JP4878445B2 - Communication apparatus and method - Google Patents

Description

  The present invention relates to a communication apparatus and method, and more particularly, to a communication apparatus and method for performing communication by frequency hopping (FH).

  Wireless communication systems are used as highly portable network systems that are not constrained by communication cables, and are dramatically improved due to improvements in the transmission speed of wireless communication sections, the spread of mobile terminals, and the emergence of applications suitable for mobile communication. Is spreading widely. For example, as a method for wirelessly connecting computer devices at a relatively short distance, a wireless LAN (Local Area Network) system using a 2.4 GHz or 5 GHz band radio wave is widely used.

  Such a wireless LAN system not only has a feature that a cable connection is not required and a free device layout in the room is possible, but if the terminal is in the vicinity of the connection point, for example, a room in a company, a meeting room It is a very convenient system that allows users to freely connect to the company's backbone LAN in different locations, and can do the same work at their desk at any location. Further, in recent years, it has become possible to connect to the Internet using a terminal owned by a connection service provider from an outdoor connection point.

  Similarly, there is an increasing demand for connecting information processing devices such as computer peripheral devices, digital cameras, and digital video cameras to printers and mobile phones. Currently, these are generally connected by a wired cable such as USB or IEEE1394, but wireless connection is also considered as a means by which a user can easily connect these devices. For example, Bluetooth is known as a wireless communication system between devices in such a close range. Such a system is different from a wireless LAN in that it is aimed at wireless connection in the surrounding environment of a person, which is considered to be about 10 meters at most, unlike a LAN, and it is called WPAN (Wireless Personal Area Network). It has been called. Currently, WPAN is being developed as a standard for IEEE802.15 standards. On the other hand, in recent years, it has been proposed to use a UWB (Ultra Wide Band) communication method as a physical layer method capable of realizing higher-speed communication than a conventional WPAN system such as a Bluetooth system. UWB is a method for spatially improving frequency utilization efficiency by limiting the radiated power to the level of radiation noise generated by ordinary devices, instead of occupying a very wide band for communication. Since the transmission level is low because the transmission level is low, it is considered that a relatively high-speed data communication can be realized because a communication path with a clear line of sight can be assumed. Therefore, it can be said that the UWB system is very suitable for communicating large-capacity data such as multimedia data at close range such as WPAN.

  In indoor wireless communication systems such as wireless LAN and WPAN, wireless signals transmitted from a transmitter are reflected by walls and ceilings, furniture and fixtures placed indoors, and directly received and delayed incoming waves at the receiver. Are received as a combined signal. Such a wireless communication environment is called a delay propagation environment or a multiple propagation environment. In such a multiple propagation path, in order to correctly demodulate transmission data at the receiver, it is necessary to correct the waveform distortion caused by the delayed wave by some method. As such a waveform distortion correction method, there is a method in which correction is performed by an adaptive equalizer or the like on the time axis, while there is also a method in which the modulation method itself has resistance against delayed waves.

  An OFDM (Orthogonal Frequency Division Multiplex) scheme is one of the communication schemes that can eliminate the effects of delayed wave interference. The OFDM system is a modulation system in which a plurality of orthogonal narrowband signals are arranged on the frequency axis of the occupied band, and has already been adopted in digital television broadcasting, wireless LAN systems, and the like. Here, these multiple narrowband signals are called subcarriers. Since each subcarrier is a signal having a low transmission rate, it has a relatively strong characteristic against delayed wave interference due to multipath. Furthermore, by providing an area called a guard interval between data symbols on the time axis, interference between data symbols due to delayed waves is further reduced. For the modulation and demodulation processing of the OFDM signal, fast Fourier transform (FFT) processing by digital calculation is used.

  A multiband OFDM scheme is currently being proposed as a communication scheme for UWB adopted as the physical layer of WPAN. The multi-band OFDM scheme is a scheme for communicating a radio signal multiplexed by the OFDM modulation scheme by switching different frequency bands for each data symbol.

  FIG. 6 is a diagram showing an operation principle of a multiband OFDM system using three different frequency bands. The multiband OFDM transmitter transmits an OFDM signal while sequentially switching three frequency bands f1, f2, and f3 as shown in (a) on the time axis as shown in (b). In the currently proposed mode, four different types of frequency hopping patterns as shown in FIGS. 8A to 8D are used to configure different radio channels. By using channels with different frequency hopping patterns, it is intended to reduce as much as possible interference between networks operating simultaneously in geographically overlapping situations.

