U.S. patent application number 14/789625 was filed with the patent office on 2017-01-05 for breaking up symbols for spectral widening.
The applicant listed for this patent is Higher Ground LLC. Invention is credited to Scott MCDERMOTT.
Application Number | 20170005697 14/789625 |
Document ID | / |
Family ID | 57609600 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170005697 |
Kind Code |
A1 |
MCDERMOTT; Scott |
January 5, 2017 |
BREAKING UP SYMBOLS FOR SPECTRAL WIDENING
Abstract
A technique for spectral widening in a communication system may
divide respective symbols of a block of symbols into symbol pieces
of shorter duration than a symbol. The symbol pieces may be
scrambled. The resulting scrambled symbol pieces may optionally be
further spread using direct-sequence spreading prior to
transmission. Error-control coding may also be used prior to
dividing the symbols into symbol pieces and scrambling the symbol
pieces. Additionally, the number of symbol pieces per symbol may be
adjustable, based on channel characteristics, performance, or
both.
Inventors: |
MCDERMOTT; Scott;
(Washington, DC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Higher Ground LLC |
Palo Alto |
CA |
US |
|
|
Family ID: |
57609600 |
Appl. No.: |
14/789625 |
Filed: |
July 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14789524 |
Jul 1, 2015 |
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14789625 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 25/03866 20130101;
H04L 1/0041 20130101; H04B 1/707 20130101; H04L 1/0045
20130101 |
International
Class: |
H04B 1/707 20060101
H04B001/707; H04L 25/03 20060101 H04L025/03 |
Claims
1. A method of data communication using spectral widening, the
method including: receiving a sequence of transmitted scrambled
symbol pieces of shorter duration than an entire symbol and
corresponding to a block of data-bearing symbols whose respective
symbols were divided into the symbol pieces, wherein a respective
number of symbol pieces for a respective symbol is adaptive;
descrambling the sequence of transmitted scrambled symbol pieces to
recover the block of data-bearing symbols; and receiving
information indicative of the number of pieces and adapting the
descrambling based on the received information.
2. The method of claim 1, wherein the descrambling comprises an
inverse operation to a pseudo-random scrambling operation used to
scramble the symbol pieces.
3. The method of claim 1, wherein the method further includes
performing error-control decoding on the block of data-bearing
symbols.
4. The method of claim 1, wherein the symbol pieces are of
substantially equal duration.
5. (canceled)
6. The method of claim 1, further including direct-sequence
de-spreading the sequence of transmitted scrambled symbol pieces
prior to descrambling.
7. The method of claim 6, wherein the direct sequence de-spreading
uses a common sequence to de-spread each of the symbol pieces.
8. A receive-side data communication apparatus, including: a
receiver configured to receive a sequence of transmitted scrambled
symbol pieces of shorter duration than an entire symbol and
corresponding to a block of data-bearing symbols whose respective
symbols were divided into the symbol pieces; and a descrambler
configured to descramble the scrambled symbol pieces to recover the
block of data-bearing symbols, wherein a number of pieces per
respective symbol is adaptive, wherein the receiver is further
configured to receive information indicative of the number of
pieces, and wherein the descrambler is further configured to be
adapted based on the received information.
9. The apparatus of claim 8, further including an error-control
decoder configured to accept and decode the block of data-bearing
symbols.
10. The apparatus of claim 8, wherein the symbol pieces are of
substantially equal duration.
11. (canceled)
12. The apparatus of claim 8, further including a direct-sequence
de-spreader configured to direct-sequence de-spread each respective
symbol piece and disposed prior to the descrambler.
13. The apparatus of claim 12, wherein the direct-sequence
de-spreader is configured to use a common sequence to de-spread the
respective symbol pieces.
14. The apparatus of claim 8, wherein the receiver is a wireless
communication receiver.
15. The apparatus of claim 8, wherein the descrambler is configured
to descramble the symbol pieces according to an inverse operation
to a pseudo-random scrambling operation used to scramble the symbol
pieces.
