(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`(43) International Publication Date
`14 July 2005 (14.07.2005)
`
` (10) International Publication Number
`
`WO 2005/062798 A2
`
`(51) International Patent Classification:
`
`Notclassified
`
`(21) International Application Number:
`PCT/US2004/042509
`
`(22) International Filing Date:
`17 December 2004 (17.12.2004)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`60/531,419
`
`19 December 2003 (19.12.2003)
`
`US
`
`(71) Applicant (for all designated States except US): IBIS
`TELECOM,INC.[US/US]; 8950 Costa Verde Boulevard
`#4433, San Diego, CA 92122 (US).
`
`(72) Inventors; and
`SCHEINERT,
`(75) Inventors/Applicants (for US only):
`Stefan [DE/US]; 8950 Costa Verde Boulevard #4433, San
`Diego, CA 92122 (US). BENDER, Daniel, M. [US/US];
`4341 Nobel Drive, #114, San Diego, CA 92122 (US).
`
`(81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW,BY, BZ, CA, CH, CN,
`CO, CR, CU, CZ, DE, DK, DM,DZ, EC, EE, EG, ES, FI,
`GB, GD, GE, GII, GM, IIR, ITU, ID, IL,IN,IS, JP, KE,
`KG,KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD,
`MG, MK, MN, MW, MX, MZ, NA,NI, NO, NZ, OM,PG,
`PH,PL, PT, RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM,
`TN,TR, TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM,
`7W.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU,TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK,EE, ES,FI,
`FR, GB, GR,ITU,IE, IS, IT, LT, LU, MC, NL, PL, PT, RO,
`SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN,
`GQ, GW, ML, MR,NE, SN, TD, TG).
`
`Published:
`
`without international search repart and to be republished
`upon receipt of that report
`
`(74) Agents: SCHMELZER,Troy, M.et al.,; Hogan & Hart-
`son L.L.P., Biltmore ‘lower, 500 South Grand Avenue, Suite
`1900, Los Angeles, CA 90071 (US).
`
`For two-letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes and Abbreviations" appearing at the begin-
`ning of each regular issue of the PCT Gazette.
`
`(54) Title: BASE STATION INTERFERENCE CONTROL USING TIMESLOT RESOURCE MANAGEMENT
`
`(57) Abstract: A personal base station configured to connectto the Internet and establish a small area of wireless coverage including
`means for controlling interference with neighboring personalbasestations using a timeslot management mechanism. Timeslot man-
`agement mechanisms include timeslot interference detection, timeslot power reduction, timeslot allocation, timeslot offset calibra-
`tion, and timeslot synchronization managementthat minimizes the numberof frequencics required to control inter-cell interference
`between neighboring personal base stations.
`
`APPLE 1009
`
`
`
`
`
`2005/062798A2IIUIMNIINAININUINNIAINITAANAGNMUTA
`
`APPLE 1009
`
`1
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`BASE STATION INTERFERENCE CONTROL USING
`
`TIMESLOT RESOURCE MANAGEMENT
`
`
`
`RelatedApplications
`
`[0001] This application claims the benefit ofU.S. provisional application no.
`60/531,419, filed December 19, 2003. This application is a continuation-in-part of
`U.S. non-provisional application serial no. 10/280,733, filed October 25, 2002.
`Field of the Invention
`
`[0002] The present invention relates generally to radio or wireless communications
`and, more particularly, to interference controlbyuse oftimeslot managementfor
`pico/personalbasestations integrated into conventional wireless networks.
`
`Backgroundofthe Invention
`[0003] In rolling out a conventional wirelesscarrier network, one of the primary
`considerationsis the process of selecting and allocating frequency channels for all
`of the cellular base stations within the system. This process, which is called
`frequency reuse or frequency planning, depends on various factors such as
`
`frequencies available for use, cell geometry, type of antenna, aid topography.