  FIG. 7 is a diagram showing a state in which two different networks are operating in a geographically overlapping region. In the figure, two terminal stations DEV1 and DEV2 constitute a network 1 that performs communication using the hopping pattern # 1 shown in FIG. Two other terminal stations DEV-A and DEV-B constitute a network 3 that performs communication using the hopping pattern # 3 shown in FIG. 8C. Here, DEV2 transmits data to and from DEV1, but at the same time DEV-A exists in the vicinity, so the hopping pattern signal used in network 3 interferes and interferes with the received signal of DEV2. There is a fear. Here, since the hopping patterns used in the two networks are different from each other, there are a symbol that causes a collision by using the same frequency at the same time point and a symbol that does not cause a collision because a different frequency is used at the same time point. Note that it exists. In this way, when different hopping patterns are used for each network, the manner in which data symbols in a radio frame collide greatly varies depending on the relationship between the hopping phases.

  In the multiband OFDM scheme, the time spreading scheme is adopted in order to reduce packet loss due to symbol collision and realize highly reliable communication. As shown in FIGS. 9 and 10, this is a system in which symbols composed of the same information data are transmitted by overlapping different symbols. In FIG. 9, information signals modulated into two data symbols with the same number are the same information signals, and the same information signals are transmitted in duplicate at different timings and different communication frequencies. As a result, a time / frequency diversity effect can be obtained, and even if one of the two symbols is destroyed due to a collision with a signal from another network as an interference source, the remaining symbols are demodulated. This makes it possible to avoid loss of the entire packet.

  However, in FIG. 9, due to the relationship of the frequency hopping phase between the desired signal and the interference signal, for example, the symbols (1) and (4) are both destroyed by collision with the interference signal. In such a state, the frame cannot be normally received by the receiving terminal, resulting in a frame loss. Conversely, in FIG. 10, the hopping phases are different from each other even though each network uses the same frequency hopping pattern as in FIG. Therefore, at least one of the two time-spread symbols transmitted in the desired signal is free from collision with the interference signal. In this case, since the entire frame is normally received by the receiving terminal, there is no frame loss.

  As described above, in frequency hopping communication employing the time spreading method represented by the multiband OFDM communication method, when each network uses another predetermined frequency hopping pattern, the other interference source Depending on how to select the hopping phase of the own network for the FH signal by the network, the situation in which packet loss due to interference occurs varies greatly. Therefore, in order to prevent frame loss, it is important to control an appropriate hopping phase using this fact.

  As a conventional technique for controlling the hopping pattern and phase in the frequency hopping communication system, for example, Japanese Patent Laid-Open No. 2003-229868 (Patent Document 1) can be cited. This document discloses a technique related to wireless communication between a base station as a control station and a remote station as a terminal station. A technique is disclosed in which, when a base station cannot correctly receive a frequency hopping signal from a remote station, a hopping pattern phase used by the remote station in retransmission is notified from the base station. The application range of this technology is limited to a network of 1-to-N topology in which a communication path is set between a control station and a terminal station. When the terminal stations communicate with each other like WPAN, it is impossible to use it for controlling the hopping phase. Also, since it is assumed that a reverse radio link has been established to notify the hopping phase information used for retransmission, this technology will not function properly if transmission of the control information fails There is a drawback.

  As another similar prior art, there is Japanese Patent No. 3150413 (Patent Document 2). This document discloses a technique for selecting a hopping phase by adopting a delay time generated from a random number when an AVM slave station serving as a terminal station performs retransmission. In this example, since the hopping phase in retransmission is simply selected by a random number, there is no guarantee that transmission can be performed with an appropriate hopping phase during retransmission, and a large effect cannot be obtained in improving packet loss.

JP 2003-229868 A Japanese Patent No. 3150413

  As described above, in the frequency hopping system using the time spreading method adopted in multiband OFDM, it is possible to realize data transmission even if a plurality of networks are operated in the same region. However, for that purpose, it was necessary to appropriately select the hopping phase to be used. In addition, in the prior art, it is difficult for the terminal on the data transmission side to transmit data at an appropriate hopping phase, so that packet collisions frequently occur between networks and the throughput of the entire network is reduced. There was a problem.

