USOO7493133B2
`
`(12) United States Patent
`Krishnan et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7493,133 B2
`Feb. 17, 2009
`
`(54) POWER CONTROL IN AD-HOC WIRELESS
`NETWORKS
`(75) Inventors: Ranganathan Krishnan, San Diego, CA
`(US); Amol Rajkotia, San Diego, CA
`(US)
`
`(73) Assignee: QUALCOMM, Incorporated, San
`Diego, CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 78 days.
`(21) Appl. No.: 10/773,629
`
`(22) Filed:
`
`Feb. 5, 2004
`
`(65)
`
`Prior Publication Data
`US 2005/0176455A1
`Aug. 11, 2005
`
`(51) Int. Cl.
`(2006.01)
`H04B 7/00
`(2006.01)
`H04O 7/20
`(52) U.S. Cl. ......................... 455/522:455/69; 455/126;
`455/67.11
`(58) Field of Classification Search ................. 455/522,
`455/69,525, 67.13, 67.11-13, 70, 126, 63.1,
`455/134, 135,137,501, 127.1, 115.1: 370/332,
`370/320
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`5,697.073 A * 12/1997 Daniel et al. ................ 455,126
`6,072,784. A
`6/2000 Agrawal et al. ............. 370,311
`
`9/2000 Shen et al. .................. 370,252
`6,118,767 A
`6/2003 Brouwer ..................... 455,522
`6,577,875 B1
`6,647,273 B2 11/2003 Parsinen et al. ............ 455,522
`6,697,634 B1
`2/2004 Hayashi r
`... 455,522
`6,778,839 B2
`8, 2004 Valkealahti
`... 455,522
`6,788,138 B2* 9/2004 Suzuki ......
`... 455,126
`6,813,254 B1 1 1/2004 Mujtaba ..................... 370,335
`6,816,717 B1
`1 1/2004 Sipila ...................... 455/2772
`2002/0137535 A1* 9/2002 Hunzinger .................. 455,522
`2002/0196766 A1* 12/2002 Hwang et al. ............... 370,342
`2003/0166407 A1* 9/2003 Qian et al. .................. 455,522
`2004/0062216 A1* 4/2004 Nicholls et al. ............. 370,320
`2004/0203462 A1* 10, 2004 Lin et al. ................. 455/67.13
`2006/0046767 A1* 3/2006 Hunzinger .................. 455,522
`
`* cited by examiner
`Primary Examiner John J Lee
`(74) Attorney, Agent, or Firm—Mary Fales; Thomas R.
`Rouse
`
`(57)
`
`ABSTRACT
`
`Systems and techniques are disclosed relating to wireless
`communications. The systems and techniques involve wire
`less communications wherein a module or communications
`device is configured to enable a closed-loop power control in
`response to a detecting a wide-band interferer and disable the
`closed-loop power control in response to not detecting inter
`ferer.
`
`20 Claims, 7 Drawing Sheets
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`ENABLE CLOSED-LOOP POWER CONTROL:
`DISABLE OPEN-LOOP POWER CONTROL
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`INTERFERER
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`DISABLE CLOSED-LOOP
`POWER CONTROL
`ENABLE OPEN-LOOP
`POWER CONTROL
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`808
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`FILTER NARROW-BAND
`INTERFERENCE
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`NARROW BAND
`INTERFERER
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`ENABLE CLOSED-LOOP POWER CONTROL
`DISABLE OFEN-LOOP POWER CONTROL
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`U.S. Patent
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`Feb. 17, 2009
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`U.S. Patent
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`US 7,493,133 B2
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`1.
`POWER CONTROLINAD-HOC WIRELESS
`NETWORKS
`
`FIELD
`
`The present disclosure relates generally to wireless com
`munications, and more specifically, to various systems and
`techniques for power control in ad-hoc wireless networks.
`
`BACKGROUND
`
`10
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`2
`In an ad-hoc network, terminals are added dynamically. As
`more terminals are added, each communicating terminal cre
`ates more interference for terminals other than the terminal
`with which it is communicating. Thus, it is desirable to con
`trol terminal transmit power to avoid adverse interference
`with other terminal communications.
`
`SUMMARY
`
`In one aspect of the present invention, a method of power
`control includes enabling closed-loop power control in
`response to detecting a wide-band interference above a
`threshold, disabling closed-loop power control in response to
`determining the wide-band interference is below a threshold,
`and sending a power feedback signal indicating a power
`transmission level if the closed-loop power control is enabled.