16. A storage device containing executable instructions configured
to result in the implementation of operations including:
descrambling a received sequence of transmitted scrambled symbol
pieces of duration shorter than a symbol and corresponding to a
block of data-bearing symbols whose respective symbols were divided
into the symbol pieces to recover the block of data-bearing
symbols, wherein a number of symbol pieces per respective symbol is
adaptive; and adapting the descrambling based on received
information indicative of the number of pieces.
17. The storage device of claim 16, wherein the descrambling
comprises an inverse operation to a pseudo-random scrambling
operation used to scramble the symbol pieces.
18. The storage device of claim 16, wherein the operations further
include performing error-control decoding on the block of
data-bearing symbols.
19. The storage device of claim 16, wherein the symbol pieces are
of substantially equal duration.
20. (canceled)
21. The storage device of claim 16, wherein the operations further
include direct-sequence de-spreading the sequence of transmitted
scrambled symbol pieces prior to descrambling.
22. The storage device of claim 21, wherein the direct sequence
de-spreading uses a common sequence to de-spread each of the symbol
pieces.
23. A communication apparatus including: at least one processing
device; and the storage device of claim 16, wherein the at least
one processing device is coupled to the storage device and is
configured to execute the executable instructions.
24. The method of claim 1, wherein the sequence of transmitted
scrambled symbol pieces comprises symbol pieces of different
symbols of the block of data-bearing symbols scrambled across the
block of data-bearing symbols to change the order of transmission
of the symbol pieces.
25. The apparatus of claim 8, wherein the sequence of transmitted
scrambled symbol pieces comprises symbol pieces of different
symbols of the block of data-bearing symbols scrambled across the
block of data-bearing symbols to change the order of transmission
of the symbol pieces.
26. The storage device of claim 16, wherein the sequence of
transmitted scrambled symbol pieces comprises symbol pieces of
different symbols of the block of data-bearing symbols scrambled
across the block of data-bearing symbols to change the order of
transmission of the symbol pieces.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/789,524, Attorney Docket No. 688956-2US,
also entitled "Breaking Up Symbols for Spectral Widening," filed on
Jul. 1, 2015, co-assigned, and incorporated by reference
herein.
FIELD OF ENDEAVOR
[0002] Aspects of the present disclosure may relate to techniques
for spreading/widening the spectrum of a communication signal.
BACKGROUND
[0003] In communication systems, one may need a symbol to contain a
certain received energy, usually termed E.sub.s, in order to
correctly decode the information carried by the symbol. However, in
some situations, one may also need the transmitted power per Hertz
(Hz) to be below some ceiling. This is often required to avoid
interfering with other signals in the same frequency band. One way
to do this may be to widen the spectrum of the transmitted signal,
i.e., to transmit the same energy over a wider bandwidth, in order
to be able to meet such a constraint. For example, if one would
like to transmit 10 kbps and would need somewhere in the 13-20 kHz
range to send it, one may need to spread that power across, e.g., 1
MHz of bandwidth.
[0004] One known way to do this is direct-sequence (DS) spreading.
In a DS spread-spectrum (DSSS) system, each symbol to be
transmitted may be multiplied by a spreading sequence, which may
be, for example, but is not limited to, a pseudo-random sequence
(to be referred to as a "PN sequence" herein). As a result, for a
particular symbol, one may multiply by, for example, an 80-chip PN
sequence, and the resulting increase in the number of transitions
(which may be in phase, frequency or amplitude or some other
characteristic) between those chips may serve to widen the
spectrum.
[0005] An issue in using DSSS is that it may make acquisition more
difficult, and the longer the PN sequence used, the more difficult
acquisition becomes. As a result, long training sequences may be
needed to provide synchronization/acquisition for DSSS systems
using long PN sequences. Therefore, it may be desirable to use
another technique to shorten the length of the PN sequence needed
or instead of using DSSS.
SUMMARY OF THE DISCLOSURE
[0006] Various aspects of the disclosure may be directed to
spectral widening techniques that may be used in conjunction with
or in lieu of DSSS. Such techniques may break up blocks of symbols
to be transmitted into pieces and may scramble (or interleave) the
pieces and transmit the scrambled pieces. At the receive side, the
pieces may be descrambled (or de-interleaved) to recover the
original symbols. Error-control coding techniques may be used in
conjunction with this breaking up and scrambling of symbols, which
may help to ensure corrected reception of information.
