A SAW-BASED COMMUTATION SIGNALING MODEM FOR BROAD-BAND INDOOR WIRELESS COMMUNICATION

Commutation signaling is a bandwidth expanding modulation scheme that is robust to multipath induced intersymbol interference making it suit able for wireless digital communications. By using multipath diversity combining, commutation signaling exploits the time diversity that is inherent in a multipath propagation environment. This paper considers a surface acoustic wave (SAW) implementation of a commutation signalin g modem for broadband indoor wireless communication. The modem employs differential encoding and a form of direct sequence spread spectrum m odulation with the following specifications: data rate 40 Mb/sec, chip rate 200 MHz, and IF frequency 1 GHz. The differential coherent detec tor is a key element of a low cost, low complexity commutation signali ng modem. A commutation signaling differential coherent detector has b een implemented using SAW and RF integrated circuit (RF IC) technologi es. The SAW devices have been fabricated on 128 degrees-rotated Y-cut, X-propagating lithium niobate using approximately 1 micron line width s. RF IC technology is used to implement the high-speed bilinear multi pliers needed for differential coherent detection as well as the low-i mpedance buffers used to drive these multipliers.