Spreading code sequence acquisition system and method that allows fast acquisition in code division multiple access (CDMA) systems

Abstract

Methods for generating code sequences that have rapid acquisition properties and apparatus which implement the methods by processing spreading codes on in-phase and quadrature channels. A first method combines two or more short codes to produce a long code. This method may use many types of code sequences, one or more of which are rapid acquisition sequences of length L that have average acquisition phase searches r=log2L. Two or more separate code sequences are transmitted over the complex channels. If the sequences have different phases, an acquisition may be done by acquisition circuits in parallel over the different code sequences when the relative phase shift between the two or more code channels is known. When the received length L codes or the length L correlation codes used to find the phase of the received codes have a mutual phase delay of L / 2, the average number of tests to find the code phase of the received code is L / 4. The codes sent on each channel may be the same code, with the code phase in one channel being delayed with respect to the other channel, or they may be different code sequences.

Description

BACKGROUND OF THE INVENTIONThe present invention generally pertains to Code Division Multiple Access (CDMA) communications, also known as spread-spectrum communications. More particularly, the present invention pertains to a new system and method employing a new code sequence design for providing fast acquisition of a received spreading code phase in a CDMA communications system.DESCRIPTION OF THE RELEVANT ARTRecent advances in wireless communications have used spread spectrum modulation techniques to provide simultaneous communication by multiple users. Spread spectrum modulation refers to modulating a information signal with a spreading code signal; the spreading code signal being generated by a code generator where the period Tc of the spreading code is substantially less than the period of the information data bit or symbol signal. The code may modulate the carrier frequency upon which the information has been sent, called frequency-hopped spreading, or may directly modulate the...

AI Technical Summary

Benefits of technology

Rapid acquisition of the correct code phase by a spread-spectrum receiver is improved by designing spreading codes which are faster to detect. The present embodiment of the invention includes a new method of generating code sequences that have rapid acquisition properties by using one or more of the following methods. First, a long code may be constructed from two or more short codes. The new implementation uses many code sequences, one or more of which are rapid acquisition sequences of length L that have average acquisition phase searches r=log2L. Sequences with such properties are well known to those practiced in the art. The average number of acquisition test phases of the resulting long sequence is a multiple of r=log2L rather than half of the number of phases of the long sequence.

Second, a method of transmitting complex valued spreading code sequences (In-phase (I) and Quadrature (Q) sequences) in a pilot spreading code signal may be used rather than transmitting real valued sequences. Two or more separate code sequences may

Problems solved by technology

Related problems of such a system include: handling multipath fading effects.

The problems associated with the prior art systems focus around reliable reception and synchronization of the receiver despreading circuits to the received signal.

The presence of multipath fading introduces a particular problem with spread spectrum receivers in that a receiver must somehow track the multipath components to maintain code-phase lock of the receiver's despreading means with the input signal.

Prior art receivers generally track only one or two of the multipath signals, but this method may not be satisfactory because the combined group of low power multipath signal components may actually contain far more power than the one or two strongest multipath components.

Such as rural telephone systems and telephone systems in underdeveloped countries, has proved to be a challenge in recent years.

The problems associated with the prior art systems focus around reliable reception and synchronization of the receiver despreading circuits to the received signal.

Since spreading code sequences in a communications system which supports a relatively large number of users may be very long with a corresponding long code period, one particular problem associated with prior spread spectrum receivers is to rapidly determine the correct code phase of a received spread spectrum signal.

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