`[0004] A key
`parameter
`in
`determining
`frequency
`reuse
`is the
`Carrier-to-Interference (C/I) ratio, which measuresthe ratio of the power level of
`the radio frequency carrier to the powerlevel of the interference signal in the
`channel. The C/I ratio helps to determine the maximum interference levelthat will
`
`still allow a cellular system configuration to provide an acceptable quality of
`
`service.
`
`2
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0005] In rolling out a new GSM outdoor macro base station network, assuming a
`standard 4/12 geometry cell cluster reuse pattern (see FIG. 1), a minimum of 12
`
`frequencies is typically required to keep the quality of service within tolerable
`
`limits. For the GSM network,that means meeting or exceeding the GSM 9 db C/I
`
`ratio specification.
`[0005] In rolling out a new GSM outdoor micro or pico base stationnetwork, one
`of several frequency planning strategies may be implemented. Onestrategy is to
`
`allocate new (unused) frequencies to the micro/pico cells, depending onthe
`
`availability of unused frequencies in the carrier's inventory. Altematively, the
`carrier may choose to share the same frequencies allocated to the existing macro
`cell network. In either case, assuming a standard 4/12 geometric cell cluster reuse
`
`pattern, a minimum of 9 to 12 frequenciesis typically required to meet or exceed
`
`the GSM 9 db C/I quality of service specification for the micro/pico cell network.
`
`The reasonfor the reduced numberoffrequenciesis that themicro or picocells are
`deployedbelowthe clutterheight, whichmeansahighersignal loss to more distant
`_ areas, effectively reducing the interference level.
`[0007] When considering therollout of yet another network of base stations,
`specifically indoor pico or personal basestations, the superior frequency planning
`
`strategy would be to allocate new (unused) frequencies,
`
`in order to avoid
`
`interference from the more powerful outdoor macro stations, particularly in high
`
`rise structures. Although allocating new (unused) frequencies is a superior strategy
`
`(easier to implement) than sharing the frequencies with the macro- and micro cells
`
`when rolling out a new indoor network, it is not always feasible, for several
`
`reasons.
`
`3
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0008] First, most carriers do not own enough additionalfrequencies to implement °
`| the unused frequency strategy. Typically, the only unused frequencies in a carrier
`bandwidth inventory are the two "guard" frequencies on the extreme ends of the
`
`carrier's licensed bandwidth. These frequencies, however, are typically unusable in
`a practical sense because ofpotential interference from frequencies licensed and
`deployed by other carriers.Secondly, even if these two guard frequencies were
`| used, they would not allow the carrier to meet or exceed the current GSM 9 db C/I
`
`ratio quality of service specification discussed above.
`
`[0009] From the carriers point of view, an ideal solution to their frequency
`planning problem wouldbe amethod or mechanism allowingthe rollout ofa GSM
`network ofindoorpico or personal basestations that fulfills the followingcriteria: a)
`use of only one or two unused frequencies, preferably guard frequencies, b)
`
`satisfaction of the GSM 9 db C/I ratio qualify of service specification, and c)
`
`seamless integration with the carriers existing outdoor macro/micro network.
`[0010] Conventional Timeslot Allocation Management: Conventional networks
`
`use time slot allocation management to help control mobile station interference
`
`within a single cell, rather than between cells. A base station or base station
`controllerallocates time slotswithin channelsto all ofthe mobile stations withinits
`
`cell, ensuring that no two mobiles are transmitting or receiving signals within the
`same timeslots, thereby avoiding any interference between mobile stations within
`
`a particular cell.
`
`In addition, the mobile station measures the signal strength or
`
`signal quality (based on the Bit Error Ratio), and passes the information to the Base
`
`Station Controller, which ultimately decides ifand when the powerlevel shouldbe
`
`changed or a handovershould beinitiated.
