JP2004297824A - Mobile communication system and mobile terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system in which throughput decrease due to the collision of reservation control packets does not exist. <P>SOLUTION: A base station periodically transmits busy-tone information that corresponds to the situation of the traffic in a service area through a response control channel or a busy-tone specific channel. Each mobile terminal having a request for data transmission controls the transmission of the reservation control packet based on the busy-tone information. Thereby, sending of the reservation control packets simultaneously generated can be controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a mobile communication system and a mobile terminal device, and more particularly, to a mobile communication system and a mobile terminal device of a reservation system to which a code division multiple access (CDMA) system is applied.

Conventionally, for example, IEE Transactions on Communications, Packet Switching in Radio Channels: Part 3-Polling and (Dynamic) Split-Channels Reservation Multiple Access, COM-24, 8 (1976) pp. 832- Page 845 (IEEE Transactions on Communications, Packet Switching in Radio Channels: Part3-Polling and (Dynamic) Split-Channel Reservation Multiple Access, COM-24, 8 (1976) pp. 832-845) (hereinafter referred to as Prior Art 1) As described in (1), there is known a communication system for performing reservation-type access control in a frequency division multiple access (FDMA) system.
In the reservation type access method, a mobile terminal having a data transmission request reserves a transmission channel to a base station using a reservation control packet, and the base station schedules a transmission channel to be allocated to the terminal and a transmission timing (time slot). Then, each terminal is notified of a transmission channel and a time slot to be used by a response control packet. According to this method, basically, no packet collision occurs in the transmission channel. As another example of the communication system of the reservation type access control, for example, a system based on a time division multiple access (TDMA) system is proposed in Japanese Patent Application Laid-Open No. Hei 6-311160 (hereinafter referred to as prior art 2). Have been.

  On the other hand, as a standard method of Future Public Land Mobile Telecommunication Systems (FPLMTS), a code division multiple access (CDMA) method is promising. A mobile communication system of the CDMA system has been proposed in, for example, Japanese Patent Application Laid-Open No. 7-38496 (hereinafter referred to as Conventional Technique 3).

JP-A-6-311160

JP-A-7-38496

  However, in the mobile communication system of the reservation type access scheme using FDMA and TDMA proposed in the prior arts 1 and 2, each mobile terminal transmits a reservation control packet asynchronously with each other on a reservation control channel. There is a high possibility that the control packet for collision collides, and retransmission of the reservation control packet accompanying the collision is repeated, which is a factor of deteriorating the throughput of the entire system. On the other hand, the prior art 3 employing CDMA does not give particularly effective information on the above problem in the reservation-type access control.

  An object of the present invention is to solve the problem of reservation control packet collision in a reservation-type access control mobile communication system, and to provide a mobile communication system and a mobile terminal device with high throughput.

  Another object of the present invention is to solve the problem of collision of reservation control packets in a mobile communication system of a reservation type access control method, and to provide a mobile communication system and a mobile terminal device with high throughput.

  In order to achieve the above object, in the mobile communication system of the present invention, in a radio communication section between a base station and a mobile terminal, an uplink data packet from the mobile terminal to the base station and an uplink data packet from the base station to the mobile terminal A plurality of transmission channels used for transmitting data packets in the downlink direction, a reservation channel used for transmitting a reservation control packet indicating a transmission channel assignment request from the mobile terminal to the base station, and a transmission channel used for transmission from the base station to the mobile terminal. And a response channel used to transmit a response control packet indicating a transmission channel to transmit and receive data, and a spectrum spread by the CDMA system is applied to each of the reservation, response, and transmission channels, and data transmission is performed. The mobile terminal having the request transmits a reservation control packet to the reservation channel at an arbitrary timing, and A response control packet transmitted to the response channel specifies a transmission channel and a time slot to be used for each mobile terminal, and each mobile terminal specifies a transmission channel and a time slot specified on the transmission channel specified by the response control packet. Data packets are transmitted and received in time slots.

  More specifically, each channel of the reservation, response, and transmission is assigned a unique spreading code, for example, pseudo noise (PN), and in particular, the reserved channel is allocated to another response and transmission. Assign a shorter spreading code than the channel. The base station identifies, using a matched filter, signals of a plurality of reservation control packets transmitted from a plurality of mobile terminals with time overlap with each other, and performs a bit signal reception process for each packet.

  According to a preferred embodiment of the present invention, upon receiving a reservation packet from a mobile terminal, the base station allocates time slots in each transmission channel by schedule control, and transmits the result to each mobile terminal in a response control packet. Notice. Further, in order to regulate the total amount of simultaneously communicated packets, the base station periodically transmits a busy tone signal according to the traffic situation, and each mobile terminal having a data transmission request responds to the busy tone signal. The reservation packet transmission control is performed. Note that a plurality of response channels may be prepared in the wireless section, and a response channel to be received for each mobile terminal may be designated.

  According to the present invention, a time slot is defined for a transmission channel, and each mobile terminal transmits and receives data in a specific time slot designated by a base station. Without the provision, each mobile terminal having a data transmission request transmits the reservation control packet at an arbitrary timing, so that the transmission operation of the reservation control packet in each mobile terminal becomes easy.

