Radio communication apparatus and method

Details Radio communication apparatus and method Radio communication apparatus and method

2001-03-14

2004-08-17

Pezzlo, John (Department: 2662)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C370S310000, C370S318000, C370S331000

Reexamination Certificate

active

06778520

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a radio communication apparatus and method used in a car telephone, a portable telephone or the like.
BACKGROUND ART
In a cellular radio communication system for a car telephone, a portable telephone or the like, as a multiple access system for transmission signals in which a plurality of stations communicate concurrently at the same frequency band, a FDMA system, a TDMA system and so on are known. Recently, a CDMA system (Code Division Multiple Access system) has been applied as a system in which higher frequency utilization is obtained and more system users are accommodated than other techniques such as the FDMA system, the TDMA system and so on.
In addition, there are a FDD system and a TDD system as a transmission system to perform a bi-directional communication of transmission data over forward link and reverse link between a mobile station and a base station in a cellular system. The FDD system utilizes different frequency bands in forward and reverse links. The TDD system utilizes the same frequency band and transmits forward link signals and reverse link signals using time slots. Accordingly, a CDMA/TDD mobile station apparatus is a mobile station apparatus using the CDMA system as a multiple access system and the TDD system as a system for discriminating the forward link and reverse link.
The configuration of a conventional CDMA/TDD mobile station apparatus will be explained below using a block diagram in FIG.
1
.
As illustrated in
FIG. 1
, a mobile station comprises antenna
101
via which data is transmitted and received to and from a base station, switch
102
to switch a time band for transmitting and receiving, RF receiving section
103
to convert the received data passed through switch
102
to baseband signals, AD converter
104
to convert the data converted at RF receiving section
103
to digital data, correlator
105
to despread the data converted at AD converter
104
with a spreading code and decoder
106
to decode the data despread at correlator
105
.
Further, the mobile station comprises synchronization circuit
107
to generate synchronization signals used in despreading at correlator
105
from an output from AD converter
104
and to generate frame synchronization signals from the decoded data, and timing generation circuit
108
to generate switching timing signals for switch
102
based on the frame synchronization signals output from synchronization circuit
107
.
Furthermore, the mobile station comprises coder
111
to code transmission data, spreading multiplexing circuit
112
to spectrum spread the data coded at coder
111
to multiplex each channel, DA converter
113
to convert the data spread at spreading multiplexing circuit
112
to analog data, and RF transmitting section
114
to convert the data converted at DA converter
113
to RF data.
Furthermore, the mobile station comprises control circuit
120
to control the whole apparatus such as transmission power, frame configuration and so on.
The mobile station configured as described above selects receiving or transmitting by switch
102
corresponding to a control signal output from timing generation circuit
108
. In the case of selecting receiving, it decodes the data received from a base station using antenna
101
, RF receiving section
103
, AD converter
104
, correlator
105
, and decoder
106
. On the other hand, in the case of selecting transmitting, it transmits transmission data to a base station using coder
111
, spreading multiplexing circuit
112
, DA converter
113
, RF transmitting section
114
and antenna
101
. The switching timing of switch
102
is provided from timing generation circuit
108
based on the frame synchronization signals generated at synchronization circuit
107
. The control of each section in the mobile station is carried out by control circuit
120
.
In the conventional CDMA/TDD system mobile station described above, when the mobile station moves from a cell of a base station in current communication to another cell of another base station for next communication, control circuit
120
performs a switching of transmission and reception frequencies or a spreading code in order to communicate with a base station for the new communication.
However, there has been a problem that the conventional CDMA/TDD system mobile station described above has no hand-over system that is efficient to switch a base station quickly, therefore it takes a time to acquire synchronization with the base station for new communication and the mobile station has to discontinue communication temporally while it moves from a cell of a base station in current communication to another cell of another base station for next communication.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a CDMA mobile station apparatus capable of switching a base station in a short time while it moves from a cell of a base station in current communication to another cell of another base station for next communication and preventing transmission property from being deteriorated even in the case where the mobile station is present around a boundary between the cells of two base stations.
The object is achieved according to the following steps:
First, a mobile station detects reception power of data received from surrounding base stations, and when a level of the received power from a base station that is not the main base station in current communication becomes higher than a predetermined level, determines this base station as a sub base station, then transmits and receives data to and from the sub base station concurrently along with the main base station. After that, when the received power from the sub base station becomes higher than that from the main base station, the mobile station switches the main base station and the sub base station so as to transmit data to a new main base station.


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Kojiro et al. “Forward Link Capacity of a DS/CDMA System with Soft Handover,” with English language preface.
PCT International Search Report dated Dec. 16, 1997.

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