`
`4
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
` [0011] Conventional Channel Structure and Use of Timeslots:
`Since radio
`spectrum is a limited resource shared by all users, a method must be devised to
`
`divide up the bandwidth among as manyusers as possible. The method chosen by
`
`_ GSM is a combination of Time and Frequency Division Multiple Access
`
`(TDMA/FDMA). The FDMA part involves division by frequencyofthe total MHz
`
`bandwidth into allocatable carrierfrequencies of200 kHz bandwidth. One or more
`
`carrier frequencies are then assigned to each basestation. Each carrier frequency
`_ consists of 2 200 kHz channels separated by a duplex distance (e.g. 45 MHz in
`
`GSM 900). One frequency is used for the downlink (BTS - MS) andthe other
`
`frequencyis used for the uplink (MS -> BTS). The pair of one 200 kHz channelsis
`
`called a duplex channel.
`
`[0012] Each of these duplex channels is then divided in time, using a TDMA
`
`scheme,into eight time slots. Groups of eight consecutive time slots form TDMA
`
`frames, each with duration of 4.615 ms. Each time slot is a burst period (BP)
`during which a transmission burst ofmodulated bits is broadcast. One timeslot is
`
`used for transmission by the mobile (uplink) and one for reception (downlink).
`
`They are separated in time so that the mobile unit does not receive and transmit at
`
`the same time, a fact that simplifies the electronics.
`
`[0013] The GSM BPlasts 15/26 milliseconds (ms) (or approximately 0.577ms).
`
`Eight burst periods are grouped into a TDMA frame (120/26ms,or approximately
`
`4.615ms), which forms the basic unit for the definition of logical channels, an
`
`endlessly recurring cycle of BP time slot transmissions.
`
`[0014] Logical channels are defined by the number and position of their
`
`corresponding burst periods or time slots. The logical channels are used to
`
`5
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`exchange information between mobile stations and base stations, The logical
`channels are divided into dedicated channels, which are allocated to a mobile
`
`station, and common channels, which are used by mobilestations in idle mode.
`Within a logical channel, the transmission (downlink) to a mobile stationoccurs 3
`
`timeslots earlier than the reception (uplink) from a mobilestation.
`
`[0015] The first carrier within a cell is called the Broadcast Control Channel
`
`(BCCH) carrier. The BCCH carrier transmits BCCH system information over
`
`timeslot 0, plus Access Grant Channels, Paging channels and most often SDCCH
`
`channels. The BCCH carrierhas to be onatall times, so the mobiles in surrounding —
`
`cells and in its cell can check the BCCHcarrier signal onall timeslots. - Another
`
`characteristic ofthe BCCHcarrier signal is the basestation transmitting the BCCH
`
`carrier signal does so with a constant output power. Eveniftraffic channelsare in
`
`active use, creating potential interference with the BCCHcarrier signal, the BCCH
`
`carrier signal is still transmitted with a constant output poweronall timeslots. All
`
`other frequency carriers of a cell (TCH carriers) can be switched of if there is no
`
`traffic on the carrier/timeslot.
`
`[0016] Conventional Power Control: To minimize co-channel interference and
`
`conserve power, both the mobiles and the base transceiver stations operate at the
`
`lowest power level that will maintain an acceptable signal quality. Power levels
`canbe stepped up or down in steps of2 dB from the peak powerfor the class down
`to a minimum of 13 dBm (20 milliwatts) or 2.5 mW in GSM 1900. The power .
`
`control is typically done on the TCH carriers. Mobile andbase stations need only
`
`transmit enough power to make a connection. Any more is superfluous, andusing
`
`less power meansless interference.
`
`6
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0017] The mobile and base stationmeasures the signal strengthand signal quality
`(based on the Bit Error Ratio), andpasses the information to the Base Station
`Controller, which ultimately decides if and when the power level should be
`
`changedin either the mobile or the base station. Power control needsto be handled
`
`carefully, since there is the possibility of instability. This arises from having a
`
`mobile increase its power in responseto increased co-channelinterference caused
`
`by another mobile increasing its power.
