Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-12-06
2003-09-30
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S349000, C455S065000, C455S134000
Reexamination Certificate
active
06628698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA reception apparatus and power control method therefor which are used for a mobile communication system and, more particularly, to a CDMA reception apparatus for performing RAKE reception and a power control method for the apparatus.
2. Description of the Prior Art
Conventionally, a mobile communication system using CDMA (Code Division Multiple Access) has been known.
In this CDMA mobile communication system, when data is to be transmitted from a mobile station to a base station, transmission data is transmitted after it is spread by using a corresponding one of spreading codes assigned to the respective mobile stations, and the base station demodulates the transmission data from each mobile station by despreading the data by using the spreading code assigned to each mobile station.
Likewise, data transmitted from a base station to a mobile station is also spread by a corresponding one of the spreading codes assigned to the respective mobile stations before it is transmitted. The resultant data is then transmitted.
In urban areas, in particular, various obstacles are present between a base station and a mobile station, and hence radio waves from the base station are often reflected by these obstacles and reach the mobile station. In such a situation, there are many reflected waves, which are reflected by various obstacles and reach the mobile station, between the base station and the mobile station as well as direct waves that directly reach the mobile station. That is, a so-called multi-path, in which there are a plurality of routes through which radio waves reach the mobile station, occurs.
The respective multi-path radio waves reach the mobile station with delay times corresponding to the respective routes. The mobile station therefore can improve reception quality owing to a path diversity effect by combining the multi-path radio waves in consideration of the delay times. This reception method will be referred to as a RAKE reception method.
A reception apparatus using this RAKE reception method needs to have fingers for despreading and the like equal in number to paths to a RAKE combiner. If, therefore, the number of paths to the RAKE combiner is too large, many fingers are required, resulting in increases in the size and cost of the apparatus. Considering that a mobile station moves all the time, the manner in which a multi-path occurs always changes. In some case, therefore, the use of too many fingers cannot allow the RAKE combiner to obtain a satisfactory reception quality improving effect, i.e., a path diversity effect.
For this reason, it is necessary to set the number of fingers to be set in the apparatus so as to obtain a reception quality improving effect by the RAKE combiner, i.e., a path diversity effect, to such an extent that the apparatus size does not increase too much.
In such a situation, in a CDMA reception apparatus having a limited number of fingers, the delay times in the respective fingers must be controlled to reliably capture multi-path radio waves.
As a conventional reception apparatus that solves this problem, the reception apparatus disclosed in Japanese Unexamined Patent Publication No. 9-181704 is available.
FIG. 1
is a block diagram showing the arrangement of a reception apparatus disclosed in Japanese Unexamined Patent Publication No. 9-181704. The first conventional apparatus will be described below with reference to FIG.
1
.
Reference numeral
100
denotes a terminal to which a reception input spread signal is input;
200
, a tracking finger for performing tracking and despreading; and
300
, a search finger for detecting the level of a reception signal in each phase.
Reference numeral
402
denotes a RAKE combining path selecting section for selecting a phase of a spreading code in accordance with signals from the search finger
300
and tracking finger
200
.
Reference numeral
403
denotes a pilot interpolation absolute synchronous detector for performing synchronous detection of the signal despread by the tracking finger
200
.
Reference numeral
404
denotes a long code spreading code replica generator for supplying, to the tracking finger
200
or search finger
300
, a spreading code replica corresponding to a specific channel to be used. The tracking finger
200
or search finger
300
uses this spreading code replica after delaying it by a predetermined amount through a spreading code replica delay section
206
or
305
.
Reference numeral
405
denotes a RAKE combiner for combining signals from the respective paths; and
410
, an output terminal.
Reference numerals
201
,
202
,
203
, and
310
denote multipliers each serving to despread a reception signal by multiplying it by a spreading code replica;
204
,
250
,
207
, and
302
, integration dump circuits each serving to perform integration for a predetermined period of time;
208
,
209
, and
303
, amplitude squaring circuits each serving to detect a signal level by performing amplitude squaring detection; and
304
, a reception level memory for storing an output from the squaring circuit
303
.
Reference numeral
210
denotes an adder for adding an output from the amplitude squaring circuit
208
to an output from the amplitude squaring circuit
209
with opposite polarities to generate a chip timing error signal associated with the spreading code replicas.
Reference numeral
211
denotes a loop filter for averaging the chip timing error signals from the adder
210
and outputting the resultant data. The data output from the loop filter
211
is input to a spreading code replica timing control signal generating section
212
. In accordance with an output from the spreading code replica timing control signal generating section
212
, the phase of the spreading code replica used by the RAKE combining path selecting section
402
for despreading.
The operation of the conventional technique shown in
FIG. 1
will be described below.
The tracking finger
200
performs despreading by using a spreading replica code corresponding to a delayed path designated by the RAKE combining path selecting section
402
on the basis of the reception level detection information of all the chip phases of the search finger
300
. The signal obtained by this despreading is demodulated.
As a demodulation scheme, delay detection, synchronous detection, or the like is available. In absolute synchronous detection, an absolute phase of reception must be estimated. In this prior art, the pilot interpolation absolute synchronous detector
403
performs absolute synchronous detection by estimating the phase of each information symbol by using a pilot signal and the phase of a pilot symbol as a reference phase.
In the tracking finger
200
, the multipliers
201
and
202
perform correlation detection by using a reception spread/modulated signal and a replica code obtained by shifting a spreading code replica phase synchronized with the spreading code phase of a reception signal from each path by ±&Dgr; phase, and the integration dump circuits
204
and
205
performs integration for a predetermined period of time. The amplitude squaring circuits
208
and
209
then perform amplitude squaring detection to remove data modulation components and instantaneous phase variation components.
The adder
210
adds the amplitude square outputs of the spreading code replica obtained by the +&Dgr; phase shift and the spreading code replica obtained by the −&Dgr; phase shift with opposite polarities to generate a chip timing error signal associated with the spreading code replicas.
The loop filter
211
averages these chip timing error signals. The phase of the spreading code replica is updated in accordance with an output signal from the loop filter
211
.
This phase update information is input to the RAKE combining path selecting section
402
. The RAKE combining path selecting section
402
manages RAKE combining paths in real time to prevent overlaps between paths.
The RAKE combining path selecting sec
Pham Chi
Scully Scott Murphy & Presser
Tran Khanh Cong
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