Wireless transmission device

Abstract

In wireless transmission systems using MIMO and TDD transmission methods, the peak of the correlation value obtained from the cross-correlation of preamble signals is amplified to detect the preamble's starting position with high accuracy. [Solution] The MIMO-OFDM modulation unit 10 of the transmitting wireless transmission device 1A applies MIMO-OFDM modulation to the data to be transmitted to generate transmission signals S1 and S2. The preamble signal insertion unit 11-1 inserts the Tx1 preamble signal at the beginning of the transmission signal S1 to form a subframe, and the preamble signal insertion unit 11-2 inserts the Tx2 preamble signal at the beginning of the transmission signal S2 to form a subframe. The Tx1 preamble signal is obtained by OFDM modulation of a signal in which a first series of ZC sequences and nulls are alternately arranged on the frequency axis. The Tx2 preamble signal is obtained by OFDM modulation of a signal in which a second series of ZC sequences and nulls are alternately arranged on the frequency axis.

Description

[Technical Field]

[0001] This invention relates to a wireless transmission device that uses MIMO (Multiple-Input Multiple-Output) transmission and TDD (Time Division Duplex) transmission methods. [Background technology]

[0002] Traditionally, wireless transmission equipment used for transmitting program materials has been called an FPU (Field Pickup Unit), and it has become an important device for transmitting broadcasted video or on-location footage to broadcasting stations. In particular, it is essential for transmitting video and audio from mobile broadcasting vehicles to broadcasting stations in live broadcasts of events such as ekiden (long-distance relay races) and marathons.

[0003] In recent years, methods have emerged that incorporate bidirectional transmission using the TDD method as a transmission method for FPUs (see, for example, Non-Patent Document 1).

[0004] Non-Patent Document 1 employs a TDD (Transmission-Driven Device) method in which subframes are transmitted alternately via an uplink (UL) that transmits subframes from a mobile station (MS) to a base station (BS) and a downlink (DL) that transmits subframes from the BS to the MS.

[0005] Figure 15 shows the configuration of a subframe using the TDD method, and illustrates the configurations of the UL subframe (UL subframe) and DL subframe (DL subframe) described in Non-Patent Document 1.

[0006] A UL subframe consists of multiple data sets, each containing a UL pilot and UL data, plus a UL preamble inserted at the beginning. A DL subframe consists of a DL preamble, DL pilot, and DL data.

[0007] In the TDD method, synchronization processing is required to detect the beginning of each UL subframe and DL subframe, and in Non-Patent Literature 1, a synchronization signal called a preamble signal is inserted at the beginning of each subframe.

[0008] Figure 16 is a diagram illustrating the preamble signal used in a conventional wireless transmission system, and shows the preamble signal described in Non-Patent Literature 1. Figure 17(1) is a diagram illustrating the Tx1 preamble signal (preamble signal for the first transmission system) in the conventional technology, and Figure 17(2) is a diagram illustrating the Tx2 preamble signal (preamble signal for the second transmission system) in the conventional technology.

[0009] As shown in Figure 16, this wireless transmission system is a MIMO transmission system with 2 transmits and M receive (2 × M, where M is an integer greater than or equal to 1) and a TDD system, and is configured with wireless transmission devices 101 and 102 that perform bidirectional transmission. Wireless transmission device 101 represents only the transmit side of the transmit and receive functions in the TDD system, and wireless transmission device 102 represents only the receive side of the transmit and receive functions in the TDD system.

[0010] Wireless transmission device 101 includes a transmitting antenna for the first transmission system (Tx1) and a transmitting antenna for the second transmission system (Tx2), and wireless transmission device 102 includes a receiving antenna for the first receiving system (Rx1), ... and a receiving antenna for the M receiving system (RxM). M is the number of receiving antennas.

[0011] In the DL from wireless transmission device 101 to wireless transmission device 102, the preamble signal transmitted from the first transmission system of wireless transmission device 101 (Tx1 preamble signal) and the preamble signal transmitted from the second transmission system (Tx2 preamble signal) are divided into two in the frequency domain.

[0012] Specifically, as the Tx1 preamble signal, only the first half of the OFDM subcarriers is used on the frequency axis of the original OFDM signal. As the Tx2 preamble signal, only the second half of the OFDM subcarriers is used.

[0013] Referring to FIGS. 17(1) and (2), on the frequency axis of the original OFDM signal, the number of subcarriers is N

[0015] (even), and the subcarrier numbers are 0, 1, 2, ···, N C -1.

[0014] As shown in FIG. 17(1), the Tx1 preamble signal in the prior art is arranged in the first half (left half) region on the frequency axis of the OFDM signal, and consists of the subcarriers between subcarrier numbers 0 and N C / 2 - 1.

[0015] At the positions of the even subcarrier numbers 0, 2, ···, N C / 2 - 2, the conventional signal is arranged, and at the positions of the odd subcarrier numbers 1, 3, ···, N C / 2 - 1 between them, null signals are arranged. Also, null signals are arranged in the second half (right half) region on the frequency axis of the OFDM signal.

[0016] Also, as shown in FIG. 17(2), the Tx2 preamble signal in the prior art is arranged in the second half region on the frequency axis of the OFDM signal, and consists of the subcarriers between subcarrier numbers N C / x2 and N C - 1.

[0017] At the positions of the even subcarrier numbers N C / 2, N C / 2 + 2, ···, N C - 2, the conventional signal is arranged, and at the positions of the odd subcarrier numbers N C / 2 + 1, N C / 2 + 3, ···, N C - 1 between them, null signals are arranged. Also, null signals are arranged in the first half region on the frequency axis of the OFDM signal.

[0018] Referring to FIG. 16, the wireless transmission device 102 receives the signal Tx1 transmitted from the first transmission system of the wireless transmission device 101 and the signal Tx2 transmitted from the second transmission system in a combined (mixed) state in the MIMO transmission path.

[0019] However, since the Tx1 preamble signal and the Tx2 preamble signal are orthogonal on the frequency axis, the wireless transmission device 102 can extract each of the Tx1 preamble signal and the Tx2 preamble signal from the received signal, and for each of the signals Tx1 and Tx2 received in the combined state, the synchronization timing can be detected with high accuracy.

[0020] The wireless transmission device 102 performs synchronization processing with the same configuration as FIG. 6 described later to detect the preamble start position of the Tx1 preamble signal, which is the start position of the subframe in the signal Tx1. Similarly, the wireless transmission device 102 detects the preamble start position of the Tx2 preamble signal, which is the start position of the subframe in the signal Tx2.

[0021] [[ID=-- -- --]] Specifically, the wireless transmission device 102 calculates the cross-correlation between the received signal and the Tx1 preamble signal in the time domain obtained by performing OFDM modulation (IFFT) on the Tx1 preamble signal in the frequency domain, and detects the peak thereof. Also, the wireless transmission device 102 calculates the cross-correlation between the received signal and the Tx2 preamble signal in the time domain obtained by performing OFDM modulation on the Tx2 preamble signal in the frequency domain, and detects the peak thereof. Then, the wireless transmission device 102 detects the preamble start position of the received signal based on these peaks.

[0022] FIG. 18 is a diagram for explaining that in the prior art, the preamble signal in the time domain is a signal formed by repeating the same waveform twice and is combined in the MIMO transmission path.

[0023] As shown in Figure 17, the frequency-domain Tx1 and Tx2 preamble signals are placed only on even-numbered subcarriers on the frequency axis of the OFDM signal. In this case, the time-domain Tx1 and Tx2 preamble signals are composed of the same waveform repeated twice, as shown in Figure 18. The time-domain Tx1 and Tx2 preamble signals are then combined in the MIMO transmission path, and the combined time-domain preamble signal is also composed of the same waveform repeated twice.

[0024] Therefore, in the synchronization process performed by the receiving wireless transmission device 102, the Tx1 and Tx2 preamble signals in the pre-set time domain used as references when calculating the cross-correlation only need to be one of the two identical waveforms. In other words, the number of samples to be processed in the synchronization process can be reduced by half.

[0025] Furthermore, since the synthesized preamble signal included in the received signal received by the receiving wireless transmission device 102 is a signal composed of the same waveform repeated twice, the noise power can be estimated by comparing the waveforms repeated twice, as shown in Patent Document 1. [Prior art documents] [Patent Documents]

[0026] [Patent Document 1] Japanese Patent Publication No. 2019-062385 [Non-patent literature]

[0027] [Non-Patent Document 1] "Portable Quasi-Microwave OFDM Digital Wireless Transmission System for Transmitting Ultra-High Definition Television Broadcast Program Materials," ARIB STD-B75 1.1, Association of Radio Industries and Businesses (ARIB) [Overview of the project] [Problems that the invention aims to solve]

[0028] However, the conventional Tx1 and Tx2 preamble signals are located in only half the frequency range of the OFDM signal, which leads to a problem of reduced effective transmission power.

[0029] When the effective transmit power decreases, the peak value obtained by calculating the cross-correlation of the preamble signals also decreases, reducing the accuracy of detecting the preamble's starting position. When the accuracy of detecting the preamble's starting position decreases, the likelihood of synchronization timing shifts increases, making it impossible to perform MIMO-OFDM demodulation processing with high accuracy, resulting in insufficient data recovery.

