Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-01-24
2002-11-19
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S440000, C455S441000
Reexamination Certificate
active
06484032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a path connection control system and control method thereof in a code division multiple access (CDMA) mobile communication system.
2. Description of the Related Art
It has been well known a mobile communication system, in which a mobile communication switching center is connected to a based station control unit through a wire circuit, a plurality of radio base stations are connected to the base station control unit through a wire circuit, and each base station is connected to a plurality of mobile terminals entering into a service area of an own station through radio circuits.
As a method for multiplexing radio communication paths in the mobile communication system, there has been known a code division multiple access (CDMA), in which information bit desired to communicate is multiplexed by spreading spectrum with several tens to several thousands bits of spreading code pattern, in addition to a frequency division multiple access (FDMA) or time division multiple access (TDMA).
CDMA is advantageous in strength against narrow barrage jamming and in capability of accommodating a plurality of paths within the same carrier wave. In current typical CDMA mobile communication system, a path connection system to establish a multiple paths for a plurality of radio base stations depending upon a condition of communication in call through one radio channel, has been employed. However, since CDMA uses a frequency band of low power in wide band, if number of paths is in excess of a certain number, radio signals arriving through such relatively large number of paths become mere noise. Therefore, connection control of the paths depending upon communication environment is particularly important in the CDMA mobile communication system.
FIG. 8
is an illustration for explaining path connection control of the conventional CDMA mobile communication system of this type.
In
FIG. 8
, the reference numeral
50
denotes mobile terminal (MS),
51
to
53
denote radio base stations (BTS),
54
denote a base station control unit (BSC),
58
denotes a mobile communication switching center (MSC).
On the other hand, in the base station control unit
54
, the reference numeral
55
denotes a field intensity data extracting portion for extracting data of electric field intensity,
56
denotes a field intensity level monitoring portion for monitoring a field intensity level of the each radio base station based on the field intensity data, and
57
denotes a path setting control portion for determining path to be connected and path to be cut based on information from the field intensity level monitoring portion
56
.
Next, path connection control of the CDMA mobile communication system shown in
FIG. 8
will be discussed hereinafter.
Upon calling from the mobile terminal
50
, a received field intensity of a pilot pattern transmitted from each radio base station
51
to
53
is measured in the mobile terminal
50
to establish call connection to the radio base station having the highest field intensity.
Here, it is assumed that the radio station having the highest field intensity is the radio base station
52
, the radio terminal
50
at first establishes a path to the radio mobile station
52
.
Even after establishing the path with the radio base station
52
, the mobile terminal
50
continues measurement of the received field intensity of the pilot pattern to sequentially report information of measured field intensity of each radio base station to the base station control unit
54
through the path established with the radio base station
52
.
In the base station control unit
54
, data relating to the field intensity of each radio base station is extracted from the signal input from the radio base station
52
to feed the extracted data to the field intensity level monitoring portion
56
for monitoring the field intensity level of each radio base station in the field intensity level monitoring portion
56
.
In hand off control while moving, when radio base station having field intensity level exceeding a threshold value to be a reference in establishing the path, newly appears, path is newly established to the newly appearing radio base station. Conversely, when the field intensity level of the radio base station, to which the path has already been established, is lowered to be lower than the threshold level to be the reference, the path to such radio base station is cut off.
Namely, in hand-off control in the conventional CDMA mobile communication system, path connection control is performed depending upon the actual field intensity level of each radio base station reported from the mobile terminal.
In the path connection control system in the conventional CDMA mobile communication system set forth above, since the path connection control is performed depending upon the actual field intensity level of each radio base station reported from the mobile terminal, the following problem is encountered.
At first, in order to re-establish paths depending upon high and low of actual field intensity level, hand-off control may cause delay when the mobile terminal is in motion at high speed to cause degradation of communication quality until completion of hand-off control.
Secondly, since path is uniformly established for the radio base stations having the field intensity level higher than or equal to the given level, the path is inherently established even for the radio base station temporarily passed through in a moment. On the other hand, in order to adapt to abrupt variation of communication environment, it becomes necessary to constantly establish a plurality of paths to waste communication resource.
It should be noted that, in Japanese Unexamined Patent Publication No. Heisei 7-322336, for “Hand-Off System for Cellular Telephone System”, as shown in
FIGS. 9
,
10
A and
10
B, a position detector
518
for detecting a current position and traveling direction of the mobile terminal is provided in the mobile terminal
50
, and a map data storage portion
522
for storing map data covering all cell area of the cellular phone system, a mobile terminal position information storage portion
521
for storing position information and traveling direction information detected by the position detector
518
and a mobile terminal traveling direction judgment portion
523
are provided in a control station
502
.
The mobile terminal traveling direction judgment portion
523
detects the cell area where the mobile terminal moves with reference to the map data on the basis of the position information and traveling direction information when degradation of field intensity associating with movement of the mobile terminal is noticed to the mobile base station of the cell area where the mobile terminal is actually present.
The system disclosed in the above-identified publication has the radio base station map to perform hand-off after narrowing down the radio base stations to hand-off on the basis of traveling direction of the mobile terminal for effectively use a part of communication resource. However, even in this technology, the foregoing problem of delay in hand-off control during high speed travel cannot be resolved and effectiveness of use of communication resource is not satisfactory.
SUMMARY OF THE INVENTION
The present invention has been worked out in view of the drawbacks in the prior art set forth above. Therefore, it is an object of the present invention to provide a path connection control system and control method thereof in a CDMA mobile communication system which can establish minimum but sufficient paths without causing degradation of communication quality due to delay of hand off control even during high speed travel.
According to the first aspect of the present invention, a path connection control system in a CDMA mobile communication system for determining a radio base station to establish a path for communication with a mobile terminal by a base station control unit, the base station control unit comprises:
means for re
Harry Andrew T
Hunter Daniel
NEC Corporation
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