United States Patent (19)
`Alamouti et al.
`
`54 METHOD FOR FREQUENCY DIVISION
`DUPLEX COMMUNICATIONS
`
`75 Inventors: Siavash Alamouti, Kirkland, Wash.;
`Eduardo F. Casas, Vancouver, Canada;
`Michael Hirano; Elliott Hoole, both of
`Redmond, Wash.; Mary Jesse,
`Issaquah, Wash.; David G. Michelson,
`North Vancouver, Canada; Patrick
`Poon, Redmond, Wash.; Gregory J.
`yeintimila, Redmond, Wash.;
`Hongliang Zhang, Redmond, Wash.
`73 Assi
`: AT&T Wireless Services I
`73 ASSignee: is sists services ine,
`IrKland, Wasn.
`
`21 Ap1. No.: 08/796,584
`21
`ppl. No
`/796,
`22 Filed:
`Feb. 6, 1997
`(51) Int. Cl. ................................................. H04Q 7/00
`52 U.S. Cl. ........................... 370/330; 370/203; 370/281
`58 Field of Search ..................................... 370/203, 206,
`370/329, 330, 337, 336,343, 344, 321,
`280, 281; 375/267, 347, 299
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`a
`4,381.562 4/1983 Acampora.
`4,644,562 2/1987 Kavehrad.
`4,723,321
`2/1988 Saleh.
`6. Smpora
`5,280.464. 2f1994 Wang
`5.367,539 11 f1994 Cop?ey
`5,6895.02 11/1997 Scott. 370/281
`FOREIGN PATENT DOCUMENTS
`
`USOO5933421A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,933,421
`Aug. 3, 1999
`
`O 653859 5/1995 European Pat. Off..
`O 653 973 12/1995 European Pat. Off..
`94/19877 9/1994 WIPO.
`97/O1256
`1/1997 WIPO.
`
`OTHER PUBLICATIONS
`
`Ojanpera et al., “Frames-hybrid multiple acceSS technol
`ogy,” 1996 IEEE 4th Int’l Symposium on Spread Spectrum
`Techniques, vol. 1, Sep. 22-25, 1996, pp. 320-324.
`C
`p
`pp
`Rohling Hetal, “Performance of an OFDM-TDMA mobile
`communication system,” 1996 IEEE 46th. Vehicular Tech
`nology Conference, Apr. 28-May 1, 1996, vol. 3, No. 46, pp.
`1589-1593, XP000595799.
`Giner, V.C., “An Approximate Analysis of TDMA Out-of
`-Slot Random Access Protocols for Microcellular Mobile
`Communications' Int’l Jour. of Wireless Information Net
`works, vol. 3, No. 1, Jan. 1996, pp. 41–53, XP002077581.
`
`Primary Examiner Jeffery A. Hofsass
`ASSistant Examiner-Clement Townsend
`
`ABSTRACT
`57
`The high quality PCS communications are enabled in envi
`ronments where adjacent PCS service bands operate with
`out-of-band harmonics that would otherwise interfere with
`the system's operation. The highly bandwidth-efficient com
`munications method combines a form of time division
`duplex (TDD), frequency division duplex (FDD), time divi
`Sion multiple access (TDMA), orthogonal frequency divi
`Sion multiplexing (OFDM), Spatial diversity, and polariza
`tion diversity in various unique combinations. The method
`provides excellent fade resistance. The method enables
`changing a user's available bandwidth on demand by assign
`ing additional TDMA slots during the user's session.
`
`O 641 096 3/1995 European Pat. Off..
`
`41 Claims, 15 Drawing Sheets
`
`OFDM TONES
`REMOTE
`TRANS/
`STATION
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`U AND W
`OFDM TONES
`s:
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`TRANS/-(y
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`SHARE
`TDMA
`
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`16
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`the
`
`ANTENNA ARRAY WITHSPATAL
`AND POLARIZATION DIVERSITY
`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 1 of 37
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 1 of 15
`
`5,933,421
`
`
`
`7 NOII WIS 3 SW8
`
`
`
`
`
`
`
`
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`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 2 of 37
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`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 2 of 15
`
`5,933,421
`
`
`
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`
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 3 of 37
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`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 3 of 15
`
`5,933,421
`
`FIC. 1.3
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`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 4 of 37
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`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 4 of 15
`
`5,933,421
`
`FIG.
