Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-07-13
2003-03-25
Le, Thanh Cong (Department: 2684)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S441000
Reexamination Certificate
active
06539005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for searching an access channel and allocating a finger for a base station, and in particular to an improved method for searching an access channel and allocating a finger for a base station which is capable of implementing a mobile communication system such as a DCS(Digital Control System) using a CDMA(Code division Multiple Access), a PCS(Personal Communication System) and a satellite communication system.
2. Description of the Background Art
Generally, a mobile communication system is a communication system capable of receiving a communication service.
In the above-described mobile communication system, a mobile station is capable of transmitting a signal to a base station for receiving a mobile communication service. At this time, the signal from the mobile station is directly transmitted to the base station or is reflected by a certain building and then is transmitted to the base station. Namely, the signals transmitted to the base station may have a certain delay time based on multiple paths. The base station demodulates the signals from the mobile station received through multiple paths and transmits to a control station.
When the mobile station requests a call transmission, in a state that the mobile station does not receive a certain service from the base station, when transmitting a short signal to the base station, an access channel is used. The above-described access channel is a CDMA channel that the mobile station transmits a signal to the base station in the reverse direction in a state that a communication channel is not set between the mobile station and the base station. In addition, in this access channel, different offsets may allocated for preventing the signals from being concurrently transmitted from a plurality of mobile stations to the base station via the access channel.
FIG. 1
is a flow chart illustrating a conventional method for searching an access channel and allocating a finger for a base station in a conventional mobile communication system.
As shown therein, the method for searching an access channel and allocating a finger for a conventional mobile communication system includes steps ST
1
through ST
3
for searching a search energy for an access channel for each antenna, comparing with a search critical value and storing an offset which exceeds the search critical value, steps ST
4
through ST
6
for selecting an offset having the highest search energy among the stored offsets, allocating the selected offset to the finger for each antenna, and demodulating the same, and steps ST
7
through ST
9
for searching a multiple path signal of the offset for each antenna, allocating the offsets which are not allocated to the finger having a search energy which exceeds the search critical value to the remaining fingers for each antenna, and demodulating the same and then feeding back to the steps ST
1
through ST
3
.
The operation of the method for searching an access channel and allocating a finger for a base station in a conventional mobile communication system will be explained with reference to the accompanying drawings.
First, in the base station for a mobile communication system, the space for smoothing a multiple path fading operation is diversed. Namely, a signal receiving state from the mobile station is improved using more than two receiving antenna. Here, two antennas are used, and a base station having four fingers is used. The finger performs a function for demodulating a signal from the mobile station to the base station.
In the step ST
1
, in the base station having two receiving antenna and four fingers, a search unit for the base station despreads a receiving signal at a certain offset interval for the receiving antenna and computes the search energy.
In the step ST
2
, the computed search energies which correspond to the same offset for each antenna are summed and compared with a set search critical value for judging whether the signal is detected from the mobile station.
In the step ST
3
, the search unit stores the offsets with respect to the signals having a search energy above the set search critical value.
In the steps ST
4
and ST
5
, the offset having the highest search energy among the stored offsets is selected and allocated to the finger. At this time, the base station allocates to the finger-
0
connected with the first antenna if the selected offset is a signal corresponding to the first antenna. If the selected offset is a signal corresponding to the second antenna, the offset is allocated to the finger_
2
connected with the second antenna. The finger_
0
and the finger_
1
are connected with the first antenna, and the finger_
2
and finger_
3
are connected with the second antenna.
The finger_
0
and finger_
2
to which the selected offsets are allocated, compute the finger energy with respect to the signal of the allocated offset and compares with the set finger critical value. If the computed finger energy is above a set finger critical value, in the step ST
6
, the signal corresponding to the offset is demodulated.
At this time, in the steps ST
7
and ST
8
, the search unit computes the search energy with respect to the offset for searching the multiple path signal for the antenna. The offsets having the highest search energy, not the offset allocated to the finger_
0
and finger_
2
among the offsets having the search energy above the search critical value, are allocated to the remaining fingers. At this time, if the signal of the offset having the highest search energy is a signal corresponding to the first antenna, the allocation is made for the finger_
1
, and if the offset signal is a signal corresponding to the second antenna, the allocation is made for the finger_
3
.
In the step ST
9
, the filger_
1
and finger_
3
having the allocated offsets demodulate the signals of the offsets.
In the step ST
1
, the search unit searches whether the signals having an energy above the search critical value provided to a new offset is received.
In the steps ST
2
through ST
4
, if the signal having a search energy above the set search critical value is received as another offset, not the offset allocated to the finger_
0
and finger_
3
, the offset of the signal having the highest search energy is selected. Thereafter, the new offset is allocated to the other finger which performs the demodulation function with respect to the offset as another offset is allocated. Namely, the offset of a newly searched signal is allocated to the finger_
0
and finger_
2
.
The finger_
0
and finger_
1
demodulate the multiple signal having a different time offset received into the first antenna, and the finger_
2
and finger_
3
demodulate the multiple signal having a different time offset received into the second antenna. Namely, one finger is connected with one antenna for thereby demodulating one access channel signal.
The search unit repeatedly performs the allocation with respect to the finger by searching a new multiple path signal. The search unit of the conventional base station allocates an access channel signal from the other mobile station to the finger in order to protect the access channel signal from the other mobile station before the decoding operation of the access channel signal with respect to one mobile station is completed.
Generally, when using a communication channel between the base station and the mobile station for the mobile communication system, the signal is spread using a spreading code which is different based on each mobile station and is transmitted from the mobile station to the base station. In addition, in the base station, the communication channel signal from the mobile station is despread based on the same spreading code as the mobile station for thereby separating the signal from the other mobile station.
The signal with respect to the offset in which the search energy of the receiving signal which despreads using the spreading code with respect to a certain mobile station exceeds a search critical value i
Chung Chae-Hun
Kim Dong-Hun
Cong Le Thanh
Greenspan Myron
Hyundai Electronics Industries Co,. Ltd.
Lackenbach & Siegel LLP
Nissen J. Harold
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