[0030] Therefore, the present invention has been made to solve the above-mentioned problems, and its objective is to provide a wireless transmission device that accurately detects the preamble leading position in a wireless transmission system using the MIMO transmission method and the TDD method by amplifying the peak of the correlation value obtained by the cross-correlation of preamble signals when performing subframe synchronization processing by the TDD method. [Means for solving the problem]

[0031] To solve the above problem, the wireless transmission device of claim 1 is a wireless transmission device in a wireless transmission system that performs wireless transmission using a MIMO transmission method and a TDD (Time Division Duplex) method, wherein the wireless transmission device functions as a transmitting device that constitutes and transmits subframes of a first transmission system (Tx1) and subframes of a second transmission system (Tx2) using the TDD method, and the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are time-domain Tx1 preamble signal and Tx2 preamble signal, respectively. A storage unit that stores data as such; a MIMO-OFDM modulation unit that applies MIMO-OFDM modulation to the data to be transmitted to generate the transmission signal S1 for the first transmission system and the transmission signal S2 for the second transmission system; a first preamble signal insertion unit that reads the time-domain Tx1 preamble signal from the storage unit and inserts the time-domain Tx1 preamble signal into the beginning of the transmission signal S1 generated by the MIMO-OFDM modulation unit to constitute a subframe of the first transmission system; and a storage unit that reads the time-domain Tx2 preamble signal from the storage unit. The system includes a second preamble signal insertion unit that reads out the ampble signal and inserts the time-domain Tx2 preamble signal at the beginning of the transmission signal S2 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the second transmission system, wherein the time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the frequency-domain Tx1 preamble signal is a signal in which the subcarrier on the frequency axis alternates between a ZC (Zadoff-Chu) sequence for Tx1 and a null. The present invention is characterized in that the time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, the frequency-domain Tx2 preamble signal is a signal in which a ZC sequence for Tx2 and nulls are alternately arranged on the frequency axis as subcarriers, and the subcarriers of the ZC sequence for Tx1 in the frequency-domain Tx1 preamble signal and the subcarriers of the ZC sequence for Tx2 in the frequency-domain Tx2 preamble signal are arranged at the same position on the frequency axis.

[0032] Furthermore, the wireless transmission device according to claim 2 is a wireless transmission device in a wireless transmission system that performs wireless transmission using a MIMO transmission method and a TDD (Time Division Duplex) method, and when the wireless transmission device functions as a transmitting device that constitutes and transmits subframes of a first transmission system (Tx1) and subframes of a second transmission system (Tx2) using the TDD method, the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are stored as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively. A storage unit; a MIMO-OFDM modulation unit that applies MIMO-OFDM modulation to the data to be transmitted to generate the transmission signal S1 for the first transmission system and the transmission signal S2 for the second transmission system; a first preamble signal insertion unit that reads the time-domain Tx1 preamble signal from the storage unit and inserts the time-domain Tx1 preamble signal into the beginning of the transmission signal S1 generated by the MIMO-OFDM modulation unit to constitute a subframe of the first transmission system; and a time-domain Tx2 preamble signal from the storage unit. The system includes a second preamble signal insertion unit which reads out a number and inserts the time-domain Tx2 preamble signal into the beginning of the transmission signal S2 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the second transmission system, wherein the time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the frequency-domain Tx1 preamble signal is a signal in which a ZC (Zadoff-Chu) sequence for Tx1 and nulls are alternately arranged on the subcarrier on the frequency axis. The Tx2 preamble signal in the time domain is a signal obtained by OFDM modulation of the Tx2 preamble signal in the frequency domain, the Tx2 preamble signal in the frequency domain is a signal in which nulls and ZC sequences for Tx2 are alternately arranged on the frequency axis as subcarriers, and the subcarriers of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarriers of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged orthogonally on the frequency axis.

[0033] Furthermore, the wireless transmission device of claim 3 is a wireless transmission device in a wireless transmission system that performs wireless transmission using the MIMO transmission method and the TDD (Time Division Duplex) method, and the wireless transmission device functions as a receiving device that receives a signal synthesized in the transmission path, detects the preamble start position of the subframe from the received signal, and restores the data to be transmitted, for each of one or more receiving systems, from the transmitting wireless transmission device, the subframe of the first transmission system (Tx1) and the subframe of the second transmission system (Tx2) using the TDD method, and detects the preamble start position of the subframe from the received signal. A storage unit stores the preamble signal used for the first transmission system and the preamble signal used for the second transmission system as a time-domain Tx1 preamble signal and a time-domain Tx2 preamble signal, respectively. The storage unit reads the time-domain Tx1 preamble signal and the time-domain Tx2 preamble signal from the storage unit, and calculates the cross-correlation value between the received signal corresponding to each of the one or more receiving systems and the time-domain Tx1 preamble signal, thereby determining the Tx1 peak position, and the received signal and the time A receiving processing unit having a preamble starting position detection unit that calculates the cross-correlation value between the region and the Tx2 preamble signal to determine the Tx2 peak position, and detects the preamble starting position of the subframe in the received signal based on the Tx1 peak position and the Tx2 peak position, and MIMO-OFDM demodulation for the received signals of all receiving systems based on the preamble starting position of all receiving systems detected by the preamble starting position detection unit of the receiving processing unit, to restore the original data to be transmitted. The system comprises an FDM demodulation unit, wherein the time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, the frequency-domain Tx1 preamble signal is a signal in which ZC (Zadoff-Chu) sequences for Tx1 and nulls are alternately arranged on the subcarrier on the frequency axis, the time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, and the frequency-domain Tx2 preamble signal is a signal in which the subcarrier on the frequency axis is,The signal is characterized by having alternating ZC sequences and nulls for Tx2, wherein the subcarriers of the ZC sequence for Tx1 in the frequency domain Tx1 preamble signal and the subcarriers of the ZC sequence for Tx2 in the frequency domain Tx2 preamble signal are located at the same position on the frequency axis.

[0034] Furthermore, the wireless transmission device according to claim 4 is a wireless transmission device in a wireless transmission system that performs wireless transmission using MIMO transmission and TDD (Time Division Duplex) transmission, and the wireless transmission device functions as a receiving device that receives a signal synthesized in the transmission path, detects the preamble start position of the subframe from the received signal, and restores the data to be transmitted, for each of one or more receiving systems, from the transmitting wireless transmission device, the first transmitting system A storage unit stores the preamble signal used for the first and the preamble signal used for the second transmission system as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively. The storage unit reads the time-domain Tx1 preamble signal and the time-domain Tx2 preamble signal from the storage unit and calculates the cross-correlation value between the received signal corresponding to each of the one or more receiving systems and the time-domain Tx1 preamble signal to determine the Tx1 peak position, as well as the received signal and the time-domain Tx2 preamble signal A receiving processing unit having a preamble leading position detection unit that calculates the cross-correlation value between the numbers to determine the Tx2 peak position and, based on the Tx1 peak position and the Tx2 peak position, detects the leading position of the preamble of the subframe in the received signal; and a MIMO-OFDM demodulation unit that performs MIMO-OFDM demodulation on the received signals of all receiving systems based on the leading positions of the preamble of all receiving systems detected by the preamble leading position detection unit of the receiving processing unit, and restores the original data to be transmitted, wherein the time domain T The x1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, wherein the frequency-domain Tx1 preamble signal is a signal in which the subcarriers on the frequency axis alternate between a ZC (Zadoff-Chu) sequence for Tx1 and nulls, and the time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, wherein the frequency-domain Tx2 preamble signal is a signal in which the subcarriers on the frequency axis alternate between a ZC sequence for Tx2 and nulls.The subcarrier of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarrier of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged orthogonally on the frequency axis.

[0035] Furthermore, the wireless transmission device of claim 5 is the wireless transmission device of claim 4, wherein the storage unit further stores in advance the ZC sequence subcarriers for Tx1 arranged in the frequency domain Tx1 preamble signal and the ZC sequence subcarriers for Tx2 arranged in the frequency domain Tx2 preamble signal, the receiving processing unit further has a channel estimation unit for each of the one or more receiving systems, the channel estimation unit reads out the ZC sequence subcarriers for Tx1 and the ZC sequence subcarriers for Tx2 from the storage unit, and the preamble detected by the preamble leading position detection unit The method is characterized by extracting a time-domain preamble signal from the received signal corresponding to the receiving system, using the starting position as a reference, generating a frequency-domain preamble signal by applying OFDM demodulation to the time-domain preamble signal, estimating the channel response between the transmitting antenna of the first transmitting system and the receiving antenna of the receiving system based on the ZC sequence subcarrier for Tx1 and the frequency-domain preamble signal, and estimating the channel response between the transmitting antenna of the second transmitting system and the receiving antenna of the receiving system based on the ZC sequence subcarrier for Tx2 and the frequency-domain preamble signal. [Effects of the Invention]

[0036] As described above, according to the present invention, in a wireless transmission system using the MIMO transmission method and the TDD method, when performing subframe synchronization processing by the TDD method, the preamble starting position can be detected with high accuracy by amplifying the peak of the correlation value obtained by the cross-correlation of the preamble signals. Furthermore, if the subcarriers of the ZC sequence are located at the same position in Tx1 and Tx2, the preamble signal can be used to estimate the noise power. Furthermore, if the subcarriers of the ZC sequence are located at orthogonal positions in Tx1 and Tx2, the preamble signal can be used to estimate the channel. [Brief explanation of the drawing]