`
`[0018] In contrast to conventional use ofGSM timeslot allocationmanagement to
`control interference, the present invention usesa timeslot allocation managementto
`
`reduce the number of frequencies required to control
`interference between
`neighboring cells (intercell
`interference control). A mechanism for such a
`capability is provided for both macro base stations and pico or personal base
`
`stations.
`
`Summaryof the Invention
`[0019] United States application no. 10/280,733, filed October 25, 2002 and
`having commonassignee, proposes a portable, low powerbase station configured .
`to convey wireless traffic between a mobile base station and a conventional
`wireless network via the Internet. The base station may be referred to as a
`“personal” or “pico” base station (“PBS”), and is configured to connect to the
`Internetat auser-selected location and establishes a small area ofwireless coverage
`
`within a greater macrocell network. Theuser sets the operating parameters of the
`
`base station. United States application no. 10/280,733 is incorporated by reference,
`
`and its subject matter has been published in corresponding International
`
`Publication No.WO 2004/040938.
`
`7
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0020] The present invention provides a method for enabling a network of indoor
`
`pico or personal base stations (PBSs) meeting the criteria set forth in the
`
`background section above. In particular, the method enables a network ofpico or
`
`personal base stations, using one or two unused frequencies,
`
`to provide an
`
`acceptable level of services within an existing carrier network of macro base
`
`stations. This is accomplished by controlling interference between neighboring
`
`pico/personal basestations using various timeslot management mechanisms.
`
`[0021] The present invention also provides a method to reduce the number of
`frequencies required to control interference between neighboring pico or personal
`base stations (PBS). The present invention comprises one or more ofthe following
`GSM TDMA timeslot resource management procedures: timeslot interference
`detection, timeslot powerreduction, timeslot allocation, timeslot offset calibration,
`and timeslot synchronization. One or more of these resource management
`
`procedures are applied to both BCCH and TCHtimeslot resources. There are many
`
`configurations (mechanisms and embodiments) to achieve this function.
`[0022] It is important to note that this invention benefits a carrier rolling out an
`indoorpico/personal base station network whetherthe carrier elects to implement
`
`either a shared or unused frequency planning strategy for the PBS network. It is
`
`also important to note that this invention is not only applicable to inter-cell
`
`interference control between PBS cells, but also between PBS and macro base
`
`station cells as well in a shared strategy.
`
`[0023] The principles underlying the PBS interference detection and resource
`
`management proceduresare straightforward. FIG. 1 shows two neighboring PBS
`
`cells with interfering mobile signals. FIG.2 illustrates the process flow modelfor .
`
`8
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`initializing, updating, and maintaining two PBS interference detection. databases.
`FIGS.3 and 4 illustrate the "Poweroff"state with the event "Power on" (Power On
`
`Startup Procedure) and "Power On" state operational procedures for timeslot
`interference detection,
`interference database updates, and timeslot
`resource
`
`management.
`
`[0024] Asillustrated in FIG.2, each PBS maintains its own interference databases.
`The two PBS databasesshown are used to track TCH and BCCH timeslot
`
`interference for neighboring PBS units. The BCCH DBis a long-term database(i.e.
`weeks and months), adjusting its active interference timeslotlist to reflect the
`comings and goings of neighboring PBS units. The TCHis a short-term database
`(i.e. minutes, hours, and days), adjusting its active interference timeslot list to
`reflect the real time mobile services provided by neighboring PBS units.
`[0025] The PBS units operate in one oftwo modes. During the "Power On Startup"
`
`procedure the PBSis in mobile mode(i.e. receive on the downlink frequency), and
`in "Power On"state the PBS switches intermittently back and forth from normal
`base station mode(i.e. transmit on the downlink frequency and receive on the
`
`uplink frequency) to sampling mode (similar to mobile mode) as mecessary to
`
`detect BCCHinterfering signal.
