Abstract:
A method for improving the hidden-node problem in a wireless network comprises detecting a power back-off initiated at a data portion of a transmitted packet.

Description:
FIELD OF THE INVENTION  
       [0001]     The present embodiments of the invention relate generally to wireless communications, and more specifically, relate to the hidden-node problem in a wireless network.  
       BACKGROUND  
       [0002]     When a station or access point (AP) transmits a high-rate packet (for example, a 54 Mbps rate packet) in a wireless local area network (WLAN), it is usually transmitted with a lower power than that of a low-rate packet (for example, a 6 Mbps packet). This is referred to as a “power back-off,” with the exact amount of power being reduced measures in decibels (dB). A typical back-off for the 54 Mbps rate versus the 6 Mbps rate is approximately 7 dB.  
         [0003]     Generally, power back-off is applied in order to meet transmit Error Vector Magnitude (EVM) and mask specifications received in the Institute of Electrical and Electronics Engineers) (IEEE) 802.11a standard (IEEE std. 802.11a-1999) [hereinafter 802.11a] and the IEEE 802.11g standard (IEEE std. 802.11g-2003) [hereinafter 802.11g].  
         [0004]     Remote stations that receive and/or detect the low-rate packet from the AP or station may not, in some situations, receive or detect the high-rate packet transmitted by this same AP or station. As a result of not detecting the high-rate packet, multiple remote stations may transmit simultaneously and cause a packet collision in the network. This problem is referred to as the “hidden node” problem.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention. The drawings, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.  
         [0006]      FIG. 1  illustrates an exemplary wireless communication station in accordance with embodiments of the invention;  
         [0007]      FIG. 2  illustrates a block diagram of a wireless network system in accordance with exemplary embodiments of the invention;  
         [0008]      FIG. 3  illustrates a time-slot diagram demonstrating the operation of a wireless network station in an exemplary scenario;  
         [0009]      FIG. 4  illustrates a time-slot diagram demonstrating the operation of a wireless network station in accordance with one embodiment of the invention;  
         [0010]      FIG. 5  is a flow diagram depicting a method according to one embodiment of the invention; and  
         [0011]      FIG. 6  is a flow diagram depicting a method according to another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0012]     An apparatus and method to improve the hidden-node problem in a wireless network are described. Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.  
         [0013]     In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art, that the embodiments of the invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.  
         [0014]     It should be understood that embodiments of the invention may be used in a variety of applications. Although the invention is not limited in this respect, embodiments of the invention may be used in many apparatuses, for example, a modem, a personal computer, a desktop computer, a mobile computer, a laptop computer, a notebook computer, a Personal Digital Assistant (PDA) device, a tablet computer, a server computer, a network, a Local Area Network (LAN), a Wireless LAN (WLAN), a modem, a wireless modem, a wireless communication device, devices and/or networks operating in accordance with the existing 802.11a, 802.11b (IEEE std. 802.11b-1999) [hereinafter 802.11b], 802.11g, 802.11n (IEEE std. 802.11bn-2003) [hereinafter 802.11n] and/or future versions of the above standards, a Personal Area Network (PAN), Wireless PAN (WPAN), Wireless Metropolitan Area Network (WMAN), Wireless Wide Area Network (WWAN), units and/or devices which are part of the above WLAN, PAN, WPAN, WMAN, and/or WWAN networks, one-way and two-way radio communication systems, and the like.  
         [0015]     Referring to  FIG. 1 , a wireless communication station in accordance with embodiment of the invention is shown. Station  110  may operate using a power back-off feature in accordance with embodiments of the invention, as described below. Throughout this description, a station may also be referred to as a remote station.  
         [0016]     In some embodiments, station  110  may include a personal computer, a desktop computer, a mobile computer, a laptop computer, a notebook computer, a Personal Digital Assistant (PDA) device, a tablet computer, a network device, a network, an internal and/or external modem, fax-modem device and/or card, a peripheral device, a WLAN device, or the like.  
