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In cooperative relaying, intermediate stations are required to enhance the end-to-end transmission performance. The performance of the cooperative relaying scheme has been investigated theoretically and via computer simulations. However, cooperative relaying using transmit diversity techniques in actual environments has not been investigated thus far. This paper presents an experimental system for distributed cooperative relaying using space-time block code and evaluations of its transmission performances in real propagation channels. To this end, four wireless stations-specifically, one source, two relays, and one destination-were developed using analog transceivers and field-programmable gate arrays for real-time digital signal processing. Sample timing and frequency synchronizations among the four wireless stations were established by using the received signals as a reference. The end-to-end error performance of distributed cooperative relaying was compared to those of noncooperative relaying schemes, and the performances of three relaying schemes were evaluated quasisimultaneously in terms of their cumulative distribution functions of the bit-error ratios (BERs). The experimental results indicated that the BER performance of the two-hop distributed cooperative relaying scheme was substantially superior to those of noncooperative two-hop relaying schemes, including a route diversity scheme.

We present some modern theories on the structure of space-time that can be classified as relational theories in the direction of Leibniz’s ontology. In particular we summarize the Leibniz’s position against Newton and Clarke on the nature of space-time, Penrose’s model of spin networks, Heisenberg’s fundamental equation for the unification of elementary particles, Finkelstein’s space-time code, Weizsäcker’s urs theory that unifies the postulates of quantum mechanics and the theory of relativity, Sorkin’s causal sets, Markopoulou’s quantum causal histories, Markopoulou and Smolin’s causal spin foams, in the last three of which the principle of causality has been introduced. In order to analyze the nature of space-time, we consider three levels of knowledge —observational, theoretical and ontological— to which the different models can be ascribed. Following similar approach to the models mentioned in the first sections, we present our theoretical model of the structure of the space-time, some physical applications and the ontological interpretation of the model. In order to implement the above models with theological aspects we present in the last sections two theologians, Pannenberg and Torrance, who have made explicit analysis of the nature of space-time from a relational point of view. Following their expositions we have presented, after some epistemological presuppositions, the connection between the Creation and the rationality of God through the structure of space-time and the communication of God to the creatures in the Incarnation through the same structure., Presentamos algunas teorías modernas sobre la estructura del espacio-tiempo que pueden ser clasificadas como relacionales siguiendo la dirección de la ontología de Leibniz. En particular resumimos la postura de Leibniz frente a la de Newton y Clarke sobre la naturaleza del espacio-tiempo, el modelo de los spin networks de Penrose, la ecuación fundamental de Heisenberg para la unificación de las partículas elementales, el código espacio-temporal de Finkelstein, la teoría de los urs de Weizsäcker, que unifica los postulados de la mecánica cuántica y la teoría de la relatividad, los conjuntos causales de Sorkin, las historias cuánticas causales de Markopoulou, los spin foams causales de Markopoulou y Smolin, donde en los tres últimos se ha introducido el principio de causalidad. Para analizar la naturaleza del espacio-tiempo consideramos tres niveles de conocimiento —observacional, teorético y ontológico— a los cuales podemos adscribir los modelos mencionados. Siguiendo las directrices de los modelos descritos en las primeras secciones, presentamos nuestro propio modelo teórico sobre la estructura del espacio-tiempo, algunas aplicaciones físicas y la interpretación ontológica del mismo. Para completar los modelos anteriores con aspectos teológicos presentamos en las últimas secciones dos teólogos, Pannenberg y Torrance, que han realizado análisis explícitos sobre la naturaleza del espacio-tiempo desde un punto de vista relacional. Siguiendo sus exposiciones hemos presentado, después de estudiar los presupuesos epistemológicos que subyacen, la conexión entre la Creación y la racionalidad de Dios a través de la estructura del espacio-tiempo, y la comunicación de Dios a las criaturas en la Encarnación a través de la misma estructura.