  The present invention has been made in view of such problems. That is, an object of the present invention is to provide a communication apparatus and method that reduce packet loss due to packet collision between networks and realize high throughput.

One aspect of the present invention relates to, for example, a communication apparatus that performs communication using a periodic predetermined frequency hopping pattern, a transmission unit that transmits the same data multiple times by a time spreading method, and a transmission by the time spreading method. Determination means for determining failure of communication of all of the first data of the same data, and when the determination means determines that communication of the first data has failed, the time spreading method The transmitting means does not change the frequency hopping pattern so that at least one of the same data transmitted by a phase relationship with the interference signal avoids a collision with an interference signal. Changing means for changing the frequency hopping phase at the time of transmission.

According to the present invention, when communication with the communication partner fails, at least one of the same data transmitted by the time spreading method has a phase relationship with the interference signal so as to avoid collision with the interference signal. Thus, since the frequency hopping phase is changed without changing the frequency hopping pattern, even if another network as an interference source communicates by the frequency hopping method, the packet loss due to the packet collision between the networks is reduced, and high Throughput can be realized.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, It shows only the specific example advantageous for implementation of this invention. In addition, not all combinations of features described in the following embodiments are indispensable as means for solving the problems of the present invention.

  FIG. 2 is a diagram illustrating a configuration of a communication device in the wireless communication system according to the present embodiment. The wireless communication system in the present embodiment is a multiband OFDM wireless communication system. In the figure, the communication apparatus includes an antenna 101, a radio frequency (RF) processing unit 102, a demodulation unit 103, a modulation unit 104, a frequency hopping unit 105, a media access control unit 106, and an application processing unit 107. The function of each part will be apparent from the following description. With this configuration, the communication device functions as a data frame transmitting terminal (transmitter) or a data frame receiving terminal (receiver).

  The communication apparatus in the present embodiment switches the OFDM signal while sequentially switching the three frequency bands f1, f2, and f3 as shown in FIG. 6A on the time axis as shown in FIG. Send. At this time, different radio channels are configured using four different types of frequency hopping patterns as shown in FIGS. In addition, this communication apparatus transmits a radio frame by a time spreading method in which the same information signal is transmitted by using different frequencies at different timings.

  Furthermore, the communication apparatus according to the present embodiment supports retransmission processing. That is, when this communication apparatus functions as a data frame transmitting side terminal, it is determined whether or not an acknowledgment (ACK) frame returned from the data frame receiving side terminal has been received at a predetermined time after data frame transmission. Based on this determination result, it is determined whether or not the data frame transmitted by the own station has been correctly received by the data frame receiving side terminal. If the data transmitting side terminal cannot receive such an ACK frame normally, it tries to retransmit the same data frame.

  A specific example of this retransmission processing will be described in detail below. In this embodiment, this retransmission processing is controlled by the media access control unit 106. FIG. 1 shows a detailed configuration of the media access control unit 106. A frame transmission / reception control unit 206 exchanges various types of control information with the following components in order to control transmission / reception of data frames in response to a request from the application processing unit 107. The frame transmission / reception control unit 206 includes an ACK timer 206a for measuring the time taken to receive an ACK frame. 201 is a reception frame analysis unit that analyzes the demodulated reception frame passed from the demodulation unit 103 and outputs the analysis result to the frame transmission / reception control unit 206. Reference numeral 202 denotes a reception FH pattern synchronization unit that synchronizes a frequency hopping pattern (hereinafter also referred to as “FH pattern”) of a reception frame passed from the demodulation unit 103. 203 is an FH pattern switching unit that switches FH patterns in accordance with transmission / reception switching control information from the frame transmission / reception control unit 206. A transmission FH pattern generation unit 204 generates a transmission FH pattern according to the frequency hopping phase control information from the frame transmission / reception control unit 206 and passes this to the FH pattern switching unit 203. Reference numeral 205 denotes a frame transmission control unit that controls output of transmission data from the frame transmission / reception control unit 206 to the modulation unit 104.

