Space–Time Coding for Multiuser Ultra-Wideband Communications

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     

On the Amplify-and-Forward Cooperative Diversity with Time-Hopping Ultra-Wideband Communications

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.     

Orthogonal Space-Time Block Codes for Binary Pulse Position Modulation

In this paper, we propose orthogonal Space-Time (ST) codes for binary Pulse Position Modulations (PPM). Unlike the well known orthogonal ST codes, the proposed schemes verify the additional constraint of achieving a full transmit diversity order without introducing any phase rotations. This renders the proposed codes suitable for Free-Space Optical (FSO) communications with direct detection and for Ultra-WideBand (UWB) communications. At the receiver side, optimal detection can be achieved with linear operations and the proposed codes can be also applied with On-Off Keying (OOK).     

Distributed Algebraic Space-Time Codes for Ultra-Wideband Communications

In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra-wideband. In particular, we present the construction of two families of distributed algebraic space-time codes. The first family 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 with various numbers of relays. Simulations performed over realistic indoor UWB channel models show important performance gains.     

Priority-aware optical shared protection: An offline evaluation study

The availability of an optical connection is considered to be a critical service differentiator in WDM optical networks. In this regard, the design of a protection scheme that improves the availability of high priority optical connections and makes efficient use of optical resources is a major challenge faced by optical network operators. In a previous study, we proposed the so-called priority-aware shared protection survivability scheme as a potential solution to this design issue.In this paper, we complement our previous study. More specifically, we develop an offline study whose main purpose is to assess the efficiency of the priority-aware shared protection scheme. Through this study, we show that the priority-aware shared protection strategy as opposed to existing protection strategies is able to achieve the best tradeoff between optical resource usage and optical connections’ availability satisfaction.     

On Space–Time Coding With Pulse Position and Amplitude Modulations for Time-Hopping Ultra-Wideband Systems

In this work, we propose novel families of space-time (ST) block codes that can be associated with impulse radio ultra-wideband (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 pulse-position 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 or 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.     

A Space-Time Coded MIMO TH-UWB Transceiver with Binary Pulse Position Modulation

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 2^k 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.     

A 2/spl times/2 antennas ultra-wideband system with biorthogonal pulse position modulation

The Golden code is a 2/spl times/2 space-time code that achieves the best known performance with all constellations carved from /spl Zopf/[i]. In this letter, we present the construction of a new coding scheme for 2M-ary biorthogonal pulse position modulations (BPPM) with M/spl ges/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/spl ges/4.     

Pulse antenna permutation and pulse antenna modulation: two novel diversity schemes for achieving very high data-rates with unipolar MIMO-UWB communications

In this paper, we consider the problem of applying the Multiple-Input-Multiple-Output (MIMO) techniques on Impulse-Radio Time-Hopping Ultra-Wideband (IR-TH-UWB) communications. In particular, we propose two novel Space-Time (ST) block codes that are suitable for UWB. The proposed encoded MIMO-UWB schemes present the main advantage of conveying the information only through the positions of the very short unipolar UWB pulses. The constraint of unipolar transmissions keeps the transceiver structures very simple since it imposes no additional constraints on the RF circuitry to control the amplitudes or the phases of the sub-nanosecond UWB pulses. Consider the case where the transmitter is equipped with P antennas and where M PPM modulation positions are available. The first proposed scheme achieves a full transmit diversity order for M ges P while transmitting at the rate of log₂(M) bits Per Channel Use (PCU). The second scheme is fully diverse with any number of antennas and transmits at a rate of M log₂(P)/P bits PCU. The proposed codes permit to achieve different levels of compromise between complexity and performance since scheme 1 necessitates M-dimensional Maximum-Likelihood (ML) decoding while scheme 2 necessitates MP-dimensional decoding. We also present a comprehensive analysis on the enhancement in terms of the data rate achieved at a certain communication distance based on realistic indoor channel models and on an exact system model that takes inter-pulse-interference and intersymbol- interference into consideration.     

Achieving full transmit diversity for PPM constellations with any number of antennas via double position and symbol permutations

We present a general technique for constructing minimal-delay rate-1 Space-Time (ST) block codes for Pulse Position Modulations (PPM) with an arbitrary number of transmit antennas. We show that the novel idea of time-domain constellation extension as well as introducing joint position and symbol permutations achieves a full transmit diversity order while maintaining unipolar transmissions. This renders the proposed scheme suitable for low-cost Time-Hopping Ultra- Wideband (TH-UWB) systems as well as Free-Space Optical (FSO) communications with direct detection.