United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,345,599
`
`Paulraj et a1.
`
`[45] Date of Patent:
`
`Sep. 6, 1994
`
`US005345599A
`
`[54]
`
`INCREASING CAPACITY IN WIRELESS
`BROADCAST SYSTEMS USING
`DISTRIBUTED
`TRANSMISSION/DIRECTIONAL
`RECEPTION (DTDR)
`
`[75]
`
`Inventors: Arogyaswami J. Paulraj, Palo Alto;
`Thomas Kailath, Stanford, both of
`Calif.
`
`[73]
`
`Assignee:
`
`The Board of Trustees of the Leland
`Stanford Junior University, Stanford,
`Calif.
`
`[21]
`
`Appl. No.: 839,624
`
`[22]
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Filed:
`
`Feb. 21, 1992
`
`Int. Cl.5 ............................................... H043 7/06
`US. Cl. ................................... 455/49.1; 455/101;
`455/105; 455/27 B; 342/367; 348/384
`Field of Search .................... 455/49.1, 51.1, 51.2,
`455/59, 60, 61, 101, 103, 105, 137, 273, 278.1;
`375/38, 40; 342/367, 463—465; 358/133, 138,
`141, 146; 370/59, 63, 64
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,750,147 6/1988 Roy, III et a1.
`..................... 364/807
`4,888,641 12/1989 Isnardi et a1. ............ 358/141
`
`..... 358/138
`4,935,813
`6/1990 Fonsalas et a1.
`
`4,965,732 10/1990 Roy, III et a1.
`...... 364/460
`
`6/1991 Schreiber ............. 358/141
`5,021,882
`
`
`5,040,211
`8/1991 Schreiber
`380/14
`.. 358/146
`5,041,909
`8/1991 Okano ........
`5,095,535
`3/1992 Fresburg .......................... 455/2781
`HIGH BANDWIDTH SOURCE SIGNAL
`20
`
`SIGNAL SPLITTER
`
`FOREIGN PATENT DOCUMENTS
`
`0164749 12/1985 European Pat. Off.
`
`.............. 375/38
`
`Primary Examiner—Reinhard J. Eisenzopf
`Assistant Examiner-Chi Pham
`Attorney, Agent, or Firm—Townsend and Townsend
`Khourie and Crew
`
`[57]
`
`ABSTRACT
`
`A method and apparatus for increasing the capacity of ‘
`wireless broadcast communications system from a cen-
`tral studio to a plurality of users in a service area is
`disclosed. Given a source signal whose high informa-
`tion rate exceeds the practical information carrying
`capacity of the available broadcast channel bandwidth,
`the invention increases the effective capacity of the
`broadcast system to effectively communicate such a
`source signal. The high-rate signal is split into several
`low-rate signals such that each can be accommodated
`within the allocated bandwidth. These low-rate signals
`are transmitted from spatially separated transmitters, all
`radiating into the service area in the same frequency
`channel. Each receiver uses a plurality of antennas to
`receive these multiple cochannel signals that arrive
`from different directions-of-arrival. The receiver ex—
`ploits the directions-of-arrival differences of these co-
`channel signals to separate them into the individually
`transmitted signals. The separated signals are then de-
`modulated to extract the information signals which are
`then combined to obtain the original high-rate source
`signal. Thus, the broadcast information capacity can be
`increased several-fold.
`
`4 Claims, 7 Drawing Sheets
`
`52
`
`O O O
`
`
`
`
`
`
`
`ESTIMATED SOURCE SIGNAL
`
`CLEARWIRE 1009
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 1 of 7
`
`5,345,599
`
`HIGH BANDWIDTH SOURCE SIGNAL
`
` COMBINER
`
`B
`
`H B
`
`ESTIMATED SOURCE SIGNAL
`
`FIG. 1
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 2 of 7
`
`5,345,599
`
`/
`
`//
`
`I;
`.
`i
`!.
`\.
`\
`
`STUDIO
`
`//-------------------\“\
`TRANSMITTING STATION 1
`BROADCAST
`\
`.
`53 /"""\~.
`
`/
`
`$032386?
