JP2003199148A - Channel assignment control method and channel assignment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a channel assignment control method and a channel assignment apparatus capable of enhancing the utilizing efficiency of a time slot and of channel assignment with high impartiality when a transmission capacity of a wireless packet is decided independently of each subscriber station. <P>SOLUTION: This invention provides the channel assignment control method that is characterized in that the method forms a wireless channel between one base station and a plurality of subscriber stations respectively, allows a plurality of the subscriber stations to share the same wireless frequency by time division multiple access/time division duplex, and allows the base station to assign a time slot used for communication by each of a plurality of the subscriber stations, when a transmission capacity per unit time in each wireless channel is decided independently of each subscriber station, a maximum data amount Q(n) assigned to one time slot is individually decided for each subscriber station depending on the transmission capacity per unit time of each subscriber station. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to TDMA (Time D).
ivision Multiple Access: Time division multiple access) / TDD
Using (Time Division Duplex) method,
P- in which one base station and a plurality of subscriber stations perform wireless communication
The present invention relates to a line allocation control method and a line allocation device used in an MP (Point-Multi Point) type fixed wireless access system, and in particular, the transmission capacity of a wireless packet determined by the modulation degree and the modulation format is independent for each subscriber station. The present invention relates to a line allocation control method and a line allocation device applied when it is determined.

[0002]

2. Description of the Related Art In a P-MP type fixed wireless access system, a wireless line is formed between one base station and a plurality of subscriber stations. Also, TDMA / TDD
In a system that communicates by using, one radio frequency is shared by a base station and a plurality of subscriber stations, the base station allocates a time slot to each subscriber station as needed, and each required subscriber Secure the communication channel of the station.

In such a system, since the capacity which can be transmitted by one radio frequency is limited in advance,
In the wireless line between the base station and each subscriber station, it is necessary to appropriately allocate the communication channel used by each subscriber station. Especially, when the traffic of a large number of subscriber stations is concentrated, the line allocation is delayed in response to the request from each subscriber station, and the transmission delay between the base station and the subscriber stations is greatly increased. May increase. In such cases, fairness among subscriber stations becomes a problem.

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 implemented by time scheduling in the base station. When performing round-robin control, buffers are provided for each subscriber station for traffic in the direction from the base station to the subscriber station (downlink) and traffic in the direction from the subscriber station to the base station (uplink). assign. Then, in accordance with a predetermined order so as to ensure fairness, the data accumulated in the buffer is sequentially allocated to the time slots and transmitted with the predetermined data amount Q as the maximum value.

[0005]

In a general fixed wireless access system or the like, in the wireless line between the base station and each subscriber station, the modulation format and the degree of modulation of the wireless packet are in all subscriber stations. It is supposed to be the same.
In such an assumption, the transmission capacity per unit time of the wireless line is the same for all subscriber stations.
By implementing the round robin control, fairness among subscriber stations can be ensured and lines can be efficiently allocated to each subscriber station.

However, generally, 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 improve the peak speed by increasing the modulation degree more than usual. On the other hand, with respect to a subscriber station with a long transmission distance, there are cases in which data errors occur at a normal modulation degree and it is difficult to establish a wireless line. For such a subscriber station, if the modulation degree is made lower than usual, the occurrence of data errors is reduced, and it is considered that the establishment of a wireless line is facilitated.

As described above, when the so-called link adaptation method in which the transmission capacity of the wireless packet is independently determined for each subscriber station is adopted, 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 is different for each subscriber station, if the maximum transmission capacity (Q) is uniformly defined as in the round-robin control, the use efficiency of time slots will deteriorate.

A specific example will be described with reference to FIG.
In FIG. 7, 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. Also, each user has a different applicable modulation method due to a difference in propagation conditions and the like. And
The amount of data that can be transmitted in one time slot is assumed to be Q for user A, 2Q for user B, and 3Q for user C.

FIG. 7A shows the case where the maximum transmission data amount assigned by the round robin control of time scheduling is uniformly Q. Figure 7 (a)
In the above example, although it is possible to transmit a larger amount of data to users B and C, only Q can transmit the amount of data in one time slot, and therefore it can be seen that the transmission band is wasted.

FIG. 7B shows the case where the maximum transmission data amount assigned by the round robin control of time scheduling is uniformly 3Q. Figure 7
In the example of (b), a useless transmission band is generated for the user B. Moreover, since most of the time slots are assigned to the user A, it is understood that the throughputs of the user B and the user C are not improved.