`In another aspect of the present invention, a wireless ter
`minal includes means for enabling closed-loop power control
`in response to detecting a wide-band interference above a
`threshold, means for disabling closed-loop power control in
`response to determining the wide-band interference is below
`a threshold, and means for sending a power feedback signal
`indicating a power transmission level if the closed-loop
`power control is enabled.
`In yet another aspect of the present invention, a wireless
`terminal includes a receiver for detecting a wide-band inter
`ference above a threshold, a baseband processor for enabling
`closed-loop power control in response to detecting the wide
`band interference, the baseband processor coupled to the
`receiver, and a transmitter for sending a power feedback
`signal indicating a powertransmission level if the closed-loop
`power control is enabled, the transmitter coupled to the base
`band processor.
`In a further aspect of the present invention, computer read
`able media embodying a program of instructions executable
`by a computer program may be used to enabe closed-loop
`power control in response to detecting a wide-band interfer
`ence above a threshold, disable closed-loop power control in
`response to determining the wide-band interference is below
`a threshold, and send a power feedback signal indicating a
`power transmission level if the closed-loop power control is
`enabled.
`It is understood that other embodiments of the present
`invention will become readily apparent to those skilled in the
`art from the following detailed description, wherein various
`embodiments of the invention are shown and described by
`way of illustration. As will be realized, the invention is
`capable of other and different embodiments and its several
`details are capable of modification in various other respects,
`all without departing from the spirit and scope of the present
`invention. Accordingly, the drawings and detailed description
`are to be regarded as illustrative in nature and not as restric
`tive.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Aspects of the present invention are illustrated by way of
`example, and not by way of limitation, in the accompanying
`drawings, wherein:
`FIG. 1 is a conceptual diagram illustrating an example of a
`piconet;
`FIG. 2 is a conceptual diagram illustrating an example of a
`Medium Access Control (MAC) frame for controlling intra
`piconet communications;
`FIG. 3 is a functional block diagram illustrating an
`example of a terminal capable of operating within a piconet;
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`In conventional wireless communications, an access net
`work is generally employed to support communications for a
`number of mobile devices. An access network is typically
`implemented with multiple fixed site base stations dispersed
`throughout a geographic region. The geographic region is
`generally Subdivided into Smaller regions known as cells.
`Each base station may be configured to serve the mobile
`devices in its respective cell. An access network may not be
`easily reconfigured when there are varying traffic demands
`across different cellular regions.
`In contrast to the conventional access network, ad-hoc
`networks are dynamic. An ad-hoc network may be formed
`when a number of wireless communication devices, often
`referred to as terminals join together to form a network.
`Terminals in ad-hoc networks can operate as either a host or
`router. Thus, an ad-hoc network may be easily reconfigured to
`meet existing traffic demands in a more efficient fashion.
`Moreover, ad-hoc networks do not require the infrastructure
`required by conventional access networks, making ad-hoc
`networks an attractive choice for the future.
`Ultra-Wideband (UWB) is an example of a communica
`tions technology that may be implemented with ad-hoc net
`works. UWB provides high speed communications over a
`wide frequency bandwidth. At the same time, UWB signals
`are transmitted in very short pulses that consume very little
`power. The output power of the UWB signal is so low that it
`looks like noise to other RF technologies, making it less
`interfering.
`Numerous multiple access techniques exist to Support
`simultaneous communications in an ad-hoc network. A Fre
`quency Division Multiple Access (FDMA) scheme, by way
`of example, is a very common technique. FDMA typically
`involves allocating distinct portions of the total bandwidth to
`individual communications between two terminals in the ad
`45
`hoc network. While this scheme may be effective for uninter
`rupted communications, better utilization of the total band
`width may be achieved when such constant, uninterrupted
`communication is not required.
`Other multiple access schemes include Time Division
`Multiple Access (TDMA). These TDMA schemes may be
`particularly effective in allocating limited bandwidth among
`a number of terminals which do not require uninterrupted
`communications. TDMA schemes typically dedicate the
`entire bandwidth to each communication channel between
`two terminals at designated time intervals.
