JPH08186533A - Radio communication system - Google Patents

Abstract

PURPOSE: To improve frequency utilizing efficiency by changing the slot interval ratio of an up line and a down line between a radio base station and a mobile station inside a service area. CONSTITUTION: Inside a service area 6, a radio base station 1 and plural mobile stations 4 perform duplex communication at the same frequency through a time division slot while using respective up channel lines 4 and down channel lines 3. This base station 1 is provided with a slot ratio changing means 7 and the slot interval ratio of up and down lines 4 and 3 is dynamically changed. Thus, the uselessness of channels can be reduced even against the communication of the asymmetrical traffic of up and down channels and frequency utilizing efficiency can be improved. Further, delay characteristics can be improved as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system, and more particularly, to dynamically change the slot interval ratio of each line in accordance with the difference in the relative amount of communication load between the uplink and downlink channels. The present invention relates to a wireless communication system for performing communication.

[0002]

2. Description of the Related Art As one of methods for performing communication by dividing a wireless channel into slots, there is, for example, Aloha with a reserved slot. In this method, when transmitting data, a reserved slot is used for Lantasem access with Aloha with a slot, and a slot for communication is assigned from a base station. As an improvement of this method, there is Japanese Patent Laid-Open No. 3-62328. In this method, a data length transmitted by a terminal is added to a reserved slot, and a slot for a base station to communicate is assigned based on the data. Furthermore, Japanese Laid-Open Patent Publication No. 32044/1988 is a method for dynamically changing the length of the reserved slot frame length and the data transmission frame length according to the data length requested by the terminal to improve delay characteristics and frequency utilization efficiency. is there. All of these schemes are schemes in which the base station controls the slot in which data is transmitted according to the traffic of the line (uplink channel) from the terminal to the base station.

In recent years, it has been considered to accommodate multimedia such as VOD (Video On Demand) and electronic publishing by an infrastructure using wireless. The only characteristic of these traffics is the data for which information is requested in the uplink channel. In the downlink, a huge amount of data such as still images, moving images, texts, etc. is transferred compared to the uplink channel. That is,
As mentioned above, slots cannot be reserved for uplink traffic. Further, in the normal Aloha with reserved slots, in such a communication in which the traffic of the downlink and uplink channels is asymmetric, the uplink channel is wasted and the frequency utilization efficiency is deteriorated.

[0004]

As described above, the uplink channel only transmits the information related to the service request,
In the downlink channel, in the case of wireless communication in which the amount of information such as still images, moving images, and texts is larger than that of the uplink channel, the conventional access using Aloha with reserved slots wastes the frequency band to be transmitted. There is a problem that ends up.

The present invention has been made to solve the above problems, and smooths time division duplex communication by changing the ratio of slot intervals according to the difference in transmission amount between the upstream channel and the downstream channel. It is an object of the present invention to provide a wireless communication system capable of performing.

[0006]

A radio communication system according to the present invention is a downlink channel line for communicating from a radio base station to a mobile radio terminal and an uplink channel for communicating from the mobile radio terminal to the radio base station. A wireless line having a line, forming a slot divided at time intervals for each channel to enable dual communication at the same frequency at the same time, and having a predetermined service area, through the downlink channel line. And a radio base station that simultaneously broadcasts the same information to a plurality of mobile radio terminals, and receives information by broadcast from the radio base station via the downlink channel in the service area,
A plurality of the mobile radio terminals performing time division duplex communication with the radio base station via the uplink channel line;
A slot ratio that dynamically changes the ratio of the slot interval of the downlink channel line to the slot interval of the uplink channel line according to the relative amount of the communication load on the uplink channel line and the communication load on the downlink channel line. And changing means.

