United States Patent (19)
`Fran
`
`54) DIRECT COMMUNICATION WIRELESS
`
`RADIO SYSTEM
`
`75 Inventor: Edward Frlan, Kanata, Canada
`73 Assignee: Nortel Networks Corporation,
`Montreal, Canada
`
`21 Appl. No.: 08/995,219
`22 Filed:
`Dec. 19, 1997
`
`(51) Int. Cl." ....................................................... H04Q 7120
`
`52 U.S. Cl. ............................................. 455/423; 455/450
`
`58 Field of Search ...................................... 455/423, 450
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,878,342 3/1999 Gustafson et al. ...................... 455/423
`5,898,928 4/1999 Karlsson et al......
`... 455/450
`5,905,956 5/1999 Young et al. .
`... 455/450
`5,909,649 6/1999 Saunders ................................. 455/450
`Primary Examiner Paul Loomis
`
`US006047178A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,047,178
`Apr. 4, 2000
`
`-
`
`-
`
`-
`
`-
`
`-
`
`ABSTRACT
`57
`A method of providing direct communication between a pair
`of mobile Stations over a single Voice channel is disclosed,
`as well as a novel mobile Station equipped with the capa
`bility to function in a So-called base-station-emulation
`(BSE) mode. A mobile switching center (MSC) first deter
`mines whether direct communication between two mobile
`Stations is possible, by Verifying that at least one of them can
`function in BSE mode. The MSC then establishes whether a
`clear radio link between the two mobile stations can be
`established and assigns a single voice channel for the
`conversation. In this way, the number of base station trans
`ceiverS required to Service a cell can be reduced. If the
`locations of the two mobile stations are known, feasibility of
`direct communication can be easily determined. Optionally,
`the MSC might order the two mobile stations to exchange
`modulated audio tones and report measured received signal
`Strengths. Direct communication is then established Subject
`to an evaluation by the MSC. The one mobile station chosen
`to operate in BSE mode is ordered to “swap” its transmit and
`receive frequencies, and the direct call is begun. Termination
`of the call by the mobile station that has remained in
`“normal” mode is detected by the mobile station in BSE
`mode, and termination of the call by the mobile station in
`BSE mode is detected by the base station.
`31 Claims, 4 Drawing Sheets
`
`108
`
`A
`
`VC 134
`
`110
`
`V
`
`1
`
`4.
`A
`A
`A
`f
`CC 321
`N-y
`A.
`A.
`A.
`A
`A
`
`114
`
`Cell Site
`106
`
`
`
`
`
`
`
`
`
`Mobile
`Switching
`Center
`102
`
`
`
`
`
`Public Switched
`Telephone Network
`104
`
`IPR2018-00556
`Exhibit 2015 / Page 1
`
`

`

`U.S. Patent
`
`Apr. 4, 2000
`
`Sheet 1 of 4
`
`6,047,178
`
`Fig. 1A
`PRIOR ART
`
`108
`
`110
`
`
`
`
`
`Mobile
`Switching
`Center
`102
`
`114
`
`Cell Site
`106
`
`
`
`
`
`
`
`Public SWitched
`Telephone Network
`104
`
`IPR2018-00556
`Exhibit 2015 / Page 2
`
`

`

`U.S. Patent
`
`Apr. 4, 2000
`
`Sheet 2 of 4
`
`6,047,178
`
`Fig. 1B
`
`108
`
`?
`CC 321 /
`N1y
`
`A
`
`VC 134
`
`110
`
`
`
`
`
`Mobile
`Switching
`Center
`102
`
`114
`
`Cell Site
`106
`
`
`
`
`
`
`
`Public Switched
`Telephone Network
`104
`
`IPR2018-00556
`Exhibit 2015 / Page 3
`
`

`

`U.S. Patent
`
`Apr. 4, 2000
`
`Sheet 3 of 4
`Fig. 2
`
`6,047,178
`
`
`
`
`
`
`
`A sends origination
`message to MSC
`202
`
`MSC pages B
`204
`
`Bresponds to MSC
`206
`
`CC
`
`CC
`
`CC
`
`VC
`
`VC
`
`
`
`
`
`
`
`
`
`
`
`NO
`
`
`
`
`
`Normal Call
`processing
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`MSC
`Verifies : is
`Direct Communication
`possible?
`208
`
`MSC assigns VC for Direct
`Communication
`210
`
`MSC tells B to go into
`BSE mode
`212
`
`B responds to MSC
`214
`
`B goes into BSE
`mode and Conversation task
`216
`
`IPR2018-00556
`Exhibit 2015 / Page 4
`
`

