JP3351277B2 - Wireless line switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for packet communication using a wireless line. The present invention is suitable for use in a communication system using a moving wireless communication terminal. In particular, the present invention relates to a technique for reducing transmission delay time.

[0002]

2. Description of the Related Art A mobile communication system using a moving wireless communication terminal is widely used. The mobile communication method includes a method of transmitting information by voice, a method of transmitting data by packetizing the data, and the like.

In the conventional radio line switching method, the cause of the error is specified from the reception level and the bit or frame error rate, and if it is specified that the cause is interference or the movement of the radio (mobile) station, the error is promptly determined. The wireless line is being switched. The detection of the reception level and the error rate may be performed by both the base station and the mobile station, or may be performed by any of the stations. When the mobile station performs the detection, it is necessary to notify the detection result to the base station having the right to switch the radio channel.

FIG. 9 is a diagram showing the relationship between the threshold F of the error rate, the threshold D of the desired reception level, and the radio line switching control. In order to recover the transmission quality, in the case of the mobile communication system, for example, the case classification as shown in FIG. 9 is performed, and when the error rate f> F and the desired wave reception level L> D, the same base station is used. When the desired signal reception level L <D, the wireless line is switched to the line of the adjacent base station. This is a control method assuming voice communication, and its purpose is to quickly restore quality.

[0005] In voice communication, quality degradation gives direct discomfort to the subscriber, and retransmission control is not performed because information must be transmitted in real time. It is strongly required to shorten the deterioration time. The above control procedure meets the requirements.

[0006]

As described above, conventionally, degradation of transmission quality is dealt with by switching between wireless links within the same base station or switching between wireless links between adjacent base stations. This is performed similarly for voice communication and data communication.

However, in data communication, especially packet communication, the effect of quality deterioration on subscribers is significantly different from that in voice communication.
It is only information transmission delay. Also, since real-time performance is not required as much as in the case of voice communication, quality compensation by retransmission of error information is possible, and line switching control for quality recovery always involves a processing delay of a certain time, etc. Therefore, it is meaningful to consider data retransmission instead of simply switching wireless channels as a method for dealing with the deterioration of transmission quality.

[0008] In particular, when the processing delay of data retransmission is smaller than the processing delay due to line switching, it is useful for reducing the transmission delay time.

[0009] Therefore, there is a need for a technique for classifying a new start condition for quality recovery control assuming data communication which has not been considered in the past.

The present invention has been made in view of such a background, and an object of the present invention is to provide a wireless communication line switching method capable of reducing a delay time associated with wireless line switching. An object of the present invention is to provide a wireless communication line switching method capable of improving transmission quality optimal for wireless packet communication. An object of the present invention is to provide a wireless packet communication system with a small transmission delay and a low error rate.

[0011]

SUMMARY OF THE INVENTION According to the present invention, switching of a radio channel is performed only when the time required for switching the radio channel is shorter than the transmission delay time estimated from the information length of transmission data and the channel quality of the radio channel. The most important feature is to do. Therefore, the quality of the radio channel used for communication is estimated, it is determined whether retransmission of error information or radio channel switching is more efficient, and radio channel switching is performed only when it is concluded that it is efficient.

Thus, when the degree of quality deterioration is light,
By using retransmission as a means of compensating for information errors rather than wireless line switching, it is possible to avoid processing delays inevitably associated with wireless line switching, thereby reducing transmission delays, which are the most important in services in data communication. it can.

That is, the present invention relates to a radio channel switching method for switching to a high quality radio channel when the reception error rate of a signal arriving from a mobile station exceeds a threshold F and deteriorates. is there. The feature of the present invention is that when the transmission delay time estimated from the information length of the transmission data and the line quality of the wireless line is shorter than the time required to switch the wireless line, the switching of the wireless line is temporarily suspended. It is where the packets are retransmitted.

Here, the transmission delay time is given by α × k / n, where α is the estimated transmission delay rate of the radio link, k is the amount of information to be transmitted, and n is the information transfer rate of the radio link.

Here, the estimated transmission delay rate α is a ratio of the retransmission frame to the entire transmitted frame.

As an example, AR of Selective Repeat method
The improvement effect in the system performing Q is shown. Sele
In the ctive Repeat method, the frame error rate is e
Then, the estimated delay rate per packet is obtained as follows: α = e / (1−e).

Further, the level of the received signal from the mobile station is detected, and when the level of the received signal is higher than the threshold value D, switching to another radio line in the same base station is performed. When it is low, it is desirable to switch to a wireless line of another base station.

At this time, the transmission delay time estimated from the information length of the transmission data and the channel quality of the wireless channel is longer than the switching time of the wireless channel in the same base station, but is longer than the switching time of the wireless channel in the adjacent base station. If the packet is too short, only the switching of the radio link within the same base station is permitted, and the packet whose attempt to improve the information error by switching to the radio link of the adjacent base station is retransmitted to reduce the information error. It is better to control to improve.

