Pulse or digital communications – Spread spectrum
Reexamination Certificate
2000-09-18
2004-11-23
Bayard, Emmanuel (Department: 2631)
Pulse or digital communications
Spread spectrum
C375S147000
Reexamination Certificate
active
06822998
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Apparatus and Method for Measuring Noise Power in CDMA Mobile Communication System” filed in the Korean Industrial Property Office on Sep. 18, 1999 and assigned Serial No. 99-40250, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to base station receiver for a CDMA mobile communication system, and in particular, to an apparatus and method for measuring noise power of a received signal.
2. Description of the Related Art
In general, a CDMA (Code Division Multiple Access) communication system performs forward and reverse power control. For reverse power control, a base station transmits a power control command to a mobile station so as to maintain a specific signal-to-noise ratio (SNR) for a specific reverse channel being received from a mobile station, thereby controlling transmission power of that mobile station. For this, the base station requires an apparatus for measuring an SNR of the reverse channel. In reverse power control mode, when a signal received from the mobile station has a low SNR, the base station commands the mobile station to increase its transmission power; otherwise, when the signal received from the mobile station has a high SNR, the base station commands the mobile station to decrease its transmission power. Here, “low SNR” implies a bad channel condition, and the “high SNR” implies a good channel condition.
As stated above, the CDMA mobile communication system controls transmission power of the mobile station through reverse power control to ensure stable and efficient data transmission for each user, thereby preventing a waste of transmission power at the mobile station.
Therefore, it is very important for the CDMA mobile communication system to accurately measure the SNR, because it is the basis on which power control is performed. That is, it is necessary to correctly measure the SNR in order to prevent a waste of mobile station transmission power and ensure effective power control.
FIG. 2
illustrates a structure of a power control apparatus included in a base station receiver for a CDMA communication system according to the prior art. Referring to
FIG. 2
, measurement of noise power for power control is conventionally performed on a signal received through an antenna ANT and a receiving filter
210
. That is, a noise power measurer
218
measures the noise power of the received signal, which is not despread. Here, the received signal is a signal transmitted from a mobile station transmitter in a CDMA mobile communication system, the transmission signal including noise components generated by the radio channel environment. Therefore, the noise power measured by the noise power measurer
218
is not only the power of noise components but also the power of some signal components.
Further, the received signal filtered by the receiving filter
210
is provided to a sync acquisition block
212
, which acquires synchronization from the filtered received signal. In order to reproduce a signal transmitted from the transmitter, the receiver must be synchronized with the transmitter, and the term “sync acquisition” means that the receiver is synchronized with the transmitter. After sync acquisition, a complex conjugate despreading sequence generator
214
generates a complex conjugate despreading sequence. The received signal provided from the receiving filter
210
is despread with the complex conjugate despreading sequence by a multiplier
216
. The complex conjugate despreading sequence is a value determined by taking the conjugate of the complex spreading sequence that is used to spread the signal at the mobile station transmitter. A PN (Pseudo Noise) code is typically used for the complex spreading sequence and the complex conjugate despreading sequence. The received signal despread by the multiplier
216
is provided to a signal power measurer
220
for signal power measurement.
Next, the noise power measured by the noise power measurer
218
and the signal power measured by the signal power measurer
220
are provided to an SNR measurer
222
. The SNR measurer
222
measures the ratio of the measured signal power to the measured noise power. The value provided from the SNR measurer
222
is compared with a power control threshold value by a comparator
226
. The power control threshold value is generated by a threshold generator
224
. A power control command generator
228
generates a power control command according to the comparison results of the comparator
226
, and the generated power control command is transmitted to the mobile station transmitter for reverse power control.
A detailed structure of the noise power measurer
218
is shown in FIG.
3
. Referring to
FIG. 3
, the conventional noise power measurer
218
estimates the power of the received signal as the noise power. As mentioned above, the received signal is a mixed signal of the signal transmitted from the mobile station transmitter and the noise components generated by the radio channel environment. Therefore, the noise power measured by the noise power measurer
218
is not the power of the noise components alone, but the power of the signal components mixed with the noise components. An averaging block
312
, to estimate the noise power, averages the power of the received signal. Since power control is performed by calculating a ratio of the signal power measured by the signal power measurer
220
to the measured noise power, the SNR is determined by
SNR=E
s
/(
E
c
+N
o
) (1)
where SNR denotes a signal-to-noise ratio, E
s
denotes signal power after despreading, E
c
denotes signal power before despreading, and N
o
denotes noise power.
Therefore, when the noise power is measured using the conventional noise power measurer, it is not possible to calculate a correct SNR, making it difficult to perform effective power control. For example, even when the actual signal power is high enough, the SNR approximation (E
s
/(E
c
+N
o
)) is lower than the power control threshold value, thus making the base station generate an erroneous power-up command. The unnecessary increase in transmission power dissipates the battery power of the mobile station. Even though SNR is measured this way in the conventional IS-95 method for power control, the signal power-before-despreading E
c
is not so high in the conventional IS-95 communication system, so that it is possible to calculate a quite correct SNR. However, future CDMA-2000 mobile communication systems transmit an increased amount of data at a high data rate, thereby increasing the signal power in proportion to the amount of the transmission data. Therefore, if the noise power is measured using the conventional IS-95 method, the error will increase to an undesirable extent. That is, the conventional noise power measuring method measures the SNR by estimating the power of the total received signal (i.e., power of the signal components + power of the noise components) as the noise power. Thus, an increase in power of the signal components (E
c
) will cause an increase in the difference between the estimated noise power (E
c
+N
o
) and the pure noise power (N
o
), making it difficult to approximate the correct SNR.
SUMMARY OF THE INVENTION
It is, therefore an object of the present invention to provide an apparatus and method for measuring only the power of the noise components in a received signal in a base station receiver for a CDMA mobile communication system.
It is another object of the present invention to provide an apparatus and method for measuring noise power using an orthogonal code, which is not presently used in a mobile station, in a base station receiver for a CDMA communication system.
It is further another object of the present invention to provide an apparatus and method for measuring only the power of the noise components in a received signal, using an orthogonal code which is orthogonal to all the orthogonal codes use
Maeng Seung-Joo
Yoon Soon-Young
Yun Yu-Suk
Bayard Emmanuel
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
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