Note: Descriptions are shown in the official language in which they were submitted.
CA 02390976 2002-07-19
1
Dynamic Allocation of Bandwidth for Transmission of Audio Signals and a Video
Signal
FIELD OF THE INVENTION
The present invention relates generally to a method
and apparatus for dynamically allocating transmission
bandwidth resources. Utilization of available bandwidth
is maximized by a using a multiple channel, multiple
carrier (MCMC) transmission scheme. The tr=ansmission
rate capability of each carrier is parsed down into
smaller slots which can be dynamically allocated and
multiplexed to facilitate any sized user, from one slot
to multiple slots. Multiple carriers a~r_~e used to
transmit the allocated data slots on available portions
of the transmission spectrum. At least one slot of
information on each carrier will be used for control
information so that channels or services can be located
on that particular carrier. Additionally, a separate
service might be used to provide system-Wide mapping or
administrative functions. As a result, a user can find
CA 02390976 2002-07-19
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any service even if a channel or service location has
changed. This transmission scheme allows for wide user
flexibility, while also maximizing use of available
transmission spectrum.
In an alternative embodiment, the present invention
generally relates to a method and apparatus for
transmitting at least one digitally encoded video signal
with at least two digitally encoded audio signals
related thereto. According to this alternative
embodiment, the video and audio digital signals are
i
combined through time division multiplexing to produce
an aggregate audio/video bitstream containing data
packets transmitted along at least two channels of fixed
bandwidth, thereby maintaining a known fixed delay
between packets of data in a given channel.
CA 02390976 2002-07-19
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BACKGROUND OF THE INVENTION
Available bandwidth on transmission systems is a
valuable commodity whose value continues to increase as
more and more users and applications crowd the spectrum.
As a result, maximizing the use of available bandwidth
is an important concern for the industry. To date,
systems have not adequately provided for user
flexibility in conjunction with maximum use of available
bandwidth.
Current technology permits modulation of a binary
base band signal into a radio frequency (RF) signal for
transmission and demodulation back into base band. As
shown in Fig. 1, the base band signal 1 enters the
modulator 3 and is converted into RF for transmission
and receipt over antennas 5, 7. Demodulator 9 converts
the received signal back into a base band signal 11.
This transmission scheme is known as single channel per
carrier (SCPC).
Modulators convert base band signals from binary
into the frequency spectrum through a variety of
modulation techniques. Common modulation techniques
include binary phase shift keying (BPSK) and quadraphase
shift keying (QPSK). BPSK has a conversion rate of
approximately 1 kilohertz (KHZ) per 1 kilobit (KB).
QPSK has a conversion rate of approximately 0.5 KHZ per
1 KB. Accordingly, QPSK is more efficient in that
nearly twice as many bits of information can be
CA 02390976 2002-07-19
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transmitted over a similar frequency bandwidth.
However, noise tradeoffs exist as data conversion rates
increase. This limits the effectiveness of increasing
bandwidth usage through modulation techniques with even
higher data conversion rates.
As shown in Fig. 2, SCPC systems generate a
separate RF carrier signal 13, 15 for each base band
input signal 14, 16. Fig. 3 shows a plot of power
'versus frequency for the carrier signals 13, 15 wherein
each signal occupies a separate center frequency 17, 19
with a separate bandwidth 21, 23. Since each channel --
with a separate carrier -- occupies different space on
the frequency spectrum, such SCPC systems are inherently
inefficient for multi-channeled systems.
Referring to Fig. 4, to maximize efficiency, the
space 25 between each carrier signal must be minimized.
However, as shown in Fig. 5, if this space is minimized
too much, then the edges, or "skirts" 27, of the carrier
signals overlap and interfere with each other. This can
lead to erroneous and noisy demodulation of the RF
signal. Alternatively, as shown in Fig. 6, the skirts
27 can be truncated via filtering, but then part of the
original carrier signal has been excluded. This again
could appear as errors or noise upon demodulation.
Current technology also includes multiple channel
per carrier (MCPC) systems as shown in Fig. 7. With
this system, multiple binary base band signals (or
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channels) 31, 33 are multiplexed via a multiplexor 35
and then fed into a modulator 37. The transmitted RF
signal is then demodulated (via 39) and demultiplexed
(via 41) into its component base band signals 43, 45.
As shown by Figs. 8(a) and 8(b), separate carriers --
that might be produced by signals 31, 33 in an SCPC
system -- would have the potentially noisy skirt overlap
49, and a collective bandwidth 47. Sy multiplexing the
signals together, the resulting RF signal shown in Fig.
8(b) would have a comparable bandwidth 51 and yet carxy
more information (e. g. up to 20% more bits), with less
noise, due to more efficient use of the carrier signal
across the corresponding bandwidth 51. Accordingly,
MCPC systems are inherently more efficient than SCPC
systems.
While MCPC systems might be more efficient, they
are often used in very inefficient ways due to the
inflexibility of existing transmission systems. For
instance, to gain the benefits of multiplexing two (or
more) signals together, information must often be
transported or transmitted back to the facility where
the MCPC multiplexing and transmission ultimately
occurs. This practice is known as "backhauling"
information. Referring to Fig. 9(a), an SCPC system 56
is shown with the resulting plot of carrier signal 57.
