Integrated video and audio signal distribution system and method for use on commercial aircraft and other vehicles

A passenger entertainment system employing an improved digital audio signal distribution system and method for use on commercial aircraft and other vehicles. A plurality of digital audio signal sources are provided for generating a plurality of compressed digital audio signals. The compressed digital audio signals are provided to a multiplexer which domain multiplexes those signals to produce a single composite digital audio data signal. The composite digital audio data signal is provided to a demultiplexer which is capable of selecting a desired channel from the composite digital audio data signal. The selected channel is provided to a decompression circuit, where it is expanded to produce a decompressed digital output signal. The decompressed digital output signal is then provided to a digital-to-analog converter and converted to an analog audio signal. The analog audio signal is provided to an audio transducer.

FIELD OF THE INVENTION 
The field of the present invention is onboard entertainment systems for use 
in large commercial aircraft and other passenger vehicles. 
Recently, substantial attention has been directed to the design and 
implementation of cabin entertainment and communications systems for use 
in large commercial aircraft. Examples of such systems are disclosed in 
U.S. Pat. No. 3,795,771, entitled "Passenger Entertainment/Passenger 
Service and Self-Test System;" U.S. Pat. No. 4,428,078, entitled "Wireless 
Audio Passenger Entertainment System (WAPES);" U.S. Pat. No. 4,774,514, 
entitled "Method and Apparatus for Carrying Out Passenger-Related and 
Flight Attendant-Related Functions in an Airplane;" U.S. Pat. No. 
4,835,604, entitled "Aircraft Service System with a Central Control System 
for Attendant Call Lights and Passenger Reading Lights;" U.S. Pat. No. 
4,866,515, entitled "Passenger Service and Entertainment System for 
Supplying Frequency-Multiplexed Video, Audio, and Television Game Software 
Signals to Passenger Seat Terminals;" and U.S. Pat. No. 5,123,015, 
entitled "Daisy Chain Multiplexer". 
As shown in FIG. 1, conventional (or prior art) passenger entertainment 
systems 1, such as those disclosed in the previously identified patents, 
generally comprise a plurality of audio signal sources 2 (e.g. compact 
disc players and audio tape players), a plurality of analog-to-digital 
(A/D) converters 3 for converting analog signals generated by the audio 
signal sources to a digital format, a multiplexer 4 for time domain 
multiplexing (combining) the converted digital signals, a signal 
distribution network 5 for conveying the multiplexed signal to a plurality 
of remote locations, at least one demultiplexer 6 for demultiplexing the 
combined signal and selecting one or more channels from the combined 
signal, a plurality of digital-to-analog (D/A) converters 7 for converting 
the selected channels to an analog format, and a plurality of audio 
transducers 8 which convert the analog signal(s) to sound waves. 
Those skilled in the art will appreciate that, while conventional compact 
disc players are capable of providing digital signal outputs, those 
digital signal outputs are simply not used in conventional passenger 
entertainment systems. One primary reason for this is that compact disc 
players generally include their own internal oscillators and, thus, if a 
plurality of conventional compact disc players are utilized, their 
respective digital outputs will be asynchronous. This makes the 
combination of a plurality of digital outputs quite difficult. Another 
primary reason that the digital outputs of conventional compact disc 
players are not utilized is that conventional compact disc players provide 
a digital signal output having a 16-bit sample size and a 44 kHz sampling 
rate. This makes it difficult to distribute a large number of channels 
(for example, fifty channels or more) over an audio signal distribution 
network without exceeding desirable power consumption levels or incurring 
significant bit error rates. For example, if a conventional compact disc 
player output having a 16-bit sample size and a 44 kHz sampling rate is to 
be utilized in a 72-channel system, a transfer rate exceeding 50 megabits 
per second would be required. However, conventional systems capable of 
achieving a 50 megabit per second transfer rate require considerably more 
power than is desirable in an aircraft environment. In addition, these 
systems require heavier circuitry, generate more heat, and occupy more 
space than is desirable in an aircraft environment. 
Those skilled in the art will appreciate also that, as data transfer rates 
are increased, cable attenuation and distortion also increase. These 
increases in cable attenuation and distortion contribute substantially to 
transmission difficulties and, in particular, to increased bit-error 
rates. 
As a means for reducing data transfer rates and eliminating many of the 
complications in data transmission which result therefrom, conventional 
passenger entertainment systems utilize the analog output signals S1 
provided by conventional compact disc players 2 and convert those output 
signals to a digital format using an analog-to-digital (A/D) converter 3. 
In this fashion, the sample size and sampling rate of the converted signal 
may be selected so as to minimize the transfer rate required to distribute 
a large number of channels. This technique, however, while making it 
possible to obtain a more desirable transfer rate, substantially 
sacrifices audio fidelity or quality. More specifically, as the sample 
size and sampling rate of the converted signal are reduced, the resolution 
of the digital representation of the original analog audio signal is 
diminished, and substantial signal degradation may result due to 
quantization error. This signal degradation places a practical limit on 
the extent to which the sample size and sampling rate may be reduced. 
Those skilled in the art will appreciate also that in an aircraft 
environment substantial background noise may be introduced into the system 
whenever a signal is distributed in an analog format. Moreover, the most 
common type of noise in an aircraft environment is produced by the 
aircraft power distribution system and has a frequency of approximately 
400 Hz. This type of noise will hereinafter be referred to as "400 Hz 
background noise." Because of this 400 Hz background noise, unless 
substantial shielding is utilized, it is very difficult on an aircraft to 
convert an analog audio source signal to a digital format without 
including substantial background noise in the resulting digital signal. As 
indicated above, however, it appears to be universally accepted among 
manufactures of conventional passenger entertainment systems that, to 
achieve satisfactory data transfer rates and satisfactory power 
consumption levels, it is necessary to utilize the analog output signals 
of conventional compact disc players and to convert those analog output 
signals to a digital format having a sufficiently low sample size and 
sampling rate. For this reason, the presence of a substantial quantity of 
quantization noise, 400 Hz background noise, signal cross-talk, and the 
like is inherent in all conventional passenger entertainment and audio 
signal distribution systems. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved passenger entertainment 
system, which employs an improved audio signal distribution system and 
method, for use in commercial aircraft and other vehicles. By employing 
the system and method of the present invention, high channel capacity and 
low power consumption are achieved, while substantial immunity to 
quantization noise, background noise, cross-talk, and the like is 
maintained. 
In one preferred form, a passenger entertainment system in accordance with 
the present invention comprises a plurality of "true" digital signal 
sources (for example, a plurality of specialized compact disc players 
capable of providing a compressed digital audio signal output), a 
multiplexer, a signal distribution network, at least one demultiplexer, at 
least one decompression circuit, at least one digital-to-analog converter, 
and at least one audio transducer. 
The digital audio signal sources receive clock and enable signals from the 
multiplexer and, in response, provide a plurality of compressed digital 
audio signals to the multiplexer. The multiplexer multiplexes the 
compressed digital audio source signals to create a composite digital 
audio signal and delivers the composite digital audio signal to the 
distribution network. The distribution network carries the digital 
composite signal to at least one remote location where a demultiplexer is 
disposed. The demultiplexer selects one or more desired channels (or 
signals) from the composite signal and provides the selected channels to a 
decompression circuit. Each decompression circuit decompresses the 
channels delivered thereto and provides each of the resulting expanded 
digital audio signals to a digital-to-analog converter. Each 
digital-to-analog converter converts the expanded digital audio signal 
delivered thereto to an analog audio signal which is then provided to an 
audio transducer disposed, for example, in a passenger headset. Finally, 
each audio transducer generates sound waves in response to the analog 
audio signal delivered thereto. 
Those skilled in the art will recognize that, because a passenger 
entertainment system in accordance with the present invention maintains 
transmitted digital audio data in a compressed digital format until that 
data reaches a remote seat location, substantial immunity to quantization 
noise, background noise, cross-talk, and the like is achieved. In 
contrast, conventional passenger entertainment systems, which require that 
all audio data be provided in an analog format and, then, be converted to 
a digital format, are inherently prone to picking up 400 Hz background 
noise which may cause substantial signal degradation. More specifically, 
any signal which exists in an analog format in the noisy environment of a 
commercial aircraft is subject to distortion or degradation resulting from 
400 Hz background noise. If an audio source signal is allowed to exist in 
an analog format that signal may become distorted as set forth above 
before it is converted to a digital format, and any signal resulting after 
an analog-to-digital conversion will represent the distorted audio signal, 
not the original audio signal. For this reason, users of conventional 
passenger entertainment systems must provide substantial shielding on 
incoming and outgoing signal lines or employ substantial decontamination 
(noise reduction) circuitry. If they do not, they must accept the presence 
of substantial noise in the transmitted audio signal. 
Finally, those skilled in the art will recognize that, by utilizing digital 
signal sources capable of providing compressed digital audio signals to 
the signal distribution network via the multiplexer and later 
decompressing those signals, the passenger entertainment system of the 
present invention achieves far superior signal reproduction than that 
which is achievable using the A/D conversion technique characteristic of 
prior art systems. More specifically, when the systems of the prior art 
(including those disclosed in the previously identified patents) convert 
analog audio signals provided by conventional compact disc players to 
digital signals having, for example, an 8-bit sample size and a 20-30 kHz 
sampling rate, signal resolution and, therefore, signal fidelity or 
quality is sacrificed substantially. In contrast, when a digital signal 
having a 16-bit sample size and a 37.8 kHz sampling rate is compressed to 
produce a digital signal having a 4-bit sample size and the same sampling 
rate in accordance with the present invention, signal degradation is 
encountered, but only to a very small degree. Stated somewhat differently, 
digital signal compression yields close to a 4-to-1 reduction in the 
volume of data to be transported over the signal distribution network 
without incurring a noticeable degradation in sound quality. 
In a preferred form, the passenger entertainment system of the present 
invention may comprise, in addition to the digital audio signal 
distribution system described above, a plurality of analog video signal 
sources, a plurality of analog audio signal sources, a passenger address 
system, a plurality of overhead video projectors, a plurality of inseat 
video displays, and a modular signal distribution network capable of 
transmitting all audio and video signals to a plurality of remote seat 
locations over a single coaxial cable. These embodiments are discussed 
more fully below in the section entitled "Detailed Description." 
