Code-rate-optimized differentially modulated near-capacity cooperation

It is widely recognized that half-duplex-relay-aided differential decode-and-forward (DDF) cooperative transmission schemes are capable of achieving a cooperative diversity gain, while circumventing the potentially excessive-complexity and yet inaccurate channel estimation, especially in mobile environments. However, when a cooperative wireless communication system is designed to approach the maximum achievable spectral efficiency by taking the cooperation-induced multiplexing loss into account, it is not obvious whether or not the relay-aided system becomes superior to its direct-transmission based counterpart, especially, when advanced channel coding techniques are employed. Furthermore, the optimization of the transmit-interval durations required by the source and relay is an open issue, which has not been well understood in the context of half-duplex relaying schemes. Hence, we first find the optimum transmission duration, which is proportional to the adaptive channel-code rate of the source and relay in the context of Code-Rate-Optimized (CRO) TDMA-based DDF-aided half-duplex systems for the sake of maximizing the achievable network throughput. Then, we investigate the benefits of introducing cooperative mechanisms into wireless networks, which may be approached in the context of the proposed CRO cooperative system both from a pure capacity perspective and from the practical perspective of approaching the Discrete-input Continuous-output Memoryless Channel (DCMC) capacity with the aid of the proposed Irregular Distributed Differential (IrDD) coding aided scheme. In order to achieve a near-capacity performance at a low-complexity, an adaptive-window-duration based Multiple-Symbol Differential Sphere Detection (MSDSD) scheme is employed in the iterative detection aided receiver. Specifically, upon using the proposed near-capacity system design, the IrDD coding scheme devised becomes capable of performing within about 1.8 dB from the corresponding single-relay-aided DDF cooperative system’s DCMC capacity

Histone posttranslational modifications and cell fate determination: Lens induction requires the lysine acetyltransferases CBP and p300

Lens induction is a classical embryologic model to study cell fate determination. It has been proposed earlier that specific changes in core histone modifications accompany the process of cell fate specification and determination. The lysine acetyltransferases CBP and p300 function as principal enzymes that modify core histones to facilitate specific gene expression. Herein, we performed conditional inactivation of both CBP and p300 in the ectodermal cells that give rise to the lens placode. Inactivation of both CBP and p300 resulted in the dramatic discontinuation of all aspects of lens specification and organogenesis, resulting in aphakia. The CBP/p300(−/−) ectodermal cells are viable and not prone to apoptosis. These cells showed reduced expression of Six3 and Sox2, while expression of Pax6 was not upregulated, indicating discontinuation of lens induction. Consequently, expression of αB- and αA-crystallins was not initiated. Mutant ectoderm exhibited markedly reduced levels of histone H3 K18 and K27 acetylation, subtly increased H3 K27me3 and unaltered overall levels of H3 K9ac and H3 K4me3. Our data demonstrate that CBP and p300 are required to establish lens cell-type identity during lens induction, and suggest that posttranslational histone modifications are integral to normal cell fate determination in the mammalian lens

