Note: Descriptions are shown in the official language in which they were submitted.
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SIGNALLING INTERFERENCE PROTECTION
This invention is concerned with signalling interterence protection.
More particularly, this invention is concerned with signalling interference
protection in a (cellular radiotelephone) channel reuse network.
BACKGROUND OF THE INVENTION
In systems employing channel reuse schemes, it is a common problem to
determine whether one is using the channel intended or an unintended
reuse of that channel. In cellular radiotelephone systems exhibiting
geographical frequency reuse, the problem is worse because cellular
radiotelephones are not fully capable of rejecting not only the same
frequency reused at the geographic separation distance, but also
insufficiently capable of rejecting adjacent frequencies within the reuse
perimeter.
US Patent No. 4,128,740 to Graziano, assigned in the instant assignee,
is useful to demonstrate the point. Figure 4 of Graziano (substantially
reproduced here as Figure 1 ) illustrates a conventional cellular
frequency reuse plan common known as the seven-cell repeat pattern. It
consists of a central cell (1 ) ringed in a clockwise direction beginning at
3-o'clock by six ring cells (2-7), completing a seven-cell pattern. That
seven-cell pattern is then itself surrounded by six other identical seven-
cell patterns. Thus, the frequencies operating in each cell are
geographically reused at a geographical reuse separation distance. It is
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this geographical frequency reuse that provides the (frequency) channel
capacity to allow a large number of radiotelephone users to share a
limited amount of (frequency) spectnrm. However, the neat geographical
reuse separation illustrated is not quite so neat when local propagation
conditions such as antenna height, buildings and obstructions) etc.) are
taken into account. Accordingly) additional protection is provided against
co-channel (same frequency) interference in the signalling by allocating
seven differentiating codes to each of the surrounding patterns. This
signalling provides some protection in that a radiotelephone is able to
differentiate the frequency on which he is speaking from an interferer of
the same frequency at the reuse separation distance but having a
different code. In conventional analog cellular systems, these codes are
Supervisory Audio Tones (SAT) and in proposed narrower band, split-
channel systems, known as Digital SAT or DSAT.
The problem solved by the instant invention is that there is insufficient
rejection in radiotelephones to fully reject adjacent channels just one
frequency above or below the one of interest.
In his patent (US 4,128,740), Graziano teaches that greater frequency
reuse (and therefore spectrum utilization) can be obtained with narrow
beam, sectored antennas. The resulting four-cell pattern is still
surrounded by six reuses of that same four cell pattern, advantageously
employing seven DSATs for improved signalling protection against co-
channel interterence. Figure 9 of Graziano (substantially reproduced
here as Figure 2) illustrates a frequency plan for his "four-cell" pattern. It
illustrates how 208 frequency channels are divided among 4 cells) each
having 6 sectors, for a total of 24 sectors (CS1-CS24). Thus, each sector
has one supervisory frequency (S1-S24) and either 7 or 8 voice
frequency channels, allowing that many simultaneous conversations in
each sector. The problem is that, although any given frequency being
used in Sector 3 of a first pattern can be differentiated from that same co-
channel frequency in Sector 3 of the pattern behind it by its DSAT, there
is no protection for a radiotelephone user in Sector 3 using frequency
196 from the next higher adjacent frequency 197 directly behind it in
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Sector 4, or from the next lower adjacent frequency 195 in Sector 2
behind and to the side of it.
This invention takes as its object to overcome these shortcomings and
to realize certain advantages presented below.
SUMMARY OF THE INVENTION
There is provided a method of signalling interference protection
comprising: transmitting, in a desired channel and an interfering channel
each within a reuse pattern, signalling information that differentiates the
desired channel and the interfering channel from one another, receiving
that transmitted differentiating information, and responding to the
desired channel while remaining unresponsive to the interfering channel
based on the differentiating information.
In addition, there is provided an apparatus for signalling interference
protection in a channel reuse radio network, comprising, operatively
coupled in series: means, in a desired channel or an interfering channel
within a reuse pattern, for transmitting signalling information that
differentiates the desired channel from interfering channels within the
reuse pattern, means for receiving that transmitted differentiating
information, and means for responding to the desired channel while
remaining unresponsive to the interfering channel based on the
differentiating information.
