CN101051998A - Block conflict resolving method of radio local net - Google Patents

Abstract

The method comprises: when the sending end sends An, it inserts the initial value of backoff counter to be used by the next packet in the sending queue into header information field of the packet to be currently sent; at the time of sending An, previously broadcasting initial values of m backoff counters corresponding to its next m packets; after other ends in serving area receives them, they extracts the initial values of backoff counters, and calculate the location of relevant reserved time slot so as to avoid sending the packets on said reserved time slot.

Description

A kind of block conflict resolving method of WLAN (wireless local area network)

Technical field

The present invention relates to communication technical field, the block conflict resolving method in particularly a kind of WLAN (wireless local area network).

Background technology

Current I EEE 802.11 standards have become the generally acknowledged international standard of WLAN (wireless local area network) access technology.Mainly defined two kinds of multiple access access protocols in IEEE 802.11FGY standard: first distributed coordination function (DCF), another one are point coordination function (PCF).A kind of multiple access that DCF is based on carrier sense and collision avoidance mechanism is access strategy at random, is inserted standard by the multiple access of industry-wide adoption.

Along with the develop rapidly of technology, the wireless local area network technology based on IEEE 802.11 has obtained using widely in recent years.On the one hand, along with increasing user uses this technology, it is more and more nervous that the frequency spectrum resource of IEEE 802.11 WLAN (wireless local area network) institute working frequency range becomes.On the other hand, the IEEE 802.11 standards block conflict resolving method recommending to use can not effectively be controlled the generation of packet collisions under the more situation of network user's number.Because the packet collisions probability is higher, so the channel utilization of system is very low.

In order to improve the performance of IEEE 802.11 multiple access access protocols, it is very important possessing an efficient and sane block conflict resolving method.Yet in present existing most of strategies, communication terminal independently produces backoff counter initial value separately mutually, so packet collisions just inevitable (especially under the bigger situation of system business amount).At American Baldwin R., Davis N., and Midkiff S. equals to go up at international periodical " ACM Mobile Computing and CommunicationsReview " in 1999 a kind of real-time multiple access access strategy of proposition, and Korean Choi J., Yoo J., Choi S., Kim C. went up in a kind of distributed channel reservation strategy that proposes at international periodical " IEEE Transactions on Mobile Computing " in 2005, send terminal when sending the current data grouping, the initial value of the backoff counter that will use ensuing packet is broadcasted away in advance.So corresponding time slot is just preengage, and uses same time slot to carry out the data transmission thereby avoided other to send terminal.But all just step reservations of the channel booking algorithm that they propose (, only finish the time slot that ensuing data grouping is about to use and preengage) promptly by sending the current data grouping.As everyone knows, transmission error is inevitable on wireless channel.When the wireless channel transmission characteristic is comparatively abominable, can not guarantee that once step reservation algorithm the channel booking information of broadcasting is away sent terminal by as much as possible other and obtains.So also just can't further avoid the generation of packet collisions.Emulation experiment shows that the performance of step reservation algorithm is to Channel Transmission mistake very responsive (significantly descending along with the increase of Channel Transmission error rate), and low performance can not satisfy the development need of WLAN (wireless local area network).

Summary of the invention

Higher in order to overcome prior art packet collisions probability, the deficiency that the system channel utilance is low the present invention proposes a kind of block conflict resolving method based on step channel reservation multi.By using this method, packet collisions can effectively be suppressed, and then has significantly improved systematic function.

