JP2006014318A - Transmission method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To switch a configuration of a preamble of an MIMO system. <P>SOLUTION: A storage part 116 stores a preamble signal prescribed for a conventional system and a preamble signal prescribed for an MIMO system. A monitoring part 112 monitors presence of a communication device corresponding to the conventional system but not corresponding to the MIMO system. A transmission path properties acquiring part 114 derives properties of a radio transmission path between the transmission device and a receiving device. A selecting part 110 selects a packet format based on the result of monitoring by the monitoring part 112. Moreover, the selecting part 110 selects arrangement of an LTS based on the properties of the radio transmission path derived by the transmission path properties acquiring part 114. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transmission technique, and more particularly to a transmission method and apparatus for transmitting a packet format signal.

  In wireless communication, effective use of limited frequency resources is generally desired. One of the technologies for effectively using frequency resources is the adaptive array antenna technology. In the adaptive array antenna technology, the antenna directivity pattern is formed by controlling the amplitude and phase of signals transmitted and received by a plurality of antennas. That is, an apparatus equipped with an adaptive array antenna changes the amplitude and phase of signals received by a plurality of antennas, adds the changed plurality of received signals, respectively, and changes the amplitude and phase (hereinafter referred to as the amount of change). A signal equivalent to a signal received by an antenna having a directivity pattern corresponding to “weight” is received. In addition, a signal is transmitted by an antenna directivity pattern corresponding to the weight.

  In the adaptive array antenna technology, an example of a process for calculating a weight is a method based on a minimum mean square error (MMSE) method. In the MMSE method, a Wiener solution is known as a condition for giving an optimum weight value, and a recurrence formula with a smaller amount of calculation than directly solving the Wiener solution is also known. As the recurrence formula, for example, an adaptive algorithm such as an RLS (Recursive Least Squares) algorithm or an LMS (Least Mean Squares) algorithm is used. On the other hand, for the purpose of increasing the data transmission rate and improving the transmission quality, there are cases where data is subjected to multicarrier modulation and a multicarrier signal is transmitted (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-2110099

  There is a MIMO (Multiple Input Multiple Output) system as a technique for increasing the data transmission speed using the adaptive array antenna technology. In the MIMO system, the transmission device and the reception device each include a plurality of antennas, and one channel is set for each antenna. That is, for the communication between the transmission device and the reception device, channels up to the maximum number of antennas are set to improve the data transmission rate. Furthermore, if a technology for transmitting a multicarrier signal is combined with such a MIMO system, the data transmission speed can be further increased. On the other hand, since the signal transmitted from the transmission apparatus is accurately received by the reception apparatus, the transmission signal generally includes a preamble that is a known signal. In general, the preamble signal is defined by a fixed pattern. However, if the preamble signal pattern changes in consideration of the characteristics of the wireless transmission path and the packet utilization efficiency, a flexible wireless communication system can be realized with respect to the characteristics of the wireless transmission path.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a transmission method and apparatus for changing the format of a preamble signal.

  In order to solve the above-described problem, a transmitting apparatus according to an aspect of the present invention includes a first known signal defined in the first wireless communication system and a second wireless communication different from the first wireless communication system. A storage unit for storing the second known signal defined by the system, a packet format in which the second known signal is arranged at the head portion, and a first known signal further arranged in the preceding stage of the second known signal A selection unit that selects one of the packet formats; and a transmission unit that transmits a signal in the packet format selected by the selection unit.

  According to this aspect, since the presence / absence of the first known signal is switched, compatibility with the first wireless communication system and improvement of packet utilization efficiency can be selected in the second wireless communication system.

  Another embodiment of the present invention is also a transmission device. This apparatus has the same number of first known signals defined in the first wireless communication system that should transmit signals using a plurality of carriers and the number of carriers for transmitting signals in the first wireless communication system. A storage unit for storing a second known signal defined by the second wireless communication system that should transmit signals from a plurality of antennas in parallel while using the same number of carriers, and the second known signal are arranged at the head part A selection unit that selects one of the received packet format, a packet format in which the first known signal is further arranged before the second known signal, and a transmission unit that transmits the signal in the packet format selected by the selection unit; .

  According to this aspect, since the presence / absence of the first known signal is switched, compatibility with the first wireless communication system and improvement of packet utilization efficiency can be selected in the second wireless communication system.

  A plurality of types of second known signals stored in the storage unit may be defined according to the number of antennas that should transmit signals in the second wireless communication system. Since the pattern of the second known signal is changed according to the number of antennas, the communication quality can be improved.

  When the selection unit selects a packet format in which the second known signal is arranged at the head part, if the number of antennas to which the signal is to be transmitted becomes one, a plurality of types of second known signals defined One of them may be arranged. Even if the number of antennas is changed from a plurality to one, since the second known signal corresponding to one of the plurality of antennas is used, switching to the first wireless communication system becomes unnecessary.

  When selecting a packet format in which the first known signal is further arranged before the second known signal, the selecting unit selects the second known signal between the first known signal and the second known signal. Information indicating that it is arranged may be arranged. Since the information indicating that the second known signal is arranged is inserted after the first known signal, it is possible to notify the communication device of the first wireless communication system of the content of the subsequent signal. it can.

  A monitoring unit that monitors the presence of a communication device that is not compatible with the second wireless communication system and that is compatible with the first wireless communication system, and the selection unit determines the packet format based on the monitoring result of the monitoring unit. You may choose. Since the switching of the presence / absence of the first known signal is performed based on the presence / absence of the terminal device of the first wireless communication system, even if the switching is performed, other communication devices are not affected.

  Another embodiment of the present invention is also a transmission device. This apparatus includes a transmission unit that transmits signals defined in a predetermined packet format in parallel from a plurality of antennas, a storage unit that stores a known signal to be placed at the beginning of the packet format, and a known signal that is stored in the packet format. When placing at the beginning, select either an arrangement in which known signals are transmitted from multiple antennas at the same timing, or an arrangement in which known signals are transmitted from multiple antennas at different timings A selection unit.

  According to this aspect, since the arrangement of known signals to be transmitted from a plurality of antennas is changed, signal transmission quality and packet utilization efficiency can be selected.

