JP4468832B2 - COMMUNICATION DEVICE, TERMINAL DEVICE, ITS COMMUNICATION METHOD, AND PROGRAM USED FOR THE SAME - Google Patents

Description

  The present invention relates to a wireless communication apparatus and an antenna pattern control method, and more particularly to an antenna pattern control technique for an adaptive array antenna in wireless communication using a CSMA / CA method.

  In recent years, wireless LAN systems have been introduced in offices and homes for reasons such as higher speed of wireless LAN systems, lower prices, and ease of device layout. For example, in homes, there are many opportunities for wireless LAN systems to be introduced for wireless video transmission in response to user requests for viewing images in a server in a living room on a TV in another room. It has become.

  There are several types of wireless LAN systems. Among them, the most popular high-speed wireless LAN system is an IEEE802.11a system standardized by IEEE. This IEEE802.11a is a system that performs multicarrier transmission using 5 GHz band radio waves, and can realize a maximum transmission rate of 54 Mbps.

  In an IEEE802.11 compliant system represented by IEEE802.11a, a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance, hereinafter referred to as “CSMA / CA” in this specification) method is adopted as an access method. It is prescribed. FIG. 4 is a diagram showing a configuration example of a basic packet format used in an IEEE802.11 compatible system adopting the CSMA / CA method. As shown in FIG. 4, a packet used in an IEEE802.11 compatible system includes a preamble 100, a header 101, and data 102. Among these, the preamble 100 is a known signal used for synchronization, frequency error correction, and the like, and the header 101 is a signal for notifying the address of the packet type, the transmission source and the destination, the address of the base station to which it belongs, and the like. In IEEE802.11, if the packet is not addressed to itself as a result of decoding the header 101, the received packet is discarded. Here, since the header 101 is not normally encrypted, the header 101 of the packet transmitted and received in the adjacent system can be decrypted to know the transmission source and destination of the packet.

  FIG. 5 is a diagram showing a basic transmission procedure of an IEEE802.11 compatible system. The description will be made on the assumption that a base station, a terminal A, and a terminal B exist. However, the terminal B shown in FIG. 5 is a terminal that is already connected to the base station, and the terminal A is a terminal that is newly connected to the base station.

  As shown in FIG. 5, in the IEEE802.11 compatible system, a terminal A desiring access to a base station first receives a beacon 110 transmitted by the base station. Here, the beacon 110 transmitted by the base station is a notification signal to all terminals belonging to the base station, and is transmitted periodically. In the terminal A, after receiving the beacon 110, the terminal A transmits a packet called an authentication request 111 to the base station. The authentication request 111 has a role such as an ID assignment request. The base station that has received the authentication request 111 transmits a packet called an authentication response 112 to the terminal A in order to notify the ID of the terminal A. Next, the terminal A transmits an association request 113 and makes an authentication request. In response to this, the base station transmits an association response 114 and permits authentication. The new terminal is authenticated by such a procedure.

  After the above authentication processing, the transmitting terminal (here, terminal A) observes the transmission status of the other terminal (terminal B) (carrier sense: observes the presence or absence of a carrier) and confirms that transmission by terminal B is not performed. After that, send the packet. If there is a terminal (terminal B) that is transmitting, the other terminal (terminal A) refrains from transmitting packets until the terminal (terminal B) that is transmitting ends the transmission. By adopting such an access method, IEEE802.11 compatible systems reduce the situation where radio waves of multiple terminals belonging to the same base station and using the same channel interfere, and realize multiple access by multiple terminals. ing.

  As main access methods different from the CSMA / CA method described above, there are FDMA (Frequency Division Multiple Access) method, TDMA (Time Division Multiple Access) method, and CDMA (Code Division Multiple Access) method. With reference to FIG. 6, these three access methods will be described based on signal power on the time axis and the frequency axis.

  The FDMA scheme shown in FIG. 6A is a scheme in which users are divided by frequency, and a plurality of users can perform transmission using different frequencies at the same time. Further, the TDMA scheme shown in FIG. 6B is a scheme in which users are divided in time, and a plurality of users use the same frequency and transmit at different times. On the other hand, the CDMA system shown in FIG. 6 (c) is a system that divides users based on codes, and a plurality of users assigned different codes respectively transmit at the same time using the same frequency. Do. FIG. 7 shows an outline of this CDMA system (in particular, the Direct Sequence-CDMA system here).

  As shown in FIG. 7, in the CDMA system, transmission data of each user is multiplied by a spreading code (for example, CODE1) assigned to each user and transmitted. Here, since the spreading code (CODE1) assigned to each user is a sequence that changes very quickly as compared with the data sequence, the spectrum 121 of the transmission signal is the original data sequence (see FIG. 7). Compared to the spectrum 120), it is spread over a wider band. The spread spectrum signal is received by the receiving side via the propagation path. Here, as described above, in the CDMA system, a plurality of users perform transmission at the same time using the same frequency, and therefore the signal received on the receiving side includes other users' signals (transmissions of other users). Signal spectra 122 and 123) are also mixed (received spectrum 124). Such a received signal is multiplied on the receiving side by the same code as that used on the transmitting side. At this time, since the signal (spectrum 126) addressed to the other user is uncorrelated with the code to be multiplied on the receiving side, a peak indicating correlation does not appear even if the correlation operation by multiplication of the code is performed.

  On the other hand, since the signal destined for the local station has a correlation with the spreading code to be multiplied on the receiving side, a correlation peak is obtained by the correlation operation by multiplication of the spreading code, and the received signal in which other users' signals (spectrum 126) are mixed From (Spectrum 124), a signal addressed to the own station can be extracted (Spectrum 125). In the CDMA system, the correlation between these codes is used to distinguish necessary signals from other users' signals, and the original data is reproduced by demodulating the extracted correlation peak value. Can do.