`
`1.6
`
`FREQUENCY
`
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 5 of 37
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`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 5 of 15
`
`5,933,421
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`FIC. 1.6
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`BINARY SOURCE
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 6 of 37
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`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 6 of 15
`
`5,933,421
`
`FIC. 1.7
`
`BINARY SOURCE
`72
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 7 of 37
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 7 of 15
`
`5,933,421
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 8 of 37
`
`

`

`US. Patent
`
`Aug. 3, 1999
`
`Sheet 8 0f 15
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`5,933,421
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`ERICSSON V. UNILOC
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`Ex. 1006 / Page 9 of 37
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 9 of 37
`
`
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
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`Sheet 9 of 15
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`5,933,421
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 10 of 37
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`

`

`U.S. Patent
`US. Patent
`
`Aug. 3, 1999
`Aug. 3, 1999
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`Sheet 10 Of 15
`Sheet 10 0f 15
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`5,933,421
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`Ex. 1006 / Page 11 of37
`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 11 of 37
`
`
`
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 11 of 15
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`5,933,421
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 12 of 37
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 12 of 15
`
`5,933,421
`
`FIC. 2. 1
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 13 of 37
`
`

`

`US. Patent
`
`Aug. 3, 1999
`
`Sheet 13 0f 15
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`5,933,421
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`ERICSSON V. UNILOC
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`Ex. 1006 / Page 14 of37
`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 14 of 37
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`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 14 of 15
`
`5,933,421
`
`FIG. 3.2
`
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`
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`
`FREQUENCY OFFSET
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 15 of 37
`
`

`

`U.S. Patent
`
`Aug. 3, 1999
`
`Sheet 15 of 15
`
`5,933,421
`
`FIG. 4.2
`
`55us
`55us
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`
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`BURSTS
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`MEASUREMENT INFORMATION
`TO UNCOMPENSATED RU
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`RU ADVANCES ITS
`TRANSMISSION BY
`MEASURED DELAY
`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 16 of 37
`
`

`

`1
`METHOD FOR FREQUENCY DIVISION
`DUPLEX COMMUNICATIONS
`
`5,933,421
`
`2
`permits the Separation and reconstruction of each user's
`message at the receiving end of the communication channel.
`There are four types of CDMA protocols classified by
`modulation: direct Sequence (or pseudo-noise), frequency
`hopping, time hopping, and hybrid Systems. The technical
`foundations for CDMA protocols are discussed in the recent
`book by Prasad entitled “CDMA for Wireless Personal
`Communications”, Artech House, 1996.
`The Direct Sequence CDMA (DS-CDMA) protocol
`Spreads a user's data Signal Over a wide portion of the
`frequency spectrum by modulating the data Signal with a
`unique code Signal that is of higher bandwidth than the data
`Signal. The frequency of the code Signal is chosen to be
`much larger than the frequency of the data Signal. The data
`Signal is directly modulated by the by the code signal and the
`resulting encoded data Signal modulates a Single, wideband
`carrier that continuously covers a wide frequency range.
`After transmission of the DS-CDMA modulated carrier
`Signal, the receiver uses a locally generated version of the
`user's unique code signal to demodulate the received signal
`and obtain a reconstructed data Signal. The receiver is thus
`able to extract the user's data Signal from a modulated
`carrier that bears many other users data Signals.
`The Frequency Hopping Spread Spectrum (FHSS) pro
`tocol uses a unique code to change a value of the narrow
`band carrier frequency for Successive bursts of the user's
`data Signal. The value of the carrier frequency varies in time
`over a wide range of the frequency spectrum in accordance
`with the unique code. The term Spread Spectrum Multiple
`Access (SSMA) is also used for CDMA protocols such as
`DS-CDMA and FHSS that use a relatively wide frequency
`range over which to distribute a relatively narrowband data
`Signal.
