2,703 research outputs found
Impulse Radio Systems with Multiple Types of Ultra-Wideband Pulses
Spectral properties and performance of multi-pulse impulse radio
ultra-wideband systems with pulse-based polarity randomization are analyzed.
Instead of a single type of pulse transmitted in each frame, multiple types of
pulses are considered, which is shown to reduce the effects of multiple-access
interference. First, the spectral properties of a multi-pulse impulse radio
system is investigated. It is shown that the power spectral density is the
average of spectral contents of different pulse shapes. Then, approximate
closed-form expressions for bit error probability of a multi-pulse impulse
radio system are derived for RAKE receivers in asynchronous multiuser
environments. The theoretical and simulation results indicate that impulse
radio systems that are more robust against multiple-access interference than a
"classical" impulse radio system can be designed with multiple types of
ultra-wideband pulses.Comment: To be presented at the 2005 Conference on Information Sciences and
System
Ultra Wideband Impulse Radio Systems with Multiple Pulse Types
In an ultra wideband (UWB) impulse radio (IR) system, a number of pulses,
each transmitted in an interval called a "frame", is employed to represent one
information symbol. Conventionally, a single type of UWB pulse is used in all
frames of all users. In this paper, IR systems with multiple types of UWB
pulses are considered, where different types of pulses can be used in different
frames by different users. Both stored-reference (SR) and transmitted-reference
(TR) systems are considered. First, the spectral properties of a multi-pulse IR
system with polarity randomization is investigated. It is shown that the
average power spectral density is the average of the spectral contents of
different pulse shapes. Then, approximate closed-form expressions for the bit
error probability of a multi-pulse SR-IR system are derived for RAKE receivers
in asynchronous multiuser environments. The effects of both inter-frame
interference (IFI) and multiple-access interference (MAI) are analyzed. The
theoretical and simulation results indicate that SR-IR systems that are more
robust against IFI and MAI than a "conventional" SR-IR system can be designed
with multiple types of ultra-wideband pulses. Finally, extensions to
multi-pulse TR-IR systems are briefly described.Comment: To appear in the IEEE Journal on Selected Areas in Communications -
Special Issue on Ultrawideband Wireless Communications: Theory and
Application
The Trade-off between Processing Gains of an Impulse Radio UWB System in the Presence of Timing Jitter
In time hopping impulse radio, pulses of duration are transmitted
for each information symbol. This gives rise to two types of processing gain:
(i) pulse combining gain, which is a factor , and (ii) pulse spreading
gain, which is , where is the mean interval between two
subsequent pulses. This paper investigates the trade-off between these two
types of processing gain in the presence of timing jitter. First, an additive
white Gaussian noise (AWGN) channel is considered and approximate closed form
expressions for bit error probability are derived for impulse radio systems
with and without pulse-based polarity randomization. Both symbol-synchronous
and chip-synchronous scenarios are considered. The effects of multiple-access
interference and timing jitter on the selection of optimal system parameters
are explained through theoretical analysis. Finally, a multipath scenario is
considered and the trade-off between processing gains of a synchronous impulse
radio system with pulse-based polarity randomization is analyzed. The effects
of the timing jitter, multiple-access interference and inter-frame interference
are investigated. Simulation studies support the theoretical results.Comment: To appear in the IEEE Transactions on Communication
A low-cost time-hopping impulse radio system for high data rate transmission
We present an efficient, low-cost implementation of time-hopping impulse
radio that fulfills the spectral mask mandated by the FCC and is suitable for
high-data-rate, short-range communications. Key features are: (i) all-baseband
implementation that obviates the need for passband components, (ii) symbol-rate
(not chip rate) sampling, A/D conversion, and digital signal processing, (iii)
fast acquisition due to novel search algorithms, (iv) spectral shaping that can
be adapted to accommodate different spectrum regulations and interference
environments. Computer simulations show that this system can provide 110Mbit/s
