Electrical and Computer Engineering

In this paper, we present two space-time schemes for
exploiting diversity in multi-antenna Impulse Radio Ultra Wideband
(IR-UWB) systems when neither the transmitter nor the
receiver has access to channel state information. The first scheme
encodes the pulses of the same data symbol by a combination of
differential phase shift keying and permutation codes and can be
associated with any number of transmit and receive antennas.
The second scheme encodes different symbols with two transmit
antennas. These schemes are associated with Rake receivers
and achieve full spatial and multi-path diversity with no data
rate loss for constant-modulus multi-dimensional constellations.
Adaptive versions of these schemes are also presented and shown
to approach the performance of coherent receivers in stationary
indoor channels.

In this paper, we propose two transmit diversity schemes for ultrawideband time-hopping (UWB-TH) communications. The performance of these schemes is evaluated for binary antipodal signalling over real UWB channels. The first proposed scheme assigns orthogonal codes to the M transmit antennas and is
capable of achieving the maximum transmit diversity of Mwith no
data rate loss compared to single antenna UWB systems. The
second scheme is the extcnsion of Alamouti’s space-time (ST)
code to UWB communications. Simulations and semi-analytical
evaluations of the mor probability show that giving rise to both
spatial and multipath diversity by associating these schemes with
partial or selective combining Rake receivers (PRake or SRake)
can result in considerablc pcrformance gains.

"In this paper, the advantage of applying space-time (ST) coding on Ultra Wideband (UWB) systems is discussed. In order to achieve very high data rates and important performance gains, combined pulse position modulation (PPM) and pulse amplitude modulation (PAM) constellations along with full diversity and full rate ST codes are used at the transmitter side. The proposed coding-decoding scheme takes into account the nature of the highly frequency selective channel and the multi-dimensional constellation. Furthermore, the coding gain is optimized over different constellations and the possibility of compromising performance to lower peak-to-average power ratios (PAPR) is discussed. Moreover, for simplified receiver structures, V-BLAST decoding scheme was adapted to multi-dimensional signals. Results show considerable performance gains and better immunity against Inter Symbol Interference (ISI) and Multi User Interference (MUI)."

"In this paper, we propose a new Space Time (ST) coding scheme for Time Hopping (TH) Ultra Wideband (UWB) systems. The proposed scheme encodes the pulses used to transmit one information symbol. This permits to achieve full rate and full diversity with a non-vanishing coding gain for all number of transmit antennas. The proposed code shows to be the optimal extension of the codes constructed from cyclic division algebras when inter-pulse coding is performed."

In this paper, we evaluate the performance of Multiple
Input Multiple Output (MIMO) Ultra-Wideband (UWB)
systems over the IEEE 802.15.3a channel model recommendation
[1]. Two schemes are considered, namely a Space-Time (ST)
coded scheme and an uncoded scheme using MMSE receivers.
In order to achieve higher data rates with lower complexity and
better performance, these schemes are associated with combined
Pulse Position Modulation (PPM) and Pulse Amplitude Modulation
(PAM). At the receiver side, the better conditioned channel
matrices offered by the highly frequency selective channel permit
linear receivers to close the gap with respect to fundamental
performance limits.

""Ultra-wideband (UWB) technology has recently attracted the entire wireless community with its great potential for short-range and high data-rate communications. On the other hand, multiantenna (or multiple-input multiple-output) techniques are considered as an effective way to improve the link reliability and transmission rate. In this paper, both aspects are studied through a complete UWB single-input multiple-output (SIMO) channel sounding campaign. The time-domain channel sounder with its antenna array is firstly detailed. Secondly, measurement results will be used to describe interesting antenna array effects and channel behavior (like correlation results and underlying spatial diversity). Finally, in order to show the utility of spatial diversity in UWB systems, the performance of a SIMO system with a Rake receiver will be presented through bit error rate simulations based on measurement results.""