Near-capacity co-located and distributed MIMO systems

Space-time transmission based colocated and distributed Multiple-Input-Multiple-Output (MIMO) systems are investigated. Generally speaking, there are two types of fundamental gains, when using multiple antennas in wireless communications systems: the multiplexing gain and the diversity gain. Spatial multiplexing techniques such as the Vertical Bell-labs LAyered Space-Time (V-BLAST) scheme exploit the associated multiplexing gain in terms of an increased bit rate, whereas spatial diversity techniques such as Space-Time Coding (STC) aim for achieving a diversity gain, which results in a reduced error rate. Firstly, we concentrate our attention on a novel space-time transmission scheme, namely on Generalized Multi-Layer Space-Time Codes (GMLST), which may be viewed as a composite of V-BLAST and STC, hence they provide both multiplexing and diversity gains. The basic decoding procedure conceived for our GMLST arrangement is a certain ordered successive decoding scheme, which combines group interference nulling and interference cancellation. We apply a specifically designed power allocation scheme, in order to avoid the overall system performance degradation in the case of equal power allocation. Furthermore, the optimal decoding order is found, in order to enhance the system’s performance with the aid of the channel state information (CSI) at the receiver. However, our decoding scheme relying on power allocation or on the optimal decoding order does not take full advantage of the attainable receive antenna diversity. In order to make the most of this source of diversity, an iterative multistage Successive Interference Cancellation (SIC) detected GMLST scheme was proposed, which may achieve the full receive diversity after a number of iterations, while imposing only a fraction of the computational complexity of Maximum Likelihood (ML)-style joint detection.Furthermore, for the sake of taking full advantage of the available colocated MIMO channel capacity, we present a low-complexity iteratively detected space-time transmission architecture based on GMLST codes and IRregular convolutional Codes (IRCCs). The GMLST arrangement is serially concatenated with a Unity-Rate Code (URC) and an IRCC, which are used to facilitate near-capacity operation with the aid of an EXtrinsic Information Transfer (EXIT) chart based design. Reduced-complexity iterative multistage SIC is employed in the GMLST decoder instead of the significantly more complex ML detection. For the sake of approaching the maximum attainable rate, iterative decoding is invoked to achieve decoding convergence by exchanging extrinsic information across the three serially concatenated component decoders. Finally, it is shown that the iteratively detected IRCC-URC-GMLST scheme using SIC strikes an attractive trade-off between the complexity imposed and the effective throughput attained, while achieving a near-capacity performance.The above-mentioned advances were also exploited in the context of near-capacity communications in distributed MIMO systems. Specifically, we proposed an Irregular Cooperative Space-Time Coding (Ir-CSTC) scheme, which combines the benefits of Distributed Turbo Codes (DTC) and serially concatenated schemes. Firstly, a serial concatenated scheme comprising an IRCC, a recursive URC and a STC was designed for the conventional single-relay-aided network for employment at the source node. The IRCC is optimized with the aid of EXIT charts for the sake of achieving a near-error-free decoding at the relay node at a minimum source transmit power. During the relay’s transmit period, another IRCC is amalgamated with a further STC, where the IRCC employed at the relay is further improved with the aid of a joint source-and-relay mode design procedure for the sake of approaching the relay channel’s capacity. At the destination node, a novel three-stage iterative decoding scheme is constructed in order to achieve decoding convergence to an infinitesimally low Bit Error Ratio (BER) at channel Signal-to-Noise Ratios (SNRs) close to the relay channel’s capacity. As a further contribution, an extended Ir-CSTC scheme is studied in the context of a twin-relay aided network, where a successive relaying protocol is employed. As a benefit, the factor two multiplexing loss of the single-relay-aided network - which is imposed by the creation of two-phase cooperation - is recovered by the successive relaying protocol with the aid of an additional relay. This technique is more practical than the creation of a full-duplex system, which is capable of transmitting and receiving at the same time. The generalized joint source-and-relay mode design procedure advocated relies on the proposed procedure of finding the optimal cooperative coding scheme, which performs close to the twin-relay-aided network’s capacity. The corresponding simulation results verify that our proposed Ir-CSTC schemes are capable of near-capacity communications in both the single-relay-aided and the twin-relay-aided networks.Having studied diverse noise-limited single-user systems, we finally investigate a multiuser space divisionmultiple access (SDMA) uplink system designed for an interference-limited scenario, where the multiple access interference (MAI) significantly degrades the overall system performance. For the sake of supporting rank-deficient overloaded systems, a maximum signal-to-interference-plus-noise ratio (MaxSINR) based SIC multiuser detection (MUD) algorithm is proposed for the multiple-antenna aided multi-user SDMA system, which is capable of striking a trade-off between the interference suppression and noise enhancement. Furthermore, the multiuser SDMA system is combined with channel codes, which assist us in eliminating the typical error floors of rank-deficient systems. Referring to the Ir-CSTC scheme designed for the single-user scenario, relaying techniques are invoked in our channel-coded SDMA systems, which benefit from extra spatial diversity gains. In contrast to the single-user Ir-CSTC schemes, interference suppression is required at both the base station (BS) and the relaying mobile station (MS). Finally, a more practical scenario is considered where the MSs have spatially correlated transmit antennas. In contrast to the conventional views, our simulation results suggest that the spatial correlation experienced at the transmitter is potentially beneficial in multiuser SDMA uplink systems, provided that efficient MUDs are invoked

A Near-Capacity Differentially Encoded Non-Coherent Adaptive Multiple-Symbol-Detection Aided Three-Stage Coded Scheme

This paper presents an Irregular Distributed Hybrid Concatenated Differential (Ir-DHCD) coding scheme contrived for the relay aided differential decode-and-forward (DDF) cooperative system using multiple-symbol differential sphere detection (MSDSD), where no channel estimation is required. We proposed a practical design framework for a cooperative system, which is capable of performing close to the network’s corresponding non-coherent Discrete-input Continuous-output Memoryless Channel (DCMC) capacity. An adaptive-window-duration based MSDSD scheme is employed to further reduce the iterative detection complexity. Specifically, upon using the proposed near-capacity system design, the Ir-DHCD coding scheme devised becomes capable of performing within about 1.8 dB from the corresponding single-relay-aided DDF cooperative system’s DCMC capacity