`Code Division Multiple Access (CDMA) techniques may
`be used in conjunction with TDMA to support multiple com
`munications during each time interval. This may be achieved
`by transmitting each communication or signal in a designated
`time interval with a different code that modulates a carrier,
`and thereby, spreads the spectrum of the signal. The transmit
`ted signals may be separated in the receiver terminal by a
`demodulator that uses a corresponding code to de-spread the
`desired signal. The undesired signals, whose codes do not
`match, are not de-spread in bandwidth and contribute only to
`O1SC.
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`3
`FIG. 4 is a conceptual block diagram illustrating an
`example of a terminal operating as a master terminal of a
`piconet;
`FIG. 5 is a conceptual block diagram illustrating an
`example of a terminal operating as a member terminal of the
`piconet;
`FIG. 6 is a flow diagram illustrating an example of power
`control operation when communications between two mem
`ber terminals is established; and
`FIG. 7 is a flow diagram illustrating an example of open
`loop power control operation when communications between
`two member terminals is established.
`
`10
`
`DETAILED DESCRIPTION
`
`4
`another under control of the master terminal 104. As to be
`explained in greater detail below, each member terminal 106
`in the piconet 102 may also be able to directly communicate
`with terminals outside the piconet.
`The master terminal 104 may communicate with the mem
`ber terminals 106 using any multiple access scheme. Such as
`TDMA, FDMA, CDMA, or any other multiple access
`scheme. To illustrate the various aspects of the present inven
`tion, the wireless communications system shown in FIG. 1
`will be described in the context of a hybrid multiple access
`scheme employing both TDMA and CDMA technologies.
`Those skilled in the art will readily understand that the present
`invention is in no way limited to Such multiple access
`schemes.
`A piconet may be formed in a variety of ways. By way of
`example, when a terminal initially powers up, it may search
`for pilot signals from piconet master terminals. The pilot
`signal broadcast by each piconet master terminal may be an
`unmodulated spread-spectrum signal, or Some other refer
`ence signal. In spread-spectrum configurations, a pSuedo
`random noise (PN) code unique to each piconet master ter
`minal may be used to spread the pilot signal. Using a
`correlation process, the terminal may search through possible
`PN codes to identify the master terminal with the strongest
`pilot signal. If the strongest pilot signal is received with
`Sufficient signal strength to support a minimum data rate, then
`the terminal may attempt to join the piconet by registering
`with the master terminal.
`A terminal may be unable to find a pilot signal because
`there is no master terminal. In some instances, a terminal may
`be unable to find a pilot signal of Sufficient signal strength to
`support the minimum data rate. This may result from any
`number of reasons. By way of example, the terminal may be
`too far from the master terminal. Alternatively, the propaga
`tion environment may be insufficient to support the requisite
`data rate. In either case, the terminal may be unable to join an
`existing piconet, and therefore, may begin operating as an
`isolated terminal by transmitting its own pilot signal. The
`isolated terminal may become the master terminal for a new
`piconet. Other terminals that are able to receive the pilot
`signal broadcast from the isolated terminal with sufficient
`strength may attempt to acquire that pilot signal and join the
`piconet of this isolated terminal.
`The master terminal 104 may use a periodic frame struc
`ture to coordinate intra-piconet communications. This frame
`is often referred to in the art as a Medium Access Control
`(MAC) frame because it is used to provide access to the
`communications medium for various terminals. It would be
`apparent to those skilled in the art that a frame may be any
`duration depending on the particular application and overall
`design constraints.
`For the purpose of discussion, a frame duration of approxi
`mately 5 ms will be used. An approximate 5 ms frame is
`reasonable to accommodate a high chip rate of approximately
`650 Mcps and a desire to support data rates down to approxi
`mately 19.2 kbps.
`An example of a MAC frame structure is shown in FIG. 2
`with n number of frames 202. Each frame may be divided into
`160 or any other number of time slots 204. The slot duration
`may be approximately 31.25 us, which corresponds to
`approximately 20,312.5 chips at approximately 650 Mcps.
`The frame may dedicate some of its slots for overhead. By
`way of example, the first slot 206 in the frame 202 may be
`used to broadcast the spread-spectrum pilot signal to the
`member terminals. The pilot signal may occupy the entire slot
`206, or alternatively, be time shared with a control channel.