  In general, some of the signals destined for the local station are received with a significant delay with respect to the preceding signal due to the length of the propagation path. Such delayed signals interfere with the FDMA and TDMA systems. Cause. On the other hand, in the CDMA system, a correlation peak value can be obtained by performing a correlation operation for multiplying a delayed signal by a code. By demodulating the signal to which all the peak values are added, the delay signal is not caused to interfere, and conversely, the delay signal power is used for demodulation without being wasted, thereby improving the demodulation characteristics. As described above, the CDMA system can be maintained in a good environment even in a propagation environment in which a delay signal exists, and is therefore adopted in third-generation mobile phone systems and the like.

  Here, generally, a correlation peak value obtained by a correlation operation between a received signal and a code is arranged on a time axis according to a delay time is called a delay profile (see FIG. 8). By obtaining this delay profile, it becomes possible to know the propagation path condition (how much delay a signal having a certain amount of power arrives). However, the preceding wave in FIG. 8 is a signal that arrives at the receiver earliest, and the delayed wave is a signal that arrives after a certain time delay from the preceding wave. At this time, when the code of the other user is known in the receiver, the delay profile of the signal of the other user can be obtained.

  As described above, the CDMA scheme is originally a scheme in which interference signals of other users are included in the received signal. Therefore, in order to improve reception characteristics and increase the number of users that can be accommodated in the system, inter-user interference is required. Suppression technology is required. As one of such interference suppression techniques, attention has been paid to an adaptive array antenna that uses a plurality of antenna elements and flexibly controls the antenna directivity according to the propagation path state by signal processing.

  As shown in FIG. 9 (a), the technique using an adaptive array antenna has different complex weights (complex weights) for received signals of antenna elements (antennas # 1, # 2 to # N-1, #N). This is a technique for controlling antenna directivity by multiplying signals # 1, # 2 to # N-1, #N) and then adding those signals. By adaptively controlling the complex weight in each antenna element of the adaptive array antenna, the antenna pattern is controlled to have a high antenna gain with respect to the arrival direction of the desired signal as shown in FIG. 9B. However, it can be controlled so that the antenna gain is very low with respect to the direction of arrival of the interference signal (null is directed).

  In this way, by controlling the antenna pattern, it is possible to suppress reception of interference signals and receive only desired signals. Here, the complex weight in each antenna element is set using an adaptive algorithm such as LMS (Least Mean Square) or RLS (Recursive Least Square) so that the mean square error between the received signal and the reference signal is minimized. The The adaptive array antenna that controls the antenna pattern (complex weight) in this way is called an adaptive array antenna based on the MMSE (Minimum Mean Square Error) standard.

  In the CDMA / TDD (Time Division Duplex) system, there is a high correlation between the channel characteristics of the uplink transmitting from the terminal to the base station and the downlink transmitting from the base station to the terminal. Is installed on the terminal side, an uplink transmission antenna pattern can be generated using a downlink reception signal. Therefore, the same antenna pattern is normally used for the reception antenna pattern used in the downlink and the transmission antenna pattern used in the next uplink. Here, at the time of reception, for the purpose of improving the error rate characteristics, an antenna pattern is generated based on the MMSE standard so that the signal power to interference plus noise power ratio (SINR) of the received signal is maximized. However, with respect to the arrival direction of the interference signal, a null is formed only to the extent that the level of the interference signal is lower than the noise level, and a very deep null cannot be formed. When transmission is performed using such a shallow antenna pattern of null, interference is transmitted to other users without much suppression, and even if the reception pattern is optimal, it is not always optimal. It is not always a transmission pattern. Therefore, unlike reception, it is considered important to generate an antenna pattern for the purpose of suppressing interference power given to other users during transmission.

  In addition, arriving waves (signals) that arrive at the antenna generally form an arriving wave group and are distributed in a certain angular spread centered on the direct wave, so there is a low degree of freedom (number of antennas −1: nulls that can be formed) Alternatively, it is important to effectively use the number of beams) to effectively form a wide null so as not to transmit an interference signal.

  From this point of view, a technique for generating different antenna patterns for reception and transmission while using the same downlink reception signal has been proposed for CDMA / TDD systems (see Non-Patent Document 1). ).

In Non-Patent Document 1, the antenna weight is obtained according to the MMSE standard based on the pseudo reception signal generated from the delay profile of each user. At this time, a deep null is obtained with respect to the arrival direction of the interference signal regardless of the interference signal power. In order to form the antenna weight, a method of calculating the antenna weight after increasing the power level of the delay profile of the interference signal by 30 dB is used (see FIG. 10). With this technique, the receiver is considered to have received an interference signal having very large power, and the antenna weight is calculated so as to form a very deep null in that direction. This technique is called Deep Null Creation Technique (DNCT). Also, in order to effectively form a wide null, only the path with the highest power in the delay profile of the interference signal is selected, and the virtual interference signal is within a certain angle centered on the arrival direction of this path. A method of generating an antenna weight based on the MMSE standard using a virtual delay profile to which is added (see FIG. 11). With this technique, the receiver is considered to have received an interference signal with a very large angular spread, and the antenna weight is calculated so as to form a very wide null in that direction. This technique is called Wide Null Creation Technique (WNCT). Non-Patent Document 1 proposes a method of forming an antenna pattern by combining the above-described DNCT and WNCT at the time of transmission and forming an antenna pattern so that the reception SINR is maximized at the time of reception.
“Yamanaka et al.,“ Study on interference suppression to neighboring cells / sectors based on propagation path control method ”, IEICE Technical Report RCS2003-72, 2003.

  As mentioned earlier, systems that support IEEE802.11 use the CSMA / CA method as an access method, so when the carrier of an adjacent system is observed by carrier sense performed prior to packet transmission. It is necessary to postpone packet transmission until the adjacent system carrier is no longer observed. Such a postponement of packet transmission occurs when systems using the same frequency band are located nearby.

  Recently, as wireless communication data, not only general text data and still image data having a relatively small capacity but also moving image data has been increasing.

