(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0159404 A1
`(43) Pub. Date:
`Oct. 31, 2002
`Raissinia et al.
`
`US 2002O159404A1
`
`(54) POWER REGULATION USING MULTI-LOOP
`CONTROL
`(75) Inventors: Ali Raissinia, Monte Sereno, CA (US);
`Vincent K. Jones IV, Redwood Shores,
`CA (US); Derek Gerlach, Mountain
`View, CA (US); Gregory G. Raleigh,
`Woodside, CA (US); Michael Pollack,
`Cupertino, CA (US)
`Correspondence Address:
`RITTER, LANG & KAPLAN
`12930 SARATOGAAE. SUTE D1
`SARATOGA, CA 95070 (US)
`(73) Assignee: Cisco Technology, Inc., A CALIFOR
`NIA CORPORATION, San Jose, CA
`95134-1706 (US)
`(21) Appl. No.:
`10/138,238
`(22) Filed:
`May 3, 2002
`Related U.S. Application Data
`(63) Continuation of application No. 09/348,719, filed on
`Jul. 6, 1999, now Pat. No. 6,408,165.
`
`Publication Classification
`
`(51) Int. Cl." ....................................................... H04Q 7/24
`(52) U.S. Cl. ............................................ 370/318; 370/338
`
`(57)
`
`ABSTRACT
`
`Improved adjustment of transmission power in a communi
`cation System is provided. In one embodiment, in a point to
`multipoint communication System, transmission power of a
`Subscriber unit is controlled based on power measurements
`made at a central access point. Power measurement infor
`mation based on transmissions occurring at irregular inter
`vals may be combined in a beneficial manner to control
`transmission output power. In one embodiment, a power
`regulation process determines a Series of difference values
`indicating the differences between desired received power
`level at the central access point and measured received
`power level. A Smoothing process is applied to the difference
`values. One or more parameters of the Smoothing proceSS
`vary with elapsed time Since a last available power mea
`Surement.
`
`I04
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`Subscriber
`Unit
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`Subscriber
`Unit
`
`
`
`102
`
`Central
`Access
`Point
`
`Subscriber
`Unit
`
`Subscriber
`Unit
`
`
`
`SubSCriber
`Unit
`
`104
`
`Subscriber
`Unit
`
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`Patent Application Publication
`
`Oct. 31, 2002 Sheet 1 of 8
`
`US 2002/0159404 A1
`
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`Patent Application Publication
`
`Oct. 31, 2002 Sheet 2 of 8
`
`US 2002/0159404 A1
`
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`Patent Application Publication Oct. 31, 2002 Sheet 3 of 8
`
`US 2002/0159404 A1
`
`I02
`
`Central
`ACCeSS Point
`
`
`
`I O2
`
`Central
`ACCeSS Point
`
`POWer
`Measurements
`
`Upstream
`Transmissions
`
`FIG. 3A
`
`POWer
`Adjustments
`
`Upstream
`Transmissions
`
`FIG. 3B
`
`I04
`
`SubSCriber
`Unit
`
`I04
`
`SubSCriber
`Unit
`
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`Patent Application Publication Oct. 31, 2002 Sheet 4 of 8
`
`US 2002/0159404 A1
`
`104
`
`Subscriber
`Unit
`
`104
`
`Subscriber
`Unit
`
`
`
`I02
`
`Central
`ACCeSS Point
`
`I02
`
`Central
`ACCeSS Point
`
`Transmit
`POWer Levels
`
`Upstream
`Transmissions
`
`FIG. 3C
`
`Channel Response
`Estimates
`
`
`
`Upstream
`Transmissions
`plus power
`levels used.
`
`FIG. 3D
`
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`Patent Application Publication
`
`Oct. 31, 2002 Sheet 5 of 8
`
`US 2002/0159404 A1
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`Patent Application Publication
`
`Oct. 31, 2002. Sheet 6 of 8
`
`US 2002/0159404 A1
`
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`Patent Application Publication Oct. 31, 2002 Sheet 7 of 8
`
`US 2002/0159404 A1
`
`Send transmission from
`Subscriber unit to Central
`access point at Current
`Set Output power.