[0037] [Figure 1] This figure shows an example configuration of a wireless transmission system consisting of the wireless transmission devices of Examples 1 and 2. [Figure 2] (1) A diagram illustrating the preamble signal of the prior art. (2) A diagram illustrating the preamble signals of Examples 1 and 2. [Figure 3] (1) This figure illustrates the preamble signal in Example 1, in which the ZC series subcarriers are arranged identically across the transmitting systems. (2) This figure illustrates the preamble signal in Example 2, in which the ZC series subcarriers are arranged orthogonally across the transmitting systems. [Figure 4] This is a block diagram showing an example configuration of the wireless transmission device on the transmitting side in Examples 1 and 2. [Figure 5] This is a block diagram showing an example configuration of the receiving wireless transmission device in Example 1. [Figure 6] This is a block diagram showing an example configuration of the preamble starting position detection unit. [Figure 7] This is a block diagram showing an example configuration of the noise power estimation unit. [Figure 8] This is a block diagram showing an example configuration of the receiving wireless transmission device in Example 2. [Figure 9] This is a block diagram showing an example configuration of the channel estimation unit. [Figure 10](1) This figure shows the specifications of the computer simulation. (2) This figure shows the channel being evaluated by the computer simulation. [Figure 11] (1) This figure illustrates the computer simulation results for calculating the Tx1 peak in Example 1. (2) This figure illustrates the computer simulation results for calculating the Tx2 peak in Example 1. [Figure 12] This figure illustrates the computer simulation results of noise power N1 in Example 1. [Figure 13] (1) This figure illustrates the computer simulation results for calculating the Tx1 peak in Example 2. (2) This figure illustrates the computer simulation results for calculating the Tx2 peak in Example 2. [Figure 14] (1) This figure illustrates the computer simulation results of the channel response of the Tx1→Rx transmission path in Example 2. (2) This figure illustrates the computer simulation results of the channel response of the Tx2→Rx transmission path in Example 2. [Figure 15] This diagram shows the subframe configuration using the TDD method. [Figure 16] This diagram illustrates the preamble signal used in conventional wireless transmission systems. [Figure 17] (1) This diagram illustrates the Tx1 preamble signal in the conventional technology. (2) This diagram illustrates the Tx2 preamble signal in the conventional technology. [Figure 18] This diagram illustrates that, in conventional technology, the time-domain preamble signal is a signal composed of the same waveform repeated twice, and that it is synthesized in a MIMO transmission path. [Modes for carrying out the invention]

[0038] The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. In a wireless transmission system using a 2xM MIMO transmission method and a TDD method, the present invention uses the entire frequency band of the OFDM signal while maintaining the ability to calculate cross-correlation and detect peaks for the Tx1 preamble signal and Tx2 preamble signal used for subframe synchronization processing by the TDD method.

[0039] Conventional techniques use half of the subcarriers in the frequency band of the OFDM signal as the preamble signal, whereas the present invention uses twice that amount of subcarriers. As a result, the peak of the correlation value obtained from the cross-correlation of the preamble signals can be expanded, and the position of the preamble start can be detected with high accuracy.

[0040] Below, we will describe two examples, 1 and 2, that use the ZC sequence as the preamble signal and are adapted to different use cases based on the arrangement of subcarriers in the OFDM signal. The preamble signal in Example 1 is a signal with the same arrangement, using only even-numbered subcarrier numbers in both the first and second transmission systems, similar to Non-Patent Document 1 mentioned above (see Figure 3(1) described later). Therefore, the time-domain preamble signal obtained by applying OFDM modulation to the frequency-domain preamble signal is a signal in which the same waveform is repeated twice, and this property can be used to estimate noise power from the received signal.

[0041] The preamble signal in Example 2 is an orthogonal arrangement signal in which only even subcarrier numbers are used in the first transmission system and only odd subcarrier numbers are used in the second transmission system (see Figure 3(2) described later). Furthermore, since the amplitude of the ZC sequence used in the preamble signal is 1, the preamble signal is used as a pilot symbol on the subcarrier, and the channel response is estimated from the preamble signal included in the received signal.

[0042] Figure 1 shows an example configuration of a wireless transmission system consisting of the wireless transmission devices of Examples 1 and 2. Similar to the wireless transmission system shown in Figure 16, this wireless transmission system uses a MIMO transmission method and a TDD method with 2 transmission and M reception (2 × M, where M is an integer of 1 or more), and is configured with wireless transmission device 1 and wireless transmission device 2 that perform bidirectional transmission via MIMO transmission path 3.

[0043] The wireless transmission device 1 has the functions of both a transmitter and a receiver in the TDD system. Here, we will describe the functions of the transmitter, which includes the transmitting antenna 4-1 of the first transmission system (Tx1) and the transmitting antenna 4-2 of the second transmission system (Tx2).

[0044] The wireless transmission device 2 has the functions of both the transmitter and receiver in the TDD system. Here, we will describe the functions of the receiver, which has receiving antennas 5-1, ... for the first receiving system (Rx1) and receiving antennas 5-M for the M receiving system (RxM). M is the number of receiving antennas.

[0045] Figure 2(1) is a diagram illustrating the preamble signal of the prior art, and Figure 2(2) is a diagram illustrating the preamble signals of Examples 1 and 2.

[0046] In conventional technology, as shown in Figure 2(1), the preamble signal uses only the first half of the entire bandwidth of the OFDM signal as the Tx1 preamble signal, and only the second half as the Tx2 preamble signal.

[0047] In contrast, the preamble signals in Examples 1 and 2, as shown in Figure 2(2), utilize the entire bandwidth in the frequency axis of the OFDM signal as the Tx1 preamble signal. Similarly, the Tx2 preamble signal also utilizes the entire bandwidth.

[0048] (Preamble signal using the ZC sequence) Next, we will describe the preamble signals of Examples 1 and 2 shown in Figure 2(2). In Examples 1 and 2, a preamble signal using a ZC sequence is used.

[0049] Figure 3(1) illustrates the preamble signal in Example 1, where the ZC series subcarriers are arranged identically across the transmitting systems, and Figure 3(2) illustrates the preamble signal in Example 2, where the ZC series subcarriers are arranged orthogonally across the transmitting systems.

[0050] Referring to Figures 3(1) and (2), the number of subcarriers in the frequency axis of the OFDM signal is N. C Let (even numbers) be used, and the subcarrier numbers be 0, 1, 2, ..., N C Set it to -1.

[0051] As shown in Figure 3(1), the Tx1 preamble signal and the Tx2 preamble signal of Example 1 are composed of a Zadoff-Chu sequence (ZC sequence) signal and a null signal, which will be described later, and are located at the same subcarrier position (in the same arrangement).

[0052] The Tx1 preamble signal is located across the entire frequency axis of the OFDM signal. Even subcarrier numbers 0, 2, ..., N C At position -2, the ZC sequence signal for Tx1 (described later) is placed, with odd subcarrier numbers 1, 3, ..., N in between. C A null signal is placed at the -1 position.

[0053] Similarly, the Tx2 preamble signal is also placed across the entire frequency domain of the OFDM signal. Even subcarrier numbers 0, 2, ..., N C At position -2, the ZC sequence signal for Tx2 (described later) is placed, with odd subcarrier numbers 1, 3, ..., N in between. C A null signal is placed at the -1 position.

[0054] In other words, the Tx1 preamble signal in Example 1 is a signal in which ZC-sequence subcarriers and nulls for Tx1 are alternately arranged on the frequency axis, and the Tx2 preamble signal is a signal in which ZC-sequence subcarriers and nulls for Tx2 are alternately arranged. Furthermore, the ZC-sequence subcarriers in the Tx1 preamble signal and the ZC-sequence subcarriers in the Tx2 preamble signal are located at the same position on the frequency axis.

[0055] On the other hand, as shown in Figure 3(2), the Tx1 preamble signal and Tx2 preamble signal of Example 2 are composed of a ZC sequence signal and a null signal that are arranged (orthogonally) at different subcarrier positions on the frequency axis of the OFDM signal.

[0056] The Tx1 preamble signal is located across the entire frequency axis of the OFDM signal. Even subcarrier numbers 0, 2, ..., N C At position -2, the ZC sequence signal for Tx1 is placed, with odd subcarrier numbers 1, 3, ..., N in between. C A null signal is placed at the -1 position.

[0057] Similarly, the Tx2 preamble signal is also placed across the entire frequency domain of the OFDM signal. Even subcarrier numbers 0, 2, ..., N C A null signal is placed at position -2, with odd subcarrier numbers 1, 3, ..., N in between. C At position -1, the ZC sequence signals for Tx2 are placed.

[0058] In other words, the Tx1 preamble signal in Example 2 is a signal in which ZC-sequence subcarriers for Tx1 and nulls are alternately arranged on the frequency axis, and the Tx2 preamble signal is a signal in which nulls and ZC-sequence subcarriers for Tx2 are alternately arranged on the frequency axis. Furthermore, the ZC-sequence subcarriers in the Tx1 preamble signal and the ZC-sequence subcarriers in the Tx2 preamble signal are located at orthogonal positions, which are different positions on the frequency axis.

[0059] (ZC series) Next, we will explain the ZC series. The ZC series ZC(n) is expressed by the following formula. [Equation 1] TIFF2026046128000002.tif24170

[0060] N ZC n indicates the sequence length, and r indicates the root of the ZC sequence. Root r and sequence length N ZC These are integers that are relatively prime to each other. n is the sequence index (n=0 to N). ZC -1) is shown. Sequence length N ZC This is the number of subcarriers N in an OFDM signal. C It will be half of that.

[0061] In Examples 1 and 2, two types of ZC sequences are prepared by changing the root r of the ZC sequence, and ZC1(n) is used for Tx1, and ZC2(n) is used for Tx2. As shown in Figures 3(1) and (2), the Tx1 preamble signal is set to the Tx1 ZC sequence ZC1(n), and the Tx2 preamble signal is set to the Tx2 ZC sequence ZC2(n).

