Multiplex communications – Communication over free space – Combining or distributing information via time channels
Patent
1997-05-23
1999-11-16
Jung, Min
Multiplex communications
Communication over free space
Combining or distributing information via time channels
370500, 370508, H04J 306
Patent
active
059870230
DESCRIPTION:
BRIEF SUMMARY
This invention relates to controlling the timing of transmission of data packets in predetermined time slots of fixed length time frames.
Time division multiplex/time division multiple access (TDM/TDMA) communication requires that signals from various subscriber units communicating with a base station must reach the base station at appropriate times, otherwise, portions of two or more data packets from different subscriber units might reach the base station at the same instant, and then the base station would not be able to receive all packets correctly. In conventional TDM/TDMA systems, such as GSM ("Global System for Mobile communications") systems, a base station sends reference timing signals to the subscriber units, having informed each subscriber unit how much in advance of the reference signal it should transmit in order that transmissions from the subscriber units are received with the correct timing at the base station. In consequence, each data packet is correctly aligned in its TDMA time slot at the base station. Without such adaptive time alignment, packets would have to be separated by sufficiently large guard periods to allow for the possible maximum time delay between subscriber units and the base station, resulting in inefficient spectrum usage.
The present invention in its various aspects is defined in the claims to which reference should now be made.
The present invention in one aspect relates to a method of controlling the timing of transmissions of data packets from at least one first transmitting and receiving unit (NTE) for reception by a second transmitting and receiving unit (BTE) in predetermined time slots within fixed length time frames, the second unit transmitting a timing reference signal to a first unit, the first unit transmitting selectably in response a relatively short first packet at a time dependent on a preset first value, the subscriber first value being a predetermined estimate of the propagation delay dependent on the approximate separation of the first unit and the second unit, the second unit determines a second value dependent upon the propagation delay from the time of reception of the first packet, and the second unit transmits an adjustment signal dependent upon the second value to the first unit to adjust the timing of subsequent transmissions of relatively long packets from the subscriber un:. in response thereto.
The timing adjustment for a first unit includes a first component representative of the second value determined by measuring the time for arrival of the pilot packet from the subscriber unit and a second component representative of the pre-set first value which is predetermined according to the approximate separation of subscriber unit and base station. The first component can be variable, and once the first component is determined, a message is sent to the subscriber unit setting the timing adjustment to be used for subsequent information packets.
Adaptive time alignment according to the present invention involves transmission of pilot packets from a subscriber unit to the base station. Pilot packets are of shorter duration than normal packets. The shorter duration of pilot packets ensures that pilot packets are received from different subscriber units at the base station such that they do not overlap in time. Pilot packets can contain system control data and/or short information messages, whereas normal packets, which are longer, can contain both system control data and other information, such as user data.
Timing control means for controlling the timing of transmission of data packets from a first transmitting and receiving unit (NTE) for reception by a second transmitting and receiving unit (BTE) in predetermined time slots within fixed length time frames, the second unit comprising timing reference signal transmission means, and the first unit comprising response means operative to transmit selectably in response to receipt of a timing reference signal a relatively short first packet at a time dependent on a preset first value, the first value
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M. de Couesnogle et al, "IRT 2000: System for telephone and data at remote sites", pp. 1-19, Systems Review, vol., 47, No. 2, Jun. 1989.
A Copy of the International Search Report.
Albrow Richard John
Black Simon Alexander
Carter Leigh
Goodings Rupert Leslie Alexander
Martin Paul Maxwell
Ionica International Limited
Jung Min
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