/pdf/convex-analysisnoer-san-nojin-zhan-nituite-5dl2rbmoyr.pdf

Convex Analysisの二,三の進展について

Real and Complex Analysis

Due to the broadcast nature of radio propagation, the wireless air interface is open and accessible to both authorized and illegitimate users. This completely differs from a wired network, where communicating devices are physically connected through cables and a node without direct association is unable to access the network for illicit activities. The open communications environment makes wireless transmissions more vulnerable than wired communications to malicious attacks, including both the passive eavesdropping for data interception and the active jamming for disrupting legitimate transmissions. Therefore, this paper is motivated to examine the security vulnerabilities and threats imposed by the inherent open nature of wireless communications and to devise efficient defense mechanisms for improving the wireless network security. We first summarize the security requirements of wireless networks, including their authenticity, confidentiality, integrity, and availability issues. Next, a comprehensive overview of security attacks encountered in wireless networks is presented in view of the network protocol architecture, where the potential security threats are discussed at each protocol layer. We also provide a survey of the existing security protocols and algorithms that are adopted in the existing wireless network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term evolution (LTE) systems. Then, we discuss the state of the art in physical-layer security, which is an emerging technique of securing the open communications environment against eavesdropping attacks at the physical layer. Several physical-layer security techniques are reviewed and compared, including information-theoretic security, artificial-noise-aided security, security-oriented beamforming, diversity-assisted security, and physical-layer key generation approaches. Since a jammer emitting radio signals can readily interfere with the legitimate wireless users, we also introduce the family of various jamming attacks and their countermeasures, including the constant jammer, intermittent jammer, reactive jammer, adaptive jammer, and intelligent jammer. Additionally, we discuss the integration of physical-layer security into existing authentication and cryptography mechanisms for further securing wireless networks. Finally, some technical challenges which remain unresolved at the time of writing are summarized and the future trends in wireless security are discussed.

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A Survey on Wireless Security: Technical Challenges, Recent Advances, and Future Trends

In this paper, we study how to optimally manage the freshness of information updates sent from a source node to a destination via a channel. A proper metric for data freshness at the destination is the age-of-information , or simply age , which is defined as how old the freshest received update is, since the moment that this update was generated at the source node (e.g., a sensor). A reasonable update policy is the zero-wait policy, i.e., the source node submits a fresh update once the previous update is delivered, which achieves the maximum throughput and the minimum delay. Surprisingly, this zero-wait policy does not always minimize the age. This counter-intuitive phenomenon motivates us to study how to optimally control information updates to keep the data fresh and to understand when the zero-wait policy is optimal. We introduce a general age penalty function to characterize the level of dissatisfaction on data staleness and formulate the average age penalty minimization problem as a constrained semi-Markov decision problem with an uncountable state space. We develop efficient algorithms to find the optimal update policy among all causal policies and establish sufficient and necessary conditions for the optimality of the zero-wait policy. Our investigation shows that the zero-wait policy is far from the optimum if: 1) the age penalty function grows quickly with respect to the age; 2) the packet transmission times over the channel are positively correlated over time; or 3) the packet transmission times are highly random (e.g., following a heavy-tail distribution).

Update or Wait: How to Keep Your Data Fresh

In this chapter we deal with the following nonlinear fractional programming problem: 

$$P:\mathop{{\max }}\limits_{{x \in s}} q(x) = (f(x) + \alpha )/((x) + \beta )$$

where f, g: R n → R, α, β ∈ R, S ⊆ R n . To simplify things, and without restricting the generality of the problem, it is usually assumed that, g(x) + β + 0 for all x ∈ S,S is non-empty and that the objective function has a finite optimal value.