[0007] Various operations may be performed by dedicated electronic
hardware devices, or alternatively, may be implemented using other
hardware, software, or firmware, or combinations thereof, including
the possibility of using a processor that may execute software
instructions, which may, e.g., be saved on a storage device, and
which may cause the operations to be implemented.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0008] Various aspects of this disclosure will now be discussed in
further detail in conjunction with the attached drawings, in
which:
[0009] FIG. 1 shows an example of a conceptual block diagram
according to various aspects of the disclosure;
[0010] FIG. 2 shows another example of a conceptual block diagram,
according to various aspects of the disclosure;
[0011] FIG. 3, consisting of FIGS. 3A-3D, shows a conceptual
example of signaling, according to an aspect of the disclosure;
[0012] FIG. 4 shows an example of a further conceptual block
diagram, according to an aspect of the disclosure;
[0013] FIG. 5 shows an example of further signaling-related
concepts, according to an aspect of the disclosure; and
[0014] FIG. 6 shows a conceptual block diagram of a technique and
components according to another aspect of the disclosure.
DETAILED DESCRIPTION OF ASPECTS OF THE DISCLOSURE
[0015] As shown in FIG. 4, a communication system may have transmit
41 and receive 43 sides, between which signals 42 may be
transmitted. Either or both sides may have both transmit and
receive capabilities, which may result in "transceivers" and may
allow for bi-directional communications. In some cases, the signals
42 may traverse one or more repeaters or transponders between the
transmit 41 and receive 43 sides, such as a geosynchronous
satellite, but the invention is not thus limited.
[0016] In some cases, a power density of a transmitted signal 42
may need to be limited. For example, a frequency band in which
signal 42 is transmitted may be allocated for other uses. In such
cases, if the power of signal 42 is maintained at a level below a
particular "noise floor," it may still be acceptable to transmit in
that frequency band. For example, in some bands in the United
States, the Federal Communications Commission ("the FCC") may
allocate frequency bands while allowing other uses of the same
bandwidth, provided that the signals corresponding to the other
uses are of sufficiently low power as not to interfere with the
signaling to which the bands are allocated. As noted above, DSSS is
one way to do this, but there may be drawbacks to doing so, and
simply transmitting signals at a sufficiently low power level may
result in it not being possible to reliably communicate.
[0017] According to an aspect of this disclosure, examples of which
are shown in FIGS. 1-3, it may be possible to use a further
technique, either alone or in combination with DSSS, which may
alleviate some of the issues stated above. As shown in FIG. 1,
information may be provided for error-control coding 11; however,
the invention is not limited to systems using error-control coding
11, and this may be omitted, according to some aspects of this
disclosure. Such information may, for example, be in the form of
binary or non-binary symbols (bits or M-ary symbols). In one
example, shown in FIG. 3A, eight symbols may be provided for
error-control coding; but the invention is not thus limited. The
error-control coding 11 is not limited to any particular coding
technique and may, for example, comprise algebraic coding,
convolutional coding, parity check coding, turbo coding, block
coding, systematic or non-systematic coding, etc. Error-control
coding 11 may be implemented, e.g., in the form of a coding chip or
chipset or other hardware, software, firmware or combination
thereof. In a relatively simple example shown in FIG. 3B, the eight
symbols of FIG. 3A may be encoded into sixteen code symbols, i.e.,
by using a rate one-half encoder. The sixteen code symbols are
labeled "1" to "16" in FIG. 3B, and for the sake of simplicity, the
eight original information symbols may correspond to code symbols
1-8, while code symbols 9-16 may correspond to "parity check"
symbols, in a systematic rate one-half code; however, it is
emphasized that the invention is not limited to this type of
encoding.