         [0017]     In the exemplary embodiment of  FIG. 1 , station  110  may include a computer  120 , which may include a processor  141 , a memory unit  142 , a storage unit  143 , a display unit  144 , an input unit  145 , a modem  146 , and an antenna  147 , all interconnected through bus  130 .  
         [0018]     Processor  141  may include, for example, a Central Processing Unit (CPU), a Digital Signal Processor (DSP), or any suitable specific, general, or multi-purpose processor or micro-processor.  
         [0019]     Memory  142  may include, for example, a Random Access Memory (RAM). Storage unit  143  may include, for example, a hard disk drive. Display unit  144  may include, for example, a monitor. Input unit  145  may include, for example, a keyboard, a mouse, or a touch-pad.  
         [0020]     Modem  146  may include, for example, a modem able to operate in accordance with one or more of the existing 802.11a, 802.11b, 802.11g, 802.11n standards and/or any future versions of these standards, or any other suitable existing or future versions of these standards. Antenna  147  may include an internal and/or external Radio Frequency (RF) antenna, for example, a dipole antenna. In some embodiments, antenna  147  may be integral to modem  146  or integrated within modem  146 .  
         [0021]     It is noted that in some embodiments, modem  146  may include a detector unit to detect properties of the signals received by station  110 . In some embodiments, such detection may be performed by other suitable components of station  110  or computer  120 , for example, processor  141  or software applications, driver, and operations systems associated with station  110  or computer  120 .  
         [0022]     It is noted that station  110  and/or computer  120  may include various other components and may be configured with additional or alternative units. Further, stations  110  and computer  120  may be implemented using any suitable combination of hardware and/or software, and may include any circuit, circuitry, unit, or combination of integrated or separate units or circuits, as are known in the art, to perform desired functionalities.  
         [0023]     It is noted that the terms “circuit” and “circuitry” as used herein, may include any suitable combination of hardware components and/or software components. For example, station  110  may include detection circuitry, analysis circuitry, selection circuitry, comparison circuitry, processing circuitry, reception circuitry, engagement circuitry, reset circuitry, storage circuitry, one or more analyzer units, comparison units, decision units, processing units, storage units, detection units, buffers, memories, and various other types of units, components, and/or circuitry, which may be used to perform methods and operations as discussed below in accordance with exemplary embodiments of the invention, and which may be implemented using any suitable combination of hardware components and/or software components (including, for example, applications, drivers, and/or operating systems) of station  110 .  
         [0024]     Referring to  FIG. 2 , a wireless network system, in accordance with embodiments of the invention, is shown. In one embodiment, system  200  may include a network access station  210  such as an access point (AP), base station, hybrid coordinator, wireless router or other device (for simplicity referred to hereafter as an AP). System  200  also includes a remote station  220  and, optionally, an additional remote station  230 . In some embodiments, system  200  may further include one or more APs similar to AP  210 , and one or more additional stations similar to station  220 . In some embodiments, AP  210  and stations  220 ,  230  are the same as station  110  as depicted in  FIG. 1 .  
         [0025]     Remote stations  220 ,  230  may be any device such as an AP or user station configured to communicate with AP  210  using one or more over-the-air (OTA) link protocols such as those contemplated by various IEEE standards for WPANs, WMANs, or WWANs. In certain embodiments, remote stations  220 ,  230  include one or more transceivers and circuitry for physical (PHY) layer and data link layer (medium access control (MAC)) processing although the embodiments are not limited in this respect.  
         [0026]     In one embodiment, AP  210  may include any suitable WLAN access point circuitry, for example, access point circuitry able to operate in accordance with one or more of the existing 802.11a, 802.11b, 802.11g, and 802.11n standards or future versions of those standards or any other suitable existing and/or future standard.  