Further, the radio communication system according to the present invention comprises a downlink channel line for communicating from the radio base station to the mobile radio terminal and an uplink channel line for communicating from the mobile radio terminal to the radio base station. , A wireless line that forms slots divided at time intervals for each channel to enable dual communication at the same frequency at the same time, and has a predetermined service area, and has a plurality of movements through the downlink channel line. The wireless base station that simultaneously broadcasts the same information to a wireless terminal, receives information from the wireless base station via the downlink channel in the service area by broadcasting, and connects the uplink channel to the wireless base station. A plurality of mobile radio terminals performing time-division duplex communication with the radio base station via the Dynamically change the ratio of the slot interval of the downlink channel line and the slot interval of the uplink channel line so as to minimize the sum of the transmission delay time due to mobile access and the transmission delay time for transmitting information of the downlink channel line. And a slot ratio changing unit for changing the slot ratio.

Further, the radio communication system comprises a downlink channel line for communicating from the radio base station to the mobile radio terminal and an uplink channel line for communicating from the mobile radio terminal to the radio base station. A wireless line that forms a slot divided at time intervals to enable dual communication at the same frequency at the same time, and has a predetermined service area, and to a plurality of mobile wireless terminals via the downlink channel line. At the same time with the wireless base station that broadcasts the same information, while receiving information from the wireless base station via the downlink channel in the service area by broadcast communication, the wireless base station via the upstream channel. A plurality of mobile radio terminals that perform time-division duplex communication with a station and random access to the uplink channel line. Slot ratio changing means for dynamically changing the ratio between the slot interval of the downlink channel line and the slot interval of the uplink channel line so as to minimize the sum of the call block ratio due to the random access of the downlink channel line and the slot loss of the downlink channel line. Prepare

[0009]

When a TDD (time division duplex) communication is attempted in a mobile communication system in which the transmission bands of the uplink channel and the downlink channel are different, the conventional random access method deteriorates the frequency utilization efficiency, and The capacity of the communication system cannot be increased.

However, according to the present invention, frequency utilization efficiency can be improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radio communication system according to the present invention comprises a downlink channel line 3 for communication from a radio base station 1 to a mobile radio terminal 2 and an uplink channel for communication from the mobile radio terminal 2 to the radio base station 1. And a predetermined service area 6 and a wireless line 5 that is provided with a line 4 and that forms slots divided at time intervals for each channel 3 and 4 to enable dual communication at the same frequency at the same time. The radio base station 1 that simultaneously broadcasts the same information to a plurality of mobile radio terminals 2 via the downlink channel line 3.
In the service area 6, information is received from the radio base station 1 via the downlink channel line 3 by broadcast communication, and is time-divided to the radio base station 1 via the uplink channel line 4. Depending on the relative amounts of the communication loads on the plurality of mobile radio terminals 2 and the uplink channel line 4 that perform duplex communication, and the communication load on the downlink channel line 3, the slot interval of the downlink channel line 3 and the uplink. Slot ratio changing means for dynamically changing the ratio to the slot interval of the channel line 4.

FIG. 2 shows a conceptual diagram of a wireless communication system according to the present invention. The terminal 2 requests the desired information from the base station 1 through the wireless line. The base station 1 loads a request from the terminal 2 from the database 9 through the network 8. Then, the loaded information is transmitted to the terminal 2 via the wireless line. Further, the database 8 may be directly connected. Next, FIG. 3 shows a frame format for wireless communication between the base station 1 and the terminal 2. A plurality of slots 10 is defined as a frame 11. Then, the inside of the frame is divided into subframes for uplink channels and subframes for downlink channels. Further, the subframe is divided to multiplex a plurality of terminals. FIG. 3 shows a case where three terminals are multiplexed in both uplink and downlink, and an uplink frame divided for multiplexing terminals is a random access subframe.
Further, a downlink frame divided for multiplexing terminals is defined as a downlink individual subframe. The random access subframe is randomly accessed by the terminal. Next, FIG. 4 shows how a plurality of terminals actually communicate in this frame format. When the user A requests data, the user A selects an arbitrary random access subframe from the uplink subframe. In FIG. 4, the first random access subframe 21 is selected. In FIG. 4, the random access subframe is composed of three slots. Next, the user A selects an arbitrary slot from the three slots and transmits it. At this time, since the other users are not transmitting at the same timing as the transmission of the user A, they are correctly received by the base station. The base station transmits the requested data to the user A in the first downlink dedicated subframe 23 corresponding to the first random access subframe 21. Similarly, focusing on the second random access sub-frame 23, user C and user D
Since the request packets are transmitted at the same time, the packets collide and the base station fails to receive the packets. User B is transmitting the request packet in the same second random access subframe 22 but the slot to be transmitted is different, so that it is correctly received by the base station. The base station transmits data addressed to user B in the second downlink dedicated subframe. on the other hand,
User C receives the second data that should be received from the base station.
Although the downlink individual subframe of 1 is received, but it is not the data addressed to the user C, the data request packet is rerequested by the method described above.

