Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-11-17
2004-05-25
Maung, Nay (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S127100, C455S127200, C455S126000, C455S114300, C375S297000, C375S296000
Reexamination Certificate
active
06741867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a non-linear distortion compensation circuit, a transmitter device to be employed in the same and a mobile communication unit. More particularly, the invention relates to a control system for a non-linear distortion compensation circuit for compensating non-linear distortion to be caused by non-linearity of an amplifier or a frequency converter.
2. Description of the Related Art
In general, it has been known a linearizer as a non-linear distortion compensation circuit for compensating non-linear distortion caused by non-linearity of an amplifier, a frequency converter or the like forming a transmitter to be used in a radio communication. As the linearizer, one taking output only non-linear signal from a transmission signal transmitted and compensating non-linear distortion by subtracting the taken out non-linear distortion signal, or one preliminarily multiplying a signal having distortion compensating characteristics to a transmission signal before radio transmission process, such as frequency conversion, amplification and so forth with taking a non-linear distortion to be caused in the transmitter into account, for compensating distortion.
On the other hand, it has been known that non-linear distortion caused by non-linearity of the amplifier, frequency converter and so forth forming the transmitter to be used in radio communication appears as a leak current in a frequency band of a channel on transmission and in a frequency band of an adjacent channel of the channel on transmission and the leak current increases according of increasing of transmission power. Particularly, a power leaking to adjacent channel is known as an adjacent-channel leak power. The adjacent-channel leak power caused by the transmitter may affect for other radio equipment communicating using the adjacent channel to cause degradation of reception characteristics.
Next, discussion will be given for influence of adjacent-channel leak power caused by radio equipment employing a spread spectrum communication system (CDMA system: Code Division Multiple Access system) performing multiplex communication by spreading spectra of communication signals as a communication system employed in a mobile communication, for other communication system.
In the CDMA system, spreading of spectra of communication signals is performed employing a spreading code, such as pseudo noise code (PN code: Pseudo random Noise code), and communication signals are identified by the spreading code. Therefore, the CDMA system is characterized by capability of simultaneous communication of a plurality of radio equipments and a plurality of channels at the same frequency. The CDMA system is also characterized by the fact that, upon demodulating a received signal, demodulation of the received signal cannot be accomplished unless multiplying the same spreading code as that used in spreading on transmission side at the same timing as that in the transmission side, and the received signal spread by different spreading code or the received signal spread at different timing, namely the signals used for communication by other radio equipments or the signals of other channels are fallen as noise within a reception band currently on reception.
Here, consideration is given for the case where a base station of mobile communication is present, where a plurality of mobile stations are present in distal position and proximal position of the base station and where communication is performed by CDMA system. When the mobile stations at distal position and the proximal position of the base station are communicating with the base station using the same frequency and the same transmission power, as viewed at a receiving end of the base station, the transmission power of the mobile station communicating at the proximal position of the base station is higher than that of the mobile station communicating at the distal position to submerge the transmission signal of the mobile station at the distal position in the transmission signal of the mobile station at the proximal position. This has been known as a far-near problem. In view of the characteristics of the CDMA system, even when the base station demodulates the signal transmitted from the distal mobile station, the transmission signal of the distal mobile station cannot be demodulated correctly since the signal of the proximal mobile station falls with the reception band as noise.
In the CDMA system, the far-near problem is solved by performing transmission power control at high precision and high accuracy relatively frequently. Namely, by performing transmission power control, a transmission power of the proximal mobile station is controlled to be lower power and a transmission power of the distal mobile station is controlled to be higher power. For transmission at higher power by the mobile station, the frequency converter and/or the amplifier forming the transmitter of the mobile station has to be operated at non-linear region thereof. As a result, non-linear distortion of the transmission signal increases at higher level of the transmission power. Namely, the adjacent-channel leak power transmitted from the transmitter is increased. Influence of the adjacent-channel leak power to other system will be discussed with reference to FIG.
6
.
FIG. 6
illustrates a mobile communication system including a mobile station
101
, a mobile station
102
, a base station
103
, a base station
104
, a cell
105
and a cell
106
. Here, consideration is given for the case where the base station
103
and the base station
104
perform communication using the CDMA system, and carriers of the base station
103
and the base station
104
are different. The cell
105
represents a service area of the base station
103
and is extended in the vicinity of the base station
104
. On the other hand, the cell
106
is the service area of the base station
104
.
When the mobile station
102
is in communication with the base station
104
at proximal position to the base station
104
and the mobile station
101
is in communication with the base station
103
with traveling from proximal position to the base station
103
to distal position thereof, the transmission power and the adjacent-channel leak power of the mobile station
101
increase according to traveling toward the distal position by transmission power control of the base station
103
to the mobile station
101
. When the mobile station
101
approaches to the base station
104
, the transmission power and the adjacent-channel leak power of the mobile station
101
arrive to the base station
104
at higher power.
If the communication frequency used by the base station
103
and the communication frequency used by the base station
104
are adjacent with each other, the transmission power transmitted from the mobile station
102
may submerge in the adjacent-channel leak power transmitted from the mobile station
101
, In such case, a problem is encountered in that the base station
104
cannot receive the signal of the mobile station
102
correctly. This is because that the transmission power of the mobile station
102
is lower power for transmission power control of the base station
104
in the mobile station
102
.
As a solution for this problem, a linearizer for compensating non-linear distortion of the transmitter is employed. As set forth above, as the linearizer, one taking output only non-linear signal from a transmission signal transmitted and compensating non-linear distortion by subtracting the taken out non-linear distortion signal, or one preliminarily multiplying a signal having distortion compensating characteristics to a transmission signal before radio transmission process, such as frequency conversion, amplification and so forth with taking a non-linear distortion to be caused in the transmitter into account, for compensating distortion. The former is not practical for increasing of current consumption due to increasing of circuit scale and for comp
Foley & Lardner
Gantt Alan T.
Maung Nay
NEC Corporation
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