Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-11-23
2001-08-14
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S143000, C375S142000, C375S150000, C375S152000, C370S342000
Reexamination Certificate
active
06275520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pseudo-noise generating apparatus for generating a pseudo-noise sequence used in the spreading modulation of a transmission signal in a CDMA (Code Division Multiple Access) communication system.
2. Description of the Related Art
In a CDMA communication system which uses a spreading code sequence whose period may extend to, for example, as much as several minutes, code synchronization must be established quickly by starting the spreading code sequence from the phase determined based on time data that the transmitting end sends through a control channel. Further, in a system in which a code sequence of a long period is divided into a plurality of sections each for use by a different station, it is required that the code sequence be quickly started from the phase to be used, and that when an assignment change request is issued to reduce mutual interference, the code sequence be restarted quickly from the assigned phase.
One possible method to arbitrarily set the phase of the pseudo-noise sequence used as a spreading code sequence is to supply a faster-than-usual clock to the pseudo-noise generator that generates the pseudo-noise sequence and shift its phase from the initial phase to the desired phase. This method, however, requires a high-speed clock to accomplish the shifting, and presents a problem particularly when the shift amount is large, because a very fast clock becomes necessary if the desired shift amount is to be obtained within a short time.
Another possible method is to utilize the shift additive nature of the pseudo-noise sequence and generate a phase-shifted code sequence by taking appropriate taps from the respective stages of a shift register in the pseudo-noise generator and EORing the tapped outputs. This method, however, has the problem that the tap positions for obtaining the desired shift amount must be determined by calculation and, if the number of shift register stages is large, it takes considerable time for calculation.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a pseudo-noise generating apparatus that can start from a desired phase in a short time.
According to the present invention, there is provided a pseudo-noise generating apparatus comprising: a pseudo-noise generator having a plurality of delay elements connected in series; a memory device for storing a selection pattern corresponding to a phase shift amount; a selector for selecting delay element outputs in the pseudo-noise generator in accordance with the selection pattern output from the memory device; and an adder for adding the delay element outputs selected by the selector, thereby outputting a phase-shifted version of a pseudo-noise sequence output from the pseudo-noise generator.
Preferably, the memory device stores a plurality of selection patterns corresponding to a plurality of different phase shift amounts, and outputs a selection pattern corresponding to one phase shift amount specified from among the plurality of phase shift amounts.
Preferably the apparatus further comprises: a shift register for accumulating therein the pseudo-noise sequence that the adder outputs; and a controller for accomplishing a desired phase shift as a sum of a plurality of phase shift amounts by issuing specification of a phase shift amount to the memory device and by transferring the pseudo-noise sequence accumulated in the shift register into the delay elements in the pseudo-noise generator.
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Mutagi, R.N. “Pseudo Noise Sequences for Engineers” Electronics & Communication Engineering Journal, vol: 8 2, Apr. 1996, pp 79-87.
Hamada Hajime
Kawabata Kazuo
Nakamura Takaharu
Obuchi Kazuhisa
Chin Stephen
Fujitsu Limited
Helfgott & Karas P.C.
Rupert Paul N
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