`The Time Hopping CDMA (TH-CDMA) protocol uses a
`Single, narrow bandwidth, carrier frequency to Send bursts of
`the user's data at intervals determined by the user's unique
`code. Hybrid CDMA systems include all CDMA systems
`that employ a combination of two or more CDMA protocols,
`Such as direct Sequence/frequency hopping (DS/FH), direct
`Sequence/time hopping (DS/TH), frequency hopping/time
`hopping (FH/TH), and direct Sequence/frequency hopping/
`time hopping (DS/FH/TH).
`The Space Division Multiple Access (SDMA) transmis
`Sion protocol forms directed beams of energy whose radia
`tion patterns do not overlap Spatially with each other, to
`communicate with users at different locations. Adaptive
`antenna arrays can be driven in phased patterns to Simulta
`neously Steer energy in the direction of Selected receivers.
`With Such a transmission technique, the other multiplexing
`Schemes can be reused in each of the Separately directed
`beams. For example, the Specific codes used in CDMA can
`be transmitted in two different beams. Accordingly, if the
`beams do not overlap each other, different users can be
`assigned the same code as long as they do not receive the
`Same beam.
`The Frequency Division Multiple Access (FDMA) pro
`tocol Services a multiplicity of users over one frequency
`band by devoting particular frequency slots to Specific users,
`i.e., by frequency division multiplexing the information
`asSociated with different users. Knowledge of the frequency
`Slot in which any Specific information resides permits recon
`Struction of each user's information at the receiving end of
`the communication channel.
`Orthogonal Frequency Division Multiplexing (OFDM)
`addresses a problem that is faced, for example, when pulsed
`Signals are transmitted in an FDMA format. In accordance
`
`25
`
`CROSS-REFERENCES TO RELATED
`APPLICATIONS
`The invention disclosed herein is related to the copending
`U.S. patent application by Gibbons, et al entitled “REMOTE
`WIRELESS UNIT HAVING REDUCED POWER OPER
`ATING MODE', Ser. No. 08/796,586, filed on the same day
`as the instant patent application, assigned to AT&T WireleSS
`Services, Inc. and incorporated herein by reference.
`The invention disclosed herein is related to the copending
`U.S. patent application by Greg Veintimilla, entitled
`“METHOD TO INDICATE SYNCHRONIZATION LOCK
`15
`OFAREMOTE STATION WITH ABASE STATION”, Ser.
`No. 08/796,492, filed on the same day as the instant patent
`application, assigned to AT&T WireleSS Services, Inc. and
`incorporated herein by reference.
`The invention disclosed herein is related to the copending
`U.S. patent application by Elliott Hoole, entitled “DELAY
`COMPENSATION', Ser. No. 08/796,491, filed on the same
`day as the instant patent application, assigned to AT&T
`Wireless Services, Inc. and incorporated herein by reference.
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention involves improvements to communica
`tions Systems and methods in a wireless, frequency division
`duplex communications System.
`2. Description of Related Art
`WireleSS communications Systems, Such as cellular and
`personal communications Systems, operate over limited
`spectral bandwidths. They must make highly efficient use of
`the Scarce bandwidth resource to provide good Service to a
`large population of users. Examples of Such communica
`tions Systems that deal with high user demand and Scarce
`bandwidth resources are wireleSS communications Systems,
`Such as cellular and personal communications Systems.
`Various techniques have been Suggested for Such Systems
`to increase bandwidth-efficiency, the amount of information
`that can be transmitted within a given Spectral bandwidth.
`Many of these techniques involve reusing the same com
`munication resources for multiple users while maintaining
`45
`the identity of each user's message. These techniques are
`generically referred to as multiple acceSS protocols. Among
`these multiple access protocols are Time Division Multiple
`Access (TDMA), Code Division Multiple Access (CDMA),
`Space Division Multiple Access (SDMA), and Frequency
`Division Multiple Access (FDMA). The technical founda
`tions of these multiple access protocols are discussed in the
`recent book by Rappaport entitled “Wireless Communica
`tions Principles and Practice', Prentice Hall, 1996.
