Title of Invention

A DIGITAL BROADCAST SYSTEM FOR TRANSMITTING A BROADCAST SIGNAL, A TERRESTRIAL REPEATER FOR RETRANSMITTING SATELLITE SIGNALS TO RECEIVERS, METHOD FOR TRANSMITTING BROADCAST SIGNAL TO A RECEIVER AND RECEIVER FOR RECEIVING BROADCAST SIGNAL

Abstract A digital broadcast system is provided which uses a satellite direct radio broadcast system (22) having different downlink options in combination with a terrestrial repeater (18) network employing different re-broadcasting options to achieve high availability reception by mobile radios (14), static radios and portable radios (14) in urban areas, suburban metropolitan areas, rural areas, including geographically open areas and geographic areas characterized by terrain having high elevations. Two-arm and three-arm receivers (14) are provided which each comprise a combined architecture for receiving both satellite and terrestrial signals, and for maximum likelihood combining of received signals for diversity purposes. A terrestrial repeater (18) is provided for reformatting a TDM satellite signal as a multicarrier modulated terrestrial signal. Configurations for indoor and outdoor terrestrial repeaters are also provided.
Full Text The present insertion relates to a digital broadcast system and method for
transmitting broadcast signal, terresterial repeater, and receiver for receiving broadcast
signal. This application is divided from Indian Patent Application No. 805/CAL/98
(hereinafter referred to as "parent application").
Field of Invention
A digital broadcast system is provided which uses a satellite direct radio
broadcast system having different downlink options in combination with a terrestrial
repeater network employing different re-broadcasting options to achieve high
availability reception by mobile radios, static radios and portable radios in urban areas,
suburban metropolitan areas, rural areas, including geographically open areas and
geographic areas characterized by terrain having high elevations.

Background of the Invention
Receivers in existing systems which provide digital audio radio service (DARS)
have been radically effected by multipath effects which create severe degradations in
signal quality, such as signal fading and inter-symbol interference (ISI). Fading effects
on broadcast channels to receivers can be sensitive to frequency, particularly in an urban
environment or geographic areas with high elevations where blockage of line of sight
(LOS) signals from satellites is most prevalent. Locations directly beneath a satellite
(hereinafter referred to as the sub-satellite point) inherently have the highest elevation
angles, while locations that depart from the sub-satellite point inherently have
decreasing elevation angles and, accordingly, an increase of the earth center angle
subtended between the sub-satellite point and the reception location. Locations that are
near the sub-satellite point typically enjoy virtually unblocked LOS reception. Thus,
the need for terrestrial reinforcement of potentially blocked LOS signals is minimal.
When the LOS elevation angle to the satellite becomes less than about 85 degrees,
however, blockage by tall buildings or geological elevations (i.e., on the order of 30
meters) becomes significant. Terrestrial re-radiation for gap filling is needed to achieve
satisfactory coverage for mobile radios, static radios, as well as portable radios. In areas
where the heights of buildings or geological sites are relatively low (i.e., on the order of
less than 10 meters), the blockage is not significant until the LOS elevation angle is
lower than 75 degrees. Thus, at the mid-latitude and high latitude locations within the
coverages of one or more broadcast satellites, terrestrial re-radiation is needed to achieve
suitable radio reception. A need exists for fully satisfactory radio reception that
combines satellite LOS transmission and terrestrial re-radiation of a satellite downlink
signal waveform.
Summary of the Invention
In accordance with one aspect of the present invention, a digital broadcast
system (DBS) is provided which overcomes a number of disadvantages associated with
existing broadcast systems and realizes a number of advantages. The DBS of the present
invention comprises a TDM carrier satellite delivery system for digital audio broadcasts

(DAB) which is combined with a network of terrestrial repeaters for the re-radiation of
satellite downlink signals toward radio receivers.
In accordance with another aspect of the present invention, a single
geostationary satellite transmits downlink signals which can be received by radio
receivers in the LOS of the satellite signal, as well as by terrestrial repeaters. Each
terrestrial repeater is configured to recover the digital baseband signal from the satellite
signal and modulate the signal using multicarrier modulation (MCM) for retransmission
toward radio receivers. Radio receivers are configured to receive both a quadrature
phase shift keyed (QPSK) modulated TDM bit stream, as well as an MCM stream.
Radio receivers are programmed to select a broadcast channel demodulated from the
TDM bit stream and the MCM bit stream, and to select the broadcast channel recovered
with the least errors using a diversity combiner.
In accordance with still another aspect of the present invention, a DBS system is
provided which comprises two geostationary satellites in combination with a network
of terrestrial repeaters. The terrestrial repeaters are configured to process satellite
downlink signals to achieve the baseband satellite signal and to modulate the signal
using MCM. Radio receivers are configured to implement a diversity decision logic to
select from among three diversity signals, including the two satellite signals and the
MCM signal. Each radio receiver employs maximum likelihood combining of two LOS
satellite signals with switch combining between the terrestrial re-radiated signal, or
MCM signal, and the output of the maximum likelihood combiner.
In accordance with another aspect of the present invention, a broadcast channel
may be selected from the three diversity signals by using maximum likelihood
combining of all three signals, that is, early and late LOS satellite signals and the MCM
signal from the terrestrial repeater.

Accordingly, the present invention provides a digital broadcasting system for transmitting a
broadcast signal, said broadcast signal being transmitted from an earth station, comprising : a satellite for
receiving said broadcast signal from said earth station and for transmitting a satellite signal comprising
said broadcast signal on a first carrier frequency; and a terrestrial repeater for receiving said satellite signal
and for generating and transmitting a terrestrial signal from said satellite signal comprising said broadcast
signal on a second carrier frequency that is different from said first carrier frequency to enable a radio
receiver configured to receive said satellite signal and said terrestrial signal to employ diversity combining
to generate an output signal from at least one of said satellite signal and said terrestrial signal, said
terrestrial signal being modulated by said terrestrial repeater in accordance with a multipath-tolerant
modulation technique.
The present invention further provides a terrestrial repeater for retransmitting satellite signals to
radio receivers comprising : a terrestrial receiver for receiving said satellite signals ; and a terrestrial
waveform modulator for generating terrestrial signals from said satellite signals, said terrestrial signals
being modulated by said terrestrial waveform modulator in accordance with multicarrier modulation ;
wherein said satellite signals are transmitted from a satellite using a first carrier frequency, and said
terrestrial waveform modulator is operable to transmit said terrestrial signals to said radio receivers using a
second carrier frequency that is different from said first carrier frequency to enable said radio receivers to
employ diversity combining to generate an output signal from at least one of said satellite signals and said
terrestrial signals.
The present invention also provides a receiver for receiving a broadcast signal in a combined
satellite and terrestrial digital broadcasting system, comprising : a first receiver arm for receiving a first
satellite signal transmitted from a first satellite on a first carrier frequency, said first satellite signal
comprising said broadcast signal and being modulated in accordance with at least one of time division
multiplexing and code division multiplexing, said first receiver arm comprising a demodulator for
recovering said broadcast signal; a second receiver arm for receiving a terrestrial signal transmitted from
a terrestrial station on a second carrier frequency, said terrestrial signal being generated at the terrestrial
station from a received said broadcast signal that has been modulated in accordance with at least one of

adaptive equalized time division multiplexing, coherent frequency hopping adaptive equalized time
division multiplexing, code division multiplexing and multicarrier modulation prior to transmission via
said second carrier frequency, said second receiver arm comprising a demodulator for recovering said
broadcast signal ; and a combiner for generating an output signal from at least one of said first satellite
signal and said terrestrial signal.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
These and other features and advantages of the present invention will be more readily
comprehended from the following detailed description when read in connection with the appended
drawings, which form a part of this original disclosure, and wherein :

Fig. 1 depicts a digital broadcast system for transmitting satellite signals and
terrestrial signals in accordance with an embodiment of the present invention;
Fig. 2 is a diagram of a digital broadcast system comprising a satellite and a
terrestrial repeater in accordance with an embodiment of the present invention;
Fig. 3 is a schematic block diagram illustrating a generation of a multicarrier
modulated (MCM) signal in accordance with an embodiment of the present invention;
Fig. 4 is a schematic block diagram depicting a radio receiver arm configured to
demodulate MCM signals in accordance with an embodiment of the present invention;
Fig. 5 is a block diagram illustrating MCM signal demodulation in accordance
with an embodiment of the present invention;
Fig. 6 is a schematic block diagram depicting a radio receiver arm configured to
demodulate time division multiplexed (TDM) signals in accordance with an
embodiment of the present invention;
Fig. 7 is a block diagram illustrating QPSK TDM signal demodulation in
accordance with an embodiment of the present invention;
Figs. 8 and 9 are schematic block diagrams illustrating respective embodiments
of the present invention for diversity combining in a radio receiver;
Fig. 10 illustrates a system of combining three diversity signals using a maximum
likelihood decision unit in accordance with an embodiment of the present invention;
Fig. 11 is a schematic block diagram illustrating TDM signal demultiplexing in
accordance with an embodiment of the present invention;
Fig. 12 illustrates a system of combining bit streams recovered at a radio receiver
using a maximum likelihood decision unit on a first satellite signal and a delayed second
satellite signal and then a diversity combiner for terrestrial repeater signal and the
output of the maximum likelihood decision unit in accordance with an embodiment of
the present invention;
Fig. 13 illustrates an arrangement for indoor reception of a broadcast signal in
accordance with an embodiment of the present invention; and
Fig. 14 illustrates an arrangement for terrestrial repeaters along a path in
accordance with an embodiment of the present invention.