  In particular, in moving image transmission, relatively long packets are transmitted continuously. Therefore, in a situation where at least one of the adjacent systems performs moving image transmission, the other system postpones packet transmission. There was a problem that the time that had to be increased. In such a situation, there is a problem in that the throughput of the system that postpones packet transmission is significantly reduced, and when both systems perform moving image transmission, smooth reproduction cannot be performed.

  An object of the present invention is to provide a wireless communication technique in which throughput is not reduced even when moving image transmission is performed.

  In the wireless communication technology of the present invention, in the system using the CSMA / CA scheme, it is determined that there is an adjacent system that performs transmission using the same frequency band as a result of carrier sense performed by the base station prior to packet transmission. In this case, it is further determined what data transmission is being performed by the adjacent system (image transmission, normal intermittent data packet transmission, etc.). Also, determine what kind of data transmission is to be performed for the own system. If at least one of the systems performs continuous transmission for a long time such as moving image transmission, it is provided in the base station and terminal. The transmission is performed in a direction that reduces the interference of the adaptive array antenna to be reduced to the adjacent system. At this time, the packet transmission is started after the directivity is formed, but the transmission is started without delaying the transmission even when the carrier of the adjacent system is observed by the carrier sense. However, if it is judged that the interference to the adjacent system cannot be reduced even if a null is formed in the direction of the adjacent system, or the transmission of the own system is hindered by the directivity formation that emphasizes the formation of the null. Stops transmission.

  In addition, when it is determined that both the adjacent system and the local system perform normal intermittent packet transmission that is not moving image transmission, the directivity of the adaptive array antenna is not formed, and the CSMA / CA method is followed. Perform normal packet transmission.

  That is, according to one aspect of the present invention, there is provided a communication apparatus in a wireless communication system that includes an adaptive array antenna including a plurality of antennas and uses a CSMA / CA method as an access method, and as a result of carrier sense, the wireless communication When a signal of a wireless communication system (non-communication target system) composed of a communication device that uses the same frequency band as the system and does not directly communicate with a communication device in the wireless communication system is observed The non-communication target system has means for discriminating the type of data transmission being performed, and the non-communication target system continuously transmits packets having a length equal to or greater than a certain threshold for a certain period of time or longer. If determined, or within a certain time of a packet having a length equal to or greater than a certain threshold. In the case of starting the transmission over a long time, the directivity of the adaptive array antenna is controlled, and it is determined that the wireless communication system and the non-communication target system do not transmit a packet having a length longer than a certain threshold for a long time. In some cases, it is preferable to control so as not to form directivity. For example, all the weights of each adaptive array antenna are set to 1.

  In addition, the antenna pattern formed when at least one of the wireless communication system or the non-communication target system transmits a packet having a length equal to or greater than a certain threshold over a certain period of time is used at the time of transmission and at the time of reception. Different antenna patterns are used. Here, the directivity control of the adaptive array antenna is performed when at least one of the packets transmitted by the wireless communication system or the non-communication target system is determined to be, for example, a moving image transmission packet.

  The antenna pattern can be obtained, for example, by applying to an MMSE (Minimum Mean Square Error) algorithm.

  A path for amplifying power is a path having high power in a delay profile of a signal transmitted from the non-communication target system.

  Further, the carrier sense performed after the antenna pattern calculation is performed by using the transmission antenna pattern.

  In the first carrier sense performed after calculating the antenna pattern, if the signal transmitted from the non-communication target system is observed with a power equal to or lower than a certain threshold value, the transmission destination in the wireless communication system indicates that communication preparation is complete. And transmitting using the formed antenna pattern. In this case, it can be determined that no interference is given to the other party.

  In the situation where the signal transmitted from the non-communication target system is observed at a power equal to or higher than a certain threshold at the time of the first carrier sense performed after the antenna pattern is calculated, the packet having a length equal to or longer than the certain threshold In the case of performing transmission over a certain period of time, it is set to reduce the number of times of transmitting a delivery confirmation signal to be sent to the base station in the wireless communication system. By reducing the delivery confirmation signal, the transmission interference is reduced as much as possible.

  According to the wireless communication technique of the present invention, when moving image transmission is performed in a system using the CSMA / CA method, the situation in which transmission is refrained by observing the carrier of an adjacent system is reduced. Furthermore, packet collisions that normally occur due to transmission regardless of the result of carrier sense can be avoided by controlling the directivity of the adaptive array antenna. For this reason, even when systems using the same frequency band are located close to each other, both systems can maintain high throughput, and smooth reproduction of moving images becomes possible.

  Hereinafter, a wireless communication technique according to an embodiment of the present invention will be described with reference to the drawings.

  First, a configuration to which the present invention is applied will be described. The radio transmission system according to the present embodiment includes a base station having an adaptive array antenna including a plurality of antennas and a terminal, and can be applied to a radio transmission system using a CSMA / CA scheme as an access scheme.

  FIG. 1 is a functional block diagram showing a device configuration example of a transceiver according to an embodiment of the present invention. As shown in FIG. 1, the transceiver according to the present embodiment first has antennas 10 to 12 and up to the same number of radio frequency RF units 13 to 15 corresponding to the antennas 10 to 12 (number of antennas N) and transmission / reception switching. Switches 16 to 18 are provided. The transmission / reception change-over switches 16 to 18 input the received signal to the antenna weight control unit 32 and the receiver 33 at the time of carrier sense and reception, and transmit the transmission signal sent from the transmitter 34 to all the antennas 10 to 10 at the time of transmission. Switch to 12 for input. However, the antennas 10 to 12 indicate N antennas constituting the adaptive array antenna (only a part of the antennas are illustrated here).