Fig. 9(b) shows an MCPC system 58 which multiplexes the
signal 57 with the backhauled signal 55 to produce the
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resulting MCPC carrier signal 59. Fig. 10 demonstrates
the relative inefficiency of backhauling; not only is
the band~ridth of signal 59 being used on the frequency
spectrum, the bandwidth of signal 55 is also being used.
Hence, the use of multiple carriers to create an MCPC
signal is relatively inefficient, particularly when
backhauling is employed, because more frequency
bandwidth is ultimately used than with the MCPC system
alone.
The applicant has recognized the need for a
multiple channel multiple carrier system (MCMC) which is
more flexible and allows users of all sizes to access
the system. Multiple carriers, each carrying multiple
channels, can be spread out over the available frequency
spectrum, thus maximizing bandwidth usage. Each carrier
will carry control header information which will allow
location and access to all possible channels spread out
over all possible carriers.
Existing transmission systems transport audio and
video data in satellite and cable TV applications. Fig.
23 illustrates an exemplary audio/video transmission
system including an audio/video encoder 400 which
communicates with a statistical remultiplexor 402 which
in turn communicates with a modulator 404. The encoder
400 receives audio and video signals along input lines
401 and 403 and outputs encoded packets of audio and
video data along lines 406 and 408, respectively. The
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statistical remultiplexor 402 combines the audio and
video uata packets (according to the format illustrated
in. Fig. 25) and outputs same as an aggregate bitstream
along line 412. The aggregate bitstream is transmitted
to a remote destination via antenna 418 by the modulator
404. Feedback lines 410 and 414 are provided to
maintain a desired timing relation between the data
transmission rates of the encoder 400, remultiplexor 402
and transmit module 404.
The transmitted bitstream is received by a
demodulator and the audio and video data packets are
demultiplexed and decoded into separate audio and video
data streams. These decoded data streams are processed
and displayed to end viewers: One such demultiplexor
and decoding system has been proposed LSI Logic
Corporation of California (Model No. L64007 MPEG-2
Transport Demultiplexor). The system proposed by LSI
Logic complies with the international standard ISO/IEC
13818-1 MPEG-2 systems specification. As shown in Fig.
25, the aggregate bitstream 450 is composed of
plurality of data packets 452, each of which includes a
data section 454 and a "presentation time stamp" 456
(explained below in more detail). As shown in Fig. 25,
the statistical multiplexor 402 (Fig. 23) intersperses
the audio and video packets in a non-uniform manner. By
way of example, a single audio packet 458 may be
followed by two video packets 460 and 462, which are
CA 02390976 2002-07-19
followed by alternating audio and video packets 464-472.
The statistical rem~:ltiplexor 402 controls the order in
which the audio and video packets 458-472 are combined.
The presentation time stamps 456 are provided
within each data packet 452 by the encoder 400 to enable
synchronization and realignment, at the downstream end,
between the audio and video signals. Each time stamp
456 represents a timing offset, with respect to a
reference time Tr, at which corresponding audio or video
packet is to be played/displayed.
However, conventional audio/video encoding and
decoding have met with limited success. These existing
systems have been unable to combine multiple audio and
video signals into a single aggregate bitstream in an
optimal manner. As explained above, conventional
systems utilize statistical remultiplexors 402 to
combine audio and video packets. ,
Fig. 26 illustrates an exemplary aggregate
bitstream produced by a statistical remultiplexor which
receives input signals from multiple audio and video
encoders. In the example of Fig. 26, it is assumed that
three audio and video encoders are utilized, denoted
encoders A, B and C. According to the conventional
technique, the statistical remultiplexor combines audio
and video packets from these multiple encoders A-C in a
statistical fashion (as shown in Fig. 26). Thus,
packets pertaining to a particular video encoder or a
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particular audio encoder may be separated by several
packets from dyfferent encoders. Time stamps generated
by a single encoder represent an offset which is reset
to a new reference time at time intervals of a duration
only sufficient to account for the maximum delay between
audio and video data packets for a single encoder.
Hence, packets statistically multiplexed from two or
more encoders exceed the time interval between reference
times. Accordingly, the statistical remultiplexor must
adjust each presentation time stamp to account for the
increased delay due to the use of multiple encoders.
These modified time stamps are denoted by reference
numerals 480-494.
However, the foregoing statistical multiplexing
process is excessively complex, slow and undesirable.
CA 02390976 2002-07-19
1
OBJECTS OF THE INVENTION
The present invention has various embodiments that
achieve one or more c~f the following features or
objects:
It is an object of the present invention to provide
a multiple channel, multiple carrier transmission system
with dynamically allocable base band signal slots (or
channels) to accommodate any sized service.
It is another object of the present invention to
provide a multiple channel, multiple carrier
transmission system wherein each carrier can by
dynamically located to maximize bandwidth usage on the
frequency spectrum.
It is a further object of the present invention to
provide a multiple channel, multiple carrier
transmission system wherein each carrier contains header
information which can provide access to all services on
the series of carriers.
It is yet a further object of the present invention
to provide a multiple channel, multiple carrier
transmission system wherein each carrier contains header
information which can provide access to all services on
the series of carriers, and wherein additional service
space is allocated for such tasks as information
transfer, service identification, and service control.
It is yet a further object of the present invention
to provide a system for digitally encoding and
CA 02390976 2002-07-19
~1
transmitting at least one digital video signal along
with multiple digital audio signals.
It is a corollary object of the present invention
to provide an audio/video encoding and transmitting
system which transmits multiple audio signals related to
a single video signal in a time division multiplexed
manner.