The switching timing between transmission and reception for the user C to perform TDD in the data transmission and reception described above will be described with reference to FIG. User C first makes random access in the second random access subchannel frame, and thus operates the transmitter during that period (2
5). Then, if the random access succeeds, it is expected that desired data will be received in the second downlink dedicated subframe, so the receiver is operated during that period (2
6). However, since the transmission of the request packet failed in the first random access, the data received by the second downlink dedicated channel is the data addressed to the user C. Therefore,
The next request packet is transmitted on the second lantam access sub-channel 22, so the transmitter is operated during that period.

Next, a method of determining the ratio of the lengths of the upstream slot and the downstream slot that minimizes the information transmission delay time according to the load applied to the upstream channel will be described.

The transmission delay of the uplink channel is determined by comparing the data length, the average number of retransmissions, the random delay width at the time of retransmission, the load applied to the uplink channel, and the slot length of the uplink channel and the downlink channel. Among these parameters, it is the load applied to the uplink channel and the ratio of the slot lengths of the uplink channel and the downlink channel that change with time.

If the load generated by the user is λ, the load on the upstream slot is λup, the slot lengths of the upstream and downstream channels are R, and the delay amount is Dup, then Dup = function (λup, R) The delay amount is a function of λup and R.

Further, λup can be described by λ, and λup =
It becomes λ (1 + R) / (2R).

The delay amount of the downlink channel is determined by comparing the data length, the load applied to the downlink channel, and the slot lengths of the uplink channel and the downlink channel.

When the load is λdown, the slot lengths of the upstream and downstream channels are R, and the delay amount is Ddown, the delay amount is a function of λdown and R as Ddown = function (λdown, R).

The load λdown of the downlink channel is determined by the load λup of the uplink channel and the random access method of the uplink channel since the information request has been successfully transmitted in the uplink channel.

The throughput of the upstream channel is S (λu
p), the load on the downlink channel is λdown = λup × (1- (λup−S (λup)))
/ Λup).

Therefore, the total delay amount D = Dup + Ddown
Is a function of λup and the throughput S (λup) at that time and R. The total delay amount D has a minimum value with respect to S.
Therefore, the ratio of the slot length of the uplink channel and the slot length of the downlink channel that minimizes the delay amount is determined by finding the S that gives the minimum value at that time while maintaining the load of the uplink channel.

That is, D = function (λup, S (λu
From p), R),

[0024]

[Equation 1] We need to find S

Actually, a description will be given on the assumption that the uplink channel is randomly accessed by the slotted Aloha and the information amount transmitted on the downlink channel is constant.

The delay amount of the slotted Aloha is Dup = C1 + exp (λup) × C2 = C1 + exp (λ (1 + R) / (2 × R)) × C2 C1, C2 It is a constant determined by the data length, the average number of retransmissions, the random delay at the time of retransmission, and the like.

