Base station and wireless communication method

The present invention relates to a base station capable of wireless communication using the OFDMA system and a wireless communication method.

In recent years, terminal devices such as PHS (Personal Handy phone System) and mobile phones have become widespread, and it has become possible to make calls and obtain information regardless of location or time. In particular, in recent years, the amount of information that can be obtained has been steadily increasing, and high-speed and high-quality wireless communication methods have been adopted to download large amounts of data.

In wireless communication such as these, it is necessary to duplicate signals in order to transmit and receive. Typical examples of the duplex method are TDD (Time Division Duplex) that switches transmission and reception by time division, and FDD (Frequency Division Duplex) that duplicates transmission and reception by different frequencies. In addition, as a method for multiple access that communicates with multiple terminal devices at the same time, TDMA (Time Division Multiple Access) that switches between multiple terminal devices by time division, and FDMA (Frequency) that divides the frequency band Typical examples are Division Multiple Access (frequency division multiple access) and CDMA (Code Division Multiple Access) in which different codes are multiplied for each terminal device.

For example, as next-generation PHS communication standards that enable high-speed digital communication, there are ARIB (Association of Radio Industries and Businesses) STD T95 (Non-Patent Document 1) and PHS MoU (Memorandum of Understanding). , OFDMA / TDMA TDD Broadband Wireless Access System (next generation PHS system) is being formulated.

OFDMA (Orthogonal Frequency Division Multiple Access) is a method of performing multiple access in OFDM (Orthogonal Frequency Division Multiplexing). OFDM is a method developed from FDM (Frequency Division Multiple). By dividing a carrier signal into a large number of subcarriers on the frequency axis and making the phase of the signal wave orthogonal between adjacent subcarriers. , This is a method of effectively utilizing the frequency band by partially superimposing the subcarrier bands. In OFDM, all subcarriers are occupied by one terminal device, but in OFDMA, several (for example, 24) subcarriers are grouped to form a subchannel, and all subchannels are shared by multiple terminal devices. By doing so, multiple connections are made. The subchannel, for example, divides the frequency band of 18 MHz into 20 pieces.

Furthermore, in the next-generation PHS system, in addition to OFDMA, multiple access is performed by TDMA. TDMA is a method of dividing a frequency into a plurality of time slots on the time axis and communicating with a plurality of partners. At present, it is assumed that the uplink (Up Link: from the terminal device to the base station) and the downlink (Down Link: from the base station to the terminal device) are each divided into four. That is, in the next-generation PHS system, communication blocks are subdivided on both the frequency axis and the time axis, and communication blocks are dynamically assigned to a large number of terminal devices for efficient communication. A communication block determined by one time slot in one subchannel is called a PRU (Physical Resource Unit), and it is assumed that 80 PRUs are used per base station.

As mentioned above, the base station can use 20 subchannels, one of which is used as a control channel (CCH) and the remaining subchannels are dynamically assigned to the terminal device (DCA:). Dynamic Channel Assign). Anchor channels or extra channels are assigned to PRUs included in the sub-channels used for communication. One anchor channel is assigned to each terminal and contains a map of PRUs to which extra channels are assigned to that terminal. The extra channel is a channel that actually contains data, and a plurality of extra channels are assigned to one terminal device according to the amount of data and the communication status. Notifying the allocation of extra channels by the map included in the anchor channel in this way is called FM-mode (Fast access channel based on Map-Mode).

The anchor channel is assigned to the PRU with the highest communication quality obtained by performing carrier sense for all PRUs. The extra channel is basically not carrier-sensed, but when the base station newly uses a PRU that is not in communication, it is assigned after carrier-sense. In this way, since the base station can dynamically change the position and number of extra channels via the anchor channel, it is possible to send and receive a large amount of data at high speed.

