JPH10174185A - Data transmission system and mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize data avoided undesirably due to mismatching between a transmission speed and a buffer capacity and invalid data losing real time performance. SOLUTION: A host station 1 designates an outgoing control physical channel structure to a radio base station 3 at the start system operation. The radio base station 3 obtains an optimum buffer capacity Cs according to an equation Cs=Vs×Te, where Vs is a transmission speed in each function channel depending on a designated control physical channel structure an Te is a time a reply wait time of a host station 1 from a mobile equipment 5 with some margin. Since the buffer capacity is selected in this way, data invalidated not in time for a reply wait of the host station 1 in a consecutive high load state are aborted before being stored in the buffer. Thus, the data sent to the mobile equipment 5 actually are all validated and then the transmission capability of a radio channel is utilized efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buffer capacity adjusting method in a communication system having a variable transmission rate, and more particularly to a buffer capacity adjusting method for increasing or decreasing a buffer capacity according to a transmission rate.

[0002]

2. Description of the Related Art In recent years, the transmission of not only voice but also images, facsimile, data and the like on telephone lines has increased rapidly, and packet communication has increased due to low-density conversational data communication and intermittent information communication. I have. In this packet communication, a data signal is divided into blocks of a fixed length, each of which is attached as a header including destination information necessary for transfer, and transmitted as a packet. Packets are sent from multiple transmitting stations,
When the packet is once stored in the exchange and the line to the other party becomes free or when the amount of transmission data is stored to some extent, the packets are arranged in time series and transmitted sequentially. If there is an error, the packet is transmitted again.

Conventionally, a receiving station stores a packet transmitted from a transmission line in a buffer memory having a variable capacity. When the amount of packets is large, the storage capacity of the buffer memory is increased. , The data is sequentially read out and subjected to signal processing by a decoding device. In this case, the buffer capacity adjusting method for adjusting the capacity of the buffer memory absorbs the difference between the input speed and the output speed of the data, shortens the time for the data to pass through the buffer for the matching buffer, and reduces the buffer fullness. There is a demand for setting an optimal buffer capacity to reduce the amount of discarded data.

The prior art is disclosed in Japanese Patent Laid-Open No. 4-113744.
There is a variable-rate packet transmission system for performing packet communication at a variable rate disclosed in Japanese Patent Application Laid-Open No. H10-260,000. In this publication, it is necessary to prevent a fluctuation that is an indefinite delay due to a waiting time when performing multiplexing processing in a packet communication path of packet communication, and when the buffer capacity is set to an allowable maximum fluctuation, In order to solve the problem, if the buffer capacity is too large, the maximum delay occurs due to reading and sending, and if the buffer amount is reduced to reduce the delay, packets that become extra cells were discarded. FIG. 3 is a block diagram showing the configuration of this embodiment.

[0005] In FIG. 3, a dummy packet generator 6 sends out dummy packets at regular intervals Td. Multiplexer 7
Transmits a signal packet and a dummy packet in a multiplexed manner. The separating unit 8 separates a signal received through the communication line into a dummy packet and a signal packet, delivers the dummy packet to the buffer control unit 9, and stores the signal packet in the variable buffer 10. The buffer control unit 9 receives the plurality of dummy packets, and receives the dummy packet reception interval average value T
u is calculated and compared with the constant interval Td. That is, in the case of the bucket communication, dummy packets are provided at regular intervals Td and signal packets are sequentially inserted by the multiplexing unit 7 and transmitted to the communication line.
d, and the transmission time of the communication line passes through various communication paths, so that the transmission time at which the fixed interval Td becomes faster or delayed is shifted. Here, Tu>
In the case of Td, it means that the traffic on the transmission line is low, so the capacity of the variable buffer 10 is reduced. Tu ≦ T
In the case of d, the discard rate is set to γ from the standard normal distribution of dummy packets determined by the reception interval average Tu, and the confidence interval T
uc = 2Tu × γ is calculated. Next, if the reception interval time ΔT of the received dummy packet belongs to the confidence interval Tuc, the capacity of the variable buffer 10 is maintained, and if it does not belong to the confidence interval Tuc, the buffer capacity is increased. Thus, the fluctuation of the communication network is detected in accordance with the delay width of the dummy packet transmitted at regular intervals, the buffer capacity of the buffer on the receiving side is increased or decreased, and the fluctuation of the network is detected by the receiving unit corresponding to the variable rate. Absorption can be prevented, and unnecessary absorption delay and packet discard can be prevented. As described above, the buffer capacity is adjusted according to the data amount of the signal packet.