Detailed Description of the Preferred Embodiments
Fig. 1 depicts a digital broadcast system (DBS) 10 comprising at least one
geostationary satellite 12 for line of sight (LOS) satellite signal reception at radio
receivers indicated generally at 14. Another geostationary satellite 16 at a different
orbital position can be provided for time and/or spatial diversity purposes as discussed
below in connection with Figs. 6 and 7. The system 10 further comprises at least one
terrestrial repeater 18 for retransmission of satellite signals in geographic areas 20 where
LOS reception is obscured by tall buildings, hills and other obstructions. The radio
receiver 14 is preferably configured tor dual-mode operation to receive both satellite
signals and terrestrial signals and to select one of the signals as the receiver output.
As stated previously, the present invention relates to a DBS 10 for optimized
static, portableand mobile radio reception. In accordance with the present invention,
the DBS 10 combines line-of-sight (LOS) reception of satellite waveforms that are
optimized for satellite delivery with re-radiation of the LOS signal from the satellite 12
or 16 via one or more terrestrial repeaters 18. The terrestrial repeaters 18 use other
waveforms which are optimized for terrestrial delivery where blockage of the satellite
LOS signal occurs. LOS signal blockage caused by buildings, bridges, trees and other
obstructions typically occurs in urban centers and suburban areas. Waveforms
particularly suitable for LOS satellite transmission are Time Division Multiplex (TDM)
and Code Division Multiple Access (CDMA). Waveforms particularly suitable for
overcoming terrestrial multipath interference encountered in blocked urban areas are
Adaptive Equalized TDM (AETDM), Coherent Frequency Hopping Adaptively
Equalized TDM (CFHATDM) and Multiple Carrier Modulation (MCM).
Frequency hopping is described in U.S. Patent No. 5,283,780, to Schuchman et
al, which is hereby incorporated herein by reference. When a terrestrial repeater 18
employs AETDM, radio receivers 14 are provided with an equalizer (not shown). For
AETDM, a TDM bit stream is received, from the satellite 12 or 16. The bit stream is
converted into a new TDM bit stream into which training sequences are inserted by a
process called puncturing. Puncturing replaces a small traction of the TDM data bits
with the training sequences. The number of bits punctured is so small that the errors
thereby produced are correctable at the receiver by forward error correction. The new

TDM bit stream is QPSK-modulated by the repeater onto a radio frequency (RF) carrier
that is transmitted at high power into the multipath environment of a central city
business district, for example. This transmitted signal is received by a receiver 14
equipped with an adaptive time domain equalizer. By using the training sequences, it
can adjust the taps of an inverse multipath processor to cause the various multipath
arrival components to add constructively. The signal thus reconstructed is next
processed to recover the bits of the TDM stream with high accuracy. The forward
error correction available in the receiver 14 corrects both the errors introduced by the
puncturing and those caused by thermal noise and receiver impairments.
In accordance with another aspect of the present invention, the combination of a
satellite-efficient LOS waveform and terrestrial multipath interference-tolerant
waveform in a DBS system is the optimum means for achieving high availability
reception by mobile radios, static radios and portable radios in urban areas, suburban
areas and in rural areas. For example, in accordance with an embodiment of the present
invention illustrated in Figs. 2-9, an MCM signal is sent from a network of terrestrial
repeaters 18 deployed to cover a blocked area with high reception availability. The
signaling techniques described in connection with the present invention are applicable
over the electromagnetic wave frequency range from 200 to 3000 MHz to facilitate the
combination of LOS satellite radiation with terrestrial re-radiation of the signal received
from the satellite 12 or 16.
Optimal satellite waveforms permit very efficient transformation of solar power,
which is collected by the solar arrays of the satellites 12 and 16 into radiated radio
frequency power. These waveforms are characterized by a low peak-to-average power
ratio (i.e., crest factor), thereby permitting operation of high power amplifiers that feed
the satellite earth-pointing antennas at or near the maximum power output and
therefore the most efficient power output. A TDM waveform is particularly useful for
permitting operation within a few tenths of a dB of maximum power output. A CDMA
waveform that uses properly selected codes allows operation at approximately 2 to 4 dB
below maximum power output. Because the MCM waveform is composed of the sum of
hundreds ot pnase modulated sinusoids, as described below with reference to Fig. 3, the
MCM waveform inherently possesses a high peak-to-average ratio. Consequently, a

MCM waveform encounters significantly greater amplitude and phase intermodulation
distortion in the satellite's high power amplifier. To achieve acceptable reception by an
LOS satellite receiver, a MCM waveform is backed in the high power amplifier and
allocated a receiver implementation impairment of at least 6 dB on the down-link
budget, as compared with a quadrature phase shift keying (QPSK) TDM waveform.
This translates to a 4-to-1 reduction in satellite power conversion, rendering the MCM
waveform an unsuitable choice for satellite LOS delivery on a DBS 10. Regarding the
ATDM and CFHATDM waveforms, these waveform are specifically designated to
combat terrestrial multipath and are not intended for, nor are they efficient for satellite
LOS delivery.
Regarding terrestrial reinforcement by re-radiation of the satellite LOS signal
from a terrestrial repeater, for example, a TDM waveform is not suitable because its
reception is severely impaired by multipath effects. Furthermore, some proposed
systems which use CDMA waveforms for reinforcement repeat the same program signal
using one CDMA channel code for LOS satellite delivery and another CDMA channel
code for terrestrial re-radiated delivery on carriers that occupy the same frequency
bandwidth. Reception is achieved by means of adaptive rake receivers. These proposed
CDMA systems are disadvantageous because an annulus zone occurs in which reception
is not possible between the region where the reinforcement signal can be received and
the region where the satellite LOS signal can be received. Receivers 14 in the annulus
are not able to receive the terrestrial re-radiated signal because the signal power level
falls below a receiver threshold for that signal. These receivers 14 are also not able to
receive the satellite LOS signal because there remains sufficient re-radiated signal to jam
LOS satellite reception. Thus, these receivers 14 in the annulus must move far enough
away from the zone of re-radiation to decrease the re-radiated signal power to below the
threshold of jamming; otherwise, LOS satellite reception is not possible.
In accordance with one embodiment of the present invention, the CDMA
waveform is adapted to make possible its use for simultaneous delivery via satellite LOS
and via terrestrial re-radiation. The CDMA channel codes are assigned for each delivery
to different RP carriers. The orthogonality thereby created permits the two signals (i.e.,

the satellite LOS signal and the terrestrial repeater signal) to be separated by RF/IF
filtering in the radio receiver.
The identification of workable and unworkable waveform combinations for
accomplishing terrestrial reinforcement of satellite LOS reception in accordance with
the present invention are listed in the TABLE 1.
TABLE 1