The present invention also provides a radio communication line switching method for switching to a high quality radio line when the reception error rate of a signal received from the mobile station and received at the mobile station exceeds a threshold value F and deteriorates. Can also be applied.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

The present invention is a radio line switching method for switching to a high quality radio line when the reception error rate of a signal arriving from the mobile station 2 _i (i = a to d) exceeds the threshold F and deteriorates. .

Here, the feature of the present invention is that when α is an estimated transmission delay rate of a wireless channel, k is an information amount to be transmitted, and n is an information transfer rate of the wireless channel, α × k / n When the given transmission delay time is shorter than the time required for switching the wireless channel, the switching of the wireless channel is temporarily suspended and the packet is retransmitted.

Also, the level of the received signal from the mobile station 2 _i is detected, and when the level of the received signal exceeds the threshold value D and is high, switching to another radio channel within the same base station 3 _j (j = a, b) is performed. was carried out, it is subjected to switching to the radio network of another base station 3 _j when the received signal level is lower than the threshold D.

Further, the above operation can be performed according to the reception error rate of a signal received on the mobile station side reported from the mobile station 2 _i .

The base station 3 _j is connected to a data communication network 7 via a PHM (Packet Handling Module) 6. The PHM 6 exchanges a protocol for connecting the data communication network 7 and the mobile packet communication system, routing to the mobile station 2 _i , and further, to the base station 3 _j toward the mobile station 2 _i for radio channel control. Notify the information length of the data to be sent.

Possible causes of quality degradation in the mobile packet communication system include collisions caused by the mobile stations 2a and 2b simultaneously trying to transmit data by judging that the radio line is idle, and the adjacent base station 3 mobile station 2a to within the wireless cell 4a or 4b constituting the _j, 2
b, interference between 2d and 2d, decrease in the reception level of the desired wave due to an increase in the distance between the base station 3a and the mobile station 2c, short-term median value fluctuation, and level reduction due to instantaneous fluctuation.
Of these, the present invention seeks to address and.

In the mobile packet communication system, a plurality of mobile stations are packet-multiplexed on one radio line, and data transmission is performed only when the line is free. FIG. 2 is a diagram showing a format of downlink information. Downlink information sent from the base station 3 _j is a format shown in FIG. 2, includes a free / busy information of the line. This downlink information is constantly transmitted on the wireless line used for packet communication.

In addition, both the base station 3 _j and the mobile station 2 _i
Error detection, error information retransmission request, and error information retransmission in response to this request can be performed.

FIG. 3 is a diagram showing a layer configuration of a communication protocol. As indicated by solid-line arrows, the data link layer includes the base station 3 _j and the mobile station 2 _i , and the base station 3 _j and the PHM
6 and the network layer consists of a mobile station and PHM
Terminate at 6. The PHM 6 performs protocol exchange for connecting the data communication network 7 to the mobile packet communication system, routing to the mobile station 2 _i , and further, for radio line control.
To the mobile station 2 _i to the base station 3 _j notifies the information length of data to be sent.

When the base station 3 _j determines that line switching within the same base station is necessary, and when it receives a request from the mobile station 2 _i that determines that line switching within the same base station is necessary, the base station 3 _j receives the interference wave. The line level is switched to the wireless line determined to be free by measuring the reception level.

Further, the mobile station 2 _i, when it is determined that it is necessary to switch the same base station line, and if the adjacent base station 3 _j the line switching is deemed necessary, the base station 3 _j, Sends a line switching request. When neighboring base station line switching is performed, the communication link between the base station 3 _j which has been communicating before cell change and the mobile station 2 _i is disconnected.

The base station 3 _j and the mobile station 2 _i measure and estimate quality, estimate the cause of quality degradation, and calculate the amount of information to be sent by the following functions. [A: Measurement and Estimation of Quality] The mobile station 2 _i measures the frame error rate of the downlink radio channel constantly transmitted from the base station 3 _j . When transmitting data from the mobile station 2 _i to the base station 3 _j , the transmission delay rate is estimated from this error rate.

Conversely, when transmitting data from the base station 3 _j to the mobile station 2 _i , the mobile station 2 _i sends back the estimated value of the transmission delay rate when receiving the first packet. Mobile station 2
_i is sent back an estimate of the transmission delay factor in the response signal of the call (synchronization) signal that is transmitted prior to the data transmitted from the base station 3 _j. As such, the base station 3 _j, reporting the quality of communication with a particular mobile station 2 _i. [B: Estimation of Cause of Quality Deterioration] Estimation of the cause of quality deterioration is performed based on whether the desired signal reception level is above or below threshold D (see FIG. 9). [C: Calculation of Information Amount] As shown by a dotted line arrow in FIG.
With respect to the data link layer in the radio section, the mobile station 2 _i directly sends the base station 3 _j from the network layer to the data link layer.
Then, the notification is made from the network layer of the PHM 6 via the data link layer. The data link layer in the wireless section calculates the number of wireless bursts required for transmission from the notified information amount.

