Zero-forcing precoding

This is an old revision of this page, as edited by Jamessungjin.kim (talk | contribs) at 11:41, 24 December 2008. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Zero-forcing precoding (or ZF-precoding) is a spatial signal processing that nulls multiuser interference at the multiple antenna transmitter in wireless communications. Regularized zero-forcing precoding is enhanced processing to consider the impact on a background noise and unknown user interference[1], where the background noise and the unknown user interference can be emphasized in the result of (known) interference signal nulling.

Performance of Zero-forcing Precoding

If the transmitter knows the downlink channel status information perfectly, ZF-precoding can achieve almost the system capacity when the number of users is large. On the other hand, wth limited channel status information at the transmitter (CSIT) the performance of ZF-precoding decrease depending on the accuracy of CSIT. ZF-precoding requires the significant feedback overhead with respect to signal-to-noise-ratio (SNR) so as to achieve the full multiplexing gain[2]. Inaccurate CSIT results in the significant throughput loss because of residual multiuser interferences. Multiuser interferences are remained since those can not be nulled with beams generated by imperfect CSIT.

Mathematical Description

In a Precoded MIMO BC system with   transmitter antennas at AP and a receiver antenna for each user  , the input-output relationship can be described as

 

where   is the   vector of transmitted symbols,   and   are the received symbol and noise respectively,   is the   vector of channel coefficients and   is the   linear precoding vector.

For the comparison purpose, we describe the mathematical description of MIMO MAC. In a MIMO MAC system with   receiver antennas at AP and a transmit antenna for each user   where  , the input-output relationship can be described as

 

where   is the transmitted symbol for user  ,   and   are the   vector of received symbols and noise respectively,   is the   vector of channel coefficients.

See Also

References

  1. ^ B. C. B. Peel, B. M. Hochwald, and A. L. Swindlehurst (Jan. 2005). "A vector-perturbation technique for near-capacity multiantenna multiuser communication - Part I: channel inversion and regularization". IEEE Trans. Commun. 53: 195–202. doi:10.1109/TCOMM.2004.840638. {{cite journal}}: Check date values in: |date= (help)CS1 maint: multiple names: authors list (link)
  2. ^ N. Jindal (Nov. 2006). "MIMO Broadcast Channels with Finite Rate Feedback". IEEE Trans. Information Theory. 52 (11): 5045–5059. doi:10.1109/TIT.2006.883550. {{cite journal}}: Check date values in: |date= (help)