JP4084086B2 - Random access communication method, wireless communication device, and wireless communication system - Google Patents

Description

【００３９】
図７のシミュレーション結果の比較図において、スロット（１−３０）はＭ＝０、Ｎ＝３０とした場合であり、前述した特開２００１−１１８１９１に開示の発明の基本設定値である。また、スロット（６−２５）はＭ＝５、Ｎ＝２５、スロット（１１−３０）はＭ＝１０．Ｎ＝２０とした場合である。図１０から明らかなようにスロット（１１−３０）が成功率、衝突確率共によい性能を示しており、本発明によるランダムアクセス方式の有効性、優位性を示している。
以上、本発明の一実施例について説明したが本発明は上記実施例に限定されるものではなく、種々の変形実施が可能であることはいうまでもない。
【００４０】
【発明の効果】
上記説明したように、本発明によれば、送信要求時にデータ送信を所定の方法で算出した時間分待機するようにしたことにより、他グループからのデータとの衝突確率を低減させ、通信の衝突回避能力を高めているので、ランダムアクセス方式を基本とした無線通信システムにおいても、通信遅延時間や通信チャンネルの利用効率の改善効果が期待できる。
【図面の簡単な説明】
【図１】無線通信システムの一実施例を示す図である。
【図２】本発明の無線通信システムにおける端末（無線通信機器）の一実施例の構成を示すブロック図である。
【図３】本発明に基く、端末のシステムモデルを示す図である。
【図４】図３のシステムモデルにおける端末のチャンネルアクセス手順を示すフローチャートである。
【図５】ビーコン制御フレームのランダム送信手順の説明図である。
【図６】図５のランダム送信手順に本発明のオフセット付きランダムアクセス方式を用いた通信手順を示すフローチャートである。
【図７】ランダムアクセス手順の性能シミュレーション結果の比較図である。
【図８】端末の一般的なシステムモデルを示す図である。
【図９】アロハ方式のチャンネルアクセス例の説明図である。
【図１０】スロットアロハ方式のチャンネルアクセス例の説明図である。
【符号の説明】
１〜４ 端末（無線端末、無線通信機器）
１３ 制御部（通信制御手段）
１００ 無線通信システム[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a random access technique when data communication is performed by sharing one communication channel with a plurality of wireless communication devices.
[0002]
[Prior art]
In the wireless communication system 100 in which a plurality of wireless communication devices (terminal 1 to terminal 4) as shown in FIG. 1 exist, a number of wireless communication devices (hereinafter referred to as terminals) share one channel. Efficient use is a challenge.
[0003]
FIG. 8 shows a system model of a general terminal. Under the wireless communication system of FIG. 1, each of the terminals 1 to 4 is in either the transmission data generation state (THmode) 31 or the random access state (RAmode) 33. Is in a state.
[0004]
The terminal in the transmission data generation state (THmode) 31 generates new data with probability δ, and the terminal in the random access state (RAmode) 33 performs channel acquisition operation with probability p, that is, channel acquisition success, that is, If the access is successful, the data is transmitted. The transmission data is repeated with probability p until channel acquisition is successful, and the terminal that has succeeded in transmission returns to the transmission data generation state (THmode) 31 to generate the next new data.
[0005]
For example, as a typical channel access method in a random access state, various methods such as an Aloha method and a slot Aloha method have been proposed. As shown in FIG. 9, the Aloha method is a method in which each terminal accesses a channel asynchronously and randomly. When a part of data overlaps with the data transmission of the terminal, the data transmission interferes with each other, affecting each data transmission. give. For this reason, the communication efficiency is not so high.
[0006]
On the other hand, as shown in FIG. 5, the slot aloha method is a method in which the data length is fixed, each terminal synchronizes with the slot unit based on this length, and randomly accesses the channel. Since transmission from the terminal is synchronized in slot units, there is no partial collision of transmission data, and channel utilization efficiency is improved compared to the Aloha method.
[0007]
[Problems to be solved by the invention]
In this way, the random access method is a method in which communication is performed while repeating channel contention and collision, so in practice, a gap depending on the random number generation process may affect communication delay time and channel utilization efficiency. There was a problem that there was.
[0008]
For example, there is a sufficient possibility that a specific terminal continuously performs data communication. As described above, when a specific terminal performs continuous data transmission, the communication of other terminals may be interrupted, which may cause an increase in delay time in communication. There is a possibility that bias may occur and adversely affect the operation of the entire wireless communication system.