In light of the above, it is an object of the present invention to provide 
an improved passenger entertainment system, which employs an improved 
digital audio signal distribution system and method, for use on commercial 
aircraft and other vehicles. 
It is a further object of the present invention to provide an improved 
passenger entertainment system, which employs an improved integrated video 
and audio signal distribution system and method, for use on commercial 
aircraft and other vehicles. 
It is a still further object of the present invention to provide a 
passenger entertainment system which is capable of distributing an 
integrated video and compressed digital audio signal over a single coaxial 
cable. 
It is a still further object of the present invention to provide a method 
for efficiently transmitting digital signal compression factors over 
digital signal distribution networks such as those utilized on commercial 
aircraft and other vehicles.

DETAILED DESCRIPTION 
In an effort to highlight various embodiments and innovative aspects of the 
present invention, a number of sub-headings are provided in the following 
discussion. In addition, where a given structure appears in several 
drawings, that structure is labeled using the same reference numeral in 
each drawing. 
Digital Audio Signal Distribution System 
Turning now to the drawings, FIG. 2 is a block diagram illustrating the 
basic components of a digital audio signal distribution system 10 in 
accordance with one form of the present invention. As shown, the digital 
audio signal distribution system 10 comprises a plurality of "true" 
digital signal sources 12, a multiplexer 14, a signal distribution network 
16, a plurality of demultiplexers 18, a plurality of decompression 
circuits 20, a plurality of digital-to-analog converters 22, and a 
plurality of audio transducers 24. 
Each digital audio signal source 12 may comprise, for example, a compact 
disc player, Model No. RD-AX7091, manufactured and sold by Matsushita 
Electronics Industrial Co., Ltd., of Osaka, Japan. Further, in a preferred 
form each digital audio signal source 12 is capable of receiving a 
plurality of clock and enable signals from the multiplexer 14 and, in 
response to those signals, generating a compressed digital audio signal 
output having a 4-bit sample size and a 37.8 kHz sampling rate. More 
specifically, prior to being stored on a compact disc (or other digital 
media), digital audio data is compressed from a 16-bit format to a 4-bit, 
compact disc interactive (CD-I), level B format by adaptive delta pulse 
code modulation (ADPCM). ADPCM compression and the CD-I level B format are 
well known in the art and, thus, they will not be discussed in further 
detail herein. 
In a preferred form, each of as many as six digital signal sources 12 
provides eight channels (4 stereo, or 8 mono) of compressed digital audio 
data to the multiplexer 14. Upon receiving the compressed digital audio 
channels from the digital audio signal sources 12, the multiplexer 14 time 
domain multiplexes (combines) the received compressed digital audio 
signals to form a single composite audio signal. In a preferred form, the 
composite audio signal has a transfer rate of 19.3536 MHz. The multiplexer 
14 delivers the composite audio signal to the signal distribution network 
16, and the signal distribution network 16 carries the composite audio 
signal to a plurality of remote locations, such as passenger seats, where 
one or more demultiplexers 18 are disposed. Each demultiplexer 18, under 
the control of a digital passenger control unit (DPCU) 134 (shown in FIG. 
3), selects one or more desired channels from the composite signal and 
provides each selected channel to a decompression circuit 20. Each 
decompression circuit 20 decompresses the channel (signal) delivered 
thereto and provides the resulting expanded digital signal to a 
digital-to-analog (D/A) converter 22. Each of the digital-to-analog 
converters 22 converts the signal delivered thereto to an analog audio 
signal which is passed on to an audio transducer 24. Finally, each audio 
transducer converts the analog audio signal delivered thereto to sound 
waves. 
As set forth above, because a passenger entertainment system 10 in 
accordance with the present invention performs only a single 
digital-to-analog conversion on each selected channel, substantial 
immunity to background noise, cross-talk, and the like is achieved. 
Moreover, the only digital-to-analog signal conversion performed by a 
system 10 in accordance with the present invention is that required to 
convert a selected decompressed digital audio signal to a form usable by 
the audio transducer(s) 24. Further, by utilizing "true" digital audio 
signal sources 12 capable of providing compressed digital audio signals to 
the signal distribution network 16 via the multiplexer 14 and later 
decompressing those signals, the passenger entertainment system 10 of the 
present invention achieves far superior signal resolution than that which 
is achievable using the A/D conversion technique characteristic of prior 
art systems. More specifically, when the systems of the prior art convert 
the analog audio signals provided by conventional compact disc players to 
digital signals having, for example, an 8-bit sample size and a 20-30 kHz 
sampling rate, signal resolution (fidelity or quality) is sacrificed 
substantially. In contrast, when a digital audio signal having a 16-bit 
sample size and a 37.8 kHz sampling rate is compressed to produce a 
digital signal having, for example, a 4-bit sample size and the same 
sampling rate, signal degradation is encountered, but only to a very small 
degree. In essence, digital signal compression yields close to a 4-to-1 
reduction in the volume of data to be transported over the signal 
distribution network without incurring a noticeable degradation in sound 
quality. 
Passenger Entertainment System Overview 
Turning now to FIG. 3, in a preferred form a passenger entertainment system 
100 in accordance with a preferred form of the present invention may 
comprise a mix of audio, video, and control signal sources including a 
plurality of true digital audio signal sources 102, a plurality of video 
signal sources 104, one or more analog audio signal sources 106, a cabin 
management terminal 108, and a cabin intercommunications data system 
(CIDS) 110. These audio, video, and control signal sources 102-110 are 
connected to each other and to a plurality of remotely located audio 
headsets 114, in-seat video monitors 116, and overhead video monitors 118 
via a combined audio and video signal distribution system comprising a 
video system control unit (VSCU) 120, a passenger entertainment system 
controller (PESC) 122, a video modulator unit (VMU) 124, a plurality of 
area distribution boxes (ADBs) 126, a plurality of floor disconnect boxes 
(FDBs) 128, a plurality of seat electronics boxes (SEBs) 130, a plurality 
of tapping units (TUs) 132, a plurality of digital passenger control units 
(DPCUs) 134, a plurality of inseat video cassette players (IVCPs) 136, and 
a plurality of video cassette player controllers (VCPCs) 138. Many of the 
above identified signal sources 102-110 and signal distribution system 
components 120-138 will be discussed in more detail below. However, it is 
believed that the following general discussion will prove helpful in 
gaining a full understanding of the structure and function of an improved 
passenger entertainment system 100 in accordance with the present 
invention. 
As set forth above in the section entitled "Digital Audio Signal 
Distribution System," it is presently preferred that each of the plurality 
of digital audio signal sources comprise a compact disc player, Model No. 
RD-AX7091, manufactured and sold by Matsushita Electronics Industrial Co., 
Ltd., of Osaka, Japan. It is preferred, also, that each of the digital 
audio signal sources 102 be capable of providing a compressed digital 
audio signal output comprising eight (8) channels (4 stereo or 8 mono) and 
having a 4-bit sample size and a 37.8 kHz sampling rate. Moreover, any 
compact disc player (CDP), digital audio tape player (DAT), or other 
digital audio signal source 102 capable of generating a digital output 
signal comprising eight (8) channels in a compact disc interactive (CD-I) 
level B format and capable of synchronizing to the frame format utilized 
by the system via provided control signals (i.e. clock and enable signals) 
may be used in accordance with the preferred form of the present 
invention. 
Each of the compressed digital audio signals generated by the digital audio 
signal sources 102 is delivered to a separate input (not shown) of the 
video system control unit (VSCU) 120. The structure and function of the 
video system control unit 120 is described in detail in the section 
entitled "VSCU Structure and Function" below. However, at this point it 
should be understood that a multiplexer (not shown) disposed within the 
video system control unit 120 time domain multiplexes the compressed 
digital audio signals delivered thereto and produces a composite pulse 
code modulated (PCM) data signal. The composite PCM data signal is then 
delivered to a filter/combiner 312 (shown in FIG. 5) for combination with 
a composite RF video signal received from the video modulator unit (VMU) 
124, and the resulting composite PCM/RF video signal is delivered to the 
passenger entertainment system controller (PESC) 122. 
In a preferred form, the passenger entertainment system controller (PESC) 
122 performs a second multiplexing operation which adds an additional 
twenty-four (24) entertainment channels and six (6) passenger address 
channels to the composite PCM/RF video signal. More specifically, the 
passenger entertainment system controller (PESC) 122 separates the 
composite PCM data/RF video signal into its respective PCM data and RF 
video components. The additional data channels are added to the PCM data 
portion of the separated signal and then the PCM data and RF video 
portions of the composite signal are recombined for further transmission. 
Next, the composite PCM/RF video signal is delivered from the passenger 
entertainment system controller (PESC) 122 to a plurality of area 
distribution boxes (ADBs) 126. The area distribution boxes (ADBs) 126 are 
arranged in a daisy-chain configuration, and it is presently preferred to 
provide a maximum of eight area distribution boxes along each daisy-chain. 
However, those skilled in the art will recognize that additional area 
distribution boxes 126 may be provided depending, for example, upon the 
type of coaxial cable (not shown) which is used to connect the area 
distribution boxes (ADBs) 126. Each area distribution box 126 taps off a 
small portion of the composite PCM/RF video signal. Then, the tapped 
composite PCM/RF video signal is amplified and split such that the 
composite PCM/RF video signal may be distributed to a plurality of floor 
disconnect boxes (FDBs) 128. It may be noted that a separate signal is 
provided to each floor disconnect box (FDB) 128. 
Each floor disconnect box (FDB) 128 acts as a signal splitter which 
services two daisy-chains of seat electronics boxes (SEBs) 130. It is 
presently preferred that each floor disconnect box 128 support a maximum 
of thirty (30) seat electronics boxes (SEBs) 130 with a maximum of fifteen 
(15) seat electronics boxes (SEBs) 130 being disposed in any given 
daisy-chain. However, it will again be noted that the number and specific 
configuration of the seat electronics boxes (SEBs) 130 may be varied from 
system to system. 
