Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM AND METHOD TO CONTROL AMPLIFIER
GAIN IN A RADIATING LINE COMMUNICATION SYSTEM
FIELD OF THE INVENTION
This invention relates to radio frequency communication systems, and, in
particular,
communication systems having multi-cascading repeater systems providing a
number of bi-
directional amplifiers in the system to compensate for losses. In particular,
in one aspect,
the present invention relates to a radio frequency communication systems
utilizing radiating
or "leaky" transmission lines and bi-directional amplifiers to amplify the
communication
signals to and from the base station.
BACKGROUND OF THE INVENTION
Radiating transmission lines are deliberately constructed as imperfect
transmission
lines so that signals in the inner conductor radiate electromagnetic fields
outwardly from the
line as the electrical signals are being transmitted down the line. The
electrical magnetic
fields radiating from the line can be picked up by mobile receivers located
remotely, but in
the vicinity, of the transmission line. Furthermore, components can be
connected directly to
the radiating transmission line to modify the signal, such as amplify it,
branch the signal to
more than one line, or receive and send communication signals such as through
radio
phones and other electrical components. Radiating transmission line
communication
systems may also transmit data and/or video signals as disclosed, for
instance, in U.S.
Patent No. 5,697,067 to Graham et al. and U.S. Patent No. 7,616,768 to Waye
assigned to
the same assignee as the present application.
Radiating transmission lines can take on several different forms. One form
comprises
an open braid coaxial cable. Other forms comprise coaxial cables having
cylindrical outer
sheaths with longitudinal slits to permit radiation.
Radiating transmission lines are commonly used in environments where
electromagnetic waves, such as radio frequency waves, do not propagate well.
This type of
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environment exists, for example, in underground mine shafts or other types of
tunnels. For
example, a worker in a mine shaft using a remote mobile communication unit,
such as a
mobile radio or walkie-talkie, cannot communicate to other workers who also
have remote
mobile communication units because the radio waves cannot propagate long
distances
down a mine shaft. However, if all of the workers are near a radiating
transmission line,
the radio waves from the first worker's remote mobile communication unit could
be
received by the transmission line, transmitted by the radiating transmission
line to the base
station, modified, and then transmitted back into the mine and radiated near
the remote
mobile communication units of other workers. In this way, communication in a
mine shaft
or other environment where radio frequency waves do not propagate well can be
effected.
In the past, several different types of communication systems utilizing
radiating
transmission lines have been used. However, a common difficulty with most of
the prior
art communication systems is that it has been difficult to gauge and control
the
amplification of the signals being transmitted along the radiating
transmission line. In
particular, because the radiating transmission line is radiating
electromagnetic energy, the
signals have a much higher degree of loss than other types of transmission
lines. It is
therefore necessary to control the gain of each of the amplification units. In
addition to
automatic gain control (AGC) of the amplification units, it is also generally
necessary to
have automatic slope control (ASC) so as to properly amplify communication
signals
across a predetermined bandwidth.
In the prior art, to accommodate the control of the communication signals
going to
and from the base station, pilot signals have been used. The downstream pilot
signals had
been selected at different frequencies to propagate downstream from the first
end of the
radiating transmission line, such as into a mine or tunnel, and upstream pilot
signals, at
different frequencies, to propagate upstream towards the first end of the
radiating
transmission line. In this way, the upstream pilot signals have been used in
the prior art
systems to determine the gain required for the signals travelling in the
upstream direction
by detecting the actual loss of the upstream pilot signal along the length of
the radiating
transmission line immediately downstream of the amplification unit. In other
words, the
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upstream pilot signals are used in the prior art system to gauge the loss that
had occurred
over a section of the transmission line immediately downstream to the upstream
communication signal travelling in the same direction as the upstream pilot
signal, and,
then amplify the upstream pilot signal and the upstream communication signal
to
compensate for the detected actual losses that occurred to the upstream pilot
signal.
Similarly, the gain required in the downstream direction has been determined
by detecting
a corresponding downstream pilot signal along the length of the radiating
transmission line
immediately upstream of the amplification unit and compensate for the actual
loss.
Further wore, having several pilot signals, whether in the upstream or
downstream, assists
in automatic slope control. This is particularly important in cases where the
bandwidth can
be 10 MHz up to 40 MHz because the longitudinal loss in a cable is generally
higher at
higher frequencies than at lower frequencies in the bandwidth.
However, difficulties arise with the prior art systems utilizing this type of
upstream
pilot signals and downstream pilot signals. In particular, pilot signals
travelling upstream
towards the first end of the radiating transmission cable may be superimposed
if there is a
branch. In other words, if the radiating transmission line has been branched
out at different
points, such as by using branching units, the upstream pilot signal from
different ends of
the radiating transmission line may be superimposed at the branching points,
thereby losing
their reference nature and no longer being useful to calibrate the loss in the
next length of
the radiating transmission line.
Other difficulties also arise with closed loop control systems. These
difficulties
may include stability problems where overshooting and ringing phenomenon are
evident in
cascaded amplifier systems. Furthermore, closed loop control systems are
associated with
constant gain settling time problems. This arises, in part, due to the fact
that the time
required for the gain of the amplifiers in the system to reach a state output
level are not
generally constant and the closed loop circuit is affected by the tolerances
of electronic
components that vary from one amplifier to another. Closed loop control
systems are also
sensitive to this type of signal modulation which are common in radiating
transmission line
cables.
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Accordingly, there is a need in the art to overcome the disadvantages of the
prior art
systems. In particular, there is a need in the art to provide an improved
system and method
to control amplifier gain and slope control.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to at least partially overcome
some of
the disadvantages of the prior art. Also, it is an object of this invention to
provide an
improved type of system and method to provide automatic gain control with a
radiating
transmission line.
