JP6494918B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a digital radio system that suppresses interference due to the same operating wave transmission in simultaneous transmission from a plurality of base station radio apparatuses.

  In the conventional digital radio system, in the simultaneous transmission of the same operating wave by a plurality of base station radio devices, each base station radio device has received from the radio network controller an instruction to start downlink transmission to a lower radio terminal device. Since it starts at each timing as an opportunity, there is a possibility that a dead zone may occur due to the influence of neighboring base station radio apparatuses.

  That is, even if the radio network controller notifies all base station radio devices of the downlink transmission start instruction, the timing at which the downlink transmission start instruction reaches each base station radio device is Due to the difference in transmission time, the timing at which a downlink transmission start instruction arrives at each base station radio apparatus differs, and simultaneous transmission should be performed at different timings at each base station radio apparatus. For this reason, in areas where radio signals from a plurality of base station radio apparatuses reach (areas where service areas of base station radio apparatuses overlap), downlink transmissions started at different timings by the plurality of base station radio apparatuses are mutually There may be a dead zone due to interference.

  Various inventions have been proposed for digital radio systems. For example, Patent Document 1 discloses an invention of a radio communication system in which a plurality of systems operating independently at normal times can be effectively used in an emergency. Is disclosed.

JP 2008-301327 A

  In order to respond to diversification of communication needs such as digital transmission, the fire and emergency radio system will change from an analog communication system using the 150 MHz band to a digital communication system using the 260 MHz band in the period up to May 31, 2016. A migration has been implemented. By introducing a digital wireless system, communication with improved secrecy and advanced communication such as data transmission can be realized. On the other hand, the propagation distance of the 260 MHz band used in the digital communication method is 1/2 of the 150 MHz band. Therefore, it is necessary to install many relay stations with digitization.

However, when adding more relay stations, there is a dead zone where the relay station's transmission waves interfere in areas where service areas overlap, so eliminating the dead zone is a challenge when migrating systems from analog to digital. It has become.
In addition, in the transition to the digitization of the current system, the system has become wider due to the merger of multiple firefighting headquarters. As the system becomes widespread, it is required that each fire-fighting headquarters has jurisdiction over a wide area, so fire-fighting emergency activities across multiple base station radio devices may be performed. For this reason, there is a concern that there will be an opportunity to conduct fire-fighting and emergency activities in the area of the dead zone.

  As described above, in a system in which a plurality of base station radio devices start downlink transmission after waiting for a start instruction from the radio network controller, the radio network controller sends a downlink transmission start command to each base station radio device all at once. Even if the notification is made, the transmission time to and from the radio network controller is not uniform, so the timing at which each base station radio apparatus receives the downlink transmission start instruction is different, and as a result, each base station radio There is a possibility that a dead zone may occur due to interference between downlink transmissions started at different timings depending on devices.

  The present invention has been made in view of the above-described conventional circumstances, and a difference in transmission time between a plurality of base station radio apparatuses that perform downlink transmission using the same frequency and a radio network controller. Regardless, it is an object to reduce the dead zone by enabling the downlink transmission to be started at the same timing and suppressing the mutual interference of the downlink transmissions from a plurality of base station radio apparatuses.

  In order to achieve the above object, the present invention provides a radio communication system having a plurality of base stations that perform downlink transmission using the same frequency, and a radio network controller that controls the plurality of base station radio apparatuses. The operation was as follows.

That is, the radio network controller and the plurality of base station radio devices operate at timing synchronized with each other, and the radio network controller transmits an instruction to start downlink transmission at the same timing to the plurality of base station radio devices. In this case, as the start timing of downlink transmission in the instruction, a timing is set with an interval corresponding to the maximum transmission time between the radio network controller and the plurality of base station radio apparatuses with respect to the transmission timing of the instruction. It was decided to.
According to such a configuration, each base station radio apparatus can start downlink transmission at the same timing regardless of the difference in transmission time with the radio network controller. For this reason, it can suppress that the downlink transmission from a some base station radio | wireless apparatus mutually interferes, and can reduce a dead zone.

