Multiplex communications – Diagnostic testing – Of a switching system
Reexamination Certificate
1997-10-21
2001-01-09
Hsu, Alpus H. (Department: 2738)
Multiplex communications
Diagnostic testing
Of a switching system
C370S465000, C370S470000, C370S468000, C370S296000, C370S294000, C370S293000, C370S260000, C370S276000, C370S278000, C370S279000, C375S241000, C375S244000
Reexamination Certificate
active
06172965
ABSTRACT:
TECHNICAL FIELD
This invention relates to duplex and to half duplex transmission schemes and more particularly to the application of such schemes in TDMA and other multiple access environments.
BACKGROUND TO THE INVENTION
Duplex and Half Duplex transmission schemes are used in a variety of voice and data services. Duplex voice schemes are generally perceived by subscribers as providing better service quality than half duplex, whereas half duplex voice schemes provide a more efficient use of system resources than duplex schemes.
FIG. 1
is a diagram representative of typical voice traffic operating over a half duplex channel. In such a scheme the listening party is prevented from transmitting a voice signal until the talking party has ceased transmitting.
FIG. 2
is a diagram representative of typical voice traffic on a duplex channel. The parties to the call have intermittent periods where both parties are talking. These periods may be considered as contention periods. Typically the parties to the call resolve these contention periods between themselves so that a mutually understandable conversation results. It is unusual for both parties to talk at the same time for an extended period.
Duplex transmission schemes have the advantage over half duplex schemes of improved call quality for subscribers. However they have the disadvantage of inefficient use of system resources, as typically one channel will be idle at any one point during a conversation.
One example of a duplex channel is a time division duplex (TDD) arrangement where both parties have alternating access to the channel. Typically, the channel may have a capacity of 72 Kbits
−1
, in an ISDN system. Each party is typically sampled at 32 Kbits
−1
for 2 ms periods. These sampled signals are transmitted along the channel at the higher data rate of 72 Kbits
−1
using 1 ms packets of data.
However with typical voice traffic, approximately half of the time slots on the TDD channel will be idle.
WO 95/04412 to Motorola provides a method and apparatus for multiplexing fixed length message data and variably coded speech. A variable rate vocoder receives and codes the speech of an unknown amount at one of full and less than full rates to produce the coded data. U.S. Pat. No. 5,124,701 to France Telecom provides a quantisation device with a variable digital coding rate.
OBJECT OF THE INVENTION
Accordingly it is an object of the present invention to reduce the disadvantages present in the prior art.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there is provided a method of multiplexing signals transmitted by a number of terminals onto a communications link; the link having a capacity less than the total capacity of the terminals; the method comprising the steps of:
i) monitoring the link for the occurrence of simultaneous transmission of signals over the link by two or more terminals; the bandwidth of the terminals exceeding the capacity of the link;
ii) assigning a portion of the link capacity to the transmitting terminals; the sum of said portions being equal to or less than the capacity of the link;
iii) varying the rate of encoding of said signals transmitted by said terminals whereby the bandwidth of the transmitted signals corresponds to the portions allocated to the terminals.
The link can be a time division duplex link, optionally with the signals being encoded using a variable bit rate encoding scheme or using an adaptive differential pulse code modulation encoding scheme. The link can be a time division duplex link and said signals can be encoded using a variable bit rate encoding scheme and wherein a 32 Kbits
−1
capacity is allocated to a terminal when only one terminal is transmitting and wherein a 32 Kbits
−1
capacity is allocated to both terminals when both are transmitting.
In accordance with another aspect of the invention, there is provided a system for the communication of signals in real time over a channel; said system adapted to vary the bandwidth of at least one signal such that the number of signals multiplexed onto said channel can be dynamically varied.
In accordance with another aspect of the invention, there is provided a communications system adapted to multiplex a plurality of signals into frames of information; said frames comprising a plurality of sub-frames; the system adapted to vary the bandwidth of transmitted signals by varying the number of sub-frames allocated to each signal.
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patent: 5001703 (1991-03-01), Johnson et al.
patent: 5124985 (1992-06-01), Hoshikawa
patent: 5347562 (1994-09-01), Candy
patent: 5379279 (1995-01-01), Backof et al.
patent: 5384807 (1995-01-01), Yatim et al.
patent: 5657420 (1997-08-01), Jacobs et al.
patent: 5790532 (1998-08-01), Sharma et al.
patent: 5864544 (1999-01-01), Serinken et al.
patent: 5950164 (1999-09-01), Takahashi
Burr Alister Graham
Edwards Keith Russell
Pearce David Andrew James
Tozer Timothy Conrad
Ho Duc
Hsu Alpus H.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
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