This paper discusses practical issues and results on the implementation of low-cost transceivers for several wireless optical LANs, covering most physical layer elements. Target optical LANs under consideration have bit-rates varying between 1Mbps and 25Mbps, and input photodiode capacitance may vary between 10pF and 50pF. PPM modulation, either in a 4-PPM or 16-PPM format, is typically used in the physical layer. Differential front-end topologies are presented, both in discrete and integrated (CMOS) implementations, targeting different LANs. Strategies for bandwidth improvement, interference reduction and dynamic range improvement have been used in some of these topologies. These strategies lead to a switched-gain transceiver with a transimpedance gain*bandwidth of 25THzΩ, achieved with a 10pF capacitance photodiode in the input. Both non-sectored and sectored transceivers are discussed. The increased complexity brought about by sectored receivers will be made clear as the design of a signal-to-noise ratio estimator and constraints on power consumption of the basic front-end design are discussed. Considerations on practical usage of MAP detection confronted with adaptive threshold detection are further presented. Clock recovery issues are also mentioned. Final comments on practical issues and evolution of these low-cost systems are presented.

In this communication we present a space-frequency pre-filtering technique, for downlink time division duplex (TDD) MC-CDMA systems, where the base station is equipped with an antenna array. We show that the pre-filtering approach can considerably reduce the multiple access interference at the mobile terminals allowing to transfer a significant part of the computational complexity to the base station, using a very low complex receiver at mobile. This approach relies on the availability of the channel state information at transmission, i.e., uses the time division duplex channel reciprocity between alternative uplink and downlink to obtain the channel state information. Simulation results are presented to demonstrate the effectiveness of the proposed prefiltering algorithm. Moreover, the performance of the proposed pre-filtering algorithm is assessed in two distinct scenarios: beamforming and diversity.