at 7-10m distance, as well as higher data rates at shorter distances under FCC
emissions limits. Due to the spreading concept of time-hopping impulse radio,
the system can sustain multiple simultaneous users, and can suppress narrowband
interference effectively.Comment: To appear in EURASIP Journal on Applied Signal Processing (Special
Issue on UWB - State of the Art
IR-UWB Detection and Fusion Strategies using Multiple Detector Types
Optimal detection of ultra wideband (UWB) pulses in a UWB transceiver
employing multiple detector types is proposed and analyzed in this paper. We
propose several fusion techniques for fusing decisions made by individual
IR-UWB detectors. We assess the performance of these fusion techniques for
commonly used detector types like matched filter, energy detector and amplitude
detector. In order to perform this, we derive the detection performance
equation for each of the detectors in terms of false alarm rate, shape of the
pulse and number of UWB pulses used in the detection and apply these in the
fusion algorithms. We show that the performance can be improved approximately
by 4 dB in terms of signal to noise ratio (SNR) for perfect detectability of a
UWB signal in a practical scenario by fusing the decisions from individual
detectors.Comment: Accepted for publishing in IEEE WCNC 201
Optimal and Suboptimal Finger Selection Algorithms for MMSE Rake Receivers in Impulse Radio Ultra-Wideband Systems
Convex relaxations of the optimal finger selection algorithm are proposed for
a minimum mean square error (MMSE) Rake receiver in an impulse radio
ultra-wideband system. First, the optimal finger selection problem is
formulated as an integer programming problem with a non-convex objective
function. Then, the objective function is approximated by a convex function and
the integer programming problem is solved by means of constraint relaxation
techniques. The proposed algorithms are suboptimal due to the approximate
objective function and the constraint relaxation steps. However, they can be
used in conjunction with the conventional finger selection algorithm, which is
suboptimal on its own since it ignores the correlation between multipath
components, to obtain performances reasonably close to that of the optimal
scheme that cannot be implemented in practice due to its complexity. The
proposed algorithms leverage convexity of the optimization problem
formulations, which is the watershed between `easy' and `difficult'
optimization problems.Comment: To appear in IEEE Wireless Communications and Networking Conference
(WCNC 2005), New Orleans, LA, March 13-17, 200
A Genetic Algorithm Based Finger Selection Scheme for UWB MMSE Rake Receivers
Due to a large number of multipath components in a typical ultra wideband
(UWB) system, selective Rake (SRake) receivers, which combine energy from a
subset of multipath components, are commonly employed. In order to optimize
system performance, an optimal selection of multipath components to be employed
at fingers of an SRake receiver needs to be considered. In this paper, this
finger selection problem is investigated for a minimum mean square error (MMSE)
UWB SRake receiver. Since the optimal solution is NP hard, a genetic algorithm
(GA) based iterative scheme is proposed, which can achieve near-optimal
performance after a reasonable number of iterations. Simulation results are
presented to compare the performance of the proposed finger selection algorithm
with those of the conventional and optimal schemes.Comment: To appear in the Proc. IEEE International Conference on Ultrawideband
(ICU-2005
Multi Detector Fusion of Dynamic TOA Estimation using Kalman Filter
In this paper, we propose fusion of dynamic TOA (time of arrival) from
multiple non-coherent detectors like energy detectors operating at sub-Nyquist
rate through Kalman filtering. We also show that by using multiple of these
energy detectors, we can achieve the performance of a digital matched filter
implementation in the AWGN (additive white Gaussian noise) setting. We derive
analytical expression for number of energy detectors needed to achieve the
matched filter performance. We demonstrate in simulation the validity of our
analytical approach. Results indicate that number of energy detectors needed
will be high at low SNRs and converge to a constant number as the SNR
increases. We also study the performance of the strategy proposed using IEEE
802.15.4a CM1 channel model and show in simulation that two sub-Nyquist
detectors are sufficient to match the performance of digital matched filter
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