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Abstract：A new 8PBF structure for 64/128 flexible point FFT processor is proposed. The processor, which is based on 8*8*2 mixed radix algorithm, can deal with multiple inputs more efficiently for MIMO applications. The 8PFB structure efficiently brings the throughput of the processor up to 1GS/s and the chances of register reverse down, reducing the power dissipation remarkably. Meanwhile the modified shift-add algorithm can remove complex multipliers in the fft processor. I. IntroductionUltra Wide band (UWB) is en emerging technology that offers great promises to satisfy the growing demand for low cost and high speed digital wireless home network. The OFDM based UWB communication system is supposed to process and transfer data at 528Mbps[1][2], which poses a challenge to realize the application of UWB system. FFT processor is one of the core modules with high computational complexity in the UWB system. How to improve the signal processing capability and to reduce the power consumption as well as the hardware cost of a FFT processor have now all become challenging targets. What's more, in 2*2 MIMO-OFDM system, which have been shown to be an efficient approach to make benefits of spatial and frequency diversities[3], the FFT processor is demanded to deal with two parallel 64-points operations. Fig. 1 and Fig. 2 respectively show the structure of SISO and MIMO UWB system. Several FFT processors have been realized different algorithms and structure in the last decade, such as [4] the processor with multi-path delay commutator (MDC) structure. It features high data transmission rate but high hardware cost.[5] has improved the MDC structure to a mixed radix multi-path delay feedback(MRMDF) structure for the 128-points FFT processor in order to decrease the hardware cost. But the MRMDF structure has a difficulty in meeting the requirement of transmission rate and the

To realize high-speed nonvolatile magnetic memory with low energy consumption, electric switching of perpendicular magnetization by spin−orbit torque in the heavy metal/ferromagnetic (HM/FM) structure has recently attracted intensive attention. Conventionally, an external in-plane magnetic field for breaking the symmetry is required for achieving electric switching of perpendicular magnetization. However, electric switching without external field is the prerequisite for the integration of magnetic functionality into the integrated circuit devices. Here, we propose a new method of utilizing a W wedge in the Pt/W/FM structure to induce a spin current gradient, which can result in an in-plane equivalent field along the wedge thickness gradient direction. We experimentally demonstrate the deterministic magnetization switching of perpendicular Co/Ni multilayers without external magnetic field when the electric current is along the wedge thickness gradient direction. Our findings shed light on free field electric switching of magnetization by a new physical parameteran asymmetric spin current induced by a bilayer wedge structure.

We present a new scheme of compact Rubidium cold-atom clock which performs the diffuse light cooling, the microwave interrogation and the detection of the clock signal in a cylindrical microwave cavity. The diffuse light is produced by the reflection of the laser light at the inner surface of the microwave cavity. The pattern of injected laser beams is specially designed to make most of the cold atoms accumulate in the center of the microwave cavity. The microwave interrogation of cold atoms in the cavity leads to Ramsey fringes whose line-width is 24.5 Hz and the contrast of 95.6% when the free evolution time is 20 ms. The frequency stability of 7.3 × 10 −13 τ −1/2 has been achieved recently. The scheme of this physical package can largely reduce the complexity of the cold atom clock, and increase the performance of the clock.

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We report an experiment on the adiabatic cooling of 87 Rb atoms in an atomic fountain to a temperature as low as 1.5 𝜇K, which is roughly twice the recoil temperature. The atomic fountain has the (1,1,1) optical geometry for cooling and launching of cold atoms. The atoms are first cooled in an optical molasses of 6 beams to 3.4 𝜇K by polarization gradient geometry and then are adiabatically cooled by decreasing the intensity of laser from 1.8𝐼𝑠 per beam to zero in 1 ms during the launching of cold atoms. We also study the dependences of atomic temperature on different laser parameters. The method we used is useful in any cold atom physics experiment.

This paper studies the feasibility of deploying intelligent reflecting surfaces (IRSs) in massive MIMO (multiple-input multiple-output) systems to improve the performance of users in the service dead zone. One question of paramount importance is as follows: if the overhead of channel training and the computational complexity of algorithm design arising from the huge number of IRS reflecting elements and base station (BS) antennas have to be controlled, can we provide reasonable performance to the users with weak direct channels? This paper provides an affirm answer to this question. Specifically, to reduce the channel training overhead, we advocate a novel protocol for the uplink communication in the IRS-assisted massive MIMO systems. Under this protocol, the IRS reflection coefficients are optimized based on the channel covariance matrices, which are generally fixed for many coherence blocks, to boost the long-term performance. Then, given the IRS reflecting coefficients, the BS beamforming vectors are designed in each coherence block based on the effective channel of each user, which is the superposition of its direct and reflected user-IRS-BS channels, to improve the instantaneous performance. Since merely the user effective channels are estimated in each coherence block, the training overhead of this protocol is the same as that in the legacy wireless systems without IRSs. Moreover, in the asymptotic regime that the numbers of IRS elements and BS antennas both go to infinity with a fixed ratio, we manage to first characterize the minimum mean-squared error (MMSE) estimators of the user effective channels and then quantify the closed-form user achievable rates as functions of channel covariance matrices with channel training overhead and estimation error taken into account. Interestingly, it is shown that the properties of channel hardening and favorable propagation still hold for the user effective channels, and satisfactory user rates are thus achievable even if simple BS beamforming solutions, e.g., maximalratio combining, are employed. Finally, thanks to the rate characterization, we design a low-complexity algorithm to optimize the IRS reflection coefficients based on channel covariance matrices.

This study presents an experiment on diffuse light cooling of atoms in a cylindrical cavity. We focus on the controlling of the shape of the atom cloud by placing the cooling beams in appropriate positions. The Gauss-like shape of the atomic cloud is demonstrated. The number of cold atoms detected in the cavity is increased, thereby improving the signal-to-noise ratio of the clock signal.