In order to operate a plurality of base station radio devices and radio channel control devices at timings synchronized with each other, for example, the following configuration may be used.
That is, each of the plurality of base station radio devices and radio network controllers outputs a reference signal having a period of 1 second and a clock signal having a period shorter than that of the reference signal based on a signal from a GPS (Global Positioning System) satellite. A GPS module is provided, the reference signal is divided by a predetermined integer based on the clock signal, the timing of the radio frame is generated, and a frame number that is reset at the timing of the reference signal is given to each radio frame.
As a result, the plurality of base station radio devices and radio channel control devices can synchronize the frame timing and frame position with other devices accurately while operating independently.

Here, as one configuration example, when a base station radio apparatus having a transmission time equal to or greater than a predetermined value exists in a plurality of base station radio apparatuses, the radio network controller is configured to have a base whose transmission time is within the predetermined value An instruction to start downlink transmission at the same timing is changed according to the station radio apparatus, and an instruction to start downlink transmission set by the change at the same timing is transmitted.
Thereby, it is possible to prevent the transmission of the downlink transmission start instruction to the base station radio apparatus from being delayed from the original schedule due to the presence of the base station radio apparatus that is too far from the radio network controller.

Further, as one configuration example, a plurality of base station radio apparatuses start downlink transmission without waiting for an instruction when a predetermined time has elapsed after receiving data targeted for downlink transmission.
As a result, it is possible to avoid a situation in which downlink transmission is not started as a result of the base station radio apparatus missing the downlink transmission start instruction from the radio network controller.

  According to the present invention, each base station radio apparatus can start downlink transmission at the same timing regardless of the transmission time difference with the radio network controller, so that a plurality of base station radio apparatuses can Can be prevented from interfering with each other, and the dead zone can be reduced.

It is a figure which shows the example of schematic structure of the fire-fighting emergency digital radio system which concerns on one Embodiment of this invention. It is a figure which shows the example of the functional block of a radio network controller. It is a figure explaining operation | movement of a super-frame counter. It is a figure which shows a mode that a transmission timing frame number is produced | generated on the basis of a transmission timing base frame number. It is a figure which shows the example of the operation | movement sequence at the time of instruct | indicating the start of downlink transmission. It is a figure which shows the example of the functional block of a base station radio | wireless apparatus. It is a figure which shows the example of the processing flow which determines transmission timing in a base station radio | wireless apparatus. It is a figure which shows a mode that a some base station radio | wireless apparatus starts downlink transmission at the same timing. It is a figure explaining the structure which provides a transmission start protection timer in a base station radio | wireless apparatus. It is a figure which shows the example of the operation | movement sequence in the structure which provides a transmission start protection timer in a base station radio | wireless apparatus. It is a figure which shows the mode of interference in case a base station radio | wireless apparatus transmits asynchronously at the same frequency. It is a figure which shows the example of distribution of BER when three base stations transmit asynchronously. It is a figure which shows the example of distribution of BER when three base stations perform synchronous transmission.

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a schematic configuration of a wireless communication system according to an embodiment of the present invention. In this example, a fire and emergency digital radio system is used as an example of a radio communication system, but the present invention can also be applied to a radio communication system for other purposes.
The wireless communication system of this example includes a wireless control console 10, a communication console 20, a management monitoring control console 30, a command console 40, a command control device 50, a radio network controller 60, a base station radio device 70, a mobile station radio device 90, and the like. Equipment and facilities.

  The wireless control stand 10 is a device that is connected to the wireless line control device 60 to centrally control wireless communication such as fire engines and ambulances. The wireless control table 10 is a facility installed on the headquarters side and may be an individual remote controller.

  The communication console 20 is a device that is connected to the wireless line control device 60 and individually performs wireless communication such as fire engines and ambulances. The communication console 20 is a facility installed on the headquarters side and may be used together with the command board 40 in an integrated manner. These conditions vary depending on the use of each fire department headquarters and the equipment design policy of the supplier.

  The management monitoring control console 30 is a device that is connected to the wireless line control device 60 and performs operation management and monitoring control of the fire and emergency digital wireless system. The management monitoring control console 30 is arranged according to the necessity in system design, and may not exist.