`52 v/
`
`
`fififififié
`
`'1: fl'
`
`:2:
`
`/
`
`\
`
`‘\
`
`RECEIVING SITE
`
`‘
`
`./
`/
`
`55
`
`
`50
`
`
`.
`
`-.
`\
`\\
`‘\
`
`55
`
`\
`TRANSMITTING STATION d
`)
`
`\\
`
`SERVICE AREA
`
`.\\
`
`/
`
`,
`
`‘\.~\...........z'
`
`58
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 3 of 7
`
`5,345,599
`
`
`
`
`SPLITTER
`
`TO Tx
`
`TO Tx
`
`TO Tx
`
`STATION 1 STATION 2
`
`STATION d
`
`FIG! 3
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 4 of 7
`
`5,345,599
`
`EQWL
`
`TRANSMITTING STATION 1
`Tx ANTENNA:
`
`
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 5 of 7
`
`5,345,599
`
`TRANSMITTER 1
`
`g \ ANTENNA 1
`52/
`I
`::
`4|
`‘~'
`‘
`ANTENNA 2
`
`74
`
`TRANSMITTER 2
`M
`
`TRANSMITTER d
`
`, /
`
`73 ANTENNA m
`,
`if ‘ 75
`
`55
`
`
`
`54
`
`80
`
`32W
`
`34
`
`75
`
`RECEIVER FRONT—ENDS
`
`.
`
`33
`
`BB
`
`SPATIAL FILTERS
`
`C ‘€
`
`3?
`
`DEMODULATOR/DECODER
`
`{II
`
`5°,
`
`35
`
`COMBINER
`
`100
`
`102
`
`TERMINAL
`
`
`
`EQUIPMENT
`
`FIG. 5
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 6 of 7
`
`5,345,599
`
`RECEIVER FRONT—END OUTPUTS
`
`SPATIAL FILTER
`
`SPATIAL FILTER
`
`INPUT 1
`85
`
`o
`
`o
`
`o
`
`INPUT m
`85
`
`. S
`
`PATIAL FILTER
`
`SPATIAL FILTER
`
`OUTPUT 1
`
`OUTPUT d
`
`TO DEMODULATOR/DECODER
`
`FIG. 5
`
`

`

`US. Patent
`
`Sep. 6, 1994
`
`Sheet 7 of 7
`
`5,345,599
`
`148
`
`148
`
`145
`
`A
`
`SIGNAL
`
`SOURCE
`
`
`
`B
`
`SIGNAL
`
`SOURCE
`
`C
`
`SIGNAL
`
`SOURCE
`
`150
`
`COMBINER
`
`HIGH BANDWIDTH
`
`COMBINED SIGNAL
`
`FIG.
`
`1
`
`DIAGRAM
`
`152
`
`SEPARATOR
`
`B
`
`FIG. 7
`
`

`

`1
`
`5,345,599
`
`INCREASING CAPACITY IN WIRELESS
`BROADCAST SYSTEMS USING DISTRIBUTED
`TRANSMISSION/DIRECTIONAL RECEPTION
`(DTDR)
`
`BACKGROUND
`
`1. Field of the Invention
`This invention relates to the field of wireless broad-
`cast of information to a multiplicity of receivers, and in
`particular to a method and apparatus for increasing the
`effective information transmission bandwidth or equiv-
`alently channel capacity by means of source signal split-
`ting, spatially distributed cochannel transmission, direc—
`tionally selective reception, and source signal recombi—
`nation.
`1. Prior Art
`
`10
`
`15
`
`In wireless broadcast systems, information generated
`by a source is transmitted by wireless means to a plural-
`ity of receivers within a particular service area. The
`transmission of such information over a fixed time inter-
`
`20
`
`val requires a finite amount of (frequency) bandwidth,
`and in current state-of-the-art, transmission of informa-
`tion from different sources must occur in different fre-
`quency bands (channels). Since there are quite a few
`services (e.g., television (TV), FM radio, private and
`public mobile communications, etc.) competing for a
`finite amount of available spectrum, the amount of spec-
`trum which can be allocated to each channel is severely
`limited. Innovative means for using the available spec-
`trum more efficiently are of great value. In current
`state-of-the-art systems such as broadcast television, a
`suitably modulated signal is transmitted from a single
`tower centrally located in the service area and propa-
`gate to receiving stations in the service area surround-
`ing the transmitter. The information transmission rate
`achievable by such broadcast
`transmission is con-
`strained by the allocated bandwidth (C. P. Sandbank,
`“Digital Television”, John Wiley, 1990 and W. F.
