Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
2000-02-23
2002-03-12
Rao, Seema S. (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C375S147000, C370S519000
Reexamination Certificate
active
06356542
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a reception path search method and searcher circuit for use in such method of a CDMA (Code Division Multiple Access) reception device.
Description of the Prior Art
The CDMA communication system enables communication with high quality to be implemented under very low Eb/No (signal power in every 1 bit
oise power in every 1 Hz). The CDMA communication system is used in conjunction with diversity technique using multi-path propagation (RAKE), the technique of large error-correcting code of coding gain, transmission power control technique and so forth. The CDMA communication system in conjunction with the above techniques brings such high quality communication. In recent years, the CDMA communication is applied extensively in mobile communication and so forth.
On the other hand, in the CDMA communication system, the reception signal is diffused using diffusion code. The diffused reception signal is subjected to inverse-diffusion by a diffusion code in the reception side. At the time of the inverse-diffusion of the diffused reception signal,
20
chip timing (reception timing) of the diffusion code should be accurately synchronized with the reception signal diffused by using the diffusion code indispensably. Particularly, in the case of mobile communication, there exist a great many reception paths which are changed from moment to moment. In such the case, the most appropriate reception path should be selected regularly. Reception timing of respective reception paths is necessary to be synchronized with reception signal to be followed correctly.
For instance, the Japanese Patent Application Laid-Open No. HEI 9-181704 (hereinafter referred to as a first prior art) discloses ‘MULTIPATH SEARCH METHOD’. In the multipath search method, the CDMA reception device is provided with a set of search-finger and plural sets of tracking-fingers. The search-finger detects intensity level of reception signal concerning reception timing corresponding to delay range of the reception path supposed previously. The search-finger selects the most suitable plural reception paths to allocate plural reception paths to respective tracking-fingers. The tracking-finger tracks the respective reception paths in detail.
FIG. 1
is a conception view showing basic operation of the above first prior art. Its (a) indicates a reception signal. The search-finger executes correlating detection with reception signal using diffusion code in which chip timing is changed gradually with information N symbol as search range. A delay profile with reception timing shown in (b) as the horizontal axis, and with intensity level of reception signal as the vertical axis is obtained. The intensity level of the reception signal is detected in such a way that the diffusion code is multiplied by the reception signal, before executing inverse-diffusion. Subsequently, such delay profile is integrated during fixed time by integrating-dump circuit. An amplitude square circuit executes amplitude square detection.
A control means shown in (d) selects three reception paths in the example of
FIG. 1
, in order of the largeness of the maximum value of the delay profile. The control means allocates the chip timing to respective tracking-fingers.
The tracking-finger shown in (c) executes inverse-diffusion of the reception signal using the diffusion code of each chip timing allocated previously to generate demodulating signal. The tracking-finger compares intensity of the reception signal which is subjected to inverse-diffusion using diffusion code whose chip phase is different by only ±&Dgr;, namely, causing the chip timing to be moved before and after, thus tracking delay variation of the reception path using DLL (Delay Lock Loop).
Furthermore, the search-finger continues search of the reception path periodically shown in (d). The reception path which is tracked by the tracking-finger overlaps with each other. When the reception path with large reception signal intensity level occurs by another cause. In such the cases, re-allocation of the reception path to the tracking-finger is implemented.
In the first prior art, the demodulating signal outputted from respective tracking-fingers are obtained above such steps. Such the demodulating signal is detected to be demodulated with phase of pilot-symbol inserted in respective time slots of reception signal as a standard, thus the output signal is obtained by the fact that RAKE-composition is executed.
It requires very large calculation quantity to obtain the delay profile while executing correlating detection with accuracy of ¼ to {fraction (1/16)} of the chip rate, for instance, in the above-described example, extending over wide search range such as extending over N symbols. For that reason, in the above-described first prior art, search of wide range according to the search-finger is restricted within fixed cycle. During this time interval, respective tracking-fingers monitor intensity level of the reception signal between two points with ±&Dgr;, before executing tracking of the reception path.
Furthermore, the official report of the Japanese Patent Application Laid-Open No. HEI 10-32523 (hereinafter referred to as a second prior art) discloses the technique for obtaining the delay profile with required accuracy. According to the technique, the reception signal undergoes sampling with relatively rough sampling frequency, for instance, a sampling frequency of ½ of the chip rate. It calculates mutual correlation between the diffusion code and, for instance, the known signal list obtained from the pilot symbol. The obtained correlation value of two samples per one chip is interpolated by an interpolation filter so that the delay profile with required accuracy is obtained.
FIG. 2
is a block diagram showing a constitution of the searcher circuit of the second prior art. The searcher circuit of
FIG. 2
comprises an A/D converter
101
for converting a complex base band signal obtained from radio band signal into a digital reception signal S, a list correlator
102
for obtaining mutual correlation between the digital reception signal S and well known signal list about fixed search range in every fixed cycle, an interpolation filter
103
for re-sampling an output signal R of the list correlator
102
with four times of sampling frequency of for instance, the A/D converter
101
, a power calculator
104
for obtaining power P of the mutual correlation signal which is re-executed sampling in the interpolation filter
103
, an averaging part
105
for obtaining the delay profile while adding to be averaged a mutual correlation signal power P extending over plural cycles, and a peak detector
106
for determining the most suitable reception timing “&tgr; opt” while obtaining peak “Popt” of the delay profile obtained by the averaging part
105
.
The digital reception signal S is indicated as time list data of complex number with in-phase component of the complex base band signal as real number part, and with orthogonal component as imaginary number part, namely as time list data of vector value.
The list correlator
102
calculates the mutual correlation value while multiplying the time list data by complex conjugate.
For instance, the sampling frequency of the A/D converter
101
is taken as two times of the chip rate. As shown in
FIG. 3
, 1 time slot is constituted by transmission signal which consists of L symbols is diffused with a diffusion rate M (number of chip of diffusion code per 1 symbol) to be transmitted. On this occasion, signal component of symbol of m+1 th order in a slot of n+1 th order is diffused to the time list data from S (2LMn+2Mn+&tgr;) to S (2LMn+2Mn+2M−1+&tgr;) when &tgr; is delay of reception path to the reception timing, namely known signal list Pn (i).
Consequently, from next formula, mutual correlation value Rnm (&tgr;) with respect to symbol concerned is obtained as a vector value.
Rnm(&tgr;)=&Sgr;i=0 to M−1S(2LMn+
a
Mn&
NEC Corporation
Rao Seema S.
Sam Phirin
LandOfFree
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