[0006]

However, in a data transmission requiring real-time performance, when a heavy load is applied to the communication system, the conventional method increases the buffer capacity in order to prevent data from being discarded.
There is a problem that it takes a long time from the time when the data is stored in the buffer to the time when the data is read, and the validity as real-time data is lost. Furthermore, if the buffer capacity is reduced to guarantee real-time performance, all data stored in the buffer becomes invalid under a continuous high load state.

[0007]

The buffer capacity adjusting method according to the present invention comprises adjusting means for increasing the buffer capacity when the transmission speed of the transmitting unit is high, and decreasing the buffer capacity when the transmitting speed is low. Buffer capacity of a typical variable capacity buffer can be set.

More specifically, the buffer capacity adjusting method according to the present invention employs a communication means having a variable transmission speed and a method for temporarily storing data in order to absorb and match the difference between the input speed and the output speed of data. It is characterized by comprising a variable capacity buffer for storing variable capacity, and adjusting means for increasing or decreasing the buffer capacity of the variable capacity buffer according to the transmission speed of the transmission unit. In the data transmission method,
The adjustment means adjusts the buffer capacity so that the buffer capacity is increased when the transmission speed of the transmission unit is high, and the buffer capacity is decreased when the transmission rate is low.

[0009] Further, the mobile communication system according to the present invention comprises:
In a digital car telephone system comprising an upper station, a base station via a line to the upper station, and a mobile station receiving radio waves transmitted from the base station, a variable capacity buffer in the base station is controlled by the control data of the mobile station. When setting the capacity value of the variable capacity buffer, the capacity value of the variable capacity buffer is set according to the transmission speed of data transmitted from the upper station. Further, in the mobile communication system, the transmission rate is a transmission rate that can be transmitted from the base station, and the capacity value of the variable capacity buffer is the time and the transmission rate returned from the upper station to the mobile station. The capacity is determined by the product of

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A first embodiment will be described with reference to the drawings. FIG. 1 shows a TDMA (Time Division Multiple Acces) for realizing the buffer capacity adjusting method according to the present embodiment.
It is a block diagram which shows the structure of the mobile communication system by a s) system. A digital car phone system as a kind of mobile communication system has a frequency band of 800 MHz band /
The frequency band is 1.5 GHz, the carrier frequency interval is 50 kHz interleaved at 25 kHz, the output of the base station is 30 W, the output of the mobile station is 0.6 to 3 W, the modulation method is π / 4 shift QPSK, and the transmission speed is Is 42kbps
The access system is operated in TDMA / FDD with the main specifications of full-rate 3ch multiplexing or half-rate 6ch multiplexing. In terms of configuration, data and voice are transmitted from a telephone to a mobile telephone exchange, a radio network controller, and a plurality of radio base stations via a public line, and data and voice are transmitted wirelessly from a radio base station antenna to a mobile station. Is transmitted.

In FIG. 1, an upper-level station 1 corresponds to a radio network controller, particularly for data transmission, and data is transmitted from a radio base station 3 to a predetermined mobile station via a dedicated or public telephone line 2. Transmission is performed in three time-division time slots, the mobile station 5 selects data addressed to itself,
The radio base station 3 receives the data of the mobile station 5 during the division and transmits the data in one of the other three divisions. This data may be digitalized audio data or data from a computer or the like.

FIG. 2 shows a conceptual diagram of the configuration of the radio base station 3. As shown in FIG. In the figure, reference numeral 12 denotes an upper station receiving unit as an interface for receiving data transmission from the upper station 1;
Reference numeral 3 denotes a buffer capacity setting value table for setting a buffer capacity from a message specifying a control physical channel structure from the upper station 1 when the message is received.
Reference numeral 4 denotes a comparator for comparing the buffer capacity set by the buffer capacity setting value table 13 with the data amount from the upper station 1, and 15 denotes a buffer usage amount to be converted into the current data amount in the physical channel structure for controlling the upper station 1. A table 16 is a capacity of a transmitting unit for transmitting the data from the upper station 1 to the plurality of mobile devices 5, and a control unit 17 controls and calculates the radio base station 3. Reference numeral 18 denotes an antenna for modulating the radio frequency with data together with the address of the mobile station 5 from the radio base station 3 to the mobile station 5 and outputting the data. It may be. Although the structure in the radio base station 3 is shown only in one direction, the structure in the reverse direction is similarly provided for relaying when data from the mobile station 5 is sent to the upper station 1.