Accordingly, in one of its aspects, this invention resides in a radio
frequency
communication system for communicating signals, said system comprising: a
radiating
transmission line having a first end; a base station coupled to the first end,
said base station
comprising a base transmitter for transmitting downstream communication
signals in a
downstream direction away from the first end at a downstream frequency band,
and, a base
receiver for receiving upstream communication signals in an upstream direction
towards
the first end at an upstream frequency band, different from the downstream
frequency band,
said base station further comprising a pilot generator for generating a first
downstream
pilot signal at a first downstream pilot frequency (fpL) and a second
downstream pilot signal
at a second downstream pilot frequency (fpH) different from the first
downstream pilot
frequency (fpL) and transmitting the pilot signals in the downstream direction
away from
the first end of the radiating transmission line; at least one hi-directional
amplification unit
coupled to said transmission line for amplifying the downstream communication
signal in
the downstream direction and amplifying the upstream communication signal in
the
upstream direction, wherein each hi-directional amplification unit comprises:
(i) a
downstream pilot detector for detecting the first and second downstream pilot
signals and
measuring losses (Lõ,fpL) and (L,õfpn) of the downstream pilot signals over
the upstream
section (n) of the radiating transmission line immediately upstream of the
amplification
unit; and (ii) an upstream loss predicting unit for predicting an anticipated
loss of the
upstream communication signal for the upstream section (n) based on measured
losses (La,
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fn) and (1-,,,fpu) of the first and second downstream pilot signals
transmitted over the
upstream section (n); and wherein the bi-directional amplification unit
amplifies the
upstream communication signal in the upstream direction to compensate for the
anticipated
loss of the upstream communication signal over in the upstream section.
In a further aspect, the present invention resides in an amplification unit
for
amplifying an upstream communication signal at an upstream frequency band in
an
upstream direction towards a first end of a radiating transmission line
connected to a base
station, said communication unit comprising: (a) an upstream connection unit
for
connecting to a section (n) of the radiating transmission line immediately
upstream of the
amplification unit; (b) an amplifier for amplifying the upstream communication
signal in
the upstream direction for transmission on the upstream section of the
radiating
transmission line connected to the upstream connection; (c) a downstream pilot
detector for
detecting at least a first downstream pilot signal at a first downstream pilot
frequencyfn
and a second downstream pilot signal at a second downstream pilot frequencyfm
different
from the first downstream pilot signalfn, entering from the upstream section
(n) of the
radiating transmission line connected to the upstream connection and measuring
losses (La,
fpi.) and (1_,,,fp H) of the first and second downstram pilot signals over the
upstream section
(n); (d) an upstream loss predicting unit for predicting an anticipated loss
of the upstream
communication signal in the upstream direction based on the measured losses
La, In and
1-,,,,fpu of the downstream pilot signals; and (e) wherein the amplification
unit amplifies the
upstream communication signal to compensate for the anticipated loss of the
upstream
communication signal and transmits the amplified upstream communication signal
through
the upstream connection to the upstream length of the radiating transmission
line.
In a still further aspect, the present invention resides a method for
amplifying an
upstream communication signal at an upstream frequency band in an upstream
direction
towards a first end of a radiating transmission line, said method comprising:
(a) receiving,
at an amplification unit, at least a first downstream pilot signal at a first
downstream pilot
frequencyfpi and a second downstream pilot signal at a second downstream pilot
frequency
fn different from the first downstream pilot frequencyfn; (b) predicting an
anticipated
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loss of the upstream communication signal in the upstream direction based on
the
measured losses L,,fpL and Lnfpfi of the downstream pilot signals; and (c)
amplifying the
upstream communication signal to compensate for the anticipated loss of the
upstream
communication signal over the upstream section of the radiating transmission
line.
Various embodiments of the present invention have one or more advantages. The
present invention provides for the prediction of system losses based on
predefined and
measured variables which do not vary greatly over time. By predicting
transmission losses,
the amplification units in the system will be able to predict the losses
before they occur and
adjust gain accordingly.
A further advantage of certain embodiments of the present invention is that
the
system performance may be optimized. In other words, the adjusted gain control
will
facilitate reliable and stable operating conditions for the overall system.
The amplifiers in
the communication system will be better controlled by implementing automatic
gain
control and automatic slope control to operate within their linear range of
amplifications.
System instability and AGC time settling issues can also be contained.
A further advantage of certain embodiments of the present invention relates to
ease
of system installation. Because the system of the present invention does not
have an
upstream pilot signal, but rather predicts the upstream losses based on the
downstream
pilot signal, this can reduce the complexity of the system alignments. For
instance,
because there are no upstream pilot signals, in the system of the present
invention, there is
no concern that the upstream pilot signal from different ends of a branch may
be
superimposed. This can save time during installation of the system in part
because the
amplifiers in the system are automatically adjusting their gains and slopes.
This approach
also decreases the demand on highly trained technicians and special alignment
tools during
installation, thereby reducing time and cost for system implementation,
installation and
deployment.
A further advantage of certain embodiments of the present invention are that
the
system can be expandable and flexible. Because of the nature of the automatic
compensation for upstream cable losses, automatic compensations due to
temperature
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variations or cable layout changes, facilitate flexibilities and
expandabilities in ever
growing under ground environments, such as underground mines.
Further aspects of the invention will become apparent upon reading the
following
detailed description and drawings, which illustrate the invention and
preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, which illustrate embodiments of the invention:
Figure 1 is a symbolic representation of a radiating transmission line
communication system according to one embodiment of the present invention.
Figure 2 is a graphical representation of the system reference points,
downstream
communication bands, upstream communication bands and preferred pilot
frequencies.
Figure 3 is a block diagram of an amplification unit according to one
embodiment
of the present invention.
Figure 4 is a flowchart illustrating steps in the method according to one
embodiment of the present invention.
Figure 5 is a representation of a radiating line longitudinal loss chart for a
particular
radiating transmission line which may be used in association with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention and its advantages can be understood by
referring to the present drawings. In the present drawings, like numerals are
used for like
and corresponding parts of the accompanying drawings.
As shown in Figure 1, one embodiment of the present invention relates to a
radio
frequency communication system, as shown generally by reference numeral 10.
The
communication system 10 comprises a radiating transmission line 12 having
several
segments shown generally by variable n, used for communicating downstream and
upstream communication signals, shown generally by CSd and CS,õ respectively.
The
communication system 10 comprises a base station 24 which is electrically
connected to
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the first end 1 of the transmission line. In a preferred embodiment, the base
station 24
comprises an rf combiner 11, a base receiver 26 and base transmitter 28 which
together
receive the upstream communication signal CSõ and re-transmit the downstream
communication signal CSd.
For ease of reference, the communication signals CS travelling away from the
first
end 1 of the transmission line are referred to as downstream communication
signals CSd
and the communication signals CS travelling towards the first end 1 of the
transmission
line 12 are referred to as upstream communication signals CS,. In one
embodiment, the
base receiver 26 receives the upstream communication signals CS, and the base
transmitter
28 re-transmits the information contained in the upstream signal CSõ as the
downstream
communication signal CSd. In this way, the base receiver 26 and transmitter 28
can act as
voice and data repeaters to repeat the infoimation contained in the upstream
communication signal CS, in the downstream communication signal CSd. In
addition,
while not shown, the base station 24 may be connected to radio and/or
computers including
the Internet, such that data or voice information contained in the upstream
data
communication signal CSõ may not be re-transmitted into the first end 1 of the
transmission line 12, but rather could be used externally from the system 10.
