JP2009296335A - Radio access system, terminal station device and radio access method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform access control, according to the number of terminal stations under each extended radio station, in a multi-cell type radio access system that uses ROF (radio over fiber) transmission. <P>SOLUTION: In the multi-cell type radio access system in which a centralized control base station and a plurality of extended radio stations are connected via a broadband transmission line; the centralized control base station is provided with a radio resource control means for respectively distributing a radio resource for ranging for transmitting a ranging signal, by which respective terminal stations under the plurality of extended radio stations perform an access request to the plurality of extended radio stations, according to the number of terminal stations having the access request; and the terminal stations transmit the ranging signal by the radio resource for ranging notified via a belonging extended radio station. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In a multi-cell wireless access system in which a centralized control base station and an extended radio station are connected via a broadband transmission line, the centralized control base station transmits a ranging signal for requesting an access request from the extended radio station. The present invention relates to a radio access system, a terminal station apparatus, and a radio access method in which ranging radio resources are distributed to each overhanging radio station, and each terminal station transmits a ranging signal using the ranging radio resource.

  In order to realize a multi-cell wireless access system relatively easily, there is a method of using a broadband transmission path as a wireless signal relay medium. Among these, the one using an optical fiber as a broadband transmission line is called ROF (Radio Over Fiber) transmission. In ROF transmission, an optical carrier is modulated with a radio signal and transmitted through an optical fiber, so that there is little propagation loss, and it is possible to deploy a radio station extending from a centralized control base station to a distant area.

  Hereinafter, a case where the number of overhanging radio stations is larger than that of the centralized control base station will be described. The central control base station performs baseband signal processing such as modulation / demodulation processing of radio signals and access control. Optical signals transmitted and received by the centralized control base station are ROF-transmitted with a plurality of overhanging radio stations. Each overhanging radio station converts the received optical signal into an electric signal, amplifies it, and transmits it as a radio signal from the transmitting antenna to the terminal station under its control. Each overhanging radio station receives a radio signal transmitted from a subordinate terminal station by a receiving antenna, converts the radio signal into an optical signal, and transmits the optical signal to the centralized control base station by ROF transmission.

  Here, when a plurality of overhanging radio stations use the same frequency for transmission and reception, and the same data is transmitted from the centralized control base station to the overhanging radio station in the downlink, the overhanging radio stations are geographically and spatially connected to each other. Even if they are separated, it is equivalent to a state in which a plurality of terminal stations exist in a single base station arrangement, and a virtual large cell can be constructed. That is, the area covered by the same frequency can be expanded and the frequency utilization efficiency can be improved. Further, in the form in which the centralized control base station and the overhanging radio station are connected with a PON (Passive Optical Network) topology, the cost of installing the optical fiber in the ROF section can be reduced.

  By the way, in order to realize a P-mP (Point to Multi-Points) type shared access in which a plurality of terminal stations are accommodated under an overhanging radio station and perform simultaneous communication, some access control is required. In the case of wireless communication, random access control such as CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) or Slotted ALOHA is often used (Non-patent Document 1). In CSMA / CA, communication is started when a terminal station senses a carrier and determines that it is not used elsewhere. In Slotted ALOHA, for example, a time slot used for transmission is randomly selected from time slots provided at regular intervals. In any case, there is a possibility that signals of a plurality of terminal stations collide with each other. In this case, a method of reducing the collision probability by retransmitting after a random time is taken.

  In the case of a radio access system using ROF transmission, depending on the positional relationship between the overhanging radio stations, a situation may occur in which the same frequency is simultaneously used by a plurality of overhanging radio stations.

  FIG. 12 shows a successful example of random access control in a radio access system using ROF transmission.

  In the figure, the centralized control base station 10 and the overhanging radio stations 20a and 20b are connected 1: 2 through the optical fiber transmission line 1 and the optical coupler 2. The overhanging radio stations 20a and 20b form independent cells #a and #b, respectively. The terminal stations 30a1 and 30a2 are under the overhanging radio station 20a, and the terminal station 30b1 is under the overhanging radio station 20b. Each terminal station is assigned a time slot t1 to t6 shared by all cells used for random access control, and makes an access start request at the same frequency.

  In the cell #a of the extended radio station 20a, the terminal station 30a1 makes an access start request in the time slot t1 and the terminal station 30a2 makes an access start request in the time slot t4 by carrier sense. In the cell #b of the overhanging radio station 20b, the terminal station 30b1 makes an access start request at time slot t5 by carrier sense. Since each access start request is different in each time slot, even if the optical coupler 2 joins, the access start request reaches the centralized control base station 10 without colliding, and each access start request is processed.

  FIG. 13 shows a collision example of random access control in a radio access system using ROF transmission.

  In the figure, the centralized control base station 10 and the overhanging radio stations 20a, 20b, and 20c are connected 1: 3 through the optical fiber transmission line 1 and the optical coupler 2. The overhanging radio stations 20a, 20b, and 20c form independent cells #a, #b, and #c. The terminal stations 30a1 and 30a2 are under the overhanging radio station 20a, and the terminal stations are under the overhanging radio station 20b. 30b1 and terminal stations 30c1, 30c2, and 30c3 are under the control of the overhanging radio station 20c. Each terminal station is assigned a time slot t1 to t6 shared by all cells used for random access control, and makes an access start request at the same frequency.