The technical solution adopted for the present invention to solve the technical problems is: consider the WLAN (wireless local area network) (present most WLAN (wireless local area network) all is network topology structures of single-hop) of a single-hop, all communication terminals in primary service area " BBS " all can " be heard " the transmission activity of other-end on channel mutually.Send packet A if send terminal A to terminal B _n(footmark " n " is represented the sequence number of this packet).For fear of packet collisions, sending A _nThe time, A will be at medium other the follow-up grouping A to be sent of its transmit queue _N+1, A _N+2..., A _N+mThe backoff counter initial value BT that will use _N+1, BT _N+2..., BT _N+mBe inserted into the current grouping A that promptly will send _nThe header information territory in (concrete reservation time slot position can calculate) by these backoff counter initial values.Like this, sending A _nThe time m grouping that it is follow-up pairing m backoff counter initial value broadcast away in advance, thereby played the purpose of channel booking.In the service area other send terminal and are receiving A _nAfter, from wherein extracting backoff counter initial value BT _N+1, BT _N+2..., BT _N+m, and calculate the position of corresponding reservation time slot, thus avoid on these time slots, sending grouping.By such booking-mechanism, can guarantee that the channel booking information broadcasted is sent terminals with very high success rate by other of periphery and obtains, and then avoid the generation of packet collisions.

If A is for sending terminal, below the realization of this method be divided into some steps specifically described:

A) calculate in the transmit queue at current transmission grouping A _nThe A of the follow-up grouping of other of Deng Daiing afterwards _N+1, A _N+2..., A _N+kThe backoff counter initial value BT that will use _N+1, BT _N+2..., BT _N+k

This step specifically describes as follows:

Be located at and send A _nIts front grouping A _N-iWhen (i 〉=1), finished follow-up grouping A _N+j(1≤j≤m _r) reservation (that is to say this m _rThe existing backoff counter initial value of individual grouping is corresponding respectively with it).Establish again and send current group A _nAfter, also remaining m in the transmit queue of A _wIndividual packet awaits sends (m _w〉=m _r), make k=min (m, m so _w), and A also need calculate k-m _rIndividual backoff counter initial value.

The method that produces each backoff counter initial value is identical, and therefore we only describe the generation algorithm of a backoff counter initial value here.If will produce with the pairing backoff counter initial value of i backoff counter be x (i).Known previous backoff counter, i.e. i-1 backoff counter, the position of the time slot of being preengage in the channel booking window is TA _I-1During initial calculation, make q=1.At first, 1 and min[q (CW _Min-1), (CW _Max-1) evenly produces a random number x] ₁As backoff counter initial value (CW _MinExpression minimum competition window size, CW _MaxThe maximum of expression backoff counter), i.e. x ₁=uniform (1, min[q (CW _Min-1), (CW _Max-1)]).If should value pairing time slot, i.e. (T _Ai-1+ x ₁) mod (1024 * m), preengage by other-end, just produce x once more ₂=uniform (1, min[q (CW _Min-1), (CW _Max-1)]).The x that continuous if L time (L 〉=1) produces ₁, x ₂..., x _LPairing time slot is all preengage by other-end, and then the value with current q adds 1.Utilization and top same method are until producing satisfactory x value as the backoff counter initial value x (i) that finally produces then.Like this, the position of time slot in the channel booking window of A preengage of i backoff counter is $T_{A_i}=(T_{A_{i-1}}+x\left(i\right))\mathrm{mod}(1024\×m).$ Based on above method, just can obtain backoff counter initial value BT _N+1, BT _N+2..., BT _N+k

B) with the backoff counter initial value BT that produces recently _N+1, BT _N+2..., BT _N+kUpgrade sending m the backoff counter that terminal is safeguarded one by one, promptly use BT _N+iUpgrade i (number backoff counter of 1≤i≤k);

C) the position T of time slot in the channel booking window of A that is preengage according to the i backoff counter _Ai, be " 1 " with the relevant position of channel booking window, thereby show that corresponding time slot is preengage;

This step specifically describes as follows: in order to note the state that channel is preengage in the service area, the bit array that it is 1024 * m position that each transmission terminal is all being kept a length voluntarily (1024 correspondences each maximum possible value that sends the terminal backoff counter), whether each of array indicates corresponding time slot by reservation (for " 1 " expression has been preengage, for " 0 " expression is not preengage as yet).Such bit array is called " channel booking window ".In addition, send pointer and m the backoff counter (m represents the channel booking step number) of also safeguarding a current time slot position of living in of indication in the terminal at each.Whenever a time slots is gone over, the current location pointer just adds 1, when it is added to maximum 1024 * m, just from newly being changed to 0.M backoff counter is used to indicate m the residing relative position of reservation time slot.

