United States Patent 55
`6,016,311
`Jan. 18, 2000
`[45] Date of Patent:
`Gilbert et al.
`
`[11] Patent Number:
`
`US006016311A
`
`[54] ADAPTIVE TIME DIVISION DUPLEXING
`METHOD AND APPARATUS FOR DYNAMIC
`BANDWIDTH ALLOCATION WITHIN A
`WIRELESS COMMUNICATION SYSTEM
`
`Altorney, Agent, or Firm—Jaquez & Associates; Martin J.
`Jaquez
`
`[57]
`
`ABSTRACT
`
`[75]
`
`Inventors: Sheldon L. Gilbert; Rami Hadar,
`Israel J. Klein, all of San Diego, Calif.
`
`[73] Assignee: Ensemble Communications, Inc., San
`Diego, Calif.
`
`[21] Appl. No.: 08/974,376
`
`[22]
`
`Filed:
`
`Nov. 19, 1997
`
`Tint, C0 ceceeeeccceeessecessnneeceetteeeeenneees H04Q 7/20
`[SL]
`[52] U.S. Ch. eens 370/280; 370/329; 370/468;
`455/450; 455/452
`[58] Field of Search oe 370/280, 329,
`370/336—-338, 345-349, 468; 455/450-453
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,420,851
`5,768,254
`
`5/1995 Seshadri et al. oer 370/29
`6/1998 Papadopouloset al.
`..........+ 370/201
`OTHER PUBLICATIONS
`
`H.C. Papadopouloset al., “Reduction of Mixed Co-channel
`Interference in Microcellular STDD Systems”, Vehicular
`Technology Conference, 1995 IEEE 45th, vol. 2, pp.
`759-763.
`
`An adaptive time division duplexing (ATDD) method and
`apparatus for duplexing transmissions on a communication
`link in wireless communication systems. Communication
`link efficiency is enhanced by dynamically adapting to the
`uplink and downlink bandwidth requirements of the com-
`munication channels. Time slots are flexibly and dynami-
`cally allocated for uplink or downlink transmissions depend-
`ing upon the bandwidth needs of a channel. Communication
`link bandwidth requirements are continuously monitored
`using sets of pre-determined bandwidth requirement param-
`eters. Communication channels are configured to haveeither
`symmetric or asymmetric uplink/downlink bandwidths
`depending upon the needs of the channel. Channel band-
`width asymmetry can be configured alternatively in favor of
`the uplink transmissions(i.c., more time slots are allocated
`for uplink transmissions than for downlink transmissions) or
`in favor of the downlink transmissions(i.e., more time slots
`are allocated for downlink transmissions than for uplink
`transmissions). A myriad oftime slot allocation schemesare
`possible. One simplified time slot allocation scheme uses a
`“frame-based” approach. A preferred channel bandwidth
`analysis technique is disclosed which monitors and updates
`bandwidth requirement parameters associated with commu-
`nication sessions, base stations and cell cluster controllers.
`In accordance with this technique, a communication session
`is preferably assigned both an “initial” and an “actual” set of
`bandwidth parameters.
`
`Primary Examiner—Melvin Marcelo
`
`45 Claims, 6 Drawing Sheets
`
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`U.S. Patent
`
`Jan. 18, 2000
`
`Sheet 1 of 6
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`6,016,311
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`

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`U.S. Patent
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`Jan. 18, 2000
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`6,016,311
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`Jan. 18, 2000
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`Jan. 18, 2000
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`U.S. Patent
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`Jan. 18, 2000
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`Sheet 6 of 6
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`6,016,311
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`CONCENTRATOR
`MULTI-SERVICE
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`CLUSTERCONTROLLER
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`6,016,311
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`1
`ADAPTIVE TIME DIVISION DUPLEXING
`METHOD AND APPARATUS FOR DYNAMIC
`BANDWIDTH ALLOCATION WITHIN A
`WIRELESS COMMUNICATION SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`This invention relates to wireless communication
`
`systems, and moreparticularly to wireless point to multi-
`point voice, data and video (“broadband”) communication
`systems.