[0018] As a rule of thumb in communication systems, there is a
certain amount of energy, E.sub.s, which must be present in each
symbol at the receiver 43 for correct reception to take place an
acceptable percentage of the time (e.g., to ensure an acceptable
average symbol error rate or bit error rate). Energy is power
multiplied by time. Thus, along the `t` axis of FIG. 3B, for a
given amount of total transmitted power per symbol and a given
signal path 42, there is some minimum amount of time that a given
code symbol, e.g., code symbol 8, must occupy in order to have
successful communication, on average (it is noted that, while this
is discussed in the context of "code symbols," the discussion may
be applicable to uncoded systems, as mentioned above, according to
other aspects of this disclosure). This time may be contiguous, as
is the case in many known communication systems; i.e., the
transmitter may begin transmitting a symbol, may continue doing so
for at least the required minimum amount of time, and may then then
stop transmitting the symbol.
[0019] However, this contiguous transmission of one symbol may
concentrate the signal's power density. A signal's power density
is, to a first order, the amount of power being transmitted,
divided by the bandwidth it occupies. The bandwidth it occupies, in
turn, is proportional to the number and character of transitions
present in the signal. In various communication techniques, the
number of transitions may be considered equal to the number of
bits, symbols, or DSSS chips sent per unit time, whichever is
greatest. According to an aspect of this disclosure, a fourth
option is added, namely, the number of pieces a single symbol is
broken into.
[0020] Thus, according to an aspect of this disclosure, the code
symbols output from error-control coding 11 may be divided 12 into
multiple pieces. In one example, as shown in FIG. 3C, code symbol 8
may be divided into sixteen pieces, 8a, 8b, . . . , 8p. They are
shown here of substantially equal length in time; however, this is
an example, and the invention is not limited to equal-duration
pieces. This may be performed, e.g., by one or more switching
devices, which may be implemented in parallel. This may be followed
by scrambling/interleaving 13.
[0021] Note that, while shown in FIG. 1 as preceding and being
separate from scrambling/interleaving 13, symbol division 12 need
not necessarily be a separate operation. For example, the
scrambling/interleaving 13 may include switching operations that
may select pieces from a block of code symbols output from
error-control coding 11 (or a block of uncoded symbols) in an order
according to a scrambling/interleaving algorithm implemented in
scrambling/interleaving 13.
[0022] It is further noted that the number of pieces into which
code symbols are divided 12 may not be fixed. While keeping the
duration of a symbol-piece fixed, the number of pieces integrated
together to make a symbol may be variable and adjustable. For
example, to which the invention is not limited, the number of
pieces into which symbols are divided may be changed based, e.g.,
on measured channel conditions or feedback received from a receiver
receiving and/or processing the transmitted signal reflecting
performance, such as, but not limited to, signal-to-noise ratio,
bit- or symbol-error rate, etc. If channel conditions are poor or
performance is not acceptable, symbol division 12 may be adjusted
to increase the number of pieces allocated to a given symbol,
increasing the amount of time over which that symbol can be
integrated, which may thus increase the total energy E.sub.s
received at receiver 43. Similarly, if channel conditions are
determined to be better than expected or performance is better than
some predetermined threshold, symbol division 12 may be adjusted to
decrease the number of pieces allocated to a given symbol, even
down to a single piece per symbol, the maximum rate of the system.
According to this aspect of the disclosure, the total occupied
bandwidth, and any spreading applied to symbol pieces, and all of
the processing and logic associated with them, may remain identical
across a wide range of ultimate symbol rates. The only change may
occur during division and re-integration of symbol pieces, which
may thus leave all the rest of the system in between unchanged.