`Schreiber, “Fundamentals of Electronic Imaging: Some
`Aspects of Image Processing”, Springer Verlag, 1991).
`Due to attenuation suffered by signals in wireless
`propagation, the same frequency channel can be reused
`in a different geographical service area. Allowable in-
`terference levels determine the maximum transmit
`
`power at each location, as a well as the minimum sepa-
`ration between service areas using the same channels.
`Currently, within a service area, the rate at which infor-
`mation can be transferred to the receivers is limited by
`the fact that use of any channel is on a one-at-a-time
`basis. Simultaneous transmission of independent signals
`requires the use of separate channels. The current in-
`vention is a new method for increasing the capacity of
`a broadcast channel several fold by employing direc-
`tional channels. Directional channels are realized by
`spatially distributing signals to be transmitted, and em-
`ploying directionally sensitive receivers, a concept
`unique to this invention.
`In prior art, increasing the capacity of point—to—point
`communication links has been proposed by S. Ander-
`son, et al. “An Adaptive Array for Mobile Communica-
`tions Systems”, IEEE Trans. Veh. Technology, Vol.40.
`February 1991, pp. 230—236, and S. C. Swales, et al.
`“The Realization of a Multi-beam Antenna for Cellular
`Mobile Land Radio System”, Mobile Radio and Per-
`sonal Communications Conf., U.K., December, 1989,
`pp. 341—348. These papers addressed means for increas-
`ing the number of simultaneous users of a wireless com-
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`2
`munication system by allowing more than one user to
`use the same frequency, and exploiting the differences
`in directions-of-arrival at the receive antenna array to
`separate the different signals. However, they do not
`address the problem of increasing capacity in a broad—
`cast channel.
`
`Also in prior art, increasing capacity of point-to-point
`communication links using directional channels was
`claimed in R. Roy, et al., “Methods for Estimating
`Signal Source Locations and Signal Parameters Using
`an Array of Signal Sensor Pairs,” U.S. Pat. No.
`4,750,147, March 1985, U.S. Cl. 364—800, and R. Roy, et
`al., “Methods and Arrangements for Signal Reception
`and Parameter Estimation,” U.S. Pat. No. 4,968,732,
`July 1987, U.S. Cl. 364-460, and in a recent patent fil-
`ing, R. Roy, et al., “Spatial Division Multiple Access
`Wireless Communication Systems”, U.S. patent appli-
`cation Ser. No. 806,695, filed Dec. 12, 1991. Therein, no
`reference is made to the broadcast problem, and increas-
`ing broadcast channel capacity is not claimed in these
`patents. Moreover, in the first two referenced patents,
`arrays used therein are required to possess a special
`structure, i.e., sensors occur in pairs of identical ele-
`ments.
`
`Spatial processing has also been used in the context of
`spatial diversity techniques wherein multiple antennas
`that are employed for reception of broadcast signals are
`scanned for the strongest signal and its output chosen
`for further processing, or some method for combining
`the such outputs is applied. Though this leads to a im-
`provement in the quality of the received signal, there is
`no increase in system capacity.
`In prior art, increasing capacity of TV broadcast
`systems and in particular for HDTV where a severe
`bandwidth constraint exists, several patents have pro-
`posed use of plural/multiple channels to increase infor-
`mation transmission: M. A. Isnardi, et al., “Extended
`Definition Widescreen Television System Using Plural
`Signal Transmission” U.S. Pat. No. 4,888,641, October
`1988, US Cl. 358—141; T. Okano, “Multichannel Video
`Signal Transmission/Reproduction System” Japan Pa-
`tent 5,041,909, December 1987, US Cl. 358—146; E. L. J.