`The Time Division Multiple Access (TDMA) protocol
`Sends information from a multiplicity of users on one
`assigned frequency bandwidth by time division multiplexing
`the information from the various users. In this multiplexing
`Scheme, particular time slots are devoted to Specific users.
`Knowledge of the time slot during which any specific
`information is transmitted, permits the Separation and recon
`Struction of each user's message at the receiving end of the
`communication channel.
`The Code Division Multiple Access (CDMA) protocol
`uses a unique code to distinguish each user's data Signal
`from other users data Signals. Knowledge of the unique
`code with which any specific information is transmitted,
`
`50
`
`55
`
`60
`
`65
`
`35
`
`40
`
`ERICSSON v. UNILOC
`Ex. 1006 / Page 17 of 37
`
`

`

`5,933,421
`
`15
`
`25
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`3
`with principles well known in the communication Sciences,
`the limited time duration of Such Signals inherently broadens
`the bandwidth of the Signal in frequency Space. Accordingly,
`different frequency channels may significantly overlap,
`defeating the use of frequency as a user-identifying
`parameter, the principle upon which FDMA is based.
`However, pulsed information that is transmitted on Specific
`frequencies can be separated, in accordance with OFDM
`principles, despite the fact that the frequency channels
`overlap due to the limited time duration of the Signals.
`OFDM requires a specific relationship between the data rate
`and the carrier frequencies. Specifically, the total signal
`frequency band is divided into N frequency Sub-channels,
`each of which has the same data rate 1/T. These data Streams
`are then multiplexed onto a multiplicity of carriers that are
`Separated in frequency by 1/T. Multiplexing Signals under
`these constraints results in each carrier having a frequency
`response that has Zeroes at multiples of 1/T. Therefore, there
`is no interference between the various carrier channels,
`despite the fact that the channels overlap each other because
`of the broadening associated with the data rate. OFDM is
`disclosed, for example, by Chang in Bell Sys. Tech. Jour.,
`Vol. 45, pp. 1775–1796, December 1966, and in U.S. Pat.
`No. 4,488,445.
`Parallel Data Transmission is a technique related to
`FDMA. It is also referred to as Multitone Transmission
`(MT), Discrete Multitone Transmission (DMT) or Multi
`Carrier Transmission (MCT). Parallel Data Transmission
`has significant calculational advantages over Simple FDMA.
`In this technique, each users information is divided and
`transmitted over different frequencies, or “tones’, rather
`than over a single frequency, as in Standard FDMA. In an
`example of this technique, input data at NF bits per Second
`are grouped into blocks of N bits at a data rate of F bits per
`Second. N carriers or "tones' are then used to transmit these
`bits, each carrier transmitting F bits per Second. The carriers
`can be spaced in accordance with the principles of OFDM.
`Both the phase and the amplitude of the carrier can be
`varied to represent the Signal in multitone transmission.
`Accordingly, multitone transmission can be implemented
`40
`with M-ary digital modulation schemes. In an M-ary modu
`lation Scheme, two or more bits are grouped together to form
`Symbols and one of the M possible signals is transmitted
`during each Symbol period. Examples of M-ary digital
`modulation schemes include Phase Shift Keying (PSK),
`Frequency Shift Keying (FSK), and higher order Quadrature
`Amplitude Modulation (QAM). In QAM a signal is repre
`Sented by the phase and amplitude of a carrier wave. In high
`order QAM, a multitude of points can be distinguished on a
`amplitude/phase plot. For example, in 64-ary QAM, 64 Such
`points can be distinguished. Since Six bits of Zeros and ones
`can take on 64 different combinations, a Six-bit Sequence of
`data Symbols can, for example, be modulated onto a carrier
`in 64-ary QAM by transmitting only one value Set of phase
`and amplitude, out of the possible 64 Such sets.
`Suggestions have been made to combine Some of the
`above temporal and spectral multiplexing techniques. For
`example, in U.S. Pat. No. 5,260,967, issued to Schilling,
`there is disclosed the combination of TDMA and CDMA. In
`U.S. Pat. No. 5,291,475, issued to Bruckert, and in U.S. Pat.
