Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-06-29
2003-10-07
Maung, Nay (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S446000, C455S453000, C455S067700, C455S125000, C455S063300, C455S115200
Reexamination Certificate
active
06631268
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a radio system, which comprises a plurality of transceivers that are arranged to communicate with each other by using a plurality of predetermined radio frequency channels. In particular, the invention relates to a system in which a maximum value is determined for the amount of interference caused to adjacent frequency channels by the transceiver frequency channel.
BACKGROUND OF THE INVENTION
In radio systems the signal to be transmitted must in general be modulated for transmission on a transmission channel. Generally, digital modulation methods are applied, by means of which the desired signal is transmitted on an allocated frequency channel. Digital modulation methods whose envelope is not constant are often employed. When employing these modulation methods, in case the transmitter is not linear, interference, which is called adjacent channel interference, is caused outside the frequency channel allocated to the signal transmission. This interference is thus mainly due to nonlinearity of the transmitter. The nonlinearity of the transmitter is closely related to the efficiency of the terminal amplifier of the transmitter. Linear amplifiers cause little interference to adjacent frequency channels, but their efficiency is poor. More nonlinear amplifiers cause more interference, whereas the efficiency is better.
In radio systems, a maximum value is in general determined for the amount of interference caused to the adjacent channels by transmitters, the purpose of which value is to enable the simultaneous use of adjacent channels for telecommunications without excessive interference. The maximum value is generally determined by simulations at the planning stage of the system. By simulating traffic on different channels and by measuring interchannel interference and transmission errors resulting therefrom, an acceptable maximum value of interference is determined.
In current systems, the maximum value of adjacent channel interference is determined to be the same within the whole system. On the basis of simulations, the value which gives a satisfactory result in the whole system, is selected. However, this method has several drawbacks. Since the whole system employs one interference value, the value has to be selected on the basis of the channel that is the most sensitive to interference. So on all frequency channels, transmitters must meet the same requirement. Consequently, in practice amplifiers that are linear but poor in efficiency must be used on all frequency channels. This causes problems, for instance power consumption of mobile telephones is high due to inefficient amplifiers.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to provide a method and a system to the effect that the above-mentioned problems can be solved. This is achieved with a transmission method in which at least one base station transceiver and terminal transceivers communicate by employing a plurality of predetermined radio frequency channels and in which method a maximum value is determined for the amount of interference caused to adjacent frequency channels by the transmitter frequency channel. The invention is characterized in that different maximum values are determined for different radio frequency channels.
The invention also relates to a radio system which comprises a plurality of transceivers that are arranged to intercommunicate by employing a plurality of predetermined frequency channels and in which radio system a maximum value is determined for the amount of interference caused to adjacent frequency channels by the transmitter. The system of the invention is characterized in that the transceivers of the system are arranged to transmit on different frequency channels using different maximum values of adjacent channel interference.
The preferred embodiments of the invention are disclosed in the dependent claims.
Several advantages are achieved with the method and system of the invention. The invention is based on the fact that, in radio systems, there are in general frequency channels whose tolerance of interference is different. For instance, the outermost frequency channels of a frequency range allocated to a system may have stricter interference requirements than the channels in the centre of the range. By means of the invention, requirements as strict as necessary can be set to the outer channels, while higher adjacent channel interference is allowed to the centre channels. This has an advantage that the centre channels may employ more nonlinear amplifiers whose power consumption is lower, on the average.
In one preferred embodiment of the invention, the maximum interference limits to different frequency channels can be set at the planning stage of the system, whereby they are fixed values that are not varied. The interference limits can also be changed, for instance, in connection with network planning modifications. In a second preferred embodiment of the invention, the values of interference limits can be changed dynamically by using, for instance, the traffic load of network channels as an adjustment criterion.
In a preferred embodiment of the invention, a base station is arranged to signal information to a terminal on the maximum value of interference allowed on the terminal frequency channel. Information on the maximum interference level can be transmitted to the terminal every time a call is established. This is particularly applicable to the embodiment in which the values are varied dynamically. Another advantage is that the terminal need not keep the values of different channels in the memory all the time. In a second preferred embodiment, information on the maximum interference level can be transmitted to the terminal every time the terminal registers in the network. This is advantageous particularly in cases where the values do not constantly vary.
In one preferred embodiment of the invention, adjacent channel interference caused by transmitters is controlled by limiting the transmitter's maximum power.
In a second preferred embodiment of the invention, adjacent channel interference caused by transmitters is controlled by adjusting the linearity of transmitters by means of biasing.
In a third preferred embodiment of the invention, the above-mentioned options are applied simultaneously.
In a fourth preferred embodiment of the invention, adjacent channel interference caused by transmitters is controlled by predistorting transmitters.
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Maung Nay
Nokia Mobile Phones Ltd.
Orgad Edan
Perman & Green LLP
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