[0009]
The present invention has been made to solve the above-described problems, and avoids a communication collision even in a communication system based on a random access method, and improves communication delay time and communication channel utilization efficiency of the communication system. An object is to provide a random access communication method, a wireless communication device, and a wireless communication system.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, a random access communication system according to a first aspect of the present invention is a channel access system used when data communication is performed by sharing one communication channel with a plurality of wireless communication devices. When a data transmission request is generated in the device, the step of waiting for data transmission for a certain period of time, the step of transmitting data with the probability of being generated at random after the waiting time has elapsed, and the transmission data is transmitted to other wireless communication When there is a collision with data transmitted from a device, the step of transmitting data with the probability of generating at random without waiting for the waiting time to elapse until there is no collision with data transmitted from another wireless communication device. If the transmission data can be transmitted without collision with data transmitted from another wireless communication device, the data transmission request is generated. Steps that you have to repeat the features a.
[0011]
The second invention includes communication control means for executing a communication procedure according to the random access communication system of the first invention, and shares one communication channel with a plurality of wireless communication devices to communicate data with each other. It is characterized by performing.
[0012]
In a third aspect of the present invention, in a wireless communication system in which a group is formed between a plurality of wireless terminals and performs wireless communication with each other, one wireless terminal in the wireless communication device group is set as a beacon station and a beacon signal is transmitted. Each wireless terminal in the group is configured to transmit data in a specific data slot assigned to each wireless terminal among the data slots following the beacon signal, and further, the wireless terminals in each group The terminal transmits data only when a beacon signal is transmitted from a beacon station in the group. When transmitting a beacon signal from a beacon station of each group, the terminal transmits data in a beacon period composed of a plurality of beacon slots. The beacon slot randomly selected based on the random number generated by the random number generation process When the beacon station of each wireless terminal group does not receive the beacon signal of another wireless terminal group before transmitting its own beacon signal, the beacon signal of its own station is transmitted. Transmit data from each wireless slot in its own group in each data slot. If a beacon signal from another wireless terminal group is received before transmitting its own beacon signal, transmit its own beacon signal. A wireless communication system that performs wireless communication between each wireless terminal group according to a random transmission procedure to be canceled, and when transmitting a beacon signal at a beacon station of each group, if the previous data transmission could not be performed, Subtract the beacon slot number of the other wireless terminal group from the previous random number generated as the beacon slot that transmits the beacon signal. When the beacon slot of the slot number is selected and the previous data transmission was possible, the beacon slot of the number Tr represented by the following formula is selected as the beacon slot for transmitting the next beacon signal. Do;
(Formula) Tr = RND (N) + M
Here, M + N = total number of beacon slots, RND (N) indicates a calculation result for generating a random number of any one of 1 to N out of the maximum integer value N, and M is a predetermined number less than the total number of beacon slots. A constant integer value.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
FIG. 1 is a diagram illustrating an embodiment of a wireless communication system. In the wireless communication system 100, a plurality of wireless communication devices (hereinafter referred to as terminals) 1 to 4 share a single communication channel. Perform data communication. Further, the terminals 1 to 4 are in either a transmission data generation state or a random access state.
[0014]
FIG. 2 is a block diagram showing the configuration of an embodiment of a terminal (wireless communication device) in the wireless communication system of the present invention. Each of the terminals 1 to 4 includes an antenna 11, a wireless communication unit 12, a control unit 13, and a memory 14. ing.
[0015]
The wireless communication unit 12 transmits and receives data via the antenna 11 according to a predetermined communication procedure under the control of the control unit 13. The control unit 13 has a microcomputer configuration including a CPU, a program storage memory such as a ROM (not shown), an internal clock 131, and peripheral circuits.
[0016]
The memory 14 is composed of a primary storage memory such as a DRAM. When the terminals 1 to 4 are started, the control program stored in the program storage memory is made resident, and the communication protocol and the communication control program in the wireless communication system of the present invention are timely. Alternatively, other processing programs and the like are read from the program storage memory and are allowed to stay for as long as necessary.
FIG. 3 is a diagram showing a system model of each terminal of FIG. 1 based on the present invention, and is a model obtained by adding an access standby state 32 to the system model of FIG. In the wireless communication system 100, the plurality of terminals 1 to 4,... Are in a transmission data generation state (THmode) 31, an access standby state (Delay) 32, or a random access state (RAmode) 33. Here, the terminal in the transmission data generation state 31 generates new data with the probability δ, and the terminal in the random access state 33 transmits data with the probability p. The transmission data is repeated with probability p until the transmission is successful, and the terminal that has succeeded in the transmission returns to the transmission data generation state 31, but does not immediately shift to the random access state 33, but the delay time (offset) in the access waiting state 32 (Time) is inserted and then the random access state 33 is entered.