`
`Reveive transmission at
`Central acCeSS point.
`
`
`
`
`
`
`
`
`
`Measure power at
`Central access point.
`
`
`
`
`
`604
`
`606
`
`608
`
`Compute channel response
`based on new measured power.
`61
`0
`
`
`
`
`
`
`
`Determine new Smoothed
`estimates for Channel
`response based on new
`value and old Smoothed
`estimate.
`
`
`
`Update smoothed
`channel response values.
`
`612
`
`Pick new transmit power
`level based on long term
`Or short term channel
`response value and desired
`receive power level.
`
`
`
`
`
`FIG. 6A
`
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`Patent Application Publication Oct. 31, 2002 Sheet 8 of 8
`
`US 2002/0159404 A1
`
`Send transmission from
`Subscriber unit to Central
`access point at Current
`set output power.
`
`
`
`
`
`Reveive transmission at
`Central access point.
`
`Measure power at
`Central access point.
`
`Determine difference
`between measured
`power level and
`desired power level.
`
`Determine Smoothed
`difference.
`
`
`
`630
`
`632
`
`634
`
`
`
`
`
`
`
`636
`
`Pick new transmit power
`level based On Smoothed
`difference.
`
`
`
`FIG. 6B
`
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`US 2002/0159404 A1
`
`Oct. 31, 2002
`
`POWER REGULATION USING MULTI-LOOP
`CONTROL
`
`BACKGROUND OF THE INVENTION
`0001. The present invention is related to digital commu
`nication Systems and more particularly to Systems and
`methods for controlling output power of Subscriber units in
`a point to multipoint communication System.
`0002 A point to multipoint wireless communication sys
`tem represents a potentially effective Solution to the problem
`of providing broadband network connectivity to a large
`number of geographically distributed points. Unlike optical
`fiber, DSL, and cable modems, there is no need to either
`construct a new wired infrastructure or Substantially modify
`a wired infrastructure that has been constructed for a dif
`ferent purpose.
`0003. In order to conserve scarce spectrum, the data
`communication devices of a point to multipoint wireleSS
`communication System may share access to a common
`frequency. In a typical Scenario a first group of one or more
`frequency channels are allocated to downstream broadcast
`communication from a central acceSS point to a plurality of
`Subscriber units. A Second group of one or more Separate
`frequency channels are allocated to upstream communica
`tion from the Subscriber units to the central access point. For
`upstream communication there is a medium access control
`(MAC) protocol that determines which subscriber unit is
`permitted to transmit at which time So as not to interfere with
`transmissions from other Subscriber units.
`0004 For a given upstream frequency, the time domain is
`divided into frames that are typically of equal duration. Each
`frame represents an individually allocable unit in the time
`domain. One Subscriber unit transmits in each frame. Res
`ervations for transmission in a particular frame are made by
`the central access point and distributed in broadcast down
`Stream transmissions. Such a Scheme is referred to as a time
`domain multiple access scheme (TDMA).
`0005. In such a point to multipoint wireless communica
`tion System, it is generally preferable to centrally control the
`transmission power of each Subscriber unit. Each Subscriber
`unit should transmit at a power Sufficient to ensure accurate
`reception of its transmission yet not So high So as to overload
`the front end of the central access point's receiver or cause
`interference to unintended receivers. Power control involves
`monitoring Subscriber unit transmitted power at the central
`access point and Sending power adjustment information
`downstream to maintain power at the desired level.
`0006 Cable modem systems also require access to a
`shared medium and Subscriber unit power control. It would
`be desirable to simply adopt a MAC protocol already
`developed for cable applications to the wireleSS context. One
`Such protocol that has been developed is referred to as the
`MCNS protocol. The MCNS protocol is described in the
`Data-over-Cable Service Interface Specifications, Radio
`Frequency Interface Specification, SP-RFI-I04-980724,
`(Cable Television Laboratories, 1997), the contents of which
`are herein incorporated by reference.