  The receiver 33 multiplies each of the weights 1 to N of the transmission / reception changeover switches 16 to 18 by the reception antenna weight multiplication unit, and inputs the result to the demodulation unit 27 and the carrier sense unit 28. Demodulated data is output from the demodulator 27 and carrier sense information is output from the carrier sense unit 28. This carrier sense information is information indicating the presence or absence of an observed carrier, and is sent to an upper layer processing unit (CPU or the like) not shown in FIG. In addition, when the carrier sense is necessary for information on the period during which the carrier is continuously observed, that is, the length of the packet used by the adjacent system for transmission / reception, the carrier sense unit 28 continuously observes the carrier. Time is counted and sent to an upper layer processing unit (not shown). Based on this carrier sense information (information on the observed packet length), a pattern generation control signal that instructs generation of an antenna pattern is generated in an upper layer processing unit (not shown).

  The transmitter 34 receives the transmission data, modulates it in the modulation unit 29, performs copying (processing for preparing the same signal for the number of antennas) in the copy unit 30, and each weight 1 to N (N is the same as the number of antennas). Are weighted by the transmission antenna weight multiplier 31 and output to the transmission / reception changeover switches 16 to 18, respectively.

  The delay profile measurement unit 19 included in the antenna weight control unit 32 measures not only the signal of the own system but also the delay profile of the signal transmitted from the adjacent system, and the measurement result is the path selection unit 20 and the reception antenna weight control. Input to the unit 24. As a method for measuring a delay profile in the delay profile measuring unit 19, a technique for obtaining a correlation between a preamble of a received signal and a transmission preamble is used. The preamble in IEEE802.11a is a known OFDM signal that is commonly added to the beginning of all packets and has excellent correlation characteristics, that is, has a sharp peak in autocorrelation similar to the spreading code in CDMA, and cross-correlation Has a characteristic that it is a substantially zero signal, and thus such a method can be used.

  The path selection unit 20 following the delay profile measurement unit 19 selects a path having the highest power from the delay profiles, and newly generates a delay profile composed only of the selected path. The changeover switch 21 performs a process of switching whether to amplify the input delay profile (the path selected by the path selection unit 20) according to the transmission source. At this time, when the received signal is a signal of the own system, the changeover switch 21 does not input the delay profile after the path selection in the path selection unit 20 to the path amplification unit 22, and transmits the antenna weight control unit 23 for transmission. To enter. Conversely, when the received signal is a signal of an adjacent system, the path selection unit 20 is controlled to input the delay profile after path selection to the path amplification unit 22. The path amplification unit 22 amplifies the input delay profile. In the transceiver according to the present embodiment, as an example, the amplification amount at this time is 30 dB.

  The transmission antenna weight control unit 23 calculates a transmission antenna weight using a plurality of input delay profiles. As an antenna weight calculation procedure in the transmission antenna weight control unit 23, first, for each input delay profile, for example, the ESPRIT algorithm (one of arrival direction estimation algorithms, which has excellent characteristics with respect to a calibration error. It is an algorithm that has been attracting attention because it has it) and estimates the direction in which the desired signal and interference signal arrive at the highest power. As a result of the arrival direction estimation processing, communication is not performed (stopped) when the direction in which the desired signal and the interference signal arrive with the highest power is within a certain angle. This is because the transmitter / receiver according to the embodiment of the present invention generates an antenna pattern having a wide and deep null in a direction in which interference is caused to an adjacent system, and performs transmission using the antenna pattern. This is because not only the interference signal but also the desired signal is suppressed when the direction of arrival is near, and the desired communication quality in the own system cannot be maintained. Conversely, if the direction in which the desired signal and the interference signal arrive with the highest power is more than a certain angle, the direction within the certain angle centered on the estimated arrival direction of each interference signal. A virtual interference signal is generated. Then, a new delay profile (virtual delay profile) is generated by adding the generated virtual interference signal, and this delay profile is stored in, for example, a memory provided in the transmitting antenna weight control unit 23.

  After the path selection, the desired signal delay profile and the interference signal virtual delay profile are convolved with different OFDM signals (with the same number of different OFDM signals as the delay profile), and after each convolution integration. Are added together to generate a pseudo received signal. Apply the pseudo reception signal generated in this way and the reference signal of the desired signal (the OFDM signal prepared in advance before the convolution integration with the delay profile of the desired signal) to the adaptive algorithm based on the MMSE standard Thus, the transmission antenna weight for each antenna is calculated.

Similarly to the processing in the transmission antenna weight control unit 23, the reception antenna weight control unit 24 performs convolution integration on the delay profiles of the input desired signal and interference signal with different OFDM signals, and performs convolution integration. Are added together to generate a pseudo received signal. And, by applying this pseudo received signal and the reference signal of the desired signal (the OFDM signal prepared in advance before performing the convolution integration with the delay profile of the desired signal) to the adaptive algorithm based on the MMSE standard, The receiving antenna weight for each antenna is calculated.
The antenna weight calculated in this way is multiplied by the transmission signal and the reception signal in the transmitter and the receiver, respectively. At this time, the transmission antenna pattern is formed with a wide and deep null in the direction of causing interference to the adjacent system, and the reception antenna pattern is formed so that the reception SINR is maximized.

  Next, the flow of control processing on the base station side according to the embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2, in the base station in the wireless communication system according to the embodiment of the present invention, when power is turned on in step 001, carrier sense is performed for a certain period of time for the channel to be used (step 002). It is determined whether there is an adjacent system to be used (step 003). As a result, if it is determined that there is no adjacent system, as shown in step 014, all antenna weights are set to 1, and normal transmission according to the CSMA / CA scheme is started. On the other hand, if it is determined that an adjacent system exists, the reception is continued and the delay profile of the interference signal coming from the adjacent system is measured (step 004). Then, the received interference signal header is demodulated (step 005), and the address of the signal transmission source is obtained. If there is a matching address between the source address obtained here and the source address stored in the memory not shown in FIG. 1, as shown in steps 006 and 007, the receiving antenna weight is set. The delay profile of the corresponding signal stored in the memory in the control unit 24 is discarded and the newly measured delay profile is stored (the delay profile is updated to a new profile).

