WO2009089241A2

WO2009089241A2 - Systems and methods for an adaptive power controlled mac protocol for wireless ad hoc networks

Info

Publication number: WO2009089241A2
Application number: PCT/US2009/030261
Authority: WO
Inventors: Pan Li; Yuguang Fang
Original assignee: University Of Florida Research Foundation, Inc.
Priority date: 2008-01-07
Filing date: 2009-01-07
Publication date: 2009-07-16
Also published as: WO2009089241A3

Abstract

An embodiment generally relates to a method of transmitting. The method includes detecting an incoming packet at a wireless network interface and determining a minimum power level based on a transmission power level contained in the incoming packet. The method also includes determining whether any neighboring nodes are transmitting and determining an allowable power level to a sender of the incoming packet. The method further includes transmitting the reply packet at the allowable power level in response to the allowable power level being greater than the minimum power level.

Description

SYSTEMS AND METHODS FOR AN ADAPTIVE POWER CONTROLLED WIAC PROTOCOL FOR WIRELESS AD HOC NETWORKS

DESCRIPTION OF THE INVENTION

Government Rights

[0001] This invention was made with government support under Contracts

DBi-0529012 and CNS-0721744 awarded by the National Science Foundation (NSF). The government has certain rights in the invention.

Related Applications

[0002] This application claims priority to U.S. Provisional Patent

Application No. 61/019,353, filed January 7, 2008, which is hereby incorporated by reference in its entirety.

Field of the Invention

[0003] This invention relates generally to wireless ad hoc networks, more particularly, to systems and methods for an adaptive power controlled media access control ("MAC") protocol for wireless ad hoc networks.

Background of the Invention

[0004] A wireless ad hoc network is a network where nodes communicate with each other via a wireless medium directly or indirectly with the assistance of other nodes. It has gained popularity recently due to its easy and quick deployment with low cost In ad hoc networks, the wireless channel is shared by all the nodes, and hence a media access control (MAC) protocol is needed to coordinate their transmissions to reduce collision events. Although it was initially standardized for wireless local area networks (WLANs), IEEE 802.11 DCF (Distributed Coordination Function), known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), with an optional use of RTS/CTS, is now also widely used in wireless ad hoc networks.

[0005] However, the IEEE 802.11 standard has two main disadvantages when used in ad hoc networks. First, energy is used inefficiently. More particularly, IEEE 802.11 specifies the same transmission power for all nodes to transmit all their packets, no matter how close a transmitter may be to its intended receiver. Second, the spatial reuse of the network is low. According to IEEE 802.1 1 , when one node is transmitting, the other nodes in its physical carrier sensing range should keep silent to avoid interference. Thus, even those transmissions that will not interfere with the ongoing one are still blocked. Accordingly, there is a need in the art for a mechanism to transmit packets efficiently and to utilize spatial reuse.

SUMMARY OF THE INVENTION

[0006] An embodiment generally relates to a method of transmitting. The method includes detecting an incoming packet at a wireless network interface of a current node and determining a minimum power level based on a reception power level collected by the wireless network interface and a transmission power level contained in the incoming packet. The method also includes determining whether any neighboring nodes are engaged in transmission and determining an allowable power level for a transmitter to transmit to its intended receiver based on a maximum power level of the neighboring nodes. The method further includes transmitting the DATA packet at the allowable power level in response to the allowable power level being larger than the minimum power level required to successfully transmit to the receiver. [0007] Another embodiment pertains generally to an apparatus configured to transmit and receive wireless packets. The apparatus includes a radio frequency interface configured to transmit and receive packets conforming to an IEEE802.11 standard and a computer interface configured to translate data from a computer to packets conforming to the IEEE802.11 standard. The apparatus also includes a network controller coupled to the radio frequency interface and the computer interface. The network controller is configured to detect an incoming packet at the radio frequency interface of a current node and to determine a minimum power ieve! based on a reception power level collected at the radio frequency interface and a transmission power Ieve! contained in the incoming packet. The network controller is also configured to determine whether any neighboring nodes are engaged in transmission and to determine an allowable power level for a transmitter to transmit to its intended receiver based on a maximum power level of the neighboring nodes. The network controller is further configured to transmit the DATA packet at the allowable power level in response to the allowable power level being greater than the minimum power level. [0008] Additional objects and advantages of the invention will be set forth in part in the description which follows, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

[0011] FIG. 1 illustrates an exemplary system in accordance with an embodiment of the present invention;

[0012] FIG. 2 shows an exemplary flow diagram executed by an adaptive power control ("APC") module in accordance with various embodiments; [0013] FIG. 3 depicts another exemplary flow diagram executed by the APC module in accordance with various embodiments; and

[0014] FIG. 4 illustrates yet another exemplary flow diagram executed by the APC module in accordance with various embodiments.