`
`[0026] As embodied in this invention, during the "Power On Startup" procedure,
`
`the PBS detects BCCHsignals from a neighboring PBS and adds interfering
`timeslots to it active list. In "Power On"state, the PBS switches intermittently to a
`
`Sampling Modeto detect BCCHsignals from a neighboring PBS and either adds
`
`timeslots (when signal is detected) or deletes timeslots (when the absence of a
`
`previously detected signal is noted over a long period oftime, e.g. months) to or
`
`—
`
`9
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`from its BCCH DB active interference list. Coincidently, as embodied in this
`invention, the PBS, when in “Power On"state, also detects TCH signals from’
`neighboring mobiles and adds or deletes timeslots in real time from its TCH DB
`
`active interferencelist.
`
`[0027] Wheneverthere is a changeofstate in either the BCCH DB or TCH DB(i.e.
`
`the addition or deletion of interfering timeslots to the DB), or various flags or
`
`counters indicate TCH or BCCHtimeslotinterferers have been detected, the PBS
`
`takes steps to manage the timeslot resources appropriately by performing one or
`
`more of several procedures, as appropriate: timeslot allocation (selecting
`non-interfering timeslots for future mobile service requests), timeslot power
`control (decreasing power on interfering timeslots and increasing power on
`non-interfering timeslots), timeslot offset calibration (offsetting BCCH TDMA
`timeframes to avoid interfering with neighboring PBS control signals), and or.
`
`timeslot synchronization (synchronizing TDMA timeframes with those of
`neighboring PBS units to avoidinterference problems associated with timeslot
`frequency drift).
`|
`
`[0028] Timeslot allocation as embodied in this invention is a procedure for
`
`selecting non-interfering timeslots that are not on the PBS active interference DB
`
`lists for use by future mobiles requests within the local PBScell.
`[0029] Timeslot power control as embodied in this invention is a procedure that
`
`reduces PBClocalcell broadcast strength on interfering timeslots in active use by
`
`neighboring PBC cells. Powerlevels are resetto their original levels when the local
`
`PBScell is no longer receiving interfering signals.
`
`10
`
`10
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0030] Timeslot offset calibration as embodiedin this invention is aprocedure for
`the local PBS cell offset its BCCH TDMA timeframe to avoid interference by
`avoiding use of the same BCCHtimeframe used by the neighboring PBScell.
`
`[0031] Timeslot synchronization as embodied in this invention is a procedure for
`the local PBS cell to synchronizeits TDMA timeframe clock with a central clock
`reference,like GPS,the Internet or those ofneighboring PBSunits in order to avoid
`
`interference problems associated with timeslot frequency drift.
`
`[0032] Other systems, methods, features, and advantages of the present invention
`will be or become apparent to one with skill in the art upon examination of the -
`following drawings and detailed description. It is intended that all such additional
`systems, methods, features, and advantagesbe included within this description, be
`within the scope of the present invention, and be protected by the application.
`
`
`BriefDescriptionoftheDrawings
`[0033] The foregoing and other systems, methods, features, and advantages ofthe
`present invention will be more readily understood upon consideration of the
`following detailed description ofthe invention,taken in conjunction with reference
`
`to the accompanying drawings. The elements (components) in the drawings are not
`
`necessarily to scale, emphasis instead being placed upon clearly illustrating the
`
`principles of the present invention and the relationships between the elements.
`Moreover, in the drawings, like (identical) text reference or text descriptions
`designate corresponding elements (components) consistently in the multiple
`
`figures or diagrams.
`
`[0034] FIG. 1 is a block diagram showing interference between mobile stations
`
`located in neighboring PBScells in adjoining apartments.
`
`10
`
`11
`
`11
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0035] FIG.2 is a block flow diagram showing how PBS TCH and BCCH DBsare
`maintained and used to manage timeslotresources.
`|
`[0036] FIG. 3 is a block flow diagram showing. the PBS Power-On Startup
`procedure.
`.
`[0037] FIG. 4 is a block flow diagram is a continuation of FIG. 3 showing the PBS
`
`operational procedures that continuously update the BCCH/TCH DBsand the
`ongoing procedures that continuously manage timeslot resources.