`

`U.S. Patent
`
`Apr. 4, 2000
`
`Sheet 4 of 4
`
`6,047,178
`
`Fig. 3
`
`POWer
`Amplifier
`334
`
`
`
`326
`
`322
`
`
`
`
`
`
`
`
`
`
`
`
`
`Duplexer
`304
`
`
`
`316
`
`OScillator
`320
`
`OScillator
`332
`
`F and
`Baseband
`
`> Low Noise
`
`Amplifier
`336
`
`328
`
`324
`
`A - normal mode
`
`B - "base station emulation" mode
`
`IPR2018-00556
`Exhibit 2015 / Page 5
`
`

`

`1
`DIRECT COMMUNICATION WIRELESS
`RADIO SYSTEM
`
`6,047,178
`
`2
`in a telecommunications network and being capable of
`operation in a normal mode and in a base Station emulation
`(BSE) mode, the network comprising a plurality of mobile
`Stations including the BSE capable mobile Station, a plural
`ity of base Stations and a mobile Switching center, the mobile
`Switching center communicating with the plurality of base
`Stations, each base Station communicating with one or more
`mobile Stations, the BSE capable mobile Station comprising:
`circuitry for switching between normal mode and BSE
`mode; wherein operation of the mobile Station in normal
`mode consists of reception over a forward channel and
`transmission over a reverse channel and operation of the
`mobile station in BSE mode consists of reception over the
`reverse channel and transmission over the forward channel;
`wherein the mobile station Switches from normal mode into
`BSE mode upon receiving an instruction from the respective
`base Station, wherein the mobile Station can establish direct
`communication with another mobile Station of the plurality
`of mobile stations.
`The present invention can be Summarized according to a
`Second broad aspect as a telecommunications network com
`prising: a plurality of mobile Stations, at least one of which
`is capable of operation in a normal mode and in a base
`station-emulation (BSE) mode, the BSE capable mobile
`Station comprising circuitry for Switching between normal
`mode and BSE mode; a plurality of base Stations, each base
`Station communicating with one or more mobile Stations,
`and a mobile Switching center communicating with the
`plurality of base Stations, wherein operation of the mobile
`Stations in normal mode consists of reception over a forward
`channel and transmission over a reverse channel and opera
`tion of the PSE capable mobile station in BSE mode consists
`of reception over the reverse channel and transmission over
`the forward channel; wherein the BSE capable mobile
`station switches from normal mode into BSE mode upon
`receiving an instruction from the respective base Station
`whereby the BSE capable mobile station establishes direct
`communication with another mobile Station of the plurality
`of mobile stations.
`The present invention can be Summarized according to a
`third broad aspect as a method of enabling direct commu
`nication between first and Second mobile Stations in a
`telecommunications network, the network comprising a
`plurality of mobile Stations, at least one of which is capable
`of operation in a normal mode and in a base-station
`emulation (BSE) mode, the BSE capable mobile station
`comprising circuitry for Switching between normal mode
`and BSE mode, a plurality of base Stations, each base Station
`communicating with one or more mobile Stations, and a
`mobile Switching center communicating with the plurality of
`base Stations, wherein operation of the mobile Station in
`normal mode consists of reception over a forward channel
`and transmission over a reverse channel and operation of the
`mobile station in BSE mode consists of reception over the
`reverse channel and transmission over the forward channel;
`wherein the mobile station Switches from normal mode into
`BSE mode upon receiving a indication from the base Station,
`the first and Second mobile Stations communicating in
`normal mode with a respective base Station among the