  The command board 40 is installed in the fire command center, is connected to the radio network controller 60 via the command control device 50, and is a device for operating the fire emergency digital radio system and other systems.・ Input, processing, display, etc. of data (non-voice information such as images and information indicating the position of the vehicle), short sentences (character strings of up to 80 bytes), etc.

As described above, the wireless control console 10, the communication console 20, the management monitoring control console 30, and the command console 40 are connected to the radio network controller 60.
The radio network controller 60 is connected to a plurality of base station radio devices 70 under its management. In this example, the radio network controller 60 uses the radio channel f1 to perform radio communication with the mobile station radio devices 90 (# 1) and (# 2), the base station radio devices 70 (# 1) to (# 3), a base station radio apparatus 70 (# 4) that performs radio communication with the mobile station radio apparatus 90 (# 3) using the radio channel f2, and a mobile station radio apparatus 90 (using the radio channel f3) A base station radio apparatus 70 (# 5) that performs radio communication with # 4) is connected, and the base station radio apparatus 70 is controlled.

The mobile station wireless device 90 is a wireless communication terminal that can be moved by vehicle or mobile, and performs wireless communication with the base station wireless device 70 whose location is included in the service area (wireless communication area). Here, the radio communication from the base station radio apparatus 70 (higher apparatus) to the mobile station radio apparatus 90 (lower apparatus) is referred to as downlink transmission, and the radio communication in the opposite direction is referred to as uplink communication.
As a wireless terminal device that performs wireless communication with the base station wireless device 70, a fixed station wireless device that is fixedly installed can be used in addition to the mobile station wireless device 90 as described above.

FIG. 2 shows an example of functional blocks of the radio network controller 60.
The radio network controller 60 includes a GPS antenna 61, a GPS module 63, a PLL (Phase Locked Loop) 64, a frame generator 62 including a superframe counter 65, and a controller 66 including a CPU (Central Processing Unit) 67. And a base station interface unit 68.
As shown in FIG. 3, the frame generation unit 62 has a configuration in which hardware modules such as a GPS module 63, a PLL 64, and a super frame counter 65 are mounted on a HUB board.

The GPS module 63 outputs a 10 MHz clock signal and a 1 PPS (Pulse Per Second) signal based on a signal transmitted from a GPS satellite and received by the GPS antenna 61. The 1PPS signal is a rectangular wave signal with a period of 1 second indicating the timing for counting seconds.
The PLL 64 outputs a 40 ms signal indicating a frame timing every 40 ms based on the 10 MHz clock signal output from the GPS module 63.
Based on the 40 ms signal output from the PLL 64 and the 1 PPS signal output from the GPS module 63, the super frame counter 65 takes a frame number for identifying a radio frame having a frame length of 40 ms for each frame timing (40 ms cycle). To notify the CPU 67 of the control unit 66.

A specific operation of the super frame counter 65 will be described with reference to FIG.
The super frame counter 65 forms a super frame that switches at the cycle (1 second cycle) of the 1PPS signal output from the GPS module 63, and further divides the super frame at the cycle of 40 ms signal output from the PLL 64 to obtain 25 frames. A radio frame is formed. At this time, frame numbers “1” to “25” indicating the position (order) in the superframe are sequentially attached to each radio frame. The assignment of the frame number is performed using a frame counter that is incremented (+1) at a cycle of 40 ms signal. This frame counter is reset to an initial value (in this example, “1”) every time a super frame is switched.
The frame number generated by the super frame counter 65 is notified to the CPU 67 of the control unit 66 at every frame timing of 40 ms cycle.

  When the CPU 67 of the control unit 66 receives a downlink transmission start instruction from a device such as the command board 40 or the like, at that time (immediately before or after reception of the downlink transmission start instruction), the CPU 67 of the frame generation unit 62 receives the instruction. Based on the notified frame number, the base station radio apparatus 70 sets a frame number (hereinafter referred to as “transmission timing frame number”) of a radio frame from which downlink transmission starts.

