US006175737B1
`(10) Patent No.:
`a2) United States Patent
`US 6,175,737 B1
`Kao
`(45) Date of Patent:
`*Jan. 16, 2001
`
`
`(54) METHOD AND APPARATUS FOR WIRELESS
`COMMUNICATIONS FOR BASE STATION
`CONTROLLERS
`
`(75)
`
`Inventor: Chiiming Kao, Saratoga, CA (US)
`
`(73) Assignee: David E. Lovejoy, Tiburon, CA (US)
`(*) Notice:
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent
`term provisions of 35 U.S.C.
`154(a)(2).
`
`.
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`(21) Appl. No.: 08/751,520
`(22)
`Filed:
`Nov. 15, 1996
`(SL) Tint C0? eee ceeeccessseseeeensssee H04Q 7/22; H04Q 7/30
`(52) U.S. Ch. oe ... 455/447; 455/560; 455/562
`
`(58) Field of Search 0... 455/422, 447,
`455/554, 560, 561, 562
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,065,449 * 11/1991 Gordon et al. oes 455/562
`
`2/1997 Searle et al. wees 455/562
`5,603,089 *
`6/1998 Haartsen 0... eeeeseeeeeeeeeeee 455/561
`5,771,453 *
`7/1998 Bannister et al. wee 455/458
`5,787,355 *
`koe
`.
`cited by examiner
`Primary Examiner—Andrew M. Dolinar
`(74) Attorney, Agent, or Firm—Law Office of Imam
`(57)
`ABSTRACT
`A cellular communication system having a plurality of
`wireless in-band channels and having a plurality of cells
`with a plurality of mobile stations in each cell where a base
`station (BTS) is the interface between mobile stations and a
`base station controller (BSC). The base station controller
`monitors and controls one or more base stations. A wireless
`trunk is established between the base station and the base
`station controller using selected ones of the allocated chan-
`nels otherwise available for mobile station communications.
`
`26 Claims, 9 Drawing Sheets
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 1 of 9
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`US 6,175,737 B1
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`FIG. 1
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 2 of 9
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`US 6,175,737 B1
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`BASE
`STATION (BSC)
`
`CONTROLLER
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 3 of 9
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`US 6,175,737 B1
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 4 of 9
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`US 6,175,737 B1
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`U.S. Patent
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`Sheet 5 of 9
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`US 6,175,737 B1
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 6 of 9
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`US 6,175,737 B1
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`7
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 7 of 9
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`US 6,175,737 B1
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`Sheet 8 of 9
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`U.S. Patent
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`U.S. Patent
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`Jan. 16, 2001
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`Sheet 9 of 9
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`US 6,175,737 B1
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`FIG. 17
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`STORE STORE
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`CELL
`LOCATION
`MAP
`
`CONTROL
`CODE
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`ALLOCATED
`FREQUENCY
`STORE
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`PROCESSOR
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`US 6,175,737 B1
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`1
`METHOD AND APPARATUS FOR WIRELESS
`COMMUNICATIONSFOR BASE STATION
`CONTROLLERS
`
`BACKGROUND OF THE INVENTION
`
`2
`several tens and several hundreds. The principal tasks of the
`base station controllers are frequency administration, the
`control of a base station, and exchange functions. The base
`station controllers assign RF carriers to support calls, coor-
`dinate the handoff of mobile users between base stations,
`and monitor and report on the status of base stations. The
`invention relates to the field of two-way
`The present
`base station controllers can be located at the samesite as the
`wireless communication systems and more specifically to
`base stations or at a different site. Base station controllers
`methods and apparatus for wireless communications in
`and base stations together form a functional unit referred to
`mobile telephone systems.
`as the base station subsystem (BSS).