[0017]
The delay time (d) is determined in consideration of the maximum data update time required for maintaining the system operation and the maximum average data transmission delay time (random number generation time, empty channel confirmation time, etc.) related to communication. it can.
[0018]
For example, if the maximum data update time is 100 msec and the maximum average data delay time is 20 msec, there is an average margin of 80 msec. Therefore, for example, for 40 msec immediately after data transmission, even if new transmission data is generated in the transmission data generation state 31, it does not shift to the random access state 33 and waits in the access standby state 32 (d = 40 msec). By not performing the above, continuous access to the channel 24 can be controlled.
[0019]
FIG. 4 is a flowchart showing the channel access procedure of the terminal in the system model of FIG. Although the delay time is 40 msec in steps S2 and S3 in FIG. 4, the delay time is not limited to 40 msec.
First, the control unit 13 of the terminal clears the initialization completion time (step S1), generates new data with a probability δ in the transmission data generation state 31, and proceeds to step S3 when new data is generated (step S2). ).
[0020]
When new data is generated in step S2, it is checked whether or not a predetermined delay time (40 msec in this example) has elapsed from the previous transmission completion time in the access standby state 32, and the predetermined delay time has elapsed. Shifts to step S4, and when the delay time has not elapsed (in this example, less than 40 msec), the standby state is repeated (step S3).
[0021]
If the predetermined delay time has elapsed in step S3, the channel acquisition operation is performed with the probability p in the random access state 33. If transmission is possible (channel acquisition is successful), that is, transmission data is transmitted from another terminal. If transmission is possible without colliding with data, the process proceeds to step S5. If transmission is not possible (channel acquisition failure), that is, transmission data collides with data transmitted from another terminal, transmission is possible. Until the transmission probability p, the channel acquisition operation is repeated. The transmission probability p is a probability depending on the generated random number after generating a random number in the random access state 33 (step S4).
[0022]
If transmission is possible in step S4, the created transmission data is transmitted (step S5), the initialization completion time is cleared, and the process returns to step S2 (step S6).
[0023]
In general, the channel access probability is reduced to reduce the channel contention probability, but the number of competing terminals can be reduced without reducing the channel access probability by adopting the channel access procedure shown in the flowchart of FIG. Therefore, it is possible to reduce the collision probability during channel access. In addition, since the delay time (offset time) is provided, the continuous communication right acquisition of a specific terminal is eliminated, which can contribute to stable operation of the entire communication system.
[0024]
[Second Embodiment]
In this embodiment, the present invention is applied to a random transmission procedure of a beacon control frame (hereinafter simply referred to as a beacon signal) in the invention (Japanese Patent Laid-Open No. 2001-118191) filed on October 20, 1999 by the applicant of the present application. The communication procedure using the random access method is shown.
[0025]
The hardware configuration of the terminal may be the same as that of the terminal shown in FIG. 1, but the control unit 13 includes a CPU, a program storage memory such as a ROM (not shown), an internal clock 131, and peripheral circuits. Based on the control of the entire device and each program stored in the program storage memory, comparison of group ID information, priority determination, correction based on the beacon time of the internal clock, and other groups Communication control in the wireless communication system of the present invention including time synchronization and delay time calculation, and execution control of necessary processing. The program storage memory includes a control program and a communication protocol for controlling the entire wireless communication apparatus, a program for performing communication control and necessary processing in the wireless communication system of the present invention, and a beacon information table (not shown). In addition, various setting values are stored.
[0026]
The memory 14 is composed of a primary storage memory such as a DRAM. When the terminal is activated, the control program stored in the program storage memory is made resident, and the communication protocol or the communication control program in the wireless communication system of the present invention or the like can be used. The processing program and the beacon information table are read from the program storage memory and are stationed only when necessary. The memory 14 stores beacons and data frames received via the wireless communication unit 12 under the control of the control unit 13.