`The control channel occupying the end of the first slot 206
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`The detailed description set forth below in connection with
`the appended drawings is intended as a description of various
`embodiments of the present invention and is not intended to
`represent the only embodiments in which the present inven
`tion may be practiced. Each embodiment described in this
`disclosure is provided merely as an example or illustration of
`the present invention, and should not necessarily be construed
`as preferred or advantageous over other embodiments. The
`detailed description includes specific details for the purpose
`of providing a thorough understanding of the present inven
`tion. However, it will be apparent to those skilled in the art
`that the present invention may be practiced without these
`specific details. In some instances, well-known structures and
`devices are shown in block diagram form in order to avoid
`obscuring the concepts of the present invention. Acronyms
`and other descriptive terminology may be used merely for
`convenience and clarity and are not intended to limit the scope
`of the invention.
`The word “exemplary” is used exclusively herein to mean
`'serving as an example, instance, or illustration.” Any
`embodiment described herein as “exemplary' is not neces
`sarily to be construed as preferred or advantageous over other
`embodiments.
`In the following detailed description, various aspects of the
`present invention may be described in the context of a UWB
`40
`wireless communications system. While these inventive
`aspects may be well Suited for use with this application, those
`skilled in the art will readily appreciate that these inventive
`aspects are likewise applicable for use in various other com
`munication environments. Accordingly, any reference to a
`45
`UWB communications system is intended only to illustrate
`the inventive aspects, with the understanding that such inven
`tive aspects have a wide range of applications.
`FIG. 1 illustrates an example of a network topology for a
`piconet in a wireless communications system. A piconet' is
`a collection of communication devices or terminals con
`nected using wireless technology in an ad-hoc fashion. The
`terminals may be stationary or in motion, Such as a terminal
`that is being carried by a user on foot or in a vehicle, aircraft
`orship. The term “terminal is intended to encompass various
`types of communications devices including cellular, PCS,
`wireless or landline phones, personal data assistants (PDA),
`laptops, external or internal modems, PC cards, and other
`similar devices.
`In at least one embodiment of the wireless communications
`system, each piconet has one master terminal and a number of
`member terminals slaved to the master terminal. In FIG. 1, a
`piconet 102 is shown with a master terminal 104 supporting
`communications between several member terminals 106. The
`master terminal 104 may be able to communicate with each of
`the member terminals 106 in the piconet. The member termi
`nals 106 may also be able to directly communicate with one
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`may be a spread-spectrum signal broadcast to all the member
`terminals at the same power level as the pilot signal. The
`master terminal may use this control channel to define the
`composition of the MAC frame.
`The master terminal may be responsible for scheduling
`intra-piconet communications. This may be accomplished
`through the use of one or more additional spread-spectrum
`control channels which occupy various time slots within the
`frame, such as time slots 208 and 210 in FIG. 2. These
`additional control channels may be broadcast by the master
`terminal to all the member terminals and include various
`scheduling information. The scheduling information may
`include time slot assignments for communications between
`terminals within the piconet. As shown in FIG. 2, these time
`slots may be selected from the data slots portion 212 of the
`frame 202. Additional information, such as the power level
`and data rate for each communication between terminals,
`may also be included. The master terminal may also grant
`transmit opportunities in any given time slot to any number of
`terminal pairs using a CDMA scheme. In this case, the sched
`uling information may also assign the spreading codes to be
`used for the individual communications between terminals.
`The master terminal may periodically set aside a fraction of
`time for peer-to-peer transmissions. During this time, the
`master terminal 104 may assign one of the member terminals
`106 to communicate with one or more isolated terminals
`and/or adjacent piconets. These transmissions may require
`high transmit power, and in some instances, can only be
`Sustained at low data rates. In the event that high power
`transmissions are needed to communicate with the isolated
`terminals and/or adjacent piconets, the master terminal may
`decide not to schedule any intra-piconet communications at
`the same time.
`FIG. 3 is a conceptual block diagram illustrating one pos
`sible configuration of a terminal. As those skilled in the art
`will appreciate, the precise configuration of the terminal may
`vary depending on the specific application and the overall
`design constraints.
`The terminal may be implemented with a front end trans
`ceiver 302 coupled to an antenna 304. A baseband processor
`306 may be coupled to the transceiver 302. The baseband
`processor 306 may be implemented with a software based
`architecture, or any other type of architecture. A micropro
`cessor may be used as a platform to run software programs
`that, among other things, provide executive control and over
`all system management functions that allow the terminal to
`operate either as a master or member terminal in a piconet. A
`digital signal processor (DSP) may be implemented with an
`embedded communications software layer which runs appli
`cation specific algorithms to reduce the processing demands
`on the microprocessor. The DSP may be used to provide
`various signal processing functions such as pilot signal acqui
`sition, time synchronization, frequency tracking, spread
`spectrum processing, modulation and demodulation func
`tions, and forward error correction.
