Vector Signal Generator Research Articles

AN EXPERIMENTAL MULTI-FREQUENCY SYSTEM FOR STUDYING DOSIMETRY AND ACUTE EFFECTS ON CELL AND NUCLEAR MORPHOLOGY IN RAT TISSUES

Simultaneous exposure to multiple electromagnetic signals with widely difiering carrier frequencies is a reality of daily life, but its possible efiects on health are unknown. In this study, we exposed rats to non-thermal levels of 900 and 2450MHz TEM-mode radiation, applied individually or simultaneously, and we obtained estimates of 1g mean SAR (speciflc absorption rate) in various tissues using a numerical model of the rat and flnite-difierence time- domain software. The experimental system comprised a GTEM (gigahertz TEM) chamber connected to two vector signal generators, a signal mixer and amplifler, a directional coupler, a spectrum analyzer and a power meter. Tissue sections from rats sacriflced 24h after exposure, and from negative controls and positive controls exposed to gamma radiation, were stained with haematoxylin-eosin for evaluation of general cell morphology and with DAPI (4', 6- diamidino-2-phenylindole) for evaluation of apoptosis. Lesions, tissue destruction and apoptosis were only observed in positive controls. The results for rats exposed to either frequency, or to both simultaneously, were similar to those of unexposed negative controls. It remains to determine whether chronic exposure is similarly innocuous.

Photonic generation of 60 GHz-band vector signals for RoF systems based on optical vector signal down-conversion

A novel photonic method of 60 GHz-band vector signal generation for RoF systems based on optical vector signal down-conversion is proposed and experimentally demonstrated in this paper. In the proposed method, the target vector signals are first generated in the optical domain with the help of mature commercial optical devices and then directly distributed to the base stations (BSs) through the fiber link. The generated vector signals can be automatically down-converted to the 60 GHz band in the BSs after O/E conversion, and then directly transmitted to the users without any further processing. With the proposed method, higher spectrum efficiency and system capacity will be obtained compared with the traditional OOK RoF systems while almost no extra system complexity and cost is brought in. According to the characteristics of different types of vector signals, two particular modulation schemes are provided, which are then verified by corresponding simulations and experiments. In the experimental 60 GHz RoF system, the 622 MSym/s 60 GHz-band 8-QAM and 4-QAM signals generated with two different schemes respectively are successfully transmitted over 50 km SMF and 5 m wireless channel without any compensation, and the power penalty are both about 1.7 dB at the BER of 10 − 9 .

Design and implementation of portable TDD-LTE vector signal generator

Design and implementation of portable TDD-LTE vector signal generator

Reconfigurable Low Area Complexity Filter Bank Architecture Based on Frequency Response Masking for Nonuniform Channelization in Software Radio Receivers

The most computationally demanding block in the digital front-end of a software defined radio (SDR) receiver is the channelizer which operates at the highest sampling rate. Channelizers are employed in the SDR receivers for extracting individual channels (frequency bands) from the digitized wideband input signal. Reconfigurability and low complexity are the two key requirements in an SDR channelizer. A new reconfigurable filter bank (FB) architecture based on frequency response masking (FRM) for SDR channelizers is proposed. The proposed FB offers reconfigurability at the architectural level and at the channel filter level and is capable of extracting channels of nonuniform bandwidths corresponding to multiple wireless communication standards from the digitized wideband input signal. Design examples show that the proposed FB offers multiplier complexity reduction of 84% over the conventional per-channel (PC) approach, which is best suitable for the extraction of channels of nonuniform bandwidth. The proposed FB has been synthesized on 0.18 μm complementary metal oxide semiconductor (CMOS) technology and compared with the PC approach. Synthesis results show that the proposed FB offers area reduction of 85%, power reduction of 48.5%, and improvement in speed of 56.7% over the PC approach. The proposed FB has been implemented on Xilinx Virtex 2v3000ff1152-4 FPGA and tested using real-time inputs from a vector signal generator.