`0007. A cable MAC layer like MCNS is already imple
`mented in low cost chip Sets. The operational characteristics
`of MCNS are well known. Furthermore, it is desirable to
`
`maintain parts commonality between wireleSS modems and
`cable modems to the extent possible.
`0008. The MCNS protocol provides for controlling the
`power of Subscriber units. In one implementation, the power
`control function is combined with monitoring of the round
`trip propagation delay between the central access point and
`individual Subscriber units. Periodically, the head end sends
`a ranging request message to a particular Subscriber unit. In
`response to the ranging request message, the Subscriber unit
`Sends a ranging response to the central acceSS point. The
`time of the response indicates the Subscriber unit's current
`understanding of the System clock as modified by the
`propagation delay. The head end then tells the Subscriber
`unit by how much to adjust its clock phase to align its
`transmissions to the System MAC layer clock maintained by
`the head end. The head end also measures the power level of
`the ranging response message. Also, the head end Sends the
`Subscriber unit power adjustment information to help the
`subscriber unit set its power so that it will be received at a
`desired level.
`0009. This combined ranging and power control opera
`tion is, however, relatively infrequent, occurring approxi
`mately every two Seconds in typical implementations. This
`MAC layer power control operation cannot easily be made
`more frequent because of the limited processing power
`provided by equipment implementing the MCNS protocol.
`In a wireleSS System, the frequency of power control opera
`tions that may be implemented practically with MCNS is
`insufficient. Channel response may vary too rapidly for the
`MCNS power control system to react. If hundreds of mil
`liseconds have passed since the last update to the Subscriber
`units power level, new data transmitted by the subscriber
`unit may be included in a transmission having an either
`excessive or insufficient power level.
`0010. One solution is to measure at the central access
`point the power of other Subscriber unit transmissions Such
`as data transmissions, acceSS request transmissions and/or
`Special power measurement transmissions. Such techniques
`are not admitted prior art to the present application and are
`discussed in the co-filed, co-assigned applications entitled
`POLLING FOR TRANSMISSION POWER CONTROL
`and OPTIMAL USE OF REQUEST ACCESS TDMA
`SLOTS FOR AUTOMATICLEVEL CONTROL.
`0011. It is desirable to base power control on power level
`measurements obtained from disparate types of upstream
`transmissions that may occur at irregular intervals. For
`example, consider a voice over IP application where the
`network is Supporting a voice telephone call made from a
`Subscriber unit location. Upstream data transmissions from
`the participating Subscriber unit will be relatively frequent
`and power measurements based on Successive data trans
`missions will be up to date for the duration of the call.
`However, when a Subscriber unit has been inactive for a long
`time the most recent power measurement may be based on
`a very old transmission. What is needed is a power control
`technique that can optimally exploit power measurements
`that occur at irregular intervals.
`
`SUMMARY OF THE INVENTION
`0012 Improved adjustment of transmission power in a
`communication System is provided by virtue of the present
`invention. In one embodiment, in a point to multipoint
`
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`US 2002/0159404 A1
`
`Oct. 31, 2002
`
`communication System, transmission power of a Subscriber
`unit is controlled based on power measurements made at a
`central access point. According to the present invention,
`power measurement information based on transmissions
`occurring at irregular intervals may be combined in a
`beneficial manner to control transmission output power. In
`one embodiment, a power regulation process determines a
`Series of difference values indicating the differences between
`desired received power level at the central access point and
`measured received power level. A Smoothing process is
`applied to the difference values. One or more parameters of
`the Smoothing process vary with elapsed time since a last
`power measurement.
`0013 A first aspect of the present invention provides
`apparatus for operating a central access point in a point to
`multipoint communication System. The apparatus includes a
`receiver System that receives a Series of transmissions from
`a Subscriber unit and measures received power levels of the
`Series of transmissions. The apparatus further includes a
`control processor that sends power adjustment information
`to the Subscriber unit to regulate output power level of the
`Subscriber unit. Influence of older ones of the received
`power levels on the output power level varies with elapsed
`time since the last one of the Series of transmissions.
