155 research outputs found
Approximation to Distribution of Product of Random Variables Using Orthogonal Polynomials for Lognormal Density
We derive a closed-form expression for the orthogonal polynomials associated
with the general lognormal density. The result can be utilized to construct
easily computable approximations for probability density function of a product
of random variables, when the considered variates are either independent or
correlated. As an example, we have calculated the approximative distribution
for the product of Nakagami-m variables. Simulations indicate that accuracy of
the proposed approximation is good with small cross-correlations under light
fading condition.Comment: submitted to IEEE Communications Lette
Spectrum Sensing in the Presence of Multiple Primary Users
We consider multi-antenna cooperative spectrum sensing in cognitive radio
networks, when there may be multiple primary users. A detector based on the
spherical test is analyzed in such a scenario. Based on the moments of the
distributions involved, simple and accurate analytical formulae for the key
performance metrics of the detector are derived. The false alarm and the
detection probabilities, as well as the detection threshold and Receiver
Operation Characteristics are available in closed form. Simulations are
provided to verify the accuracy of the derived results, and to compare with
other detectors in realistic sensing scenarios.Comment: Accepted in IEEE Transactions on Communication
Non-Orthogonal Contention-Based Access for URLLC Devices with Frequency Diversity
We study coded multichannel random access schemes for ultra-reliable
low-latency uplink transmissions. We concentrate on non-orthogonal access in
the frequency domain, where users transmit over multiple orthogonal subchannels
and inter-user collisions limit the available diversity. Two different models
for contention-based random access over Rayleigh fading resources are
investigated. First, a collision model is considered, in which the packet is
replicated onto available resources, of which are received
without collision, and treated as diversity branches by a maximum-ratio
combining (MRC) receiver. The resulting diversity degree depends on the
arrival process and coding strategy. In the second model, the slots subject to
collisions are also used for MRC, such that the number of diversity branches
is constant, but the resulting combined signal is affected by multiple
access interference. In both models, the performance of random and
deterministic repetition coding is compared. The results show that the
deterministic coding approach can lead to a significantly superior performance
when the arrival rate of the intermittent URLLC transmissions is low.Comment: 2019 IEEE 20th International Workshop on Signal Processing Advances
in Wireless Communications (SPAWC) - Special Session on Signal Processing for
NOMA Communication System
Co-primary inter-operator spectrum sharing over a limited spectrum pool using repeated games
We consider two small cell operators deployed in the same geographical area,
sharing spectrum resources from a common pool. A method is investigated to
coordinate the utilization of the spectrum pool without monetary transactions
and without revealing operator-specific information to other parties. For this,
we construct a protocol based on asking and receiving spectrum usage favors by
the operators, and keeping a book of the favors. A spectrum usage favor is
exchanged between the operators if one is asking for a permission to use some
of the resources from the pool on an exclusive basis, and the other is willing
to accept that. As a result, the proposed method does not force an operator to
take action. An operator with a high load may take spectrum usage favors from
an operator that has few users to serve, and it is likely to return these
favors in the future to show a cooperative spirit and maintain reciprocity. We
formulate the interactions between the operators as a repeated game and
determine rules to decide whether to ask or grant a favor at each stage game.
We illustrate that under frequent network load variations, which are expected
to be prominent in small cell deployments, both operators can attain higher
user rates as compared to the case of no coordination of the resource
utilization.Comment: To be published in proceedings of IEEE International Conference on
Communications (ICC) at London, Jun. 201
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