2,151 research outputs found
A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals
Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility
A digital polar transmitter for multi-band OFDM Ultra-WideBand
Linear power amplifiers used to implement the Ultra-Wideband standard must be
backed off from optimum power efficiency to meet the standard specifications and
the power efficiency suffers. The problem of low efficiency can be mitigated by polar
modulation. Digital polar architectures have been employed on numerous wireless
standards like GSM, EDGE, and WLAN, where the fractional bandwidths achieved
are only about 1%, and the power levels achieved are often in the vicinity of 20 dBm.
Can the architecture be employed on wireless standards with low-power and high
fractional bandwidth requirements and yet achieve good power efficiency?
To answer these question, this thesis studies the application of a digital polar transmitter
architecture with parallel amplifier stages for UWB. The concept of the digital
transmitter is motivated and inspired by three factors. First, unrelenting advances
in the CMOS technology in deep-submicron process and the prevalence of low-cost
Digital Signal processing have resulted in the realization of higher level of integration
using digitally intensive approaches. Furthermore, the architecture is an evolution
of polar modulation, which is known for high power efficiency in other wireless applications.
Finally, the architecture is operated as a digital-to-analog converter which
circumvents the use of converters in conventional transmitters.
Modeling and simulation of the system architecture is performed on the Agilent Advanced
Design System Ptolemy simulation platform. First, by studying the envelope
signal, we found that envelope clipping results in a reduction in the peak-to-average
power ratio which in turn improves the error vector magnitude performance (figure
of merit for the study). In addition, we have demonstrated that a resolution of three
bits suffices for the digital polar transmitter when envelope clipping is performed.
Next, this thesis covers a theoretical derivation for the estimate of the error vector
magnitude based on the resolution, quantization and phase noise errors. An analysis
on the process variations - which result in gain and delay mismatches - for a
digital transmitter architecture with four bits ensues. The above studies allow RF
designers to estimate the number of bits required and the amount of distortion that
can be tolerated in the system.
Next, a study on the circuit implementation was conducted. A DPA that comprises
7 parallel RF amplifiers driven by a constant RF phase-modulated signal and 7
cascode transistors (individually connected in series with the bottom amplifiers)
digitally controlled by a 3-bit digitized envelope signal to reconstruct the UWB
signal at the output. Through the use of NFET models from the IBM 130-nm
technology, our simulation reveals that our DPA is able to achieve an EVM of -
22 dB. The DPA simulations have been performed at 3.432 GHz centre frequency
with a channel bandwidth of 528 MHz, which translates to a fractional bandwidth
of 15.4%. Drain efficiencies of 13.2/19.5/21.0% have been obtained while delivering
-1.9/2.5/5.5 dBm of output power and consuming 5/9/17 mW of power.
In addition, we performed a yield analysis on the digital polar amplifier, based
on unit-weighted and binary-weighted architecture, when gain variations are introduced
in all the individual stages. The dynamic element matching method is also
introduced for the unit-weighted digital polar transmitter. Monte Carlo simulations
reveal that when the gain of the amplifiers are allowed to vary at a mean of 1 with a
standard deviation of 0.2, the binary-weighted architecture obtained a yield of 79%,
while the yields of the unit-weighted architectures are in the neighbourhood of 95%.
Moreover, the dynamic element matching technique demonstrates an improvement
in the yield by approximately 3%.
Finally, a hardware implementation for this architecture based on software-defined
arbitrary waveform generators is studied. In this section, we demonstrate that the error vector magnitude results obtained with a four-stage binary-weighted digital polar
transmitter under ideal combining conditions fulfill the European Computer Manufacturers
Association requirements. The proposed experimental setup, believed to
be the first ever attempted, confirm the feasibility of a digital polar transmitter architecture
for Ultra-Wideband. In addition, we propose a number of power combining
techniques suitable for the hardware implementation. Spatial power combining, in
particular, shows a high potential for the digital polar transmitter architecture.