However, the PRU in the OFDMA system has a problem that it is susceptible to interference from adjacent PRUs. Various proposals have been made as proposals to prevent interference in wireless communication. For example, in Patent Document 1, a downlink frame is divided into resource blocks of substantially the same size, transmission data is scheduled from the beginning within the resource block, and data having a capacity exceeding the resource block is a resource block allocated to another sector. Schedule to be sent from the end of. As a result, it is possible to prevent endless communication in the same channel sector and reduce interference on the same channel.<patcit num="1"><text>Special Table 2006-515141 Gazette</text></patcit><nplcit num="1"><text>ARIB (Association of Radio Industries and Businesses) STD-T95</text></nplcit>

<p> As described above, in the OFDMA / TDMA TDD system, it is possible to communicate with more terminal devices (users) and more communication blocks (PRU) than in the conventional TDMA-TDD. However, since the communication status and the distance from the base station differ for each terminal device, and the modulation method, power, and delay amount may differ accordingly, interference may occur between adjacent PRUs. As for the amount of delay, interference can be effectively prevented by the guard band in TDMA. However, since OFDMA has overlapping subcarrier frequency bands, if the modulation method and power are significantly different, it will be affected by the radio waves of adjacent PRUs.</p><p> When an error is detected in the extra channel due to interference, it can be compensated by making a retransmission request such as ARQ (Automatic Repeat reQuest) or HARQ (Hybrid-Automatic Repeat reQuest). However, since the anchor channel contains information (map) on the number and position of extra channels, communication itself becomes impossible if the anchor channel becomes unavailable due to interference from other PRUs.</p><p> On the other hand, as described above, the anchor channel is assigned by performing carrier sense, and the position of the PRU of the anchor channel does not change until the communication is disconnected. Therefore, it is possible to determine whether or not there is interference with the predetermined PRU at the time of performing carrier sense, but it is not possible to determine whether or not there is interference with the predetermined PRU at the next and subsequent frame timings. Therefore, even if the communication status of the PRU to which the anchor channel is assigned deteriorates during communication, it cannot be dealt with.</p><p> As a specific example, extra channels are dynamically assigned, so other PRUs adjacent to the anchor channel (especially adjacent in the frequency axis direction) after the anchor channel has been assigned based on the carrier sense results. Terminal equipment extra channels may be assigned. In particular, when the extra channel uses a high-output modulation method (for example, 256QAM (Quadrature Amplitude Modulation)), the anchor channel may be interfered with by the extra channel of another terminal device, and communication may not be possible.</p><p> In view of such a problem, the present invention can minimize the interference received by the anchor channel and stabilize it by devising the position of the PRU to which the anchor channel and the extra channel used by one terminal device are assigned. It is an object of the present invention to provide a base station and a wireless communication method capable of communicating with each other.</p>

<p> In order to solve the above problems, a typical configuration of the present invention is a base station that wirelessly communicates with one or more terminal devices by using the OFDMA system, and an extra channel used for data communication and an extra. It includes an anchor channel containing a map showing the location of the PRU to which the channel is assigned, and a channel allocation unit that allocates the channel to the PRU. It is characterized by allocating the extra channel.</p><p> With the above configuration, since only the anchor channel is assigned to the PRU in the predetermined frequency region, the frequency region of the PRU to which the anchor channel is assigned and the frequency region of the PRU to which the extra channel is assigned can be reliably separated. Therefore, after the anchor channel is assigned, the extra channel of another terminal device is not assigned to the PRU adjacent to the anchor channel, so that the interference of the extra channel with the anchor channel can be prevented. This makes it possible to improve the stability of communication.</p><p> The predetermined frequency domain may be adjacent to the frequency domain to which the control channel is assigned.</p><p> Since the control channel is transmitted intermittently, the control channel does not communicate from after the control channel is transmitted to before the next control channel is transmitted. Therefore, the PRU to which the control channel is assigned has less interference with the adjacent PRU. Therefore, according to the above configuration, it is possible to reduce the interference with the anchor channel and improve the stability of communication.</p><p> The above-mentioned predetermined frequency region may be biased to the highest frequency or the lowest frequency among the frequencies used by the base station.</p><p> When the predetermined frequency region is set to the region in the middle of the frequency used by the base station, the PRU to which the anchor channel is assigned is an extra channel assigned to the PRU having a frequency higher or lower than the predetermined frequency region of the PRU. May be interfered with by. On the other hand, according to the above configuration, the number of PRUs adjacent to the PRU to which the anchor channel is assigned can be halved when the predetermined frequency domain is in the middle of the frequency, and the extra adjacent to the anchor channel can be halved. It is possible to reduce the interference caused by the channel.</p><p> A typical other configuration of the present invention is a wireless communication method using one or more terminal devices and a base station using the OFDMA system, wherein the base station is an extra channel used for data communication. , An anchor channel containing a map showing the location of the PRU to which the extra channel is assigned, and when assigning to the PRU, the anchor channel is assigned to the PRU in the predetermined frequency domain, and the extra channel is assigned to the PRU other than the predetermined frequency domain to which the anchor channel is assigned. Is characterized by assigning.</p><p> The components corresponding to the above-mentioned technical idea in the base station and their explanations can also be applied to the wireless communication method.</p>