The switching operation of the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a flowchart showing the switching operation of the embodiment of the present invention. Line switching controller 5a and 5b are respectively provided in the base station 3 _j. The line switching control unit 5a and 5b performs wireless line switching according to a request from its own judgment or mobile station 2 _i.

The switching control is performed as shown in FIG.
Is less than or equal to the threshold F (S1), data transmission is performed normally (S10). If the error rate f exceeds the threshold F, (S
1), preparation for switching is performed (S2). Here, the threshold value F takes a different value according to the information length in a communication system in which packets of various information lengths are mixed as assumed in the embodiment of the present invention. Therefore, the comparison between the error rate f and the threshold value F is performed using different F values for different information lengths.

At this time, if α × k / n <τ, the switching of the radio line is suspended (S4), and instead, the packet in which the information error has occurred is retransmitted (S5).
Here, τ is the time required for wireless line switching within the same base station,
α is the estimated transmission delay rate of the wireless channel used for communication, k is the amount of information to be transmitted (frames), and n is the information transfer rate (frames / sec) of this wireless channel.

If α × k / n ≧ τ is satisfied (S3), and if α × k / n ≧ τ ′ is satisfied (S6), the wireless channel is switched (S9).
As described above, this wireless line switching detects the level of the received signal from the mobile station 2 _i, and when the received signal level exceeds the threshold value D and is high, switches to another wireless line within the same base station 3 _j . performed, to switch the radio channel of another base station 3 _j when the received signal level is lower than the threshold D. Here, τ ′ is the time required for switching the line between adjacent base stations, and usually τ <τ ′.

Also, α × k / n ≧ τ (S3), and α × k / n <τ ′ (S6), and the radio channel switching to be performed is performed by the radio channel switching within the same base station. If it is (S7), the wireless channel switching within the same base station is executed (S8). However, if the wireless channel switching to be performed is a wireless channel switching between adjacent base stations (S7), the wireless channel switching is suspended (S4), and the packet having the information error is retransmitted (S7).
5).

For estimating the quality deterioration factor, it is necessary to measure the reception level of the desired signal. Therefore, the data is transmitted from the mobile station that constantly measures the reception level of the desired signal, and the data is transmitted from the base station _3j. When transmitting data, the sequence is different. When transmitting data from the base station _3j , the desired signal reception level is measured by the response signal of the mobile station, or the desired signal reception level is notified from the mobile station in the response signal.

[0041] When transmitting data from the base station 3 _j, the mobile station, transmission delay rate in a radio channel used for communication α
Must be notified to the base station _3j , it is efficient to report the desired wave (downlink) reception level in the same signal, and the measurement value is more accurate.

The sequence for estimating the quality deterioration factor is shown in FIGS. Figure 5 is a sequence diagram showing a case you decide to perform wireless line switching between adjacent base stations when transmitting data from the base station 3 _j, 6 mobile station 2 _i
From a sequence diagram showing a case you decide to switch radio line between adjacent base stations when transmitting data, Fig. 7 is to perform switching within the same base station radio channel when transmitting data from the base station 3 _j is a sequence diagram showing a case where determined, FIG. 8 is a sequence diagram showing a case you decide to switch within the same base station radio channel when transmitting data from the mobile station 2 _i.

As shown in FIG. 5, the base station 3a
Send a call signal to _i . The mobile station _i includes
The base station 3a is notified by inserting information of the transmission delay rate α and the reception level measured when the paging signal is received. The base station 3a respects this transmission delay factor α and the reception level is carried out between adjacent base station radio channel switching instruction to the mobile station 2 _i. Mobile station 2 _i is prepares to deal with switching radio line between adjacent base stations, it transmits a radio line switch request between adjacent base stations to the base station 3b when the preparation is completed.
The base station 3b performs this receiving by switching a radio channel between adjacent base stations, and transmits a radio line switching permission between adjacent base stations, and a radio packet channel specifying information to the mobile station 2 _i. The mobile station 2 _i receives this and deals with the wireless channel switching between adjacent base stations, and after completing this measure, transmits a wireless packet line designation response to the base station 3 b. The base station 3b receives this and starts data transmission via the designated wireless channel.

As shown in FIG. 6, the base station 3a constantly transmits downlink information. The mobile station 2 _i measures the transmission delay α and the reception level of the radio channel by receiving the downlink information. The mobile station 2 _i considers this measurement result and transmits a wireless channel switching request between adjacent base stations to the base station 3 b. The base station 3b performs switching radio line between adjacent base stations receiving this, sends a radio channel switching permission between adjacent base stations to the mobile station 2 _i. The mobile station 2 _i receives this and deals with wireless channel switching between adjacent base stations. The mobile station 2 _i starts transmitting data to the base station 3 b after completing this measure.

