Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-02-09
2001-05-29
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
Reexamination Certificate
active
06240076
ABSTRACT:
The present invention relates to a method for transmitting data over the radio path in a mobile communications system based on time division multiple access (TDMA), in which system several time-slots of a frame may be allocated to a mobile station for data transmission.
British Patent Application No. GB-2,232,562, applied by Philips, discloses method for transmitting data over a time-division duplex channel. In accordance with the proposed method, one or more channels are allocated for data transmission. Each channel consists of a pair of time-slots. When it is detected that data transmission is or will be asymmetric, the unused time-slots in the other direction are released, and they may be re-allocated for other purposes.
In the GSM system (Groupe Speciale Mobile) one TDMA frame is 4.615 ms in length, and consists of eight time-slots, which are numbered from zero to seven. The number of the time-slot is marked with an abbreviation TN (Time Slot Number). A full rate traffic channel TCH/F intended for transmitting speech and data consists of time-slots from successive frames, having the same time-slot number, so that from the point of view of the network, it is possible to form eight traffic channels on one carrier wave. The traffic in the direction from a mobile station to a base station (uplink) and the traffic in the direction from the base station to the mobile station (downlink) is arranged so that reception takes place in the base station three bursts later than transmission. Thus, the time-slot number TN of the time-slot in the transmission frame and that TN of the time-slot in the reception frame are identical. Correspondingly, in the mobile station, transmission takes place some three burst periods later than reception. These events are illustrated from the point of view of the mobile station in
FIGS. 1A-1E
.
FIG. 1A
shows successive time-slots of a mobile station located near a base station. Rx represents the reception time-slot, TX represents the transmission time-slot, and M stands for monitoring of adjacent cells. Transmission, reception and monitoring take place on different frequencies.
FIG. 1B
shows the time-slots of the reception frequency of the mobile station, and
FIG. 1C
shows the time-slots of the transmission frequency of the mobile station. The transmission and reception time-slots are marked with diagonal lines. During the time between transmission and reception the mobile station monitors the BCCH carrier waves of the adjacent cells.
FIG. 1D
shows the time-slots of the BCCH carrier wave of an adjacent cell, and
FIG. 1E
the time-slots of the BCCH carrier wave of a second adjacent cell. The-arrows combining the time-slots in the Figures illustrate the frequency changes that must be carried out by the radio part of the mobile station between reception, transmission and monitoring.
Transmission takes place in the transmission time-slot in form of a burst. A standard burst consist of two modulated 58-bit sequences with a 26-bit training sequence between them. At the beginning and at the end of the burst there are three tail bits. In order that the successive received bursts would not overlap, there is a guard-time at the end of each burst. The actual duration of the guard-time depends on the envelope of the transmission burst, but the usual duration of the guard-time is in the order of 30 microseconds. The guard-time is required as the mobile stations transmitting on the same radio carrier wave are within a random distance from the base station, and the propagation time of the radio waves from the base station to the mobile station thus varies from time-slot to time-slot. Therefore, the duration of the bursts transmitted in the time-slots must be slightly shorter than the time-slot in order to avoid overlapping of the bursts transmitted in adjacent time-slots during the reception at the base station. In order that the guard-time would be as short as possible and the mobile station could still be remote from the base station, the propagation delay of the transmission of a mobile station located remote from the base station must be compensated. Therefore the system is arranged to be such that the base station adjusts the transmission time of each mobile station dynamically on the basis of the bursts received from them. The base station provides the mobile station with a so-called timing advance TA, according to which the mobile station adjusts the starting moment of its transmission. Thus, in a mobile station located remote from the base station the time between reception and transmission is remarkably shorter than in a mobile station located near the base station.
In accordance to what has been stated above and
FIGS. 1B-1C
, the GSM system is optimized to use as a traffic channel a pair consisting of one time-slot of successive downlink frames and a corresponding time-slot of successive uplink frames. Thus, it is possible to employ in the mobile station just a simple radio part, which synthesizes the different frequencies for reception, transmission and listening to the adjacent cells. In order that the frequency synthesizer would have sufficient time to tune in and settle on a new frequency in order to carry out the required changes of frequency, the transmission of the mobile station is determined to take place in the way described above with a delay with respect to reception. Correspondingly, a sufficient time still remains between transmission and reception for monitoring the frequencies of the adjacent cells.
The prior art traffic channel arrangement described above is attended by the drawback that the use of only one traffic channel time-slot from each frame allows a very small capacity, e.g. in the GSM system the maximum data transfer rate on one traffic channel is 9.6 kbit/s. In the last few years there has been a remarkable increase in the demand for high-speed data services in the mobile communications networks. For making use of ISDN (Integrated Services Digital Network) circuit switched digital data services, for instance, transfer rates of at least 64 kbit/s would be required. Data services of a public switched telephone network PSTN, such as modems and telefax terminals of the class G3 require higher transfer rates, such as 14.4 kbit/s. An expanding area of mobile data transmission requiring higher data transfer rates than 9.6 kbit/s are mobile video services. The minimum data transfer rate in video transmission can be e.g. 16 or 31 kbit/s.
The transfer rates of the present mobile communications networks are not sufficient, however, for meeting these new demands.
For increasing the data transfer rate, various methods have been studied in connection with the development work carried out at ETSI (European Telecommunications Standard Institute). These methods are herein generally referred to as HSCSD (High Speed Circuit Switched Data). Suggestions have been made e.g. for changing the frame structure. It is a complicated way, however, since it would require changes in the present GSM system. Another suggested way of increasing the data transfer rate is to employ more than one pair of channels, that is, several TDMA time-slots from each frame for one mobile station. A high-speed data signal is distributed at the transmitting end into parallel channels mentioned above for transmitting them over the radio path, and it is combined again at the receiving end. It is thus possible to offer data transmission services having a data transfer rate which is up to eight-fold as compared with the standard data transfer rate, depending on the number of the allocated traffic channels. This is termed as a multi-slot access technique. It is characterized in that there is an equal number of time-slots available both in the transmitting direction and in the receiving direction, i.e. it is symmetric and provides an identical transmission capacity in both directions. In this respect it is similar to connections of a fixed network, which are usually symmetric in both directions.
The symmetric HSCSD method employing several time-slots is attended by a few dra
Hamalainen Jari
Jokinen Harri
Kanerva Mikko
Marcelo Melvin
Nokia Telecommunications Oy
Pillsbury & Winthrop LLP
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