We present some modern theories on the structure of space-time that can be classified as relational theories in the direction of Leibniz’s ontology. In particular we summarize the Leibniz’s position against Newton and Clarke on the nature of space-time, Penrose’s model of spin networks, Heisenberg’s fundamental equation for the unification of elementary particles, Finkelstein’s space-time code, Weizsäcker’s urs theory that unifies the postulates of quantum mechanics and the theory of relativity, Sorkin’s causal sets, Markopoulou’s quantum causal histories, Markopoulou and Smolin’s causal spin foams, in the last three of which the principle of causality has been introduced. In order to analyze the nature of space-time, we consider three levels of knowledge —observational, theoretical and ontological— to which the different models can be ascribed. Following similar approach to the models mentioned in the first sections, we present our theoretical model of the structure of the space-time, some physical applications and the ontological interpretation of the model. In order to implement the above models with theological aspects we present in the last sections two theologians, Pannenberg and Torrance, who have made explicit analysis of the nature of space-time from a relational point of view. Following their expositions we have presented, after some epistemological presuppositions, the connection between the Creation and the rationality of God through the structure of space-time and the communication of God to the creatures in the Incarnation through the same structure., Presentamos algunas teorías modernas sobre la estructura del espacio-tiempo que pueden ser clasificadas como relacionales siguiendo la dirección de la ontología de Leibniz. En particular resumimos la postura de Leibniz frente a la de Newton y Clarke sobre la naturaleza del espacio-tiempo, el modelo de los spin networks de Penrose, la ecuación fundamental de Heisenberg para la unificación de las partículas elementales, el código espacio-temporal de Finkelstein, la teoría de los urs de Weizsäcker, que unifica los postulados de la mecánica cuántica y la teoría de la relatividad, los conjuntos causales de Sorkin, las historias cuánticas causales de Markopoulou, los spin foams causales de Markopoulou y Smolin, donde en los tres últimos se ha introducido el principio de causalidad. Para analizar la naturaleza del espacio-tiempo consideramos tres niveles de conocimiento —observacional, teorético y ontológico— a los cuales podemos adscribir los modelos mencionados. Siguiendo las directrices de los modelos descritos en las primeras secciones, presentamos nuestro propio modelo teórico sobre la estructura del espacio-tiempo, algunas aplicaciones físicas y la interpretación ontológica del mismo. Para completar los modelos anteriores con aspectos teológicos presentamos en las últimas secciones dos teólogos, Pannenberg y Torrance, que han realizado análisis explícitos sobre la naturaleza del espacio-tiempo desde un punto de vista relacional. Siguiendo sus exposiciones hemos presentado, después de estudiar los presupuesos epistemológicos que subyacen, la conexión entre la Creación y la racionalidad de Dios a través de la estructura del espacio-tiempo, y la comunicación de Dios a las criaturas en la Encarnación a través de la misma estructura.

We focus on space-time block code (STBC) OFDM system with four transmit antennas. A block diagonal (BD) non-orthogonal STBC is proposed for full-rate transmission of complex data. To estimate the channel response, a BD STBC matrix has to be nonsingular for all possible transmitted BD STBC data matrices. A diagonal weighting constant is proposed to assure the nonsingularity. A phase-direct technique can be used to further improve the subspace-based semi-blind channel estimation. From computer simulation the proposed channel estimation is shown to be effective and we can also see that a large weighting constant improves channel estimation at the cost of a degraded bit error rate., APSIPA ASC 2009: Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference. 4-7 October 2009. Sapporo, Japan. Poster session: Signal Processing and Implementations in Communications (6 October 2009).

APSIPA ASC 2009: Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference. 4-7 October 2009. Sapporo, Japan. Poster session: Signal Processing and Implementations in Communications (6 October 2009)., We focus on space-time block code (STBC) OFDM system with four transmit antennas. A block diagonal (BD) non-orthogonal STBC is proposed for full-rate transmission of complex data. To estimate the channel response, a BD STBC matrix has to be nonsingular for all possible transmitted BD STBC data matrices. A diagonal weighting constant is proposed to assure the nonsingularity. A phase-direct technique can be used to further improve the subspace-based semi-blind channel estimation. From computer simulation the proposed channel estimation is shown to be effective and we can also see that a large weighting constant improves channel estimation at the cost of a degraded bit error rate.

We focus on space-time block code (STBC) OFDM system with four transmit antennas. A block diagonal (BD) non-orthogonal STBC is proposed for full-rate transmission of complex data. To estimate the channel response, a BD STBC matrix has to be nonsingular for all possible transmitted BD STBC data matrices. A diagonal weighting constant is proposed to assure the nonsingularity. A phase-direct technique can be used to further improve the subspace-based semi-blind channel estimation. From computer simulation the proposed channel estimation is shown to be effective and we can also see that a large weighting constant improves channel estimation at the cost of a degraded bit error rate., APSIPA ASC 2009: Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference. 4-7 October 2009. Sapporo, Japan. Poster session: Signal Processing and Implementations in Communications (6 October 2009).

We address the problem of designing a linear precoder for space-time coded multiple-input multiple-output (MIMO) system with imperfect knowledge of channel state information at the transmitter (CSIT), subject to a total transmit power constraint. Assuming an uncorrelated flat-fading channel and using a maximum likelihood decoder at the receiver, we analytically reveal that the derived precoder is a function of the noise variance, the eigenvalues of the estimated channel matrix and the eigenvalues of the codeword distance matrix. Furthermore, the power allocation on the eigenvalues of the precoder is shown to follow the water-pouring policy and hence the proposed precoder allocates more power to the stronger channels.

We address the problem of designing a linear precoder for space-time coded multiple-input multiple-output (MIMO) system with imperfect knowledge of channel state information at the transmitter (CSIT), subject to a total transmit power constraint. Assuming an uncorrelated flat-fading channel and using a maximum likelihood decoder at the receiver, we analytically reveal that the derived precoder is a function of the noise variance, the eigenvalues of the estimated channel matrix and the eigenvalues of the codeword distance matrix. Furthermore, the power allocation on the eigenvalues of the precoder is shown to follow the water-pouring policy and hence the proposed precoder allocates more power to the stronger channels.

