JP3977639B2 - Line assignment control method and line assignment apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a TDMA (Time Division Multiple Access) / TDD (Time Division Duplex) system to perform wireless communication between one base station and a plurality of subscriber stations. -With regard to a line allocation control method and a line allocation apparatus used in an MP (Point-Multi Point) type fixed radio access system, the transmission capacity of a radio packet determined by a modulation degree, a modulation format, etc. is independent for each subscriber station. The present invention relates to a line allocation control method and a line allocation apparatus that are applied in the case of being determined.
[0002]
[Prior art]
In the P-MP type fixed wireless access system, a wireless line is formed between one base station and a plurality of subscriber stations. In a system that communicates using TDMA / TDD, a base station and a plurality of subscriber stations share one radio frequency, and the base station assigns time slots to each subscriber station as necessary. Secure a communication channel for each subscriber station.
[0003]
In such a system, since the capacity that can be transmitted at one radio frequency is limited in advance, the communication channel used by each subscriber station is appropriately set in the radio channel between the base station and each subscriber station. Need to be assigned.
In particular, when traffic from a large number of subscriber stations occurs in a concentrated manner, line assignment is delayed in response to requests from each subscriber station, and transmission delay between the base station and the subscriber station is greatly increased. May increase. In such a case, fairness among subscriber stations becomes a problem.
[0004]
Conventionally, round robin control has been adopted as traffic control at the layer 2 level in order to ensure fairness among subscriber stations. This round robin control is generally performed by time scheduling in a base station.
When round-robin control is performed, a buffer is provided for each subscriber station for traffic in the direction from the base station to the subscriber station (downward) and for traffic in the direction from the subscriber station to the base station (upstream). assign. Then, in accordance with a predetermined order so as to ensure fairness, a predetermined amount of data Q is set as a maximum value, and data stored in the buffer is sequentially allocated and transmitted to time slots.
[0005]
[Problems to be solved by the invention]
In general fixed wireless access systems, it is assumed that the modulation format and degree of modulation of radio packets are the same in all subscriber stations in the radio link between the base station and each subscriber station. . Under such assumptions, the transmission capacity per unit time of the radio line is the same for all subscriber stations, so that round-robin control ensures efficient fairness among subscriber stations. A line can be assigned to each subscriber station.
[0006]
However, in general, the transmission distance between the base station and each subscriber station is different for each subscriber station. For example, for a subscriber station with a short transmission distance, it is possible to increase the transmission capacity of wireless packets and increase the peak speed by increasing the modulation degree than usual.
On the other hand, for a subscriber station having a long transmission distance, there is a case where data errors occur frequently and establishment of a radio line is difficult with a normal modulation degree. For such a subscriber station, it is considered that if the modulation degree is lowered than usual, the occurrence of data errors is reduced, so that the establishment of a radio link is facilitated.
[0007]
As described above, when the so-called link adaptation method in which the transmission capacity of the wireless packet is determined independently for each subscriber station is employed, a problem occurs when the conventional round robin control is performed. That is, since the data capacity that can be transmitted in each time slot differs for each subscriber station, if the maximum transmission capacity (Q) is uniformly defined as in round robin control, the use efficiency of the time slot deteriorates.
[0008]
A specific example will be described with reference to FIG. In FIG. 7, the horizontal axis represents time or time slots (TS), and the vertical axis represents the amount of data that can be transmitted in one time slot.
In this example, it is assumed that three users (that is, subscriber stations) A, B, and C each communicate with a base station. Each user has a different modulation scheme that can be applied due to a difference in propagation conditions. The amount of data that can be transmitted in one time slot assumes that user A is Q, user B is 2Q, and user C is 3Q.
[0009]
FIG. 7A shows a case where the maximum transmission data amount assigned by round robin control of time scheduling is uniformly Q.
In the example of FIG. 7 (a), although a larger amount of data can be transmitted to users B and C, only the amount of data can be transmitted in one time slot, resulting in wasted transmission bandwidth. I understand that.
[0010]
FIG. 7B shows a case where the maximum transmission data amount assigned by round robin control of time scheduling is uniformly 3Q.
In the example of FIG. 7B, a useless transmission band is generated for the user B. Further, since most time slots are allocated to the user A, it can be seen that the throughput of the user B and the user C is not improved.
