Jocelyn Fiorina

On the asymptotic distribution of the correlation receiver output for time-hopped UWB signals

In ultra-wideband (UWB) communications based on time-hopping (TH) impulse radio, one of the most frequently studied receivers is the correlation receiver. The multiuser interference (MUI) at the output of this receiver is sometimes modeled as a Gaussian random variable. In order to justify this assumption, the conditions of validity of the Central Limit Theorem (CLT) have to be studied in an asymptotic regime where the number of interferers and the processing gain grow toward infinity at the same rate, with the channel degree being kept constant. An asymptotic study is made in this paper based on the so-called Lindebergs condition for the CLT for martingales. Nonsynchronized users sending their signals over independent multipath channels are considered. These users may also have different powers. It is shown that when the frame length grows and the repetition factor is kept constant, then the MUI does not converge in distribution toward a Gaussian random variable. On the other hand, this convergence can be established if the repetition factor grows at the rate of the frame length. In this last situation, closed-form expressions for the signal-to-interference-plus-noise ratio (SINR) are given for TH pulse amplitude modulation (PAM) and pulse position modulation (PPM) UWB transmissions

P-order metric UWB receiver structures with superior performance

The generalized Gaussian probability density function is shown to better approximate the probability density function of the multiple access interference in ultra-wide bandwidth systems than the Gaussian approximation and the Laplacian density approximation. Two ultra-wide bandwidth receiver structures based on this new approximation using a p-order metric receiver decision statistic are investigated for the detection of time-hopping ultra-wide bandwidth wireless signals in multiple access interference channels. The first receiver outperforms both the conventional matched filter ultra-wide bandwidth receiver and the soft-limiting ultra-wide bandwidth receiver when only multiple access interference is present in UWB channels. The second new receiver with adaptive limiting threshold outperforms the conventional matched filter ultra-wide bandwidth receiver, the soft-limiting ultra-wide bandwidth receiver, and the adaptive threshold soft limiting ultra-wide bandwidth receiver in all multiple access interference-plus-noise environments. In multipath channels, a new Rake receiver based on the p-order metric receiver is proposed for signal detection. Mathematical analysis and numerical results show that this new Rake receiver can achieve larger signal-to-interference-plus-noise ratio than the standard matched filter Rake receiver when multipath components are resolvable in UWB channels.

WLC28-2: A Simple IR-UWB Receiver Adapted to Multi-User Interferences

We propose in this paper a simple receiver adapted to multi user interferences (MUI) in impulse radio ultra wide band (IR-UWB). It is known that MUI distribution is not Gaussian in several cases. The classical correlation receiver which is adapted to Gaussian noise, is not adapted to the particular form of UWB MUI and is often far from the performance computed through the standard Gaussian approximation. We show that modeling MUI by a generalized Gaussian distribution helps in deriving a simple receiver which increases the performances and may also outperform the standard Gaussian approximation which was considered formerly to be too optimistic.

Combining UWB with Time Reversal for improved communication and positioning

This work investigates the use of Time Reversal (TR) applied to UWB systems for communication and positioning applications. Potential performance boosts, that are achievable over a single UWB communication link by the sole adoption of TR, are investigated. In the case of multiuser UWB communications, it is shown that TR modifies the distribution of Multi User Interference (MUI) and that further performance improvement can be obtained by adapting the receiver to the specific MUI distribution characteristics. As regards UWB positioning, an enhancement in position estimation accuracy can be achieved when TR reinforces DOA estimation thanks to increased robustness to decreased homogeneity in the propagation medium.

Revisiting TH-IR-UWB performance limits dependency on essential system parameters using the Generalized Gaussian Approximation

The huge potential of Ultra Wide Band Impulse Radio (UWB IR) with Multiple Access was initially evaluated using the Standard Gaussian Approximation (SGA) which assumed Multi-User Interference to be representable as classical Gaussian noise. Thus, under the reference scenario of free space propagation and perfect power control, closed form expressions allowed to express performance in function of the essential system parameters (number of users, impulse waveform, and number of slots per frame). However the derivations of the closed form expressions were based on the Standard Gaussian Approximation which has been proven later to be not valid. We propose here to revisit performance using the more accurate Generalized Gaussian Approximation (GGA).