In the cell #a of the extended radio station 20a, the terminal station 30a1 makes an access start request at time slot t3 and the terminal station a2 makes an access start request at time slot t5 by carrier sense. In the cell #b of the extended radio station 20b, the terminal station 30b1 makes an access start request at the time slot t3 by carrier sense. In the cell #c of the extended radio station 20c, the terminal stations 30c1, 30c2, and 30c3 make access start requests in time slots t1, t4, and t5, respectively, by carrier sense. Each access start request is simply added by the optical coupler 2, the access start requests of the terminal stations 30a1 and 30b1 overlap at time slot t3, and the access start requests of the terminal stations 30a2 and 30c3 overlap at time slot t5. However, they cannot be recognized, and only the access start requests of the terminal stations 30c1 and 30c2 are processed.
FATobagi, "Distributions of Packet Delay and Interdeparture Time in Slotted ALOHA and Carrier Sense Multiple Access", Journal of the Association for Computing Machinery, Vol.29, No.4, pp.907-927, 1982

  In a multi-cell wireless access system in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line, random access control widely used in wireless communication is performed between terminal stations under each overhanging radio station. The access start request collision probability can be kept low. However, when the radio cells formed by each overhanging radio station exist apart from each other, carrier sense of each radio cell is difficult, so as shown in FIG. 13, between the terminal stations under each overhanging radio station in the uplink The probability of collision of access start requests increases. For this reason, each terminal station may fall into a deadlock state where an access opportunity cannot be obtained, and there is a problem that efficient communication cannot be performed.

  The present invention relates to a radio access system, a terminal station apparatus, and a radio access method capable of efficiently performing access control according to the number of terminal stations under each overhang radio station in a multi-cell radio access system using ROF transmission. The purpose is to provide.

  A first invention is a multi-cell wireless access system in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line, wherein the centralized control base station is a terminal under each of the plurality of overhanging radio stations A radio station is provided with radio resource control means for distributing ranging radio resources for transmitting a ranging signal for requesting an access request to a plurality of extended radio stations according to the number of terminal stations having access requests. In this configuration, a ranging signal is transmitted using a ranging radio resource notified via an overhanging radio station.

  The radio resource control means in the radio access system of the first invention measures the total received power of the ranging radio resources distributed to each of the plurality of overhanging radio stations, and the ranging radio resource according to the total received power ratio And a ranging radio resource is redistributed to each of the plurality of overhanging radio stations.

  The centralized control base station in the radio access system of the first invention broadcasts a control signal including information on ranging radio resources distributed to a plurality of overhanging radio stations to the plurality of overhanging radio stations, and the overhanging radio station The overhanging radio station recognizes the ranging radio resource distributed to itself from the broadcast control signal and inserts the ranging radio resource into the radio frame. Is notified to the terminal stations under control.

  A second invention is a multi-cell type wireless access system in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line, and the centralized control base station requests access under the plurality of overhanging radio stations. In accordance with the number of terminal stations having a certain number, the period during which each overhanging radio station is activated sequentially is controlled, and the ranging radio resource for transmitting a ranging signal for requesting access by the terminal station is transmitted via the active overhanging radio station. Radio resource control means for notifying a subordinate terminal station is provided, and the terminal station is configured to transmit a ranging signal using a ranging radio resource notified from an active overhanging radio station.

  The radio resource control means in the radio access system of the second invention measures the total received power of the ranging radio resources during the active period of each of the plurality of overhanging radio stations, and each overhanging radio station according to the total received power ratio The active period is determined, and a plurality of overhanging radio stations are sequentially controlled to be active.

  The terminal station in the first or second radio access system repeats transmission of the ranging signal until a communication connection with the centralized control base station is established, and transmission power control means for increasing the transmission power of the ranging signal at each repetition. Prepare.

  According to a third aspect of the present invention, in the terminal station apparatus in the first or second radio access system, transmission of the ranging signal is repeated until a communication connection with the centralized control base station is established, and the transmission power of the ranging signal is increased for each repetition. A transmission power control means for increasing is provided.

  According to a fourth aspect of the present invention, there is provided a multi-cell wireless access method in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission path, wherein the centralized control base station is a terminal under each of the plurality of overhanging radio stations. A ranging radio resource for transmitting a ranging signal for requesting access by a station is distributed to each of the plurality of overhanging radio stations according to the number of terminal stations having access requests. A ranging signal is transmitted using the notified ranging radio resource.

  The centralized control base station in the wireless access method of the fourth invention broadcasts a control signal including information on ranging radio resources distributed to the plurality of overhanging radio stations to the plurality of overhanging radio stations, and The overhanging radio station recognizes the ranging radio resource distributed to itself from the broadcast-reported control signal, inserts the ranging radio resource into the radio frame, and controls the subordinate radio station. Notify the terminal station.

  According to a fifth aspect of the present invention, there is provided a multi-cell wireless access method in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line, wherein the centralized control base station requests access under the plurality of overhanging radio stations. In accordance with the number of terminal stations having a certain number, the period during which each overhanging radio station is activated sequentially is controlled, and the ranging radio resource for transmitting a ranging signal for requesting access by the terminal station is transmitted via the active overhanging radio station. The terminal station is notified, and the terminal station transmits a ranging signal using the ranging radio resource notified from the active overhanging radio station.