Here, the transmission timing frame number is set in consideration of the transmission time from the radio network controller 60 to the base station radio device 70.
Specifically, based on the frame number of the radio frame used by the radio network controller 60 to transmit the downlink transmission start instruction to the base station radio device 70 (hereinafter referred to as “transmission timing base frame number”), A frame number with an interval corresponding to at least a transmission time is specified with respect to the transmission timing base frame number, and the specified frame number is set as a transmission timing frame number. That is, a frame number obtained by adding at least the number of radio frames corresponding to the transmission time to the transmission timing base frame number is set as the transmission timing frame number.

In this example, after the installation of each base station radio apparatus 70, the transmission time with the radio network controller 60 is measured, and the result of adjusting the measured value in a predetermined time unit (eg, 100 ms unit) is obtained. The number of radio frames corresponding to the transmission time is stored in the memory of the radio network controller 60 and stored in the memory, and is referred to when calculating the transmission timing frame number. You may implement | achieve by other structures, such as referring when calculating a number.
The transmission timing frame number set by the CPU 67 of the control unit 66 is transmitted to the base station radio apparatus 70 via the base station interface unit 68 together with a downlink transmission start instruction.

With reference to FIG. 4, a process for generating a transmission timing frame number based on the transmission timing base frame number will be described.
FIG. 4 shows an example of the waveform of the 1PPS signal in order from the top, an example in which one cycle (1 second) of the waveform of the 1PPS signal is enlarged, and one superframe corresponding to one cycle of the 1PPS signal is divided by integer values. An example in which 25 radio frames (frame length 40 ms) are formed, an example of a transmission timing base frame number in the radio network controller 60, and an example of a transmission timing frame number in the base station radio device 70 (# 1) are shown. .
In the example of FIG. 4, when the transmission timing base frame number in the radio network controller 60 is “1”, the transmission time from the radio network controller 60 to the base station radio device 70 (# 1) is taken into account. “3” is set as the transmission timing frame number of the station radio apparatus 70 (# 1).

FIG. 5 shows an example of an operation sequence when instructing the start of downlink transmission.
When receiving a downlink transmission instruction from the user, the command board 40 transmits a downlink transmission start instruction to the radio network controller 60 (process T11).
When receiving a downlink transmission start instruction from the command board 40, the radio network controller 60 determines a transmission timing frame number based on the transmission timing base frame number and gives it to the downlink transmission start instruction (process T12). It transmits to the base station radio | wireless apparatus 70 as a start message (process T13).
Note that the operation sequence of this example is an example in which downlink transmission is started by a user instruction received at the command board 40, but manually or automatically by another device such as the wireless control board 10, the communication console 20, or the like. The same applies to various downlink transmissions that occur in

FIG. 6 shows an example of functional blocks of the base station radio device 70.
The base station radio apparatus 70 includes a GPS antenna 71, a frame generation unit 72 including a GPS module 73, a PLL 74, and a super frame counter 75, a control unit 76 including a CPU 77, and a radio unit 78. .
Note that the frame generation unit 72 has a configuration in which hardware modules such as a GPS module 73, a PLL 74, and a super frame counter 75 are mounted on the HUB board in the same manner as the frame generation unit 62 of the radio network controller 60 (see FIG. 3). ing.
In addition, an antenna duplexer 80 having a radio antenna 81 is connected to the base station radio apparatus 70.

The GPS module 73 outputs a 10 MHz clock signal and a 1 PPS signal based on a signal transmitted from a GPS satellite and received by the GPS antenna 71.
The PLL 74 outputs a signal indicating the frame timing every 40 ms based on the 10 MHz clock signal output from the GPS module 73.
Based on the 40 ms signal output from the PLL 74 and the 1 PPS signal output from the GPS module 73, the super frame counter 75 takes a frame number for identifying a radio frame having a frame length of 40 ms for each frame timing (40 ms period). And notifies the CPU 77 of the control unit 76 of the transmission timing frame number. Here, since the specific operation of the super frame counter 75 is the same as that of the super frame counter 65 of the radio network controller 60, the description thereof is omitted.

When the CPU 77 of the control unit 76 receives a transmission start message for downlink transmission (instruction to start downlink transmission with a transmission timing frame number) from the radio network controller 60, the transmission timing specified by the transmission start message. The frame number is compared with the transmission timing frame number notified from the super frame counter 75, and downlink transmission is started at the timing when these match. That is, when the respective transmission timing frame numbers coincide with each other, a downlink transmission signal is supplied to the radio unit 78.
The radio unit 78 outputs the downlink transmission signal supplied from the control unit 76 to the antenna duplexer 80 and causes the radio antenna 81 to perform radio transmission.