DESCRIPTION OF THE DRAWINGS
Additional objects, features and advantages of the invention will be
more clearly understood and the best mode contemplated for practicing
it in its preferred embodiment will be appreciated (by way of unrestricted
example) from the following detailed description, taken together with the
accompanying drawings in which:
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Figure 1 is a cellular geographical reuse diagram which is a substantial
reproduction of Figure 4 of US Patent No. 4,128,740 to Graziano,
assigned in the instant assignee.
Figure 2 is a cellular frequency reuse plan which is a substantial
reproduction of Figure 9 of US Patent No. 4,128,740 to Graziano,
assigned in the instant assignee.
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Figure 3 is a cellular geographical reuse diagram and cellular frequency
reuse plan of the network in which the invention operates in accordance
with the preferred embodiment.
Figure 3 is a cellular geographical reuse diagram and cellular frequency
reuse plan of the network in which the invention operates in accordance
with the preferred embodiment.
Once again) the problem illustrated in Figure 3 is that, although any
given frequency being used in Sector 3 of a first pattern of a mobile
radiotelephone subscriber can be differentiated from that same co-
channel frequency in Sector 3 of the pattern behind it by its DSAT, there
is no protection for a radiotelephone user in Sector 3 using frequency
196 from the next higher adjacent frequency 197 directly behind it in
Sector 4, or from the next lower adjacent frequency 195 in Sector 2
behind and to the side of it: Present systems simply do not provide
protection against the most likely source of interference) an adjacent
channel within its own pattern.
The instant invention provides a solution to the problem by utilizing the
signalling to provide additional interference protection, not from co-
channel (same frequency) interferences at the geographic reuse separation
distance but from adjacent channels within the same pattern. It provides
that radiotelephone receivers (and base cell site equipment) reject
adjacent interferers on the basis of evenness and oddness of the
frequency. For example) if a mobile radiotelephone subscriber in
Sector 3 is assigned nominal channel frequency 196 (actual frequency
abc.xyz MHz) - an "even" channel, his receiver would reject adjacent
channel frequency 197 (actually some 12.5, 15) 25 or 30 KHz higher) in
Sector 4 directly behind and channel frequency 195 (actually some
12.5, 15, 25 or 30 KHz below) in Sector 2 behind and to the side, based
upon their "oddness". This substantially reduces the possibility of a
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receiver improperly acting upon a transmission intended for another on
an adjacent channel.
If "evenness" and "oddness" were not otherwise determinable (and
inherently associated with each carrier), a bit could be transmitted along
with each carrier frequency to indicate "evenness" and "oddness" as by
either setting or clearing that bit field. Similarly) if additional protection
from interferers were desired) a one-of-n state binary word could be
included in the signalling protocol for each of n partitions of the frequency
spectrum. However, the usual distance 5 BCH code provides sufficient
assurance that the single bit will be recoverable.
The attendant advantage of this invention clearly includes signalling
protection against adjacent channel interferers within the pattern in
addition to the usual SAT co-channel interference protection from outside
the pattern.
Thus, there has been provided a mechanism for signalling interterence
protection comprising: transmitting) along with adjacent channel
frequencies, an odd/even bit associated with odd/even channels that
differentiates adjacent channel frequencies from one another, receiving
transmitted an odd/even bit associated with odd/even channels that
differentiates adjacent channel frequencies from one another, and
responding to ones) of interest while remaining unresponsive to other
than that of interest.
It will be appreciated by those ordinarily skilled in the art that the means
for carrying out the invention are readily available and their operation
well understood. While the preferred embodiment of the invention has
been described and shown, it will be appreciated by those skilled in this
field that other variations and modifications of this invention may be
implemented. For example) "evenness" and "oddness" could be
determined from frequencies discrimination (channel spacing) or made
inherent to the channels through slight variations in the bit rates used on
"odd" versus "even" channels. Although the foregoing discussion has
included a discussion in terms of channel frequencies, the technique is
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equally applicable to other channel structures such as, time slot channels
or code division channels and the like.
These and all other variations and adaptations are expected to fall within
the ambit of the appended claims.
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