AETDM waveforms can be satisfactorily implemented and operated in
multipath environments characterized by signal propagation delays as long as 20
microseconds (µs). Care must be exercised to ensure that signal arrivals from distant
repeaters 18 do not exceed this bound. The adaptively equalized re-radiated waveform
can be received by radio receivers 14 designed to use the parent non-equalized TDM
waveform when the former does not exhibit severe multipath. This compatibility
prevents obsolescence of direct LOS non-equalized TDM radios when the AETDM re-
radiation is turned on.
The CFHATDM waveform can be satisfactorily implemented and operated in
multipath environments characterized by delays as long as 65 µs. Care must be exercised
to ensure that signal arrivals from distant repeaters 18 do not exceed this bound. The

waveform cannot be received by radio receivers 14 designed to use the parent non-
equalized TDM waveform.
The MCM waveform can be satisfactorily implemented and operated in
multipath environments characterized by delays as long as 65 µs. The maximum delay is
affected by the guard time assignment given to the waveform's periodic symbol period
assignment. Care must be exercised to ensure that signal arrivals from distant repeaters
18 do not exceed this bound. The waveform cannot be received by radio receivers 14
designed to use the parent non-equalized TDM waveform.
The CDMA waveform can be satisfactorily implemented and operated in
multipath environments characterized by delays determined by the span of the time
delays implemented in the rake paths at the receivers 14. Care must be exercised to
ensure that all signal arrivals from distant repeaters 18, multipath reflections and
different satellites do not exceed this bound. The waveform cannot be received by radio
receivers 14 designed to use the parent non-equalized TDM waveform.
The satellite signals can be transmitted from one satellite 12 or 16 or from two
satellites 12 and 16. Use of two geostationary satellites 12 and 16 sufficiently separated
in their orbits creates diversity in the LOS elevation and azimuth angles to enhance
signal reception availability. Also, time diversity achieved by repeating a satellite signal
from a single satellite 12 or 16, or by transmitting a signal from two satellites 12 and 16
with the properly selected time difference, further enhances the reception availability.
In accordance with a preferred embodiment of the present invention, a
waveform comprising multiple channel TDM with QPSK, Offset QPSK, Differential
QPSK, Differentially Coded QPSK, or Minimum Shift Keyed (MSK) modulation is
used for the transmission of signals from a satellite for LOS reception by a radio
receiver 14. Terrestrial re-radiation is preferably implemented using an MCM
waveform designed to carry a TDM bit stream of a capacity of up to 3.68 Mbit/s.
MCM is preferably implemented which creates between 400 and 1200 multiple carriers
by means of an Inverse Fast Fourier Transform as described below in connection with
Fig. 3, resulting in a symbol period between 200 and 300 µs. A guard interval of
between 55 to 65 microseconds is included in each symbol period. The MCM
waveform is designed to accommodate Doppler carrier frequency shifts among

multipath components occurring simultaneously. Puncturing is preferably used to
eliminate bits or pairs of bits from the TDM bit stream to reduce the rate to a value of
between 70% to 80% of the 3.68 Mbit/s rate. A special symbol is inserted between each
of a selected number of FFT-generated symbols periods to provide a means to recover
symbol period timing and carrier frequency synchronization . In the receiver 14, a
Viterbi soft decision trellis decoder is preferably implemented to re-establish the bits or
bit pairs punctured at the repeater 18, as well as all other bits transmitted, by use of an
erasure technique. In this technique, the decoder simply ignores the bits in locations
known to have been punctured at the repeater 18.
TDM carrier satellite delivery of the DBS 10 is discussed in U.S. Patent
Specification No. 6,201,798,— the entire subject matter of which is hereby
incorporated herein by reference for all purposes. Briefly, with reference to Fig. 2, the
broadcast segment 22 preferably includes encoding of a broadcast channel into a 3.68
Megabits per second (Mbps) time division multiplex (TDM) bit stream, as indicated in
block 26. The TDM bit stream comprises 96 16 kilobits per second (kbps) prime rate
channels and additional information for synchronization, demultiplexing, broadcast
channel control and services. Broadcast channel encoding preferably involves MPEG
audio coding, forward error correction (FEC) and multiplexing. The resulting TDM
bit stream is modulated using quadrature phase shift keying (QPSK) modulation, as
shown in block 28, prior to transmission via a satellite uplink 30.
TDM satellite delivery achieves the greatest satellite on-board payload efficiency
possible in terms of the conversion of solar power to electromagnetic wave power. This
is because single TDM carrier per tube operation permits each satellite traveling wave
tube to operate at its saturated power output, which is its most efficient operating point.
The TDM carrier in a typical application is designed to deliver 96 prime bit rate
increments, each bearing 16 kbit/s, to small, economical radio receivers 14 located in
the beams of the satellite 12 or 16. From one to eight prime rate increments are
grouped to constitute a broadcast channel. A broadcast channel can be divided into a
number of service channels for delivery of audio, video, data and multimedia.
The power density delivered to the earth by TDM carriers from satellites 12 and
16 can made very high and hence provide excellent LOS reception by radio receivers 14

in automobiles and trucks when traveling on open highways in the country side and in
suburban areas. However, in urban areas where tall buildings abound, or in forests
where tall towering damp foliage trees abound, LOS reception is blocked, thus
inhibiting suitable operation of the receiver 14 for LOS reception. Attempting to
overcome these conditions by raising the satellite power is both excessively expensive
and technically impractical. Accordingly, a more practical alternative is to augment the
direct LOS satellite reception by adding a network of terrestrial repeaters 18.
Concerning the nature of the blockage of LOS reception consider the following.
Locations directly beneath the satellite 12 or 16 (i.e., the sub-satellite point) inherently
have the highest elevation angles, while locations that depart from the sub-satellite point
inherently have decreasing elevation angles and an increase of the earth center angle
subtended between the sub-satellite location and the reception location. Receivers 14 at
locations that are near the sub-satellite point are permitted virtually unblocked LOS
reception and the need for terrestrial reinforcement is minimal. However, when the
LOS elevation angle to the satellite becomes less than about 85 degrees, blockage by tall
buildings (i.e., >30 m) becomes significant. Accordingly, terrestrial re-radiation for
gap-filling is needed to achieve satisfactory coverage for mobile radio receivers. In areas
where building heights are low (e.g., LOS elevation angle is lower than 75 degrees. At the mid-latitude and high latitude
locations within the 6 degree beam width coverages of the satellites 12 and 16, terrestrial
re-radiation of the TDM waveform is needed to achieve suitable mobile reception.
Thus, fully satisfactory mobile reception requires a system that combines satellite LOS
and terrestrial re-radiation of the satellite waveform.
The DBS 10 of the present invention re-radiates the LOS satellite signal from a
multiplicity of terrestrial repeaters 18 which are judiciously spaced and deployed within
the central part of a city, as well as in metropolitan areas and suburban areas, to achieve
maximum coverage. This type of deployment is a recognized art for terrestrial digital
audio broadcast (DAB) and cell telephone systems, and can be extended in accordance
with the present invention to terrestrial re-radiation of the TDM satellite LOS signal.
The deployment utilizes a mix of radiated power levels (EIRP) ranging from as little as
1 to 10 watts for short range fill-in repeaters 18 (out to 1 km radius) to as great as 100 to

10,000 watts for re-radiators or repeaters having wide area coverage (from 1 km to 10
km radius).
Two preferred embodiments for a DBS 10 having a satellite-LOS/terrestrial-re-
radiation configuration are described below. The first embodiment involves one
geostationary orbit (GSO) satellite 12 or 16 having a judiciously selected longitude along
the GSO arc which operates in coordination with a network of the terrestrial repeaters
18. The second embodiment involves two satellites 12 and 16 having different
judiciously spaced GSO longitudes to achieve space and time diversity.
The embodiment for a DBS 10 using one GSO satellite 12 with at least one
terrestrial repeater 18 is shown in Fig. 2 for illustrative purposes. For each terrestrial
repeater 18, the LOS satellite signal is received by an antenna 32 operating in
conjunction with a radio receiver 34 to demodulate and recover the digital baseband
signal from the signal radiated from the satellite 12. The digital baseband signal is
supplied to a terrestrial waveform modulator 36 that generates a waveform which is
judiciously designed to make possible the recovery of the digital baseband signal after
the waveform has been transmitted from the terrestrial repeater 18 and received by a
radio receiver 14. The modulated waveform is then frequency translated to a carrier
frequency and amplified, as indicated by block 38. The terrestrial re-radiated waveform
is specifically chosen to withstand the dynamic multipath encountered over the
terrestrial path between the transmitter antenna 40 and the receiver 14. This multipath
is caused by reflections and diffractions from and around obstacles such as buildings 44
and terrain and from troposphere wavebending and reflections.
The antenna 32 is designed to have high gain (> 10dBi) toward the satellite 12,
while achieving low gain in other directions such that the LOS signal is received with
low interference and consequently very high quality (i.e. error rate demodulator and other reception elements in the receiver 34 are those designed for the
LOS radio receivers 14 used in the DBS 10 and described in the aforementioned
U.S. Patent No. 6,201,798. The radio receivers 18 are
designed to receive the 3.68 Mbit/s QPSK modulated TDM bit stream. As stated
previously, the digital baseband is preferably a 3.68 Mbit/s digital waveform TDM bit
stream that carries 96 16 kbit/s prime bit rate digital channels organized into broadcast