`0.014) A second aspect of the present invention provides
`apparatus for operating a Subscriber unit in a point to
`multipoint communication System. The apparatus includes a
`transmitter System that transmits a Series of transmissions
`from the Subscriber unit to a central access point. The
`apparatus further includes a control processor that regulates
`transmitted power level of the Series of transmissions in
`accordance with power measurements made on the Series of
`transmissions. The influence of older ones of Said power
`measurements on the transmitted power level varies with the
`elapsed time Since a most recent one of the power measure
`mentS.
`Further understanding of the nature and advantages
`0.015
`of the invention herein may be realized by reference to the
`remaining portions of the Specification and the attached
`drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0016 FIG. 1 depicts a point to multipoint communica
`tion System according to one embodiment of the present
`invention.
`0017 FIG. 2 depicts the interchange of messages
`between physical layer and MAC layer entities at a sub
`Scriber unit and a central acceSS point according to one
`embodiment of the present invention.
`0.018
`FIGS. 3A-3D depict alternative operation schemes
`of a power control loop according to one embodiment of the
`present invention.
`0.019
`FIG. 4 depicts elements of a central access point of
`a point to multipoint communication System according to
`one embodiment of the present invention.
`0020 FIG. 5 depicts elements of a subscriber unit of a
`point to multipoint communication System according to one
`embodiment of the present invention.
`0021
`FIG. 6A is a flowchart describing steps of control
`ling Subscriber unit output power in a point to multipoint
`
`communication System according to a first alternative
`embodiment of the present invention.
`0022 FIG. 6B is a flowchart describing steps of control
`ling Subscriber unit output power in a point to multipoint
`communication System according to a Second alternative
`embodiment of the present invention.
`
`DESCRIPTION OF SPECIFIC EMBODIMENTS
`0023 FIG. 1 depicts a point to multipoint wireless com
`munication network 100 Suitable for implementing one
`embodiment of the present invention. Network 100 includes
`a central access point or head end 102 and multiple Sub
`scriber units 104. All communication is typically either to or
`from central access point 102. Communication from central
`access point 102 to one or more subscriber units 104 is
`herein referred to as downstream communication. Commu
`nication from any one of Subscriber units 104 to central
`access point 102 is herein referred to as upstream commu
`nication. In one embodiment, different frequencies are allo
`cated to upstream and downstream communication. In alter
`nate embodiments, Subscriber units 104 may communicate
`directly with one another.
`0024. Each of one or more upstream frequencies is com
`mon to multiple Subscriber units. To prevent collisions
`between Subscriber units when accessing the shared
`medium, a medium access control (MAC) protocol is pro
`Vided. According to one embodiment of the present inven
`tion, a MAC protocol developed for data transmission over
`cable systems may be used to coordinate upstream commu
`nications in wireless network 100. An exemplary MAC
`protocol of this type is the so-called MCNS protocol
`described in the Data-over-Cable Service Interface Specifi
`cations, Radio Frequency Interface Specification, SP-RFI
`I04-980724, (Cable Television Laboratories, 1997).
`0025 MCNS employs a time domain multiple access
`(TDMA) Scheme to allocate access to the shared upstream
`frequency among multiple subscriber units 104. The entities
`controlling operation according to the MAC protocol at
`central access point 102 and subscriber units 104 are
`referred to collectively as the MAC layer. This identifies
`these entities as representing a layer in a multi-layer com
`munication model. In reference to the well-known OSI
`multi-level model of data communications, the MAC layer
`as it is discussed here corresponds to a lowest Sublayer of the
`data link layer. Underneath the MAC layer is the physical
`layer, which is responsible for transmitting and receiving
`bits over the wireless channel. The MAC layer implements
`a TDMA scheme for upstream communication. Each of one
`or more frequencies is divided into a Series of frames or
`minislots in the time domain.
`0026 FIG. 2 depicts interactions between central access
`point 102 and one of subscriber units 104. Central access
`point 102 includes a central access point MAC layer block
`202 and a central access point physical layer block 204.