`Conventional Cellular Systems
`Mobile Services Switching Center
`Cellular mobile telephone systems have developed due to
`The mobile services switching center (MSC)is the inter-
`a large demand for mobile services. Cellular systems “reuse”
`face between the cellular system and the PSTN. The MSC is
`frequency within a number of cells to provide wireless
`a switching exchange (switch) for routing calls from the
`two-way radio frequency (RF) communication to large
`numbers of users (mobile stations). Each cell covers a small
`fixed PSTN network through the base station controllers
`(BSC) and the base stations (BTS) to individual mobile
`geographic area and collectively groups of adjacent cells
`stations (MS). The MSC switch provides the network with
`cover a larger geographic region. Eachcell hasafraction of
`the total amount of RF spectrum which is available to
`data about individual mobile stations. Depending on the
`cellular network size, one or more interfaces to the fixed
`support cellular users located in the cell. Cells are of
`different sizes (macro-cell or micro-cell) and are generally
`PSTN network may exist through one or more switches. The
`limited to a fixed capacity. The shapes andsizes of cells are
`numberofbase stations controlled by a single MSC depends
`functions of the terrain,
`the man-made environment,
`the
`upon the traffic at each base station, the cost of intercon-
`quality of communication and user capacity. Cells are con-
`nection between the MSC andthe basestations, the topology
`nected to each other via land lines or microwave links and
`of the service area and other similar factors.
`to the public-switched telephone network (PSTN) through
`Operation and Maintenance Center
`The operation and maintenance center (OMC) hasaccess
`telephone switches. The switches provide for the hand-off of
`to both the MSC switches and the base station controllers in
`users from cell to cell and thus from frequency to frequency
`as mobile users move betweencells.
`order to process error messages coming from the network
`and to controlthe traffic load of the BSC controllers and the
`Base Station (BTS)
`BTS base stations. The OMC configures the BTS base
`In conventional cellular systems, base stations, or base
`transceiver stations (BTS),are the interface between mobile
`stations through the BSC and allows components of the
`system to be checked.
`stations and the rest of the communications system. A base
`A handoff between base stations occurs, for example,
`station is usually located in the center of a cell. The
`
`transmitting powerof a base station determinesthe cell size. when a mobile user travels fromafirst cell to an adjacent
`35
`second cell. Handoffs also occurto relieve the load on a base
`A basestation typically has between one and sixteen trans-
`ceivers where each transceiver uses separate RF channels.
`Base stations have RF transmitters and RF receivers co-sited
`for transmitting and receiving communications to and from
`cellular users (mobile stations) in the cell. The base stations
`employ forward RF frequency bands (forward carriers) to
`transmit forward channel communications to users and
`employ reverse RF bands (reverse carriers)
`to receive
`reverse channel communications from users in the cell.
`Conventional forward channel communicationsare static in
`that they employ fixed power,at fixed frequencies and have
`fixed sectors if sectorized antennae are used.
`The forward and reverse channel communications use
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`separate frequency bandsso that simultaneous transmissions
`in both directions are possible. This operation is referred to
`as frequency domain duplex (FDD) signaling. Although
`time domain duplex (TDD)signaling, in which the forward
`and reverse channels take turns using the same frequency
`band is possible, such operation is not part of any wide-
`spread current cellular implementation.
`The base station in addition to providing RF connectivity
`to users also provides connectivity to a Mobile Telephone
`Switching Office (MTSO). In a typical cellular system, one
`or more MTSO’s will be used over the coverage region.
`Each MTSO can service a number of base stations and
`
`associated cells in the cellular system and supports switch-
`ing operations for routing calls between other systems (such
`as the PSTN) and the cellular system or for routing calls
`within the cellular system.
`Base Station Controllers
`
`In conventional cellular systems, base station controllers
`(BSC) monitor and control one or more base stations. The
`number of base stations controlled typically is between
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`station that has exhausted its traffic-carrying capacity or
`where poor quality communication is occurring. The handoff
`is a communication transfer for a particular user from the
`basestation for thefirst cell to the base station for the second
`cell. During the handoff in conventional cellular systems,
`there is a transfer period of time during which the forward
`and reverse communications to the mobile user are severed
`with the base station forthe first cell and are not established
`
`with the second cell. A typical conventional cellular system
`has the transfer period designed to be less than 100 milli-
`seconds.