  Also, each mobile terminal spreads the spectrum of the reservation control packet with a spreading code having a shorter cycle than the data packet transmitted on the transmission channel, and the base station receives the signal of the reservation channel by a matched filter. In this case, even if two or more control packets spectrally spread by the same spreading code partially overlap on the time axis, if there is a timing shift of one chip or more on the spreading code between each packet, the matched filter is Since the received packet can be identified, even if a plurality of mobile terminals each generate a reservation control packet at an arbitrary timing, it is extremely unlikely that the mobile terminal becomes unreceivable due to collision.

  As is clear from the above description, the present invention applies CDMA to a mobile communication system of a reservation type packet access control method, so that even when each mobile terminal transmits a reservation control packet at an arbitrary timing, This is to reduce the possibility of occurrence of retransmission due to collision and improve throughput.

  According to the present invention, for example, a plurality of mobile terminals transmitted a reservation control packet asynchronously with each other by applying a short spreading code to the reservation control packet and causing the base station to perform synchronous acquisition using a matched filter. Even in this case, each reservation packet can be identified at high speed by the base station. In addition, transmission efficiency can be improved by using a local address (own address) or a link number (destination address) shorter than the original address number for terminal address information set in each packet. Furthermore, when each terminal device controls transmission of a reservation control packet in response to a busy tone signal from a base station, it is possible to avoid an excessive amount of simultaneous communication packets and to guarantee good communication. .

  FIG. 1 shows an example of the configuration of a mobile communication network to which the present invention is applied.

  Reference numeral 1 denotes a public network accommodating fixed terminals 3 such as telephones, and 2 denotes a mobile communication network accommodating a plurality of base stations 4 (4a, 4b,...) And connected to the public network. Communicates with the mobile terminals 5 (5a, 5b,...) Located in the respective service areas (cells) via the wireless channel 6. On the wireless channel, CDMA packet transmission suitable for communication of multimedia information in which data, sound, and images are mixed is applied.

  FIG. 2 shows a transmission / reception protocol of the wireless communication system according to the present invention.

  FIG. 2A shows a protocol of a call setup process. There are two types of call setup processing. One is a process of first assigning a local ID (local address) in a service area to a wireless terminal, and the other is a process of assigning another destination terminal to a wireless terminal. This is a process for assigning a link number for communicating with. The local ID is an address number shorter than a unique address number given to each wireless terminal in advance, and the packet length can be reduced by using the local ID. Link numbers have a similar effect.

  The procedure of the call setup process is common to both the above-described assignment of the local ID and the assignment of the link number, and the transmitting terminal transmits the control packet 10 a for call setup reservation to the base station using the reservation channel 7. Then, using the response channel 8, the base station transmits a control packet 11a for call setup response to the transmitting terminal. Address information indicating a transmission source is set in the reservation control packet 10a. In the response control packet, a transmitting terminal address to be subjected to the receiving operation and a time slot on the transmission channel 9 to be subjected to the receiving operation are specified. As a result, the transmitting terminal specified by the response control packet includes the location registration information (local ID number) or the link information (link number) transmitted by the base station in the specified time slot on the transmission channel 9. The data packet 12a for call setup is received. If the control packet has a margin, the location registration information or the link information can be transmitted and processed by the call setup response control packet 11a without using the call setup data packet 12a.

  The reservation, response, and transmission channel are selected depending on the PN code to be applied. In addition, the base station allocates time slots on each transmission channel by, for example, referring to a management table and allocating, from among the vacant channels, a vacant slot that is temporally closest after the transmission slot of the response control packet. And so on.

  FIG. 2B shows a protocol for information transmission.

  Each transmitting terminal having a data transmission request transmits the reservation control packet 10b to the base station using the reservation channel 7. In response to this, the base station transmits the response control packet 8b to the transmitting terminal using the response control channel 8, and specifies the transmission channel 9 and the time slot to be used by the transmitting terminal for the transmission operation. When each transmission terminal that has transmitted the reservation packet receives the response control packet 11b addressed to its own station, it uses a specific time slot in the transmission channel 9 designated therein to transmit a data packet for information transmission to the base station. 12b is sent out.

  The data packet 12b is temporarily received by the base station. The base station checks the destination address of the data packet and, if the destination terminal (receiving terminal) is a mobile terminal located in the service area, utilizes the response channel 8 to communicate with the receiving terminal using a transmission channel to be operated. Then, after transmitting the control packet 13 specifying the time slot, the receiving packet 12b from the transmitting terminal is transferred in the specified time slot. The receiving terminal receives the data packet 14 transferred by the base station in the time slot of the transmission channel 9 specified by the control packet 13.

  According to the information transmission protocol described above, a control packet for reservation is required for uplink data transfer from the mobile terminal to the base station, but a reservation control packet is required for downlink data transfer from the base station to the mobile terminal. No control packet is required. The base station gives a reference timing in the transmission / reception operation to each mobile terminal by the pilot signal, and each mobile terminal can receive the data packet 14 for information transmission from the base station and the pilot signal with the same delay time. Therefore, if the pilot signal is referred to, the synchronization of the data packet can be easily performed.

