Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-07-02
2001-04-03
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S477000, C348S388100, C348S423100
Reexamination Certificate
active
06212201
ABSTRACT:
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 transmission 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 are 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 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 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.
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 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 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
. By multiplexing the signals together, the resulting RF signal shown in FIG.
8
(
b
) would have a comparable bandwidth
51
and yet carry 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 resulting MCPC carrier signal
59
.
FIG. 10
demonstrates the relative inefficiency of backhauling; not only is the bandwidth 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 statistical remultiplexor
402
combines the audio and video data 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 p
Fish Laurence A.
Hinderks Larry W.
Lerner Ian
Roberts, III Roswell R.
Hsu Alpus H.
McAndrews Held & Malloy Ltd.
Ryan Robert C.
StarGuide Digital Networks, Inc.
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