In low power wide area (LPWA) networks, low-cost end devices (EDs) such as sensors communicate with a central base station (BS) using pure ALOHA protocol. In particular, half-duplex is considered wherein the BS switches from receiving to transmitting mode after receiving a packet successfully from an ED in order to send the acknowledgement. Since the EDs can not know at the moment when the BS turns to the receiving mode, the packets transmitted by the EDs during the receiving mode of the BS are lost. To investigate performance of such half-duplex pure ALOHA systems, this paper develops a semi-Markov (SM) process model for pure ALOHA channel with infinite population. Furthermore, the SM process is approximated with an M/M/1 system in order to analyze the system with finite population. As results, this paper presents how the performance of half-duplex system is influenced by switching time, backoff interval of EDs, and stability criteria of the system, which are verified through system simulations.

In this paper, we propose a hybrid division cooperative transmission (HDCT) scheme for system throughput enhancement in enterprise femtocell systems. In HDCT scheme, a cooperative transmission (CT) scheme is applied to user equipments (UEs) located at the edge of a serving femtocell base station (fBS), whereas conventional scheme is applied to UEs located near the fBS. In the zone where CT is applied, a UE is capable of receiving desired signal from serving fBS as well as from an adjacent fBS. Thus, the UE achieves an improved signal to interference plus noise ratio (SINR) by using two time synchronized signals from two adjacent fBSs. Performance of the proposed scheme is evaluated in terms of call level quality of service (QoS) (i.e., call blocking probability) and packet level QoS (i.e., outage probability). We first measure the resource utilization and call blocking probability for the downlink channel for various offered load. Based on that, we obtain the outage probability and effective throughput of the system by computer simulations. Finally, the results of the simulation yield the optimum hybrid zone for achieving the maximum system throughput.

In this paper, we investigate the performance of the Mobile Multi-hop Relay (MMR) uplink (UL) system with a non-transparent mode Relay Station (RS) which is used for coverage extension. We first develop analytical models to calculate the blocking probability and the utilization of the access zone in UL subframe. Based on that, the outage probability of the system is simulated. Performance is presented in terms of call blocking probability, channel utilization, outage probability and system throughput for various offered load in multicell environments with three types topologies. The numerical examples show that the MMR UL system achieves the maximum system throughput when the MR-BS to RS coverage ratio is seven fur specified system parameters.

In this paper, we investigate the performance of a reuse partitioning (RUP) based cellular uplink system in a multicell environment. In a RUP scheme, a cell is divided into several concentric regions and each region has a different reuse factor. The model presented in this paper accounts for channel selection of a mobile station (MS) using a two-dimensional Markov, and co-channel interference (CCI) level in the cell. Performance is presented in terms of channel utilization, call blocking probability, outage probability and effective throughput. For specified system parameters, the RUP based cellular system achieves the maximum system throughput when the distance from the center of a cell to the inner zone boundary to radius of a cell ratio is 0.6.

In this paper, we investigate the performance of MMR system in non-transparent mode. The IEEE 802.16j MMR system has two mode of operation, single-frame mode and multi-frame mode. In the analysis, we assume that channel interference between MR-BS and RS, or between RSs anywhere in the given area is negligible. The performance is presented in terms of frame efficiency by varying number of RS and BS coverage to RS coverage ratio and maximum coverage area of a BS by varying traffic density. Analytical results show that the single-frame mode is more efficient than multi-frame mode in frame efficiency and coverage extension.

MOTIVATION: Conventional Monte Carlo and molecular dynamics simulations of proteins in the canonical ensemble are of little use, because they tend to get trapped in states of energy local minima at low temperatures. One way to surmount this difficulty is to use a non-Boltzmann sampling method in which conformations are sampled upon a general weighting function instead of the conventional Boltzmann weighting function. The multiensemble sampling (MES) method is a non-Boltzmann sampling method that was originally developed to estimate free energy differences between systems with different potential energies and/or at different thermodynamic states. The method has not yet been applied to studies of complex molecular systems such as proteins. RESULTS: MES Monte Carlo simulations of small proteins have been carried out using a united-residue force field. The proteins at several temperatures from the unfolded to the folded states were simulated in a single MC run at a time and their equilibrium thermodynamic properties were calculated correctly. The distributions of sampled conformations clearly indicate that, when going through states of energy local minima, the MES simulation did not get trapped in them but escaped from them so quickly that all the relevant parts of conformation space could be sampled properly. A two-step folding process consisting of a collapse transition followed by a folding transition is observed. This study demonstrates that the use of MES alleviates the multiple-minima problem greatly. AVAILABILITY: Available on request from the authors.

MOTIVATION: The solvent accessibility of amino acid residues plays an important role in tertiary structure prediction, especially in the absence of significant sequence similarity of a query protein to those with known structures. The prediction of solvent accessibility is less accurate than secondary structure prediction in spite of improvements in recent researches. The k-nearest neighbor method, a simple but powerful classification algorithm, has never been applied to the prediction of solvent accessibility, although it has been used frequently for the classification of biological and medical data. RESULTS: We applied the fuzzy k-nearest neighbor method to the solvent accessibility prediction, using PSI-BLAST profiles as feature vectors, and achieved high prediction accuracies. With leave-one-out cross-validation on the ASTRAL SCOP reference dataset constructed by sequence clustering, our method achieved 64.1% accuracy for a 3-state (buried/intermediate/exposed) prediction (thresholds of 9% for buried/intermediate and 36% for intermediate/exposed) and 86.7, 82.0, 79.0 and 78.5% accuracies for 2-state (buried/exposed) predictions (thresholds of each 0, 5, 16 and 25% for buried/exposed), respectively. Our method also showed slightly better accuracies than other methods by about 2-5% on the RS126 dataset and a benchmarking dataset with 229 proteins. AVAILABILITY: Program and datasets are available at http://biocom1.ssu.ac.kr/FKNNacc/ CONTACT: [email protected].