  FIG. 3 shows an access control method in a conventional reservation-type wireless communication system.

  As described with reference to FIG. 2, the reservation method is a method of transmitting a reservation packet before transmitting a data packet for information transmission and transmitting a data packet after the reservation is established. First, a reservation channel 7 and a response channel 8 are prepared. Channel division is performed by frequency division (see prior art 1) or time division (see prior art 2).

  In FIG. 3, the time 21 is shown on the horizontal axis. When the wireless terminal transmits a control packet for reservation to the base station on the reservation channel 7, the base station performs scheduling 24 of time slots on the transmission channel, and indicates the reservation result to the wireless terminal using the response channel 8. Send a control packet. According to the conventional method, there is a possibility that reservation packets from a plurality of mobile terminals collide on a reservation channel, as shown by 22a and 22b. After transmitting the reservation control packet, if each phase terminal does not return a response control packet addressed to itself after waiting for a certain period of time, it determines that a collision has occurred on the reservation channel, and The control packet is retransmitted (23a, 23b). The throughput of the reservation scheme is limited depending on the above-mentioned reservation packet collision.

  FIG. 4 shows a case where an access control method based on CDMA (Code Division Multiple Access) is applied to a reserved channel according to the present invention.

  The present invention is different from the conventional reservation system in that access to the reservation control channel is controlled by the CDMA system (see Prior Art 3). In the reserved channel 7 shown in FIG. 3, the horizontal axis represents time 21 and the vertical axis represents the transmitting terminal 25, which represents a situation where reserved packets from a plurality of terminals are partially overlapped and transmitted on the time axis. I have.

  In the CDMA system, each symbol ("1", "0") of transmission data is replaced with a spread code (orthogonal code or PN code) of a plurality of chips having a pattern unique to a channel, thereby performing spectrum spreading. . For example, in the direct spreading method, when a plurality of transmitting terminals spread spectrum data using the same PN (Pseudo Noise) sequence and transmit data at the same carrier frequency, the data transmission timing is set to 1 If there is a time lag of more than a chip, the receiving side can identify each transmission data independently.

  According to the present invention, CDMA packet communication is applied to a reservation channel, and a plurality of mobile terminals are transmitted with a reservation control packet at an arbitrary timing. If the transmission timings of the reservation control packets from a plurality of terminals completely match, it means that the packets collided, but such perfect matches are rare, and as shown by 26 (26a, 26b), If the two packets have a timing difference of one chip or more even if they overlap in time, collision has been avoided and there is no need for retransmission. Therefore, according to the method of the present invention, the throughput is significantly improved as compared with the conventional reservation method.

  In the present invention, each mobile terminal having a data transmission request transmits a control packet for reservation of a transmission channel time slot at an arbitrary timing on a reservation channel, and is designated by a response control packet transmitted by a base station on a response channel. The transmission data is transmitted in the designated time slot of the transmission channel. Data transmission is performed in units of time slots in principle, and when transmission data covers a plurality of time slots, a reservation is made for each time slot. However, in order to impose a reservation process efficiently, one reservation control packet is used. The transmission channel of a plurality of time slots is set to be reservable, and the base station responds to one reservation control packet with one response control packet or a plurality of response control packets for each time slot. A time slot may be assigned.

  In the present invention, the reservation packet is allowed to be transmitted at an arbitrary timing, but the transmission and reception of the response control packet and the information transmission data packet are performed in synchronization with a predetermined fixed time slot. Dividing the response channel and each transmission channel into time slots having a fixed length facilitates high-speed synchronization between each wireless terminal and the base station. That is, the base station continues to transmit a pilot signal generated by spread spectrum using a PN sequence having an appropriate period on a common channel (pilot channel), and each wireless terminal monitors the pilot signal to generate a synchronization signal. (Reference signal) is extracted, and a time slot synchronized with the base station is set in the response channel and each transmission channel. Since the pilot signal is intended for synchronizing the spread code, the content of the transmission information may be anything. Therefore, instead of using a dedicated pilot channel, the pilot signal can use, for example, a control channel for response.

  FIG. 5 shows a format of a packet used in the mobile communication system of the present invention.

  As shown in FIG. 5A, the reservation control packet includes, in order from the beginning, a preamble 31a for acquiring synchronization, and a reservation type 432b indicating the type of the packet (for position registration, link securing, and information transmission). , A source address 33 (use a local ID if the location is already registered), a destination address 34 (use a link number if a link is already secured), the number of transmission packets (number of time slots) 35 to be reserved, and a CRC (error detection code). (Cyclic Redundancy Check) 36a. It should be noted that the number of transmitted packets is unnecessary in the call setup processing for location registration or link reservation.