[0027]
FIG. 5 is an explanatory diagram of a beacon random transmission procedure. In the above Japanese Patent Laid-Open No. 2001-118191, one terminal in a terminal group (wireless communication equipment (FIG. 5A) mounted on each vehicle in a vehicle group) is set as a beacon station and a beacon signal is generated. Each terminal in the group is configured to transmit data in a specific data slot allocated to each terminal among the data slots (FIG. 5B) following the beacon signal. The terminal within the group transmits data only when a beacon signal is transmitted from a beacon station within the group, and when a beacon signal is transmitted from a beacon station of each group, it is composed of a plurality of beacon slots. In the beacon period (FIG. 5C), the beacon slot randomly selected based on the random number generated by the random number generation process. If the beacon station of each terminal group does not receive a beacon signal of another terminal group before transmitting its own beacon signal (= collision with data of other terminals) If not, the terminal transmits a beacon signal of its own station and transmits data in each data slot from a terminal in its own group (= successful channel acquisition). When a beacon signal of a group is received (= when colliding with data of another terminal), transmission of the beacon signal of the own station is stopped (= channel acquisition failure), between vehicles (= A vehicle-to-vehicle wireless communication system that performs wireless communication between terminals) is disclosed.
[0028]
That is, when forming a group between a plurality of terminals and performing wireless communication with each other, the communication channel acquisition control is executed by randomly transmitting the beacon during the beacon period 45 shown in FIG. Yes. This beacon period 45 is composed of a plurality of beacon slots, and competition control with other terminals (other groups) is realized by randomly selecting a beacon slot to be transmitted.
[0029]
Summarizing this beacon transmission procedure, the following (1) to (7) are obtained;
(1) The beacon period is composed of beacon slots 1 to 30;
(2) A beacon is transmitted in one of the beacon slots in synchronization with the beacon period;
(3) A beacon slot to be transmitted that becomes a random delay time is determined by random (random numbers 1 to 30);
(4) If a beacon is received before the beacon transmission, beacon transmission is stopped;
(5) A terminal (group) that has successfully transmitted a beacon acquires a communication channel and transmits data in a subsequent data period;
(6) A terminal (group) that has not acquired a communication channel acquires a random value during the next beacon period. ;
(7) Terminals (groups) that have not acquired a communication channel subtract the time elapsed this time to obtain a random value for the next beacon period.
[0030]
A communication procedure using the random access method with an offset according to the present invention described in the first embodiment is shown in the flowchart of FIG. 6 as the random transmission procedure of (1) to (7).
[0031]
In the flowchart of FIG. 6, the control unit 13 of the terminal checks whether or not the beacon period is reached. If the beacon period is reached, the process proceeds to step T2, and if it is not the beacon period, the beacon period is awaited (step T1). .
[0032]
When the beacon period is reached, the random delay time Tr is set in the internal clock 131 (step T2), and it is checked whether the channel access is successful. If the channel access is successful, the process proceeds to step T4, where the channel access is performed. If it fails, access is repeated until it succeeds. At this time, if a beacon is received from another terminal, the channel access operation is stopped and the process proceeds to step T7 (step T3).
[0033]
If channel access is successful in step T3, data transmission is performed in the subsequent data period (step T4), a communication channel is acquired (step T5), and random access delay time Tr = RND (N) + M where RND ( N) indicates a calculation result for generating a random number from 1 to N among the maximum integer values N, M is a predetermined integer value that is equal to or less than the total number of beacon slots, and M + N = maximum random delay time ( = Total number of beacon slots), the random access delay time Tr (that is, the beacon slot number) is calculated based on the calculation formula, and the process returns to step T1 (step T6).
[0034]
If a beacon is received from another terminal in step T3, the beacon start time Tw is calculated (step T7), and the random delay time is updated as random delay time Tr = Tr-Tw. The process returns to T1 (step T8).
[0035]
Although the communication procedure shown in the flowchart of FIG. 6 has 30 beacon slots, the present invention is not limited to this. Further, when a new random delay time is acquired, as shown in step T6, the random access delay time Tr = RND (N) + M where R + N = maximum random delay time. Since 30 beacon slots are calculated, for example, if M = 10 and N = 20, when a random delay time is newly acquired, at least 10 terminals of beacon slots are obtained. The period will wait without sending. That is, this period is a period in which other terminals (groups) can preferentially transmit.
[0036]
Next, the performance comparison simulation result of the random access procedure with offset according to the present embodiment (second embodiment) is shown in the performance simulation result comparison diagram of FIG. The simulation parameters are shown in the table below. In the simulation, the following conditions (a) to (c) are used to simplify the calculation.
[0037]
(A) Does not consider propagation delay time, transmission / reception switching time, etc .;
(B) The propagation path model assumes an ideal propagation path and there are no communication errors other than the occurrence of a collision;
(C) When communication collides, the communication shall be failed.
