Pulse or digital communications – Transmitters – Antinoise or distortion
Reexamination Certificate
2000-09-13
2004-08-10
Tse, Young T. (Department: 2634)
Pulse or digital communications
Transmitters
Antinoise or distortion
C375S140000, C375S308000, C370S208000
Reexamination Certificate
active
06775331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a transmission band limiting filter apparatus and a transmission apparatus. More specifically, the present invention is directed to a transmission band limiting filter and the like, which are used to execute a transmission band limiting process operation of transmission data for a portable telephone and a base station system.
2. Description of the Related Art
In a wireless mobile communication system, more particularly, in a cellular portable telephone system, a multiple access system is used in order to simultaneously establish communications between a base station and a plurality of mobile stations (communication terminals). In this multiple access system, a base station and/or plural mobile stations access empty wireless lines so as to establish wireless communications. This multiple access system is mainly subdivided into a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, and a code division multiple access (CDMA) system. Then, a base station allocates such a multiple access parameter corresponding to a multiple access system employed in a relevant wireless communication system with respect to a mobile station.
In the FDMA system, a plurality of channels are formed by varying the frequency. In the TDMA system, a plurality of channels are formed by slightly shifting time. To the contrary, in the CDMA system, while all of the frequencies and time are used, since the channels are discriminated from each other based upon the specific codes transmitted with being multiplexed on the signals, there are such drawbacks that the frequency components would be broadened, the frequency utilizing efficiency would be lowered, and thus, the broad band line should be used. However, this TDMA system may own such a feature that since the codes are multiplexed to convert the signals, the high secrecy characteristic could be maintained. Therefore, this TDMA system has been widely used.
On the other hand, in the CDMA system, in particular, while a multiplexing process operation is carried out, there are certain possibilities that a large current instantaneously flows. A so-called “limiter function” capable of limiting transmission power may constitute a major important factor in this CDMA system.
Conventionally, a transmission apparatus equipped with a peak amplitude suppression function is disclosed in, for example, Japanese Patent Laid-open Patent No. Hei(JPA)-9-18451.
As indicated in
FIG. 24
, a transmission band limiting apparatus employed in such a CDMA system that while a spread spectrum communication system is employed, a plurality of users are stored within the same frequency band, is constituted by a transmission data input dynamic range limiter processing unit
2401
, and also an n-times oversampling ROF unit
2402
. The transmission data input dynamic range limiter processing unit
2401
limits an amplitude of multiplexed data. The n-times oversampling ROF unit
2402
samples the output data of this transmission data input dynamic range limiter processing unit
2401
, and cuts off such output data having a large amplitude.
First, the transmission data which are multiplexed and are entered from an input terminal “i
data
” and another input terminal “q
data
” are inputted into the transmission data input dynamic range limiter processing unit
2401
. Then, this transmission data input dynamic range limiter processing unit
2401
performs the input dynamic range limit with respect to such input transmission data having a value larger than a preset value, so that the maximum value of the transmission data is suppressed.
Next, the transmission data whose maximum value has been suppressed by the transmission data input dynamic range limiter processing unit
2401
is entered to the n-times oversampling transmission band limiting filter unit
2402
so as to be processed by the transmission band limiting process operation thereof. Then, the transmission data which have been processed by the band limiting process operation by the n-times oversampling transmission band limiting filter unit
2402
are transferred via an output terminal “i
out
” and another output terminal “q
out
” to a post stage.
On the other hand, as shown in
FIG. 25
, the transmission data which has been processed by the band limiting process operation by the n-times oversampling transmission band limiting filter unit
2402
is further processed by an instantaneous peak suppression processing unit
2503
so as to suppress an instantaneous peak of this transmission data. The above-described apparatus has been proposed. Similar to the first-mentioned apparatus shown in
FIG. 24
, in this apparatus, transmission data which are multiplexed and entered from an input terminal “i
data
” and another input terminal “q
data
” are inputted into a transmission data input dynamic range limiter processing unit
2501
. This transmission data input dynamic range limiter processing unit
2501
performs an input dynamic range limiting operation with respect to such input data having a value larger than a set value in order to suppress the amplitude of the transmission data.
Next, the transmission data whose maximum value has been suppressed by the transmission data input dynamic range limiter processing unit
2501
is entered to an n-times oversampling transmission band limiting filter unit
2502
so as to be processed by the transmission band limiting process operation thereof. Then, the transmission data which has been processed by the band limiting process operation by the n-times oversampling transmission band limiting filter unit
2502
produces a peak value different from such a peak value which is suppressed by the peak value producing factor owned by the n-times oversampling transmission band limiting filter unit
2502
, although the amplitudes of the transmission data have been suppressed by the transmission data input dynamic range limiter unit
2501
. As a consequence, with respect to the transmission data outputted from the n-times oversampling transmission band limiting filter unit
2502
, the processing unit
2503
equipped with both the transmission power detection function and the instantaneous peak suppression function suppresses both an instantaneous peak and a peak value of such a signal having a value larger than the value which is again set. Next, the data outputted from this processing unit
2503
are transferred via the output terminal “i
out
” and another output terminal “q
out
” to the post stage.
In the transmission control system shown in
FIG. 24
arranged by the transmission data input dynamic range limiter unit
2401
and the n-times oversampling transmission band limiting filter unit
2402
, in such a case that the transmission power variation in the time axis by the transmission data entered into the input terminals “i
data
” and “q
data
” represent such a large fluctuation characteristic as indicated in
FIG. 17
, the band limiting process operation (limiting process) is carried out by the transmission data input dynamic range limiter unit
2401
in response to the set limited value. As a consequence, while the instantaneous peak value is suppressed and the upper limit value of the transmission power variation is removed (see FIG.
18
), such transmission data having no transmission power variation can be obtained.
However, in the case that the transmission data which has been limiter-processed by the transmission data input dynamic range limiter unit
2401
is inputted into the n-times oversampling transmission band limiting filter unit
2402
, the transmission power variation again owns such a characteristic having a high instantaneous peak, as indicated in FIG.
19
. Although the instantaneous peak of the transmission power variation has been suppressed as illustrated in
FIG. 18
, another instantaneous peak value which is caused by a different occurrence factor would occur. This instantaneous peak value is caused by the convolution process operation with respect to both
Pearne & Gordon LLP
Tse Young T.
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