HK1151168A - Method and apparatus for resolving blinded-node problems in wireless networks - Google Patents

Description

Method and apparatus for solving blind node problem in wireless network

Technical Field

Aspects of the present disclosure relate generally to wireless network protocols and, more particularly, to methods and apparatus for solving blind node problems in wireless networks.

Background

The Institute of Electrical and Electronics Engineers (IEEE)802.11 Wireless Local Area Network (WLAN) standard has gained significant popularity in recent years. The family of standards covers a wide range of wireless networks with various system designs for handling various traffic and user scenarios. Many other wireless network designs, such as home and business wireless networks, mesh networks, ad hoc networks, wireless sensor networks, etc., are also based on the IEEE 802.11 standard.

In IEEE 802.11-based wireless networks, various nodes of the network reserve access to the wireless medium using control messages, such as Request To Send (RTS)/Clear To Send (CTS). The RTS/CTS mechanism is used to reduce or minimize interference and collisions between network nodes wishing to communicate over the medium. However, when one or more nodes cannot detect an RTS/CTS exchange because the node is listening for the wrong RTS/CTS exchange, a medium reservation failure using the RTS/CTS exchange may occur. This situation is referred to as the "blind node problem," which is consistent with well-accepted terminology such as the hidden node problem and the exposed node problem. This problem may occur in all communication systems where RTS/CTS control packets are used to reserve the medium. The blind node problem degrades throughput and delay performance both locally to the wireless network and across the network.

Therefore, there is a need in the art for a solution to the blind node problem that occurs in wireless networks that rely on RTS/CTS wireless medium reservation mechanisms.

Disclosure of Invention

The solution disclosed herein solves the blind node problem by letting the node stop processing data packets that are not destined for it, so that it can reserve its resources to detect control packets and other packets destined for it.

According to one aspect, a wireless communication method is implemented, comprising: receiving a packet comprising at least one header and non-header information; and decoding the at least one header to determine whether the non-header information should be processed.

According to another aspect, a computer program product for wireless communications is implemented having a computer-readable medium including code executable by at least one computer for receiving a packet including at least one header and non-header information; and decoding the at least one header to determine whether the non-header information should be processed.

According to still another aspect, there is implemented a wireless communication apparatus having: means for receiving a packet comprising at least one header and non-header information; and means for decoding the at least one header to determine whether the non-header information should be processed.

According to yet another aspect, a wireless communications apparatus is implemented having a receiver configured to receive a packet including at least one header and non-header information; and a decoder configured to decode the at least one header to determine whether the non-header information should be processed.

According to yet another aspect, an access point is implemented having an antenna; a receiver for receiving a packet including at least one header and non-header information through the antenna; and a decoder coupled to the receiver, the decoder configured to decode the at least one header to determine whether the non-header information should be processed.

In accordance with yet another aspect, an access terminal is implemented having a receiver for receiving a packet including at least one header and non-header information. The access terminal further comprises a decoder coupled to the receiver, the decoder configured to decode the at least one header to determine whether the non-header information should be processed; and a user interface for providing an indication based on the non-header information.

Drawings

FIG. 1 is a network diagram for describing the blind node problem;

FIG. 2 is a timing diagram for describing the blind node problem;

FIG. 3 is a flow chart of a first scheme for solving the blind node problem;

FIG. 4 is a flow chart of a second scheme for solving the blind node problem;

FIG. 5 is a timing diagram for describing the scheme of FIGS. 3 and 4;

fig. 6 is a block diagram of a node component configured to implement the schemes of fig. 3 and 4.

Fig. 7 is a second block diagram of a node component configured to implement the aspects of fig. 3 and 4.

Detailed Description

Various aspects of the disclosure are described below. It should be apparent that the teachings of the present application may be implemented in a variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings of the present application, one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the apparatus may be implemented or the method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. Further, an aspect may include at least one feature of a claim.

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. Further, the description also makes use of networks associated with the IEEE 802.11 standard, and networks utilizing other protocols may also benefit from the various techniques and systems disclosed herein.

The communication problem, referred to herein as the "blind node" problem, may be illustrated using a simple 5-node network 100 as shown in fig. 1, in which a station STA1104 and an access point AP 1102 are within range of each other, where "within range" indicates that the 2 transceivers (e.g., station STA1104 and access point AP 1102) are able to communicate with each other. Similarly, as shown in fig. 1, station STA3108 and access point AP2110 are within range of each other. In addition, station STA2106 is within range of AP 1102 and station STA 3108. However, station STA1104 and station STA2106 are associated with access point AP 1102, and station STA3108 is associated with access point AP 2110. Further, access point AP 1102 and station STA3108 are not within range of each other, and station STA1104 and station STA2106 are not within range of each other.

