Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-10-02
2002-11-12
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S514000, C375S325000, C455S063300
Reexamination Certificate
active
06480479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CDMA cellular radio transmission system for use in digital cellular mobile communication and the like.
2. Description of the Related Art
In digital cellular mobile communication, a multiple access method means a line connection method when a plurality of stations simultaneously communicate with one another in the same band zone. CDMA, that is, Code Division Multiple Access is a technique in which multiple access is performed by means of spectrum spread communication for transmitting an information signal spectrum by spreading the spectrum over a band sufficiently wide in comparison with the original information band width and may also be called Spectrum Spread Multiple Access (SSMA). A direct spread method is a method of multiplying an information signal directly by a spread sequence code in the spread process.
Of the detection method in digital communication, a coherent detection method has excellent static characteristics in comparison with a delay detection method and is a method in which Eb/IO necessary for obtaining a certain mean bit error rate is lowest. Moreover, a coherent detection scheme with interpolation has been proposed to compensate transmission signal distortion due to fading (Masaichi Sanbe “Method of Compensating for Fading Distortion of 16 QAM for Land Mobil Communication” JECS Paper B-11, Vol. J72-B-11 No. 1 pp. 7-15, 1989). According to this method, a pilot symbol
701
is, as shown in
FIG. 7
, inserted in an information symbol to be transmitted with each period T so as to make wave detection by estimating a channel transfer function, that is, the circuit condition. Further, a method which apply the above method to the direct spread CDMA has been proposed (Azuma, Taguchi, Ohono “Characteristics of Insert-Type Coherent detection RAKE in DS/CDMA” JECS Technical Paper RCS94-98, 1994). There is also a pilot channel as a method enabling coherent detection in the direct spread CDMA. As shown in
FIG. 8
, in this method, one pilot channel
801
as a reference detection signal is continuously transmitted to be independent of channels for transmitting information data.
FIG. 4
shows the structure of a base station in a conventional CDMA cellular radio transmission system using a pilot channel. In a forward-link, transmission data (
2
) to (m) of mobile stations m−1 (1<m) are each spread by spread codes (
2
) to (m), and the spread data are then multiplies by weight before being multiplexed. A channel for use in transmitting the transmission data from each mobile station such as information data, control data and the like is called a “communication channel”. The aforementioned weight is used for transmission power control in the forward-link so as to add weight to transmission power among transmission channels. In a pilot channel
401
, on the other hand, transmission data (
1
)
402
is spread by a spread code (
1
)
403
in a spread circuit
404
, and the spread data is multiplied by weight W (
1
). The spread data in the communication channels
406
to
411
are then multiplexed in a multiplex circuit
412
, and the multiplexed data is up-converted by a radio transmission unit
413
before being transmitted from an antenna
414
. At this time, since no information needs to be transmitted with the transmission data (
1
)
402
, it may be unmodulated data (totally 0 or 1).
FIG. 5
shows the structure of a mobile station in the conventional CDMA cellular radio transmission system using a pilot channel. As shown in
FIG. 5
, the signal received from an antenna
501
is down-converted in a radio reception unit
502
. In a pilot channel
503
, a phase estimation circuit
511
detects phase information
512
from the output of a correlation circuit
505
, and transfers the detected result to the detection circuit
516
of a communication channel
513
. In the communication channel
513
, a detection circuit
516
subjects the signal inversely spread with a spread code i (i=2 to m) in a correlation circuit
515
to coherent detection on the basis of the phase information
512
,and a binary value decision circuit
517
outputs reception data
518
.
On the other hand, the pilot channel can be used as information other than coherent detection. In
FIG. 5
, reception power for each sampling (phase) is calculated in a power detection circuit
506
from the output of the correlator of the pilot channel
503
, and a chip synchronous signal
508
is output by integrating (filtering) the reception power with a predetermined time constant in a chip synchronous circuit
507
. This chip synchronous signal
508
is used to determine the phase of inverse spread with a spread code (i)
514
in the correlation circuit
515
of the communication channel
513
. In the case of a system wherein any other cell transmits pilot channels and the same spread code (
1
)
504
is used with shifting the phase, it is possible to obtain other-cell signal level information
510
from the output of the power detection circuit via an other-cell monitor circuit
509
. At this time, the transmission power of the pilot channel required to obtain the chip synchronous signal
508
and the other-cell signal level information
510
can be lower than the power required for coherent detection, because the output of the power detection circuit is integrated in the chip synchronous circuit
507
and the other-cell monitor circuit
509
.
Moreover, Unexamined Japanese Patent Publication (kokai) No. 7-76049 discloses that the base station controls the directivity of a transmission antenna on a communication channel to make transmission so as to deal with the suppression of interference.
FIG. 6
shows the situation in which the directivity is controlled. A base station
601
transmits signals to three mobile stations
602
,
603
,
604
while controlling the directivity of communication channels in the three directions of A, B, C. On the other hand, a pilot channel to be transmitted as a reference signal for coherent detection needs transmitting without directivity, because the pilot channel is commonly used for the communication channels. At this time, the propagating path of the pilot channel is different from that of the communication channel. Namely, as shown in
FIG. 6
, paths
605
,
606
refer to the situation in which the pilot channel transmitted without directivity has propagated through the path different from that of the communication channel, that is, the communication channel transmitted to have the directivity A never pass through the paths
605
,
606
. Therefore, the phase information of the pilot channel signal differs from that of communication channel signal.
In the conventional multiple transmission of a pilot channel, it is necessary to transmit the pilot channel with relatively strong power with respect to any other communication channel which may interfere with the pilot channel in order to increase the reliability of the pilot channel and improve coherent detection performance. More specifically, with reference to
FIG. 4
, the weight W (
1
)
405
tends to become large in value (W
1
>Max W
2
. . . Wm) as compared with the communication channel. If, however, W (
1
) is increased, the reliability of the reference signal for coherent detection is increased on one hand but since interference with communication channels (of any other station) is also increased, there arises a problem resulting in lowering communication channel quality.
Moreover, when the base station controls the directivity of the transmission antenna on a communication channel basis, the phase information of the pilot channel is impossible to use for making the coherent detection of the communication channel since the phase information obtained from the pilot channel differs from the detection phase of the communication channel.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an excellent CDMA cellular radio transmission system capable of reducing the interference (interference among stati
Kato Osamu
Miya Kazuyuki
Watanabe Masatoshi
Chin Wellington
Matsushita Electric - Industrial Co., Ltd.
Tran Maikhanh
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