  As shown in FIG. 5B, the response control packet indicates the destination address 34 and the packet type (for position registration, for link securing, for uplink information transmission, and for downlink information transmission) in order from the beginning. It comprises a response type 32b, a PN type 37 indicating a spreading code of an assigned channel, timing information 38 indicating an assigned transmission timing, and a CRC 36b. In the present invention, the response control packet does not require a preamble. This is because each mobile terminal (wireless terminal) constantly monitors a pilot signal, and based on the pilot signal, synchronizes each time slot in a response channel and can capture and process each response packet. As shown in FIG. 5C, the data packet for information transmission is, in order from the beginning, a preamble 31b, a packet type (for position registration, link securing, uplink information transmission, and downlink information transmission) 32c, and transmission. Source address 33 (use local ID if location registered), destination address 34 (use link number if link secured), data 39 (PN code of information transmission channel or response control channel, transmission or reception timing , Transmission information) and a CRC 36c. Since the response control channel and the information transmission channel are time-slotted, it is necessary to standardize the packet size to a fixed length even if the packet type is different. For this reason, for example, a dummy bit is inserted into an address part located in front of each packet, and the start position of each field thereafter is adjusted. Note that in the downlink communication, the preamble can be omitted as in the case of the response control packet.

  FIG. 6 is a block diagram showing a schematic configuration of the base station 4. As shown in FIG.

  The base station includes an antenna 41, a CDMA transmitting / receiving unit 50, a packet control unit 90, and a BSC interface 42 connected to a control device (BSC 43) interposed between the base station and the mobile communication network.

  FIG. 7 is a block diagram showing a detailed configuration of the CDMA transmitting / receiving unit 50 of the base station.

  Reference numerals 52 and 53 denote wireless modules for reception and transmission, respectively, which perform modulation / demodulation of baseband signals and transmission / reception processing at high / intermediate frequencies.

  The control packet for response transmitted by the base station is input to the encoding circuit 58a via the response channel signal line 45a, and after encoding for error correction using, for example, a convolutional code, the multiplier 56a In, the spectrum is spread by the orthogonal code for the response channel output from the orthogonal code generator 59 and input to the adder 60. Similarly, the transmission data output to the plurality of signal lines 45b corresponding to the transmission channels is encoded by the encoding circuit 58b, and subjected to spectrum spreading by the multiplier 56b using orthogonal codes corresponding to the respective transmission channels. Is supplied to the vessel 60. The pilot signal output to the signal line 45c is also encoded by the encoding circuit 58c, spectrum-spread by a multiplier 56c with an orthogonal code unique to the pilot channel, and supplied to the adder 60.

  The output of the adder 60 is spread in a multiplier 56 with a PN (long code) unique to each base station output from a PN generator 57a, and is then supplied to the wireless module 53 for transmission. .

  On the other hand, the signal received and processed by the receiving wireless module 52 is input to a reserved channel matched filter 70a and a plurality of transmission channel matched filters 70b to 70b '.

  The received packet of the reserved channel is subjected to despreading processing of the received signal by a matched filter 70a using a PN unique to the reserved channel, and is received by a packet separating circuit 80 by separating packets having a temporal overlap. . In this case, as will be described later with reference to FIGS. 8 and 9, if the period of the PN sequence applied to the despreading is set equal to the number of taps of the matched filter, the output of the matched filter becomes the result of the despreading process. High-speed synchronization becomes possible. The reserved packets separated from each other are supplied to the packet control unit 90 after being subjected to a decoding process with error correction such as Viterbi decoding in the decoding circuit 55a.

  The received signal of the transmission channel is first subjected to synchronous acquisition in matched filters 70b to 70b ', and thereafter, from the acquired timing, a PN generator 57b generates a PN sequence corresponding to each channel, and a multiplier. In 56-56 ', despreading is performed by multiplying the received signal by the PN sequence corresponding to each channel generated from the PN generator 57b, and the despread results for one symbol are accumulated in accumulators 54-54'. Is supplied to the packet control unit 90 via the decoding circuits 55 to 55 '.

  FIG. 8 shows a process of receiving a reservation control packet by the matched filter 70a.

  (A) of the figure is a principle diagram of a matched filter. The matched filter includes a plurality of multi-stage connected delay elements 71 having a delay time T equal to the chip width of the PN sequence, a plurality of coefficient multipliers 72 provided for the input tap of the first stage and the output tap of each delay element, and The received signal input for each chip time propagates between the taps with a delay time T71. Therefore, if the delay time of each delay element is made equal to the chip width of the PN sequence for the reserved channel, and the period length (number of chips) of the PN sequence is made equal to the number of taps of the matched filter, the first chip of the input signal becomes the right end. , The PN sequence for one cycle is simultaneously visible in the tap output. Each tap output is multiplied by a binary PN code (“1” or “−1”) for the reserved channel set in each coefficient multiplier 72, and the sum is obtained by an accumulator 73 to obtain a correlation value. Is output, the time when the correlation value that changes after the chip time reaches the peak value is the time of synchronization acquisition. The output value at this time indicates a demodulated value obtained by performing inverse spectrum spreading of the received signal. In the present invention, the spreading code length and the number of taps of the matched filter are made equal so that the output value of the matched filter becomes information (symbol code) for one bit of the reserved packet. Further, by applying a short code as a PN sequence for the reserved channel, the number of taps of the matched filter is reduced, and synchronization supplementation is facilitated.

