United States Patent [19]
`Paulraj et al.
`
`[54] SPATIAL MULTIPLEXING IN A CELLULAR
`NETWORK
`
`[75] Inventors: Arogyaswami J. Paulraj, Stanford;
`Robert W. Heath, Jr., Hayward;
`Per00r K. Sebastian; David J.
`Gesbert, both of Mountain View, all of
`Calif.
`
`[73] Assignee: Gigabit Wireless, Inc., Mountain View,
`Calif.
`
`[21] Appl. No.: 09/364,146
`[22]
`Filed:
`Jul. 30, 1999
`
`[51] Int. Cl.7 .......................... .. H04Q 7/28; H04B 7/216;
`H04B 7/185; H03D 3/22
`[52] U.S. Cl. ......................... .. 370/329; 370/342; 370/341
`[58] Field of Search ................................... .. 370/328, 329,
`370/347, 341, 342, 326, 319, 431, 464,
`310; 455/13.1, 507, 509, 524, 560; 375/299
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`9/1994 Paulraj et a1. .
`5,345,599
`4/1996 Lee .
`5,504,936
`1/1997 Briskman .............................. .. 455/506
`5,592,471
`6/1997 Roy, III et a1. ....................... .. 370/329
`5,642,353
`3/1998 Kostreski et a1. .
`5,729,825
`3/1998 Tangemann et al. .
`5,732,075
`5,828,658 10/1998 Ottersten etal. ..................... .. 370/329
`5,841,971 11/1998 Longginou et a1. .
`
`OTHER PUBLICATIONS
`
`Arogyaswami J. Paulraj and Constantinos B. Papadias
`“Space—Time Processing for Wireless Communications”,
`IEEE Signal Processing Magazine, Nov. 1997.
`
`Primary Examiner—Chi H. Pham
`Assistant Examiner—Brenda H. Pham
`
`/
`
`US006067290A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,067,290
`May 23, 2000
`
`Attorney, Agent, or Firm—Beyer Weaver Thomas &
`Nguyen
`[57]
`
`ABSTRACT
`
`The present invention provides methods and apparatus for
`implementing spatial multiplexing in conjunction with the
`one or more multiple access protocols during the broadcast
`of information in a wireless network. A wireless cellular
`network for transmitting subscriber datastream(s) to corre
`sponding ones among a plurality of subscriber units located
`within the cellular network is disclosed. The wireless cel
`lular network includes base stations and a logic. The base
`stations each include spatially separate transmitters for
`transmitting, in response to control signals, selected sub
`streams of each subscriber datastream on an assigned chan
`nel of a multiple access protocol. The logic communicates
`with each of the base stations. The logic assigns an available
`channel on which to transmit each subscriber datastream.
`The logic routes at least a substream of each datastream to
`at least a selected one of the base stations. The logic also
`generates control signals to con?gure the at least a selected
`one of the base stations to transmit the selected substreams
`to a corresponding one among the plurality of subscriber
`units on the assigned channel. A subscriber unit for use in a
`cellular system is also disclosed. The subscriber unit
`includes: spatially separate receivers, a spatial processor,
`and a combiner. The spatially separate receivers receive the
`assigned channel composite signals resulting from the spa
`tially separate transmission of the subscriber downlink
`datastream(s). The spatial processor is con?gurable in
`response to a control signal transmitted by the base station
`to separate the composite signals into estimated substreams
`based on information obtained during the transmission of
`known data patterns from at least one of the base stations.
`The spatial processor signals the base stations when a
`change of a spatial transmission con?guration is required.
`The combiner combines the estimated substreams into a
`corresponding subscriber datastream.
`
`47 Claims, 31 Drawing Sheets
`
`Circuit/Packet Switched
`
`SPATIAL MULTIPLEX
`
`Page 1 of 52
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`U.S. Patent
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`May 23, 2000
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`Sheet 1 0f 31
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`6,067,290
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`@2256 “9.08235
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`Page 2 of 52
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`May 23, 2000
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`Sheet 2 0f 31
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`May 23, 2000
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`Sheet 3 0f 31
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`Page 4 of 52
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`U.S. Patent
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`May 23, 2000
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`Sheet 4 of 31
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`May 23, 2000
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`May 23, 2000
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`Page 31 of 52
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`U.S. Patent
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`May 23, 2000
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`Page 32 of 52
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`6,067,290
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`1
`SPATIAL MULTIPLEXING IN A CELLULAR
`NETWORK
`
`BACKGROUND OF THE INVENTION
`
`Copyright Authorization
`
`A portion of the disclosure of this patent document
`contains material which is subject to copyright protection.
