Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-04-15
2001-11-13
Patel, Ajit (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S208000, C370S335000, C375S130000
Reexamination Certificate
active
06317422
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of wireless communication systems and more particularly, to systems and methods of creating spreading codes in a CDMA system which are substantially orthogonal in a quasi-synchronous situation and thus resistant to misalignment caused by multi-path delays and/or time jitter of the system and/or misalignment of signals received from different users.
BACKGROUND OF THE INVENTION
For severely multipath dispersive environments, the downlink capacity of cellular Code Division Multiple Access (CDMA) systems, such as IS95, is limited by intra-cell interference. Downlink signals in a cell are orthogonal or substantially orthogonal at the transmitter (hereinafter the term orthogonal or substantially orthogonal includes the terms orthogonal and/or substantially orthogonal), but tend to suffer a loss of orthogonality due to multi-path propagation, time jitter (imprecise implementation errors), etc. The uplink capacity of CDMA systems, such as IS95, is also limited because the uplink signals are not orthogonal. However, orthogonal signals may be used for the uplink if different user symbols are received with timing alignment.
For nondispersive channels, time alignment of the signals results in orthogonality and rejection of the intra-cell interference. In reality, however, wireless channels are dispersive and propagation along multiple paths causes time misalignment in which case multi-path components will interfere with other multi-path components having a different delay. In this case it is generally only possible to align a single component from each signal. Therefore, orthogonality is partially lost due to the interference between non-aligned terms.
Accordingly there exists a need for a system and method of spreading which is resistant to misalignment (delay) caused by multi-path delays.
There also exists a need for a system and method of spreading which is resistant to interference caused by time jitter of the system.
A need also exists for a system and method of spreading which is resistant to interference caused by misalignment of the signals received from different users.
Accordingly it is an object of the present invention to provide systems and methods of spreading in CDMA systems which are resistant to effects of misalignment caused by multi-path propagation delays.
It is another object of the present invention to provide systems and methods of generating spreading codes which are resistant to effects of time jitter of the system.
It is a further object of the present invention to provide systems and methods of generating spreading codes which are resistant to effects of misalignment of signals from different users.
It is still another object of the invention to provide such codes which do not affect the data rate of the system.
These and other objects of the invention will become apparent to those skilled in the art from the following description thereof.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, these and other objects may be accomplished by the present systems and methods of generating spreading codes which are resistant to misalignment caused by multi-path delays and/or time jitter of the system and/or misalignment of signals received from different users in CDMA systems. An embodiment of the present invention includes an apparatus for generating spreading codes including means for generating a substantially orthogonal code, and means for inserting at least one zero into a code generated by the substantially orthogonal code generating means.
In an exemplary embodiment of the invention, the system includes an apparatus for generating spreading codes including means for generating a substantially orthogonal code, means for generating a pseudonoise (PN) code, means for combining a PN code generated by the PN code generating means with a code generated by the substantially orthogonal code generating means and means for inserting zeros into a code generated by the combining means.
In another embodiment of the invention, the system includes an apparatus for generating spreading codes including a pseudonoise (PN) code generator and a logic controlled multiplexor logically connected to the PN code generator. The multiplexor may be configured to alter a PN code generated by the PN code generator by replacing at least a portion of the PN code with at least one zero. The embodiment further includes a Walsh code generator and a multiplier logically connected to the Walsh code generator and to the PN code generator and configured to combine a Walsh code generated by the Walsh code generator with the altered PN code.
In an embodiment of the invention, the system includes an apparatus for generating spreading codes including a pseudonoise (PN) code generator and a logic controlled multiplier logically connected to the PN code generator and configured to alter a PN code generated by the PN code generator by multiplying at least a portion of the PN code by zero. The apparatus further includes a Walsh code generator; a multiplier connected to both the Walsh code generator and to the PN code generator and configured to combine a Walsh code generated by the Walsh code generator with the altered PN code.
In another embodiment of the invention the system includes an apparatus for generating spreading codes including a pseudonoise (PN) code generator, a microprocessor connected to the PN code generator and configured to alter a PN code generated by the PN code generator. The system further includes a Walsh code generator, a multiplier connected to both the Walsh code generator and to the PN code generator and configured to combine a Walsh code generated by the Walsh code generator with the altered PN code.
In another embodiment of the invention the system includes a method of generating spreading codes by generating a substantially orthogonal code made up of chips and generating a new substantially orthogonal code by inserting at least one zero into the substantially orthogonal code.
In yet another embodiment of the invention the system includes a method of generating time delay resistant spreading codes by generating a pseudonoise (PN) code including multiple chips, generating a new PN code from the PN code by replacing at least one of the chips by a zero, such that the new PN code includes at least one zero chip and at least one non-zero chip. The method further includes generating a substantially orthogonal code including multiple chips and combining the new PN code with the substantially orthogonal code by multiplying the non-zero PN code chips by the substantially orthogonal code chips on a chip by chip basis.
The invention will next be described in connection with certain exemplary embodiments; however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit or scope of the claims.
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patent: 5603096 (1997-02-01), Gilhousen et al.
patent: 5751705 (1998-05-01), Sato
patent: 5812938 (1998-09-01), Gilhousen et al.
patent: 5933424 (1999-08-01), Muto
patent: 5982763 (1999-11-01), Sato
patent: 6091762 (2000-07-01), Davis et al.
Khaleghi Farideh
Secord Norman P.
Strawczynski Leo
Cobrin & Gittes
Haszko Dennis R.
Nortel Networks Limited
Patel Ajit
Phunkulh Bob A.
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