It is a further object of the present invention to
provide a digital encoding and transmitting system which
avoids the need to adjust presentation time stamps
generated within each encoder by maintaining a fixed
delay between data packets from different encoders.
It is yet a further object of the present invention
to provide a digital encoding and transmitting system
25 which assigns fixed bandwidths to each audio and video
signal to be transmitted.
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SUMMARY OF THE INVENTION
The disclosed invention overcomes the
aforementioned inefficiencies of prior transmission
systems by providing a transmission system that is
flexible and efficient. The present invention provides
a multiple channel, multiple carrier transmission system
with dynamically allocable slots (or channels) that can
be combined to form any sized service. Slots could be
allocated sequentially or nonsequentially. The data
rate of each slot is relatively small compared .to the
data rate of the whole system. This allows each user to
purchase and use only the necessary number of bits for
a particular application. As user needs change, the
slots can be dynamically reallocated without affecting
the efficiency of the system, the ease of use by the
user without affecting other slots used by different
users.
Each carrier signal contains reserved header data
regarding all other carriers associated with the
transmission system. This allows all services (e. g.
allocated combinations of slots) to be located
regardless of which carrier signal contains that service
to be located. Accordingly, a plurality of services --
each consisting of one or many slots - can be spread
out over a plurality of carrier signals and so
transmitted. When operating with a plurality of
carriers, each carrier signal can be dynamically tuned
CA 02390976 2002-07-19
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to fill available spaces in the transmission frequency
spectrum, thus maximizing use of all available
transmission bandwidth.
In an alternative embodiment, a method and
apparatus are provided for digitally encoding and
transmitting at least one video signal and at least two
related audio signals. According to this alternative
embodiment, a video encoder is provided along with at
least two audio encoders. The audio and video encoders
generate corresponding audio and video bitstreams, each
of which comprises a plurality of packets containing
data sections. The audio and video bitstreams are
delivered to a multiplexor which effects time division
multiplexing upon to combine the audio and video
bitstreams into an aggregate audio/video bitstream. The
aggregate audio/video bitstream contains at least two
independent channels of fixed bandwidth for separately
transmitting designated ones of the video and audio
bitstreams. A modulator transmits the aggregate
audio/video bitstream. According to the above described
alternative embodiment, fixed delays are maintained
between packets within a single channel, thereby
avoiding the need to adjust any presentation time stamps
which may be generated by the encoders.
Additional features and advantages of the present
invention will become apparent to one skilled in the art
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upon consideration of the following detailed description
of the present invention.
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BRIEF DESCRIPTIONS OF THE DRAWINGS
Figure 1 is a block diagram illu:,~trating a single
channel per carrier (SCPC) transmission scheme.
Figure 2 is a block diagram illustrating the
generation of two separate carrier signals from two
separate SCPC translniasion schemes.
Figure 3 is a plot of power versus frequency for
..the two carrier signals of Figure 2.
Figure 4 is a plot of power versus frequency for
two example carrier signals showing the desire to
minimize the frequency spacing between the two signals.
Figure 5 is a plot of power . versus frequency for
two example carrier signals wherein the frequency
spacing has been minimized to the point that the carrier
signal skirts overlap.
Figure 6 is a plot of power versus frequency for an
example carrier signal wherein the skirts have been
filtered off.
Figure 7 i.s a block diagram illustrating a multiple
channel per carrier transmission scheme.
Figure 8 (a) is a plot of power versus frequency for
two example carrier signals showing skirt overlap for a
given bandwidth.
Figure 8 (b) is a plot of power versus frequency for
the two example carrier signals of Figure 8(a) which
have been multiplexed before modulation.
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Figure 9(a) shows a block diagram of an SCPC system
and a resulting plot of power versus frequency for a
carrier signal with a given bandwidth.
Figure 9(b) shows a block diagram of an MCPC
system, along with an SCPC system for backhauling, and
a resulting plot of power versus frequency for the MCPC
generated signal.
Figure 10 is a plot of power versus frequency for
the MCPC signal and the SCPC signal of Figure 9(b).
Figure 11 shows a block diagram of an MCPC system
with a plurality of input and output channels.
Figure 12 shows a block diagram of the multiplexor
and demultiplexor sections of the MCPC system of Figure
11, with different channels allocated for different
services.
Figure 13 a block diagram of the multiplexor and
demultiplexor sections of the MCPC system of Figure 11,
with yet other channels allocated for other services.
.:
Figure 14 is a table showing the type of
information which allows a user to locate and use a
particular service on a system-wide basis.
Figure 15 is a plot of power versus frequency for
a carrier signal, with a given center frequency and
bandwidth, which contains the services of Figures 13 and
14.
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Figure 16 is a block diagram illustrating an MCPC
system with four slots and secondary multiple~cors for
services spanning more than one slot.
Figure 17 is a table showing the bitstream patterns
of the MCPC system of Figure 16, and the resulting
multi-slot service bitstream.
Figure 18 is a plot of power versus frequency
showing two unaccessible bandwidth areas and three
carrier signals oriented in the available spaces between
the unaccessible areas.
Figure 19 is a block diagram illustrating a
multiple channel, multiple carrier transmission scheme,
with multiple services, corresponding to the carrier
signals of Figure 18.
Figure 20 is a table showing the type of
information which allows a user to locate and use a
particular service on the MCMC system of Figures 18 and
19.
