130 research outputs found
On Physically Secure and Stable Slotted ALOHA System
In this paper, we consider the standard discrete-time slotted ALOHA with a
finite number of terminals with infinite size buffers. In our study, we jointly
consider the stability of this system together with the physical layer
security. We conduct our studies on both dominant and original systems, where
in a dominant system each terminal always has a packet in its buffer unlike in
the original system. For N = 2, we obtain the secrecy-stability regions for
both dominant and original systems. Furthermore, we obtain the transmission
probabilities, which optimize system throughput. Lastly, this paper proposes a
new methodology in terms of obtaining the joint stability and secrecy regions.Comment: 7 Pages, 8 Figures, Allerton 200
Throughput Optimal Multi-user Scheduling via Hierarchical Modulation
We investigate the network stability problem when two users are scheduled
simultaneously. The key idea is to simultaneously transmit to more than one
users experiencing different channel conditions by employing hierarchical
modulation. For two-user scheduling problem, we develop a throughput-optimal
algorithm which can stabilize the network whenever this is possible. In
addition, we analytically prove that the proposed algorithm achieves larger
achievable rate region compared to the conventional Max-Weight algorithm which
employs uniform modulation and transmits a single user. We demonstrate the
efficacy of the algorithm on a realistic simulation environment using the
parameters of High Data Rate protocol in a Code Division Multiple Access
system. Simulation results show that with the proposed algorithm, the network
can carry higher user traffic with lower delays.Comment: 4 pages, 2 figures, submitte
Reliable multi-hop routing with cooperative transmissions in energy-constrained networks
We present a novel approach in characterizing the optimal reliable multi-hop virtual multiple-input single-output (vMISO) routing in ad hoc networks. Under a high node density regime, we determine the optimal cardinality of the cooperation
sets at each hop on a path minimizing the total energy cost per transmitted bit. Optimal cooperating set cardinality curves are derived, and they can be used to determine the optimal routing strategy based on the required reliability, transmission power, and path loss coefficient. We design a new greedy geographical
routing algorithm suitable for vMISO transmissions, and demonstrate the applicability of our results for more general networks
On Security and Reliability using Cooperative Transmissions in Sensor Networks
Recent work on cooperative communications has demonstrated benefits in terms of improving the reliability of links through diversity and/or increasing the reach of a link
compared to a single transmitter transmitting to a single receiver (single-input single-output or SISO). In one form of cooperative transmissions, multiple nodes can act as virtual antenna elements and provide such benefits using space-time coding. In a multi-hop sensor network, a source node can make use of its neighbors as relays with itself to reach an intermediate node, which will use its neighbors and so on to reach the destination. For the same reliability of a link as SISO, the number of hops between a source and destination may be reduced using cooperative transmissions.
However, the presence of malicious or compromised nodes in
the network impacts the use of cooperative transmissions. Using more relays can increase the reach of a link, but if one or more relays are malicious, the transmission may fail. In this paper, we analyze this problem to understand the conditions under which cooperative transmissions may fare better or worse than SISO transmissions
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