Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-03-18
2003-04-22
Kincaid, Lester G. (Department: 2685)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S335000, C455S069000, C455S127500, C455S522000
Reexamination Certificate
active
06553018
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a communication terminal apparatus by means of CDMA (Code Division Multiple Access) utilizing spread spectrum system, and especially to a method of and an apparatus for controlling transmission power in one communication terminal apparatus in case of conducting multi-code transmission in which a plurality of spreading code channels are allocated to the communication terminal apparatus, and thereby, transmission capacity is enlarged.
In a mobile communication system having a base station and a plurality of mobile communication terminals, as a connection method in which the number of terminals capable of being accommodated in the system is increased, and which is capable of flexibly corresponding to a change of a transmission speed, CDMA in which a spread spectrum system is applied has been watched.
In case of mobile communication by means of the CDMA, especially in case of using Direct Sequence (DS) as a method of spread spectrum, if transmission power from the mobile communication terminals is the same as each other, since a reception electric field at the base station is generally in inverse proportion to a square of a distance between the base station and the mobile communication terminals, a weak radio wave from the terminal far from the base station is strongly interfered with a strong radio wave from the terminal near the base station, and a radio wave from the remote terminal cannot be normally received at the base station. Accordingly, it is necessary to control the transmission power for each terminal so that strength of received radio waves from each terminal is almost the same as each other at a position of the base station.
Conventionally, in the mobile communication system by means of the CDMA, it is usual that one code channel is allocated to one terminal that is used by a user. Here, the code channel is a communication channel that is specified by a spreading code (pseudorandom noise code) being used for spreading.
FIG. 7
is a block diagram simply showing a conventional mobile terminal
101
in accordance with a CDMA method from an aspect of transmission power control, and here, it is assumed that data transmission is conducted from the mobile terminal
101
to a base station
102
using only one code channel. The data to be transmitted is supplied to the mobile terminal
101
from a signal source
104
connected to the mobile terminal
101
.
The data to be transmitted is often a voice signal, and is sometimes a high speed multi-media data that is output from a computer. In any event, it is assumed that the signal source
104
is for outputting a data stream at a bit rate of R bits/second.
Provided in the mobile terminal
101
are a receiver
112
connected to a reception antenna
111
, a transmitter
114
connected to a transmission antenna
113
, a spreading circuit
115
to which a data stream from the signal source
104
is input, a D/A (Digital/Analog) converter
116
for converting a digital signal output from the spreading circuit
115
into an analog signal, a modulator
117
for applying orthogonal modulation to a carrier wave based on an output from the D/A converter
116
, a variable gain circuit
118
inserted between an output of the modulator
117
and an input of the transmitter
114
. An oscillation circuit
119
for generating a high frequency signal that is a carrier signal is connected to the modulator
117
.
After applying error correction coding and a process such as interleave and encrypt to a data stream from the signal source
104
, the spreading circuit
115
spreads using a spreading code corresponding to an allocated code channel, and outputs a base band signal. Here, the spreading circuit
115
is constructed as a digital signal processing circuit, and spreads the data stream from the signal source
104
to generate a signal and outputs a multilevel digital signal as a base band signal, which represents an instant value of this signal every moment. Also, in the modulator
117
, orthogonal modulation is conducted by means of four phases PSK (phase shift modulation) (QPSK (Quadrature Phase Shift Keying)), and accordingly, an in-phase component I and an orthogonal component Q of the base band signal are output from the spreading circuit
115
as a multilevel digital signal, respectively, and the D/A converter
116
independently converts the in-phase component I and the orthogonal component Q into analog signals, respectively, and the modulator
117
receives these in-phase component I and orthogonal component Q and conducts modulation.
Here, an arrangement of the spreading circuit
115
will be explained using FIG.
8
. This spreading circuit
115
is for applying direct sequence (DS) system as spread spectrum system to the input data stream. In
FIG. 8
, values in parentheses show typical examples of a data speed, a chip rate and so forth.
A data stream of a data speed 128 kbps (bps is the number of bits per second) for example is input from the signal source, and a serial/parallel conversion circuit
121
with one input and two outputs (
1
→
2
) is provided for dividing this input data stream into two series of data streams with a data speed (64 kbps in this example) that is a half compared with the input data stream. One data stream from the serial/parallel conversion circuit
121
corresponds to the in-phase component I in the orthogonal modulation, and the other data stream corresponds to the orthogonal component Q. Disposed are a PN code generator
122
for generating a pseudorandom noise code (PN code) as a spreading code for the in-phase component I, and a PN code generator
123
for generating a pseudorandom noise code (PN code) as a spreading code for the in-phase component Q. The data stream and spreading code on a side of the in-phase component I are input to an adder
124
, and thereby, the data stream corresponding to the in-phase component I is spreaded. In the same manner, the data stream and spreading code on a side of the orthogonal component Q are input to an adder
125
, and thereby, the data stream corresponding to the orthogonal component Q is spreaded. The adders
124
and
125
are for calculating exclusive OR between the input data stream and the spreading code. A chip rate of a signal after spreading which is output from each of the adders
124
and
125
is 4.096 Mcps (cps is the number of chips per second), for example. The signals after spreading from the adders
124
and
125
are input to FIR (finite impulse response) filters
126
and
127
that function as a low pass filter, respectively, and thereby, a multilevel digital signal (8 bits value signal, for example) is output every moment, which represents an instant value of a base band signal of the in-phase component I and the orthogonal component Q.
In this manner, spread spectrum is applied to the data stream, and a transmission signal with a predetermined frequency band can be obtained from an output of the modulator
117
. A level adjustment for this transmission signal is conducted by the variable gain circuit
118
, and thereafter, this transmission signal is transmitted from the transmitter
114
. The variable gain circuit
118
is constructed of an amplifier capable of varying a gain or an attenuator capable of varying an amount of attenuation. As mentioned below, a gain (or an amount of attenuation) in the variable gain circuit
118
is controlled by a TPC (Total Power Control) signal from the receiver
112
1 dB by 1 dB, for example.
Now, it is assumed that a bit rate of the data stream from the signal source
104
is R [bits/second], and a band width of the transmitted signal is W [Hz],
G=W/R
(1)
is called a spreading gain.
After receiving such a transmission signal from the mobile terminal
101
, the base station
102
applies de-spreading, decoding, de-interleave and error correction to this signal. It is assumed that signal power per bit necessary for fully receiving this signal in the base station
102
is E
b
, noise power per Hertz i
Dickstein Shapiro Morin & Oshinsky LLP.
Kincaid Lester G.
NEC Corporation
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