[0023] FIG. 6 shows an example of a block diagram of a system that
may be used to implement adaptive symbol division. On the transmit
side 61, which may include symbol division 12, either or both of
channel condition measurement 63 or reception of information
indicative of performance or channel conditions 64 may be
performed. A channel condition measurement block 63 may receive
signals and estimate, for example, a signal-to-noise ratio (SNR) or
similar indication of channel conditions. The indication of channel
conditions may be provided to control logic 65 and processed to
determine whether or not to adjust symbol division 12 and, if so,
how to adjust it. For this purpose, control logic 65 may perform
one or more comparisons of values received from channel condition
measurement 63, e.g., with one or more predetermined or adaptive
thresholds, to determine a number of pieces into which symbol
division 12 may divide code symbols. As an alternative, or in
conjunction with channel condition measurement 63, the transmit
side 61 may receive feedback from a receive side 62. This feedback
may be in the form of channel condition measurements or indications
thereof (e.g., SNR, received signal strength indicator (RSSI),
etc.) and/or performance-related information (e.g., bit-error rate,
symbol-error rate, received signal power/energy, etc., or
indication(s) thereof (e.g., but not limited to, numerical
indicators or quantized versions thereof)). For this purpose, a
receiver 64 may receive such feedback and may provide it to control
logic 65. Control logic 65 may, again, analyze the received
feedback, e.g., using one or more threshold comparisons (which,
again, may use predetermined thresholds and/or adaptive
thresholds), and may thereby determine how to control symbol
division 12. Note that channel condition measurement 63 and/or
performance or channel condition feedback receiver 64 may both be
present and may both provide one or more types of information to
control logic 65, which may perform various combinations,
comparisons, etc., of the information received from blocks 64 and
65 to determine how to control symbol division 12. For example,
feedback information may be weighted more heavily than local
measurements. Control of symbol division 12 by control logic 65 may
be by provision to symbol division 12 of a number of pieces into
which symbols are to be divided or an indication to increment or
decrement (or neither) a number of pieces used for symbol
division.
[0024] While not shown in FIG. 6, it may also be necessary to adapt
the scrambler/interleaver 13, based on the number of pieces per
symbol. Scrambler/interleaver 13 may receive a control signal from
control logic 65 to indicate the number of pieces per symbol, which
affects the number of pieces per block, and this may be used to
adapt the scrambler/interleaver 13, e.g., by selecting a
scrambling/interleaving scheme appropriate to the number of pieces.
It is further noted that, for purposes of coordination, the number
of pieces into which symbols are being divided may be transmitted
to receive side 62 and may be used, e.g., to control
de-scrambler/de-interleaver 22 to similarly adapt (which may,
again, be by selecting an appropriate scheme).
[0025] Continuing the example shown in FIG. 3,
scrambling/interleaving 13 may select various pieces of various
symbols and arrange them according to some scrambling/interleaving
scheme. FIG. 3D shows a non-limiting example of what the pieces in
the eighth symbol period may look like after scrambling. In this
example, the particular symbol interval includes pieces of all
sixteen symbols, 16i, 4k, 11n, 8q, . . . , but the invention is not
limited to any particular scrambling/interleaving scheme. Note that
the scrambling/interleaving 13 may be optimized to ensure that
there are no or minimal peaks in the spectrum of the resulting
signal and may, therefore, use some pseudo-random technique; such a
technique may help to ensure that the pieces of a given symbol are
disposed sufficiently "randomly" so as to prevent or minimize
spectral peaks. It is also noted that the scrambling/interleaving
13 may be implemented in the form of a dedicated hardware block (a
"scrambler" or "interleaver"), which may be a chip or chipset, or
using hardware, software, firmware, or a combination thereof
[0026] To elaborate further, the result of scrambling the symbol
pieces as shown in FIG. 3D may, in general, be to increase the
number of transitions (in phase, frequency, amplitude, or other
characteristic) per unit time. Whereas the time period for symbol 8
in FIG. 3B had zero transitions, the same time period in FIG. 3D
may have up to 15 transitions (on average, if the data were random
binary data, this may typically be seven or eight transitions). By
increasing the number of transitions per unit time, the signal's
power density decreases; but by having each symbol occupy the same
total amount of time in both FIG. 3B and FIG. 3D, total symbol
energy E.sub.s is not affected, given the same transmitted
power.
[0027] As further shown in FIG. 1, scrambling/de-interleaving 13
may be followed by spreading 14, e.g., DSSS spreading. Spreading 14
may optionally be used, for example, if the spectral widening
effected by breaking up the symbols into pieces is not sufficient
to lower the energy level of the signal sufficiently to meet
requirements of the frequency band on which the signal may be
transmitted. However, as a result of the breaking up of the symbols
into pieces 12 and the scrambling/interleaving 13, at least some
degree of spectral widening may be obtained, so if additional
spreading 14 is needed, it may be to a lesser degree than may
otherwise be needed, e.g., to meet energy level requirements in a
frequency band of interest (in one example of an implementation,
spreading 14 may use a shorter spreading sequence that may be
easier to acquire than a spreading sequence that might be used to
obtain a similar degree of spectral widening, if the symbols were
not broken up into pieces). Note that DSSS spreading may be
implemented using any of a number of known hardware or software
implementations (e.g., a sequence generator and a multiplier that
may multiply the pieces by the sequence) and that the DSSS
spreading may use a common spreading sequence for each piece.