According to the present invention, when the transmission capacity of a wireless packet is independently determined for each subscriber station, the efficiency of use of time slots is improved and a circuit allocation control method capable of highly fair circuit allocation. And a line allocation device.

[0012]

According to a first aspect of the present invention, a radio line is formed between one base station and a plurality of subscriber stations, and the same radio frequency is provided by time division multiple access / time division duplex. A channel allocation control method for sharing time among a plurality of subscriber stations and for allocating a time slot used by a base station for each communication of a plurality of subscriber stations, and a transmission capacity per unit time in each wireless channel. When the number is decided independently for each subscriber station, the maximum data amount to be assigned to one time slot must be individually determined for each subscriber station according to the transmission capacity per unit time of each subscriber station. Is characterized by.

According to the first aspect of the present invention, when assigning a wireless line to each subscriber station, data is assigned to each time slot with the maximum data amount individually set for each subscriber station as an upper limit. That is, 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 assigned to a time slot in a single process, so that the data assigned in that process is assigned to one All can be transmitted in time slots.

Therefore, unlike the example shown in FIG. 7B, the same user (A) does not continuously use a plurality of time slots, and the fairness among the subscriber stations can be improved. Further, since a large amount of data corresponding to the transmission capacity is assigned to a subscriber station with a high degree of modulation and a large transmission capacity of a wireless line in one process, when the transmission capacity of one time slot is large. Can transmit a large amount of data in one time slot, and can prevent a wasteful transmission band from being generated in the time slot.

According to a second aspect of the present invention, a radio line 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 shared and is determined independently for each subscriber station, the base station assigns a time slot used for each communication of a plurality of subscriber stations. A line assignment device used for assigning, a management table that independently holds, for each subscriber station, the maximum amount of data associated with the transmission capacity per unit time in the radio line of each subscriber station,
Scheduling for sequentially allocating the data accumulated in the buffer allocated to each subscriber station to time slots and determining the maximum amount of data to be allocated to one time slot for each subscriber station based on the contents of the management table. And means are provided.

According to another aspect of the present invention, the maximum data amount associated with the transmission capacity per unit time in the wireless line of each subscriber station is stored in the management table independently for each subscriber station. The maximum amount of data to be allocated to one time slot can be determined for each subscriber station.

Therefore, as in the first aspect, the fairness among the subscriber stations can be enhanced and useless transmission band can be prevented from occurring in each time slot.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a line allocation control method and a line allocation device of the present invention will be described with reference to FIGS. This form corresponds to all the claims.

FIG. 1 is a flow chart showing the line allocation operation in this embodiment. FIG. 2 is a block diagram showing a configuration example of a fixed wireless access system. FIG. 3 is a schematic diagram showing 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. Figure 6
FIG. 3 is a schematic diagram showing the structure of a frame generally used in TDMA / TDD communication.

In this embodiment, the management table and the scheduling means of claim 2 are respectively the management table 12
5 and the time scheduling circuit 104.
In this form, it is assumed that the present invention is applied to a fixed wireless access system as shown in FIG. The base station embodying the present invention forms a wireless line with each of a plurality of subscriber stations 111, and relays signals between each subscriber station 111 and the IP network 121. In addition, in this example, the radio frequency in the quasi-millimeter wave band is used in the radio communication between the base station and the subscriber station 111.

As a communication method between the base station and the subscriber station 111, TDMA / TDD is adopted. 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 needed. Also, 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.

Actually, communication is performed using a frame having a structure 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 transmitting broadcast information transmitted from the base station to the subscriber station 111 on the downlink. The time slot TSB is used by the base station to transmit user data to the corresponding subscriber station 111 in the downlink. The time slot TSC is used by each subscriber station 111 to transmit user data to the base station on the uplink. The time slot TSD is used for random access in the upstream direction from the subscriber station 111.

As shown in FIG. 2, the base station includes an antenna 1
A high frequency circuit 106 and a signal processing circuit 109 are provided. Further, the high frequency circuit 106 is provided with a receiver 107 and a transmitter 108. Signal processing circuit 1 of base station
09 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.

The base station uses an IP (Internet Protocol) network 121 via a network interface circuit 101.
Connected with. The LLC control circuit 102 has a built-in buffer circuit for temporarily storing transmission / reception signal data. Further, the LLC control circuit 102 has a function of adding a sequence number used for retransmission control and a tag for identifying a service class of data.