`Conventional cellular implementations employ one of
`several techniques to reuse RF bandwidth from cell to cell
`over the cellular domain. The powerreceived from a radio
`signal diminishes as the distance between transmitter and
`receiver increases. All of the conventional frequency reuse
`techniques rely upon power fading to implement reuse
`plans. In a frequency division multiple access (FDMA)
`system, a communications channel consists of an assigned
`particular frequency and bandwidth (carrier) for continuous
`transmission. If a carrier is in use in a given cell, it can only
`be reused in cells sufficiently separated from the given cell
`so that the reuse site signals do not significantly interfere on
`the carrier in the given cell. The determination of how far
`away reuse sites must be and of what constitutes significant
`interference are implementation-specific details. The cellu-
`lar Advanced Mobile Phone System (AMPS) currently in
`use in the United States employs FODMA communications
`between base stations and mobile cellular telephones.
`In time division multiple access (TDMA) systems, mul-
`tiple channels are defined using the same carrier. The
`separate channels each transmit discontinuously in bursts
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`US 6,175,737 B1
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`3
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`whichare timed so as not to interfere with the other channels
`cellular multi environment, multiple copies of the burst are
`received over some delay spread corresponding to multipath
`on that carrier. Typically, TDMA implementations also
`reception over reflected paths of varying lengths. A digital
`employ FDMAtechniques. Carriers are reused from cell to
`signal processing technique known as equalization is com-
`cell
`in an FDMA scheme, and on each carrier, several
`monly used in RF communications to correct for multipath
`channels are defined using TDMA methods.
`delay spreading and fading. After equalization,
`the base
`In code division multiple access (CDMA)systems, mul-
`station can measure a single skewing delay time for the user
`tiple channels are defined using the same carrier and with
`synchronization burst. The base station then commands the
`simultaneous broadcasting. The transmissions employ cod-
`user to correct for this delay time by time advancing the user
`ing schemessuchthat to a given channel on a given carrier,
`bursts by an equal time interval. Thus each individual user
`the power from all other channels on that carrier appears to
`has a time base set by the base station to ensure that the
`be noise evenly distributed across the entire carrier band-
`transmissions from al users will arrive back at
`the base
`width. One carrier may support many channels and carriers
`station in synchronization with the base station time base.
`may be reused in everycell.
`These burst structures are detailed for two typical con-
`In space division multiple access (SDMA) systems, one
`ventional cellular TDMA implementations. Under the
`carrier is reused several times over a cellular domain by use
`European-defined “Global system for mobile communica-
`of adaptive or spot beam-forming antennae for eitherter-
`tions” (GSM) standard, which is substantially copied in the
`restrial or space-based transmitters.
`United States within the PCS 1900 standard, each RF carrier
`TDMAConventional Cellular Architectures
`occupies 200 kHz of bandwidth. Each carrieris divided into
`In TDMAsystems, time is divided into time slots of a
`time slots of 577 us, organized into 8-slot frames lasting
`specified duration. Time slots are grouped into flames, and
`4.615 ms. Each physical channel receives one time slot per
`the homologoustime slots in each frame are assigned to the
`frame, and a variety of logical channels may be constructed
`same channel. It is common practice to refer to the set of
`on a physical channel. The digital coding scheme used in
`homologous time slots over all frames as a time slot. Each
`GSM hasabit length of 3.69 us. A normal speech burst
`logical channelis assigned a timeslot or slots on a common
`consists of 148 bits of information followed by 8.25 bits of
`25
`carrier band. The radio transmissions carrying the commu-
`guard time. Thus for GSM, the standard is T,=8.25 bits=
`nications over each logical channel are thus discontinuous.
`30.44 us. The reverse channel synchronization (in GSM
`The radio transmitter is off during the time slots not allo-
`terminology, the random access) burst has 88bits of signal-
`cated to it.