Likewise,
data, voice and other information and signals external from the system 10 can
be received
at the base station 24 and transmitted into the first end 1 of the
transmission line 12 base
receiver as a downstream communication signal CSd. In this way, the base
station 24 can
act as a headend for the system 10.
Generally, the base receiver will receive the upstream communication signal
CSõ in
an upstream frequency band and then the base transmitter 28 may transmit the
downstream
communication signals CSd in a downstream frequency band which is different
from the
upstream frequency bandThis is done in order to avoid hamionics and other
interference
between the communication signals CSõ, CSd.
The radio frequency communication system 10 also comprises a number of
amplifiers, as shown generally by the symbols "Amp 01, Amp 02, etc.". Between
each
amplifier is a separate section n of the transmission line 12. The amplifiers
AMP are
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preferably hi-directional amplifiers and amplify the upstream communication
signal CS, in
the upstream direction towards the first end 1 of the transmission line 12
connected to the
base station 24 and the downstream communication signal CSd in the downstream
direction
away from the first end 1 of the transmission line 12 connected to the base
station 24. The
system 10 may also comprise branches 31 which provide a branch from the
radiating
transmission line 12. The branch 31 will also lead away from the first end 1
of the
transmission line. In this way, the downstream communication signal CSd will
travel down
the transmission line 12 as well as the branches 31 of the transmission line
12. Similarly,
the upstream communication signal CS u will travel upstream along the branches
31
towards the first end 1 of the transmission line 12. The system 10 also
preferably
comprises several portable radios 32 or other types of mobile communication
units (not
shown). In this way, radio waves being radiated from the radiating
transmission line 12
may be received and sent from a remotely located mobile communication unit,
such as the
portable radio 32, located near the transmission line 12. This is disclosed,
for instance, in
U.S. Patent No. 5,692,067 to Graham and U.S. Patent No. 7,616,968 B2 to Waye.
In a preferred embodiment, the upstream communication signal CS u will be
separated into two upstream data bands; one for the upstream data M=1 and the
other for
the upstream voice M=3. Similarly, the downstream communication signal CSd
will be
separated into two downstream data bands; one for the downstream data m=4 and
the other
for the downstream voice m=2. The following is a table showing the four bands
m (two in
the upstream direction and two in the downstream direction) for the
communication signals
CSd and CS u according to one preferred embodiment of the invention:
Band No. Band Name Frequency, MHz.
m=1 Upstream Data 5-42 MHz
m=2 Downstream Voice 155-158 MHz
m=3 Upstream Voice 172-175 MHz
m=4 Downstream Data 220-232 MHz
Table 1, Preferred Embodiment System Frequency Plan
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The base station 24 also preferably comprises a pilot generator 30 to general
pilot
signals P. The pilot generator 30 generates at least a first downstream pilot
signal PSL at a
first frequencyfn and a second downstream pilot signal PSH at a second
downstream pilot
frequeneyfm, different from the first downstream pilot signalfn. In a further
preferred
embodiment, the pilot generator also generates a third downstream pilot signal
PSM at a
third frequeneyfpm.
In one preferred embodiment, the above downstream pilot frequenciesfi,L,fpm
and
fill also represent the preferred reference frequencies for the downstream
communication
signal CSd in bands m=2 and m=4. In this way, these downstream pilot
frequencies can be
used to determine the loss of the downstream communication signal CSd and this
loss can
be used to deteithine the gain and slope that should be used for the
downstream
communication signals CSd as is known in the art.
Accordingly, in one preferred embodiment, the frequencies of the reference
pilot
signal will be as follows:
Pilot Frequency (MHz)
fpt 157.325
/PM 219.5
232.5
Table 2, Pilot Frequencies and, in a preferred embodiment, downstream band
reference
point frequency
As indicated in Tables 1 and 2, these downstream pilot signals PL, PM and PH
fall
within bands m=2 and m=4.
With respect to the upstream communication signals CS, in a preferred
embodiment, the upstream reference point frequencies may be as follows:
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Reference Points Frequency (MHz) _
fi 5.00
f2 42.00
.f3 172.325
Table 3, Upstream Bands Reference Points-Frequencies
These frequencies are preferred reference points in cases where the upstream
communication signals CSu have the upstream communication bands m=1, m=3,
shown in
Table 1 above. For convenience, the reference frequencies and the pilot
frequencies_ii,i,
fpm andfpm for this preferred embodiment are graphically shown in Figure 6.
It has been appreciated that the system losses, which may be represented by
reference symbol L, for each section n of the transmission line 12 generally
consist of two
components. The first component may be called cable longitudinal loss CL,
which is
mainly due to the longitudinal losses of the section n of the radiating
transmission line 12.
Furthermore, the cable longitudinal loss CL is generally a function of the
length of the
section n of the transmission line 12 and also varies with the frequency of
the signal. It has
also been appreciated that the second component of the system loss L is not a
frequency
dependent component and is mainly caused by insertion losses with
miscellaneous active
and passive units installed in the system 10 and specifically along the
section n of the
transmission line 12. This second component of the system losses L may be
called
insertion losses (IL). The insertion losses of these sections n are typically
of a flat radio
frequency response where the attenuations are almost the same over the entire
frequency
spectrum of these sections n of the radiating transmission line 12. An example
of these
miscellaneous active and passive units which cause insertion loss IL may
include branch
units (such as power dividers or splitters) as well as cable splice boxes for
joining two
sections of cables together and other types of non-frequency dependent
factors. In this
way, the two types of losses, namely the frequency specific cable longitudinal
loss CL and
the non-frequency specific insertion loss IL may be detei ________ mined for
each section n of the a
transmission line 12 to determine the total loss and therefore the accurate
gain
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compensation for each amplifier in the system for the corresponding frequency
band M=1,
M=2, M=3 and M=4.
For ease of reference, the system losses referred to above in each cable
section n
can be represented by the following equation:
= CLnrn+ ILõ (1)
where, Lndõ represents the total system loss in one section n of the cable 12
at
frequency band m.
CLõ,õ, represents the longitudinal cable loss in one section n of the cable
12. These
losses are a function of the cable section n and the frequency f, for each
frequency band m.
These losses are generally measured in dB.