Here, the data to be subjected to downlink transmission may be supplied to the base station radio apparatus 70 together with the downlink transmission start instruction, and supplied to the base station radio apparatus 70 prior to the downlink transmission start instruction. It may be in a form to keep. In other words, when the base station radio apparatus 70 receives a downlink transmission start instruction, it is only necessary that the downlink transmission can be started promptly at the reception timing (radio frame of the transmission timing frame number).
The downlink transmission data transmitted from the base station radio apparatus 70 is either SB0 (Synchronous Burst0) or SC (Service Channel) defined by the radio channel, and the base station radio apparatus 70 has received an instruction to start downlink transmission At this time, transmission is started according to the transmission timing frame number. Regarding the contents of the transmission data, since the contents of RICH (Radio Information Channel) differ depending on the state of the base station radio apparatus 70, not all base station radio apparatuses 70 that can be synchronized necessarily transmit the same data. Absent. The type of data may be voice or non-voice including data.

FIG. 7 shows an example of a processing flow for determining the transmission timing in the base station radio apparatus 70.
When the CPU 77 of the control unit 76 receives the transmission start message for downlink transmission from the radio network controller 60, the CPU 77 acquires the transmission timing frame number FN1 from the transmission start message (step S11).
Thereafter, the transmission timing frame number FN2 notified from the super frame counter 75 is acquired for each frame timing (step S12), and it is determined whether or not the transmission timing frame number FN1 and the transmission timing frame number FN2 match (step S12). S13).

If the transmission timing frame number FN1 and the transmission timing frame number FN2 do not match (step S13; FALSE), it waits until the next frame timing, and acquires the transmission timing frame number FN2 notified from the super frame counter 75. Then, the process of comparing with the transmission timing frame number FN1 is repeated.
On the other hand, when the transmission timing frame number FN1 and the transmission timing frame number FN2 match (step S13; TRUE), control is performed to start downlink transmission (step S14).
That is, the base station radio apparatus 70 waits until the timing of the transmission timing frame number set by the radio network controller 60, and starts downlink transmission when the timing has arrived.

Next, a process in which a plurality of base station radio apparatuses 70 start downlink transmission at the same timing will be described with reference to FIG.
In FIG. 8, in order from the top, an example of a transmission timing base frame number in the radio network controller 60, an example of a transmission timing frame number in the base station radio device 70 (# 1), and in the base station radio device 70 (# 2) Examples of transmission timing frame numbers,..., An example of transmission timing frame numbers in the base station radio apparatus 70 (#N) are shown.
In the example of FIG. 8, the radio network controller 60 sets an interval corresponding to the maximum value of the transmission time between the plurality of base station radio devices 70 (# 1) to (#N) that are to be subjected to downlink transmission. The transmission timing frame number is set and notified to the base station radio devices 70 (# 1) to (#N).

In other words, the transmission timing frame number is set in accordance with the transmission time of the base station radio device 70 farthest from the radio network controller 60, and the base station radio device 70 farthest from the radio network controller 60 instructs to start downlink transmission. Is made to wait for another base station radio apparatus 70 to arrive.
Thereby, since all base station radio | wireless apparatuses 70 can start downlink transmission at the same timing, it becomes possible to suppress the interference by the shift | offset | difference of the same wave transmission, and can reduce a dead zone.

  Here, in the radio communication system of this example, each of the radio network controller 60 and the base station radio device 70 has a function of receiving and processing a GPS signal, and generating a frame timing by a common technique. Therefore, the frame timing can be accurately synchronized while each device independently generates the frame timing. Also, a 1 PPS signal cycle (1 second cycle) indicating the timing of ticking seconds is assigned to a super frame, and this is divided into a predetermined number based on a 10 MHz clock signal to form a radio frame, which is reset at the cycle of 1 PPS signal. Thus, the frame position (frame number) at each frame timing can be easily matched in each device. In addition, in this example, since these processes are performed by hardware, there is no processing delay caused by CPU load or memory shortage when performed by software, and the radio network controller 60 and the base station radio apparatus 70 Accurate timing synchronization between the devices can be realized.

