A downlink transmit diversity scheme is proposed for [1] WCDMA low chip rate (1.28 Mcps) Time Division Duplex (LCR-TDD) systems. In the proposed Time Switched Transmit Diversity (TSTD) scheme, two spatially separated antennas are alternately used at a base station in order to transmit consecutive sub-frames on the downlink physical channels. The proposed TSTD scheme takes advantage of the frame structure of the WCDMA LCR-TDD, where TSTD transmission is possible with a single power amplifier. Simply adding switching components in front of the transmit antennas yields a considerable gain compared with a non-diversity mode system. A new power control algorithm is also proposed for generating power control command for efficient use of TSTD. A performance gain of up to 5 dB, compared with a non-diversity scheme, is achieved in terms of the frame error rate for varying Eb/No and mobile speeds. From the viewpoint of both complexity and performance, the TSTD scheme is a simple and effective transmit diversity method that can increase downlink capacity in the WCDMA LCR-TDD systems.

In this paper, an ultra low power analog front-end for EPCglobal Class 1 Generation 2 RFID tag is presented. The proposed RFID tag removes the need for high frequency clock and counters used in conventional tags, which are the most power hungry blocks. The proposed clock-free decoder employs an analog integrator with an adaptive current source that provides a uniform decoding margin regardless of the data rate and a link frequency extractor based on a relaxation oscillator that generates frequency used for backscattering. A dual supply voltage scheme is also employed to increase the power efficiency of the tag. In order to improve the tolerance of the proposed circuit to environmental variations, a self-calibration circuit is proposed. The proposed RFID analog front-end circuit is designed and simulated in 0.25 µm CMOS, which shows that the power consumption is reduced by an order magnitude compared to the conventional RFID tags, without losing immunity to environmental variations.