  FIG. 12B is a diagram illustrating an operation of identifying a reserved packet by the matched filter 70a, taking as an example a case where two reserved packets A and B are partially overlapped on the time axis and issued. Starting from the point in time when the output of the accumulator 73 shows the peak value (synchronization supplementary point), the subsequent filter output signals appearing in the accumulator 73 in the PN cycle (symbol cycle) are grouped and belong to the same reserved packet. The reproduced bit data sequence can be reproduced.

  In the illustrated example, the signal value (“1” or “−1”) 76-2, 76-3, 76-4, which starts from the first peak value 75-1 and thereafter appears every PN cycle 75, .. Are collected as one bit data group, the reservation packet (A) 76 can be reproduced. Starting from the peak value 77-1 appearing asynchronously with the bit data group, signal values ("1" or "-1") appearing every PN cycle 75-2, 77-3, 77-4, .. Are collected as one bit data group, the reservation packet (B) 77 can be reproduced. As a result, even if packets are temporally overlapped, in principle, if there is a phase shift of one chip or more, they can be identified as separate packets.

  FIG. 9 shows an example of the configuration of the packet separation circuit 80.

  The output signal 79a of the matched filter 70a is input to an absolute value circuit (ABS) 81, and the comparator 83a compares the absolute value of the matched filter output signal 79a with a predetermined threshold output from the threshold circuit 82. When the absolute value is larger than the threshold value, the output of the comparator 82 is turned on ("1" state) and input to the AND circuit 84a. The other input signals of the AND circuit 84a are off in the initial state, and are inverted and input. Therefore, the AND circuit 84a is opened by the output of the comparator, and the output signal is turned on ( "1" state). The ON output of the AND circuit 84a is input to AND circuits 84b and 84d.

  In the AND circuit 84b, a negative signal of the output of the timer 85a is input to the other input terminal. In the initial state, the output of the timer 85a is off ("0"), so that when the output of the AND circuit 84a turns on, the output of the AND circuit 84b also turns on. The ON output of the AND circuit 84b is input as an enable signal to the timing register 86a. At this time, the value of the counter 87 that counts at the chip cycle of the PN code and returns to the initial value at the symbol cycle is set in the register 86a. You. Note that the output value of the counter 87 indicates the chip position (synchronous capture timing) at the time of synchronization capture described in FIG. 8B.

  The ON output of the AND circuit 84b activates a timer 85a that controls the other input of the AND circuits 84b and 84d. The timer 85a keeps its output on until one packet period of the reservation packet elapses, closes the AND circuit 84b until this period elapses, and stores another counter value in the timing register 86a. To be set.

  When the next peak value is output from the matched filter before the timer 85 times out, the ON output output from the AND circuit 84a is output to the AND circuit 84d which is open by the output of the timer 85a and the next output. The signal is input to an enable terminal of the next timing register 86b via an AND circuit 84b 'paired with the timing register 86b. As a result, the output value of the counter 87 is set in the timing register 86b. At this time, the timer 85b paired with the register 86b is started, and by the same operation as the above-described timer 85a, setting of another value to the register 86b is prohibited until one packet period elapses, and the next time. It operates to input the generated enable signal to the next register 86c.

  In this embodiment, since four timing registers 86a to 86d are provided, by repeating the same operation, of a plurality of reserved packets which are generated in time overlap, four packets are generated in the order of generation. The synchronization acquisition timing is stored.

  The value of the synchronization acquisition timing set in the timing register 86a is compared with the output value of the counter 87 in the comparator 83b. Each time the counter value matches the synchronization acquisition timing set in the timing register 86a, the comparator 83b The output of 83b is turned on. The ON output of the comparator is input to the enable terminal of the data register 87a through the AND circuit 84c that is open while the timer 85a is ON. As a result, the output of the matched filter at the synchronization acquisition timing is input to the data register 87a. The other timing registers 86b to 86d operate in the same manner as described above, and the output of the matched filter for each reserved packet is stored in the data registers 87b to 87d.

  Since data is input to the data registers 87a to 87d according to the synchronization capture timing of each reservation packet, the contents of the data registers 87a to 87d are synchronized with the clock of the bit period generated by the clock generation circuit 88. Are transferred to the output registers 88a to 88d, and the received data of each reservation packet is transferred from the output registers 88a to 88d to the decoding circuit 55a shown in FIG.

  FIG. 10 shows a detailed configuration of the packet control unit 90 of the base station 4.

  The packet control unit 90 has a digital signal processor (DSP) 91. After the received data (contents of the reserved packet) of the reserved channel is decrypted by the decryption routine 92 of the DSP 91, it is transmitted by the uplink schedule control routine 93. , A transmission channel and a time slot are allocated (scheduled). The transmission channel and the time slot determined by the uplink schedule control routine 93 are transmitted to the response packet generation circuit 97, and the response packet generated by the response packet generation circuit 97 and transmitted to each terminal is transmitted on the response channel. It is possible to make the uplink transmission packet from the base station to the base station perform according to the scheduling of the base station.

