A new layered space-time detection algorithm for frequency selective fading multiple-input multiple-output channels based on particle filter

In this paper, a new observation equation of non-Gaussian frequency selective fading Bell Labs layered space time （BLAST） architecture system is proposed, which is used for frequency selective fading channels and non-Gaussian noise in an application environment of BLAST system. With othogonal matrix triangularization （QR decomposition） of the channel matrix, the static observation equation of frequency selective fading BLAST system is transformed into a dynamic state space model, and then the particle filter is used for space-time layered detection. Making the full use of the finite alphabet of the digital modulation communication signal, the optimal proposal distribution can be chosen to produce particle and update the weight. Incorporated with current method of reducing error propagation, a new space-time layered detection algorithm is proposed. Simulation result shows the validity of the proposed algorithm.

Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems

A particle filter is proposed to perform joint estimation of the carrier frequency offset （CFO） and the channel in multiple-input multiple-output orthogonal frequency division multiplexing （MIMO-OFDM） wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling （SIS）, and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling （SIR）. Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations.

Frequency Switches at Transition Temperature in Voltage-Gated Ion Channel Dynamics of Neural Oscillators

Understanding of the mechanisms of neural phase transitions is crucial for clarifying cognitive processes in the brain. We investigate a neural oscillator that undergoes different bifurcation transitions from the big saddle homoclinic orbit type to the saddle node on an invariant circle type, and the saddle node on an invariant circle type to the small saddle homoclinic orbit type. The bifurcation transitions are accompanied by an increase in thermodynamic temperature that affects the voltage-gated ion channel in the neural oscillator. We show that nonlinear and thermodynamical mechanisms are responsible for different switches of the frequency in the neural oscillator. We report a dynamical role of the phase response curve in switches of the frequency, in terms of slopes of frequency-temperature curve at each bifurcation transition. Adopting the transition state theory of voltagegated ion channel dynamics, we confirm that switches of the frequency occur in the first-order phase transition temperature states and exhibit different features of their potential energy derivatives in the ion channel. Each bifurcation transition also creates a discontinuity in the Arrhenius plot used to compute the time constant of the ion channel.

New Channel Simulator for Adaptive HF Communication Systems

The high frequency (HF) channel simulators with time-varying parameters based on the Watterson model are analyzed. The methods of simulating the HF channel with time-varying parameters are proposed. The linearly time-varying delay spread is introduced into the channel simulators to simulate the transition states between two channel modes of CCIR520-1. Two signals, including a 500 Hz and a 1 000 Hz bandwidth signal are respectively input into the standard Watterson HF channel model and the proposed channel model with time-varying parameters. Some simulation results prove that the proposed HF channel model with time-varying parameters can reflect the time-varying characteristics of frequency selected fading of HF channel.

Low-complexity fractional phase estimation for totally blind channel estimation

To remove the scalar ambiguity in conventional blind channel estimation algorithms, totally blind channel estimation （TBCE） is proposed by using multiple constellations. To estimate the unknown scalar, its phase is decomposed into a fractional phase and an integer phase. However, the maximum-likelihood （ML） algorithm for the fractional phase does not have closed-form solutions and suffers from high computational complexity. By ex- ploring the structures of widely used constellations, this paper proposes a low-complexity fractional phase estimation algorithm which requires no exhaustive search. Analytical expressions of the asymptotic mean squared error （MSE） are also derived. The theo- retical analysis and simulation results indicate that the proposed fractional phase estimation algorithm exhibits almost the same performance as the ML algorithm but with significantly reduced computational burden.

Joint channel and carrier frequency offset estimation for multi-user MIMO-OFDM uplink transmissions

This article proposes a new algorithm of joint channel and carrier frequency-offset OCCFO） estimation for multi-user multi-input and multi-output orthogonal frequency division multiplexing （MIMO-OFDM） systems. A least square （LS） channel estimation and a carrier frequency offset （CFO） correlation estimation are combined in this contribution. CFOs are generally estimated using training sequences in a special synchronization timeslot. In this contribution, CFO estimation is further improved by taking advantages of channel estimation based on pilot symbols in traffic timeslots. The CFOs can be first obtained from the primary channel estimation. And then, with the knowledge of the CFOs estimated, channel estimation can be enhanced greatly. Computer simulation results indicate that the proposed JCCFO scheme is of good performance. Besides, the computational complexity is low.

Design and application of wireless signal strength measurement system on the near-ground

The wireless communication system's performance is greatly constrained by the wireless channel characteristics,especially in some specific environment.Therefore,signal transmission will be greatly impacted even if not in a complicated topography.Testing results show that it is hardly to characterize the radio propagation properties for the antenna installed on the ground.In order to ensure a successful communication,the radio frequency(RF)wireless signal intensity monitor system was designed.We can get the wireless link transmission loss through measuring signal strength from received node.The test shows that the near-ground wireless signal propagation characteristics still can be characterized by the log distance propagation loss model.These results will conduce to studying the transmission characteristic of Near-Earth wireless signals and will predict the coverage of the earth's surface wireless sensor network.

Effect of gate engineering in submicron GaAs MESFET for microwave frequency applications

We present an approach of GaAs MESFET incorporating the gate engineering effect to improve immunity against the short channel effects in order to enhance the scaling capability and the device performance for microwave frequency applications. In this context, a physics-based model for I–V characteristics and various microwave characteristics such as transconductance, cut-off frequency and maximum frequency of oscillation of submicron triple material gate（TM） GaAs MESFET are developed. The reduced short channel effects have also been discussed in combined designs i.e. TM, DM and SM in order to show the impact of our approach on the GaAs MESFETs-based device design. The proposed analytical models have been verified by their good agreement with 2D numerical simulations. The models developed in this paper will be useful for submicron and microwave analysis for circuit design.

Comparison of Achievable Rates of OFDM and Single Carrier Communication Systems

This paper presents a theoretical comparison of a single carrier system and a multi-carrier system through an analysis of the achievable rate under frequency selective fading with channel state information at the receiver. A scheme was designed to compare the achievable rates of a single carrier system and an Or- thogonal Frequency Division Multiplexing （OFDM） system. A thorough theoretical analysis of the two-path channel was conducted, and simulations were also used to analyze practical stochastic channels. Analysis and simulation results show that the achievable rates of the two approaches are comparable when the channel is flat fading. However, when the channel is frequency selective fading, the single carrier system outperforms the OFDM system. The achievable rate of the OFDM system is about 10% lower than that of the single carrier system at higher SNRs.