Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-08-20
2004-04-27
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S701000, C714S746000
Reexamination Certificate
active
06728919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile telephone system, and more particularly to a mobile telephone system which adopts the site diversity reception wherein a signal from a mobile station is received by a plurality of base stations to choose the most available base station.
2. Description of the Related Arts
Mobile telephone systems such as portable telephone systems have been popularized widely. In a mobile communication system of the cellular system, for example, each of a plurality of base stations has an area called cell covered by it, and the cells are disposed without any gap among them to allow a mobile station to communicate over a wide area.
In the cellular mobile telephone system, when a mobile station moves into a new cell, the communication is switched over from the present base station to the base station which covers the new cite without being suffered from interruption of the communication. The switch over of communication is called as “hand over”.
Where a plurality of cells form an area in which they overlap each other on the boundary between or among them, if a mobile station roams into the overlapping area, it can communicate with all of the base stations which cover the overlapping area, or in other words, can communicate with a plurality of base stations simultaneously.
This fact is utilized in a conventional mobile telephone system (for example, a spread spectrum system) so that, when a mobile station is roaming around the boundary of two base stations, the mobile station communicates with the two base stations simultaneously. The method just described is adopted by the diversity hand over which is disclosed, for example, in “From the Beginning to Applications of the CDMA (Code Division Multiple Access) Technique” by Takuro Satoh, published by Linearize Company.
The diversity hand over described in the “CDMA Technique” is one of the communication system described above, a reception of an upward link signal from a mobile station to base station is utilized a site diversity reception among a plurality of related base stations.
The conventional site diversity reception among related base stations selection is described below.
FIG. 1
is a schematic block diagram of a usual mobile telephone system.
Referring to
FIG. 1
, base station
1
covers cell
2
, and base station
3
covers cell
4
. Base station
1
and base station
3
communicate through base station controller
6
. Connector
7
to different networks is, for instance, a mobile communication switch or a gateway switch for connecting to a public telephone network.
The conventional mobile telephone system has the space diversity configuration. In particular, when cell
2
and cell
4
have an overlapping area among them and mobile station
5
is roaming within the overlapping area as seen in
FIG. 1
, mobile station
5
communicates with both of base stations
1
and
3
simultaneously. The signals received by the two base stations from mobile station
5
are combined by a host station, i.e., base station controller
6
, and then transmitted to the other party of communication.
FIG. 2
is a block diagram showing a structure of a conventional base station and base station controller.
Base station
1
includes receiver
1
b
for receiving a radio signal from mobile station
5
through reception antenna
1
a
, analog to digital converter
1
c
for converting the analog signal from receiver
1
b
into a digital signal, counter spreader
1
d
for counter spreading the signal from analog to digital converter
1
c
, decoder
1
e
for decoding the signal from counter spreader
1
d
, error detector
1
f
for detecting whether the signal from decoder
1
e
contains some error or not, and reception level measurement unit
1
g
for measuring the reception level of the signal from counter spreader
1
d
. The signal from mobile station
5
after the error detection by error detector
1
f
is transmitted to base station controller
6
. Also the information of a result of the detection by error detector
1
f
representing whether some error is included or not is transmitted to base station controller
6
. Further, also the reception level measured by reception level measurement unit
1
g
is transmitted to base station controller
6
.
Also base station
3
similarly includes receiver
3
b
, analog to digital converter
3
c
, counter spreader
3
d
, decoder
3
e
, error detector
3
f
, and reception level measurement unit
3
g
. Base station
3
transmits a signal from mobile station
5
after error detection by error detector
3
f
to base station controller
6
, transmits information of a result of detection by error detector
3
f
whether some error is found or not to base station controller
6
, and further transmits a reception level measured by reception level measurement unit
3
g
to base station controller
6
.
Base station controller
6
includes selective composition controller
6
m
, data buffer
6
b
for storing a signal from base station
1
, and data buffer
6
c
for storing a signal from base station
3
.
FIG. 3
is a block diagram showing an internal structure of selective composition controller
6
m
shown in FIG.
2
.
A signal from mobile station
5
transmitted through base station
1
is inputted to and stored into data buffer
6
b
. A signal from mobile station
5
transmitted through base station
3
is inputted to and stored into data buffer
6
c.
Selective composition controller
6
m
includes no error data selector
6
f
, and highest reception level data selector
6
k.
No error data selector
6
f
refers to information of presence/absence of an error received from base stations
1
and
3
and controls data buffers
6
b
and
6
c
to select that one of the data stored in data buffers
6
b
and
6
c
(signals from mobile station
5
received through base stations
1
and
3
) which includes no error.
If both information of presence/absence of error received from base stations
1
and
3
indicates absence of error, then either information may be selected. On the other hand, if both information of presence/absence of error received from base stations
1
and
3
indicates presence of error, no error data selector
6
f
informs highest reception level data selector
6
k
of the presence of error.
If both information of presence/absence of error received from base stations
1
and
3
indicates presence of error, then highest reception level data selector
6
k
refers to reception levels received from base stations
1
and
3
, and controls data buffers
6
b
and
6
c
to be selected either one having higher reception level data.
In this manner, that one of the data stored in data buffers
6
b
and
6
c
which is selected by selective composition controller
6
m
is transmitted to connector
7
to a different network.
As described above, in the conventional mobile telephone system, a signal from a mobile station to a base station (upward link signal) is received by a plurality of base stations, and each of the base stations performs error detection detecting an error detection signal included periodically (for example, at intervals of 10 ms) in the received signal and measurement of the reception level. Then, each of the base stations sends results of the error detection and the measurement of the reception level to a base station controller which is connected to the base stations and acts as a controlling apparatus to them. The base station controller selects one of the signals sent thereto from the base stations which is free from an error, but if all of the received signals contain an error, then the base station controller selects that one of the received signals which has the highest reception level, thereby to assure augmented reception quality.
In a mobile telephone system, a signal is divided into units called frames before it is transmitted from a mobile station to a base station. Error detection code mentioned above is provided for each frame formed with a time width of, for example, 10 ms, so that a transmission error can be
Kondo Takayuki
Nagata Yoshinori
Chung Phung M.
NEC Corporation
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