In FIG. 1, first, when starting up the mobile radio system, the upper station 1 transmits information for designating a control physical channel structure to the radio base station 3, and the radio base station 3 A message specifying the physical channel structure for use is received by the upper station receiving unit 12, the optimum buffer capacity is calculated, and the calculated buffer capacity is sent to the buffer capacity setting value table 13. Set.

Next, the upper station 1 transmits a request for data transmission of its own data to the mobile station 5 to the radio base station 3 via the line 2 and starts counting by the response waiting timer 11. Upon receiving the data transmission request, the upper station receiving unit 12 notifies the comparator 14 of the length of data to be stored in the variable capacity buffer 4. The comparator 14 compares the length of the buffer capacity setting value with the current buffer usage amount stored in the buffer usage amount table. If the buffer capacity of the buffer capacity setting value is small, NG is ranked higher as the comparison result. Notify the station receiving unit 12. On the other hand, if the buffer capacity is large or equal, OK is notified as the comparison result. The upper station receiving unit 12 discards the data when the comparison result is NG. On the other hand, if the comparison result is OK, the data is written into the variable capacity buffer 4 and the newly written data length is added to the buffer usage table and updated. The transmission unit for mobile unit 16 transmits data in the slot of the corresponding function channel while taking the timing in the superframe, and subtracts the used data in the buffer usage table by the data that has been transmitted.

In other words, the wireless base station 3 receiving the data transmission request from the upper station 1 stores the data to be transmitted to the mobile station 5 in the variable capacity buffer 4 and The timing on the frame is taken and transmitted to the mobile device 5 in the slot. The mobile device 5 transmits a response to the received data or newly created data to the radio base station 3, and the radio base station 3 transmits a response or data via the line 2. When the upper station 1 receives the response,
If the response waiting timer 11 started earlier has timed out, the received response is invalidated and discarded. If the response waiting timer 11 is operating, the timer count is stopped and the next response is accepted.

FIG. 2 shows the structure of a physical channel for downlink control from the upper station 1 to the mobile station 5 in the digital car telephone system based on the TDMA system. In the downlink control physical channel, regardless of the function channel type, 1
The data that can be transmitted in a slot is defined as 17 bytes, and a superframe is one repetition unit, and the slot of the same function channel is repeated every superframe of 720 ms.

In the figure, BCCH is a broadcast channel, which is a one-way channel for broadcasting information from the circuit network to the mobile device 5, and includes broadcast information, information for location registration, information on a channel structure, and a system. B indicates a BCCH slot. The SCCH is a signaling channel for an individual cell, is a bi-directional channel for transferring information between the circuit network and the mobile device 5, and is used when a serving cell of the mobile device 5 is registered on the circuit network side. Independent information is transferred for each cell using different frequency resources, the uplink channel is randomly accessed, and S indicates an SCCH slot. Also, PC
H is a paging channel, which is a one-way channel for simultaneously transferring the same information to a wide area (paging area) from the circuit network to the mobile station 5, and is used for paging. Shows a slot.

In FIG. 2A, one super slot is 36 slots, and one slot is divided into three channels by the TDMA method and divided into three channels. One slot is transmitted in 20 ms. / 3m
It is repeatedly transmitted every s, and one channel includes a data transmission amount of 36 × (20/3) = 240 ms in 36 slots. Here, Ab is the BC between B and B
indicates the number of channel slots, As1 indicates the number of SCCH slots between SS after BCCH, Ap indicates the number of PCH slots between PP, and next As2 indicates the number of SS between SS after PCH.
Indicates the number of CCH slots, and the last remainder is 36 between SS.
Specify the number of extra slots in slots. These A
b, As1, Ap, As2 are variable parameters set by the upper station 1.

FIG. 2B is an example showing a specific 36-slot superslot, where Ab = 3, A
This is a slot sequence when s1 = 3, Ap = 1, As2 = 1, and Np = 15. Here, for example, in the case of SCCH data, transmission is performed in units of 17 bytes in the slot indicated by “S” in the figure.

