Pulse or digital communications – Spread spectrum
Reexamination Certificate
1999-06-14
2001-08-28
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
C370S503000
Reexamination Certificate
active
06282229
ABSTRACT:
BACKBROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a method and apparatus for receiving a spread spectrum (SS) signal which is to be synchronized with a Pseudo-Noise (PN) sequence for de-spreading.
2. Description of the Prior Art
The synch chip timing between the spread spectrum (SS) signal and the Pseudo-Noise (PN) sequence which is used for de-spreading is detected by independent antennas to combine the multipath signals from each antennas, as disclosed, for example, in JP 9-64845 A (1997).
In a conventional SS signal receiver under a direct sequence (DS) system as shown in
FIG. 5
, independent receiving units
111
to
11
K with antennas
101
to
10
K are connected in parallel with antenna diversity combining unit
121
. Here, receiving units
111
to
11
K are identical.
The signal received by antenna
101
and the spread spectrum (SS) sequence from PN sequence generator
6
are inputted into sliding correlation calculation means
7
.
The calculation of the sliding correlation is a multiplication and summation of the SS signal and the PN sequence over a prescribed period which is given by one to several symbol periods in general.
The correlation sequence level outputted from sliding correlation calculation means
7
has peaks at the synch chip timings of a plurality of multipath signals received by antenna
101
, as shown in FIG.
2
.
Then, the correlation sequence is inputted into correlation averaging means
8
which averages the correlation values in each of the chip timings over a prescribed period. Then, correlation averaging means
8
outputs delay profile
91
.
Peak detector means
9
outputs N synch chip timings of the multipath signals, by detecting N peaks in delay profile
91
. For example, peak detector means
9
detects N peaks in the order of their levels which are distant by one or more chips with each other.
Then, the synch chip timings corresponding to the N peaks are inputted into delay circuits
21
to
2
N, respectively.
The PN sequences outputted from PN sequence generator
6
are inputted into delay circuits
21
to
2
N, and then, inputted into multipliers
31
to
3
N to be multiplied by an SS signal from antenna
101
.
The de-spread SS signals are inputted into coherent detector means
41
to
4
N which compensates for the phase shift of de-spread SS signal on the propagation path and are combined by path combining means
5
.
Further, the outputs from path combining means in each of receiving units
111
to
11
K are fed into antenna diversity combining means
121
.
In general, the correlation sequence which is outputted from sliding correlation calculation means
7
has peaks at the synch chip timings of the multi-path waves received by antenna
101
. The peak levels at the synch chip timings vary due to the fading caused by the movement of the connected mobile station, as shown in FIG.
3
.
Therefore, it is difficult to detect the synch chip timings due to the fading.
In order to discriminate the peaks of the correlation level of the synch chip timings from the noise level, the correlation at each of the chip timings outputted from sliding correlation calculation means
7
is averaged over a prescribed period by correlation averaging means
8
. Thus, correlation averaging means
8
can output delay profile
91
which is clearly discriminated from the noise level.
However, it takes a long time to complete the averaging procedure in correlation averaging means
8
.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a spread spectrum (SS) signal receiver, wherein the synch chip timings of multipath signals can be detected rapidly, even when a doppler frequency is low due to a slow movement of a mobile station.
In the method and apparatus for receiving spread spectrum (SS) signals of the present invention, SS signals are received by a plurality of antennas. Then, a delay profile as a correlation between an SS signal and a prescribed PN sequence for each antenna is calculated. Then, the delay profiles calculated for every antenna are combined. Then, the synch chip timings are detected from the combined delay profile. Then, the detected synch timings are utilized commonly by each receiving unit. Then, each multipath signal is de-spread on the synch chip timing. Then, the de-spread multipath signals are combined in each receiving unit to obtain a path diversity effect. Finally, the combined signals in each of the receiver units are combined to obtain an antenna diversity effect.
In short, each SS signal received by each antenna is used to calculate each delay profile in parallel, from which a synch chip timing is detected. The detected timing is fed commonly to each antenna.
According to the present invention, a stable delay profile can be obtained in a shorter period of time, in comparison with the conventional technique wherein the correlation is averaged before combining the delay profiles. In the present invention, the synch chip timing is detected after combining the delay profiles from a set of independent antennas.
Accordingly, the tracking capability can be improved, even when the synch chip timing varies rapidly, due to the fast movement of mobile station.
Further, according to the present invention, the number of peak detector means is reduced, because the peak is detected after combining the delay profiles.
REFERENCES:
patent: 5237587 (1993-08-01), Schoolcraft
patent: 5652765 (1997-07-01), Adachi et al.
patent: 5790588 (1998-08-01), Fukawa et al.
patent: 5844935 (2000-07-01), Shoji
patent: 6067293 (2000-05-01), Shoji
patent: 6081547 (2000-07-01), Miya
patent: 6094449 (2000-07-01), Komatsu
patent: 7-74687 (1995-03-01), None
patent: 9-64845 (1997-03-01), None
patent: 10-65591 (1998-03-01), None
Corrielus Jean
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Pham Chi
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