<p> According to the base station and wireless communication method according to the present invention, it is possible to minimize the interference with the anchor channel by devising the position of the PRU to which the anchor channel and the extra channel used by one terminal device are assigned. It is possible to perform stable communication.</p>

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in such an embodiment are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to omit duplicate description, and elements not directly related to the present invention are not shown. To do.

Terminal devices such as PHS terminals and mobile phones construct a wireless communication system that wirelessly communicates with wireless communication devices (base stations) that are fixedly arranged at predetermined intervals. In this embodiment, the entire wireless communication system will be described for easy understanding, and then the specific configuration of the base station as a wireless communication device and the PHS terminal as a terminal device will be described. Further, in the present embodiment, a PHS terminal is mentioned as a terminal device, but not limited to such a case, a mobile phone, a notebook personal computer, a PDA (Personal Digital Assistant), a digital camera, a music player, a car navigation system, and a portable TV. , Game devices, DVD players, remote controllers, and various other electronic devices capable of wireless communication can also be used as terminal devices.

(Wireless communication system 100) FIG. 1 is a diagram showing a schematic connection relationship of a wireless communication system. The wireless communication system 100 includes a PHS terminal 110 (110A, 110B), a base station 120 (120A, 120B), an ISDN (Integrated Services Digital Network) line, an Internet, a communication network 130 composed of a dedicated line, and the like. It is configured to include a relay server 140.

In the wireless communication system 100, when a user connects a communication line from his / her own PHS terminal 110A to another PHS terminal 110B, the PHS terminal 110A makes a wireless connection request to a base station 120A within the communicable range. .. Upon receiving the wireless connection request, the base station 120A requests the relay server 140 to make a communication connection with the communication partner via the communication network 130, and the relay server 140 refers to the location registration information of the other PHS terminal 110B and PHS. For example, base station 120B within the wireless communication range of terminal 110B is selected, a communication path between base station 120A and base station 120B is secured, and communication between PHS terminal 110A and PHS terminal 110B is established.

In such a wireless communication system 100, various techniques are adopted in order to improve the communication speed and communication quality between the PHS terminal 110 and the base station 120. In this embodiment, for example, next-generation PHS communication technology such as ARIB STD T95 or PHS MoU is adopted, and wireless communication based on the OFDMA / TDMA-TDD method is executed between the PHS terminal 110 and the base station 120. .. In the present embodiment, an anchor channel for transmitting control information such as MCS (Modulation and Coding Scheme), communication channel map, and error information in such wireless communication is assigned to a PRU in a predetermined frequency domain to improve communication stability. Try. Hereinafter, a specific configuration of the base station 120 in such a wireless communication system 100 will be described.

(Base station 120) FIG. 2 is a block diagram showing a schematic configuration of a base station. The base station 120 includes a base station control unit 210, a base station memory 212, a base station wireless communication unit 214, and a base station wired communication unit 216.