The blind node problem arises when communication between station STA1104 and access point AP 1102 is severely impeded by station STA2106 during operation of the node according to the IEEE 802.11 protocol. The blind node problem is described with reference to fig. 1, where the data packets sent by station STA3108 to access point AP2110 blind station STA 2106. When station STA2106 locks on and receives the data packet, it misses the CTS message sent by access point AP 1102. Since station STA2106 is not aware that station STA1104 will transmit data packets to access point AP 1102, when station STA2106 wants to transmit information to access point AP 1102, station STA2106 will transmit an RTS message to access point AP 1102, thereby interfering with and possibly corrupting the data packets that access point AP 1102 is receiving from station STA 1104.

The following is a detailed description and refers to the timing diagram 200 as shown in fig. 2, where station STA3108 performs a process of transmitting a long frame to access point AP 2110. Station STA3108 will send an RTS message 212 and receive a CTS message 202 from AP2110 before station STA3108 begins to send data packet 214. Since station STA2106 is within range of station STA3108, station STA2106 will detect the preamble from station STA3108 and continue accumulating bits of the packet from station STA3108 according to the operational specifications of the protocol. If data packet 214 is decoded and contains a destination address that does not match station STA2106, data packet 214 will be discarded by station STA 2106. During this time period, however, station STA2106 may have set its NAV 252 based on RTS message 212. When station STA1104 sends an RTS message 222 to access point AP 1102, access point AP 1102 will respond with a CTS message 232 because it is not affected by the communication between station STA3108 and access point AP2110 and station STA1104 will start sending data packet 224 to access point AP 1102. The CTS message 232 from access point AP 1102 will not be detected by station STA2106 because STA2106 locked to data packet 214 from station STA 3108. Once data transmission between station STA3108 and access point AP2110 is complete, station STA2106 will probe the medium in its vicinity as idle, as indicated by ACK message 216, because it is not within transmission range of station STA1104 and does not detect an RTS/CTS message exchange between station STA1104 and access point AP 1102. Station STA2106 may then begin sending an RTS message 242 (or data) to access point AP 1102, which would collide with the ongoing transmission of data packet 224 between station STA1104 and access point AP 1102. Note that if aggregation is used, the data frame between station STA1104 and access point AP 1102 may be large and several retransmissions from station STA2106 may be attempted within the frame duration. These collisions will cause errors in the decoding of frames from station STA1104 at access point AP 1102.

Note that the reason station STA2106 attempts to transmit to access point AP 1102 is that it misses the CTS message 232 from access point AP 1102 and is out of range of station STA 1104. Therefore, station STA2106 will decode packets not destined for it. Note also that reserved packets such as RTS and CTS are sent at a rate that can be decoded at low SNR, a problem that has been referred to as the blind node problem because station STA2106 is "blind" to other packets in the medium because it is trying to decode the data packet 214 from station STA 3108.

The illustration of 2 access points and 3 stations in the previously described example is arbitrary. The same problem occurs in many other situations. For example, all 5 nodes in the network may be STAs in an Independent Basic Service Set (IBSS), or equivalent sensor nodes in a wireless sensor network, or Mesh Points (MPs) and STAs and Mesh Access Points (MAPs) in an extended service set Mesh (ESS Mesh).

To address the blind node problem, a node that is blinded by packets destined for other nodes should be able to stop decoding such packets and be able to receive and decode the retained packets in the medium. To solve this problem, two schemes may be adopted. The first scheme involves implementation in the Physical (PHY) layer, while the second scheme involves the Medium Access Control (MAC) layer.

Fig. 3 shows a first procedure 300 for solving the blind node problem, implemented in the PHY layer of a node, starting with step 302, the node entering an idle state after initialization. During the idle state, a node will attempt to detect another node's transmission. Further, during the idle state, the node may have set its NAV period based on previously received packets. The operation of the first procedure 300 will be described with reference to fig. 5 and the network configuration shown in fig. 1, where the "node" referred to in the description is station STA2106, except that station STA2106 now operates in accordance with the first procedure 300 to solve the blind node problem.