The above-mentioned three function channels are arranged in the physical channel for downlink control. Among them, the PCH is divided into groups, and the mobile station 5 is determined to which group the mobile station 5 belongs to by a unique identification number. When the machine 5 waits, the BC
The control channel structure is recognized based on the broadcast information of the CH, and the PCH waits for the simultaneous paging of the PCH by the PCH slot of the group to which it belongs. Np is the number of PCH groups in one control channel.

One superframe is composed of 36 slots. In the physical channel for downlink control, BCCH,
SCCH and PCH slots are arranged according to system parameters specified at the start of system operation. Therefore, at the start of system operation, the upper station 1 sends effective data including data for setting the storage capacity of the variable capacity buffer of the radio base station 3 in consideration of its own transmission speed and its own data amount. The transmission rate of each functional channel constituting this changes in proportion to the number of slots allocated in one superframe. The upper station 1 specifies a downlink control physical channel structure to the wireless base station 3 via the line 2 at the start of system operation. The radio base station 3 sets the optimal buffer capacity of each functional channel according to the specified downlink control physical channel structure, and starts operation.

A method of setting the buffer capacity of the variable capacity buffer 4 of the radio base station 3 will be described using SCCH as an example.

When one superframe is composed of 36 slots, the number Ns of SCCH slots in the frame is the number Ab of BCCH slots which are parameters designated by the upper station 1, the number Ap of PCH slots per group, and the physical number for control. It is obtained as follows from the number Np of PCH groups in the channel.

Ns = 36−Ab− (Ap × Np) The data that can be transmitted in one slot (20 ms) on the physical channel for downlink control is 136 bits (17 bytes). Required.

Vs = 136 × Ns × 1000 {720}
189 × Ns [bps] A certain margin τ is set for a time Tr during which the upper station 1 waits for a response after requesting the wireless base station 3 to transmit data to the mobile station 5, that is, a time during which the transmission data is valid. Assuming that the estimated time is Te (Tr + τ), the optimum buffer capacity Cs for the downlink SCCH buffer is obtained as follows.

Cs = Vs × Te ≒ 189 × Ns × Te [bit] ≒ 23.6 × Ns × Te [byte] The optimum capacity Cs is determined by the number Ns of SCCH slots for data transmission expected by the upper station 1. When the system including the wireless base station 3 is started up, the capacity of the variable capacity buffer 4 is set. The margin τ at the time Te, which takes into account the time Tr for waiting for a response after making a data transmission request and a certain margin τ, is small with respect to the time Tr, and the transmission speed according to the specifications of the digital car telephone system is 42 kbps. If it is determined that the data amount has been sent in 36 slots of one super slot, and BCCH is 1 slot and PCH is 2 slots, S
1. CCH 33 slots, Te round-trip without margin
Assuming 44 s, the transmission speed Vs is Vs = 189 × 33 =
6237 [bps], and the optimal buffer capacity Cs is C
s = 23.6 × 33 × 1.44 = 1121 [bytes]
Becomes The transmission speed of 42 kbps according to the specifications is a combined speed of all the channels. The transmission speed of one control physical channel is 42/3 (multiplex number) = 14 kbps. , Wireless base station 3
Since it includes the number of bits for synchronizing between them, there is a difference of more than twice compared with the speed of transmitting data from the upper station 1 stored in the variable capacity buffer 4 substantially.

As described above, the optimum capacity Cs greatly changes depending on the transmission speed. However, by setting the variable capacity buffer 4 to this optimum capacity Cs, the effectiveness as real-time data is lost. Without this, data can be efficiently communicated between the upper station 1 and the mobile station 3.

In general, the relationship between the transmission speed Vh of the line 2 and the transmission speed Vs of the SCCH of the radio line is as follows.

Vh >> Vs Since the SCCH is used for transmitting data to an unspecified number of mobile stations 5, the SCCH is stored in the variable capacity buffer 4 in consideration of a load exceeding the transmission capacity of the radio channel. Data that cannot be deleted is discarded. Since the buffer capacity is set to an optimal value as described above, all responses from the mobile station 5 to data that could be actually transmitted to the mobile station 5 are received before the response waiting timer of the upper station 1 times out. Is done. Also, it is not necessary to discard unnecessary data.