  In the present invention, ranging radio resources are distributed to each overhanging radio station according to the number of terminal stations requested to access under each overhanging radio station. The terminal station transmits an access request using the distributed ranging radio resources, thereby reducing the probability of collision between the terminal stations of each overhanging radio station and between the terminal stations under each overhanging radio station. Access control becomes possible.

  In addition, by using the fact that the total received power measured in the ranging radio resource section changes dynamically according to the number of terminal stations that have access requests under each overhanging radio station, the total sum of ranging radio resources is obtained. Redistributing ranging radio resources using the received power ratio. This enables efficient access control while effectively using the ranging radio resources.

  The present invention controls the active period of each overhanging radio station according to the number of terminal stations having access requests under each overhanging radio station, and sequentially activates each overhanging radio station. The terminal stations under the active overhanging radio station transmit the access request using the common ranging radio resource, thereby increasing the probability of collision between the terminal stations of each overhanging radio station and between the terminal stations under each overhanging radio station. Reduction and efficient access control becomes possible.

  In addition, by using the fact that the total received power measured in the ranging radio resource section changes dynamically according to the number of terminal stations that have access requests under each overhanging radio station, the total sum of ranging radio resources is obtained. The active period of each overhanging radio station is varied using the received power ratio. This enables efficient access control while effectively using the ranging radio resources.

  In addition, the terminal station performs autonomous transmission power control, and by reflecting the access request of the terminal station to the total received power of the ranging radio resource, it is possible to redistribute the ranging radio resource advantageously and adjust the active period. Thus, it is possible to reduce the occurrence probability of deadlock in which random access continues to fail.

(First embodiment)
FIG. 1 shows a first embodiment of the wireless access system of the present invention.
In the figure, the centralized control base station 10 and a plurality of overhanging radio stations 20 (one in the figure) are connected via an optical fiber transmission line 1 and an optical coupler (not shown), and the overhanging radio station 20 and the terminal station 30 are connected. Are connected via a wireless line. Here, the optical fiber transmission line 1 is shown as a broadband transmission line, and it is assumed that an optical signal is branched / joined by an optical coupler, but other transmission media that realize the same function may be used.

  The centralized control base station 10 includes a radio signal processing unit 11, a ranging area allocation control unit 12, an optical signal transmission / reception unit 13, and a total received power measurement unit 14 as involved in the present embodiment. The radio signal processing unit 11 performs baseband signal processing such as modulation / demodulation processing of radio signals transmitted / received to / from the terminal station 30 via the overhanging radio station 20 and access control. The ranging area allocation control unit 12 outputs a ranging area allocation control signal that notifies the ranging area to be allocated to each overhanging radio station 20. The optical signal transmission / reception unit 13 converts the radio signal to be transmitted to the terminal station 30 and the ranging area allocation control signal to be transmitted to the extended radio station 20 into an optical signal, and sends the optical signal to the optical fiber transmission line 1. The received optical signal is converted into a radio signal and output to the radio signal processing unit 11. The ranging area allocation control signal is transmitted to each overhang radio station 20 using, for example, a downlink control signal channel. The total received power measurement unit 14 receives the reception signal processed by the radio signal processing unit 11, measures the total received power of the ranging area allocated to each overhanging radio station 20, and based on the result, each overhanging radio station 20 The ranging area to be redistributed is notified to the ranging area allocation control unit 12.

  The overhanging radio station 20 includes an optical signal transmission / reception unit 21, a ranging area allocation signal generation unit 22, an addition unit 23, an amplifier 24, and a transmission / reception antenna 25. The optical signal transmission / reception unit 21 performs mutual conversion between an optical signal transmitted / received to / from the centralized control base station 10 and a radio signal transmitted / received to / from the terminal station 30 under its control, and is transmitted from the centralized control base station 10 The ranging area allocation control signal is received and notified to the ranging area allocation signal generator 22. The ranging area allocation signal generation unit 22 detects the ranging area of the overhanging radio station 20 notified by the ranging area allocation control signal, generates a ranging area allocation signal to be notified to the subordinate terminal station 30, and is subordinated by the addition unit 23. Is superimposed on the radio signal to be transmitted to the terminal station 30. A radio signal transmitted / received to / from the subordinate terminal station 30 is amplified via the amplifier 24 and transmitted / received by the transmission / reception antenna 25.

  The terminal station 30 includes a transmission / reception antenna 31, a radio signal processing unit 33, a ranging processing unit 33, and a transmission power control unit 34 as those involved in the present embodiment. The transmission / reception antenna 31 transmits and receives radio signals to and from the overhanging radio station 20. The radio signal processing unit 32 performs baseband signal processing such as modulation / demodulation processing of radio signals transmitted / received to / from the centralized control base station 10 via the overhanging radio station 20 and access control. The ranging processing unit 33 performs a ranging process for an access start request and terminal transmission power control before the terminal station starts data communication. Here, a signal transmitted by the terminal station 30 for ranging is referred to as a ranging signal. The ranging area assignment signal transmitted from the overhanging radio station 20 is received, and the ranging signal is transmitted in the notified ranging area. For example, power measurement in a predetermined frequency band is performed by carrier sense, and when it is determined that the same radio resource is not used around its own terminal, a ranging signal is transmitted in the ranging time slot notified as the ranging area . At this time, the terminal station 30 randomly selects one slot from the plurality of assigned ranging time slots. With this access control, it is possible to keep the collision probability of ranging signals between terminal stations under the overhanging radio station low. The transmission power control unit 34 controls the transmission power of the ranging signal as necessary.