`2. Description of Related Art
`A wireless communication system facilitates two-way
`communication between a plurality of subscriber radio sta-
`tions or subscriber units (either fixed or portable) anda fixed
`network infrastructure. Exemplary systems include mobile
`cellular telephone systems, personal communication sys-
`tems (PCS), and cordless telephones. The objective of these
`wireless communication systems is to provide communica-
`tion channels on demand between the subscriber units and
`the base station in order to connect the subscriber unit user
`with the fixed network infrastructure (usually a wired-line
`system).
`In the wireless systems using multiple access
`schemes, frames of time are the basic transmission unit.
`Each frameis divided into a plurality of slots of time. Some
`time slots are used for control purposes and sometimeslots
`are used for information transfer. Information is typically
`transmitted during time slots in the frame where the time
`slots are assigned to a specific subscriber unit. Subscriber
`units typically communicate with the base station using a
`“duplexing” scheme which allows for
`the exchange of
`information in both directions of connection.
`Transmissions from the basestation to the subscriber unit
`are commonly referred to as “downlink” transmissions.
`Transmissions from the subscriber unit to the base station
`are commonly referred to as “uplink” transmissions.
`Depending upon the design criteria of a given system, the
`prior art wireless communication systems have typically
`used either time division duplexing (TDD) or frequency
`division duplexing (FDD) methodsto facilitate the exchange
`of information between the base station and the subscriber
`
`units. Both the TDD and FDD duplexing schemesare well
`knownin theart.
`
`In FDD systems, duplexing of transmissions between a
`base station and its subscriber units is performed in the
`frequency domain. Different sets of frequencies are allo-
`cated for uplink and downlink transmissions. For example,
`two well-known FDD systems are the pan-European GSM
`system (also known as Global System for Mobile
`Communication) and the North American IS-54 and IS-136
`wireless communication systems. Both of these systems use
`a TDMA(time-division multiple access) with an FDD
`duplexing approach. See, e.g., D. J. Goodman, “Second
`Generation Wireless Information Networks,” IEEE Trans.
`Veh. Tech., VI-40, No. 2, pp. 366-374, May 1991. The
`IS-54 air interface uses TDMA/FDDtechnology with three
`channels per 30-kHz AMPScarrier. The GSM air interface
`is characterized by an eight-order TDMA scheme with FDD.
`The available frequency band in Europe is 2*25 MHz,with
`radio channel spacing of 200 kHz. In both wireless systems,
`a base station transmits information to a plurality of sub-
`scriber units during a given first set of time slots and using
`a pre-determined set of downlink frequencies. Subscriber
`units transmit information to the base station using a pre-
`determinedset of uplink frequencies. The uplink and down-
`link frequenciesare offset or spaced in the frequency domain
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`by a knownspacing value. The duplex spacing in both the
`GSM and IS-54 systems is 45 MHz (ie.,
`the downlink
`frequency of a given subscriber unit is separated by 45 MHz
`from the uplink frequency of that subscriber unit).
`Disadvantageously, FDD systems require frequency sepa-
`ration between the uplink and downlink frequency bands.
`The bandwidth allocation schemes needed to provide a
`given service are made more complex and therefore more
`costly than those used by TDD systems. FDD systemsalso
`disadvantageously require that a duplexor be provided with
`the subscriber unit antenna in order to separate the trans-
`mission and reception signals from each otherat the antenna.
`Consequently, the complexity and costs associated with the
`subscriber unit are increased. Although FDD systems are
`effective in reducing interference between the uplink and
`downlink transmissions, FDD systems havelimited flexibil-
`ity and limited available frequency spectrum which is espe-
`cially disadvantageous in broadband wireless communica-
`tion systems. FDD systemsallocate an equal or symmetrical
`bandwidth for both the uplink and downlink transmissions.
`However, many broadband services have asymmetrical
`bandwidth requirements (i.e., the percentage of downlink
`transmissions far outnumber the percentage of uplink
`transmissions, or vice versa). An FDD approach therefore
`results in under-utilized spectrum when used to duplex
`transmissions in a broadband communication system. The
`FDD approach also disadvantageously requires that
`adequate frequency spectrum be available for both uplink
`and downlink transmissions when converting to another
`frequency band for a related application.
