JP4283644B2 - Wireless communication system and wireless channel control method - Google Patents

Description

  The present invention relates to a radio communication system and a radio channel control method, and more particularly to a configuration of a radio communication system using time division multiple access and a radio channel control method of the system.

  In the field of wireless communication, introduction of wireless communication systems having various configurations has been attempted. Of these, a personal handyphone system (hereinafter referred to as PHS) is used, and a plurality of channels are assigned to a predetermined frame using a time division multiple access (hereinafter referred to as TDMA) technique. A wireless communication system that performs time-division multiplexing and transmission / reception of information is detailed in the configuration and operation of a standard called “RCR STD-28” by Association of Radio Industries and Businesses (hereinafter referred to as ARIB). It is a wireless communication system that is widely spread and operated.

  A wireless communication system is a system in which a terminal moves and is used, and the state of the radio wave propagation path between the terminal and the base station changes. Therefore, when the communication quality changes during communication, the channel being used A technology called “channel switching (sometimes referred to as handover or handoff)” is adopted in which information communication is continued by switching from a channel in use to another empty channel. The procedure is determined in detail (for example, Chapter 4.3.8.5 of the above standard (Non-patent Document 1) (see pages 440-450)).

Note that the above-mentioned standard has a procedure determined so that channel switching can be performed smoothly, and the determination of in which communication state channel switching (handover) is performed depends on the specifications of each carrier and the equipment manufacturer's equipment. Depending on the function, various channel switching realization methods have been proposed (see, for example, Patent Document 1).
JP 2001-169323 A RCR STD-28 3.3 edition, published by The Radio Industry Association

  PHS is a system that was built on the premise that the terminal moves at a slow speed such as walking in the presence of a plurality of relatively narrow radio wave ranges (hereinafter referred to as zones) having a radius of about 200 m from the base station. When compared with other wireless communication systems on the assumption that the terminal moves at high speed, the frequency of channel switching can be reduced.

  With recent urban development, the number of buildings where radio waves are likely to be reflected has increased, and a multipath with multiple radio wave arrival paths between the base station and the terminal can be created. A situation in which a moving body that reflects radio waves moves at high speed is likely to occur. For this reason, an event that the radio wave arrival path between the base station and the terminal fluctuates or is interrupted only for a short time has occurred frequently. When such an event occurs, the radio wave propagation state of the channel communicating between the base station and the terminal seems to change suddenly for a short time, so the channel is switched every time the state changes. In the system, channel switching occurs frequently and places a burden on the processing capability of the base station. In addition, when a channel is switched, a communication interruption occurs in principle. Therefore, the number of times that a communication voice during communication is interrupted increases, which is not desirable for the user of the terminal.

  In the case of the above event, a data error or the like may occur instantaneously due to a rapid change in the propagation state for a short time, but the state of radio wave propagation returns to the original state after the event. In other words, since the quality of the communication channel originally used between the base station and the terminal after the occurrence of the event is maintained, the load on the base station and the increase in the number of interruptions of the call that the user feels are not done without channel switching. It has also been found that the overall system operation and user convenience are improved. It is desired to realize a wireless communication system that can provide stable communication for users of carriers and terminals that provide a wireless communication system by performing channel switching in consideration of the actual propagation situation.

  On the other hand, depending on the state of radio wave propagation, communication quality may be significantly degraded and channel switching may be required, and it is possible that an appropriate service cannot be maintained simply by raising the standard for switching channels.

  In view of the above, an object of the present invention is to provide a radio communication system and a radio channel control method capable of controlling the execution of channel switching according to the state of radio wave propagation that changes suddenly for a short time. In addition, the present invention provides wireless communication that does not cause frequent channel switching, has excellent communication quality, suppresses an increase in the load on the base station, and an increase in the number of call interruptions felt by the user, improving the operation of the entire system and user convenience. It is an object of the present invention to provide a communication system and a radio channel control method. An object of the present invention is to provide a radio communication system and a radio channel control method with a simpler configuration and procedure.

According to the first solution of the present invention,
This is a radio channel control method for controlling channel switching for switching a channel used for radio communication between a radio terminal and a base station to another channel of the same base station, and handover for switching to a channel of another base station. And
The control device of the base station obtains a reception level of the radio signal received from the radio terminal and a frame error rate based on an error occurring in the frame at a predetermined time or every predetermined number of frames;
The control device compares the determined frame error rate with a predetermined first rate threshold value, and the determined frame error rate with a second rate threshold value that is greater than the predetermined first rate threshold value. and a step frame error rate is less than the first rate threshold value, less than the first rate threshold value or higher than the second rate threshold value, or, to determine whether it is above a second rate threshold value,
The control device compares the determined reception level with a predetermined level threshold, and determines whether the reception level is less than the level threshold or greater than or equal to the level threshold;
Controller, a frame error rate is less than the first rate threshold value or higher than the second rate threshold value, and a first and a second counter for receiving levels corresponding to each of the above below the level threshold and level threshold, the frame Among the third and fourth counters corresponding to the error rate equal to or higher than the second rate threshold and the reception level lower than the level threshold and higher than the level threshold, a predetermined counter is counted according to the determination result. Up or down or resetting;
The control device compares the value of each counter with the first to fourth continuous number thresholds corresponding to each counter,
The control device includes a step of performing channel switching or handover when the value of any of the first to fourth counters is equal to or greater than the corresponding first to fourth consecutive times threshold,
The third continuous number threshold is set to ensure communication quality by switching channels even in a relatively short time,
The first and fourth continuous frequency thresholds are set so as to ensure communication quality by switching channels when the state continues for a relatively longer time than the time corresponding to the third continuous frequency threshold. ,
The radio channel control method set to perform channel switching when the second continuous frequency threshold is continued longer than any of the times corresponding to the first , third, and fourth continuous frequency thresholds. Provided.