         [0027]     Optionally, stations  220 ,  230  may include one or more antennas  225 ,  235 . Antenna  225 ,  235  may include an internal and/or external RF antenna, for example, a dipole antenna. In some embodiments, antenna  225 ,  235  may be integral to the circuitry of station  220 ,  230  or otherwise integrated within station  220 ,  230 . In certain embodiments, multiple antennas may be used for each station  220 ,  230  to facilitate multiple input multiple output (MIMO) communications.  
         [0028]     It will be appreciated that the term “signal” as used herein may include, for example, a signal, a packet, a frame, a data structure, a preamble, a header, a content and/or a data portion, which may be transmitted and received in accordance with various formats and standards.  
         [0029]     It will be appreciated that, although the scope of the invention is not limited in this respect, the term “receive”, and its derivative terms (e.g., “receiving”, “reception”), as used herein, may include, for example, physically receiving a signal using an antenna, receiver, transceiver, and/or modem. It may also include physically receiving a wireless communication transmission, receiving energy indicating a wireless communication transmission, and/or physically receiving a signal over a wireless communication link, network, and/or WLAN.  
         [0030]     Referring to  FIG. 3 , a time-slot diagram is shown. The time-slot diagram  300  depicts the operation of a WLAN system. The WLAN system includes an AP  330  and two remote stations  340 ,  350 .  
         [0031]     The AP  330  may transmit a signal  310  to a remote station in the WLAN system, such as remote station  340 . Signal  310  is a high-rate transmission packet that may consist of a preamble portion  312  and a data portion  314 . As signal  310  is a high-rate data transmission packet, AP  330  transmits the signal  310  with a power back-off in order to meet requirements of various wireless standards.  
         [0032]     However, in some situations, station  350  may not receive or even detect the high-rate packet  310 . For example, referring to  FIG. 2 , the range of a 54 Mbps transmission has a much smaller radius than the range of a 6 Mbps transmission, due to the power requirements for each transmission rate. As a result, station  350  may not receive a packet transmitted at 54 Mbps. If station  350  does not detect packet  310 , it may transmit its own packet  320  and cause a collision in the network. This is generally known as the “hidden node” problem.  
         [0033]     Referring to  FIG. 4 , a time-slot diagram in accordance with embodiments of the present invention, is shown. The time-slot diagram  400  depicts the operation of a WLAN system in accordance with embodiments of the present invention. In one embodiment, WLAN system is the same as WLAN system  200  as depicted in  FIG. 2 , and includes an AP  210 , and two remote stations  220 ,  230 .  
         [0034]     AP  210  may transmit a signal  410 , including preamble portion  412  and data portion  414 , to a remote station in the WLAN system  200 , such as remote station  220 . In some embodiments, the preamble portion  312  of the packet may include Physical Layer Convergence Procedures (PLCP). Signal  410  is a high-rate transmission packet, such as an 802.11a/g Orthogonal Frequency Division Multiplexing (OFDM) packet. However, in lieu of applying a power back-off to the entire high-rate packet  410 , the AP  210  applies a power back-off to the data portion  414  of the packet  410  and not to the preamble portion  412 .  
         [0035]     The preamble portion  412  of the packet  410  is digitally boosted with high power so that all of the remote stations  220 ,  230  may detect the signal  410 . Although the preamble portion  412  may be distorted due to the transmission rate and power level, it can be properly decoded by the remote stations  220 ,  230  to determine the length of the packet  410 . Once the stations determine the length of the packet  410 , they will be able to wait until the end of the transmission to send their own packets.  
         [0036]     Remote station  220  may send an acknowledgement packet  420  once it has received the high-rate data packet  410 . In this way, collision is prevented because remote station  230 , which would normally not detect the high-rate packet, detects a packet being transmitted in the WLAN system  200  and waits to send its own non-colliding packet  430 . As a result, the number of hidden nodes in the WLAN system  200  will drop dramatically (assuming uniform distribution of stations in the cell).  