As shown in FIG. 7, base station 3 _j is mobile station 2
Send a call signal to _i . The mobile station 2 _i inserts the information of the transmission delay rate α and the reception level measured when the paging signal was received into the response signal, and transmits the response signal to the base station 3 _j . The base station 3 _j respects this transmission delay factor α and the reception level, performed within the same base station radio channel switching, transmits the same base station radio channel switching instruction to the mobile station 2 _i. In response, the mobile station 2 _i responds to switching of the base station 3 _j 's intra-base-station wireless channel. The mobile station 2 _i transmits a response to the same base station radio channel switching instruction to the base station 3 _j upon completion of this countermeasure. The base station _3j receives this and starts data transmission.

As shown in FIG. 8, the base station 3 _j constantly transmits downlink information. In response to this, the mobile station 2 _i measures the transmission delay rate α and the reception level, and transmits a request for switching the radio link within the same base station to the base station 3 _j in consideration of the measurement results. The base station 3 _j performs the same base station radio channel switching response to this, transmits the same base station radio channel switching permission to the mobile station 2 _i. In response to this, the mobile station 2 _i copes with the switching of the radio channel within the same base station by the base station 3 _j and starts data transmission after the coping is completed.

When switching the wireless channel between adjacent base stations, P
The retransmission of data from the HM 6 to the mobile station 2 _i is performed by the adjacent base station 3
through _j .

As described above, it is possible to avoid the processing delay inevitably associated with the wireless line switching according to the degree of the quality deterioration, so that the effect of reducing the transmission delay can be obtained.
The transmission delay of τ−α × k / n can be reduced from the required time τ of the wireless channel switching required according to the estimated cause. However, the amount of information k [b
it], and the information transfer rate of the wireless line is n [bit / sec].

[0049]

As described above, according to the present invention,
Delay time associated with wireless line switching can be reduced. Further, it is possible to improve transmission quality optimal for packet communication. As a result, a wireless packet communication system with a small transmission delay and a low error rate can be realized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a format of downlink information.

FIG. 3 is a diagram showing a layer configuration of a communication protocol.

FIG. 4 is a flowchart illustrating a switching operation according to the embodiment of the present invention.

FIG. 5 is a sequence diagram showing a case where it is decided to perform wireless channel switching between adjacent base stations when transmitting data from a base station.

FIG. 6 is a sequence diagram showing a case where it is decided to perform wireless channel switching between adjacent base stations when transmitting data from a mobile station.

FIG. 7 is a sequence diagram showing a case where it is decided to perform wireless channel switching within the same base station when transmitting data from the base station.

FIG. 8 is a sequence diagram showing a case where it is decided to perform wireless channel switching within the same base station when transmitting data from a mobile station.

FIG. 9 shows an error rate threshold F and a desired reception level threshold D
FIG. 3 is a diagram showing a relationship between the control of the wireless channel switching.

[Explanation of symbols]

 2a to 2d Mobile station 3a, 3b Base station 4a, 4b Wireless cell 5a, 5b Line switching control unit 6 PHM 7 Data communication network

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 H04Q ⁷ /00-7/38

Claims (5)

(57) [Claims] 1. A wireless line switching method for switching to a high-quality wireless line when a reception error rate of a signal arriving from a mobile station exceeds a threshold value F, the information length of transmission data and the line of the wireless line When the transmission delay time estimated from the quality is shorter than the time required for performing the switching of the wireless channel, the switching of the wireless channel is temporarily suspended and the packet is retransmitted. 2. The transmission delay time is given by α × k / n, where α is an estimated transmission delay rate of a radio link, k is an information amount to be transmitted, and n is an information transfer rate of the radio link. Item 2. The wireless line switching method according to Item 1. 3. A level of a received signal from the mobile station is detected, and when the level of the received signal is higher than a threshold value D, switching to another radio line in the same base station is performed. 2. The wireless communication line switching method according to claim 1, wherein switching to a wireless line of another base station is performed when the wireless communication line is low. 4. A radio channel switching method for switching to a radio channel of high quality when a reception error rate of a signal received on the mobile station side reported from the mobile station exceeds a threshold F and deteriorates. When the transmission delay time estimated from the information length and the line quality of the wireless line is shorter than the time required for switching the wireless line, the wireless line switching is temporarily suspended to retransmit the packet. Method. 5. The transmission delay time is given by α × k / n, where α is an estimated transmission delay rate of a wireless link, k is an information amount to be transmitted, and n is an information transfer rate of the wireless link. Item 5. The wireless line switching method according to Item 4.