According to the second solution of the present invention,
An antenna for transmitting and receiving information wirelessly with a wireless terminal;
A reception level measuring unit for measuring a reception level of a radio signal received from a radio terminal via the antenna;
A frame error monitoring unit for monitoring a frame error and obtaining a frame error rate;
A channel having a memory in which a predetermined threshold value is stored in advance, channel switching for switching a channel used for wireless communication with a wireless terminal to another channel of the same base station, and handover for switching to a channel of another base station A control device for controlling,
The controller is
Means for obtaining a reception level and a frame error rate based on outputs of the reception level measurement unit and the frame error monitoring unit at a predetermined time or every predetermined number of frames;
The frame error rate is compared with each of the determined frame error rate and a predetermined first rate threshold value, and the determined frame error rate is compared with a second rate threshold value greater than the predetermined first rate threshold value. rate is less than the first rate threshold value, less than the second rate threshold value or more first rate threshold value, or means for determining whether it is equal to or higher than the second rate threshold value,
Means for comparing the obtained reception level with a predetermined level threshold and determining whether the reception level is less than the level threshold or greater than or equal to the level threshold;
Frame error rate is less than the first rate threshold value or higher than the second rate threshold value, and a first and a second counter for receiving levels corresponding to each of the above below the level threshold and level threshold, the frame error rate is the A predetermined counter is counted up or down among the third and fourth counters corresponding to the rate threshold value of 2 or more and the reception level being less than the level threshold value and greater than or equal to the level threshold value, Or means for resetting;
Means for comparing the value of each counter with the first to fourth consecutive number thresholds corresponding to each counter;
Means for performing channel switching or handover when any value of the first to fourth counters is greater than or equal to the corresponding first to fourth consecutive times threshold;
Including
The third continuous number threshold is set to ensure communication quality by switching channels even in a relatively short time,
The first and fourth continuous number thresholds are set so as to ensure communication quality by switching channels when the state continues for a relatively longer time than the time corresponding to the first continuous number threshold. ,
A wireless communication system is provided in which the second continuous frequency threshold is set to perform channel switching when it continues for longer than any of the times corresponding to the first , third, and fourth continuous frequency thresholds. The

  According to the present invention, even when the state of radio wave propagation suddenly changes in a short time, channel switching can be limited depending on the state of radio wave propagation, and channel switching can be performed when communication quality continues to deteriorate. In addition, according to the present invention, channel switching does not occur frequently, the communication quality is excellent, and the increase in the load on the base station and the increase in the number of call interruptions felt by the user are suppressed, improving the overall system operation and user convenience. A communication system can be provided. According to the present invention, it is possible to provide a radio communication system and a radio channel control method with a simpler configuration and procedure.

  The base station measures the radio wave level and the error rate of the propagated frame (hereinafter referred to as FER) as the radio wave propagation state, and switches the channel based on the level, the value of the FER and their duration ( The execution / non-execution of handover (which may be described as Tch switching in the following description and drawings) or handover (which may be described as HO in the following description and drawings) is finely controlled. Hereinafter, embodiments of a wireless communication system and a wireless channel control method according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a network configuration diagram showing a configuration of a wireless communication system.
The wireless communication system 10 is connected to a plurality of terminals (PS) 140, a plurality of base stations (CS) 130 each having a zone 120 that is a radio wave arrival area to the terminals, and a plurality of base stations 140. A base station control station (CSC) 110 that controls the system 10 is provided, and information is transmitted and received between the terminals 140. Information is transmitted and received between the terminal 140 and the base station 130 by the frame 160 through the radio propagation path 150.

  In the figure, terminal 1 (PS1) 140-1 transmits / receives information to / from the base station (CS1) via radio propagation path 150-1 using slot 1 among a plurality of channels time-division multiplexed on frame 160. It shows how they are doing. In the figure, “O” shown in each slot indicates that the slot is in use (communication), and “i” means empty. Further, “f1” described on the left of the frame 160 indicates the frequency of the wireless propagation path 150-1 that propagates the frame. When the terminal 140 communicates with another terminal belonging to a communication network other than the wireless communication system, the terminal 140 is not shown in the figure via another communication network (for example, public communication network) 100 from the base station control station (CSC) 110. Information is transmitted and received with other terminals.

  In the wireless communication system 10, Tch switching or H.264 is performed when the state of the wireless propagation path 150 suddenly changes in a short time. Control is performed so that O does not occur frequently. Here, the Tch switching means that what was communicated in slot 1 of frame 160 in the same figure is an empty slot (slots 2 to 4) of the same zone in the same zone, or another frame (same frequency in the same zone) ( The communication is continued by switching to an empty slot (not shown) having a good radio wave condition. H. O is the one that is communicating in slot 1 of frame 160 in the same figure to another slot (for example, 120-2) in another zone (for example, 120-2) and switches to any slot in which the radio wave condition is good. To do. In the following description of the present embodiment, the above slot may be referred to as a channel.

FIG. 2 is a block diagram showing a configuration of a base station provided in the wireless communication system.
The base station 130 transmits / receives information to / from the terminal 140, such as an antenna 200 that transmits / receives information to / from the terminal 140, a combiner 210 that combines / separates information to be transmitted / received, and a radio signal converted into an electrical signal. A transmission system radio apparatus 220 and a reception system radio apparatus 230 that perform the above processing, a signal control apparatus 240 that performs processing (for example, modulation and demodulation) of signals transmitted and received between the base station control station 110 and the terminal 140, and base station control It has a wired line control device 250 that processes signals transmitted to and received from the station 110, and a control device 260 that controls the entire base station 130. These are connected by a control line 270, respectively.

