Telecommunications – Transmitter and receiver at separate stations – Single message via plural carrier wave transmission
Reexamination Certificate
1994-09-09
2001-04-03
Vo, Nguyen (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Single message via plural carrier wave transmission
C455S447000
Reexamination Certificate
active
06212363
ABSTRACT:
THE FIELD OF INVENTION
This invention is concerned with signalling interference 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. U.S. Pat. No. 4,128,740 to Graziano, assigned to the instant assignee, is useful to demonstrate the point. FIG. 4 of Graziano (substantially reproduced here as
FIG. 1
) illustrates a conventional cellular frequency reuse plan commonly 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 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) spectrum. 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 (U.S. Pat. No. 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 interference. FIG. 9 of Graziano (substantially reproduced here as
FIG. 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 (CS
1
-CS
24
). Thus, each sector has one supervisory frequency (S
1
-S
24
) and either 7 or 8 voice frequency channels, allowing 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 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 and apparatus for signalling interference protection comprising: transmitting, in, inter alia, 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 one(s) of interest while remaining unresponsive to other than that of interest.
REFERENCES:
patent: 4128740 (1978-12-01), Graziano
patent: 4345334 (1982-08-01), Nordahl
patent: 4500984 (1985-02-01), Shimbo et al.
patent: 4654867 (1987-03-01), Labedz et al.
patent: 4677653 (1987-06-01), Weiner et al.
patent: 4696027 (1987-09-01), Bonta
patent: 4754453 (1988-06-01), Eizenhofer
patent: 4850030 (1989-07-01), Hashimoto et al.
patent: 4850033 (1989-07-01), Eizenhofer et al.
patent: 4876740 (1989-10-01), Levine et al.
patent: 4914651 (1990-04-01), Lusignan
patent: 55-93335 (1980-07-01), None
patent: 1170232 (1989-07-01), None
DeClerck William Paul
Longshore Theodore F.
Motorola Inc.
Motsinger F. John
Sonnetag Richard A.
Vo Nguyen
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