Mobility Management and Resource Allocation towards 5G ...
Transcript of Mobility Management and Resource Allocation towards 5G ...
Mobility Management and Resource Allocationtowards 5G Radio Access Networks (RANs)
Konstantinos AlexandrisEmail: [email protected]
PhD thesis defenceCommunication Systems Dep., EURECOM
March 9, 2018
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Outline
1 Introduction
2 Mobility (HO) management in LTE/LTE-A and beyond
3 Multi-connectivity resource allocation towards 5G RANs
4 Conclusion & Future directions
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Introduction
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5G: Ushering a new era
2020: 50B devices to be prevalent
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5G: Ushering a new era
2020: 50B devices to be prevalent
5G architecture
X SCs → UDNs
X New paradigms
H2M, M2M
X New technologies
Massive MIMOmm-wave
X Network management
SDN, MEC
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5G: Ushering a new era
2020: 50B devices to be prevalent
What are the 5G requirements?
5G Services: xMBB, uRLLC, mMTC
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5G: Ushering a new era
2020: 50B devices to be prevalent
What are the 5G requirements?
5G Services: xMBB, uRLLC, mMTC
5G Use cases
X Media and Broadband
X E-health
X IoT
X V2X
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5G: Ushering a new era
2020: 50B devices to be prevalent
What are the 5G requirements?
5G Services: xMBB, uRLLC, mMTC
5G Use cases
X Media and Broadband
X E-health
X IoT
X V2X
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5G: Ushering a new era
2020: 50B devices to be prevalent
What are the 5G requirements?
5G Services: xMBB, uRLLC, mMTC
5G Use cases
X Media and Broadband
X E-health
X IoT
X V2X
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5G: Ushering a new era
2020: 50B devices to be prevalent
What are the 5G requirements?
5G Services: xMBB, uRLLC, mMTC
5G Use cases
X Media and Broadband
X E-health
X IoT
X V2X
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5G Networks
Macrocell
Wi-Fi
LTE
UDN
CN
Internet
RNsD2D
D2D D2D
V2X
D2D
SDN
LTE
D2D
Massive MIMO
D2D
D2D
MC
SC
SC
Multi-connectivity
Multi-connectivity
C-RAN
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From 4G to 5G: Contributions
New algorithms
Centralized architectureLTE/LTE-A RAN control
Mobility mgt (RRC)
X2 Handover (HO)Load + HO in HetNets
Multi-connectivity resourceallocation (MAC)
Air + BH limitationsOpportunistic scheduling
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From 4G to 5G: Contributions
New algorithms
Centralized architectureLTE/LTE-A RAN control
Mobility mgt (RRC)
X2 Handover (HO)
Load + HO in HetNets
Multi-connectivity resourceallocation (MAC)
Air + BH limitationsOpportunistic scheduling
Konstantinos Alexandris 6 / 52
From 4G to 5G: Contributions
New algorithms
Centralized architectureLTE/LTE-A RAN control
Mobility mgt (RRC)
X2 Handover (HO)Load + HO in HetNets
Multi-connectivity resourceallocation (MAC)
Air + BH limitationsOpportunistic scheduling
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From 4G to 5G: Contributions
New algorithms
Centralized architectureLTE/LTE-A RAN control
Mobility mgt (RRC)
X2 Handover (HO)Load + HO in HetNets
Multi-connectivity resourceallocation (MAC)
Air + BH limitationsOpportunistic scheduling
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X2 Handover in LTE/LTE-A
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X2 Handover in LTE/LTE-A
MME
X2eNB0 eNB1
S1-U S1-U
S-GW
S1-MME S1-MME
S11
UEUE
UEUE
UE
S1 vs X2
HO: Procedure to transfer a UE andits context from source to targeteNB
X2 HO: Reduce EPC signaling loadby 6x!
Goals & Challenges:
Study of X2 handover parameters
Handover latency evaluation
Implementation in OpenAirInterface
Contrary to prior-art:
Open to experimenters community
HO parametirization
Flexibility + Accessibility
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X2 Handover in LTE/LTE-A
MME
X2eNB0 eNB1
S1-U S1-U
S-GW
S1-MME S1-MME
S11
UEUE
UEUE
UE
S1 vs X2
HO: Procedure to transfer a UE andits context from source to targeteNB
X2 HO: Reduce EPC signaling loadby 6x!