  The signal control device 240 includes a reception level measurement unit 241 that measures the reception level of a frame (wireless signal) received from the terminal, a frame error monitoring unit 242 that monitors errors occurring in the frame and obtains a frame error rate. Is provided. The reception level measurement unit 241 may be configured to be included in the reception wireless device 230. Also, the reception level measuring unit 241 and the frame error monitoring unit 242 store the measured reception level and frame error rate in, for example, the memory 262 or a memory in the own device.

  The control device 260 includes a control microcomputer (processor) 261 and a memory 262 for storing operation programs and data of the base station 130, and performs radio channel control such as channel switching according to the present embodiment described in detail below. The program Tch / CNT263 for operating is configured. The program 263 includes a reception level of a frame received from the terminal measured by the reception level measurement unit 241 (hereinafter simply referred to as a level, which may be described as LEVEL or L in the drawing), a frame error monitoring unit 242 Based on the measured value of the frame error rate FER, the level, and the duration of the FER, it is determined whether or not the channel can be switched. The channel switching is controlled according to the state / usage status of the radio propagation path 150. Specifically, when the radio wave propagation state suddenly changes for a short time and returns to the original state, channel switching is not performed, and when the radio wave propagation state changes for a long time, the channel is switched to a better state. Control to execute channel switching (or handover).

  Before explaining the details of the radio communication system and the radio channel control method of the present invention, the state change of radio wave propagation and the events that occur in the radio communication system 10 will be explained. FIG. 3 is an explanatory diagram (1) for explaining a change in a radio wave propagation state and an occurrence event in a wireless communication system.

As shown in FIG. 3A, when the terminal 140 moves on the road R between the buildings B1 and B2 while communicating with the base station 130 using the slot (channel) 1 of the frame 160, The state changes as follows:
(1) At time T1, the terminal 140 is at the position 140-a, and the frame 160-a (shown in FIG. 3B) is transmitted and received via the radio propagation path 150-a.
(2) When the terminal 140 moves to the position 140-b at time T2, the radio wave from the radio propagation path 150-a is framed via the radio propagation path 150-b that is blocked by the building B2 and reflected by the building B1. 160-b is transmitted and received.
(3) Further, when the terminal 140 moves to the position 140-c at time T3, the base station 130 becomes visible from the terminal 140, and therefore the frame 160-c is transmitted / received via the radio propagation path 150-c. .

  That is, in the vicinity of time T2, frames are transmitted / received via the radio propagation path 150-b having a long propagation path reflected by the building B1, and therefore, as shown in FIG. The reception timing of 150 is shifted by 160-t.

  FIG. 4 is an explanatory diagram (2) illustrating a change in radio wave propagation state and an occurrence event in the wireless communication system. Depending on the position of the terminal, a multipath can be generated and an interference wave is generated or the reception level changes. The information 1600 in slot 1 cannot be correctly received due to this timing shift, the influence of interference waves, or a change in reception level, and an error occurs in the synchronization word UW 1640 or error correction code CRC 1680 in the information 1600, and a frame error is detected. However, such an event is restored to the original error-free state in a short time if the terminal 140 moves to the position 140-c at time T3 in FIG. The numbers in the information 1600 shown in FIG. 4 are the number of bits, and each piece of information includes R: ramp time for transient response, SS: start symbol, PR: preamble, UW: synchronization word, CI: channel type, SA : SACCH (accompanying control channel), G: guard bit, CRC: cyclic redundancy check bit.

  In the above situation, the quality of the communication channel originally used between the base station and the terminal is maintained. Therefore, if the channel is not switched, the load on the base station 130 and the number of interruptions of the call that the user feels increase. It is suppressed, and the operation of the entire system and user convenience are improved. Therefore, the radio communication system according to the present embodiment is provided with a function for controlling channel switching in base station 130 in consideration of propagation situations that may actually occur.

  FIG. 5 is an explanatory diagram showing an example of a state change of a radio propagation path that has occurred specifically. FIG. 6A shows an event in which the state of radio wave propagation as described above suddenly changes for a short time (FER deteriorates for a short time) and returns to the original state. FIG. 5B shows an event in which the state change of radio wave propagation is large and continues for a long time (level decrease and FER deterioration continue). In particular, the level is low and the continuous number of times the FER threshold is exceeded is a predetermined number. An example of exceeding is shown. The radio communication system according to the present embodiment does not perform channel switching in the case of FIG. 11A, and performs channel switching to a good channel in the case of FIG. In addition, as will be described separately with reference to the drawing (FIG. 10), whether or not channel switching is possible is controlled in detail according to the contents of the event (degree of change and duration).

  6, 7, and 8 are operation flowcharts (1) to (3) illustrating the operation of the program Tch / CNT 263 provided in the base station 130, respectively. FIG. 9 is an explanatory diagram for explaining the measurement principle of the radio propagation path state executed during the operation of the program 263. Further, FIG. 10 is an explanatory diagram showing an example of channel switching logic executed by the program 263. Hereinafter, the radio channel control function will be described in detail with reference to these drawings. In the drawings and in the following description, F1: first FER threshold value (%), F2: second FER threshold value (%), where F1 <F2, a, b, c, d: first To fourth continuous number counter (times), a0, b0, c0, d0: first to fourth continuous number threshold values (times), where a0 <b0, c0 <d0, L0: level threshold value (dBμV) Show.