To Cooperate or Not: A Capacity Perspective

It is widely recognized that differential decode-and-forward (DDF) cooperative transmission scheme is capable of providing a superior performance compared to classic direct transmissions employing differential detection, where no channel coding is used. However, the diversity gains achieved by the cooperative system become modest in practical channel coded scenarios, where the interleaving and channel coding gains dominate. Therefore, when a cooperative wireless communication system is designed to approach the maximum achievable spectral efficiency by taking the cooperation-induced multiplexing loss into account, it is not obvious, whether or not the relay-aided system becomes superior to its direct-transmission based counterpart, especially, when advanced channel coding techniques are employed. Hence in this paper the capacity of the single-relay-assisted DDF based cooperative system was studied in comparison to that of its direct-transmission based counterpart in order to answer the above-mentioned dilemma

Near-capacity cooperative space-time coding employing irregular design and successive relaying

In this paper, we develop a capacity-approaching Cooperative Space-Time Coding CSTC scheme employing irregular design for a twin-relay aided network as an extension of our previous work cast in the context of a half-duplex single-relay-aided network. For the sake of recovering the multiplexing loss imposed by a half-duplex three-terminal network, we employ a successive relaying protocol in this paper, where an additional relay node is activated. Hence, in order to design a near-capacity coding system, first the capacity and the achievable information-rate of a specific space-time coding aided scheme are quantified for the successive relaying aided channel. More specifically, the cooperative space-time codes employed at the source and the relays are jointly designed with the aid of EXtrinsic Information Transfer EXIT charts for the sake of high-integrity operation at Signal-to-Noise Ratios SNRs close to the corresponding successive relaying channel's capacity. Furthermore, unlike in the half-duplex single-relay based system, the destination node performs frame-by-frame Successive Interference Cancellation SIC aided iterative detection, in order to mitigate the efforts of multiple-access interference. Finally, our numerical results demonstrate that our proposed Irregular Cooperative Space-Time Coding Ir-CSTC scheme is capable of near-capacity operation in the successive relaying aided network, which is an explicit benefit of our joint source-and-relay transceiver desig

Multiple-relay aided distributed turbo coding assisted differential unitary space-time spreading for asynchronous cooperative networks

This paper proposes a cooperative space-time coding (STC) protocol, amalgamating the concepts of asynchronous cooperation, non-coherent detection as well as Distributed Turbo Coding (DTC), where neither symbol-level time synchronization nor CSI estimation is required at any of the cooperating nodes, while attaining a high performance even at low SNRs. More specifically, a practical cooperative differential space-time spreading (CDSTS) scheme is designed with the aid of interference rejection spreading codes, in order to eliminate the effect of synchronization errors between the relay nodes without the assistance of channel estimation or equalization. Furthermore, a set of space-time codewords are constructed based on Differential Linear Dispersion Codes (DLDC), which allows our CDSTS system to support an arbitrary number of relay nodes operating at a high transmission rate due to its flexible design. Rather than using conventional single-relay assisted DTCs, novel multi-relay-assisted DTCs and a three-stage iteratively-decoded destination receiver structure are developed. In our simulations the system parameters are designed with the aid of EXIT chart analysis, followed by the characterization of the achievable BER performance for various synchronization delay values as well as for various diversity-multiplexing relationships in frequency-selective fast and/or quasi static Rayleigh fading environments

Us Housing Price Cycle after 2008 Recession

Pricing volatility has long been a tough topic because there is no research that can confidently pinpoint the volatility to any set of fundamental values like interest rate, earning, or construction cost. It is especially important to get an understanding for price volatility because there are financial, social, and economical consequences if consumers make decisions without understanding the dynamics. Literatures such as Glaeser et al. (2008) and Huang and Tang (2012) believe supply constraints have a huge effect on the price volatility from 1982 to 2009. There are two major types of supply constraints: regulatory and geographic. I focused on regulatory constraints. With data from after the 2008 recession, I reexamine the relationship between regulatory constraints and price change. I am able to find that greater regulatory constraint is linked to greater price appreciation, but the relationship is less clear when consequences of the recession, like unemployment rate, is factored in. Glaeser et al. (2008) faced similar problems in his paper, and it is shown by Huang and Tang (2012) that the sampling period is very important when estimating the relationship between regulatory constraint and price change. This can potentially indicate that each housing cycle has different factors that contribute to the price volatility