Figure 21 is a block diagram of a multiplexor
configuration as used in an embodiment of the MCMC
system.
Figure 22 is a block diagram of a receiver
configuration as used in an embodiment of the MCMC
system.
Fig. 23 illustrates a block diagram of an exemplary
conventional audio/video encoding and transmitting
system.
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18
Fig. 24 illustrates a block diagram of an
alternative embodiment of an audio/video encoding system
according to the present invention.
Fig. 25 illustrates a portion of an aggregate
audio/video bitstream transmitted by the conventional
system of Fig. 23.
Fig. 26 illustrates an exemplary aggregate
audio/video bitstream generated according to the system
of Fig. 23 for multiple audio and video encoders.
Fig. 27 illustrates an exemplary aggregate
audio/video bitstream generated by the system of the
alternative embodiment of Fig. 24 of the present
invention.
Fig. 28 illustrates a block diagram of an exemplary
decoder for use in connection with the alternative
embodiment of Fig. 24 of the present invention.
CA 02390976 2002-07-19
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DETAILED DESCRIPTION OF TFiE PREFERRED-EMBODIMENT
Referring now to Figure 11, an MCPC system 60 is
shown with a plurality of input channels 61 and a
plurality of output channels 63. As with other MCPC
systems a multiplexor 65 combines tie various channels
into a single bitstream which enters the modulator 67.
The modulator 67 converts the bitstream into an RF
signal 69 which enters the demodulator 71 and is
converted back into a binary signal. The binary signal
enters the demultiplexor 73 which separates the signal
back into its component channels 63.
While each channel of an MCPC system 60 might
handle a variety of data rates from large to small, the
preferred embodiment uses a relatively small, fixed data
rate for each channel. Referring to Figure 12 the
multiplexor and demultiplexor portion of the MCPC system
60 is shown is more detail. As shown for purposes of
example; for the plurality of channels 61 (numbered 0
through N), each channel (or slot) operates at 8
kilobits per second (KBS). This allows for services 75
to be tailored to each user's size and data rate needs.
For example, Services utilizes four slots to give the
user a 32 KBS capability. Service2 utilizes only 1 slot
for a 8 KBS capability: Similarly, Service3 utilizes
only 1 slot for a 8 KBS capability.
The allocation of slots for services does not have
to be sequential. As shown in Figure 13, ServiceN 81
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spans slot 1 (83), slot 2 (85), slot 4 (89), and slot 6
(93) thu creating a service with a 32 KBS data rate
capability. ServiceW 97 spans slot 3 (87) and slot 5
(91) thus creating a service with a 16 KBS data rate
capability. The slot data then enters multiplexor 99
and is modulated into an RF signal and demodulated back
to binary (not shown). The demodulated binary signal
then enters demultiplexor 101 for separation back into
the appropriate slot and service data.
Figure l5 shows the resulting carrier signal 110
which is generated and transmitted by the MCPC system of
Figure 13. Signal 110 is centered about frequency f~ 111
and has a bandwidth (bw) indicated by, 113. Carrier
signal 110 contains all of the multiplexed slot
information which can be extracted if the location of
the services is known.
Figure 14 shows a table of the type of information
that would allow a user to locate and use a particular
' service on a system-wide basis (e. g. a slot allocation
table, along with carrier center frequencies and
bandwidths). It is preferable that the center frequency
and bandwidth of a particular carrier be known to
receive and demodulate the carrier signal. It is also
preferable that the total number of multiplexed slots
(for that particular carrier) be known to facilitate
decoding of the demodulated bitstreame Optionally, the
center frequency, bandwidth and/or the total number of
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multiplexed slots may be computed using related
information, such as bandwidth and the like. For each
service, the total number of slots used for that
particular service should be known, as well as the
particular slot numbers used. As Figure 14 shows,
ServiceN can be located and demodulated at center
frequency f~ with a bandwidth bw. The total number of
slots in this MCPC system is eight. ServiceN uses 4
total slots with slot numbers 1, 2, 4 and 6, for a 32
KBS data rate capability. Similarly, and as part of the
same carrier, ServiceW can be located and demodulated at
center frequency f~ with a bandwidth bw. Again, the
total number of slots in this MCPC system is eight.
ServiceW uses 2 total slots with slot numbers 3 and 5 for
a data rate capability of 16 KBS.
With this table of information, the user can locate
and use the services transmitted on a particular carrier
signal. In the preferred embodiment, the slots used for
each service on a particular carrier are transmitted as
auxiliary header information on a designated, hardwired
slot. While this designated slot might be any of the
total number of slots for each MCPC system, the
preferred embodiment hardwires the ~eroth slot 103 as a
convenient location for such slot allocation
information. Hence, upon demodulating any carrier
signal as configured above, the user can demultiplex the
slot data and get a "map" of all services within that
CA 02390976 2002-07-19
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particular carrier by looking at the zeroth slot data.
With this "map" then all the services on that carrier
can be digitally reconstructed and retrieved.
Referring now to Figure 16, in order for any
particular service to use more than one slot (albeit
sequential or nonsequential), a secondary set of
multiplexors is used to partition the signal down to the
data rate for each of the particular slots. In this
example embodiment, the MCPC system 120 has four slots,
each with a 8 KBS data rate. The zeroth slot I23, 143
is reserved for slot allocation data. The input base
band signal 121 (or service) has a 16 KBS data rate and
uses nonsequential slots 127 and 128 on the primary
multiplexor 130. The secondary multiplexor 132 is used
to partition the 16 KBS signal down into two bitstreams
of 8 KBS as applied to slots 124, 126.
