5,209 research outputs found
Performance Analysis and Enhancement of Multiband OFDM for UWB Communications
In this paper, we analyze the frequency-hopping orthogonal frequency-division
multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless
personal area networks (WPANs) based on ultra-wideband (UWB) transmission.
Besides considering the standard, we also propose and study system performance
enhancements through the application of Turbo and Repeat-Accumulate (RA) codes,
as well as OFDM bit-loading. Our methodology consists of (a) a study of the
channel model developed under IEEE 802.15 for UWB from a frequency-domain
perspective suited for OFDM transmission, (b) development and quantification of
appropriate information-theoretic performance measures, (c) comparison of these
measures with simulation results for the Multiband OFDM standard proposal as
well as our proposed extensions, and (d) the consideration of the influence of
practical, imperfect channel estimation on the performance. We find that the
current Multiband OFDM standard sufficiently exploits the frequency selectivity
of the UWB channel, and that the system performs in the vicinity of the channel
cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading
algorithm improve the system power efficiency by over 6 dB at a data rate of
480 Mbps.Comment: 32 pages, 10 figures, 1 table. Submitted to the IEEE Transactions on
Wireless Communications (Sep. 28, 2005). Minor revisions based on reviewers'
comments (June 23, 2006
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
Novel wireless modulation technique based on noise
In this paper, a new RF modulation technique is presented. Instead of using sinusoidal carriers as information bearer, pure noise is applied. This allows very simple radio architectures to be used. Spread-spectrum based technology is applied to modulate the noise bearer. Since the transmission bandwidth of the noise bearer can be made very wide, up to ultra-wideband regions, extremely large processing gains can be obtained. This will provide robustness in interference-prone environments. To avoid the local regeneration of the noise reference at the receiver, the Transmit-Reference (TR) concept is applied. In this concept, both the reference noise signal and the modulated noise signal are transmitted, together forming\ud
the bearer. The reference and modulated signals are separated by applying a time offset. By applying different delay times for different channels (users) a new multiple access scheme results based on delay: Delay Division Multiple Access (DDMA). A theoretical analysis is given for the link performance of a single-user and a multi-user system. A testbed has been built to demonstrate the concept. The demonstrator operates in a 50 MHz bandwidth centered at 2.4 GHz. Processing gains ranging from 10¿30 dB have been tested. The testbed confirms the basic behavior as predicted by the theory
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