  (1) When communication (information transmission / reception) starts between the terminal 140 and the base station 130 based on the procedure defined in the RCR STD-28, the control microcomputer 261 of the control device 260 (hereinafter simply referred to as the control device). The counter is started (FIG. 6: S1000) and counts the number of consecutive occurrences of the radio wave state (in the present embodiment, the first to fourth counters indicated by a, b, c, and d). (4 counters) is initialized (FIG. 6: S1010). These counters may be provided in the memory 262 as appropriate, or dedicated hardware may be provided.

  (2) The control device 260 uses the reception level measurement unit 241 and the frame error monitoring unit 242 to measure the level and FER every 100 mS (20 frames), for example, based on the operation principle of FIG. 9 (FIG. 6: S1020-1040). Specifically, as shown in FIG. 9, level and FER are measured with 20 frames as one measurement unit 3000 (FIG. 6: S1020), and measurement results 300 for 240 frames (1200 mS in 12 measurement units) are collected. From the time (FIG. 6: S1030), the level obtains the average value L in 240 frames, and the FER obtains the FER total F for 240 frames (FIG. 6: S1040). As the FER total F, the total or average of FERs every 20 frames, the number of errors of 240 frames, and the like can be used. The first and second FER thresholds F1 and F2 are obtained by calculating the FER total F, unit It can be set appropriately depending on the situation. After the processing for the first 240 frames 300-1 is completed, the control device 260 inserts the newly obtained measurement results for 20 frames, removes the measurement results for the oldest 20 frames, and similarly L and F are obtained for 240 frames (300-2 to N). The control device 260 determines that the number of times that the L and F for these 240 frames exceed the threshold is N times in succession and the Tch switching / H. Perform O. N uses four types of a0, b0, c0, and d0 depending on the reception level and the FER level.

  As shown in FIG. 10, the radio channel switching control is performed by dividing the state of determining whether or not channel switching is possible based on the values of L and F and the number of continuations thereof. Channel switching is controlled based on six states (4000 to 4050) divided by two threshold values (F1 and F2) of threshold values L0 and F. In the present embodiment, when F is smaller than the first FER threshold value F1 (4000 and 4010 in FIG. 10), it is assumed that channel switching or the like is not performed. Counter e and a fifth continuous number threshold e0 may be provided to switch channels.

  (3) The control device 260 compares F of the present embodiment with the first FER threshold value F1 (for example, 30% in the present embodiment) (FIG. 6: S1050), and if F is smaller than F1, Then, it is determined that there is no problem in the operation of the wireless communication system, and the process returns to step S1020, and the above measurement (2) is continued. On the other hand, when F is greater than or equal to F1 (FIG. 6: S1050), F is further compared with a second FER threshold F2 (for example, 50% in the present embodiment) (FIG. 7: S1060), and F is greater than F2. The processing is divided according to the case of small (F1 ≦ F <F2) and the case of F2 or more (F2 ≦ F). The handling when F is equal to each of the threshold values F1 and F2 can be determined as appropriate. The same applies to the handling when the level L and each counter are equal to each threshold value.

  (4) When F is equal to or greater than F1 and smaller than F2, the control device 260 performs 1 addition of the second counter b and 0 reset of the third counter c and the fourth counter d (FIG. 7: S1070). Thereafter, L is compared with a threshold value L0 (for example, 25 dBμV in the present embodiment) (FIG. 7: S1080).

  (5) When L is smaller than L0, the control device 260 adds 1 to the first counter a (FIG. 7: S1100). On the other hand, when L is equal to or larger than L0, the control device 260 sets the first counter a. Reset to 0 (FIG. 7: S1110). Next, the control device 260 determines the value of the first counter a and the threshold value (first continuous threshold value) a0 (for example, 19 in the present embodiment, state 4020 in FIG. Low state) is compared with 19 consecutive times (about 3 Sec.), And the value of the second counter b and the threshold value (second continuous threshold value) b0 of the counter (for example, this embodiment) Then, 39 is compared with the state 4030 in FIG. 10 (indicating that the FER is small but the level is high) continued 39 times (about 5 Sec.) (FIG. 7: S1120).

  (6) If either the first counter a or the second counter b is greater than or equal to the respective threshold values a0 and b0 (S1120), the control device 260 moves to step S1180 and performs channel switching (or handover). (FIG. 8: S1180) and the process ends (FIG. 8: S1190). On the other hand, in step S1120, the controller 260 does not perform channel switching in cases other than the above, returns to step S1020, repeats the above (2) to (6), and continues the processing. When channel switching is performed, processing is started for a new channel after switching (FIG. 6: S1000).

  (7) In S1060, when F is greater than or equal to F2, the control device 260 performs 1 addition of the second counter b and the fourth counter d (FIG. 8: S1130), and then compares L with the threshold L0. (FIG. 7: S1140).

  (8) When L is smaller than L0, the control device 260 adds 1 to the first counter a and the third counter c (FIG. 8: S1150). On the other hand, when L is equal to or larger than L0, The first counter a and the third counter c are reset to 0 (FIG. 8: S1160). Next, the control device 260 determines the value of the third counter c and the threshold value (third continuous threshold value) c0 (for example, 4 in the present embodiment, state 4040 in FIG. The value of the fourth counter d and the threshold value of the counter (fourth continuous). Threshold value d0 (for example, 19 in the present embodiment, indicating that state 4050 in FIG. 10 (the state in which the FER is high but the level is high) has continued 19 times (about 3 Sec.)) Is compared (see FIG. 8: S1170).