IL, represents the total insertion loss of units installed on the section n of
the cable
12. These insertion loss IL losses are characteristics of the particular
system components
measured in dB. The value of the insertion loss of a particular unit is
approximately the
same for the entire frequency spectrum of the unit's operation (non-frequency
dependent
component). For example, the insertion loss of a branch unit 31 is
approximately 3.5 dB
for entire frequency span (5-232 MHz).
n identifies the cable section n of the radiating transmission line 12 in the
system 10
as illustrated, for example, in Fig. 1.
m identifies the band number of the communication signal CS of the system 10
as
illustrated in Fig. 6 and shown in Table 1, above, in one preferred
embodiment.
Accordingly, in a preferred embodiment, the three pilot signals PL, PH and PM
will
be generated at the pilot generator 30 at the base station 24. The pilot
signals PL, PH and
PM as indicated above, preferably, are selected to be within the downstream
voice and data
bands as also illustrated in Fig. 6. In this way, the low pilot PL will
propagate within the
downstream voice band m=2 at frequency,fpL, the mid-point pilot PM will
propagate at the
lower end of the downstream data band m=4 at frequencyfpm and the high-pilot
PH will
propagate at the upper end of the downstream data band at frequencyfm,
according to one
preferred embodiment. In this way, the downstream pilots PL, PM, PH, may be
used to
determine the gain and slope of the downstream communication signals CSd as is
known in
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the art.
As is also known in the art, the amplitude of the pilots PF, PM and PH will be
set
by the pilot generator 30 at the system headend 24 to the reference power
levels, PL0, PM,
and Pflo, respectively, when transmitted. Also, after each amplification unit
AMP, the
pilot signals PL, PM and PH will again be re-amplified or re-set to the
original reference
same levels PL,õ PMõ and PH0 in order to permit each subsequent amplifier AMP
in the
system 10 to be able to detect the losses of the pilot signals P from the
original power level
PL0, PM0 and PHo. It is understood that these original power levels, PL0, PK,
and PH() will
be set at the time of manufacture and/or updated whenever the system 10 is re-
set.
According to one preferred embodiment of the invention, at least two
downstream
pilot signals PL and PH are used to predict the anticipated loss of the
upstream
communication signal CSõ and the upstream cable section n over which the
downstream
communication signal CSd and the downstream pilots PL and PH have been
transmitted.
In one preferred embodiment, only two of the three reference pilot signals are
required to
predict the gain in the upstream direction CS,. For ease of explanation, the
lower pilot
signal PL and the higher pilot signal PH will be used to determine the gain
for the upstream
signal CSu, but it is understood that any other downstream pilot signals at
any two
particular frequencies could be used.
As indicated above, in the case where the lower pilot signal PL and the higher
pilot
signal PH also correspond to the downstream frequency band for the downstream
communication signals CSd, the losses of the downstream pilots PL and PH will
be
equivalent to the losses for the reference frequencies for the downstream band
of the
downstream communication signal CSd, namely m=2 and m=4, respectively.
Therefore, in
this preferred embodiment, the losses for the pilot signals PL and PH, will
also be
equivalent to the cable losses for the downstream bands m=2 and m=4, and PL
and PH will
be interchangeable with m=2 and m=4 in this particular preferred embodiment.
Therefore, the losses of the low pilot PL and high pilot PH will basically be
the
differences between the original power levels for these pilots PLõ and PH,, at
the headend
and the measured levels of these pilots when they are detected and measured at
each of the
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amplification units AMP. Each amplifier will also re-amplify the pilot signals
PL and PH
to the original levels PLõ and PT-I0 for re-transmission down the next section
n+1 of the
transmission line 12.
In this preferred embodiment, the system losses L of the low pilot PL at
frequency
,fiL, shall also be considered the system losses L for the downstream voice
band m=2 and
may be represented as follows:
= L0,2 = PLO-PLõ (2)
Similarly, the system losses for the high pilot frequency PH at frequencyfm,
which
in this preferred embodiment also represents the reference frequency for the
downstream
data m=4, may be represented as:
L0A-1= 4.4 = PHo PH, (3)
In this way, the total system losses L of the first cable section have been
measured
for the low pilot frequencyfn and the high powered frequeneyfm, which, in this
preferred
embodiment, also corresponds to the loss, and therefore the gain required, for
the
downstream voice and data bands m=2, 4. However, the general value of CL,,m
for
different frequencies and the insertion loss ILn have not yet been determined.
Re-writing equation (1) for the total system loss of any cable section n in
the
downstream direction for bands m=2 and m=4, which in this preferred embodiment
also
correspond to the frequencies of the low frequency pilot PL and the high
frequency pilot
PH, we have the following:
CLn>fPL + IL = L,õPL = L,2 = CL02 + IL,, (4)
wherefn=M=2 for this preferred embodiment
CLn,fpli + IL = LnJH = Lro = CLI,4 + IL, (5)
wherefpL=M=4 for this preferred embodiment
At this point, it is advantageous to define the relationship between the
longitudinal
losses of the radiating transmission cable 12 at various frequencies including
the pilot
frequenciesfn,fpH, which in this preferred embodiment corresponds to the
downstream
frequency bands m=2 and m=4. This relationship can be used to relate the
system losses
Lõ, PL of the low pilot signal PL in terms of the system losses Ln,py of the
high frequency
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pilot PH and vice versa. For ease of reference, this is identified below by
the downstream
low pilot to high pilot cable loss ratio RD defined as follows:
RD = Cable Loss (frt (6a)
Cable Loss @fp.H
As discussed above, in the preferred embodiment where the frequenciesfn
and,fPn
correspond to the downstream bands m=2, m=4, this can be re-written as:
RD = Cable Loss (-&,fpi = CLn,2 (6b)
Cable Loss @fpL = CLn,4
The cable loss curve R for different frequencies, including the downstream
cable
loss ratio RD illustrated in equations (6a) and (6b) above, can be determined
for different
frequencies and different cables, or can be obtained from the cable
manufacturers and is
often available in many reference manuals. A sweep test can also be conducted
on a
particular type of radiating transmission line 12, commonly used in
communication
systems 10 in order to determine the cable loss curve R and, more
particularly, specific
cable ratios, such as the downstream cable ratio RD for the low frequency
pilot PL and the
high frequency pilot PH. The results of one such test are shown in Fig. 5. As
is apparent
from Fig. 5, the ratio can be generally approximated as a linear slope or
curve R.