`In TDD systems, duplexing of transmissions between a
`base station and its subscriber units is performed in the time
`domain. A selected subscriber unit typically communicates
`with a selected base station using a specific pre-defined radio
`frequency. The channel is time-divided into repetitive time
`periods or time “slots” which are employed for uplink and
`downlink transmissions. In contrast to FDD systems, fre-
`quencyallocation or frequency reuse patterns are simplified
`because there is no requirement of frequency separation
`between the uplink and downlink transmissions. Both the
`uplink and downlink transmissions occur during different
`pre-determined time slots using the identical radio fre-
`quency. However, the subscriber units in the TDD systems
`disadvantageously must accommodate an increased instan-
`taneousbit rate which is required dueto the time sharing of
`the channel. The modemsin the subscriber units of TDD
`systemsare typically active only one-half of the time. As a
`consequence, in order to achieve the same averagebit-rates,
`the typical TDD modem is more complex than it would be
`in a system which would allow the modems to always
`remain active. Therefore, the TDD modems are more com-
`plex and therefore more costly than necessary to achieve a
`given average bit rate.
`One well-known application for the TDD approach is
`found in digital cordless telephone (DCT) systems. Trans-
`mission standards or specifications have been developed in
`both Japan and Europe for use in designing DCT systems.
`Eachof the transmission standards use a TDD technique for
`two-way communication. The Japanese DCT transmission
`standard specifies the use of a plurality of individual carrier
`signals having a frequency separation of 300 kHz within an
`overall system bandwidth of about 23 MHz between
`approximately 1,895 MHz to 1,918 MHz. Each carrier
`signal must support four channels in a TDMA format
`employing TDD for two-way communication.In particular,
`for each frame of time (5 ms) there are four transmit time
`slots (one for each channel) and four receive time slots (one
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`6,016,311
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`for each channel). Each slot is approximately 625 micro-
`seconds duration with a guard time of approximately 30
`micro-seconds provided within each slot.
`By contrast, the European DCT system, or Digital Euro-
`pean Cordless Telecommunication (DECT) system specifies
`a series of carriers spaced 1,728 MHzapart within an overall
`bandwidth of approximately 17.28 MHz. The DECTstan-
`dard provides a network architecture in addition to an air
`interface physical specification and protocols. Ten carrier
`frequencies are employed in conjunction with twenty-four
`time slots per carrier and ten carriers per 20 MHz of
`frequency spectrum. A TDD approach is used for transmis-
`sion between the cordless telephone andthe base station. A
`transmission channel is formed via a combination of a time
`slots and frequencies. Transmissions occur during a ten
`millisecond time frame wherein each frame comprises
`twenty-four time slots. Twelve of the time slots are used for
`transmissions from the base station to the handset (downlink
`transmissions) while twelve are used for transmissions from
`the handset to the base station (uplink transmissions).
`Because the DECT channels allocate an equal amount of
`time (and thus bandwidth) for both the uplink and downlink
`transmissions, the DECT TDD duplexing schemeis said to
`be “symmetrical” in nature. A symmetrical duplexing sys-
`tem is sufficient for systems (such as the DECT system)
`where, on the average, an equal amount of bandwidth is
`required for reception and transmission of information.
`However, symmetrical duplexing systems are inefficient in
`communication systems offering services requiring an
`asymmetric information exchange between the base station
`and subscriber stations. This is especially true in wireless
`communication systems offering wideband or “broadband”
`services such as voice, data and video services.
`In wireless communication networks offering broadband
`services there is no guarantee that the uplink and downlink
`transmissions will have equal or symmetrical bandwidth
`requirements. In fact,
`in many scenarios currently being
`contemplated, it is likely that the bandwidth requirements
`will be unequal and asymmetrical. There are several factors
`driving this observation. First,
`the ratio of uplink and
`downlink bandwidth requirements is somewhat dependent
`upon the service provided over the link. For example, a
`typical telephony voice service (“POTS”-type service) has a
`largely symmetric uplink/downlink bandwidth requirement.
