A nonlinear transmitter pre‑equalization technique that cancels known intersymbol or inter‑stream interference before transmission by using a causal feedback filter combined with a modulo operation on finite constellations, thereby converting a problematic channel into one with reduced residual interference at the receivers.

Principle

THP implements successive interference pre‑subtraction at the transmitter: a feedback filter removes the effect of previously generated transmitted symbols (given known channel or interference structure), and a modulo operation confines signal amplitude to the constellation region to control transmit power and maintain decodability via the receiver’s inverse modulo operation.

Demonstration

Situation: A transmitter serving two spatial streams over a channel with known inter‑stream coupling. Recognition: The transmitter knows the channel coupling and the symbol sequence to be sent. Action: It applies a feedback filter that subtracts the predicted interference from the current symbol, then applies a modulo operation to wrap the result into the constellation region; the receiver applies the inverse modulo and decodes. Consequence: The receiver sees substantially reduced inter‑stream interference without relying on receiver‑side decision feedback; wrong or absent modulo inversion at the receiver produces symbol ambiguity.

Misapplication

Treating THP as a linear precoder: the error is to ignore the feedback and modulo nonlinearity that distinguish THP; replacing THP by a linear matrix multiply removes the modulo mechanism and typically increases transmit power or residual interference for the same constellation constraints.

Consequence

When applicable, THP can achieve performance comparable to receiver decision‑feedback equalizers while shifting complexity to the transmitter and avoiding error propagation at receivers; misconfiguration (e.g., missing inverse modulo) creates decoding ambiguity and can increase symbol error rate.

Reversal

THP relies on accurate transmitter‑side knowledge of channel coupling and on finite constellations supporting modulo arithmetic; if channel knowledge is absent, rapidly varying, or if the system uses coding/constellations incompatible with modulo operations, THP’s benefits disappear and linear or receiver‑side equalization may be preferable.

Boundary

Clearly within: transmitter‑side preequalization using causal feedback filtering plus modulo mapping for finite constellations. Boundary case: precoding with feedback but no modulo (which raises transmit dynamic range). Clearly outside: purely linear precoding without feedback or receive‑side decision‑feedback equalizers acting after reception.

Semantic Tension

THP ↔ Receiver Decision‑Feedback Equalization — both use successive interference cancellation concepts but place feedback at the transmitter (THP) versus at the receiver (DFE); the choice trades transmitter complexity and modulo operations against receiver complexity and error propagation risk.

Synthesis

THP moves successive interference cancellation to the transmitter, using modulo arithmetic to bound signal excursions; this nonlinear strategy can reduce receiver complexity and error propagation but requires transmitter channel knowledge and compatible modulation structure.