  3 and 4 show an example of a sequence related to the data frame transmission operation of the communication apparatus according to the present embodiment. FIG. 3 shows a sequence when frame transmission can be normally executed, and FIG. 4 shows normal frame transmission. This shows the sequence in the case where cannot be executed.

  In FIG. 3, the data frame transmitting side terminal is represented as “DEV1”, and the data frame receiving side terminal is represented as “DEV2”. Assume that the internal configurations of both DEV1 and DEV2 are as shown in FIGS. When the application processing unit 107 of DEV1 holds data requesting transmission to DEV2, the application processing unit 107 requests the media access control unit 106 to perform a transmission operation. Specifically, the frame transmission / reception control unit 206 of the media access control unit 107 gives transmission data to the frame transmission unit 205 to start the transmission operation, and at the same time, transmits the frequency hopping phase control information during transmission to the transmission FH pattern generation unit. Give to 204. In the modulation unit 104 that has received the transmission data from the frame transmission unit 205, the transmission data is configured into a multiband OFDM frame, modulated into a high-frequency radio signal by the RF processing unit 102, and then transmitted from the antenna 101 into the space. . Further, the communication apparatus according to the present embodiment generates a frequency hopping pattern by the frequency hopping unit 105 based on the phase control information from the transmission FH pattern generation unit 204 selected by the FH pattern switching unit 203 according to the multiband OFDM scheme. The carrier frequency is switched over time. At this time, the data frame is transmitted one symbol at a time in three different frequency bands as described with reference to FIG. 6, for example.

  As shown in FIG. 3, the DEV 1 that has transmitted the data frame activates an ACK timer 206a provided in the frame transmission / reception control unit 206 in order to wait for reception of an ACK frame for the data frame. In the WPAN protocol proposed for use in the UWB communication system, the period from the end of data frame transmission to the start of ACK frame return for the data frame is defined as a Short Frame Interspace (SIFS) period. This is determined based on the time generally required for the communication apparatus to switch between transmission and reception, and is usually several μs to several tens μs.

  This data frame reaches DEV2 as a receiving station, and DEV2 similarly receives this data frame from the radio space via the antenna 101. In DEV2, the RF processing unit 102 down-converts the data frame into a baseband signal, and then the demodulation unit 103 performs data demodulation and decoding. The received data obtained by the demodulation is transmitted to the media access control unit 106. In the media access control unit 106, the received data is analyzed by the received frame analysis unit 201 provided therein. Here, if the identifier of the data frame, such as the transmission destination address and ID number, is the same as that assigned to the local station, and the error detection function determines that the received data does not contain an error, the data frame Is sent back to DEV1 in order to notify DEV1 that is the transmission source. In FIG. 3, since the ACK frame is received from DEV2, which is the destination of the data frame, before the ACK timer times out, DEV1 ends the series of data transfer processes assuming that the data frame transfer is successful.

  FIG. 4 is a sequence diagram when the data frame from DEV1 is not normally transmitted to DEV2. Also in the figure, first, DEV1, which is a data frame transmitting side terminal, transmits a data frame to the receiving side terminal DEV2 in the same procedure as described above. If this data frame is not normally received by DEV2 due to interference from other networks, DEV2 naturally does not perform ACK transfer to DEV1. Therefore, DEV1, which has not received an ACK frame during the ACK timeout period, tries to transmit the same data frame again. As described above, the communication apparatus according to the present embodiment retransmits the data frame that failed to be transmitted by the ACK protocol.

  It should be noted that in the WPAN protocol using the UWB communication method, if an ACK for the previous data transmission could not be received, the data frame transmission side waits for the reception slot time from the SIFS period described above. The terminal DEV1 is a point that immediately transmits a retransmission frame. As described above, since the data frame is retransmitted in a relatively short time in the WPAN protocol, there is a high possibility that the frame from the other network that has become an interference source at the previous data frame transmission continues to be communicated as it is. Therefore, when DEV1 retransmits a data frame, if transmission is performed with the same phase as the previous hopping, the frequency transition of the interference source signal and the hopping again have the same phase relationship, and there is a possibility that the frame collision will reoccur.

