his work proposes adaptive buffer-aided distributed space-time coding schemes and algorithms with feedback for wireless networks equipped with buffer-aided relays. The proposed schemes employ a maximum likelihood receiver at the destination and adjustable codes subject to a power constraint with an amplify-and-forward cooperative strategy at the relays. Each relay is equipped with a buffer and is capable of storing blocks of received symbols and forwarding the data to the destination if selected. Different antenna configurations and wireless channels, such as static block fading channels, are considered. The effects of using buffer-aided relays to improve the bit error rate (BER) performance are also studied. Adjustable relay selection and optimization algorithms that exploit the extra degrees of freedom of relays equipped with buffers are developed to improve the BER performance. We also analyze the pairwise error probability and diversity of the system when using the proposed schemes and algorithms in a cooperative network. Simulation results show that the proposed schemes and algorithms obtain performance gains over previously reported techniques.his work proposes adaptive buffer-aided distributed space-time coding schemes and algorithms with feedback for wireless networks equipped with buffer-aided relays. The proposed schemes employ a maximum likelihood receiver at the destination and adjustable codes subject to a power constraint with an amplify-and-forward cooperative strategy at the relays. Each relay is equipped with a buffer and is capable of storing blocks of received symbols and forwarding the data to the destination if selected. Different antenna configurations and wireless channels, such as static block fading channels, are considered. The effects of using buffer-aided relays to improve the bit error rate (BER) performance are also studied. Adjustable relay selection and optimization algorithms that exploit the extra degrees of freedom of relays equipped with buffers are developed to improve the BER performance. We also analyze the pairwise error probability and diversity of the system when using the proposed schemes and algorithms in a cooperative network. Simulation results show that the proposed schemes and algorithms obtain performance gains over previously reported techniques.T

The toxic effects of ionizing radiation to DNA are thought to be due to the generation of the superoxide radical, O-j. Superoxide dismutase (SOD), which scavenges O-j, has been invoked as a protecting enzyme against ionizing radiation in viruses, bacteria, mammalian cells in culture, and live mice. We now demonstrate that SOD is involved in the resistance of Drosophila melanogaster against irradiation. The protection is greatest when flies carry the S form of the enzyme (which exhibits highest in vitro specific activity), intermediate when they carry the F form of the enzyme, and lowest when they are homozygous for N, an allele that reduces the amount of the enzyme to 3.5% of the normal level. Natural selection experiments show that the fitness of the high-activity S allele is increased in an irradiated population relative to the nonirradiated control. These results point towards a possible adaptive function of the S/F polymorphism found in natural populations of D. melanogaster.The superoxide dismutases (SOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) are a family of metalloenzymes that provide organisms with protection against oxygen toxicity by scavenging the superoxide radical anion, O2 (1, 2).Cu,Zn SOD is found in the cytosol of animals, plants, and fungi.In Drosophila melanogaster the gene (Sod) coding for this enzyme has been mapped in the third chromosome, locus 32.5 or 34.6 (3). The enzyme is a dimer consisting of two identical subunits, each with a molecular weight of 16,000 (4). Two alleles, S and F, are present with variable frequencies in natural populations, although the F allele is always the most abundant. (The S, for "slow," and F, for "fast," designations refer to the relative mobility of the encoded enzymes in assays by standard gel electrophoresis.) The F and S polypeptides differ by a single amino acid substitution and also in various biochemical properties (5). Relevant for the present purposes is that the S allozyme exhibits higher specific activity than the F form; the purified S enzyme is typically capable of scavenging O-* at a rate about 2.7 times faster than the F enzyme (5).SOD has been shown to protect against ionizing radiation damage to DNA, viruses, bacteria, mammalian cells in culture, and even whole mice (6-13). We have now tested this property in D. melanogaster in two ways: (i) by measuring the reduction in viability of larvae of different genetic constitutions exposed to increasing doses of ionizing radiation and (ii) by following the change in allelic frequencies over several generations in populations subject to x-irradiation every generation. Our results corroborate the role of this enzyme in providing biological protection against ionizing radiation. The results also show that the higher-activity S form of the enzyme provides greater protection than the F allozyme. This, in turn, identifies a possible adaptive role for the S and F polymorphism found in natural populations of Drosophila. Sod", "null" allele) that in homozygous condition yields only 3.5% ...

Abstract-In this paper, a joint power allocation algorithm with minimum mean-squared error (MMSE) receiver for a cooperative Multiple-Input and Multiple-Output (MIMO) network which employs multiple relays and a Decode-and-Forward (DF) strategy is proposed. A Distributed Space-Time Coding (DSTC) scheme is applied in each relay node. We present a joint constrained optimization algorithm to determine the power allocation parameters and the MMSE receive filter parameter vectors for each transmitted symbol in each link, as well as the channel coefficients matrix. A Stochastic Gradient (SG) algorithm is derived for the calculation of the joint optimization in order to release the receiver from the massive calculation complexity for the MMSE receive filter and power allocation parameters. The simulation results indicate that the proposed algorithm obtains gains compared to the equal power allocation system.