`However, in contrast, a broadcast video service requires a
`largely asymmetric uplink/downlink bandwidth require-
`ment. Most of the information provided during a broadcast
`video service is uni-directional (most of the information is
`transmitted from the base station to the subscriber unit via
`
`the downlink, with very little or no information transmitted
`via the uplink). Therefore, the uplink bandwidth requirement
`of such a service is negligible as compared to the downlink
`bandwidth requirement.
`Second, the ratio of uplink/downlink bandwidth desired
`will vary between channels in a broadband services system
`because each channel shall carry a multitude of diverse
`services Each service shall have its own unique bandwidth
`requirements for transmission and reception. Third, the need
`for symmetrical or asymmetrical communication in a chan-
`nel varies depending upon the type of user. For example, in
`cases where a small business accesses the broadbandser-
`
`vices network for video conferencing or computer network-
`ing applications,
`the uplink/downlink bandwidth require-
`ments shall be largely equal and symmetric. In contrast, in
`cases where a residential user accesses the broadbandser-
`vices network for video-on-demand (VOD)applications,the
`uplink/downlink bandwidth requirements shall be unequal
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`and asymmetric. In these cases, the downlink shall require
`much more bandwidth than the uplink.
`Therefore, a need exists for a method and apparatus which
`can flexibly and dynamically allocate uplink and downlink
`bandwidths in a time division duplexing scheme. The
`method and apparatus should be responsive to the needs of
`a particular link. The bandwidth needs may vary due to
`several factors, including the type of service provided over
`the link and the user type. The prior art systems have
`attempted to accommodate the need for asymmetric links by
`utilizing different modulation schemesfor the uplink and the
`downlink. Underthis approach,all typical bandwidth need
`scenarios are “averaged.” This results in using a more
`spectrum efficient modulation scheme for the downlink. For
`example, a QAM-16 modulation scheme may be selected
`over a GMSKscheme. However,the prior art systems using
`this approach disadvantageously share the communication
`channel equally in time between the uplink and downlink
`transmissions. Consequently,
`the prior art solutions have
`been sub-optimal because they solve the asymmetry prob-
`lem bysatisfying the “average” bandwidth requirement.
`However, as described above, the uplink and downlink
`bandwidths required in broadband networks and by broad-
`band services are very unpredictable. In one sense, there is
`no average or typical scenario. Therefore, a need exists for
`an adaptive time division duplexing method and apparatus
`which can flexibly, efficiently, and dynamically allocate the
`uplink and downlink bandwidths for use in a broadband
`service network. The present
`invention provides such a
`adaptive time division duplexing method and apparatus.
`SUMMARYOF THE INVENTION
`
`The present invention is an adaptive time division duplex-
`ing (ATDD) method and apparatus for duplexing transmis-
`sions in wireless communication systems. The present
`ATDDinvention facilitates the efficient use of communica-
`tion channels in wireless communication systems by adapt-
`ing to the uplink and downlink bandwidth requirements of
`the channels. In accordance with the present invention, the
`communication link bandwidth requirements are continu-
`ously monitored using sets of pre-determined bandwidth
`requirement parameters. The present ATDD invention flex-
`ibly and dynamically allocates time slots for either uplink or
`downlink transmissions in response to the changing band-
`width needs of the communication links. The present inven-
`tion is particularly useful in widebandor broadband wireless
`communication systems, although it may also be used in any
`data communication system where an adaptive and dynamic
`time division duplexing transmission schemeis desirable.
`In contrast to the TDD systemsofthe prior art which have
`time slots dedicated for either uplink or downlink
`transmissions,
`the present ATDD invention dynamically
`changes the time slot designation as either an uplink or
`downlink transmission period. Consequently,
`the uplink/
`downlink bandwidth allocation can be changed to accom-
`modate the uplink/downlink bandwidth requirements of the
`link. The present ATDD invention thus advantageously
`allows channels to use either a symmetric or asymmetric
`uplink/downlink time slot allocation depending upon the
`needs of the channel. In the case of asymmetric time slot
`allocation, the present ATDD invention alternatively allows
`asymmetry in favor of the uplink (i.e., allocates more uplink
`time slots than downlink time slots) or in favor of the
`downlink (i.e., allocates more downlink time slots than
`uplink time slots).