In essence, the secondary multiplexor acts like a
commutative switch 134. By switching back and forth
between the two slots 124 , 126, the 16 KBS bitstream is
halved into two 8 KBS bitstreams by alternatingly
dividing the incoming bits into two different
directions. Larger systems (not shown) might have an
even larger multiple of input lines into the multiglexor
and demultiplexor devices. Hence, the commutative
switching must occur between a large number of input
lines and be programmably alterable as the allocations
of the services are altered or updated. Such selective,
CA 02390976 2002-07-19
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commutative switching between the multiple input lines
could easily be achieved by a device such as a Field
Programmable Gate Array (FPGA) or Programmable Logic
Array (PLA) that has been configured for such a task.
The primary multiplexor 130 also acts like a
commutative switch 136. Multiplexor 130 switches down
across each of the slots 123, 124, 125, and 126, and
thus combines the four 8 KBS bitstreams into a 32 KBS
bitstream 138. Bitstream 138 is modulated, transmitted
as an RF signal, and then demodulated (not shown) back
into a 32 KBS signal 139. The resulting demodulated 32
KBS signal 139 is fed into the primary demultiplexor 140
which similarly acts as a commutative switch 147 to
divide the 32 KBS signal into four slots 143, 144, 145,
and 146 of 8 KBS each. The secondary demultiplexor 150
is connected across slots 144 and 146. Demultiplexor
150 also acts as a commutative switch 152 to alternate
between the 8 KBS bitstreams of slots 144, 146 and
combine them into a resulting 16 KBS signal 154.
Figure 17 demonstrates, in tabular form, the
commutative switching effect of the primary and second
multiplexors and demultiplexors. Referring also to
Figure 16, the demodulated 32 KBS signal 139 is
comprised of a sequence of bits as indicated by row 161.
This sequence 161 is repeatedly divided across the four
slots (numbered 0 through 3), by the commutative action
of the demultiplexor'140, as indicated by row 163. The
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bitstreams are ultimately comprised of service bits
which are labeled as S°S, as shown by :160. According to
this notation, the superscript b represents the ongoing
number of times the series of slots (O through 3) is
sampled on the primary multiplexor. Hence b also
represents the ongoing bit number emerging from each
slot. The subscript s represents the particular slot
number.
Using this notation the assignment of the bits of
the transmitted bitstream 139 to each slot 0 through 3
(elements 143-146) is shown by row 165. As the
commutative action of the multiplexor 140 progresses,
each bit of the incoming bitstream 139 is sequentially,
and repeatedly, assigned to each slot. Slot 1 (element
144) , for example, will have the bitstream S°1, 511, SZ1
. . and so on. (see element 156). Accordingly, the bits
of available data emerging across the four available
Slots would be S°°, S°1, S°2, S°3,
S1°, 511, S12 r 513, Sz°, S21 r
522, S23, . . . and so on. By adding the secondary
demultiplexor 150 across slots 1 and 3 (elements 144,
146), the two 8 KBS bitstreams can be combined into the
16 KBS service bitstream 154 by the commutative action
152 of the demultiplexor 150. As shown by row 167, this
resulting bitstream would include S°l, S°3, S11, S13, 521,
S23, . . and so on.
Using the principles described above, a multi-
channel, multi-carrier (MCMC) transmission system is
CA 02390976 2002-07-19
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even more efficient at utilizing available bandwidth.
With such an MCMC system, a plurality of services could
be allocated across a plurality of MCPC systems.
Referring now to Figure 19, an example MCMC system is
shown. In this example, three MCPC systems 170, 172,
174 are shown which generate RF carrier frequencies 171,
173, 175. Each MCPC system has, for purposes of
example, four slots per multiplexor/demultiplexor.
Services (Svl) utilizes slots 1 and 2 (elements 191
and 192) of the primary multiplexor 220 of MCPC system
170. Hence a secondary multiplexor 222 is used to
divide Svl between the two slots. Sv2 utilizes slot 3
(element 193) of the primary multiplexor 220 of MCPC
system 170. Sv3 utilizes slot 1 (element 195) of the
primary multiplexor 230 of MCPC system 172. Sv4 utilizes
slots 2 and 3 (elements 196 and 197) of the primary
multiplexor 230 of MCPC system 172. Hence a secondary
multiplexor 232 is used to divide Sv4 between the two
slots. Svs utilizes slots 1, 2, and 3 (elements 199,
200, and 201) of the primary multiplexor 240 of the MCPC
system 174. Hence a secondary multiplexor 242 is used
to divide SvS between the three slots.
Referring also to Figure 18, the outputs of the
primary multiplexors 220, 230; and 240 are modulated
into three separate carrier signals 171, 173, and 175.
In Figure 18, two areas of unusable (or already used)
bandwidth 300 and 302 are shown. As a result, carrier
CA 02390976 2002-07-19
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signal 171 has been tuned to have a center frequency fl
- (element 191) and a bandwidth bwl (element 192) so that
signal 171 fits on the transmission spectrum before
signal portion 300. Carrier signal 173 has been tuned
to have a center frequency f2 (element 193) and a
bandwidth bw2 (element 194) so that signal 173 fits on
the transmission spectrum between signals 300 and 302.