`ing information followed by 68.25 bits of guard time. Thus
`for GSM,the T,,=68.25 bits=252 us.
`Under the IS136 TDMAstandard, each RFcarrier occu-
`pies 30 kHz of bandwidth. Each carrier is divided into time
`slots of 6.67 ms, organized into 6-slot frames lasting 40 ms.
`Each logical channel receives two timeslots per frame. The
`bit length for IS136 is 20.58 us. A normal reverse channel
`burst consists of 6 guard bits, 6 ramp bits, and 312 bits of
`mixed control signaling and data. Thus for IS136, T,=6
`bits=123.48 is. The reverse channel synchronization burst
`has a longer guard period of 38 bits, so that T,,=38
`bits=782.0 us for IS136.
`In accordance with the above background,there is a need
`for improved wireless communication systems which over-
`come the limitations of conventional cellular systems.
`SUMMARYOF THE INVENTION
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`Each separate radio transmission, which should occupy a
`single time slot, is called a burst. Each TDMA implemen-
`tation defines one or more burst structures. Typically, there
`are at least two burst structures, namely, a first one for the
`initial access and synchronization of a user to the system,
`and a second one for routine communications once a user
`has been synchronized. Strict timing must be maintained in
`TDMAsystemsto prevent the bursts comprising one logical
`channel from interfering with the bursts comprising other
`logical channels in the adjacent time slots. When bursts do
`not interfere, they are said to be isolated.
`The isolation of one burst from the preceding and fol-
`lowing bursts is crucial for TDMA systems. The defined
`burst structures are constructed to assist in the isolation
`
`its
`theoretically cannot completely fill
`process. A burst
`allotted time slot because radio transmitters neither com-
`mence nor cease transmitting instantaneously. TDMA
`implementations therefore allow time for radio signal
`strength to ramp up and to ramp downin each ofthe defined
`burst structures. During normal communicationsto and from
`a synchronized user, each burst does not quite fill
`its
`specified time slot. A guard period, T., is inserted before or
`after each normal burst to allow for timing mismatches,
`multipath delays, and inaccuracies within the system. The
`initial synchronization bursts for accessing the system fill
`even less of a time slot than do normal bursts. The long
`guard period, T,, for synchronization bursts is used to
`overcome the timing mismatches caused by the unknown
`separation between a user and the basestation.
`Within a cell, the base station maintains a time base which
`users synchronize to during initial access. User synchroni-
`zation to a particular base station is achieved using synchro-
`nization bursts sent periodically on a specific carrier by that
`base station and the reply synchronization bursts sent by the
`user. Those reply transmissions will arrive delayed at the
`given basestation by the propagation time for radio signals
`over the separation between the user and the given base
`station. The separation is generally unknown because the
`users are mobile. Not only is a burst delayed, but in the
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`The present invention is a cellular communication system
`having a plurality of wireless in-band channels and having
`a plurality of cells with a plurality of mobile stations in each
`cell where a base station (BTS) is the interface between
`mobile stations and a base station controller (BSC). The base
`station controller monitors and controls one or more base
`stations. In the present invention, a wireless trunk is estab-
`lished between the base station and the base station control-
`
`ler using selected ones of the allocated channels otherwise
`available for mobile station communications.
`
`The base station is formed with a base unit including a
`first
`transceiver operating with a first wireless interface
`formedoffirst ones of the in-band channels for broadcasting
`the forward channel communications and for receiving the
`reverse channel communications. Also, the base station is
`formed with a trunk unit including a second transceiver
`operating with a second wireless interface formed of second
`ones of the in-band channels for transmitting the forward
`channel communications and for receiving the reverse chan-
`nel communications. The base unit connects the channel
`communicationsto and from the trunk unit and the trunk unit
`connects the channel communications to and from the base
`unit.
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`US 6,175,737 B1
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`The mobile stations include a mobile station transceiver
`for receiving the forward channel communications and for
`broadcasting the reverse channel communications over the
`first wireless interface.