`Fonsalves, “System of Transmitting High-Definition
`Television Pictures via a Relatively Narrow Passband
`Channel, and Also a Transmitter and Receiver Suitable
`for the System”, U.S. Pat. No. 4,935,813, March 1988,
`U.S. CL. 358—138, W. F. Schreiber. “Definition Televi-
`sion Systems” U.S. Pat. No. 5,021,882, April. 1989, US
`Cl. 358—141. In W. F. Schreiber, “Reliable Television
`Transmission Through Analog Channels”, U.S. Pat.
`No. 5,040,211 October 1988, US Cl. 380—14, a system
`for spatially processing the acquired TV image, divid-
`ing it into spatiotemporal frequency components, fol-
`lowed by coding of the information prior to transmis-
`sion is disclosed. However, none of this prior art men-
`tions the use of spatial processing or directional chan-
`nels to increase capacity. The word channel in all the
`above cases refers to frequency channels, and multiple
`channels require additional spectrum. Reuse of the same
`frequency channel by transmitters at different spatial
`locations is unique to this invention.
`LIMITATIONS OF PRIOR ART
`
`The fundamental limitation of prior art is that it is
`constrained by the limited bandwidth of each channel
`and the number of available channels. The limited band-
`width constrains the rate at which information can be
`
`

`

`5,345,599
`
`3
`transferred to the users in each channel, and the number
`of available channels is the number of simulcast trans-
`missions possible. Current attempts to overcome the
`limited bandwidth problem primarily include data com-
`pression and efficient modulation. M. A. Isnardi et al.,
`“A Single Channel NTSC Compatible Widescreen
`EDTV System” Image Technology, April 1988, pp.
`118—119. Fukinuki et al., “Extended Definition TV
`Fully Comaptible with Existing Standards” IEEE
`Trans. COM-32, No.8, August 1984, pp.948—953. These
`methods try to alleviate the limited bandwidth problem
`by making the most effective use of the available band-
`width of the broadcast channel. However, due to enor-
`mous demands for increased definition (fidelity)
`in
`broadcast video, music, etc.,
`these compression and
`modulation techniques offer at best a temporary respite
`for the problem. A fundamentally new means of in-
`creasing effective transmission bandwidth is needed. (R.
`Hopkins,
`“Advanced Television Systems”,
`IEEE
`Trans. Consumer Electronics, February 1988, pp.
`l-15).
`Current proposals for improved broadcast services
`either use a combination of the above techniques or
`involve new spectrum allocation. For example,
`the
`proposed expansion of HF broadcast services involves
`changing from the current double sideband modulation
`standard to a more spectrally efficient single sideband
`modulation standard. In addition, a fresh allocation of
`spectrum (in the 5 to 26 Mhz band) is also planned.
`Another example of a severely constrained broadcast
`system is the proposed terrestrial digital HDTV stan-
`dard. Therein, a combination of data compression, effi-
`cient channel modulation and the allocation of limited
`
`additional spectrum (taboo channels) are all planned.
`Despite this, because of the very high data rate of high
`definition full-motion video, such a system may demand
`excessive transmission power thereby increasing the
`attendant simulcast and co-channel interference prob-
`lems in an attempt to keep the costs of digital HDTV
`receivers at reasonable (marketable) levels.
`Therefore, in view of the basic principle that broad-
`casting of information requires bandwidth, the funda-
`mental limitation of the amount of usable spectrum
`available has become a serious barrier to expanding the
`quality and capacity of wireless broadcast systems. As
`demonstrated over the last decade, the amount of prac~
`tically usable frequency spectrum cannot keep pace
`with the demand for new broadcast services. Thus there
`is a critical need for new technology to increase spec-
`trum utilization. The current invention directly ad-
`dresses this need.
`
`OBJECTS AND ADVANTAGES
`
`The present invention is directed to a method and
`apparatus for increasing information transmission ca-
`pacity or equivalently effective transmission bandwidth
`of wireless broadcast communication systems. The in-
`vention essentially consists of splitting a potentially
`high information rate source signal, whose frequency
`content may exceed the allocated channel bandwidth,
`into several low-rate signal components, and transmit-
`ting the low-rate components, each of which occupy
`some or all of the allocated bandwidth,
`in the same
`frequency channel from spatially separated transmitters.
