JP3464162B2 - Wireless packet transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a communication system in which a plurality of channels exist as an uplink from a mobile station to a center station and which has a large propagation delay such as satellite communication. In particular, it relates to channel assignment in a wireless packet transmission system.

[0002]

2. Description of the Related Art (Prior Art 1) ICMA-PE (Idle-signal Casting Multiple Access with Part)
ialEcho) is adopted in the digital car phone system. FIG. 8 shows a sequence of channel assignment according to this method. Reference numerals (a) to (d) indicate the order of processing. The center station 2 monitors the upstream channel use status and broadcasts the free channel information 73 to each mobile station. Each mobile station 8
Numerals 1 and 87 access the vacant channels based on the vacant channel information from the center station to make channel reservations.

Specifically, channel reservation is performed by each mobile station 81,
This is performed by adding the packet length to the packet 91 to be transmitted by the 87 and transmitting the packet. The center station 2, which receives the packet without collision, sends a time corresponding to the packet length to all mobile stations including the mobile station,
Free channel information 73 indicating that the channel is reserved and partial echo 92 which is a part of the bit string of the packet are broadcast.

Since there is a delay before the free channel information 73 indicating that the channel has been reserved reaches the mobile stations 81 and 87, a plurality of mobile stations 81,
87 may transmit a packet. In this case, the mobile stations 81 and 87 compare the partial echo 92 with the packet transmitted by the local station to determine whether the channel reservation is successful. The mobile station 87, which has failed in the reservation, retransmits the packet 91 to another empty channel. In this method, since the channel reservation described above is performed for each packet, the channel reservation is also made for each packet generated after that. (Prior Art 2) ICMA-BR Method (Idle-sign
al Casting Multiple Access with Block Reservation)
FIG. 9 shows a sequence of channel allocation of the above. Reference numerals (a) to (d) indicate the order of processing. In this method, the center station 2 monitors the usage status of the upstream channel, and each mobile station 8
The free channel information 73 is broadcast to 1 and 87. Each of the mobile stations 81 and 87 accesses a free channel based on the free channel information 73 from the center station 2 to make a channel reservation.

Specifically, channel reservation is performed by each mobile station 81,
This is performed by transmitting the packet length 101 of the packet to be transmitted by 87 as a reservation packet. The center station 2, which has received the reservation packet without collision, broadcasts the free channel information 73 in which the channel is reserved for a time corresponding to the packet length.

Since there is a delay before the free channel information for which the channel has been reserved reaches the mobile stations 81 and 87, there is a possibility that a plurality of mobile stations 81 and 87 may transmit reservation packets to the channel. In this case, the center station 2 uses the channel 7 assigned individually to each mobile station 81, 87.
Return 6,84. In this method, since the channel reservation described above is performed for each packet, the channel reservation is also made for each packet generated after that.

FIG. 10 is a diagram showing a sequence when a second packet occurs during transmission of the first packet in the ICMA-BR system. Reference numerals (a) to (c) indicate the order of processing. However, as shown in FIG. 10, when the second packet 113 is generated during the transmission of the first packet 112, the mobile station 1 immediately after the transmission of the first packet 112, the packet length 114 of the second packet 113 Send and request additional transmission.

[0008]

In a wireless packet transmission system that broadcasts the channel usage status to each mobile station, free channel information that informs that the channel has been reserved after the center station detects a reservation packet The reservation collision cannot be completely eliminated because there is a delay due to the propagation delay until the mobile station reaches each mobile station.

Therefore, in the prior art 1, when a reservation collision occurs, the mobile station detects the reservation success or failure by the broadcast partial echo. However, in this method, a mobile station that fails in channel reservation makes a channel reservation again, resulting in a large delay.

On the other hand, in the prior art 2, the mobile stations that have collided with the channel reservation do not need to make the channel reservation again because the center station individually allocates the channels. However, while the prior art 1 makes a channel reservation at the same time when a packet is transmitted, the prior art 2 makes a packet transmission after the channel is reserved, so that the packet is delayed by the propagation delay time between the mobile station and the center station. Will be delayed.

FIG. 11 is a diagram showing timing of channel reservation and channel release in the ICMA-PE system. FIG. 12 is a diagram showing timings of channel reservation and channel release in the ICMA-BR system. Next, assuming bursty traffic such as the Internet in which packets are concentrated in a certain time and the packet length and the packet generation interval are not constant, the conventional technique 1
Then, as shown in FIG. 11, the channel reservation 41 and the channel release 42 are repeated for each data packet. Also,
According to the conventional technique 2, as shown in FIG. 12, when the time interval between the packet 51 and the packet 52 is small, the channel reservation 53 and the release 54 are not repeated, but when the processing of the packet 55 is completed, the next packet 51 is released. If has not arrived, channel reservation 53 and release 57 are again repeated.