  The deriving unit that derives the characteristics of the radio transmission path to which the signal is to be transmitted and the selection unit may select the arrangement of the known signals based on the derived characteristics of the radio transmission path. Since the change of the configuration of the known signal to be transmitted from a plurality of antennas is executed based on the quality of the radio transmission path, the configuration of the known signal suitable for the quality of the radio transmission path can be selected.

  Yet another embodiment of the present invention is a transmission method. This method is the same as the first known signal defined in the first wireless communication system to transmit signals using a plurality of carriers and the number of carriers for transmitting signals in the first wireless communication system. The second known signal defined by the second wireless communication system that should transmit signals from a plurality of antennas in parallel while using the number of carriers is defined, and the second known signal is arranged at the head portion. The packet format and the packet format in which the first known signal is further arranged in the previous stage of the second known signal are selected, and the signal is transmitted.

  Yet another aspect of the present invention is also a transmission method. The method stores a first known signal defined in a first wireless communication system and a second known signal defined in a second wireless communication system different from the first wireless communication system. Selecting a packet format in which the second known signal is arranged at the head part, and a packet format in which the first known signal is further arranged in the preceding stage of the second known signal, and a step of selecting Transmitting a signal in the selected packet format.

  Yet another aspect of the present invention is also a transmission method. This method is the same as the first known signal defined in the first wireless communication system to transmit signals using a plurality of carriers and the number of carriers for transmitting signals in the first wireless communication system. Storing a second known signal defined by the second wireless communication system to transmit signals from a plurality of antennas in parallel while using the number of carriers, and the second known signal is arranged at the head portion A packet format, a step of selecting one of the packet formats in which the first known signal is further arranged in the previous stage of the second known signal, and a step of transmitting the signal in the packet format selected in the selecting step. .

  The second known signal stored in the storing step may be defined in a plurality of types according to the number of antennas that should transmit signals in the second wireless communication system. The step of selecting, when selecting the packet format in which the second known signal is arranged at the head part, is provided with a plurality of types of second known signals if the number of antennas to transmit the signal is one. One of them may be arranged. The step of selecting includes selecting the second known signal between the first known signal and the second known signal when selecting a packet format in which the first known signal is further arranged before the second known signal. Information indicating that is placed may be placed.

  The method further comprises the step of monitoring the presence of a communication device compatible with the first wireless communication system without being compatible with the second wireless communication system, and the selecting step is based on the monitoring result in the monitoring step. May be selected. The second known signal stored in the storing step includes a plurality of portions having different signal patterns, and the selecting step transmits at least one of the plurality of portions from the plurality of antennas at the same timing. The arrangement of the second known signals and the arrangement of the second known signals that respectively transmit at least one of the plurality of portions at different timings from the plurality of antennas may be selected. In the step of deriving and selecting the characteristics of the wireless transmission path on which the signal is to be transmitted, the second known signal arrangement may be selected based on the derived characteristics of the wireless transmission path.

  Yet another aspect of the present invention is also a transmission method. This method has an arrangement in which a known signal is transmitted from a plurality of antennas at the same timing with respect to a known signal to be arranged at the beginning of a packet format of a signal to be transmitted in parallel from a plurality of antennas One of arrangements is selected so that signals are transmitted from a plurality of antennas at different timings.

  Yet another aspect of the present invention is also a transmission method. This method includes a step of transmitting a signal defined in a predetermined packet format in parallel from a plurality of antennas, a step of storing a known signal to be arranged at the head portion of the packet format, and a step of storing the known signal at the head portion of the packet format. Selecting an arrangement in which known signals are transmitted from a plurality of antennas at the same timing, and an arrangement in which known signals are transmitted from a plurality of antennas at different timings. Is provided. In the step of deriving the characteristics of the radio transmission path to which the signal is to be transmitted and the selection step, the arrangement of the known signals may be selected based on the derived characteristics of the radio transmission path.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the transmission method and apparatus which change the format of a preamble signal can be provided.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a MIMO system configured by a transmission apparatus having a plurality of antennas and a reception apparatus having a plurality of antennas. In addition, the MIMO system according to the present embodiment transmits a signal by multi-carrier, specifically, OFDM (Orthogonal Frequency Division Multiplexing) modulation, and the transmitted signal is defined in a packet format. A preamble signal is arranged at the beginning of the packet format, and a receiving apparatus that receives the signal performs AGC (Automatic Gain Control) setting, timing synchronization, carrier reproduction, and the like based on the preamble signal. In a MIMO system, independent signals are transmitted from a plurality of antennas of a transmission apparatus, and a reception apparatus demodulates a desired signal by separating the received signals by adaptive array signal processing.

  On the other hand, there may be a receiving device that does not support the MIMO system around the transmitting device (hereinafter, a system that does not support the MIMO system is referred to as a “conventional system”). The conventional system transmits a signal by the OFDM modulation method as in the MIMO system. However, unlike the MIMO system, the signal is transmitted by setting one channel between the transmission device and the reception device. Here, if a preamble signal corresponding to only the MIMO system is added, the signal redundancy in the packet format in the MIMO system can be reduced. However, since the conventional system cannot recognize such a preamble signal, it recognizes the arrival of the signal. There are cases where it is not possible. This corresponds to the fact that if the conventional system uses CSMA, the carrier sense is not accurately executed, and it is determined that the signal is not transmitted, and the signal is transmitted by itself. The probability of occurrence increases.

  On the other hand, in the MIMO system, if the preamble signal corresponding to the conventional system is added before the preamble signal corresponding to only the MIMO system, the reception device of the conventional system can also recognize the preamble signal. Is less likely to occur. However, since the preamble signals corresponding to the two systems are added, the signal redundancy in the packet format of the MIMO system increases. Therefore, the transmitting apparatus according to the present embodiment adds a preamble signal corresponding to the conventional system to the head of the packet format if the receiving apparatus corresponding to the conventional system exists in the vicinity, while supporting the conventional system. If the receiving apparatus is not present in the vicinity, a preamble signal corresponding to the conventional system is not added to the head of the packet format.

