JP2855100B2 - 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 relates to a wireless packet transmission system, and more particularly to a wireless packet transmission system that employs a random access method as an access method from a plurality of mobile stations to a base station.

[0002]

2. Description of the Related Art Conventionally, an Aloha system, a slot Aloha system, a reservation system, and the like have been known as a multiple access system for performing communication from a plurality of mobile stations to a base station in a wireless packet transmission using a common access channel. The Aloha system and the slot Aloha system are random access systems.If a plurality of packets arrive from the mobile station at the same time, packet collision occurs in the base station, and in the worst case, all packets are discarded. Will be lost.

Therefore, as a method of avoiding packet collision in the base station, a plurality of directional antennas having different directivity directions are arranged in the base station, and packets are received by switching the directional antennas. A method has been proposed to improve the efficiency of
A Slotted ALOHA Packet Radio System with Multiple
Antennas and Receivers ”IEEE TRASACTION ON VEHICUL
AR TECHNOLOGY, VOL.39, NO.3, August 1990, 218
226). Hereinafter, this method is referred to as a “slot antenna switching method”.

FIG. 7 is a diagram for explaining an antenna beam of a directional antenna of a base station in the slot antenna switching system. In this figure, the base station 10
At 0, a directional antenna group 101 is installed. The directional antenna group 101 includes {a, {b, {c...}}
a plurality of directional antennas 101a, 10a having an antenna beam 120 having a plurality of different directional directions indicated by n
1b, 101c... 101n. And each antenna service area 130a, 130b, 130c by each directional antenna 101a-101n.
.. 130n cover a base station service area 140 called a cell.

The operation of the slot antenna switching system will be described with reference to a time chart of FIG. In this figure,
The three mobile stations 210, 220 and 230 existing in each of the antenna service areas 130a to 130n
Shows an example in which random access is performed to the base station 100. As shown in this figure, in this method, the time axis of the communication channel is divided into slots of a fixed time unit, and each of the mobile stations 210 to 230 transmits a fixed-length packet equal to the slot length at the beginning of each slot. ing. The base station 100 measures the received power received by each of the directional antennas 101a to 101n at the beginning of each slot (omnidirectional carrier search), selects the directional antenna 101i having the largest received power, and does not show it. A receiver is fixedly connected to the directional antenna 101i during the slot period to receive the packet. According to this scheme, even when packets arrive from the mobile stations 210 and 220 at the same time, as in the slot indicated by A in FIG. Since only the received packet is received, both packets are not discarded.

[0006]

According to such a slot antenna switching method, collision of received packets can be avoided in the base station as described above.
The time axis of the communication channel is divided into slots in fixed time units, the received power received by each directional antenna at the beginning of each slot is measured, and the directional antenna connected to the receiver is selected. Therefore, if the base station and each mobile station need to synchronize with each other and control the timing of packet transmission at the mobile station, or if the packet length transmitted by the mobile station does not match the slot length, There is a problem that the characteristics of the system are deteriorated.

Accordingly, an object of the present invention is to provide a high-efficiency wireless packet transmission system that eliminates the need for packet transmission timing control in a mobile station and restrictions on packet length.

[0008]

To achieve the above object, a wireless packet transmission system according to the present invention comprises a base station and a plurality of mobile stations, and performs random transmission of uplink packets from each mobile station to the base station. a wireless packet transmission system employing the access method, the mobile station, the data of the previous
Start flag indicating start and end flag indicating end of data
Packet having a flag part having a tag and a data body part
Is configured to transmit packets at any time.
Ri, the base station is different from a plurality of directional antennas having directivity direction, and a carrier detecting means for detecting a carrier signal of a packet arriving from the mobile station of the base station service area, the packets arriving from the mobile station A flag detecting means for detecting the flag portion, and when the packet arriving from the mobile station is not received, the carrier detecting means detects the output signals of all the directional antennas in the base station service area. Is in a carrier search state for searching for a carrier signal of a packet arriving from a mobile station, and when the carrier signal is detected by the carrier detection means, the packet is received by one directional antenna detecting the carrier signal. while, audit the full <br/> lug part included in the received packet by the flag detecting means And, when the flag detecting means detects the end flag, or, when the carrier detecting means detects no carrier signal is what is adapted to again return to the carrier search state.