`Subscriber unit 104 includes a subscriber unit physical layer
`block 206 and a subscriber unit MAC layer block 208. In one
`embodiment, central access point MAC layer block 202 and
`subscriber unit MAC layer block 208 collectively operate
`according to the MCNS protocol.
`0027 Data from higher layers and MAC layer network
`management information are passed between MAC layer
`
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`US 2002/0159404 A1
`
`Oct. 31, 2002
`
`block 202 and 208 via physical layer blocks 204 and 206
`which are directly responsible for exchange of bits acroSS
`the wireleSS channel. Central access point 102 has exclusive
`access to at least one frequency for downstream transmis
`Sions. Subscriber unit 104, however, shares access to one or
`more upstream transmission frequencies in accordance with
`the operative MAC protocol.
`0028. Each subscriber unit 104 is assigned one or more
`MAC layer addresses. In MCNS applications, the MAC
`layer addresses are known as SIDS. Multiple SIDs are
`assigned to individual data Services at a Subscriber unit. For
`example, Voice traffic at a particular Subscriber unit may be
`designated by a given SID with other types of data being
`assigned a different SID. The various SID values may be
`assigned when a Subscriber unit powers on and registers to
`the central acceSS point. Each Subscriber unit has a primary
`SID that uniquely identifies the subscriber unit.
`0029. One class of network management messages
`eXchanged between central access point MAC layer block
`202 and Subscriber unit MAC layer block 208 implements
`ranging, the process of establishing the round trip propaga
`tion delay between central access point 102 and subscriber
`unit 104. There are ranging requests transmitted from central
`access point MAC layer block 202 to subscriber unit MAC
`layer block 208 and ranging responses Sent back from
`subscriber unit MAC layer block 208 to central access point
`MAC layer block 202. The power level of the ranging
`responses may be measured within central access point
`physical layer block 204. Central access point MAC layer
`block 202 and subscriber unit MAC layer 208 also act as
`data interfaces to higher layers.
`0030 Application data including, e.g., voice, Video, com
`puter files, etc. is exchanged between the MAC layer blockS.
`Higher layer entities Serve as the origin and destination for
`this data. When subscriber unit MAC layer block 208 has
`application data ready for upstream transmission to central
`access point MAC layer block 202, it transmits a special
`network management message known as an acceSS request
`(RA). TDMA-oriented MAC layer protocols such as MCNS
`allocate certain time domain slots for transmission of acceSS
`requests. In response to acceSS requests, central access point
`MAC layer block 202 sends grants downstream to the
`various Subscriber units 104. A downstream grant message
`includes SIDS for various Subscriber unit data services
`accompanied by times reserved for their upstream transmis
`Sion of data.
`0.031
`Point to multipoint communication system 100
`regulates the transmission power level of each Subscriber
`unit 104 so that the received power is at a desired level. The
`desired received power level may be set the same for each
`subscriber unit 104. The desired received power level may
`be set at a level high enough to assure accurate reception of
`data by central access point 102 while not being Set So high
`So as to Saturate receiver equipment within central acceSS
`point 102 or cause interference to unintended receivers.
`0.032 To regulate power to the desired level central
`access point 102 measures the received power level from
`each of subscriber units 104. A received power level may be
`measured on each type of upstream transmission depicted in
`FIG. 2. According to the present invention, power control
`may be based on power measurements made on disparate
`types of transmissions arriving at central acceSS point 102 at
`disparate times.
`
`0033 FIGS. 3A-3D illustrate message traffic relating to
`power control and various alternative divisions of power
`control responsibilities between central access point 102 and
`subscriber unit 104. Methods for determining transmitter
`power level will be described with reference to FIGS.
`6A-6B. In FIG. 3A, central access point 102 makes succes
`Sive power measurements on upstream transmissions
`received form subscriber unit 104. Central access point 102
`Sends information indicating the raw power measurement
`levels back to Subscriber unit 104.