Each seat electronics box (SEB) 130 may include a directional tap 702, a 
band splitting filter 704, a demultiplexer 706, a decompression circuit 
708, and a plurality of video processing circuits 714 and 716 (all shown 
in FIG. 9) depending upon the features (audio or video) provided at a 
given passenger seat location. The directional tap 702 functions to tap 
off a small portion of the composite PCM/RF video signal for use within 
the seat electronics box (SEB) 130 and to pass the composite PCM/RF video 
signal with only a small amount of loss to the next seat electronics box 
(SEB) 130 in a given daisy-chain. The band splitting filter 704 separates 
the tapped composite PCM/RF video signal into its respective PCM data and 
RF video components. The RF video component is delivered to a tuner 714 of 
each of the video processing circuits, and the PCM data signal is 
delivered to the demultiplexer (IVAS gate array) 706 via a linear analog 
amplifier 730 and an amplitude comparator 732. The demultiplexer 706, 
under the control of one of a plurality of digital passenger control units 
(DPCUs) 134, selects one or more desired channels from the composite PCM 
data signal and provides each selected channel to a decompression circuit 
708 (ADPCM gate array shown in FIG. 9). Each decompression circuit 708, in 
turn, decompresses the channel(s) delivered thereto and provides the 
resulting expanded digital audio signal to a pair of digital-to-analog 
(D/A) converters 710. The digital-to-analog converters 710 convert the 
expanded digital audio signals to analog signals. The resulting analog 
audio signals are amplified by an amplifier 712 and delivered to a 
transducer (not shown) disposed in, for example, a passenger headphone 
114. 
The RF video portion of the split signal is delivered to a plurality of 
video processing circuits each comprising a tuner 714 and a tuner control 
circuit 716 via a signal splitter 734 (all of which are shown in FIG. 9). 
The signal splitter 734 functions to isolate the individual tuners 714 
from one another, and the tuner control circuits 716 are controlled via a 
microprocessing unit (MPU) 718 and one of a plurality of digital passenger 
control units (DPCUs) 134. Each tuner 714 is controlled by an associated 
video control circuit 716 which receives control signals from the 
microprocessing unit 718, and each tuner 714 is capable of selecting a 
desired video channel from the composite RF video signal. After a 
particular video channel is selected, the video processing circuit 
delivers that channel to a seat display unit (SDU) 116 for display. 
The in-seat video cassette players (IVCPs) 136 are controlled by the video 
cassette player controllers (VCPCs) 138 and provide an additional source 
of video signals for display on the seat display units (SDUs) 116. In a 
preferred form, the inseat video cassette players (IVCPs) 136 may 
comprise, for example, Part No. RD-AV1203, manufactured and sold by 
Matsushita Electronics Industrial Co., Ltd., of Osaka, Japan. The in-seat 
video cassette players (IVCPs) 136 are controlled in a conventional 
fashion by the video cassette player controllers (VCPCs) 138, and when 
enabled, provide analog audio and video signals which are passed through 
the seat electronics box (SEB) to a seat display unit (SDU) 116 and 
passenger headset (not shown). 
VMU Structure and Function 
Turning now to FIG. 4, in a preferred form the video modulator unit (VMU) 
124 receives at separate balanced input ports 202 a plurality of analog 
video signals generated by the video signal sources 104. Each of the 
analog video signals delivered to the video modulator unit 124 is provided 
to an amplitude modulator 204 disposed within the video modulator unit 
124, and the amplitude modulators 204 modulate each of the supplied video 
signals on a selected carrier frequency. It is believed that amplitude 
modulation is well known in the art and, thus, it will not be discussed in 
further detail herein. However, it may be noted that it is presently 
preferred to modulate each supplied video signal on a selected carrier 
frequency between 135 MHz and 300 MHz. Further, each modulator 204 is 
electronically coupled to and controlled by a micro-processing unit (MPU) 
205. The micro-processing unit (MPU) 205 provides a means for varying the 
operating parameters of the modulator units 204 and, in doing so, provides 
a means for programmably selecting desired carrier frequencies. More 
specifically, the micro-processing unit (MPU) 205 communicates with a 
central processing unit (CPU) 316 (shown in FIG. 5) disposed within the 
video system control unit (VSCU) 120 via an RS-232 interface 207, and the 
micro-processor 205 sets the carrier frequencies in response to signals 
received from the video system control unit (VSCU) 120. It is presently 
preferred to set each carrier frequency to a default frequency (between 
135 MHz and 300 MHz), absent circumstances which dictate otherwise. 
Presently preferred default frequencies are set forth in TABLE 1 below. 
TABLE 1 
______________________________________ 
Channel Frequency Channel Frequency 
______________________________________ 
NORMAL CHANNELS 
01 151.25 MHz 07 223.25 MHz 
02 163.25 MHz 08 235.25 MHz 
03 175.25 MHz 09 247.25 MHz 
04 187.25 MHz 10 259.25 MHz 
05 199.25 MHz 11 271.25 MHz 
06 211.25 MHz 12 283.25 MHz 
PREVIEW CHANNELS 
PR1 139.25 MHz PR2 295.25 MHz 
______________________________________ 
It should be noted, however, that it is not intended to limit the scope of 
the present invention to the particular carrier frequencies listed above, 
as those frequencies merely comprise preferred carrier frequencies. 
Moreover, as set forth above, it is preferred that the carrier frequencies 
utilized by the passenger entertainment system 100 of the present 
invention be programmable, such that if, for example, interference is 
encountered at a particular frequency, that frequency may be changed by 
entering a new carrier frequency into a database stored in memory at the 
cabin management terminal 108. The carrier frequency of a particular 
modulator 204 may also be varied in the event that a particular video 
input signal is not available (i.e. in the event that a particular video 
source 104 becomes inoperative). For example, if a particular video 
recording is to be broadcast upon channel 1, and the video source 104 
feeding channel one becomes inoperative, the video recording may be played 
by another video source 104 and the modulator coupled to that source may 
be configured, as set forth above, to modulate the signal delivered 
thereto up to 151.25 MHz (the carrier frequency of channel 1). 
After modulation, each video signal is delivered to a separate input 206 of 
one of a plurality of primary combiner circuits 208. Each primary combiner 
circuit 208 combines three video input signals to form a combined video 
signal, and each resulting combined signal is delivered to one input of a 
secondary combiner circuit 210. The signal produced by the secondary 
combiner circuit 210 is referred to herein as the composite RF video 
signal. 
Prior to being distributed throughout the passenger entertainment system 
100, the composite RF video signal is passed through a low pass filter 
212, amplified by an amplifier 214, and split by a 4-way splitter 216. 
Thus, in a preferred form the composite RF video signal is provided to 
four separate output terminals 218 of the video modulator unit (VMU) 124. 
Referring now also to FIG. 3, the video modulator unit (VMU) 124 is coupled 
to a plurality of tapping units (TUs) 132 which are, in turn, coupled to a 
plurality of video projectors or video monitors 118. Each tapping unit 
(TU) 132 may comprise, for example, a TU Model No. RD-AA5101, presently 
manufactured and sold by Matsushita Electronics Industrial Co., Ltd., of 
Osaka, Japan. Further, each tapping unit 132 comprises a video tuner 
(shown in FIG. 4(a)) for selecting a desired channel from the composite RF 
video signal, and each tapping unit 132 is capable of driving up to three 
(3) different video monitors or projectors 118 (all displaying the same 
channel). Although the tapping units 132 receive the composite RF video 
signal from the video modulator unit 124, the tapping units 132 are 
controlled by the central processing unit (CPU) 316 (shown in FIG. 5) 
disposed within the video system control unit (VSCU) 120. More 
specifically, the central processing unit (CPU) 316 disposed within the 
video system control unit (VSCU) 120 controls the selection of channels by 
the tapping units 132, as well as, the function of the video monitors or 
projectors 118. 
Tapping Unit Structure and Function 
Turning now also to FIG. 4(a), each tapping unit 132 comprises a 
directional tap 220, a tuner 222, a turner control circuit 224, and three 
video signal amplifiers 226. The directional tap 222 functions to tap off 
a small portion of the composite RF video signal generated by the video 
modulator unit 124 and to pass the remaining portion of the composite RF 
video signal to the next tapping unit 132 along a given daisy-chain with 
only a small amount of signal loss. The tuner control circuit 224 is 
coupled to the central processing unit 316 disposed within the video 
system control unit (VSCU) 120 and, in response to signals received 
therefrom, controls the tuner 222. The tuner 222 selects a desired channel 
for viewing the video monitors 118 in response to signals received from 
the tuner control circuit 224 and delivers the selected channel to the 
amplifiers 226. 
VSCU Structure and Function 
Turning now to FIG. 5, in a preferred form the video system control unit 
(VSCU) 120 of the present invention provides the central control function 
for the audio and video portions of a passenger entertainment system 100 
in accordance with the present invention. Moreover, the video system 
control unit (VSCU) 120 receives database and program selection 
information from the cabin management terminal (CMT) 108 and, based on 
that information, provides control signals to the video signal sources 
104, the digital audio signal sources 102, the video modulator unit (VMU) 
124, and a plurality of tapping units (TUs) 132. 
In addition to providing the central control function for a passenger 
entertainment system 100 in accordance with a preferred form of the 
present invention, the video system control unit (VSCU) 120 receives and 
multiplexes all video sourced audio signals generated by the video signal 
sources 104 and all compressed digital audio signals provided by the 
digital audio signal sources 102. The signal which results upon completion 
of the multiplexing operation performed by the video system control unit 
(VSCU) 120 is referred to herein as the composite PCM data signal. 
The video system control unit (VSCU) 120 distributes the composite PCM data 
signal to a plurality of remote locations via the passenger entertainment 
system controller (PESC) 122, a plurality of area distribution boxes 
(ADBs) 126, a plurality of floor disconnect boxes (FDBs) 128, and a 
plurality of seat electronics boxes (SEBs) 130. 
