Another important system design parameter is the peak-to-average-power ratio (PAPR) that measures the implementation feasibility of the power amplifiers at the transmitter.
In the previous mentioned works, the implementation of linear or non-linear precoding techniques at the transmitter are considered with perfect knowledge of CSI to the users.
An alternative to avoid this problem is Tomlinson-Harashima precoding (THP [5, 6], which can be seen as the implementation of the DFE receiver's feedback filter at the transmitter.
To achieve a good trade-off between the performance and implementation cost, the transmit-antenna-selection (TAS) is used at the transmitter.
After this point, blocks in the receiver are the counterpart of those at the transmitter, including an efficient ad hoc Viterbi implementation for the decoder block.
Both techniques use block transmission and employ a cyclic prefix at the transmitter which ensures orthogonality and enables efficient implementation of the system using the fast Fourier transform (FFT) and one tap scalar equalization per subcarrier at the receiver.
In the article "Experimental Investigation of TDD Reciprocity-Based Zero-Forcing Transmit Precoding" by Zetterberg [10], the author describes an implementation on a wireless testbed of zero-forcing linear precoding when CSI at the transmitter is acquired by exploiting time-division-duplex (TDD) reciprocity.
Unfortunately, most beamforming algorithms considered assume availability of perfect channel state information at the transmitter, which presents a big challenge to their practical implementation (references [9, 10] and references therein contain an overview of the subject).
At the transmitter side, the complexity is significantly reduced in comparison with the standard implementation of the CC method.
DSTTD employs two space time block codes at the transmitter.