`0034). In FIG.3B, central access point 102 determines the
`desired power adjustment for subscriber unit 104 based on
`received power measurements. Central access point 102
`sends power adjustments downstream to subscriber unit 104.
`In one embodiment, Subscriber unit 104 Smoothes the
`adjustment amounts received over time to obtain a Smoothed
`adjustment to actually use in modifying transmit power.
`Alternatively, subscriber unit 104 simply modifies its output
`power in response to the adjustments.
`0035) In FIG.3C, central access point 102 determines the
`desired transmission power levels for subscriber unit 104
`based on received power measurements. Central acceSS
`point 102 sends these levels downstream to subscriber unit
`104. In one embodiment, Subscriber unit 104 Smoothes the
`power levels over time before using them. Alternatively,
`subscriber unit 104 simply changes its output power to the
`level indicated in the downstream transmission.
`0036). In FIG. 3D, the upstream transmissions used for
`power measurements include a numeric value indicating the
`power level used for the transmission. The numeric value is
`embedded as data in the upstream transmissions. Central
`access point 102 may then estimate a channel response
`magnitude by dividing the power measurement for a par
`ticular transmission by the transmitter power level. Channel
`response estimates derived from Successive transmissions
`are then sent downstream to Subscriber unit 104.
`0037 FIG. 4 depicts elements of central access point 102
`according to one embodiment of the present invention.
`Central access point 102 includes a CPU 402 that controls
`overall operation. A MAC layer processor 404 is primarily
`responsible for controlling MAC layer functions and Serving
`as an interface to higher layer entities. MAC layer processor
`404 controls the transmission and reception of messages
`shown in FIG. 2 as being transmitted or received by central
`access point MAC layer block 202. In one embodiment,
`central access point MAC layer processor 404 may be a
`BCM3210B integrated circuit available from Broadcom,
`Inc. of Irvine Calif. Central acceSS point physical layer block
`204 is depicted as including a physical layer control pro
`cessor 406 and a physical layer transceiver 408. Physical
`layer transceiver 408 is equipped with a transmitter antenna
`410 and a receiver antenna 412. In one embodiment, CPU
`402 also incorporates the functions of physical layer pro
`cessor 406 and/or MAC layer processor 404.
`0038 Physical layer transceiver 408 includes a modem
`for converting received analog Signals to digital data and for
`converting digital data to be transmitted to analog signals.
`Physical layer transceiver 408 also incorporates necessary
`RF and IF Subsystems both for upconverting analog trans
`mitter Signals to RF frequency and downconverting received
`RF signals to baseband. Physical layer transceiver 408 also
`incorporates hardware for measuring power of individual
`
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`IPR2021-01376
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`US 2002/0159404 A1
`
`Oct. 31, 2002
`
`transmissions from Subscriber units. These power measure
`ments are forwarded to physical layer control processor 406.
`0.039 The primary source of digital transmission data for
`physical layer transceiver 408 is the downstream MAC layer
`data and higher layer data forwarded by MAC layer pro
`cessor 404. Also, however, there is power adjustment infor
`mation to be sent downstream that is received from physical
`layer control processor 406. As was described in reference
`to FIGS. 3A-3D, the power adjustment information may be,
`e.g., power adjustment commands, raw power measure
`ments, channel estimates, etc. Physical layer transceiver 408
`Sends this power adjustment information downstream in a
`manner that is transparent to MAC layer operation. One
`Scheme for downstream transmission of this power adjust
`ment information is described in the co-filed co-assigned
`application entitled COMMUNICATION OF PHYSICAL
`LAYER CONTROL PARAMETERS
`0040 Physical layer control processor 406 receives
`power measurements from physical layer transceiver 408
`from various Subscriber units and formats the information
`for forwarding to CPU 402. Physical layer control processor
`406 determines power adjustment information based on
`these power measurements and Sends the power adjustment
`to physical layer transceiver 408 for downstream transmis
`Sion. As is shown in FIG. 4, CPU 402 may also perform the
`determination of power adjustment information. The func
`tionality of CPU 402, physical layer control processor 406,
`and MAC layer processor 404 may be, e.g., combined in one
`unit of divided in any way among multiple units.