[0011]
The present invention relates to a line allocation control method and a line allocation capable of improving the use efficiency of time slots and performing a highly fair line allocation when the transmission capacity of a radio packet is determined independently for each subscriber station. An object is to provide an apparatus.
[0012]
[Means for Solving the Problems]
In the first aspect, a radio channel is formed between one base station and a plurality of subscriber stations, and the same radio frequency is shared by a plurality of subscriber stations by time division multiple access / time division duplex. A line allocation control method for a base station to allocate time slots used for communication of each of a plurality of subscriber stations, wherein one time is provided between a buffer corresponding to each subscriber station and a radio communication means. A maximum value of the amount of data transmitted in the slot is determined and held according to the transmission rate of the corresponding subscriber station, and a time slot is allocated to each subscriber station according to round robin, and data transmitted in the time slot scheduling an upper limit the maximum value of each subscriber data amount determined in correspondence with the station data transfer between the buffer and the wireless communication unit according to And wherein the door.
[0013]
In claim 1, when assigning a radio channel to each subscriber station according to round robin, the maximum data amount individually determined for each subscriber station is used as an upper limit, for example, from a buffer corresponding to the subscriber to a radio communication means A data transfer process is scheduled, and an appropriate amount of data is assigned to the assigned time slot according to the transmission capability of each subscriber station .
In other words, for a subscriber station with a low modulation degree and a small transmission capacity of a wireless line, a small amount of data corresponding to the transmission capacity is handled from a buffer corresponding to the transmission capacity in a single process ( or from a wireless communication means ). was transferred to the buffer) to, is allocated to the subscriber's time slot, it is possible to transmit all of the data allocated in the processing in one time slot.
[0014]
Therefore, as in the example shown in FIG. 7B in which the amount of data transferred from the buffer to the wireless communication means is set in accordance with the subscriber having a large transmission capacity, data exceeding the amount of data that can be transmitted in one time slot. Since the same user (A) does not use a plurality of time slots continuously, the fairness among subscriber stations can be improved.
Also, for subscriber stations with a high degree of modulation and a large transmission capacity of the radio channel, a large amount of data corresponding to the transmission capacity is transferred between the corresponding buffer and the radio communication means in a single process. When the transmission capacity of one time slot is large, a large amount of data can be transmitted in one time slot, and it is possible to prevent useless transmission bands from occurring in the time slot.
[0015]
According to claim 2, a radio link is formed between one base station and a plurality of subscriber stations, and the same radio frequency is shared by a plurality of subscriber stations by time division multiple access / time division duplex. In a wireless communication system in which the transmission capacity per unit time in each wireless line is determined independently for each subscriber station, in order for the base station to allocate time slots used for communication of each of the plurality of subscriber stations A line allocating device to be used, which determines the maximum amount of data to be transmitted in one time slot between a buffer corresponding to each subscriber station and the wireless communication means in accordance with the transmission rate of the corresponding subscriber station. A time table assigned to each subscriber station according to the round robin, and the buffer and the data buffer for the data to be transmitted in the time slot. Characterized by providing a scheduling means for scheduling the maximum data amount determined in correspondence to each subscriber station the data transfer between the wireless communication unit as the upper limit.
[0016]
In claim 2, since the maximum data amount associated with the transmission capacity per unit time in the radio channel of each subscriber station is held in the management table independently for each subscriber station, Gets the amount to transfer between the buffer corresponding to the subscriber station is one time slot in Oite wireless communication means for each subscriber station as the data to be transmitted, the corresponding appropriate amount of data A schedule can be determined.
[0017]
Accordingly, the fairness among subscriber stations can be improved as in the first aspect, and it is possible to prevent the useless transmission band from being generated in each time slot.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a line allocation control method and a line allocation apparatus according to the present invention will be described with reference to FIGS. This form corresponds to all the claims.
[0019]
FIG. 1 is a flowchart showing a line allocation operation in this embodiment. FIG. 2 is a block diagram illustrating a configuration example of the fixed wireless access system. FIG. 3 is a schematic diagram illustrating a configuration example of the management table. FIG. 4 is a time chart showing an operation example of the present invention. FIG. 5 is a schematic diagram showing a specific example of the downlink time slot allocation operation. FIG. 6 is a schematic diagram showing a frame configuration generally used in TDMA / TDD communication.
