This paper discusses the design and implementation of a burst mode Continuous Phase Modulation (CPM) modem over flat, Rayleigh fading channels in the 220MHz frequency band. Our design focused on bandwidth efficiency while maintaining good synchronization performance and low complexity. The designed preamble is based on the combination of Minimum Shift Keying (MSK) signals and 3RC (Raised Cosine) signals. The use of MSK allows a closed form result for an initial Maximum Likelihood (ML) timing estimate. The 3RC signal, which has a better timing characteristic than MSK, is used to refine the timing and frequency estimates. The payload uses 3RC signals. Pilot symbol assisted modulation (PSAM) is used to assist channel estimation. The designed packet structure meets the Federal Communications Commission (FCC) frequency emission mask for 220MHz frequency band. A CPM modem using the designed packet structure has been implemented on the testbed and the simulation, bench test, and field test results are presented in this paper.
In order to develop electroluminescent and laser devices based on the ultraviolet exciton emission of ZnO, it will be important to fabricate good p-n junctions. As-grown ZnO is normally of n-type because of oxygen vacancies and zinc interstitials acting as donors. Making p-type ZnO has been more difficult, believed due to self-compensation by intrinsic defects such as the donors V<SUB>o</SUB> and Zn<SUB>i</SUB>, or possibly by hydrogen as an unintentional extrinsic donor. In this work, we demonstrate that reactively sputtered, vacuum- annealed ZnO films can be changed from n-type to moderate p- type by adjusting the oxygen/argon ratio in the sputtering plasma. We report the properties of p-n homojunctions fabricated in this way and characterize transport in the films by Hall measurements. Ohmic contacts were formed by deposition of Au/Al. Our finding of p-type conductivity in apparently intrinsic ZnO formed by reactive sputtering is not inconsistent with calculated defect formation enthalpies if account is taken of the higher chemical potential of the atomic (ionic) oxygen reservoir represented by the sputter plasma, compared to the molecular oxygen reservoir assumed in the calculation of formation enthalpies. Photoluminescence of the sputtered and annealed films is characterized mainly by the 3.27 eV exciton peak at room temperature.