`The terminal may also include various user interfaces 308
`coupled to the baseband processor 306. The user interfaces
`may include a keypad, mouse, touch screen, display, ringer,
`vibrator, audio speaker, microphone, camera and/or other
`input/output devices.
`FIG. 4 is a conceptual block diagram illustrating an
`example of a terminal operating as a master terminal. The
`baseband processor 306 is shown with the transceiver 302.
`The transceiver 302 may include a receiver 402. The receiver
`402 provides detection of desired signals in the presence of
`noise and interference. The receiver 402 may be used to
`extract the desired signals and amplify them to a level where
`
`6
`information contained in the received signal can be processed
`by the baseband processor 306.
`The transceiver 302 may also include a transmitter 404.
`The transmitter 404 may be used to modulate information
`from the baseband processor 306 onto a carrier frequency.
`The modulated carrier may be upconverted to an RF fre
`quency and amplified to a sufficient power level for radiation
`into free space through the antenna 3.04.
`The baseband processor 306 may enable a scheduler 406
`when operating as a master terminal. In the software based
`implementation of the baseband processor 306, the scheduler
`406 may be a software program running on a microprocessor.
`However, as those skilled in the art will readily appreciate, the
`scheduler 406 is not limited to this embodiment, and may be
`implemented by any means known in the art, including any
`hardware configuration, Software configuration, or combina
`tion thereof, which is capable of performing the various func
`tions described herein.
`The scheduler 406 may be used to schedule intra-piconet
`communications in a way that optimizes the capacity of the
`piconet. This may beachieved in a variety of ways. By way of
`example, the scheduler 406 may be used to carefully select the
`terminal pairs that will engage in simultaneous communica
`tions. A transmission power level may be scheduled for each
`of the simultaneous communications that satisfies a target
`quality parameter for each of the receiving terminals. The
`target quality parameter may be a desired carrier-to-interfer
`ence (C/I) ratio at the receiving terminal, or any other quality
`parameter known in the art.
`FIG. 5 is a conceptual block diagram illustrating an
`example of a terminal operating as a member terminal. The
`scheduler 406 is shown with phantom lines illustrating that it
`is not enabled by the baseband processor 306 during opera
`tion as a member terminal. The configuration of the trans
`ceiver 302 is the same whether the baseband processor 306 is
`operating as a master or member terminal, and therefore, will
`not be discussed further. The transceiver 302 is shown in FIG.
`5 for completeness.
`As discussed earlier in connection with the baseband pro
`cessor 306 configured as a master terminal, the scheduling
`assignments may be broadcast to all the member terminals in
`the piconet on one or more control channels. The signal
`processor 412 on the receiving end may employ spread-spec
`trum processing to extract the scheduling information from
`the control channel and provide it to a controller 418. The
`scheduling information may include the time slot assign
`ments for the various transmissions to and from the member
`terminal, as well as the power level and data rate for each.
`The controller 418 may be used to provide data rate and
`spreading information to the signal processor 412 on the
`receiving end for the scheduled transmissions to the member
`terminal. Using this information, the signal processor 412
`may recover communications from other member terminals
`at the appropriate times and provide the recovered commu
`nications to the various user interfaces 308.
`The controller 418 may also provide power level informa
`tion to the computational module 408 for each transmission
`from another terminal (not shown). The computational mod
`ule 408 may use this information to compute a path loss from
`the transmitting terminal by using the signal strength mea
`surement from the transceiver 302 during scheduled trans
`missions. The path loss information computed by the com
`putational module 408 may be stored in memory 410 and
`provided to the signal processor 416 on the transmitting end
`during the scheduled time for the control channel broadcast.
`In various embodiments of the terminal employing a GPS
`receiver (not shown), it may be used to provide coordinate
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`US 7,493,133 B2
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`information to the master terminal over a control channel
`broadcast via the signal processor 416 and the transceiver
`3O2.
`The signal processor 416 may be used to spread commu
`nications to various member terminals within the piconet.