For the above reasons, when the prior arts 1 and 2 are applied to a system such as satellite communication in which the propagation delay between the center station and the mobile station is large, the influence of the propagation delay due to the channel reservation becomes large. Therefore, the throughput is reduced.

Further, for traffic such as the Internet, the number of times of channel reservation is increased and the influence of propagation delay is increased, so that the throughput is lowered.

The present invention has been made against such a background, and it is possible to simultaneously transmit a data packet and reserve a channel, and to separately channel all mobile stations that have collided. It is an object of the present invention to provide a wireless packet transmission system capable of allocating packets. An object of the present invention is to provide a wireless packet transmission system that does not repeat channel reservation and release even in the case of bursty traffic such as the Internet. An object of the present invention is to provide a wireless packet transmission system in which throughput does not decrease even when applied to wireless communication with a large propagation delay between a center station and a mobile station.

[0015]

SUMMARY OF THE INVENTION The present invention comprises a plurality of mobile stations and one center station connected to the mobile stations via a radio line, and an uplink line from the mobile station to the center station. In the wireless packet transmission system, a plurality of channels are set in the center station, and the center station includes means for monitoring the usage status of the upstream channel and means for broadcasting free channel information to the mobile station.

Here, the feature of the present invention resides in that the mobile station adds a reservation flag to the channel selected by the means for selecting a channel in accordance with the empty channel information at the start of communication. Transmitting the first packet, the center station stores the combination of the channel used by the mobile station and the mobile station number assigned to each mobile station, and the mobile station. Means for detecting a reservation flag added to the first packet transmitted from the mobile station, and the channel used by the mobile station for transmitting the first packet according to the combination stored in the storing means is not reserved. Assign the channel to the mobile station and select another channel from unused channels when the channel is reserved by another mobile station. The mobile station comprises means for allocating to the mobile station and means for notifying the mobile station of the allocated channel as a notification channel. And a means for transmitting a release packet to the center station when the packet to be transmitted is completed, the center station detecting means for detecting the release packet transmitted from the mobile station. According to the detection result of the detecting means, the corresponding channel is released and the combination of the channel and the mobile station number is deleted from the storing means.

As described above, by transmitting the packet in which the information to be transmitted is written as the first packet, the delay time can be reduced as compared with the conventional technique. In addition, since the mobile station can secure the channel from the first packet to the release packet, it is not necessary to reserve and release the channel for each packet when multiple packets are transmitted at short intervals. The delay time can be reduced as compared with the related art.

The broadcasting means may comprise means for broadcasting at regular time intervals. In this case, since the mobile station knows in advance the time slot in which the free channel information is broadcast, it may perform the operation of receiving the free channel information only in that time slot. By this means, the reception operation of the free channel information can be completely stopped during the other time period when the broadcast is not performed, so that the processing procedure of the free channel information can be simplified. Further, even if the mobile station fails to receive the free channel information due to deterioration of the wireless channel quality, the free channel information can be received again at the next broadcast of the free channel information.
It is possible to cope with the deterioration of the wireless line quality.

Alternatively, the broadcasting means may comprise means for broadcasting immediately after the free channel information in the center station changes. In this case, the mobile station must always continue the operation of receiving the empty channel information, but the center station needs to broadcast only when the empty channel information changes, so that the empty channel information is transmitted. The procedure can be simplified.

The means for transmitting the release packet may include means for transmitting when there is no packet to be transmitted to the mobile station for a predetermined time or longer. In this case, the mobile station can set the optimum release packet transmission timing for the mobile station by statistically setting the predetermined time from the packet transfer pattern that the mobile station frequently performs.

Alternatively, a means for accumulating packets to be transmitted to the mobile station is provided in advance, and the means for transmitting the release packet is such that the number of packets accumulated in the accumulating means is equal to or less than a predetermined number after the start of communication. It can be provided with a means for transmitting when it is reduced. In this case, the release packet can be transmitted in advance before the transfer of the packet is completed, and the delay time required for the release processing in the center station can be compensated. As a result, when the transfer of the packet from the mobile station is completed, the invalid channel hold time can be extremely shortened.
The channel can be used effectively.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention will be described with reference to FIGS. FIG. 1 is a diagram showing a configuration of a wireless packet transmission system of the present invention. FIG. 2 is a block diagram of the essential parts of a mobile station according to the first embodiment of the present invention. FIG. 3 is a block diagram of a main part of the center device. FIG. 4 is a block diagram of the essential parts of a mobile station according to the second embodiment of the present invention.