  If it is determined in step 006 that the corresponding signal is received for the first time, the delay profile is newly stored in the memory in the receiving antenna weight control unit 24. At this time, the path selection unit 20 (FIG. 1) selects only the path having the highest power among the newly measured delay profiles, and the path amplification unit 21 (FIG. 1) amplifies the path. The new delay profile generated in this way is stored in the memory in the transmitting antenna weight control unit 23 (step 008). Such a process is continued for a time set in advance as the initial carrier sense time, and all the delay profiles of the observed interference signals are measured (step 009).

  Even if the initial carrier sense process as described above is performed, if the signal of the adjacent system is not observed, the base station transmits a beacon and starts authenticating the terminal according to the IEEE802.11 procedure shown in FIG. At the time of this authentication, the terminal transmits an authentication request or an association request to the base station. The base station measures a delay profile from the preamble of these desired signals and stores it in the memory in the receiving antenna weight control unit 24. Remember. Further, only the path having the highest power in the delay profile of the desired signal is selected by the path selection unit 20 and stored in the memory in the transmission antenna weight control unit 23 (step 011). However, the beacon transmission at the base station, the authentication response at the time of authentication, and the transmission of the association response are performed by an omnidirectional antenna pattern (all transmission complex weights are set to 1).

  Next, based on the result of demodulating the header of the signal arriving from the adjacent system performed in step 005, it is determined what data transmission is performed by the adjacent system. In the target system here, moving image transmission in which long packets are continuously transmitted and data transmission in which short packets are intermittently transmitted are performed, and what kind of data transmission is performed on the header. Or information indicating the packet length is included. Therefore, the demodulated result of this header is sent to an upper layer processing unit (not shown in FIG. 1). In the upper layer processing unit, whether the adjacent system performs moving image transmission or intermittent short data transmission. Is determined (step 012). Also, depending on the system, the header may not include information indicating the type of data transmission or the packet length. In such a case, the length of the packet transmitted in the adjacent system is roughly measured. Thus, it is possible to determine what data transmission is performed. Such a rough measurement of the packet length can be realized by measuring the time during which continuous long packets are observed in the carrier sense unit 28 as described above. The packet length measurement result by the carrier sense unit 28 is sent to an upper layer processing unit (not shown in FIG. 1), and what antenna pattern is generated is determined as a transmission antenna weight control unit 23 and a reception antenna weight control unit 24. This is used to generate a pattern generation control signal instructing. In this case, for example, when a packet having a packet length of 1000 bytes or more is transmitted, it is determined that moving image transmission is performed.

  If it is determined that moving image transmission is being performed in the adjacent system as a result of determining the type (for example, packet length) of data transmission performed in the adjacent system, the process proceeds to step 015. If it is determined that intermittent short data transmission is being performed, the process proceeds to step 013 to determine what kind of data transmission the own system performs. If it is determined in step 013 that the own system performs moving image transmission, the process proceeds to step 015. If it is determined that intermittent short data transmission is performed, the process proceeds to step 014, where all antenna weights are set to 1, and normal transmission according to the CSMA / CA scheme is started.

  That is, when both the adjacent system and the own system transmit intermittent short data packets, the antenna pattern is not formed, and the packet transmission according to the normal CSMA / CA scheme is controlled. On the other hand, when either the adjacent system or the own system continuously transmits a long packet, for example, when moving image transmission is performed, the antenna pattern is set so as to reduce interference to the adjacent system in a system that starts communication later. Is controlled to form.

  When it is determined that at least one of the adjacent system and the own system performs moving image transmission, as shown in step 015, the transmission antenna weight control unit 23 estimates the arrival directions of the desired signal and the interference signal. Is done. As described above, in this embodiment, this direction-of-arrival estimation is performed using the ESPRIT algorithm. Then, as shown in step 016, the angle difference between the arrival directions of the desired signal and the interference signal is calculated, and the magnitude relationship between the angle difference and a predetermined angle is determined.

  As a result, when it is determined that the arrival directions of the desired signal and the interference signal are within a predetermined angle, the terminal of the desired communication destination is formed by forming an antenna pattern so as not to interfere with the adjacent system. Therefore, it is presumed that even if communication is started, good characteristics cannot be secured. Therefore, in this case, as shown in step 017, the terminal is notified of the suspension of communication, and the control is terminated. Conversely, when it is determined that the difference in the angle of arrival between the desired signal and the interference signal is greater than a predetermined angle, an antenna pattern that can ensure the communication quality of the local system while reducing interference with adjacent systems. Therefore, the transmission / reception antenna weight is calculated by the subsequent control.

  In the calculation of transmission / reception antenna weights shown in step 018, a transmission antenna weight calculation procedure will be described first. Here, the transmission antenna weight is calculated in the transmission antenna weight control unit 23 as described above. As this procedure, a virtual interference signal is generated within a certain angle around the estimated arrival direction of the interference signal. Then, a new delay profile (virtual delay profile) is generated by adding the generated virtual interference signal. Then, the delay profile of the desired signal after path selection and the virtual delay profile of the interference signal are convolution integrated with different OFDM signals (the same number of different OFDM signals as the delay profiles are prepared), and the convolution integration after each convolution integration The signals are added to generate a pseudo received signal. Apply the pseudo reception signal generated in this way and the reference signal of the desired signal (the OFDM signal prepared in advance before the convolution integration with the delay profile of the desired signal) to the adaptive algorithm based on the MMSE standard Thus, the transmission antenna weight for each antenna is calculated.

  The reception antenna weight is calculated by the reception antenna weight control unit 24. This procedure is almost the same as the processing in the transmitting antenna weight control unit 23. That is, the desired signal and the interference signal delay profiles (no path selection / path amplification) are convolutionally integrated with different OFDM signals, and the signals after convolution integration are added to generate a pseudo reception signal. And, by applying this pseudo received signal and the reference signal of the desired signal (the OFDM signal prepared in advance before performing the convolution integration with the delay profile of the desired signal) to the adaptive algorithm based on the MMSE standard, The receiving antenna weight for each antenna is calculated.

