576 research outputs found
Auction-Based Coopetition between LTE Unlicensed and Wi-Fi
Motivated by the recent efforts in extending LTE to the unlicensed spectrum,
we propose a novel spectrum sharing framework for the coopetition (i.e.,
cooperation and competition) between LTE and Wi-Fi in the unlicensed band.
Basically, the LTE network can choose to work in one of the two modes: in the
competition mode, it randomly accesses an unlicensed channel, and interferes
with the Wi-Fi access point using the same channel; in the cooperation mode, it
delivers traffic for the Wi-Fi users in exchange for the exclusive access of
the corresponding channel. Because the LTE network works in an
interference-free manner in the cooperation mode, it can achieve a much larger
data rate than that in the competition mode, which allows it to effectively
serve both its own users and the Wi-Fi users. We design a second-price reverse
auction mechanism, which enables the LTE provider and the Wi-Fi access point
owners (APOs) to effectively negotiate the operation mode. Specifically, the
LTE provider is the auctioneer (buyer), and the APOs are the bidders (sellers)
who compete to sell their channel access opportunities to the LTE provider. In
Stage I of the auction, the LTE provider announces a reserve rate. In Stage II
of the auction, the APOs submit their bids. We show that the auction involves
allocative externalities, i.e., the cooperation between the LTE provider and
one APO benefits other APOs who are not directly involved in this cooperation.
As a result, a particular APO's willingness to cooperate is affected by its
belief about other APOs' willingness to cooperate. This makes our analysis much
more challenging than that of the conventional second-price auction, where
bidding truthfully is a weakly dominant strategy. We show that the APOs have a
unique form of the equilibrium bidding strategies in Stage II, based on which
we analyze the LTE provider's optimal reserve rate in Stage I.Comment: 32 page
A new One-time Password Method
AbstractOne-Time Passwords (OTP) can provide complete protection of the login-time authentication mechanism against replay attacks. In this paper, we propose TSOTP: a new effective simple OTP method that generates a unique passcode for each use. The calculation uses both time stamps and sequence numbers. A two-factor authentication prototype for mobile phones using this method has been developed and has been used in practice for a year
Geometry of power flows and convex-relaxed power flows in distribution networks with high penetration of renewables
AbstractRenewable energies are increasingly integrated in electric distribution networks and will cause severe overvoltage issues. Smart grid technologies make it possible to use coordinated control to mitigate the overvoltage issues and the optimal power flow (OPF) method is proven to be efficient in the applications such as curtailment management and reactive power control. Nonconvex nature of the OPF makes it difficult to solve and convex relaxation is a promising method to solve the OPF very efficiently. This paper investigates the geometry of the power flows and the convex-relaxed power flows when high penetration level of renewables is present in the distribution networks. The geometry study helps understand the fundamental nature of the OPF and its convex-relaxed problem, such as the second-order cone programming (SOCP) problem. A case study based on a three-node system is used to illustrate the geometry profile of the feasible sub-injection (injection of nodes excluding the root/substation node) region
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