  The present embodiment is characterized in that, when a data frame is retransmitted in this way, retransmission is performed at a phase different from the previous frequency hopping phase. For example, the pattern period of the hopping pattern of the interference signal is 6 symbols as shown in FIGS. 9 and 10, and the frequency hopping time slot length is Ts. Then, if transmission of a retransmission frame is started at a timing 6 × n × Ts (where n is a natural number) from the start of the previous data frame transmission, a symbol collision with the interference signal will occur as in the previous case. . In this example, 6 × Ts represents the frequency hopping period (see FIG. 8), and it will be understood that the above 6 × n × Ts represents an integer multiple of the frequency hopping period.

  The frame transmission / reception control unit 206 recognizes that the current frame transmission is a retransmission of the previous data frame based on the timeout of the ACK timer 206a. At this time, the phase control information given to the transmission FH pattern generation unit 204 is different from the previous data frame transmission, for example, a phase that is shifted from the integer multiple of the frequency hopping cycle by one frequency hopping time slot time Ts. Stipulate. Thus, even if there is a symbol that causes a collision due to the phase relationship with the interference signal as shown in FIG. 9 at the previous transmission frame timing, the phase relationship with respect to the interference signal of the transmission frame at the time of retransmission is shown in FIG. As shown in FIG. 10, the state changes to a state in which a collision can be avoided in all Time spreading symbols. As a result, at least one of each Time spreading symbol can be normally transmitted over the entire frame, and the occurrence of frame loss is suppressed.

  By performing retransmission processing as described above, it becomes possible to avoid collision of hopping symbols with interference signals during retransmission, and normal transmission of data frames can be performed.

(Modification)
By the way, as long as DEV2 is a communication device having the same configuration as DEV1, it has the ability to execute the retransmission processing as described above. Therefore, as a modified example, an example will be described in which DEV1 performs data frame retransmission processing without controlling the frequency hopping phase, while DEV2 controls frequency hopping phase and performs ACK frame retransmission processing.

  FIG. 5 is a diagram showing a modified example of the sequence related to the data frame transmission operation of the communication apparatus, and is a sequence diagram when the receiving terminal cannot normally transmit the ACK frame. As in the example shown in FIG. 4, DEV1 holding transmission data transmits the first data frame to DEV2. When DEV2 normally receives the data frame and recognizes that it is a frame for itself without error, DEV2 returns an ACK frame to DEV1. However, this ACK frame may not be normally received by DEV1 due to the influence of the interference signal. In this case, after the timeout period of the ACK timer 206a expires, DEV1 retransmits the data frame that failed to be transmitted last time. At this time, DEV1 does not control the frequency hopping phase as in the example of FIG.

  DEV2 receives both the first transmitted data frame and the retransmitted data frame, but since this wireless communication system supports retransmission control, it is possible to detect duplication of transmitted frames. Therefore, DEV2 recognizes that the same data frame has been retransmitted despite the return of the ACK frame. Thus, DEV2 can determine that the ACK frame transmitted from its own station has not been normally received by DEV1. In this case, DEV2 returns the ACK frame again for the received retransmission data frame, but at this time, the frequency hopping phase is changed from the frequency hopping phase at the time of the previous ACK frame transmission to perform transmission. Also at this time, for example, as described above, for example, a phase having a timing shifted by one frequency hopping time slot time Ts from an integer multiple of the frequency hopping period is given. As a result, the retransmitted ACK frame avoids interference from the interference signal and is normally received by DEV1. Thus, as shown in the sequence of FIG. 5, DEV1, which has normally received this retransmission ACK frame, recognizes that the frame transmission has succeeded and ends a series of data transfer processing.

  By applying this modification, even when the first ACK frame has a symbol collision, the retransmitted ACK frame can avoid the symbol collision, and the frame transfer sequence can be normally completed. As a result, the throughput in the network can be improved.

  To summarize the configuration of the communication apparatus according to the embodiment described above, after transmitting a data frame as a data transmission side terminal, it is determined whether an expected recognition (ACK) frame is received from the data reception side terminal, and data frame transmission is performed. If it is determined that the packet has failed, the packet is retransmitted. Here, at the time of retransmission, transmission is performed in a phase relationship such that a collision with a frequency hopping signal used in another network serving as an interference source does not affect communication in the time spreading method. By appropriately changing the hopping phase during retransmission in this way, it is possible to avoid a situation in which all of the multiple data symbols transmitted in duplicate by the time spreading method are destroyed due to collision with the interference source (that is, frame loss). can do.