`The copyright owner has no objection to the facsimile
`reproduction by any one of the patent disclosure, as it
`appears in the U.S. Patent and Trademark Office patent files
`or records, but otherwise reserves all copyright rights what-
`soever.
`
`1. Field of Invention
`
`The field of the present invention relates in general to the
`field of wireless broadcast of information using one or more
`multiple access protocols and in particular to methods and
`apparatus for implementing spatial multiplexing in conjunc-
`tion with the one or more multiple access protocols during
`the broadcast of information.
`
`2. Description of the Related Art
`In wireless broadcast systems, information generated by a
`source is transmitted by wireless means to a plurality of
`receivers within a particular service area. The transmission
`of such information requires a finite amount of bandwidth,
`and in current state of the art transmission of information
`from different sources, must occur in different channels.
`
`Since there are quite a few services (e.g. television, FM
`radio, private and public mobile communications, etc.)
`competing for a finite amount of available spectrum, the
`amount of spectrum which can be allocated to each channel
`is severely limited. Innovative means for using the available
`spectrum more efficiently are of great value. In current state
`of the art systems, such as cellular telephone or broadcast
`television, a suitably modulated signal is transmitted from a
`single base station centrally located in the service area or cell
`and propagated to receiving stations in the service area
`surrounding the transmitter. The information transmission
`rate achievable by such broadcast
`transmission is con-
`strained by the allocated bandwidth. Due to attenuations
`suffered by signals in wireless propagation, the same fre-
`quency channel can be re-used in a different geographical
`service area or cell. Allowable interference levels determine
`
`the minimum separation between base stations using the
`same channels. What is needed is a way to improve data
`transfer speed in the multiple access environments currently
`utilized for wireless communications within the constraints
`of available bandwidth.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides methods and apparatus for
`implementing spatial multiplexing in conjunction with the
`one or more multiple access protocols during the broadcast
`of information in a wireless network.
`
`In an embodiment of the invention, a wireless cellular
`network for transmitting subscriber datastream(s) to corre-
`sponding ones among a plurality of subscriber units located
`within the cellular network is disclosed. The wireless cel-
`
`lular network includes base stations and a logic. The base
`stations each include spatially separate transmitters for
`transmitting in response to control signals and selected
`substreams of each subscriber datastream on an assigned
`channel of a multiple access protocol. The logic communi-
`cates with each of the base stations. The logic assigns an
`available channel on which to transmit each subscriber
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`datastream. The logic routes at least a substream of each
`datastream to at least a selected one of the base stations. The
`logic also generates control signals to configure at least a
`selected one of the base stations to transmit the selected
`substreams to a corresponding one among the plurality of
`subscriber units on the assigned channel.
`In an embodiment of the invention, a subscriber unit for
`use in a cellular system with base stations, each including
`spatially separate transmitters for transmitting selected sub-
`streams of at least one of a plurality of subscriber downlink
`datastream(s) on an assigned channel of a multiple access
`protocol, is disclosed. The subscriber unit includes: spatially
`separate receivers, a spatial processor, and a combiner. The
`spatially separate receivers receive the assigned channel
`composite signals resulting from the spatially separate trans-
`mission of the subscriber downlink datastream(s). The spa-
`tial processor is configurable in response to a control signal
`transmitted by the base station to separate the composite
`signals into estimated substreams based on information
`obtained during the transmission of known data patterns
`from at least one of the base stations or by using blind
`training techniques. The spatial processor signals the base
`stations when a change of a spatial transmission configura-
`tion is required in order to resolve the composite signals into
`estimated downlink datastream(s). The combiner combines
`the estimated substreams into a corresponding subscriber
`datastream.
`
`In another embodiment of the invention, a wireless cel-
`lular network for
`transmitting subscriber downlink
`datastream(s) from a first network to subscribers located
`within the wireless cellular network is disclosed. The wire-
`less cellular network includes: base stations, subscriber units
`and a logic. The base stations are each configured for
`spatially separate transmission of selected substreams of
`each subscriber downlink datastream on an assigned channel
`of a multiple access protocol. The subscriber units are each
`configured for spatially separate reception on the assigned
`channel of the selected substreams, for combining the sub-
`streams into the corresponding subscriber datastream and for
`initiating a change signal to at least one of the base stations
`when a change of a spatial transmission configuration is
`required in order to separate the selected substreams. The
`logic communicates with each of the base stations and to the
`first network. The logic is configured to route at least a
`substream of each subscriber downlink datastream to at least
`
`a selected one of the base stations and further configured to
`vary the routing between a single base station and multiple
`base stations to vary a spatial transmission configuration of
`the selected substreams.