  The first feature of the present embodiment is that each ranging radio station 20 is divided and assigned so that the ranging time slots do not overlap. As a result, the terminal stations 30 subordinate to each overhanging radio station 20 transmit ranging signals using the assigned ranging time slots, thereby avoiding ranging signal collisions between terminal stations under different overhanging radio stations. it can. Furthermore, the second feature of the present embodiment is that the number of ranging time slots allocated to each overhanging radio station 20 is adjusted according to the access request status of the terminal station 30 under its control. Thereby, the collision probability of the ranging signal between the terminal stations under the overhanging radio station can be reduced.

  Hereinafter, the control of the first feature and the second feature of the present embodiment will be specifically described with reference to FIGS. FIG. 2 shows a processing procedure in the first embodiment of the wireless access system of the present invention. 3 and 4 show an operation example of the first embodiment of the wireless access system of the present invention. FIG. 1 also shows a procedure for generating a ranging area allocation signal from the ranging area allocation control signal in the overhanging radio station 20.

  First, the centralized control base station 10 arbitrarily distributes the ranging time slots of the overhanging radio stations 20 (FIG. 2: S11). Then, ranging time slot information distributed to each overhanging radio station 20 is transmitted as a ranging area allocation control signal (FIG. 2: S12). Each overhanging radio station 20 receives the ranging area allocation control signal, generates a ranging area allocation signal indicating the allocated ranging time slot, and transmits it to the subordinate terminal station 30 (FIG. 2: S21). In the example shown in FIG. 3, when the time slots for ranging shared by each overhanging radio station are t1 to t6, the time slots t1 and t2 in the cell #a of the overhanging radio station 20a and the cell #b of the overhanging radio station 20b are set. Time slots t3 and t4 and time slots t5 and t6 are equally allocated to the cell #c of the overhanging radio station 20c.

  The processing in which the centralized control base station 10 notifies the ranging time slot to the subordinate terminal stations 30 via the overhanging radio station 20 is performed as follows, for example. An area for inserting a ranging area allocation signal is formed in a part of a radio frame transmitted from the radio signal processing unit 11 of the centralized control base station 10 to the terminal station 30, and this area is nullified when transmitted from the centralized control base station 10. And In the example of the radio frame in FIG. 1, an area for inserting a ranging area allocation signal is formed in a part of the header area h. This radio frame is transmitted as an optical signal from the optical signal processing unit 13 of the centralized control base station 10 to the optical signal processing unit 21 of the overhanging radio station 20, converted back to the radio frame, and output to the adding unit 23.

  On the other hand, a different ID is assigned to each overhanging radio station in advance, and the ranging area allocation control unit 12 generates a ranging area allocation control signal that specifies a ranging time slot for each ID, for example, using a control signal channel. Broadcast to each overhanging radio station 20. The ranging area allocation signal generation unit 22 of the overhanging radio station 20 outputs a ranging area allocation signal a corresponding to the ID of the own station from the received ranging area allocation control signal, and inputs the ranging area allocation signal a to the adder 23 to input the null of the radio frame. Inserted into the part. The ranging area allocation signal generation unit 22 holds each radio signal pattern of ranging time slot information notified from the centralized control base station 10 in a memory, and the radio signal pattern as a ranging area allocation signal to be inserted into a radio frame. By selecting and outputting, it is possible to generate a radio frame including a ranging area allocation signal that is different for each overhanging radio station.

  Next, the terminal station 30 under the overhanging radio station 20 receives the radio frame, extracts the ranging area allocation signal, and notifies the ranging processing unit 33 (FIG. 2: S31). The ranging processing unit 33 transmits the ranging signal in the ranging time slot assigned as the ranging area (FIG. 2: S32). In the example shown in FIG. 3, the terminal stations 30a1 and 30a2 under the overhanging radio station 20a transmit ranging signals in the assigned time slots t1 and t2, respectively. If the terminal stations 30a1 and 30a2 select the same ranging time slot, both ranging signals collide and random access fails, but in FIG. 3, the respective ranging signals are in time slots t1 and t2. A distributed example is shown.

  The terminal station 30b1 under the overhanging radio station 20b transmits the ranging signal in the time slot t3 among the assigned time slots t3 and t4. The terminal stations 30c1, 30c2, and 30c3 under the overhanging radio station 20c transmit ranging signals in the assigned time slots t6, t5, and t6, respectively. In the extended radio station 20c, since there are only two ranging time slots for three terminal stations, at least two terminal stations select the same ranging time slot, and ranging signals collide, resulting in random access failure. Probability is high. However, since different ranging time slots are assigned to the respective overhanging radio stations 20a, 20b, and 20c, ranging signal collisions do not occur between the terminal stations under the different overhanging radio stations.

Next, the overhanging radio station 20 converts the ranging signal transmitted by the subordinate terminal station 30 into an optical signal and transfers it to the centralized control base station 10. The centralized control base station 10 is transferred from the overhanging radio station 20. A ranging signal is received (FIG. 2: S13). Then, the total received power measuring unit 14 measures the total received power in the ranging time slot section allocated to each overhanging radio station (FIG. 2: S14). The total received power may be averaged from the result of receiving the ranging signal a plurality of times. In the example shown in FIG. 3, the ratio of the total received power Pa, Pb, Pc in the ranging time slot section allocated to the overhanging radio stations 20a, 20b, 20c is
Pa: Pb: Pc = 2: 1: 3
It becomes. In the ranging time slot t6, the ranging signals of the terminal stations 30c1 and 30c3 collide, and the received power increases by about 3 dB due to the interference.