[0062] In Example 1, referring to Figure 3(1), the carrier number 0 of the Tx1 preamble signal is set to ZC series ZC1(0), and the carrier number Nc-2 of the Tx1 preamble signal is set to ZC series ZC1(N ZC -1) is set. Also, the carrier number 0 of the Tx2 preamble signal is set to ZC series ZC2(0), and the carrier number Nc-2 of the Tx2 preamble signal is set to ZC series ZC2(N ZC -1) is set.

[0063] In Example 2, referring to Figure 3(2), the carrier number 0 of the Tx1 preamble signal is set to ZC series ZC1(0), and the carrier number Nc-2 of the Tx1 preamble signal is set to ZC series ZC1(N ZC-1) is set. Also, the carrier number 1 of the Tx2 preamble signal is set to ZC series ZC2(0), and the carrier number Nc-1 of the Tx2 preamble signal is set to ZC series ZC2(N ZC -1) is set.

[0064] Generally, ZC sequences have a high cross-correlation value with their own sequences, meaning they exhibit excellent autocorrelation characteristics, and low cross-correlation values ​​between different sequences. By utilizing this property, the receiving wireless transmission device 2 can detect the peak positions of the Tx1 preamble signal and the Tx2 preamble signal from the received signal.

[0065] Thus, by using the Tx1 preamble signal and Tx2 preamble signal of Example 1 shown in Figure 3(1), the receiving wireless transmission device 2 can expand the peak of the correlation value obtained by cross-correlation while maintaining its ability to detect the respective peak positions.

[0066] Furthermore, similar to conventional technology, the time-domain preamble signal received by the receiving wireless transmission device 2 (a signal obtained by combining the time-domain Tx1 preamble signal and the Tx2 preamble signal) is a signal with the same waveform repeated twice. Therefore, by using this double-repeated signal, the noise power can be estimated. Details will be described later.

[0067] Furthermore, by using the Tx1 preamble signal and Tx2 preamble signal of Example 2 shown in Figure 3(2), the receiving wireless transmission device 2 can expand the peak of the correlation value obtained by cross-correlation while maintaining its ability to detect the respective peak positions.

[0068] Furthermore, since the ZC sequence has an amplitude of 1, the Tx1 and Tx2 preamble signals can be used as pilot signals. In other words, the channel response can be estimated using the Tx1 and Tx2 preamble signals. Details will be described later.

[0069] [Transmitter-side wireless transmission device 1 / Examples 1, 2] Next, we will describe the transmitting wireless transmission device 1 in Examples 1 and 2 shown in Figure 1. Figure 4 is a block diagram showing an example configuration of the transmitting wireless transmission device 1 in Examples 1 and 2.

[0070] The transmitting wireless transmission device 1A of this Embodiment 1 includes a MIMO-OFDM modulation unit 10, preamble signal insertion units 11-1, 11-2, a storage unit 12, and transmitting antennas 4-1, 4-2. The transmitting wireless transmission device 1B of Embodiment 2 also has the same components as in Embodiment 1. Note that Figure 4 shows only the components related to the present invention, and components unrelated to the invention have been omitted.

[0071] The MIMO-OFDM modulation unit 10 receives the data to be transmitted, and applies MIMO-OFDM modulation such as encoding, interleaving, serial / parallel conversion, carrier modulation, and OFDM modulation to the data to be transmitted, generating a time-domain transmission signal S1 for the first transmission system Tx1 and a time-domain transmission signal S2 for the second transmission system Tx2. The MIMO-OFDM modulation unit 10 then outputs the transmission signal S1 to the preamble signal insertion unit 11-1 and the transmission signal S2 to the preamble signal insertion unit 11-2.

[0072] The preamble signal insertion unit 11-1 reads the time-domain Tx1 preamble signal from the storage unit 12 and receives the transmit signal S1 from the MIMO-OFDM modulation unit 10. The preamble signal insertion unit 11-1 then constructs a subframe by inserting the time-domain Tx1 preamble signal at the beginning of the transmit signal S1.

[0073] The subframe formed by the preamble signal insertion unit 11-1 is transmitted from the transmitting antenna 4-1 as the modulated wave of Tx1.

[0074] The preamble signal insertion unit 11-2 reads the time-domain Tx2 preamble signal from the storage unit 12 and receives the transmit signal S2 from the MIMO-OFDM modulation unit 10. The preamble signal insertion unit 11-2 then constructs a subframe by inserting the time-domain Tx2 preamble signal at the beginning of the transmit signal S2.

[0075] The subframe formed by the preamble signal insertion unit 11-2 is transmitted from the transmitting antenna 4-2 as a modulated wave of Tx2.

[0076] The memory unit 12 stores the Tx1 preamble signal in the time domain used for the first transmission system and the Tx2 preamble signal in the time domain used for the second transmission system.

[0077] Specifically, the memory unit 12 of Embodiment 1 stores the time-domain Tx1 preamble signal and Tx2 preamble signal obtained by OFDM modulation of the frequency domain Tx1 preamble signal and Tx2 preamble signal shown in Figure 3(1). As mentioned above, the frequency domain Tx1 preamble signal and Tx2 preamble signal are signals in which ZC sequence signals are placed at the same subcarrier position.

[0078] Furthermore, the memory unit 12 of Embodiment 2 stores the time-domain Tx1 preamble signal and Tx2 preamble signal obtained by OFDM modulation of the frequency domain Tx1 preamble signal and Tx2 preamble signal shown in Figure 3(2). As described above, the frequency domain Tx1 preamble signal and Tx2 preamble signal are signals in which ZC sequence signals are placed at orthogonal subcarrier positions.

[0079] As described above, according to the transmitting wireless transmission devices 1A and 1B of Examples 1 and 2, the MIMO-OFDM modulation unit 10 applies MIMO-OFDM modulation to the data to be transmitted and generates a time-domain transmission signal S1 for Tx1 and a time-domain transmission signal S2 for Tx2.

[0080] The preamble signal insertion unit 11-1 constructs a subframe by inserting a time-domain Tx1 preamble signal at the beginning of the transmitted signal S1. This subframe is transmitted from the transmitting antenna 4-1 as a modulated wave of Tx1.

[0081] The preamble signal insertion unit 11-2 constructs a subframe by inserting a time-domain Tx2 preamble signal at the beginning of the transmitted signal S2. This subframe is transmitted from the transmitting antenna 4-2 as a modulated Tx2 wave.

[0082] Then, the modulated waves Tx1 and Tx2 transmitted from the transmitting wireless transmission devices 1A and 1B of Examples 1 and 2 are combined in the MIMO transmission path 3, and the receiving wireless transmission devices 2A and 2B of Examples 1 and 2, described later, receive the combined modulated wave. Since the Tx1 preamble signal and the Tx2 preamble signal use different ZC sequences, the respective peak positions of the Tx1 preamble signal and the Tx2 preamble signal can be detected from the received signal of the combined modulated wave.

[0083] Then, through the synchronization processing of subframes by wireless transmission devices 2A and 2B, the cross-correlation value between the received signal and the time-domain Tx1 preamble signal and Tx2 preamble signal is calculated and a peak is detected, thereby detecting the preamble start position. MIMO-OFDM demodulation is then applied to the received signal to restore the original data that was to be transmitted.

[0084] By using such Tx1 and Tx2 preamble signals, in both arrangements shown in Figures 3(1) and 3(2), the ability to detect peak positions in each of the Tx1 and Tx2 preamble signals is maintained, similar to the case of Non-Patent Document 1 mentioned above, while the effect of expanding the peaks detected by cross-correlation calculation is obtained compared to Non-Patent Document 1.

[0085] In other words, in wireless transmission systems using MIMO and TDD transmission methods, a preamble signal spanning the entire bandwidth of the OFDM signal is used. As a result, when the receiving wireless transmission devices 2A and 2B perform subframe synchronization processing using the TDD method, the peak of the correlation value obtained from the cross-correlation of the preamble signals can be amplified, and the preamble starting position can be detected with high accuracy.

[0086] [Receiver's Wireless Transmission Device 2 / Example 1] Next, we will describe the receiving wireless transmission device 2 of Example 1 shown in Figure 1. Figure 5 is a block diagram showing an example configuration of the receiving wireless transmission device 2 in Example 1.

[0087] The receiving wireless transmission device 2A of this embodiment 1 includes receiving antennas 5-1, ..., 5-M, receiving processing units 20-1, ..., 20-M, a storage unit 21, and a MIMO-OFDM demodulation unit 22. The receiving processing unit 20-1 includes a preamble starting position detection unit 30-1 and a noise power estimation unit 40-1, and the receiving processing units 20-2, ..., 20-M also include the same components as the preamble starting position detection unit 30-1 and the same components as the noise power estimation unit 40-1. Note that Figure 5 shows only the components related to the present invention, and components unrelated to the invention are omitted.

[0088] In the first embodiment shown in Figure 4, the modulated waves transmitted from the transmitting antennas 4-1 and 4-2 of the transmitting wireless transmission device 1A are combined in the MIMO transmission path 3, and the combined modulated waves are received by the receiving antennas 5-1, ..., 5-M of the receiving wireless transmission device 2A.

[0089] The preamble starting position detection unit 30-1 of the receiving processing unit 20-1 receives the signal of the synthesized modulated wave as a received signal R1 via the receiving antenna 5-1. The preamble starting position detection unit 30-1 also reads out the time-domain Tx1 preamble signal (hereinafter simply referred to as "Tx1 preamble signal") and the time-domain Tx2 preamble signal (hereinafter simply referred to as "Tx2 preamble signal") from the storage unit 21.