DESCRIPTION OF THE EMBODIMENTS

[0015] For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of wireless network systems, and that any such variations do not depart from the true spirit and scope of the present invention. Moreover, in the following detailed description, references are made to the accompanying figures, which illustrate specific embodiments. Electrical, mechanical, logical and structural changes may be made to the embodiments without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the present invention is defined by the appended claims and their equivalents.

[0016] Embodiments relate generally to systems, methods and apparatus for an adaptive power controlled MAC protocol for wireless ad hoc networks. More particularly, a network interface card can be configured with an adaptive power control ("APC") module. The APC module can be configured to operate with a modified 802.1 1 protocol. Two additional fields, transmission power, P₁, and an interference level, Piπter_f. have been added to RTS (request-to-send) and CTS (clear-to-seπd) frames of the 802.1 1 standard. The ACK frames also include an additional field, transmission power, P₁.

[0017] The APC module can also maintain a neighboring node table. The neighboring node table can have a schema of a node identification ("ID") field, a minimum power, P_mi_π, field, a maximum power, Pr_713x, field, and a NAV field. The node ID field can identify a selected neighboring node. The minimum power field can indicate the minimum power to transmit to the selected neighboring node. The maximum power field can indicate the maximum allowable power value to the selected neighboring node. The NAV field can indicate whether or not the selected neighboring node is transmitting.

[0018] According to some embodiments, the APC module can be configured to detect an incoming CTS packet. The APC module can then collect a reception power value, P_n, from the wireless interface and get the transmission power value, P_t, contained in the CTS packet, Subsequently, the APC module can determine a minimum power value, P_miπt for the current node to successfully transmit packets to the sender of the CTS packet. The P_min field in the respective table can be updated accordingly. Moreover, the P_max field in the respective table can also be updated based on the P-_misri included in the CTS packet. [0019] If this CTS packet is for the current node, the APC module can transmit a DATA packet after the SIFS period. If this CTS packet is not for the current node and this node has packets to transmit, the APC module can then determine whether any of the neighboring nodes are engaged in transmission. If any of the other neighboring nodes are actively transmitting, the APC module can then determine the allowable power level to transmit a packet to the current transmission without interfering with the current transmissions of the neighboring nodes,

[0020] The APC module determines whether the allowable power level is greater than the minimum power level required to transmit to the intended receiver, which can be obtained by checking the respective table as mentioned previously. If the allowable power level is greater, the APC module can transmit the DATA packet after SlFS period at the allowable power level. Thus, the current node detecting an incoming CTS packet can transmit a DATA packet at the same time as the intended receiver of the CTS packet. If the allowable power is less than the minimum power level, the APC module cannot transmit any packets. [0021] In other embodiments, the APC module can be configured to detect an RTS packet The APC module can then collect the reception power level value, P₀ and retrieve the transmission power level, P₁, from the RTS packet. Subsequently, the APC module can determine a minimum power level, P_min> for the current node to successfully transmit packets to the send of the RTS packet. The P_min field in the respective table can be updated accordingly. Moreover, the Pmax field in the respective table can also be updated based on the P_inter_f included in the RTS packet.

[0022] if this RTS packet is for the current node, the APC module can determine the maximum average interference level, P_lπterfl to insert into the reply packet, i.e., the CTS packet, and transmit the CTS packet after the SIFS period. Thus, this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's DATA reception. If this RTS packet is not for the current node and this node has packets to transmit, the APC module can then determine whether any of the other neighboring nodes are engaged in transmission.