`
`[0038] FIG. 5 is a block diagram showing logical timeslot allocation and power
`
`reduction resource management to control interference between neighboring PBS
`
`cells.
`
`[0039] FIG.6 is a block diagram showinginitialPBS Startup withBCCHtimeslot
`
`offset calibration, and subsequenttimeslot resource management.
`[0040] FIG. 7 is a block diagram showing the impact on field strength when
`timeslots between base stations become asynchronous. |
`Detailed Description ofthe Preferred Embodiments
`
`[0041] Introduction
`
`[0042] United States application no. 10/280,733, filed October 25, 2002 and
`having common assignee, proposes a portable, lowpowerbase station configured
`to convey wireless traffic between a mobile base station and a conventional
`wireless network via the Internet. The base station may be referred to as a
`
`“personal”or “pico” base station (“PBS”), and is configuredto connect to the
`
`Internet at a user-selected location and establishes a small area ofwireless coverage
`within a greater macrocell network. The user sets the operating parameters ofthe
`base station. United States application no. 10/280,733 is incorporated by reference,
`
`11
`
`12
`
`12
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509 |
`
`and its subject matter has been published in corresponding International
`Publication No. WO 2004/040938.
`
`[0043] 1.0 Implementation
`
`[0044] The embodiment of the present invention can be viewed asa method
`
`consisting of one or more of the following resource management procedures:
`
`timeslot interference detection and database update, timeslot power reduction,
`
`timeslot allocation, timeslot offset calibration, and timeslot synchronization. One
`
`or more of these resource management procedures is applied to both TCH and
`
`BCCH GSM TDMA timeslot resources. Section 2.0 describes thePBS Startup
`
`procedures that
`initially detects interference between neighboring PBS cells
`(Figure 1), fills the interference BCCH/TCH DBs(Figure 2), and subsequently
`
`.
`
`implements timeslot resource startup management (Figures 3-7).
`Section 3.0
`describes the PBS Operational procedures that continuously detect interference, |
`update the interference BCCH/TCH DBs, and continuously manage timeslot
`resources (Figures 2 -7).
`|
`
`[0045] 2.0 PBS Startup Power On Procedure
`[0046] ‘When a new PBSis initially activated or an existing PBS comes alive
`following some eventsuch as a connectionto the Internet or power outage,it starts
`
`the Power On Startup procedure illustrated in Figure 3. Embodiments of these
`
`Power OnStartup proceduresare described below in Sections 2.1 through 2.6
`[0047] 2.1 Power On Startup
`[0048] One embodimentof the Power Onprocedure occurs whenever a PBS loses
`
`electrical power, either because of a power outage or becauseits on-off switch was
`
`12
`
`13
`
`13
`
`

`

`wo 2005/062798
`PCT/US2004/042509
`toggled to the offposition. Following the power outage or toggling of the on-off .
`switch to the "on" position, the PBSresets itselfto the Startup Mode.
`[0049] Another embodiment of Power On occurs whenever
`the PBS is
`disconnected from the Internet. When the PBS is reconnected to the Internet, the
`
`PBSresets itself to the Startup Mode.
`
`[0050] Another embodiment of Power On occurs whenever the PBS comparesthe
`
`most recent TCH data entry with ihe current time clock. Ifthe time difference (TD)
`between the most recent entry and the current time clock is greater than a specified .
`
`time difference limit (TD-int), such as 7 days, then the PBSresets itself to the ©
`Startup Mode.
`_
`
`-
`
`[0051] 2.2 Delete DB Entries
`[0052] Each PBS maintains its own interference databases (see Figure 2): The two
`
`PBS databases are used to track TCH and BCCH timeslot interference for
`
`neighboring PBS units (see FIG. 1). The BCCH DBis a long-tenD database(i.e.
`weeks and months), adjusting its active interference timeslot list to reflect the
`comings and goings ofneighboring PBSunits. The TCH is a short-term database
`
`(i.e. minutes, hours, and days), adjusting its active interference timeslotlist to
`
`reflect the real time mobile services provided by neighboring PHS units.
