Telecommunications – Receiver or analog modulated signal frequency converter – Modulation distortion or cross talk correction or elimination
Reexamination Certificate
1999-11-19
2004-07-20
Trost, William (Department: 2684)
Telecommunications
Receiver or analog modulated signal frequency converter
Modulation distortion or cross talk correction or elimination
C455S078000, C455S230000, C330S296000
Reexamination Certificate
active
06766156
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a radio transmitter-receiver of so called a simultaneous transmitting and receiving system, capable of receiving a downstream radio signal transmitted from a base station while transmitting an upstream radio signal having amplitude variation components, such as a mobile terminal apparatus employing the CDMA (Code Division Multiple Access) scheme.
BACKGROUND ART
Recently, a cellular radio communications system has been rapidly widespread in accordance with the increase in the needs for the mobile communications and the development of the communications techniques.
A mobile terminal apparatus used in the cellular radio communications system, for example, receives a radio frequency signal transmitted from a base station, by an antenna, inputs the signal to a receiving radio-frequency unit via an antenna duplexer, high-frequency-amplifies the signal, removes unnecessary waves outside the receiving band from the signal, converts the signal to an intermediate frequency signal, demodulates the intermediate frequency signal by a demodulator, and converts the signal into a baseband signal. The transmitting baseband signal is subjected to a predetermined signal process, input to a modulator, which modulates a carrier wave signal. The modulated carrier wave signal is converted into a radio frequency by a transmitting radio-frequency circuit and amplified to a predetermined transmitting power, and transmitted to the base station from the antenna via the duplexer.
Incidentally, the receiving radio-frequency unit uses a low noise amplifier as a radio-frequency amplifier. In a conventional analog mobile terminal apparatus employing the FM scheme as its modulation scheme, for example, the distortion characteristics of the low-noise amplifier is generally set to be such that the input tertiary interception point (IIP3) can be about −3 [dBm], at which the apparatus can bear the mutual modulation disturbance generated by adjacent and the following adjacent channels. In this case, the low-noise amplifier can be implemented with the consumed current of a few [mA].
In the mobile terminal apparatus employing the CDMA scheme, however, its own transmitting wave has amplitude variation components as shown in, for example, FIG.
1
. For this reason, when a narrow-band disturbance tone signal in the analog cellular system using a near-field band of the CDMA cellular system exists near the desired receiving wave, the amplitude variation components of its own transmitting wave which cannot be attenuated by the duplexer causes the cross modulation resulting from the tertiary distortion of the low-noise amplifier to be generated, and overlap the disturbance tone signal as shown in
FIG. 2
, and part of it is added to the receiving band as interference.
The CDMA cellular system employs what is called open-loop transmission power control, which allows the transmitting signal power of the mobile terminal apparatus to be increased when the mobile terminal apparatus is remote from the base station and when the received signal level is low. When the mobile terminal apparatus exists in a place where the received signal level is low, such a case where the mobile terminal apparatus exists in, for example, a fringe area of a cell, deterioration of the receiving characteristics is accelerated because of the interference caused by the cross modulation effect, which may cause the communications to be interrupted in a worst case.
To solve this problem, the IIP3 of the low-noise amplifier provided in the receiving radio-frequency unit needs to be set at about 5-7 dB. In order to implement this, however, the consumed current needs to be increased to about 10 to about 20 [mA], and this will cause the standby time of the CDMA mobile terminal apparatus to be made remarkably shorter, which is not very preferable.
On the other hand, some measures to be taken, i.e. further increasing the attenuation amount of the transmitting frequency band on the receiving side of the duplexer and further lowering the signal level at which its own transmitting wave is input to the receiving radio-frequency unit, can be considered. With these measures, however, the duplexer is excessively large, which may disturb miniaturization of the mobile terminal apparatus and the reduction of the weight thereof.
As described above, in the radio transmitter-receiver for simultaneously transmitting/receiving the radio signal having the amplitude variation components, such as the mobile terminal apparatus used in the CDMA cellular system, the interference to the receiving band, which results from the cross modulation between the near-field disturbance tone signal of the desired receiving wave and its own transmitting wave, occurs and therefore, some measures need to be taken. According to the conventionally considered measures, however, the standby time is shortened by increasing the consumed current of the receiving radio-frequency unit, and the radio transmitter-receiver is made larger by making the duplexer larger, and thus, the effective measures have been desired.
The present invention is accomplished in consideration of the above circumstances, and its object is to provide a radio receiver, a receiving radio-frequency unit thereof, and a control unit, capable of preventing deterioration of the receiving sensitivity caused by its own transmitting wave and the disturbance wave as well as restricting the increase in the current consumption of the receiving radio-frequency unit, and thus extending the standby time or communications time with preferable receiving distortion characteristics.
DISCLOSURE OF INVENTION
According to one aspect of the present invention, there is provided a radio transmitter-receiver for simultaneously transmitting/receiving a radio signal including an amplitude variation component, comprising: a receiving radio-frequency unit having a first operation mode in which an operation is executed at a predetermined first current consumption value and a predetermined first distortion characteristics, and a second operation mode in which an operation is executed at a second current consumption value larger than the first current consumption value and a second distortion characteristics having less distortion than the first distortion characteristics; and a mode changing control means allowing the receiving radio-frequency unit to be operated in the second operation mode in a period in which the radio signal is transmitted, or in the first operation mode in a period in which the radio signal is not transmitted.
Therefore, according to the present invention, since the receiving radio-frequency unit is operated in the low-distortion mode, in the period in which the radio signal is transmitted, the deterioration of the receiving sensitivity which is caused by the interference to the receiving band resulting from the cross modulation between the near disturbance wave of the desired receiving wave and its own transmitting wave, is suppressed, and the receiving distortion characteristics can be thereby kept preferable.
On the other hand, since the receiving radio-frequency unit is operated in the low current consumption mode, in the non-transmission period during which occurrence of the cross modulation as the standby period needs not to be considered, the current consumption of the receiving radio-frequency unit is reduced and thereby the standby time can be extended.
That is, according to the present invention, the standby time can be extended while the receiving distortion characteristics at the transmitting/receiving operation are kept preferable.
The receiving radio-frequency unit may comprise an amplification means for amplifying a signal received by an antenna, and the mode changing control means may change an operation mode of the amplification means.
Further, the receiving radio-frequency unit may comprise an amplification means for amplifying a signal received by an antenna and a mixer means for mixing the output from the amplification means and the recei
D'Agosta Stephen
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Trost William
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