Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-08-10
2002-12-17
Cumming, William (Department: 2684)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S441000
Reexamination Certificate
active
06496497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for managing walsh code channels allotted from a base station in a mobile communication system based on a code division multiple access (CDMA) system, and more particularly, to a method for managing walsh code channels in which excellent walsh codes are allotted with priority from a base station so as to improve quality of service.
2. Background of the Related Art
Generally, a mobile communication system based on a CDMA system spreads frequency width of a channel and gives different codes to users through this spread channel. Accordingly, the mobile communication system has an advantage that a plurality of subscribers can simultaneously use the communication system through one channel. Such a mobile communication system based on a CDMA system increases frequency capacity by 10 to 20 times as compared with a related art analog communication system and has a relatively high frequency efficiency. Furthermore, the mobile communication system can facilitate data communication and has a relatively better security as compared with other communication systems.
FIG. 1
is a block diagram illustrating a related art mobile communication system based on a CDMA system.
Referring to
FIG. 1
, a plurality of PCS/cellular terminals MT
1
-MTn for mobile communication are respectively connected to their base stations BTS
1
-BTS
32
through a radio communication link. The respective base stations BTS
1
-BTS
32
are respectively connected to a mobile switching center MSC
1
through their base station controllers BSC
1
-BSC
4
. At this time, home location register/visitor location register (HLR/VLR) which manages moving location of the mobile terminals MT
1
-MTn is connected to the mobile switching center MSC
1
.
Origination operation of the respective mobile terminals in the aforementioned mobile communication system will be described below.
If the mobile terminal MT
1
transmits an origination message to the base station BTS
1
, the base station BTS
1
detects the origination message and reports contents of the origination message to the base station controller BSC
1
.
If it is determined that a frame-offset from the base station controller BSC
1
is appropriate to be allotted to the base station BTS
1
, the base station controller BSC
1
allots the frame-offset to the base station BSC
1
. If not, the base station controller BSC
1
proceeds with frame-offset negotiation over maximum three times.
Subsequently, if the frame-offset negotiation has been successfully proceeded, the base station BTS
1
allots a traffic channel for communication. Then, the base station allots a walsh code channel.
Subsequently, null data are transmitted from the base station BTS
1
to the mobile terminal MT
1
.
The frequency allocation (FA), walsh codes, and the frame-offset, which are allotted from the base station BTS
1
, are transmitted to the mobile terminal MT
1
through a paging channel. Accordingly, the base station BTS
1
can temporarily synchronize with the base station controller BSC
1
when the null data are transferred from the mobile terminal MT
1
. If the base station BSC
1
synchronizes with the mobile terminal MT
1
, ring back tone from the switching center MSC
1
is transferred to the mobile terminal MT
1
. Thus, origination sound occurs in the mobile terminal MT
1
so that the origination call access procedures are finished.
Walsh code allocation technology for dividing channels in the mobile terminal MT
1
which requests call access or handoff, at the base station BTS
1
and spreading transmission data will be described in more detail.
In a CDMA system by Qualcomm in the United States, there are provided 64 different walsh codes which are respectively 64 bits. There are provided 64 channels W
0
,W
1
,W
2
,W
3
, . . . , W
63
in the walsh codes. The channel W
0
is used as a pilot channel which catches the location of channels and controls power when initiating the mobile terminal MT
1
. The channels W
1
-W
7
are used as paging channels which inform the mobile terminal MT
1
of a paging signal. The channel W
32
is used as a synchronization channel which synchronizes the mobile terminal MT
1
with the base station BTS
1
. The other 55 channels are used as traffic channels, respectively.
According to the communication system based on the CDMA system, if each mobile terminal MT
1
requests call access or handoff, a channel manager provided in the base station BTS
1
allots walsh codes. The channel manager allows walsh codes of 55 traffic channels W
8
-W
31
, W
33
-W
63
to be on standby using a FIFO type queue and allots walsh codes to corresponding mobile terminals, sequentially, as occasion demands. At this time, 55 traffic channels W
8
-W
31
, W
33
-W
63
turns on the base station BTS
1
so that various processor boards load corresponding software(S/W) and are initiated when a task of each software is driven. In other words, a queue is initiated when software to the channel manager is normally operated. Thus, if a particular mobile terminal requests call access or handoff from the base station, the channel manager determines whether or not there are available walsh codes in the walsh codes which are be on standby in the queue. Subsequently, if there exist available walsh codes, the channel manager allots the walsh codes sequentially and performs call access procedures. If there do not exist available walsh codes, the channel manager informs the mobile terminal of the status of the current communication service, which is not available.
The walsh code allocation method is performed in such a manner that the walsh codes for 55 traffic channels which are sequentially initiated are sequentially allotted in the order of the first walsh code which is not allotted. In this regard, the walsh code for the traffic channel W
8
is first allotted. However, if a certain time passes, it is not easy to recognize what walsh codes are allotted ahead.
As aforementioned, if the base station allots the walsh codes sequentially, the walsh code having poor peak factor characteristic may be allotted, which occurs due to unique periodicity of the walsh code. The peak factor is a parameter that expresses peak power in association with average power. If the peak factor characteristic is good, load exerted on a base station amplifier
20
shown in
FIG. 2
is reduced. For example, if any system requires average power of 10 W that satisfies signal to noise ratio (SNR) and if the peak factor is expressed as 10:1, the base station amplifier should be designed to cover 100 W.
In that case, quality of service which is not relatively good is provided to the mobile terminal to which the walsh code having poor peak factor characteristic is allotted. In other words, if the peak factor characteristic is not good, large load is instaneously applied to an input terminal of the amplifier
20
. For this reason, a parameter such as adjacent channel power ratio (ACPR) increases, and the range for securing linearity of an output signal is exceeded at an output terminal of the amplifier, thereby causing distortion of CDMA signal. As a result, interference between adjacent channels increases and thus it is difficult to achieve optimal quality of service.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method for managing walsh code channels in a mobile communication system, that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for managing walsh code channels in a mobile communication system, in which a base station manages peak factor characteristic of each walsh code through one queue or two queues so that the walsh code having excellent peak factor characteristic can be allotted ahead.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and
Cho Sang Hyun
Lee Jong Il
Cumming William
Fleshner & Kim LLP
LG Information & Communications Ltd.
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