Carrier signal 175 has been tuned to have a center
frequency f3 (element 195) and a bandwidth bw3 (element
196) so that signal 175 fits on the transmission
spectrum after signal 302.
By tuning each carrier frequency used by the MCMC
system to fit within the available transmission
bandwidth on the frequency spectrum, usage of the
spectrum is maximized. The Carrier signals 171, 173,
and 175 are then demodulated by their respective
demodulators 226, 236, and 246. The demodulated base
band signals are then fed into their respective primary
demultiplexors 228, 238, and 248. As described above,
the service bits on the autgut slots 250 through 261 are
multiplexed by secondary multiplexors 229, 239, and 249
to reconstruct the bitstreams for services 1 through 5
(Svl through Svs -- 180, 182, 184, 186, and 188).
The preferred embodiment also utilizes one complete
service -- exemplified here as services -- for a variety
of administrative or "housekeeping" tasks. The number
of slots allocated for this administrative service could
CA 02390976 2002-07-19
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vary depending upon the needs of the particular MCMC
system in question. The bits in this service might be
used, among other things, to perform the following
functions: downloading (or uploading) software to (or
from) a particular customer as needed; alphanumeric
identification of services or carriers within the MCMC
system or community; turning on or off various services
within the MCMC system as required; and/or providing a
revision number for the slot allocation table as
contained in zeroth slot data.
As for transferring software, the MCMC network host
might provide its service subscribers with periodic
upgrades of software used to interact with the MCMC
system. By allocating separate bits for this task, the
service subscribers would be minimally affected by such
upgrades. This would promote continual development of
related software by the host and would likely result in
more optimal system performance and bandwidth savings.
Similarly, the services data might provide
alphanumeric names for the various services within the
MCMC network. Often this is much more useful to a user
or service subscriber than a service number or other
minimal identification means.
Occasionally, entire services might need to be
turned on or. off for maintenance and/or billing
purposes. The services data might provide such
CA 02390976 2002-07-19
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individualized control over the various services within
the MCMC network.
As for the slot allocation table revision number,
the zeroth slot -- with its slot allocation table -
will always be found in the ame place on any particular
demodulated and demultiplexed carrier signal; thereby
acting as a "beacon" for the user to learn about that
particular carrier signal. However, the remaining slots
which comprise the various MCMC services can be
dynamically altered and reallocated as the needs of the
many users change. As a result, the slot allocation
table will be revised and carry with it a new revision
number. As indicated above, the administrative service
(e. g: services) will show the most recent revision
number. If a user is operating with an outdated version
of the slot allocation table, the zeroth slot can be
decoded to provide updated slot allocation information
on an as needed basis.
As detailed above, the zeroth slots (input slots
190, 194, 198 and output slots 250, 254 ,258) are used
for slot allocation data information which will allow
the user to locate, demodulate and reconstruct the
various services within each particular carrier. As
combined with the Services data, a full "map" of the MCMC
system can be quickly derived by the user. In
operation, the disclosed device will internally switch
back and forth between slot zero and Services data as
CA 02390976 2002-07-19
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needed and carry the data on an In-Band Carrier Channel
(See Figures 21 and 22) for processing. -
For instance, upon startup of the system, a
designated carrier is acquired and the slot zero data is
processed via the Ln-Band Carrier Channel. Once the
Slot Allocation Table for the carrier is acquired, the
system automatically switches over to process Services
data. Services data can provide a system-wide "map" of
the MCMC system, and/or it can provide the other
aforementioned Services functions. However, if the
revision number of the slot allocation table changes,
the system will automatically switch back to read slot
zero data until a new and updated slot allocation table
is acquired. As a result, Services is the "steady state"
condition for the data on the In-Band Carrier Channel.
Only when a new carrier is acquired or when the slot
allocation table changes does the In-Band Carrier
Channel carry slot zero again data for processing.
Referring to Figure 20, an example table is shown
with the type of slot zero data and/or Services data
necessary to locate and reconstruct all service data on
all the MCMC carrier signals for this particular system.
The zeroth slot will carry the slot allocation data for
each particular carrier. The Services data will provide
such system-wide data as the center carrier frequencies
and the carrier bandwidths for all carriers in the MCMC
system. By internally switching, as necessary, between
CA 02390976 2002-07-19
these two data sources, a complete set of system-wide
information (as shown in Figure 20) can be collected and
maintained more efficiently than placing all such data
on only one data path. By providing this full "map" to
5 the system, any service can be dynamically allocated and
reallocated without affecting a users ability to find
all of the services within a particular MCMC
transmission system.
Accordingly, the MCMC transmission system of the
10 present invention provides an efficient and versatile
way to transmit data across available bandwidth on the
transmission spectrum. The present invention utilizes
the benefits of multiplexing multiple channels of
information before modulating and transmitting the
15 information as a carrier signal. Additionally, the
present invention allows for users of all sizes to
utilize only the particular amount of data transfer
capability that they need. Hence, individual services
can range in size from the basic rate of one slot (e. g.