  The data received from each transmission channel is input via signal lines 44b to 44b 'to reception processing circuits 96b to 96b' provided for each transmission channel, and is transferred as a data packet to the BSC interface. On the other hand, the downstream data packets are temporarily stored in the transmission buffer 99, and then subjected to transmission control according to the schedule performed by the downstream schedule control routine 95 of the DSP. That is, according to the downlink schedule, first, the response packet created by the response packet structure creation circuit 97 is transmitted from the response channel, and then the transmission packet structure is transmitted at a predetermined time slot of the transmission channel determined by the downlink schedule. The data packets generated by the generating circuits 98a to 98a 'are transmitted.

  In this embodiment, in order to suppress the issue of the reservation packet from the mobile terminal when the transmission channel is busy, the number of reservation packets received on the reservation channel and the uplink schedule control routine 93 are determined. The busy tone value calculation routine 94 of the DSP 91 generates busy tone information in accordance with the use state information of the transmission channel being used, and notifies each mobile terminal of the busy tone information through the response channel 45a.

  FIG. 11 is a block diagram illustrating a configuration of the mobile terminal (wireless terminal) 5.

  The mobile terminal includes an antenna 100, a CDMA transmitting / receiving unit 110 connected to the antenna, a packet control unit 130 connected to the CDMA transmitting / receiving unit 110, and a data processing device connected to the packet control unit 130. . The data processing device includes a microprocessor (MPU) 101, a memory 102 for storing data and programs, and a plurality of input / output devices connected to an internal bus via an I / O interface 103. Examples of the input / output device include a camera 104a, a speaker 104b, a display 104c, a keyboard 104d, and the like.

  FIG. 12 shows a detailed configuration of the CDMA transmitting / receiving section 110 of the mobile terminal.

  Reference numerals 112 and 113 denote wireless modules that perform modulation / demodulation of a baseband signal and reception processing and transmission processing at high / intermediate frequencies.

  In the transmitting circuit, in each of the reserved channel and the transmission channel, the encoding circuits 120a and 120b perform error correction encoding of the transmission packet, and then generate a PN sequence unique to each channel generated by the PN generators 121a and 121b. , The transmission packets are spread by the multipliers 114 a and 114 b and sent to the transmission wireless module 113. At this time, the spreading process in the transmission channel is performed in synchronization with the reference timing 105c generated from the PN generator 119.

  On the other hand, in the receiving circuit, the received signal output from the receiving wireless module 112 is input to the multiplier 114c, and the spectrum is despread using the PN code unique to the base station generated by the PN generator 119. The output of the multiplier 114c is input to multipliers 114d, 114e, and 114f provided for a response channel, a transmission channel, and a pilot channel, and is despread by an orthogonal code unique to each channel generated by an orthogonal code generator 117. You. In the response channel and the transmission channel, the signals despread by the orthogonal code are input to decoding circuits 116d and 116e via accumulators 115d and 115e, respectively, and the error-corrected decoded signals are output to signal lines 105d and 105d. The packet is transferred to the packet control unit 130 via 105e. In the pilot channel, a pilot signal despread with an orthogonal code is input to a DLL (Delay Locked Loop) circuit 118 via an accumulator 115f, and synchronously tracked. The PN generator 119 generates a PN sequence in synchronization with the output of the DDL circuit 118. The decoding circuits 116d and 116e operate in synchronization with the pilot signal output from the accumulator 115f.

  FIG. 13 shows an example of the configuration of the packet control unit 130 of the mobile terminal.

  The decoded data of the response channel is decoded by a monitoring routine 132 of the DSP 131, and the contents of the response packet are supplied to an uplink schedule control routine 134 and a downlink schedule control routine 135. The busy tone signal received on the response channel is a busy tone signal. It is supplied to a calculation routine 133.

  The packet reception processing circuit 136 on the downlink transmission channel is controlled by the output of the downlink schedule control routine 135 and the reference timing signal 105c. The transmission data is temporarily stored in the transmission buffer 138, input to the transmission packet structure creation circuit 139 according to the control signal from the uplink schedule control routine 134, and the data packet is transmitted to the transmission channel.

  The upstream schedule control routine 134 generates a transmission channel designation signal 106 for transmitting a transmission packet according to the contents of the response packet, and activates the transmission packet structure creation circuit 139 at the timing of the time slot designated by the base station. . The PN generator 121b generates a PN code of the channel specified by the transmission channel specifying signal 106.

  Further, the busy tone value calculation routine 133 calculates a busy tone value from a busy tone signal received on the response channel, and notifies traffic status information to the uplink schedule control routine 134. The uplink schedule control routine 134 controls the generation of a reservation packet according to the traffic situation. When there is transmission data in the transmission buffer and there is no instruction to suppress the reservation packet from the base station, the reservation packet structure at any timing. It activates the creation circuit 137 and instructs transmission of a reservation packet. The transmission processing of the transmission packet is also performed in a time slot synchronized with the reference timing 105c.

