Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-05-12
2002-12-03
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C370S329000
Reexamination Certificate
active
06490453
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 providing 4 quasi-orthogonal functions (QOF), which are used in association with 256 Walsh codes in a forward link, in a base station transceiver system (BTS) and a base station controller (BSC).
2. Description of the Related Art
Existing IS-95A/B CDMA communication systems spread a radio channel with a Walsh function. However, as the IS-2000 standard introduces new channels to the forward and reverse links, the existing conventional communication system lacks the necessary amount of Walsh codes to maintain orthogonality between channels
Accordingly, there is a need for a method for increasing the number of the channels, without decreasing the orthogonality between the existing channels. For the IS-2000 forward link, several methods have been proposed. One method is to define a quasi-orthogonal function (QOF) necessary for the mobile station thereby to assign 4 times the channels as compared with the case when the existing Walsh function is used, and another method is to expand the existing Walsh function which can generate 64 Walsh codes, so as to generate 256 Walsh codes. The quasi-orthogonal function (QOF) is commonly applied to IS-2000 forward channels, such as the fundamental channel (FCH), the dedicated control channel (DCCH) and the supplemental channel (SCH). However, existing base stations can only support 64 Walsh code channels.
Now, reference will be made to the types of the channels used in the IMT-2000 (International Mobile Telecommunications 2000) standard. IMT-2000 includes UMTS (Universal Mobile Telecommunication Service) and CDMA-2000/IS-2000.
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 another 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, the only required operation is to assign this logical channel to the previously established physical channel.
The physical channel can be divided into dedicated channels and common channels according to its characteristics. Dedicated channels are exclusively used for communication between the BTS and a particular mobile station (MS), and include a fundamental channel (FCH), a dedicated control channel (DCCH) and a supplemental channel (SCH). The fundamental channel is used to transmit voice, data and signaling signals. Such a fundamental channel is compatible with TIA/EIA-95-B. The dedicated control channel is used to transmit data and signaling signals. The dedicated control channel supports a discontinuous transmission (DTX) mode in which data is only transmitted when the upper layer generates transmission data. Because of this property, the dedicated control channel is suitable for effectively providing a packet service. The supplemental channel is used to transmit large amounts of data.
In addition to the dedicated channels stated above, the physical channel includes a common channel which is used in common 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-95B.
The logical channels to be assigned on the above physical channels include a dedicated signaling channel (dsch) and a dedicated traffic channel (dtch). The dedicated signaling channel can be assigned to the fundamental channel and the dedicated control channel, which are physical channels. The dedicated traffic channel can be assigned to the fundamental channel, the dedicated control channel and the supplemental channel. The dedicated signaling channel is used when the base station and the mobile station exchange a control signal. The dedicated traffic channel is used when the base station and the mobile station exchange user data.
The common logical channel to be assigned on the common physical channel is divided into a common signaling channel (csch) used to transmit control signal, and a common traffic channel (ctch) use to transmit user data. The common logical channels are assigned on the paging channel for the forward link, and are assigned on the access channel for the reverse link.
FIG. 1
shows a structure of a general mobile communication system. More specifically,
FIG. 1
shows a reference model of a 3G IOS (Interoperability Specifications) for a digital air interface between a mobile switching center (MSC) and a base station, and between base stations in the common mobile communication system.
Referring to
FIG. 1
, between MSC
20
and BSC
32
, a signal is defined as an A
1
interface and user information is defined as an A
2
/A
5
(circuit data) interface. An A
3
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 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 A
3
interface. An A
7
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 the CDMA mobile communication system, a 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 forward and reverse links. The MSC
20
includes a call control and mobility management block
22
and a switching block
24
. Further, the MSC
20
is connected to a data network such as the Internet through an interworking function (IWF) block
50
. 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.
FIG. 2
shows a procedure for exchanging signals between the BTS and the BSC (more specifically, the SDU function block in the BSC, BSC-SDU) according to the prior art. The operation can be performed either between the BSC
32
(or BSC-SDU
34
) and the BTS
36
in the source BS
30
, or between the BSC
42
and the BTS
44
in the target BS
40
.
FIG.2
is independent of types of the required physical channel, i.e., DCCH, FCH, SCH or whatever. That is, the invention in this document can be applied to all types of physical channels.
Referring to
FIG. 2
, the BTS determines forward and reverse channels to be established with the MS and then generates a signaling message (more specifically, a connect message) necessary for channel establishment, in step
201
. The generated signaling message includes a frame selector (or channel type) and channel information. The detailed operation of step
201
will be described later with reference to FIG.
3
. The BTS sends the generated connect message to the BSC in step
203
. Upon receipt of the connect message, the BSC analyzes the received connect message to check the channel assigned to the MS, and generates a connect ACK message to be transmitted to the BTS, in step
205
. The detailed operation of receiving the connect message will be described later with reference to FIG.
4
. The BSC sends the generated connect ACK message to the BTS in step
207
. The connect ACK message includes information for acknowledging establishment of the channel requested by the BTS. The BTS then
Chang Yong
Lee Hyun-Seok
Cong Le Thanh
Corsaro Nick
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