As shown in FIG. 1, the present invention comprises a plurality of mobile stations 1 and one center station 2 connected to the mobile stations 1 via a radio line. A plurality of channels are set in the uplink to the center station 2, and as shown in FIG. 3, the center station 2 monitors the usage state of the uplink channel and broadcasts the free channel information to the mobile station 1 to transmit the free channel information. A wireless packet transmission system including a unit 331.

Here, the feature of the present invention is that the mobile station 1, as shown in FIG. 2, has a free channel information processing unit 222 which is a means for selecting a channel according to the free channel information at the start of communication. The center station 2 moves as shown in FIG. 3, including a reservation flag addition unit 21 that is a means for transmitting a first packet with a reservation flag added to the channel selected by the free channel information processing unit 222. A combination storage unit 37 for storing a combination of a channel used by the station 1 and a mobile station number assigned to each mobile station 1, and a reservation added to the first packet transmitted from the mobile station 1. According to the combination stored in the combination storage unit 37 and the flag control unit 36 that is a unit for detecting a flag, the channel used by the mobile station 1 to transmit the first packet is When booking when assigned the channel to the mobile station 1 the channel is reserved by another mobile station 1 is a means for assigning to the mobile station 1 separately select a channel among the unused channels combination determining section 3
8 and a channel information transmission unit 39 that is means for notifying the mobile station 1 of the assigned channel as a notification channel.
As shown in FIG. 2, the mobile station 1 includes a channel storage unit 27 that is a means for transmitting a packet following the first packet to a notification channel from the center station 2 for the first packet, and When the packet to be processed is completed, the center station 2 is provided with a release packet generating unit 26 which is a unit for transmitting the release packet. In the center station 2, as shown in FIG.
The release packet transmitted from the combination storage unit 3 is detected.
7 is to release the corresponding channel according to the detection result of the flag control unit 36 and delete the combination of the channel and the mobile station number.

Free channel information transmitter 331 shown in FIG.
Broadcasts idle channel information at regular time intervals, but in another embodiment, it may be broadcast immediately after the idle channel information in the center station 2 changes.

The release packet generator 26 shown in FIG. 2 transmits a release packet to the mobile station 1 when there is no packet to be transmitted for a predetermined period of time or longer, but as another embodiment, it is shown in FIG. As described above, the buffer 6 which is a means for accumulating the packets to be transmitted in advance is provided, and the release packet generation unit 26 releases the release packet when the number of packets accumulated in the buffer 6 is reduced to a certain number or less after the start of communication. To send.

[0027]

(First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a diagram showing a channel reservation and channel release sequence in the present invention. FIG. 6 is a diagram showing a sequence when a plurality of mobile stations according to the present invention cause channel reservation collision. FIG. 7 is a diagram showing timings of channel reservation and channel release in the present invention.

As shown in FIG. 1, the wireless packet transmission system of the present invention comprises a plurality of mobile stations 1, a center station 2 and a satellite 3. The center station 2 is connected via a GW (gateway) 4. Connected to the Internet 5. FDMA is used for the uplink from the mobile station 1 to the center station 2.
(Frequency division multiple access) is used, and TDM (time division multiplexing) is used for the downlink from the center station 2 to the mobile station 1.

Next, the sequence of the channel allocation method of the present invention is shown in FIG. Reference numerals (a) to (e) indicate the order of processing. Uplink frequencies 71 are set from channel # 1 to channel #N, and center station 2 broadcasts free channel information 73, which is information about the usage status of the channels, to all mobile stations 1. The mobile station 1 selects a channel based on the free channel information 73, adds a reservation flag 75 to the packet, and transmits the packet. On the other hand, the center station 2 returns the assigned original channel number 76 to indicate that the channel reservation is successful.
The mobile station 1 transmits the packet 77 generated after that to the returned channel. Further, the mobile station 1 releases the release flag 7 when the packet does not occur in the own station for a certain time or longer.
The packet assigned 8 is transmitted to the center station 2 to release the channel.

By the way, since there is a propagation delay between when the center station 2 detects the reservation packet and when the free channel information 73 for which the channel has been reserved reaches each mobile station 1, there is a plurality of mobile stations 1. May cause reservation conflicts for the same channel. The sequence at this time is shown in FIG.
Shown in. Reference numerals (a) to (b) indicate the order of processing. The center station 2 which receives the packet 76 with the reservation flags of a plurality of mobile stations 81 and 87 from the same channel returns the original channel number 76 to the mobile station 81 to which the packet arrived first, and Thereafter, another channel number 84 is assigned and returned to the mobile station 87 where the packet arrives.

