Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-05-12
2004-05-04
Tran, Sinh (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S067110, C455S450000, C455S422100, C370S342000, C370S328000
Reexamination Certificate
active
06731948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a method for enabling a base station to support a discontinuous transmission (DTX) mode in a dedicated control channel and a supplemental channel.
2. Description of the Related Art
Existing CDMA mobile communication systems have mainly provided voice service. However, in the near future, CDMA mobile communication systems will support the IMT-2000 (International Mobile Telecommunication-2000) standard which can provide data service as well as voice service. The IMT-2000 mobile communication system can support high-quality voice service, moving picture service and Internet search service.
A CDMA mobile communication system includes a base station (BS), which is comprised of a base station transceiver system (BTS) and a base station controller (BSC), a mobile switching center (MSC), and a mobile station (MS). A radio link existing between the MS and the BTS is divided into a forward link for transmitting a signal from the BTS to the MS and a reverse link for transmitting a signal from the MS to the BTS.
Every channel is divided into a physical channel and a logical channel. The logical channel is established over the physical channel, and several logical channels can be established on a single physical channel. If the physical channel is released, the logical channel established over the physical channel is automatically released. It is not necessary to establish the physical channel in order to establish a certain logical channel. When a physical channel to be established for a logical channel is already established for another logical channel, a required operation is only to assign this logical channel to the previously established physical channel.
The physical channel can be divided into a dedicated channel and a common channel according to its property. The dedicated channel is exclusively used for communication between the BTS and the MS, and includes a fundamental channel (FCH), a dedicated control channel (DCCH) and a supplemental channel (SCH). The fundamental channel is used to transmit voice signal, data signal and signaling signal. Such a fundamental channel is compatible with TIA/EIA-95-B. The dedicated control channel is used to transmit the data signal and signaling signal. The supplemental channel is used when large amounts of data need to be transmitted. The common channel is the physical channel other than the dedicated channel, and is commonly used by the base station and several mobile stations. A physical channel for the forward link transmitted from the BTS to the MS is called a paging channel, and a physical channel for the reverse link transmitted form the MS to the BTS is called an access channel. These common channels are compatible with IS-95-B.
In a mobile communication system, data communication has the characteristic that periods of bursty data transmission alternate with long periods of no data transmissions. Therefore, future mobile communication systems employ a discontinuous transmission (DTX) mode for assigning the dedicated channel only when data is transmitted during the data communication service.
The DTX mode refers to a mode in which a wired system or a mobile communication system transmits data on a frame unit basis only when there is data to transmit. That is, the DTX mode refers to a mode in which the wired system or the mobile communication system does not transmit data when there is no transmission data for a predetermined time period. The DTX mode has various advantages as follows. Since data is transmitted on a frame unit basis only when there is actual data, it is possible to minimize transmission power. Further, the overall interference of the system decreases in strength, thus increasing the overall system capacity.
However, since the frames are irregularly transmitted by the transmitter, the receiver cannot know beforehand whether frames have been transmitted or not. Accordingly, the BTS cannot independently perform forward power control. More specifically, if the receiver in the MS does not exactly know when the frame has been transmitted at the transmitter, the decision parameters of the decoder, including the cyclic redundancy code (CRC), and the decoding results are unreliable. Accordingly, in DTX mode, it is not possible to precisely control transmission power of the MS by applying the same method used in the continuous transmission mode.
The DTX mode is supported in the dedicated control channel and the supplemental channel. The dedicated control channel supports the DTX mode in which data is transmitted only when the upper layer generates transmission data. Because of such a property, the dedicated control channel is proper to be used as a control channel to effectively provide packet service. For this DTX period, it is possible to perform power control by transmitting a null frame over the dedicated control channel. The supplemental channel also supports the DTX mode for transmitting no data in a period where there is no data to transmit. In such a DTX period, no frame is transmitted over the supplemental channel. The DTX mode connects the dedicated traffic channel and control channel only in a period where the data is actually transmitted, and releases the dedicated channels when no data is transmitted for a predetermined time period, in consideration of the limited radio resources, the base station capacity, and the power consumption of the mobile station. When the dedicated channels are released, communication is performed through the common channel only, thereby increasing utilization efficiency of the radio resources. For such a DTX mode, there are required several states according to the channel assignment situation and existence
onexistence of state information.
FIG. 1
shows a state transition diagram of a mobile communication system for a common packet service. Referring to
FIG. 1
, the states for the packet service are divided into an active state
11
, a control hold state
12
, a suspended state
13
, a dormant state
14
, a packet null state
15
, and an initial state
10
. In the control hold state
12
, the active state
11
, and suspended state
13
, a service option is connected. In the other states, the service option is not connected. It should be noted that the present invention relates to the base station (BSC and BTS) for supporting the DTX mode in the supplemental channel and the dedicated channel in the active state
11
and the control hold state
12
.
FIG. 2
shows a reference model of a 3G IOS (Interoperability Specifications) for a digital air interface between the MSC and the base station, and between the base stations in the common mobile communication system.
Referring to
FIG. 2
, between MSC
20
and BSC
32
, a signal is defined as an A1 interface and user information is defined as A2/A5 (circuit data) interface. An A3 interface is defined to connect a target BS
40
to a frame selection/distribution unit (SDU) function block
34
of a source BS
30
for soft/softer handoff between the base stations. The signaling and user traffic between the target BS
40
and the SDU function block
34
of the source BS
30
are transmitted through the A3 interface. An A7 interface is defined for signal exchange between the target BS
40
and the source BS
30
, for soft/softer handoff between the base stations. In a CDMA mobile communication system, the wired communication link between the base station
30
and the base station
40
, and between the base station
30
and the MSC
20
, is comprised of a forward link transmitted from the MSC
20
to the base station
30
, a reverse link transmitted from the base station
30
to the MSC
20
. Generally, a wired bi-directional line connected between the MSC
20
and the base station
30
carries the reverse and forward links. The wired line exists over all the interfaces in the RAN, e.g., MSC-BSC, BS-BS, BSC-BTS, BSC-Target BTS and so on. The MSC
20
includes a call co
Chang Yong
Lee Hyun-Seok
Afshar Kamran
Dilworth & Barrese LLP
Tran Sinh
LandOfFree
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