channels, and side information needed to synchronize, demultiplex and control the
broadcast channels and the services they bare. The terrestrial waveform modulator 36
and the waveform that it generates is designed to allow reception unimpeded by the
multipath vagaries indicated at 42 of the terrestrial path as described previously.
Possible multipath-tolerant waveforms are adaptive equalized TDM, adaptive equalized
multiple carrier frequency hoppers with adaptive equalization, Fast Fourier Transform
multiple carrier modulation and CDMA with rake receivers. The repeater 18 is
equipped to assemble the multipath-tolerant waveform, to frequency convert the
waveform to the desired re-radiator transmitter RF frequency at the selected power
level via the RF translator 38, and to radiate the waveform from antenna 40. The
antenna 40 is preferably configured to provide omni-directional or sector directional
propagation in the horizontal plane and high directive toward the horizon. The net
antenna gain is expected to range from 10 to 16 dBi. The antenna 40 can be located on
top of a building and/or on a tower at a desired height. As previously mentioned, the
radiated power level can range from 1 to 10,000 watts of EIRP depending on the
application.
A particularly desirable multipath-tolerant re-radiated waveform uses
multicarrier modulation (MCM). The manner in which the waveform is generated is
shown in Fig. 3. A digital stream such as the 3.68 Mbit/s TDM stream is time-domain-
divided into a number of parallel paths (block 102), for example, 460 parallel paths with
each parallel path carrying 8000 bits per second. The bits on each of these paths are
paired into 2 bit symbols with one bit identified as the I (imaginary) component and the
other as the Q (Real) component of a complex number. This creates a complex symbol
rate of 4000 per second. These bits are fed as 460 parallel complex number frequency
coefficient inputs to a Discrete Inverse Fourier Transform converter implemented using
a 512 coefficient Inverse Fast Fourier Transform (EFFT) 104. It is well known in the
current state of the art that the Fast Fourier Transform algorithm must operate with 2n
input and output coefficients where n is any integer. Thus, for n = 9, 29 = 512. Since
the number of coefficients is 460, the remaining 52 missing input coefficients are set
equal to zero. This is done by assigning 23 zero-valued coefficients at each the
uppermost and lower most IFFT inputs, thus leaving the 460 center coefficients assigned

to non-zero values. The output 104 of the IFFT is a set of 460 QPSK-modulated,
orthogonal sine coefficients which constitute 460 narrow band orthogonal carriers, each
supporting a symbol rate of 4000 per second and consequently having a symbol period
of 250 µs. No carriers appear at the output of the IFFT 104 for the coefficients that are
set equal to zero.
The IFFT multicarrier output 104 is further processed to create a guard interval
105 for the set of 460 complex symbol narrow band orthogonal carriers (block 106). It
is assumed that a fraction f of a symbol period Ts is to be allocated to guard time. To do
this the symbol duration must be reduced to a value Ts = (1-f) Ts. For the example
considered above Ts = 250 µs. If 25 % of the symbol time is to be allocated guard time,
then f =0.25 and Ts = 187.5 µs. To do this, the symbol period output of the IFFT is
stored in a memory every 250 µs and then played back in 187.5 µs. To fill the 250 µs
symbol interval, the first samples of the IFFT output are again played back during the
62.5 µs guard interval. This procedure causes an increase in the bandwidth of the
multicarrier output by a multiplication of (l-f)-l. Thus, the bandwidth needed for the
multicarrier modulator output is multiplied by 1.33 to a value of 4000 x 460 x 1.33 =
2.453 MHz.
Finally, to complete the multicarrier modulator processing, a symbol 106
containing a synchronization symbol is introduced periodically, as indicated by block
108. This is done to provide the means for synchronizing a sampling window of 187.5
µs duration at the receiver 14 to the center of the group of multipath arrivals every 250
µs. Also, a phase reference symbol for differential reference coding of the symbol
information is also added periodically. The synchronization and phase reference
symbols are preferably introduced every 20 to 100 symbol periods depending on the
design requirements.
An additional feature of the modulation design is to puncture the TDM digital
bit stream, as indicated by phantom block 110, at the input to the modulator 36 to
reduce the final bandwidth of the multicarrier waveform. Puncturing means selective,
sparse elimination of real data bits from the data stream applied at the input to the IFFT
104. This can be done for a fraction of the bits of the stream in anticipation that the
forward error correction scheme applied at the receiver 14 will simply treat the

punctured bits as errors and correct them. This has the consequence of increasing the
signal to noise ratio (Eb/No) for a desired reception BER objective by 1 to 3 dB,
depending on the fraction of bits removed by the puncturing. The design for the
punctured waveform proportionately reduces the bandwidth of the multicarrier
modulation. For example, if the bit rate of the TDM stream is reduced by 75% , the
bandwidth will also be reduced by 75%. For the example previously given, the bit rate
is reduced to 2.76 Mbit/s and the multicarrier bandwidth to 1.84 MHz. Such bandwidth
compression can be necessary in applications where the available frequency spectrum
would otherwise be insufficient to carry the desired capacity.
It is to be understood that the terrestrial repeater described with reference to
Figs. 2 and 3 is used to recover a TDM satellite downlink signal, and to demodulate and
reformat the TDM signal via baseband processing into a different waveform using, for
example, CDMA, AETDM, MCM or CFIFATDM. It is to be understood, however,
that the DBS 10 can comprise terrestrial repeaters 18 which are co-channel or non-co-
channel repeaters. For example, terrestrial repeaters 18 can be provided which are co-
channel gap-fillers which merely amplify and repeat a received satellite signal on the
same carrier as the satellite signal. Alternatively, terrestrial repeaters can be provided
which are non-co-channel gap-fillers which amplify and repeat a satellite signal on a
different carrier frequency via frequency translation. In either case, baseband processing
of the satellite signal is not performed at the repeater. These types of gap-fillers can be
used, for example, indoors (Fig. 10) or along a roadway (Fig. 11).
At a radio receiver 14 shown in Fig. 4, the multicarrier modulated RF waveform
is received by the antenna 201 operating in conjunction with a low noise RF front end
202, mixer 203, local oscillator 204, first intermediate frequency (IF) 205, second mixer
206, second local oscillator 207, second IF 208 to recover the multicarrier modulated
carrier. A multicarrier demodulator 209 recovers the TDM digital baseband signal. To
demodulate the multicarrier waveform, the received modulated signal is digitally
sampled by a sampler 211, as shown in Fig. 5, at a rate equal to two of four times the
bandwidth of the modulation. These samples are taken during a window of 187.5 µs
duration which is optimally centered on the cluster of time dispersed multipath arrivals
during each symbol period once every 250 µs. The samples are rate down converted by

a buffer memory 212 to expand them to the 460 complex time domain samples in the
original 250 µs duration window. These samples are then processed by an 512
coefficient FFT 213 to recover the bits of the TDM bit stream. The receiver 14 next
synchronizes to the TDM masterframe frame preamble via unit 214, demultiplexes and
aligns the prime rate bits via unit 215 and then recovers the bits of a selected broadcast
channel via unit 216. These bits are then forward error corrected using concatenation of
a soft decision Viterbi decoder 217, a de-interleaver 218, followed by a Reed Solomon
decoder 219, to recover the broadcast channel (BC). This recovered BC is supplied as
one input to a decision/combiner unit 240, as described below in connection with Fig.
6.
For a two-arm receiver 14, as depicted Fig. 6, the MCM signal is received as
described with reference to Fig. 4. The QPSK modulated satellite TDM RF waveform
is also received by the antenna 201 operating in conjunction with the low noise RF
front end 202, a mixer 220, a local oscillator 221, a first IF 222, a second mixer 223, a
second local oscillator 224, and a second IF 225, to recover the QPSK-modulated TDM
carrier. As shown in Fig. 7, a QPSK TDM carrier demodulator 226 comprises a QPSK
demodulator 227 which recovers the TDM digital baseband. The receiver 14 next
synchronizes to the TDM masterframe frame preamble 228, demultiplexes and aligns
the prime rate bits 229 and then recovers the bits of a selected broadcast channel. These
bits are then forward error corrected 230 using the concatenation of a soft decision
Viterbi decoder 231, a de-interleaver 232, and a Reed Solomon decoder 232, to recover
the broadcast channel. This recovered BC is supplied as a second input to the
decision/combiner unit 240.
The diversity combiner 240 selects which of the two input BCs is to be
submitted for further processing. It does this based on selecting that BC which is
recovered with the least errors. Estimates of the error counts are available from the soft
decision data supplied by the Viterbi decoders 217 and 231 or the Reed Solomon
decoders 219 and 233. The decision is preferably made with a hysterisis logic which
requires that several errors of difference exist before the decision is reversed. This
process is needed to prevent chattering between the two BCs when the decisions are

