93 research outputs found
Average Error Probability Analysis in mmWave Cellular Networks
In this paper, a mathematical framework for the analysis of average symbol
error probability (ASEP) in millimeter wave (mmWave) cellular networks with
Poisson Point Process (PPP) distributed base stations (BSs) is developed using
tools from stochastic geometry. The distinguishing features of mmWave
communications such as directional beamforming and having different path loss
laws for line-of-sight (LOS) and non-line-of-sight (NLOS) links are
incorporated in the average error probability analysis. First, average pairwise
error probability (APEP) expression is obtained by averaging pairwise error
probability (PEP) over fading and random shortest distance from mobile user
(MU) to its serving BS. Subsequently, average symbol error probability is
approximated from APEP using the nearest neighbor (NN) approximation. ASEP is
analyzed for different antenna gains and base station densities. Finally, the
effect of beamforming alignment errors on ASEP is investigated to get insight
on more realistic cases.Comment: Presented at IEEE VTC2015-Fal
MIMO Wireless Communications Under Statistical Queueing Constraints
The performance of multiple-input multiple-output (MIMO) wireless systems is investigated in the presence of statistical queueing constraints. Queuing constraints are imposed as limitations on buffer violation probabilities. The performance under such constraints is captured through the effective capacity formulation. A detailed analysis of the effective capacity is carried out in the low-power, wideband, and high signal-to-noise ratio (SNR) regimes. In the low-power analysis, expressions for the first and second derivatives of the effective capacity with respect to SNR at SNR = 0 are obtained under various assumptions on the degree of channel state information at the transmitter. Transmission strategies that are optimal in the sense of achieving the first and second derivatives are identified. It is shown that while the first derivative does not get affected by the presence of queueing constraints, the second derivative gets smaller as the constraints become more stringent. Through the energy efficiency analysis, this is shown to imply that the minimum bit energy requirements do not change with more strict limitations but the wideband slope diminishes. Similar results are obtained in the wideband regime if rich multipath fading is being experienced. On the other hand, sparse multipath fading with bounded number of degrees of freedom is shown to increase the minimum bit energy requirements in the presence of queueing constraints. Following the low-SNR study, the impact of buffer limitations on the high-SNR performance is quantified by analyzing the high-SNR slope and the power offset in Rayleigh fading channels. Finally, numerical results are provided to illustrate the theoretical findings, and to demonstrate the interactions between the queueing constraints and spatial dimensions over a wide range of SNR values
A Delay-Aware Caching Algorithm for Wireless D2D Caching Networks
Recently, wireless caching techniques have been studied to satisfy lower
delay requirements and offload traffic from peak periods. By storing parts of
the popular files at the mobile users, users can locate some of their requested
files in their own caches or the caches at their neighbors. In the latter case,
when a user receives files from its neighbors, device-to-device (D2D)
communication is enabled. D2D communication underlaid with cellular networks is
also a new paradigm for the upcoming 5G wireless systems. By allowing a pair of
adjacent D2D users to communicate directly, D2D communication can achieve
higher throughput, better energy efficiency and lower traffic delay. In this
work, we propose a very efficient caching algorithm for D2D-enabled cellular
networks to minimize the average transmission delay. Instead of searching over
all possible solutions, our algorithm finds out the best pairs,
which provide the best delay improvement in each loop to form a caching policy
with very low transmission delay and high throughput. This algorithm is also
extended to address a more general scenario, in which the distributions of
fading coefficients and values of system parameters potentially change over
time. Via numerical results, the superiority of the proposed algorithm is
verified by comparing it with a naive algorithm, in which all users simply
cache their favorite files
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