[0023] If any of the other neighboring nodes are activefy transmitting, the

APC module can then determine the allowable power level to transmit a packet to its intended receiver without interfering with the current transmissions of the neighboring nodes. The APC module can be configured to determine whether the allowable power level is larger than the minimum power level, P_miπ, required to transmit to the intended receiver. If the allowable power level is larger, the APC module can transmit the DATA packet after 2*SIFS + TJCTS} period at the allowable power level where T_{CTS} is the transmission time of the CTS packet. Thus, the current node detecting an incoming RTS packet can transmit a DATA packet at the same time as the transmitter of the RTS packet. If the allowable power level is less than the minimum power level, P_min, the APC module cannot transmit any packet.

[0024] In other embodiments, the APC module can be configured to detect an ACK packet. The APC module can then collect a reception power value, P_n and get the transmission power value, P₁, contained in the ACK packet. Subsequently, the APC module can determine a minimum power level, P_min, for the current node to successfully transmit packets to the sender of the ACK packet. The P_miπ field in the respective table can be updated accordingly. If this packet is for the current node, the APC module can determine the maximum average interference level, P_Tπler_f, to insert into a next RTS frame so that this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's CTS reception for the next DATA transmission. If this packet is not for the current node, the current node does nothing. [0025] FIG. 1 illustrates an exemplary network interface card 100 in accordance with various embodiments. It should be readily apparent to those of ordinary skill in the art that the network interface card 100 depicted in FIG. 1 represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. Moreover, the network interface card 100 may be implemented using software components, hardware components, or combinations thereof.

[0026] As shown in FIG. 1 , the network interface card ("NIC") 100 can comprise a radio frequency ("RF") interface 105, a network controller 110, and a computer interface 120. The RF interface 105 can be configured to provide a communication interface between the NIC 100 and a wireless medium such as radio frequency band. The RF interface 105 can transmit and receive packets conforming to the 802.11 network standard.

[0027] The network controller 110 can be configured to manage and control the operation of the NIC card 100 as described previously and in greater detail below. The network controller 110 can be implemented with a microprocessor, a digital signal processor, an application specific integrated circuit, an EEPROM or other similar programmable computing device. In some embodiments, the NIC card 100 can perform at least a conversion of wireless data packets between computer data format to the wireless format of IEEE802.11 standard. [0028] The computer interface 120 can be configured to provide an interface between a host computing device (such as personal computer, laptop computer, personal digital assistance or other mobile computing device) and the NIC 100. The computer interface 120 can receive and transmit data to the NIC card through this interface.

[0029] In some embodiments, the network controller 110 can store and execute an adaptive power control ("APC") module 1 15. The APC module 115 can be configured to operate with a slightly modified 802.11 protocol. For instance, two additional fields, transmission power, P_t, and interference level, PiπtGrf, have been added to RTS and CTS frames of the 802.1 1 standard. The ACK frames also include an additional field, i.e., transmission power, P_t. Further, for instance, a single-radio, single-channel, multi-rate protocol can be implemented to improve the spatial reuse by controlling the transmission power so that multiple transmissions can be enabled at the same time without interfering with each other.

[0030] The APC module 115 can also maintain a neighboring node table.

The neighboring node table can have a schema of a node identification ("ID") field, a minimum power, P_min, field, a maximum power, P_max, field, and a NAV field. The node ID field can identify a selected neighboring node. The minimum power field can indicate the minimum power to transmit to the selected neighboring node. The maximum power field can indicate the maximum power value to the selected neighboring node. The NAV field can indicate whether or not the selected neighboring node is transmitting.

[0031] According to some embodiments, the APC module 115 can be configured to detect an incoming CTS packet. The APC module 115 can then collect a reception power value, P_r, from the wireless interface and get the transmission power value, P_tl contained in the CTS packet. Subsequently, the APC module 115 can determine a minimum power value, P_miπι for the current node to successfully transmit packets to the send of the CTS packet. The P_min field in the respective table can be updated accordingly. Moreover, the P_max field in the respective table can also be updated based on the Pinter_f included in the CTS packet.

[0032] If this CTS packet is for the current node, the APC module 115 can transmit a DATA packet after the SIFS period. If this CTS packet is not for the current node and this node has packets to transmit, the APC module 1 15 can then determine whether any of the neighboring nodes are engaged in transmission. If any of the other neighboring nodes are actively transmitting, the APC module 1 15 can then determine the allowable power level to transmit a packet to the current transmission without interfering with the current transmissions of the neighboring nodes.