For this curve R, the downstream ratio RD may be calculated for this preferred
embodiment to have the value RD = 0.792. It is understood that any other type
of specific
downstream ratio values RD can be determined based on the cable loss ratio
curve R
illustrated in Fig. 5 and any specific cable loss ratio is deteiniined for
specific frequency for
each type of radiating transmission cables 12. It is also understood that in
general, the
curve R does not change with time and is a constant property of the specific
radiating
transmission 12 and can be determined from the cable frequency response,
published by the
cable manufacturer or deteiiiiined by a sweep test as indicated above.
It is also generally understood that the curve R does not change appreciably
with
changes in temperature or other environment or conditions, or, any such
environmental
changes will affect all frequencies substantially equally, such that the curve
R stays
substantially the same.
CA 02789768 2012-09-14
- 16 -
Following equation 6 above, we now have related equation:
CL,õfpL = RD*CLn,fpu (7a)
which, for this specific embodiment, can be re-written as:
CLn,2 = 0.792 CLn,4 (7b)
where PL and PH reflect the reference frequencies for downstream bands m=2, 4
and RD is the downstream ratio for these specific frequencies,fpLJNi and this
particular
transmission line determined above to be RD = 0.792. It is understood if
different types of
cables are used, the curve R will change and therefore the value of RD would
be adjusted
accordingly. Similarly, if different frequencies PL and PH are used, the value
for RD will,
of course, also change because the frequenciesfpL andfm are different.
Substituting equation 7 into 4 and re-arranging, we have the following
equation:
Lfpt = RD*CLnfPu + TL (8a)
where for the preferred embodiment discussed above reduces to:
L,,,, = 0.792 CLõ,4 + ILn
This can be re-written to solve ILn as follows:
IL n = LJL - RD * CLn.4 (8b)
wherefor this preferred embodiment reduces to:
IL,, = 4,2 - 0.792 CL,.4
Substituting equations (8) into (5) and solving for the cable loss CLn,4, we
have the
following:
GENERAL SPECIFIC TO THIS PREFERRED
EMBODIMENT
L,,,fpH = + LnfPL - RD*CL,LPH L,4 = CLn,4 + L2-0.792*CL,4
LõIpi = (1 + Lõ,fpL 4,4= 0.208*CLn.4 + 4,2
CLn,PH = PH PL) C4,4 = Ln 4 1-11
(1-RD) (9a) 0.208 (9b)
Based on the above derivations (9a) and (9b), the longitudinal cable loss CL
for the
higher pilot signal PH has been calculated in terms of the measured losses of
the higher
CA 02789768 2012-09-14
- 17 -
pilot signal L,f,pH and the measured losses of the lower pilot signal PL,
namely Lõ,fpL.
Using the underlying principle in equation 1, that the total system losses Liõ
will have the
frequency component based on the cable loss CL and the non-frequency component
based
on the insertion IL, the insertion loss IL for section n of transmission cable
12, regardless
of the frequency, can be re-written as follows:
IL,, = LõfpH - CLII2ipH = LifPH - - Lii/PL) (10a)
1-RD
wherefor the preferred embodiment reduces to:
IL n =L,4 - CL,4 = Ln,4 In 4 __ L) (10b)
0.208
The insertion loss, IL for the section n of the radiating transmission line 12
will be
the same for the downstream communication bands m=2, m=4 and the upstream
communication system bands m=1, m=3 because IL, is not frequency specific.
As indicated above, using the measured losses Ln,pH and LPL, the gain for the
downstream band m=2 and m=4 can then be deteiinined. Therefore, the gain of
these
bands in the downstream direction to the next section n + 1 of the
transmission line 12 can
be found and compensated for in each amplification unit AMP as is known in the
art.
Furtheimore, now that the insertion loss IL, for the section n has been
determined
as well as the cable losses CLfn and CLõ,fini, the anticipated loss of the
upstream
communication signals CS,, in the upstream bands m = 1,3, can be predicted and
the
upstream communication signal CS,, being transmitted into the same section n
immediately
upstream of the amplification unit AMP can then be amplified to adjust and
compensate
for the anticipated losses that have yet to occur, but have been predicted
will occur based
on the downstream pilot signal PL,PH.
Specifically, using equation (1) above, the system losses for the upstream
communication bands, in this case m=1 and m=3, respectively, may be defined by
the
following:
= CLõ, + IL,, (12)
Ln,3 = CL.3 (13)
CA 02789768 2012-09-14
- 18 -
The insertion loss ILn has already been detelmined above, and, as indicated
above,
is non-frequency specific and therefore this value in equations (12) and (13)
has already
been determined.
Using the reference frequenciesfi,f2 andf3 as shown in Fig. 6, the predicted
signal
losses in the upstream frequency band can be determined. For ease of
reference, the
following references will be used according to a preferred embodiment:
represents the frequency of a reference point at lower end of the data
upstream
band. This point is not used in calculating the gain of the upstream data
band. However, it
is used to calculate the slope as shown below.
f2 represents the frequency of a reference point at an upper end of the
data upstream
band m=1. This point is used in calculating the gain of the upstream data band
m=1. The
losses at this frequency represent the losses at the upstream data band, m=1.
This reference
point is selected to be the point of maximum losses in this band. Frequencyf2
is also used
to calculate the slope in the upstream data band m=1 as will be shown below.
f3 represents the frequency of a reference point within the upstream voice
band m=3.
This point is used when calculating the gain of the upstream voice band m=3.
The losses
at this frequency represent the losses of the upstream voice band, m=3. The
frequency f3 is
also used to determine the slope as shown below.
Similar to the downstream cable loss ratio, RD, determined from the curve R
(shown in Fig. 5) to define a relationship between the downstream pilot
signals PL and PH,
upstream cable loss ratios RU can be determined to define relationships
between the cable
loss at other frequencies, such as the reference downstream pilot
frequenciesfpL,fm and
the upstream reference frequenciesfi,f2 andf3 as defined above.
In this particular relationship, the following ratios, RU1, RU2 and RU3 for
the cable
loss ratios with respect to the low frequency pilotfi>L can be determined from
curve R:
CA 02789768 2012-09-14
- 19 -
RU1 = Cable Loss gfn (14a)
Cable Loss @fi
which for this preferred embodiment where the low pilot frequencyfn is the
same as the
reference frequency for band m=2:
RU1 = CL,7 (14b)
CL,,f;
Similarly, the band ratio RU2 for the cable loss ratio between cable losses at
low
pilot frequencyfn and the cable losses atf2, may be represented as follows:
RU2= Cable Loss (ii),fpt (15a)
Cable Loss @f7
which for this preferred embodiment where the low pilot frequencyfn is the
same as the
reference frequency for band m=2:
RU, = CLõ (15b)
CLõf2
Similarly, for the third frequency RU, the upstream cable loss ratio RU3
between
the low pilot frequency JPL and the cable loss atf3 may be represented as:
RU3= Cable Loss (fp.t (16a)
Cable Loss @f3
which for this preferred embodiment where the low pilot frequencyfPL is the
same as the
reference frequency for band m=2:
RU3 =CLn 2 (16b)
CL,õf3
Using the preferred embodiment shown in Fig. 5, and the preferred
frequenciesfi,
f3 andfp1-2 andfm=4 the values RU1, RU2 and RU3 may be determined to be RU1=
4.000, RU2 = 1.927 and RU3 = 0.981.