`plurality of base Stations, the method comprising:
`A) the first mobile Station sending, via the respective base
`Station, a message to the mobile Switching center indi
`cating that the Second mobile Station is being called;
`B) the mobile Switching center Sending a page message to
`the Second mobile Station via the Specific base Station;
`C) the Second mobile station responding to the page mes
`Sage,
`
`FIELD OF THE INVENTION
`This invention relates to wireleSS communications net
`WorkS and more specifically to a method of enabling pairs of
`mobile Stations in a wireleSS network to communicate
`directly with each other.
`Background of the Invention
`Modern cellular telecommunications networks are
`divided into cells which service mobile stations (mobile
`phones) in a defined area. Each cell contains a base Station
`which exchanges voice and control information with mobile
`Stations located within the cell's coverage area, and base
`Stations from various cells communicate with each other
`through a mobile Switching center.
`In a fixed wireleSS network, mobile Stations are con
`Strained to a Small geographic area, usually within the same
`cell. Installation of Such networks is common when tele
`communications are required in regions not equipped with a
`prior communications infrastructure, e.g., new housing
`developments or relatively affluent third world communities.
`Furthermore, it is often the case that telephone calls placed
`by members of a cell reach users within the Same cell, Such
`as neighbourhood friends.
`A large part of the cost of a cellular network, be it fixed
`or truly mobile, lies with the numerous base Stations that
`need to be deployed. Base Station cost, for its part, is largely
`concentrated in the transceivers required to maintain com
`munication with the mobile stations. When two mobile
`Stations within the same cell communicate with one another,
`they each take up one voice channel at the base Station,
`occupying a total of two transceivers per pair of communi
`cating mobile Stations.
`The number of intra-cell calls that a base Station can
`handle is therefore on the order of half the available
`channels, a corollary being that free channels will expire
`approximately twice as fast as calls are made. When all of
`a base Station's transceivers are busy, mobile Stations not
`actively involved in a conversation cannot place or receive
`calls until a channel is liberated. Worse still, if both the
`originator and potential recipient of a new call reside within
`the same cell (whose base station transceivers are occupied),
`then the call cannot be effected until two channels are freed
`at the base Station.
`Yet other problems are inherent to current wireless sys
`tems. For example, in a conventional network, two mobile
`Stations in close proximity to each other but located rela
`tively far from their common base station may find that their
`connection Suffers from poor voice quality or is Sometimes
`dropped. The explanation lies in the Severe degradation that
`plagues the Signal from one mobile Station as it makes its
`way to the base Station and again and towards the other
`mobile Station. Furthermore, establishing communication
`with a distant base station (Sometimes as far away as 20
`kilometers) demands Substantial power consumption on the
`part of the mobile stations. This has the deleterious effect of
`reducing the time interval between recharges of a mobile
`Station.
`
`5
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`SUMMARY OF THE INVENTION
`It is an object of the present invention to mitigate or
`obviate one or more disadvantages of the prior art.
`To this end, the present invention can be Summarized
`according to a first broad aspect as a mobile Station for use
`
`65
`
`IPR2018-00556
`Exhibit 2015 / Page 6
`
`