The above studies demonstrate the feasibility of the digital polar architecture with
good power efficiency for a wideband wireless standard with low-power and high
fractional bandwidth requirements
Millimeter-wave Communication and Radar Sensing â Opportunities, Challenges, and Solutions
With the development of communication and radar sensing technology, people are able to seek for a more convenient life and better experiences. The fifth generation (5G) mobile network provides high speed communication and internet services with a data rate up to several gigabit per second (Gbps). In addition, 5G offers great opportunities of emerging applications, for example, manufacture automation with the help of precise wireless sensing. For future communication and sensing systems, increasing capacity and accuracy is desired, which can be realized at millimeter-wave spectrum from 30 GHz to 300 GHz with several tens of GHz available bandwidth. Wavelength reduces at higher frequency, this implies more compact transceivers and antennas, and high sensing accuracy and imaging resolution. Challenges arise with these application opportunities when it comes to realizing prototype or demonstrators in practice. This thesis proposes some of the solutions addressing such challenges in a laboratory environment.High data rate millimeter-wave transmission experiments have been demonstrated with the help of advanced instrumentations. These demonstrations show the potential of transceiver chipsets. On the other hand, the real-time communication demonstrations are limited to either low modulation order signals or low symbol rate transmissions. The reason for that is the lack of commercially available high-speed analog-to-digital converters (ADCs); therefore, conventional digital synchronization methods are difficult to implement in real-time systems at very high data rates. In this thesis, two synchronous baseband receivers are proposed with carrier recovery subsystems which only require low-speed ADCs [A][B].Besides synchronization, high-frequency signal generation is also a challenge in millimeter-wave communications. The frequency divider is a critical component of a millimeter-wave frequency synthesizer. Having both wide locking range and high working frequencies is a challenge. In this thesis, a tunable delay gated ring oscillator topology is proposed for dual-mode operation and bandwidth extension [C]. Millimeter-wave radar offers advantages for high accuracy sensing. Traditional millimeter-wave radar with frequency-modulated continuous-wave (FMCW), or continuous-wave (CW), all have their disadvantages. Typically, the FMCW radar cannot share the spectrum with other FMCW radars.\ua0 With limited bandwidth, the number of FMCW radars that could coexist in the same area is limited. CW radars have a limited ambiguous distance of a wavelength. In this thesis, a phase-modulated radar with micrometer accuracy is presented [D]. It is applicable in a multi-radar scenario without occupying more bandwidth, and its ambiguous distance is also much larger than the CW radar. Orthogonal frequency-division multiplexing (OFDM) radar has similar properties. However, its traditional fast calculation method, fast Fourier transform (FFT), limits its measurement accuracy. In this thesis, an accuracy enhancement technique is introduced to increase the measurement accuracy up to the micrometer level [E]
Channel Dynamics and SNR Tracking in Millimeter Wave Cellular Systems
The millimeter wave (mmWave) frequencies are likely to play a significant
role in fifth-generation (5G) cellular systems. A key challenge in developing
systems in these bands is the potential for rapid channel dynamics: since
mmWave signals are blocked by many materials, small changes in the position or
orientation of the handset relative to objects in the environment can cause
large swings in the channel quality. This paper addresses the issue of tracking
the signal to noise ratio (SNR), which is an essential procedure for rate
prediction, handover and radio link failure detection. A simple method for
estimating the SNR from periodic synchronization signals is considered. The
method is then evaluated using real experiments in common blockage scenarios
combined with outdoor statistical models
Turbo-Coded Adaptive Modulation Versus Space-Time Trellis Codes for Transmission over Dispersive Channels
Decision feedback equalizer (DFE)-aided turbocoded wideband adaptive quadrature amplitude modulation (AQAM) is proposed, which is capable of combating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo-coding rates capable of maintaining the target bit-error rate while aiming for achieving a highly effective bits per symbol throughput. As a design alternative, we also employ multiple-input/multiple-output DFE-aided spaceâtime trellis codes, which benefit from transmit diversity and hence reduce the temporal channel quality fluctuations. The performance of both systems is characterized and compared when communicating over the COST 207 typical urban wideband fading channel. It was found that the turbo-coded AQAM scheme outperforms the two-transmitter spaceâtime trellis coded system employing two receivers; although, its performance is inferior to the spaceâtime trellis coded arrangement employing three receivers. Index TermsâCoded adaptive modulation, dispersive channels, spaceâtime trellis codes
Fixed point dual carrier modulation performance for wireless USB
Dual Carrier Modulation (DCM) is currently used
as the higher data rate modulation scheme for Multiband
Orthogonal Frequency Division Multiplexing (MB-OFDM) in the
ECMA-368 defined Ultra-Wideband (UWB) radio platform.