[0020]
In this form, the management table and scheduling means of claim 2 correspond to the management table 125 and the time scheduling circuit 104, respectively.
In this embodiment, it is assumed that the present invention is applied to a fixed wireless access system as shown in FIG. A base station that implements the present invention forms a radio channel with each of a plurality of subscriber stations 111 and relays signals between each subscriber station 111 and the IP network 121. In this example, the radio frequency between the base station and the subscriber station 111 uses a quasi-millimeter wave band radio frequency.
[0021]
TDMA / TDD is adopted as a communication method between the base station and the subscriber station 111. That is, the same frequency is shared by a plurality of subscriber stations 111, and a plurality of time slots separated by time are allocated for communication of each subscriber station 111 as necessary. Further, the same frequency is used for the downlink in the direction from the base station to the subscriber station 111 and the uplink in the direction from the subscriber station 111 to the base station.
[0022]
Actually, communication is performed using a frame configured as shown in FIG. This frame is composed of four types of time slots TSA, TSB, TSC, and TSD.
The time slot TSA is used for transmission of broadcast information transmitted from the base station to the subscriber station 111 on the downlink. The time slot TSB is used for transmitting user data to the corresponding subscriber station 111 on the downlink by the base station. The time slot TSC is used for each subscriber station 111 to transmit user data to the base station on the uplink. The time slot TSD is used for uplink random access from the subscriber station 111.
[0023]
As shown in FIG. 2, the base station includes an antenna 110, a high frequency circuit 106, and a signal processing circuit 109. The high frequency circuit 106 is provided with a receiving unit 107 and a transmitting unit 108.
The signal processing circuit 109 of the base station includes a network interface circuit 101, an LLC (logical link control) control circuit 102, a MAC (media access control) control circuit 103, a time scheduling circuit 104, a modulation / demodulation circuit 105, and a management table 125. Yes.
[0024]
The base station is connected to an IP (Internet Protocol) network 121 via the network interface circuit 101.
The LLC control circuit 102 has a built-in buffer circuit for temporarily storing transmission / reception signal data. The LLC control circuit 102 has a function of assigning a sequence number used for retransmission control, a tag for identifying a data service class, and the like.
[0025]
The MAC control circuit 103 assigns a device identification ID (MAC-ID) at the layer 2 level to transmission / reception signal data, and dynamically assigns a time slot for information transmission using the time scheduling circuit 104.
[0026]
The modem circuit 105 modulates the signal to be transmitted and demodulates the received signal. That is, the baseband signal output from the MAC control circuit 103 is modulated by the modulation / demodulation circuit 105 and applied to the transmission unit 108 of the high frequency circuit 106. A reception signal (intermediate frequency signal) output from the reception unit 107 of the high frequency circuit 106 is demodulated by the modulation / demodulation circuit 105 and applied to the MAC control circuit 103 as a baseband signal.
[0027]
The transmission unit 108 converts the intermediate frequency signal input from the modulation / demodulation circuit 105 to a radio frequency, performs power amplification of the signal, and supplies the signal to the antenna 110. The receiving unit 107 receives the high frequency signal received by the antenna 110 and amplifies it with low noise, performs frequency conversion, and outputs a received signal having an intermediate frequency to the modulation / demodulation circuit 105.
[0028]
In the time scheduling circuit 104 of the base station, the data stored in each buffer BF is sequentially transmitted as shown in FIG. 5 so that the data of each subscriber station 111 is transmitted using the radio channel fairly. Assign to a time slot.
Actually, for the uplink, each subscriber station 111 transmits the number of frames corresponding to the amount of data stored in the transmission buffer on the subscriber station 111 to the base station as a line allocation request. The number of frames (Pr (n)) is managed on the management table 125, and time slots are allocated accordingly.
[0029]
For the downlink, since the base station has a transmission buffer for each subscriber station 111, the number of frames (Pt (n)) corresponding to the amount of data stored in each transmission buffer is stored on the management table 125. And assigns time slots accordingly.
That is, time slots are assigned in the order shown by the arrows in FIG.
