Multiplex communications – Communication over free space – Combining or distributing information via time channels
Patent
1997-06-17
2000-07-04
Nguyen, Chau
Multiplex communications
Communication over free space
Combining or distributing information via time channels
455561, 370350, H04J 300
Patent
active
060848685
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/FI95/00688, filed Dec. 19, 1995 which designated the U.S.
FIELD OF THE INVENTION
The invention relates to a base station for a mobile communication system comprising one or more switching centres and base stations connected to it by telecommunication links, each base station comprising an antenna for transmitting radio signals divided into time-slots by means of a frame structure, a controller unit for controlling the base stations, means for generating a frame alignment signal, a transmitter for generating a radio signal, the transmitter further comprising digital means for producing a digital signal to be modulated.
BACKGROUND OF THE INVENTION
Frame Structure and Modulation
The air interface of GSM mobile communication systems (GSM=Global System for Mobile Communications) is based on the TDMA technique (TDMA=Time Division Multiple Access), according to which a number of simultaneous calls may be transmitted on a same radio frequency. Calls transmitted on the same radio frequency are separated from each other in the time domain, i.e. the time on the radio path is divided into slices, i.e. time-slots, and each time-slot may be used for transmitting a separate call. This time-division forms a frame structure, which determines how many calls may be transmitted on one radio channel in the GSM system, it is possible to transmit up to eight calls in one frame structure on a full-rate speech channel. The frame structure of the GSM system is disclosed in M. Mouly & M. -B. Pautet, The GSM System for Mobile Communications, 1992, Mouly & Pautet, Palaiseau, France (in the following referred to as M & P), especially FIG. 4.15.
The properties of a transmitter of a GSM base station are described in two GSM specifications: GSM 05.04, January 1991, Recommendation GSM 05.04: Modulation, ETSI/PT 12 (3 pages in total), and GSM 05.05, March 1991, GSM Recommendation 05.05: Radio Transmission and Reception, ETSI/PT 12 (19 pages in total). Briefly, the above-mentioned recommendations make the following three demands for a transmitter: the broadest allowable frequency band (GSM 05.05 ANNEX 1), the maximum allowable phase error in modulated data (GSM 05.05, section 4.6), and power adjustment control for modulated data during a time-slot (GSM 05.05 ANNEX 2).
GSM recommendations define a TDMA frame to be used in GSM mobile communication systems, the time of which frame is divided into eight different time-slots. The maximum number of calls on one radio channel is thus eight when full-rate coding is employed. Naturally, it is also possible to use other rates, such as half-rate coding. The length of each time-slot is 156.25 bits, or they may alternatively be arranged so that the first and the fourth time-slot are longer, i.e. 157 bits in length, the other ones being 156 bits in length. In such a case, the lengths of the time-slots are in succession as follows: 157, 156, 156, 156, 157, 156, 156, 156 bits. This succession is disclosed in GSM recommendation GSM 05.10, January 1991: Radio Sub-system Synchronization, ETSI/PT 12 (6 pages in total), section 5.7. In that case, the length of each bit is 3.69 .mu.s.
Each time-slot contains 148 bits of data to be transmitted, and a guard-time of 8.25 bits. The binary data, i.e. the 148 bits transmitted during each time-slot contain a training sequence of 26 bits. This sequence of bits is known both by the transmitter and by the receiver, and its location is always the same. By means of a training sequence, it is possible to determine the location of the start and the end of a time-slot when the location of a training sequence of the transmission is detected within a time-slot. The training sequence is also described in M & P, in particular in chapter 4.3.1.1 and table 4.3. The training sequence may thus be used for synchronizing the transmitter and the receiver.
The guard-time, i.e. the 8.25 bits remaining from said 148 bits is intended for power adjustment carried out between different time-slots (M & P: FIG. 4.23)
REFERENCES:
patent: 5237592 (1993-08-01), Nonami
patent: 5384828 (1995-01-01), Brown et al.
patent: 5528593 (1996-06-01), English et al.
GSM System for Mobile Communications; Michel Mouly, Marie Bernadette Pautet, 1992.
Recommendation GSM 05.04, Jan. 1991, pp. 1-3.
Recommendation GSM 05.05, Mar. 1991, pp. 1-19.
Recommendation GSM 05.10, Jan. 1991, pp. 1-6.
Lee Chiho Andrew
Nguyen Chau
Nokia Telecommunications Oy
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