In a preferred form the video system control unit (VSCU) 120 is capable of 
accepting up to forty-eight (48) compressed digital audio channels from a 
plurality of compact disc players (CDPs) 102 (eight channels per player) 
and up to forty-eight (48) analog audio channels from a mix of video 
cassette players 104 (four channels per player) and analog audio 
reproducers 106 (twelve channels per player), to a maximum of seventy-two 
(72) channels total. More specifically, the video system control unit 
(VSCU) 120 is configured to accommodate three blocks of input channels 
comprising twenty-four (24) channels each, and a given block of input 
channels may comprise channels of only one type (i.e. either compressed 
digital audio channels or analog audio channels). Accordingly, in the 
preferred form the video system control unit may be configured to 
accommodate either twenty-four (24) analog audio channels and forty-eight 
(48) compressed digital audio channels or forty-eight (48) analog audio 
channels and twenty-four (24) compressed digital audio channels for a 
maximum of seventy-two (72) channels total. 
The analog audio channels received from the audio reproducers 106 and video 
sources 104 are converted to a digital format having a 16-bit sample size 
using analog-to-digital converters 302, and the resulting digital signals 
are then compressed to a format having a 4-bit sample size by adaptive 
delta pulse code modulation. In a preferred form, the analog-to-digital 
conversion process is performed by one of up to forty-eight (48) MASH 
(Multi-Stage Noise Shaping) analog-to-digital converters 302 (twenty-four 
per analog audio board 301). Each MASH analog-to-digital converter 302 is 
capable of receiving a single analog input signal, converting that signal 
to a digital format, and multiplexing the resulting digital signal with 
another converted digital signal (i.e. a signal from another MASH 
analog-to-digital converter 302) to form a single digital output signal 
having two channels. MASH conversion is well known in the art and, 
therefore, it will not be discussed in further detail herein. Further, in 
a preferred form the MASH converters may comprise MASH DAC chips Part No. 
MN6460A sold by Matsushita Electronics Corp. of Osaka, Japan. After the 
MASH analog-to-digital signal conversion process is completed, the 
resulting digital signals comprising two channels each are delivered to 
separate input terminals 304 of a plurality of ADPCM gate arrays 302. It 
is presently preferred to utilize three (3) ADPCM gate arrays 306, each 
being coupled to eight (8) separate MASH analog-to-digital converters 306. 
The four (4) digital signals comprising two (2) channels each, which are 
received by each ADPCM gate array 306, are compressed by adaptive delta 
pulse code modulation and then multiplexed to form a single compressed 
digital output signal having eight channels. The resulting three (3) 
compressed digital output signals are then delivered from the ADPCM gate 
arrays 306 to separate inputs 308 of an integrated video audio system 
(IVAS) gate array 310. 
The integrated video audio system (IVAS) gate array 310, in turn, combines 
the compressed digital audio signals generated by the digital audio signal 
sources 102 with the compressed digital output signals generated by the 
ADPCM gate array 310 to form the composite PCM data signal. The function 
of the IVAS gate arrays 306 is discussed in more detail below. However, at 
this point it is sufficient to understand that the integrated video audio 
system (IVAS) gate array 310 time domain multiplexes the compressed 
digital audio signals received from the digital audio signal sources 102 
and the converted and compressed signals received from the ADPCM gate 
arrays 310 to form a composite pulse code modulated (PCM) data signal. The 
integrated video audio system (IVAS) gate array 310 then delivers the 
composite PCM data signal to a filter/combiner 312 which combines that 
signal with a composite RF video signal provided by the video modulator 
unit (VMU) 124. The filter (not shown) in the filter/combiner 312 reduces 
the amplitude of the composite PCM data signal and shapes the resulting 
waveform so as to create an analog waveform similar in frequency and other 
characteristics to a modulated radio frequency (RF) signal. In doing so, 
the composite PCM data signal is converted to a form which may be passed 
through the passive signal processing components (i.e. directional taps, 
splitters, and the like) as well as the linear analog amplifiers disposed 
within the area distribution boxes (ADBs) 126 and floor disconnect boxes 
(FDBs) 128. The combiner (not shown) of the filter/combiner 312 combines 
the filtered composite PCM data signal with the composite RF video signal 
to form a composite PCM/RF video signal. The resulting composite PCM/RF 
video signal is then delivered to the passenger entertainment system 
controller (PESC) 122 for further processing and, ultimately, distribution 
to the remote seat locations. 
As further illustrated in FIG. 5, in a preferred form the video system 
control unit (VSCU) 120 may comprise as many as nine (9) subsystem boards 
including: two analog signal conversion boards 301; a central processing 
unit (CPU) board 303; an ARINC interface board 305; a local area network 
(LAN) board 307; a digital audio board 309; a tuner board 311; a power 
supply board (not shown); and a mother board 313. For convenience, dashed 
lines are utilized herein to indicate which circuit components reside on a 
given subsystem board. 
Each audio signal conversion board 301 comprises twenty-four (24) audio 
signal input ports 302, twenty-four (24) MASH analog-to-digital converters 
314, and three ADPCM gate arrays 306. The audio signal input ports 314 
receive analog audio signals from a plurality of video sources 104 and 
audio reproducer units 106 and, in turn, pass those signals on to the MASH 
analog-to-digital converters 302. The MASH analog-to-digital converters 
302 each convert a single incoming analog audio signal to a digital audio 
signal, and pairs of resulting digital audio signals are multiplexed to 
form a single digital output signal comprising two (2) channels and having 
a 16-bit sample size and a 37.8 kHz sampling rate. Each of the converted 
audio signals comprising two (2) channels is then delivered to an input 
terminal 304 of one of three (3) ADPCM gate arrays 306, where it is 
compressed and combined with three other converted audio signals to form a 
compressed digital output signal having eight (8) channels. Each of the 
three (3) ADPCM gate arrays 306 generates a separate compressed digital 
output signal, and each of the three (3) compressed digital output signals 
is then delivered to the digital audio board 309 whereon the integrated 
video audio system (IVAS) gate array 310 is disposed. 
The integrated video audio system (IVAS) gate array 310 disposed on the 
digital audio board 309 receives compressed digital audio signals from the 
digital audio signal sources 102 and the ADPCM gate arrays 306 and 
multiplexes those signals to produce the composite PCM data signal 
referred to above. The composite PCM data signal is then provided to the 
filter/combiner 312 of the mother board. 
As discussed more fully below, the integrated video audio system (IVAS) 
gate array 310 of the digital audio board 309 also functions as a channel 
selector or demultiplexer. More specifically, the integrated video audio 
system (IVAS) gate array 310 may be utilized to select preview audio 
channels for listening at the cabin management terminal 108. In this mode, 
the integrated video audio system (IVAS) gate array 310 in response to 
control signals generated by the central processing unit (CPU) 316 selects 
the desired audio channel(s) (1 for mono or 2 for stereo) from the 
composite PCM data signal. The selected audio channels, which comprise 
compressed digital audio data, are delivered to an ADPCM gate array 318 
for decompression to a 16-bit format and then passed to a pair of MASH 
digital-to-analog converters 320 (preferably MASH DAC chips Model No. 
MN6475A sold by Matsushita Electronics Corp. of Osaka, Japan) for 
separation (i.e. demultiplexing) and conversion to an analog format. The 
resulting analog preview channels are then delivered to a gain control 
circuit 322 and, finally, to the cabin management terminal 108 for 
listening via an audio transducer disposed in, for example, a stereophonic 
headset (not shown). 
The tuner board comprises tuner control circuitry 324 and a tuner circuit 
326. The tuner circuit 326 receives the composite RF video signal 
generated by the video modulator unit (VMU) 124 and, in response to 
control signals generated by the central processing unit 316, is capable 
of selecting a preview video channel from the composite RF video signal. 
More specifically, the tuner control 324 receives control signals from the 
central processing unit (CPU) 316 and, in response thereto, adjusts the 
operating parameters of the tuner 326 to select a desired RF video 
channel. Referring back to TABLE 1, in a preferred form the carrier 
frequency of the channel to be previewed is set to either 139.25 MHz or 
295.25 MHz and, thus, the tuner 326 is also set to select either a 
frequency of 139.25 MHz or 295.25 MHz depending upon which preview carrier 
frequency is utilized. Finally, the selected RF video channel is 
demodulated by the tuner 326 and passed to the cabin management terminal 
108 for viewing. In this fashion, channels may be previewed prior to 
distribution throughout the passenger entertainment system 100. If, on the 
other hand, it is desired to merely monitor a video channel, the carrier 
channel of that video channel may be selected by the tuner 326 in the 
manner set forth above, and the channel to be monitored will be passed to 
the cabin management terminal 108 for viewing. 
The CPU board comprises a central processing unit 316 (preferably a 68,000 
series micro-processor of the type manufactured by Motorola, Inc. of 
Phoenix, Ariz., Part No. MC68HC000RC16), a crystal controlled oscillator 
328 having a crystal frequency of 19.66 MHz, a frequency divider circuit 
330, a plurality of memory components 332, and a microprocessor supervisor 
circuit 334. 
The central processing unit 316 performs a number of functions including 
initialization, sub-system control, and sub-system communications 
management. Chip initialization is accomplished by writing programming 
commands to peripheral chips to control the mode of operation of those 
chips. It may be noted that, as part of performing the initialization 
function, the central processing unit 316 must receive a system 
configuration database from the cabin management terminal (CMT) 108. 
Communication between the central processing unit (CPU) 316 and other 
peripheral devices (or sub-systems) is implemented as follows. The central 
processing unit (CPU) 316 communicates with the cabin management terminal 
(CMT) 108 via the local area network (LAN) 319 to obtain configuration 
information and execution commands used for controlling video system 
functions. The central processing unit (CPU) 316 communicates with the 
microprocessor 205 of the video modulator unit (VMU) 124 via an RS-232 
interface 338 to control the frequencies of the modulators 204 disposed 
therein and to run diagnostic functions. The central processing unit (CPU) 
316 communicate with the cabin intercommunications data system (CIDS) 110 
over one of the ARINC-429 interfaces 336. The central processing unit 
(CPU) 316 controls selected video signal sources 104 via an RS-232 
interface 338 which corresponds to the selected video signal source 104. 
More specifically, upon receiving commands to control certain functions of 
the video signal sources 104 from the cabin management terminal (CMT) 108, 
the central processing unit (CPU) 316 executes the commands by 
communicating with an appropriate video signal source 104 via the RS-232 
interface 338 which corresponds to that video signal source 104. 