The timing of channel reservation and channel release of the mobile station 1 is shown in FIG. Time zone when packets are concentrated and bursty like the Internet, that is, ON
Assuming the traffic in which the time zone 61 of 1 and the time zone of non-occurrence, that is, the time zone 62 of OFF are repeated, the channel reservation 63 is performed in the first packet of the time zone 61 of ON.
In the OFF time zone 62, it is detected that the packet does not occur in the local station for a certain time or longer, and the channel is released 65. Therefore, unlike the prior art 1 and the prior art 2, channel reservation and channel release are not repeated even in the ON time zone.

Next, the detailed configuration of the mobile station 1 is shown in FIG. The mobile station 1 inputs the packet from the packet generation source 22 of the mobile station 1 to the modulator 24 via the packet sensor 23. The packet sensor 23 clears the timer value of the timer unit 25 every time a packet passes.

On the other hand, the timer unit 25 increases the timer value every moment, and when the timer value reaches a certain value, the timer value is cleared and the release packet generating unit 26 generates a packet to which a release flag is added. The packet from the packet sensor 23 and the packet from the release packet generator 26 are input to the modulator 24. At this time, the channel used by the modulator 24 is the one stored in the channel storage 27. Then, the modulated packet is transmitted from the small antenna 28.

The demodulation unit 29 demodulates the signal received from the small antenna 28, and the packet contents are decoded by the packet control unit 224. When the contents are the assigned channel number or free channel information, they are input to the channel information processing unit 221 and the free channel information processing unit 222, respectively, and in other cases, they are input to the packet processing unit 223. It

The channel information processing unit 221 stores the channel in the channel storage unit 27 when the assigned channel number and the channel number stored in the channel storage unit 27 are different. The empty channel information processing unit 222 randomly selects a channel from the empty channel information and stores the channel in the channel storage unit 27 when nothing is stored in the channel storage unit 27, and at the same time, the reservation flag addition unit. The reservation flag generated in 21 is added to the packet from the packet generation source 22.

Next, the detailed configuration of the center station 2 is shown in FIG. The signal received by the large antenna 31 is demodulated by the demodulation group unit 32.
To the channel used for transmission from the mobile station 1 (k is a channel number, 1 to N
The packet is demodulated by an arbitrary natural number (33), and the demodulated packet is extracted from the center station 2 to the outside by the packet input / output unit 35 via the packet reception control unit 34. In the packet reception control unit 34, when the release flag or the reservation flag is attached to the packet, the combination of the channel number and the mobile station number assigned to the mobile station is
Input to the flag control unit 36. When the release flag is input to the flag control unit 36, the combination is deleted from the combination storage unit 37.

When the reservation flag is input, the combination determination unit 38 determines whether the combination is stored in the combination storage unit 37, and if not stored, the combination is stored, and another combination is already stored. If so, after selecting a channel from the unreserved channels, a new combination with this selected channel is stored, and at the same time the channel information transmitter 39 transmits the finally selected channel to the mobile station. To do. Also, the free channel information transmission unit 33
1 retrieves an unreserved channel from the combination storage unit 37,
Free channel information is created and broadcasted to all mobile stations 1 at certain time intervals. The packet input from the packet input / output unit 35 is controlled by the packet from the channel information transmitting unit 39 and the idle channel information transmitting unit 331 and the packet transmission control unit 332, and the modulator unit 3
After being modulated by 33, it is transmitted from the large antenna 31. (Second Embodiment) A mobile station configuration according to the second embodiment of the present invention will be described with reference to FIG. In the second embodiment of the present invention, the mobile station 1 is provided with the buffer 6 and the queue length detection unit 7, and the release packet generation unit 26 reduces the number of packets accumulated in the buffer 6 to a certain number or less after the start of communication. Send a release packet to.

By this means, it is possible to transmit the release packet in advance before the transfer of the packet is completed and compensate for the delay time required for the release processing in the center station 2. Therefore, when the transfer of the packet from the mobile station 1 is completed, the invalid channel holding time can be extremely shortened, so that the channel can be effectively used.

[0039]

As described above, according to the present invention, it is possible to simultaneously transmit a data packet and reserve a channel, and individually allocate channels to all mobile stations that have collided. be able to.
As a result, it is possible to realize a wireless packet transmission system that does not repeat channel reservation and release even in the case of bursty traffic such as the Internet. Therefore, particularly in a system such as satellite communication having a large propagation delay, high throughput can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a wireless packet transmission system of the present invention.