If frequencyf2 is the reference frequency for the upstream data m=1, then we
may
substitute CL,,,i into equation (15) and obtain the following:
CL,i = CL11J1 = CLidpi (17a)
RU,
which, for a preferred embodiment where PL is the same as the reference
frequency for
band m=2 reduces to:
CA 02789768 2012-09-14
- 20 -
CL,1 = CLI1J ¨ CL (17b)
(17b)
1.927
Therefore, the predicted total system losses for the upstream data band m=1 in
the
section n, which is immediately upstream from the amplifier, can be predicted
from
equation (12) as follows:
L,,,] =CLJ TL, (18a)
RU7
which the above values CL, PL and IL, have already been deteimined for the
section n
immediately upstream from the amplifier AMP, and, for this preferred
embodiment, can be
reduced to the following:
CL, 2 IL, (18b)
1.927
The total system loss in the upstream voice band represented by L3 can be
found
using the following:
Ln,3 ¨ CLiztPL (19a)
RU3
which all of the above values CL,õ PL, RU3 and IL, have been determined as
identified
above. In this way, the anticipated system loss in section n immediately
upstream from the
amplifier AMP can be predicted and compensated for by amplifying the upstream
communication signal CS,, in the band m=3 by the value L1,3. In this preferred
embodiment, this value can be determined as follows:
L,3 ¨ CLõ, ILõ (19b)
0.981
At this point, the components of the system loss have been determined for both
upstream bands. The gains of the amplifiers in the upstream bands m=1, m=3
have been
determined. The amplifier can then amplify the upstream signals CS, to
compensate for
this anticipated loss as described more fully below. Accordingly, based on the
above, the
amplifiers AMP will amplify the upstream signals CS,,, to compensate for the
anticipate
loss which the upstream signals CS, in bands m=1 and m=3 will experience when
the
upstream signal CSõ propagates through the upstream section n of the cable 12.
CA 02789768 2012-09-14
-21 _
In cases where the bands m=1, m=2, m=3 and m=4 have a wide bandwidth, such as
more than 10 MHz, the radio frequency response of the cable section n will
vary over this
bandwidth such that it will have a shape or negative slope, sometimes referred
to as a Tilt
across the bandwidth m. The longitudinal loss in the cable in the higher
frequencies will,
of course, be higher than the loss at the lower frequencies which is also
illustrated from the
curve R as shown in Fig. 5. For example, cable sweep tests have shown that for
a cable
length of 350 meters, negative slope of approximately 2 dB, were produced
within the data
downstream band m=4 which, at least in this preferred embodiment, is 12 MHz
between
220 - 232 MHz. The upstream data band m=1, which in this preferred embodiment
is 5 -
42 MHz can have a slope or tilt of 6 dB because it is a bandwidth of about 37
MHz.
In order to measure the slope in the bandwidth, it is preferred that the wider
band
widths of 10 MHz or wider have two reference pilots, one at the upper end and
one at the
lower end to be able to accuragely determine the slope T.
As indicated above, based on the curve R and the low pilot PL and high pilot
PH, it
would be possible to determine losses at any other frequency including the
downstream
mid-point pilot PM. However, in order to improve the accuracy of the system,
and given
that the downstream pilots PL, PM, PH are relatively simple to manage because
they all
travel away from the first end 1 of the radiating transmission line 12, in a
preferred
embodiment, three downstream pilot signals PL, PM and PH are used. Otherwise,
the
middle pilot signal PM representing the lower end of the downstream data band
m=4,
could be predicted using the equations above and the curve R.
To calculate the slope in the downstream data band, the system losses for the
pilots
PM and PH may be used. The losses added to PH have been calculated in equation
(3)
above.
The losses for the mid-point pilot PM, when it is used, may be calculated as
follows:
LnfpM ¨ PM0 - PMn (20)
where PMo is the original level of the pilot PM and PMn is the measured value
of PM.
The slope in the downstream data band can then be calculated as follows:
CA 02789768 2012-09-14
- 22 -
T4 = 1-m,4 - LniPM (21)
where T4 is the slope for the data downstream band m=-4 in this preferred
embodiment and
the losses Ln,4 represent the losses of the high frequency pilot signalfpu.
Next, the slope for the upstream data band m=1 may be calculated. This slope
may
be represented by T1. To calculate the slope Ti, the cable longitudinal losses
CLn,f1 and
CLõ,f2 at the two references pointsfi andf2 of band m-1, respectfully are
required.
From equations 14 and 15 above and using the cable loss ratios RU1 and RU2,
the
following equation can be derived:
CLJj=CLPL (22a)
RU1
which for this preferred embodiment is:
CLõ,fi = CL n 2 (22b)
4.999
If the second reference frequencyf2 is considered to be the reference for band
m=1,
then CL,,f2 is the same as CLõ,i, which was calculated in equation (17) above.
Using this equation, the slope Ti and the upstream data band m=1 can be
calculated
as follows:
T1 = CLõ,f2 - CLf (23)
It is apparent where a comparison from equations (21) and (23) that for the
upstream data band m=1, the cable loss values CL,õf2 and CLõ,fi may be used to
determine
the slope Ti. In contrast, equation 21 the total losses Lõ,fpH - Lnii,m are
used because the
actual loss Lnym has been measured in this preferred embodiment. However,
because the
only difference between the total loss L and the cable loss CL is the
insertion loss IL,
which is non-frequency dependent, the slope T should be substantially the same
whether
the total loss L is used or the cable loss CL is used.
On this basis, in case only two pilot signals are used, namely PL and PH, then
the
slope for the downstream data band m=4 may be the following:
T4 = CL,/PH CLniPM
where CLõ,pm may be determined from the curve R and the measured losses L of
the low
CA 02789768 2012-09-14
- 23 -
pilot PL and high pilot pH and CLn,fpH has been determined above in equation
(9).