The MAC control circuit 103 applies a device identification ID (MAC) at the layer 2 level to the data of the transmission / reception signal.
-ID) is assigned and a time slot for information transmission is dynamically assigned using the time scheduling circuit 104.

The modulation / demodulation circuit 105 modulates a signal to be transmitted and demodulates a received signal. That is, the baseband signal output from the MAC control circuit 103 is modulated by the modulation / demodulation circuit 105, and the transmission unit 108 of the high frequency circuit 106.
Applied to. The reception signal (intermediate frequency signal) output from the receiving unit 107 of the high frequency circuit 106 is the modulation / demodulation circuit 10.
MAC control circuit 1 demodulated by 5 and used as a baseband signal
03 is applied.

The transmitter 108 frequency-converts the intermediate frequency signal input from the modulation / demodulation circuit 105 into a radio frequency, amplifies the power of the signal, and supplies the amplified signal to the antenna 110. The receiving unit 107 inputs the high frequency signal received by the antenna 110, performs low noise amplification, performs frequency conversion, and modulates / demodulates the intermediate frequency received signal.
Output to.

Base station time scheduling circuit 10
4, the data accumulated in each buffer BF is sequentially allocated to each time slot as shown in FIG. 5 so that the data of each subscriber station 111 is transmitted fairly using the wireless line. Actually, for the uplink, each subscriber station 111 transmits the number of frames corresponding to the amount of data accumulated in the transmission buffer on the subscriber station 111 to the base station as a channel allocation request, so that the base station is requested. The number of frames (Pr (n)) is managed on the management table 125, and the time slot is allocated according to the management.

For the downlink, the subscriber station 111
Since the base station is provided with each transmission buffer, the number of frames (Pt (n)) according to the amount of data accumulated in each transmission buffer is managed on the management table 125, and time slots are allocated accordingly. I do. That is, time slot allocation is performed in the order shown by the arrows in FIG.

However, if a time slot is assigned to each subscriber station 111 so that all the data in the buffer is transmitted, the subscriber station 111 with a lot of traffic occupies the radio line for a longer time. Therefore, inequity occurs among the subscriber stations 111. Therefore, the amount of data that the time scheduling circuit 104 allocates in one process is limited.

Incidentally, 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 the wireless packet transmitted in one time slot and increase the peak speed by increasing the modulation degree more than usual. On the other hand, with respect to a subscriber station with a long transmission distance, there are cases in which data errors occur at a normal modulation degree and it is difficult to establish a wireless line. For such a subscriber station, if the modulation degree is made lower than usual, the occurrence of data errors is reduced, and it is considered that the establishment of a wireless line is facilitated.

Therefore, in this embodiment, it is assumed that the modulation format and the modulation degree in the wireless line are independent for each subscriber station 111. Therefore, the transmission capacity per unit time that can be transmitted in one time slot differs for each subscriber station 111. In such a circumstance, the time scheduling circuit 10 may be used for time slot allocation.
If the data amount 4 is uniformly assigned to all subscriber stations 111 in a single process, the problem shown in FIG. 7 arises.

Therefore, in this embodiment, as shown in FIG. 3, the management table 125 manages the value of the maximum data amount Q (n) which is independent for each subscriber station 111. These maximum data amounts Q (n) correspond to the modulation format and the 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 that employs a modulation format or a modulation degree with a large transmission capacity per unit time, and a modulation format with a small transmission capacity per unit time. A small value is assigned to the maximum data amount Q (n) with respect to the subscriber station 111 that adopts the modulation factor.

In practice, since the modulation format and the modulation degree are determined at the time of link activation for each subscriber station 111, a value according to the modulation format and the modulation degree is determined immediately after that and the maximum value is stored in the management table 125. The data amount Q (n) is registered and used together with the subscriber station number. Time scheduling circuit 1
04 executes the processing shown in FIG.
Scheduling for time slot allocation is performed according to the contents of.

The processing shown in FIG. 1 will be described below.
Note that here, the number of subscriber stations accommodated in the base station is Umax.
The case of is assumed. The subscriber station number is MAC-
It corresponds to the 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, the first subscriber station 111 is the first
Allocate time slots to (1).