If the current time slots position indicator pointer that A safeguarded is T _A, the position T of the time slot of reservation in the channel booking window of A _AiComputing formula be:

$T_{A_i}=(T_A+\underset{j=1}{\overset{i}{\mathrm{\Σ}}}B{T}_{n+j})\mathrm{mod}(1024\×m)(1\≤i\≤k)...\left(1\right)$

The backoff counter initial value BT that d) will just produce _N+1, BT _N+2..., BT _N+mBe inserted into the current grouping A that promptly will send _nThe header information territory in;

The specific descriptions of this step are as follows:

Every value of DIBCR-Num	Corresponding channel booking step number m
		000	1
001	2
		010	3
011	4

100	5
		101	6
110	7
		111	8

The channel booking step number that every value in table 1 DIBCR-Num territory is corresponding with it

Among the present invention,, defined an expanded data subtype frame, thereby guaranteed that the present invention can keep well compatible with present IEEE 802.11 MAC based on IEEE 802.11 MAC data frame structures.

Among the present invention, an additional field of definition (being called the DIBCR-Num territory) is used for indicating the number of broadcasting counter in the header information territory of MAC Frame.The DIBCR-Num length of field is decided to be 3 bits, promptly allows to send the channel booking (its definition is shown in Table 1) that terminal supported for 8 steps at most.Next, a variable-length territory of definition (being called the DIBCR-Timer territory) is used for carrying m channel booking value (m is provided by the DIBCR-Num territory).Each reservation value (comprises 1 and 1023) between 1 to 1023, so each reservation value just can be represented with 10.Like this, the total length in DIBCR-Timer territory is 10 * m bit, with the backoff counter initial value BT that produces _N+1, BT _N+2..., BT _N+mBe inserted in this variable-length territory.

E) with packet A _nSend;

F) establish terminal B and listen to the grouping A that transmission terminal A is sent _nFrom the DIBCR-Timer territory that receives packet, obtain k ' (≤m) individual counter initial value x ₁, x ₂..., x _k';

G) calculate the time slot position that these counter initial values are preengage;

If the current time slots position indicator pointer that B safeguarded is T _B, time slot pairing time slot position in the channel booking window of B of being preengage of terminal A is respectively so $T_{B_j}=(T_B+\underset{i=1}{\overset{j}{\mathrm{\Σ}}}{x}_i)\mathrm{mod}(1024\×m)(1\≤j\≤k^{\′}).$

H) the B terminal is labeled as " being preengage " state with these locational time slots.

The invention has the beneficial effects as follows: compare with single step channel booking algorithm, adopt the present invention can effectively avoid the generation of packet collisions, thereby significantly improve the percent of pass of system.Emulation experiment shows, compares and the single step channel booking method, and under the wireless communications environment that transmission error rate be can not ignore, the present invention can improve system's percent of pass nearly 40%.

The present invention is further described below in conjunction with drawings and Examples.

Description of drawings

Fig. 1 is the data structure diagram that the present invention sends terminal.

Fig. 2 is a growth data frame assumption diagram of the present invention.

Fig. 3 is the present invention and prior art system throughput comparison diagram.

Fig. 4 is the average packet transmission delay contrast of the present invention and prior art.

Fig. 5 is that the present invention sends channel booking window and the backoff counter schematic diagram that terminal A is safeguarded constantly at k+1.

Fig. 6 is that k+2 of the present invention sends channel booking window and the backoff counter figure that terminal A is safeguarded constantly.

Embodiment

Under the k+1, the state of channel booking window, current time slots position indicator pointer and two backoff counter of transmission terminal A as shown in Figure 5 constantly.The current time slots position indicator pointer has pointed to next time slot position (i.e. No. 3 time slot positions), and No. 1 backoff counter value subtracts 1 simultaneously.Further hypothesis sends grouping without any sending terminal at moment k+1 on the channel.Therefore, after the idle time slots, system will enter next time slot, promptly enter k+2 constantly.