[0033] The APC module 1 15 determines whether the allowable power level is greater than the minimum power level required to transmit to the intended receiver, which can be obtained by checking the respective table as mentioned previously. If the allowable power level is greater, the APC module 115 can transmit the DATA packet after SlFS period at the allowable power level. Thus, the current node detecting an incoming CTS packet can transmit a DATA packet at the same time as the intended receiver of the CTS packet. If the allowable power is less than the minimum power level, the APC module cannot transmit any packets.

[0034] in other embodiments, the APC module 1 15 can be configured to detect an RTS packet. The APC module 115 can then collect the reception power level value, P_r, and retrieve the transmission power level, P_t, from the RTS packet. Subsequently, the APC module 115 can determine a minimum power level, P_mι_π, for the current node to successfully transmit packets to the send of the RTS packet. The P_mi_π field in the respective table can be updated accordingly. Moreover, the P_max field in the respective table can also be updated based on the Pinter_f included in the RTS packet. If this RTS packet is for the current node, the APC module 115 can determine the maximum average interference level, Pinter_f, to insert into the reply packet, i.e., the CTS packet, and transmit the CTS packet after the SIFS period.

[0035] Thus, this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's DATA reception. If this RTS packet is not for the current node and this node has packets to transmit, the APC module 115 can then determine whether any of the other neighboring nodes are engaged in transmission. If any of the other neighboring nodes are actively transmitting, the APC module 115 can then determine the allowable power level to transmit a packet to its intended receiver without interfering with the current transmissions of the neighboring nodes.

[0036] The APC module 115 can be configured to determine whether the allowable power level is larger than the minimum power level, P_mι_π, required to transmit to the intended receiver. If the allowable power level is larger, the APC module 115 can transmit the DATA packet after 2*SIFS + T_{CTS} period at the allowable power level where T_{CTS} is the transmission time of the CTS packet. Thus, the current node detecting an incoming RTS packet can transmit a DATA packet at the same time as the transmitter of the RTS packet If the allowable power level is less than the minimum power level, P^n, the APC module 115 cannot transmit any packet.

[0037] In other embodiments, the APC module 115 can be configured to detect an ACK packet. The APC module 115 can then collect a reception power value, P_n and get the transmission power value, P₁, contained in the ACK packet. Subsequently, the APC module 115 can determine a minimum power level, P_mtn, for the current node to successfully transmit packets to the sender of the ACK packet. The Pm_in field in the respective table can be updated accordingly. If this packet is for the current node, the APC module 1 15 can determine the maximum average interference level, P_iπter_f. to insert into a next RTS frame so that this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's CTS reception. If this packet is not for the current node, the current node does nothing.

[0038] FlG. 2 illustrates an exemplary flow diagram 200 executed by the

APC module 115 in accordance with various embodiments. It should be readily apparent to those of ordinary skill in the art that the flow diagram 200 depicted in FIG. 2 represents a generalized schematic illustration and that other steps may be added or existing steps may be removed or modified. [0039] As shown in FlG. 2, the APC module 1 15 can be configured to detect a CTS packet, in step 205, The APC module 115 can receive the CTS packet via the RF interface 105. [0040] In step 210₁ the APC module 1 15 can be configured to collect or retrieve the reception power level, P_n from the RF interface 105 as known to those skilled in the art. For example, the APC module 115 can be configured to determine the reception power level by using equation (1):

(D Λ =c.|

where P_t is the transmission power level; C is a constant related to the antenna profiles of the transmitter and the receiver, wavelength, and other variables; and dij is the distance between node i and node j. The APC module 115 can also retrieve the transmission power value from the respective field of the CTS packet. [0041] In step 215, the APC module 115 can be configured to determine the minimum power level by using equation (2):

where RXu₁ is the receiver sensitivity (or minimum power level) required for correctly receiving a signal. The APC module 115 can temporarily buffer the minimum power level for the received CTS packet The APC module 115 can then update the minimum power level field, P_mι_π, in the respective table for the sender of the CTS packet.