         [0037]     Transmitting the packet  410  using digitally-boosted, higher power in the preamble  412  may impose a problem to a conventional receiver that would set its automatic gain control (AGC) and calculate its equalizer according to the higher-power preamble  412 . In order to receive the data in the data portion  414 , an improved receiver may implement one of two alternate arrangements.  
         [0038]     Referring to  FIG. 5 , a method according to one embodiment of the invention is shown. The method  500  implements one arrangement for a receiver to receive high-rate, low-power data portions of a packet with a digitally-boosted preamble.  
         [0039]     At processing block  510 , a power-back off in a data portion of a received packet is detected. Then, the incoming data is buffered in a buffer mechanism at processing block  520 . At processing block  530 , the digital gain of the detected power-back off is calculated. Then, at processing block  540 , the digital gain is set so that the data will be properly received. At processing block  550 , the data is passed on from the buffer mechanism.  
         [0040]     It should be noted that other storage means may be implemented in lieu of a buffer mechanism. Any means that provide temporary storage for data while the receiver calculates and sets the gain may be utilized in embodiments of the invention.  
         [0041]     The buffering of data in method  500  may create a high latency which could be problematic with short packets. Therefore, in one embodiment, power back-off during data transmission of short packets is not implemented.  
         [0042]     With the embodiment described above, power back-off during data transmission can be applied to all remote stations and APs. For example, the embodiment could be implemented in an ad hoc network among various remote stations.  
         [0043]     Furthermore, this embodiment allows Network Interface Card (NIC) vendors, and not only APs, to introduce this feature and contribute to the improvement of the hidden node problem. As a result, NIC vendors may contribute to the Basic Service Set (BSS) capacity.  
         [0044]     Referring to  FIG. 6 , a method according to another embodiment of the invention is shown. The method  600  implements an alternative arrangement for a receiver to receive high-rate, low-power data portions of a packet with a digitally-boosted preamble portion.  
         [0045]     At processing block  610 , each remote station receives the exact power back-off for each transmission rate from the AP. Then, at processing block  620 , the receiver detects a power back-off in the data portion of a received packet. At processing block  630 , the receiver sets the preliminarily-known digital gain value accordingly to receive the data. In some embodiments, the digital gain value is a function of the RATE field in the PLCP. Then, at processing block  640 , the data is received.  
         [0046]     In this embodiment, power back-off is not calculated when a power back-off is detected because the receiver already knows the exact power back-off. Also, as the receiver already knows the power back-off, it does not have to buffer the data while it calculates the power back-off. However, power back-off during data transmission may only be implemented by the AP transmitter. As such, remote station to remote station transmissions may not implement power back-off.  
         [0047]     In some embodiments, stations that are not able to receive a packet with power back-off, such as legacy stations, will only receive the preamble portion and wait an Extended InterFrame Space (EIFS) instead of a Distributed InterFrame Space (DIFS) before transmitting.  
         [0048]     During an association period, the AP and remote stations exchange their capabilities regarding support of power back-off only in the data section of a packet. In some embodiments, such a capability exchange may include: a bit to indicate the ability to receive the data back-off packet; minimal payload length for which data back-off is implemented; and a list of power back-offs for each rate to support receivers that preliminary know the power back-off values. In some embodiments, the AP controls whether or not the “data power back-off” mechanism is turned on in the stations by using a beacon with a dedicated one bit field.  
         [0049]     Various embodiments of the invention may be provided as a computer program product, which may include a machine-readable medium having stored thereon instructions, which may be used to program a computer (or other electronic devices) to perform a process according to various embodiments of the invention. The machine-readable medium may include, but is not limited to, floppy diskette, optical disk, compact disk-read-only memory (CD-ROM), magneto-optical disk, read-only memory (ROM) random access memory (RAM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic or optical card, flash memory, or another type of media/machine-readable medium suitable for storing electronic instructions. Moreover, various embodiments of the invention may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer to a requesting computer by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).  
         [0050]     Similarly, it should be appreciated that in the foregoing description, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.  
         [0051]     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims, which in themselves recite only those features regarded as the invention.