  (9) If either the third counter c or the fourth counter d is greater than or equal to the respective threshold value c0 · d0, the control device 260 performs channel switching (or handover) (FIG. 8: S1180). The process ends (FIG. 8: S1190). On the other hand, in step S1170, the control device 260 does not perform channel switching in cases other than the above, returns to step S1020, repeats the above (2) to (9), and continues the processing. When channel switching is performed, processing is started for a new channel after switching (FIG. 6: S1000). In step S1170, the control device 260 compares the value of the first counter a and the value of the second counter b with the threshold values a0 and b0, respectively (S1170). Channel switching may be performed (S1180).

  As described above, considering the propagation situation that can actually occur, (i) If there are many errors and the level is low, the communication quality is extremely bad, so the channel is switched even in a short time to ensure the communication quality, (Ii) If there are many errors but the level is high, or if there are some errors and the level is low, if the event lasts longer than the above event duration, channel switching is performed to ensure communication quality. (Iii) Further, if the level is high even if there are some errors, it is assumed that the communication quality is not so bad, and the channel is switched only when the event lasts longer than the above event. Control.

  Referring to FIG. 5, FIG. 5B shows the case of (i) described above. Since the case where L is low and FER is large continues four times, channel switching is performed. FIG. 9A shows the cases (ii) and (iii) described above. Even if the state where the FER is large four times continues, the L is large and the FER returns to the original state, so the channel is switched. It continues to operate. In this way, when the quality of the communication channel used between the base station 130 and the terminal 140 is maintained, channel switching is not performed, thereby increasing the load on the base station 130 and the number of calls that the user feels. The increase in the number of interruptions is suppressed, and the overall system operation and user convenience are improved.

In the above-described embodiment, as described separately, the length is 5 mSec., Which is defined by RCR STD-28, the frequency band is 1.89 to 1.92 GHz, and 4 channels (slots) are multiplexed. In the wireless communication system based on the PHS that repeatedly transmits and receives the above frame, an example in which channel switching control is performed with six appropriate states (FIG. 10: 4000 to 4050) and each threshold value has been described. Depending on the installation environment, usage status, and user requirements of the PHS, even if the control is finer than the control shown in the above-described embodiment, or on the contrary, rough control is acceptable. Thus, the channel switching control according to the present embodiment can be applied by changing the number and values of the FER rate threshold , the L level threshold, the number of counters, and the continuous frequency threshold of each counter.

  FIG. 11 is an operation sequence diagram showing the operation of the wireless communication system, and shows the operation of Tch switching. The operation will be described below with reference to FIGS.

  Prior to communication, the terminal (PS1) 140-1 and the base station (CS1) 130-1 establish communication (S2000) according to the outgoing / incoming procedure defined in 4.4.3.8 of RCR STD-28. Then, communication is possible in which information can be transmitted and received in the assigned slot (for example, slot 1 of the frequency f1 frame in the present embodiment) (S2100).

  When communication is started, degradation of the level and FER occurs according to the movement status of the terminal (PS1) 140-1 and changes in the surrounding environment (S2200), but the base station (CS1) 130-1 Channel switching control as described with reference to FIG. For example, if the timing deviation 160-t in FIG. 3 is small and returns to the original state in a short time, the communication is continued without switching the channel, but if the low level state or the large FER state continues for a predetermined time, the Tch switching is performed. Execute.

  Specifically, another empty slot (for example, in this embodiment, in the same zone 120-1 by the Tch switching procedure defined in 4.4.3.8.5.1 of RCR STD-28. Channel 4 is selected by selecting slot 4) of frequency f2 frame (S2300), and thereafter, terminal (PS1) 140-1 and base station (CS1) 130-1 use slot 4 of frequency f2 frame to transmit information. Transmission / reception is continued (S2400).

  FIG. 12 is an operation sequence diagram showing the operation of the wireless communication system. The operation of O is shown. The operation will be described below with reference to FIGS.

  Prior to communication, the terminal (PS1) 140-1 and the base station (CS1) 130-1 establish communication (S2000) according to the outgoing / incoming procedure defined in 4.4.3.8 of RCR STD-28. Then, communication is possible in which information can be transmitted and received in the assigned slot (for example, slot 1 of the frequency f1 frame in the present embodiment) (S2100).

  When communication is started, degradation of the level and FER occurs (S2200) according to the movement status of the terminal (PS1) 140-1 and changes in the surrounding environment (S2200). The base station CS1 uses FIGS. Perform the channel switching control as described. For example, if the timing shift 160-t in FIG. 3 is small and returns to the original state in a short time, the communication is continued without switching the channel, but the terminal 140-1 moves to the vicinity of the adjacent zone 120-2 and has a low level. When the state or the state where the FER is large continues for a predetermined time, the base station control station (CSC) 110 and, for example, the base station (CS2) 130-2 work in conjunction with the H.264 standard. O is executed.

  Specifically, the H.264 standard defined in 4.4.3.8.5.4 of RCR STD-28. In the O procedure, another vacant slot in another zone 120-2 (for example, slot 4 of the frequency f2 frame in this embodiment) is selected and channel switching is performed (S2350), and then the terminal (PS1) 140-1 and the base station (CS2) 130-2 continue to transmit and receive information using slot 4 of the frequency f2 frame (S2450).

(First determination method for each threshold)
Next, each numerical value determination of the threshold values F1, F2, L0, a0, b0, c0, and d0 will be described.
FIG. 13 is an explanatory diagram showing an example of the reception level, FER, and channel switching occurrence. The example shown in FIG. 13 is a graph in which the reception level and FER are measured for a plurality of base stations in various environments, and the relationship between the level and FER is represented in a graph in a wireless communication system in operation.

