Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-06-05
2001-01-23
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
C375S134000, C375S136000, C375S142000, C375S145000, C455S522000
Reexamination Certificate
active
06178193
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a spread spectrum receiver. More specifically, the invention relates to a fading period detecting system for a synchronization acquisition and a transmission power control.
2. Description of the Related Art
In a multiple access system for mutual communication between a plurality of stations utilizing assigned frequency band, there has been proposed various communication systems, such as a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, code division multiple access (CDMA) system and so forth. In most of these systems, a base station is arranged in each of cells which is established by dividing a service area into small areas, and a subscriber terminal communicates with another subscriber terminal via the base station.
Amongst, the CDMA system which does not require burst synchronization, is suitable for a communication system having a large number of subscribers and is strong against interference and jamming. Therefore, the CDMA system has been attracting attention. The CDMA system employing a spread spectrum communication system is a multiple access system assigning mutually distinct spreading code series for respective users and performing spread modulation utilizing the same. Accordingly, even in one cell, the same frequency can be used by a plurality of users.
As is well known, the spread spectrum communication system is premised to use a spreading code synchronized with the spreading code used at the transmission side in demodulation by despreading of a reception signal. For example, when the diffusion signal is shifted over one chip due to influence of variation of propagation path delay or so forth due to multiple path or so forth, it becomes difficult to accurately demodulate data. Therefore, a technology for synchronization acquisition (initial synchronization) for reducing a phase difference of transmission side and reception side spreading code series (normally, less than or equal to half chip) and synchronization tracking (synchronization holding) for maintaining a necessary chip accuracy so as not to lose track of the once acquisited synchronization position due to influence of noise or demodulation, are indispensable.
Conventionally, this kind of synchronization acquisition circuit is employed for the purpose of acquisition of chip phase synchronization of the spreading code in the spread spectrum receiver, as disclosed in Japanese Unexamined Patent Publication No. Heisei 7-202843, for example.
FIG. 11
is a block diagram showing one example of the conventional spread spectrum receiver and its synchronization acquisition circuit. As shown in
FIG. 11
, the conventional spread spectrum receiver has an orthogonal demodulator
11
connected to a reception antenna
10
, an A/D converter
12
for performing analog-to-digital conversion of an output of the orthogonal demodulator
11
, a RAKE demodulator
30
connected to an output of the A/D converter
12
, a synchronization acquisition tracking unit
40
similarly connected to the output of the A/D converter
12
and a decoder
14
connected to the output of the RAKE demodulator
30
.
The RAKE demodulator
30
performs maximum ratio synthesis of upper three outputs in the order of electric power among correlated demodulation output. Each correlated demodulation output by each of three demodulation circuits
31
-
1
to
31
-
3
which perform correlated demodulation on the basis of phase information obtained from the synchronization acquisition tracking unit, is output with synthesis by a RAKE synthesizing circuit
32
.
In the synchronization acquisition tracking unit
40
, a correlated power is calculated by a correlator
41
. The correlated power is integrated by an integrator
42
. An integrated output of the integrator
42
is sequentially switched by a switch
43
at a period Tr (about Tw/100) which is sufficiently shorter than a Rayleigh fading period Tw (about several Hz to 100 Hz). The correlated power integrated by each of these periods are integrated by inputting to N in number of integrators
44
-
1
to
44
-N. Then at a timing where a preliminarily designated fixed integration period is reached, a switch
45
is switched for outputting phase shifting amounts corresponding to integrators among the integrators
44
-
1
to
44
-N outputting largest three integrated values. In a manner set forth above, synchronization acquisition is performed.
A problem encountered in the prior art set forth above is that the predeterminarily designated and fixed integration period does not match with an actual fading period. If the set fixed integration period is short, when the fading period is long, it is possible to perform integration for a falling down portion of fading. On the other hand, if the set integration period is long, when the fading period is short, integration can be performed for unnecessarily long period to slow-down follow-up of the path and whereby to cause degradation of synchronization acquisition ability.
The reason is that since the fading frequency is sequentially varied depending upon moving speed of a mobile terminal, an integration period of an optimal correlated value cannot be obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a spread spectrum receiver which can improve reception characteristics by enabling obtaining of an integration period of an optimal correlated value even upon variation of fading period.
According to one aspect of the present invention, a spread spectrum receiver for receiving a spread spectrum signal and demodulating the received signal on the basis of a synchronization phase detected by despreading of the received signal, comprises:
correlation computing means for controlling a phase of a spreading code over a search range and deriving correlation between the received signal and the spreading code;
integrating means for integrating correlation outputs of the correlation computing means in each phase condition of the spreading code over an integration period;
peak detecting means for deriving a synchronization phase by detecting a peak path from output of the integrating means;
demodulation means for demodulating the received signal according to the synchronization phase;
fading period computing means for deriving a relative transmission power on the basis of a transmission power offset with extracting a transmission power control information of a predetermined period transmitted from a counterpart for controlling a transmission power and deriving the integration period depending upon the relative transmission power; and
transmission means for deriving the transmission power according to the transmission power information and transmitting the derived transmission power.
According to another aspect of the present invention, a transmission power control method in a spread spectrum receiver for receiving a spread spectrum signal and demodulating the received signal on the basis of a synchronization phase detected by despreading of the received signal, comprises:
correlation computing step of controlling a phase of a spreading code over a search range and deriving correlation between the received signal and the spreading code;
integrating step of integrating correlation outputs of the correlation computing step in each phase condition of the spreading code over an integration period;
peak detecting step of deriving a synchronization phase by detecting a peak path from output of the integrating step;
demodulating step of demodulating the received signal according to the synchronization phase;
fading period computing step of deriving a relative transmission power on the basis of a transmission power offset with extracting a transmission power control information of a predetermined period transmitted from a counterpart for controlling a transmission power and deriving the integration period depending upon the relative transmission power; and
transmitting step of deriving the transmission power according
Chin Stephen
Ghayour Mohammad
McGuireWoods LLP
NEC Corporation
LandOfFree
Spread spectrum receiver and transmission power control method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spread spectrum receiver and transmission power control method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spread spectrum receiver and transmission power control method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2501949