Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-03-19
2002-12-10
Olms, Douglas (Department: 2732)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
Reexamination Certificate
active
06493332
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mobile communication system in which base station apparatuses based on the IS-95 scheme and W-CDMA (Wide band-CDMA (Code Division Multiple Access)) scheme of the CDMA schemes as access schemes in mobile communication systems share the same frequency band within the same service area.
As a mobile communication system using the CDMA scheme, a system using the IS-95 scheme is currently used in the U.S., Korea, and the like. It is, however, expected that this system will be replaced with a system used in IMT-2000 (International Mobile Telecommunications-2000) that is a multimedia mobile communication system in the process of standardization by the ITU (International Telecommunication Union).
The W-CDMA scheme is one of the schemes, the application of which to IMT-2000 has been studied. If this W-CDMA scheme is used for IMT-2000, the currently available IS-95 scheme and W-CDMA scheme may coexist. In consideration of the effective use of frequencies as well, the IS-95 scheme and the W-CDMA scheme may use the same frequency band within the same service area.
FIGS. 19
shows the arrangement of base station apparatuses in such a case.
Referring to
FIG. 19
, three base station apparatuses
1
are base station apparatuses based on the IS-95 scheme, and base station apparatuses
4
are base station apparatuses based on W-CDMA scheme. When a mobile station communication system based on the IS-95 scheme and a mobile station communication system based on the W-CDMA scheme are established in the same service area, base station apparatuses based on the respective schemes coexist in the area, as shown in FIG.
19
.
In the communication system based on the CDMA scheme, a plurality of communication channels can use the same frequency band. This is because each communication channel is spread-modulated with codes having orthogonality on the transmission side, and each communication can be specified by spread-demodulation (despreading) with the same codes on the reception side.
This orthogonality is made imperfect by propagation delay differences due to geographical and weather conditions and the like and time deviations due to multipath in the propagation path between the mobile station and the base station, and multipath associated with irrelevant codes, i.e., irrelevant communication, and multipath associated with relevant codes, i.e., relevant communication, have correlation components in some case. These correlation components become interference components in the relevant communication, resulting in a deterioration in communication quality. Since interference components are generated by such a factor, interference components increase as the number of communication channels increases.
The number of communication channels that can commonly use the same frequency band is therefore limited. If the total transmission power exceeds a predetermined threshold in this band, predetermined communication quality cannot be obtained. In the worst case, communication failures occur.
The arrangement of the conventional base station apparatus
1
in
FIG. 19
will be described next with reference to FIG.
20
.
As shown in
FIG. 20
, the IS-95 base station apparatus
1
is comprised of a transmission/reception amplification section
10
and a modulation/demodulation section
20
. The transmission/reception amplification section
10
amplifies a reception RF (Radio Frequency) signal from a mobile station and outputs the amplified signal to the modulation/demodulation section
20
. The transmission/reception amplification section
10
also amplifies a transmission RF signal from the modulation/demodulation section
20
and transmits the amplified signal to each mobile station through an antenna.
The modulation/demodulation section
20
is made up of a radio section
21
, a radio base station control section
22
, a FACH (Forward Access CHannel) baseband signal processing section
23
, an SDCCH (Stand alone Dedicated Control CHannel) baseband signal processing section
24
, a TCH (Traffic CHannel) baseband signal processing section
25
, and a wire transmission path interface section
26
.
The radio section
21
spreads baseband signals from the FACH baseband signal processing section
23
, the SDCCH baseband signal processing section
24
, and the TCH baseband signal processing section
25
with spreading codes, and synthesizes the resultant signals. The radio section
21
then D/A-converts the synthetic signal, converts the analog signal into a transmission RF signal by quadrature modulation, and outputs the signal to the transmission/reception amplification section
10
. In addition, the radio section
21
converts a reception RF signal from the transmission/reception amplification section
10
into an IF (Intermediate Frequency) signal, A/D-converts it, and performs quadrature demodulation of the digital signal.
The FACH baseband signal processing section
23
is made up of an encoding section
30
, a decoding section
31
, and a base station FACH transmission power calculation section
32
. The encoding section
30
encodes a signal from the wire transmission path interface section
26
and outputs the encoded signal as a baseband signal to the radio section
21
. The decoding section
31
decodes a signal demodulated by the radio section
21
and outputs the decoded signal to the wire transmission path interface section
26
.
The base station FACH transmission power calculation section
32
calculates a base station FACH transmission power value from a perch CH transmission power value, a perch CH reception SIR value, a rate correction value, and FACH specified reception SIR value according to equation (1) below. The base station FACH transmission power value is a power value required to transmit a FACH signal from the base station apparatus.
base station
FACH
transmission power value=perch
CH
transmission power value−(mobile station perch
CH
reception
SIR
value−mobile station
FACH
specified reception
SIR
value)/
FACH
rate correction value (1)
The FACH is a one-way channel for transmitting control information or user packet data from a base station to a mobile station. The FACH is used when the cell in which a mobile station is present is known. A FACH-L is used to transmit a relatively large amount of information, whereas a FACH-S is used to transmit a relatively small amount of information. The transmission formats for the FACH-S include a normal mode and an ACK mode. The normal mode is a mode for transmitting information about layer
3
or upper layers and packet control/user information. The ACK mode is a mode for transmitting an ACK (ACKnowledge) signal in response to a RACH (Random Access CHannel) signal received from a mobile station.
The perch CH transmission power value is a power value required to transmit a perch CH signal. This value is determined by operation information held in a base station. The perch CH is a channel for which systematic control information for each cell or sector is transmitted from a base station to a mobile station. Information whose contents change with time, e.g., SFN (System Frame Number) information and uplink interference power, is transmitted via this channel.
The perch CH reception SIR value is an SIR value obtained when a mobile station receives a perch CH signal transmitted from a base station. This information is transmitted from the mobile station to the base station via an RACH or SDCCH. The SIR (Signal Interference Ratio) is the ratio of the level of a desired signal to the level of a signal that interferes with the desired signal.
The FACH rate correction value is a value obtained by equation (2) below. This value is used to correct the influences of different transmission rates in the respective channels.
FACH
rate correction value=10×log (
FACH
transmission rate/perch
CH
transmission rate) (2)
The mobile station FACH specified reception SIR value is an SIR value to be obtained by a mobile station when it receives a
Olms Douglas
Pizarro Ricardo M.
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