[0042] in step 220, the APC module 115 can be configured to retrieve the maximum average interference value, P_Meril from the CTS packet and update the Pmax field in the respective table of the current node. The APC module 115 can calculate P_max by using equation (3): p ■ P

(9,\ P — '""-'¹^ '

\°> Λtinx - 7; — [0043] In step 225, the APC module 115 can determine whether the CTS packet is for the current node. If the CTS packet is for the current node, the APC module 115 can transmit a DATA packet after a SIFS period, in step 230, Otherwise, if the CTS packet is not for the current node, the APC module 1 15 can be configured to determine whether any neighboring nodes are actively transmitting or engaged in transmission, in step 235. If none of the neighboring nodes are transmitting, the APC module 115 can set the transmission power level is at P_max, in step 260. The APC module 1 15 can then transmit a reply packet at the Pπiax, in step 265.

[0044] Returning to step 235, if any of the neighboring nodes are engaged in transmission, the APC module 115 can be configured to determine the allowable power level, P_an_ow, by using equation (4), in step 240:

(4) P_allm. = {min,_es {?,L }// S ≠ 0; P,_ux if S =ϋ} where S is the set of the active neighboring nodes and it can be obtained by checking the table previously described, and P_MAX is the maximum transmission power allowed for the wireless interface card.

[0045] In step 245, the APC module 1 15 can be configured to determine whether the allowable power level is greater or larger than the minimum power level. If the allowable power level is greater, the APC module 115 can transmit a DATA packet at the allowable power level after SIFS, in step 250. Otherwise, the APC module 115 can not transmit the reply packet, in step 255. [0046] FIG. 3 illustrates another exemplary flow diagram 300 executed by the APC module 115 in accordance with various embodiments. It should be readily apparent to those of ordinary skill in the art that the flow diagram 300 depicted in FIG. 3 represents a generalized schematic illustration and that other steps may be added or existing steps may be removed or modified.

[0047] As shown in FlG. 3, the APC module 115 can be configured to detect a RTS packet, in step 305, The APC module 115 can receive the RTS packet via the RF interface 105.

[0048] In step 310, the APC module 115 can be configured to collect or retrieve the reception power level, P_n from the RF interface 105 as known to those skilled in the art and retrieve the transmission power level from the respective field in the RTS packet.

[0049] In step 315, the APC module 1 15 can be configured to determine the minimum power level by using equation (2). The APC module 115 can then update the minimum power level field, P_miπ, in the table for the sender of the RTS packet.

[0050] In step 320, the APC module 115 can be configured to retrieve the maximum average interference value, Ptπtβr_f, from the RTS packet and update the

Pmax field in the respective table of the current node. The APC module 115 can be configured to calculate P_1713x based on equation (3).

[0051] In step 325, the APC module 115 can determine whether the RTS packet is for the current node. If the RTS packet is for the current node, the APC module 115 can be configured to determine the minimum power level, P_mι_n, by using equation (2), and update the minimum power level field, P_mln, in the respective table, in step 326.

[0052] In step 327, the APC module 115 can determine the maximum average interference level, P|_nterf, by using equation (5); (5) P -. ^P> ^{~ SINR} - ^P^ V ' """* N - (\ + β) - SINR

[0053] In embodiments, in a multi-rate protocol, the maximum average interference level, Pjnier_f, can be caiculated by using equation (6):

(6) p. - ^Pr -^mRr ^p***

^{'m af} N - (l + β) - SINR, where SINR₁ is the signai-to interference plus noise ratio required to support the data rate, R₁ , the transmitter has chosen.

[0054] In step 328, the APC module 115 can be configured to insert the maximum average interference level, Pt_nter_f, in the CTS packet. Accordingly, this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's DATA reception, in step 330, the APC module 115 can transmit a CTS packet after a SiFS period,

[0055] Contrary, if the RTS packet is not for the current node, the APC module 115 can be configured to determine whether any neighboring nodes are actively transmitting or engaged in transmission, in step 335. If none of the neighboring nodes are transmitting, the APC module 115 can set the transmission power level is at P_max, in step 360. The APC module 1 15 can then transmit a reply packet at the P_maχ, in step 365.

[0056] Returning to step 335, if any of the neighboring nodes are engaged in transmission, the APC module 1 15 can be configured to determine the allowable power level, P_aI|_QW) by using equation (4), in step 340. [0057] In step 345, the APC module 115 can be configured to determine whether allowable power level is greater or larger than the minimum power level. If the allowable power level is greater, the APC module 115 can transmit a DATA packet at the allowable power level after a period of 2*SIFS + T_{CTS}, in step

350. Otherwise, the APC module 115 can not transmit the reply packet, in step

355.