  Here, the centralized control base station 10 detects the ranging signals of the terminal stations 30a1 and 30a2 subordinate to the overhanging radio station 20a in the ranging time slots t1 and t2, and detects the ranging signal of the overhanging radio station 20b in the ranging time slot t3. The ranging signal of the subordinate terminal station 30b1 is detected. Furthermore, the centralized control base station 10 detects only the ranging signal of the terminal station 30c2 because the ranging signals of the terminal stations 30c1 and 30c3 subordinate to the overhanging radio station 20c collide in the ranging time slots t5 and t6. However, it can be estimated from the total received power of the ranging time slots t5 and t6 that a terminal station other than the terminal station 30c2 is transmitting a ranging signal.

  Next, the centralized control base station 10 compares the number of terminal stations in which ranging signals are detected in the ranging time slot assigned to each overhanging radio station 20 with the total received power, and whether or not a ranging signal collision has occurred. It is determined whether or not (FIG. 2: S15). If it is determined that there is a collision of ranging signals, the number of ranging time slots (integer ratio) allocated to each overhanging radio station is calculated so as to be proportional to the total received power ratio measured in step S14. Distribute (FIG. 2: S16). In the example shown in FIG. 3, the time slots for ranging assigned to the overhanging radio stations 20a, 20b, and 20c are redistributed as (t1, t2), (t3), and (t4, t5, t6).

  The centralized control base station 10 establishes a communication connection with the terminal station that has detected the ranging signal for each ranging time slot in parallel with the processing of steps S14 to S16, and sets the corresponding overhanging radio station. Data communication is started (FIG. 2: S17, S33). In the example shown in FIG. 3, the ranging signals of the terminal stations 30a1 and 30a2 under the overhang radio station 20a, the terminal station 30b1 under the overhang radio station 20b, and the terminal station 30c2 under the overhang radio station 20c are detected. The centralized control base station 10 starts data communication with these terminal stations. On the other hand, the terminal stations 30c1 and 30c3 under the overhanging radio station 20c transmit the ranging signal repeatedly because the communication signal with the central control base station 10 is not established although the ranging signal is transmitted. At this time, the transmission power control unit 34 of the terminal stations 30c1 and 30c3 gradually increases the transmission power every time the ranging signal is transmitted, thereby reflecting the redistribution of the ranging time slots allocated to the overhanging radio station 20c, You may set so that the collision of a ranging signal may be avoided. Details will be described as a third embodiment.

  Next, the centralized control base station 10 returns to step S12, and transmits a ranging area allocation control signal based on the redistribution of the ranging time slot in step S16 to each overhanging radio station 20. Similarly, the ranging signal is transmitted in the ranging time slot distributed from the terminal station 30 under the control of each overhanging radio station 20. In the example shown in FIG. 4, the time slots t1 and t2 are in the cell #a of the overhanging radio station 20a, the time slot t3 is in the cell #b of the overhanging radio station 20b, and the time slots t4, t5 are in the cell #c of the overhanging radio station 20c. Each of t6 is assigned, and a ranging signal is transmitted from each terminal station under each overhanging radio station.

  By repeating the above processing, a collision of ranging signals generated between the terminal stations 30 under the control of each overhanging radio station 20 is avoided, and a communication connection is established with each terminal station 30 to start data communication. be able to.

(Second Embodiment)
The overhanging radio station 20 of the first embodiment receives ranging area allocation control signals from the centralized control base station 10 and transmits ranging area allocation signals indicating the individually allocated ranging areas to the subordinate terminal stations 30. Each terminal station 30 transmits a ranging signal within the ranging area.

  The present embodiment is different in a method for realizing the first feature and the second feature in the first embodiment.

  FIG. 5 shows a second embodiment of the wireless access system of the present invention. In the figure, the centralized control base station 10 includes a radio signal processing unit 11, a ranging area allocation control unit 12, an optical signal transmission / reception unit 13, and a total received power measurement unit 14 as those involved in the present embodiment. The overhanging radio station 20 includes an optical signal transmission / reception unit 21, an operation control unit 26, an amplifier 24, and a transmission / reception antenna 25 that are involved in this embodiment. The terminal station 30 includes a transmission / reception antenna 31, a radio signal processing unit 33, a ranging processing unit 33, and a transmission power control unit 34 as those involved in the present embodiment. Although the basic functions of the respective parts common to the first embodiment are the same, functions unique to the present embodiment will be described below.

  The radio signal processing unit 11 of the centralized control base station 10 generates a radio frame including ranging area allocation information r for notifying each overhanging radio station 20 of a common ranging time slot, and transmits it in a frame cycle. This radio frame is transferred as it is to the subordinate terminal station 30 via the overhanging radio station 20.

  On the other hand, the ranging area allocation control unit 12 determines a prescribed number of frames that is a period in which each overhanging radio station 20 is activated, and a sleep control signal that suspends the operation except for the period of the prescribed number of frames assigned to each overhanging radio station. Send. The operation control unit 26 of the overhanging radio station 20 receives the sleep control signal, and sets it to be inactive except for the period of the specified number of frames allocated to the own station. Therefore, the radio frame transmitted from the centralized control base station 10 is transmitted to the terminal station 30 under the overhang radio station 20 and does not reach the terminal stations 30 under the other overhang radio station 20. .

