We propose a new broadcast strategy for a multiple-input multiple-output (MIMO) system with N transmit antennas at the transmitter and M≤N single antenna receivers. The proposed method, based on dirty-paper coding (DPC), spatially separates the M users but does not suffer from the power loss of classical spatial division multiple access (SDMA). For the special case of M=N=2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO transmission system that doubles the symbol rate of MIMO space-time block code (STBC) systems from one to two symbol per transmission time. It is proved theoretically and experimentally that the proposed scheme provides the same performance level as that of MIMO STBC systems (i.e., the Alamouti scheme) for the first symbol, and the same performance as the Bell labs layered space-time (BLAST) system for the second symbol. When compared to the BLAST system, the proposed scheme has the same symbol rate, but achieves significantly better performance, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.

Inspired by the success of the low-density parity-check (LDPC) codes in the field of error-control coding, in this paper we propose transforming the downlink multiuser multiple-input multiple-output scheduling problem into an LDPC-like problem using the normal graph. Based on the normal graph framework, soft information, which indicates the probability that each user will be scheduled to transmit packets at the access point through a specified angle-frequency sub-channel, is exchanged among the local processors to iteratively optimize the multiuser transmission schedule. Computer simulations show that the proposed algorithm can efficiently schedule simultaneous multiuser transmission which then increases the overall channel utilization and reduces the average packet delay.

With the rapid advances in wireless network communication, multimedia presentation has become more applicable. However, due to the limited wireless network resource and the mobility of Mobile Host (MH), QoS for wireless streaming is much more difficult to maintain. How to decrease Call Dropping Probability (CDP) in multimedia traffic while still keeping acceptable Call Block Probability (CBP) without sacrificing QoS has become an significant issue in providing wireless streaming services. In this paper, we propose a novel Dynamic Resources Adjustment (DRA) algorithm, which can dynamically borrow idle reserved resources in the serving cell or the target cell for handoffing MHs to compensate the shortage of bandwidth in media streaming. The experimental simulation results show that compared with traditional No Reservation (NR), and Resource Reservation in the six neighboring cells (RR-nb), and Resource Reservation in the target cell(RR-t), our proposed DRA algorithm can fully utilize unused reserved resources to effectively decrease the CDP while still keeping acceptable CBP with high bandwidth utilization.

We propose a new mobility management scheme using Label Switched Path (LSP) of Multi Protocol Label Switching (MPLS) for seamless service in Broadband Convergence Network (BcN) in Korea, and verify that the proposed scheme has lower latency time than the existing ones through the separation of control plane from data plane for handover signaling.

This paper discusses the behavior of the second-order modes (Hankel singular values) of linear continuous-time systems under variable transformations with positive-real functions. That is, given a transfer function H(s) and its second-order modes, we analyze the second-order modes of transformed systems H(F(s)), where 1/F(s) is an arbitrary positive-real function. We first discuss the case of lossless positive-real transformations, and show that the second-order modes are invariant under any lossless positive-real transformation. We next consider the case of general positive-real transformations, and reveal that the values of the second-order modes are decreased under any general positive-real transformation. We achieve the derivation of these results by describing the controllability/observability Gramians of transformed systems, with the help of the lossless positive-real lemma, the positive-real lemma, and state-space formulation of transformed systems.

In this letter, a Tomlinson-Harashima precoding (THP) scheme is proposed for the downlink of multiuser MIMO systems with multiple antennas at each receiver. Assuming single data stream communication for each user, joint transmitter and receiver design is done to maximize the signal to noise ratio (SNR) for each user. Furthermore, a heuristic user ordering algorithm is proposed to optimize the encoding order and improve the bit error rate (BER) performance. Simulation results have shown that the proposed approach is superior to some existing precoding schemes.

Based on an analysis of the error patterns in lattice-reduction (LR) precoding in a multiple-antenna broadcast channel, this paper proposes a simple precoding technique that can reduce the quantization error. The proposed scheme establishes a lattice list to provide more candidates for transmission power reduction based on the analysis of the patterns of the error in the LR precoding method [9]. Simulation results show that the proposed scheme matches the BER performance of more complex precedents (such as the vector perturbation using sphere encoding) with significant saving in complexity.