[0058] FIG. 4 illustrates yet another exemplary flow diagram 400 executed by the APC module 1 15 in accordance with various embodiments, it should be readily apparent to those of ordinary skill in the art that the flow diagram 400 depicted in FIG. 4 represents a generalized schematic illustration and that other steps may be added or existing steps may be removed or modified.

[0059] As shown in FIG. 4, the APC module 115 can be configured to detect an ACK packet over the RF interface 105, in step 405. In step 410, the

APC module 1 15 can be configured to collect the reception power level, P_n from the RF interface 105 and retrieve the transmission power, P_t, contained in the

ACK packet.

[0060] In step 415, the APC module 115 can process the received ACK packet to determine whether the ACK packet is for the current node. If the ACK packet is for the current node, the APC module 115 can be configured to determine the minimum power level, P_m|_π, by using equation (2). The APC module 115 can then update the minimum power level field, P_m\n, in the table for the sender of the RTS packet.

[0061] In step 425, the APC module 115 can determine the maximum average interference level, P_]n(erft by using equation (5). In embodiments, in a multi-rate protocol, the maximum average interference level, Piπtert, can be calculated by using equation (6).

[0062] In step 430, the APC module 115 can be configured to insert the maximum average interference level, P|_πlerfl in the RTS packet. Accordingly, this node's neighboring nodes can update the maximum allowable transmission power not to affect the current node's DATA reception.

[0063] Returning to step 415, if the ACK packet is not for the current node, the APC module 115 can drop the ACK packet and enter an idle state to wait for the next packet, in step 435.

[0064] Other embodiments of the present invention are described in the attached Attachment A and is hereby incorporated by reference in its entirety. [0065] Certain embodiments may be performed as a computer program.

The computer program may exist in a variety of forms both active and inactive. For example, the computer program can exist as software program(s) comprised of program instructions in source code, object code, executable code or other formats; firmware program (s); or hardware description language (HDL) files. Any of the above can be embodied on a computer readable medium, which include storage devices and signals, in compressed or uncompressed form. Exemplary computer readable storage devices include conventional computer system RAM (random access memory), ROM (read-only memory), EPROM (erasable, programmable ROM), EEPROM (electrically erasable, programmable ROM), and magnetic or optical disks or tapes. Exemplary computer readable signals, whether modulated using a carrier or not, are signals that a computer system hosting or running the present invention can be configured to access, including signals downloaded through the Internet or other networks. Concrete examples of the foregoing include distribution of executable software program(s) of the computer program on a CD-ROM or via Internet download. In a sense, the Internet itself, as an abstract entity, is a computer readable medium. The same is true of computer networks in general. [0066] While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments without departing from the true spirit and scope. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the method has been described by examples, the steps of the method may be performed in a different order than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope as defined in the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A method of transmitting, the method comprising: detecting an incoming packet at a wireless network interface of a current node; determining a minimum power level based on a reception power level and a transmission power level contained in the incoming packet; determining whether any neighboring nodes are transmitting; determining an allowable power level to a sender of the incoming packet based on a maximum power level of the neighboring nodes; and transmitting the reply packet at the allowable power level in response to the allowable power level being greater than the minimum power level.

2. The method of claim 1 , further comprising collecting the reception power level from a wireless interface, wherein the reception power level is related p to the transmission power level by P_r = c * -^J~. dl

3. The method of claim 2, wherein the minimum power level is based

„ P. • RX ,,, on p ⁱ ιπm . = — p ^

4. The method of claim 1 , wherein the allowable power level is based on P_al!m. = {min_te, fc_x },/ S ≠ 0; P_mx ifS = θ}.

5. The method of claim 1 , further comprising transmitting the reply packet at maximum power in response to none of the neighboring nodes transmitting.

6. The method of claim 1 , further comprising transmitting the reply packet at the minimum power level in response to the allowable power level being greater than the minimum power level,

7. The method of claim 1 , further comprising: retrieving a maximum average interference, Pmtβr_f. from the incoming packet; and determining a maximum power based on the maximum average interference.

