Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-10-01
2002-02-26
Vu, Huy D. (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S441000, C375S350000, C375S148000, C375S343000
Reexamination Certificate
active
06351462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) receiving apparatus for a mobile communication system, particularly for a car phone/portable phone system (cellular system), and a reception method therefor.
2. Description of the Related Art
The CDMA reception method has an advantage that the same frequency is usable between all cells and within a cell, and a path diversity effect of composing plural arrival path signals can be obtained by a simple RAKE receiver. However, it has a problem that the interference between channels cannot be perfectly extinguished. In order to solve this problem, Japanese Laid-open Patent Application No. Hei-7-170242 has disclosed a method of removing interference by using an adaptive despreading filter.
FIG. 4
shows the construction of the conventional CDMA receiving apparatus disclosed in the above publication.
The conventional CDMA includes a reception antenna
101
for receiving a radio signal transmitted from a communication partner station (i.e., a station with which a station concerned communicates), a radio reception unit
102
for demodulating the radio signal received by the reception antenna
101
to convert the radio signal to a base band signal, an analog/digital converter (A/D)
103
for converting the base band signal to a digital signal and outputting it as a reception signal, a data accumulator
104
for accumulating the reception signal converted by the analog/digital converter
103
, a channel signal processor
105
and a clock generator
106
for transferring a clock signal clk to each block of the channel signal processor
105
.
In each block of the channel signal processor
105
, a signal having a twice period of the chip rate serving as a reference time unit of the frequency spreading processing is formed by using the clock signal clk, and each block operates on the basis of the signal thus formed.
Further, the channel signal processor
105
comprises an adaptive despreading filter
110
, an adaptive controller
111
, a judgment unit
112
and an autocorrelative inverse matrix calculator
113
.
The adaptive despreading filter
110
comprises a transversal filter, and it applies filtering processing to the reception signal r by performing despreading with a variable coefficient vector a.
The adaptive controller
111
renews the variable coefficient vector a so that the error power between the output signal re and the judgment data rd is minimum.
The judgment unit
112
makes a judgment on the output signal re of the adaptive despreading filter
110
so that the output signal re is set to the data of a transmission series of a transmitter which transmits the radio signal, and outputs the judgment result as the judgment data rd. That is, the judgment data rd is the data obtained by removing noises from the output signal data re.
The autocorrelative inverse matrix calculator
113
calculates the inverse matrix of an autocorrelative matrix of the reception signal re, and transfers the inverse matrix thus calculated to the adaptive controller
111
.
FIG. 5
is a block diagram showing the adaptive despreading filter
110
. The adaptive despreading filter
110
comprises sampling circuits
201
,
205
, a shift register
202
, a variable coefficient multiplier
203
and an adder
204
.
The sampling circuit
201
samples the reception signal r at the twice period of the chip rate, and outputs it to the shift register
202
.
The shift register
202
successively stores the reception signal r sampled by the sampling circuit
201
to generate and output a tap output vector u.
The variable coefficient multiplier
203
multiplies the tap output vector u and the variable coefficient vector a with each other.
The adder
204
adds the multiplication results of the variable coefficient multiplier
203
.
The sampling circuit
205
samples the addition value of the adder
204
at the period of a symbol rate, and outputs it as the output signal re.
Next, the operation of the conventional CDMA receiving apparatus thus constructed will be described hereunder.
First, the radio signal received by the reception antenna
101
is demodulated by the demodulator
102
to be converted to the base band signal, converted to the digital reception signal r in the analog/digital converter
103
, and then accumulated in the data accumulator
104
.
The reception signal r accumulated in the data accumulator
104
is sampled at the twice period of the chip rate in the sampling circuit
201
, and then input to the shift register
202
.
Representing the spreading rate of CDMA by M, for the shift register
202
, the tap interval is equal to the half of the period of the chip rate, and the number of taps is equal to
6
M.
In the autocorrelative inverse matrix calculator
113
, the inverse matrix of the autocorrelative matrix of the reception signal r is calculated, and transferred to the adaptive controller
111
. In the adaptive controller
111
, the variable coefficient vector a={a
0
, a
1
, a
2
, . . . , a
6
M−1} serving as a filter coefficient of the adaptive despreading filter
110
is generated by using the inverse matrix thus calculated.
Thereafter, in the adaptive despreading filter
110
, the reception signal r is sampled by the sampling circuit
201
, and successively stored in the shift register
202
to generate the tap output vector u={u
0
,u
1
,u
2
, . . . , u
6
M−1} and output the tap output vector to the adaptive controller
111
. Further, in the adaptive despreading filter
110
, the tap output vector u is weighted with the variable coefficient vector a and added in the adder
204
, then sampled at the period of the symbol rate in the sampling circuit
205
, and then output as the output signal re. In the judgment unit
112
, noises are removed from the output signal re, and the resultant signal is output as the judgment data rd.
Here, the adaptive controller
111
controls the variable coefficient vector a so that the error power between the output signal re and the judgment data rd is minimum. A known training signal is transmitted/received at a transmission side/reception side from the time just after reception of a burst signal is started until the variable coefficient vector a of the adaptive despreading filter
110
is converged. After the variable coefficient vector a is converged, correct data are output for the judgment data from the judgment unit
112
, so that the variable coefficient vector a is successively judged so that the adaptive controller
111
minimizes the error power between the output signal re from the adaptive despreading filter
110
and the judgment data rd from the judgment unit
112
, whereby the variation of the transmission path characteristics can be tracked. As an adaptive control algorithm for minimizing the error power have been known an LMS (Least Mean Square Algorithm) which is simple, but low in converging rate, an RLS algorithm which is high in converting rate, but complicate, etc.
Signal components (interference signals) addressed to other receivers and noises of the receiver cause errors in the self-receiving apparatus. Accordingly when power of interference signal noise power of receiver, the adaptive despreading filter
110
operates to cancel the interference signal.
In the conventional CDMA receiving apparatus, the composite path length, that is, the tap number of the adaptive despreading filter
110
is fixed to the maximum value in advance. Therefore, when a communication is made under a severe radio environment like a metropolitan region containing many buildings or the like in which multipath occur frequently because the radio transmission path status is bad, the multiple paths can be added without omission by composing many paths. Therefore, S/N is increased and an error rate is reduced, and thus this is extremely effective. However, for example when a communication is made under a radio environment like a clear suburb in which multipath occur rarely because the radio transmission
Ostrolenk Faber Gerb & Soffen, LLP
Phan Tri H.
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