`The communications may be originated from the various user
`interfaces 308 and stored in a buffer 420 until the scheduled
`transmission. At the scheduled time, the controller 418 may
`be used to release the communications from the buffer 420 to
`the signal processor 416 for spread-spectrum processing. The
`data rate, spreading code and transmission power level of the
`communications may be programmed into the signal proces
`sor 416 by the controller 418. Alternatively, the transmission
`power level may be programmed by the controller 418 at the
`transmitter 404 in the transceiver 302.
`FIG. 6 is a flow diagram illustrating an example of power
`control operation when communications between two mem
`ber terminals is established. In an embodiment, communica
`tion between a terminal A and a terminal B is bidirectional.
`When terminal Asends signals other than a feedback signal to
`terminal B, terminal A is the transmitting terminal and termi
`nal B is the receiving terminal. When terminal B sends signals
`other than a feedback signal to terminal A, terminal B is the
`transmitting terminal and terminal A is the receiving terminal.
`The receiving terminal performs the power control opera
`tion of FIG. 6. In an embodiment, the power control operation
`of FIG. 6 is performed periodically. In an embodiment, the
`power control operation is performed every time slot. In
`another embodiment, the power control operation is per
`formed every frame. It would be apparent to those skilled in
`the art that the time period between successive executions of
`the power control operation of FIG. 6 depends on the wireless
`application. It would also be apparent to those skilled in the
`art that the time period between successive executions of the
`power control operation of FIG. 6 can be programmable.
`In step 800, closed-loop power control is enabled and
`open-loop power control is disabled. Closed-loop power con
`trol involves a feedback signal being sent by the receiving
`terminal to the transmitting terminal to provide the transmit
`ting terminal feedback regarding the power of signals
`received at the receiving terminal. Open-loop power control
`involves setting transmission power as shown in FIG. 7 and
`described herein below. In an embodiment, the receiving
`terminal sends a feedback signal indicating the status of
`closed-loop power control. Such as an enable/disable bit. In an
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`embodiment, the receiving terminal sends a feedback signal
`indicating the status of open-loop power control Such as
`enable/disable bit.
`In step 802, the receiving terminal determines whether
`there is an interferer. If an interferer is not detected, then in
`step 804, closed loop power control is disabled and open-loop
`power control is enabled. Then, the flow of control loops back
`to step 802 for a next time period. If an interferer is detected,
`then in step 806, the receiving terminal determines whether
`the interferer is a narrow-band interferer or a wide-band inter
`ferer. A narrow-band interferer is a source that emits a signal
`within a bandwidth narrow enough to be substantially filtered
`below a threshold. A wide-band interferer is a source that
`emits a signal that is not within a bandwidth narrow enough to
`be substantially filtered below a threshold.
`If the interferer is a narrow-band interferer, then in step
`808, the narrow-band interference from the narrow-band
`interferer is filtered out by a notch filter. After the narrow
`band interference is filtered out, then the flow of control goes
`to step 802 and the receiving terminal determines whether
`there is another interferer. If in step 806, the receiving termi
`nal determines there is no narrow-band interferer, then in step
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`810, closed-loop power control between the receiving termi
`nal and the transmitting terminal is enabled and open-loop
`power control is disabled. Then, the flow of control goes to
`step 802 for a next time period.
`In an embodiment, the receiving terminal receives radio
`frequency (RF) signals via antenna 304. Receiver 402 ampli
`fies and frequency downconverts the received RF signals to
`intermediate frequency (IF) signals, and filters the IF signals.
`The IF signals are output to signal processor 412 for digital
`processing.
`In an embodiment, receiver 402 also includes circuitry for
`performing an analog measurement of total received signal
`power from the transmitting terminal. This power measure
`ment is used to generate a feedback signal that is provided to
`transmitter 404. In an embodiment, a feedback signal is gen
`erated by a feedback generator included in the controller 418.
`In another embodiment, a feedback signal is generated by a
`feedback generator included in the computational module
`408. It would be apparent to those skilled in the art that a
`feedback signal may be generated by any terminal module
`coupled to the receiver 402 and coupled to the transmitter 404
`Such that the terminal module receives the analog measure
`ment and provides a feedback signal to the transmitter 404.
`A feedback signal is sent by the receiving terminal to the
`transmitting terminal to provide the transmitting terminal
`feedback regarding the receipt of signals received at the
`receiving terminal. In an embodiment, an exemplary feed
`back signal indicates a transmission power level (hereinafter
`power feedback signal). The power feedback signal is a
`request by the receiving terminal that the transmitting termi
`nal transmit at a transmission powe