  FIG. 1 shows a spectrum of a multicarrier signal according to an embodiment of the present invention. This corresponds to a multicarrier signal transmitted by the conventional system and a multicarrier signal transmitted from one antenna of the MIMO system. Here, it is assumed that the conventional system is a wireless LAN (Local Area Network) compliant with the IEEE 802.11a standard (hereinafter, the wireless LAN compliant with the IEEE 802.11a standard is also referred to as “conventional system”). One of a plurality of carriers in the OFDM system is generally called a subcarrier, but here, one subcarrier is designated by a “subcarrier number”. As shown in the figure, the IEEE 802.11a standard defines 53 subcarriers from subcarrier numbers “−26” to “26”. The subcarrier number “0” is set to null in order to reduce the influence of the DC component in the baseband signal. Each subcarrier is modulated by BPSK (Binary Phase Shift Keying), QSPK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), and 64QAM.

  FIG. 2 shows a configuration of a packet format according to the embodiment of the present invention. This corresponds to the call channel of the conventional system. In the OFDM modulation system, generally, the total of the Fourier transform size and the number of symbols in the guard interval is used as one unit. This single unit is an OFDM symbol in this embodiment. In the conventional system, since the size of the Fourier transform is 64 (hereinafter, one FFT (Fast Fourier Transform) point is referred to as an “FFT point”) and the guard interval has 16 FFT points, the OFDM symbol is 80 FFT. It corresponds to a point.

  In the packet signal, “preamble” of “4 OFDM symbol”, “signal” of “1 OFDM symbol”, and “data” of an arbitrary length are arranged from the head. The preamble is a known signal transmitted for AGC setting, timing synchronization, carrier reproduction, and the like in the receiving apparatus. The signal is a control signal, and the data is information to be transmitted from the transmission device to the reception device. Furthermore, as shown in the figure, the “preamble” of “4OFDM symbol” is separated into “STS (Short Training Sequence)” of “2OFDM Symbol” and “LTS (Long Training Sequence)” of “2OFDM Symbol”. The STS is composed of ten signal units “t1” to “t10”, and one unit “t1” or the like is 16 FFT points. As described above, the STS uses the unit of the time domain as 16 FFT points, but uses 12 subcarriers among the 53 subcarriers shown in FIG. 1 in the frequency domain. The STS is particularly used for AGC setting and timing synchronization. On the other hand, the LTS is composed of two signal units “T1” and “T2” and a guard interval “GI2” that is twice as long, and one unit “T1” is 64 FFT points. “GI2” is 32 FFT points. The LTS is particularly used for carrier reproduction.

「１+ｊ」は、ＱＰＳＫ変調されたＳＴＳの信号点を示す。 The signal in the frequency domain as shown in FIG. 1 is indicated as S− ₂₆ , _26, and the subscript indicates the subcarrier number. If such a notation is used, the STS of the conventional system is expressed as follows.

“1 + j” indicates a signal point of STS subjected to QPSK modulation.

  FIG. 3 shows a concept of the communication system 100 according to the embodiment of the present invention. The communication system 100 includes a transmission device 10 and a reception device 12. Further, the transmission device 10 includes a first transmission antenna 14 a and a second transmission antenna 14 b that are collectively referred to as a transmission antenna 14, and the reception device 12 is a first reception antenna 16 a that is generally referred to as a reception antenna 16. And the second receiving antenna 16b.

  The transmitting apparatus 10 transmits a predetermined signal, but transmits different signals from the first transmitting antenna 14a and the second transmitting antenna 14b. The receiving device 12 receives signals transmitted from the first transmitting antenna 14a and the second transmitting antenna 14b by the first receiving antenna 16a and the second receiving antenna 16b. Furthermore, the receiving device 12 separates the received signals by adaptive array signal processing, and independently demodulates the signals transmitted from the first transmitting antenna 14a and the second transmitting antenna 14b. Here, the transmission path characteristic between the first transmission antenna 14a and the first reception antenna 16a is h11, the transmission path characteristic between the first transmission antenna 14a and the second reception antenna 16b is h12, 2 If the transmission path characteristic between the transmission antenna 14b and the first reception antenna 16a is h21, and the transmission path characteristic between the second transmission antenna 14b and the second reception antenna 16b is h22, the receiving apparatus 12 operates by enabling only h11 and h22 by adaptive array signal processing and independently demodulating the signals transmitted from the first transmitting antenna 14a and the second transmitting antenna 14b.

第１受信用アンテナ１６ａで受信した信号の１６ＦＦＴ単位での強度は、次のように示される。

Here, the problem when the preamble signal of the conventional system, for example, the STS is transmitted from the first transmitting antenna 14a and the second transmitting antenna 14b in FIG. 3 will be described. If the signal transmitted from the first transmitting antenna 14a is S1 (t), the signal transmitted from the second transmitting antenna 14b is S2 (t), and the noise is n1 (t) and n2 (t), A signal received by the first receiving antenna 16a is represented by X1 (t), and a signal received by the second receiving antenna 16b is represented by X2 (t) as follows.

The intensity in units of 16 FFT of the signal received by the first receiving antenna 16a is shown as follows.

送信される信号Ｓ1（ｔ）とＳ2（ｔ）が同一であり、さらにh１１＝−h２１の場合は、受信した信号の強度が０になるので、受信装置１２のＡＧＣは正確に動作しない。さらに、一般的にはデータ区間ではＸｃが０とみなせる程度に小さくなるので、データ区間の受信電力は｜ｈ１１｜^２＋｜ｈ２２｜^２となる。従って、データ区間とＳＴＳ区間の受信電力の差は、数４の右辺第３項で示されるように、２Ｒｅ［ｈ１１ｈ*２１Ｘ*ｃ］となる。これから分かるように、ＳＴＳ区間のＸｃが大きい場合には、ＳＴＳ区間の電力とデータ区間の電力が大きく異なるため、ＡＧＣが正常に動作しない。従って、ＭＩＭＯシステムに対して、従来システムのＳＴＳと別のＳＴＳが必要となり、かつ、それらの相互相関値は低い方が望ましい。 Here, using the relationship of ΣS * 1 (t) S2 (t) = Xc, ΣS * i (t) nj (t) = 0, | nj (t) | ² ≈0, the intensity is as follows: Shown in

When the transmitted signals S1 (t) and S2 (t) are the same and h11 = −h21, the received signal strength becomes 0, so the AGC of the receiving device 12 does not operate correctly. Further, generally, Xc becomes small enough to be regarded as 0 in the data interval, so the reception power in the data interval becomes | h11 | ² + | h22 | ² . Therefore, the difference in received power between the data section and the STS section is 2Re [h11h * 21X * c] as shown by the third term on the right side of Equation 4. As can be seen, when Xc in the STS section is large, the power in the STS section and the power in the data section are greatly different, and AGC does not operate normally. Therefore, an STS different from the STS of the conventional system is required for the MIMO system, and it is desirable that their cross-correlation values are low.