[Second Embodiment] In a communication system in which the transmission rate is variable, if a large transmission buffer is secured for a low transmission rate, the transmission data is stored in the buffer during a high load, and then the transmission data is actually stored. The time required for transmission is long, and the validity of data required as real-time properties is lost. Therefore, if the high load state continues, all data to be transmitted becomes invalid.

Conversely, if the transmission buffer capacity is small for a high transmission speed, the data cannot be stored in the buffer, but the data must be discarded, despite the transmission capability that can be transmitted while the data is valid. I will not get it. By optimally adjusting the buffer capacity according to the setting of the transmission rate, it is possible to store only the data that can be transmitted within the valid time of the data in the buffer to the maximum.

In the mobile communication system based on the TDMA system as shown in FIG. 1, the downlink control channel structure is based on the SCCH as shown in FIG.
The capacity of the variable capacity buffer 4 can be set at the start of the system by making As1 and As2 indicating the number of slots variable, and the transmission speed of each functional channel changes according to the channel structure. One slot (2
0 ms), the data that can be transmitted is 136 bits (17
Bytes). Therefore, one superframe (720m
If the number of SCCH slots in s) is Ns, the transmission rate Vs is: Vs = 136 × Ns × 1000 × 720 ≒ 189 × Ns
[Bps].

The time T taking into account a certain margin with respect to the time for waiting for a response from the mobile station 5 after the host station 1 requests data transmission to the radio base station 3 via the line 2.
Assuming that e seconds is the time when the transmission data is valid, SCC
The optimum buffer capacity Cs for the H transmission buffer is Cs = Vs × Te ≒ 189 × Ns × Te [bit] ≒ 23.6 × Ns × Te [byte].

When the control channel structure is determined at the start of system operation, by setting the buffer capacity according to the above equation, it is possible to minimize transmission data that becomes invalid.

That is, if a large transmission buffer is secured for a low transmission rate, the time from when transmission data is stored in the buffer to when it is actually transmitted becomes longer under high load, and real-time data is transmitted. The effectiveness as is lost. Therefore, if the high-load state continues, all data to be transmitted becomes invalid. Conversely, if the transmission buffer capacity is small for a high transmission rate, the data must be discarded because it cannot be stored in the buffer, despite the transmission capacity that can be transmitted while the data is valid. I will. Thus, the optimal buffer capacity is the maximum buffer capacity that can be transmitted before the last stored data loses validity.

[0036]

As described above, the buffer capacity adjusting method according to the present invention has a structure in which the optimum buffer capacity is set according to the transmission speed of the transmission unit, so that invalidated data is minimized. This has the effect that only valid data can be transmitted and received while making the most of the transmission capacity of the communication line.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a system for realizing a buffer capacity adjustment method according to the present invention.

FIG. 2 is a block diagram showing a configuration for realizing a buffer capacity adjustment method according to the present invention.

FIG. 3 is a diagram illustrating a structure of a physical channel for downlink control in the TDMA scheme.

FIG. 4 is a block diagram showing a configuration of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper station 2 Circuit 3 Radio base station 4 Variable capacity buffer 5 Mobile station

Claims (4)

[Claims] Communication means having a variable transmission rate; a variable capacity variable buffer for temporarily storing data for absorbing and matching a difference between an input rate and an output rate of data; Adjusting means for increasing or decreasing the buffer capacity of the variable buffer in accordance with the transmission speed of the transmission unit. 2. The data transmission system according to claim 1, wherein said adjusting means adjusts the buffer capacity so that the buffer capacity is increased when the transmission speed of the transmission unit is high, and the buffer capacity is decreased when the transmission speed of the transmission unit is low. A data transmission method characterized by: 3. A digital car telephone system comprising an upper station, a base station via a line to the upper station, and a mobile station receiving radio waves transmitted from the base station, wherein the base station is controlled by control data of the mobile station. A mobile communication system, wherein when setting a capacity value of a variable capacity buffer in a station, the capacity value of the variable capacity buffer is set according to a transmission speed of data transmitted from the upper station. 4. The digital car telephone system according to claim 3, wherein the transmission rate is a transmission rate at which transmission is possible from the base station, and the capacity value of the variable capacity buffer is from the upper station to the mobile station. A mobile communication system having a capacity determined by a product of a return time and the transmission rate.