If the flag detecting means does not detect a start flag within a certain period of time from the start of receiving a packet from the mobile station, the base station returns to the carrier search state. It is to return to.
Furthermore, the base station further includes a directivity direction storage means for storing information on a directivity direction, and the flag detection means does not change until a predetermined time has elapsed since the start of reception of a packet from the mobile station. If the start flag is not detected, the directional direction storage means stores directional direction information corresponding to the directional direction of the directional antenna that is receiving the packet, and the directional direction storage means While ignoring the carrier detection in the stored directivity direction and deleting the carrier in the directivity direction, the directivity direction information stored in the directivity storage means is deleted. Is configured.

Further, the CSMA system is adopted as a random access system for uplink from the mobile station to the base station, and the antenna beam width of each directional antenna provided in the base station is set to Has the same size as the carrier detectable area in which the mobile station can detect the state of communication performed by another mobile station, or has a size smaller than the carrier detectable area.

[0011]

FIG. 1 shows the overall configuration of a wireless packet transmission system according to the present invention. As shown, this system is similar to the base station 100 shown in FIG.
And a plurality of mobile stations 210, 220,... The base station 100 includes a directional antenna group 101 including a plurality of directional antennas 101a, 101b,.
Reference numeral 40 denotes each directional antenna 101a, 101b...
1n respectively corresponding to a plurality of directional antenna beams 1
20 (♯a, ♯b... ♯n) are covered by an antenna service area 130 (♯a, ♯b... ♯n). The base station 100 includes a plurality of mobile stations 210, 220 existing in the base station service area 140.
.. Can be received by the directional antennas 101a, 101b,.

FIG. 2 is a block diagram showing a configuration example of the base station 100 used in the wireless packet transmission system of the present invention. In this figure, 101a, 101b... 101
n is a directional antenna forming the directional antenna group 101, and each has a different directional direction. The positions of the antenna beams of the directional antennas 101a to 101n may be arbitrarily set or may be fixed in advance. Reference numeral 102 denotes each directional antenna 101a based on the selection instruction signal supplied from the carrier detection unit 103.
A signal selection unit that selects any one of the received signals input from the receivers 104 to 101n and inputs the selected signal to the receiver 104.

Reference numeral 103 denotes each directional antenna 101a.
.. To 101n, and each mobile station 210, 220.
And a carrier detection unit for detecting a carrier signal of a packet arriving from the PDU, and supplying an instruction signal for selecting the directional antenna to the signal selection unit when the carrier signal is detected. Further, the carrier detection unit 103 includes a directional direction storage unit 1 for storing information on the directional directions of the directional antennas 101a to 101n.
06 is provided.
The carrier signal detected from the directional antenna corresponding to the directional direction stored in is stored so as to be ignored when the carrier signal is detected. A receiver 104 receives the output of the signal selection unit 102 and receives a packet transmitted from each mobile station. A receiver 105 detects a flag portion of a packet from a signal received by the receiver 104. Department.

FIG. 3 shows the structure of a packet 300 transmitted from each mobile station 210, 220. As shown in this figure, each transmission packet 300 includes a synchronization preamble 301 used for establishing synchronization of the physical layer, a start flag 302 indicating the head of data, a data body 303, and an end flag 304 indicating the end of the packet. It is configured. As described above, since the start flag 302 and the end flag 304 are provided, the length of the data body 303 can be arbitrary, and the transmission packet 300 can be of variable length.

The operation of the embodiment of the present invention configured as described above will be described with reference to the time chart of FIG. 4 and the flowchart of FIG. In the time chart of FIG. 4, the number of mobile stations is 3 (mobile stations 210, 220, and 230), the number of directional antennas is 3 (directional antennas 101a, 101b, and 101c).
220 and 230 are directional antennas 101a and 1
13 shows a case where the mobile terminal exists in the service area 01b or 101c.

When no mobile station is transmitting a packet (time T0 to T1), base station 100 searches all areas of base station service area 140 for the presence or absence of a carrier signal (omnidirectional search). Is performed by the carrier detection unit 103. This is the directional antenna 10
This is performed by simultaneously inputting the signals received by 1a, 101b, and 101c to the carrier detection unit 103, or by sequentially switching the directional antennas 101a, 101b, and 101c and connecting to the carrier detection unit 103 (step S501). , S502). At this time, nothing is stored in the directivity storage means 106.