  Next, a problem when a preamble signal such as STS suitable for the MIMO system as described above is added to the head portion of the packet format will be described. When a packet signal to which a preamble signal suitable for the MIMO system is added is transmitted from the transmission device 10, the reception device 12 can receive the packet signal. On the other hand, a reception device of a conventional system (not shown) also receives a packet signal to which a preamble signal suitable for a MIMO system is added. However, since the preamble signal in the conventional system held in advance by the receiving apparatus is different from the preamble signal added to the packet signal, even if correlation processing is performed between them, the correlation value is higher than a predetermined value. Does not grow. As a result, the receiving device cannot detect the packet signal. Further, if the receiving device and the transmitting device integrally form a communication device, the above-described operation corresponds to the fact that no packet signal is detected by the communication device, so the communication device transmits a signal. This corresponds to the fact that carrier sense is not correctly executed in the communication device, and therefore, signal collision is likely to occur.

  FIG. 4 shows the configuration of the transmission apparatus 10. The transmission device 10 includes a data separation unit 20, a first modulation unit 22a, a second modulation unit 22b, an Nth modulation unit 22n, which are collectively referred to as a modulation unit 22, a first radio unit 24a, a second radio unit 24, and a second radio unit 24. A radio unit 24b, an Nth radio unit 24n, a control unit 26, and an Nth transmission antenna 14n are included. The first modulation unit 22a includes an error correction unit 28, an interleaving unit 30, a preamble addition unit 32, an IFFT unit 34, a GI unit 36, and an orthogonal modulation unit 38. The first radio unit 24a includes a frequency conversion unit 40, An amplification unit 42 is included.

  The data separator 20 separates data to be transmitted according to the number of antennas. The error correction unit 28 performs encoding for error correction on the data. Here, it is assumed that convolutional encoding is performed, and the encoding rate is selected from predetermined values. The interleave unit 30 interleaves the convolutionally encoded data. The preamble adding unit 32 adds a preamble signal to the head of the packet signal. Here, a plurality of types of preamble signals to be added by the preamble adding unit 32 are defined, and one of them is selected based on an instruction from the control unit 26. Details thereof will be described later.

  The IFFT unit 34 performs IFFT (Inverse Fast Fourier Transform) in units of FFT points, and converts a frequency domain signal using a plurality of subcarrier carriers into a time domain signal. The GI unit 36 adds a guard interval to the time domain data. As shown in FIG. 2, guard intervals added to the preamble signal and the data signal are different. The quadrature modulation unit 38 performs quadrature modulation. The frequency converter 40 converts the orthogonally modulated signal into a radio frequency signal. The amplifying unit 42 is a power amplifier that amplifies a radio frequency signal. Finally, signals are transmitted from the plurality of transmitting antennas 14 in parallel. In this embodiment, it is assumed that the directivity of the transmission antenna 14 is non-directional, and the transmission apparatus 10 does not perform adaptive array signal processing. The control unit 26 controls the timing and the like of the transmission apparatus 10 and selects a preamble signal to be added by the preamble adding unit 32.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of an arbitrary computer, and in terms of software, it is realized by a program having a reservation management function loaded in memory. The functional block realized by those cooperation is drawn. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 5 shows the configuration of the control unit 26. The control unit 26 includes a selection unit 110, a monitoring unit 112, a transmission path characteristic acquisition unit 114, and a storage unit 116.

  The storage unit 116 stores a preamble signal specified in the conventional system and a preamble signal specified in the MIMO system. As described above, the conventional system transmits signals using a plurality of subcarriers, and the MIMO system uses the same number of subcarriers as the number of subcarriers of the conventional system in parallel from the plurality of transmitting antennas 14. Transmit the signal. Further, a plurality of types of preamble signals defined by the MIMO system are defined according to the number of transmitting antennas 14 to which signals are to be transmitted. A plurality of types of prescribed preamble signals will be described later. Similarly to the preamble signal of the conventional system shown in FIG. 2, the preamble signal of the MIMO system is defined to include STS and LTS. Here, STS and LTS have different signal patterns.

  The monitoring unit 112 monitors the presence of a communication device that does not correspond to the MIMO system but corresponds to the conventional system. Here, it is assumed that the transmission apparatus 10 and a reception apparatus (not shown) integrally constitute a communication apparatus, for example, a base station apparatus compatible with a MIMO system. The receiving device searches for the signal received from the communication device of the conventional system among the received signals. That is, it is determined whether the packet format of the received packet signal corresponds to the packet format of the conventional system shown in FIG. The monitoring unit 112 determines that there is no communication device corresponding to the conventional system when the receiving device does not detect a packet signal defined by the conventional system over a predetermined period. On the other hand, when the receiving apparatus detects a packet signal defined by the conventional system within a predetermined period, it is determined that there is a communication apparatus corresponding to the conventional system.

  The transmission path characteristic acquisition unit 114 derives the characteristics of the wireless transmission path with the receiving device 12. The characteristics of the wireless transmission path are measured by a predetermined method. One method is measurement by the reception device 12 of FIG. 3, and another method is measurement by a communication device including the transmission device 10. The former corresponds to the characteristic of the wireless transmission path from the transmission apparatus 10 to the reception apparatus 12, and the latter corresponds to the characteristic of the wireless transmission path from the reception apparatus 12 to the transmission apparatus 10. In the former case, the communication device including the receiving device 12 notifies the communication device including the transmitting device 10 of the measurement result. Here, the characteristics of the wireless transmission path include reception power, delay profile, delay spread, error rate, and the like.