  In this embodiment, the data frame transmitting terminal changes the frequency hopping phase and retransmits the data frame. As a modification, the data frame receiving terminal changes the frequency hopping phase and retransmits the ACK frame. However, it is also possible to selectively use or combine the configurations that realize these two examples.

FIG. 1 is a diagram showing a configuration of a media access control unit in the embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a communication device in the wireless communication system according to the embodiment of the present invention. FIG. 3 is a diagram showing an example of a sequence related to the data frame transmission operation of the communication apparatus according to the embodiment of the present invention, and is a sequence diagram in a case where frame transmission can be normally executed. FIG. 4 is a diagram showing an example of a sequence related to the data frame transmission operation of the communication apparatus according to the embodiment of the present invention, and is a sequence diagram when frame transmission cannot be executed normally. FIG. 5 is a diagram showing a modification of the sequence related to the data frame transmission operation of the communication apparatus according to the embodiment of the present invention, and is a sequence diagram when the receiving terminal cannot normally transmit the ACK frame. FIG. 6 is a diagram illustrating the principle of the multiband OFDM communication system. FIG. 7 is a conceptual diagram showing a state in which a plurality of networks overlap. FIG. 8 is a diagram illustrating an example of a frequency hopping pattern in the multiband OFDM communication scheme. FIG. 9 is a diagram for explaining the occurrence of symbol collision in radio frame transmission. It is a figure explaining the avoidance of the symbol collision by Time spreading method.

Explanation of symbols

101 ... antenna
102 ... RF processing section
103 Demodulator
104: Modulator
105 ... frequency hopping section
106 ... Media access control unit
107: Application processing section
201 ... Received frame analysis unit
202 ... Reception FH pattern synchronization section
203 ... FH pattern switching part
204 ... Transmission FH pattern generator
205: Frame transmission control unit
206 ... Frame transmission / reception controller

Claims (8)

A communication device that performs communication using a periodic predetermined frequency hopping pattern,
A transmission means for transmitting the same data multiple times by the time spreading method;
Determining means for determining failure of all communication of the first data of the same data transmitted by the Time spreading method ;
The interference in which at least one of the same data transmitted by the time spreading method avoids a collision with an interference signal when the determination unit determines that the communication of the first data has failed Changing means for changing a frequency hopping phase when transmitting the data by the transmitting means without changing the frequency hopping pattern so as to be in a phase relation to a signal ;
A communication apparatus comprising:   Retransmission means for retransmitting the data by a time spreading method at a phase different from the frequency hopping phase when the data is transmitted by the transmission means when the determination means determines that the communication of the data has failed. The communication device according to claim 1, further comprising:   The determination unit determines that the transmission of the data has failed when the recognition signal returned from the device that has received the data is not received within a predetermined time after the transmission of the data by the transmission unit. The communication device according to claim 1, wherein the communication device is a communication device. 4. The communication apparatus according to claim 1, wherein the changing unit changes a phase when the data is transmitted by the transmitting unit to a value other than an integer multiple of a frequency hopping period. 5. It said changing means, according to claim 4, characterized in that to change the data to a phase displaced by one partial frequency hopping time slots from an integer multiple of the frequency hopping cycle phase in sending by the transmission means Communication device. A communication method for performing communication using a periodic predetermined frequency hopping pattern,
A transmission step of transmitting the same data multiple times by the time spreading method;
A determination step of determining failure of all communication of the first data of the same data transmitted by the Time spreading method ;
The interference in which at least one of the same data transmitted by the time spreading method avoids a collision with an interference signal when it is determined in the determination step that the communication of the first data has failed A change step of changing a frequency hopping phase when transmitting the data in the transmission step without changing the frequency hopping pattern so as to be in a phase relation to a signal ;
A communication method characterized by comprising: Before Symbol Data communication device according to any one of claims 1 to 5, characterized in that a recognition signal sent back in response to the reception of the information transmitted from the communication partner. Said determination means within a predetermined time after return the recognition signal by said transmitting means, if the same information as information transmitted by the communication partner is received again, the communication of the recognition signal has failed The communication device according to claim 7 , wherein the communication device is determined.

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