Transmitter-Based Equalization for Wireless LAN's

In a high-speed mobile communications network, it is desirable tooff-load as much hardware complexity as possible from mobile terminalsto the base station. A system architecture is presented where allequalization-related computations, requiring most hardware resources,can be performed at the base station. A conventional decision-feedbackequalizer (DFE) is used to equalize the received transmissions, and amodified Tomlinson–Harashima precoding method (Tx-THP) is appliedto pre-equalize the transmitted data sequence. The Tx-THP scheme canalso be extended to differentially coherent detection, to suit thesystems where perfect frequency synchronization is not available. Amodified DQPSK receiver is presented to process the extendedconstellations. To avoid the side effect of severe noise multiplication,an alternative receiver structure is developed, incorporating adiscrete-time phase tracker to allow the reduction of the constellationsize prior to the correlation operation. With a 2nd-order estimatorfilter, this receiver approaches the performance of coherent detectionfor Tx-THP.