  The selection unit 110 selects a packet format based on the monitoring result from the monitoring unit 112. Here, two types of packet formats are defined. 6A to 6B show packet formats selected by the selection unit 110. FIG. FIG. 6A shows a packet format in which a preamble signal corresponding to the MIMO system is arranged at the head portion (hereinafter referred to as “dedicated format”). Here, it is assumed that signals are transmitted from the first transmitting antenna 14a and the second transmitting antenna 14b among the transmitting antennas 14, the packet format of the signal transmitted from the first transmitting antenna 14a is shown in the upper stage, 2 shows the packet format of the signal transmitted from the transmitting antenna 14b. “STS1” and “LTS1” are transmitted as preamble signals from the first transmitting antenna 14a, and “STSa” and “LTSa” are transmitted as preamble signals from the second transmitting antenna 14b. Here, “STS1” and “STSa”, and “LTS1” and “LTSa” are signals having different patterns. Details of these signals will be described later.

  FIG. 6B shows a packet format in which a preamble signal corresponding to the conventional system is further arranged before the preamble signal corresponding to the MIMO system (hereinafter referred to as “mixed format”). Here, the STS and LTS of the preamble signal corresponding to the conventional system are indicated as “conventional STS” and “conventional LTS”, respectively. Note that the pattern of the conventional STS is as described in FIG. The part corresponding to the preamble signal of the MIMO system is the same as that shown in FIG. Here, a “signal” is arranged between the preamble signal corresponding to the conventional system and the preamble signal corresponding to the MIMO system. “Signal” includes information indicating that a preamble signal corresponding to the MIMO system is arranged. Therefore, even if the communication apparatus of the conventional system receives the packet signal, the packet signal may be discarded from the content of “signal”. Further, the information indicating that the preamble signal is arranged may be the length of the packet signal, that is, it is only necessary to determine that some signal continues for a certain period of time.

  Since the dedicated format has few redundant signal components, the use efficiency of packets can be improved. On the other hand, the mixed format is detected by a communication apparatus compatible with the conventional system since a packet signal corresponding to the conventional system is added. If the monitoring unit 112 does not detect a communication device compatible with the conventional system, the selection unit 110 selects a dedicated format. If the monitoring unit 112 detects a communication device compatible with the conventional system, the selection unit 110 Select a mixed format.

  Further, the selection unit 110 selects an LTS arrangement based on the characteristics of the wireless transmission path derived by the transmission path characteristic acquisition unit 114. 7A to 7B show the format of the LTS selected by the selection unit 110. FIG. FIGS. 7A to 7B are described in a dedicated format, but may be a mixed format, in which case the preamble signal portion of the MIMO system is illustrated. FIG. 7A shows a case where LTSs are transmitted from a plurality of transmitting antennas 14 at the same timing (hereinafter, such a format is referred to as “continuous format”). "Is transmitted, and" LTSa "is transmitted from the second transmitting antenna 14b. FIG. 7B shows a case where LTSs are transmitted from a plurality of transmitting antennas 14 at different timings (hereinafter, such a format is referred to as “separation format”), and “LTS1” and “LTSa” are illustrated as shown. "Is transmitted at a different timing.

  Since the continuous format has few redundant signal components, the use efficiency of packets can be improved. On the other hand, in the separation format, “LTS1” and “LTSa” are transmitted at different timings, and interference between signals is reduced. Therefore, estimation of transmission path characteristics, response vectors, and weights performed by the receiving apparatus 12 described later are performed. Vector estimation is accurate and communication quality is improved. If the wireless channel characteristics acquired by the channel characteristics acquisition unit 114, for example, the error rate is not worse than the threshold value, the selection unit 110 selects the continuous format, and the error rate is worse than the threshold value. If so, the selection unit 110 selects the separation format.

  FIG. 8 shows the relationship used when selecting by the selection unit 110, and shows the relationship between the number of transmitting antennas and the STS pattern transmitted from the transmitting antenna. In addition, although description is abbreviate | omitted here about LTS, suppose that it selects similarly. Here, the number of transmission antennas 14 is shown in the vertical direction in the figure, and the transmission antenna 14 to be used and the STS corresponding thereto are shown in the horizontal direction in the figure according to the number of transmission antennas 14. Yes. That is, when the number of transmitting antennas 14 is “1”, the conventional STS is transmitted from the first transmitting antenna 14a. Note that, in the case of the dedicated format, the selection unit 110 may transmit “STS1” defined by the MIMO system if the number of transmission antennas 14 to which a signal is to be transmitted becomes one. Thereby, switching to the preamble signal corresponding to the conventional system can be omitted.

  When the number of transmitting antennas 14 is “2”, “STS1” is transmitted from the first transmitting antenna 14a, and “STSa” is transmitted from the second transmitting antenna 14b. Further, when the number of transmitting antennas 14 is “3”, “STS1” is transmitted from the first transmitting antenna 14a, “STS2” is transmitted from the second transmitting antenna 14b, and the third transmitting antenna 14c. “STSb” is transmitted. Here, “STS1”, “STSa”, “STS2”, and “STSb” are defined by values that reduce the cross-correlation value in order to solve the above-described problems.

  Further, “STSa” transmitted from the second transmitting antenna 14b when the number of transmitting antennas 14 is “2” and from the third transmitting antenna 14c when the number of transmitting antennas 14 is “3”. It has a function of notifying the receiving apparatus 12 of the number of transmitting antennas 14 that are transmitting signals, depending on the pattern difference between “STSb” to be transmitted. Therefore, these STSs are different to the extent that “STSa” and “STSb” can be identified from the signal received by the receiving device 12. That is, the cross-correlation value between “STSa” and “STSb” is defined to be small.