Using the above equations, the amplification units AMP in the system 10 can
amplify the downstream signals CSd into the next, or downstream, section n+1
of the
communication system 10 using the measured losses L in the pilots PL, PH and,
if used,
PM. The controlled gain for the upstream communication signals CSõ may be
predicted
using the anticipated loss of the upstream signals CSõ into the upstream
section n of the
radiating transmission line 12 immediately upstream from the amplification
unit AMP
based on the measured losses from the downstream pilot signals PL and PH and,
if used,
PM transmitted through the upstream section n.
Figure 3 illustrates a block diagram of an amplification unit AMP, identified
generally by reference numeral 100, according to one preferred embodiment.
As shown in Figure 3, the amplification unit 100 preferably comprises an
upstream
connection unit 102 for connecting to an upstream section n of the radiating
transmission
line 12. It is understood that the upstream connection unit 102 will receive
radio
frequencies RF representing the downstream communication signals CSd and send
RF
frequencies representing the upstream communication signals CS. However,
because the
connection unit 102 is connected to the section n of the radiating
transmission line 12
immediately upstream from the amplification unit 100, this connection unit 102
will be
referred to as the upstream communication unit 102 for ease of reference.
Similarly, the
amplification unit 100 has a downstream connection unit 104 for connection to
the section
n+1 of the radiating transmission line 12 that is immediately downstream from
the
amplification unit 100. The downstream connection unit 104 will receive radio
frequency
RF signals representing the amplified downstream communication signal CSd and
receive
radio frequency RF signals representing the upstream communication signal
CSii.
As is also illustrated in Figure 3, the downstream connection unit 104 will
also
transmit the re-amplified pilot signals PL,, and PH,, and where a third signal
is used, PM,. It
is understood that re-amplified pilot signals will have the same amplitude as
the signals
that emanated originally from the pilot generator 30 at the base station 24.
Similarly, the
upstream connection unit 102 will receive the downstream pilot signals PL and
P1-1 and,
CA 02789768 2012-09-14
=
, .
- 24 -
where used, PM, which have traveled down the upstream section n of the
radiating
transmission line 12. It is understood that the pilot signals PL and PH and,
where used,
PM, will have experienced a loss in transmission over the upstream section n
of the
radiating transmission line 12. It is also understood that the pilot signals P
would have
emanated either from the base station 24 or from another amplification unit
100 and, in
either case, would have initially entered into the upstream section n of the
radiating
transmission line 12 having the same amplitude as when originally generated by
the pilot
generator 30 in the base station 24.
As is also known in the art, the amplification unit 100 will have various
radio
frequency combiners, filters, wave guides and other electronics which would be
known to a
person skilled in the art and are not necessarily represented in the general
graphical
representation of the amplification unit 100 as shown in Figure 3. However,
Figure 3 does
illustrate various filters 136 between the internal components of the
amplification unit 100
and the connection units 102, 104. As also illustrated in Figure 3, the
amplification unit
100 preferably comprises a directional coupler 138 which separates the
downstream
communication signal CS(.1 from the downstream pilot signals PL, PH and, where
used,
PM. The pilot signals PL, PM and PH, as shown in Figure 3, pass through
further filters
139 and then enter into the respective detectors, namely the low pilot PL
detector 130 PL,
the mid-pilot detector 130 PM and the high pilot detector 130 PH. Emanating
from each of
the detectors 130 is the corresponding measured loss signal LiõfpL,
and Lnipli, which
is then received by the microcontroller 120.
It is understood that the microcontroller 120 would perform several functions
in
controlling the amplification unit 100. It is also understood that the
amplification unit 100
may have more than one microcontroller 120, but for ease of reference, only
one
microcontroller 120 is illustrated in Figure 3. Furthermore, the
microcontroller 120 in a
further embodiment will comprise an insertion loss component 122, a cable loss
component 124 and a slope deteimining component 126. It is understood that
each of these
components 122, 124, 126 could be software or hardware components controlled
by, or
foiming part of, the microcontroller 120. It is also understood that the
components 122,
CA 02789768 2012-09-14
-25 _
124 and 126 could be stand alone units and may have a separate microcontroller
or
processor, such as in cases where the amplification unit 100 has been
retrofitted with this
hardware. In a preferred embodiment, the microcontroller 120 will have the
hardware and
software capacity to include the components 122, 124 and 126. Therefore, the
microcontroller 120 performs the function of an upstream loss prediction unit.
It is understood that the insertion loss component 122 will receive the
measured
losses L,õfpl , Lfpm and Lndepi) and determine the various values and,
specifically, the
insertion loss IL, for each section based on the equation (10) indicated
above. It is noted
that Figure 1 illustrates the calculated insertion losses ILn for the sections
n of this
preferred embodiment. The distance D of each section n is also shown in Figure
1. In
order to perfoim these calculations, it is understood that the microcontroller
120 of each
amplification unit AMP 100 will have been previously programmed with software
and/or
supplied with hardware to perform the functions indicated by the equations
above,
including information regarding the curve R illustrated in Figure 5.
Similarly, the cable loss component CL, 124 will perfoim the calculations
determined to perform the cable loss for both the downstream signals CSd and
the upstream
signals CS. It is understood that in the preferred embodiment where the pilot
signals PL
and PH also correspond to the reference frequencies for the downstream bands
m=2, m=4,
the downstream cable loss calculation and downstream insertion loss
calculation will
simply be a subtraction of the measured values L,õfpL and 1_,,,,fPn from the
original values
PL0 and PH0 as indicated in equations (2) and (3) above. For the upstream
communication
signals CSõ, the upstream predicted cable losses 4,1 and L03 will be based on
the measured
losses of downstream pilots PL and PH as indicated in equations (18) and (19)
above.
Similarly, the slope T will be determined for any communication signals CS
that
have a bandwidth of greater than 12 MHz and preferably greater than 10 MHz. In
this
preferred embodiment, as indicated above, the slope T will be calculated for
the
downstream data band m=1 (Ti) and the upstream data band M=4 (T4). As
indicated
above, in cases where the system 10 does not have a midpoint downstream pilot
PM, the
lower end of the cable loss CL at the lower end of the data band M=4 can be
determined
CA 02789768 2012-09-14
- 26 -
and the slope T4 calculated from equation (24). In the preferred embodiment,
where a
downstream midpoint pilot PM is used, the actual measured losses Lii,fpx and
Lõ,fpm will
be used to determine the slope T4 based on equation (21). For the upstream
communication signal CSõ, in this preferred embodiment, the upstream data band
m=1 has
a bandwidth greater than 10 MHz, such that the slope T1 for bandwidth m=1
would need to
be calculated. In this case, as indicated above, the slope T1 for bandwidth
m=1 would be
calculated based on equation (23).