In the above description, the transmission timing frame number is set in accordance with the transmission time of the base station radio device 70 farthest from the radio network controller 60. For example, a threshold is provided for the transmission time, and the transmission time is equal to or greater than the threshold. If there is a base station radio apparatus 70 to be transmitted, the transmission timing frame number is changed according to the base station radio apparatus 70 to be transmitted by excluding this, and downlink transmission is performed based on the changed transmission timing frame number. A start instruction may be issued.
That is, when there is a base station radio apparatus 70 whose transmission time is equal to or greater than the threshold, the radio network controller 60 excludes the base station radio apparatus 70 and transmits a transmission timing frame according to the base station radio apparatus 70 to transmit. The number is changed, and a downlink transmission start instruction in which the same start timing is set based on the changed transmission timing frame number is transmitted.

According to such a configuration, it is possible to prevent the transmission of the downlink transmission start instruction to the base station radio apparatus 70 from being delayed due to the presence of the base station radio apparatus 70 that is too far from the radio network controller 60. . For this reason, for example, a situation where downlink transmission of audio data from the base station radio apparatus 70 to the mobile station radio apparatus 90 is started later than originally scheduled, and the audio output is interrupted at the mobile station radio apparatus 90. Can be prevented.
For the base station radio apparatus 70 whose transmission time is equal to or greater than the threshold, a transmission timing frame number is set and notified so that downlink transmission can be started with a radio frame assigned to the base station radio apparatus 70 in the next superframe. That's fine.

Next, as an extended example, a configuration will be described in which an upper limit is set for the elapsed time from when the base station radio apparatus 70 receives data to be downlink transmitted until it receives a downlink transmission start instruction.
That is, the base station radio apparatus 70 includes a transmission start protection timer that measures the elapsed time since reception of data targeted for downlink transmission, and the transmission start protection timer times out without receiving a downlink transmission start instruction. In this case (when the upper limit of elapsed time is exceeded), downlink transmission is started.
Here, the upper limit value of the elapsed time may be the same in each base station radio apparatus 70 or may be different. However, the upper limit value of the elapsed time needs to be longer than the transmission time considered when the radio network controller 60 determines the transmission timing frame number.

Normally, as shown in FIG. 9 (a), since a downlink transmission start instruction can be received before the transmission start protection timer times out, the mobile station radio apparatus 90 is notified in response to the reception of the downlink transmission start instruction. Starts downlink transmission.
On the other hand, if a frame cannot be generated due to a failure of the GPS module 63 in the radio network controller 60, or if the transmission timing frame number from the radio network controller 60 is missed in the base station radio device 70, the mobile station Downlink transmission to the wireless device 90 cannot be started. Therefore, as shown in FIG. 9B, when the transmission start protection instruction cannot be received before the transmission start protection timer times out, the downlink to the mobile station radio device 90 is promptly performed after the transmission start protection timer times out. Start sending.

FIG. 10 shows an example of an operation sequence in a configuration in which the base station radio apparatus 70 is provided with a transmission start protection timer.
When receiving a downlink transmission instruction from the user, the command board 40 transmits a downlink transmission start instruction to the radio network controller 60 (process T21).
When receiving the downlink transmission start instruction from the command board 40, the radio network controller 60 determines the transmission timing frame number based on the transmission timing base frame number and assigns it to the downlink transmission start instruction (process T22). It transmits to the base station radio | wireless apparatus 70 as a start message (process T23).

The base station radio apparatus 70 activates a transmission start protection timer in response to reception of data to be subjected to downlink transmission (process T24), and receives a transmission start message to determine whether or not a transmission timing frame number has been acquired. These determinations are repeated (process T25).
If the transmission timing frame number can be acquired before the transmission start protection timer times out, downlink transmission is started from the radio frame corresponding to the acquired transmission timing frame number (process T27). On the other hand, when the transmission start protection timer times out without acquiring the transmission timing frame number (process T26), downlink transmission is started from the radio frame immediately after that (process T27).