  First, the occurrence status of FER at each reception level is acquired. For example, about 13,000 plots are acquired for one base station. The reception level is represented by an integer value as shown in FIG. 13, for example. The quality of the radio section is preferably judged from the median value (circled in FIG. 13) because an error is likely to occur when sudden FER degradation occurs when judged by the average value. If FER occurs during communication, the quality may be affected. Therefore, in the present embodiment, Tch switching / H. A reception level threshold value L0 is set as a criterion for determining whether to start O processing. That is, the threshold L0 of the reception level is obtained as the median value of the acquired FER for each reception level, and is set to the lowest reception level (25 dBμV in FIG. 13) among the reception levels whose median is 0. . In addition to the reception level whose median is 0, the lowest reception level among the reception levels satisfying an appropriate standard such as several percent or less may be used.

  The FER threshold values (F1, F2) are considered based on the suddenly generated FER. Since the suddenly generated FER is likely to return to the original state even in a short time, the thresholds F1 and F2 can be set so as to limit channel switching in this state. For example, an approximate value curve (approximate expression) is created from the maximum value of FER generated at each reception level (indicated by a triangle in FIG. 13), and the received level determined with reference to the FER approximate value curve (approximate expression) The FER value for L0 is obtained. In addition to creating an approximate value curve using the maximum value of FER, it is also possible to appropriately use data that is considered to have occurred suddenly, for example, using an average of an appropriate number of data from the larger FER. Good. The FER threshold values F1 and F2 can be set to about 5 to 10% before and after the obtained value. For example, F1 may be a threshold set in a conventional base station.

For example, in FIG. 13, an approximate value curve of the maximum value of FER represented by a dotted line is referenced with respect to the level threshold L0 of 25 dBμV, and a value of less than 50% is obtained as the FER. Therefore, the second rate threshold value F2 can be set to 50 [%]. The first rate threshold value F1 may be 40 [%] or the like, but in the present embodiment, 30 [%] set in the conventional base station is used.

  Next, there are F1 and F2 determined as described above, and c0 and d0 set in the conventional base station, for example, describing the setting of the continuous frequency thresholds a0 to d0. The continuous frequency threshold values a0 and b0 in the state where the FER is F1 to F2 are determined under the conditions of a0> c0, b0> d0, and a0 <b0. For example, when c0 = 1.5 s (4 consecutive times) and d0 = 3 s (19 consecutive times), a0 is 2 s, 2.5 s, 3 s..., B0 is 3.5 s, 4 s, 4.5s, 5s... Are added little by little (for example, every 0.5 seconds), and the quality state of the call and the overall effect state based on traffic data are confirmed for each combination. The step size to be changed can be set to an appropriate time other than the 0.5 s step as described above. H. of the points determined as observation points (for example, places where reception timing is delayed or where interference waves are likely to occur) during the execution of these combination tests. The conditions are gradually relaxed until the average number of times of O + Tch switching becomes about once every 10 minutes in relation to the call time. Note that the criterion of about once every 10 minutes can be appropriately changed according to the processing capability of the base station. In addition, the number of times of switching when a0 and b0 are changed can be measured, and a0 and b0 can be set so as to be the minimum switching value.

  FIG. 14 is a diagram illustrating the relationship between the continuous frequency threshold and the switching frequency. Tch switching is performed when the base station is activated (500 in the figure) and when the terminal is activated (510 in the figure). Therefore, simply increasing the continuous frequency threshold does not necessarily reduce the total number of Tch switching (520 in the figure). Therefore, as described above, a0 and b0 are changed, the number of times of Tch switching at the point determined as the observation point is measured, and the total number of terminal activation switching and base station activation switching is minimized (or minimized). It is also possible to set a0 and b0. As a result, for example, values of a0 = 3 s (19 consecutive times) and b0 = 5 s (39 consecutive times) are obtained.

(Second determination method for each threshold)
First, as described above, in a predetermined base station, the occurrence status of FER at each reception level is obtained, and F1, F2, and L0 are obtained. Here, for example, the value of L0 is a reception level for the purpose of ensuring quality, but a lower value can be set when quality degradation to the extent that the actual user does not feel is not a problem. . Actually, in field tests, it is often possible to talk without problems even if the value is less than the value determined from the data, and even if the value is too low, the quality of the call deteriorates. It is known that the O / Tch switching operation is not performed (HO takes time). Moreover, since the values obtained from the acquired data for F1 and F2 can be said to be the maximum values from the viewpoint of maintaining quality, the actual determined values can be made lower than that. Therefore, in addition to a0 and b0, the respective threshold values can also be determined by changing the values of the obtained F1, F2, and L0. Further, c0 and d0 may be similarly changed.

  As for the change of a0 and b0, for example, the change is made under the conditions of a0> c0, b0> d0, and a0 <b0, starting from c0 and d0 set in the conventional base station, for example. For example, when c0 is 1.5 s and d0 is 3 s, a0 is 2 s, 2.5 s, 3 s..., B0 is 3.5 s, 4 s, 4.5 s, 5 s. The number is incremented (for example, every 0.5 seconds), and the call quality state and the overall effect state based on the traffic data are confirmed for each combination.

On the other hand, for L0, separately, the level threshold determined from the acquired data is assumed to be the maximum value that can be set, and the level threshold is divided downward from there and sequentially changed. For example, 25 dB determined from the acquired data as described above can be used as a starting point, and can be lowered to 20 dB and 15 dB, and a0 and b0 can be changed for each level threshold value. Note that the separation width can be an appropriate width. Also, 25 dB determined from the acquired data may not be tested, and the test may be started from 20 dB.

  When changing L0, if the value is too low, the call quality will be poor. O / Tch switching operation is not performed (HO takes time). At the point to be O (for example, 30 to 35 dB at the PS level). Measure the number of times of O / Tch switching. It is determined whether or not it takes time to start O, and for example, 20 dB can be selected first.

