A New Family of Space-Time Codes for Pulse

2009

In this paper, we consider the problem of Space- Time (ST) coding with unipolar Pulse Position Modulations (PPM) and propose a novel ST code that satisfies a large number of construction constraints rendering it superior to the existing PPM encoding schemes. In particular, the proposed 2 × 2 code achieves a full transmit diversity order while transmitting at a rate of 1 PPM symbol per channel use. The proposed scheme can be associated with M-ary PPM constellations for all even values of M without introducing any constellation expansion. This renders the proposed scheme suitable for low cost carrier-less Ultra Wideband (UWB) systems where information must be conveyed only by the time delays of the modulated sub-nanosecond pulses without introducing any amplitude amplifications or phase rotations. Finally, the proposed scheme can be associated with a reduced complexity optimal Maximum-Likelihood (ML) decoder that takes the structure of the proposed code into consideration in order to simplify the decoding procedure. We also propose a simple diversity-preserving suboptimal decoder that requires approximately half the number of multiplications compared to the ML decoder. Possible extensions to transmitters equipped with three antennas are also discussed in situations where a certain number of feedback bits is available.

International Conference on Signal Processing & Communications (SPCOM), 2004, 2004

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.

IEEE Journal on Selected Areas in Communications, 2008

In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log₂(M-1)/n log₂(M).

Ultrawideband (UWB) radio is a promising solution for low and high data rate wireless communications over short ranges. Space-time (ST) coding techniques are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. So far, few contributions have looked over multiple-inputs multiple-outputs (MIMO) UWB systems. In this paper we introduce two new families of ST codes suitable for binary pulse modulated (BPM) and pulse position modulated (PPM) UWB systems. The codes are characterised by full-rate, full-diversity and low complexity at the receiver side. The probability of error resulting from the use of these space-time codes in a typical MIMO UWB channel is analytically derived. Simulations support analysis for various numbers of transmit and receive antennas in order to show that the two methods can effectively enlarge the transmission range of UWB devices.

IEEE Transactions on Wireless Communications, 2015

In this paper, we present a general technique for constructing minimal-delay unitary differential Space-Time (ST) block codes for Pulse Position Modulation (PPM) with an arbitrary number of transmit antennas and signal set cardinality. A typical application corresponds to Multiple Input Multiple Output (MIMO) Impulse-Radio Ultra-Wideband (IR-UWB) systems where neither the transmitter nor the receiver knows the channel. The proposed scheme is a pulse-based solution where the information is encoded differentially through the relative shifts of the pulses in one block with respect to the pulse positions in the previous block where each block extends over P symbol durations with P standing for the number of transmit antennas. This technique of time-domain encoding avoids all types of amplitude constellation expansions and achieves a full transmit diversity order while maintaining a single unipolar pulse transmission per symbol in a way that is completely equivalent to singleantenna PPM communications. We also propose a simplified decoder that can be associated with the proposed ST code and we perform a detailed complexity analysis that allows to quantify the reduction in the number of operations offered by this simplified decoding strategy. Finally, the results are validated numerically and through a semi-analytical evaluation of the conditional symbol error rate.

2009

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 ≥ 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.

The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications , 2006

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).

IEE proceedings, 2006

Ultra wide-band (UWB) systems have recently attracted much research interest owing to their appealing features in short-range mobile communications. These features include high data rates, low power consumption, multiple access communications, and precise positioning capabilities. Space-time coding techniques, such as the block coding scheme or the trellis coding scheme, are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. So far, few contributions have looked over multiple inputs multiple outputs UWB systems. In this paper, a method to adapt the space-time block coding technique to single band UWB signalling is proposed. A space-time block codec, based on orthogonal pulses to achieve spatial diversity and collect the multipath diversity is developed. A theoretical analysis is conducted to enlighten the performance enhancements provided by the proposed scheme compared to the classic single link scheme. Simulations support analysis, for various numbers of transmit and receive antennas, several types of channel scenarios, and different detection techniques. In a typical studied UWB environment, the results revealed that our proposed scheme improves the bit error rate performances compared to those of a single link scheme and it provides a strong immunity against timing jitter.

2007

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.

2016

Abstract—Ultra wide-band (UWB) systems have recently at-tracted much research interest owing to their appealing fea-tures in short-range mobile communications. These features include high data rates, low power consumption, multiple access communications, and precise positioning capabilities. Space-time coding techniques, such as the block coding scheme or the trellis coding scheme, are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. So far, few contributions have looked over multiple inputs multiple outputs UWB systems. In this paper, a method to adapt the space-time block coding technique to single band UWB signalling is proposed. A space-time block codec, based on orthogonal pulses to achieve spatial diversity and collect the multipath diversity is developed. A theoretical analysis is conducted to enlighten the performance enhancements provided by the proposed scheme compared to the classic single link sch...