[0030]
However, if a time slot is allocated so that all the data on the buffer is transmitted for each subscriber station 111, the subscriber station 111 with a lot of traffic will occupy the radio line for a longer time. Unfairness occurs between subscriber stations 111. Therefore, there is a limit on the amount of data that the time scheduling circuit 104 allocates in one process.
[0031]
By the way, the transmission distance between the base station and each subscriber station is generally different for each subscriber station. For example, for a subscriber station with a short transmission distance, it is possible to increase the transmission capacity of radio packets transmitted in one time slot by increasing the modulation degree than usual, thereby improving the peak speed.
On the other hand, for a subscriber station having a long transmission distance, there is a case where data errors occur frequently and establishment of a radio line is difficult with a normal modulation degree. For such a subscriber station, it is considered that if the modulation degree is lowered than usual, the occurrence of data errors is reduced, so that the establishment of a radio link is facilitated.
[0032]
Therefore, in this embodiment, it is assumed that the modulation format and modulation degree in the radio channel are independent for each subscriber station 111. Therefore, the transmission capacity per unit time that can be transmitted in one time slot is different for each subscriber station 111.
In such a situation, in time slot allocation, if the amount of data to be allocated by the time scheduling circuit 104 in a single process is uniformly determined for all the subscriber stations 111, the problem shown in FIG. 7 occurs.
[0033]
Therefore, in this embodiment, as shown in FIG. 3, the management table 125 manages the value of the maximum data amount Q (n) independent for each subscriber station 111. These maximum data amounts Q (n) correspond to the modulation format and modulation degree of each subscriber station 111. That is, a large value is assigned to the maximum data amount Q (n) for the subscriber station 111 adopting a modulation format or a modulation factor with a large transmission capacity per unit time, and a modulation format with a small transmission capacity per unit time. For the subscriber station 111 adopting the modulation factor, a small value is assigned to the maximum data amount Q (n).
[0034]
Actually, since the modulation format and the modulation degree are determined when the link for each subscriber station 111 is started up, a value corresponding to the modulation format and the modulation degree is determined immediately thereafter, and the maximum data amount Q is stored in the management table 125. Register and use with the subscriber station number as (n).
The time scheduling circuit 104 executes the processing shown in FIG. 1 and performs scheduling for time slot allocation according to the contents of the management table 125.
[0035]
The process shown in FIG. 1 will be described below. Here, it is assumed that the number of subscriber stations accommodated in the base station is Umax. The subscriber station number corresponds to the MAC-ID.
In step S10, an initial value 1 is assigned to the variable n. The value of the variable n corresponds to the number of the subscriber station 111. That is, for the first time, a time slot is assigned to the first subscriber station 111 (1).
[0036]
In step S11, the nth data, that is, the maximum data amount Q (n), the downlink data amount Pt (n), and the uplink data amount Pr (n) for the nth subscriber station 111 are acquired from the management table 125. .
In step S12, the downlink data amount Pt (n) (data amount in the transmission buffer on the base station) for the nth subscriber station 111 (n) and the maximum data amount Q for the nth subscriber station 111 (n). Compare with (n). If “Pt (n)> Q (n)”, the process proceeds to step S13. If “Pt (n) ≦ Q (n)”, the process proceeds to step S14.
[0037]
In step S13, scheduling is performed such that a data amount equal to Q (n) is transmitted to the nth subscriber station 111 (n). That is, the amount of data to which time slots are allocated in one process is limited to Q (n).
In step S14, scheduling is performed so as to transmit all the requested data (Pt (n)) to the nth subscriber station 111 (n).
[0038]
In step S15, the upstream data amount Pr (n) (data amount in the transmission buffer on the subscriber station) for the nth subscriber station 111 (n) and the maximum data amount for the nth subscriber station 111 (n). Compare Q (n). If “Pr (n)> Q (n)”, the process proceeds to step S16. If “Pr (n) ≦ Q (n)”, the process proceeds to step S17.
In step S16, scheduling is performed on the subscriber station 111 (n) so that the nth subscriber station 111 (n) transmits a data amount equal to Q (n). That is, the amount of data to which time slots are allocated in one process is limited to Q (n).
