Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Patent
1997-05-28
2000-05-09
Hsu, Alpus H.
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
370458, 370468, H04B 7212, H04J 316, H04L 1243
Patent
active
060613408
DESCRIPTION:
BRIEF SUMMARY
The invention relates to digital data transmission in time slots within fixed length time frames, in particular, time division multiplexing/time division multiple access (TDM/TDMA) digital telephony.
Conventional TDM/TDMA systems, such as GSM ("Global System for Mobile communications") systems are not suited to the transmission of non-speech data and facsimile. As discussed in Cellular Radio Systems, D M Balston & R C V Macario (Editors), Artech House Inc. 1993, Chapter 14, Pages 315 to 323, GSM equipment performs erratically in transmitting Group 3 facsimile signals, and cannot handle Group 4 facsimile. A key problem is the limited bandwidth which is available. Each data or telefax transmission is sent at a conventional rate in a designated slot in successive TDMA frames. Also, ISDN (Integrated Services Digital Network) transmissions require increased bandwidth.
The present invention is defined in the claims, to which reference should now be made.
The present invention preferably provides a method of transmitting a digital data message between a sending unit and a receiving unit using a TDMA data transmission scheme, a slot or slots in successive TDMA frames being assigned for transmission of the message, in which at least a portion of the message is detected to determine a parameter of the message, at least one further slot is selectively assigned for transmission of the message dependent on said parameter. The message is allocated to the assigned slots for transmission then reconstituted at the receiving unit. The first slot or slots and the further slot or slots are preferably included in each frame.
The number of slots which are used to carry a message can be increased, or decreased, without terminating the call connection between the sending unit and the receiving unit. The effect of adding an additional slot or slots is to provide more bandwidth within which to transmit the message. As the assignment of slots is varied depending on need, it is not necessary to have full knowledge, when a call is first established, of what bandwidth might be required.
Preferably, the sending unit and receiving unit are a base station and subscriber unit. The assignment of slots is preferably undertaken by the base station. When a call is first established, the system does not know whether the message is speech on the one hand, or non-speech voice-band data on the other hand, such as from a modem or facsimile machine, or an ISDN message. Facsimile messages are preferably carried in two slots per frame unless a second slot is unavailable due to the large amount of communication traffic on the system at that time. Using two slots per frame effectively doubles the data transmission rate. ISDN messages are preferably carried on two to five slots per frame, with the corresponding multiplication of transmission rate.
The detection process preferably occurs at the base station to determine the parameter which indicates whether a faster transmission rate is desirable. If so, a decision is made to assign a further slot or slots.
A detection process occurs at the base station to determine whether the message being transmitted in a first slot is speech or voice-band data. A detector at the base station can perform this function, in particular, by detecting whether the message includes standard modem answertone or facsimile handshake or ISDN call set-up signalling or any other characteristic expected if the call includes voice-band data. If this characteristic is detected, a decision to assign an additional slot or slots is made.
The present invention also preferably provides communication means for communicating a digital message using a TDMA data transmission scheme, the communication means including a sending unit and a receiving unit, at least one of said units including first slot assignment means operative to assign a slot in successive TDMA frames, and second slot assignment means operative to selectively assign a second or subsequent slot, the sending unit including means operative to divide the message between the assign
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Wai-Choong Wong et al, "Integrated data and speech transmission using packet reservation multiple access", IEEE International Conference on Communications '93, vol., 1, pp. 172-176.
Copy of the International Search Report.
Albrow Richard John
Black Simon Alexander
Carter Leigh
Goodings Rupert Leslie Alexander
Martin Paul Maxwell
Hsu Alpus H.
Ionica International Limited
Qureshi Afsar M.
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