nearly equally likely. The broadcast channel selected by the diversity combiner 240 is
next supplied to the appropriate source decoder 244 to recover the service(s).
The embodiment of the DBS 10 which uses two GSO satellites 12 and 16 with
terrestrial repeater 18 is shown in Fig. 8. In this configuration, two satellites 12 and 16
are separated by between 30 degrees to 40 degrees longitude along the GSO circle. One
satellite repeats a signal sent from a ground station, and the other satellite repeats the
same signal sent from the same ground station but delays the signal as much as 5 to 10
seconds. The use of two satellites 12 and 16 separated in space results in elevation angle
diversity in the LOS paths between a radio receiver 14 on the earth and each satellite 12
and 16. The time delay between the two satellite signal arrivals results in time diversity.
Each of these types of diversity taken alone can significantly improve the availability of
the LOS signal for a moving mobile receiver 14, and the improvement in availability is
further significantly enhanced by both space and time diversity. Space and time
diversity are particularly important when a mobile receiver 14 is traveling in a suburban
area or in a rural area where the LOS signal blockage is due to bridges, trees and low
buildings. However, for central city and metropolitan areas, where tall buildings
abound, terrestrial re-radiation of the signal is also supplied in accordance with the
present invention to achieve acceptable total area coverage for mobile reception. Thus,
this two-satellite diversity configuration operates essentially the same way as the single
satellite configuration with regard to the diversity between direct LOS satellite
reception and terrestrial re-radiated reception, but adds the time and space diversity
provided by the two satellites. The signal from the early satellite is the one re-radiated
by the terrestrial repeater 18. Choice of the early signal allows any delay encountered in
the signal processing at the repeater 18 or the receiver 14 to be absorbed. The terrestrial
re-radiation network is otherwise implemented in the same way as previously described
for the single satellite configuration.
Another difference between the two-satellite system and the one-satellite system
resides in the three-arm radio receiver 14. The receiver 14 introduces appropriate
/compensating delays via delay units 309 and 310 to achieve simultaneous signal
reception among the three received signals and implement a diversity decision logic
which selects among the three diversity signals. The radio receiver diversity logic design

is shown in Fig. 8. It incorporates a maximum likelihood combiner 240 for the Early
and Late LOS satellite signals with a switched combiner 307 between the terrestrial re-
radiated signal and the output of the maximum likelihood combiner 240. When both
signals are degraded, maximum-likelihood combining can improve the quality of
reception. The improvement can be as much as 3 dB in terms of threshold Eb/No when
both signals are equally degraded. The radio receiver 14 is equipped with two receiver
chains 301 and 302 that individually receive and recover the TDM signals from the
Early and Late satellites, respectively, and selects a desired broadcast channel from each.
This is done for each received signal in the same manner as previously described for
LOS satellite reception in Fig. 6. Next, the broadcast channel signal derived from the
early satellite is delayed by a delay unit 309 comprising a memory device to align it
precisely, that is, symbol by symbol, with the symbols of the broadcast channel derived
from the late satellite signal. This can be done by aligning the two broadcast channels
relative to one another so as to cause coincidence of their service control header
preamble correlation spikes. This coincidence is detected in a correlation comparitor
unit in the delay unit 309. The next step is to use the maximum likelihood combiner
240 to combine the bits of the two broadcast channels, bit-by-bit, each bit expressed in
soft decision form. The maximum likelihood combining coefficients are determined
over 1 ms blocks of bits. Next, the output of the maximum likelihood combiner 240 is
applied as one input to the switched combiner 307, with the other input coming from
the terrestrial re-radiated signal receiver arm 308. The choice of which input is to be
passed to the output is based on selecting that BC which is recovered with the least
errors. In accordance with another embodiment of the present invention, one of the
TDM signal receiver chains (e.g., receiver chain 302 for the late satellite TDM signal)
can be maximum likelihood combined with the signal from the terrestrial re-radiated
signal receiver arm 308, as shown in Fig. 9. Thus, the switched combiner 307 selects
from between the output of the maximum likelihood combiner 240 and the other
satellite signal receiver arm (e.g., arm 301), as shown in Fig. 9. The delay units 309 and
310 can be configured to store the entire recovered bit stream for delay purposes, which
requires more buffering but simplifies combining. Alternatively, the delay units 309

and 310 can be configured to store only a portion of the recovered TDM bit stream;
however, synchronization requirements for combining become more complicated.
With regard to switched combiner 307, estimates of the error counts are
available from the soft decision data supplied by the Viterbi decoders 217 and 231 or the
Reed Solomon decoders 219 and 233. The decision is made with a hysterisis logic which
requires that several errors of difference exist before the decision is reversed. This
process is prevents chattering between the two BCs when the decisions are nearly
equally likely. Alternatively, a simple switching logic may be used in which the switch
always favors the choice of the BC having the least errors. Hysterisis is used to prevent
chattering. The latter implementation avoids the more complex maximum likelihood
combining. Yet another alternative could be maximum likelihood combining of the
three input BCs (e.g., from receiver arms 301, 302 and 308), as shown in Fig. 10.
The diversity combiner shown in Fig. 10 combines three signals. Two are
received from two spatially separated satellites 12 and 16, one broadcasting an early
signal and the other broadcasting a late signal. The third signal is received from a
terrestrial repeater 18 which rebroadcasts the early satellite signal. These signals are
received by receiver arm 301 for the early satellite 12, receiver arm 302 for the late
satellite 16 and receiver arm 308 for the early signal retransmitted by the repeater 18.
The diversity combiner 312 combines the symbols in the three signals by maximum
likelihood ratio combining. By this method, the samples of the symbol appearing at the
output have the highest probability of representing the original transmitted symbol. To
do this, the early satellite 12 and repeater 18 signals are delayed relative to the late
satellite signal by delay units 309 and 310 to realign the individual symbols of the three
signals causing them to be in time coincidence. Simple a priori adjustment of the delay
units 309 and 310 suffices to coarsely align the output of the delay units 309 and 310 to
within a TDM frame of 138 µs. Thus, fine alignment of the symbols to the master
frame preamble (MFP) of a TDM frame is nonambiguous. To align the symbols of the
three signals precisely, the MFPs for each signal stream are aligned by fine tuning the
delay units 39 and 310 to within a small fraction of a symbol.
With continued reference to symbol combining in unit 312, the normalized
variance σx2 for the signal symbols, as contained in the background of noise, and

uncorrelated multipath interference, is calculated from the observed samples. These
variances are calculated for the early (E), late (L) and repeater 18 or gap-filler (G) signal
symbols. The respective signal samples of the symbols for the early, late and gap-filler
signals are then multiplexed by their variance ratios , which are
defined as follows:

The weighting factors are inversely proportional to the estimated variance and are
normalized such that