`No. 5,319,634 issued to Bartholomew, the combination of
`TDMA, FDMA, and CDMA is suggested.
`Other Suggestions have been made to combine various
`temporal and Spectral multiple-access techniques with Spa
`tial multiple-access techniques. For example, in U.S. Pat.
`No. 5,515,378, filed Dec. 12, 1991, Roy Suggests “separat
`ing multiple messages in the same frequency, code, or time
`
`4
`channel using the fact that they are in different spatial
`channels.” Roy Suggests Specific application of his tech
`nique to mobile cellular communications using an “antenna
`array'. Similar Suggestions were made by Swales et. al., in
`the IEEE Trans. Veh. Technol. Vol. 39. No. 1 February 1990,
`and by Davies et. al. in A.T.R., Vol. 22, No. 1, 1988 and in
`Telecom Australia, Rev. Act., 1985/86 pp. 41-43.
`Gardner and Schell Suggest the use of communications
`channels that are “spectrally disjoint in conjunction with
`“spatially separable” radiation patterns in U.S. Pat. No.
`5,260,968, filed Jun. 23, 1992. The radiation patterns are
`determined by restoring "Self coherence' properties of the
`Signal using an adaptive antenna array. “An adaptive
`antenna array at a base Station is used in conjunction with
`Signal processing through Self coherence restoral to Separate
`the temporally and Spectrally overlapping Signals of users
`that arrive from different specific locations.” See the
`Abstract of the Invention. In this patent, however, adaptive
`analysis and Self coherence restoral is only used to deter
`mine the optimal beam pattern; ". . . conventional Spectral
`filters . .
`. are used. . . to separate spatially inseparable
`filters.
`WinterS Suggests “adaptive array processing in which
`“the frequency domain data from a plurality of antennas
`are . . . combined for channel Separation and conversion to
`the time domain for demodulation,” in U.S. Pat. No. 5,481,
`570, filed Oct. 20, 1993. Column 1 lines 66–67 and Column
`2, lines 14-16.
`Agee has shown that “the use of an M-element multiport
`antenna array at the base Station of any communication
`network can increase the frequency reuse of the network by
`a factor of M and greatly broaden the range of input SINRS
`required for adequate demodulation . . . ” (“Wireless Per
`Sonal Communications: Trends and Challenges', Rappaport,
`Woerner and Reed, editors, Kluwer Academic Publishers,
`1994, pp. 69-80, at page 69. See also, Proc. Virginia Tech.
`Third Symposium on Wireless Personal Communications,
`June 1993, pp. 15-1 to 15-12.)
`Gardner and Schell also suggest in U.S. Pat. No. 5,260,
`968, filed Jun. 23, 1992, “time division multiplexing of the
`Signal from the base station and the users” ... “in order to
`use the same frequency for duplex communications . . . '
`“Reception at the base station from all mobile units is
`temporally Separated from transmission from the base Sta
`tion to all mobile units.” Column 5, lines 44ff. In a similar
`vein, in U.S. Pat. No. 4,383,332 there is disclosed a wireless
`multi-element adaptive antenna array SDMA system where
`all the required adaptive Signal processing is performed at
`baseband at the base station through the use of “time
`division retransmission techniques.”
`Fazel, “Narrow-Band Interference Rejection in Orthogo
`nal Multi-Carrier Spread-Spectrum Communications”,
`Record, 1994 Third Annual International Conference on
`Universal Personal Communications, IEEE, 1994, pp.
`46-50 describes a transmission Scheme based on combined
`spread spectrum and OFDM. A plurality of Subcarrier fre
`quencies have components of the spreaded vector assigned
`to them to provide frequency-diversity at the receiver Site.
`The Scheme uses frequency domain analysis to estimate
`interference, which is used for weighting each received
`Subcarrier before despreading. This results in Switching off
`those Subcarriers containing the interference.
`Despite the Suggestions in the prior art to combine certain
`of the multiple acceSS protocols to improve bandwidth
`efficiency, there has been little Success in implementing Such
`combinations. It becomes more difficult to calculate opti
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`S
`mum operating parameters as more protocols are combined.
