Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1998-10-26
2003-01-07
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S347000, C370S395100
Reexamination Certificate
active
06504836
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a communication system and in particular, the present invention relates to a communication system for transmitting data packets via a plurality of virtual wireless communication links established between a base station and a plurality of operational mobile stations and having a variable transmission capacity.
BACKGROUND OF THE INVENTION
Wireless communication networks for transmitting data and audio information are increasingly in use. Wireless communication networks are able to serve mobile stations as well as fixedly located end stations. A data transmission in such networks is often performed using multiplex techniques, where a plurality of communication links is transmitted via a single transmission channel. Such a transmission channel may, e.g. be a radio frequency band. Examples for wireless communication networks are mobile communication networks, e.g. networks according to the GSM-standard.
In communication networks employing multiplex techniques individual radio channels are partitioned into a plurality of time frames, itself each partitioned into a plurality of time slots. Each of these time slots can now be used for transmitting data for one communication link in that a sending station places data to be transmitted via one of the communication links onto particular time slots of the time frame. At a receiving station, it is known, which time slots are used for transmitting data intended for the receiving station and thus all data transmitted via the communication link can be recovered at the receiving station. For example, the receiving station combines the short data segments transmitted on the time slots to a continuous audio signal.
In general, different techniques may be employed to transmit data of a plurality of communication links via a common medium. It is a widely used method to employ a fixed assignment of time slots of a transmission frame to communication links. Such a fixed assignment, for example, is generally in use in GSM-systems.
If it is assumed that for example data of four communication links are to be transmitted via a common medium, each of the transmission frames of the medium could be divided into four time slots, and a first communication link could be established via the first time slot of each transmission frame, a second communication link could be established via the second time slot and analogously, the other communication links could be established via the third and fourth time slots.
Thus, the transmission medium is made available to each of the communication links at a fixed point in time. A fixed assignment of time slots to communication links thus allocates a predetermined and fixed capacity to each of the communication links. In general therefore the same channel capacity is made available to a communication link, which is used for the transmission of speech signals and accompanying speech pauses, as it is made available to a communication link used for the transmission of data, e.g. between two computers. However, in order to enable an efficient usage of a communication system it is desirable to adapt the capacity assigned to a communication link to the actual requirements of the amount of data to be transmitted.
A second generally used method for assigning of time slots to communication links enables an adaptation to the capacity requirements of a communication link. Here, a repetitive and fixed assignment of time slots of a communication channel to communication links it is not performed any longer, the assignment is performed dynamically corresponding to the amount of data to be transmitted.
One of the connection-oriented multiplex switching techniques is ATM (Asynchronous Transfer Mode). In ATM data belonging to a communication link are not necessarily transmitted periodically on a transmission medium and it becomes possible to allocate transmission bandwidth for subscribers as required, without encountering problems, if one of the subscribers requests to use a large bandwidth. ATM combines advantages of packet-switched networks and line-switched networks.
ATM covers layer
1
and large parts of layer
2
of the ISO-OSI-reference model. The OSI-reference model of the ISO (International Standardization Organization) describes a protocol layering for a communication between open systems, i.e. systems not in accordance with a standard, and distributed systems. Layer
1
of the OSI-reference model is the physical layer, layer
2
is the link layer.
In an ATM transmission so-called message cells of a predetermined length are transmitted as transmission units, using address information contained in a header. In general, ATM cells contain messages concerning the virtual connection, i.e. the communication link, as well as information concerning virtual communication channels, wherein a communication link may be divided into a plurality of virtual channels. Corresponding to the amounts of data individual channels may occupy more or less time slots.
A communication-oriented transmission of data via virtual communication links has been to date used particularly in communication networks with fixed lines, as for example in LANs (Local Area Networks).
It is, however, desirable to apply the advantages of a requirement-oriented data transmission to wireless communication networks. But in this endeavor it shows that data rates and bit error rates in communication networks with fixed lines and requirement-oriented transmission, e.g., a switching based on ATM, do not allow to readily use these techniques in wireless communication networks. For example, ATM for a data transmission in fixed networks provides a typical data and bit error rate of 155 Mbit/s and 10e-14, respectively. For providing the services of fixed networks with variable communication link capacity in mobile communication networks, an adaptation to a low channel capacity (25 Mbit/s) and a high bit error rate (10e-2) for radio channels (25 MHz channels in the 5 MHz range) is required.
Rules for an adaptation of connection-oriented switching techniques are, e.g. specified in the MAC (Medium Access Control) protocol. The MAC-protocol occupies a sub-layer of the layer
2
of the OSI-reference model.
The MAC-protocol consists of a number of messages, which are transmitted between mobile stations and a base station and determine the usage of the transmission medium. The MAC-protocol enables to establish a plurality of virtual communication links with communication-oriented transmission capacity using multiplex techniques. A MAC-protocol in general consists of different protocol data units for transmitting the above messages. Therefore, the efficiency and flexibility of a MAC-protocol is closely linked with the definition of different types of protocol data units (PDU).
A definition of protocol data units for a wireless requirement-oriented ATM communication is, e.g. known from “Design Principles for a MAC-protocol of an ATM air interface”, D. Petras, A. Krämling, A. Hettich, Mobile Telecommunications Summit, Granada, Spain, Nov. 27-29, 1996. In this document four types of protocol data units are described, transmitted in a transmission frame divided into an uplink and a downlink transmission portion. Here, in a uplink transmission portion data are transmitted from a mobile station to a base station and in a downlink transmission portion data are transmitted from a base station to a mobile station.
A Sig-PDU for uplink transmission contains a reservation message for a following transmission frame and further control information, e.g. for controlling access to time slots reserved for a transmission from an arbitrary mobile station.
A ATM-cell-PDU for downlink transmission contains an ATM-cell having a LLC (Logic Link Control) header with an overall length of 55 Byte.
A Sig-PDU, used for uplink transmission, contains, e.g., a capacity request or acknowledgments having a length of roughly 3 Byte.
A ATM-cell-PDU, used in uplink portions of the transmission frame contains an ATM-cell, a LLC (Logic Link Control) header and a capacity requ
Bautz Gregor
Khun-Jush Jamshid
Li Hui
Thielecke Jörn
Nguyen Brian
Olms Douglas
Telefonaktiebolaget LM Ericsson (publ)
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