`

`6,047,178
`
`3
`D) the mobile Switching center determining whether at least
`one of the first and Second mobile Stations is capable of
`operating in BSE mode and identifying the one mobile
`station that is to operate in BSE mode;
`E) the mobile Switching center determining whether a clear
`radio link between the first and Second mobile Stations can
`be maintained;
`F) if steps d) and e) result in a positive determination, the
`mobile Switching center assigning forward and reverse
`channels for the call;
`G) the mobile Switching center Sending, via the respective
`base Station, a request message to the mobile Station
`identified in Step d) instructing it to operate in BSE mode;
`H) the BSE capable mobile station responding to the request
`message and Switching into BSE mode,
`I) the BSE capable station establishing a direct call with the
`other of the first and second mobile stations.
`
`15
`
`4
`Telephone (NMT) network and the Total Access Commu
`nication System (TACS).
`When in use, i.e., when in a So-called “conversation
`State', each mobile Station transponds a Supervisory audio
`tone (SAT) to the base station over the RVC. The base
`station continually monitors the SAT and if at any time the
`mobile Station fails to transpond the SAT, e.g., due to
`obstruction of the wireless link, the MSC in charge of the
`base Station will initiate a call release routine. A mobile
`Station may also trigger the call release routine by Sending
`a signalling tone (ST) to the base station, also over the RVC,
`and Subsequently ceasing transmission. This procedure is
`commonly referred to as “hanging up'.
`A traditional approach to Setting up a call between two
`mobile stations A and Blocated within the same cell is now
`briefly described with reference to FIG. 1A. Assuming that
`mobile Station A wishes to place a telephone call to mobile
`Station B, it communicates this intention to the base Station
`via the control channel, Say 321; the base Station Subse
`quently informs the MSC. If mobile station B is ready to
`accept the call, and if there are at least two available
`transceivers at the base Station, the MSC will assign one
`Voice channel, Say 134, to mobile Station A and another, Say
`58, to mobile station B. The MSC communicates this
`information to the base station which informs each mobile
`Station of its respective assigned Voice channel Via the
`control channel.
`Conventionally, therefore, a telephone call between two
`co-cellular mobile Stations A and B passes through the base
`Station, occupying two voice channels, i.e., two base Station
`transceivers. Specifically, the base Station transmits to
`mobile station A over the FVC of channel 134 and mobile
`station A transmits to the base station over the RVC of
`channel 134. Similarly, the base Station Similarly exchanges
`voice information with mobile station B over the FVC and
`RVC of channel 58.
`In contrast, the present invention lets both mobile Stations
`A and B communicate directly with each other, using the
`Same Voice channel, thus allowing the base Station to Simul
`taneously process more calls or to be designed for accom
`modating fewer transceivers. A key ingredient that permits
`direct communication between a pair of mobile Stations is
`the ability of at least one mobile station to Switch into a
`so-called “base station emulation” (BSE) mode, in which
`transmission over the FVC and reception over the RVC of a
`given voice channel is enabled. Referring now to FIG. 1B,
`mobile station B is empowered with BSE mode capability
`and direct communication between the two mobile Stations
`can take place on Voice channel 134, effectively liberating
`voice channel 58 and allowing other connections to be
`established by the actual base station in the cell. The control
`channel 321 is still used to maintain communication
`between the mobile Stations and the base Station.
`A sequence of Steps for Setting up a call between mobile
`Station A and mobile Station B in accordance with the present
`invention is now described with reference to FIG.2. The two
`mobile Stations are assumed to be located within a common
`cell Served by a base Station and a mobile Switching center
`(MSC). Moreover, a single control channel is used to
`communicate control information between the base Station
`and mobile stations A and B.
`Although it is preferable that two mobile Stations wishing
`to establish direct communication be located within the
`Same cell, the present invention is also applicable in cases
`where the mobile Stations are in adjoining cells but proxi
`mate each other, and therefore close to the cells common
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The preferred embodiment of the present invention will
`now be described with reference to the following figures, in
`which:
`FIG. 1A shows part of a prior art wireless cellular
`telecommunications network,
`FIG. 1B illustrates direct communication between a pair
`of mobile Stations as contemplated by the present invention;
`FIG. 2 is a flowchart illustrating the steps required to
`enable direct communication of two mobile Stations in
`accordance with the present invention; and
`FIG. 3 is a block diagram of RF circuitry used in a mobile
`Station that has been adapted to possess base Station emu
`lation functionality.
`
`25
`
`35
`
`40
`
`45
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`In FIG. 1A is shown part of a wireless cellular telecom
`munications network, consisting of a mobile Switching
`center (MSC) 102 connected to a base station 106 at a given
`cell site and to the remainder of the network 104. Mobile
`stations A and B communicate with the base station 106
`through wireleSS links established between respective anten
`nas 108,110 at the mobile stations A,B and an antenna 114
`at the base station 106.
`The base Station exchanges control information with
`mobile Stations over a control channel (CC), separated into
`a forward control channel (FCC) and a reverse control
`channel (RCC) usually shared among the mobile Stations.
`On the other hand, separate voice channels (VCs) carry
`50
`voice information over the same wireless link, each VC
`separated into a forward voice channel (FVC) for base
`Station-to-mobile-Station voice communication and a
`reverse voice channel (RVC) that Supports voice communi
`cation in the opposite direction.
`An exemplary analog system currently in use and in
`respect of which the present invention applies is the
`Advanced Mobile Phone Service (AMPS, specified by the
`Electronics Industries Association EIA-553 specification,
`and hereby incorporated by reference herein), which pro
`vides 333 commonly available channels, each occupying a
`different frequency range further bisected into a portion for
`the forward channel and another for the reverse channel. A
`cell usually shares these 333 channels with six neighbours,
`and is usually assigned a total of 48 (s333/7) channels for
`use within the cell. The present invention also applies to
`other analog cellular standards such as the Nordic Mobile
`
`55
`
`60
`
`65
`
`IPR2018-00556
`Exhibit 2015 / Page 7
`
`