  After the transmission / reception antenna weight is calculated in this way, as shown in step 019, the transmission antenna weight is set in the weight multiplication unit of the receiver, and carrier sense is performed in the transmission antenna pattern. This is because the amount of interference coming from the adjacent system observed when carrier sense is performed in the transmission pattern is considered to be approximately equal to the amount of interference given to the adjacent system during transmission. This is because the amount of interference given to the system can be predicted.

  As a result of this carrier sense, if an interference amount equal to or greater than the threshold value is observed, communication termination is notified to the terminal as shown in step 021. This is because even if a null is formed in the direction of the adjacent system, it is determined that interference with the adjacent system cannot be suppressed and communication of the adjacent system that has already been started is hindered. In this case, the control is terminated without starting communication in the own system. On the other hand, if the observed interference amount is less than or equal to the threshold, as shown in step 022, the terminal is notified that the communication preparation is completed.

  Through the above processing, the transmission / reception antenna pattern formation in the base station is completed. After this, if there is a notification that the terminal is ready for communication, a transmission antenna pattern is formed during transmission, and a reception antenna pattern is formed during reception for communication.

  However, it is preferable that the carrier sense is omnidirectional (the reception antenna weights are all set to 1), and transmission is performed even when a signal from an adjacent system (a system to which a null is directed) is observed. During this carrier sense, the transmission antenna weight may be set as the reception antenna weight. This is because, in a system according to the normal CSMA / CA scheme, transmission is refrained when a signal from an adjacent system is observed at the time of carrier sense. This is because even if transmission is performed regardless of the result of carrier sense, the influence on the adjacent system is reduced.

  Next, the flow of control processing on the terminal side according to the embodiment of the present invention will be described with reference to FIG. As shown in FIG. 3, the control on the terminal side according to the present embodiment is almost the same as the control on the base station side, and the following description is also substantially the same as the description on the base station side control described above.

  As shown in FIG. 3, when the power is turned on in step 050, the used channel is carrier sensed for a certain period of time (step 051), and it is determined whether there is an adjacent system using the same channel (step 052). ). As a result, if it is determined that there is no adjacent system, as shown in step 063, all antenna weights are set to 1, and normal transmission according to the CSMA / CA scheme is started. On the other hand, if it is determined that the adjacent system exists, the reception is continued and the delay profile of the interference signal coming from the adjacent system is measured (step 053). Then, the received interference signal header is demodulated (step 054), and the address of the signal source is acquired. If there is a matching address between the source address obtained here and the source address stored in the memory (not shown in FIG. 1), as shown in steps 056 and 057, the receiving antenna weight is set. The delay profile of the corresponding signal stored in the memory of the control unit 24 is discarded and the newly measured delay profile is stored (the delay profile is updated). If it is determined in step 055 that the corresponding signal is received for the first time, the delay profile is newly stored in the memory in the receiving antenna weight control unit 24. At this time, the path selection unit 20 (FIG. 1) selects only the path having the highest power among the newly measured delay profiles, and the path amplification unit 21 (FIG. 1) amplifies the path. Thus, the generated new delay profile is stored in the memory in the transmitting antenna weight control unit 23 (step 057). Such processing is continued for a time set in advance as the initial carrier sense time, and the delay profile of the observed interference signal is measured without exception (step 058).

  After such an initial carrier sense, a beacon is transmitted at the base station, so that the terminal receives it and starts an authentication process according to the IEEE802.11 procedure shown in FIG. At the time of this authentication, the terminal receives an authentication response and an association response, measures a delay profile from the preamble of these desired signals, and stores it in a memory in the receiving antenna weight control unit 24. Further, only the path having the highest power in the delay profile of the desired signal is selected by the path selection unit 20 and stored in the memory in the transmission antenna weight control unit 23 (step 060). However, it is assumed that the authentication request and the association request are transmitted using an omnidirectional antenna pattern (all transmission complex weights are set to 1).

  Next, from the demodulation result of the header of the signal arriving from the adjacent system performed in step 054, it is determined whether the adjacent system performs moving image transmission or intermittent short data transmission (step 061). ). Alternatively, as described above, the length of packets continuously observed in the carrier sense unit 28 may be roughly measured to estimate what kind of packet transmission is performed in the adjacent system. If it is determined in step 061 that moving image transmission is being performed in the adjacent system, the process proceeds to step 064. If it is determined that intermittent short data transmission is being performed, the process proceeds to step 062, where it is determined what kind of data transmission the own system will perform. If it is determined in step 062 that the own system performs moving image transmission, the process proceeds to step 064. If it is determined that intermittent short data transmission is performed, the process proceeds to step 063. In step 063, all antenna weights are set to 1, and normal transmission according to the CSMA / CA system is started.

  If it is determined that at least one of the adjacent system and the own system performs moving image transmission, as shown in step 064, the transmitting antenna weight control unit 23 determines the arrival direction of the desired signal and the interference signal. Estimation is performed. As described above, this direction-of-arrival estimation is performed using the ESPRIT algorithm. Then, as shown in step 065, the angle difference between the arrival directions of the desired signal and the interference signal is calculated, and the angle difference and a predetermined angle are determined. As a result, when it is determined that the direction of arrival of the desired signal and the interference signal is within a predetermined angle, as shown in step 066, the base station is notified of the suspension of communication and the control is finished. . Conversely, when it is determined that the difference in the angle of arrival between the desired signal and the interference signal is greater than a predetermined angle, an antenna pattern that can ensure the communication quality of the local system while reducing interference with adjacent systems. Therefore, the transmission / reception antenna weight is calculated by the subsequent control.