"""In this paper, we describe a global distributed solution that enables the simultaneous performance of time synchronization and positioning in ultra-wideband (UWB) ad hoc networks. On the one hand, the proposed synchronization scheme basically relies on cooperative two-way-ranging/time-of-arrival transactions and a diffusion algorithm that ensures the convergence of clock parameters to average reference values in each node. Although the described solution is generic at first sight, its sensitivity to time-of-arrival accuracy imposes the choice of an impulse-radio ultra-wideband physical layer in the very context. On the other hand, a distributed algorithm coupled with this synchronization scheme mitigates the impact of non-line-of-sight ranging errors on positioning accuracy without any additional protocol hook. More particularly, the realistic UWB ranging error models we use take into account UWB channel effects, as well as detection noises and relative clock drifts. Then, it is demonstrated that a cooperative and distributed maximization of the log-likelihood of range estimates can reduce the uncertainty on estimated positions in comparison with classical distributed weighted least squares approaches. Finally, the proposed distributed maximum log-likelihood algorithm proves to preserve a reasonable level of complexity in each node by approximating asynchronously the positive gradient direction of the log-likelihood function. For both distributed synchronization and positioning algorithms, simulation results are provided to illustrate the relevance of such a solution."""

In this paper, we present a new full rate scheme for exploiting diversity in multi-antenna ultra-wideband (UWB) systems. The independent data streams that are transmitted simultaneously from the different antennas are rendered orthogonal by the use of modified Hermite pulses. At a second time, appropriate real rotations enhance the transmit diversity level. We also consider, for the first time, the problem of Maximum Likelihood (ML) detection with multi-dimensional PPM and hybrid PPM-PAM constellations that can be used in conjunction with the proposed scheme.

In this paper, we extend the Amplify-and-Forward (AF) cooperative
diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we apply a space-time (ST) coding scheme based on totally-real cyclic division algebras in order to achieve full diversity with no data rate losses. At a second time, the pulse repetitions are exploited in order to enhance the performance of the first scheme and to propose a new scheme that achieves comparable performance with lower complexity. These schemes are associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM).

This paper presents the construction of new totallyreal space-time coding schemes suited for carrier-less ultrawideband transmissions. These schemes are associated with pulse position modulation and with hybrid pulse amplitude and position modulation where the input data is modulated onto both the pulse amplitudes and positions. The new schemes have a uniform average transmitted energy per antenna and achieve full rate and full diversity with hybrid M-PPM-M
-PAM for all values of M
and for M ≥ 3, M ≥ 5 and {M = 5,M ≥ 7} with n = 2, 3 and 4 transmit antennas respectively.

In this paper, we study the achievable diversitymultiplexing gain (D-MG) tradeoffs over the IEEE 802.15.3a channel model. In particular, we give an exact expression of the D-MG tradeoff for single antenna systems. This expression is based on a statistical model of the integrated energy of the considered channels. At a second time, we evaluate lower and upper bounds on the D-MG tradeoffs of multi-antenna systems. This formulation gives us more insights on the real potential of multi-antenna techniques with UWB systems. It is shown that even though the asymptotical diversity gain has an infinite value, the multi-antenna techniques can be very beneficial in the practical range of signal-to-noise ratios.

In this paper, we extend the Decode-and-Forward cooperative diversity scheme to the context of impulse radio ultrawideband (IR-UWB). We develop coherent and non-coherent schemes that exploit the spatial diversity in a distributed manner among the different terminals of a wireless network. These schemes are specific to IR-UWB and they take advantage of the pulse repetitions used to convey each information symbol. If Nf is the number of pulses per symbol, the coherent scheme is based on joint symbol and pulse coding and it achieves full diversity with any number of relays for Nf > 1. The non-coherent scheme is based on pulse coding and it achieves full diversity with a maximum number of Nf -1 relays.

The Golden code [1] is a 2 × 2 space-time code that achieves the best known performance with all constellations carved from Z[i]. In this letter, we present the construction of a new coding scheme for 2M-ary biorthogonal pulse position modulations (BPPM) with M ≥ 4. The proposed code satisfies all of the construction constraints of the Golden code and it has the additional advantage of being totally real making it suitable for low cost carrier-less ultra-wideband terminals. Namely, this totally real construction achieves full rate and full diversity with the best known coding gain and without any shaping losses for 2M-BPPM with M ≥ 4.

The golden code [1] is a 2×2 space-time (ST) code that achieves the best known performance with all constellations carved from Z[i]. On the other hand, impulse radio (IR) timehopping (TH) ultra wideband (UWB) is a carrier-less baseband transmission technique. Therefore, being complex-valued, the golden code can not be associated with IR-UWB systems. In this paper, we propose a new ST code that satisfies all of the construction constraints of the golden code and that has the additional advantage of being totally real making it suitable for low cost carrier-less UWB terminals. Unlike the golden code that can be associated with all constellations carved from Z[i], the proposed code is optimal with binary pulse position modulation (PPM) which is a popular modulation scheme for TH-UWB. Moreover, the proposed scheme permits to achieve full transmit diversity with hybrid pulse position and amplitude modulations (PPAM) having two modulation positions.