`
`The base station controller operates to transmit the for-
`ward channel communications and receive the reverse chan-
`nel communications over the second wireless interface.
`
`In the present invention, channels are assigned tothefirst
`or second wireless interfaces in a mannerthat avoids inter-
`
`the present
`ference between the channels. Accordingly,
`invention permits in-band wireless connections between
`base stations and basestation controllers without the need of
`wired connections or the need for out-of-band frequency
`channels.
`
`The foregoing and other objects, feats and advantages of
`the invention will be apparent from the following detailed
`description in conjunction with the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 depicts a block diagram of a cellular communica-
`tions system connected to the public switched telephone
`network.
`
`FIG. 2 depicts a block diagram of a base station sub-
`system used in the cellular communications system of FIG.
`1.
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`FIG. 3 depicts a block diagram of a wireless trunk unit
`used in the base station subsystem of FIG. 2.
`FIG. 4 depicts a block diagram of a RF/IF unit used in the
`wireless trunk unit of FIG. 3.
`
`FIG. 5 depicts a block diagram ofa star configuration of
`base stations in accordance with the present invention.
`FIG. 6 depicts a block diagram of a hop configuration of
`base stations in accordance with the present invention.
`FIG. 7 depicts a block diagram of a data interface for base
`stations in accordance with the present invention.
`FIGS. 8a through 8d depict representations of signals in
`a GSM cellular system.
`FIG. 9 depicts a representation of three adjacent cells in
`a cellular system.
`FIG. 10 depicts a representation of five adjacent cells in
`a cellular system.
`FIG. 11 depicts a representation of twelve cells in a cellar
`system that have a frequency reuse pattern of 4.
`FIG. 12 depicts a representation of sixteen cells in a
`cellular system that have a frequencyreusepattern of 4 using
`six wireless trunks.
`
`FIG. 13 depicts a representation of twelve cells in a
`cellular system that have a frequencyreusepattern of 4 using
`three wireless trunks.
`
`FIG. 14 depicts a representation of a seven cell cluster in
`a cellular system that uses seven wireless trunks.
`FIG. 15 depicts a representation of a seven cell cluster in
`a cellular system that uses two wireless trunks.
`FIG. 16 depicts a representation of twenty-eight cells in a
`cellular system that have a frequencyreusepattern of 7 using
`two wireless trunks per 7-cell cluster.
`FIG. 17 depicts a block diagram of the frequency assign-
`ment apparatus for making mobile station and trunk fre-
`quency assignments.
`DETAILED DESCRIPTION
`
`In FIG. 1, a cellular communications system 9 is con-
`nected to a central office switch (CO) 2 of the public
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`switched telephone network 6 through a mobile switching
`center (MSC) 5. The cellular communications system 9
`includesa plurality of cells 3-1, 3-2, .
`.
`.
`, 3-c where each of
`the cells 3 connects through the mobile switching center
`(MSC) 5 to the PSTN 6.
`In FIG. 1, each of the cells 3 includes a plurality of
`cellular users (mobile stations) 1, including mobile stations
`1-1.1-2,..., 1-n. Each of the cells 3 includes a base station
`subsystem (BSS) 12. Particularly, cells 3-1, 3-2, ... , 3-c
`include base station subsystems 12-1, 12-2, ... , 12-c,
`respectively. Each base station subsystem 12 has a first
`wireless interface, W,,,,, to the mobile stations 1 in the cell
`and a wireline interface, A,
`to a mobile switching center
`(MSC)5.
`The base station subsystems 12 each include a base
`station (BTS) 7 and a base station controller (BSC) 8.
