A Space-Time Spreading Assisted Multicarrier DS-CDMA System using OVSF Codes Employing Adaptive Mode Switching Thresholds and Adaptive Modulation

The Concept of Space-Time Spreading (STS) assisted, Adaptive Quadrature Amplitude Modulation (AQAM) aidedMC DS-CDMAis introduced. The AQAMmode-switching thresholds are determined using an on-line real-time Bit-Error-Ratio (BER) based learning procedure. Four different schemes were studied, designed for maintaining a given target BER of 10?2, 10?3, 10?4 and 10?5 both with and without turbo channel coding. The effect of using different number of STS antennas ranging from1 to 8 was also characterized in terms of the achievable effective throughput, characterising the associated system design trade-offs

LAS-CDMA using Various Time Domain Chip-Waveforms

LAS CDMA exhibits a significantly better performance than that of classic random code based DS-CDMA, when operating in a quasi-synchronous scenario. Classic frequency-domain raised cosine Nyquist filtering is known to show the best possible performance, but its complexity may be excessive in highchip-rate systems. Hence in these systems often low-complexity time-domain waveform shaping is considered. Motivated by this fact, the achievable performance of LAS-CDMA is investigated in conjunction with three different time-limited chipwaveforms, which exhibit an infinite bandwidth. The raised cosine time-domain waveform based DS-CDMA system is shown to achieve the best performance in the context of a strictly band-limited system, because its frequency-domain spectral side-lobes are relatively low

Coherently manipulating cold ions in separated traps by their vibrational couplings

Recent experiments [K. R. Brown, et al., Nature 471, 196 (2011); and M. Harlander, et al., Nature 471, 200 (2011)] have demonstrated the coherent manipulations on the external vibrations of two ions, confined individually in the separated ion traps. Using these recently developed techniques, we propose here an approach to realize the coherent operations, e.g., the universal quantum gates, between the separated ion-trap qubits encoded by two internal atomic states of the trapped ions. Our proposal operates beyond the usual Lamb-Dicke limits, and could be applied to the scalable ion traps coupled by their vibrations.Comment: 4 pages, 2 figure

Spin-orbit couplings between distant electrons trapped individually on liquid helium

We propose an approach to entangle spins of electrons floating on liquid helium by coherently manipulating their spin-orbit interactions. The configuration consists of single electrons, confined individually on liquid helium by the microelectrodes, moving along the surface as the harmonic oscillators. It has been known that the spin of an electron could be coupled to its orbit (i.e., the vibrational motion) by properly applying a magnetic field. Based on this single electron spin-orbit coupling, here we show that a Jaynes-Cummings (JC) type interaction between the spin of an electron and the orbit of another electron at a distance could be realized via the strong Coulomb interaction between the electrons. Consequently, the proposed JC interaction could be utilized to realize a strong orbit-mediated spin-spin coupling and implement the desirable quantum information processing between the distant electrons trapped individually on liquid helium.Comment: 12 pages, 4 figure