Photonic vector signal generation employing a novel optical direct-detection in-phase/quadrature-phase upconversion

This work demonstrates the feasibility of the generation of an RF direct-detection vector signal using optical in-phase/quadrature-phase (I/Q) upconversion. The advantage of the proposed transmitter is that no electrical mixer is needed to generate the RF signal. Therefore, I/Q data of RF signals are processed at baseband at the transmitter, which is independent of the carrier frequency of the generated RF signal. A 10 Gb/s 16 quadrature amplitude modulation signal is experimentally demonstrated. Following transmission over a 50 km single-mode fiber, the power penalty is negligible. Moreover, I/Q imbalance of the proposed transmitter is studied and compensated by digital signal processing, which is both numerically and experimentally verified.

Photonic vector signal generation at microwave/millimeter-wave bands employing an optical frequency quadrupling scheme

To the best of our knowledge, a novel photonic architecture to generate vector signals at microwave/millimeter-wave bands employing an optical frequency quadrupling technique based on an external dual-parallel modulator is proposed for the first time. A 312.5 MSym/s quadruple phase-shift keying signal at 25 GHz is experimentally demonstrated using properly precoding driving signal at 6.25 GHz, and optical power penalty is negligible following 50 km single-mode fiber transmission.

Radio Over Fiber for Picocellular Network Architectures

We have studied RF transmission over various multimode fibers (MMFs) and a standard single-mode fiber, targeting picocellular networks for voice, data, and video applications. Bandwidth requirements of MMF links that are based on vertical-cavity surface-emitting laser (VCSEL) have been extensively studied. The performance of the radio-over-fiber link is assessed in terms of the error vector magnitude. Also conducted was a full system analysis, including the investigation of an achievable dynamic range and a noise figure for different low-cost architectures. This was compared to coax-based RF transmission. The IEEE 802.11 a/b/g standard, as well as other applications like radio frequency identification tracking, was considered. For experimental investigations, we have used both commercial wireless access points and a vector signal generator as a signal source, with two types of directly modulated VCSELs - 850-nm sources and 1310-nm high-speed uncooled single-mode AlGaInAs/InP VCSELs. A robust system performance was demonstrated in both 2.4- and 5-GHz RF bands, and record multimode and standard single-mode fiber transmission distances were achieved. A transponder design that can meet system requirements in terms of sensitivity ( 95 dBldrHz2/3) for a dual-band wireless LAN (WLAN) fiber-radio picocellular network was developed. A full 14-cell experimental WLAN system with cells of 4-m radius was implemented to study networking issues such as handoff and cochannel interference.

A comparative study of STBC transmissions at 2.4 GHz over indoor channels using a 2 × 2 MIMO testbed

AbstractIn this paper we employ a 2 × 2 Multiple‐Input Multiple‐Output (MIMO) hardware platform to evaluate, in realistic indoor scenarios, the performance of different space‐time block coded (STBC) transmissions at 2.4 GHz. In particular, we focus on the Alamouti orthogonal scheme considering two types of channel state information (CSI) estimation: a conventional pilot‐aided supervised technique and a recently proposed blind method based on second‐order statistics (SOS). For comparison purposes, we also evaluate the performance of a Differential (non‐coherent) space‐time block coding (DSTBC). DSTBC schemes have the advantage of not requiring CSI estimation but they incur in a 3 dB loss in performance. The hardware MIMO platform is based on high‐performance signal acquisition and generation boards, each one equipped with a 1 GB memory module that allows the transmission of extremely large data frames. Upconversion to RF is performed by two RF vector signal generators whereas downconversion is carried out with two custom circuits designed from commercial components. All the baseband signal processing is implemented off‐line in MATLAB®, making the MIMO testbed very flexible and easily reconfigurable. Using this platform we compare the performance of the described methods in line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) indoor scenarios. Copyright © 2007 John Wiley & Sons, Ltd.