BCA4021
HYBRID SATELLITE-TERRESTRIAL NETWORKS; A NOVEL CONCEPT
FOR INTERACTIVE DIGITAL TELEVISION
I. Koffman, MSc.
Runcom Technologies, Ltd. Israel
I. ABSTRACT
The concept of Hybrid Networks that combine both the Satellite and Terrestrial infrastructures has
the potential to offer a cost effective solution for the Satellite DBS operators that will enable them
to successfully compete versus the Digital Cable TV and Cable Modem Operators with interactive
applications and added value services such as TV Web browsing, TV commerce, TV voting,
Video on Demand, plane broadband IP connectivity, etc.
The main features of this solution are:
• The Satellites will be used for what they are good for (broadcasting and
multicasting) and the wireless terrestrial channel for unicast and mobile
applications.
• The Satellite broadcaster can use the Terrestrial downlink to broadcast the local TV
channels and not waste the satellite resource for limited audience.
• The solution in the subscriber unit consists of a “Plug and Play” extension board
(with indoor UHF antennas) to existing Satellites IRD's or Set-Top-Boxes (STB's)
without the need of professional installation and track and roll efforts.
• The solution is scalable; the satellite broadcaster can build wireless terrestrial base
stations in hot spot areas and build the system in parallel to the growth in the
subscribers’ base and applications availability.
• In addition the Satellite broadcasters in the US can take advantage of the new FCC
Auctions and acquire the needed spectrum for this operation in the "attractive"
UHF band that can allow Non-Line of Sight and indoor operation.
This paper presents the concept and the business justification of Hybrid systems based on the
OFDMA technology and the DVB-RCT standard it complies with.
II. BACKGROUND
Despite the fact that Digital Satellite TV still has a leading edge over the cable and terrestrial
counterparts in terms of worldwide installed base of digital Set Top Boxes (65% satellite vs. 29%
cable and 6% terrestrial in 2002 [14]), it looks that this leading edge is deteriorating in an
increasing pace as the compound average annual growth of the satellite subscribers base scores the
lowest numbers (27% satellite, 46% cable and 119% terrestrial [14]), One of the major reasons for
this trend is the lack of suitable return channel that will enable Interactive TV applications and
“Triple Play” ( Video Voice and Data) to satellite subscribers compared to the return channel
options available to the cable and terrestrial competitors.
1
The main options available today for return channel to satellite Set Top Boxes like PSTN or
Satellite return channels have major disadvantages such as: not “always on”, narrow band and
operator-dependent for the PSTN return channel option and expensive and long delays for the
satellite return channel option.
Recent trends in the Digital Terrestrial TV arena bring a unique opportunity to combine between
these two technologies in order to provide a better service to the digital satellite TV subscribers
and an increased ARPU (average return per user) to the Satellite operators and content providers.
Among the trends in the Terrestrial TV markets are: the approval of the DVB-RCT standard by
ETSI in 2002, the massive deployment plans for Digital Terrestrial Television networks
worldwide, the UHF spectrum availability due to the “analogue switch off” (Many governments
world wide will switch off the analogue TV transmission when a substantial percentage of the
population will have a digital TV solution and free valuable spectrum in the UHF band for other
applications) and UHF spectrum Auctions by the FCC in the US, etc.
In the following chapters a Hybrid system concept that combines satellite and terrestrial solutions
is presented as well as its business rationale and its supporting OFDMA technology.
III. HYBRID SYSTEM DESCRIPTION
The Hybrid Satellite-Terrestrial (“HST”) nomenclature has been used by many for different kind
of systems using combined satellite and terrestrial technologies and equipment, in the context of
this paper we refer to HST Networks, to systems, like the one depicted in Figure-1, that include a
satellite down stream link and a wireless terrestrial bi-directional link (upstream and downstream).
Figure-1: Hybrid satellite terrestrial network concept
2
The leading DVB-T/RCT Standard is proposed as cellular, point-to-multipoint terrestrial bidirectional link that will complement the satellite broadband down link. This solution exploits the
unique advantages of both worlds by using the satellite link for broadcasting, multicasting and
caching and the terrestrial link for unicasting. The main features of the terrestrial bi-directional
link are depicted in Table –1 below:
Parameter
Uplink
Downlink
Standard
DVB-RCT
DVB-T
Technology
OFDMA
COFDM
Spectral Efficiency 3.5 bits/sec/Hz 4 bits/sec/Hz
Channel Bandwidth 6,7 and 8 MHz
6,7 and 8
MHz
Modulation
QPSK, 16,
QPSK, 16,
64QAM
64QAM
Cell size
Up to 60 Km Up to 60 Km
Table-1. Terrestrial bi-directional link
The up link portion of the terrestrial bi-directional link will be used as the return channel for the
STB’s for all the interactive applications whereas the down link channel will be used for
applications such as Video on Demand, broadcasting of local TV channels (in order to save the
satellite transponders for national and multinational TV channels).
