Cocktail parties, busy streets, and other noisy environments pose a difficult challenge to the auditory system: how to focus attention on selected sounds while ignoring others? Neurons of primary auditory cortex, many of which are sharply tuned to sound frequency, could help solve this problem by filtering selected sound information based on frequency-content. To investigate whether this occurs, we used high-resolution fMRI at 7 tesla to map the fine-scale frequency-tuning (1.5 mm isotropic resolution) of primary auditory areas A1 and R in six human participants. Then, in a selective attention experiment, participants heard low (250 Hz)- and high (4000 Hz)-frequency streams of tones presented at the same time (dual-stream) and were instructed to focus attention onto one stream versus the other, switching back and forth every 30 s. Attention to low-frequency tones enhanced neural responses within low-frequency-tuned voxels relative to high, and when attention switched the pattern quickly reversed. Thus, like a radio, human primary auditory cortex is able to tune into attended frequency channels and can switch channels on demand.
Ultra-wideband (UWB) communication is an emerging technique for wireless transmission in the 3.1-10.6 GHz unlicensed band with signal bandwidths of 500 MHz or greater. A non-coherent receiver based on energy collection reduces complexity, cost, and power consumption at the cost of channel spectral efficiency. The receiver collects the signal energy in two time windows and determines the transmitted bits based on which window has greater energy. This thesis explains the implementation of low-complexity detection, synchronization, and decoding algorithms for a non-coherent ultra-wideband receiver. The receiver is modeled in MATLAB to measure performance. The UWB receiver performs effectively in noisy channels. At the signal-to-noise ratio (SNR) of 0 dB, the receiver achieves a detection miss rate of 2.1% and a false alarm rate of 1.2%. The synchronization error (within ±2 chip periods) rate is 0.5%. The bit error rate is 8.6%, but it drops sharply to 0.1% at an SNR of 5 dB. Moreover, the detection and the synchronization processes take 19.72 p.s and 22.53 pts, respectively. The digital system is implemented in Verilog, which is mapped to hardware (FPGA). In the final system, a radio frequency and an analog front-end interface with the FPGA...
Conference Paper; Mobile users' capacity is limited by the fact that within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. We are proposing a new form of diversity, whereby diversity gains are achieved via the cooperation of in-cell users. Results show that, even though the inter-user channel is noisy, cooperation leads not only to an increase in capacity but also to a more robust system, where users' achievable rates are less susceptible to channel variations.; Nokia
As wireless systems proliferate worldwide, interference is becoming one of the main problems for system designers. Interference, which occurs when multiple transmissions
take place over a common communication medium, limits system performance. Wireless devices can coordinate the use of scarce radio resources in order to manage the interference and establish successful communication. To effectively deal with the interference problem, some wireless devices must have a certain level of knowledge about the interference. In practice, this knowledge comes at the expense of using more resources (such as employing a proper channel training mechanism). With the remaining available resources, the question is how to achieve reliable communication? This thesis investigates an information theoretic approach and employs several coding techniques to improve system performance by either cancelling the interference or extracting knowledge from it about the information signal.
The first part of this thesis considers the transmission of information signals over a fading channel that is disturbed with additional interference. The system's information
theoretic limit in terms of mean square error distortion is assessed. Moreover, hybrid coding schemes are proposed and analyzed to obtain an achievable performance.
As an extension to this problem...
As the wireless cellular market reaches competitive levels never seen before, network operators need to focus on maintaining Quality of Service (QoS) a main priority if they wish to attract new subscribers while keeping existing customers satisfied.
Speech Quality as perceived by the end user is one major example of a characteristic in constant need of maintenance and improvement.
It is in this topic that this Master Thesis project fits in. Making use of an intrusive method of speech quality evaluation, as a means to further study and characterize the performance of speech codecs in second-generation (2G) and third-generation (3G) technologies. Trying to find further correlation between codecs with similar bit rates, along with the exploration of certain transmission parameters which may aid in the assessment of speech quality.