In this paper, a fiber with two inhomogeneous sector holes around the core is proposed, and propagation characteristics of polarization maintaining region and single-polarization region are numerically analyzed by circular Fourier expansion method. In each case of the single-polarization region and the polarization maintaining region, a fiber is designed so as to satisfy the zero total dispersion at wavelength of 1.55 µm. Then, the single-polarization bandwidth for the single-polarization region and the modal birefringence for the polarization maintaining region are examined as the specific characteristics in each region. In addition, the power concentrating into the core region and distributions of Poynting vector is also discussed.

We propose a new linear array for multiplication in GF(2m) which outperforms most of the existing linear multipliers in terms of the area and time complexity. Moreover we will give a very detailed comparison of our array with other existing architectures for the five binary fields GF(2m), m=163,233,283,409,571, recommended by NIST for elliptic curve cryptography.

In this paper, we propose a leakage-resilient and proactive authenticated key exchange (called LRP-AKE) protocol for credential services which provides not only a higher level of security against leakage of stored secrets but also secrecy of private key with respect to the involving server. And we show that the LRP-AKE protocol is provably secure in the random oracle model with the reduction to the computational Diffie-Hellman problem. In addition, we discuss about some possible applications of the LRP-AKE protocol.

The low complexity tree-structure based user scheduling algorithm is extended into up-link MLD-based multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing access (OFDMA) wireless systems. The system sum capacity is maximized by careful user selection on a defined tree structure. The calculation load is reduced by selecting the M most possible best branches and sampling in frequency dimension. The performances of the proposed scheduling algorithm are analyzed within three kinds of OFDMA systems and compared with conventional throughput-based algorithm. Both the theoretical analysis and simulation results show that the proposed algorithm obtains better performance with much low complexity.

Reliable end-to-end delivery service is one of the most important issues for wireless sensor networks in large-scale deployments. In this paper, a reliable data transport protocol, called the Data Forwarding Protocol (DFP), is proposed to improve the end-to-end delivery rate with minimum transport overhead for recovering from data loss in large-scale wireless sensor environments consisting of low speed mobile sensor nodes. The key idea behind this protocol is the establishment of multi-split connection on an end-to-end route, through the Agent Host (AH), which plays the role of a virtual source or a sink node. In addition, DFP applies the local error control and the local flow control mechanisms to multi-split connections, according to network state. Extensive simulations are carried out via ns-2 simulator. The simulation results demonstrate that DFP not only provide up to 30% more reliable data delivery, but also reduces the number of retransmission generated by data loss, compared with the TCP-like end-to-end approach.

Normalization transform is known to be very useful for finding the overall trend of time-series data since it enables finding sequences with similar fluctuation patterns. Previous subsequence matching methods with normalization transform, however, would incur index overhead both in storage space and in update maintenance since they should build multiple indexes for supporting query sequences of arbitrary length. To solve this problem, we adopt a single-index approach in the normalization-transformed subsequence matching that supports query sequences of arbitrary length. For the single-index approach, we first provide the notion of inclusion-normalization transform by generalizing the original definition of normalization transform. To normalize a window, the inclusion-normalization transform uses the mean and the standard deviation of a subsequence that includes the window while the original transform uses those of the window itself. Next, we formally prove the correctness of the proposed normalization-transformed subsequence matching method that uses the inclusion-normalization transform. We then propose subsequence matching and index-building algorithms to implement the proposed method. Experimental results for real stock data show that our method improves performance by up to 2.52.8 times compared with the previous method.

In this paper, we propose an adaptive guard symbol insertion method for one-cell reuse TDMA cellular systems in which co-channel interference is reduced by adaptively selecting the best transmit-pulse waveform with different guard (null-) symbols according to the average error power (AEP) corresponding to signal-to-interference and noise power ratio (SINR), even though the same frequency channel is used at all base stations. Using the proposed system, current TDMA-based systems are readily extensible to one-cell reuse systems, which achieves higher spectrum efficiency. The system capacity is enhanced using the proposed method; moreover, the required qualities such as blocking probability and outage probability are retained.

