1,098 research outputs found
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Linearisation Method of DML-Based Transmitters for Optical Communications Part III: Pulse Amplitude Modulation
A new linearization method for optical transmitters based on directly modulated lasers (DMLs), named the Stretched A method, was proposed in Parts I and II of this work. Parts I and II presented the theoretical framework of the method for non-return-To-zero (NRZ) modulation and related detailed simulation and experimental results. Here, we extend the method to pulse amplitude modulation schemes (PAM). Focussing on 4-level PAM (PAM-4), we present the theoretical background and discuss implementation options. A simplified variation of the method for the generation of PAM signals with a significantly lower number of sub-currents is proposed. Simulation studies for PAM-4 transmission at 50 GBaud (100 Gb/s) and an experimental proof-of-principle demonstration at 16 GBaud (32 Gb/s) are reported based on 850 nm vertical-cavity surface-emitting lasers (VCSELs). For PAM-4, products of effective eye diagram areas ({\boldsymbol{PS}}) of 0.6 × 10-5 and 43 × 10-5 before and after applying the Stretched A method were measured, demonstrating an improvement ratio of ∼72. The sensitivity and tolerances of the method are analyzed using simulation and experiment
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Linearisation Method of DML-based Transmitters for Optical Communications Part II: Experimental Demonstration and Implementation Methods
In this paper, we report the first experimental demonstration of the Stretched A linearisation method. The theoretical framework of the method and related simulation studies have been presented in Part I of this work. Here, we apply the method on an 850 nm multimode vertical-cavity surface-emitting laser (VCSEL) specified for operation at 10 Gb/s and demonstrate good quality optical output waveforms with little non-linear distortion at 16 Gb/s using non-return-to-zero (NRZ) modulation. An experimental sensitivity analysis on the generation of the required modulating current components demonstrates large tolerance to parameter mismatch. In addition, it is shown that an adaptive gain scheme can improve the tolerance to the timing offset between the current components. Potential hardware implementations using either analog or digital electronics are also discussed
Reduction of Proximity Effects on UHF Passive RFID Systems by Using Tags with Polarization Diversity
A new technique that enables passive ultra high fre-
quency (UHF) radio frequency identification (RFID) tags to be
read when they are placed in close proximity in an array is pre-
sented. This paper demonstrates that, in a linear tag array with
a tag separation of 1 cm, the interaction between the backscat-
tered waves and incident wave causes a significant degradation in
tag sensitivity. It is found that the use of tags that have polariza-
tion diversity can improve the read performance when they are
placed in close proximity to one another compared with conven-
tional linear tags. Two ways of achieving polarization diversity are
studied in this paper, namely: 1) using a circularly polarized tag
and 2) using a cross-polarized tag pair. Both methods show an
improvement in close proximity read performance and it is exper-
imentally demonstrated that by using cross-polarized tag pairs in
an array, one achieves on average a 2.6-dB increase in read power
margin for a 57-tag array with 1 cm separation compared with
using conventional linearly polarized tags.This work has been supported by UK Engineering and
Physical Science Research Council
via the COPOSII project.This is the final published version. It first appeared at http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7042269
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Low-Cost MIMO radio over fiber system for multiservice das using double sideband frequency translation
In this paper, a novel low-cost DSB frequency translation system is experimentally demonstrated and its theory is mathematically proved. The new system is capable of transmitting wideband LTE MIMO signals and supporting multiple services. Experimentally, 2×2 LTE MIMO channels with 20MHz bandwidth, and a 700MHz carrier frequency, are transmitted simultaneously along with an IEEE 802.11g signal (54Mbps) over a 300m length of multi-mode fiber (MMF). The MIMO channel matrix of the system is retrieved and the condition number is calculated. It can be seen in the experimental results that the system is well conditioned, has a low error vector magnitude (EVM) and the transmission of the MIMO signals has negligible effect on the IEEE 802.11g signal. The use of a preamplifier minimizes the non-linearity introduced by the frequency mixers, resulting in a high spurious-free dynamic range (SFDR). Compared to a single sideband (SSB) system, where multiple filters are used and two channels encounter different EVMs, the new DSB system avoids unnecessary filtering and the impairments introduced will be the same for both channels. Therefore it can be concluded that the improved MIMO over fiber system using DSB frequency translation technology is a potential low-cost solution for multiservice MIMO-enabled distributed antenna systems (DAS).This work was supported in part of the UK Engineering and Physical Sciences Research Council via the COPOS II grant and the European Community via the FP7 programme Quaternian project.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/JLT.2016.258208
Power margin reduction in linear passive UHF RFID tag arrays
This paper studies the power margin reduction
in linear passive UHF RFID tag arrays due to proximity effects.
It is shown experimentally that a 40% reduction in tag power
margin occurs when two tags are placed with a separation of
less than 2cm. Major causes of tag sensitivity degradation due
to proximity in arrays are analyzed by experiment and
simulation, including tag detuning, shadowing and re-emission
cancellation. It is shown that tag detuning has a significant
effect when tags are separated by less than 7mm. At larger
separations in excess of 1cm, the tag shadowing effect and
interactions between the backscattered waves cause more
significant degradation for large tag arrays.This work has been supported by UK Engineering and
Physical Science Research Council via the COPOSII project.This is the author accepted manuscript. The final version is available at http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=6934248
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