In step 304, the node detects a signal that may belong to a packet transmission and proceeds to step 306 where the node decodes the preamble and PLCP header in step 306. Then, at step 308, it is determined whether a packet is detected during the NAV period. If the node is not in a NAV period, e.g., before time T0 of fig. 5, operation continues to step 314 where the packet is processed normally (e.g., decoded to determine the sender and receiver, and responded to if, for example, the packet is destined for the node) at step 314, and then the node returns to its idle state at step 302. If the node is currently in a NAV period, such as NAV period 552 at time T1 in FIG. 5, operation continues to step 310.

At step 310, where the node is currently in a NAV period, the node will not send any requests. A node is only interested in messages such as RTS/CTS packets, which will extend the NAV period, e.g., at time T2 in fig. 5, setting NAV period 554 at time T2, which NAV period 554 will extend the time the node is in the NAV period due to the existing NAV period 552. Thus, at step 310, the node will determine whether the packet contains an RTS/CTS packet, e.g. an RTS message 512 or a CTS message 502, relating to the exchange between station STA3108 and access point AP2110 for transmitting data packet 514; or an RTS message 522 or a CTS message 532 related to the exchange between station STA1104 and access point AP 1102 for sending data packet 524. According to one aspect, the node determines whether the packet contains an RTS/CTS packet by checking the packet duration contained in the PLCP header, since the RTS/CTS packet has a fixed duration. Note that the time taken for the RTS/CTS packet is fixed and therefore may be "hard coded" into the PHY layer processing entity. If the duration field indicates that the frame may be an RTS/CTS packet, the node performs all required procedures to decode the packet. According to another aspect, a node may determine whether a packet contains an RTS/CTS packet by checking the MAC header (which will contain type information). If the message is not an RTS/CTS packet, operation continues to step 316. Otherwise, if the message is an RTS/CTS packet, operation continues to step 312. Further, the ACK message (e.g., ACK message 516) may be ignored by the node or processed to confirm that the previously set NAV period (e.g., NAV period 516) may be terminated.

In step 316, where the message has been determined by the node to be a non-RTS/CTS packet, the node will ignore the packet. In particular, if the node decodes the preamble and PLCP header and the duration field indicates that the packet is not an RTS or CTS packet (e.g., at time T1 in fig. 5) but a data packet (e.g., data packet 514), the node determines that this corresponds to a previous RTS or CTS (e.g., RTS message 512 or CTS message 502) data packet and is therefore not addressed to the node. The node then stops accumulating any further bits to decode the packet and returns to the mode of probing the preamble of any other new packet. The operation will then return to step 302 where the node again enters its idle state to listen for other preambles. Note that although a node may not be able to receive either an RTS or CTS packet due to low SINR, it may operate accordingly as long as it receives either.

At step 312, the packet has been previously determined to be an RTS/CTS packet and the node will determine the destination of the packet. If the packet is destined for the node, operation continues to step 314 where the packet is processed normally at step 314. However, if the destination of the packet is not the node, operation will continue to step 318.

At step 318, when a node determines that it decoded an RTS/CTS packet (e.g., RTS message 512/522 or CTS message 502/532) for which data is destined for a node other than the node, e.g., at time T1 or T2 in fig. 5, the node will set or extend its NAV period, e.g., NAV period 552 by an additional amount based on NAV period 554, respectively. In general, based on the time of receipt of the RTS/CTS packet, a node can determine the time Tn at which a data frame will arrive and how long the packet transmission of the data is to last.

Typically, within the duration indicated by the NAV, the node operates according to standard protocols, i.e., it checks each preamble, PLCP layer to determine whether the packet has an RTS/CTS duration. Packets with a duration different from the RTS/CTS packet duration are not processed further and the node continues to detect other preambles. For RTS/CTS packets, the NAV of a node may be extended from the new RTS/CTS packet if the packets are successfully decoded by the node.

As can be seen in fig. 5, data packet 524 to be transmitted from station STA1104 to access point AP 1102 is not interrupted by transmissions from station STA 2106. Station STA2106 will wait for an ACK message to be sent from access point AP 1102 (e.g., ACK message 516 sent by station STA3 acknowledging receipt of data packet 514 from station STA 1104) before attempting to transmit.

Fig. 4 shows a second procedure 400 for solving the blind node problem, implemented in the MAC layer of a node, which begins at step 402, where the node enters an idle state after initialization. During the idle state, a node will attempt to detect another node's transmission. The operation of the second process 400 will be described with reference to fig. 5.