At time T1, when a packet is generated in mobile station 210 and transmission of the packet to base station 100 is started, base station 100 detects a carrier signal present in the received signal of directional antenna 101a. Part 10
3 (step S502), and the carrier detection unit 10
3 is a directional antenna 101a for the signal selection unit 102.
(Step S503). As a result, the base station 100 starts receiving the packet arriving from the mobile station 210 via the directional antenna 101a at the receiver 104. The packet signal received by the receiver 104 and transmitted from the mobile station 210 is transmitted to the upper layer and also to the flag detector 105 at the same time.

The flag detection unit 105 includes a start flag 302 indicating the start of a packet within a predetermined time from the start of reception.
Is determined (step S504).
When the start flag is detected within a predetermined time, the packet is received (step S505). When the end flag 304 indicating the end is detected at time T2 (step S506), the carrier detection unit 103 is notified of the fact. Notice. If the start flag is not detected within a predetermined time in the determination in step S504, the process returns to step S501, and the omnidirectional search is started again.

At time T2, the carrier detection unit 103 notified of the detection of the end flag 304 restarts the search for the presence or absence of a carrier signal in all areas of the base station service area 140 through the directional antennas 101a, 101b, and 101c again. (Steps S501 and S502), the base station 1
00 is in the same state as at times T0 to T1. Also, the carrier detecting unit 103 performs the same operation when the carrier is not detected during the packet reception (S506). Further, when the packet is normally received, the base station 100 notifies the transmitting mobile station of “normal reception”.

At time T3, when a packet is generated in mobile station 220 and transmission of the packet to base station 100 is started, base station 100 receives the packet from mobile station 210 described above (time T1). In this case, the carrier detection unit 103 instructs the signal selection unit 102 to select a signal from the directional antenna 101b in step S503.

At time T4 while mobile station 220 is transmitting a packet to base station 100, mobile station 230
A packet is generated at the mobile station 230 and the base station 100
, The signal input to the receiver 104 of the base station 100 is
01b, the packet arriving from the mobile station 230 is transmitted to the mobile station 220 at the base station 100.
It does not interfere with the reception of packets arriving from.

When the packet transmission of mobile station 220 is completed at time T5, base station 100 performs the same operation as the above-described operation at time T2, and performs carrier detection section 103.
The search for carrier signals in all areas of the base station service area 140 is started again (step S50).
1, S502). At this time, as shown in FIG.
Is transmitting a packet, the carrier detection unit 103
Immediately detects the carrier from the directional antenna 101c, and instructs the signal selection unit 102 to select a signal from the directional antenna 101c (step S503).

As a result, the base station 100
Starts receiving packets coming from the mobile station 230 at
The start flag is detected by the flag detection unit 105 (step S504).
4, since the transmission is started from the middle of the packet, the start flag is not detected within a predetermined time from the start of the reception. If the start flag detection is not notified from the flag detection unit 105 by a predetermined time after the carrier is detected (time T6), the carrier detection unit 103 selects the directivity currently selected by the signal selection unit 102. Information (directivity direction information) corresponding to the antenna (101c) is stored in the directivity information storage means 106, and the base station 100
The omnidirectional carrier sensing operation similar to 0 to T1 is restarted (S501, S502). As a result, it is possible to prevent a packet from being received in the middle.

The carrier detection unit 103 invalidates carrier detection from the directional antenna (101c) corresponding to the information stored in the storage unit 106 at the time of the omnidirectional search in S501, and the directional antenna (101 101
The signal from c) is not received (time T6 to T8).
Note that the directional information stored in the directional information storage means 106 is the directional antenna (101
When the carrier is no longer detected in c) (time T8), the carrier is deleted from the storage means 106. As a result, carrier detection by the directional antenna corresponding to the information deleted from the directional information storage unit 106 is enabled, and a new packet input to the directional antenna can be received.
Even though the packet was sent, "normal reception"
Is not notified from the base station 100, the mobile station that transmitted the packet (in this case, the mobile station 230) performs error processing such as retransmission.