Their sum constitutes the maximum likelihood ratio combined symbols. These are
then passed on to the time demultiplexer/FEC decoder/BC remultiplexer unit 250 (Fig.
11), the components of which have previously been described above in connection with
Fig. 5, to recover the maximum likelihood ratio combined symbols by decision
processing.
The diversity combiner shown in Fig. 12 first combines signals received from
two satellites 12 and 16, one broadcasting an early signal and the other broadcasting a
late signal. The result of this is next combined by minimum bit error decision with
reception of the early signal that has been retransmitted by a gap-filler repeater 18
located on the ground. The individual signals are received by the receiver arm 301 for
the early satellite, the receiver arm 302 for the late satellite and the receiver arm 308 for
the early signal retransmitted by the gap-filler repeater 18. The maximum likelihood
ratio diversity combiner 412 combines the symbols of the early and late satellite signals

in the same manner described above in connection with combiner 312 in Fig. 10 for
three signals. By this method, the final symbol appearing at the output of unit 412 has
the highest probability of representing the original transmitted symbol.
The result from unit 412 is next combined with that from the terrestrial repeater
18 by minimum BER select unit 417. Within the unit 417, there are preferably two
units 250 that make FEC-decoded symbol decisions for an entire broadcast channel
frame of the signals applied at their inputs. One unit 250 makes its decisions on the
output from maximum likelihood decision unit 412, and the other unit 250 from the
signal received from the terrestrial repeater 18. These decisions also provide the number
of errors made with each decision observed over the duration of a broadcast frame. A
BER compare unit 414 operates in conjunction with a minimum BER select unit 417 to
select the symbols of that broadcast frame with the least error, as determined from
inputs from Viterbi FEC units 217 and 231. To implement the necessary delay
operations, the early and gap-filler signals are delayed by delay units 309 and 310 to
realign their individual symbols to be in symbol time coincidence with the symbols'
received from the late satellite. The delay alignment method used here is the same as
that described for the implementation of Fig. 10.
In accordance with another aspect of the present invention, an indoor re-
radiation system 450 is provided which is illustrated in Fig. 13. Since LOS reception of
a satellite signal at a radio receiver located inside a building or other structure is
generally not available, unless the radio receiver 14 is located at a window in LOS of the
satellite 12 or 16, indoor reinforcement of satellite signals for more complete coverage.
As shown in Fig. 13, an antenna 452 can be located externally with respect to a
building so as to achieve LOS reception of satellite signals. A tuned RF front-end unit
454 is connected to the antenna 452 and is preferably configured to select the portion of
the RF spectrum that contains the essential frequency content of the satellite signal and
by doing so with very low added noise. An interconnecting cable 456 is provided to
supply the signal at the output of the tuned RF front-end unit 454 to an amplifier 458.
The amplifier 458 is connected to a re-radiating antenna 460 located within the building.
The amplifier 458 is configured to increase the power of the satellite signal to a
level that, when re-radiated, by the antenna 460, is sufficient to permit satisfactory

indoor reception for a radio receiver. The power level radiated from the antenna 460 is
sufficiently high to achieve satisfactory indoor reception at locations which are not in
the LOS of the satellite, but not so high as to cause instability by signals returned by the
path between the indoor antenna 460 and one or more of the receiving antennas 452.
Thus, high isolation (i.e., on the order of 70-80 dB) is preferred between the indoor
antenna 466 and the outdoor antenna 452.
Reception areas will be present (e.g., through windows or other openings to the
building or structure) where indoor re-radiated signals combine with an outdoor signal
transmitted directly from the satellite. To assure that the combination of these signals
does not occur in an manner which is destructive to signal content, the time delay
between an outdoor signal and an indoor signal in the region of combination is
preferably less than a fraction of the symbol width of the signal being transmitted. For
example, for a symbol width of approximately 540 nanoseconds, a time delay between
50 and 100 nanoseconds can be tolerated. The time delay is generally due to the time
required for a signal to travel the path comprising the outdoor antenna 452, the cable
(where signals generally travel at two-thirds the speed of light), and onward to the
indoor antenna 460. Another delay occurs as the signal travels from the indoor antenna
460 to the radio receiver 14 in an area covered by the indoor antenna. This time delay
is preferably only 20% of the symbol width, that is, not more than 100 nanoseconds for
a system in which the symbol width is 540 nanoseconds.
The purpose of a terrestrial repeater is to repeat a signal received from the
satellite into areas where the signal is otherwise blocked. A multiplicity of these
terrestrial repeaters 18 may be placed along a roadway or other path at a height h and
separated by distances d, as shown in Fig. 14. The heights and separation distances
between the terrestrial repeaters need not be equal. A terrestrial repeater 18 comprises a
receive antenna 462 that is pointed at the satellite 12 or 16, a receiver (not shown) that
recovers the signal and amplifies it with a gain that is sufficient to drive a transmit
antenna 464 such as to a power flux density in the path below which is comparative to
that normally expected from the satellite. The transmit antenna 464 is shielded so as to
prevent the transmitted signal from reaching the terrestrial repeater receive antenna 462
at a level sufficient to create instability. The transmit antenna 464 radiates its power

over an aperture of length L sufficient to cause path length diversity over several
wavelengths between the transmitter 464 and the vehicle's receive antenna at the carrier
frequency.
As a vehicle drives along the path, the radio receiver 14 therein receives signals
coming from more than one terrestrial repeater 18. For example, in position A, a
vehicle is nearest to terrestrial repeater 18b and that terrestrial repeater's signal
dominates and be responsible for reception. Signals from terrestrial repeaters 18a and
18b are low because of distance and antenna pattern and cause little interference. If the
vehicle is at position B, the radio receiver 14 therein receives signals from both
terrestrial repeaters 18c and 18d. Since the distances are nearly equal, and assuming that
the time difference between signals radiated from terrestrial repeaters 3 and 4 is adjusted
to zero, the time difference of arrival between the signals received at the vehicle are
sufficiently small so as to cause constructive reinforcement. By proper choice of the
distances h and d in relationship with the symbol period of the digital signal being
received, this condition can be achieved.
It is important to cause diversity in the signals that arrive at the vehicle from the
different terrestrial repeaters. If this is not done, then the signals from two terrestrial
repeaters, as would be received in the location B, would combine alternately in-phase
and out-of-phase and phases in between. When they are in phase, the signals reinforce,
and when out-of-phase the signals cancel. When signal cancellation occurs, the signal is
completely lost. In addition, the resulting carrier phase of the signal created by addition
of the terrestrial repeater carriers rotates at a rate equal to a nearly monochromatic
Doppler difference, making it difficult to recover the QPSK modulation. The spread in
arrival times caused by the diversity transmission resulting from distribution of the
transmitted signal over the aperture L, or over an equivalent time difference of L/C
where C = speed of light, eliminates the amplitude cancellation and provides the
possibility of correcting the impact of the phase rotation by application of adaptive
equalization techniques. This applied to all vehicle locations between locations A and
B.
An example of the proper choice of distances in relationship to symbol period is
seen by considering a signal having a symbol period on the order of 540 to 550

nanoseconds. The spacing d and height h is selected so as to cause the time delay in
transversing the slant distance (d2 + h2)½ to cause a delay of no greater than a quarter
of a symbol period. In this example, the slant distance is 550/d = 137.5 ft. One
nanosecond is equivalent to one foot at the speed of light. Thus, if the height is 20 feet,
the distance d is 180 feet. The height h is preferably relatively small when compared to
distance d so as to cause the difference in distance between the vehicle and each
terrestrial repeater 18 to change by an amount sufficient to assure that the signal level
from any one terrestrial repeater is attenuated by 10 dB or more compared to that from
a terrestrial repeater immediately overhead. The length L is preferably between 5 to 10
feet to provide sufficient path length diversity at L-band frequencies. If an equalizer
unit is incorporated in the vehicle's mobile receiver 14, the time difference in arrival can
be extended to several symbols, thus increasing the distance between the terrestrial
repeaters to over 1000 feet. An equivalent time difference would be to transmit the
signal several times from the same source over a spread not exceeding 5-10 nanoseconds.
While various embodiments have been chosen to illustrate the invention, it will
be understood by those skilled in the art that various changes and modifications can be
made therein without departing from the scope of the invention as defined in the
appended claims.

