報告人:蘇蕙蕙
指導教授:陳偉業
班級:碩資管二甲
學號:MA390204
Ref: Ozcan Ozturk, Madhavan Vajapeyam(2013), “ Performance of VoLTE
and Data Traffic in LTE Heterogeneous Networks , ” , Globecom Communications QoS, Reliability and Modelling Symposium .
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Abstract
INTRODUCTION
BACKGROUND
RESULTS AND ANALYSIS
CONCLUSION
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VoLTE (Voice over LTE)
◦ provide voice services.
◦ increasing need for much higher data capacity as a result of
smartphone proliferation.
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VoLTE and data users
◦ evaluate the performance of LTE Downlink.
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data performance and VoLTE capacity
◦ HetNet with Pico cell range expansion significantly improves
both the system.
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The LTE radio access downlink system performance
when both data and voice users are present.
In Section II
In Section III
In Section IV
Section V
a
background
on
the
VoLTE
considered scenarios are provided.
the simulation model and assumptions
are discussed.
we present the simulation results with
analyses.
includes concluding remarks.
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The
advantage
of VoLTE
SPS
HetNet
•Reuses the LTE radio access to carry voice traffic.
• Utilizes the IP Multimedia Subsystem (IMS) in the core
network which can support richer media services.
•That LTE can provide significant capacity at the required
QoS.
•The usual mode of scheduling in LTE is dynamic.
• Downlink (DL) and Uplink (UL) assignments are
signaled on every subframe on the Physical Downlink
Control Channel (PDCCH).
•The deployment of base stations (eNB) with lower power
such as Picos and Femtos is envisioned.
•A key solution to increase the system capacity to meet the
(exponentially increasing) data traffic.
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The channel model and cell layout are based on 3GPP
simulation D1 model for LTE , with minor
modifications. Main simulation parameters are
summarized in Table I.
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A. Scheduler
◦ The downlink scheduling uses a dynamic sub-band scheduler.
◦ MIMO is enabled for all users and Discontinuous Reception
(DRX) is disabled for all users.
◦ Each scheduled user is assigned a PDCCH resource to signal
the transport format and the resource allocation. For the
availability of PDCCH resources, two options were simulated:
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Up to 5 PDCCH (control channel limitation).
No limit on the number of PDCCH available.
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B. VoLTE
◦ VoLTE traffic is modeled using a two-state Markov model
based on AMR 12.65 wideband vocoder.
◦ Assume that
 Robust Header Compression (RoHC) is used which reduces the
UDP/IP/PDCP header size to 3 bytes.
 The VoLTE frames are not segmented or bundled at the source;
however these may occur due to scheduling choices of the TB
sizes for a user.
◦ The system capacity for VoLTE is reached when the number of
users in outage is more than 5% of the total VoLTE users.
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C. SPS
◦ modeled by assigning static RBs to VoLTE users in active
state.
◦ When a full frame voice frame is scheduled for the first time
for a user, an SPS grant of 2RBs is scheduled with periodicity
of 20ms.
◦ SPS grants are given higher priority over other VoLTE
transmissions
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D. HetNet
◦ no association bias is used so that users are served by the best
cell in terms of DL received power.
◦ In order to enable CRE, two association biases of 9dB and
16dB were simulated, corresponding to different Pico cell
range expansion and amounts of offloading.
◦ Three options of (6, 2), (5,3), and (4, 4) were tried for both
9dB and 16dB biases.
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The simulation duration was 20 seconds. Performance
statistics were collected for VoLTE packets (delay,
dropped, lost), FB throughput, and PDCCH and RB
usage.
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A. Macro Only
◦ FB user throughput comparing the Macro case is shown in
Table II.
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The impact of VoLTE users on FB performance is
mainly through two aspects:
◦ the main cause of FB throughput decline with increased
number of VoLTE users.
◦ Can be alleviated to some degree by relaxing the absolute
priority of VoLTE users.
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HetNet can provide significant gains for both VoLTE
and FB.
◦ The offloading of users to Pico cells
◦ Reduced control channel limitation
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Table III shows the gains of HetNet over Macro
usingdifferent CRE biases for 5 PDCCH limitation.
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Table IV shows the gains without PDCCH limitation.
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Fig 3 shows the edge and median user throughput with
5 PDCCH limit for 0dB bias.
It is seen that the Pico users have very good
performance compared to the Macro users.
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This can be seen by comparing Fig. 5 and Fig. 6 where
the Macro 5% and median throughputs are always
higher than Pico ones in Fig.6 and vice versa in Fig.5.
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A further comparison can be seen from the user
throughput CDF curves Fig. 7 and Fig. 8.
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SPS provides gains similar to no PDCCH limitation for
the FB performance as shown in Fig.2.
◦ Even though the allocation of RBs is fixed and channel
insensitive for SPS, this under-utilization has little impact on
FB performance.
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The VoLTE capacity based on outage criteria for the 5
PDCCH was limited by this control channel bound in
all cases except for SPS. These are shown in Table V.
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VoLTE capacity would be higher if there were no data
users in the system since, even though the scheduler
gives higher priority to VoLTE users within a cell, the
data users generate additional inter-cell interference.
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LTE-Advanced systems
◦ the performance of mixed VoLTE and data traffic.
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The simulation results show
◦ the data throughput decreases almost linearly.
◦ the number of VoLTE users increases.
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Control channel capacity is limited.
◦ data users have less multi-user diversity gains due to PDCCH
availability
◦ cannot be scheduled due to PDCCH blocking.
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The implementation of SPS
◦ help with the control channel limitation issue.
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The VoLTE capacity is less
◦ obtained under dynamic scheduling.
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HetNet
◦ provide significant gains by offloading the users to Pico cells.
◦ alleviating the PDCCH limitation.
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A positive CRE bias and ABS
◦ partitioning can provide gains for both data throughput.
◦ VoLTE capacity where the data gain increases with more
VoLTE users.
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Found by simulation
◦ the optimal partitioning choices for the two bias options.
◦ Consistent with offloading statistics.
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