  With such a configuration, even when the base station cannot receive a downlink transmission start instruction from the radio network controller 60, the base station automatically starts downlink transmission due to a timeout of the transmission start protection timer. Therefore, downlink transmission starts even when a frame cannot be generated due to a failure of the GPS module 63 in the radio network controller 60 or when the transmission timing frame number from the radio network controller 60 is missed in the base station radio device 70. It is possible to avoid the situation of being left untouched.

Here, in the description so far, a superframe having a period of one second is divided into 25 to form a radio frame having a period of 40 ms. However, the frame length of each frame is not limited to this, and wireless communication is not limited. What is necessary is just to set suitably according to the use etc. of a system.
Further, in the wireless communication system of this example, the length of one wireless frame is 40 ms, which conforms to “ARIB STD T-61” that defines a narrowband digital communication system. Generation of a radio frame of 40 ms is easy to control when n = 25 when using pulses of 1 / n second intervals, but not necessarily n = 25.

Next, a simulation result by the wireless communication system to which the present invention is applied will be described in comparison with a case where the present invention is not applied.
FIG. 11 shows the state of interference in the case of simultaneous transmission asynchronously using the same frequency in a narrowband SCPC (Single Channel Per Carrier) wireless system for public service. In the figure, it is assumed that the mobile station radio device 90 exists in an overlapping portion between the service area A1 of the base station radio device 70 (# 1) and the service area A2 of the base station radio device 70 (# 2). Yes.

  Each base station radio apparatus 70 is connected to the radio network controller 60 by an asynchronous approach line. This approach line is configured using a communication company's wired line, a self-operated optical line, a microwave multiplex radio apparatus, or the like, in order to ensure line quality.

  Here, in a narrowband SCPC radio system for public service, if radio waves transmitted simultaneously from different base stations in an overlapping area of service areas are regarded as a desired wave (Desired) and an interference wave (Undesired), the desired wave and the interference wave It is stipulated in “Radio Law-related Examination Criteria Attachment 2 Examination Criteria by Purpose No. 2 Public Service Radio Station” that the ratio (DU ratio) is 21 dB or more. The content of 21 dB is the theoretical required CIR (Carrier) under a fading environment at BER (Bit Error Rate) = 3%, which is the limit performance of speech coding when the information of the interference wave is random noise. to Interference Rate (carrier-to-interference ratio) = 15 dB, with a fixed degradation margin of 6 dB.

FIG. 11 shows an area A3 where the DU ratio <21 dB and an area A4 where the DU ratio <10 dB with respect to the position of the mobile station radio apparatus 90. There is a possibility that the sound cannot be correctly reproduced under an environment where the DU ratio <21 dB. In particular, there is a high possibility that the sound cannot be reproduced under a fading environment when the DU ratio <10 dB.
In the SCPC wireless system for public business, generally, when sound cannot be reproduced correctly, the sound is silent. As a phenomenon, the sound is interrupted or the sound is continuously silenced.
Even if there is no fading, the limit of the DU ratio is about 10 dB, and if the distance from a plurality of base stations is about the same, the DU ratio cannot be secured. Can not.

FIG. 12 shows an example of BER distribution obtained by simulation when three base stations simultaneously transmit asynchronously for (a) single reception and (b) diversity reception. In FIG. 12, the position of each base station is indicated by Δ.
The simulation is performed under the following conditions.
[Base station arrangement] 3 base stations, 10 km interval [Base station antenna height] 15 m
[Terminal station antenna height] 3m
[Frequency] 270 MHz
[Propagation loss model] Hata, small and medium city model [Propagation model] Rayleigh fading
It is assumed that there is no delay spread in the path from each base station. [Maximum Doppler frequency] 15Hz 60km / h (@ 270MHz) equivalent [Terminal station noise figure] 8dB
[External noise (urban noise)] None [Effective radiation power] 5W
[Transmission / Reception Antenna Gain] 0dBi

The BER that can be used in a narrowband SCPC radio system for public service is approximately 10 ^-2.5 or less.
In the single reception when each base station performs asynchronous transmission, as shown in FIG. 12A, the BER is 10 ^−2.5 or more except in the vicinity of the base station, and cannot be used for reception in a wide range. .
Also, in diversity reception when each base station transmits asynchronously, as shown in FIG. 12B, although the BER is slightly better than in the case of single reception, most of the areas cannot be used for reception. is there.
Further, in both single reception and diversity reception, an intermediate area between base stations cannot be used for reception at all.
Thus, when performing asynchronous transmission from each base station, it can be used for reception in an individual area centered on each base station, but it can be used for reception in a wide range including an intermediate area between each base station. You can see that it is not available.