`
`[0053] One embodiment of the Delete DB Entries procedure is to delete all active.
`
`entries from the PHS TCH and BCCH DBs(FIG.2) whenever the PHSdetects that
`
`it is in the Startup Mode, based on the embodiments for Power Onset forth in
`
`Section 2.1 above.
`
`[0054] 2.3 Set PBS in MS Mode
`
`13°
`
`14
`
`14
`
`

`

`WO 2005/062798
`
`|
`
`PCT/US2004/042509
`
`[0055] When the PBSis powered-on,it initially enters into a startup mobile station
`
`mode rather then the base station mode. While in mobile mode, the PHS can
`receive downlink data sent by other base stations, just like any other mobile station.
`While in the mobile modé,itis importantto note that the PHS transmits no signals.
`[0056] The exemplary embodiments for Setting the PHS in MS modearesimilar to
`
`the embodimentsset forth in Section 2.2 above for the Delete DB Entries procedure.
`
`One embodiment of the Set PHS in MS Mode procedure is to have the PHS
`automatically enter the Startup Mobile Mode whenever the PHS detectsthatit is in
`
`the Startup Mode, based on the embodiments set forth in Section 2.1 above.
`[0057] 2.4 Start BCCH Detection
`
`[0058] Whenin Mobile Mode, the PHS does not transmit or provide servicesto the
`
`mobiles, but searches for other neighboring PHScells broadcasting BCCHsignals
`
`on the assigned frequency. Thisis illustrated in FIG. 1. While scanning in mobile
`
`mode, the PBSdetects interfering timeslots using one or more procedures.
`[0059] One exemplary embodiment of interference detection is the following
`
`procedure. While in Mobile Mode, the PBS scans for BCCHsignals in all timeslots
`
`on the assigned frequency.
`
`If the PBS can detect any BCCH messagesin the
`
`downlink path it will add this timeslot to the BCCH DB.
`
`that any BCCH timeslot
`requires
`[0060] Another exemplary embodiment
`interference signals detected needto exceed a preset FS-BCCH threshold. If that
`threshold is exceeded, aFlag (F-int) or anyyes/no binaryindicator is set to indicate
`an interference condition is occurring for a particular timeslot(e.g. true), indicating
`
`BCCHDetection. For example, BCCH timeslot interference is detected ifPBS can
`
`14
`
`15
`
`15
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`receive BCCH messages and the received field strength of the downlink path
`exceeds FS_BCCH(e.g. -80 dBm).
`|
`|
`
`[0061] Another embodimentfor interference detection is entirely independent of
`the absolute field strength. While in Startup Mobile Mode, the PBS scans for
`
`BCCH signals on assigned frequencies. Whenever a decoded BCCH signal is
`detected, interference is occurring and the timeslot interference Flag or yes/no
`
`binary indicatoris set (e.g. true), indicating BCCH Detection.
`
`[0062] 2.5 Set BCCH Offset
`
`-
`
`[0063] The Set BCCH Offset procedure sets its own BCCH timeslot for a PBS
`
`during the Power On procedurethatits timeframeis offset by one or more timeslot
`
`increments against interfering BCCH timeslots. An example of BCCH timeslot
`
`offset may be seen in Figure 6.
`[0064] One embodiment ofthe Set BCCH Offset procedure is as follows: Before
`
`the Offset occurs, a PBS detects one or more BCCHsignals from interfering PBS -
`
`cell(s) on one or moreofits timeslots(e.g. timeslot 2 in FIG. 6) using one of the
`BCCHdetection embodimentprocedures describedin Section 2.4 above. The PBS
`then resets (recalibrates) its TDMA framing so that the interfering BCCH signal
`
`originally detected in one PBStimeslot(e.g. timeslot 2 in FIG. 6) is subsequently
`
`detected in a different timeslot(e.g. timeslot 6 in FIG. 6). Note that because this
`
`procedure is done in "mobile mode", the offset must take into consideration the
`
`BS-MSdelay offset. The BCCH offset procedure is considered "correct", if later,
`
`after the PBS switches to base station mode, its own BCCH timeslot and all
`interfering BCCH timeslots from neighboring PBScells are not overlapped.