[0090] The preamble leading position detection unit 30-1 detects the preamble leading position P1 of the received signal R1 based on the received signal R1, the Tx1 preamble signal, and the Tx2 preamble signal, and outputs the preamble leading position P1 to the noise power estimation unit 40-1 and the MIMO-OFDM demodulation unit 22.

[0091] Figure 6 is a block diagram showing an example configuration of the preamble starting position detection unit 30-1. This preamble starting position detection unit 30-1 includes a peak calculation unit 31 and a peak detection unit 32. The peak calculation unit 31 includes cross-correlation units 33-1 and 33-2.

[0092] The cross-correlation unit 33-1 of the peak calculation unit 31 receives the received signal R1 and reads out the Tx1 preamble signal from the storage unit 21.

[0093] The cross-correlation unit 33-1 calculates the cross-correlation value between the received signal R1 and the Tx1 preamble signal as the Tx1 peak calculation result for causing a peak in the Tx1 preamble signal, and outputs this to the peak detection unit 32.

[0094] The cross-correlation unit 33-2 of the peak calculation unit 31 receives the received signal R1 and reads out the Tx2 preamble signal from the storage unit 21.

[0095] The cross-correlation unit 33-2 calculates the cross-correlation value between the received signal R1 and the Tx2 preamble signal as the Tx2 peak calculation result for causing a peak in the Tx2 preamble signal, and outputs this to the peak detection unit 32.

[0096] The peak detection unit 32 receives the Tx1 peak calculation result from the cross-correlation unit 33-1 and the Tx2 peak calculation result from the cross-correlation unit 33-2. Based on the Tx1 peak calculation result, the peak position of the Tx1 preamble signal (Tx1 peak position) is detected, and based on the Tx2 peak calculation result, the peak position of the Tx2 preamble signal (Tx2 peak position) is detected. Based on both peak positions, the peak detection unit 32 detects the preamble start position P1 of the received signal R1 and outputs this to the noise power estimation unit 40-1 and the MIMO-OFDM demodulation unit 22.

[0097] The peak detection unit 32 may, for example, detect the peak position that appears in the cross-correlation result of the Tx1 preamble signal as the preamble starting position P1, or it may detect the higher peak position of the cross-correlation result of the Tx1 preamble signal and the Tx2 preamble signal as the preamble starting position P1. There are various methods for peak detection, but regardless of the method, the larger the value of the peak calculation result, the more accurately the preamble starting position P1 can be detected.

[0098] Furthermore, the Tx1 peak calculation result and Tx2 peak calculation result, which are cross-correlation values ​​calculated by the cross-correlation units 33-1 and 33-2, always show the peak position appearing twice at a fixed interval (for example, 512 samples in the computer simulation results shown in Figure 11, which will be described later).

[0099] This property can be used to prevent false detection of peak positions in the following way. The peak detection unit 32 determines, for each of the Tx1 preamble signal and the Tx2 preamble signal, whether another peak position is detected a predetermined number of samples (e.g., 512 samples) before or after the detected peak position. If the peak detection unit 32 determines that the peak position has appeared twice in the predetermined number of samples, it treats the detected peak position as the correct peak position. If it determines that the peak position has not appeared twice, it treats the detected peak position as an incorrect peak position. This also prevents false detection of peak positions.

[0100] As described above, there are various methods for peak detection, but regardless of the method, the larger the peak calculation result, the more accurately the preamble starting position P1 can be detected.

[0101] Returning to Figure 5, the noise power estimation unit 40-1 of the receiving processing unit 20-1 receives the received signal R1 as input, along with the preamble starting position P1 from the preamble starting position detection unit 30-1. The noise power estimation unit 40-1 then uses the property that the preamble signal is repeated twice with the same waveform, based on the preamble starting position P1 of the received signal R1, to estimate the noise power N1 contained in the received signal R1, and outputs this to the MIMO-OFDM demodulation unit 22.

[0102] Figure 7 is a block diagram showing an example configuration of the noise power estimation unit 40-1. This noise power estimation unit 40-1 includes a preamble signal first half extraction unit 41, a preamble signal second half extraction unit 42, and a signal difference / noise power calculation unit 43.

[0103] The preamble signal first half extraction unit 41 receives the received signal R1 as input, and also receives the preamble starting position P1 from the preamble starting position detection unit 30-1. Then, using the preamble starting position P1 of the received signal R1 as a reference, the preamble signal first half extraction unit 41 identifies the portion where the same waveform is repeated twice, and extracts the first half of that waveform portion from the received signal R1 as the first half of the received preamble signal. The preamble signal first half extraction unit 41 outputs the first half of the received preamble signal to the signal difference / noise power calculation unit 43.

[0104] The preamble signal second half extraction unit 42 receives the received signal R1 as input, and also receives the preamble starting position P1 from the preamble starting position detection unit 30-1. Then, using the preamble starting position P1 of the received signal R1 as a reference, the preamble signal second half extraction unit 42 identifies the portion where the same waveform is repeated twice, and extracts the latter half of that waveform portion from the received signal R1 as the second half of the received preamble signal. The preamble signal second half extraction unit 42 outputs the second half of the received preamble signal to the signal difference / noise power calculation unit 43.

[0105] The signal difference / noise power calculation unit 43 receives the first half of the received preamble signal from the preamble signal first half extraction unit 41, and also receives the second half of the received preamble signal from the preamble signal second half extraction unit 42.

[0106] The signal difference / noise power calculation unit 43 calculates the difference between the first half of the received preamble signal and the second half of the received preamble signal, divides the square of the difference by 2, and averages it to estimate the noise power N1, and outputs the noise power N1 to the MIMO-OFDM demodulation unit 22.

[0107] Returning to Figure 5, the receiving processing units 20-2, ..., 20-M perform the same processing as the receiving processing unit 20-1. The receiving processing unit 20-2 outputs the preamble starting position P2 and noise power N2 to the MIMO-OFDM demodulation unit 22, ..., and the receiving processing unit 20-M outputs the preamble starting position PM and noise power NM to the MIMO-OFDM demodulation unit 22.

[0108] The memory unit 21 stores, similar to the memory unit 12 in Embodiment 1 shown in Figure 4, a time-domain Tx1 preamble signal corresponding to the frequency-domain Tx1 preamble signal used for the first transmission system, and a time-domain Tx2 preamble signal corresponding to the frequency-domain Tx2 preamble signal used for the second transmission system.

[0109] Specifically, the memory unit 21 stores the time-domain Tx1 preamble signal and Tx2 preamble signal obtained by OFDM modulation of the frequency domain Tx1 preamble signal and Tx2 preamble signal shown in Figure 3(1).

[0110] The MIMO-OFDM demodulation unit 22 receives the received signals R1,...,RM, and also receives the preamble starting position P1 and noise power N1,..., as well as the preamble starting position PM and noise power NM from the receiving processing units 20-1,...,20-M.

[0111] The MIMO-OFDM demodulation unit 22 uses the preamble starting position P1 and noise power N1, ..., and the preamble starting position PM and noise power NM to perform MIMO-OFDM demodulation on the received signals R1, ..., RM, including OFDM demodulation (FFT (Fast Fourier Transform)), channel estimation, carrier demodulation, parallel / serial conversion, deinterleaving, and code decoding, to restore and output the original transmitted data.

[0112] (Computer simulation results / Example 1) Next, the results of the computer simulation in Example 1 will be described. Figure 10(1) shows the specifications of the computer simulation, and Figure 10(2) shows the channel to be evaluated by the computer simulation.

[0113] As shown in Figure 10(1), the specifications for the computer simulation use the 1K full mode described in Non-Patent Document 1 above, with N subcarriers of OFDM. CThe number of lines is set to 860, the number of FFT points to 1024, and the FFT clock to 20.450743MHz. For the specifications of MIMO transmission line 3, the 11-pass slice fading model described in Non-Patent Literature 1 is used. The number of cross-correlation samples is set to 512, and the first 512 samples are used as the reference for both the Tx1 preamble signal and the Tx2 preamble signal. The received C / N is -5dB.

[0114] Number of subcarriers N C Since there are 860 strands, the sequence length of the ZC series is N. ZC This becomes half, 430. Also, the root r of the ZC series is set to r=1 for ZC1 for Tx1 and r=429 for ZC2 for Tx1.

[0115] As shown in Figure 10(2), the target of evaluation by computer simulation is a 2x1 MISO channel in a wireless transmission system with 2 transmitting antennas and M receiving antennas. This is because the processing in Example 1 is performed similarly for each of the M receiving antennas 5-1, ..., 5-M, so it is sufficient to evaluate only one of them, receiving antenna 5-1. In other words, by evaluating one receiving system which is a 2x1 MISO channel, a similar evaluation can be obtained for each receiving system of the 2xM MIMO channel.

[0116] The same computer simulation conditions described above also apply to the computer simulation in Example 2, which will be described later.

[0117] Figure 11(1) illustrates the computer simulation results of the Tx1 peak calculation results in the prior art and Example 1, and Figure 11(2) illustrates the computer simulation results of the Tx2 peak calculation results in the prior art and Example 1.