  The terminal station 30 that has received this radio frame transmits a ranging signal in the ranging time slot (t1 to t6 in the example of FIG. 8) notified by the ranging area allocation information r. Accordingly, although the ranging time slot is shared by all the terminal stations 30, the terminal stations 30 under the overhanging radio station that can use the ranging time slot are selected by sequentially activating each of the overhanging radio stations 20.

  Note that sleep control (active control) for the overhanging radio station 20 transmits a sleep signal or a CTS signal for instructing the terminal station under control of the overhanging radio station to stop operation for a certain period of time, and stops signal transmission of the terminal station. A method of suspending transmission / reception in the overhanging radio station for a certain period of time and rejecting acceptance of the transmission signal of the terminal station, or a dedicated optical communication channel is set between the centralized control base station 10 and the overhanging radio station In this case, a method of discarding the optical communication channel at the centralized control base station can be used.

  Hereinafter, the control of this embodiment will be specifically described with reference to FIGS. FIG. 6 shows a processing procedure in the second embodiment of the wireless access system of the present invention. 7 to 9 show examples of the operation of the second embodiment of the wireless access system of the present invention.

  First, the centralized control base station 10 determines the prescribed number of frames during which each overhang radio station 20 is active, and actively controls one overhang radio station (FIG. 6: S41, S51). Next, a radio frame including the ranging area allocation information r is generated and transmitted at a frame period. This radio frame is transferred as it is to the subordinate terminal station 30 via the active overhanging radio station 20 (FIG. 6: S41). In the example shown in FIG. 7, the prescribed frame numbers of the overhanging radio stations 20a, 20b, and 20c are set to 2, 1, and 3, respectively, and the overhanging radio station 20a transfers the radio frames 1 and 2 to the terminal stations under the overhanging radio station 20a. The radio station 20b transfers the radio frame 3 to the subordinate terminal station, and the overhang radio station 20c transfers the radio frames 4 to 6 to the subordinate terminal station. Further, the total number of ranging time slots allocated to each overhanging radio station 20 is substantially set according to the number of ranging time slots and the specified number of frames that determine the active period of each overhanging radio station 20. In the example of FIG. 8, the ranging time slots are t1 to t6, the total number of ranging time slots allocated to the overhanging radio station 20a is 6 × 2, and the total number of ranging time slots allocated to the overhanging radio station 20b is Thus, the total number of ranging time slots allocated to the overhanging radio station 20c is 6 × 3.

  Next, the terminal station 30 under the active overhanging radio station 20 receives the radio frame, extracts the ranging area allocation information r, and notifies the ranging processing unit 33 (FIG. 6: S61). The ranging processing unit 33 transmits a ranging signal in the notified ranging time slot (FIG. 6: S62). In the example shown in FIGS. 7 and 8, the terminal stations 30a1 and 30a2 subordinate to the overhanging radio station 20a perform ranging at t1 and t4 in the ranging time slots t1 to t6 during the period in which the radio frame 1 is received. Send a signal. When the terminal stations 30a1 and 30a2 select the same ranging time slot, both ranging signals collide with each other and random access fails, but in FIG. 8, the respective ranging signals are in time slots t1 and t4. A distributed example is shown.

  Next, the overhanging radio station 20 converts the ranging signal transmitted by the subordinate terminal station 30 into an optical signal and transfers it to the centralized control base station 10. The centralized control base station 10 is transferred from the overhanging radio station 20. A ranging signal is received (FIG. 6: S43). Then, the total received power measuring unit 14 measures the total received power in the ranging time slot section (FIG. 6: S44). The total received power may be the average received power in the ranging time slot section of one frame, or may be the sum or average of the received power of the ranging signals in the total ranging time slot section of the specified number of frames.

  Next, the centralized control base station 10 establishes a communication connection with the terminal station 30 that has detected the ranging signal, and starts data communication via the extended radio station 20 (FIG. 6: S45, S63).

  Next, the centralized control base station 10 repeats the processes of steps S42 to S45 until the number of radio frames transmitted to the active overhanging radio station 20 reaches the specified number of frames (FIG. 6: S46). When the specified number of frames is reached for one overhanging radio station 20, the overhanging radio station is controlled to sleep (FIG. 6: S47, S52), and access control for all overhanging radio stations 20 is completed (see FIG. 6: S48), the processing of steps S41 to S47 is repeated for the next overhanging radio station 20. In the example of Fig. 7 and Fig. 9, the overhanging radio station 20a goes to sleep in the radio frame 3, and the overhanging radio station 20b The terminal station 30b1 becomes active and transmits a ranging signal at t3 of the ranging time slots t1 to t6 during a period in which the radio frame 3 is received.

  When the access control for the extended radio station 20 is completed in the radio frames 1 to 6, the total received power measuring unit 14 totals the total received power of the ranging signals in the radio frame for each extended radio station and is proportional to the total received power ratio. As described above, the prescribed number of frames (integer ratio) corresponding to each overhanging radio station is calculated and redistributed (FIG. 6: S49).