`

`6,047,178
`
`6
`defined as the Strength of a Signal between two mobile
`Stations, one in each Sub-region, relative to a nominal value.
`For a given pair of Sub-regions, the RSSI value is either
`measured directly during installation or modelled using
`radio propagation theory. It is convenient to represent the
`RSSI information on the form of a matrix, where R is the
`RSSI between sub-regions X and y of the cell:
`
`S
`boundary. If the MSC has information pertaining to the
`location of each mobile Station, which it may well in a fixed
`wireless network, then it is possible for the MSC to initiate
`direct communication with the two mobile stations in the
`Same manner as for the case in which both mobile Stations
`are within the same cell. Since each cell ordinarily uses
`different voice channels from those of its neighbours, one of
`the two mobile stations would be ordered to tune to a
`channel, i.e., a frequency range, that is not normally used
`within its own cell.
`Step 202
`Mobile Station A, upon attempting to reach mobile Station
`B, automatically sends an origination message destined for
`the MSC. This message is first sent to the base station via the
`control channel, and is relayed to the MSC by the base
`Station.
`Step 204
`The MSC instructs the base station to page mobile station
`B over the control channel.
`Step 206
`Mobile station B “wakes up” and responds to the base
`Station over the control channel, indicating that it is ready for
`a conversation. The base Station relays this message to the
`MSC.
`Step 208
`The MSC now checks to see whether direct communica
`tion between the two mobile Stations is possible, i.e., if two
`essential criteria are Satisfied. The order in which they are
`tested is not essential to the present invention. First, at least
`one of the two mobile stations must be capable of function
`ing in BSE mode. This can be determined, for example, by
`searching for the mobile identification number of either
`mobile Station in a database containing mobile identification
`numbers of mobile stations manufactured with BSE mode
`capability.
`If the first criterion is met, the base station must then
`determine whether the two mobile stations are in Sufficient
`proximity to each other that a clear radio signal can be
`maintained. This can be achieved in a variety of ways, Such
`as utilizing So-called extended 911 Services or consulting a
`received signal strength indicator (RSSI) matrix. Extended
`911 (or E911) services, akin to the familiar 911 services in
`the North American wireline network, allow the MSC to
`calculate the position of any mobile Station in order to
`dispatch emergency Services to a Subscriber. The practical
`implication with regard to the present invention is that if
`mobile station B is found to be within a certain threshold
`distance (say, less than 1 kilometer (km) in a radio propa
`gation environment with little Signal attenuation or fading
`due to buildings and other obstructions) of mobile Station A,
`then direct communication between the two mobile Stations
`is deemed possible.
`In a fixed wireless network, the use of E911 services is not
`necessary, as relatively accurate knowledge of the position
`of each mobile Station is readily available upon installation
`of the network. However, the size and geography of a cell
`does not necessarily permit direct communication between
`any pair of mobile stations in the cell. RSSI information in
`the form of a matrix can be used in order to evaluate the
`feasibility of direct communication between mobile stations
`in different Sub-regions of a cell.
`In an exemplary embodiment of a cell, there may be four
`Sub-regions a,b,c,d which in an urban Setting could be
`considered as large neighbourhoods having diameters of
`approximately 1 km. The RSSI between two sub-regions is
`
`RSS =
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Another way of determining the feasibility of direct
`communication is for the mobile Switching center ordering
`a first “candidate” mobile station to send a known modulated
`audio tone of a certain duration to a Second "candidate'
`mobile Station over a pre-assigned Voice channel. The Sec
`ond candidate measures the received signal Strength and
`then forwards this data to the base Station. A reciprocal
`transmission and detection are performed, the results of
`which are relayed to the base station by the first candidate.
`The reception quality data for both directions of communi
`cation are sent to the MSC, which compares these results to
`Some known values in deciding whether a clear radio link
`can be established between the two candidate mobile sta
`tions. Clearly, use of this technique requires that both mobile
`Stations be adapted for transmission and reception of Suit
`able modulated audio tones, which in practical terms would
`mean that they would have to be BSE capable mobile
`Stations according to the present invention.
`Irrespective of the evaluation methods employed, if either
`criterion is not met, i.e., if direct communication between
`the two mobile stations A and B is not achievable, then
`Subsequent Steps for placing the call correspond to the
`known procedure as used in the prior art.
`Step 210
`On the other hand, if direct communication between
`mobile stations A and B is possible, the MSC must find a free
`Voice channel that will be assigned to carry the telephone
`call, say VC1.
`Step 212
`Since both criteria outlined in step 208 have necessarily
`been passed at this stage, at least one mobile Station is
`capable of functioning in BSE mode. The MSC will already
`know this fact and, by way of the base Station, now orders
`one mobile station to enter BSE mode. Clearly, if both
`mobile stations have BSE mode capability, a straightforward
`algorithm can be applied to choose the one mobile Station
`that will actually be requested to enter BSE mode.
`For the Sake of argument, it is assumed that mobile Station
`B has been selected to emulate a base station. The base
`Station will use So-called “blank and burst' Signalling over
`the FVC on VC1 (the assigned voice channel) to tell mobile
`station B to enter BSE mode. In the AMPS standard, for
`example, the Order field in the FVC would be set to “local
`control” and a “base station emulation' command would be
`Set in the Local/Message Type field.
`Step 214
`Upon recognizing that it is being requested to enter BSE
`mode, mobile Station B complies by responding to the base
`station over the RVC of VC1. It then enters BSE mode,
`which consists of “Swapping its transmitter and receiver,
`i.e., mobile station B now transmits on the FVC and receives
`on the RVC of VC1.
`
`IPR2018-00556
`Exhibit 2015 / Page 8
`
`