`[0065] 2.6 Fill BCCH DB
`
`15
`
`16
`
`16
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0066]The BCCH DBis a long-term database, adjusting its active interference
`timeslot list to reflect the comings and goings ofneighboring PBS units. One
`embodimentof the Fill BCCH DB procedure for a PBS in the Mobile Mode uses
`the timeslotinterference flags or any otherbinary indicators that were set to "True":
`in the Start BCCH Detection Procedure (see Section 2.4) above in order toidentify
`
`and add active interference timeslots to the BCCH DB. Even though the
`
`maintenance of the BCCH DB might be a long term process, the initial fill
`
`_ procedure occurs in a matter of seconds.
`
`.
`.
`[0067] 2.7 Set PBS in BS mode
`[0068] Afterfilling the BCCH DB,the PBS switches from MS mode to BS mode.
`
`While in BS mode, the PBS receives inthe frequency band where the mobiles are
`transmitting and transmits in the frequencybandwhereotherbasestations transmit.
`In other words, it receives in uplink and transmits in downlink, like any. other
`standard basestation.
`
`[0069] 2.8 Start Other Procedures
`[0070] During the "power on" transition, several messages are sent to initiate
`different processes (procedures); so that once the "power on"state is reached these
`
`functions are active. Start Other Procedures includes the following, examples.
`"Start TCH detection" which starts the TCH detection process and continuously
`monitors
`the timeslots.
`"Start Power Control", which:
`starts
`the power
`control/power reduction process, Similar is "Start BCCH detection" and "Start
`synchronization". The details are described in the following paragraphs.
`
`[0071] 3.0 PBS in "Power on" State
`
`16
`
`17
`
`17
`
`

`

`WO 2005/062798
`
`PCT/US2004/042509
`
`[0072] Once a PBSis in "Power On" state, more processes becomeactive (see
`
`above) and generate events described in figure 4. The procedures in "Power On"
`state are described below in Sections 3.1 through 3.6.
`
`[0073] Start TCH Detection (TCH Detection / TCH Missing)
`
`[0074] In order to control. inter-cell timeslot interference, the present invention
`
`detects interference occurrences (TCH Detection) or absence ofoccurrences (TCH
`Missing) bymonitoring measuredfield strength ofits idle time slots in thepersonal
`
`basestation and counting interference occurrences (see FIG.5).
`
`[0075] One exemplary embodiment of interference occurrence monitoring and
`counting begins by defining a field strength threshold interference limit: FS-int
`
`(e.g. - 75 dBm). Using this threshold limit, timeslot signal samples are taken
`(monitored) and the number of timeslot
`interference occurrences identified
`
`(counted). A duration for timeslot signal monitoringis set (e.g., a duration ofone
`timeslot, although it might be shorter to account for asynchronous issues) and for
`each sample signal above or below the threshold limit FS-int, a counter N-int is
`modified (i.e. incremented or decrementedby somevalue, as appropriate).
`[0076] One exemplary embodiment ofTCH Detection (interference occurrence)is
`
`the following procedure. Whenever a sampled timeslot measured field strength
`
`(FS) exceeds the FS-int threshold, a counter (N-int) will be incrermented by a
`
`designated number(e.g. 1). Conversely, if the FS-int threshold is not reached, the
`counter N-int will be decremented by a designated number(e.g. 1). A's soon as the
`
`counter N-int reaches a limit UP-int (e.g. 3), the interference condition is met,
`indicating TCH Detection. The counter N-int is allowed to increase until an upper
`
`limit UPPER-int (e.g. 5.) is reached.
`
`If a sample does not reach