`A myriad of time slot allocation schemes are possible.
`One simplified time slot allocation scheme uses a “frame-
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`6,016,311
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`5
`based” approach which allows the system to dynamically
`allocate a first numberof time slots of a frame for downlink
`(alternatively, uplink) transmissions only while configuring
`the remaining time slots of the frame for uplink
`(alternatively, downlink)
`transmissions. An alternative
`frame-based approach similarly allows the system to
`dynamically allocate a first numberof time slots of a frame
`for downlink (alternatively uplink) transmissions only, how-
`ever the remaining timeslots of the frame maybe allocated
`for either uplink or downlink transmissions, depending upon
`the channel bandwidth needs.
`
`The present ATDD inventionis particularly advantageous
`when used in a wireless communication system offering
`broadband data, video and telephone services. The wireless
`communication system preferably comprises a plurality of
`cells organized into cell clusters, each cell including a base
`station having an associated active antenna array, and each
`base station providing wireless connectivity to a plurality of
`customer sites having a plurality of customer premises
`equipment. The customers are presently contemplated to be
`either residential or small business users. The coordination
`
`of cell activity within a cell cluster is preferably controlled
`by a cluster controller. The broadband services include
`telephone services and data services such as fast internet,
`10-BaseT data service, local area network and wide area
`network connectivity. Video services include broadcast
`video and video-on-demandservices for residential users,
`and video conferencing and distance learning for business
`users.
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`FIG. 2 is a timing diagram showing asymmetric uplink
`and downlink time slot allocations in accordance with the
`
`present invention.
`FIGS. 3a and 3b are timing diagrams showing frame-
`based adaptive time slot allocation schemes in accordance
`with the present invention.
`FIG. 4 is a block diagram of an exemplary broadband
`wireless communication system for use with the present
`invention.
`
`FIG. 5 is a block diagram of a communication hub used
`in the wireless communication system of FIG. 4.
`FIG. 6 is a block diagram of cell site used in the wireless
`communication system of FIG. 4.
`FIG. 7 is a block diagram of a preferred residential
`customer premises equipment (CPE) used in the wireless
`communication system of FIG. 4.
`FIG. 8 is a block diagram of a preferred business customer
`premises equipment (CPE) used in the wireless communi-
`cation system of FIG. 4.
`FIG. 9 is a block diagram ofa cell configuration showing
`the cells of FIG. 4 groupedinto a cell cluster wherein the cell
`cluster comprises seven contiguouscells.
`Like reference numbers and designations in the various
`drawings indicate like elements.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`In one preferred embodiment of the present invention,
`channel efficiency and data bandwidth improvements are
`achieved by using bandwidth requirement parameters to
`monitor and update the communication link timeslotallo-
`cations.
`In accordance with the present
`invention, each
`communication session is preferably assigned both an “ini-
`tion system. Without significantly altering existing wireless
`tial” and an “actual” set of bandwidth parameters. The initial
`communication systems, the present ATDD invention facili-
`set of bandwidth parameters can be established when the
`tates the efficient use of communication channels by adapt-
`system is first installed. The actual set of bandwidth param-
`ing to the uplink and downlink bandwidth requirements of
`eters are created and maintained by the system using the
`the channels. The invention is particularly useful in wide-
`monitoring and updating technique of the present invention.
`band or broadband wireless communication systems,
`Once the system learns about the exact nature of a commu-
`although it may be used with any data communication
`nication session’s bandwidth requirements it updates the
`system where an adaptive and flexible time division duplex-
`initial values to accurately reflect
`the actual bandwidth
`ing transmission schemeis desirable or necessary.
`requirements of the channel.
`In addition to assigning,
`As described above,
`the typical TDD system uses a
`monitoring, and updating session bandwidth parameters,the
`symmetric allocation of uplink and downlink transmissions.