In this paper, we propose a method of controlling personal data disclosure based on LooM (Loosely Managed Privacy Protection Method) that prevents a malicious third party from identifying a person when he/she gets context-aware services using personal data. The basic function of LooM quantitatively evaluates the anonymity level of a person who discloses his/her data, and controls the personal-data disclosure according to the level. LooM uses a normalized entropy value for quantifying the anonymity. In this version of the LooM, the disclosure control is accomplished by adding two new functions. One is an abstracting-function that generates abstractions (or summaries) from the raw personal data to reduce the danger that the malicious third party might identify the person who discloses his/her personal data to the party. The other function is a unique-value-masking function that hides the unique personal data in the database. These functions enhance the disclosure control mechanism of LooM. We evaluate the functions using simulation data and questionnaire data. Then, we confirm the effectiveness of the functions. Finally, we show a prototype of a crime-information-sharing service to confirm the feasibility of these functions.

Wireless content sharing where peers share content and services via wireless access networks requires user contributions, as in fixed P2P content sharing. However, in wireless access environments, since the resources of mobile terminals are strictly limited, mobile users are not as likely to contribute as ones in fixed environments. Therefore, incentives to encourage user contributions are more significant in wireless access environments. Although an incentive service differentiation architecture where the content transfer rate is adjusted according to the contributions of each downloading user has been already proposed for fixed P2P, it may not work well in wireless access environments because several factors effect wireless throughput. In this paper, we propose a novel architecture for contribution-based transfer-rate differentiation using wireless quality of service (QoS) techniques that motivates users to contribute their resources for wireless content sharing. We also propose a radio resource assignment method for our architecture. Computer simulations and game-theoretic calculations validate our architecture.

The performance of multiuser MIMO downlink systems with block diagonalization (BD) relies on the channel state information (CSI) at the transmitter to a great extent. For time division duplex TDD systems, the transmitter estimates the CSI while receiving data at current time slot and then uses the CSI to transmit at the next time slot. When the wireless channel is time-varying, the CSI for transmission is imperfect due to the time delay between the estimation of the channel and the transmission of the data and severely degrades the system performance. In this paper, we propose a linear method to suppress the interferences among users and data streams caused by imperfect CSI at transmitter. The transmitter first sends pilot signals through a linear spatial precoding matrix so as to make possible that the receiver can estimate CSI of other users, and then the receiver exploits a linear prefilter to suppress the interference. The numerical results show that the proposed schemes achieve obvious performance enhancement in comparison to the BD scheme with imperfect CSI at the transmitter.

The IEEE 802.15.4 standard for Low Power Wireless Personal Area Networks (LoWPANs) has emerged as a promising technology to bring the envisioned ubiquitous paradigm, into realization. Considerable efforts are being carried on to integrate LoWPANs with other wired and wireless IP networks, in order to make use of pervasive nature and existing infrastructure associated with IP technologies. Provisioning of service discovery and network selection in such pervasive environments puts heavy communication and processing overhead in networks with highly constrained resources. Localization of communication, through accessing the closest services, increases the total network capacity and increases the network life. We present a hierarchical service discovery architecture based on SSLP, in which we propose directory proxy agents to act as cache service for directory agent, in order to localize the service discovery communication and access the closest services. We also propose algorithms to make sure that service users are connected to the closest proxy agent in order to access the closest service in the vicinity. The results show that our architecture and algorithms help finding the closest services, reduce the traffic overhead for service discovery, decrease the service discovery time, and save nodes' energy considerably in 6LoWPANs.

We describe a way to write state machines inductively. The proposed method makes it possible to use the standard techniques for proving theorems on inductive types to verify that state machines satisfy invariant properties. A mutual exclusion protocol using a queue is used to exemplify the proposed method.

Recently, many studies reported various advanced e-Health service systems in patient care monitoring utilizing sensor networks and questionnaire systems. We propose an informant driven e-Health service system for the identification of heart rate related mental stress factors with a simple operation of informant-client model. Through performance analysis, we show that the proposed system is a cost-effective stress identification system applicable to mobile wireless networks.