Satellite Antenna
IRD or STB
To PC
TV
Extension Card for
Terrestrial
communication
Communicationwith
with
Internal UHF
internal
UHF antenna
antenna
Figure-2. Terrestrial link added to existing satellite STB
3
One of the main advantages of this solution is the ability of the terrestrial link to operate in an
indoor-to-outdoor environment, the meaning of this capability is that there is no need to install an
outdoor UHF antenna to the STB in order to communicate with the base station, for most cases an
small indoor antenna on top of the STB will be sufficient. A major outcome of this attribute, is the
possibility to upgrade a major portion of the existing satellite subscriber base STB’s using an
extension card or external modem without the need for “track and roll”, professional installation
and additional cables in the subscribers houses, The extension card could be distributed through
the traditional retailing channels and installed by the subscribers using the plug and play method.
A possible subscriber installation scenario is depicted in Figure-2 herein.
IV. THE BUSINESS MODEL
The business model for the Hybrid concept is based on the following assumptions:
a. The solution should enable Interactive TV and “triple play” services to subscribers
b. The concept should support the satellite existing subscriber base without the need
of massive replacement of STB’s.
c. The solution will not require professional installation.
d. The concept will be able to compete with the other Interactive Digital TV delivery
methods
Based on the above assumptions the average cost of data traffic (in $ per Megabyte) for the
different return channel options were calculated and is depicted in Table-2 below.
Return Channel Method
$ Per Megabyte
Satellite
0.12 to 0.33
Terrestrial
0.03 to 0.06
Cable
0.05 to 0.12
The numbers above are based on 50% utilization and include the infrastructure, equipment and operational expenses needed to operate the serviced.
Table-2. Cost off data traffic in the return channel
The estimated price for the extension card for the terrestrial bi directional link is $60 to $80 each,
and the infrastructure and operational cost per subscriber are $10 to $20, assuming that the service
provider will be able to increase the average revenue per subscriber by a conservative amount of
$10/month due to the additional interactive services given, than the return on investment (ROI)
will be between 7 to 10 months.
V. THE OFDMA TECHNOLOGY AND DVB-RCT STANDARD
The object of this and the following chapters is the DVB-RCT Standard, covering the
VHF/UHF bands [2]. The propagation characteristics in this band allow a certain level of obstacle
penetration, which are both a blessing and a challenge. While it allows coverage at long distance
and in NLOS scenarios, a commercial system can only be implemented with techniques that
efficiently mitigate the impairments of fading and multipath.
The most prominent present wireless application of OFDM is the European standard DVB-T
(Digital Video Broadcasting – terrestrial). The DVB-T approach called Coded OFDM (COFDM)
4
involves a series of principles that are also applied in the IEEE 802.16a. In [4] it is given a review
of the COFDM and a thorough discussion on its advantages over single carrier.
f(t)
DATA
IN
FEC
&
INTERLEAVING
an
bn
IDFT
f0
MODULATOR
CHANNEL
T
DEMOD
DFT
FEC
DATA
&
DEINTEROUT
LEAVER
Figure 3. Simplified diagram of an OFDM system
A generic simplified diagram for an OFDM system is shown in Figure 3. The mathematical
background is widely available in literature. The transmitted sequence {bn} is obtained from the
input information sequence {an} through an N-point inverse digital Fourier transform (IDFT). The
{an} is created from the source data passed through a forward error correction (FEC) encoder, then
interleaved and mapped into a constellation that can be QPSK, 16QAM or 64QAM. The IDFT
converter receives and presents the information in blocks of N samples. The resulting waveform is
a sum of sine waves separated in frequency at 1/NT, modulated by an and filtered in baseband with
f(t) – the anti-aliasing filter. The quadrature modulator shifts the frequency to the carrier frequency
f0.
5
Figure 4. Example of time delay profile and frequency response of a 6 MHz NLOS channel.