Goals & Challenges:
Study of X2 handover parameters
Handover latency evaluation
Implementation in OpenAirInterface
Contrary to prior-art:
Open to experimenters community
HO parametirization
Flexibility + Accessibility
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X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
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X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
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X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
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X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
Konstantinos Alexandris 9 / 52
X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
Konstantinos Alexandris 9 / 52
X2 Handover experimentation in oaisim
Run in OAI emulator
3GPP TS 36.331, 36.423PHY/MAC/RLC/PDCP/RRC
UE
MovingeNB 0
eNB 1
Fixed location
(2680,4800)
Fixed location
(4000,4800)
Mobile location
(1800,4800)↔(4700,4840)
Network components
2 eNBs: source/target1 UESISO link (Tx/Rx)
Grid topology
eNBs: Fixed positionUE: Mobility tracesStraight line movement
Traffic:
UL/DL UDP traffic
Configuration:
.config/.xml filesSpecifically: RF, protocol,mobility, traffic params
Output:
pcap/log files, messagesignalling
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OAI X2 HO UE measurements
0 50 100 150 200 250 300−138
−136
−134
−132
−130
−128
−126
time (ms)
Filt
ered
RS
RP
(dB
m)
Filtered RSRP measurements with S=2
eNB0−S=2−realeNB1−S=2−realeNB0−S=2−smoothedeNB1−S=2−smoothed
Serving cell
Target cell
Handover is triggered
0 50 100 150 200 250 300−138
−136
−134
−132
−130
−128
−126
time (ms)
Filt
ered
RS
RP
(dB
m)
Filtered RSRP measurements with S=5
eNB0−S=5−realeNB1−S=5−realeNB0−S=5−smoothedeNB1−S=5−smoothed
Target cellServing cell
Handover is triggered
Handover criterion:
r dBmn [k] + S > r dBm
s [k],
where S = ofn + ocn − ofs − ocs − hys − off . (HO parameters)
Handover triggering: S > 0: high signaling overheadS < 0: high probability of failure
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OAI X2 HO network measurements
10
15
20
25
30
35
40
45
50
55
60
UE (connected to idle) UE (idle to connected)
X2 handover measurements
Del
ay (
ms)
Handover delay:
DelayHO = TBefore HO + THO Preparation + THO Execution + THO Completion + TMargin︸ ︷︷ ︸detach time ≤ 65ms
Remarks:
Measured detach time adheres to the 3GPP standards
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RF X2 Handover experimentation in OAI
X Real-world OAI X2 handover RF testbed measurements!
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OAI RF X2 HO UE measurements (1/2)
Network information and RSRP measurements before/after the HO process
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OAI RF X2 HO network measurements (2/2)
UE
MovingeNB 0
eNB 1
Different type of experiments:
Exp. Param. Value Param. Value#1 prach config index 0 Ch. atten. Ch0: 12, Ch1:16#2 prach config index 14 Ch. atten. Ch0: 12, Ch1:16#3 prach config index 0 Ch. atten. Ch0: 12, Ch1:10#4 prach config index 14 Ch. atten. Ch0: 12, Ch1:10
X2 handover measurements
1 2 3 4
Experiments
0
20
40
60
80
100
120
Del
ay (
ms)
UE (connected to idle)
UE (idle to connected)
Remarks:
prach config index=14 reduces delay: more chances to PRACH detection byeNB (Exp. 1/2 & Exp. 3/4)
Interference in DL is varying: additional delay to detect RRC/RAR messages
Channel attenuation, i.e., Ch0>Ch1 vs Ch1>Ch0 (Exp. 1/3 & Exp. 2/4)
Measured detach time > 65ms: Optimization is needed for 3GPP compliance
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Take away messages
� Handover is an “expensive” process → Delay cost
� UE synchronization overwhelms the network in terms of delay
� Contention-free preamble process can be used to help inreducing such latency in the network
� S-like offsets can impact the HO triggering
� Such offsets can be expressed as functions of different metricsprovided by SDN-like mobility mgt schemes
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Load-aware Handover Decisionalgorithm in Next-generation HetNets
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Handover (HO) in HetNets
3GPP X2 HO applies a conventionalRSS-based algorithm
Prior art:
Beyond 3GPP legacyconventionalities
Other methods based on:
1 speed2 distance3 interference mgt
What about asymmetrical transmissionpower environments in HetNets?
3GPP Rel.9 introduces SCs asHeNBs
Goals and Challenges:
Macrocell (MC) BSs deteriorate thearea in terms of power
RSS-based HO: UE stays connectedto overloaded MCs whileunderloaded picocells are around
Scale-down power factors have been
proposed based on distance criteria:
No consideration of QoSmetrics (i.e., delay,throughput)
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Handover (HO) in HetNets
3GPP X2 HO applies a conventionalRSS-based algorithm
Prior art:
Beyond 3GPP legacyconventionalities
Other methods based on:
1 speed2 distance3 interference mgt
What about asymmetrical transmissionpower environments in HetNets?