[0038]
[Table 1]

[0039]
In the comparison diagram of the simulation results of FIG. 7, slot (1-30) is a case where M = 0 and N = 30, and is a basic setting value of the invention disclosed in the above-mentioned JP-A-2001-118191. The slot (6-25) has M = 5, N = 25, and the slot (11-30) has M = 10. This is a case where N = 20. As is clear from FIG. 10, the slot (11-30) shows good performance in both success rate and collision probability, and shows the effectiveness and superiority of the random access method according to the present invention.
As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, It cannot be overemphasized that various deformation | transformation implementation is possible.
[0040]
【The invention's effect】
As described above, according to the present invention, when a transmission request is made, data transmission is waited for a time calculated by a predetermined method, thereby reducing the probability of collision with data from other groups and causing communication collisions. Since the avoidance capability is enhanced, an effect of improving communication delay time and communication channel utilization efficiency can be expected even in a wireless communication system based on a random access method.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of a wireless communication system.
FIG. 2 is a block diagram showing a configuration of an embodiment of a terminal (wireless communication device) in the wireless communication system of the present invention.
FIG. 3 is a diagram showing a system model of a terminal based on the present invention.
4 is a flowchart showing a channel access procedure of a terminal in the system model of FIG.
FIG. 5 is an explanatory diagram of a random transmission procedure of a beacon control frame.
6 is a flowchart showing a communication procedure using the random access method with an offset of the present invention in the random transmission procedure of FIG.
FIG. 7 is a comparison diagram of performance simulation results of a random access procedure.
FIG. 8 is a diagram illustrating a general system model of a terminal.
FIG. 9 is an explanatory diagram of an example of Aloha channel access;
FIG. 10 is an explanatory diagram of a channel access example of a slot aloha system.
[Explanation of symbols]
1-4 terminals (wireless terminals, wireless communication devices)
13 Control unit (communication control means)
100 Wireless communication system

Claims (3)

A channel access method for performing data communication with each other by sharing one communication channel with a plurality of wireless communication devices,
When a data transmission request occurs in the wireless communication device, waiting for data transmission for a certain period of time;
A step of transmitting data with a probability generated at random after the waiting time has elapsed;
When the transmission data collides with data transmitted from another wireless communication device, it is generated at random without waiting for the waiting time to elapse until there is no collision with data transmitted from another wireless communication device. Repeating the process of transmitting data with probability,
If the transmission data can be transmitted without collision with data transmitted from other wireless communication devices, the process after the request for data transmission has been repeated,
A random access communication system characterized by   A wireless communication system comprising: a communication control unit that executes a communication procedure according to the random access communication system according to claim 1; machine. In a wireless communication system in which a group is formed between a plurality of wireless terminals and performs wireless communication with each other, one wireless terminal in the wireless communication device group is set as a beacon station to generate a beacon signal. Each wireless terminal is configured to transmit data in a specific data slot assigned to each wireless terminal among the data slots following the beacon signal. Further, the wireless terminal in each group transmits data. It is only when a beacon signal is transmitted from a beacon station in the group, and when a beacon signal is transmitted from a beacon station of each group, it is generated by a random number generation process in a beacon period composed of a plurality of beacon slots. A beacon signal is transmitted in a beacon slot randomly selected based on a random number. In this case, if the beacon station of each wireless terminal group does not receive the beacon signal of another wireless terminal group before transmitting its own beacon signal, it transmits its own beacon signal and Data is transmitted from each wireless slot in each data slot, but if a beacon signal of another wireless terminal group is received before transmission of the beacon signal of the local station, the transmission of the beacon signal of the local station is stopped by a random transmission procedure. A wireless communication system for performing wireless communication between each wireless terminal group,
When transmitting a beacon signal at the beacon station of each group,
If the previous data transmission was not possible, select the beacon slot of the slot number that is the number of the beacon slot that transmits the next beacon signal minus the beacon slot number of the other wireless terminal group previously generated from the previously generated random number,
A radio communication system characterized by selecting a beacon slot of the number Tr represented by the following formula as a beacon slot for transmitting the next beacon signal when data was transmitted last time;
(Formula) Tr = RND (N) + M
Here, M + N = total number of beacon slots, RND (N) indicates a calculation result for generating a random number of any one of 1 to N out of the maximum integer value N, and M is a predetermined number less than the total number of beacon slots. A constant integer value.

Images