  The number of transmitting antennas 14 is determined by the control unit 26. The control unit 26 determines the number of transmission antennas 14 according to the characteristics of the wireless transmission path acquired by the transmission path characteristic acquisition unit 114. That is, if the characteristics of the wireless transmission path are good, the number of transmitting antennas 14 is increased. The control unit 26 may determine the number of transmission antennas 14 based on the capacity of information to be transmitted. For example, if the capacity of information to be transmitted is large, the number of transmitting antennas 14 is increased.

  FIG. 9 shows the configuration of the receiving device 12. The receiving device 12 includes an N-th receiving antenna 16n, a first wireless unit 50a collectively referred to as a wireless unit 50, a second wireless unit 50b, an N-th wireless unit 50n, and a first processing unit 52a collectively referred to as a processing unit 52. A second processing unit 52b, an N-th processing unit 52n, a first demodulating unit 54a, a second demodulating unit 54b, an N-th demodulating unit 54n, a data combining unit 56, and a control unit 58, which are collectively referred to as a demodulating unit 54, are included. Further, as signals, a first radio reception signal 200a, a second radio reception signal 200b, an Nth radio reception signal 200n, which are collectively referred to as a radio reception signal 200, and a first baseband reception signal 202a, which is generically referred to as a baseband reception signal 202, A second baseband received signal 202b, an Nth baseband received signal 202n, a first synthesized signal 204a collectively referred to as a synthesized signal 204, a second synthesized signal 204b, and an Nth synthesized signal 204n are included.

  The radio unit 50 performs frequency conversion processing, amplification processing, AD conversion processing, and the like between the radio frequency radio reception signal 200 and the baseband baseband reception signal 202. Here, the radio frequency of the radio reception signal 200 corresponds to the 5 GHz band. Furthermore, correlation processing is also performed for timing detection. The processing unit 52 performs adaptive array signal processing on the baseband received signal 202 and outputs a composite signal 204 corresponding to the transmitted plurality of signals. The demodulator 54 demodulates the composite signal 204. Further, guard interval removal, FFT, deinterleaving, and decoding are also executed. The data combiner 56 combines the signals output from the demodulator 54 corresponding to the data separator 20 in FIG. The control unit 58 controls the timing of the receiving device 12 and the like.

  FIG. 10 shows a configuration of the first radio unit 50a. The first radio unit 50 a includes an LNA unit 60, a frequency conversion unit 62, an orthogonal detection unit 64, an AGC 66, an AD conversion unit 68, and a correlation unit 70.

  The LNA unit 60 amplifies the first radio reception signal 200a. The frequency conversion unit 62 performs frequency conversion between a radio frequency 5 GHz band and an intermediate frequency on a signal to be processed. The AGC 66 automatically controls the gain so that the amplitude of the signal is within the dynamic range of the AD converter 68. In the initial setting of the AGC 66, the STS of the received signal is used, and control is performed so that the strength of the STS approaches a predetermined value. The AD converter 68 converts an analog signal into a digital signal. The quadrature detection unit 64 performs quadrature detection on the intermediate frequency signal, generates a baseband digital signal, and outputs it as the first baseband reception signal 202a. In general, a baseband signal contains two components, an in-phase component and a quadrature component, so it should be indicated by two signal lines. Shown by signal line. The same applies to the following.

  In order to detect STS from first baseband received signal 202a, correlator 70 performs correlation processing using first baseband received signal 202a and previously stored STS, and outputs a correlation value. In the MIMO system, since the STS is set for each transmission antenna 14, the correlation unit 70 performs correlation processing on each of the plurality of STSs and outputs a plurality of correlation values. The correlation value is input to the control unit 58 in FIG. 9 through a signal line (not shown). The control unit 58 determines the reception start of the packet signal based on the plurality of correlation values input from the plurality of correlation units 70, and notifies the processing unit 52, the demodulation unit 54, and the like to that effect. In addition, in order to demodulate a plurality of signals, assignment of the processing unit 52 and the demodulation unit 54 to each signal is determined and notified to the processing unit 52, the demodulation unit 54, and the like.

  FIG. 11 shows the configuration of the correlation unit 70. The correlation unit 70 includes a conventional STS correlation unit 330, an STSa correlation unit 332, an STSb correlation unit 334, and a selection unit 336.

  The STSa correlation unit 332 stores in advance a signal sequence obtained by converting STSa into the time domain, and calculates a correlation value between the stored signal sequence and the received signal sequence (hereinafter referred to as “two-antenna correlation value”). . The STSb correlation unit 334 stores in advance a signal sequence obtained by converting the STSb into the time domain, and calculates a correlation value between the stored signal sequence and the received signal sequence (hereinafter referred to as “3-antenna correlation value”). .

  Conventional STS correlation section 330 stores in advance a signal sequence obtained by converting the above-described conventional STS into the time domain, or a signal sequence obtained by converting some subcarrier signals of conventional STS into the time domain. Further, the conventional STS correlation unit 330 calculates a correlation value between the stored signal sequence and the received signal (hereinafter referred to as “correlation value for one antenna”). Note that the signal sequence stored by the conventional STS correlator 330 may correspond to an STS corresponding to the MIMO system, for example, STS1 in FIG.

  The selection unit 336 compares the magnitudes of the two-antenna correlation value, the three-antenna correlation value, and the one-antenna correlation value, and selects the maximum correlation value. An estimation unit (not shown) determines the number of transmission antennas 14 transmitting data based on the selected correlation value. That is, if the correlation value for two antennas is large, the number of transmission antennas 14 is determined as “2”. If the correlation value for three antennas is large, the number of transmission antennas 14 is determined as “3”. If the value is large, the number of transmitting antennas 14 is determined to be “1”.

FIG. 12 shows the configuration of the first processing unit 52a. The first processing unit 52a includes a synthesis unit 80, a reception response vector calculation unit 82, and a reference signal storage unit 84. The synthesizer 80 includes a first multiplier 86a, a second multiplier 86b, an Nth multiplier 86n, and an adder 88, which are collectively referred to as a multiplier 86. The signal includes a first reception weight signal 206a, a second reception weight signal 206b, an Nth reception weight signal 206n, and a reference signal 208, which are collectively referred to as a reception weight signal 206.
The reference signal storage unit 84 stores LTS1 and the like. In addition, it is assumed that the LTS is also selected according to the STS selected by the conventional STS correlation unit 330.

