Multiplex communications – Channel assignment techniques – Combining or distributing information via code word channels...
Reexamination Certificate
1997-08-26
2001-06-26
Marcelo, Melvin (Department: 2663)
Multiplex communications
Channel assignment techniques
Combining or distributing information via code word channels...
C375S139000
Reexamination Certificate
active
06252882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a chirp spread spectrum signal multiple access apparatus in which a signal multiple access is carried out by offsetting a plurality of signals in view of time under application a chirp signal as a spread spectrum code.
2. Brief Description of the Related Art
As the prior art signal multiple access system using spread spectrum, it is possible to provide a code division multiple access communication apparatus disclosed in a gazette of Japanese Patent Laid-Open No. Hei 7-50649, for example. In this code division multiple access communication apparatus, an information code is processed in direct-spread with a spread code and its major constitution is as indicated in FIG.
8
.
In the code division multiple access communication apparatus shown in
FIG. 8
, the multiple access number (n) is defined as
2
and a symbol interval of the information code is defined as Ts. A transmission side of the code division multiple access communication apparatus is comprised of information code generators
201
,
202
, spreading circuits
203
,
204
, spread code generator
205
, delay circuit
206
, adder
207
and modulator
208
. At the receiving side, it is comprised of a de-spreading filter
210
, delay circuit
211
and samplers
212
,
213
.
At the receiving side of the code division multiple access communication apparatus, transmission code generated at the information code generator
202
is convolved by the spreading circuit
204
with a spreading code outputted from the spread code generator
205
so as to spread it. In addition, at the transmission side of it, the transmission code generated from the information code generator
201
is also convolved with the spread code outputted from the spread code generator
205
so as to spread it.
If the outputs from the spreading circuits
203
,
204
are added and made composite by the adder
207
, an output from the spreading circuit
203
and an output from the spreading circuit
204
can not be discriminated at the receiving side and further an output from the information code generator
201
and an output from an information code generator can not be separated at the receiving side. In view of this fact, at the transmission side, a delay spreading code in which a spreading code outputted from the spreading code generator
205
is delayed only by Ts/2 with the delay circuit
206
is supplied to the spreading circuit
203
.
Output signals from the spreading circuit
203
and the spreading circuit
204
are added by the adder
207
and outputted as one adding signal. At the modulator
208
, modulation for converting a signal into a signal format which can easily be transmitted in respect to the adding signal is carried out and then a modulation signal is transmitted and outputted from the modulator
208
.
In turn, at the receiving side, a correlative calculation is carried out with a demodulation signal and the same spreading code as the spreading code generated by the spreading code generator
205
by the inverse spreading filter
210
having a modulation signal received and inputted thereto. Filtering signals outputted from the inverse spreading filter
210
are displaced by Ts/2 and divided into two segments, respectively, one of the segments is extracted by a sampler
212
and the other segment is delayed by the delay circuit
211
only by Ts/2, thereafter it is extracted with the sampler
213
at the same timing as that for the sampler
212
so as to attain a sample signal supplied to the demodulation receiving processing.
In this way, if the timings for the spreading codes are displaced to perform a signal multiple access processing, it becomes possible to perform a faster signal transmission under the same frequency range width.
A case in which a signal multiple access processing with a direct spreading using the aforesaid spreading code will be studied in reference to a case in which it is applied to a portable terminal and the like, for example. In general, a chip rate of the spreading code in the direct spreading system is set to be more than ten times of a symbol rate (1/Ts) of the information code, although due to this fact, there may occur a problem that a calculation speed of the spreading circuit may become remarkably fast and a power consumption of element is increased. In particular, since the portable terminal uses battery cells as its power supply, it is difficult to employ a communication system showing a high power consumption.
SUMMARY OF THE INVENTION
The present invention has been completed in order to solve the aforesaid problems and it is an object of the present invention to provide a chirp spread spectrum code multiple access apparatus capable of realizing a more total superior signal transmission under such a circumstance as one in which a small-sized and light weight device or low power consumption is required even if a transmission characteristic is slightly deteriorated as found in the portable terminal.
According to one aspect of the invention, there is provided a spread spectrum signal multiple access apparatus comprised of a transmission device and a receiving device performing a signal multiple access processing under application of spread spectrum, wherein
the transmission device includes:
a separator for dividing transmission data into n signals (n is integer more than 1), distributing and outputting it as the number n of divided signals;
delay means for applying a different delay time to each of the number n of divided signals and outputting them as the number of (n) of transmission delay signals;
adder for adding the number n of transmission delay signals and outputting the transmission added signals;
a chirp filter for convolving the transmission added signals to chirp signals and outputting them as transmission convolving signals; and
a modulator for modulating the transmission convolving signals and outputting them as modulated signals,
the receiving device includes:
an inverse chirp filter for receiving and inputting the modulation signal, convolving it with a signal having an inverse characteristic opposite to the chirp signal and outputting it as a received convolving signal;
the number of n−1 of delay circuits for delaying each of the receiving convolving signals and outputting them as receiving delay signals;
the number of n samplers for sampling the number n−1 of receiving delay signals and the receiving convolving signals and outputting sample signals; and
an adder for adding and combining the number n of sample signals and outputting the receiving added signals as demodulation receiving signals.
According to another aspect of the invention, there is provided a spread spectrum signal multiple access apparatus comprised of a transmission device and a receiving device performing a signal multiple access processing under application of spread spectrum, wherein
the transmission device includes:
a separator for time sharing the number n of transmission data signals (n is an integer more than 1), distributing and outputting them as time-shared signals;
the number n of chirp filters for generating and outputting transmission chirp filter signals in which only absolute delay times in respect to the chirp signals in an impulse response for the number of (n) of time-shared signals are different, respectively;
an adder for adding the number n of transmission chirp filter signals and outputting the transmission added signals; and
a modulator for modulating the transmission added signals and outputting them as modulated signals; and
the receiving device includes:
an inverse chirp filter for receiving and inputting the modulated signals, convolving them with a signal having a characteristic opposite to that of the chirp signal, and outputting them as received convolving signals;
the number n−1 of delay circuits for delaying each of the received convolving signals in different delay time, respectively, and outputting them as received delay signals;
the number n of samplers for sampling the number n−1 of rece
Kwoh Jasper
Marcelo Melvin
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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