At time T7, when a packet is generated again in mobile station 210 and transmission is started, mobile station 230 is transmitting a packet, and carrier detecting section 103 of base station 100 transmits directional antenna 101a, Although the carrier is detected by both of the directional antennas 101c, the detection by the directional antenna 101c is ignored as described above, and the signal selection unit 102 is instructed to select a signal from the directional antenna 101a (S503). As a result, the base station 100
Can be received without being disturbed by the packet arriving from the mobile station 230. When the packet from the mobile station 210 ends at time T9 in this way, the omnidirectional search is started again. In this way, it is possible to avoid collision of received packets without synchronizing the timing of packet transmission at each mobile station, without having to match the slot length with a fixed packet length.

A CSMA (Carrier Sence Multip) is used in such a random access method of the wireless packet transmission system.
le access) scheme, the probability of packet collision at the base station can be further reduced. That is, each mobile station detects whether or not there is another mobile station that is transmitting a packet, and determines whether or not the mobile station can transmit its own packet, thereby reducing the probability of packet collision at the base station. Can be done. In the CSMA system, as generally known as a hidden terminal problem, the characteristics deteriorate when there is a mobile station that cannot detect the presence or absence of packet transmission of another mobile station due to radio wave propagation conditions and the like. .

FIG. 6 shows an antenna beam 1 of each directional antenna 101i in the embodiment using the wireless packet transmission system of the present invention together with the CSMA system.
Antenna service area 130 covered by 20
FIG. 5 is a diagram showing a relationship between the mobile station 210 and a carrier sense area 211 of the mobile station 210. As shown in the figure, by setting the antenna service area 130 smaller than the carrier sense area where the mobile station 210 can determine whether or not another mobile station is transmitting a packet, the mobile station 210 Can reliably detect the presence / absence of packet transmission of another mobile station existing in the same antenna service area as the own station. Therefore, the characteristics do not deteriorate as described above.

As described above, the antenna service area 130
In order to set the relationship between the directional antenna and the carrier sense area 211, the position of the antenna beam of the directional antenna can be set arbitrarily, and the service area 130 using the directional antenna is set centering on the mobile station that is always communicating. If possible, the radius of the service area 130 may be set so that (radius of the service area 130) ≦ (radius of the carrier sense area 211). Also, the antenna beam formed by the directional antenna is fixed, and
If it is not possible to always set the center of the mobile station during communication, the radius of the service area 130 may be set so that (service area 130 radius) ≦ (carrier sense area 211 radius) / 2.

As described above, the mobile station limits the service area radius during packet transmission as described above,
In a mobile station that is newly starting communication, it is possible to detect a carrier of a communicating mobile station existing in the service area 130 using the same directional antenna, and to perform CSM.
The influence of the hidden terminal, which is a problem in the A method, can be completely eliminated, and packet collision at the base station can be completely avoided.

[0030]

As described above, according to the present invention,
The base station detects the carrier of the packet arriving from the mobile station, receives the packet only from the directional antenna from which the carrier is detected, monitors the flag in the packet, receives the packet, and controls the start / end of the carrier search. , The probability of occurrence of packet collision at the base station can be reduced, and the need for packet transmission timing control and restrictions on packet length at the mobile station can be eliminated. Can be transmitted.

Further, the effect can be expected by using it together with the CSMA system. In particular, by limiting the beam width of one directional antenna, the influence of the hidden terminal in the CSMA system can be completely eliminated. Packet collision at the station can be completely eliminated.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment of a wireless packet transmission system according to the present invention.

FIG. 2 is a block diagram illustrating a configuration example of a base station in the wireless packet transmission system according to the present invention.

FIG. 3 is a configuration diagram of a packet transmitted from a mobile station in the wireless packet transmission system of the present invention.

FIG. 4 is a time chart for explaining the operation of the wireless packet transmission system of the present invention.

FIG. 5 is a flowchart showing the operation of the wireless packet transmission system of the present invention.

FIG. 6 is a diagram illustrating a relationship between a service area covered by each antenna beam of a directional antenna and a carrier sense area of a mobile station according to another embodiment of the present invention.

FIG. 7 is a conceptual diagram illustrating an antenna beam of a directional antenna of a base station according to the related art.

FIG. 8 is a time chart of the operation in the conventional technique.

