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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 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 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 space-time (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 extend the Decode-and-Forward cooperative diversity scheme to the context of impulse radio ultra-wideband (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.

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, 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 two transmit diversity schemes for ultra-wideband 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 M with no data rate loss compared to single antenna UWB systems. The second scheme is the extension of Alamouti's space-time (ST) code to UWB communications. Simulations and semi-analytical evaluations of the error 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 considerable performance gains.

The performance prediction and simulation of new communication and positioning systems based on UWB technology require an important effort to reach a deep knowledge of the physical channel. The multipath nature of the indoor channel is the limiting factor for positioning accuracy and communication capabilities of UWB systems in real environments, in particular ISI for high data rate applications. Most of the measurement performed to characterise the UWB channel have been performed in the time-domain by using a sampling oscilloscope with resolution greater than 1 ns. This paper describes a frequency approach based on a vector network analyser with a subnanosecond resolution in accordance with usually UWB pulse width. After an introduction the measurement technique is described and the performances of the sounding chain evaluated. Then an experimental methodology is proposed in order to assess the channel characteristics at different scale levels (small, medium, large). Finally the statistical post-processing for the future measurements is described.

In this paper, we present two space-time schemes for exploiting diversity in multi-antenna impulse radio ultra wide-band (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.