ECMA-368 has been chosen as the physical radio platform for
many systems including Wireless USB (W-USB), Bluetooth 3.0
and Wireless HDMI; hence ECMA-368 is an important issue to
consumer electronics and the userâs experience of these products.
In this paper, Log Likelihood Ratio (LLR) demapping method
is used for the DCM demaper implemented in fixed point model.
Channel State Information (CSI) aided scheme coupled with the
band hopping information is used as the further technique to
improve the DCM demapping performance. The receiver
performance for the fixed point DCM is simulated in realistic
multi-path environments
Radio-Communications Architectures
Wireless communications, i.e. radio-communications, are widely used for our different daily needs. Examples are numerous and standard names like BLUETOOTH, WiFI, WiMAX, UMTS, GSM and, more recently, LTE are well-known [Baudoin et al. 2007]. General applications in the RFID or UWB contexts are the subject of many papers. This chapter presents radio-frequency (RF) communication systems architecture for mobile, wireless local area networks (WLAN) and connectivity terminals. An important aspect of today's applications is the data rate increase, especially in connectivity standards like WiFI and WiMAX, because the user demands high Quality of Service (QoS). To increase the data rate we tend to use wideband or multi-standard architecture. The concept of software radio includes a self-reconfigurable radio link and is described here on its RF aspects. The term multi-radio is preferred. This chapter focuses on the transmitter, yet some considerations about the receiver are given. An important aspect of the architecture is that a transceiver is built with respect to the radio-communications signals. We classify them in section 2 by differentiating Continuous Wave (CW) and Impulse Radio (IR) systems. Section 3 is the technical background one has to consider for actual applications. Section 4 summarizes state-of-the-art high data rate architectures and the latest research in multi-radio systems. In section 5, IR architectures for Ultra Wide Band (UWB) systems complete this overview; we will also underline the coexistence and compatibility challenges between CW and IR systems
LTE performance evaluation with realistic channel quality indicator feedback
In the context of mobile communications, the availability of new services and mobile applications along with the constant evolution in terminals run up the need of higher data rates. In order to fulfill such expectations, mobile operators are continually optimizing and upgrading their networks. The Long Term Evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) seems to be the path to follow in a very short term.
The objective of this project is to study the behaviour of the radio resource assignment in LTE under realistic conditions. The scheduling is a key process in the functioning of the radio interface. Thus, two types of schedulers can be identified, the opportunistic, where the scheduler considers the state of the radio channel to make the best allocation possible, and the non-opportunistic, where the allocation has no knowledge of the radio channelâs state.
As the opportunistic option adapts to the radio channel conditions it requires the transmission of a certain level of signalling from users informing about how the channel evolves along time. One of the objectives of this project is to evaluate the system performance under different degrees of feedback. To do this, different CQI reporting methods have been programmed and simulated. So, to achieve this objective it is obvious that a second one is necessary: program and simulate in a more realistic way the LTE radio channel.
The followed methodology has been fundamentally the programming of different mathematical models and algorithms, as well as its simulation. In concrete, one of the main tasks in this work has been to extent a software platform of the research group Wicomtec to obtain more realistic results through dynamic simulations over a dynamic radio channel
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