The base station control unit 210 manages and controls the entire base station 120 by a semiconductor integrated circuit including a central processing unit (CPU). Further, the base station control unit 210 controls the communication connection of the PHS terminal 110 to the communication network 130 and other PHS terminals 110 by using the program of the base station memory 212.

The base station memory 212 is composed of ROM, RAM, EEPROM, non-volatile RAM, flash memory, HDD, etc., and stores programs, time information, and the like processed by the base station control unit 210.

The base station wireless communication unit 214 establishes communication with the PHS terminal 110 and transmits / receives data. It is also possible to determine the optimum MCS for efficient communication according to the communication quality with the PHS terminal 110, and request the MCS from the PHS terminal 110 through the anchor channel 180.

The base station wired communication unit 216 can be connected to various servers including the relay server 140 via the communication network 130.

Further, in the present embodiment, the base station control unit 210 also functions as a channel allocation unit 220. As described above, in the OFDMA / TDMA-TDD system, the communication blocks are subdivided on both the frequency axis and the time axis, and the communication blocks are dynamically assigned to a large number of terminal devices for efficient communication. A communication block determined by one time slot in one subchannel is called a PRU (Physical Resource Unit).

The channel allocation unit 220 allocates an extra channel (hereinafter referred to as EXCH) and an anchor channel (hereinafter referred to as ANCH) to the PRU. One ANCH is assigned to each terminal and contains a map of PRUs to which EXCH is assigned for that terminal. EXCH is a channel that actually contains data, and a plurality of EXCHs are assigned to one terminal device according to the amount of data and the communication status.

In the above PRU allocation, the channel allocation unit 220 allocates ANCH to the PRU in the predetermined frequency domain, and allocates EXCH to the PRU other than the predetermined frequency domain to which the ANCH is assigned. As a result, the frequency domain of the PRU to which the ANCH is assigned and the frequency domain of the PRU to which the EXCH is assigned can be reliably separated. Therefore, after the ANCH is assigned to the PRU, the EXCH of another PHS terminal 110 is not assigned to the PRU adjacent to the ANCH, so that it is possible to prevent the EXCH from interfering with the ANCH.

FIG. 3 is a diagram for explaining a frame configuration of data transmitted and received in wireless communication using the OFDMA method, and FIG. 3 (a) shows a frame configuration by conventional PRU allocation, and FIG. 3 (b). ) Indicates the frame configuration by PRU allocation according to this embodiment. OFDMA (or OFDM) has a two-dimensional map in the time axis direction and the frequency direction, and a plurality of subchannels 160 are arranged in the frequency axis direction with a uniform baseband distance, and each subchannel 160 is arranged. PRU170 is arranged for each time slot (TDMA slot) 162.

For example, if the effective frequency band of an OFDM carrier is 18 MHz, this is divided into 480 subcarriers, and 24 subcarriers are bundled to form one subchannel 160, 20 subchannels 160 are configured in one carrier. The occupied band of one subchannel 160 is 900kHz. Also, for example, if one time slot is 5 msec, it will be 2.5 msec each when divided into upstream and downstream by TDD. And since 2.5 msec is divided into four by TDMA, one time slot 162 is 625 μsec.

Therefore, PRU170 is defined by an occupied band of 900 kHz according to the baseband distance and a time length of 625 μsec by time division. A frame used for communication with a specific PHS terminal 110 is composed of ANCH 180 related to a control signal and EXCH 182 for storing data.

ANCH180 is an FM-Mode control signal and includes, for example, MI (Mcs Indicator), MR (Mcs Requirement), ACK field, and map. Here, MI indicates the MCS identifier of MCS when the data is modulated. MR is an MCS request for data sent to itself. In terms of time, MI indicates the MCS used to modulate the data transmitted at the same time as the MCS identifier, and MR indicates the desired MCS from the next time onward. The ACK field shows the error detection result of the demodulated data. Also, the map exists only in the transmission frame from the base station 120 to the PHS terminal 110 and shows the allocation of EXCH182.