Communication between the central processing unit (CPU) 316 and the 
digital audio signal sources 102 is accomplished in a similar fashion. 
Finally, communications between the central processing unit (CPU) 316 and 
the video display units (VDUs) 118 and tapping units (TUs) 132 are carried 
over RS-485 interfaces 340. 
The memory components 332 coupled to the central processing unit 316 
comprise a pair of RAM memories (128K.times.8 each) for data storage, a 
pair of EPROMs (512K.times.8 each) for program storage, and a pair of 
EEPROMs (64K.times.8 each) for storing built in test equipment (BITE) 
information, configuration data, and a downloadable data base. 
The microprocessor supervisor circuit 334 provides the reset line (not 
shown) of the central processing unit 316, and the primary function of the 
supervisor circuit 334 is to guarantee continuous system performance. More 
specifically, if the central processing unit 316 should become caught in 
an infinite loop, the supervisor circuit 334 will detect that condition 
and reset the central processing unit 316. In addition, the supervisor 
circuit 334 is capable of detecting potential power interruptions and 
failures. Thus, upon detecting a power interruption or failure, the 
supervisor circuit 334 signals the central processing unit 316, and the 
central processing unit 316 may begin an orderly shut down process or 
backup critical data. 
The ARINC interface board 305 comprises four (4) ARINC-429 ports 336, 
nineteen (19) RS-232 ports 338, and three (3) RS-485 ports 340. The RS-232 
ports 338 provide communication between the central processing unit 316 
and the digital audio signal sources 102, the video sources 104, and the 
video modulator unit (VMU) 124. The RS-485 ports 340 provide communication 
between the central processing unit 316 and the tapping units (TUs) 132, 
and the ARINC-429 ports 336 provide communication between the central 
processing unit 316 and the cabin intercommunication data system (CIDS) 
110. 
PESC Structure and Function 
Turning now to FIG. 6, in a preferred form the passenger entertainment 
system controller (PESC) 122 comprises two (2) analog signal conversion 
boards 401 and 403, a mother board 405, a CPU board 407, a local area 
network (LAN) board 409, a power supply board (not shown), and an ARINC 
interface board 411. As in the case of the video system controller unit 
(VSCU) 120, dashed lines are utilized to indicate which circuit components 
are disposed on a given board. 
The first analog signal conversion board 401 comprises the same components 
as the audio signal conversion boards 301 disposed in the video system 
control unit (VSCU) 120. More specifically, the first analog signal 
conversion board 301 comprises twenty-four (24) audio signal input ports 
402, twenty-four (24) analog-to-digital MASH converters 404, and three 
ADPCM gate arrays 406. The audio signal input ports 402 receive analog 
audio signals from a plurality of audio reproducer units 106 and, in turn, 
pass those signals on to the MASH analog-to-digital converters 404. The 
MASH analog-to-digital converters 404 convert each incoming analog audio 
signal to a digital format, and pairs of the resulting digital signals are 
multiplexed to form a single digital audio signal comprising two (2) 
channels and having a 16-bit sample size and a 37.8 kHz sampling rate. 
Each of the converted audio signals is then delivered to an input terminal 
408 of one of three (3) ADPCM gate arrays 406, where it is compressed and 
combined with three other converted audio signals to form a compressed 
digital output signal having eight (8) channels. Each of the three (3) 
ADPCM gate arrays 406 generates a separate compressed digital output 
signal, and each of the three (3) compressed digital output signals is 
then delivered to the second analog signal conversion board 403 whereon an 
integrated video audio system (IVAS) gate array 410 is disposed. 
The second analog signal conversion board 403 comprises several of the 
components disposed on the first analog signal conversion board 401, as 
well as an integrated video audio system (IVAS) gate array 410. Moreover, 
the second analog signal conversion board comprises ten (10) audio signal 
input ports 412(a)-(f) and 414, six (6) MASH analog-to-digital converters 
416, one ADPCM gate array 418, and an integrated video audio system (IVAS) 
gate array 410. 
It is presently preferred to provide four (4) voice operated switch (VOX) 
passenger address (PA) audio channels and six (6) other PA audio channels 
to the audio signal input ports 412 and 414 of the second analog signal 
conversion board 403 of the passenger entertainment system controller 
(PESC) 122. However, only six (6) PA audio channels are passed to the MASH 
analog-to-digital converters 416 at any given time. More specifically, 
voice operated switching (VOX) circuits 420 detect the presence or absence 
of audio signals at the VOX PA input terminals 414 and provide control 
signals to a four channel (2 to 1) multiplexer 421 which selects between 
the VOX PA inputs 414 and the first four PA audio channels 412(a-d). Each 
channel of the multiplexer 421 is controlled by a separate VOX circuit 
420, such that, when a VOX circuit 420 detects an audio signal at its 
input, a signal is conveyed to the multiplexer 421 prompting the 
multiplexer 421 to replace the PA audio input 412 with the VOX PA audio 
input 414. 
The analog-to-digital MASH converters 416 and ADPCM gate array 418 function 
as described above and, thus, their function will not be discussed in 
further detail at this point. 
The primary function of the IVAS gate array 410 of the passenger 
entertainment system controller (PESC) 122 is to add additional audio, 
control and passenger address signals to the composite PCM/RF video 
signal. More specifically, the IVAS gate array 410 time domain multiplexes 
the PCM data portion of the composite PCM/RF video signal, the compressed 
signals received from the ADPCM gate arrays 406 and 418, and CPMS/PSS data 
messages received from the microprocessor 430, thus adding the compressed 
signals delivered from the ADPCM gate arrays 406 and 418 and the CPMS/PSS 
data signals to the composite PCM data signal. The resulting "complete" 
composite PCM data signal is then delivered to a filter/combiner 422 for 
combination with the RF video signal, and the "complete" composite PCM/RF 
video signal is then passed from the RF combiner 422 to a plurality of 
area distribution boxes (ADBs) 124. It may be noted that the 
filter/combiner 422 of the passenger entertainment system controller 122 
functions in the same manner as the filter/combiner 312 disposed within 
the video system control unit 120. 
A separator 424 disposed on the mother board 405 of the passenger 
entertainment system controller (PESC) 122 separates the composite PCM/RF 
video signal delivered to it by the video system control unit (VSCU) 120 
and provides the PCM data portion of that signal to the integrated video 
audio system (IVAS) gate array 410. The separator 424 performs the 
separation function based on frequency, such that all frequency elements 
below approximately 50 MHz are routed to the PCM audio board 403, while 
all frequency elements above approximately 100 MHz are routed through the 
RF video board 405. The RF video portion of the separated signal is 
provided by the separator 424 to the filter/combiner 422 for recombination 
with the PCM data signal. 
The CPU board 407 of the passenger entertainment system controller (PESC) 
122 comprises the same circuitry as does the CPU board 303 disposed in the 
video system controller unit (VSCU) 120. More specifically, the CPU board 
407 comprises a microprocessor 430, a supervisor circuit 432, an 
oscillator 434, a frequency divider 436, and a plurality of memories 438. 
These components function in a similar fashion as those on the CPU board 
303 of the video system control unit (VSCU) 120. However, they are 
configured to accommodate the functions of the passenger entertainment 
system controller (PESC) 122 which are set forth above. 
ADB Structure and Function 
Turning now to FIG. 7, in a preferred form each area distribution box (ADB) 
126 serves as a zone controller which distributes power, audio, video, and 
service data to a plurality of floor disconnect boxes (FDBs) 128. The area 
distribution boxes (ADBs) 124 are arranged in a daisy-chain configuration 
with a maximum of eight (8) area distribution boxes (ADBs) 124 disposed 
along each daisy-chain. Those skilled in the art will appreciate, however, 
that the number of area distribution boxes (ADBs) 126 may be varied as set 
forth above. Interconnection between the area distribution boxes (ADBs) 
126 is achieved using a single coaxial cable and up to two (2) twisted 
pair data busses (DATA 1 and DATA 2 busses). 
The primary function of each area distribution box (ADB) 126 is to tap off 
a small portion of the composite PCM/Rf video signal and to pass the 
remaining portion of the composite PCM/RF video signal to the next area 
distribution box (ADB) 126 disposed along a given daisy-chain with only a 
small amount of signal loss. The area distribution box (ADB) then 
amplifies and splits the tapped portion of the composite PCM/RF video 
signal for further distribution within the passenger entertainment system 
100. More specifically, the composite PCM/RF video signal delivered to 
each of the area distribution boxes (ADBs) 126 is applied to a first 
directional tap 502 which taps off a small portion of the signal for use 
by the receiving area distribution box (ADB) 126 and passes the remaining 
portion of the signal to the next area distribution box (ADB) 126 disposed 
along the daisy-chain (if another ADB is present). The tap output of the 
directional tap 502 is then delivered to a band separation filter 504 
which separates the tapped PCM/RF video signal into its respective PCM 
data and RF video portions. Each portion of the tapped PCM/RF video signal 
is then passed to an amplifier 506 or 508 where it is amplified, and each 
of the resulting amplified signals is delivered to a combiner 510 for 
recombination. Next, the recombined PCM/RF video signal is passed to a 
series of 2-way splitters 512, 514 or 516 which split the PCM/RF video 
signal to form four (4) PCM/RF video output signals. Finally, the PCM/RF 
video output signals are passed to separate floor disconnect boxes (FDBs) 
128. 
The area distribution boxes (ADBs) 126 also provide a number of control 
functions and implement an address assignment protocol. More specifically, 
control data, configuration information, database information and other 
messages are downloaded from the passenger entertainment system controller 
(PESC) 122 to the area distribution boxes (ADBs) 126 via a DATA 1 bus. An 
RS-485 port 520 provides an interface between the DATA 1 bus and the area 
distribution box (ADB) 126, and the RS-485 port 520 provides data received 
from the DATA 1 bus to a communications controller 522. Upon receiving a 
message, the communications controller 522 will first acknowledge receipt 
of the received message and then determine whether to store (i.e. keep and 
act on the message data) or to pass the message downline. This 
determination is made by comparing address information contained within 
the message to the address of the area distribution box (ADB) 126 as 
determined by the discrete address inputs 524 to a particular area 
distribution box (ADB) 126. 