6
Figure 4 above displays a simulated 6 MHz channel response similar to those expected in an urban
NLOS environment. Its RMS delay time (τRMS) – an integral measure of the channel multipath – is
1.4 µs. Figure 4 shows also the corresponding frequency response – upper curve. The lower curve
is the noise plus the interference (SNR) coming from a nearby cell. The average channel SNR is
15 dB, but the SNR for every carrier, the difference between the two curves, is very irregular.
In order to demodulate the data, a single carrier (SC) system would have to employ an equalizer in
order to bring the system response as close as possible to a Nyquist equivalent. As a result the
information at equalizer’s output features an SNR close to the average channel SNR. If this is high
enough, it will result in virtually error free demodulation. The OFDM system performs the
equalization by means of a simple multiplier bank followed by demodulation in frequency
domain.
As a result each piece of information comes with the SNR of its generating carrier. As some have
a very poor SNR, the demodulation will present irreducible bit error rate (BER) even when the
average SNR is quite high. Therefore an OFDM system cannot work in a fading channel without
FEC. The OFDM requires FEC correction with frequency domain interleaving in order to scatter
the low SNR information. Furthermore the signal and noise for each carrier can be tracked,
estimated and fed as CSI (channel state information) to the FEC decoder. This can be the case with
Turbo codes, or Viterbi algorithms that use the CSI as weighting factor in local metric
calculations, or with erasure marking in Reed Solomon (RS) codes. The advantage of OFDM in
selective fading channels resides in the relative ease of frequency domain separation of the noisy
information from the “clean” one and its subsequent beneficial use with error correction codes.
This is in essence the rationale for the adoption of COFDM in Europe DVB-T and thereafter in
802.16a.
VI. PERFORMANCE GOALS AND MAIN PARAMETERS
For a successful mass deployment solution, an Interactive Hybrid system has to provide for a
predictable business case. It implies that once a broadcaster sets up a Base Station aiming at a
service area, a very high percent of subscribers will technically be able to get the service. A
broadcaster should be able to avoid situations where one house or apartment gets the service and
the neighbor does not, or situations of erratic service outages due to variable propagation or
interference conditions. Technologically this translates in system features designed to mitigate the
multipath fading and the variety of link budget and interference scenarios.
Another aspect directly related to the operations cost is the installation. It has to involve short and
inexpensive operations up to customer’s self-installation, eventually indoor.
The wireless channels related to these scenarios resemble those encountered in the mobile cellular
environment. In [7] is presented a review of measurements and models for mobile cellular
channels. For cells with radius of 1 to 10 Km – macrocells – the values of τRMS encountered are
between 0.1 to 10 µs, while in worst cases they can reach more than 20 µs. The operating range
intended for Interactive Hybrid Networks exceeds10 Km.
The fundamental parameter that relates to multipath is the number of carriers N. The basic
assumption for the OFDM demodulation involving equalization only with a multiplier bank is that
the individual carriers pass through a channel with a spaced-frequency correlation function that is
7
close to 1, a flat fading channel [9], which is generally accepted when the symbol time TS >
100τRMS. The DVB-T specifies 2048 or 8192 carriers for the downstream (COFDM), and the
DVB-RCT specifies 1024 or 2048 carriers for the upstream (OFDMA). For the 2048 option in a
USA MMDS channel of 6 MHz, the TS is 298.66 µs, therefore such a system can withstand
environments with roughly τRMS around 3 µs. This comes towards the DVB-T that with maximum
of 8192 carriers is aiming at a longer operating range.
Not all the channel bandwidth is filled with carriers. Guard bands are necessary to allow the signal
PSD (power spectral density) to roll off under the required out-of-band spectral mask, so that a
number of marginal carriers are set to zero. Some carriers are used as pilots to transmit
pseudorandom sequences for channel estimation and tracking purposes. Similarly in the time
domain, the OFDM symbols come with a guard interval in between in order to mitigate the
symbol lengthening due to the convolution with the channel response.
VII. THE COFDM AND OFDMA MODES
The downstream terrestrial link is based on the DVB-T (COFDM) and the return channel
(upstream link) on the DVB-RCT (OFDMA).
In the COFDM all carriers are transmitted at once. The downstream data is time division
multiplexed (TDM).
In OFDMA the FFT space (2048 and 1024 carriers) is divided into subchannels. They are used in
downstream for separating the data into logical streams. Those streams employ different
modulation, coding and amplitude to address subscribers with different channel characteristics. In
upstream the subchannels are used for multiple access. The subscribers are assigned on
subchannels through MAP (Media Access Protocol) messages sent in downstream.