`
`In another embodiment of the invention, a wireless cel-
`lular network for receiving subscriber datastreams at corre-
`sponding ones among a plurality of base stations located
`within the cellular network is disclosed. The wireless cel-
`
`lular network includes: subscriber units and logic. The
`subscriber units each include spatially separate transmitters
`for transmitting,
`in response to control signals, selected
`substreams of each subscriber datastream on an assigned
`channel of a multiple access protocol. The logic communi-
`cates with each of the base stations. The logic generates
`control signals to configure selected ones of the base stations
`to receive composite signals resulting from the spatially
`separate transmission of the selected substreams from a
`corresponding one among the plurality of subscriber units on
`the assigned channel. The logic also converts the composite
`signals into estimate substreams and combines the estimated
`substreams of each subscriber datastream into each sub-
`scriber datastream.
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`In another embodiment of the invention, a wireless cel-
`lular network for
`transmitting subscriber downlink
`datastream(s) from a first network to subscribers located
`within the wireless cellular network is disclosed. The wire-
`
`less cellular network includes base stations and logic. The
`base stations include at least one transmitter, for transmitting
`in response to control signals selected substreams of each
`subscriber datastream on an assigned channel of a multiple
`access protocol. The logic communicates with each of the
`base stations. The logic for assigns an available channel on
`which to transmit each subscriber datastream. The logic
`routes at least a substream of each datastream to at least a
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`selected one of the base stations. The logic further generates
`control signals to configure the at least a selected one of the
`base stations to transmit the selected substreams to a corre-
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`sponding one among the plurality of subscriber units on the
`assigned channel.
`In an embodiment of the invention, a method for trans-
`mitting subscriber downlink datastream(s) from base sta-
`tions to corresponding ones among a plurality of subscriber
`units is disclosed. The method includes the acts of:
`
`routing at least a substream of each subscriber downlink
`datastream to selected one of the base stations;
`transmitting the at least a substream of each subscriber
`downlink datastream from the selected one of the base
`
`stations on an assigned channel of a multiple access
`protocol; and
`re-routing at least a substream of each subscriber down-
`link datastream between a single base station and
`multiple base stations responsive to a determination
`that a change of a spatial transmission configuration of
`the at least a substream of each subscriber downlink
`
`datastream signal is required.
`In another embodiment of the invention, a method for
`receiving subscriber downlink datastream(s)
`transmitted
`from a plurality of spatially separate transmitters is dis-
`closed. The method includes the acts of:
`
`least one of the
`receiving signals generated from at
`plurality of spatially separate transmitters;
`determining a number of substreams to be derived from
`the signals;
`separating the signals into the number of substreams
`determined in said act of determining; and
`combining the substreams into a corresponding subscriber
`downlink datastream.
`In another embodiment of the invention, a wireless cel-
`lular network for transmitting subscriber datastream(s) to
`corresponding ones among a plurality of subscriber units
`located within the cellular network is disclosed. The wireless
`cellular network includes:
`
`means for routing at least a substream of each subscriber
`downlink datastream to selected ones of the base sta-
`tions;
`means for transmitting the at least a substream of each
`subscriber downlink datastream from the selected ones
`
`of the base stations on an assigned channel of a multiple
`access protocol; and
`means for re-routing the at least a substream of each
`subscriber downlink datastream between a single base
`station and multiple base stations responsive to a signal
`from a corresponding one of the subscriber units
`requesting a change of spatial transmission configura-
`tion.
`In another embodiment of the invention, a subscriber unit
`for use in a cellular system with base stations each including
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`spatially separate transmitters for transmitting selected sub-
`streams of at least one of a plurality of subscriber downlink
`datastream(s) on an assigned channel of a multiple access
`protocol is disclosed. The subscriber unit includes:
`means for receiving signals generated from at least one of
`the plurality of spatially separate transmitters;
`means for determining a number of substreams to be
`derived from the signals;
`means for separating the signals into the number of
`substreams determined in said act of determining;
`means for combining the substreams into a corresponding
`subscriber downlink datastream; and
`means for signaling the base when a change of a spatial
`transmission configuration is required in order to
`resolve the composite signals into estimated sub-
`streams.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other features and advantages of the present
`invention will become more apparent to those skilled in the
`art from the following detailed description in conjunction
`with the appended drawings in which:
`FIG. 1 shows a wireless cellular network incorporating
`spatial multiplexing and multiple access according to the
`current invention.
`FIG. 1B is a detailed view of selected cells within the
`cellular network shown in FIG. 1A.
`
`FIG. 1C shows a cell architecture that provides overlap-
`ping regions suitable for multi-base spatial multiplexing.
