CDMA wireless systems
View Patent ↗Information symbols are transmitted simultaneously on independent streams using the same spreading code but from different transmit antennas at the transmitter. These simultaneous data stream could be intended for the same user (and thereby the data rate for any particular user can be increased) or for different users (thereby increasing the system capacity). Each stream of data can belong to a different signal constellation and use a different channel code. At the receiver, a number of receive antennas equal to at least the number of multiple data streams is used to separate the different data streams. We consider two different cases. The first one when no transmit diversity is used (this case can also include the case when transmit diversity with simple antenna weighting is used) and the second when transmit diversity with space-time block coding is used.
1. A communication system for a data stream of digital information symbols comprising:
a plurality of transmitters each having means for splitting the data stream into a plurality of independent data streams each having data that is independent of the data in the other of the split data streams;
each of the plurality of transmitters having a respective plurality of antennas for transmitting a respective independent data stream; and a receiver comprising:
a plurality of antennas, equal in number to the number of antennas of one transmitter of said plurality of transmitters for receiving the plurality of independent data streams from the antennas of said plurality of transmitters;
a channel decoder means for applying information to the data stream produced by a combining means to produce a decoded data stream;
means for making a tentative decision of the reliability of the decoded data stream based on the format of a signal constellation of the receiver;
means for performing iterative canceling of interference of the data stream of the tentative decision and making a soft decision of the correspondence of the data stream to the receiver;
means for decoding the data stream of the soft decision;
wherein each of the antennas of the receiver receives direct and multipath reflected independent data stream signals modulated using different signal constellations and having different channelization codes;
means for suppressing interference produced by the plurality of direct and multipath received signals;
means for extracting said independent data streams from the plurality of direct and multipath received signals after interference suppression;
wherein the means for combining combines said extracted independent data streams back into the data stream;
wherein said means for suppressing further comprises:
a plurality of finger interference suppression units each of which receives at least one of the direct and multipath signals containing said independent data streams;
means for determining the reliability of each of the independent data streams output by each said finger suppression unit;
means for extracting the most reliable independent data streams from each said finger suppression unit; and
means for combining the extracted most reliable independent data streams into the data stream; and
means for assembling the received independent data streams back into the data stream of digital information symbols.
2. A communication system for a data stream of digital information symbols comprising:
a plurality of transmitters each having means for splitting the data stream into a plurality of independent data streams each having data that is independent of the data in the other of the split data streams;
each of the plurality of transmitters having a respective plurality of antennas for transmitting a respective independent data stream; and
a receiver comprising:
a plurality of antennas equal in number to the number of antennas of one transmitter of said plurality of transmitters for receiving the plurality df independent data streams from the antennas of said plurality of transmitters;
a channel decoder means for applying information to the data stream produced by a combining means to produce a decoded data stream;
means for making a tentative decision of the reliability of the decoded data stream based on the format of a signal constellation of the receiver;
means for performing iterative canceling of interference of the data stream of the tentative decision and making a soft decision of the correspondence of the data stream to the receiver;
means for decoding the data stream of the soft decision,
wherein each of the antennas of the receiver receives direct and multipath reflected independent data stream signals modulated using different signal constellations and having different channelization codes;
means for suppressing interference produced by the plurality of direct and multipath received signals;
means for extracting said independent data streams from the plurality of direct and multipath received signals after interference suppression;
wherein means for combining combines said extracted independent data streams back into the data stream;
wherein said means for suppressing comprises:
an interface suppression block that receives all of the direct and multipath signals containing all of said independent data streams;
means for determining the reliability of each of the independent data streams output by said suppression block;
means for extracting the most reliable independent data streams; and
means for combining the extracted most reliable independent streams into the data system; and
means for assembling the received independent data streams back into the data stream of digital information symbols.