We address the problem of designing a linear precoder for space-time coded multiple-input multiple-output (MIMO) system with imperfect knowledge of channel state information at the transmitter (CSIT), subject to a total transmit power constraint. Assuming an uncorrelated flat-fading channel and using a maximum likelihood decoder at the receiver, we analytically reveal that the derived precoder is a function of the noise variance, the eigenvalues of the estimated channel matrix and the eigenvalues of the codeword distance matrix. Furthermore, the power allocation on the eigenvalues of the precoder is shown to follow the water-pouring policy and hence the proposed precoder allocates more power to the stronger channels.

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M, 1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new, class, of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels.

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M, 1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new, class, of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels.

Coding and modulation for multiple-antenna systems have. gained much attention in wireless communications. This paper investigates a noncoherent trellis-coded scheme based on differential unitary space-time modulation when neither the transmitter nor the receiver know the channel. In a time-varying flat Rayleigh fading environment, we derive differentially noncoherent decision metrics and obtain performance measures for systems with either an ideal interleaver or no interleaver. We demonstrate that with an ideal interleaver, the system performance is dominated by the minimum Hamming distance of the trellis code, while without an interleaver, the performance is dominated by the minimum free squared determinant distance (a novel generalization of the Euclidean distance) of the code. For both cases, code construction is, described for Ungerboeck-type codes. Several examples that are based on diagonal cyclic group constellations and offer a good tradeoff between the coding advantage and trellis complexity are provided. Simulation results show that, by applying the soft-decision Viterbi decoder, the proposed scheme can achieve very good performance even with few receive Antennas. Extensions to trellis-coded differential space-time block codes are also discussed.

Coding and modulation for multiple-antenna systems have. gained much attention in wireless communications. This paper investigates a noncoherent trellis-coded scheme based on differential unitary space-time modulation when neither the transmitter nor the receiver know the channel. In a time-varying flat Rayleigh fading environment, we derive differentially noncoherent decision metrics and obtain performance measures for systems with either an ideal interleaver or no interleaver. We demonstrate that with an ideal interleaver, the system performance is dominated by the minimum Hamming distance of the trellis code, while without an interleaver, the performance is dominated by the minimum free squared determinant distance (a novel generalization of the Euclidean distance) of the code. For both cases, code construction is, described for Ungerboeck-type codes. Several examples that are based on diagonal cyclic group constellations and offer a good tradeoff between the coding advantage and trellis complexity are provided. Simulation results show that, by applying the soft-decision Viterbi decoder, the proposed scheme can achieve very good performance even with few receive Antennas. Extensions to trellis-coded differential space-time block codes are also discussed.

Coding and modulation for multiple-antenna systems have. gained much attention in wireless communications. This paper investigates a noncoherent trellis-coded scheme based on differential unitary space-time modulation when neither the transmitter nor the receiver know the channel. In a time-varying flat Rayleigh fading environment, we derive differentially noncoherent decision metrics and obtain performance measures for systems with either an ideal interleaver or no interleaver. We demonstrate that with an ideal interleaver, the system performance is dominated by the minimum Hamming distance of the trellis code, while without an interleaver, the performance is dominated by the minimum free squared determinant distance (a novel generalization of the Euclidean distance) of the code. For both cases, code construction is, described for Ungerboeck-type codes. Several examples that are based on diagonal cyclic group constellations and offer a good tradeoff between the coding advantage and trellis complexity are provided. Simulation results show that, by applying the soft-decision Viterbi decoder, the proposed scheme can achieve very good performance even with few receive Antennas. Extensions to trellis-coded differential space-time block codes are also discussed.

The effects of Rayleigh fading on a wireless communications link and the diversity techniques that are available to combat fading are explored in this thesis. The thesis consists of two main portions; an exploration on the use of spatial diversity and an exploration on the use of space-frequency diversity. In harnessing spatial diversity, the use of space-time coding is proposed to combat fading. Several codes of diversity two and four are explored, including Quasi-Orthogonal (QO) codes that are able to achieve a unity rate. The concept of constellation rotation for QO codes to maximize the available diversity is studied. QO codes are shown by simulation to be able to achieve full diversity, despite the fact that the codes are non-orthogonal. The use of space-time-frequency (STF) code to harness both space and frequency diversity is also explored. Simulations were performed for a variety of channel correlations to simulate varying degrees of frequency-selectivity. Results show that STF codes are very effective when the correlations in frequency response are less than 0.5. STF codes also have a power advantage over space-time codes with comparable diversity and bandwidth efficiency., Military Expert 5, Republic of Singapore Air Force, Approved for public release; distribution is unlimited.