Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-06-08
2002-04-09
Luther, William (Department: 2644)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C375S143000, C375S152000
Reexamination Certificate
active
06370130
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread spectrum communication system.
2. Background of the Invention
Spread spectrum communication systems have received attention due to their high frequency efficiency as the number of users of the land mobile communication steeply increases. Among various types of spread spectrum communication, the DS-CDMA cellular system is going to be standardized by an international committee on communication.
The DS-CDMA system is classified into two types: strictly synchronous base stations and asynchronous base stations. The global positioning system (GPS) or other systems are used in the synchronous system for synchronization. The acquisition is easy for the synchronous system only by a synchronization of a long code which is common to every base station. Each base station has a delay time of the long code different from the delay times of other base stations. The peripheral cell search for the hand-over is quick because a mobile station receives a delay information from base stations.
In the asynchronous system, different spreading code sequences are allocated to the base stations from one another. The initial cell (sector) search takes a longer time for the mobile station because it is necessary to identify a spreading code sequence. It takes a lot of time when the spreading code is long. However, the search time may be decreased by information on the spreading code from base stations of adjacent cells, and it is advantageous that synchronization by signals from satellites is unnecessary.
A cell search method for quick acquisition in the asynchronous system is proposed in “Two-stage Rapid Long Code Acquisition Scheme in DS-CDMA Asynchronous Cellular System” by Kenichi HIGUCHI, Mamoru SAWAHASH
1
and Fumiyuki ADACHI, Technical Report of IEICE, CS96-19, RCS96-12(1996-05). Composite codes are generated by corresponding long codes LC0 to LCX for identifying base stations and short codes SC0 to SCY for identifying channels. The short codes are common in all the cells and the code SC0 is allocated to common control channel (perch channel). The mobile station despreads a first short code SC0 by a matched filter that detects the timing of the long code. Then, the long codes are identified by the matched filter or a sliding correlator. The number of cells search is decreased to be (Length and Phase of spreading code) compared to the number of (Number of spread code length×Number of spread code phases) in the asynchronous system above.
Multi-media communication is required for transmitting a plurality of signals of different transmission rates. In the DS-CDMA cellular system, a type of variable spread ratio and a parallel multi-code type are proposed. Fading compensation is indispensable for these systems for high quality service.
FIG. 47
shows a conventional receiver of a DS-CDMA system having a receiver antenna
101
for receiving a spread spectrum signal, a high frequency receiving portion
102
for converting the spread spectrum signal into an intermediate frequency signal, a divider
103
for dividing the intermediate frequency signal into two signals which are input to multipliers
106
and
107
. A signal (cos &ohgr;t) of the intermediate frequency is generated by an oscillator
104
to be input to the multiplier
106
. A signal from the oscillator
104
is shifted by &pgr;/2 by a phase shifter
105
and is input to the multiplier
107
. The multipliers
106
and
107
multiply the divided signals by the signal from
104
and
105
, respectively. The outputs from the multipliers
106
and
107
are passed through low-pass filters
108
and
109
so that the base band signal of an in-phase component (I-component) and a quadrature component (Q-component) is extracted.
The I- and Q-components are multiplied at a complex matched filter
110
by PN code sequence supplied from a EN generator
111
so as to be despread. In the multi-path environment, the despread components have a plurality of peaks. The despread I- and Q-components are processed successively by a delay detection circuit
112
, a signal level detector
114
and a phase correction portion
116
.
The delay detection circuit
112
detects a signal of one path, for example the first path, of a plurality of paths and inputs the signal to a frame synchronization detector
113
. The received signal has a pilot symbol already-known and four symbols are included in a slot. The frame synchronization detector
113
judges whether the four symbols are identical to a predetermined delay pattern so as to detect the frame synchronization. The detector outputs a frame synchronization signal to the phase correction portion
116
. The level detection portion
114
detects the signal level of the I- and Q-components. The multi-path selection portion
115
selects a plurality of paths with higher power from the maximum power and outputs a signal to the phase correction portion.
The phase correction portion
116
has a plurality of phase correction means corresponding to the number of multi-paths and a selector for inputting the despread I- and Q-components according to the signal from the portions
113
and
115
. The despread signal of the matched filter
110
is input through the selector at timing of the phase correction means so that the phase correction means performs fading compensation of the despread signal.
It is necessary in frame synchronization that a multiplication of analog signals is implemented by a large circuit. Accordingly, a lot of electrical power is consumed.
FIG. 48
shows a receiver for a semi-direct conversion for a spread spectrum communication. The receiver has an antenna
200
for receiving a signal of a band-pass filter (BPF)
211
, a low noise amplifier (LNA)
212
and a frequency converter
213
for outputting a signal of intermediate frequency, fc, by mixing a local oscillation signal of frequency fL. The frequency fL, is for example, a boundary frequency of a frequency band of the received signal. In the final output, a DC offset is reduced but a frequency offset remains. When the received signal is a spread spectrum signal, despreading is performed after the direct conversion. The direct conversion is more useful for other systems such as PHS than spread spectrum communication systems.
The output of the frequency conversion is in the frequency domain at the positive and negative side on the frequency coordinate. A channel of a frequency exists in the negative domain equal to the frequency of the signal to be received. These two signals are separated by a channel filter having a complex coefficient. The output of the converter
213
is quadrature detected and over-sampled, then transformed by a Hirbert transformation portion
215
.
The output of I- and Q-components of the portion
215
is input to the channel filter
216
so that signals of adjacent channels are reduced and input to a demodulator
217
. The demodulated signal is reproduced to the data transmitted by a data decision portion
218
.
The Hirbert transformation needs rather complicated circuit.
SUMMARY OF THE INVENTION
The present invention solves the above-discussed conventional problems and has an object to provide a spread spectrum communication system capable of high speed cell search.
The present invention has another object to provide a spread spectrum communication system applicable to multi-media communication.
The present invention has another object to provide a spread spectrum communication system of high reception quality even during multi-path fading.
The present invention has another object to provide a spread spectrum communication system capable of high speed frame synchronization.
The present invention has another object to provide a semi-direct conversion receiver of a simple and small scale circuit.
According to the present invention, a receiver for receiving a traffic channel and a common control channel has a plurality of matched filters at least one of which is selectively available for the traffic or the common control cha
Shou Guoliang
Suzuki Kunihiko
Yamamoto Makoto
Zhou Changming
Zhou Xuping
Luther William
Pillsbury WInthrop LLP
Yozan Inc.
LandOfFree
Spread spectrum communication system 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 communication system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spread spectrum communication system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893471