1,181 research outputs found
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
Performance evaluation of non-prefiltering vs. time reversal prefiltering in distributed and uncoordinated IR-UWB ad-hoc networks
Time Reversal (TR) is a prefiltering scheme mostly analyzed in the context of centralized and synchronous IR-UWB networks, in order to leverage the trade-off between communication performance and device complexity, in particular in presence of multiuser interference. Several strong assumptions have been typically adopted in the analysis of TR, such as the absence of Inter-Symbol / Inter-Frame Interference (ISI/IFI) and multipath dispersion due to complex signal propagation. This work has the main goal of comparing the performance of TR-based systems with traditional non-prefiltered schemes, in the novel context of a distributed and uncoordinated IR-UWB network, under more realistic assumptions including the presence of ISI/IFI and multipath dispersion. Results show that, lack of power control and imperfect channel knowledge affect the performance of both non-prefiltered and TR systems; in these conditions, TR prefiltering still guarantees a performance improvement in sparse/low-loaded and overloaded network scenarios, while the opposite is true for less extreme scenarios, calling for the developement of an adaptive scheme that enables/disables TR prefiltering depending on network conditions
One-Bit Massive MIMO: Channel Estimation and High-Order Modulations
We investigate the information-theoretic throughout achievable on a fading
communication link when the receiver is equipped with one-bit analog-to-digital
converters (ADCs). The analysis is conducted for the setting where neither the
transmitter nor the receiver have a priori information on the realization of
the fading channels. This means that channel-state information needs to be
acquired at the receiver on the basis of the one-bit quantized channel outputs.
We show that least-squares (LS) channel estimation combined with joint pilot
and data processing is capacity achieving in the single-user,
single-receive-antenna case.
We also investigate the achievable uplink throughput in a massive
multiple-input multiple-output system where each element of the antenna array
at the receiver base-station feeds a one-bit ADC. We show that LS channel
estimation and maximum-ratio combining are sufficient to support both multiuser
operation and the use of high-order constellations. This holds in spite of the
severe nonlinearity introduced by the one-bit ADCs
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