An exemplary message format is illustrated in FIG. 7(a) and comprises a 
start flag 750, a destination seat electronics box (SEB) number 752, a 
PCU/SDU code 754, destination area distribution box (ADB) number 756, a 
destination floor disconnect box (FDB) number 758, a destination column 
address 759, a source seat electronics box address 760 and PCU/SDU code 
761, a plurality of data/control bytes 762, a checksum code 764, two 
cyclic redundancy check bytes 766 and 768, and an end of message flag 770. 
Further, in a preferred form, the communications protocol comprises a 
command-response protocol which is centrally controlled by the area 
distribution box (ADB) 126. More specifically, the each area distribution 
box (ADB) 126 must initialize any addresses of seat electronics boxes 
(SEBs) coupled thereto and activate those seat electronics boxes (SEBs) 
130 before commencing normal communications. 
The communications protocol employed by the area distribution boxes (ADBs) 
126 and seat electronics boxes (SEBs) 130 will now be described. Polling 
of the seat electronics boxes (SEBs) 130 is performed by the area 
distribution boxes (ADBs) 126 in sequence and by address. It is presently 
preferred to utilize two types of polls, an active poll (APOLL) and an 
inactive poll (IPOLL). These poll types correspond to the "activity 
states" of the seat electronics boxes (SEBs) 130. A seat electronics box 
(SEB) 130 is active when an area distribution box (ADB) 126 allows it to 
participate in normal link communications, however, an active seat 
electronics box (SEB) 130 may only transmit after receiving an APOLL 
message addressed to it. An active seat electronics box (SEB) 130 can 
respond with several types of messages including: acknowledge (ACK), byte 
results (BRES), active status (ASTA), and PSS data. It may be noted that a 
seat electronics box (SEB) 130 powers up in an inactive mode and can only 
become active upon command from an area distribution box (ADB) 126. A seat 
electronics box (SEB) 130 is inactive if it is not permitted to 
participate in normal link communications. Further, an inactive seat 
electronics box (SEB) 130 can only transmit in response to IPOLL messages 
addressed to it from an area distribution box (ADB) 126. After receiving 
such a message, a seat electronics box (SEB) 130 may only respond with 
inactive status (ISTA) or byte result(s) (BRES). 
Turning now also to FIG. 7(b), the following process is used to assign the 
seat electronics boxes (SEBs) 130 addresses on each column. The addressing 
process may be initiated by either the passenger entertainment system 
controller (PESC) 122 or an area distribution box (ADB) 126 by sending a 
programming mode (PMODE) command to the seat electronics box (SEB) 130. 
When received by a seat electronics box (SEB) 130, the PMODE command 
causes a communications relay 736, which is normally closed, to open. In 
this fashion, communications between a given area distribution box (ADB) 
126 and a single pair of seat electronics boxes (SEBs) 130 may be 
established. Moreover, once a PMODE command is distributed over the DATA 1 
bus, only seat electronics boxes (SEBs) which are directly adjacent a 
floor disconnect box (FDB) 128 are able to communicate with their 
associated area distribution boxes (ADBs) 126. Further, as shown in FIG. 
7(b), the lines of the DATA 1 bus, which connect a given area distribution 
box (ADB) 126 to a pair of seat electronics box (SEB) daisy chains 738 and 
740, are inverted with respect to each other within the floor disconnect 
box (FDB) 128. Further, the seat electronics boxes (SEBs) 130 are 
configured such that they cannot correctly interpret inverted data. Thus, 
if an area distribution box (ADB) 126 is to communicate with one of a pair 
of seat electronics box (SEB) columns (or daisy-chains) 738 it may provide 
a non-inverted message transmission. However, if that area distribution 
box (ADB) 126 is to communicate with the other column 740 it must provide 
an inverted message over the DATA 1 bus. In this fashion, a given area 
distribution box (ADB) 126 may communicate with a single seat electronics 
box (SEB) at a time when assigning addresses. Once a given seat 
electronics box (SEB) 130 has been addressed, the area distribution box 
(ADB) 126 will activate that seat electronics box (SEB) 130 causing it to 
close its relay and, thus, to establish communication between the area 
distribution box (ADB) 126 and the next seat electronics box (SEB) 130 to 
be addressed. This process continues until all functioning seat 
electronics boxes (SEBs) 130 have been addressed and activated. Further, 
by addressing the seat electronics boxes (SEBs) 130 in this fashion, it is 
possible to identify those seat electronics boxes (SEBs) 130 which are 
inoperative and to flag those seat electronics boxes (SEBs) 130, which are 
inoperative, for repair. If all seat electronics boxes (SEBs) 130 are 
correctly addressed and no defective seat electronics boxes (SEBs) 130 are 
identified, the link status is reported from the area distribution box 
(ADB) 126 to the passenger entertainment system controller (PESC) 122 as 
"normal." If any error is detected while addressing the seat electronics 
boxes (SEBs) 130, the area distribution box (ADB) 126 will terminate 
programming of the defective seat electronics box (SEB) 130 by commanding 
that seat electronics box (SEB) 130 to disable its transmitter (not 
shown), enter an inactive state, and close its relay 736. 
Once "normal" mode is verified, the communication protocol between the area 
distribution boxes (ADBs) 126 and the seat electronics boxes (SEBs) 130 
proceeds as follows. The seat electronics boxes (SEBs) 130 are polled by 
the area distribution box (ADB) 126 in sequence, and are not allowed to 
transmit information unless polled. When polled, the seat electronics 
boxes (SEBs) 130 can transmit various responses but will always send at 
least a status message. More specifically, when a message is transmitted 
to a seat electronics box (SEB) 130, the seat electronics box (SEB) 130 
will always respond with at least an acknowledgement (ACK) or 
no-acknowledgement (NAK) message. 
FDB Structure and Function 
Turning now to FIG. 8, in a preferred form each floor disconnect box (FDB) 
128 comprises a PCM/RF video signal splitter and two (2) digital data 
signal splitters 604 and 606. The PCM/RF video signal splitter 602 
receives the composite PCM/RF video signal from an area distribution box 
(ADB) 126, splits that signal, and delivers each of the resulting split 
PCM/RF video signals to a separate seat electronics box (SEB) 130. The 
digital data signal splitters 604 and 606, which split the DATA 1 and DATA 
2 signals and function in a similar fashion. However, after splitting, the 
polarity of one of the resulting split DATA signals is reversed. 
SEB Structure and Function 
Turning now to FIG. 9, each seat electronics box (SEB) 130 comprises a 
signal input board 701, an audio signal processing board 703, a video 
signal processing board 705, and a microcontroller unit (MCU) board 707. 
The input board 701 contains passive circuitry connecting each seat 
electronics box (SEB) 130 to a floor disconnect box (FDB) 128 or another 
seat electronics box (SEB) 130 (i.e. the next SEB along a daisy-chain). 
The composite PCM/RF video signal delivered to each of the seat 
electronics boxes (SEBs) 130 is applied to a directional tap 702 which 
taps off a small portion of the signal for use by the receiving seat 
electronics box (SEB) 130 and passes the remaining portion of the signal 
to the next seat electronics box (SEB) 130 disposed along the daisy-chain 
(if another SEB is present). The tap output of the directional tap 702 is 
filtered by band-splitting filters 704 prior to further distribution 
within the seat electronics box (SEB) 130. More specifically, the 
band-splitting filters 704 comprise a high pass filter and a low pass 
filter (not shown). The RF video portion of the composite signal is passed 
by the high pass filter and the PCM portion of the composite signal is 
passed by the low pass filter. After filtering, the PCM portion of the 
composite signal is delivered to the audio board 703, and the RF video 
portion of the composite system is delivered to the video board 705. Upon 
reaching the audio board 703, the PCM portion of the composite signal is 
passed through an analog amplifier 730, passed through an amplitude 
comparator 732, and applied to one input of an integrated video audio 
system (IVAS) gate array 706. The IVAS gate array 706 functions as a 
decoder and is capable of selecting desired PCM data channels from the 
composite PCM data signal. After one or more channels are selected by the 
IVAS gate array 706, those channels are delivered to an ADPCM gate array 
708 for decompression. After decompression, the selected channels are 
delivered to a pair of MASH digital-to-analog (D/A) converters 710, where 
they are separated, converted to analog audio signals, and passed on to a 
headphone amplifier 712. 
In a particularly innovative aspect of the present invention, the IVAS gate 
array 706 of a given seat electronics box (SEB) 130 may be instructed to 
select a non-existent channel from the composite PCM data signal and, in 
doing so, to provide a "zero channel" output to the ADPCM gate array 708. 
A zero channel output is an output channel which comprises a constant 
value and, thus, when converted to an analog format does not vary in 
amplitude. Accordingly, when a zero channel is converted to an analog 
format and delivered to an audio transducer, no audio is produced. 
Moreover, when a zero channel output is processed by the ADPCM gate array 
708, the MASH digital-to-analog converter 710, and the headphone amplifier 
712 as set forth above, an analog audio signal having no amplitude 
variation is produced and may be provided to a noise cancelling headset 
(not shown). The noise cancelling headset may be utilized by a passenger 
wearing that headset to block out substantially all flight noise, cabin 
noise and the like. It is appreciated that one of the compressed digital 
audio channels might be used as a zero channel in an alternative 
embodiment. However, it is presently preferred to provide a maximum number 
of audio channels for passenger listening, and providing a separate zero 
channel would reduce the number of channels available for that purpose. 
In another innovative aspect, the passenger entertainment system 100 of the 
present invention may be configured to maintain the delivery of a 
previously selected audio channel to a passenger's headset, when that 
passenger selects a video channel for viewing and that video channel is 
not accompanied by any audio channel(s). More specifically, the IVAS gate 
array 706 of the seat electronics box (SEB) 130 may be configured or 
programmed by the microprocessor 718 to switch audio channels only when a 
new audio channel is selected either directly or implicitly by a passenger 
using the digital passenger control unit (DPCU) 134. 