`The transmitters radiate into the broadcast area on the
`
`same frequency (channel), and a plurality of antennas
`are used to receive the transmitted signals. Separation of
`the signals arriving in the same frequency channel, but
`
`4
`is performed. The different
`from different directions,
`transmitted signals are thus extracted, then combined to
`reconstruct the original high rate source signal. Thus,
`the broadcast information capacity is increased several
`fold without increasing the frequency bandwidth allo-
`cation. Unique to this invention is the transmission of
`different information signals in the same frequency band
`from spatially separated transmitters such that these
`cochannel signals arrive from distinct angles of arrival
`at the receiver. There, a multiplicity of antennas and
`appropriate spatial processing is used to separate the
`signals. The advantage of the Distributed-Transmit
`Directional-Receive (DTDR) system is that informa-
`tion can be transmitted to receivers at a higher rate in a
`prescribed frequency bandwidth than is possible in cur-
`rent state-of-the-art.
`
`One major application of the current invention is in
`the burgeoning field of high-definition television
`(HDTV). Though the invention is not restricted to this
`application, it forms an appropriate basis for a descrip-
`tion of the methods and apparatus of DTDR invention.
`In current state-of-the-art television broadcast systems,
`a finite amount of bandwidth has been allocated to the
`transmission of video information in each of many fre-
`quency channels. In the United States,
`the Federal
`Communications Commission (FCC) has licensed the
`use of radio frequency (RF) spectrum in 6 MHz chan-
`nels for the purpose of video transmission, an amount
`adequate for past and present television technology.
`However, recent advances in semiconductor and video
`display technology have made increased resolution
`economically viable. Unfortunately, increasing the res-
`olution over the current state—of-the-art requires trans-
`mission of more information.
`The objective in HDTV is to increase the horizontal
`and vertical resolution of full-motion Video and this
`leads to substantial increase in information rate in the
`
`the absence of information compression. To expand the
`transmission bandwidths of the current transmission
`systems would be incompatible with the broad installed
`base of current television systems. Therefore, introduc-
`tion and acceptance of HDTV into the US. market-
`place hinges on the ability to at least restrict the trans-
`mission bandwidth to be compatible witch the current
`state-of-the-art, i.e., 6 MHz. Since the current analog
`video transmission system occupies nearly all of the
`available bandwidth, increasing the bandwidth beyond
`that obtained by using the taboo channel is not accept-
`able; thus information compression is seen as a neces-
`sity. Since information compression is an exceedingly
`difficult task to perform on analog signals, most propo-
`nents of HDTV agree that the video source signal must
`first be digitized before attempting to remove redundant
`information (i.e., compressing it). This further exacer-
`bates the bandwidth problem since analog signals are
`inherently more bandwidth efficient than their digital
`(unencoded) counterparts. Coupled with the fact that
`for full-motion video at twice the current resolution to
`be acceptable the current screen refresh rate (30 MHz in
`the US.) must also be doubled, there is something of a
`data rate explosion prior to transmission. This explosion
`places severe requirements on the amount of lossless
`compression required to meet the bandwidth specifica-
`tions (A. Netravali et al., “A High Quality Digital
`HDTV Codec”, Proc. of 25th Asilomar Conf. on Cir-
`cuits, Sys. and Comp., November 1991, pp. 451—455).
`This will not only make such compression (and decom-
`pression in the receivers) extremely expensive, lossless
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`

`

`5,345,599
`
`6
`
`70.
`72.
`74.
`76.
`78.
`80.
`82.
`86.
`
`DTDR receive system
`receive antenna 1
`receive antenna 2
`receive antenna m
`antenna 1 output
`antenna 2 output
`antenna m output 84. m channel receiver front-end
`m receiver front-end outputs to spatial filters
`88. d channel spatial filters
`90. d spatial filter outputs to channel demodulators/de-
`coders
`92. d channel demodulators/decoders
`96. d demodulator/decoder outputs to combiner
`98. combiner
`
`100. estimated source stream (signal)
`102. terminal equipment
`110. tapped delay line connecting input 1 with summer
`1
`
`112. tapped delay line connecting input 1 with summer
`d
`
`20
`
`5
`compression is also very difficult to achieve and a full
`quality HDTV will be near impossible to develop. The
`availability of additional bandwidth will can greatly
`improve the cost and quality of HDTV system. The aim
`of the present invention is to provide such increased 5
`transmission bandwidth within the available channel
`bandwidth allocation.