[0039]
In step S17, scheduling is performed on the subscriber station 111 (n) so that the nth subscriber station 111 (n) transmits all requested data (Pt (n)).
When scheduling for the nth subscriber station 111 (n) is completed, scheduling for the next subscriber station 111 (n + 1) is executed. When scheduling for the last subscriber station 111 (Umax) is completed, the process returns from step S18 to S10, and scheduling for the first subscriber station 111 (1) is executed again.
[0040]
By executing the processing shown in FIG. 1, for example, data of each subscriber station (user) is assigned to each time slot as shown in FIG. In FIG. 4, the horizontal axis represents time or time slot (TS), and the vertical axis represents the amount of data that can be transmitted in one time slot.
In this example, it is assumed that three users (that is, subscriber stations) A, B, and C each communicate with a base station. Each user has a different modulation scheme that can be applied due to a difference in propagation conditions. The amount of data that can be transmitted in one time slot is assumed when user A is M, user B is 2M, and user C is 3M.
[0041]
Therefore, in this example, M, 2M, and 3M are allocated to users A, B, and C, respectively, as the maximum data amount Q (n) of the management table 125.
In the example of FIG. 4, one time slot is assigned to all users A, B, and C in order. Accordingly, there is no unfairness among users regarding the assignment of wireless lines. In addition, since a data amount equal to the capacity that can be transmitted in each time slot is allocated to each time slot, useless transmission bandwidth does not occur. Therefore, each user's data can be transmitted efficiently using the time slot.
[0042]
【The invention's effect】
As described above, according to the present invention, even when the modulation format and the modulation degree in the radio channel are different for each subscriber station, the time slot with the maximum data amount individually determined for each subscriber station as an upper limit. Therefore, it is possible to prevent a specific user station from using a large number of time slots in succession and improve fairness among subscriber stations. Further, it is possible to prevent a useless transmission band from occurring in the time slot.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a line allocation operation in an embodiment.
FIG. 2 is a block diagram illustrating a configuration example of a fixed wireless access system.
FIG. 3 is a schematic diagram illustrating a configuration example of a management table.
FIG. 4 is a time chart showing an operation example of the present invention.
FIG. 5 is a schematic diagram showing a specific example of a downlink time slot allocation operation.
FIG. 6 is a schematic diagram showing a frame configuration generally used in TDMA / TDD communication.
FIG. 7 is a time chart showing an operation example of the prior art.
[Explanation of symbols]
101 network interface circuit 102 LLC control circuit 103 MAC control circuit 104 time scheduling circuit 105 modulation / demodulation circuit 106 high frequency circuit 107 reception unit 108 transmission unit 109 signal processing circuit 110 antenna 111 subscriber station 121 IP network 125 management table TS time slot BF buffer

Claims (2)

A radio channel is formed between one base station and a plurality of subscriber stations, and the same radio frequency is shared by a plurality of subscriber stations by time division multiple access / time division duplex. A channel allocation control method for allocating time slots used for communication of each subscriber station when the transmission capacity per unit time in each radio channel is determined independently for each subscriber station ,
Determining and holding the maximum value of the amount of data transmitted in one time slot between the buffer corresponding to each subscriber station and the wireless communication means according to the transmission rate of the corresponding subscriber station;
A time slot is assigned to each subscriber station according to round robin, and data transfer between the buffer and the wireless communication means related to data to be transmitted is determined corresponding to each subscriber station in the time slot. A line allocation control method, wherein scheduling is performed with the maximum value of the data amount as an upper limit. A radio channel is formed between one base station and a plurality of subscriber stations, and the same radio frequency is shared by a plurality of subscriber stations by time division multiple access / time division duplex. In a wireless communication system in which a transmission capacity per unit time is independently determined for each subscriber station, a line allocating device used by a base station to allocate time slots used for communication of each of a plurality of subscriber stations Because
A management table that determines and holds the maximum value of the amount of data transmitted in one time slot between the buffer corresponding to each subscriber station and the wireless communication means according to the transmission rate of the corresponding subscriber station ;
A time slot is assigned to each subscriber station according to round robin, and data transfer between the buffer and the wireless communication means related to data to be transmitted is determined corresponding to each subscriber station in the time slot. And a scheduling means for scheduling with the maximum value of the data amount as an upper limit.

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