In step S11, the management table 125
From the nth data, that is, the nth subscriber station 111
The maximum data amount Q (n), the downlink data amount Pt (n), and the uplink data amount Pr (n) are obtained. Step S12
Then, 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 (n for the nth subscriber station 111 (n). ) With. If "Pt (n)> Q (n)", the process proceeds to step S13, and if "Pt (n) ≤Q (n)", the process proceeds to step S14.

In step S13, the n-th subscriber station 1
The scheduling is performed so that the data amount equal to Q (n) is transmitted to 11 (n). That is, the amount of data to which the time slot is assigned in one process is limited to Q (n). In step S14, the n-th subscriber station 111 (n)
To all the requested data (Pt (n)).

In step S15, the n-th subscriber station 1
Uplink data amount Pr (n) for 11 (n) (data amount in the transmission buffer on the subscriber station) and the nth subscriber station 1
The maximum data amount Q (n) for 11 (n) is compared. "P
If "r (n)> Q (n)", the process proceeds to step S16 and "P
If r (n) ≦ Q (n) ”, the process proceeds to step S17. In step S16, scheduling is performed for 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 the time slot is assigned in one process is limited to Q (n).

In step S17, the n-th subscriber station 1
11 (n) schedules the subscriber station 111 (n) to transmit all requested data (Pt (n)). When the scheduling for the nth subscriber station 111 (n) is completed, the scheduling for the next subscriber station 111 (n + 1) is executed. When the scheduling for the last subscriber station 111 (Umax) is completed, the process returns from step S18 to S10, and the scheduling for the first subscriber station 111 (1) is executed again.

By executing the processing shown in FIG. 1, data of each subscriber station (user) is assigned to each time slot as shown in FIG. 4, for example. In FIG.
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, 3 users (ie subscriber stations)
It is assumed that A, B, and C each communicate with the base station. Also, each user has a different applicable modulation method due to a difference in propagation conditions and the like. The amount of data that can be transmitted in one time slot is assumed to be M for user A, 2M for user B, and 3M for user C.

Therefore, in this example, M, 2M, and 3M are assigned to the 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 equally assigned to all the users A, B, and C in order. Therefore, there is no unfairness among the users regarding the allocation of the wireless line. Further, since a data amount equal to the transmittable capacity in each time slot is assigned to each time slot, no useless transmission band is generated. Therefore, the data of each user can be efficiently transmitted by using the time slot.

[0042]

As described above, according to the present invention, even if the modulation format and the modulation degree in the wireless line are different for each subscriber station, the maximum data amount individually determined for each subscriber station can be obtained. As an upper limit, data is allocated to the time slots, so that it is possible to prevent a specific user station from continuously using a large number of time slots and improve fairness among subscriber stations. Further, it is possible to prevent a wasteful transmission band from being generated in the time slot.

[Brief description of drawings]

FIG. 1 is a flowchart showing a line allocation operation in an embodiment.

FIG. 2 is a block diagram showing a configuration example of a fixed wireless access system.

FIG. 3 is a schematic diagram showing 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 configuration of a frame generally used in TDMA / TDD communication.

FIG. 7 is a time chart showing an operation example of a conventional technique.

[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 Receiver 108 transmitter 109 signal processing circuit 110 antenna 111 Subscriber station 121 IP network 125 management table TS time slot BF buffer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fumihiro Honma             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5K028 AA11 BB06 CC02 CC05 KK12                       LL12 MM05 RR02                 5K033 AA01 CA11 CB06 CB13 DA17                 5K067 AA12 CC04 DD17 EE22 EE71                       GG06 HH22 HH23

Claims (2)

[Claims] 1. A radio line 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 circuit allocation control method for a base station to allocate a time slot used for communication of each of a plurality of subscriber stations, wherein the transmission capacity per unit time in each wireless channel is independent for each subscriber station. When determined, the maximum data amount to be assigned to one time slot is individually set for each subscriber station according to the transmission capacity per unit time of each subscriber station. 2. A radio line 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 independently determined for each subscriber station, a base station allocates a time slot used for each communication of a plurality of subscriber stations. It is a circuit allocation device to be used, and it has a management table that holds the maximum amount of data that corresponds to the transmission capacity per unit time in the wireless line of each subscriber station independently for each subscriber station, and for each subscriber station. The data accumulated in the allocated buffers are sequentially allocated to the time slots, and the maximum data amount allocated to one time slot is determined based on the contents of the management table. Line allocation apparatus characterized by comprising a scheduling means for determining for each subscriber station.