[0028] Using the above operations/blocks, fixed-energy symbols may
be decomposed into first pieces and then, optionally, into chips
that, when taken together in groups corresponding to an individual
one of the symbols, may contain substantially the same fixed amount
of energy as was in the original symbol, but with more transitions
per unit time and hence a lower power density. The resulting pieces
or chips may be modulated onto a signal 42 and transmitted to a
receive side 43. Transmission may be by means of radio frequency
(RF) or other wireless communications.
[0029] FIG. 2 shows a conceptual diagram of the reverse
blocks/operations that may be used at a receive side to process a
signal that was processed using the techniques of FIG. 1. Standard
receiver front-end operations (e.g., filtering, amplification) may
performed, and this may be followed by demodulation. If spreading
was used, de-spreading 21 may be used at the receive side. The
de-spreader 21 output may be provided for
descrambling/de-interleaving 22; again, if there was no additional
spreading 14, de-spreading 21 may be omitted.
Descrambling/de-interleaving 22 may be performed on a block of
received scrambled/interleaved symbol pieces (a part of which may
be similar to what is shown in FIG. 3D). The result may be
descrambled/de-interleaved symbol pieces, a non-limiting example of
which is shown in FIG. 3C. The resulting symbols, which may
correspond to the code symbols (if coding was used), as in FIG. 3B
may then be decoded 23, using a decoder corresponding to the
error-control coding 11 used at the transmit side 41 (again, if
coding was used), and the information symbols may thereby be
recovered. Again, implementations may correspond to those described
above for the various corresponding operations.
[0030] As an example, suppose that one would like to transmit a 10
kbps signal spread by a factor of 80, in order to meet energy level
requirements. The 10 kbps signal may nominally have transitions
every 0.1 ms. To spread by a factor of 80, transitions may need to
occur every 1.25 .mu.s. In one example, each symbol may be divided
into five pieces, of 0.02 ms, and the pieces may be scrambled.
Then, each piece may be further spread using a 16-chip PN sequence
for each 0.02 ms piece. The result may be a sequence of chips that
may nominally have transitions every 1.25 .mu.s. In another
variation, using the example of FIG. 3, in which the symbols are
divided into 16 pieces, each piece may be spread using a 5-chip
sequence, which taken together may provide a similar overall
spreading factor.
[0031] Referring again to FIGS. 2 and 4, in order to correctly
de-spread 21 and/or descramble/de-interleave 22 the received signal
content, one may need to acquire at least some degree of timing
synchronization. Such synchronization may be obtained, for example,
by the use of a known synchronization sequence 51 in signal 42,
e.g., as shown in FIG. 5. The synchronization sequence 51 may be
followed by other control/coordination signaling, data, etc. 52,
and may be repeated at regular intervals.
[0032] In a particular implementation, the synchronization sequence
51 may comprise a short framing sequence. For example, if frames of
length 0.5 s are used, a framing sequence lasting 6-8 ms may be
used. That is, a new frame, and thus a copy of the framing
sequence, is sent every 0.5 s. In the example discussed above, with
a 10 kbps information signal and a spreading factor of 80, this
repeated framing sequence may provide sufficient granularity to
synchronize timing to within one-third of a chip, which may, in
turn, be sufficient to synchronize a sampling device at the receive
side 43 to sample the received signal so as to recover at least one
sample per chip. The synchronization may be implemented at the
receive side 43 using any one of a number of known techniques, for
example, but not limited to, sliding correlation or matched
filtering.
[0033] Various aspects of the disclosure have been presented above.
However, the invention is not intended to be limited to the
specific aspects presented above, which have been presented for
purposes of illustration. Rather, the invention extends to
functional equivalents as would be within the scope of the appended
claims. Those skilled in the art, having the benefit of the
teachings of this specification, may make numerous modifications
without departing from the scope and spirit of the invention in its
various aspects.
* * * * *