Interference Cancellation and Detection for More than Two Users - Interference Cancellation Using Space-Time Processing and Precoding Design - page 50

Finally, we provide results for different number of users each with 4 transmit
antennas and one receiver with 4 receive antennas in Fig. 3.7 .We can see that although
we can still achieve full diversity for each user, the coding gain for each user will
be reduced significantly. In order to keep the coding gain on a satisfactory level, the
number of transmit antennas and the number of receive antennas should be larger
than the number of users as shown in the previous figures.
3.6 Conclusions
We have considered interference cancellation for a system with more than two users
when users know each other's channels. We have proposed a system to achieve the
maximum possible diversity of 16 with low complexity for 4 users each with 4 trans-
mit antennas and one receiver with 4 receive antennas. Besides diversity, our proposed
scheme also provides the best performance among all existing schemes with simple
array processing decoding. Our main idea is to design precoders, using the chan-
nel information, to make it possible for different users to transmit over orthogonal
directions. Then, using the orthogonality of the transmitted signals, the receiver can
separate them and decode the signals independently. We have analytically proved
that the system provides full diversity to each user and extended the results to any
number of users each with any number of transmit antennas and one receiver with
any number of receive antennas. Further work includes the extension of our scheme
to the situation with only limited feedback.
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