A) calculate in the transmit queue at current transmission grouping A _K+2The A of the follow-up grouping of other of Deng Daiing afterwards _K+3, A _K+4The backoff counter initial value BT that will use _K+3, BT _K+4

During moment k+2, the state of channel booking window, current time slots position indicator pointer and two backoff counter of transmission terminal A as shown in Figure 6.The current time slots position indicator pointer has pointed to next time slot position (i.e. No. 4 time slot positions, this time slot position just in time is that terminal A has preengage), and No. 1 backoff counter value reduces to 0 simultaneously.Therefore, terminal A enters and sends the current data Packet State.

Send before the current group, A has carried out preengaging (its corresponding backoff counter initial value is 6) to No. 10 time slots, and therefore the A position that only need calculate 1 reservation time slot again gets final product here.During initial calculation, make q=1.At first, 1 and min[q (CW _Min-1), (CW _Max-1) evenly produces a random number x] ₁(make CW as the backoff counter initial value _Min=31, CW _Max=1024), i.e. x ₁=uniform (1, min[q (CW _Min-1), (CW _Max-1)]).If x ₁=20, its pairing time slot position is (10+20) mod (1024 * 2)=30, is preengage by other-end, so just produce x once more ₂=uniform (1, min[q (CW _Min-1), (CW _Max-1)]).If x ₂=2, its pairing time slot position is (10+2) mod (1024 * 2)=12.If the position is 12 time slot also to be sent terminals by other and not to preengage, so x ₂The=2nd, the new backoff counter initial value that produces.So obtain two backoff counter initial value: BT respectively _K+3=6, BT _K+4=2.

B) with the backoff counter initial value BT that produces recently _K+3=6, BT _K+4=2 upgrade m=2 the backoff counter that the transmission terminal is safeguarded one by one, promptly use BT _K+3=6 upgrade the number one backoff counter, use BT _K+4=2 upgrade No. second backoff counter;

C) the position T of time slot in the channel booking window of A that preengages according to number one and No. second backoff counter _A1And T _A2, be " 1 " with the relevant position of channel booking window, thereby show that corresponding time slot is preengage;

The current time slots position indicator pointer that A safeguarded in this example is T _A=4, the position T of the time slot of reservation in the channel booking window of A _A1And T _A2Computing formula be:

${\mathrm{<figure-callout\; id="1"\; label="T\; A"\; filenames="A20071001781600101.png,A20071001781600121.png"\; state="\{\{state\}\}">T</figure-callout>}}_{A_{}}=(T_A+{\mathrm{BT}}_{k+3})\mathrm{mod}(1024\&times;2)$

$=(4+6)\mathrm{mod}(1024\&times;2)=10$

${\mathrm{<figure-callout\; id="2"\; label="T\; A"\; filenames="A20071001781600101.png,A20071001781600111.png"\; state="\{\{state\}\}">T</figure-callout>}}_{A_{}}=(T_A+{\mathrm{BT}}_{k+3}+{\mathrm{BT}}_{k+4})\mathrm{mod}(1024\&times;2)$

$=(4+6+2)\mathrm{mod}(1024\&times;2)=12$

The backoff counter initial value BT that d) will just produce _K+3=6, BT _K+4=2 are inserted into the current grouping A that promptly will send _K+2The header information territory in;

Owing to have only two backoff counter initial values, so the value in DIBCR-Num territory is " 001 " (seeing Table 1).Next, in the DIBCR-Timer territory, deposit following two backoff counter initial values, i.e. BT _K+3=6, BT _K+4=2, and respectively account for 10.

E) with packet A _K+2Send.

F) establish terminal B and listen to the grouping A that transmission terminal A is sent _K+2From the DIBCR-Timer territory that receives packet, obtain k '=2 (≤m) individual counter initial value x ₁=6, x ₂=2;

G) calculate the time slot position that these counter initial values are preengage;

If the current time slots position indicator pointer that B safeguarded is T _B=120, time slot pairing time slot position in the channel booking window of B of being preengage of terminal A is respectively (120+6) mod (1024 * 2)=126 and (120+6+2) mod (1024 * 2)=128 so.