In this paper, we examine the impact of spatial diversity on ultra-wideband (UWB) systems. This diversity is exploited by deploying two antennas at the UWB terminals. For single-antenna systems, spatial diversity is exploited in a distributed manner where a neighboring node can help the source in delivering its message to a destination. In particular, two spacetime (ST) coding schemes are proposed. The first one is optimal among all totally-real codes having a constant transmitted energy per antenna. Unlike the classical approach of constructing ST codes over infinite fields, the second construction takes the structure of 2-dimensional constellations into consideration in order to propose an appropriate modulation-specific code. These schemes are associated with multi-antenna arrays and with virtual arrays based on the amplify-and-forward (AF) strategy.

In this paper, we present the construction of full rate, fully diverse, and totally real space–time (ST) codes for ultrawideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple access interference (MAI). Simulations performed over realistic indoor UWB channels verify the theoretical claims and show high
performance levels and better immunity against MAI.

In this paper, we study the impact of Inter- Symbol-Interference (ISI) and Multi-User-Interference (MUI) on Multiple-Input-Multiple-Output (MIMO) Ultra-Wideband (UWB) communication systems. At the transmitter side, we consider the two cases where the transmitted data flows are either uncoded or encoded by a convenient Space-Time (ST) block code. These transmission schemes are associated with pulse amplitude modulation (PAM), pulse position modulation (PPM) or joint pulse position and amplitude modulation (PPM-PAM). The receiver is composed of a Rake receiver followed by a maximum-likelihood decoder. The proposed scheme constitutes a candidate solution for very high data rate UWB communications. The considered system model takes the ISI and MUI into account and permits to analyze the performance over the highly frequency selective UWB channels.

In this paper, we propose for the first time a 2 × 2 Space-Time (ST) block code that can be applied with Pulse Position Modulation (PPM) without introducing any constellation extension. This encoding scheme is adapted to low cost carrierless Time-Hopping Ultra-Wideband (TH-UWB) systems where information must be conveyed only by the time delay of the modulated signal that has a very low duty cycle. The proposed scheme permits to achieve full transmit diversity with M-ary PPM constellations for all values of M. Moreover, it permits to overcome the additional phase rotations or amplitude amplifications that are introduced by all the known ST codes such as the Alamouti code [1], the rate-1 codes proposed in [2], [3] for PSK and the diversity schemes proposed in [4] for TH-UWB systems with PAM or PPM.

In this paper, we propose a new Multiple-Input- Multiple-Output (MIMO) transceiver for Time-Hopping Ultra- Wideband (TH-UWB) communications. We consider the problem of Space-Time (ST) coding with binary Pulse Position Modulation (PPM) and we propose the first known family of rate-1 ST codes that can be associated with binary PPM without introducing any additional constellation extension. We prove that the proposed encoding scheme can achieve a full transmit diversity order with 2k transmit antennas. At the receiver side, we propose a Maximum-Likelihood (ML) decoder that is adapted to the structure of the considered multi-dimensional constellation that does not have the structure of a lattice.

In this work, we propose novel families of space–time (ST) block codes that can be associated with impulse radio ultrawideband
(IR-UWB) communication systems. The carrier-less nature of this nonconventional totally real transmission technique necessitates
the construction of new suitable coding schemes. In fact, the last generation of complex-valued ST codes (namely, the perfect codes) cannot be associated with IR-UWB systems where the phase reconstitution at the receiver side is practically infeasible. On the other hand, while the perfect codes were considered mainly with quadrature amplitude modulation (QAM) and hexagonal (HEX) constellations, IR-UWB systems are often associated with pulseposition modulation (PPM) and hybrid PPM-PAM (pulse-amplitude modulation) constellations. In this paper, instead of adopting the classical approach of constructing ST codes over infinite fields ( [i] or [j] for the perfect codes), we study the possibility of constructing modulation-specific codes that are exclusive to PPM and PPM-PAM. The proposed full-rate codes are totally real, information lossless, and have a uniform average energy per transmit antenna. They permit to achieve a full diversity order with any number of transmit antennas. In some situations, the proposed schemes have an optimal nonvanishing coding gain and satisfy all the construction constraints of the perfect codes in addition to the constraint of being totally real. Simulations performed over realistic indoor UWB channels showed that the proposed schemes outperform the best known codes constructed from cyclic division algebras.