ANCH180 is individually assigned to each PHS terminal 110 and occupies one PRU170. A PRU 170 with high communication quality is assigned to the ANCH 180 based on the result of the carrier sense of the base station 120. Here, the carrier sense is performed based on the signal-to-interference ratio (SINR: Signal to Interference and Noise Ratio) and the bit error rate in the PRU 170 of the frame in which transmission / reception to / from the PHS terminal 110 is performed.

EXCH182 is a PRU 170 assigned to each user as a communication path in FM-Mode, and can be assigned to one PHS terminal 110 in plurality as shown by a broken line in FIG. Such EXCH182 is assigned based on the result of carrier sense that determines whether PRU170 is being used by another user. The assigned results are then shown on the ANCH180 map as described above.

Further, in FIG. 3, among the frequencies used by the base station 120, the control channel 184 (CCH: Control CHannel hereinafter referred to as CCH) is assigned to the PRU 170 in the highest frequency region. Such CCH184 is intermittently transmitted from the base station 120, and the PHS terminal 110 recognizes the identifier (CSID) and the received electric field strength (RSSI) of the base station 120 which is a candidate for communication target by receiving the CCH184. can do. In the present embodiment, CCH184 is assigned to PRU170 in the highest frequency region, but the present invention is not limited to this, and CCH184 can be assigned to PRU170 other than such a region.

In the conventional allocation of PRU170 to ANCH180 and EXCH182, ANCH180 is assigned to PRU170 with high communication quality and EXCH182 is assigned to PRU170 not used by other users based on the result of carrier sense of base station 120. As a result, as shown in FIG. 3A, the PRU170 to which the ANCH180 was assigned was adjacent to the PRU170 to which the EXCH182 was assigned. When the EXCH182 uses a high-output modulation method (for example, 256QAM), the EXCH182 interferes with the ANCH180 and the communication quality deteriorates.

In order to solve the above problem, in the present embodiment, as shown in FIG. 3B, the channel allocation unit 220 allocates ANCH180 to PRU170 in the predetermined frequency region 190, and assigns ANCH180 to a frequency region other than the predetermined frequency region to which ANCH180 is assigned. Allocate EXCH182 to PRU170 in region 192.

By separating the frequency domain of PRU170 to which ANCH180 is assigned and the frequency domain of PRU170 to which EXCH182 is assigned as described above, only ANCH180 is assigned to PRU170 in the predetermined frequency domain 190, and after ANCH180 is assigned. The allocation of EXCH182 to the PRU170 adjacent to the ANCH180 can be avoided. Therefore, the interference of EXCH182 on ANCH180 can be reduced, and the stability of communication can be improved.

The predetermined frequency domain 190 of the PRU 170 to which the ANCH 180 is assigned is preferably adjacent to the frequency domain to which the CCH 184 is assigned, and more preferably to the highest frequency or the lowest frequency used by the base station 120. It should be biased.

Since CCH184 is transmitted intermittently, it may not be communicating. Therefore, since the PRU 170 to which the CCH 184 is assigned has less interference with the adjacent PRU 170, by assigning the ANCH 180 to the PRU 170, the interference to the PRU 170 to which the ANCH 180 is assigned can be reduced.

Further, by biasing the predetermined frequency region 190 to the highest frequency or the lowest frequency among the frequencies used by the base station 120, the number of PRU 170s adjacent to the predetermined frequency region 190 can be reduced. Therefore, it is possible to reduce the interference of the adjacent PRU170 with the PRU170 to which the ANCH180 is assigned.

Further, a blank area 194 in which neither ANCH 180 nor EXCH 182 is allocated may be provided adjacent to the predetermined frequency domain 190 for allocating ANCH 180. When ANCH180 and EXCH182 are adjacent to each other in the frequency axis direction, the communication quality of ANCH180 deteriorates. However, even if the allocation of ANCH180 is limited to the predetermined frequency domain 190, ANCH180 and EXCH182 are adjacent to each other at the boundary. It ends up. However, by providing the blank area 194 as described above, the ANCH 180 and the EXCH 182 can be separated more reliably, and the interference can be extremely reduced.