`Though the advantages above have been described in
`the context of wireless HDTV broadcast, there are a
`number of other broadcast applications such as digital
`audio broadcast (DAB) services that can profit by this
`invention. Also the increased capacity made possible by
`this invention can be used for increasing the number of
`program channels in addition to increasing the defmi-
`tion (quality) of the broadcast channels. Further in-
`creased bandwidth can be traded for reduced transmit-
`
`10
`
`15
`
`improved signal quality, etc., as is well
`ted power,
`known in the state-of-the—art. Further objects and ad-
`vantages will become apparent from a consideration of
`the drawings and ensuing description of it.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`25
`
`30
`
`35
`
`FIG. 1 is a diagram of the DTDR invention indicat-
`ing the increased information transmission capacity
`obtained using distributed transmission and directional
`reception, a concept unique to this invention.
`FIG. 2 is an illustration a central broadcast studio that
`outputs multiple low rate signals that are communicated
`to spatially separated transmitters for radiation into the
`service area in the same frequency channel.
`FIG. 3 is an illustration of the high rate source signal
`being split into multiple low rate signals which are sent
`to the transmitting stations.
`FIG. 4 is an illustration of the operation of the trans-
`mitting stations.
`FIG. 5 is an illustration of the functionality of the
`receiving station wherein impinging signals are sepa-
`rated by exploiting the distinct directions-of-arrival.
`FIG. 6 is a diagram of the spatial filter that takes as
`inputs the m receive antenna signals and processes these 40
`to estimate the d distinct transmitted source signal com-
`ponents.
`FIG. 7 is a diagram of a system for transmitting multi-
`ple signals as a composite signal in accordance with the
`invention.
`
`45
`
`REFERENCE NUMERALS IN‘ DRAWINGS
`
`18.
`source equipment
`20.
`source stream (signal)
`22.
`transmission equipment at station 1
`24.
`transmission equipment at station 2
`26.
`transmission equipment at station d
`34.
`signal splitter
`36.
`transmit antenna 1
`38.
`transmit antenna 2
`40. transmit antenna d
`
`50
`
`55
`
`.
`50. broadcast studio
`52. signal substream from splitter to transmitting station
`1
`
`54. signal substream from splitter to transmitting station 60
`2
`
`‘56. signal substream from splitter to transmitting station
`d
`58. service area
`60. representative receiving station
`62. transmitting station 1
`64. transmitting station 2
`66. transmitting station d
`
`65
`
`114. tapped delay line connecting input In with summer
`1
`
`116. tapped delay line connecting input in with summer
`d
`
`120. connection from tapped delay line 1 input 1 to
`summer 1
`
`122. connection from tapped delay line 1 input m to
`summer 1
`124. connection from tapped delay line (1 input 1 to
`summer d
`
`126. connection from tapped delay line d input In to
`summer (:1
`140. summer 1
`142. summer (1
`146. weight adjustment circuit
`148. Signal sources
`150. Signal combiner
`152. Signal separator
`DETAILED DESCRIPTION
`
`.In this discussion, the following definitions are em-
`ployed. The term source equipment (18) includes all
`manner of information generating devices including but
`not limited to still or motion video camera (including
`HDTV cameras), audio microphones and amplifiers,
`computers with necessary hardware and software to
`generate graphics, sound, data, video/audio/data stor-
`age devices, etc.. The term carrier-to-interference ratio
`(C/I) refers to the ratio of the power of the desired
`signal from a given transmitting station to the total
`power of the undesired interfering signals from the
`other transmitting stations. The term source data stream
`(20) refers to any digital or analog signal generated by
`source equipment and which is to be transmitted to a
`plurality of receivers in the service area.
`
`DTDR—Description
`
`In the interest of clarity of exposition, it is assumed
`that the source stream (signal) is available in a digital
`format from the source equipment and likewise is deliv—
`ered to terminal equipment in a digital format. Other
`signal formats can also be used. Digital modulation of
`the wireless transmission is also assumed for the pur-
`poses of discussion. Again, analog modulation can also
`be employed.