[0118] The left side of Figure 11(1) shows the Tx1 peak calculation result of the conventional technology, and the right side shows the Tx1 peak calculation result of Example 1 calculated by the cross-correlation unit 33-1 shown in Figure 6. Similarly, the left side of Figure 11(2) shows the Tx2 peak calculation result of the conventional technology, and the right side shows the Tx2 peak calculation result of Example 1 calculated by the cross-correlation unit 33-2 shown in Figure 6. The horizontal axis represents the sample number, where sample number 0 is the ideal position as the preamble starting position P1. The vertical axis represents the cross-correlation output (absolute value). This cross-correlation output is the Tx1 peak calculation result and Tx2 peak calculation result output by the cross-correlation units 33-1 and 33-2 shown in Figure 6.

[0119] From the Tx1 peak calculation results for the conventional technology and Example 1 shown in Figure 11(1), and the Tx2 peak calculation results for the conventional technology and Example 1 shown in Figure 11(2), it can be seen that the peak position occurs twice with an interval of 512 samples (see *1).

[0120] In this computer simulation, the number of FFT points is 1024. Therefore, by OFDM modulating a frequency-domain preamble signal with 1024 points, a time-domain preamble signal with 1024 samples is generated. In Example 1, in the time-domain preamble signal with 1024 samples, the waveform of the first 512 samples and the waveform of the second 512 samples are identical. As a result, the peak position occurs twice, with an interval of 512 samples between them.

[0121] The peak detection unit 32 shown in Figure 6 can detect the peak position by utilizing this property.

[0122] Furthermore, the results shown in Figures 11(1) and (2) indicate that in both the Tx1 peak calculation result and the Tx2 peak calculation result, Example 1 was able to obtain higher peak values ​​than the conventional technology. In other words, in the synchronization process of the receiving wireless transmission device 2A, the peak of the correlation value obtained by the cross-correlation of the preamble signals can be amplified, and the preamble starting position P1 can be detected with high accuracy.

[0123] Figure 12 illustrates the results of a computer simulation of noise power N1 in Example 1. Here, the number of samples extracted to estimate the noise power N1 is set to 256, and the latter 256 samples are extracted from both the waveform of the first 512 samples and the waveform of the latter 512 samples. The horizontal axis represents the noise power [dB] added in the computer simulation (value when the signal power is set to 1), and the vertical axis represents the estimated noise power [dB].

[0124] As can be seen from the computer simulation results shown in Figure 12, the estimated noise power is almost the same as the noise power added in the computer simulation.

[0125] In other words, the signal difference noise power calculation unit 43 of the noise power estimation unit 40-1 shown in Figure 7 can estimate the noise power N1 with high accuracy, similar to conventional technology, by utilizing the property that the same signal is repeated twice.

[0126] As described above, according to the receiving wireless transmission device 2A of Example 1, the modulated waves transmitted from the transmitting antennas 4-1 and 4-2 of the transmitting wireless transmission device 1A of Example 1 are combined in the MIMO transmission path 3, and the combined modulated waves are received by the receiving antennas 5-1, ..., 5-M.

[0127] The preamble leading position detection unit 30-1 of the receiving processing unit 20-1 calculates the cross-correlation value of the received signal R1 and the Tx1 preamble signal as the Tx1 peak calculation result, and calculates the cross-correlation value of the received signal R1 and the Tx2 preamble signal as the Tx2 peak calculation result. Then, the preamble leading position detection unit 30-1 detects the peak position based on the Tx1 peak calculation result and the peak position based on the Tx2 peak calculation result, and detects the preamble leading position P1 of the received signal R1 based on these peak positions.

[0128] The noise power estimation unit 40-1 of the receiving processing unit 20-1 estimates the noise power N1 contained in the received signal R1 by using the property that the preamble signal is repeated twice with the same waveform, with reference to the preamble starting position P1 of the received signal R1.

[0129] Similarly, the receiving processing units 20-2, ..., 20-M also detect the preamble starting positions P2, ..., PM of the received signal R1 and estimate the noise power N2, ... NM.

[0130] The MIMO-OFDM demodulation unit 22 uses the preamble starting position P1 and noise power N1, ..., and the preamble starting position PM and noise power NM to perform MIMO-OFDM demodulation on the received signals R1, ..., RM to restore the original transmitted data.

[0131] Here, the Tx1 preamble signal and the Tx2 preamble signal are signals obtained by OFDM modulation of the frequency domain Tx1 preamble signal and Tx2 preamble signal using different ZC sequences, as shown in Figure 3(1). The peak positions of the Tx1 preamble signal and the Tx2 preamble signal can be detected in each of the received signals R1, ..., RM.

[0132] By using such Tx1 and Tx2 preamble signals, it is possible to maintain the ability to detect peak positions in both the Tx1 and Tx2 preamble signals, similar to the case of Non-Patent Document 1 mentioned above, while also achieving the effect of expanding the peaks detected by cross-correlation calculation compared to Non-Patent Document 1.

[0133] In other words, in wireless transmission systems using MIMO and TDD transmission methods, a preamble signal spanning the entire bandwidth of the OFDM signal is used. As a result, when wireless transmission device 2A performs subframe synchronization processing, the peak of the correlation value obtained from the cross-correlation of the preamble signals can be amplified, and the preamble starting position can be detected with high accuracy.

[0134] Furthermore, the preamble signals contained in the received signals R1,...,RM are signals in which the same waveform is repeated twice. By utilizing this property, the noise power N1,...,NM can be estimated from the received signals R1,...,RM.

[0135] [Receiver's Wireless Transmission Device 2 / Example 2] Next, we will describe the receiving wireless transmission device 2 of Embodiment 2 shown in Figure 1. Figure 8 is a block diagram showing an example configuration of the receiving wireless transmission device 2 in Embodiment 2.

[0136] The receiving wireless transmission device 2B of this embodiment 2 includes receiving antennas 5-1, ..., 5-M, receiving processing units 23-1, ..., 23-M, a storage unit 24, and a MIMO-OFDM demodulation unit 25. The receiving processing unit 23-1 includes a preamble starting position detection unit 30-1 and a channel estimation unit 50-1, and the receiving processing units 23-2, ..., 23-M also include the same components as the preamble starting position detection unit 30-1 and the same components as the channel estimation unit 50-1. Note that only the components related to the present invention are shown in Figure 8, and components unrelated to the present invention are omitted.

[0137] In the second embodiment shown in Figure 4, the modulated waves transmitted from the transmitting antennas 4-1 and 4-2 of the transmitting wireless transmission device 1B are combined in the MIMO transmission path 3, and the combined modulated waves are received by the receiving antennas 5-1, ..., 5-M of the receiving wireless transmission device 2B.

[0138] The preamble starting position detection unit 30-1 of the receiving processing unit 23-1 receives the signal of the synthesized modulated wave as the received signal R1 via the receiving antenna 5-1. The preamble starting position detection unit 30-1 also reads out the Tx1 preamble signal and the Tx2 preamble signal from the storage unit 24. Then, the preamble starting position detection unit 30-1 performs the same processing as the preamble starting position detection unit 30-1 shown in Figure 5 and outputs the preamble starting position P1 to the channel estimation unit 50-1 and the MIMO-OFDM demodulation unit 25.

[0139] The channel estimation unit 50-1 of the reception processing unit 23-1 receives the received signal R1 and also receives the preamble starting position P1 from the preamble starting position detection unit 30-1. The channel estimation unit 50-1 also reads out the ZC sequences ZC1(n) and ZC2(n) from the storage unit 24.

[0140] The channel estimation unit 50-1 extracts the received preamble signal from the received signal R1, using the preamble starting position P1 of the received signal R1 as a reference. Based on the received preamble signal and the ZC sequences ZC1(n) and ZC2(n), it estimates the channel response between the transmitting antenna 4-1 and the receiving antenna 5-1 (channel response of the Tx1→Rx transmission path) and the channel response between the transmitting antenna 4-2 and the receiving antenna 5-1 (channel response of the Tx2→Rx transmission path). The channel estimation unit 50-1 then outputs these channel responses as channel estimation result H1 to the MIMO-OFDM demodulation unit 25.

[0141] Figure 9 is a block diagram showing an example configuration of the channel estimation unit 50-1. This channel estimation unit 50-1 includes a preamble signal extraction unit 51, an OFDM demodulation unit 52, and a signal comparison unit 53.

[0142] The preamble signal extraction unit 51 receives the received signal R1 as input, and also receives the preamble starting position P1 from the preamble starting position detection unit 30-1. Then, the preamble signal extraction unit 51 extracts the received preamble signal from the received signal R1, using the preamble starting position P1 of the received signal R1 as a reference, and outputs this to the OFDM demodulation unit 52.

[0143] The OFDM demodulation unit 52 receives the received preamble signal from the preamble signal extraction unit 51, performs OFDM demodulation on this time-domain received preamble signal to generate a frequency-domain received preamble signal, and outputs this to the signal comparison unit 53.

[0144] The signal comparison unit 53 receives the frequency-domain received preamble signal from the OFDM demodulation unit 52 and reads out the ZC sequences ZC1(n) and ZC2(n) from the storage unit 24. The signal comparison unit 53 then estimates the channel response between the transmitting antenna 4-1 and the receiving antenna 5-1 by comparing the two signals based on the frequency-domain received preamble signal and the ZC sequence ZC1(n). There are various methods for estimating the channel response, but for example, it can be obtained by dividing the received preamble signal by a known preamble signal. The signal comparison unit 53 also estimates the channel response between the transmitting antenna 4-2 and the receiving antenna 5-1 by comparing the two signals based on the frequency-domain received preamble signal and the ZC sequence ZC2(n).

[0145] The signal comparison unit 53 outputs these channel responses as channel estimation result H1 to the MIMO-OFDM demodulation unit 25.