8. The method of claim 7, wherein the maximum average interference

is based on P. , ... = ^P''→ ^{' P}' .

9. The method of claim 1, wherein the reply packet is a DATA packet in response to the incoming packet is a CTS packet.

10. The method of claim 1, wherein the reply packet is a CTS packet in response to the incoming packet is a RTS packet, the method further comprises: collecting reception power, P_r; retrieving transmission power, P₁; and determining a maximum average interference level, Pin_ter_f. based on Pr and P_t.

11. The method of claim 10, wherein the maximum average interference p SΓNR P level is based on P_n. _ιrf = -£ — "^olκ , m^teιf N - (\ + β) - SINR

12. The method of claim 1O₁ wherein the maximum average interference

P — SINR • P level is based on P. _rr = -= - — ^ in a multi-rate protocol.

"^lUr/ N - (\ + β) - SINR₁ ^κ

13. The method of claim 1 , wherein the incoming packet is an ACK packet, the method further comprises: collecting reception power, P_r; retrieving transmission power, P_t; and determining a maximum average interference level, P_iπ[erf_t based on Pr and P_t.

14. The method of claim 13, wherein the maximum average interference

level is based on P_ml ,„. = -^ — ""'"^■' .

™^u* N • (1 + β) ^■ SINR

15. The method of claim 13, wherein the maximum average interference

P — SINR • P level is based on /L ₇., = -^£ — ≤^- in a multi-rate protocol. m^af N -(\ + β) - SINR, ^H

16. An apparatus configured to transmit and receive wireless packets, the apparatus comprising: a radio frequency interface configured to transmit and receive packets conforming to an IEEE802.11 standard; a computer interface configured to translate data from a computer to packets conforming to the 1EEE802.11 standard; a network controller coupled to the radio frequency interface and the computer interface, wherein the network controller is configured to detect an incoming packet at the radio frequency interface of a current node; to determine a minimum power level based on a transmission power level contained in the incoming packet; to determine whether any neighboring nodes are transmitting; to determine an allowable power level to a sender of the incoming packet based on a maximum power level of the neighboring nodes; and to transmit the reply packet at the allowable power level in response to the allowable power level being greater than the minimum power level.

17. The apparatus of claim 16, wherein the network controller collects a p reception power level, which is related to the transmission power by P_r = C •-^L ₇.

18. The apparatus of claim 16, wherein the minimum power level is

P - RY based on P_miπ = —— ' — — .

19. The apparatus of claim 16, wherein the allowable power level is based on P_allιm, = {min_Aεi,

S =θ}.

20. The apparatus of claim 16, wherein the network controller is further configured to transmit the reply packet at maximum power in response to none of the neighboring nodes transmitting.

21. The apparatus of claim 16, wherein the network controller is further configured to transmit the reply packet at the allowable power level in response to the allowable power level being greater than the minimum power level.

22. The apparatus of claim 16, wherein the network controller is further configured to maintain a neighboring node table.

23. The apparatus of claim 16, wherein the neighboring node table further comprises a node identification field, a minimum power field, a maximum power field, and a NAV field.

24. The apparatus of claim 16, wherein the network controller is configured to retrieve a maximum average interference, P_tπter_f, from the incoming packet and to determine a maximum power based on the maximum average interference.

25. The apparatus of claim 24, wherein the maximum average

interference is based on P_ΛHΛ. mt crrf - P₁

26. The apparatus of claim 16, wherein the reply packet is a DATA packet in response to the incoming packet is a CTS packet.

27. The apparatus of claim 16, wherein the reply packet is a CTS packet in response to the incoming packet is a RTS packet.

28. The apparatus of claim 16, wherein the incoming packet is an ACK packet, the network controller is further configured to collect reception power, P_r;to retrieve transmission power, P₁; and to determine a maximum average interference level, Pi_ntert. based on P_r and P_t.

29. The apparatus of claim 28, wherein the maximum average

P — f/Λ/7? P interference level is based on R_n. _ιrf = — '- —≡SUL . m^U>f N - (\ + β) ' SINR

30. The apparatus of claim 28, wherein the maximum average

interference level is based on P_11110-, = — ' ^' '"""^■' in a multi-rate protocol. m^ury N- (\ + β) - SINR, ^κ