`Particularly, the base station subsystems 12-1, 12-2,...,
`12-c include the base stations 7-1, 7-2, ... , 7-c and the base
`station controllers 8-1, 8-2, . .. , 8-c. The base stations 7 and
`the base station controllers 8 are connected by either a
`conventional wireline A,,, interface or, in accord with the
`present invention, a wireless trunk interface, W,, that sup-
`ports a wireline A,,, interface. Particularly, the base station
`subsystems 12-1 and 12-2 include a wireless interface that
`supports a wireline A,;, interface while the base station
`subsystem 12-c is of conventional design and only includes
`a wireline A,,, interface. Accordingly, the base stations 7-1
`and 7-2 connect to the base station controllers 8-1 and 8-2,
`respectively, by a wireless trunk having wireless interfaces,
`W,, and hence do not require wireline connections between
`base stations 7-1 and 7-2 and the base station controllers 8-1
`and 8-2. The absence of the need for wireline connections
`between the base stations (BTS) and the base station con-
`trollers (BSC) provides great flexibility for the installation
`and location of base stations and base station controllers.
`
`Wireless Base Station Subsystem—FIG. 2
`In FIG. 2, the base station subsystem 12 includes a base
`station (BTS) 7 and a base station controller (BSC) 8
`connected by a wireless interface W,. The base station 7
`includes a conventional base unit 20 which includes a
`transmitter/receiver unit (TRX) 20-1, a CPU processor 20-2
`and an E1 interface unit 20-3. The external connections from
`and to the base unit 20 include a conventional wireless
`interface, W,,,,, from the transmitter/receiver unit 20-1 (for
`communication with mobile stations through antenna 24)
`and a conventional wireline A,,, interface from and to the E1
`unit 20-3 (for communication directly or indirectly with a
`base station controller). The A,,, interface from and to the
`E1 unit 20-3 in a normal wireline base station subsystem
`would connect directly to a conventional base station
`controller, like controller base unit 22 in FIG. 2. Controller
`22 includes an E1 interface unit 224 that has a conventional
`wireline A,,;,
`interface (for communication with a base
`station), a CPU processor 22-3, a coder/decoder (CODEC)
`22-2, and an A interface unit 22-1 providing a wireline A
`interface (for communication with the MSC 5 of FIG. 1).
`In FIG. 2, the wireless interface, W,, is controlled by the
`wireless trunk units 21-a and 21-b for base station 7 and base
`station controller 8, respectively. The wireless trunk unit 21a
`has a conventional wireline A,,, interface from and to the E1
`interface unit 20-3 of the base unit 20. The wireless trunk
`
`unit 215 has a conventional wireline A,,, interface from and
`to the El interface unit 224 of the controller base unit 22.
`Each of the wireless trunk units 21-a and 21-b connect to
`
`each other through the wireless interface Wt and transmis-
`sions between antennae 30-a and 30-b. In operation, the
`wireless trunk units 21-a and 21-b logically connect the
`13
`
`13
`
`

`

`US 6,175,737 B1
`
`7
`wireline A,,, interface of the E1 interface unit 20-3 of the
`base unit 20 to the wireline A,,, interface of the E1 interface
`unit 22-4 of the controller base unit 22.
`The wireless trunk (WLT) units 21-a and 21-b use a
`proprietary communication interface W, to provide a wire-
`less physical layer interface between the BTS basestation 7
`and the BSC base station controller 8 of a GSM cellular
`
`system. Typically, the wireless trunk interface supports a
`duplex data service with a basic data transfer rate of 2x64
`Kbps in each direction, and can be upgraded to duplex
`32x64 Kbps data service. With flexible modular design, the
`wireless trunk units 21-a and 21-b replace conventional
`wired E1/DSO interfaces.