  In addition, for F2 and F1, the point determined as the observation point while testing the combination satisfying the condition of F1 <F2 in increments of 10%, with F1 and F2 determined from the acquired data as the upper limit. (For example, a place where reception timing is delayed or an interference wave is likely to occur as described above) Conditions are gradually relaxed until the number of times of O + Tch switching becomes a value of about once every 10 minutes in relation to the call time. Note that the order in which the conditions are relaxed (values are changed) can be, for example, the order of F2, a0, b0, and F1. This can be considered as the order with little influence on the sound quality. The call quality deteriorates as conditions are relaxed. Priority is given to lowering the O / Tch switching frequency, and as a result, a0 = 3s, b0 = 5s, F1 = 30%, and F2 = 50% are obtained.

It is also possible to measure the number of times of Tch switching when each threshold value is changed and set each threshold value so as to be the minimum switching value. When the vertical axis represents the number of switching times and the horizontal axis represents a0, b0, c0, and d0, a graph similar to FIG. 14 is obtained. Further, even if F2, a0, b0, and F1 are shown on the horizontal axis, the result is that the total number of switching times has the minimum value as shown in FIG.

  In this way, starting from the values set so far and the threshold value determined from the acquired data, the conditions are gradually relaxed, the communication state at that time is confirmed, and the H.D. This can be determined by whether or not the request for lowering the O / TCH switching frequency is satisfied.

It is a network block diagram which shows the structure of a radio | wireless communications system. It is a block diagram which shows the structure of the base station with which a radio | wireless communications system is equipped. It is explanatory drawing (1) explaining the electromagnetic wave propagation state change and generation | occurrence | production event of a radio | wireless communications system. It is explanatory drawing (2) explaining the electromagnetic wave propagation state change and generation | occurrence | production event of a radio | wireless communications system. It is explanatory drawing which showed an example of the radio | wireless propagation path state change which generate | occur | produced in the radio | wireless communications system. It is an operation | movement flowchart (the 1) which shows operation | movement of a channel switching control program. It is the operation | movement flowchart (the 2) which shows operation | movement of a channel switching control program. It is an operation | movement flowchart (the 3) which shows operation | movement of a channel switching control program. It is explanatory drawing explaining the measurement principle of a wireless propagation path state. It is explanatory drawing which showed an example of the channel switching control logic. It is an operation | movement sequence diagram which shows the operation example of a radio | wireless communications system. It is an operation | movement sequence diagram which shows another operation example of a radio | wireless communications system. It is explanatory drawing which showed an example of reception level, FER, and channel switching generation | occurrence | production. It is a figure which shows the relationship between a continuous frequency threshold value and the frequency | count of switching.

Explanation of symbols

10 radio communication system 110 base station control station 120 zone 130 base station 140 terminal 150 radio propagation path 160 frame 200 antenna 210 coupler 220 transmission radio apparatus 230 reception radio apparatus 240 signal control apparatus 241 reception level measurement unit 242 frame error monitoring Part 250 Wired line control device 260 Control device 261 Control microcomputer (processor)
262 Memory 270 Control line 500 Base station activation switching number 510 Terminal activation switching number 520 Total switching number

Claims (11)

