Modulo loss reduction for Tomlinson-Harashima precoding in a multi-beam satellite forward link

SNR maximization and modulo loss reduction for Tomlinson-Harashima precoding

“…We proposed in [17,18] an alternative detection strategy to reduce the MoL compared to the CD. Let us denote by S C ⊆ {1, .…”

“…The verification for user n can be accomplished by checking whether a n (k) − (ν n (k)) (for PAM) or a n (k) − ν n (k) (for QAM) is within the modulo boundaries for all symbol indices k belonging to the frame; for growing frame size K, this condition becomes equivalent to C(n). Next, the TX informs the users accordingly; this requires the transmission of only one (properly encoded) bit of channel information per user and per frame, which typically represents a very small overhead [18].…”

“…Originally, THP has been introduced to avoid intersymbol interference on frequency-selective single-input single-output channels [2,3], but THP has also been applied to spatial multiplexing systems operating over flat channels. Depending on the scenario, one distinguishes between single-user (SU) multiple-input multipleoutput (MIMO) THP, where the both the TX and the RX are equipped with multiple antennas [4][5][6] multi-user (MU) multiple-input single-output (MISO) THP, where a multi-antenna TX sends to several single-antenna RXs [7][8][9][10][11][12][13][14][15][16][17][18]; and MU-MIMO THP, involving a multi-antenna TX sending to several multi-antenna RXs [19][20][21]. Moreover, THP is envisaged also in communication systems providing physical-layer security [22], and for simultaneous wireless information and power transfer (SWIPT) [23].…”

“…Based on the observation that, depending on the channel realization, part of the users can omit the modulo operation at the RX during an entire frame, an alternative detector is introduced in [17,18], which applies the modulo operation only when the TX instructs the RX to do so; this way, the MoL is reduced compared to the conventional detector, for which the modulo operation is always active. At the same time, in [17,18], the constellations are rotated to maximize the number of users which can discard the modulo operation.…”

“…In this contribution, we consider MU-MISO THP and we assume that perfect channel information is available at the TX and the RX. We investigate how the constellation rotations and the reordering of the users affect the SNR and the MoL of the alternative detector from [17,18]. Besides applying some existing and some new algorithms which optimize over either the user ordering or the constellation rotations, this contribution also jointly maximizes the SNR at the detector and reduces the MoL, by optimizing over both the ordering and the rotations.…”