In step 404, the node detects a signal that may belong to a packet transmission and proceeds to step 406 where the node decodes the preamble, PLCP header, and MAC header.

Specifically, when the node receives the preamble and PLCP of any packet, then the node then accumulates and decodes enough bits corresponding to the MAC header, step 406. While processing the MAC header, the node will continue to accumulate subsequent bits/symbols of the packet. However, the node continues to decode the header bits without waiting for the complete packet to accumulate. The MAC header is used to determine whether the indicated destination address corresponds to the node or whether the packet is a broadcast packet or a control packet (e.g., an RTS/CTS packet) at step 408.

If the node is indeed the destination of the frame or if the packet is a broadcast packet or an RTS/CTS or other control packet, the complete frame is accumulated and decoded at step 412.

If the node is not the destination, the packet decoding and accumulation function at the node terminates at step 410 and the node returns to the mode of probing the preamble of any other new packets.

Either or both of the above procedures may be implemented in an 802.11 device. The PHY layer only scheme of fig. 3 has the benefit of not invoking packet decoding functionality for packets determined to be not RTS/CTS packets. Thus, the node may save power resources. However, the PHY layer only scheme is not useful in a network in which the RTS/CTS method for medium reservation is rarely used. In addition, the PHY layer only scheme may cause packet loss destined for the node because the determination is made based only on the duration field. The MAC layer scheme of fig. 4 is useful in all situations and may require the invocation of a packet decoder to process packets.

Fig. 6 shows a configuration of a receiver portion 600 of a node configured to implement the PHY layer only scheme of fig. 3 and the MAC layer scheme of fig. 4. As shown, receiver portion 600 includes an antenna module 602 for receiving radio signals carrying various packets received by the node. The antenna module 602 may also be used to transmit radio signals. The receiver module 604 is coupled to the antenna module 602. The receiver module 604 is configured to receive packets transmitted via radio signals received by the antenna module 602. The decoder module 606 is coupled to the receiver module 604. The decoder module 606 is configured to decode the header and other portions of the packet received by the receiver module 604.

Fig. 7 shows a second configuration of a receiver portion 700 of a node configured to implement the PHY layer only scheme of fig. 3 and the MAC layer scheme of fig. 4. The receiver portion 700 includes a module 702 for receiving a packet including at least one header and non-header information, and a module 704 for decoding the at least one header to determine whether the non-header information should be processed.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure

The steps of a method or algorithm described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. Further, according to some aspects, any suitable computer program product may comprise a computer-readable medium comprising code (e.g., executable by at least one computer) relating to one or more aspects of the present disclosure. According to some aspects, a computer program product may include packaging materials.

The teachings of this application can be incorporated into (e.g., implemented in or performed by) a variety of apparatus (e.g., devices). For example, each node may be configured or referred to in the art as an access point ("AP"), a nodeb, a radio network controller ("RNC"), an eNodeB, a base station controller ("BSC"), a base transceiver station ("BTS"), a base station ("BS"), a transceiver function ("TF"), a wireless router, a wireless transceiver, a basic service set ("BSs"), an extended service set ("ESS"), a wireless base station ("RBS"), or some other terminology. Some nodes may also be referred to as subscriber stations. A subscriber station can also be called a subscriber unit, mobile station, remote terminal, access terminal, user agent, user device, or user equipment. In some implementations, a subscriber station may include a cellular telephone, a cordless telephone, a session initiation protocol ("SIP") phone, a wireless local loop ("WLL") station, a personal digital assistant ("PDA"), a handheld device having wireless connection capability, or other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal digital assistant), an entertainment device (e.g., a music or video device or a satellite radio), a global positioning system device, or any other suitable device configured to communicate over a wireless medium.

The wireless devices may communicate over one or more wireless communication links that are based on or otherwise support any suitable wireless communication technology. For example, according to some aspects, a wireless device is associated with a network. According to some aspects, the network may comprise a body area network or a personal area network (e.g., an ultra-wideband network). According to some aspects, the network may comprise a local area network or a wide area network. The wireless device may support or otherwise use one or more wireless communication technologies, protocols, or standards, such as CDMA, TDMA, OFDM, OFDMA, WiMAX, and Wi-Fi. Similarly, a wireless device may support or otherwise use one or more corresponding modulation or multiplexing schemes. The wireless device may thus include appropriate components (e.g., air interfaces) to establish and communicate over one or more wireless communication links using the above-described or other wireless communication techniques. For example, a device may include a wireless transceiver with associated transmitter and receiver components, which may include various components (e.g., signal generators and signal processors) that facilitate communication over a wireless medium.