`FIG. 1 is a diagram indicating the signal flow in one
`embodiment of the DTDR invention. A high band-
`width source signal (20) with a frequency bandwidth in
`
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`5,345,599
`
`7
`excess of the channel bandwidth (B) is decomposed by
`a signal splitter (34) into d signal components (52,56),
`each with frequency bandwidth less than or equal to B
`and broadcast into a service area on the same frequency
`channel of bandwidth B, where it is received by a plu-
`rality of users. An m—element antenna array receives d
`signals and a directional receiver (70) separates these
`signals that arrive at different angles-of-arrival and re-
`covers the .d signal components (96) which are then
`assembled in a combiner (98) to reconstruct the esti-
`mated source signal (100). This diagram illustrates that
`increased information transmission capacity is obtained
`using distributed transmission and directional reception.
`FIG. 2 shows the overall scenario of the central
`broadcasting studio (50), d transmitting stations (62, 64,
`66) and a representative receiving station (60). The
`system can effectively broadcast a high data rate signal
`using a low capacity channel by reusing this frequency
`channel through exploitation of the differences in direc-
`tions between a receiving station and the transmitting
`stations. The service area (58) is that geographical area
`served by the broadcast system. The (1 low rate data
`streams generated in the broadcast studio are sent to the
`transmitting stations using state-of-the-art point-to-
`point communication techniques.
`FIG. 3 shows the generation of the high rate source
`stream (20) by the source equipment (18) and its decom-
`position (splitting) into multiple low rate substreams. In
`one embodiment, the signal splitter is a simple d-way
`demultiplexer.
`In other embodiments, coding tech-
`niques established in current state-of-the-art can be used
`to improve robustness to channel errors. The d signal
`substreams (52, 54, 56) output by the signal splitter are
`then communicated to the d remote transmitting sta-
`tions.
`
`FIG. 4 shows spatially separated transmitting stations
`(62, 64, 66) where the substreams received from the
`studio are processed by the transmission equipment (22,
`24, 26), then coupled to the transmit antennas (36, 38,
`40) for transmission into the service area. The functions
`of the transmission equipment include channel coding,
`modulation and front—end processing and these methods
`are well established in the state-of-the-art. All transmit-
`ters radiate their different substreams in the same fre-
`quency channel. If several program channels are to be
`broadcast simultaneously, each program channel will
`use a different frequency channel as is done in current
`state-of-the-art.
`
`FIG. 5 shows operation of a representative receiving
`station. A receiving station located within the service
`area will receive all d signals in the same frequency
`channel. Receiving stations use a receive antenna array
`that contains in subarrays (or elements) (72, 74, 76). The
`number of subarrays m must be equal to or greater than
`(1, the number of transmitters. In one embodiment, the
`antenna array consists of m V/UHF Yagi antennas as
`the individual subarrays is located on the roof of a
`dwelling with suitable separation and arranged so that
`each subarray points to a different transmitting station.
`The outputs of the m subarrays/antennas (78, 80, 82)
`are sent to a set of m receiver front-ends (84). The term
`receiver front-end refers to the unit which contains the
`amplifier, filler, and frequency downconverter, etc.
`These receiver front-ends are well established in the
`current state-of-the-art.
`
`The m receiver front-end outputs (86) are input to the
`spatial filter (88) which uses these m signals to estimate
`the d separate impinging signals. The spatial filter con-
`
`10
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`15
`
`20
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`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`8
`sists of d processing channels (one for each transmitted
`signal) where each of these selectively pass one desired
`signal while rejecting other interfering signals,
`The d spatial filter outputs signals (90) are now pro-
`cessed by the d-channel demodulator and decoder (92)
`that first demodulates the signals to obtain the digital
`data streams which are then decoded to generate the d
`substreams that correspond to those output by the sig-
`nal splitter at the broadcasting studio. These methods
`are well established in the state-of-the—art.
`The demodulator outputs (96) are fed to the combiner
`(98) where these d streams are merged. In one embodi-
`ment, the combiner is simply a d-way multiplexer. In
`another embodiment where coding is employed in the
`signal splitter, the combiner must perform the appropri—
`ate decoding. These methods are well established in the
`current state-of-the-art.