`Wireless Trunk Unit—FIG. 3
`
`In FIG. 3, the wireless trunk unit 21 is typical of the
`wireless trunk units 21-a and 21-b of FIG. 2. The wireless
`trunk unit 21 includes a transmitter/receiver(transceiver) 30,
`an RF/IF unit 31, a modem/CPUprocessorunit 33 and an E1
`interface unit 34. The transceiver 30 and RF/IF unit 31 in
`one preferred embodiment operate at a compatible in-band
`frequency of the current standard cellular systems (GSM:
`900 MHz, DCS1800: 1800 MHz, PCS1900: 1900 MHz) to
`achieve a BER (Bit Error Rate) of less than 10-’ with the
`wireless trunk distance, D,,,, between wireless trunk units
`typically ranging from 50 m to 10 Km. The wireless trunk
`
`10
`
`15
`
`20
`
`8
`unit 21 is flexibly designed with three modules that are a
`transceiver (TRX) unit 32, a modem/CPUprocessor unit 33,
`and an E1 interface unit 34. The El interface unit 34 is a
`
`conventional circuit card or other device for providing
`physical layer links to interface with base stations (BTES)
`ani base station controllers (BCS). The modem/CPU pro-
`cessor unit 32 includes an El card or other device 33-1 to
`
`provide a physical layer interface to the E1 interface unit 34
`and a DSPunit 33-2 for baseband processing functions. The
`TRX unit 32 includes an antenna 30 for transmitting and
`receiving electromagnetic signals and an RF/F unit 31 that
`is shown in further detail in FIG. 4.
`
`REF/F Unit—FIG. 4
`
`In FIG. 4, the RF/IF unit 31 includes a diplexer 40 for
`separating the transmit and receive RF signals. The receive
`channel includes a received RF signal low-noise amplifier
`43, a down-converter 44 (connected to local oscillator 45)
`for shifting the received RF signal downto an IF frequency
`and an IF unit 46. The transmit channel includes an upcon-
`verter 42 (connected to local oscillator 45) for shifting the IF
`frequency signal to RF and a transmit RF power amplifier 41
`for amplifying the RF signal to be broadcast. Further details
`of the wireless trunk design specification parameters are
`given in TABLE1 as follows:
`
`TABLE1
`
`WIRELESS TRUNK PARAMETERS
`
`1. Operation Frequency: 900 MHZ, 1800 MHz, 1900 MHz.
`2.
`Receiver Performance Requirement: BER < 107’.
`Eb/No: >6 dBHz.
`Encoder method: Convolutional Code with constraint length K = 7, rate r = %.
`Decoder method: Viterbi decoder.
`3. Operation Range: 50 m to 10 km.
`Path Loss (without considering the multipath loss):
`L(GB) = 20Log[d(Km)] + 20Log[F(MHz)] + 32.4
`d = operation distance in Km
`F = operation frequency in MHZ
`Path loss (dB):
`900 MHZ: -65 to -112 dB
`1800 MHZ: -71 to -118 dB
`1900 MHZ: -71.5 to -118.5 dB
`With the multiple path fading effect included,
`a 5 to 10 dB loss should be added to the total path loss,i.e.
`900 MHZ: -75 to -122 dB
`1800 MHZ: -81 to -128 dB
`1900 MHZ: -81.5 to -128.5 dB
`4. Antenna Type: Parabolic Dish Antenna: Diameter = D,efficiency k = 55%.
`Antenna Gain (G):
`
`2
`
`G=k Lp
`
`
`
`Gain for D = 1.0 m: 16.9 dB at 900 MHz, 22.9 dB at 1800 MHz, 23.4 dB at 1900 MHz.
`3 dB Beamwidth (BW):
`
`pw220~D
`
`BW:23.3° at 900 MHz, 11.6° at 1800 MHz, 11.1° at 1900 MHz.
`Transmit Power:
`
`5.
`
`EIRP = TX power x AntennaGain
`For TX_Power = 100 mW = -10 dBW
`EIRP(dBW) = 6.9 at 900 MHZ, 12.9 at 1800 MHZ, 13.4 at 1900 MHZ.
`For TX_Power = 50 mW = -13 dBW
`1.0 m Antenna: EIRP(dBW) = 3.9 at 900 MHZ, 9.9 at 1800 MHZ, 10.4 at
`1900 MHZ.
`Receive Power:
`
`RXPower = TX EIRP - Path Loss + RX Antenna Gain
`
`6.