`present ATDD invention also maintains a set of bandwidth
`FIG. 1 is a timing diagram showing equal use of time slot
`parameters for both the base stations and the cluster con-
`allocations for the uplink and downlink transmissions as
`trollers of the wireless communication system. The base
`present in a typical TDD system of the prior art. As shown
`station parameters are used in controlling the uplink/
`50
`in FIG. 1, an uplink transmission occurs duringafirst time
`downlink timeslot allocations for a given cell. The cluster
`slot Ta. During the first time slot Ta, a selected subscriber
`parameters are used in controlling the uplink/downlink time
`station transmits information to a selected base station over
`slot allocations for all of the cells in a given cluster. One
`preferred technique of monitoring and controlling the
`uplink/downlink bandwidths is described. The technique
`described comprises two phases: an initialization phase and
`a tracking or monitoring phase. Other monitoring techniques
`can be used with the present invention.
`The details of the preferred and alternative embodiments
`of the present invention are set forth in the accompanying
`drawings and the description below. Once the details of the
`invention are known, numerousadditional innovations and
`changes will become obvious to one skilled in the art.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`Throughout this description, the preferred embodiment
`and examples shown should be considered as exemplars,
`rather than as limitations on the present invention.
`The present invention is an adaptive time division duplex-
`ing (ATDD) method and apparatus for duplexing transmis-
`sions over a communication link in a wireless communica-
`
`a pre-determined radio frequency. Similarly, a downlink
`transmission occurs during a second time slot Tb. During
`this second time slot Tb, the selected base station transmits
`information to the selected subscriber unit over the same
`
`pre-determined radio frequency. As shown in FIG. 1, the
`communication channel continues to alternate symmetri-
`cally between uplink and downlink transmissions in the
`subsequent time slots. For example, during a third time slot
`Ta’ an uplink transmission occurs over the channelas in the
`first time slot Ta. Similarly, during a fourth time slot Tb', a
`downlink transmission occurs as in the second time slot Tb,
`and so forth in the fifth time slot Ta".
`
`FIG. 1 is a timing diagram showing symmetric timeslot
`allocations for uplink and downlink transmissionsas used by
`prior art time division duplexing methods.
`
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`The TDD systemsoftheprior art fail to accommodate the
`dynamic and asymmetric bandwidth needs of a broadband
`communications network and associated broadband ser-
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`6,016,311
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`7
`vices. The present invention addresses these needs by pro-
`viding an adaptive time division duplexing (ATDD) method
`and apparatus for use in a wireless communication system.
`The present ATDDinvention flexibly and dynamically allo-
`cates the uplink and downlink bandwidths based upon the
`bandwidth requirement of a particular link. As described
`hereinabove, the uplink and downlink bandwidth require-
`ments of a selected link in a wireless communication system
`vary due to the types of services and users of the selected
`link. The present ATDD method and apparatus adapts the
`time slot uplink/downlink ratio to meet the uplink/downlink
`bandwidth requirements of a given service and for a given
`user type.
`FIG. 2 is a timing diagram showing how the present
`ATDD invention advantageously allocates time slots for
`uplink and downlink transmissions. In contrast to the TDD
`systems of the prior art wherein each timeslot is fixed and
`dedicated for either an uplink or a downlink transmission,
`the present ATDD invention allows timeslots to be flexibly
`and adaptively used for either uplink or downlink transmis-
`sions. Further, while the prior art channels shared bandwidth
`equally between the uplink and downlink transmissions, the
`present ATDD invention allows channels to be either sym-
`metric or asymmetric in nature, depending upon the band-
`width needs of a particular link. FIG. 2 shows one possible
`time slot allocation scheme. However, it should be appre-
`ciated that the present invention is notlimitedto the time slot
`allocation shown in FIG. 2. Rather,
`the present ATDD
`invention contemplates a myriad of time slot allocations,
`wherein virtually any combination of uplink and downlink
`transmissions are possible.
`As shownin FIG. 2, an uplink transmission occurs during
`a first time slot Ta. Similar to the timing diagram of FIG. 1,
`a downlink transmission occurs during a second time slot
`Tb. However, in contrast to the prior art TDD approaches,
`the ATDD method and apparatus of the present invention
`allows multiple contiguous and consecutive downlink (or,
`alternatively, uplink) transmissions to occur over a given
`channel. For example, as shown in FIG. 2, a second down-
`link transmission occurs during a third time slot Tc.
