Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-07-06
2004-01-27
Tran, Sinh (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S561000
Reexamination Certificate
active
06684074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching device in a digital unit of a multi-sector base station in a code division multiple access (CDMA) mobile communication system, and more particularly to a switching device in a digital unit of a multi-sector base station, which switching device uses switching elements incorporated in the digital unit and adapted to switch 3 sectors into multiple sectors, thereby being capable of implementing a multi-sector base station system allowing a softer handoff among all sectors.
2. Description of the Related Art
Recently, it has been generalized to use, rather than mono media consisting of single media, a plurality of mono media, by virtue of continued developments in performances of representation media, transfer media, and operating systems thereof, as well as continued developments in data compression techniques for storage media and transfer media. For this reason, future radio communication systems must support high-speed multimedia services associated with not only audio data, but also high-speed data and image data. In order to allow radio communication systems to accommodate high-speed multimedia services, it is, first of all, necessary to provide radio channels of a large capacity because those radio communication systems have limited frequency resources. For this reason, introduction of the concept of micro cells, which have a cell radius of several hundred meters, or pico cells, which have a cell radius of several ten meters, has been highlighted in order to efficiently reuse limited frequency resources.
In the case of micro cell systems, however, there may be a problem in that since those micro cell systems have a cell size considerably smaller than those of macro cell systems, handoff occurs frequently between adjacent base stations, thereby resulting in a degradation in speech quality. Handoff occurring between adjacent base stations in a cellular system is called “soft handoff”. This soft handoff is conducted using channel resources allocated to both base stations, thereby resulting in a waste of channel resources. Furthermore, a lengthened period of time is taken to process handoff because it is necessary to establish a channel for a new base station. On the other hand, “softer handoff” is a handoff occurring between adjacent sectors in a 3-sector base station. Accordingly, it is unnecessary to allocate additional channel elements (CEs). Also, a reduce handoff time is taken for the softer handoff, as compared to the soft handoff. In order to implement a micro cell system using a plurality of micro cells, therefore, it is necessary to design that system in such a fashion that softer handoff is made between adjacent cells. It is also necessary to develop a system capable of managing a plurality of cells in a centralized fashion.
A multi-sector base station system is a base station system capable of satisfying the above mentioned requirements.
Conventional base station systems are configured to have a maximum of three sectors. For this reason, a multi-sector base station system having a multi-sector configuration has been implemented using a plurality of
1
FA 3-sector base station systems having the same FA.
FIG. 1
is a block diagram illustrating the case in which a 6-sector base station system is implemented using two conventional
1
FA 3-sector base station systems.
As shown in
FIG. 1
, the 6-sector base station system includes a base station controller (BST)
10
, a base station interconnection network (BIN)
20
for conducting a data interface with respect to the base station controller
10
, and a base station control processor (BCP)
30
for controlling the overall operation of the base station controller
10
. The system also includes a pair of 3-sector digital units, that is, a first 3-sector digital unit
40
and a second 3-sector digital unit
50
, for processing and interfacing data between the base station controller
10
and each of sectors
81
to
86
, a radio frequency unit (RU)
60
connected to both the first and second digital units
40
and
50
and adapted to process transmission and reception radio frequency signals, and a transmission medium (TM)
70
arranged between the radio frequency unit
60
and the sectors
81
to
86
and adapted to conduct a signal interconnection between the radio frequency unit
60
and the sectors
81
to
86
.
The first digital unit
40
includes at least one shelf control and routing card assembly (SRCA)
41
for interfacing with the base station interconnection network
20
, transmitting/receiving packet data of the digital unit
40
, and collecting information about the status of the digital unit
40
, at least one CDMA digital channel card assembly (CDCA)
42
for processing a CDMA digital signal, and at least one baseband and intermediate frequency conversion card assembly
43
(BICA)
43
arranged between the CDMA digital channel card assembly
42
and the RF unit
60
and adapted to conduct a digital interface with respect to the CDMA channel card assembly
42
while providing an interface with respect to the RF unit
60
at an intermediate frequency (IF) of 4.95 MHz.
Similarly to the first digital unit
40
, the second digital unit
50
includes at least one shelf control and routing card assembly
51
, at least one CDMA digital channel card assembly
52
, and at least one baseband and IF conversion card assembly
53
.
Each of the CDMA channel card assemblies
42
and
52
includes a controller and input/output (I/O) unit for conducting control and input/output operations, and 12 cell site modems (CSMs).
Practically, there are a plurality of shelf control and routing card assemblies
51
in one digital unit. Similarly, 10 CDMA channel card assemblies
52
are provided for one digital unit. There are also 3 baseband and IF conversion card assemblies
53
in one digital unit.
In the above mentioned conventional case, a multi-sector base station system, namely, a 6-sector base station system, is implemented by simply coupling together two conventional 3-sector base station systems having the same FA.
That is, the first digital unit
40
covers the sectors
81
to
83
whereas the second digital unit
40
covers the sectors
84
to
86
. Accordingly, where a mobile station moves about within a zone covering the sectors
81
to
83
or within a zone covering the sectors
81
to
83
, a softer handoff occurs. However, where a mobile station moves between the zone covering the sectors
81
to
83
and the zone covering the sectors
84
to
86
, a soft handoff occurs. When a soft handoff occurs, it is possible to avoid a speech cut-off phenomenon because prior to a disconnection from the current base station, the mobile station is allocated with the channel element of a new base station so as to keep speech communications with the counterpart. In this case, however, a lengthened handoff processing time is taken. Furthermore, the efficiency of using channel resources is degraded because two channel elements are consumed.
Moreover, it is impossible to allocate idle channel elements, present in the first digital unit
40
, for the sectors
84
to
86
covered by the second digital unit
50
. Similarly, it is impossible to allocate idle channel elements, present in the second digital unit
50
, for the sectors
81
to
83
covered by the first digital unit
40
. For this reason, there is a problem in association with a flexible allocation of channel elements in the setting of a traffic channel.
As well known, conventional multi-sector base station systems have an advantage in that it is possible to implement a multi-sector base station system without any substantial hardware or software modification, in particular, in the case in which two
1
FA 3-sector systems having the same FA are used.
However, there is a drawback in that increased costs are imposed for the construction of a desired system because a plurality of system units should be used. As mentioned above, there are also drawbacks of a lengthened handoff processing
Hong Sung Uk
Kang Shin Ha
Lee Ho Jin
Hyundai Electronics Industries Co,. Ltd.
Nguyen Huy D
Tran Sinh
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