2,272 research outputs found
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
Multi-channel Hybrid Access Femtocells: A Stochastic Geometric Analysis
For two-tier networks consisting of macrocells and femtocells, the channel
access mechanism can be configured to be open access, closed access, or hybrid
access. Hybrid access arises as a compromise between open and closed access
mechanisms, in which a fraction of available spectrum resource is shared to
nonsubscribers while the remaining reserved for subscribers. This paper focuses
on a hybrid access mechanism for multi-channel femtocells which employ
orthogonal spectrum access schemes. Considering a randomized channel assignment
strategy, we analyze the performance in the downlink. Using stochastic geometry
as technical tools, we model the distribution of femtocells as Poisson point
process or Neyman-Scott cluster process and derive the distributions of
signal-to-interference-plus-noise ratios, and mean achievable rates, of both
nonsubscribers and subscribers. The established expressions are amenable to
numerical evaluation, and shed key insights into the performance tradeoff
between subscribers and nonsubscribers. The analytical results are corroborated
by numerical simulations.Comment: This is the final version, which was accepted in IEEE Transactions on
Communication
Open, Closed, and Shared Access Femtocells in the Downlink
A fundamental choice in femtocell deployments is the set of users which are
allowed to access each femtocell. Closed access restricts the set to
specifically registered users, while open access allows any mobile subscriber
to use any femtocell. Which one is preferable depends strongly on the distance
between the macrocell base station (MBS) and femtocell. The main results of the
paper are lemmas which provide expressions for the SINR distribution for
various zones within a cell as a function of this MBS-femto distance. The
average sum throughput (or any other SINR-based metric) of home users and
cellular users under open and closed access can be readily determined from
these expressions. We show that unlike in the uplink, the interests of home and
cellular users are in conflict, with home users preferring closed access and
cellular users preferring open access. The conflict is most pronounced for
femtocells near the cell edge, when there are many cellular users and fewer
femtocells. To mitigate this conflict, we propose a middle way which we term
shared access in which femtocells allocate an adjustable number of time-slots
between home and cellular users such that a specified minimum rate for each can
be achieved. The optimal such sharing fraction is derived. Analysis shows that
shared access achieves at least the overall throughput of open access while
also satisfying rate requirements, while closed access fails for cellular users
and open access fails for the home user.Comment: 26 pages, 8 figures, Submitted to IEEE Transactions on Wireless
Communication
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