Physical layer network coding (PNC) has been studied to serve wireless network MIMO systems with much lower backhaul load than approaches such as Cloud Radio Access Network (Cloud-RAN) and coordinated multipoint (CoMP). In this paper, we present a design guideline of engineering applicable PNC to fulfil the request of high user densities in 5G wireless RAN infrastructure. Unlike compute-and-forward and PNC design criteria for two-way relay channels, the proposed guideline is designed for uplink of network MIMO (N-MIMO) systems. We show that the proposed design criteria guarantee that 1) the whole system operates over binary system; 2) the PNC functions utilised at each access point overcome all singular fade states; 3) the destination can unambiguously recover all source messages while the overall backhaul load remains at the lowest level. We then develop a two-stage search algorithm to identify the optimum PNC mapping functions which greatly reduces the real-time computational complexity. The impact of estimated channel information and reduced number of singular fade states in different QAM modulation schemes is studied in this paper. In addition, a sub-optimal search method based on lookup table mechanism to achieve further reduced computational complexity with limited performance loss is presented. Numerical results show that the proposed schemes achieve low outage probability with reduced backhaul load.Index Terms-adaptive PNC, industrial applicable, backhaul load, unambiguous detection.

This paper presents a physical layer network coding (PNC) approach for network MIMO (N-MIMO) systems to release the heavy burden of backhaul load. The proposed PNC approach is applied for uplink scenario in binary systems, and the design guideline serves multiple mobile terminals (MTs) and guarantees unambiguous recovery of the message from each MT. We present a novel PNC design criterion first based on binary matrix theories, followed by an adaptive optimal mapping selection algorithm based on the proposed design criterion. In order to reduce the real-time computational complexity, a twostage search algorithm for the optimal binary PNC mapping matrix is developed. Numerical results show that the proposed scheme achieves lower outage probability with reduced backhaul load compared to practical CoMP schemes which quantize the estimated symbols from a log-likelihood ratio (LLR) based multiuser detector into binary bits at each access point (AP).Index Terms-binary PNC, backhaul load reduction, unambiguous detection, adaptive optimal mapping selection.

With the fast growing number of wireless devices and demand of user data, the backhaul load becomes a bottleneck in wireless networks. Physical‐layer network coding (PNC) allows access points to relay‐compressed, network‐coded user data, therefore reducing the backhaul traffic. In this paper, an implementation of uplink network‐coded modulation (NetCoM) with PNC is presented. A five‐node prototype NetCoM system is established using Universal Software Radio Peripherals, and a practical PNC scheme designed for binary systems is utilized. An orthogonal frequency‐division multiplexing waveform implementation and the practical challenges (eg, device synchronization and clock drift) of applying orthogonal frequency‐division multiplexing to NetCoM are discussed. To the best of our knowledge, this is the first PNC implementation in an uplink scenario in radio access networks, and our prototype provides an industrially applicable implementation of the proposed NetCoM with PNC approach.

An adaptive distributed space-time coding (DSTC) scheme and algorithms are proposed for two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE) receivers and an amplify-and-forward (AF) cooperation strategy are considered. In the proposed DSTC scheme, an adjustable matrix obtained by a feedback channel is employed to transform the space-time coded matrix at the relay node. Linear MMSE expressions are devised to compute the parameters of the adaptive matrix and the linear receive filter. A stochastic gradient algorith m is also developed to compute the parameters of the adaptive matrix with reduced computational complexity. We also derive the upper bound of the error probability of a cooperative MIMO system employing the randomized space-time coding scheme first.The simulation results show that the proposed algorithms obtain significant performance gains as compared to existing DSTC schemes.

Abstract-An adaptive distributed space-time coding (DSTC) scheme is proposed for two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE) receive filters and adjustable code matrices are considered subject to a power constraint with an amplify-and-forward (AF) cooperation strategy. In the proposed adaptive DSTC scheme, an adjustable code matrix obtained by a feedback channel is employed to transform the space-time coded matrix at the relay node. The effects of the limited feedback and the feedback errors are assessed. Linear MMSE expressions are devised to compute the parameters of the adjustable code matrix and the linear receive filters. Stochastic gradient (SG) and least-squares (LS) algorithms are also developed with reduced computational complexity. An upper bound on the pairwise error probability analysis is derived and indicates the advantage of employing the adjustable code matrices at the relay nodes. An alternative optimization algorithm for the adaptive DSTC scheme is also derived in order to eliminate the need for the feedback. The algorithm provides a fully distributed scheme for the adaptive DSTC at the relay node based on the minimization of the error probability. Simulation results show that the proposed algorithms obtain significant performance gains as compared to existing DSTC schemes.