`The networks implementing combined multiple access pro
`tocols become more complex and expensive. Accordingly,
`the implementation of high-bandwidth efficiency communi
`cations using a combination of multiple acceSS protocols
`continues to be a challenge.
`
`SUMMARY OF THE INVENTION
`The invention enables high quality PCS communications
`in environments where adjacent PCS service bands operate
`with out-of-band harmonics that would otherwise interfere
`with the system's operation. The highly bandwidth-efficient
`communications method combines a form of time division
`duplex (TDD), frequency division duplex (FDD), time divi
`Sion multiple access (TDMA), orthogonal frequency divi
`Sion multiplexing (OFDM), spatial diversity, and polariza
`tion diversity in various unique combinations. The invention
`provides excellent fade resistance. The invention enables
`changing a user's available bandwidth on demand by assign
`ing additional TDMA slots during the user's session.
`In one embodiment of the invention, TDD, FDD, TDMA,
`and OFDM are combined to enable a base station to effi
`ciently communicate with many remote Stations. The
`method includes the Step of receiving at the base Station a
`first incoming wireleSS Signal comprising a plurality of first
`discrete frequency tones that are orthogonal frequency divi
`sion multiplexed (OFDM) in a first frequency band from a
`first remote Station during a first time division multiple
`access (TDMA) interval. Then the method includes the step
`of receiving at the base Station a Second incoming wireleSS
`Signal comprising a plurality of Second discrete frequency
`tones that are orthogonal frequency division multiplexed
`(OFDM) in the first frequency band from a second remote
`Station during the first time division multiple access
`(TDMA) interval. The first and second stations accordingly
`have different Sets of discrete frequency tones that are
`orthogonal frequency division multiplexed.
`Then the method includes the Step of receiving at the base
`Station a third incoming wireleSS Signal comprising a plu
`rality of the first discrete frequency tones that are orthogonal
`frequency division multiplexed (OFDM) in the first fre
`quency band from a third remote Station during a Second
`time division multiple access (TDMA) interval. The first and
`third Stations accordingly are time division multiplexed by
`Sharing the same Set of discrete frequency tones in different
`TDMA intervals.
`Then the method includes the Step of receiving at the base
`Station a fourth incoming wireleSS Signal comprising a
`plurality of the Second discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`first frequency band from a fourth remote Station during the
`second time division multiple access (TDMA) interval. The
`Second and fourth Stations accordingly are time division
`multiplexed by sharing the same Set of discrete frequency
`tones in different TDMA intervals.
`Then the method includes the Step of transmitting at the
`base Station the first outgoing wireleSS Signal comprising a
`plurality of third discrete frequency tones that are orthogonal
`frequency division multiplexed (OFDM) in a second fre
`quency band to the first remote Station during a third time
`division multiple access (TDMA) interval. The first remote
`Station and the base Station accordingly are time division
`duplexed (TDD) by transmitting their respective signals at
`different TDMA intervals. In addition, the first remote
`Station and the base Station accordingly are frequency divi
`Sion duplexed (FDD) by transmitting their respective signals
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`6
`on different Sets of discrete frequency tones in different
`frequency bands.
`Then the method includes the Step of transmitting at the
`base Station the Second outgoing wireleSS Signal comprising
`a plurality of fourth discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`Second frequency band to the Second remote Station during
`the third time division multiple access (TDMA) interval.
`The Second remote Station and the base Station accordingly
`are time division duplexed (TDD) by transmitting their
`respective signals at different TDMA intervals. In addition,
`the Second remote Station and the base Station accordingly
`are frequency division duplexed (FDD) by transmitting their
`respective Signals on different Sets of discrete frequency
`tones in different frequency bands.
`Then the method includes the Step of transmitting at the
`base Station the third outgoing wireleSS Signal comprising
`the plurality of the third discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`Second frequency band to the third remote Station during a
`fourth time division multiple access (TDMA) interval. The
`third remote Station and the base Station accordingly are time
`division duplexed (TDD) by transmitting their respective
`signals at different TDMA intervals. In addition, the third
`remote Station and the base Station accordingly are fre
`quency division duplexed (FDD) by transmitting their
`respective Signals on different Sets of discrete frequency
`tones in different frequency bands.