20 8 KBS) on up to the entire capability of the entire MCMC
transmission system. Moreover; the present MCMC system
utilizes multiple carrier signals to transmit the
allocated data services. A slot of header data is
reserved in each carrier signal which provides the
25 location of all services within that carrier. A
separate service (e.g. one or many slots) might also be
CA 02390976 2002-07-19
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allocated for system administration and/or system-wide
mappi~:g
Referring now to Figure 21, a block diagram of the
multiplexor configuration is shown as used in the
preferred embodiment of the disclosed MCMC system. A
microprocessor 300 is used to control the flow of the
incoming service data. Accompanying hardware to the
microprocessor 300 includes a flash memory 318 for
program storage, a ram 320 for storage of variables and
processor operation, and NV memory 322 for parameter
storage. While any microprocessor might adequately
perform such control, the preferred embodiment uses a
Motorola 68302 and was chosen because of its preferred
instruction set, data handling capabilities, reasonable
cost and development toolset available.
The microprocessor 300 writes information relating
to the aforementioned slot allocation table into a dual
port RAM 318. As detailed above, the slot allocation
table contains information regarding the various carrier
center frequencies, the carrier bandwidths, and the
slots used for each service (e.g. "format information").
Such format information might enter the microprocessor
from a~ variety of sources. The preferred embodiment
uses a separate computer system, known as a Network
Management System (NMS) 316, to solicit and manage this
format information. The NMS 316 uses a Windows
application program to query and accept format
CA 02390976 2002-07-19
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information from an operator. The format information is
then fed into the iaicroprocessor 300 via a serial RS232
data link 317.
As shown in this embodiment, Parts A through XX
(elements 301 through 306) represent input ports for
individual services (henceforth service ports) which are
composed of one or more data slots (e,g. 8 KBS slots as
discussed above). Since each service port might consist
of one or more data slots, each service port has its own
clock rate based upon the number of data slots
designated for that particular service on that
particular service port. For instance, a service port
using five 8 KBS slots would have a higher clock rate
(e.g. 4o kilohertz) than a service port using only one
8 KBS slot. As with other synchronous systems, this
embodiment utilizes one clock cycle per bit. Such
control data is maintained and transmitted via an In
Band Control Channel 324 which carries information
gleaned from the zeroth"slot and the administrative
service (previously exemplified as Services).
The service ports 301-306 are queued into a
multiplexor control device 308 via a series of FIFO
(first in, first out) buffers 307-312. The FIFO outputs
enter the multiplexor control device 308 through a bus
313 in the order requested by the multiplexor control.
The multiplexor request sequence is a function of the
information format for the MCMC system. As mentioned
CA 02390976 2002-07-19
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above, such multiplexor control and processing is
achieved through a programmable device such as an FPGA.
The FIFO'ed service port data is then multiplexed via
multiplexor control 308 into an aggregate data stream
314 which is output to a modulator (not shown) for
modulation and transmission to a respective receiver.
Referring now to Figure 22, a block diagram of the
r-eceiver configuration is shown as used in the preferred
embodiment of the disclosed MCMC system. In this
configuration, a demodulator 350 converts the
transmitted carrier signal (not shown) into an aggregate
data stream 352 which enters a demultiplexor control
block 354. As with the multiplexor before,
demultiplexor control is also achieved via an FPGA
device.
The demodulator 350 is controlled via a
microprocessor 356. As with the multiplexor
configuration, accompanying hardware to this separate
microprocessor 356 includes a flash memory 358 for
program storage, a ram 360 for storage of variables and
processor operation, and NV memory 362 for parameter
storage. Again, a Motorola 68302 was used for similar
reasons and advantages as stated above.
The microprocessor 356 gleans format information
data (e. g. slot zero and administrative Services
information) from an In-Band Control Channel 364 as fed
from demultiplexor control 354. Such format information
CA 02390976 2002-07-19
34 -
is written into a Dual Port RAM 366 in the form of a
Slot Allocation Table. The demultiplexor control 354
then reads this Slot Allocation Table data from the Dual
Port RAM 366 and uses this data in order to properly
demultiplex the demodulated bitstream 352 into the
various services. Once properly demultiplexed, the
services are output as the various service Ports A-F
(elements 368-373). As comparable to the multiplexor
configuration, each service port might consist of one or
more data slots, with each service port having its own
clock rate based upon the number of data slots
designated for that particular service on that
particular service port. Having now been received and
decoded, the MCMC services of this particular system can
now accessed via the service ports 368-373.
Fig. 24 illustrates an alternative embodiment of
the present invention. In the embodiment of Fig. 24, a
system 500 is provided for digitally encoding and
transmitting multiple audio and video signals related to
one another. The system 500 includes a plurality of
encoders 502-508 which receive corresponding input
signals along lines 510-516. The input signals at lives
510-516 may be analog or digital. If the input signals
represent digital signals, the encoders 502-580 may
include A/D converters to provide digital input signals.
The input signals at lines 510-516 may represent any
combination of audio and video signals.
CA 02390976 2002-07-19
- 35 -
By way of example; the input signal at line 510 may
represent a video signal, while the remaining input
signals at lines 512-516 represent audio signals.
Optionally, the audio signais at lines 512-516 may
relate to the video signal at line 510. For instance,
each of lines 512-536 may carry the speech portion of a
television show, sports event and. the like in separate
languages. Hence, line 510 may carry the video signal
for a movie, while line 512 carries the audio signal for
l0 the movie in English, line 514 carries the audio signal
for the movie in French and line 516 carries the audio
signal for the movie in German.
Optionally, the input lines 510=516 may carry any
desired combination of audio and video signals, such as
one audio signal with three video signals, one video
signal with four audio signals, two video signals with
six audio signals and the like.
For purposes of explanation, the alternative
embodiment contemplates using a single video signal at
line 510 with multiple related audio signals at lines
512-516 carrying audio signals of different languages.