  The reception response vector calculation unit 82 calculates a reception weight signal 206 from the baseband reception signal 202 and the reference signal 208 as reception response characteristics of the reception signal with respect to the transmission signal. The calculation method of the reception weight signal 206 may be arbitrary, but is executed based on correlation processing as shown below as an example. It is assumed that the reception weight signal 206 and the reference signal 208 are input not only from within the first processing unit 52a but also from the second processing unit 52b and the like through a signal line (not shown). The first baseband received signal 202a is denoted by x1 (t), the second baseband received signal 202b is denoted by x2 (t), the reference signal 208 corresponding to the first transmitting antenna 14a is S1 (t), and the second transmitting band is transmitted. If the reference signal 208 corresponding to the antenna 14b is expressed as S2 (t), x1 (t) and x2 (t) are expressed by the following equations.

ここで、雑音は無視する。第１の相関行列Ｒ１は、Ｅをアンサンブル平均として、次の式で示される。

Here, noise is ignored. The first correlation matrix R1 is expressed by the following equation, where E is an ensemble average.

参照信号２０８間の第２の相関行列Ｒ２も次の式のように計算される。

The second correlation matrix R2 between the reference signals 208 is also calculated as follows:

最終的に、第２の相関行列Ｒ２の逆行列と第１の相関行列Ｒ１を乗算し、次の式で示される受信ウエイト信号２０６が求められる。

Finally, the inverse matrix of the second correlation matrix R2 and the first correlation matrix R1 are multiplied to obtain a reception weight signal 206 represented by the following equation.

なお、受信ウエイト信号２０６は、ＬＭＳアルゴリズムなどの適応アルゴリズムによって導出されてもよい。

The reception weight signal 206 may be derived by an adaptive algorithm such as an LMS algorithm.

  Multiplier 86 weights baseband received signal 202 with received weight signal 206, and adder 88 adds the outputs of multiplier 86 and outputs synthesized signal 204.

  FIG. 13 is a flowchart illustrating a procedure of transmission processing in the transmission device 10. The monitoring unit 112 monitors whether there is a communication device compatible with the conventional system. If there is a communication device compatible with the conventional system (Y in S10), the selection unit 110 selects a mixed format (S12). On the other hand, if there is no communication device compatible with the conventional system (N in S10), the selection unit 110 selects a dedicated format (S14). Further, the selection unit 110 selects STSs and LTSs corresponding to the number of transmission antennas 14 from the storage unit 116 (S16), and arranges them in the selected format. The transmission device 10 transmits a packet signal (S18).

  FIG. 14 is another flowchart showing the procedure of the transmission process in the transmission apparatus 10. The transmission path characteristic acquisition unit 114 acquires the characteristics of the wireless transmission path, for example, the error rate. If the characteristics of the wireless transmission path are good (Y in S50), that is, if the error rate is lower than the threshold value, the selection unit 110 selects a continuous format (S52). On the other hand, if the characteristics of the wireless transmission path are not good (N in S50), the selection unit 110 selects a separation format (S54). Further, the selection unit 110 selects STSs and LTSs corresponding to the number of transmission antennas 14 from the storage unit 116 (S56), and arranges them in the selected format. The transmission device 10 transmits a packet signal (S58).

  According to the embodiment of the present invention, the preamble signal in the conventional system is added to the head part of the packet signal, so that the communication apparatus in the conventional system can receive the packet signal. In addition, compatibility with conventional systems can be maintained. In addition, it is possible to inform the communication device of the conventional system of the presence of the packet signal. Further, since signal transmission by the communication device of the conventional system can be prevented, the probability of signal collision can be improved. In addition, since the presence / absence of a preamble signal in the conventional system is switched, compatibility with the conventional system and improvement in packet utilization efficiency can be selected. Further, since the switching of the presence / absence of the preamble signal of the conventional system is executed based on the presence / absence of the terminal device of the conventional system, it does not affect other communication devices.

  Further, since the preamble signal pattern is changed according to the number of antennas, the communication quality can be improved. Even if the number of antennas is changed from a plurality to one, since a preamble signal corresponding to one of the plurality of antennas is used, switching to a conventional system is not necessary. Further, since the signal is inserted after the preamble signal of the conventional system, the content of the subsequent signal can be notified to the communication device of the conventional system. In addition, since the configuration of the preamble signal to be transmitted from a plurality of antennas is changed, the signal transmission quality and the packet utilization efficiency can be selected. Since the configuration of the preamble signal to be transmitted from the plurality of antennas is changed based on the quality of the wireless transmission path, a preamble configuration suitable for the quality of the wireless transmission path can be selected.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment of the present invention, a wireless LAN conforming to the IEEE 802.11a standard is illustrated as a conventional system. However, the present invention is not limited to this, and other communication systems may be used. Furthermore, although the communication system 100 has been described as a MIMO system, it may be another communication system. Moreover, it is not necessary to transmit a multicarrier signal. According to this modification, the present invention can be applied to various communication systems 100. That is, the conventional system and the communication system 100 only need to have some compatibility such as the same radio frequency.

It is a figure which shows the spectrum of the multicarrier signal which concerns on the Example of this invention. It is a figure which shows the structure of the packet format which concerns on the Example of this invention. It is a figure which shows the concept of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the transmitter of FIG. It is a figure which shows the structure of the control part of FIG. 6A to 6B are diagrams illustrating packet formats selected by the selection unit in FIG. FIGS. 7A to 7B are diagrams showing the format of the LTS selected by the selection unit of FIG. FIG. 6 is a diagram illustrating a relationship used when selecting by the selection unit in FIG. 5 and a relationship between the number of transmitting antennas and an STS pattern transmitted from the transmitting antenna. It is a figure which shows the structure of the receiver of FIG. It is a figure which shows the structure of the 1st radio | wireless part of FIG. It is a figure which shows the structure of the correlation part of FIG. It is a figure which shows the structure of the 1st process part of FIG. It is a flowchart which shows the procedure of the transmission process in the transmitter of FIG. It is another flowchart which shows the procedure of the transmission process in the transmitter of FIG.