VIII. OFDMA AND THE SUBCHANNELS
The subchannel is a subset of carriers out of the total set of available carriers. In order to mitigate
the selective fading, the carriers of one subchannel are spread along the channel spectrum. The
Figure 5a depicts the principles of division into subchannels. The usable carrier space is divided
into a number of NE subchannels. Each subchannel contains a number of NG successive carriers,
after excluding the initially assigned pilots. For N = 2048, NG = 29 and NE = 59, while in N =
1024, NG = 29 and NE = 29.
In essence the principle of OFDMA consists in different users sharing the upstream FFT space,
while each one transmits one or more subchannels. The division in subchannels is a form of
FDMA (frequency division multiple access), where the subscriber transmits 1/NE = 1/59 of the
available channel bandwidth – for the 2048 carrier OFDMA. A low upstream data rate is
consistent with the traffic asymmetry where the streams from each subscriber add up in a
multipoint to point regime, while in downstream all the subchannels are transmitted together. So
the OFDMA allows for fine granulation of bandwidth allocation, consistent with the needs of most
of the subscribers, while the high consumers of upstream bandwidth are allocated more than one
subchannel. Figure 5b shows the structure of subchannels in the upstream framing.
8
Group 1
Group 2
Group N G
Group 3
NG SUBCHANNELS
…..
RANGING SUBCHA NNELS
STB A
STB B
STB C
.
.
.
.
.
.
.
FFT
SYMBOL
STB D
Subchannel A
STB F
STB E
The active FFT carriers space
TIM E
Subchannel B
b. Subchannels in the upstream signal space.
a. The principle of division in subchannels
Figure 5. Subchannels in OFDMA.
The most important aspect of the upstream subchannels is related to coverage. The terrestrial
downstream system involves a high power transmitter in the Base Station and a multitude of low
cost, low transmission power extension cards. For the OFDMA option of N = 2048, the extension
card concentrates its power into a subchannel that has 1/59 of the channel bandwidth. For
equivalent modulation and coding, this results in 18 dB premium for the upstream link budget
against the downstream. For a 6 MHz channel, one subchannel has an equivalent bandwidth of
97.1 KHz. But this low bandwidth signal does not undergo flat fading as its 29 carriers are spread
across the entire channel bandwidth.
In as regarding the interference, the subchannels constitute a form of frequency hopping spread
spectrum (FHSS) [11]. In every group an extension card transmits one pseudo-randomly selected
carrier out of NE possible ones. A STB in an interfering cell does the same type of selection but
statistically independent. The probability of collision is 1/NE. This is a classic scenario of FHSS
with partial band jammer. The hopping scenario repeats for every group in an FFT symbol. For N
= 2048 there are NG = 29 such groups. The data from carriers with low SNR is corrected through
interleaving and coding. The parameter that characterizes the degree of spreading in a spreadspectrum system is the processing gain - GP. It can be expressed as a function of W the group
bandwidth, R the bit rate of one carrier and RS its symbol rate by:
W N E RS N E 59
GP =
=
=
=
(1)
R
mRS
m
m
Where m is the modulation density: 2 for QPSK, 4 for 16-QAM, and 6 for 64-QAM. The
processing gain is important in cellular systems because it relates to the interference withstanding
of the modulation and coding scheme, or the carrier to interference ratio at quasi-error-free
operation – C/I, which is the major capacity limiting factor:
R ⋅ EB
1  EB 
C 


=
=
(2)
 
 I  at BER =10-6 W ⋅ N 0 GP  N 0  at BER =10-6
9
There is no upstream interference within the cell as its subchannels are orthogonal – each group
element is used by only one subchannel.
Figure 5b illustrates the OFDMA upstream signal space. Some subchannels are reserved for PHY
processes such as ranging, while others carry subscriber data according to the MAP allocations.
IX. OUTDOOR TO INDOOR OPERATION
The vision of customer installed extension card is a main condition for the success of the
Hybrid concept presented in this paper. Customers should be able to buy the card unit in a store,
and then install it near the television set, then sign-on for the service with the local broadcaster.
Such capabilities would place the Hybrid solution on high competitive grounds.
These scenarios extend the amount of channel impairments, the multipath fading and the path
loss range. Following we shall present the OFDMA mechanisms meant to mitigate those
impairments.