Due to some limitations concerning the audio analyzer equipment that was to be employed, a different system for recording the test samples was sought out. Although the new designed system is not standard, after extensive testing and optimization of the system's parameters, final results were found reliable and satisfactory. Tests include a set of high and low bit rate codecs for both 2G and 3G, where values were compared and analysed...
We consider a wideband spectrum sharing system where a secondary user can
share a number of orthogonal frequency bands where each band is licensed to an
individual primary user. We address the problem of optimum secondary transmit
power allocation for its ergodic capacity maximization subject to an average
sum (across the bands) transmit power constraint and individual average
interference constraints on the primary users. The major contribution of our
work lies in considering quantized channel state information (CSI)(for the
vector channel space consisting of all secondary-to-secondary and
secondary-to-primary channels) at the secondary transmitter. It is assumed that
a band manager or a cognitive radio service provider has access to the full CSI
information from the secondary and primary receivers and designs (offline) an
optimal power codebook based on the statistical information (channel
distributions) of the channels and feeds back the index of the codebook to the
secondary transmitter for every channel realization in real-time, via a
delay-free noiseless limited feedback channel. A modified Generalized
Lloyds-type algorithm (GLA) is designed for deriving the optimal power
codebook. An approximate quantized power allocation (AQPA) algorithm is also
Spectrum sensing is a fundamental component in cognitive radio. A major
challenge in this area is the requirement of a high sampling rate in the
sensing of a wideband signal. In this paper a wideband spectrum sensing model
is presented that utilizes a sub-Nyquist sampling scheme to bring substantial
savings in terms of the sampling rate. The correlation matrix of a finite
number of noisy samples is computed and used by a subspace estimator to detect
the occupied and vacant channels of the spectrum. In contrast with common
methods, the proposedmethod does not need the knowledge of signal properties
that mitigates the uncertainty problem. We evaluate the performance of this
method by computing the probability of detecting signal occupancy in terms of
the number of samples and the SNR of randomly generated signals. The results
show a reliable detection even in low SNR and small number of samples.
One successful detection technique for high-energy cosmic rays is based on
the radio signal emitted by the charged particles in an air shower. The LOPES
experiment at Karlsruhe Institute of Technology, Germany, has made major
contributions to the evolution of this technique. LOPES was reconfigured
several times to improve and further develop the radio detection technique. In
the latest setup LOPES consisted of 10 tripole antennas. With this, LOPES 3D
was the first cosmic ray experiment measuring all three vectorial field
components at once and thereby gaining the full information about the electric
field vector. We present an analysis based on the data taken with special focus
on the benefits of a direct measurement of the vertical polarization component.
We demonstrate that by measuring all polarization components the detection and
reconstruction efficiency is increased and noisy single channel data can be
reconstructed by utilising the information from the other two channels of one
antenna station.; Comment: Proceedings of 33rd International Cosmic Ray Conference, RIO 2013
Probabilistic broadcast has been widely used as a flooding optimization
mechanism to alleviate the effect of broadcast storm problem (BSP) in mobile ad
hoc networks (MANETs). Many research studies have been carried-out to develop
and evaluate the performance of this mechanism in an error-free (noiseless)
environment. In reality, wireless communication channels in MANETs are an
error-prone and suffer from high packet-loss due to presence of noise, i.e.,
noisy environment. In this paper, we propose a simulation model that can be
used to evaluate the performance of probabilistic broadcast for flooding in
noisy environment. In the proposed model, the noise-level is represented by a
generic name, probability of reception (pc) (0<=pc<=1), where pc=1 for
noiseless and <1 for noisy environment. The effect of noise is determined
randomly by generating a random number \zeta (0<=\zeta<1); if \zeta<=pc means
the packet is successfully delivered to the receiving node, otherwise,
unsuccessful delivery occurs. The proposed model is implemented on a MANET
simulator, namely, MANSim. The effect of noise on the performance of
probabilistic algorithm was investigated in four scenarios. The main
conclusions of these scenarios are: the performance of probabilistic algorithm
suffers in presence of noise. However...
For systems and devices, such as cognitive radio and networks, that need to
be aware of available frequency bands, spectrum sensing has an important role.
