Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2000-03-24
2002-06-11
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S561000, C455S063300, C455S067700, C455S424000
Reexamination Certificate
active
06405020
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method and a base station system for voice transmission via a radio interface in a digital radio communication system, in particular in a digital mobile radio system or in a wireless subscriber access system or access network system.
A base station system is a part of a digital radio communication system which may correspond, for example, to the GSM mobile radio network (Global System for Mobile Communications), as is known, inter alia, from the publication “Mobilfunk und intelligente Netze” [Mobile radio and intelligent networks], by J. Biala, Vieweg Publishers, 1995, in particular pages 57 to 92. In particular, the radio communication system may alternatively correspond to a third generation mobile radio system (UMTS—Universal Mobile Telecommunications System) which in general will have the same system configuration as the GSM mobile radio network, or an access network system as is known from the article “Drahtlos zum Freizeichen” [Wireless to the call connected signal], by M. Rei&bgr;, telcom report 18, 1995, pages 34 to 37.
Such radio communication systems allow communication links to be set up to transmit information, in particular voice information, via a radio interface between base stations and subscriber radio stations. The radio stations may in this case be configured, for example, as mobile stations in a mobile radio system, or as wireless network access units in an access network system.
Various methods are used for subscriber separation. These methods are generally based on a frequency-division multiplexing method FDMA (Frequency Division Multiple Access) with a given frequency bandwidth being split up into a plurality of frequency channels for use. If a plurality of subscribers on a common carrier frequency in the radio interface are separated by different timeslots, then a time-division multiplexing method TDMA (Time Division Multiple Access) is also involved, as is also used, for example, in the GSM mobile radio system. If the subscribers on the same carrier frequency are separated by different codes, then a code-division multiplex method (CDMA—Code Division Multiple Access) is involved, as is known, inter alia, from the article “Effizienter Teilnehmerzugriff für 3. Generation der Mobilkommunikation” [Efficient subscriber access for 3
rd
generation mobile communication], by T. Ketseglou, T. Zimmermann, telcom report 16, 1993, pages 38 to 41. Such a CDMA method is intended for both, second and third generation mobile radio systems and for access network systems. Furthermore, Published Non-Prosecuted German Patent Application DE 195 49 148 discloses a hybrid of these two methods for subscriber separation, which has time-division multiplex subscriber separation in addition to CDMA subscriber separation.
A radio communication system includes at least one base station system which contains, for example, a base station controller which is connected to a plurality of base stations. The base stations each supply a radio area, also called a radio cell, with radio resources. In this case, each base station may have only a limited supply of radio resources, in order to avoid interference. The radio areas of adjacent base stations overlap at the boundary regions of the radio cells or as a result of the radio cells being formed hierarchically, as is planned for second and third generation mobile radio systems. In mobile radio systems, the connection of a plurality of base stations to one base station controller allows a handover procedure between two base stations in order to make it possible for a mobile subscriber to have unrestricted freedom of movement with his mobile station.
The base station controller in this case carries out the function of switching and management of the radio channels in the base station, and administration and implementation of handover procedures.
In digital radio communication systems, digital voice codecs are used for coding voice information. In a GSM mobile radio system, these voice codecs include, for example, a voice coder and a downstream channel coder. In the voice coder, the 64 kbit/s data rate of PCM30 channels is reduced, for example, to a data rate of 13 kbit/s, which is called the net bit rate since it contains only the pure coded voice information. Additional redundancy is then added to the voice signal in the channel coder through the use of an error correction method, so that the bit rate is increased, for example, to 22.8 kbit/s, the gross bit rate. This example relates to a full-rate codec. As a further development, half-rate codecs have also been introduced in the GSM mobile radio system, which use only half the data rate for voice transmission. Such a compression of the voice signals is necessary since the available radio resources are limited and the aim is to supply as many subscribers as possible using the mobile radio system.
The proportion of error protection in the gross data rate (=net data rate of the wanted data+error protection) with the voice codecs in use is in general high, and is excessive if the transmission channel conditions are good. For this reason, the use of adaptive multirate voice codecs (AMR—Adaptive Multi Rate) is proposed, where the proportion of error protection is varied as a function of the transmission conditions on the radio interface. By reducing the error protection, it is possible to increase the bit rate after voice coding, and thus to improve the voice quality, or to reduce the gross data rate and thus create capacities for further subscribers.
The bit error rate determined by the receiving radio station may be used, for example, as a parameter for determining the error protection. However, this parameter has the disadvantage that the bit error rate can change very quickly as a result of short-term disturbances, such as shadowing by obstructions and, in particular, resulting from the movement of subscribers of mobile radio systems, so that the voice codec is unable to follow such a fast change. Furthermore, it is hardly possible to estimate the future transmission conditions from values measured in the past.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a base station system which overcome the above-mentioned disadvantages of the heretofore-known methods and systems of this general type and which allow improved voice and channel coding, irrespective of fluctuations, in particular short term variations, in the transmission channel characteristics.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for voice transmission via a radio interface in a digital radio communication system including a base station connected to a base station controller, and a radio station located in a radio coverage area of the base station. The method includes the steps of:
transmitting a signal via a radio interface between a radio station and a base station;
determining, from the signal, a characteristic value relating to transmission conditions of the radio interface;
storing the characteristic value in a storage device for providing a stored characteristic value;
performing, with a voice and channel codec, a voice and channel coding at a transmitter side for a voice transmission; and
controlling the voice and channel coding at the transmitter side by taking into account a currently determined characteristic value and the previously determined stored characteristic value.
In other words, in the method according to the invention for voice transmission via a radio interface in a digital radio communication system which has at least one base station which is connected to a base station controller, as well as at least one first radio station which is located in the radio coverage area or radio supply area of the base station, at least one signal is transmitted via the radio interface between the first radio station and the base station. At least one characteristic value relating to the transmis
Farber Michael
Kottkamp Meik
Oestreich Stefan
Mayback Gregory L.
Perez-Gutierrez Rafael
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