[Explanation of symbols]

 Reference Signs List 100 base station 101 directional antenna group 101a to 101n directional antenna 102 signal selection unit 103 carrier detection unit 104 receiver 105 flag detection unit 106 directional direction information storage unit 120 antenna beam 130 antenna service area 140 base station service area 210; 220, 230 Mobile station 211 Carrier sense area 300 Transmission packet 301 Synchronization preamble 302 Start flag 303 Data body 304 End flag

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihide Yamada 1-32 Shinrashima-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture RP Corporation Mobile Communication Technology Laboratory (56) References JP-A-7- 131411 (JP, A) JP-A-4-140933 (JP, A) JP-A-3-143123 (JP, A) Patent 2743018 (JP, B2) IEEE GLOBECOM '89, Global Telecommunications Conference and Exhibition, Violet. 2, Tak-Shing Yum et al, "DESIGN ALGO RITHMS FOR MULTIHO P PACKET RADIO NET WORKS WITH MULTIPLE E DIRECTIONAL DIRECTIONAL STATE NATIONS", page. 717-722 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 39 NO. 3, AUGUST 1990, View TL. et al, "A Slotted ALOHA Package Radio System with Multiple Antennas and Receivers", pages. 218-226 IEEE INTERNATIONAL CONNECTION CONNECTION CONNECTION CONTROL. VOL. 1, Lau C.I. et al, "ANTENNA SELECTION IN A MULTI-SECTOR PACKET RADIO NE TWORK", Pages. 188-192 ELECTRONICS LETTE RS 6th, Vol. 26 No. 25, DECEMBER 1990, Zander J. et al. "SLOTTED ALOHA MULTIHOP PACKET RA DIO NETWORKS WITH DIRECTIONAL ANTENNN AS", pages. 2098-2100 (58) Fields surveyed (Int. Cl. ⁶ , DB name) H04L 12/28 H04Q 7/38 INSPEC (DIALOG) JICST file (JOIS) WPI (DIALOG)

Claims (4)

(57) [Claims] 1. A wireless packet transmission system comprising a base station and a plurality of mobile stations, and adopting a random access scheme for uplink packet transmission from each mobile station to the base station, wherein the mobile station has a head of data. Start flag and de
A flag part having an end flag indicating the end of data and the data
Packet with the data body
Is configured to signal the base station, a plurality of directional antennas having different directivity direction, and a carrier detecting means for detecting a carrier signal of a packet arriving from the mobile station of the base station service area, It has and a flag detection means for detecting the flag portion of the packet arriving from the mobile station, when not receiving a packet arriving from the mobile station, the output of all the directional antennas in said carrier detection means In a carrier search state for searching for a carrier signal of a packet arriving from a mobile station in a base station service area from a signal, and when the carrier signal is detected by the carrier detection means, one direction in which the carrier signal is detected. Receiving the packet with the antenna, and including the packet in the received packet by the flag detecting means. The flag portion monitors that, when the flag detecting means detects the end flag, or, when the carrier detecting means detects no carrier signal, is configured to again return to the carrier search state A wireless packet transmission system. 2. The base station returns to the carrier search state when a start flag is not detected by the flag detecting means until a predetermined time has elapsed after starting reception of a packet from the mobile station. The wireless packet transmission system according to claim 1, wherein the wireless packet transmission system is configured to return. 3. The base station further comprises directional direction storage means for storing information on a directional direction, wherein the base station starts receiving a packet from a mobile station until a predetermined time elapses. If the flag detection means does not detect the start flag, the directional direction storage means stores the directional direction information corresponding to the directional direction of the directional antenna that is receiving the packet, While ignoring the carrier detection in the directivity direction stored in the direction storage means, and when the carrier is no longer detected in the directivity direction, the directivity direction information stored in the directivity direction storage means is ignored. 3. The wireless packet transmission system according to claim 2, wherein the wireless packet transmission system is configured to delete the packet. 4. The mobile station adopts a CSMA scheme as an uplink random access scheme from the mobile station to the base station, and the antenna beam width of each directional antenna provided in the base station is set to The mobile communication system according to claim 1, wherein the state of communication performed by another existing mobile station is equal to or smaller than a carrier detectable area in which the mobile station can detect. Item 4. The wireless packet transmission system according to any one of Items 1 to 3.