[0146] Returning to Figure 8, the receiving processing units 23-2, ..., 23-M perform the same processing as the receiving processing unit 23-1. The receiving processing unit 23-2 outputs the preamble starting position P2 and the channel estimation result H2 to the MIMO-OFDM demodulation unit 25, ..., and the receiving processing unit 23-M outputs the preamble starting position PM and the channel estimation result HM to the MIMO-OFDM demodulation unit 25.

[0147] Similar to the storage unit 21 shown in Figure 5, the storage unit 24 stores a time-domain Tx1 preamble signal corresponding to the frequency-domain Tx1 preamble signal used for the first transmission system, and a time-domain Tx2 preamble signal corresponding to the frequency-domain Tx2 preamble signal used for the second transmission system.

[0148] Furthermore, the memory unit 24 pre-stores the ZC sequences ZC1(n) and ZC2(n). Specifically, as shown in Figure 3(2), the memory unit 24 pre-stores the ZC sequence ZC1(n) used for the Tx1 preamble signal and the ZC sequence ZC2(n) used for the Tx2 preamble signal. Sequence index n = 0 to N ZC It is -1.

[0149] The MIMO-OFDM demodulation unit 25 receives the received signals R1,...,RM, and also receives the preamble starting position P1 and channel estimation result H1,..., as well as the preamble starting position PM and channel estimation result HM from the receiving processing units 23-1,...,23-M.

[0150] The MIMO-OFDM demodulation unit 25 uses the preamble starting position P1 and channel estimation results H1, ..., and the preamble starting position PM and channel estimation result HM to perform MIMO-OFDM demodulation on the received signals R1, ..., RM, including OFDM demodulation, carrier demodulation, parallel / serial conversion, deinterleaving, and code decoding, to restore and output the original data to be transmitted.

[0151] (Computer simulation results / Example 2) Figure 13(1) illustrates the computer simulation results of the Tx1 peak calculation results in the prior art and Example 2, and Figure 13(2) illustrates the computer simulation results of the Tx2 peak calculation results in the prior art and Example 2.

[0152] The left side of Figure 13(1) shows the Tx1 peak calculation result of the conventional technology, and the right side shows the Tx1 peak calculation result of Example 2 calculated by the cross-correlation unit 33-1 shown in Figure 6. Similarly, the left side of Figure 13(2) shows the Tx2 peak calculation result of the conventional technology, and the right side shows the Tx2 peak calculation result of Example 2 calculated by the cross-correlation unit 33-2 shown in Figure 6. The horizontal axis represents the sample number, where sample number 0 is the ideal position as the preamble starting position P1. The vertical axis represents the cross-correlation output (absolute value). This cross-correlation output is the Tx1 peak calculation result and Tx2 peak calculation result output by the cross-correlation units 33-1 and 33-2 shown in Figure 6.

[0153] From the Tx1 peak calculation results for the prior art and Example 2 shown in Figure 13(1), and the Tx2 peak calculation results for the prior art and Example 2 shown in Figure 13(2), it can be seen that the peak position occurs twice with an interval of 512 samples, similar to Figures 11(1) and (2) (see *1).

[0154] The peak detection unit 32 shown in Figure 6 can detect the peak position by utilizing this property.

[0155] Unlike Example 1 shown in Figures 11(1) and (2), in Example 2, in the 1024-sample time-domain preamble signal generated by OFDM modulation of a 1024-point frequency-domain preamble signal, the Tx1 preamble signal has the same waveform for the first 512 samples and the same waveform for the second 512 samples, but the Tx2 preamble signal does not have the same waveform for the first 512 samples and the second 512 samples. However, the waveform for the second 512 samples is a repeating waveform obtained by multiplying the waveform for the first 512 samples by -1. By utilizing this property and taking the Tx1 peak calculation result and Tx2 peak calculation result output from the cross-correlation units 33-1 and 33-2 shown in Figure 6 to the peak detection unit 32 as absolute values, the peak position can be generated twice with an interval of 512 samples.

[0156] Furthermore, the results shown in Figures 13(1) and (2) indicate that in both the Tx1 peak calculation result and the Tx2 peak calculation result, Example 2 was able to obtain higher peak values ​​than the conventional technology. In other words, in the synchronization process of the receiving wireless transmission device 2B, the peak of the correlation value obtained by the cross-correlation of the preamble signals can be amplified, and the preamble starting position P1 can be detected with high accuracy.

[0157] Figure 14(1) illustrates the computer simulation results of the channel response of the Tx1→Rx transmission path in Example 2. Figure 14(2) illustrates the computer simulation results of the channel response of the Tx2→Rx transmission path in Example 2. These figures show the results in the absence of noise.

[0158] The left and right sides of Figure 14(1) show the real and imaginary parts of the channel response for the Tx1→Rx transmission path, respectively, and the left and right sides of Figure 14(2) show the real and imaginary parts of the channel response for the Tx2→Rx transmission path, respectively.

[0159] The Tx1→Rx transmission path represents the transmission path from transmitting antenna 4-1 to receiving antenna 5-1, and the Tx2→Rx transmission path represents the transmission path from transmitting antenna 4-2 to receiving antenna 5-1. In Figures 14(1) and (2), the horizontal axis represents the subcarrier number, and the vertical axis represents the channel response amplitude. The solid line represents the actual channel response, and the circles represent the channel estimation result H1 (channel response) estimated by the channel estimation unit 50-1 shown in Figure 9.

[0160] Here, the channel estimation results indicated by ○ are calculated for subcarrier numbers where the ZC sequence is placed. That is, the channel response of the Tx1→Rx transmission path shown in Figure 14(1) is calculated for even-numbered subcarrier numbers where the ZC sequence is placed in the Tx1 preamble signal shown in Figure 3(2). The channel response for odd-numbered subcarrier numbers where no ZC sequence is placed (where a null is placed) is calculated by interpolation using the channel response of even-numbered subcarrier numbers.

[0161] Similarly, the channel response of the Tx2→Rx transmission path shown in Figure 14(2) was calculated for odd-numbered subcarrier numbers where the ZC sequence is placed in the Tx2 preamble signal shown in Figure 3(2). The channel response for even-numbered subcarrier numbers where the ZC sequence is not placed (where a null is placed) is calculated by interpolation using the channel response of odd-numbered subcarrier numbers.

[0162] From Figures 14(1) and (2), the solid line representing the channel response and the circle representing the channel estimation result H1 follow almost the same trajectory, indicating that the channel estimation result H1 is almost identical to the actual channel response.

[0163] In other words, the channel estimation unit 50-1 shown in Figure 8 can accurately estimate the actual channel response using the preamble signal extracted from the received signal R1.

[0164] As described above, according to the receiving wireless transmission device 2B of Example 2, the modulated waves transmitted from the transmitting antennas 4-1 and 4-2 of the transmitting wireless transmission device 1B of Example 2 are combined in the MIMO transmission path 3, and the combined modulated waves are received by the receiving antennas 5-1, ..., 5-M.

[0165] The preamble leading position detection unit 30-1 of the receiving processing unit 23-1 calculates the cross-correlation value of the received signal R1 and the Tx1 preamble signal as the Tx1 peak calculation result, and calculates the cross-correlation value of the received signal R1 and the Tx2 preamble signal as the Tx2 peak calculation result. Then, the preamble leading position detection unit 30-1 detects the peak position based on the Tx1 peak calculation result and the peak position based on the Tx2 peak calculation result, and detects the preamble leading position P1 of the received signal R1 based on these peak positions.

[0166] The channel estimation unit 50-1 of the receiving processing unit 23-1 extracts the preamble signal from the received signal R1, using the preamble starting position P1 of the received signal R1 as a reference, and estimates the channel response between the transmitting antenna 4-1 and the receiving antenna 5-1 and the channel response between the transmitting antenna 4-2 and the receiving antenna 5-1 as the channel estimation result H1 based on the preamble signal and the ZC sequences ZC1(n) and ZC2(n).

[0167] Similarly, the receiving processing units 23-2, ..., 23-M also detect the preamble starting positions P2, ..., PM of the received signal R1 and estimate the channel estimation results H2, ..., HM.

[0168] The MIMO-OFDM demodulation unit 25 uses the preamble starting position P1 and channel estimation results H1, ..., and the preamble starting position PM and channel estimation result HM to perform MIMO-OFDM demodulation on the received signals R1, ..., RM to restore the original data to be transmitted.

[0169] Here, the Tx1 preamble signal and the Tx2 preamble signal are obtained by OFDM modulation of the frequency domain Tx1 preamble signal and Tx2 preamble signal using a ZC sequence, as shown in Figure 3(2). The ZC sequences in both signals are arranged orthogonally on the frequency axis. Therefore, the peak positions of the Tx1 preamble signal and the Tx2 preamble signal can be detected in each of the received signals R1,...,RM.

[0170] By using such Tx1 and Tx2 preamble signals, it is possible to maintain the ability to detect peak positions in both the Tx1 and Tx2 preamble signals, similar to the case of Non-Patent Document 1 mentioned above, while also achieving the effect of expanding the peaks detected by cross-correlation calculation compared to Non-Patent Document 1.

[0171] In other words, in wireless transmission systems using MIMO and TDD transmission methods, a preamble signal spanning the entire bandwidth of the OFDM signal is used. As a result, when the wireless transmission device 2B performs subframe synchronization processing, the peak of the correlation value obtained from the cross-correlation of the preamble signals can be amplified, and the preamble starting position can be detected with high accuracy.