`FIGS. 2A—F show alternate embodiments for the sub-
`scriber units utilized in the wireless cellular network shown
`in FIGS. 1A—B.
`
`FIG. 3 shows a detailed hardware block diagram of a
`single base station and subscriber unit for use in the wireless
`cellular network shown in FIGS. 1A—B.
`
`FIGS. 4A—J show detailed hardware block diagrams of
`the multiple access hardware for controlling the transmis-
`sion of subscriber datastream(s) from one or more of the
`base stations within the wireless network.
`
`FIGS. 5A—B show detailed hardware block diagrams of
`the hardware associated with the receipt of multiple sub-
`scriber datastream(s) at
`the base stations of the wireless
`network of the current invention.
`
`FIG. 6 shows a detailed view of the signals and the
`symbols associated with the transmission and receipt of
`spatially multiplexed signals according to an embodiment of
`the current invention.
`
`FIGS. 7A—B show detailed hardware block diagrams of
`the configurable spatial processor associated with the
`receiver circuitry receiver, according to an embodiment of
`the current invention.
`
`FIGS. 7A—D show detailed hardware block diagrams of a
`configurable space and space-time processor associated with
`the configurable spatial receiver according to an embodi-
`ment of the current invention.
`
`FIG. 8 shows in-band training and data signals for cali-
`brating the spatially configurable receiver during the trans-
`mission of spatially multiplexed data, according to an
`embodiment of the current invention.
`
`FIGS. 9A—B are respectively detailed hardware block
`diagrams of a spatially multiplexed transmitter and receiver
`implementing a time-division multiple access protocol
`(TDMA), according to an embodiment of the current inven-
`tion.
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`FIGS. 10A—B are respectively detailed hardware block
`diagrams of a spatially multiplexed transmitter and receiver
`implementing a frequency-division multiple access protocol
`(FDMA), according to an embodiment of the current inven-
`tion.
`
`FIGS. 11A—B are respectively detailed hardware block
`diagrams of a spatially multiplexed transmitter and receiver
`implementing a code-division multiple access protocol
`(CDMA), according to an embodiment of the current inven-
`tion.
`
`FIGS. 12A—B are respectively detailed hardware block
`diagrams of a spatially multiplexed transmitter and receiver
`implementing a space-division multiple access protocol
`(SDMA), according to an embodiment of the current inven-
`tion.
`
`FIGS. 13A—B are process flow diagrams showing the acts
`associated with respectively the spatially multiplexed trans-
`mission and reception of datastream(s) in any one of a
`number of multiple access protocols, according to an
`embodiment of the invention.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`A method and apparatus is disclosed which allows for
`both spatial multiplexed and non-spatial wireless commu-
`nications between portable units and corresponding selected
`ones among a plurality of base stations. The methods and
`apparatus of the current invention may be implemented on
`a dedicated wireless infrastructure or may be superimposed
`on existing wireless communications systems, such as cel-
`lular telephone and paging services, which are currently in
`place around the world. The methods and apparatus include
`implementation in any of a number of multiple access
`protocols.
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`Spatial Multiplexing and Multiple Access
`
`Spatial multiplexing (SM) is a transmission technology
`which exploits multiple antennas at both the base station(s)
`and at
`the subscriber units to increase the bit rate in a
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`wireless radio link with no additional power or bandwidth
`consumption. Under certain conditions, spatial multiplexing
`offers a linear increase in spectrum efficiency with the
`number of antennas. Assuming, for example, N=3 antennas
`are used at
`the transmitter and receiver,
`the stream of
`possibly coded information symbols is split into three inde-
`pendent substreams. These substreams occupy the same
`channel of a multiple access (MA) protocol, the same time
`slot in a time-division multiple access (TDMA) protocol, the
`same frequency slot in frequency-division multiple access
`(FDMA) protocol,
`the same code/key sequence in code-
`division multiple access (CDMA) protocol or the same
`spatial
`target
`location in space-division multiple access
`(SDMA) protocol. The substreams are applied separately to
`the N transmit antennas and launched into the radio channel.
`
`Due to the presence of various scattering objects (buildings,
`cars, hills, etc.) in the environment, each signal experiences
`multipath propagation. The composite signals resulting from
`the transmission are finally captured by an array of receive
`antennas with random phase and amplitudes. For every
`substream the set of N received phases and N received
`amplitudes constitute its spatial signature.
`At the receive array, the spatial signature of each of the N
`signals is estimated. Based on this information, a signal
`processing technique is then applied to separate the signals,
`recover the original substreams and finally merge the sym-
`bols back together. Linear or nonlinear receivers can be used
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`providing a range of performance and complexity trade-offs.