WE CLAIM:
1. A digital broadcasting system for transmitting a broadcast signal, said broadcast signal being
transmitted from an earth station, comprising :
a satellite for receiving said broadcast signal from said earth station and for transmitting a satellite
signal comprising said broadcast signal on a first carrier frequency; and
a terrestrial repeater for receiving said satellite signal and for generating and transmitting a
terrestrial signal from said satellite signal comprising said broadcast signal on a second carrier frequency
that is different from said first carrier frequency to enable a radio receiver configured to receive said
satellite signal and said terrestrial signal to employ diversity combining to generate an output signal from
at least one of said satellite signal and said terrestrial signal, said terrestrial signal being modulated by said
terrestrial repeater in accordance with a multipath-tolerant modulation technique.
2. A system as claimed in claim 1, wherein said terrestrial repeater is operable to modulate said
terrestrial signal using at least one of adaptive equalized time division multiplexing, coherent frequency
hopping adaptively equalized time division multiplexing, multicarrier modulation and code division
multiplexing.
3. A system as claimed in claim 1, wherein said satellite signal is modulated in accordance with at
least one of time division multiplexing and code division multiplexing.
4. A system as claimed in claim 1, wherein said terrestrial repeater is operable to modulate said
terrestrial signal using multicarrier modulation.
5. A system as claimed in claim 4, wherein said terrestrial repeater to operable to receive said
satellite signal and demodulates said satellite signal into a baseband signal prior to modulating said
baseband signal using multicarrier modulation.
6. A system as claimed in claim 1, wherein said satellite signal is assigned a first code division
multiplex access channel code and said terrestrial signal is assigned a second code division multiplex
access channel code.

7. A system as claimed in claim 1, comprising a second satellite, said second satellite being operable
to receive said broadcast program from said earth station and to transmit a second satellite signal
comprising said broadcast signal on said first carrier frequency and delayed a predetermined period of time
with respect to the transmission of the first satellite signal.
8. A terrestrial repeater for retransmitting satellite signals to radio receivers comprising :
a terrestrial receiver for receiving said satellite signals; and
a terrestrial waveform modulator for generating terrestrial signals from said satellite signals, said
terrestrial signals being modulated by said terrestrial waveform modulator in accordance with multicarrier
modulation;
wherein said satellite signals are transmitted from a satellite using a first carrier frequency, and said
terrestrial waveform modulator is operable to transmit said terrestrial signals to said radio receivers using a
second carrier frequency that is different from said first carrier frequency to enable said radio receivers to
employ diversity combining to generate an output signal from at least one of said satellite signals and said
terrestrial signals.
9. A terrestrial repeater as claimed in claim 8, wherein said terrestrial waveform modulator
comprises:
a time division demultiplexer for demultiplexing said satellite signals from a serial time division
multiplexed bit stream into a plurality of parallel bit streams; and
an inverse fast Fourier transform device for generating a digital analog signal comprising a
plurality of discrete Fourier transform coefficients.
10. A system as claimed in claim 1, wherein:
said satellite is a first satellite configured to receive said broadcast program from said earth station
and to transmit a time division multiplexed satellite signal comprising said broadcast signal; and
said terrestrial repeater is configured to receive said satellite signal and to generate and transmit a
terrestrial signal from said satellite signal comprising said broadcast signal, said terrestrial signal being
modulated by said terrestrial repeater in accordance with at least one of adaptive equalized time division

multiplexing, coherent frequency hopping adaptive equalized time division multiplexing, code division
multiplexing and multicarrier modulation.
11. A digital broadcasting system as claimed in claim 10, wherein said satellite signal is transmitted
using a first carrier frequency, and said terrestrial signal is transmitted using a second carrier frequency that
is different from said first carrier frequency.
12. A digital broadcasting system as claimed in claim 10, comprising at least one radio receiver
configured to receive said satellite signal and said terrestrial signal, said radio receiver comprising a
diversity combiner for generating an output signal from at least one of said satellite signal and said
terrestrial signal.
13. A digital broadcasting system as claimed in claim 10, comprising a second satellite configured to
receive said broadcast signal from said earth station and to transmit a second time division multiplexed
satellite signal comprising said broadcast signal, said second satellite signal being delayed with respect to
said first satellite signal by a selected time delay.
14. A digital broadcasting system as claimed in claim 13, comprising at least one radio receiver
configured to receive said first satellite signal, said second satellite signal and said terrestrial signal, to
delay at least one of said first satellite signal and said terrestrial signal in accordance with said selected
time delay, and to generate an output signal from at least one of said first satellite signal, said second
satellite signal and said terrestrial signal.
15. A digital broadcasting system as claimed in claim 14, wherein said radio receiver comprises a
diversity combiner and a switched combiner, said radio receiver using said diversity combiner to perform
maximum likelihood decision combining of said first satellite signal and said second satellite signal and
said switch combiner to select between the output of said diversity combiner and said terrestrial signal
depending on which of said output of said diversity combiner and said terrestrial signal has the least
number of bit errors.

16. A digital broadcasting system as claimed in claim 14, wherein said radio receiver comprises a
diversity combiner to perform maximum likelihood decision combining of said first satellite signal, said
second satellite signal and said terrestrial signal.
17. A receiver for receiving a broadcast signal in a combined satellite and terrestrial digital
broadcasting system, comprising:
a first receiver arm for receiving a first satellite signal transmitted from a first satellite on a first
carrier frequency, said first satellite signal comprising said broadcast signal and being modulated in
accordance with at least one of time division multiplexing and code division multiplexing, said first
receiver arm comprising a demodulator for recovering said broadcast signal;
a second receiver arm for receiving a terrestrial signal transmitted from a terrestrial station on a
second carrier frequency, said terrestrial signal being generated at the terrestrial station from a received
said broadcast signal that has been modulated in accordance with at least one of adaptive equalized time
division multiplexing, coherent frequency hopping adaptive equalized time division multiplexing, code
division multiplexing and multicarrier modulation prior to transmission via said second carrier frequency,
said second receiver arm comprising a demodulator for recovering said broadcast signal; and
a combiner for generating an output signal from at least one of said first satellite signal and
said terrestrial signal.
18. A receiver as claimed in claim 17, comprising :
a third receiver arm for receiving a second satellite signal from a second satellite that is delayed
with respect to said first satellite signal in accordance with a selected time delay, said second satellite
signal comprising said broadcast signal and being modulated in accordance with the corresponding at least
one of time division multiplexing and code division multiplexing employed by said first satellite signal,
said third receiver arm comprising a demodulator for recovering said broadcast signal; and
a delay device for delaying said first satellite signal in accordance with said selected time delay,
said combiner generating an output signal from at least one of said first satellite signal, said second satellite
signal and said terrestrial signal.

19. A method of transmitting a broadcast signal to a radio receiver, comprising the steps of:
modulating said broadcast signal for transmission to said radio receiver as a first signal,
accordance with at least one of time division multiplexing and code division multiplexing;
transmitting said first signal to said radio receiver from a first satellite on a first carrier frequency;
modulating said broadcast signal at a terrestrial station for transmission to said radio receiver as a
second signal in accordance with at least one of adaptive equalized time division multiplexing, coherent
frequency hopping adaptive equalized time division multiplexing, code division multiplexing, and
multicarrier modulation; and
transmitting said second signal to said radio receiver from said terrestrial station on a second carrier
frequency that is different from said first carrier frequency to enable said radio receiver to employ diversity
combining to generate an output signal from at least one of said first signal and said second signal.
20. A method as claimed in claim 19, wherein said step of modulating said broadcast signal as said
second signal comprises the steps of:
receiving said first signal at said terrestrial station; and
performing baseband processing of said first signal prior to modulating in accordance with at least
one of adaptive equalized time division multiplexing, coherent frequency hopping adaptive equalized time
division multiplexing, code division multiplexing, and multicarrier modulation.
21. A method as claimed in claim 20, comprising the step of receiving said first signal and said second
signal using at said radio receiver.
22. A method as claimed in claim 21, comprising the step of demodulating each of said first signal and
said received second signal to remove said respective modulations and to recover a first recovered
broadcast signal and a second recovered broadcast signal, respectively.
23. A method as claimed in claim 22, comprising the step of generating an output broadcast signal
from said first recovered broadcast signal and said second recovered broadcast signal.

24. A method as claimed in claim 23, wherein said generating step comprises the step of performing
maximum likelihood combining of said first recovered broadcast signal and said second recovered
broadcast signal.
25. A method as claimed in claim 19, comprising the steps of:
modulating a broadcast signal for transmission to said radio receiver as a third signal in accordance
with at least one of time division multiplexing and code division multiplexing;
transmitting said third signal to said radio receiver from a second satellite, said transmission being
delayed with respect to said first signal by a predetermined period of time.
26. A method as claimed in claim 25, comprising the steps of:
receiving said first signal, said second signal and said third signal at said radio receiver;
demodulating each of said first signal, said second signal and said third signal to remove said
respective modulations and to recover a first recovered broadcast signal, a second recovered broadcast
signal and a third recovered broadcast signal, respectively; and
generating an output broadcast signal from at least one of said first recovered broadcast signal, said
second recovered broadcast signal and said third recovered broadcast signal.
27. A method as claimed in claim 19, wherein a time division multiplexed bit stream is converted into
a plurality of multicarrier modulated signals at a terrestrial repeater, the method comprising the steps of:
receiving said time division multiplexed bit stream from the first satellite;
dividing said time division multiplexed bit stream into a plurality of parallel bit paths;
representing each of a predetermined number of bits in each of said plurality of bit paths as a
symbol comprising an imaginary component and a real component;
providing said symbols to parallel inputs of an inverse Fourier transform converter as complex
number frequency coefficient inputs to generate outputs which comprise modulated, narrow-band,
orthogonal carriers; and
transmitting said modulated, narrow-band, orthogonal carriers from said terrestrial repeater.