  In the calculation of transmission / reception antenna weights shown in step 067, a transmission antenna weight calculation procedure will be described first. Here, the transmission antenna weight is calculated in the transmission antenna weight control unit 23 as described above. As this procedure, a virtual interference signal is generated within a certain angle around the estimated arrival direction of the interference signal. Then, a new delay profile (virtual delay profile) is generated by adding the generated virtual interference signal. Then, the delay profile of the desired signal after path selection and the virtual delay profile of the interference signal are convolved with different OFDM signals (prepare the same number of different OFDM signals as the delay profile), and after each convolution integration Are added together to generate a pseudo received signal. Applying the pseudo received signal generated in this way and the reference signal of the desired signal (the OFDM signal prepared in advance before convolution integration with the delay profile of the desired signal) to an adaptive algorithm based on the MMSE standard Thus, the transmission antenna weight for each antenna is calculated.

  The reception antenna weight is calculated in the reception antenna weight control unit 24. This procedure is almost the same as the processing in the transmitting antenna weight control unit 23. The delay profiles of the desired signal and the interference signal are convolution integrated with different OFDM signals, and the signals after convolution integration are added and simulated. Generate a received signal. Then, by applying this pseudo received signal and the desired signal reference signal (the OFDM signal prepared in advance before performing the convolution integration with the desired signal delay profile) to the adaptive algorithm based on the MMSE standard, The receiving antenna weight for each antenna is calculated. After the transmission / reception antenna weight is calculated in this way, as shown in step 068, the transmission antenna weight is set in the weight multiplication unit of the receiver, and carrier sense is performed in the transmission antenna pattern.

  As a result of this carrier sense, when an interference amount equal to or greater than the threshold value is observed, it is determined whether or not the own system performs moving image transmission again as shown in step 070. As a result, when it is determined that the system performs continuous and large-capacity data communication such as moving image transmission, Ack transmission is performed using the modulation scheme and coding rate that are the lowest transmission rate. The transmission power is lowered accordingly. At this time, the control for setting the modulation scheme and the coding rate low may not be performed, and the processing for reducing only the transmission power may be performed. However, it is more preferable to set the modulation scheme and the coding rate in conjunction with the transmission power. It is possible to avoid a situation in which an error occurs. Furthermore, the number of Ack transmissions is set to be smaller than usual (for example, it is reduced to 1 / M times normal: M is an integer of 2 or more), and the base station is notified of the completion of communication preparation. By performing such control, it is possible to ensure the characteristics of the adjacent system and the own system even when the influence on the adjacent system cannot be removed by only the formation of the antenna pattern. This is because, when performing image transmission, almost all signals transmitted from the terminal are Ack. Therefore, it is possible to reduce interference caused to adjacent systems by reducing the transmission power of Ack and further reducing the number of transmissions. It is. If it is determined in step 070 that the local system does not transmit moving images, it is highly likely that long packets are transmitted frequently from the terminal, but this affects the adjacent system. Therefore, in this case, the process proceeds to step 066 to notify the base station of the suspension of communication and finish the control. If the observed interference amount is equal to or smaller than the threshold value as a result of step 069, the base station is notified of the completion of communication preparation and prepares for subsequent communication.

  With the above processing, the transmission / reception antenna pattern formation at the terminal is completed. If a communication preparation completion notification at the base station is received before or after this, the transmission antenna pattern is formed at the time of transmission and the reception antenna pattern is formed at the time of reception. And communicate. However, similar to the control in the base station described above, carrier sense is omnidirectional (the receiving antenna weights are all set to 1), and signals from neighboring systems (systems to which nulls are directed) are observed. Is also configured to transmit.

  By performing the configuration as described above and control using an antenna pattern with nulls directed toward the adjacent system at the time of transmission, it is possible to avoid collision of packets when the adjacent system or the own system performs moving image transmission, which is favorable. Reception characteristics can be obtained. Therefore, even when systems using the antenna pattern control method according to the present embodiment are adjacent to each other, even when at least one of the systems performs moving image transmission, the other system transmits packets. Therefore, it is possible to ensure high throughput in both systems.

  As described above, the present invention has been described according to the embodiment. However, the present invention is not limited to these examples, and various modifications can be made.

  The present invention can be applied to a wireless transmission system, and is particularly effective when a plurality of systems that handle data having a large transmission capacity in a narrow area coexist.

It is a figure which shows the structural example of the transmitter / receiver in this Embodiment. It is a flowchart figure which shows the flow of the base station side control in this Embodiment. It is a flowchart figure which shows the flow of the terminal side control in this Embodiment. FIG. 2 is a diagram illustrating a configuration of a packet format in IEEE 802.11. It is a figure which shows the example of the transmission procedure in IEEE802.11. It is a figure which shows the example of the signal power of (a) FDMA, (b) TDMA, (c) CDMA system. It is a figure which shows the outline | summary of a CDMA system. It is a figure which shows the example of a delay profile. It is a figure which shows the structure (a) and antenna pattern (b) of an adaptive array antenna. It is a figure which shows the power amplification (a) and antenna pattern (b) of a delay profile. It is a figure which shows the delay profile (a) and antenna pattern (b) which added the virtual signal.

Explanation of symbols

10, 11, 12 ... Antenna
13, 14, 15 ... high frequency RF section
16, 17, 18 ... Transmission / reception selector switch
19… Delay profile measurement unit
20 ... Path selection part
21 ... Changeover switch
22: Path amplification unit
23 ... Transmitter antenna weight controller
24 ... Receiving antenna weight controller
25 ... Antenna weight changeover switch
27. Demodulator
28 ... Career Sense Department
26 ... Receiving antenna weight multiplier
29… Modulation section
30 ... Copy section
31 ... Transmitter antenna weight multiplier
32 ... Antenna weight control unit
33 ... Receiver
34 ... Transmitter
100 ... Preamble
101 ... Header
102 ... Data
110 ... Beacon packet
111 ... Authentication request packet
112 ... Authentication response packet
113 ... Association request packet
114 ... Association response packet
115, 116 ... data packets
120 ... Transmission data spectrum
121 ... Transmitted signal spectrum of desired user
122, 123 ... Transmission signal spectrum of other users
124 ... Received signal spectrum
125 ... Spectrum after extraction of desired signal
126 ... interference spectrum by other users
130 ... Demodulator