`Similarly, a third consecutive downlink transmission occurs
`during a fourth time slot Td. The pattern repeats itself at a
`fifth time slot Ta'. As shown in FIG. 2, during the fifth time
`slot Ta', an uplink transmission occurs over the channelas in
`the first time slot Ta. Similarly, during a sixth time slot Tb',
`a downlink transmission occurs as in the second time slot
`
`Tb. During a seventh time slot Tc', a second consecutive
`downlink transmission occurs as in the third time slot Te,
`and so forth in an eighth time slot Td’.
`The present ATDD inventionis particularly advantageous
`when used in a wireless communication system capable of
`providing wideband or broadband services, such as data,
`voice and video services. As described hereinabove,
`the
`present ATDD invention allows uplink and downlink band-
`widths to be varied depending uponthe particular needs of
`a communication channel and a particular user type. For
`example,
`the timing diagram shown in FIG. 2 allows
`seventy-five percent of the available bandwidth to be used
`for downlink communications and twenty-five percent for
`uplink communications. This uplink/downlink bandwidth
`ratio may be appropriate for some types of broadband data
`and video services, and for some types of network users.
`The present ATDD method and apparatus is flexible in
`that it can use any given time slot for either an uplink or a
`downlink transmission. As described in more detail
`hereinbelow,the average bandwidth requirementfor a given
`channel can be calculated using a variety of techniques. The
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`time slot allocation fora link (i.e., the ratio of time slots used
`for uplink and downlink transmissions) is typically directly
`related to the bandwidth requirementsof the link. Thus, once
`the average bandwidth requirement for a given link is
`determined, the time slot allocation can be established for
`that link using the present ATDDinvention. For example, an
`average bandwidth requirementcan be performedat the time
`that a selected link is first installed in the communication
`network. The average bandwidth requirement can depend
`upon such factors as the service profile or the system
`environment. The communication system uses the average
`bandwidth requirement information to configure the ratio of
`time slots used for the uplink and downlink transmissions
`over a given channel.
`As an alternative to establishing the time slot ratio upon
`link installation, the ATDD method and apparatus of the
`present
`invention can also adaptively and dynamically
`change the time slot ratio for a link based upon the con-
`stantly varying service and user bandwidth requirements.
`The method and apparatus of the present invention prefer-
`ably dynamically monitors and analyzes the service types
`and service bandwidth requirements presently active in the
`wireless communication network, and more specifically,
`active on any given radio communications link. The com-
`munication system can continuously monitor each link and
`gather information about each link’s bandwidth require-
`ments. The information gathered by the communication
`system can be used to re-examine, from time to time, the
`ratio of uplink and downlink time slots. The system can
`dynamically re-configure the time slot ratio according to
`each link’s bandwidth needs. Consequently, a far improved
`channel bandwidth utilization and increased channel effi-
`
`ciency is achieved using the ATDD method and apparatus of
`the present invention. The increase in channel efficiency
`consequently translates into an increase in the numberof
`users served and in the number of services offered by the
`communication system.
`A simplified time slot allocation process can be achieved
`by using a “frame-based” allocation scheme as shown in
`FIGS. 3a¢ and 3b. As shown in FIGS. 3a—3b, a frame is
`defined as comprising N consecutive time slots (where N
`remains constant).
`In the first “frame-based” approach
`shown in FIG. 3a, the communication system dynamically
`configures the first N, time slots (where N is greater than or
`equal to N,) for downlink transmissions only. The remaining
`N, time slots are dynamically configured for uplink trans-
`missions only (where N., equals N-N,).
`A second frame-based approach for allocating time slots
`in a communication channel is shown in FIG. 3b. This
`frame-based allocation schemeis similar to that shown in
`FIG. 3a, with the exception that the remaining N,timeslots
`are no longer configured only for uplink transmissions.
`Specifically, as shown in FIG. 36, and identically to the first
`frame-based approach of FIG. 3a,
`the first N, time slots
`(where N is greater than or equal to N,) are dynamically
`configured for downlink transmissions only. However, in
`contrast to the frame-based approach of FIG. 3a, the remain-
`ing N, (where N. equals N-N,) timeslots are not configured
`for uplink transmiss