In the present embodiment, two subchannels 160 are arranged in the predetermined frequency domain 190 for allocating the ANCH 180, but the present invention is not limited to this, and the number of the subchannels 160 to be arranged is arbitrarily set. It is possible. For example, when the base station 120 is installed in an area with a low population density, the number of subchannels 160 to be arranged is set to 1. As a result, the number of sub-channels 160 allocated in the region 192 other than the predetermined frequency region can be increased, and the number of PRU 170s to which the EXCH 182 is allocated can be increased. Therefore, it is possible to improve the communication speed between the PHS terminal 110 and the base station 120. In addition, for example, in a base station 120 located in a place with a large number of connections such as a downtown area, by increasing the number of sub-channels 160 allocated to the predetermined frequency domain 190, stable communication that the ANCH 180 is hard to disconnect can be performed while increasing the number of simultaneous connections. It can be carried out.

The band (the number of subchannels 160) allocated to the predetermined frequency domain 190 can be semi-fixed as a parameter for each base station 120. In addition, the number of sub-channels can be switched by remote control or dynamically changed according to the number of connected terminals.

In the wireless communication system 100 described above, the frequency domain of the PRU 170 to which the ANCH 180 is assigned and the frequency domain of the PRU 170 to which the EXCH 182 are assigned are separated, and the base station 120 allocates the ANCH 180 to the PRU 170 of the predetermined frequency region 190 and assigns the ANCH 180. EXCH182 will be assigned to PRU170 in the area 192 other than the assigned predetermined frequency domain. As a result, the interference of EXCH182 on ANCH180 can be reduced, and the stability of communication can be improved. Next, a wireless communication method for performing wireless communication using the above-mentioned base station 120 will be described.

(Wireless communication method) FIG. 4 is a flowchart showing a processing flow of the wireless communication method according to the present embodiment. The base station 120 performs carrier sense on the PRU 170 adjacent to the CCH 184, that is, the PRU 170 in the predetermined frequency domain 190, and assigns the ANCH 180 to the PRU 170 with less interference and high communication quality (S300: ANCH allocation step). Next, the base station 120 performs carrier sense on the PRU 170 in the region 192 other than the predetermined frequency region, determines whether the PRU 170 is being used by another user, and determines whether the PRU 170 is being used by another user. Assign EXCH182 (S302: EXCH allocation step).

Then, the position and number of PRU170 of EXCH182 are written in the map of ANCH180 as allocation information, and notified for each terminal device (PHS terminal 110) (S304: map writing step). The PHS terminal 110 reads the ANCH 180 and communicates by acquiring the EXCH 182 according to the map included in the ANCH 180. At this time, since the interference with ANCH180 is extremely reduced, stable communication can be performed.

Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, which naturally belong to the technical scope of the present invention. Understood.

It should be noted that each step in the wireless communication method of the present specification does not necessarily have to be processed in chronological order in the order described as a flowchart, and may include processing in parallel or by a subroutine.

The present invention can be used for base stations and wireless communication methods capable of wireless communication using the OFDMA system.

<figref num="1">It is a figure which showed the schematic connection relation of the wireless communication system.</figref><figref num="2">It is a block diagram which showed the schematic structure of a base station.</figref><figref num="3">It is a figure for demonstrating the frame structure of the data transmitted and received in the wireless communication using the OFDMA system.</figref><figref num="4">It is a flowchart which showed the process flow of the wireless communication method which concerns on this Embodiment.</figref>

Code description

100 ... wireless communication system 110 ... PHS terminal 120 ... base station 130 ... Communication network 140 ... Relay server 160 ... subchannel 162 ... Timeslot 170 ... PRU 180 ... ANCH 182 ... EXCH 184 ... CCH 190 ... predetermined frequency domain 192 ... Area other than the specified frequency region 194 ... blank area 210 ... Base station control unit 212 ... Base station memory 214 ... Base Station Wireless Communication Department 216 ... Base Station Wired Communication Department 220 ... Channel Allocation