H) the B terminal is labeled as " being preengage " state with these locational time slots.

Claims (4)

1, a kind of block conflict resolving method of WLAN (wireless local area network) is characterized in that comprising the steps:

(a) calculate in the transmit queue at current transmission grouping A _nThe A of the follow-up grouping of other of Deng Daiing afterwards _N+1, A _N+2..., A _N+kThe backoff counter initial value BT that will use _N+1, BT _N+2..., BT _N+k

(b) with the backoff counter initial value BT that produces recently _N+1, BT _N+2..., BT _N+kUpgrade sending m the backoff counter that terminal is safeguarded one by one, promptly use BT _N+iUpgrade i (number backoff counter of 1≤i≤k);

(c) the position T of time slot in the channel booking window of A that is preengage according to the i backoff counter _Ai, be " 1 " with the relevant position of channel booking window, thereby show that corresponding time slot is preengage;

The backoff counter initial value BT that (d) will just produce _N+1, BT _N+2..., BT _N+mBe inserted into the current grouping A that promptly will send _nThe header information territory in;

(e) with packet A _nSend;

(f) establish terminal B and listen to the grouping A that transmission terminal A is sent _n, from the DIBCR-Timer territory that receives packet, obtain k ' (≤m) individual counter initial value x ₁, x ₂..., x _k';

(g) calculate the time slot position that these counter initial values are preengage;

If the current time slots position indicator pointer that B safeguarded is T _B, time slot pairing time slot position in the channel booking window of B of being preengage of terminal A is respectively so $T_{B_j}=(T_B+\underset{i=1}{\overset{j}{\mathrm{\&Sigma;}}}{x}_i)\mathrm{mod}(1024\&times;m)(1\&le;j\&le;k^{\&prime;});$

(h) the B terminal is labeled as " being preengage " state with these locational time slots.

2, according to the block conflict resolving method of a kind of WLAN (wireless local area network) of claim 1, it is characterized in that described step (a):

Will produce with the pairing backoff counter initial value of i backoff counter be x (i); The position of the time slot that known previous backoff counter is preengage in the channel booking window is T _Ai-1During initial calculation, make q=1; At first, 1 and min[q (CW _Min-1), (CW _Max-1) evenly produces a random number x] ₁As backoff counter initial value (CW _MinExpression minimum competition window size, CW _MaxThe maximum of expression backoff counter); If the pairing time slot of this value is preengage by other-end, just produce x once more ₂=uniform (1, min[q (CW _Min-1), (CW _Max-1)]); If the continuous x that produces for L time ₁, x ₂..., x _LPairing time slot is all preengage by other-end, and then the value with current q adds 1; Utilization and top same method are until producing satisfactory x value as the backoff counter initial value x (i) that finally produces then; Like this, the position of time slot in the channel booking window of A preengage of i backoff counter is $T_{A_i}=(T_{A_{i-1}}+x\left(i\right))\mathrm{mod}(1024\&times;m).$

3, according to the block conflict resolving method of a kind of WLAN (wireless local area network) of claim 1, it is characterized in that described step (c): the position T of the time slot of reservation in the channel booking window of A _AiComputing formula be

$T_{A_i}=(T_A+\underset{j=1}{\overset{i}{\mathrm{\&Sigma;}}}{\mathrm{BT}}_{n+j})\mathrm{mod}(1024\&times;m)(1\&le;i\&le;k).$

4, according to the block conflict resolving method of a kind of WLAN (wireless local area network) of claim 1, it is characterized in that described step (d):, define an expanded data subtype frame based on IEEE 802.11MAC data frame structure; DIBCR-Num territory by 3 bit lengths provides channel booking value m; Define a variable-length territory and be used for carrying m channel booking value; Each reservation value (comprises 1 and 1023) between 1 to 1023, the total length of DIBCR-Timer is 10 * m bit.

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