  As described above, in the present invention, the possibility of retransmission due to packet collision is reduced by applying a CDMA scheme to a reservation channel even when each mobile terminal transmits a control packet for reservation at an arbitrary timing. Now you can. However, when a plurality of packets are generated with a time overlap, the packet signals affect each other as noise. Therefore, when the number of simultaneously generated packets increases, all of the packet signals are buried in the noise, and the receiving side There is a problem that cannot be identified by the

  In the mobile communication system of the present invention comprising a reservation control channel, a response control channel, and a plurality of information transmission channels, the total amount of response control packets and data packets can be controlled by the base station. Since the control packet is issued autonomously by each mobile terminal, it cannot be directly controlled by the base station. In order to solve the problem of the total packet amount regulation, in one embodiment of the present invention, the base station generates a busy tone signal indicating a traffic situation, and each mobile terminal refers to the busy tone signal to generate a reservation control packet. Sending is controlled. The busy tone signal may be transmitted on a dedicated channel for the busy tone, or may use an idle time period that periodically appears in a response control channel that is a downlink control channel.

  FIG. 14 is a diagram illustrating a control method for transmitting a busy tone signal using an idle time zone of a response control channel.

  In the figure, “t−1”, “t”, and “t + 1” are time slot numbers in the response control channel, and 143 indicates a busy tone signal transmitted in an idle time zone in the response control channel. 148 is a reservation control packet, R (t) is the number of reservation control packets transmitted by the mobile terminal in time slot t, and R (t) 'is a transmission request number of reservation control packets in time slot t. Is the data packet for information transmission, I (t) is the number of data packets generated in the time slot t, T is the number of stations capable of permitting simultaneous transmission (the number of simultaneously permitted packets), and P (t) is the control packet for reservation. Shows the transmission probability of. Here, R (t) 'and R (t) are numbers normalized by the length of the data packet for information transmission.

  First, the following equation (1) is assumed.

This equation is derived as follows. First, the number R (t) ′ of reservation control packets of all mobile terminals in the service area in the time slot “t” and the number R (t) of reservation control packets in the immediately preceding time slot “t−1”. -1) 'is estimated to be equal.

  If R (t-1) 'is rewritten using the number of reservation control packets R (t-1) known by the base station, it becomes equal to the right side of equation (1). Hereinafter, R (t) 'is estimated from Expression (1), and if the total amount of communication packets exceeds the allowable value T and Expression (2)

, The busy tone control is performed so that the transmission probability P (t) complies with equation (3), and the amount of reservation control packets actually transmitted from each mobile terminal is suppressed. And the sum of the number of data packets for information transmission and the allowable value T.

Here, since the number of reservation control packets to be transmitted is determined stochastically, it is necessary to consider setting T to be small in consideration of a margin. On the other hand, equation (4)

, The transmission probability P (t) follows Expression (5).

That is, all the reservation control packets requested to be transmitted are transmitted. The transmission probability of Expression (3) or Expression (4) becomes busy tone information.

  As shown in FIG. 2, the response control channel is converted into a time slot corresponding to the data packet length in the information transmission channel based on the pilot signal. Here, it is assumed that the response control packet length is set shorter than the data packet length, and each time slot set based on the pilot signal is further subdivided in accordance with the response packet length. If the packet length is 512 bits and the response packet length is 42 bits, 12 response packet subslots can be set in one time slot, and an empty time zone of 8 bits is finally formed. The busy tone 143 in FIG. 14 is periodically transmitted at intervals of one slot of the information transmission channel using the idle time zone obtained in this manner.

FIG. 1 is a diagram showing an example of a configuration of a mobile communication network to which the present invention is applied. FIG. 3 is a diagram for explaining a transmission / reception protocol in the wireless communication system of the present invention. FIG. 7 is a diagram for explaining a channel access control method in a conventional wireless communication system. FIG. 3 is a diagram for explaining a channel access control method in the wireless communication system of the present invention to which the CDMA method is applied. FIG. 2 is a diagram showing a packet format used in the mobile communication system of the present invention. FIG. 2 is a block diagram showing a configuration of a base station. FIG. 2 is a block diagram showing a configuration of a CDMA transmitting / receiving unit 50 of the base station. FIG. 4 is a diagram showing a configuration of a matched filter 70 and a process of receiving a reservation control packet. FIG. 3 is a diagram showing a configuration of a packet separation circuit 80. The figure which shows the structure of the packet control part 90 of a base station. FIG. 2 is a block diagram showing a configuration of a mobile terminal. FIG. 2 is a diagram illustrating a configuration of a CDMA transmitting / receiving unit 110 of a mobile terminal. FIG. 3 is a diagram illustrating a configuration of a packet control unit 130 of the mobile terminal. FIG. 4 is a diagram for explaining busy tone control.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 public network, 2 mobile communication network, 4 base station, 5 mobile terminal, 7 reserved channel, 8 response channel, 9 transmission channel, 41, 100 antenna,
50, 110: CDMA transmitting / receiving unit, 90, 130: packet control unit,
42 BSC interface, 101 MPU, 102 memory
103: input / output interface, 55, 116: decoder, 57, 121: PN generator,
118 DLL, 58, 120 encoder, 70 matched filter, 83 comparator
84 AND circuit, 85 timer, 86 register, 87 counter, 88 clock.