The RF video portion of the composite signal is delivered from the board 
splitting filters 704 to the video board 705. More specifically, the RF 
video portion of the composite signal is delivered to a signal splitter 
734 and then to one of up to three (3) video signal tuners 714, each of 
which is controlled by a tuner control circuit 716. It may be noted that 
the signal splitter 734 isolates the video tuners 714 from one another. As 
set forth above, the tuner control circuits 716 are controlled via the 
microprocessing unit (MPU) 718 and one of a plurality of digital passenger 
control units (DPCUs) 134. The video tuner control circuits 716 are each, 
in turn, coupled to a single video tuner 714 which is capable of selecting 
a desired video channel from the composite RF video signal. After a 
particular video channel is selected, the video processing circuit 
delivers that channel to a seat display unit (SDU) 116 for display. 
The microcontroller unit (MCU) board 707 comprises a micro-controller 718, 
an RS-485 port 720 for communication with the DATA 1 bus, an address 
assignment relay 721, and a DPCU interface 722 for communication with the 
digital passenger control units (DPCUs) 134. The micro-controller 718 
receives and transmits communication data on the DATA 1 bus via the RS-485 
port 720, provides serial communications to the digital passenger control 
units (DPCUs) 134 via the DPCU interface 722, and controls the internal 
operations (i.e. channel selection by the IVAS gate array 706 and video 
processing circuits 714) of the seat electronics box (SEB) 130 via an 
internal bus 724. In a preferred form, the micro-controller 718 comprises 
an eight (8) bit controller having 512 bytes of static RAM and an internal 
analog-to-digital converter (not shown). 
In a particularly innovative aspect of the present invention, the 
microcontroller 718 of one seat electronics box (SEB) 130 may be 
configured to communicate with the microcontroller 718 of another seat 
electronics box (SEB) 130 via the DATA 1 bus. This enables a digital 
passenger control unit (DPCU) 134 disposed at a first seat location to 
provide video channel selection data through a first seat electronics box 
(SEB) servicing that seat location to a second seat electronics box (SEB) 
130 servicing a seat location one row forward of the first seat location. 
Thus, a seat display unit (SDU) 116, which receives selected video signals 
from the second seat electronics box (SEB) 130 and is mounted in the back 
of the forward seat, may be controlled using the digital passenger control 
unit (DPCU) 134 disposed at the rearward seat without providing an 
additional communications link between the two seats. 
IVAS Gate Array Structure and Function 
The structure and function of the integrated video audio system (IVAS) gate 
arrays 310, 410, and 706 shall be explained with reference to FIGS. 10-12. 
However, it should be understood that the structure of the integrated 
video audio system (IVAS) gate arrays 310, 410, and 706 does not vary 
throughout the passenger entertainment system 100; only the function of 
the integrated video audio system (IVAS) gate arrays 310, 410, and 706 is 
varied. Moreover, an integrated video audio system (IVAS) gate arrays 310, 
410, or 706 comprises a single chip which functions in a different manner 
depending upon where it is disposed within the passenger entertainment 
system 100. Thus, in a preferred form the same IVAS gate array chip may be 
used in the video system control unit (VSCU) 120, the passenger 
entertainment system controller (PESC), or any of the seat electronics 
boxes (SEBs) 130. The function of the chip will vary, however, depending 
upon where it is disposed. 
Referring first to FIG. 10, each IVAS gate array 310, 410, or 706 comprises 
nine (9) functional blocks including a plurality of pre-scalers 802, a 
test tone generator 804, a Manchester decoder 806, a audio formatter 808, 
an audio buffer 810, timing and control logic 812, a communications 
controller 814, a PSS/CPMS buffer 816, and a Manchester encoder 818. 
The pre-scalers 802 comprise one portion of a phase lock loop circuit (not 
shown) and divide down by a programmable factor the frequency of a 
plurality of signals delivered to their inputs (not shown). The phase lock 
loop circuit comprises a phase detector, filter circuitry, and a voltage 
controlled oscillator (VCO) (none of which are shown), each disposed 
externally of the IVAS gate array, and the pre-scalers 802 disposed within 
the IVAS gate array. Each phase lock loop generates a clock phase locked 
to the PCM data signal. The clock frequencies are programmable multiples 
or sub-multiples of a clock derived from the bit rate (i.e. the data 
transfer rate) and are provided to the ADPCM gate arrays 306, 318, 406, 
418, and 708 and the MASH analog-to-digital and digital-to-analog 
converters 302, 320, 404,416, and 710. In this fashion, sync is maintained 
throughout the passenger entertainment system 100 based on the frame 
transfer rate of 37.8 kHz. 
The Manchester decoder 806 receives clock and serial audio data in 
Manchester code from a baseband receiver interface 820. The Manchester 
decoder 806 decodes the received serial audio data into NRZ (non-return to 
zero) and detects a unique data pattern used for system synchronization. 
Upon detecting the synchronization signal a pulse is generated by the 
Manchester decoder 806 and passed to the timing and control logic block 
812. In addition, the NRZ serial audio data is delivered from the 
Manchester decoder 806 to the audio buffer 810, the Manchester encoder 
818, and the CPMS buffer 816. 
The test tone generator 804, which comprises a shift register, a counter, 
and a control logic (not shown), is used for testing signal distribution 
within the passenger entertainment system 100. More specifically, the test 
tone generator 804 is capable of generating a square wave having a 
programmable frequency and providing that square wave to one input of a 
MASH analog-to-digital converter (not shown) disposed within the passenger 
entertainment system control (PESC) 122. The MASH analog-to-digital 
converter converts the square wave to a digital format and passes the 
converted digital signal to an ADPCM gate array 410 as set forth above. 
The ADPCM gate array 410 compresses the converted digital signal and 
provides the resulting compressed signal to one input of the IVAS gate 
array 410, where it is multiplexed into the compressed PCM data signal and 
distributed throughout the passenger entertainment system 100. Test tone 
detection circuits (not shown) disposed in the seat electronics boxes 
(SEBs) 130 detect the presence or absence of the test tone within the PCM 
data signal and provide an indication of the existence or non-existence of 
the test tone to the passenger entertainment system controller (PESC) 122. 
The audio formatter 808 comprises nine 32-bit audio sample shift registers 
(one shift register per eight audio input channels) and a 64-bit RF sample 
shift register (none of which are shown). The primary function of the 
audio formatter 808 is to insert bit stream data received from the 
compressed digital audio signal sources 102 and the ADPCM gate arrays 306, 
406, and 418 into the composite PCM data signal. More specifically, the 
audio formatter 808, under control of the timing and control logic block 
812, inserts audio, range, and filter data into the composite PCM data 
signal in the frame format illustrated in FIG. 11. A fixed relationship is 
provided between each input port 820 of the audio formatter 808 and the 
time slots into which audio and control data are inserted. 
As shown in FIG. 11, each frame 902 of the composite PCM data signal 
comprises eight (8) sync bits 904, sixty-four (64) cabin passenger 
management system (CPMS) data bits 906, thirty-two (32) range and filter 
factor (R/F) bits 908, six (6) channels comprising twenty-four (24) bits 
of passenger address (PA) audio 910, twenty-four (24) channels comprising 
ninety-six (96) bits of passenger entertainment system controller (PESC) 
audio 912, twenty-four (24) channels comprising ninety-six (96) bits of 
video system controller unit (VSCU) digital audio 914, twenty-four (24) 
channels comprising ninety-six (96) bits of video system controller unit 
(VSCU) analog audio 916, and twenty-four (24) channels comprising 
ninety-six (96) bits of video system controller unit (VSCU) optional 
digital or analog audio 918. The term "analog," as used in the preceding 
sentence, denotes that a particular signal was originally generated by an 
analog audio source. Accordingly, in a preferred form a maximum of 512 
bits are provide per frame 902. It should be noted, however, that the 
frame format may be varied substantially depending upon the number data 
types and number of bits per data type which are to be carried over the 
signal distribution network. Moreover, it is also preferred that the frame 
format of the IVAS gate array be programmably variable, such that it may 
be altered to accommodate the needs of a given passenger entertainment 
system or aircraft environment. 
Turning now also to FIGS. 12(a) and 12(b) and TABLE 2, those skilled in the 
art will appreciate that, when digital data is compressed using adaptive 
delta pulse code modulation to the CD-I, level B format, the data is not 
merely compressed from a 16-bit format to a 4-bit format. Additional range 
and filter factors 908 are added to the data. These factors, thus, become 
an essential component of the composite PCM data signal and present 
difficult problem in the context of frame formatting. More specifically, 
ADPCM compression produces one 4-bit range factor and one 4-bit filter 
factor for each channel in a twenty-eight frame audio sample. Thus, if 102 
channels of ADPCM compressed digital audio (six PA channels, twenty-four 
PESC audio channels, and seventy-two VSCU audio channels) are to be 
distributed throughout a passenger entertainment system 100, a 4-bit range 
factor and a 4-bit filter factor must be provided for each of those 102 
channels every twenty-eight frames. In a worst case scenario, transmission 
of the range and filter (R/F) factors could require that a 816-bit data 
block be dedicated solely to range and filter factors and accompany each 
frame of compressed digital audio. In contrast, when a frame format in 
accordance with the present invention is utilized, only 32-bits are 
provided per frame to accommodate the range and filter (R/F) factors. This 
substantial reduction in the number of bits per frame needed to 
accommodate the range and filter factors is accomplished by staggering the 
range and filter factors over a number of frames as indicated in TABLE 2. 
TABLE 2 
______________________________________ 
AUDIO BLOCK TRANSMISSION FORMAT 
COAX AUDIO RANGE/FILTER SAMPLE NO. 1 
FRAME SYNC CHANNEL NO.s CHANNEL NO.s 
______________________________________ 
1 1 -- 
2 0 -4 - 
3 0 -6 
4 0 1-4 1-8 
5 0 5-8 
6 0 9-12 9-16 
7 0 13-16 
8 0 17-20 17-24 
9 0 21-24 
10 0 25-28 25-32 
11 0 29-32 
12 0 33-36 33-40 
13 0 37-40 
14 0 41-44 41-48 
15 0 45-48 
16 0 49-52 49-56 
17 0 53-56 
18 0 57-60 57-64 
19 0 61-64 
20 0 65-68 65-72 
21 0 69-72 
22 0 73-76 73-80 
23 0 77-80 
24 0 81-84 81-88 
25 0 85-88 
26 0 89-92 89-96 
27 0 93-96 
28 0 -- 
29 1 -- 
30 0 -4 - 
31 0 -6 
32 0 1-4 1-8 
33 0 5-8 
34 0 9-12 9-16 
35 0 13-16 
. . . . 