28. A method as claimed in claim 27, comprising the step of generating a guard interval for said
carriers.
29. A method as claimed in claim 28, wherein said generating step comprises the steps of:
allocating a fraction of the symbol period corresponding to the duration of each of said symbols to
guard time; and
reducing the duration of each of said symbols.
30. A method as claimed in claim 29, wherein said reducing step comprises the steps of:
storing said outputs of said inverse Fourier transform converter in a memory device every said
symbol period; and
reading from said memory device after each said fraction of said symbol period has elapsed.
31. A method as claimed in claim 28, wherein said generating step comprises the step of filling said
guard interval with a subset of said outputs of said inverse Fourier transform.
32. A method as claimed in claim 27, comprising the step of inserting a synchronization symbol every
predetermined number of said symbol periods to synchronize a sampling window corresponding to said
fraction of said symbol period with respect to said carriers every said symbol period at a receiver for said
plurality of multicarrier modulated signals.
33. A method as claimed in claim 27, comprising the step of puncturing said time division multiplexed
bit stream to reduce the total bandwidth associated with said carriers.
34. A method as claimed in claim 33, wherein said puncturing step comprises the step of selectively
eliminating bits from said time division multiplexed bit stream prior to providing said symbols to parallel
inputs of an inverse Fourier transform converter.

35. A receiver as claimed in claim 17, wherein there is provided an indoor reinforcement system for
receiving satellite signals transmitted by a digital broadcasting system when the receiver is located
indoors, the indoor reinforcement system comprising :
a line of site antenna for receiving line of site satellite signals;
a radio frequency front-end unit connected to said line of site antenna for passing frequency
spectrum comprising said satellite signals with low noise;
an indoor amplifier;
a cable for connecting said radio frequency front-end unit to said indoor amplifier; and
an indoor re-radiating antenna connected to said indoor amplifier, said indoor re-radiating antenna
having a power level selected to be sufficiently high to achieve satisfactory indoor reception of said
satellite signals at radio receivers at indoor locations where line of site reception of said satellite signals is
not possible and sufficiently low to prevent interference by said satellite signals transmitted between said
indoor re-radiating antenna and said line of site antenna.
36. A receiver as claimed in claim 35, wherein said satellite signals are characterized by a selected
symbol period, and the duration of the transmission of said satellite signals between said line of site
antenna and said indoor re-radiating antenna is maintained to be less than a selected amount of said symbol
duration by limiting the length of said cable.
37. A receiver as claimed in claim 36, wherein said duration of the transmission of said satellite signals
between said line of site antenna and said indoor re-radiating antenna is no more than between 20 percent
and 25 percent of said selected symbol period.
38. A digital broadcasting system as claimed in claim 1, having a reinforcement system for receiving
satellite signals transmitted by a digital broadcasting system using a radio receiver located outdoors,
wherein said satellite signals are characterized by a selected symbol period, said reinforcement system
comprising at least two terrestrial repeaters, said terrestrial repeaters being characterized by a heighth and
being spaced apart by a distance d, the slant distance (d2 + h2)1/2 from one of said terrestrial repeaters to
said radio receiver being selected to limit a delay in reception of said satellite signals at said radio receiver
from one of said terrestrial repeaters to between 20 percent and 25 percent of said symbol period.

39. A system as claimed in claim 1, wherein :
said satellite signal and said terrestrial signal are each modulated using a multipath-tolerant
modulation technique.
40. A system as claimed in claim 39, wherein said satellite signal is modulated in accordance with
code division multiplexing.
41. A system as claimed in claim 39, wherein said terrestrial signal is modulated in accordance
with at least one of adaptive equalized time division multiplexing, coherent frequency hopping adaptive
equalized time division multiplexing, code division multiplexing, and multicarrier modulation.
42. A receiver as claimed in claim 17, comprising an indoor reinforcement system for receiving
satellite signals transmitted by a digital broadcasting system, when the radio receiver is located indoors, the
reinforcement system comprising:
a line of site antenna for receiving line of site satellite signals;
a radio frequency front-end unit connected to said line of site antenna for passing frequency
spectrum comprising said satellite signals with low noise;
an indoor amplifier;
a cable for connecting said radio frequency front-end unit to said indoor amplifier; and
an indoor re-radiating antenna connected to said indoor amplifier, said indoor re-radiating antenna
having a power level selected to be sufficiently high to achieve satisfactory indoor reception of said
satellite signals at radio receivers at indoor locations where line of site reception of said satellite signals is
not possible and sufficiently low to prevent interference by said satellite signals transmitted between said
indoor re-radiating antenna and said line of site antenna.
43. A digital broadcast system as claimed in claim 1, comprising a reinforcement system for receiving
satellite signals transmitted by a digital broadcasting system using a radio receiver located outdoors,
wherein said satellite signals are characterized by a selected symbol period, said reinforcement system
comprising at least two terrestrial repeaters, said terrestrial repeaters being characterized by a height

h and being spaced apart by a distance d, the slant distance (d2 + h2)1/2 from one of said terrestrial repeaters
to said radio receiver being selected to limit a delay in reception of said satellite signals at said radio
receiver from one of said terrestrial repeaters to between 20 percent and 25 percent of said symbolperiod.
44. A digital broadcasting system, substantially as herein described, particularly with reference to
and as illustrated in the accompanying drawings.
45. A terrestrial repeater, substantially as herein described, particularly with reference to and as
illustrated in the accompanying drawings.
46. A receiver for receiving a broadcast signal, substantially as herein described, particularly with
reference to and as illustrated in the accompanying drawings.

A digital broadcast system is provided which uses a satellite direct radio
broadcast system (22) having different downlink options in combination with a
terrestrial repeater (18) network employing different re-broadcasting options to achieve
high availability reception by mobile radios (14), static radios and portable radios (14)
in urban areas, suburban metropolitan areas, rural areas, including geographically open
areas and geographic areas characterized by terrain having high elevations. Two-arm
and three-arm receivers (14) are provided which each comprise a combined architecture
for receiving both satellite and terrestrial signals, and for maximum likelihood
combining of received signals for diversity purposes. A terrestrial repeater (18) is
provided for reformatting a TDM satellite signal as a multicarrier modulated terrestrial
signal. Configurations for indoor and outdoor terrestrial repeaters are also provided.

Documents:

692-kol-2004-granted-abstract.pdf

692-kol-2004-granted-claims.pdf

692-KOL-2004-GRANTED-CORRESPONDENCE.pdf

692-kol-2004-granted-description (complete).pdf

692-kol-2004-granted-drawings.pdf

692-kol-2004-granted-examination report.pdf

692-kol-2004-granted-form 1.pdf

692-kol-2004-granted-form 18.pdf

692-kol-2004-granted-form 2.pdf

692-kol-2004-granted-form 3.pdf

692-kol-2004-granted-form 5.pdf

692-kol-2004-granted-gpa.pdf

692-kol-2004-granted-reply to examination report.pdf

692-kol-2004-granted-specification.pdf


Patent Number 227278
Indian Patent Application Number 692/KOL/2004
PG Journal Number 02/2009
Publication Date 09-Jan-2009
Grant Date 05-Jan-2009
Date of Filing 08-Nov-2004
Name of Patentee WORLDSPACE MANAGEMENT CORPORATION
Applicant Address 2400, N. STREET, N. W., WASHINGTON, D.C. 20037-1153
Inventors:
# Inventor's Name Inventor's Address
1 CAMPANELLA JOSEPH S 18917, WHETSTONE GAITHERSBURG, MD 20879
PCT International Classification Number H04N 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/079,591 1998-03-27 U.S.A.
2 09/058,663 1998-04-10 U.S.A.