The encoders 502-508 output encoded audio and
video signals along lines 518-524 as packetized bit
streams which are formatted, as explained above. The
individual streams of packetized data are supplied to a
multiplexor 526 which combines the input signals to form
an aggregate bitstream output along line 532. The
CA 02390976 2002-07-19
- 36 -
multiplexor 526 combines the data packets from lines
518-524 in a time division multiplexed manner to form
the aggregate bit stream 550 (Fig. 27). The aggregate
bitstream is supplied to a modulator 528 which outputs
same via link 530. Optionally, the encoders,
multiplexor and modulator may include internal memory
and buffers to temporarily store data. Data is
transmitted to and read from this temporary storage in
a first-in-first-out manner.
Control lines 534-542 are provided as feedback to
control the transmission rate at which packets of data
are transmitted from the encoders 502-508 to the
multiplexor 526 and from the muitiplexor 526 to the
modulator 528. Optionally, the transmission rates and
timing of the encoders, multiplexor and modulator may be
controlled from a remote processor (not shown).
Next, the discussion turns to Fig. 27 which
illustrates an exemplary aggregate bitstream 550
generated by the multiplexor 526 based on a time
division multiplexing technique. The aggregate
bitstream 550 includes a plurality of data sets 555,
each of which inc3udes a single slot or channel 554
assigned to each encoder 502-508.
During operation, the multiplexor 526 accesses the
multiplexer~s internal memory/buffers for each of lines
518-524 to obtain a set of data packets containing a
single data packet associated with each input line 518
CA 02390976 2002-07-19
- 37 -
524. The multiplexor 526 combines this set of data
packets as illustrated in Fig. 27 in a time division
multiplexed manner. Consecutive slots 554 receive a
corresponding data packet from the assigned input line
518-524. Thus, each slot 554 of a data set 555 includes
a single data packet 556-562 for each encoder 502-508.
Optionally, each of packets 556-562 includes a
presentation time stamp 564-570. The presentation time
stamps 564-570 represent offsets with respect to
internal reference timers of corresponding encoders 502-
508 as explained.
Once the data set 555 is formed in the multiplexor
526, the set 556 is transmitted to the modulator 528.
Thereafter, the multiplexor 526 generates a next data
set 572 of packets 574-580. This process may be
continually repeated throughout operation.
While the preferred embodiment of Fig. 24
illustrates far encoders, it is understood that any
number of encoders may be utilized. Each data set 555,
572 of data slots 554 will be modified to include one
slot per encoder.
Fig. 28 generally illustrates a decoding system 600
according to the present invention. The decoding system
600 includes a demultiplexor 602 which receives the
aggregate bitstream 604 as its input. The demultiplexor
602 separates each data set 555 (Fig. 27) of data
packets 556-562. The demultiplexor 602 and transmits a
CA 02390976 2002-07-19
- 38 -
data packet from a single slot 554 in the set 555 along
a corresponding output line 606 and 608.
More specifically, decoder demultiplexor 602
includes one output port 610-616 for each slot 554 of an
incoming data set 555. For a given data set 555, the
demultiplexor 602 delivers the data packet from slot #1
to the first port (e. g., 610), the data packet from slot
#2 to the second port (e . g . , port 612 ) , and the l ike .
The decoding system 600 may connect decoders 618 and 620
l0 to predetermined output ports of the demultiplexor 602
through switches 609 and 611. The connected output
ports correspond to slots 554 in the aggregate bitstream
which contain desired data.
In the example of Fig. 28, it is desirable to
decode the data streams from the first and third
encoders (502 and 506 in Fig. 24). Hence, decoders 618
and 620 are connected at switches 609 and 611 along
lines 606 and 608 to output ports 610 and 614,
respectively.
With reference to Fig. 27, decoder 618 decodes all
packets 556 within the first slot of each data set 555.
Decoder 620 decodes all packets 560 received within the
third slot 553. The decoders 618 and 620 may output
analog signals corresponding to the decoded bitstreams
along lines 622 and 624, respectively. The analog
signals are supplied to a display 626 which presents
corresponding audio and video information to a viewer.
CA 02390976 2002-07-19
- 39 -
By way of example, when the aggregate bitstream 604
includes a single video signal (such a~ corresponding to
a movie) and a plurality of audio signals (such as
corresponding to the soundtrack for the movie recorded
in multiple languages), decoder 618 may decode the video
signal, while decoder 620 decodes an associated audio
signal for a desired language (e. g., English, French,
German and the like). Thus, the display 626 may play a
movie with a French soundtrack. Alternatively, by
l0 connecting the decoder 620 to one of ports 612 and 616,
the display 626 may output the audio track in a
different language.
According to the example explained above, the
preferred embodiment of the present invention enables
multiple audio signals to be transmitted in different
languages with a single related video signal. Hence,
the need is avoided for transmitting separate video
signals for each audio signal.
While several alternative embodinvents, of the
invention have been described hereinabove, those of
ordinary skill in the art will recognize that the
embodiments may be modified and altered without
departing from the central spirit and scope of the
invention. Thus; the embodiments described hereinabove
are to be considered in all respects as illustrative and
not restrictive, the scope of the invention being
indicated by the appended claims, rather than by the
CA 02390976 2002-07-19
40 -
foregoing descriptions, and all changes which come
within the meaning and range of equivalency of the
claims are intended to be embraced herein.