A. Power Concentration in Subchannels
Studies documented in the literature [12] tell of additional path loss of 12-17 dB at 2.3-2.5
GHz due to the building penetration or 10-15dB adapted to UHF frequencies. This affects
especially the upstream as the extension card has low transmission power due to limitations of cost
and safety. The use of subchannels partially compensates this imbalance by providing an 18 dB
advantage for the upstream.
Recieve Antenna 0
Recieve Antenna 1
FFT
0
FFT
1
I
Q
I
Ch. Estimator
0
Q
Ch. Estimator
1
∑
FEC
Figure 6. The Receive Antenna Diversity
10
B. Receive Antenna Diversity
To enhance the downstream and upstream performance, an enhanced configuration would
employ two diversity antennas for the receiver with two parallel FFT processors, fed from the
same clock, see Figure 6. This involves no processing or protocol overhead for the transmitter.
The maximal-ratio receiver-combining (MRRC) algorithm is performed on each carrier
independently using its channel and noise estimations. For perfectly de-correlated diversity
antennas in Rayleigh channel, the MRRC can bring up to 10 dB of improvement in EB/N0 at quasi
error-free BER (Bit Error Rate).
The signal received at each antenna has different channel characteristics. Each signal is passed to
the FFT block where it is transferred into frequency domain. Then each signal is passed into the
Channel Estimator block, which determines the channel characteristics per each carrier. The
signals coming from the different Channel Estimators are then combined using MRCC into a
single stream, which is then passed into the FEC decoder.
C. Coding and modulations schemes
A variety of coding and modulations schemes are allocated selectively to each subscriber, both in
upstream and downstream. There are trade-offs between throughput and robustness with an EB/N0
span of 15 dB, see Table 3. They provide efficient utilization of the spectrum, with subscribers in
difficult positions taking the robust schemes with low throughput. Those in better positions
employ higher throughput schemes and are able to transmit the same amount of data in shorter
allocations.
X. UPSTREAM SYSTEM CAPACITY
Upstream capacity is investigated, as it is the critical aspect in the economics of a mass-deployed
two-way system. We consider a cellular deployment as shown in Figure 7. A minimal cost system
with no sectorization is presented. The interference scenarios in upstream involve subscribers of
like of S1 that point their antennas toward their base station H1 but their antenna pattern hits also
the H0 antenna. The interference level they create in the H0 receiver will be further referenced as
I.
XI. OFDMA SYSTEM ENGINEERING ASPECTS
The upstream subchannels and their FHSS interference lead to scenarios similar to those of
CDMA mobile cellular. In the scenario of Figure 7 we consider the most challenging frequency
reuse scheme, where all the cells share the same frequency resource. A Monte Carlo simulation is
used, where the cells are populated with a large number of randomly distributed subscribers.
Various coding and modulation schemes are used for each subchannel, but each extension card
creates the same average traffic. The system capacity is determined by the interference I created
by the surrounding cells into the receiver of cell H0. The signal from each H0 subscriber and the I
are related through (2). From here the average activity of STB’s and subsequently the capacity.
11
Modulation and coding schemes:
M1
M2
M3
H2
D0
H0
d1
H2
S1
H1
Interfering
Subscribers
H3
H1
H0
Cellular layout. First two layers interfering with H0.
H3
H0: Allocation of modulation and coding schemes to subscribers.
H1,H2, H3: Only for the subscribers interfering with H0
Figure 7. Capacity simulation layout
The cell-to-cell interference depends on propagation conditions such as terrain, foliage, buildings,
type and height of base station antennas, the subscriber antennas and the nature of their
installation. The general statistical model used for coverage and capacity estimation expresses the
path loss L in dB as:
D
L = LR + 10n log
+ Lσ
(3)
DR
In this formula D is the distance, DR is the model’s reference distance, LR the reference path loss, n
is the propagation model exponent and Lσ is the shadow fading factor, a zero centered random
variable with variance σ. For a given area, the bibliography [7], [8] for urban and suburban
scenarios mention n in the range of 2.5 to 5 and σ in the range of 3 to 14 dB. The extension card
transmission power is adjusted according to the path loss from its base station to create the
reference level in the base station receiver. The interference propagates to the nearby cell as a
different stochastic process, with different Lσ.