Claims (18)

A communication apparatus in a wireless communication system that includes an adaptive array antenna including a plurality of antennas and uses a CSMA / CA method as an access method,
As a result of carrier sense, a wireless communication system that uses the same frequency band as the wireless communication system, and includes a communication device that does not directly communicate with a communication device in the wireless communication system (non-communication target system) Means for determining the type of data transmission performed by the non-communication target system when
When it is determined that the non-communication target system continuously transmits a packet having a length equal to or greater than a certain threshold, or a certain number of packets having a length equal to or greater than a certain threshold When starting transmission over time, the communication apparatus controls the directivity of the adaptive array antenna. The antenna pattern formed when at least one system of the wireless communication system or the non-communication target system transmits a packet having a length equal to or greater than a certain threshold over a certain period of time is as follows: The communication apparatus according to claim 1 , wherein different antenna patterns are used. The communication apparatus according to claim 2 , wherein the antenna pattern used at the time of transmission is an antenna pattern in which a null is formed in a direction in which a signal transmitted from a communication apparatus in the non-communication target system arrives. Means for measuring a delay profile of the received signal, means for generating a virtual delay profile from the measured delay profile, and means for generating a pseudo received signal from the delay profile and the transmission signal ,
The antenna pattern used at the time of transmission includes a delay profile of a signal transmitted from a transmission destination (communication partner) in the wireless communication system, a pseudo reception signal generated from the transmission signal, and a signal transmitted from the non-communication target system. A pseudo reception signal obtained by adding a virtual delay profile generated from the transmission signal of the non-communication target system and a pseudo reception signal generated from the non-communication target system is used as an input signal, and a transmission signal of the wireless communication system is used as a reference signal. The communication apparatus according to claim 3 , wherein the communication apparatus is an antenna pattern generated so as to reduce an error between the signal and the input signal. A means for selecting only a path having a power equal to or higher than a certain threshold among a plurality of paths in the measured delay profile, a means for amplifying the power of the selected path by a certain value, and estimating the arrival direction of the selected path 5. The method according to claim 4 , further comprising: means for adding a path having the same power as the selected path within an angle centered on an arrival direction of the selected path, and generating the virtual delay profile. The communication apparatus as described in. Path for amplifying the power, communication apparatus according to claim 5, characterized in that the path in the delay profile of the signal transmitted from the non-communication systems. Wherein the direction in which signals transmitted from the transmission destination in a wireless communication system comes with a highest power, angular difference between the direction signal transmitted from the non-communication target system arrives at the highest power, is The communication apparatus according to claim 5 or 6 , wherein transmission is performed using the formed antenna pattern on condition that the angle is equal to or greater than a certain angle. Wherein the direction in which signals transmitted from the transmission destination in a wireless communication system comes with a highest power, angular difference between the direction signal transmitted from the non-communication target system arrives at the highest power, is 8. The communication apparatus according to claim 5 , wherein a transmission destination in the wireless communication system is notified that communication is stopped on condition that the angle is equal to or less than a certain angle. 9. 9. The communication apparatus according to claim 3 , wherein the carrier sense performed after the antenna pattern is calculated is performed using a transmission antenna pattern. The communication apparatus according to claim 9 , wherein carrier sense performed by the transmission antenna pattern is performed only once for the first time after the antenna pattern is calculated. In carrier sensing to be performed after the antenna pattern calculation, or the second and subsequent carrier sense result ignore, or claim 9 or 10 carrier sense from the second time, characterized in that to start transmission without performing The communication apparatus as described in. In the first carrier sense performed after calculating the antenna pattern, if the signal transmitted from the non-communication target system is observed with a power equal to or lower than a certain threshold value, the transmission destination in the wireless communication system indicates that communication preparation is complete. The communication apparatus according to claim 9, wherein transmission is performed using the formed antenna pattern. During the first carrier sensing to be performed after calculating the antenna pattern, wherein when observed at the threshold or more power there is a signal transmitted from the non-communication systems, the transmission destination of the effect to stop the communication in the wireless communication system The communication apparatus according to any one of claims 9 to 12, wherein a process of notifying a message is performed. In the situation where the signal transmitted from the non-communication target system is observed at a power equal to or higher than a certain threshold at the time of the first carrier sense performed after the antenna pattern is calculated, the transmitting communication device of the wireless communication system is equal to or higher than a certain threshold. when not performing a predetermined time or longer-term transmission of a packet having a length, a communication apparatus according to claim 13, characterized in that notification of canceled communication to the transmitting-side communication device. When carrier sense to be performed after antenna pattern calculation, the in situations observed at the threshold or more power there is a signal transmitted from the non-communication systems, the threshold value longer than there is transmission side communication apparatus of the wireless communication system When transmitting a packet having a certain length over a predetermined time, the transmission power of the delivery confirmation signal sent to the transmission side communication device is set lower than the transmission power of the signal in the packet having a length equal to or greater than a certain threshold. The communication apparatus according to claim 9, wherein the communication apparatus is characterized in that The communication apparatus according to claim 15, in accordance with the transmission power of the acknowledgment signal set the low and sets a low modulation scheme of the acknowledgment signal. When carrier sense to be performed after antenna pattern calculation, the in situations observed at the threshold or more power there is a signal transmitted from the non-communication systems, the threshold value longer than there is transmission side communication apparatus of the wireless communication system 17. The transmission device according to claim 9 , wherein the transmission confirmation signal is transmitted to the transmission side communication device when the transmission of the packet having a certain length of time is performed over a predetermined time . The communication apparatus as described in . The communication apparatus according to claim 2 , wherein the antenna pattern used at the time of reception is an antenna pattern controlled in a direction in which the received signal power to interference and noise power ratio (SINR) is maximized.

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