FIG. 2 is a block diagram of a main part of a mobile station according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a main part of a center device.

FIG. 4 is a block diagram of a main part of a mobile station according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a channel reservation and channel release sequence according to the present invention.

FIG. 6 is a diagram showing a sequence when a plurality of mobile stations cause a channel reservation collision according to the present invention.

FIG. 7 is a diagram showing timings of channel reservation and channel release in the present invention.

FIG. 8 is a diagram showing a channel reservation sequence in the ICMA-PA system.

FIG. 9 is a diagram showing a channel reservation sequence in the ICMA-BR system.

FIG. 10 is a diagram showing a sequence when a second packet occurs during transmission of the first packet in the ICMA-BR system.

FIG. 11 is a diagram showing timing of channel reservation and channel release in the ICMA-PE system.

FIG. 12 is a diagram showing timing of channel reservation and channel release in the ICMA-BR system.

[Explanation of symbols]

1, 81, 87 mobile stations 2 center stations 3 satellites 4 gateway 5 Internet 6 buffers 7 Queue length detector 21 Reservation flag addition section 22 Packet generation source 23 Packet sensor 24 Modulator 25 Timer section 26 Release Packet Generator 27 channel storage 28 small antenna 29 Demodulator 31 large antenna 32 demodulation group section 33 Demodulator 34 Packet reception control unit 35 Packet input / output unit 36 flag control unit 37 Combination Storage Unit 38 Combination determination unit 39 Channel information transmitter 41, 53, 63 Reserved 42, 54, 57, 65 Release 51, 52, 55, 77, 91 packets 61 ON time zone 62 OFF time 71 Uplink frequency 73 Free channel information 75 Reserved flag 76 channel # 3 78 Release flag 84 channel # 2 92 Partial Echo 101 packet length 111 First packet length 112 First packet 113 Second packet 114 Second packet length 221 channel information processing unit 222 Free channel information processing unit 223 Packet processing unit 224 Packet control unit 331 Free channel information transmitter 332 Packet transmission control unit 333 Modulator section

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-209956 (JP, A) JP-A-10-135928 (JP, A) JP-A-62-230231 (JP, A) JP-A-4- 354221 (JP, A) JP-A-7-154363 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 12/28 300 H04B 7/204

Claims (5)

(57) [Claims] 1. A mobile station comprising a plurality of mobile stations and one center station connected to the mobile station via a radio line, wherein a plurality of channels are set in an uplink from the mobile station to the center station, In the wireless packet transmission system, wherein the center station includes means for monitoring the usage status of an upstream channel and means for broadcasting free channel information to the mobile station, the mobile station is configured to check the free channel information at the start of communication. Therefore, it is provided with means for selecting a channel and means for transmitting a first packet in which a reservation flag is added to the channel selected by the selecting means, wherein the center station has the channel used by the mobile station and the channel used by the mobile station. Means for storing a combination with a mobile station number assigned to each mobile station, and a reservation flag added to the first packet transmitted from the mobile station When the channel used by the mobile station for transmitting the first packet is not reserved according to the combination stored in the storage means and the storage means, the channel is assigned to the mobile station and the channel is moved by another mobile station. The mobile station further comprises means for separately selecting a channel from unused channels when it is reserved by the station and assigning it to the mobile station, and means for notifying the mobile station of the assigned channel as a notification channel. Comprises means for transmitting a packet following the first packet to the notification channel from the center station for the first packet, and means for transmitting a release packet to the center station when the packet to be transmitted is completed. The center station detects a release packet transmitted from the mobile station, and a means for detecting the release packet. The wireless packet transmission system is provided with means for releasing the corresponding channel according to the detection result and deleting the combination of the channel and the mobile station number from the means for storing. 2. The broadcasting means comprises means for broadcasting at regular time intervals.
The described wireless packet transmission system. 3. The wireless packet transmission system according to claim 1, wherein the means for broadcasting comprises means for broadcasting immediately after the free channel information in the center station changes. 4. The wireless packet transmission system according to claim 1, wherein the means for transmitting the release packet comprises means for transmitting when there is no packet to be transmitted to the mobile station for a predetermined time or longer. 5. The mobile station is provided with means for accumulating packets to be transmitted in advance, and the means for transmitting the release packet is such that the number of packets accumulated in the accumulating means is a fixed number after the start of communication. The wireless packet transmission system according to claim 1, further comprising means for transmitting when reduced below.