of terminal station n. Nn is the bit length of the input signal addressed to the terminal station n. M is the bit length that can be transmitted by the modulation method, K is the number of subcarriers, and S is the number of spatial multiplexing.

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