`

`25
`
`Step 216
`Mobile Station B Subsequently enters conversation State,
`during which it exchanges Voice information with mobile
`station A over VC1 and continually monitors the SAT from
`mobile Station A in the manner of a true base Station.
`Naturally, an aspect of wireleSS telephony that is just as
`important as Setting up a call is the procedure by which a call
`is terminated, or torn down. A conventional approach to
`tearing down a call between two mobile Stations A and B
`consists of the base Station detecting from one of the mobile
`stations either a loss of the SAT or the presence of a ST and
`Subsequently instructing the other mobile Station to cease
`transmission. When two mobile stations are in direct com
`munication with each other, however, the mobile Station in
`BSE mode is not monitored or controlled by the base station,
`and must take its call termination cues from the other mobile
`Station.
`For explanatory purposes, it is assumed that of two mobile
`Stations A and B in direct communication with each other
`over a voice channel VC1, mobile station B is in BSE mode.
`Clearly, either mobile station can be the first to release the
`call. In the case that mobile Station B terminates the call, it
`will switch out of BSE mode (and back into “normal”
`mode), Subsequently sending an ST to the base station over
`the RVC of VC1 and ceasing transmission. The base station
`detects this ST and, using the FVC of VC1, directs mobile
`Station A, which has always been in normal mode, to cease
`transmission.
`If mobile station A is first in releasing the call, it will send
`the ST over the RVC of VC1, which will be detected by
`mobile station B (in BSE mode), and then cease transmis
`Sion. Mobile station B subsequently acts as if it were
`releasing the call, Sending its own ST to the base Station over
`the RVC of VC1 after having Switched back into normal
`mode. Preferably, therefore, an ST to be transmitted by
`mobile station A and intercepted by mobile station B.
`Alternatively, mobile station B could be designed to
`monitor the SAT sent out by mobile station A over the RVC
`of VC1. If at any time mobile station. A fails to transpond a
`40
`SAT then this will be detected by both the base station and
`mobile station B. Mobile station B thus assumes that mobile
`Station A has hung up, and proceeds with the call release
`mechanism. This inferential method does not rely on a direct
`command to tear down a call, but concludes from lack of a
`SAT that mobile station A wishes to end communication.
`It is to be understood that out of two mobile stations
`wishing to establish direct communication, only one mobile
`station need have BSE mode capability. Hence, an ordinary
`mobile phone is not necessarily precluded from participating
`in direct communication, So long as its “partner can func
`tion in BSE mode. Moreover, if direct communication is not
`possible, then communication in the usual (prior art) way is
`established.
`Several features that at least one mobile Station in a pair
`must possess in order that both may benefit from direct
`wireless communication are now described. Most
`importantly, BSE mode capability requires that transmission
`and reception from a mobile Station, which normally occur
`over the respective RVC and FVC of a voice channel, can
`instead be made to take place over the FVC and RVC,
`respectively. To this end, FIG. 3 is a simplified block
`diagram of a configurable channel Swapping radio as would
`be used in a BSE capable mobile station.
`An antenna 302 serves to transmit and receive radio
`frequency Signals which are merged by a duplexer 304 with
`three ports 306,308,310 tuned to specific frequencies. There
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`7
`
`6,047,178
`
`15
`
`8
`are four Sets of Single-pole double-throw reflective Switches
`312,314,316,318 with possible positions of A or B. In