`The combiner output (100) is then sent to the terminal
`equipment (102) which includes all manner of informa-
`tion signal sinking devices such as TV receivers (includ-
`ing HDTV), audio receivers, computers, and other such
`equipment which can exploit the received source data
`stream.
`
`FIG. 6 is a diagram of one embodiment of the spatial
`filter (88). Therein, the m signals (86) received from the
`receiver front-ends are separated into the d distinct
`transmitted components. In this embodiment, there are
`d spatial filter channels each accepting the same In in-
`puts and operating on these with (1 single or multitap
`tapped delay line filters (110,112,114,116) with adjust-
`able weights and whose outputs are then added in sum-
`mers (140,142).
`to yield the d desired outputs. The
`weight adjustment circuit (146) uses apriori informa-
`tion, input and output signals of the spatial filter to
`determine the optimum weights. The d outputs of the
`spatial filter are sent to the demodulator/decoder for
`further processing. Techniques for spatial filtering that
`selectively receive a signal arriving at an antenna array
`from a specified direction while rejecting interfering
`signals arriving from other directions are well known in
`the current state-of-the-art and include optimum beam-
`forming, interference rejection, adaptive hulling, etc..
`See several texts including R. T. Compton, “Adaptive
`Arrays: Concepts and Performance”, Prentice Hall,
`1988; R. A. Monzingo and T. W. Miller, “Introduction
`to Adaptive Arrays”, John Wiley, 1980; for techniques
`to construct such spatial filters for various signal and
`antenna types.
`FIG. 7 is a diagram of another embodiment of the
`invention in which signals A, B, C from independent
`sources 148 are combined at 150 and then transmitting
`using the flow diagram of FIG. 1. The combined re-
`ceived signals are then separated into the signals A, B,
`and C. As noted above, this embodiment of the inven-
`tion increases the definition (quality) of the broadcast
`channels. In this embodiment, increased bandwidth is
`traded for reduced transmitting power and improved
`signal quality for each of the signals A, B, and C.
`OPERATION OF THE INVENTION
`
`Definitions
`
`65
`
`In this discussion, the following definitions are em-
`ployed. The term steering vector refers to the vector of
`receiver outputs (appropriately normalized) which re-
`sult from a single signal impinging on the antenna array.
`The steering vector is a function of the direction-of-
`arrival of the signal. The term array covariance refers to
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`5,345,599
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`9
`the covariance matrix formed from outer products of
`the antenna array outputs. The term array characteriz-
`ing data refers to the set of data that characterizes the
`array’s spatial environment, and includes the set of all
`steering vectors, the array covariance, and other data
`such as the ambient noise covariance matrix commonly
`used in spatial filtering.
`DTDR—The Invention
`
`Again, digital signals and digital modulation is as-
`sumed. The methods of this invention are also applica-
`ble to analog signals and analog modulation as well
`however.
`The essential elements of the DTDR operation is as
`follows:
`
`1. The source equipment (18) generates the high rate
`source stream (20) after suitable data compression.
`2. This source data stream is input to splitter (34) where
`it is split into (1 substreams, each at a lower bitrate
`than the source stream.
`
`3. The signal splitter outputs (52, 54, 56) are communi-
`cated one each to the d transmitting stations (62, 64,
`66) by d links using any state-of-the-art point-to-point
`communication technique.
`4. At each of the transmitting stations (62, 64, 66), the
`corresponding substream received from the studio is
`input
`to the transmission equipment
`(22, 24, 26)
`where it is processed in the channel encoder, modula-
`tor and the transmit front-end for broadcasting into
`the service area. All transmitters use the same as-
`signed frequency channel, and can use the entire
`allocated bandwidth of this channel.
`
`5. All C] cochannel transmitted signals are received by
`each of the multiplicity of receiving stations within
`the service area. At a representative receiving station
`(60), an antenna array consisting of m subarrays or
`elements (72,74, 76) receives the d impinging signals.
`6. Each of the in subarray outputs (78, 80, 82) will con-
`tain a mixture of all the d impinging signals p