FIG. 13 shows distribution examples of BER obtained by simulation when three base stations perform synchronous transmission for (a) single reception and (b) diversity reception, respectively. Further, in FIG. 13, the positions of the respective base stations are indicated by Δ.
The simulation is performed under the same conditions as in the case of asynchronous transmission.

In the single reception when each base station transmits synchronously, as shown in FIG. 13A, the BER is 10 ^−2.5 or less compared to the single reception when asynchronous transmission is performed (FIG. 12A). The area to be expanded is very wide.
Further, even in diversity reception when each base station transmits synchronously, as shown in FIG. 13B, BER is 10 ^−2.5 or less compared to diversity reception when asynchronous transmission is performed (FIG. 12B). The area has expanded very extensively.
In both single reception and diversity reception, an intermediate area between base stations that could not be used for reception by asynchronous transmission can be used for reception by synchronous transmission.
As described above, it can be seen that, in the case of asynchronous transmission, radio interference is reduced and reception can be performed satisfactorily by transmitting each base station synchronously in an area that could not be used for reception at all.

  As described above, the present invention has been described based on the embodiments. However, the configuration of the system and apparatus according to the present invention is not necessarily limited to the above-described configuration, and various configurations may be used. In addition, the present invention is provided in the form of, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a storage medium storing such a program. Is also possible.

  The present invention is applied to various types of radio communication systems having a plurality of base station radio apparatuses that perform downlink transmission using the same frequency and a radio network controller that controls the plurality of base station radio apparatuses. Can do.

10: Radio control table, 20: Communication console, 30: Management monitoring control console, 40: Command console, 50: Command control device, 60: Radio channel control device, 70: Base station radio device, 90: Mobile station radio device,
61: GPS antenna 62: Frame generation unit 63: GPS module 64: PLL 65: Super frame counter 66: Control unit 67: CPU 68: Base station interface unit
71: GPS antenna, 72: Frame generation unit, 73: GPS module, 74: PLL, 75: Super frame counter, 76: Control unit, 77: CPU, 78: Radio unit, 80: Duplexer, 81: Radio antenna

Claims (4)

In a radio communication system having a plurality of base station radio devices that perform downlink transmission using the same frequency, and a radio network controller that controls the plurality of base station radio devices,
The radio network controller and the plurality of base station radio devices each include a GPS module, and generate radio frames in which the same frame number is set at a synchronized frame timing based on a reference signal from the GPS module. And
When transmitting an instruction to start downlink transmission at the same timing to the plurality of base station radio apparatuses, the radio network controller uses the transmission timing of the instruction as the frame number of the downlink transmission start timing in the instruction. Specify the frame number of the timing with at least an interval corresponding to the maximum value of the transmission time between the radio network controller and the plurality of base station radio devices ,
The plurality of base station radio devices start downlink transmission at a frame number specified by the radio network controller ;
A wireless communication system. The radio network controller according to a base station radio apparatus having a transmission time within the predetermined value when a base station radio apparatus having a transmission time equal to or greater than a predetermined value exists in the plurality of base station radio apparatuses. change the frame number to start downlink transmission, it transmits the instruction frame number after the change specified in the start timing of the downlink transmission,
The wireless communication system according to claim 1. The plurality of base station radio devices start downlink transmission without waiting for the instruction when a predetermined time has elapsed after receiving data targeted for downlink transmission,
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The reference signal from the GPS module is a 1PPS signal,
The radio network controller and the plurality of base station radio devices form a radio frame obtained by dividing a superframe having a period of the 1PPS signal by an integer value, and reset the frame number of the radio frame at the timing of the 1PPS signal To
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system.

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