Telecommunications – Transmitter and receiver at separate stations – Distortion – noise – or other interference prevention,...
Reexamination Certificate
1999-04-12
2002-01-15
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Distortion, noise, or other interference prevention,...
C455S069000, C455S561000
Reexamination Certificate
active
06339697
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for setting a service level in a digital mobile communication system, and to a digital mobile communication system.
BACKGROUND OF THE INVENTION
The quality of the service offered to a mobile communication subscriber within a mobile communication network is determined by the joint effect of several factors. In the present application quality of service is understood to mean the technical quality of a radio connection, e.g. the transmission rate and the accuracy of the information transmitted, and the accessibility of the radio channel at a desired moment. The term service level is used to refer to the level of the above quality of service.
Within a digital data communication system, transmission errors deteriorating the quality of the signal transmitted occur on a transmission path during speech or data transmission. On the radio path transmission errors occur when a signal encounters interference e.g. due to multipath propagation, an interference signal or a high level of background noise. Channel coding of the digital signal to be transmitted improves the quality of transmission and the tolerance for transmission errors. In channel coding, redundancy is added to a coded speech or data bit sequence by means of error check bits calculated from the original signal. In a receiver, channel coding is decoded in a channel decoder, which allows using error check bits for detecting or even correcting errors occurring during transmission.
Channel coding increases the number of bits transmitted. For instance, when error check bits with a transmission rate of 9.8 kbit/s are added to a full rate speech signal of 13 kbit/s in a GSM system, the total transmission rate is 22.8 kbit/s. The level of protection provided by channel coding is arranged according to need. For rapid transmission of a large quantity of data, channel coding is reduced in order to allow more payload data to be transmitted on the transmission channel. Channel coding may be arranged to detect well and also to correct errors occurring during transmission, or to detect errors only. Channel coding may also be left out altogether. In this case the transmission is totally unprotected against transmission errors. In the GSM system, the bits to be transmitted are classified according to their significance into different groups, where channel coding is effected at a predetermined level. The problem with this solution is that efficient channel coding of the most important bits always reserves transmission capacity on the radio path. Transmission errors do not always occur during transmission. In such cases channel coding has unnecessarily blocked radio channels. On the other hand, unprotected high-speed information transmission causes problems in an environment subject to interference.
FIG. 1
of the attached drawing presents a simplified block diagram of the Pan-European GSM mobile communication system. A Mobile Station MS is connected over the radio path to a Base Transceiver Station BTS, which in the case of
FIG. 1
is base station BTS
1
. A Base Station System BSS comprises a Base Station Controller BSC and base stations BTS controlled by it. Usually a Mobile Services Switching Centre MSC controls several base station controllers BSC. A mobile services switching centre MSC has an interface to other mobile services switching centres and, via a Gateway Mobile Services Switching Centre GMSC, to a public telephone network. The operation of the whole system is controlled by an Operation and Maintenance Centre OMC. Subscriber information concerning a mobile station MS is permanently stored in the system's Home Location Register HLR and temporarily in a Visitor Location Register VLR within the area of which the mobile station MS is currently located.
Cellular mobile communication systems use several slightly over-lapping radio cells for producing radio coverage. In radio network planning, cell coverage in areas requiring high traffic capacity is arranged by means of small micro cells. As a mobile station MS moves from one cell to another, handover to a new radio cell is performed on the basis of specific handover criteria. The aim is to perform handover with minimum interference to the call in progress. However, problems arise with micro cells with small cell coverage; in them, handover must be performed fairly frequently, which increases the risk of failure in handover.
The mobile station MS and the base transceiver station BTS serving it continuously measure the level and the quality of the signal on a radio connection, for instance in case of any handover or power adjustment. The mobile station MS measures the signals from the base station BTS serving it and from the base stations BTS closest to its area of location, regularly transmitting the results of the measurement as a report message through the base transceiver station BTS serving it to the base station controller BSC. A base station BTS performs measurements of the level and quality of the signal on ongoing radio connections and possibly also other measurements indicating the general level of interference in the network.
When the level and/or quality of the signal on an individual radio connection drops below the desired level, adjustment of the transmission power can be performed at a base station BTS or/and in a mobile station MS for improving the radio connection. The transmission power of the mobile station MS is usually adjusted from a fixed network by means of a specific power adjustment algorithm. The mobile station MS measures the reception level (field strength) and the quality of a downlink signal received from the base station BTS
1
of the cell serving it, and the base station BTS
1
of the cell serving the MS in turn measures the reception level (field strength) and the quality of an uplink signal received from the mobile station MS. On the basis of these measurement results and the power adjustment parameters set, a power adjustment algorithm defines a suitable level of transmission power which is then announced to the mobile station MS in a power adjustment command. Power is adjusted continuously during the call. The problem with increasing transmission power is that it increases the level of interference in the network, for which reason the transmission power is to be kept as low as possible.
In digital Time Division Multiple Access TDMA radio systems, a group of mobile stations MS can use on a time-division basis the same carrier frequency, or radio channel, for communicating with a base station BTS. The carrier wave has been divided into successively recurring frames which are further divided into time slots, e.g. into eight time slots which are allocated to users according to need. Short data bursts are transmitted in the time slots. From the point of view of the network, eight traffic channels, for instance, can thus be created on a single carrier wave.
In a conventional TDMA system, each mobile station is allocated one traffic channel time slot for data transmission. According to the available bandwidth and the channel coding used in transmission, the maximum transmission rate on a single traffic channel is restricted at a fairly low level, being 9.6 kbit/s or 12 kbit/s in a GSM system. During the past few years, need for high-speed data services in mobile communication networks has increased significantly. One way of increasing transmission rate is to use more than one channel pair, which means that several TDMA time slots in a frame are allocated for a single mobile station. At the transmission end, a high-speed data signal is divided between such parallel channels for the duration of the transfer over the radio path, and then coded again at the receiving end. This enables offering data transmission services with a multiple transmission rate, depending on the number of channels used, as compared with the conventional transmission rate.
The operation of a Code Division Multiple Access CDMA in radio systems is based on spread-spectrum transmission. The data signal to be transmitted is mul
Altera Law Group LLC
Nokia Telecommunications Oy
Vo Nguyen T.
LandOfFree
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