1,208 research outputs found
Outage and Local Throughput and Capacity of Random Wireless Networks
Outage probabilities and single-hop throughput are two important performance
metrics that have been evaluated for certain specific types of wireless
networks. However, there is a lack of comprehensive results for larger classes
of networks, and there is no systematic approach that permits the convenient
comparison of the performance of networks with different geometries and levels
of randomness.
The uncertainty cube is introduced to categorize the uncertainty present in a
network. The three axes of the cube represent the three main potential sources
of uncertainty in interference-limited networks: the node distribution, the
channel gains (fading), and the channel access (set of transmitting nodes). For
the performance analysis, a new parameter, the so-called {\em spatial
contention}, is defined. It measures the slope of the outage probability in an
ALOHA network as a function of the transmit probability at . Outage is
defined as the event that the signal-to-interference ratio (SIR) is below a
certain threshold in a given time slot. It is shown that the spatial contention
is sufficient to characterize outage and throughput in large classes of
wireless networks, corresponding to different positions on the uncertainty
cube. Existing results are placed in this framework, and new ones are derived.
Further, interpreting the outage probability as the SIR distribution, the
ergodic capacity of unit-distance links is determined and compared to the
throughput achievable for fixed (yet optimized) transmission rates.Comment: 22 pages, 6 figures. Submitted to IEEE Trans. Wireles
A Mobile Satellite Experiment (MSAT-X) network definition
The network architecture development of the Mobile Satellite Experiment (MSAT-X) project for the past few years is described. The results and findings of the network research activities carried out under the MSAT-X project are summarized. A framework is presented upon which the Mobile Satellite Systems (MSSs) operator can design a commercial network. A sample network configuration and its capability are also included under the projected scenario. The Communication Interconnection aspect of the MSAT-X network is discussed. In the MSAT-X network structure two basic protocols are presented: the channel access protocol, and the link connection protocol. The error-control techniques used in the MSAT-X project and the packet structure are also discussed. A description of two testbeds developed for experimentally simulating the channel access protocol and link control protocol, respectively, is presented. A sample network configuration and some future network activities of the MSAT-X project are also presented
Random Access Game in Fading Channels with Capture: Equilibria and Braess-like Paradoxes
The Nash equilibrium point of the transmission probabilities in a slotted
ALOHA system with selfish nodes is analyzed. The system consists of a finite
number of heterogeneous nodes, each trying to minimize its average transmission
probability (or power investment) selfishly while meeting its average
throughput demand over the shared wireless channel to a common base station
(BS). We use a game-theoretic approach to analyze the network under two
reception models: one is called power capture, the other is called signal to
interference plus noise ratio (SINR) capture. It is shown that, in some
situations, Braess-like paradoxes may occur. That is, the performance of the
system may become worse instead of better when channel state information (CSI)
is available at the selfish nodes. In particular, for homogeneous nodes, we
analytically present that Braess-like paradoxes occur in the power capture
model, and in the SINR capture model with the capture ratio larger than one and
the noise to signal ratio sufficiently small.Comment: 30 pages, 5 figure
Massive MIMO for Crowd Scenarios: A Solution Based on Random Access
This paper presents a new approach to intra-cell pilot contamination in
crowded massive MIMO scenarios. The approach relies on two essential properties
of a massive MIMO system, namely near-orthogonality between user channels and
near-stability of channel powers. Signal processing techniques that take
advantage of these properties allow us to view a set of contaminated pilot
signals as a graph code on which iterative belief propagation can be performed.
This makes it possible to decontaminate pilot signals and increase the
throughput of the system. The proposed solution exhibits high performance with
large improvements over the conventional method. The improvements come at the
price of an increased error rate, although this effect is shown to decrease
significantly for increasing number of antennas at the base station
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