`A linear spatial multiplexing receiver can be viewed as a
`bank of superposed spatial weighting filters, where every
`filter aims at extracting one of the multiplexed substreams
`by spatially nulling the remaining ones. This assumes, of
`course, that the substreams have different signatures.
`If the transmitter is equipped with M antennas, while the
`receiver has N antennas,
`the rate improvement factor
`allowed by spatial multiplexing is the minimum of these two
`numbers. Additional antennas on the transmit or receive side
`
`are then used for diversity purposes and further improve the
`link reliability by improving, for example,
`the signal-to-
`noise ratio or allowing for smaller fading margins, etc.
`Effectively spatial multiplexing allows a transmitter receiver
`pair to communicate in parallel
`through a single MA
`channel, hence allowing for a possible N-fold improvement
`of the link speed. More improvement is actually obtained if
`we take into account
`the diversity gain offered by the
`multiple antennas (for
`instance,
`in a Raleigh fading
`channel). Such performance factors are derived ideally
`under the assumption that
`the spatial signatures of the
`substreams are truly independent from each other. In reality,
`the level of independence between the signatures will deter-
`mine the actual
`link performance. The performance,
`however, usually exceeds that obtained by a single antenna
`at the transmitter and receiver. For example, at two GHZ,
`assuming the base station and the subscriber unit are spaced
`apart by one mile and using three antennas at each end of the
`link, a scattering radius of about 30 feet (both ends) is
`enough to achieve maximum performance.
`FIG. 1A shows a plurality of subscriber units wirelessly
`coupled over a cellular network to a network 100. Network
`100 may include: a local area network (LAN), a wide area
`network (WAN), a public switched telephone network
`(PSTN), Public Land Mobile Network (PLMN), an adhoc
`network, a virtual private network, an intranet or the inter-
`net. The wireless system includes: a central office (CO) 102,
`a master switch center (MSC) 106, a ground based relay
`station 110, satellites (112), base stations 120, 126 and 132
`(BTS) and subscriber units 156, 138, 144, 150 and 162. The
`subscriber units may be mobile, fixed or portable. The base
`stations may be fixed or mobile. The base stations may
`include: a tower, satellites, balloons, planes, etc. The base
`station may be located indoors/outdoors. The cellular net-
`work includes one or more base stations, where each base
`station includes one or more spatially separate transmitters.
`The central office 102 is coupled to the network 100.
`Network 100 may be circuit switched (e.g. point-to-point) or
`packet switched network. The central office is coupled to a
`master switching center 106. The MSC in traditional cellular
`systems is alternately identified as: a mobile telephone
`switching office (MTSO) by Bell Labs, an electronic mobile
`Xchange (EMX) by Motorola, an AEX by Ericcson, NEAX
`by NEC, a switching mobile center (SMC) and a master
`mobile center (MMC) by Novatel. The MSC is coupled via
`data/control line 108 to the satellites via relay station 110
`and to the base stations. In an alternate embodiment of the
`
`invention, base station controllers (BSC) may serve as
`intermediary coupling points between the MSC and the base
`stations.
`In the embodiment shown, each of the BTS
`includes an array of spatially separate antennas for trans-
`mission and/or reception. The BTS may also include tradi-
`tional antenna for whichever of the receive/transmit side of
`its communication capability lacks spatially separate
`antenna and associated circuitry. Antennas of a transmitter/
`receiver are defined to be spatially separate if they are
`capable of transmitting/receiving spatially separate signals.
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`Physically separate antenna may be used to transmit/receive
`spatially separate signals. Additionally, a single antenna may
`be used to transmit/receive spatially separate signals pro-
`vided it includes the ability to transmit/receive orthogonal
`radiation patterns. Hereinafter, the phrase “spatially sepa-
`rate” shall be understood to include any antenna or trans-
`mitter or receiver capable of communicating spatially sepa-
`rate signals. The base stations are configured to
`communicate with subscriber units of a traditional type, i.e.
`those lacking either spatially separate transmission/
`reception as well as spatially enabled subscriber units, i.e.
`those including either or both spatially separate reception
`and transmission capabilities.
`In operation, distinct subscriber datastream(s) 170, 176
`and 182 are received by CO 102. The CO performs the initial
`routing of the data streams to the appropriate one of a
`plurality of MSCs which may be located across the country.
`The MSC performs several functions. It controls the switch-
`ing between the PSTN or network 100 and the BTSs for all
`wireline-to-subscriber, subscriber-to-wireline and
`subscriber-to-subscriber calls.
`It processes/logic data
`received from BTSs concerning subscribe