This is a radio channel control method for controlling channel switching for switching a channel used for radio communication between a radio terminal and a base station to another channel of the same base station, and handover for switching to a channel of another base station. And
The control device of the base station obtains a reception level of the radio signal received from the radio terminal and a frame error rate based on an error occurring in the frame at a predetermined time or every predetermined number of frames;
The control device compares the determined frame error rate with a predetermined first rate threshold value, and the determined frame error rate with a second rate threshold value that is greater than the predetermined first rate threshold value. Determining whether the frame error rate is less than a first rate threshold, greater than or equal to a first rate threshold, less than a second rate threshold, or greater than or equal to a second rate threshold;
The control device compares the determined reception level with a predetermined level threshold, and determines whether the reception level is less than the level threshold or greater than or equal to the level threshold;
The control apparatus includes first and second counters each having a frame error rate equal to or greater than a first rate threshold and less than a second rate threshold, and corresponding to reception levels less than the level threshold and greater than or equal to the level threshold, Among the third and fourth counters corresponding to the error rate equal to or higher than the second rate threshold and the reception level lower than the level threshold and higher than the level threshold, a predetermined counter is counted according to the determination result. Up or down or resetting;
The control device compares the value of each counter with the first to fourth continuous number thresholds corresponding to each counter,
The control device includes a step of performing channel switching or handover when the value of any of the first to fourth counters is equal to or greater than the corresponding first to fourth consecutive times threshold,
The third continuous number threshold is set to ensure communication quality by switching channels even in a relatively short time,
The first and fourth continuous frequency thresholds are set so as to ensure communication quality by switching channels when the state continues for a relatively longer time than the time corresponding to the third continuous frequency threshold. ,
The radio channel control method, wherein the second continuous frequency threshold is set so that channel switching is performed when the second continuous frequency threshold continues longer than any of the times corresponding to the first, third, and fourth continuous frequency thresholds. The level threshold is
Referring to the relationship between the reception level measured at a predetermined base station and the frame error rate, the median of the frame error rate corresponding to each reception level is obtained, and the minimum of the reception levels with the median being 0 The radio channel control method according to claim 1, wherein a reception level is set as the level threshold. The first and second rate thresholds are:
Referring to the relationship between the reception level measured at a given base station and the frame error rate, create an approximate curve or approximate expression based on the maximum value of the frame error rate corresponding to each reception level, and create the approximate curve Alternatively, a frame error rate with respect to a predetermined level threshold is obtained based on an approximate expression, and the value of the frame error rate or a value within a predetermined range before and after the frame error rate is used as the first rate threshold and / or the second rate threshold. The radio channel control method according to claim 2, wherein the radio channel control method is set. The first and second continuous frequency thresholds are:
The first continuous number threshold is larger than the third continuous number threshold, the second continuous number threshold is larger than the fourth continuous number threshold, and the first continuous number threshold is smaller than the second continuous number threshold. The number of channel switching and handover switching times in a predetermined base station is measured sequentially with a predetermined step size, and the value at which the total number of switching times is the minimum or within a desired range is measured. The radio channel control method according to claim 1, wherein the radio channel control method is set as a continuous frequency threshold value. The third and fourth consecutive thresholds are:
On the condition that the third continuous number threshold is smaller than the fourth continuous number threshold, the total number of channel switching and handover switching times in the predetermined base station is changed to the minimum or desired The radio channel control method according to claim 4, wherein values within a range are set as the third and fourth continuous frequency thresholds, respectively. The level threshold value refers to a relationship between a reception level measured at a predetermined base station and a frame error rate, obtains a median value of a plurality of frame error rates corresponding to each reception level, and the median value is 0. With a minimum reception level threshold of a certain reception level as an upper limit, sequentially decrease by a predetermined step size,
The first and second rate threshold values are approximate curves based on the maximum value of the frame error rate corresponding to each reception level with reference to the relationship between the reception level measured at a predetermined base station and the frame error rate. Create an approximate expression, calculate the frame error rate for the level threshold based on the generated approximate curve or approximate expression, and successively increase the frame error rate value or a value within a predetermined range before and after the frame error rate at a predetermined step size. Change
The first and second continuous count thresholds are greater than the third continuous count threshold, the second continuous count threshold is greater than the fourth continuous count threshold, and the first continuous count threshold. The number threshold is sequentially changed at a predetermined step size on the condition that the number threshold is smaller than the second continuous number threshold,
The number of channel switching and handover switching times in a predetermined base station is measured for each threshold combination, and a value when the total number of switching times is minimum or within a desired range is set as each threshold value. The radio channel control method according to 1. The step of counting up or down, or resetting,
The control device adds 1 to the second counter when the frame error rate is greater than or equal to the first rate threshold and less than the second rate threshold, and further reduces the first counter when the reception level is less than the level threshold. Adding 1;
The control device adds 1 to the fourth counter and / or the second counter when the frame error rate is equal to or higher than the second rate threshold, and further adds the third counter when the reception level is smaller than the level threshold. And / or a step of adding 1 to the first counter. The step of counting up or down, or resetting,
The control device resets the third and fourth counters when the frame error rate is greater than or equal to the first rate threshold and less than the second rate threshold, and further when the reception level is not less than the level threshold, Resetting the counter of
The control device further includes a step of resetting the first counter and / or the third counter when the frame error rate is equal to or higher than the second rate threshold and the reception level is not lower than the level threshold. The radio channel control method according to 1.   The wireless channel control method according to claim 1, wherein the wireless communication is wireless communication in a personal handyphone system. The control device counts up, down, or resets a fifth counter whose frame error rate is lower than a first threshold and whose reception level is lower than a level threshold, depending on a determination result;
The control device compares the value of the fifth counter with a corresponding fifth consecutive frequency threshold value;
2. The radio channel control method according to claim 1, further comprising a step of performing channel switching or handover when the fifth counter is equal to or greater than a corresponding fifth consecutive frequency threshold. An antenna for transmitting and receiving information wirelessly with a wireless terminal;
A reception level measuring unit for measuring a reception level of a radio signal received from a radio terminal via the antenna;
A frame error monitoring unit for monitoring a frame error and obtaining a frame error rate;
A channel having a memory in which a predetermined threshold value is stored in advance, channel switching for switching a channel used for wireless communication with a wireless terminal to another channel of the same base station, and handover for switching to a channel of another base station A control device for controlling,
The controller is
Means for obtaining a reception level and a frame error rate based on outputs of the reception level measurement unit and the frame error monitoring unit at a predetermined time or every predetermined number of frames;
The frame error rate is compared with each of the determined frame error rate and a predetermined first rate threshold value, and the determined frame error rate is compared with a second rate threshold value greater than the predetermined first rate threshold value. Means for determining whether the rate is less than a first rate threshold, greater than or equal to a first rate threshold, less than a second rate threshold, or greater than or equal to a second rate threshold;
Means for comparing the obtained reception level with a predetermined level threshold and determining whether the reception level is less than the level threshold or greater than or equal to the level threshold;
A first and second counter corresponding to a frame error rate that is greater than or equal to a first rate threshold and less than a second rate threshold, and whose reception level is less than a level threshold and greater than or equal to a level threshold; A predetermined counter is counted up or down among the third and fourth counters corresponding to the rate threshold value of 2 or more and the reception level being less than the level threshold value and greater than or equal to the level threshold value, Or means for resetting;
Means for comparing the value of each counter with the first to fourth consecutive number thresholds corresponding to each counter;
Means for performing channel switching or handover when any value of the first to fourth counters is greater than or equal to the corresponding first to fourth consecutive times threshold;
Including
The third continuous number threshold is set to ensure communication quality by switching channels even in a relatively short time,
The first and fourth continuous frequency thresholds are set so as to ensure communication quality by switching channels when the state continues for a relatively longer time than the time corresponding to the third continuous frequency threshold. ,
The wireless communication system configured to perform channel switching when the second continuous frequency threshold value continues longer than any of the times corresponding to the first, third, and fourth continuous frequency threshold values.