In Hybrid networks the subscribers may be considered fixed and they can employ directive
antennas. This limits the number of STB’s that actually interfere with a nearby cell. Environmental
and esthetics restrict the subscriber antenna sizes and the resulting directivity. In a NLOS
environment the actual directivity is affected by intense scattering so that for interference
estimation, the directivity has to be significantly understated. Figure 7 shows the interferers
locations in the first two layers of cells surrounding cell H0. For simplification a two-value
antenna pattern is considered, with the main lobe width of 70° - about 2-3 times the spec of
commonly used antenna, in order to account for the scattering effects. The area of interfering
subscribers is not a pie sector.
Managing the whole range of modulation and coding schemes specified in the standard can
optimize the capacity. To maximize the capacity we want to assign as many subscribers as
12
possible to the schemes with highest throughput. But these schemes also have the higher C/I
requirement and will transmit higher power, creating more interference. The optimal strategy is to
assign the schemes with their C/I in reverse relation to their path loss, so that the higher C/I
schemes are assigned to extension cards in locations with lower path loss (generally those closer to
base station). This is also consistent with the coverage, where we want to minimize the
transmission power of subscribers in challenging locations. The Table 3 shows the set of three
modulation and coding schemes, M1, M2, M3 used in the simulation. At cell extremities we
assign the most robust scheme to locations with path loss: L > L0 – K, where L0 is the mean path
loss at cell radius D0 and K is a capacity optimization system engineering parameter that says how
deep inside the cell we want to keep with the most robust, but lowest throughput scheme. Figure 7
shows an example of assigning the three schemes to a population of subscribers in cell H0, with
parameters n = 3, σ = 4, K = 10 dB. All the cells have the same distribution of schemes, but only
the interfering locations are shown. The three modulations and coding scheme are detailed in
Table 3. The EB/N0 ratings are for Rayleigh channel with diversity.
Modulation
Coding
m
GP [dB]
EB/N0 [dB]
C/I [dB]
Throughput
per
subchannel
[Kb/s]
Total
Channel
Payload
Throughput
[Mb/s]
M1
QPSK
Turbo
RC =
1/2
2
14.7
5
-9.7
M2
16QAM
Turbo
RC =
1/2
4
11.7
9
-2.7
M3
64QAM
Turbo
RC =
1/2
6
9.9
13
3.1
96.1
192.3
288.4
5.67
11.35
17.0
Table 3. Three modulation and coding schemes for OFDMA – 2048 in 6 MHz channel
A. Simulation Results
Figure 8 shows the results of simulations performed on the mentioned scenario as a function of the
path loss exponent n and the system engineering parameter K. The results show the net expected
payload data throughput, per cell, using one 6 MHz channel, after excluding all the expected
overheads in MAC and PHY. It is worth comparing the results with the last line in Table 3 that
shows the throughput of the channel fully loaded with all the 32 carriers for each one of the
schemes.
The simulation accounts for severely altered directivity of subscriber antenna, with beam width of
70° and front to back ratio of only 20 dB. For n = 2.5 which is close to free space, the capacity is
13
low due to high cell to cell interference. This generally applies to suburban scenarios with low
houses and high base station antennas. As OFDMA system is generally intended for NLOS
scenarios, higher values of n are more relevant. For higher n the cells are quite insulated from each
other, and the capacity is higher – this applies to mini-cells in urban scenarios.
Similarly to a CDMA system, the capacity of an OFDMA system can be enhanced by
sectorization. This involves a slight increase in the base station cost as several receivers are used,
each one with a sector antenna.
Cell Capacity in a 6 MHz Channel [Mb/s]
9
8
n=4
7
6
n = 3.5
5
4
n=3
3
2
1
0
n = 2.5
10
20
30
40
50
K [dB]
Figure 8. Upstream OFDMA cell capacity as a function of propagation coefficient and K.
XII. CONCLUSIONS
This article presented a novel method to enable the delivery of Interactive TV and broadband data
services to existing and future satellite digital TV subscribers. The method is based on the Hybrid
satellite-terrestrial concept that combines the advantages of both technologies into a cost effective
solution. The technical analysis and business model presented herein show the advantages of the
OFDMA based terrestrial return channel over the cable and whole satellite solutions. Finally it
should emphasized that the ingredients for the Hybrid solution are practically available since
DVB-RCT based components are currently offered in the market.
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[1]
[2]
[3]
[4]
[5]
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14
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Digital Set-Top Boxes; Satellite, Cable and Terrestrial Opportunities – Market Research by Allied Business Intelligence, Published
1Q 2002
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