`
`14
`
`14
`
`

`

`US 6,175,737 B1
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`9
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`10
`
`TABLE 1-continued
`
`WIRELESS TRUNK PARAMETERS
`
`Received power with three different transmitted power, 100 mW, 50 mW,
`and 25 mWarelisted as follows (1 dBW = 30 dBm):
`900 MHZ (dBm)
`1800 MHZ (dBm)
`1900 MHZ (dBm)
`-11.2 to -58.2
`-5.2 to -52.2
`-4.7 to -51.7
`-16.7 to -63.7
`-14.2 to -61.2
`-8.2 to -55.2
`-19.7 to -66.7
`-17.2 to -64.2
`-11.2 to -58.2
`
`Tx_power
`100 mW
`50 mW
`25 mW
`
`8.
`
`7. Modulation Method:
`0.3 GMSK: 160 KHz (approximate bandwidth requirement).
`Transmission Rate and Channel Bandwidth:
`Data Rate: 128 Kbps.
`Channel Rate: 256 Kbps.
`Bandwidth: compatible with the GSM specification (200 KHz).
`
`20
`
`25
`
`30
`
`35
`
`40
`
`nels by time division multiplexing as shown in FIG. 8c. In
`BTS Array Around BCS—FIG. 5
`In FIG. 5, an array ofbase stations (BTS) 7 with wireless
`FIG. 8c, the eight time slots TS,, TS,,..., TS, are shown
`interfaces to a central base station controller (BSC) 8 as
`for a typical one of the channels CH,of FIG. 8b. Each of the
`shown. Each of the base stations 7 is located at a different
`time slots of FIG. 8c in a GSM system is defined to include
`156.25 bits spread over a duration of 577x10~° seconds.
`angular position from the base station controller to help in
`These bits in each time slot are selected as a logical 1 or a
`isolating the trunk wireless interfaces between the base
`stations and the base station controller.
`logical O for transmitting information including data and
`control information.
`In-line Base Station Controller Configuration—FIG. 6
`In FIG. 6, the base stations (BTS) 7-1 and 7-2 are colinear
`Typical GSM Cells—FIG. 9
`In FIG. 9, three GSM cells C1, C2 and C3 are shown with
`with the base station controller 8. Since the radiation path in
`the basestation (BTS) 7-1 havinga first wireless interface to
`FIG. 6 is colinear, greater frequency isolation between the
`wireless interfaces between the base stations 7-1 and 7-2 are
`the mobile stations (MS) 9-1, 9-2, 9-3, ..., 9-n, for cell C,,
`with the base station 7-2 having a first wireless interface to
`required in order to avoid interference at the base station
`controller 8.
`the mobile stations 9-1, 9-2, 9-3, ... , 9-n, for cell C2 and
`with the base station 7-3 having a first wireless interface to
`Wireless Data System—FIG. 7
`In FIG. 7, a wireless trunk unit 73 is used to connect data
`the mobile stations 9-1, 9-2, 9-3, .. .
`, 9-1, for the cell C3.
`Each cell nominally has a radius R within which are located
`devices, such as a laptop computer 70 or other portable
`computer or such as a video coder/decoder (codec) 71 to a
`the mobile stations 9 of the cell. The cells Cl and C3 may
`base station (BTS) 7. The wireless trunk unit 73 includes an
`be adjacent or separated by one or more cells, such as cell
`C2 in FIG. 9.
`interface unit 75 that connects through interfaces (such as
`standard interfaces RS232, V.35 and RS449) to data devices
`The propagation path-loss of radio signals between a base
`(such as computer 70 or video codec 71).
`station 7 and mobile stations 9 is inversely proportional to
`R®, where a lies between 2 (for free space propagation) and
`In order to achieve a low bit error rate (BER) for low
`5 (for propagation with multi-path fading). Due to the need
`signal-to-noise ratio (SNR) signals, a bank of digital track-
`and trend for small cell sizes (moving from macrocells
`ing filters is implemented for a QPSK threshold extension
`typically having radii R of 1-25 km toward microcells
`demodulator. This design is implemented in field program-
`typically having ra