  If the terminal station 30 under the overhanging radio station 20 transmits the ranging signal, but the communication connection with the centralized control base station 10 is not established, the terminal station 30 repeats the ranging signal while receiving the radio frame. Send. At this time, the transmission power control unit 34 of the terminal station 30 gradually increases the transmission power every time the ranging signal is transmitted, thereby reflecting the redistribution of the specified number of frames so as to avoid the collision of the ranging signals. It may be set. Details will be described as a third embodiment.

  By repeating the above processing, a collision of ranging signals generated between the terminal stations 30 under the control of each overhanging radio station 20 is avoided, and a communication connection is established with each terminal station 30 to start data communication. be able to.

(Third embodiment)
The function of the transmission power control unit 34 in the terminal station 30 of the first embodiment and the second embodiment will be described with reference to FIG.

  In a general wireless communication system, in order to solve the problem of near-far in uplink transmission, that is, the problem that radio waves emitted from terminal stations far from the base station are masked by radio waves emitted from terminal stations near the base station, A transmission power control function is installed. In order to suppress interference with other terminal stations, a terminal station having a transmission power control function controls transmission power gradually when initial transmission is performed, and gradually increases transmission power when a communication link is not established. .

  In the first embodiment and the second embodiment, when a ranging signal collision occurs between the terminal stations 30 under the overhanging radio station 20, the central control base station 10 cannot determine the ranging signal. Cannot establish communication connection with. A situation where a collision occurs is when a plurality of terminal stations accidentally transmit ranging signals in one ranging time slot, or when the number of terminal stations is larger than the total number of ranging time slots.

  The following description will be made in correspondence with the first embodiment. However, in the second embodiment, the distribution of ranging time slots may be read as the distribution of the prescribed number of frames.

  In FIG. 10 (1), as shown in FIG. 3, the overhanging radio station 20a accommodates two terminal stations 30a1 and 30a2, the overhanging radio station 20b accommodates one terminal station 30b1, and the overhanging radio station 20c has 3 When accommodating two terminal stations 30c1, 30c2, and 30c3, ranging time slots t1 to t3, t4 to t6, and t7 to t9 are evenly distributed to the overhanging radio stations, and the terminal stations under each of the overhanging radio stations are respectively This shows a state in which a ranging signal is transmitted in the ranging time slot. Here, since the terminal stations 30c1 and 30c3 of the overhanging radio station 20c both transmit ranging signals in the ranging time slot t9 and collide, the centralized control base station 10 cannot detect the ranging signals of the terminal stations 30c1 and 30c3. However, it can be seen from the total received power of the ranging time slots t7 to t9 that a terminal station other than the terminal station 30c2 is transmitting a ranging signal.

In the first embodiment, when the communication connection for the ranging signal transmitted from the terminal station 30 cannot be established, the terminal station 30 repeatedly transmits the ranging signal. At this time, the transmission power control unit 34 of the terminal stations 30c1 and 30c3 gradually increases the transmission power every time the ranging signal is transmitted. At this time, when the total received power in the ranging time slots t7 to t9 measured by the total received power measuring unit 14 of the centralized control base station 10 increases from 3 to 4 and becomes as shown in FIG. The ratio of the total received power Pa, Pb, Pc of the ranging time slot allocated to the stations 20a, 20b, 20c is
Pa: Pb: Pc = 2: 1: 4
It becomes. Therefore, the number of ranging time slots (integer ratio) allocated to each overhanging radio station is calculated. At this time, the ranging time slots to be allocated to the overhanging radio stations 20a, 20b, and 20c reflecting the increase in the transmission power of the ranging signals of the terminal stations 30c1 and 30c3 are (t1 to t3) as shown in FIG. , (T4 to t5), (t6 to t9). Thereby, in the overhanging radio station 20c, four ranging time slots are allocated to the three terminal stations, and the collision probability of the ranging signal is reduced.

FIG. 11 shows an example of actual measurement of the total received power.
In the figure, on the basis of the received power after the DC component cut of the ranging signals a1 and a2, when the ranging signals a1 and a2 interfere, it increases by about 3 dB, and increases by about 6 dB as the transmission power of the ranging signal a1 increases. When the increasing ranging signal a1 and the ranging signal a2 interfere, it increases by about 7 dB. In this way, it is possible to easily distinguish whether the reception power is an interference caused by a collision of ranging signals or an increase in transmission power and reflect it in the redistribution of the ranging time slots.

  In the second embodiment and the third embodiment, the total received power Pa, Pb, Pc of the ranging time slot allocated to the extended radio stations 20a, 20b, 20c is measured by the centralized control base station 10. Instead, the total received power in the ranging time slot section to which each overhanging radio station is assigned may be measured, and the measurement result may be notified to the central control base station 10.

  In the above description, the ranging time slot for time-sharing radio resources is described as an example of the ranging area allocated to each overhanging radio station 20 and the terminal station 30 under the radio station 20 but is not limited thereto. For example, the radio resource may be frequency-divided or code-divided, or a combination of those including time division may be distributed as the ranging area of each overhanging radio station 20. For example, when a CDMA (Code Division Multiple Access) code is used as a ranging signal, a CDMA code to be transmitted is randomly selected, and radio resources provided as a ranging area (an area surrounded by a certain number of time slots and subcarriers) The CDMA code may be transmitted by selecting an arbitrary area from the above.

