463 research outputs found
Multi-standard programmable baseband modulator for next generation wireless communication
Considerable research has taken place in recent times in the area of
parameterization of software defined radio (SDR) architecture. Parameterization
decreases the size of the software to be downloaded and also limits the
hardware reconfiguration time. The present paper is based on the design and
development of a programmable baseband modulator that perform the QPSK
modulation schemes and as well as its other three commonly used variants to
satisfy the requirement of several established 2G and 3G wireless communication
standards. The proposed design has been shown to be capable of operating at a
maximum data rate of 77 Mbps on Xilinx Virtex 2-Pro University field
programmable gate array (FPGA) board. The pulse shaping root raised cosine
(RRC) filter has been implemented using distributed arithmetic (DA) technique
in the present work in order to reduce the computational complexity, and to
achieve appropriate power reduction and enhanced throughput. The designed
multiplier-less programmable 32-tap FIR-based RRC filter has been found to
withstand a peak inter-symbol interference (ISI) distortion of -41 dB
Electro-optic frequency response shaping using embedded FIR filters in slow-wave modulators
A novel method is presented to embed finite-impulse-response filters in slow-wave Mach-Zehnder modulators. This allows to adjust the electro-optic frequency response to the designer's needs. The filter is embedded by adding optical delay lines and optical crossings between phase shifter segments. The position of the delay lines and crossing in the modulator and the delay line length determine the final response. In this work, we provide a full analysis and modeling approach of the proposed technique and apply it to a silicon photonic modulator. However, the technique is generally applicable to slow-wave modulators and thus not limited to a silicon photonics platform. The modeling is verified using measurements on the manufactured devices. A shaped modulator is used in C-band transmission experiments with 56 Gb/s NRZ data over 3 km fiber to counteract chromatic dispersion and show the advantage over a standard modulator
Design and Validation of a Software Defined Radio Testbed for DVB-T Transmission
This paper describes the design and validation of a Software Defined Radio (SDR) testbed, which can be used for Digital Television transmission using the Digital Video Broadcasting - Terrestrial (DVB-T) standard. In order to generate a DVB-T-compliant signal with low computational complexity, we design an SDR architecture that uses the C/C++ language and exploits multithreading and vectorized instructions. Then, we transmit the generated DVB-T signal in real time, using a common PC equipped with multicore central processing units (CPUs) and a commercially available SDR modem board. The proposed SDR architecture has been validated using fixed TV sets, and portable receivers. Our results show that the proposed SDR architecture for DVB-T transmission is a low-cost low-complexity solution that, in the worst case, only requires less than 22% of CPU load and less than 170 MB of memory usage, on a 3.0 GHz Core i7 processor. In addition, using the same SDR modem board, we design an off-line software receiver that also performs time synchronization and carrier frequency offset estimation and compensation
Design of Analog-to-Digital Converters with Embedded Mixing for Ultra-Low-Power Radio Receivers
In the field of radio receivers, down-conversion methods usually rely on one (or more)
explicit mixing stage(s) before the analog-to-digital converter (ADC). These stages not
only contribute to the overall power consumption but also have an impact on area and can
compromise the receiver’s performance in terms of noise and linearity. On the other hand,
most ADCs require some sort of reference signal in order to properly digitize an analog
input signal. The implementation of this reference signal usually relies on bandgap
circuits and reference buffers to generate a constant, stable, dc signal. Disregarding this
conventional approach, the work developed in this thesis aims to explore the viability
behind the usage of a variable reference signal. Moreover, it demonstrates that not only
can an input signal be properly digitized, but also shifted up and down in frequency,
effectively embedding the mixing operation in an ADC. As a result, ADCs in receiver
chains can perform double-duty as both a quantizer and a mixing stage. The lesser known
charge-sharing (CS) topology, within the successive approximation register (SAR) ADCs,
is used for a practical implementation, due to its feature of “pre-charging” the reference
signal prior to the conversion. Simulation results from an 8-bit CS-SAR ADC designed in
a 0.13 μm CMOS technology validate the proposed technique
Machine Learning in Digital Signal Processing for Optical Transmission Systems
The future demand for digital information will exceed the capabilities of current optical communication systems, which are approaching their limits due to component and fiber intrinsic non-linear effects. Machine learning methods are promising to find new ways of leverage the available resources and to explore new solutions. Although, some of the machine learning methods such as adaptive non-linear filtering and probabilistic modeling are not novel in the field of telecommunication, enhanced powerful architecture designs together with increasing computing power make it possible to tackle more complex problems today. The methods presented in this work apply machine learning on optical communication systems with two main contributions. First, an unsupervised learning algorithm with embedded additive white Gaussian noise (AWGN) channel and appropriate power constraint is trained end-to-end, learning a geometric constellation shape for lowest bit-error rates over amplified and unamplified links. Second, supervised machine learning methods, especially deep neural networks with and without internal cyclical connections, are investigated to combat linear and non-linear inter-symbol interference (ISI) as well as colored noise effects introduced by the components and the fiber. On high-bandwidth coherent optical transmission setups their performances and complexities are experimentally evaluated and benchmarked against conventional digital signal processing (DSP) approaches. This thesis shows how machine learning can be applied to optical communication systems. In particular, it is demonstrated that machine learning is a viable designing and DSP tool to increase the capabilities of optical communication systems
Transmission of 120 Gbaud QAM with an all-silicon segmented modulator
Segmenting a silicon modulator can substantially increase its electro-optic bandwidth without sacrificing modulation
efficiency. We demonstrate a segmented silicon IQ modulator
and experimentally explore both modulator design and operating
point to optimize systems trade-offs in coherent detection. An
electro–optic bandwidth of greater than 40 GHz is measured for
a 4-mm-long segment, and greater than 60 GHz for a 2-mmlong segment. We evaluate optical transmission experimentally
at 120 Gbaud for 16-ary quadrature amplitude modulation
(QAM) and 32QAM. The segments are operated in tandem with
identical data at each segment. We present an experimental
method to align data timing between the segments. Through
the optimization of segment biasing and linear compensation,
we have achieved a bit error rate (BER) of 16QAM well below
the 20% forward error correction (FEC) threshold (2 × 10−2
).
Adding nonlinear pre-compensation allows for 32QAM with a
BER below the 24% FEC threshold (4.5 × 10−2
), enabling a
net rate of 483 Gbs per polarization. The modulator can also
be operated as an optical digital analogy converter for complex
optical signal generation, for which 100 Gbs is achieved for a
proof of concept
Implementing the SC-FDMA transmission technique using the GNURadio platform
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaFCT/MEC - (PTDC/EEA- TEL/120666/2010),
MANY2COMWIN (EXPL/EEI-TEL/0969/2013) and ADIN (PTDC/EEI-TEL/2990/2012
- …