Nonlinear Fractional Programming

In this paper, we consider two-way orthogonal frequency division multiplexing (OFDM) relay channels, where the direct link between the two terminal nodes is too weak to be used for data transmission. The widely known per-subcarrier decode-and-forward (DF) relay strategy, treats each subcarrier as a separate channel, and performs independent channel coding over each subcarrier. We show that this per-subcarrier DF relay strategy is only a suboptimal DF relay strategy, and present a multi-subcarrier DF relay strategy which utilizes cross-subcarrier channel coding to achieve a larger rate region. We then propose an optimal resource allocation algorithm to characterize the achievable rate region of the multi-subcarrier DF relay strategy. The computational complexity of this algorithm is much smaller than that of standard Lagrangian duality optimization algorithms. We further analyze the asymptotic performance of two-way relay strategies including the above two DF relay strategies and an amplify-and-forward (AF) relay strategy. The analysis shows that the multi-subcarrier DF relay strategy tends to achieve the capacity region of the two-way OFDM relay channels in the low signal-to-noise ratio (SNR) regime, while the AF relay strategy tends to achieve the multiplexing gain region of the two-way OFDM relay channels in the high SNR regime. Numerical results are provided to justify all the analytical results and the efficacy of the proposed optimal resource allocation algorithm.

Technical Report on "Capacity Region Bounds and Resource Allocation for Two-Way OFDM Relay Channels"

We consider the problem of tracking an unstable stochastic process $X_t$ by using causal knowledge of another stochastic process $Y_t$. We obtain necessary conditions and sufficient conditions for maintaining a finite tracking error. We provide necessary conditions as well as sufficient conditions for the success of this estimation, which is defined as order $m$ moment trackability. By-products of this study are connections between statistics such as Renyi entropy, Gallager's reliability function, and the concept of anytime capacity.

On the Trackability of Stochastic Processes.

This paper presents a cooperative transmission strategy for uplink cellular systems, especially for the case that the base station (BS) is mounted with many antennas, but the mobile terminal (MT) and relays each has much fewer antennas. Single userpsilas maximal rate of the proposed strategy is derived. We consider power allocation and time slot scheduling to increase the data rate. The simulation results show that this strategy achieves a great increase of the userpsilas data rate than that in non-relay systems. Moreover, our cooperative transmission strategy can increase the spectral efficiency of half-duplex relay networks by allowing the hops for different users to reuse the same time slot. The simulation results show that our approach achieves a higher system throughput (multiple users) than the existing strategy from literatures.

A cooperative transmission strategy for uplink cellular systems

This paper presents a fully distributed power allocation al gorithm for decode-and-forward (DF) relay networks with a large number of sources, relays, and destination nodes. The well known mathematical decomposition based distributed optimization techniques cannot directly be applied to DF relay networks, because the achievable rate of DF relaying is not strictly co ncave, and thus the local power allocation subproblem may have non-unique solutions. We resolve this non-strict concavity problem by using the idea of proximal point method, which adds some quadratic terms to make the objective function strictly concave. While traditional proximal point methods require a two-layer nested iteration structure, our proposed algorithm has a single-layer iteration structure , which is desirable for on-line implementation. Moreover, our algorithm only needs local information exchange among the source, relay, and destination nodes of each DF relay link, and can easily adapt to variations of network size and topology. In this paper, we establish the convergence and optimality of our fully distributed single-layer iterative algorithm. Numerical results are provided to illustrate the benefits of our proposed algorithm. Index terms− Decode-and-forward, distributed power allocation, wireless relay network.

Optimal Distributed Power Allocation for Decode-and-Forward Relay Networks

WiFi usage significantly reduces the battery lifetime of handheld devices such as smartphones and tablets, due to its high energy consumption. In this paper, we propose "Life-Add": a Lifetime Adjustable design for WiFi networks, where the devices are powered by battery, electric power, and/or renewable energy. In Life-Add, a device turns off its radio to save energy when the channel is sensed to be busy, and sleeps for a random time period before sensing the channel again. Life-Add carefully controls the devices' average sleep periods to improve their throughput while satisfying their operation time requirement. It is proven that Life-Add achieves near-optimal proportional-fair utility performance for single access point (AP) scenarios. Moreover, Life-Add alleviates the near-far effect and hidden terminal problem in general multiple AP scenarios. Our ns-3 simulations show that Life-Add simultaneously improves the lifetime, throughput, and fairness performance of WiFi networks, and coexists harmoniously with IEEE 802.11.

Yin Sun

Papers

Technical Report on "Capacity Region Bounds and Resource Allocation for Two-Way OFDM Relay Channels"

On the Trackability of Stochastic Processes.

A cooperative transmission strategy for uplink cellular systems

Optimal Distributed Power Allocation for Decode-and-Forward Relay Networks

Life-Add: Lifetime Adjustable Design for WiFi Networks with Heterogeneous Energy Supplies