The delivery rate of data when the amount of information is constant is μ
And ρdown = λdown / μ,

[0028]

[Equation 2] Becomes

As a result, the comparison R of the uplink channel and the downlink channel that minimizes the delay is

[0030]

(Equation 3) You just have to find R.

When actually calculated

[0032]

[Equation 4] Where ρ = λ and λ is the user's tramock μ is the downlink channel transmission capacity ^μ

[0033]

In the wireless communication system that communicates by TDD, the upstream channel is mainly for information request,
In the communication in which the requested information is mainly delivered to the downlink channel, by dynamically changing the load on the uplink and the ratio of the uplink slot interval and the downlink slot interval according to the load on the downlink, The frequency utilization efficiency can be improved and the delay characteristic can be improved.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a first basic concept of the present invention.

FIG. 2 is a system configuration diagram showing an entire wireless communication system of the present invention.

FIG. 3 is a frame configuration diagram showing a frame used in the wireless communication system of the present invention.

FIG. 4 is an explanatory diagram showing an example of the operation of the wireless communication system of the present invention.

FIG. 5 is an explanatory diagram showing an operation of a transceiver as a terminal of the wireless communication system of the present invention.

[Explanation of symbols]

 1 radio base station 2 mobile radio terminal 3 downlink channel line 4 uplink channel line 5 radio line 6 service area 7 slot ratio changing means

Claims (3)

[Claims] 1. A downlink channel line for communicating from a radio base station to a mobile radio terminal and an uplink channel line for communicating from the mobile radio terminal to the radio base station, wherein each channel is divided at time intervals. A wireless line that forms a designated slot to enable dual communication at the same frequency at the same time, and has a predetermined service area, and transmits information to a plurality of mobile wireless terminals by time division through the downlink channel line. With the wireless base station communicating with the wireless base station, receiving information communicated from the wireless base station via the downlink channel line in the service area, and time-sharing to the wireless base station via the uplink channel line. A plurality of mobile radio terminals that perform duplex communication with each other, and a communication load on the uplink channel line and a communication load on the downlink channel line In response to the relative amounts, wireless communication system and a slot ratio changing means for dynamically changing the ratio of the slot interval of the downlink channel line slot interval between the uplink channel access. 2. A downlink channel line for communicating from a radio base station to a mobile radio terminal and an uplink channel line for communicating from the mobile radio terminal to the radio base station, each of which is divided at time intervals. A wireless line that forms a designated slot to enable dual communication at the same frequency at the same time, and has a predetermined service area, and transmits information to a plurality of mobile wireless terminals by time division through the downlink channel line. With the wireless base station communicating with the wireless base station, receiving information communicated from the wireless base station via the downlink channel line in the service area, and time-sharing to the wireless base station via the uplink channel line. A plurality of mobile radio terminals that perform duplex communication with each other, a transmission delay time and a downlink channel due to random access of the uplink channel line. Slot ratio changing means for dynamically changing the ratio of the slot interval of the downlink channel line and the slot interval of the uplink channel line so as to minimize the sum of the transmission delay time for transmitting the line information. Wireless communication system. 3. A downlink channel line for communicating from a radio base station to a mobile radio terminal and an uplink channel line for communicating from the mobile radio terminal to the radio base station, and each channel is divided at time intervals. A wireless line that forms a designated slot to enable dual communication at the same frequency at the same time, and has a predetermined service area, and transmits information to a plurality of mobile wireless terminals by time division through the downlink channel line. With the wireless base station communicating with the wireless base station, receiving information communicated from the wireless base station via the downlink channel line in the service area, and time-sharing to the wireless base station via the uplink channel line. A plurality of mobile radio terminals that perform duplex communication with each other, a call loss rate due to random access of the uplink channel line and a downlink channel line Wireless communication system and a slot ratio changing means for dynamically changing the ratio of the slot interval of the downlink channel line and the slot interval of the uplink channel line to the sum of the blocking probability by random access to a minimum.