Claims (13)

A plurality of transmission channels used for transmitting an uplink data packet from the mobile terminal to the base station and a downlink data packet from the base station to the mobile terminal in a wireless communication section between the base station and the plurality of mobile terminals. A reservation channel used to transmit a reservation control packet indicating a transmission channel assignment request from the mobile terminal to the base station, and a response control packet indicating a transmission channel to transmit and receive data from the base station to the mobile terminal And a response channel used to transmit a data transmission request in a mobile communication system in which a code division multiple access (CDMA) method using a unique spreading code is applied to each of the reservation, response, and transmission channels. The mobile terminal having has transmitted a reservation control packet to the reservation channel at an arbitrary timing, and A response control packet transmitted to the response channel specifies a transmission channel and a time slot to be used for each mobile terminal, and each mobile terminal specifies a transmission channel and a time slot specified on the transmission channel specified by the response control packet. A mobile communication system wherein data packets are transmitted and received in time slots. Each mobile terminal having a data transmission request applies a spreading code specific to a reservation channel having a shorter cycle than a spreading code applied to a data packet transmitted on the transmission channel to spread the spectrum of each of the reservation control packets. The base station processes a received signal by a matched filter in which a spreading code unique to the reserved channel is set, and outputs the output of the matched filter to a plurality of signal streams corresponding to packets using the periodicity of the spreading code. The mobile communication system according to claim 1, wherein the mobile communication system is separated. The base station assigns, to each mobile terminal, a local address shorter than address information unique to each terminal, and each mobile terminal sends the local address to a destination in a response control packet transmitted on the response channel. The mobile communication system according to claim 1, wherein the mobile communication system performs reception processing of a packet included as an address. The base station provides each mobile terminal with a link number shorter than address information unique to each terminal, and each mobile terminal transmits a data packet including the link number as a destination address to a transmission channel. The mobile communication system according to claim 1, wherein The base station has means for periodically transmitting busy tone information according to the traffic situation in the service area through the response control channel or busy tone dedicated channel, and each mobile terminal having a data transmission request is The mobile communication system according to claim 1, wherein transmission of a reservation control packet is controlled based on the busy tone information. The base station, based on the number of control packets for reservation received in the past fixed period,
Means for estimating the number of control packets for reservation occurring in the next predetermined period, and generating the busy tone information based on the estimated value and the number of packets scheduled to be transmitted in the next predetermined period. The mobile communication system according to claim 5, wherein: 7. The mobile communication system according to claim 1, wherein each of the mobile terminals requests transmission of a plurality of data packets with one reservation control packet. 4. The mobile communication system according to claim 3, wherein the base station specifies a response channel on which the mobile terminal should perform a receiving operation by a control packet for assigning a local address to the mobile terminal. The base station continuously transmits a pilot signal including a synchronization signal component on a pilot channel or the response channel, and each mobile terminal identifies a time slot of the transmission channel based on the received pilot signal. The mobile communication system according to claim 1, wherein: A base station and a plurality of wireless terminals perform code division multiple access (CDMA) in a wireless section.
A) a wireless communication system adapted to communicate via a reservation channel, a response channel and a plurality of transmission channels,
Each wireless terminal requesting data transmission transmits a reservation control packet to the reservation channel asynchronously with each other,
The base station separates a plurality of reservation control packet signals partially overlapping on the period axis received on the reservation channel into packets corresponding to each other and performs reception processing. A response control packet for designating a transmission channel and a time slot to be used for a wireless terminal is transmitted on the response channel,
A wireless communication system, wherein each of the wireless terminals transmits a data packet in a specified time slot on a transmission channel specified by the response control packet. The base station transmits, to the wireless terminal specified by the destination address of the data packet received from the transmission channel, a response control packet for designating a transmission channel and a time slot to be operated by the response channel. After transmitting, transmit the received data packet to a specified time slot on the specified transmission channel,
The wireless terminal according to claim 10, wherein the wireless terminal that is the destination of the response control packet performs a data packet receiving operation in a specified time slot of a transmission channel specified by the response control packet. Communications system. A wireless terminal device for wirelessly communicating with a base station,
Means for transmitting a reservation control packet processed with a spreading code specific to a reservation channel to the base station asynchronously with the base station;
Means for receiving a response control packet processed with a spreading code specific to the response channel transmitted from the base station at a predetermined time slot timing synchronized with the base station;
Means for transmitting or receiving a data packet processed with a spreading code specific to the transmission channel at a specific time slot timing on a specific transmission channel specified by the response control packet. A wireless terminal device characterized by the above-mentioned. A wireless communication system for communicating with a plurality of wireless terminals each having a unique address via a reserved channel, a response channel, and a plurality of transmission channels associated with a unique spreading code by using a spread spectrum packet. Base station for
Means for receiving a reservation control packet signal for a transmission channel access request transmitted by the plurality of wireless terminals asynchronously with each other from the reservation channel, and performing reception processing separately for each reservation control packet;
Means for transmitting, via the response channel, a response control packet specifying a transmission channel and a time slot to be used to the transmission source wireless terminal of the reservation control packet;
A base station apparatus comprising: means for performing a receiving process of a data packet transmitted by a wireless terminal or a transmitting process of a data packet addressed to a wireless terminal in each time slot of a transmission channel.

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