The non validity of the gaussian approximation for multi-user interference in ultra wide band impulse radio: from an inconvenience to an advantage - transactions papers

The huge potential of ultra wide band impulse radio (UWB IR) with multiple access was initially evaluated using the standard Gaussian approximation which assumed that multi user interference could be approximated as classical Gaussian noise. Later the standard Gaussian approximation has been proved to be invalid in several cases. Thus the performance of the classical UWB IR correlation receiver dramatically reduces. We show in this paper how the non Gaussianity of the multi user interference can be exploited, turning the non Gaussianity into an advantage, increasing the performance with respect to the Gaussian interference case which was supposed to be too optimistic until now.

On the Benefit of a One-Bit Sampling Receiver and Hard Decoding in Impulse Radio Ultra Wide Band Communications With Multi-User Interferences

We propose in this paper to show how a one-bit sampling receiver can be more efficient in some cases than the classical correlation receiver for impulse radio ultra wide band (IR-UWB) communications with high multi user interferences (MUI). This one-bit sampling receiver can also be seen as a hard decoding process of the classical repetition code used in UWB IR. Thus hard decoding can be more efficient than soft decoding in some cases. Such a result is based on the special distribution of UWB MUI. It is known that MUI distribution is not Gaussian in several cases. The classical correlation receiver which is adapted to Gaussian noise, is not adapted to the particular form of UWB MUI. We show that modeling MUI by a generalized Gaussian distribution helps in deriving a receiver which in some cases is nearly equivalent to the one-bit sampling receiver

Cognitive Radio and Networking for Heterogeneous Wireless Networks

This book, written by leading experts from academia and industry, offers a condensed overview on hot topics among the Cognitive Radios and Networks scientific and industrial communities (including those considered within the framework of the European COST Action IC0902) and presents exciting visions for the future. Examples of the subjects considered include the design of new filter bank-based air interfaces for spectrum sharing, medium access control design protocols, the design of cloud-based radio access networks, an evolutionary vision for the development and deployment of cognitive TCP/IP, and regulations relevant to the development of a spectrum sharing market. The concluding chapter comprises a practical, hands-on tutorial for those interested in developing their own research test beds. By focusing on the most recent advances and future avenues, this book will assist researchers in understanding the current issues and solutions in Cognitive Radios and Networks designs.

Trade-off between the number of fingers in the prefilter and in the rake receiver in time reversal IR-UWB

In this paper we investigate the trade-off between the number of fingers in the prefilter of a TR-IR-UWB system versus the number of fingers in the rake receiver. This allows studying the gain brought by time reversal when the complexity is switched from the receiver to the transmitter i.e. when the number of fingers is increased in the prefilter, while it is reduced in the rake receiver.

A New Family of Low-Complexity STBCs for Four Transmit Antennas

Space-Time Block Codes (STBCs) suffer from a prohibitively high decoding complexity unless the low-complexity decodability property is taken into consideration in the STBC design. For this purpose, several families of STBCs that involve a reduced decoding complexity have been proposed, notably the multi-group decodable and the fast decodable (FD) codes. Recently, a new family of codes that combines both of these families namely the fast group decodable (FGD) codes was proposed. In this paper, we propose a new construction scheme for rate-1 FGD codes for 2a transmit antennas. The proposed scheme is then applied to the case of four transmit antennas and we show that the new rate-1 FGD code has the lowest worst-case decoding complexity among existing comparable STBCs. The coding gain of the new rate-1 code is optimized through constellation stretching and proved to be constant irrespective of the underlying QAM constellation prior to normalization. Next, we propose a new rate-2 FD STBC by multiplexing two of our rate-1 codes by the means of a unitary matrix. Also a compromise between rate and complexity is obtained through puncturing our rate-2 FD code giving rise to a new rate-3/2 FD code. The proposed codes are compared to existing codes in the literature and simulation results show that our rate-3/2 code has a lower average decoding complexity while our rate-2 code maintains its lower average decoding complexity in the low SNR region. If a it time-out sphere decoder is employed, our proposed codes outperform existing codes at high SNR region thanks to their lower worst-case decoding complexity.