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Radio Networks represent a fast-to-implement solution, reducing the costs of fixed infrastructure. The main issues that arise are related to the security of the communication. In this article we propose a solution for fast and reliable radio network, intelligent and self-configurable, which can be used in many applications, from traffic-related ones to intelligent building management.
The present paper describes an Ultra-Wideband (UWB) communication system based on the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. The system uses a small number of sub-carrier frequencies which allow the straightforward implementation of the OFDM modulator and demodulator without the use of Discrete Fourier Transform (DFT). An experimental RF transceiver based upon the proposed...
In this paper, two estimators are proposed for calculating fine timing and channel impulse response (CIR) of a CD-OFDM based communication system. The proposed low complexity algorithms are designed to operate with asynchronous nodes having independent timing and carrier frequency offsets. These algorithms fully exploit the specially designed structure of time domain preamble used for cooperative...
This paper presents the design of a 12 Mb/s COFDM baseband processor compatible with the standard IEEE 802.11a. In this case, the architecture was described in VHDL, without use of IP cores or automatic generators, and the COFDM baseband processor with a cyclic prefix includes coarse and fine time synchronization system, and a channel coding system composed of a convolutional encoder with interleaver...
We propose a maximum a-posteriori (MAP) based blind algorithm for carrier frequency offset (CFO) and symbol timing offset (STO) estimation, for a convolutionally coded orthogonal frequency division multiplexing (COFDM) system, in an additive white Gaussian noise (AWGN) channel. We derive the MAP estimators mathematically. It is observed that though the MAP metric for CFO estimation gives a good performance...
Robust, efficient and low complexity design methodologies for high speed multi-band orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) is presented. The proposed design is implemented in 0.13μm CMOS technology with the core area of 2.66mm × 0.94mm. Operating at 132MHz clock frequency, the estimated power consumption is 170mW.
Acoustic communication is transmission technology with sound and data by using speaker and microphone. In this paper, we propose a parallel acoustic communication system that is able to transmit text data in office environment using unused high frequency band in audio signal. So, we analyze the performance of acoustic communication. This system sends both sound in low frequency band and OFDM (orthogonal...
Traditional OFDM based transmission system uses Cyclic Prefix (CP) in an OFDM symbol in order to maintain orthogonality of transmission. Present days' Ultra-Wideband (UWB) systems use Multi-Band OFDM (MB-OFDM) techniques for transmission in application like Wireless Personal Area Network (WPAN). UWB based systems are power limited by the regulation of FCC. CP introduces correlation in the transmitted...
A simple, highly-effective, DSP-free, optical OFDM(OOFDM) synchronous clock recovery technique preserving system performance and enhancing stability is proposed and experimentally demonstrated, for the first time, in real-time end-to-end, 11.25Gb/s 64-QAM OOFDM, directly-modulated-DFB-based, 25km IMDD systems.
Recent real-time optical OFDM (OOFDM) research progress is reviewed extensively in terms of adaptive transceiver design, intensity modulators, synchronisation techniques and network architectures. Results indicate that OOFDM is feasible for mass deployment in PONs.
We propose a novel method to achieve precise symbol synchronization using one training symbol in DSB optical fast OFDM (FOFDM). World-first FOFDM transmission experiment using field-installed fiber verifies its robustness to the noise and CD.
In the uplink, while macrocell mobile stations (mMSs) are synchronized to the macrocell base station (mBS), their signals will arrive asynchronously at the femtocell base station (fBS). For OFDMA, if the timing misalignment among the mMSs is greater than the cyclic prefix duration, intersymbol interference (ISI) and intercarrier interference (ICI) will occur in the received signal at the femtocell...
This paper presents a FFT architecture, which processes FFT frames of various size in a continuous-flow fashion. The organization is based on the Single-path Delay Feedback (SDF) scheme and it computes mixed radix FFT algorithms with radixes 2, 22, 23 and 24. The proposed SDF is able to execute FFT of size varying from 128 to 2048 in continuous-flow by exploiting the memory of each stage for efficiently...
Unique word - orthogonal frequency division multiplexing (UW-OFDM) is a novel OFDM concept that uses deterministic sequences, which we call unique words, as guard intervals instead of the conventional cyclic prefixes. Since unique words represent known sequences, they can advantageously be used for synchronization, channel estimation, but also for improving the bit error ratio (BER) behavior of a...
In this paper, a new method of timing synchronization was proposed for 802.16e OFDMA downlink which consists of coarse frame detection and fine timing synchronization. In coarse frame detection a method had been proposed, which reduced the uncertainty existing in conventional method. For fine timing synchronization, another method was represented to improve timing precision based on special preamble...
In cooperative relay systems, relayed signals propagate through different channels and are received at the destination node with distinct timing and carrier frequency offsets (CFOs). This feature makes synchronization a rather challenging task as compared with centralized multiple-input multiple-output systems. Unlike conventional preamble designs with good correlation properties only in time domain...
For non-contiguous OFDM (NC-OFDM) based cognitive radio (CR) systems, one of huge challenges is to establish spectrum synchronization before data transmissions. In this paper, we propose a novel active subchannel detection scheme for the NC-OFDM receiver without out-of-band spectrum synchronization information. The key idea of the proposed scheme is to employ the received training symbol to calculate...
The optimal detector for CP (Cyclic Prefix)-OFDM (Orthogonal Frequency Division Multiplexing) signal with inherent periodic pilots in low signal to noise ratio environments relies on perfect time synchronization. In this paper, we modify the optimal detector and propose a new suboptimal sensing scheme based on pilots estimation (SSS-BPE). In the proposed SSS-BPE, the likelihood criterion and periodicity...
TCH (Tomlinson, Cercas and Hughes) sequences have been studied for code-spreading and channel coding, but their true purpose is for synchronization and channel estimation. This is due to their property of being (virtually) orthogonal to all of their sequences obtained via circular shifts, and the use of the FFT (Fast Fourier Transform) for decoding. This property is extremely useful for time-offset...
In this paper, we present a novel technique for coarse timing synchronization for Asymmetrically-Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) systems. This technique is tailored specifically for the ACO-OFDM waveform, and performs coarse symbol timing synchronization without the need for training data. By using a specific symmetry property of the ACO-OFDM time-domain signal,...
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