[0172] Furthermore, since the amplitude of the ZC sequence used in the Tx1 and Tx2 preamble signals is 1, the Tx1 and Tx2 preamble signals can be used as pilot symbols on the subcarrier. In other words, the channel response can be estimated from the preamble signals contained in the received signals R1,...,RM.

[0173] Although the present invention has been described above with reference to Examples 1 and 2, the present invention is not limited to Examples 1 and 2, and can be modified in various ways without departing from the technical concept. [Explanation of symbols]

[0174] 1,1A,1B,2,2A,2B,101,102 Wireless transmission equipment 3 MIMO transmission lines 4-1, 4-2 Transmitting antenna 5-1,5-M receiving antenna 10 MIMO-OFDM Modulation Section 11-1, 11-2 Preamble signal insertion section 12,21,24 Storage part 20-1, 20-M, 23-1, 23-M Receiving Processing Unit 22,25 MIMO-OFDM demodulation section 30-1 Preamble leading position detection unit 31 Peak Calculation Unit 32 Peak detection unit 33-1, 33-2 Cross-correlation section 40-1 Noise Power Estimation Unit 41. Extraction section of the first half of the preamble signal 42. Extraction section of the latter half of the preamble signal 43 Signal Difference / Noise Power Calculation Unit 50-1 Channel Estimation Unit 51 Preamble signal extraction section 52 OFDM demodulation unit 53 Signal Comparison Section S1, S2 Transmitted Signals R1,RM Received signal P1,PM Preamble starting position N1,NM Noise Power H1, HM channel estimation results

Claims

1. A wireless transmission device in a wireless transmission system that performs wireless transmission using MIMO transmission method and TDD (Time Division Duplex) method, When the wireless transmission device functions as a transmitting device that constitutes and transmits subframes of the first transmission system (Tx1) and the second transmission system (Tx2) using the TDD method, A storage unit in which the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are stored as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively, A MIMO-OFDM modulation unit that applies MIMO-OFDM modulation to the data to be transmitted to generate the transmission signal S1 for the first transmission system and the transmission signal S2 for the second transmission system, A first preamble signal insertion unit reads the time-domain Tx1 preamble signal from the storage unit and inserts the time-domain Tx1 preamble signal into the beginning of the transmission signal S1 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the first transmission system. The system includes a second preamble signal insertion unit that reads the time-domain Tx2 preamble signal from the storage unit and inserts the time-domain Tx2 preamble signal into the beginning of the transmission signal S2 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the second transmission system. The aforementioned time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the aforementioned frequency-domain Tx1 preamble signal is a signal in which a ZC (Zadoff-Chu) sequence for Tx1 and nulls are alternately arranged on the frequency axis subcarrier. The time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, and the frequency-domain Tx2 preamble signal is a signal in which a ZC sequence for Tx2 and nulls are alternately arranged on the subcarrier on the frequency axis. A wireless transmission device characterized in that the subcarrier of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarrier of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged at the same position on the frequency axis.

2. A wireless transmission device in a wireless transmission system that performs wireless transmission using MIMO transmission method and TDD (Time Division Duplex) method, When the wireless transmission device functions as a transmitting device that constitutes and transmits subframes of the first transmission system (Tx1) and the second transmission system (Tx2) using the TDD method, A storage unit in which the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are stored as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively, A MIMO-OFDM modulation unit that applies MIMO-OFDM modulation to the data to be transmitted to generate the transmission signal S1 for the first transmission system and the transmission signal S2 for the second transmission system, A first preamble signal insertion unit reads the time-domain Tx1 preamble signal from the storage unit and inserts the time-domain Tx1 preamble signal into the beginning of the transmission signal S1 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the first transmission system. The system includes a second preamble signal insertion unit that reads the time-domain Tx2 preamble signal from the storage unit and inserts the time-domain Tx2 preamble signal into the beginning of the transmission signal S2 generated by the MIMO-OFDM modulation unit, thereby constituting a subframe of the second transmission system. The aforementioned time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the aforementioned frequency-domain Tx1 preamble signal is a signal in which a ZC (Zadoff-Chu) sequence for Tx1 and nulls are alternately arranged on the frequency axis subcarrier. The time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, and the frequency-domain Tx2 preamble signal is a signal in which nulls and ZC sequences for Tx2 are alternately arranged on the subcarrier on the frequency axis. A wireless transmission device characterized in that the subcarrier of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarrier of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged orthogonally on the frequency axis.

3. A wireless transmission device in a wireless transmission system that performs wireless transmission using MIMO transmission method and TDD (Time Division Duplex) method, When the wireless transmission device functions as a receiving device that receives a signal synthesized in the transmission path from the transmitting wireless transmission device, where subframes of the first transmission system (Tx1) and subframes of the second transmission system (Tx2) are transmitted from the transmitting wireless transmission device using the TDD method for each of one or more receiving systems, detects the preamble start position of the subframe from the received signal, and reconstructs the data to be transmitted, A storage unit in which the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are stored as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively, Read out the Tx1 preamble signal and the Tx2 preamble signal from the time domain from the storage unit. A receiving processing unit has a preamble starting position detection unit that, for each of the one or more receiving systems, calculates the cross-correlation value between the received signal corresponding to the receiving system and the Tx1 preamble signal in the time domain to determine the Tx1 peak position, calculates the cross-correlation value between the received signal and the Tx2 preamble signal in the time domain to determine the Tx2 peak position, and detects the starting position of the preamble of a subframe in the received signal based on the Tx1 peak position and the Tx2 peak position. The system includes a MIMO-OFDM demodulation unit that performs MIMO-OFDM demodulation on the received signals of all receiving systems, using the preamble starting position of all receiving systems detected by the preamble starting position detection unit of the receiving processing unit as a reference, to restore the original data to be transmitted. The aforementioned time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the aforementioned frequency-domain Tx1 preamble signal is a signal in which a ZC (Zadoff-Chu) sequence for Tx1 and nulls are alternately arranged on the frequency axis subcarrier. The time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, and the frequency-domain Tx2 preamble signal is a signal in which a ZC sequence for Tx2 and nulls are alternately arranged on the subcarrier on the frequency axis. A wireless transmission device characterized in that the subcarrier of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarrier of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged at the same position on the frequency axis.

4. A wireless transmission device in a wireless transmission system that performs wireless transmission using MIMO transmission method and TDD (Time Division Duplex) method, When the wireless transmission device functions as a receiving device that receives a signal synthesized in the transmission path from the transmitting wireless transmission device, where subframes of the first transmission system (Tx1) and subframes of the second transmission system (Tx2) are transmitted from the transmitting wireless transmission device using the TDD method for each of one or more receiving systems, detects the preamble start position of the subframe from the received signal, and reconstructs the data to be transmitted, A storage unit in which the preamble signal used for the first transmission system and the preamble signal used for the second transmission system are stored as a time-domain Tx1 preamble signal and a Tx2 preamble signal, respectively, Read out the Tx1 preamble signal and the Tx2 preamble signal from the time domain from the storage unit. A receiving processing unit has a preamble starting position detection unit that, for each of the one or more receiving systems, calculates the cross-correlation value between the received signal corresponding to the receiving system and the Tx1 preamble signal in the time domain to determine the Tx1 peak position, calculates the cross-correlation value between the received signal and the Tx2 preamble signal in the time domain to determine the Tx2 peak position, and detects the starting position of the preamble of a subframe in the received signal based on the Tx1 peak position and the Tx2 peak position. The system includes a MIMO-OFDM demodulation unit that performs MIMO-OFDM demodulation on the received signals of all receiving systems, using the preamble starting position of all receiving systems detected by the preamble starting position detection unit of the receiving processing unit as a reference, to restore the original data to be transmitted. The aforementioned time-domain Tx1 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx1 preamble signal, and the aforementioned frequency-domain Tx1 preamble signal is a signal in which a ZC (Zadoff-Chu) sequence for Tx1 and nulls are alternately arranged on the frequency axis subcarrier. The time-domain Tx2 preamble signal is a signal obtained by OFDM modulation of the frequency-domain Tx2 preamble signal, and the frequency-domain Tx2 preamble signal is a signal in which the subcarrier on the frequency axis, the ZC sequence for Tx2, and nulls are arranged alternately. A wireless transmission device characterized in that the subcarrier of the ZC sequence for Tx1 in the Tx1 preamble signal in the frequency domain and the subcarrier of the ZC sequence for Tx2 in the Tx2 preamble signal in the frequency domain are arranged orthogonally on the frequency axis.

5. In the wireless transmission device according to claim 4, The memory unit further stores in advance the ZC sequence subcarrier for Tx1, which is placed in the frequency domain Tx1 preamble signal, and the ZC sequence subcarrier for Tx2, which is placed in the frequency domain Tx2 preamble signal. The receiving processing unit further includes a channel estimation unit for each of the one or more receiving systems. The channel estimation unit, Read the ZC sequence subcarrier for Tx1 and the ZC sequence subcarrier for Tx2 from the storage unit. Based on the preamble leading position detected by the preamble leading position detection unit, a time-domain preamble signal is extracted from the received signal corresponding to the receiving system, and a frequency-domain preamble signal is generated by applying OFDM demodulation to the time-domain preamble signal. Based on the ZC sequence subcarrier for Tx1 and the frequency domain preamble signal, the channel response between the transmitting antenna of the first transmitting system and the receiving antenna of the receiving system is estimated, A wireless transmission device characterized by estimating the channel response between the transmitting antenna of the second transmitting system and the receiving antenna of the receiving system based on the ZC sequence subcarrier for Tx2 and the frequency domain preamble signal.

Images