`0041. In the embodiment of FIG. 3A, the power adjust
`ment information developed by physical layer control pro
`cessor 406 consists of the raw power measurements. In the
`embodiment of FIG. 3B, the power adjustment information
`includes power adjustment values. Physical layer control
`processor 406 then computes the power adjustments to Send
`downstream in decibels. In the embodiment of FIG. 3C, the
`power adjustment information includes the power transmis
`sion level to be used by Subscriber unit 104.
`0042. In the embodiment of FIG. 3D, from each trans
`mission having its power measured, physical layer trans
`ceiver 408 also extracts a data value corresponding to the
`output transmission power level used by the Subscriber unit.
`Physical layer control processor 406 then estimates the
`channel response magnitude by dividing the measured
`received power by the Subscriber unit transmission power
`level value. The power adjustment information Sent down
`Stream then consists of these channel response magnitude
`values.
`0043. In many systems, there may be limited capacity
`available to Send power adjustment information downstream
`to numerous Subscriber units. Physical layer control proces
`sor 406 may maintain a FIFO queue (not shown) of power
`adjustment information data items awaiting downstream
`transmission to Subscriber units. The power adjustment
`information data items are the raw power measurements,
`power adjustment values, requested transmission power
`levels, or channel estimates, etc. shown in FIGS. 3A-3D.
`Each such data item is identified in the queue by a MAC
`layer address of a particular subscriber unit. In an MCNS
`application, the MAC layer address may be the primary SID
`assigned to the particular Subscriber unit.
`0044 New power adjustment information for a particular
`Subscriber unit may be generated by physical layer control
`
`processor 406 before previously generated power adjust
`ment information has been transmitted downstream and
`removed from the queue. The previously generated power
`adjustment information is thus now obsolete and should not
`be transmitted downstream. In one embodiment, when new
`power adjustment information for a particular Subscriber
`unit is ready for transmission downstream, physical layer
`control processor 406 checks whether that subscriber unit
`already has an entry in the queue. If there is no entry in the
`queue, the new power adjustment information is written to
`the back of the queue. If there is a previous untransmitted
`entry in the queue, the new power adjustment information
`overwrites the old entry and assumes the old entry's position
`in the queue.
`004.5
`FIG. 5 depicts elements of a representative sub
`scriber unit 104 according to one embodiment of the present
`invention. A CPU 502 is responsible for overall control. A
`MAC layer processor 504 Substantially implements the
`functionality of subscriber unit MAC layer block 208. MAC
`layer processor 504 also acts as a data interface to higher
`layers. In an MCNS embodiment, MAC layer processor 504
`may be a BCM3300 integrated circuit provided by Broad
`CO.
`0046) A physical layer control processor 506 and a physi
`cal layer transceiver 508 together implement the function
`ality of subscriber unit physical layer block 206 shown in
`FIG. 2. Physical layer transceiver 508 is equipped with a
`transmitter antenna 410 and a receiver antenna 512. Physical
`layer transceiver 508 includes a modem for transforming
`digital data into analog modulated Signals for transmission
`and for transforming received modulated analog signals into
`digital data. Physical layer transceiver 508 also incorporates
`an RF receiver system for downconverting a received RF
`Signal to a baseband Signal while providing necessary fil
`tering and amplification. Physical layer transceiver 508 also
`includes an RF transmitter System that upconverts baseband
`and provides necessary filtering and amplification. Physical
`layer transceiver 508 is capable of setting its output trans
`mitter power level in response to power adjustment com
`mands received from physical layer control processor 506.
`This may be done by varying RF amplification, IF (inter
`mediate frequency) amplification, digital Scaling, or a com
`bination of these.
`0047 Physical layer transceiver 508 receives its digital
`data for transmission from MAC layer processor 504.
`Received digital data output by physical layer transceiver
`508 is primarily MAC layer data and higher layer data which
`is forwarded to MAC layer processor 504. There is also
`power adjustment information