Explanation of symbols

  10 transmitting apparatus, 12 receiving apparatus, 14 transmitting antenna, 16 receiving antenna, 20 data separating section, 22 modulating section, 24 radio section, 26 controlling section, 28 error correcting section, 30 interleave section, 32 preamble adding section, 34 IFFT section, 36 GI section, 38 orthogonal modulation section, 40 frequency conversion section, 42 amplification section, 100 communication system, 110 selection section, 112 monitoring section, 114 transmission path characteristic acquisition section, 116 storage section.

Claims (16)

A storage unit for storing a first known signal defined in the first wireless communication system and a second known signal defined in a second wireless communication system different from the first wireless communication system;
A selection unit that selects one of a packet format in which the second known signal is arranged in a head portion and a packet format in which the first known signal is further arranged in a preceding stage of the second known signal;
A transmitter for transmitting a signal in the packet format selected by the selector;
A transmission device comprising: A second wireless communication system to transmit a first known signal defined by the first wireless communication system to which an inverse fast Fourier transformed signal is to be transmitted and a signal to which an inverse fast Fourier transform is transmitted in parallel from a plurality of antennas. A storage unit for storing a second known signal defined in
A selection unit that selects one of a packet format in which the second known signal is arranged in a head portion and a packet format in which the first known signal is further arranged in a preceding stage of the second known signal;
A transmission unit that transmits a signal subjected to inverse fast Fourier transform in the packet format selected by the selection unit;
A transmission device comprising: The first known signal defined in the first wireless communication system to transmit signals using a plurality of carriers, and the same number of carriers as the number of carriers for transmitting signals in the first wireless communication system A storage unit for storing a second known signal defined in the second wireless communication system to transmit signals from a plurality of antennas in parallel while using
A selection unit that selects one of a packet format in which the second known signal is arranged in a head portion and a packet format in which the first known signal is further arranged in a preceding stage of the second known signal;
A transmitter for transmitting a signal in the packet format selected by the selector;
A transmission device comprising:   The second known signal stored in the storage unit is defined in a plurality of types according to the number of antennas to which signals should be transmitted in the second wireless communication system. The transmitting device according to 1.   When the selection unit selects a packet format in which the second known signal is arranged at the head portion, if the number of antennas to which the signal is to be transmitted becomes one, a plurality of types of second known signals 5. The transmission apparatus according to claim 4, wherein one of the signals is arranged.   The selection unit selects between the first known signal and the second known signal when selecting a packet format in which the first known signal is further arranged in a preceding stage of the second known signal. 6. The transmission apparatus according to claim 2, wherein information indicating that the second known signal is arranged is arranged. A monitoring unit that monitors the presence of a communication device compatible with the first wireless communication system without supporting the second wireless communication system;
The transmission device according to claim 2, wherein the selection unit selects a packet format based on a monitoring result in the monitoring unit. The second known signal stored in the storage unit includes a plurality of portions having different signal patterns,
The selection unit includes an arrangement of the second known signals that respectively transmits at least one of the plurality of portions from a plurality of antennas at the same timing, and at least one of the plurality of portions at different timings from the plurality of antennas. 8. The transmission apparatus according to claim 2, wherein an arrangement of the second known signals is selected so that one signal is transmitted. A deriving unit for deriving the characteristics of the wireless transmission path through which the signal is to be transmitted;
The transmission device according to claim 8, wherein the selection unit selects an arrangement of the second known signals based on the derived characteristics of the wireless transmission path.   The selection unit selects one of a packet format in which the second known signal is arranged at a plurality of antennas at the same timing and a packet format in which the second known signal is arranged at a plurality of antennas at different timings. The transmission device according to claim 2, wherein the transmission device is a transmission device. A transmitter for transmitting in parallel a signal defined by a predetermined packet format from a plurality of antennas;
A storage unit for storing a known signal to be placed at the beginning of the packet format;
When placing a known signal at the beginning of a packet format, an arrangement in which the known signal is transmitted from multiple antennas at the same timing, and an arrangement in which the known signal is transmitted from multiple antennas at different timings A selection section for selecting one of
A transmission device comprising: A transmitter for transmitting in parallel a signal defined by a predetermined packet format from a plurality of antennas;
A storage unit for storing a plurality of types of known signals to be arranged at the beginning of the packet format;
A first selection unit that selects a known signal from a plurality of types of known signals stored in the storage unit;
When the known signal selected by the first selection unit is arranged at the head portion of the packet format, the packet format in which the selected known signal is arranged at a plurality of antennas at the same timing, and the selected known signal A second selection unit that selects one of packet formats arranged at different timings on a plurality of antennas;
A transmission device comprising: A transmitter for transmitting in parallel a signal defined by a predetermined packet format from a plurality of antennas;
A storage unit for storing a plurality of types of known signals to be arranged at the beginning of the packet format;
When placing known signals at the beginning of the packet format, a packet format in which known signals of different patterns are placed on multiple antennas, and a packet in which known signals with different transmission timings are placed on multiple antennas A selection section for selecting one of the formats,
A transmission device comprising: A derivation unit for deriving the characteristics of the wireless transmission path to which the signal is to be transmitted;
The transmission device according to claim 11, wherein the selection unit selects an arrangement of known signals based on the derived characteristics of the wireless transmission path.   The first known signal defined in the first wireless communication system to transmit signals using a plurality of carriers, and the same number of carriers as the number of carriers for transmitting signals in the first wireless communication system A packet in which a second known signal defined in the second wireless communication system that should transmit signals in parallel from a plurality of antennas is defined, and the second known signal is arranged at the head portion A transmission method comprising: selecting a format and a packet format in which the first known signal is further arranged in a preceding stage of the second known signal, and transmitting the signal. An arrangement in which a known signal is transmitted from a plurality of antennas at the same timing with respect to a known signal to be arranged at the beginning of a packet format of a signal to be transmitted in parallel from a plurality of antennas, and a plurality of known signals A transmission method for selecting one of the arrangements such that the antennas are transmitted at different timings.

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