The figure which shows 1st Embodiment of the radio | wireless access system of this invention. The sequence diagram which shows the process sequence in 1st Embodiment of the radio | wireless access system of this invention. The figure which shows the operation example of 1st Embodiment of the radio | wireless access system of this invention. The figure which shows the operation example of 1st Embodiment of the radio | wireless access system of this invention. The figure which shows 2nd Embodiment of the radio | wireless access system of this invention. The sequence diagram which shows the process sequence in 2nd Embodiment of the radio | wireless access system of this invention. The figure which shows the operation example of 2nd Embodiment of the radio | wireless access system of this invention. The figure which shows the operation example of 2nd Embodiment of the radio | wireless access system of this invention. The figure which shows the operation example of 2nd Embodiment of the radio | wireless access system of this invention. The figure which shows the control example of 3rd Embodiment of the wireless access system of this invention. The figure which shows the example of measurement of total received power. The figure which shows the successful example of the random access control in the radio | wireless access system using ROF transmission. The figure which shows the example of failure of the random access control in the radio | wireless access system using ROF transmission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber transmission line 2 Optical coupler 10 Centralized control base station 11 Wireless signal processing part 12 Ranging area allocation control part 13 Optical signal transmission / reception part 14 Sum total received power measurement part 20 Overhang radio station 21 Optical signal transmission / reception part 22 Ranging area allocation signal generation Unit 23 addition unit 24 amplifier 25 transmission / reception antenna 26 operation control unit 30 terminal station 31 transmission / reception antenna 32 radio signal processing unit 33 ranging processing unit 34 transmission power control unit

Claims (10)

In a multi-cell radio access system in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line,
The centralized control base station transmits a ranging radio resource for transmitting a ranging signal for requesting an access request by a terminal station subordinate to each of the plurality of overhanging radio stations according to the number of terminal stations having an access request. Radio resource control means for distributing to each radio station,
The radio access system, wherein the terminal station is configured to transmit the ranging signal using a ranging radio resource notified through an overhanging radio station to which the terminal station belongs. The radio access system according to claim 1,
The radio resource control means measures the total received power of ranging radio resources distributed to the plurality of overhanging radio stations, determines a distribution ratio of the ranging radio resources according to the total received power ratio, and A radio access system characterized in that the radio resources for ranging are redistributed to each overhanging radio station. The radio access system according to claim 1,
The centralized control base station broadcasts a control signal including information on the ranging radio resources distributed to the plurality of overhanging radio stations to the plurality of overhanging radio stations, and transmits a predetermined radio to the overhanging radio station. A configuration for transmitting frames,
The overhanging radio station recognizes the ranging radio resource distributed to itself from the broadcast-reported control signal, and inserts the ranging radio resource into the radio frame and notifies the subordinate terminal station. A wireless access system characterized by having a configuration. In a multi-cell radio access system in which a centralized control base station and a plurality of overhanging radio stations are connected via a broadband transmission line,
The centralized control base station controls a period in which each overhang radio station is sequentially activated according to the number of terminal stations having access requests under the control of the plurality of overhang radio stations, and the terminal station makes an access request. Radio resource control means for notifying a terminal station under control of a ranging radio resource for transmitting a ranging signal via an active overhanging radio station,
The radio access system, wherein the terminal station is configured to transmit the ranging signal using a ranging radio resource notified from the active overhanging radio station. The radio access system according to claim 4,
The radio resource control means measures the total received power of ranging radio resources in each active period of the plurality of overhanging radio stations, determines the active period of each overhanging radio station according to the total received power ratio, A radio access system characterized by being configured to actively control a plurality of overhanging radio stations sequentially. The radio access system according to claim 2 or 5,
The terminal station includes transmission power control means for repeating transmission of the ranging signal until a communication connection with the centralized control base station is established, and increasing transmission power of the ranging signal for each repetition. Wireless access system. In the terminal apparatus of the radio | wireless access system of Claim 2 or Claim 5,
A terminal station apparatus comprising transmission power control means for repeating transmission of the ranging signal until a communication connection with the centralized control base station is established, and increasing transmission power of the ranging signal at each repetition. In a multi-cell type wireless access method in which a centralized control base station and a plurality of overhanging wireless stations are connected via a broadband transmission line,
The centralized control base station transmits a ranging radio resource for transmitting a ranging signal for requesting an access request by a terminal station subordinate to each of the plurality of overhanging radio stations according to the number of terminal stations having an access request. Distributed to each radio station,
The wireless access method, wherein the terminal station transmits the ranging signal using a ranging radio resource notified through an overhanging radio station to which the terminal station belongs. The wireless access method according to claim 8,
The centralized control base station broadcasts a control signal including information on the ranging radio resources distributed to the plurality of overhanging radio stations to the plurality of overhanging radio stations, and transmits a predetermined radio to the overhanging radio station. Send a frame,
The overhanging radio station recognizes the ranging radio resource distributed to itself from the broadcast-reported control signal, and inserts the ranging radio resource into the radio frame and notifies the subordinate terminal station. Wireless access method characterized in that In a multi-cell type wireless access method in which a centralized control base station and a plurality of overhanging wireless stations are connected via a broadband transmission line,
The centralized control base station controls a period in which each overhang radio station is sequentially activated according to the number of terminal stations having access requests under the control of the plurality of overhang radio stations, and the terminal station makes an access request. Sends ranging radio resources to transmit ranging signals to the terminal stations under control via the active overhanging radio station,
The radio access method, wherein the terminal station transmits the ranging signal using a ranging radio resource notified from the active overhanging radio station.

Images