The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit ("IC"), an access terminal, or an access point. The IC may include a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electronic components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute code or instructions that are internal to the IC, external to the IC, or both. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (24)

1. A method of wireless communication, comprising:

receiving a packet comprising at least one header and non-header information; and

decoding the at least one header to determine whether the non-header information should be processed.

2. The method of claim 1, wherein receiving the packet is at a receiving node, and decoding the at least one header comprises:

determining a destination of the packet; and

returning to monitoring for transmission of another packet when it is determined that the destination is a node other than the receiving node.

3. The method of claim 2, further comprising: setting a first timing parameter when it is determined that the destination is a node other than the receiving node.

4. The method of claim 3, wherein the first timing parameter is a Network Allocation Vector (NAV) during which the receiving node refrains from requesting a transmission to send (RTS).

5. The method of claim 2, further comprising: stopping further processing of the non-header information when it is determined that the destination is a node other than the receiving node.

6. The method of claim 1, wherein coding the at least one header comprises:

determining a type of the packet; and

processing the non-header information when the type is determined to be a control packet.

7. The method of claim 6, wherein the control packet is one of a Request To Send (RTS) packet and a Clear To Send (CTS) packet.

8. A computer program product for wireless communications, comprising:

a computer-readable medium comprising code executable by at least one computer for:

receiving a packet comprising at least one header and non-header information; and

decoding the at least one header to determine whether the non-header information should be processed.

9. A wireless communications apparatus, comprising:

means for receiving a packet comprising at least one header and non-header information; and

means for decoding the at least one header to determine whether the non-header information should be processed.

10. The wireless communications apparatus of claim 9, wherein receiving the packet is at a receiving node, and the means for decoding the at least one header comprises:

means for determining a destination of the packet; and

means for returning to monitoring for transmission of another packet when it is determined that the destination is a node other than the receiving node.

11. The wireless communications apparatus of claim 10, further comprising: means for setting a first timing parameter when it is determined that the destination is a node other than the receiving node.

12. The wireless communications apparatus of claim 11, wherein the first timing parameter is a Network Allocation Vector (NAV) during which the receiving node refrains from requesting transmission of a Request To Send (RTS).

13. The wireless communications apparatus of claim 10, further comprising: means for stopping further processing of the non-header information when it is determined that the destination is a node other than the receiving node.

14. The wireless communications apparatus of claim 9, wherein the means for coding the at least one header comprises:

means for determining a type of the packet; and

means for processing the non-header information when the type is determined to be a control packet.

15. The wireless communications apparatus of claim 14, wherein the control packet is one of a Request To Send (RTS) packet and a Clear To Send (CTS) packet.

16. A wireless communications apparatus, comprising:

a receiver configured to receive a packet comprising at least one header and non-header information; and

a decoder configured to decode the at least one header to determine whether the non-header information should be processed.

17. The apparatus of claim 16, wherein the receiver is a receiving node, and the decoder is further configured to:

determining a destination of the packet; and

returning to monitoring for transmission of another packet when it is determined that the destination is a node other than the receiving node.

18. The apparatus of claim 17, wherein decoder is further configured to set a first timing parameter when it is determined that the destination is a node other than the receiving node.

19. The apparatus of claim 18, wherein the first timing parameter is a Network Allocation Vector (NAV) during which the receiving node refrains from requesting a transmission to send (RTS).

20. The apparatus of claim 17, wherein the decoder is further configured to stop further processing of the non-header information when it is determined that the destination is a node other than the receiving node.

21. The apparatus of claim 16, wherein the coder is further configured to:

determining a type of the packet; and

when it is determined that the type is a control packet, the non-header information is processed.

22. The apparatus of claim 21, wherein the control packet is one of a Request To Send (RTS) packet and a Clear To Send (CTS) packet.

23. An access point, comprising:

an antenna;

a receiver for receiving a packet including at least one header and non-header information through the antenna; and

a decoder coupled to the receiver, the decoder configured to decode the at least one header to determine whether the non-header information should be processed.

24. An access terminal, comprising:

a receiver for receiving a packet comprising at least one header and non-header information;

a decoder coupled to the receiver, the decoder configured to decode the at least one header to determine whether the non-header information should be processed; and

a user interface to provide an indication based on the non-header information.