Fast and reliable time and frequency synchronization is crucial for packet-based orthogonal frequency division multiplex (OFDM) systems. In this paper we compare and analyze preambles for OFDM systems based on repeated OFDM data symbols or repeated short pseudonoise sequences (PN-sequences). We make an analytical evaluation for AWGN channels and simulate the performance in oneand two-tap Rayleigh fading channels. The PN-based preamble gives better detection properties in terms of lower false detection probability and lower probability of missing the synchronization signal. The PN-based preamble has low peak-to-average power ratio and it makes it possible to use an ADC with one-bit quantization in stand-by mode. For frequency offset estimation both preambles give similar performance, but the PN-based preamble allows for a greater reduction in stand-by mode power consumption.

Time and Frequency Synchronization for BRAN using PN-sequence Preambles

With the rapid development of social economy, the importance of ecological civilization is increasing day by day. The level of environmental monitoring will directly affect the control of total pollution sources and the evaluation of environmental quality. Crowd sensing is to use the group computing power of users with smart devices to quickly collect surrounding multidimensional data, analyze and calculate based on these massive perception data, and then dig out group behavior patterns and other regular information. In order to meet the basic requirements of environmental protection work put forward by the government in the new era, this paper proposes mobile positioning and crowd sensing technologies, explains the distribution map method and adaptive weighting data fusion related algorithms, and designs and develops a mobile positioning system based on mobile positioning. The system of crowd sensing of urban healthy street monitoring is designed, and then we use this PM2.5 monitoring system to monitor the relevant environmental data of a street in Shanghai and use normalization to process the experimental data. The experimental data and statistical results show that this performance of the system is good, and the accuracy of image PM2.5 monitoring reaches 90%–95%. More than 90% of street residents are also very satisfied with this system, believing that it can play a role in supervising urban healthy street.

/pdf/crowd-sensing-urban-healthy-street-monitoring-based-on-4h10rmqdo3.pdf

Crowd Sensing Urban Healthy Street Monitoring Based on Mobile Positioning System

In optical and wireless communications systems, the goal is to reach 10 Gbps or above data rates. In order to support such extremely high data rates, the physical layer generally uses orthogonal frequency division multiplexing (OFDM) modulation. Unlike serial transmission of symbols, the OFDM modulation transmits data with many parallel sub-carriers, which help to provide high bandwidth. Field programmable gate arrays (FPGAs) and digital signal processors (DSPs) are usually employed to process OFDM blocks in real time. However, FPGAs and DSPs are not cost effective, and they are difficult to adapt to new standards. One of the most computationally intensive functions in OFDM systems is the fast Fourier transform (FFT) computation process. This paper aims to accelerate the FFT process to achieve high communication throughput in real time. Two parallel approaches are implemented for two different NVIDIA graphics processing unit (GPU) architectures. To obtain the best performance values, several optimizations are implemented. Our general purpose graphics processing unit (GPGPU)-based FFT computation achieves up to 24 Gbps throughput in real time.

Real-Time FFT Computation Using GPGPU for OFDM-Based Systems

In this paper, a baseband receiver design and its FPGA implementation for an OOFDM system aimed at the NG-PON (passive optical network) applications are presented. A low cost IMDD (intensity modulation, direct detection) architecture is adopted and baseband DSP measures are employed to compensate various optical impairments. Targeting a 4GSps throughput rate, an 8-way parallel architecture is developed to perform the synchronization, FFT and equalization each with massive parallelism. A real valued FFT module taking advantage of the Hermitian spectrum is also developed to reduce the circuit complexity significantly. The simulation results show the proposed baseband receiver is capable of achieving an 8Gbps (effective) transmission bandwidth for 64-QAM coded OFDM symbols over a 25km long single mode fiber network. The uncoded BER reaches 10−3 when the received optical power is −16dBm. Due to the speed and resource limitation, the FPGA implementation obtains a fully functional but speed degraded system. The maximum working frequency is 250 MHz, which is one half of the 500MHz required for real time processing. The design occupies 21,423 logic slices and 56 embedded multiplier modules.

Design and implementation of an optical OFDM baseband receiver in FPGA

Orthogonal frequency division multiplexing (OFDM) technique has been widely adopted in wireless communication systems. However, the study of OFDM technique for optical transmission system is still emerging in the research field. In this paper, we propose a baseband receiver architecture for the optical OFDM system. The baseband receiver contains frame detection, carrier frequency offset (CFO) estimation and compensation, channel estimation, and equalization. This paper also proposes a fast Fourier transform (FFT) processor with highly parallel architecture for the high-throughput requirement in the optical system. Finally, the FFT processor is designed and implemented using 90nm UMC CMOS technology. The measurement result shows that this chip achieves 2.67GS/s throughput for the optical OFDM system.

A baseband receiver for optical OFDM systems

This paper presents a noise-robust mobile positioning system based on received signal strength (RSS) estimators, particle filters and a convex optimization processor. The positioning system uses a code-aided noise cancellation technique to refine the (RSS) signals and improve the positioning accuracy. This study also presents a virtual base-station transform (VBST) and convex optimization algorithm to deal with the none-light-of-sight (NLOS) travelling problem of the microwave transmission. The proposed positioning processor consists of four code-aided SNR/RSS estimators and four latency-reduced particle filters to refine the RSS signals from four base stations and estimate their distances to the mobile station. Then, the estimated distances are delivered to a convex optimization processor with the VBST algorithm to locate the mobile station. This work implemented the positioning algorithm on Xilinx Virtex-4 FPGA and RF modules to verify the positioning performance. The measurement and analysis results show that the proposed convex-optimized positioning system reduces 20 % RMSE in the mixed NLOS/LOS environment compared to the sole particle filtering approach. The RSS estimator can further improve the positioning performance in the noisy environments.

A Noise-Robust Convex-Optimized Positioning System Based on Code-Aided RSS Estimation and Virtual Base Station Transform

This paper presents the design and implementation of a positioning system based on particle filters and a convex optimization processor. The positioning system uses a virtual base-station transform (VBST) and convex optimization algorithm to deal with the none-light-of-sight (NLOS) problem in wireless communication systems. This study designs a modified resampling particle filter to reduce the processing latency with little performance loss. The proposed system uses four modified particle filters to adopt RSS signals from at most four base stations to estimate their distances to the mobile station. Then, the estimated distances are delivered to a convex optimization processor with the VBST algorithm to locate the mobile station. This work implemented the positioning algorithm on Xilinx Virtex-4 FPGA and RF modules to verify the positioning performance. The measurement and analysis results show that the proposed convex-optimized positioning system reduces 20% RMSE in the mixed NLOS/LOS environment compared to the sole particle filtering approach.

Design and implementation of a convex-optimized positioning system on wireless RF/FPGA platform

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A baseband receiver for optical OFDM systems

A Noise-Robust Convex-Optimized Positioning System Based on Code-Aided RSS Estimation and Virtual Base Station Transform

Design and implementation of a convex-optimized positioning system on wireless RF/FPGA platform