`position A the mobile Station acts as a conventional cellular
`phone. An oscillator 320 produces a carrier Signal in the
`frequency range of the RVC, which multiples an
`intermediate-frequency (IF) transmit signal 322, yielding a
`radio-frequency (RF) transmit signal 326. The RF transmit
`signal 326 passes through port 308 of the duplexer 304 on
`its way to the antenna 302 via port 306.
`Conversely, a Signal arriving at the antenna 302 passes
`through port 306 of the duplexer and emerges from it at port
`310 as a RF receive signal 328. This signal is multiplied by
`a carrier Signal in the frequency range of the FVC generated
`by an oscillator 332, i.e., the RF receive signal 328 is
`effectively demodulated down to an IF receive signal 324.
`When the mobile station enters BSE mode, the B position
`is engaged, and the IF transmit Signal 322 is modulated up
`to a RF transmit signal 326 by the output of oscillator 332,
`which is in the frequency range of the FVC, and finds its way
`towards the antenna 302 through ports 310 and 306 of the
`duplexer 304. Similarly, through ports 306.308 of the
`duplexer 304 and Switch 312 in position B arrives a RF
`receive signal 328, which is now demodulated down to an IF
`receive signal 324 by the output of oscillator 320 in the
`frequency range of the RVC.
`It will be apparent to one skilled in the art that a power
`amplifier 334 and a low-noise linear amplifier are usually
`added in Series with respective radio-frequency transmit and
`receive signals 326.328 and that filtering not shown in the
`illustration may be required to isolate certain frequency
`components at various Stages of a Signals path.
`In Summary, mobile Stations need to possess certain
`hardware and Software/firmware capabilities in order to
`function in BSE mode. In particular, additional hardware
`elements required by the present invention include circuitry
`for Switching between normal and BSE modes and when in
`BSE mode, transmitting and receiving over both the FVC
`and RVC of a given voice channel and detecting an ST (and
`optionally an SAT) from another mobile station. Mobile
`Station Software or firmware must also be enhanced to
`include additional functionality for interpreting and
`responding to a request from the MSC for the mobile station
`to enter BSE mode, Switching into and out of BSE mode
`and, while in BSE mode, controlling SAT cutoff and ST
`detection (and optionally SAT cessation detection.) If, in
`addition, “interactive' measurement of modulated audio
`tone levels is to be performed, then a capability to transmit
`and detect Suitable modulated audio tones would be
`required.
`Although the preferred embodiment of the present inven
`tion is best described within the context of an analog cellular
`System, additional Signal processing in the mobile Stations,
`along with modifications to presently used digital air
`interface Standards Such as the Telecommunication Indus
`tries Association IS-54 (Time Division Multiple Access or
`TDMA) specification and the Global System for Mobile
`Communications (GSM), can enable direct communication
`between mobile Stations in a digital network.
`While the preferred embodiment of the invention has been
`described and illustrated it will be apparent to one skilled in
`the art that variations in the design may be made. The Scope
`of the invention, therefore, is only to be limited by the claims
`appended hereto.
`I claim:
`1. A mobile Station for use in a telecommunications
`network and being capable of operation in a normal mode
`
`IPR2018-00556
`Exhibit 2015 / Page 9
`
`

`

`6,047,178
`
`15
`
`25
`
`9
`and in a base station emulation (BSE) mode, the network
`comprising a plurality of mobile Stations including the BSE
`capable mobile Station, a plurality of base Stations and a
`mobile Switching center, the mobile Switching center com
`municating with th