A major challenge in this area is the requirement of a high sampling rate in
the sensing of a wideband signal. In this paper a wideband spectrum sensing
method is presented that utilizes a sub-Nyquist sampling scheme to bring
substantial savings in terms of the sampling rate. The correlation matrix of a
finite number of noisy samples is computed and used by a non-linear least
square (NLLS) estimator to detect the occupied and vacant channels of the
spectrum. We provide an expression for the detection threshold as a function of
sampling parameters and noise power. Also, a sequential forward selection
algorithm is presented to find the occupied channels with low complexity. The
method can be applied to both correlated and uncorrelated wideband multichannel
signals. A comparison with conventional energy detection using Nyquist-rate
sampling shows that the proposed scheme can yield similar performance for SNR
above 4 dB with a factor of 3 smaller sampling rate.; Comment: IEEE Dyspan 2011. arXiv admin note: substantial text overlap with
We consider a spectrum sharing communication scenario in which a primary and
a secondary users are communicating, simultaneously, with their respective
destinations using the same frequency carrier. Both optimal power profile and
ergodic capacity are derived for fading channels, under an average transmit
power and an instantaneous interference outage constraints. Unlike previous
studies, we assume that the secondary user has a noisy version of the cross
link and the secondary link Channel State Information (CSI). After deriving the
capacity in this case, we provide an ergodic capacity generalization, through a
unified expression, that encompasses several previously studied spectrum
sharing settings. In addition, we provide an asymptotic capacity analysis at
high and low signal-to-noise ratio (SNR). Numerical results, applied for
independent Rayleigh fading channels, show that at low SNR regime, only the
secondary channel estimation matters with no effect of the cross link on the
capacity; whereas at high SNR regime, the capacity is rather driven by the
cross link CSI. Furthermore, a practical on-off power allocation scheme is
proposed and is shown, through numerical results, to achieve the full capacity
at high and low SNR; Comment: 12 pages...
The basic idea of device-to-device (D2D) communication is that pairs of
suitably selected wireless devices reuse the cellular spectrum to establish
direct communication links, provided that the adverse effects of D2D
communication on cellular users is minimized and cellular users are given a
higher priority in using limited wireless resources. Despite its great
potential in terms of coverage and capacity performance, implementing this new
concept poses some challenges, in particular with respect to radio resource
management. The main challenges arise from a strong need for distributed D2D
solutions that operate in the absence of precise channel and network knowledge.
In order to address this challenge, this paper studies a resource allocation
problem in a single-cell wireless network with multiple D2D users sharing the
available radio frequency channels with cellular users. We consider a realistic
scenario where the base station (BS) is provided with strictly limited channel
knowledge while D2D and cellular users have no information. We prove a
lower-bound for the cellular aggregate utility in the downlink with fixed BS
power, which allows for decoupling the channel allocation and D2D power control
problems. An efficient graph-theoretical approach is proposed to perform the
In these series of multi-part papers, a systematic study of fundamental
limits of communications in interference networks is established. Here,
interference network is referred to as a general single-hop communication
scenario with arbitrary number of transmitters and receivers, and also
arbitrary distribution of messages among transmitters and receivers. It is
shown that the information flow in such networks follows similar derivations
from many aspects. This systematic study is launched by considering the basic
building blocks in Part I. The Multiple Access Channel (MAC), the Broadcast
Channel (BC), the Classical Interference Channel (CIC) and the Cognitive Radio
Channel (CRC) are proposed as the main building blocks for all interference
networks. First, a brief review of existing results regarding these basic
structures is presented. New observations are also presented in this regard.
Specifically, it is shown that the well-known strong interference conditions
for the two-user CIC do not change if the inputs are dependent. Next, new
capacity outer bounds are established for the basic structures with two
receivers. These outer bounds are all derived based on a unified framework. By
using the derived outer bounds, some new capacity results are proved for the
CIC and the CRC; a mixed interference regime is identified for the two-user
discrete CIC where the sum-rate capacity is established. Also...