The results from the components 122, 124 and 126 are then processed and sent
to
the downstream digital attenuator 140d and downstream slope control 142d in
order to
shape the downstream communication CSd. The downstream digital attenduator
140d and
downstream soap control 142d and amplifier 145 will generally amplify the
downstream
communication signal CSõ as is currently done and based on the downstream
pilot signals
PL, PH and, where used, PM.
The controller 120 will also provide results from the components 122, 124 and
126
to the upstream digital attenuator 140u, the upstream slope control 142u and
the amplifier
145 to amplify the upstream communication signals CSõ. In this case, however,
the
upstream communication signal CSõ will be attenuated and the slope will be
controlled
based on the anticipated loss the upstream communication signal CSõ will
experience over
the section n of the radiating transmission line 12 immediately upstream from
the
communication signal 100. Therefore, the gain and slope of the upstream
communication
signal CS,, will be controlled to compensate for the anticipated loss that the
upstream
communication signal CS, will experience based on the predicted loss for the
upstream
communication signal CSõ in bands m=1, m=3 based on the losses measured from
the
downstream pilot signals PL, PH and, where used, PM.
Once the downstream signals CSd exit the slope control 142d, it will be
amplified
by amplifiers 145, passed through the filter 136 and exit through the
downstream
connection 104. Similarly, once the upstream communication signals CS, exits
the
upstream slope control 142u, it will be amplified by the amplifier 145, passed
through the
filter 136 and exit though the upstream connection 102 into the upstream
section n of the
CA 02789768 2012-09-14
_ 77 _
radiating transmission line 12. It is understood, however, that the downstream
communication signals CSd leaving from the amplification unit 100 will have
been
amplified to compensate for the losses that occurred after the downstream
communication
signals CSd passed through the upstream section n of the cable 12 and
therefore the signal
CSd will have an amplitude similar to that which would normally have when it
exited from
the base transmitter 28 of the base station 24. In contrast, the upstream
communication
signal CS,, leaving the amplification unit 100 will have been amplified to
compensate for
the anticipated losses which the upstream communication signal CS,, will
experience when
it is transmitted through the upstream section n of the radiating transmission
line 12, based
on the downstream pilots PL, PH and where used PM. In this way, the upstream
communication signals CS,, that is received, either by the base receiver 26 if
this is the first
amplifier in the first communication system 10, or, the next upstream
amplification unit
100 in the system 10, will be substantially similar to the unamplified
upstream
communication signal CS.
Figure 4 is a flow chart illustrating the steps in a method according to one
preferred
embodiment of the present invention. As illustrated in Figure 4, the flow
chart 400
comprises a start section 401 which leads to setting variables 402. The
variables include
the pilot levels at the head end, namely PLõ, PM0, PH,, as well as the cable
loss ratios based
on curve R that will be used for the particular frequenciesf,f2 andfi as well
as the pilot
signalsfpL,fm and, where used,fpm=
In section 404 that data is inputted meaning that the detectors 130 in each
amplification unit 100 measure the input levels of the downstream pilots PL,
PH and PM
and these values are then stored in microprocessor 120 or memory (not shown).
In section 406, various calculations are made based on the equations 1 to 24
as
outlined above. For instance, step 501 calculates the band m=2 system loss
based on
equation (2). In step 502, the band m=4 system losses are calculated based on
equation (4).
Subsequently, in step 503, the band m=4 cable loss is calculated based on
equation (9).
Subsequent to that, in step 504, the section insertion loss ILn is calculated
based on
equation (10). Finally, the band m=2 cable loss can be calculated in step 505
based on
CA 02789768 2012-09-14
- 28 -
equation (7).
In section 407 of the flow chart 400, the upstream band m=1 cable loss is
calculated
and in step 506 based on equation (14), and the band m=3 cable loss is
calculated in step
507 based on equation (16). In step 508, the total system loss for upstream
band m=1 is
calculated and in step 509 based on equation (18), and, the upstream
communication signal
CSi, band m=3 total system loss Ln3 is calculated in step 509 based on
equation (19).
In section 408, of the flow chart 400, the system gains are then determined
for each
of the bands m=1, m=2, m=3 and m=4, which are essentially equivalent to the
actual
measured losses for the downstream communication signal bands m=2, m=4 and the
anticipated losses for the upstream communication bands m=1, m=3.
In section 409 of the flow chart 400, the system tilts for the bandwidths
greater than
MHz are calculated. Specifically, in step 511, the upstream data band cable
losses are
determined through both reference frequenciesfi andf2 of the upstream data
band m=1. In
step 512 in cases where the third pilot signal PM is used, the total system
loss for Ln,finvi is
determined. Finally, in step 513, the upstream and downstream data band tilts
T1, Tzt are
calculated based on equations (23) and (21), respectively.
In section 410 of the flow chart 400, the microprocessor 120 outputs the
variable
attenuators adjustment gains GI, G2, G3 and G4 to the downstream digital
attenuator 140d
and upstream attenuator 140u, respectively. Finally, in step 514, the
microprocessor
outputs the slopes T1 and T4 to the downstream slope control 142d and upstream
slope
control 142u at step 152. In section 411 of the flow chart 400, there is a
repeat step 516
after a short period of time.
To the extent that a patentee may act as its own lexicographer under
applicable law,
it is hereby further directed that all words appearing in the claims section,
except for the
above defined words, shall take on their ordinary, plain and accustomed
meanings (as
generally evidenced, inter alia, by dictionaries and/or technical lexicons),
and shall not be
considered to be specially defined in this specification. Notwithstanding this
limitation on
the inference of "special definitions," the specification may be used to
evidence the
appropriate, ordinary, plain and accustomed meanings (as generally evidenced,
inter alia,
CA 02789768 2012-09-14
- 29 -
by dictionaries and/or technical lexicons), in the situation where a word or
term used in the
claims has more than one pre-established meaning and the specification is
helpful in
choosing between the alternatives.
It will be understood that, although various features of the invention have
been
described with respect to one or another of the embodiments of the invention,
the various
features and embodiments of the invention may be combined or used in
conjunction with
other features and embodiments of the invention as described and illustrated
herein.
Although this disclosure has described and illustrated certain preferred
embodiments of the invention, it is to be understood that the invention is not
restricted to
these particular embodiments. Rather, the invention includes all embodiments,
which are
functional, electrical or mechanical equivalents of the specific embodiments
and features
that have been described and illustrated herein.
