In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we present the construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB. The first family encodes adjacent symbols and is based on totally-real cyclic division algebras. The second family encodes the pulses used to transmit one information symbol and permits to achieve high performance levels with lower complexity. Both families of codes achieve full rate, full diversity with non-vanishing determinants for various number of relays. These schemes can be associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM). The third family of codes is information-lossless and does not require any pulse repetitions. It is specific to M-PPM-M'-PAM with M ges 3 and for all values of M'. Simulations performed over realistic indoor UWB channels are provided to verify the theoretical results.

This paper presents the construction of new totally-real space-time coding schemes suited for carrier-less ultra-wideband 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 ges 3, M ges 5 and {M = 5, M ges 7} with n = 2, 3 and 4 transmit antennas respectively

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)

In this paper, we present the construction of full-rate, fully diverse, and totally real space–time (ST) codes for ultra-wideband (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). Performance over realistic indoor UWB channels verify the theoretical claims, and show high performance levels and better immunity against MAI.

In this paper, we present the construction of full rate, fully diverse, and totally real space-time (ST) codes for ultra-wideband (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

Presents recent radio communications research work carried out by LETI (Laboratoire d'Electronique, de Technologie et d'Instrumentation), which is a laboratory belonging to the French Atomic Energy Commission. At the outset, a team from the LETI was involved in a programme to develop robot intervention in hostile environments. One of the first problems to be solved was to find a reliable and robust radio modulation technique for multi-path environments. In this type of situation, conventional radio solutions are unsuccessful and provide only extremely low data rates. The performance of wireless transmissions is much poorer than conventional communications using cables and they have to cope with a transmission channel that is subject to much more interference. In particular, multi-path transmission of radio waves leads to interference phenomena such as widening of the channel impulse response, fading and Doppler noise, which reduce the quality of the transmission. A novel reception structure, implementing direct-sequence spread-spectrum techniques combined with a diversity system, actually benefits from the multi-path phenomena which usually damage conventional radio transmissions. The first receivers developed were based on a surface acoustic wave filter and were subsequently replaced by dedicated digital circuits that perform all the base band processing. The resulting flexibility has made the design of CDMA and high-data-rate wireless systems possible. This research has potential applications in a wide variety of areas, e.g. video surveillance and track-to-train communications in underground systems and factory communications for machine synchronisation.