Information security in critical infrastructure sectors has become a crucial issue in recent years. A drastic increase of mobile device usage for accessing to corporate networks could expose the critical systems to major security risks. The paper provides an overview of research and practice trends in mobile device security focusing on critical infrastructure. This includes access control, next-generation firewall, BYOD control mechanism, and BYOD management and policy. Confidentiality, integrity, and availability issues related on the research and practice trends are discussed, followed by the conclusion.

In this paper we propose a positioning approach based on the time different of arrival (TDOA) algorithm from light emitting diodes to localize mobile targets in indoor environments. The hexagonal lattice alignment of LED transmitters is proposed to reduce the coverage holes and the areas of overlapping radiation. The accuracy of the position estimation is compared to the one in a typical rectangular grid alignment. In addition, an extended Kalman filter is adopted together with the TDOA method to enhance the position estimation performance.

The empirical performance studies on the emerging IEEE 802.11n technology by an independent and vendor-neutral party have not really been explored. In this paper, we conduct performance measurements for the IEEE 802.11n network using a mixture of commercially available IEEE 802.11n devices from various manufacturers. With the same standard 20-MHz channel width configuration, the results demonstrate that IEEE 802.11n significantly outperforms the IEEE 802.11g network. The performance improvements of IEEE 802.11n are measured to be roughly about 85% for the downlink UDP traffic, 68% for the downlink TCP traffic, 50% for the uplink UDP traffic, and 90% for the uplink TCP traffic. We also observe that the UDP throughputs are largely imbalanced for the uplink and downlink traffics in most test networks, while the downlink and uplink TCP throughput results are quite balanced for all test networks. In addition, the 40-MHz channel configurations only provide marginal performance improvements. Unlike other existing work, here we also capture and analyze the IEEE 802.11n packets transferred during the performance tests in order to technically explain the measured performance results. It is observed that when the frame aggregation and block acknowledgement mechanisms are utilized, the superior performance results are achieved. However, the decisions on how and when to use these mechanisms are very hardware dependent.

In this paper, we propose a modified backoff mechanism that can be used in conjunction with the existing backoff algorithms for medium access sharing among wireless stations via the CSMA protocol. With a proper design, the resulting scheme can achieve better short-term throughput fairness performance without degradation in the average throughput performance. The main idea of the proposed scheme is to virtually create a transmission cycle for each wireless station. After getting a turn to access the medium, each wireless station is not allowed to start the backoff procedure for its next transmission until it has waited for some additional number of backoff slots. Moreover, the average throughput performance of the proposed scheme is analytically evaluated in this work via the Markov chain approach. The simulation results show that the performance analysis model derived here for the proposed scheme is valid and accurate. In addition, the proposed scheme noticeably improves the short-term throughput fairness performance of the conventional backoff scheme.

In this paper, a new technique to design improved high-rate space-time (ST) codes is proposed based on the concept of concatenated ST block code (STBC) and outer trellis-coded modulation (M-TCM) encoder constructions. Unlike the conventional rate-lossy STBC-MTCM schemes, the proposed designs produce higher rate ST codes by expanding the codebook of the inner orthogonal STBC. The classic set partitioning concept is adopted to realize the STBC-MTCM designs with large coding gains. The proposed expanded STBC-MTCM designs for the two-, three-, and four-transmitter cases are illustrated. Simulation results show the proposed STBC-MTCM designs significantly outperform the traditional ST-TCM schemes. Furthermore, decoding complexity of the proposed scheme is low because signal orthogonality is exploited to ease data decoding.

In this paper, we propose a new technique for designing an improved high-rate space-time code. The proposed code construction is based on a typical concatenation of a space-time block code and an outer TCM/MTCM encoder. However, unlike the existing STB-MTCM schemes which are rate-lossy, the proposed technique produces higher-rate space-time codes by expanding the cardinality of the available orthogonal space-time signal points before concatenating with an outer M-TCM encoder. The set partitioning concept is then employed to realize large coding gains. Here, we present design examples for the 2-transmitter and 3-transmitter cases. The new space-time codes considerably outperform the existing designs. Furthermore, signal orthogonality is exploited to keep decoding complexity of the proposed construction relatively low.

In this paper, we propose a new technique for constructing improved high-rate space-time codes. The proposed code construction is based on a concatenation of an orthogonal spacetime block code and an outer M-TCM encoder. However, unlike the existing STB-MTCM schemes which are rate-lossy, the proposed construction yields higher-rate space-time codes by expanding the cardinality of the orthogonal space-time block code before concatenating with an outer M-TCM encoder. An advantage of the proposed construction is that the standard techniques for designing a good TCM code, such as the classic set partitioning concept, can be adopted to realize the STB-MTCM designs with large coding gains. We present several design examples of improved full-rate space-time codes for a system with 2 transmit antennas. Simulation results show that the new space-time codes considerably outperform the existing ST-TCM designs. For example, the new 4-state 2-bits/symbol QPSK space-time code performs even better than the original 32-state design, while performance of the new 32-state QPSK code is only 1.5 dB away from the outage probability limit. Moreover, decoding complexity of the proposed M-TCM construction is made reasonably low by exploiting signal orthogonality.

This article provides a new formulation for the pairwise error probability for any coherently demodulated system in arbitrarily correlated Rayleigh fading. The novelty of the result is that the error probability expression can be described as a function of the eigenvalues of a "signal"-only matrix. We also provide the relationship between the pole location of the characteristic function and the resulting error probability. This result allows us to approximate and bound the desired probability. A new simple bound on the pairwise error probability is derived that is better than the standard Chernoff bound and asymptotically tight with the signal-to-noise ratio (SNR) to the true probability.

The problem of estimating the channel parameters of a new user in a multiuser code-division multiple-access (CDMA) communication system is addressed. It is assumed that the new user transmits training data over a slowly fading multipath channel. The proposed algorithm is based on maximum-likelihood estimation of the channel parameters. First, an asymptotic expression for the likelihood function of channel parameters is derived and a re-parametrization of this likelihood function is proposed. In this re-parametrization, the channel parameters are combined into a discrete time channel filter of symbol period length. Then, expectation-maximization algorithm and alternating projection algorithm-based techniques are considered to extract channel parameters from the estimated discrete channel filter, to maximize the derived asymptotic likelihood function. The performance of the proposed algorithms is evaluated through simulation studies. In addition, the proposed algorithms are compared to previously suggested subspace techniques for multipath channel estimation.

This paper provides a new formulation for the pair-wise error probability for any coherently demodulated system in flat Rayleigh fading. The novelty of the result is that the resulting error rate expression is a polynomial function of the eigenvalues of a 'signal' matrix. This view also enables a simple new asymptotically tight bound on the pair-wise error probability. Examples of single and multiple transmit antenna systems are considered.