`Then the method includes the Step of transmitting at the
`base Station the fourth outgoing wireleSS Signal comprising
`the plurality of the fourth discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`Second frequency band to the fourth remote Station during
`the fourth time division multiple access (TDMA) interval.
`The fourth remote Station and the base Station accordingly
`are time division duplexed (TDD) by transmitting their
`respective signals at different TDMA intervals. In addition,
`the fourth remote Station and the base Station accordingly are
`frequency division duplexed (FDD) by transmitting their
`respective Signals on different Sets of discrete frequency
`tones in different frequency bands.
`In another embodiment of the invention, TDD, FDD,
`TDMA, OFDM, and space diversity are combined to enable
`a base Station to efficiently communicate with many remote
`Stations. This is possible because of the multiple element
`antenna array at the base Station that is controlled by
`despreading and spreading weights. The spreading weights
`enable the base Station to Steer the Signals it transmits to
`remote Stations that are have a Sufficient geographic Sepa
`ration from one another. The despreading weights enable the
`base Station to Steer the receive Sensitivity of the base Station
`toward the Sources of Signals transmits by remote Stations
`that have a Sufficient geographic Separation from one
`another.
`The method includes the Step of receiving at the base
`Station a first incoming wireleSS Signal comprising a plural
`ity of first discrete frequency tones that are orthogonal
`frequency division multiplexed (OFDM) in a first frequency
`band from a first remote Station at a first geographic location
`during a first time division multiple access (TDMA) inter
`val. Then the method includes the step of receiving at the
`base Station a Second incoming wireleSS Signal comprising a
`plurality of the first discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`first frequency band from a Second remote Station at a
`Second geographic location during the first time division
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`ERICSSON v. UNILOC
`Ex. 1006 / Page 19 of 37
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`7
`multiple access (TDMA) interval. Then the method includes
`the Step of Spatially despreading the first and Second incom
`ing Signals received at the base Station by using spatial
`despreading weights. Spatial diversity is provided because
`the despreading weights enable the base Station to Steer the
`receive sensitivity of the base station toward the first remote
`Station and the Second remote Station, respectively.
`Later, the method performs the Step of Spatially spreading
`a first and Second outgoing wireleSS Signals at the base
`Station by using Spatial spreading weights. Then the method
`includes the Step of transmitting at the base Station the first
`outgoing wireleSS Signal comprising a plurality of third
`discrete frequency tones that are orthogonal frequency divi
`sion multiplexed (OFDM) in a second frequency band to the
`first remote Station at the first geographic location during a
`third time division multiple access (TDMA) interval. Then
`the method includes the Step of transmitting at the base
`Station the Second outgoing wireleSS Signal comprising a
`plurality of the third discrete frequency tones that are
`orthogonal frequency division multiplexed (OFDM) in the
`Second frequency band to the Second remote Station at the
`Second geographic location during the third time division
`multiple access (TDMA) interval. Spatial diversity is pro
`Vided because the Spreading weights enable the base Station
`to Steer the Signals it transmits to the first and Second remote
`Stations, respectively.
`In another embodiment of the invention, TDD, FDD,
`TDMA, OFDM, and polarization diversity are combined to
`enable a base Station to efficiently communicate with many
`remote Stations. This is possible because the antenna at the
`base Station and the antennas at the remote Stations are
`designed to distinguish orthogonally polarized signals. Sig
`nals exchanged between the base station and a first remote
`Station are polarized in one direction, and Signals exchanged
`between the base Station and a Second remote Station are
`polarized in an orthogonal direction.
`The method includes the Step of receiving at the base
`Station a first incoming wireleSS Signal polarized in a first
`polarization direction comprising a plurality of first discrete
`frequency tones that are orthogonal frequency division mul
`tiplexed (OFDM) in a first frequency band from a first
`remote Station during a first time division multiple acceSS
`(TDMA) interval.