. . . . 
. . . . 
______________________________________ 
More specifically, as shown in FIGS. 11, 12(a) and 12(b) range and filter 
(R/F) factors 908 corresponding to only four channels of compressed 
digital audio data are provided in a given frame, and range and filter 
(R/F) factors 908 corresponding to distinct groups of four channels each 
are provided in successive frames. In this fashion, the range and filter 
(R/F) factors 908 corresponding to all 102 compressed digital audio 
channels are provided over the course of a total of twenty-six frames 
(e.g. frame Nos. 2-26 as shown in TABLE 2). Further, it is presently 
preferred to stagger samples of PA and audio data over the course of 
twenty-eight frames (i.e. one sample per channel per frame). More 
specifically, each sample of PA or audio data comprises eight channels (or 
time slots). Thus, twenty-eight samples of each group of eight channels 
(i.e. one sample per frame) are provided within each block of PA and audio 
data. The samples are ordered such that the first sample (Sample 1) of a 
given eight channel group falls within the frame containing the range and 
filter (R/F) factors 908 corresponding to the first channel in the group. 
For example, the range and filter (R/F) factors 908 corresponding to audio 
channel No. 1 are placed in frame No. 3, and thus, the first sample 
(Sample No. 1) of audio channel Nos. 1-8 is also placed in frame No. 3. 
Similarly, the range and filter (R/F) factors 908 corresponding to audio 
channel No. 9 are placed in frame No. 5, and thus, the first sample 
(Sample No. 1) of audio channel Nos. 9-16 is also placed in frame No. 5. 
It will also be noted that it is presently preferred to place even 
numbered audio samples in odd numbered frames and odd numbered audio 
samples in even numbered frames on the coaxial transmission cable. Turning 
now also to FIGS. 13(a) and 13(b), the reason for this is that digital 
audio data, which is received by the audio formatter 808 during a given 
frame, is not simultaneously delivered to the coaxial downlink (not 
shown). Instead, digital audio data received by the audio formatter 808 
during one frame is delivered to the coaxial downlink during the following 
frame. Further, range and filter data 908, which is received by the audio 
formatter 808 during one frame, is split and delivered to the coaxial 
downlink over the course of the following two frames. When digital audio 
data is received by the audio buffer, the digital audio data from a given 
frame is stored in a current data register during that frame and shifted 
to an output register during the next frame. In contrast, range and filter 
factor data is read and shifted out, as soon as the register assigned 
thereto is filled (i.e. every two frames). For these reasons, it is 
preferred that the audio sampling rate of the audio formatter 808 and the 
audio buffer 810 be set equal to the frame transfer rate (i.e. equal to 
approximately 37.8 kHz), and that synchronization within the passenger 
entertainment system 100 be maintained based upon the frame transfer rate. 
It should be understood that it is not intended to limit the present 
invention to the particular frame format depicted in FIG. 11, 12(a), 
12(b), 13(a) and 13(b), as that format may be varied substantially in 
accordance with the present invention. For example, it will be noted that 
the composite PCM data signal comprises a plurality of compression blocks 
having F frames per block, C digital audio channels per frame, and P 
compression parameters per channel per block; and any of these parameters 
(especially the number of digital audio channels C provided per frame) may 
be varied. However, in a preferred form the multiplexer 14 or IVAS gate 
array 310 or 410, as the case may be, will be configured to allocate N 
time slots per frame for the compression parameters (N being an integer 
equal to or greater than (CxP)/F) and to assign selected groups of the 
compression factors (each group comprising N of said compression factors) 
to selected frames within each compression block. 
As for the sync signals 904 and 905, a unique audio sync pattern 904 (such 
as that shown in FIG. 11) is provided within the composite PCM data signal 
once every twenty-eight frames, and the inverse of that pattern, the frame 
sync pattern 905, is provided between all other frames, as shown in FIGS. 
12(a) and 12(b). 
Turning again to FIG. 10, the audio buffer 810 comprises four pairs of 
4-bit shift registers, twelve 8-bit shift registers, and four 16-bit shift 
registers (none of which are shown). The pairs of 4-bit shift registers 
are used to acquire left and right channel audio samples for each of up to 
four passenger seats. When the samples of each pair are acquired, the 
contents of each pair of shift registers are transferred into a single 
8-bit shift register. The channels are then transferred out of the 8-bit 
shift register as a single eight bit signal comprising two multiplexed, 
compressed, digital audio channels. The resulting signal is then delivered 
to one input of an ADPCM gate array 706. The remaining eight 8-bit shift 
registers are used for acquiring the compression factors for the left and 
right channels for each of up to four passenger seats. When the 
compression (range and filter) factors are acquired, they are transferred 
into the 16-bit shift registers and then shifted out on the same 
multiplexed output lines as the compressed digital audio sample to which 
they correspond. 
Control of the data selection process is provided by the timing and control 
logic 812, which generates control signals for enabling the shift 
registers to shift in selected audio channels. More specifically, the 
timing and control logic 812, in response to signals received from, for 
example, a digital passenger control unit (DPCU) 134, enables the shift 
registers to receive data located at a selected channel number time slot. 
A counter, which is reset upon receipt by the timing and control logic 812 
of a sync signal, is utilized to provide channel number information. Thus, 
when a channel number selected by the digital passenger control unit 
(DPCU) 134 reaches the timing and control logic 812, the data located in 
the corresponding time slot is passed to the shift registers. Thus, during 
operation a first shift register of a pair will acquire an audio data 
sample from the composite PCM data stream and pass that sample to the 
second register of the pair. The second shift register will then pass the 
acquired sample to the ADPCM interface, as the first shift register 
acquires another sample from the following frame of the PCM data stream. 
It may be noted that in the "zero channel" mode described above, a channel 
number of a non-existent channel is provided by the digital passenger 
control unit (DPCU) 134 to the timing and control logic 812. As the timing 
and control logic 812 never receives data corresponding to the channel 
selected, no new data is entered into the first shift register, and any 
data previously entered into the first shift register will be repeatedly 
passed on to the second shift register and eventually to the ADPCM gate 
array 708. 
The timing and control logic 812 controls all timed operations within the 
IVAS gate array 310, 410, and 708. For example, when the IVAS gate array 
310, 410, or 708 acts as a demultiplexer, the control logic 812 steers 
selected audio channels to the audio buffers 810 and divides down the 
clock to provide proper timing references for the serial interfaces. The 
timing and control logic 812 also provides address decoding to enable 
appropriate registers (not shown) for communication with the 
micro-controllers 430 or 718 or the central processing unit 316. 
The IVCP communications controller 814 manages the communication protocol 
between the IVAS gate array 706 (of the SEB 130) and the in-seat video 
cassette players (IVCPs) 138. 
The PSS/CPMS buffer 816 comprises a 16-bit shift register, a mod 8 bit 
counter, a 32 byte FIFO, a status register, a control register, a 16-bit 
address register and control logic (none of which are shown). This 
hardware is controlled to operate in one of two different modes depending 
upon whether the IVAS gate array is disposed within a seat electronics box 
(SEB) 130 or the passenger entertainment system controller (PESC) 122. 
When disposed within a seat electronics box (SEB) 130, the PSS/CPMS buffer 
816 is configured to perform a receive function. A start of message byte 
920 (shown in FIG. 11) is used to determine the start and end of a 
message. Each bit in the start of message byte 920 except the first bit 
921 corresponds to a data byte 924 in the CPMS field 906. When a start of 
message bit 922 is high, the channel may be idle or a new message may 
begin in the message byte 924 corresponding to that start of message bit 
922. When the start of message bit 922 is low, message data is present. 
After the message ends, the start of message bit will return to a high 
state for the next data byte indicating that the message has ended and 
that a new message is potentially starting. The control logic also 
compares the address field in each message against the address of the 
local unit. An interrupt signal may be provided to the microcontroller 718 
when the addresses are the same. 
When disposed within the passenger entertainment system controller (PESC) 
122, the PSS/CPMS buffer 816 performs the reverse of the function 
performed in the seat electronics box (SEB) 130. More specifically, the 
PSS/CPMS buffer 816 will accept messages from the microcontroller 
interface one byte at a time. The bytes are queued up in a FIFO. The 
timing and control logic 812 provides an envelope signalling when the 
PSS/CPMS buffer may place data into the serial bit stream (PCM data 
signal). The queued bytes are strobed into a shift register and shifted 
out while the envelope is active. Further, as set forth above, the start 
of message byte is inserted before the message bytes. The control logic 
also makes sure that the first byte of a message is the first byte after 
the start of message byte. 
The Manchester encoder 818 encodes the formatted bit stream and generates a 
programmable sync pattern at appropriate times. The Manchester encoder 818 
comprises a 16-bit register, a 16-bit shift register, a multiplexer, a 
plurality of gates and a flip-flop (non of which are shown). The register 
holds the sync pattern loaded by the host processor. During most of a 
downlink frame, the sync pattern is constantly loaded into the shift 
register. When the sync is to be transmitted, the shift register shifts 
out the sync at twice the bit rate. An XOR gate is used to control the 
polarity of the sync. The multiplexer selects between the sync or data 
based on an external control signal (sync enable signal provided by the 
timing and control logic 812). The flip-flop is used to reclock the edges 
after encoding the data. 
While the present invention is susceptible to various modifications and 
alternative forms, specific representations and illustrations thereof have 
been shown, by way of example, in the drawings and are herein described in 
detail. It should be understood, however, that it is not intended to limit 
the invention to the particular systems and methods disclosed, but on the 
contrary, the invention is to cover all modifications, equivalents, and 
alternatives falling within the spirit and scope of the invention as 
defined by the appended claims.