1,321 research outputs found
Scheduling Policies in Time and Frequency Domains for LTE Downlink Channel: A Performance Comparison
A key feature of the Long-Term Evolution (LTE) system is that the packet scheduler can make use of the channel quality information (CQI), which is periodically reported by user equipment either in an aggregate form for the whole downlink channel or distinguished for each available subchannel. This mechanism allows for wide discretion in resource allocation, thus promoting the flourishing of several scheduling algorithms, with different purposes. It is therefore of great interest to compare the performance of such algorithms under different scenarios. Here, we carry out a thorough performance analysis of different scheduling algorithms for saturated User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) traffic sources, as well as consider both the time- and frequency-domain versions of the schedulers and for both flat and frequency-selective channels. The analysis makes it possible to appreciate the difference among the scheduling algorithms and to assess the performance gain, in terms of cell capacity, users' fairness, and packet service time, obtained by exploiting the richer, but heavier, information carried by subchannel CQI. An important part of this analysis is a throughput guarantee scheduler, which we propose in this paper. The analysis reveals that the proposed scheduler provides a good tradeoff between cell capacity and fairness both for TCP and UDP traffic sources
Multi-user Scheduling Schemes for Simultaneous Wireless Information and Power Transfer
In this paper, we study the downlink multi-user scheduling problem for a
time-slotted system with simultaneous wireless information and power transfer.
In particular, in each time slot, a single user is scheduled to receive
information, while the remaining users opportunistically harvest the ambient
radio frequency (RF) energy. We devise novel scheduling schemes in which the
tradeoff between the users' ergodic capacities and their average amount of
harvested energy can be controlled. To this end, we modify two fair scheduling
schemes used in information-only transfer systems. First, proportionally fair
maximum normalized signal-to-noise ratio (N-SNR) scheduling is modified by
scheduling the user having the jth ascendingly ordered (rather than the
maximum) N-SNR. We refer to this scheme as order-based N-SNR scheduling.
Second, conventional equal-throughput (ET) fair scheduling is modified by
scheduling the user having the minimum moving average throughput among the set
of users whose N-SNR orders fall into a certain set of allowed orders Sa
(rather than the set of all users). We refer to this scheme as order-based ET
scheduling. The feasibility conditions required for the users to achieve ET
with this scheme are also derived. We show that the smaller the selection order
j for the order-based N-SNR scheme, and the lower the orders in Sa for the
order-based ET scheme, the higher the average amount of energy harvested by the
users at the expense of a reduction in their ergodic capacities. We analyze the
performance of the considered scheduling schemes for independent and
non-identically distributed (i.n.d.) Ricean fading channels, and provide
closed-form results for the special case of i.n.d. Rayleigh fading.Comment: 6 pages, 3 figures. Submitted for possible conference publicatio
Study on Scheduling Techniques for Ultra Dense Small Cell Networks
The most promising approach to enhance network capacity for the next
generation of wireless cellular networks (5G) is densification, which benefits
from the extensive spatial reuse of the spectrum and the reduced distance
between transmitters and receivers. In this paper, we examine the performance
of different schedulers in ultra dense small cell deployments. Due to the
stronger line of sight (LOS) at low inter-site distances (ISDs), we discuss
that the Rician fading channel model is more suitable to study network
performance than the Rayleigh one, and model the Rician K factor as a function
of distance between the user equipment (UE) and its serving base station (BS).
We also construct a cross-correlation shadowing model that takes into account
the ISD, and finally investigate potential multi-user diversity gains in ultra
dense small cell deployments by comparing the performances of proportional fair
(PF) and round robin (RR) schedulers. Our study shows that as network becomes
denser, the LOS component starts to dominate the path loss model which
significantly increases the interference. Simulation results also show that
multi-user diversity is considerably reduced at low ISDs, and thus the PF
scheduling gain over the RR one is small, around 10% in terms of cell
throughput. As a result, the RR scheduling may be preferred for dense small
cell deployments due to its simplicity. Despite both the interference
aggravation as well as the multi-user diversity loss, network densification is
still worth it from a capacity view point.Comment: 6 pages, 7 figures, Accepted to IEEE VTC-Fall 2015 Bosto
A Framework for Uplink Intercell Interference Modeling with Channel-Based Scheduling
This paper presents a novel framework for modeling the uplink intercell
interference (ICI) in a multiuser cellular network. The proposed framework
assists in quantifying the impact of various fading channel models and
state-of-the-art scheduling schemes on the uplink ICI. Firstly, we derive a
semianalytical expression for the distribution of the location of the scheduled
user in a given cell considering a wide range of scheduling schemes. Based on
this, we derive the distribution and moment generating function (MGF) of the
uplink ICI considering a single interfering cell. Consequently, we determine
the MGF of the cumulative ICI observed from all interfering cells and derive
explicit MGF expressions for three typical fading models. Finally, we utilize
the obtained expressions to evaluate important network performance metrics such
as the outage probability, ergodic capacity, and average fairness numerically.
Monte-Carlo simulation results are provided to demonstrate the efficacy of the
derived analytical expressions.Comment: IEEE Transactions on Wireless Communications, 2013. arXiv admin note:
substantial text overlap with arXiv:1206.229
Selective Fair Scheduling over Fading Channels
Imposing fairness in resource allocation incurs a loss of system throughput,
known as the Price of Fairness (). In wireless scheduling, increases
when serving users with very poor channel quality because the scheduler wastes
resources trying to be fair. This paper proposes a novel resource allocation
framework to rigorously address this issue. We introduce selective fairness:
being fair only to selected users, and improving by momentarily blocking
the rest. We study the associated admission control problem of finding the user
selection that minimizes subject to selective fairness, and show that
this combinatorial problem can be solved efficiently if the feasibility set
satisfies a condition; in our model it suffices that the wireless channels are
stochastically dominated. Exploiting selective fairness, we design a stochastic
framework where we minimize subject to an SLA, which ensures that an
ergodic subscriber is served frequently enough. In this context, we propose an
online policy that combines the drift-plus-penalty technique with
Gradient-Based Scheduling experts, and we prove it achieves the optimal .
Simulations show that our intelligent blocking outperforms by 40 in
throughput previous approaches which satisfy the SLA by blocking low-SNR users
Multiuser Switched Diversity Scheduling Schemes
Multiuser switched-diversity scheduling schemes were recently proposed in
order to overcome the heavy feedback requirements of conventional opportunistic
scheduling schemes by applying a threshold-based, distributed, and ordered
scheduling mechanism. The main idea behind these schemes is that slight
reduction in the prospected multiuser diversity gains is an acceptable
trade-off for great savings in terms of required channel-state-information
feedback messages. In this work, we characterize the achievable rate region of
multiuser switched diversity systems and compare it with the rate region of
full feedback multiuser diversity systems. We propose also a novel proportional
fair multiuser switched-based scheduling scheme and we demonstrate that it can
be optimized using a practical and distributed method to obtain the feedback
thresholds. We finally demonstrate by numerical examples that
switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the
ultimate network capacity of full feedback systems in Rayleigh fading
conditions.Comment: Accepted at IEEE Transactions on Communications, to appear 2012,
funded by NPRP grant 08-577-2-241 from QNR
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