3GPP Rel.9 introduces SCs asHeNBs
Goals and Challenges:
Macrocell (MC) BSs deteriorate thearea in terms of power
RSS-based HO: UE stays connectedto overloaded MCs whileunderloaded picocells are around
Scale-down power factors have been
proposed based on distance criteria:
No consideration of QoSmetrics (i.e., delay,throughput)
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Handover (HO) in HetNets
3GPP X2 HO applies a conventionalRSS-based algorithm
Prior art:
Beyond 3GPP legacyconventionalities
Other methods based on:
1 speed2 distance3 interference mgt
What about asymmetrical transmissionpower environments in HetNets?
3GPP Rel.9 introduces SCs asHeNBs
Goals and Challenges:
Macrocell (MC) BSs deteriorate thearea in terms of power
RSS-based HO: UE stays connectedto overloaded MCs whileunderloaded picocells are around
Scale-down power factors have been
proposed based on distance criteria:
No consideration of QoSmetrics (i.e., delay,throughput)
Konstantinos Alexandris 17 / 52
Handover (HO) in HetNets
3GPP X2 HO applies a conventionalRSS-based algorithm
Prior art:
Beyond 3GPP legacyconventionalities
Other methods based on:
1 speed2 distance3 interference mgt
What about asymmetrical transmissionpower environments in HetNets?
3GPP Rel.9 introduces SCs asHeNBs
Goals and Challenges:
Macrocell (MC) BSs deteriorate thearea in terms of power
RSS-based HO: UE stays connectedto overloaded MCs whileunderloaded picocells are around
Scale-down power factors have been
proposed based on distance criteria:
No consideration of QoSmetrics (i.e., delay,throughput)
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System assumptions
Air-interface model
RSRP signal:
The signal at time k is:
rdBmi [k] , PdBm
Tx ,i︸ ︷︷ ︸Tx power
+ PdBL,i (d
ki )︸ ︷︷ ︸
Pathloss
+ ψdBi [k]︸ ︷︷ ︸
Shadowing
where i ∈ {m, pj} and ψdBi [k] ∼ N
(0, σ2
dB,i/ξ2)
.
EMA (L3) filtering:
The output signal is:
rdBmi [k] , (1− α)rdBm
i [k − 1] + αrdBmi [k]
where α , 2−q/2 and q ∈ N.
Traffic model
Network users:
a) Static users (SU):
Active users (AU): on-going traffic
Disconnected (DU): switched-off
b) Mobile users (MU):
Always active
M/G/1/PS system is adopted
non-GBR traffic/flow size with mean Y
New flows total arrival rate is:
λki = λ
(Nk
MU,i + NkAU,i
)
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Load-aware (LA) decision algorithm
Input: Dkm, Dk
pj, rp,th
Output: user cell association
Proposed algorithm:
j∗ = arg maxj
rpj
if(rpj∗ [k] > rp,th
)then
if rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
thenconnect to picocell
elseconnect to macrocell
end ifend if
Assuming M/G/1/PS ⇒
Predicted avg delay: Dki =
1
µki − λk
i
,
for a service rate µki .
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Load-aware (LA) decision algorithm
Input: Dkm, Dk
pj, rp,th
Output: user cell association
Proposed algorithm:
j∗ = arg maxj
rpj
if(rpj∗ [k] > rp,th
)then
if rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
thenconnect to picocell
elseconnect to macrocell
end ifend if
Assuming M/G/1/PS ⇒
Predicted avg delay: Dki =
1
µki − λk
i
,
for a service rate µki .
The handover rule is:
rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
Konstantinos Alexandris 19 / 52
Load-aware (LA) decision algorithm
Input: Dkm, Dk
pj, rp,th
Output: user cell association
Proposed algorithm:
j∗ = arg maxj
rpj
if(rpj∗ [k] > rp,th
)then
if rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
thenconnect to picocell
elseconnect to macrocell
end ifend if
Assuming M/G/1/PS ⇒
Predicted avg delay: Dki =
1
µki − λk
i
,
for a service rate µki .
The handover rule is:
rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
Exponential family is selected for f (·):
f(Dk
m, Dkpj
), exp
[−cDk
m/Dkpj
], c ≥ 1
Konstantinos Alexandris 19 / 52
Load-aware (LA) decision algorithm
Input: Dkm, Dk
pj, rp,th
Output: user cell association
Proposed algorithm:
j∗ = arg maxj
rpj
if(rpj∗ [k] > rp,th
)then
if rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
thenconnect to picocell
elseconnect to macrocell
end ifend if
Assuming M/G/1/PS ⇒
Predicted avg delay: Dki =
1
µki − λk
i
,
for a service rate µki .
The handover rule is:
rpj∗ [k] > f(Dk
m, Dkpj∗
)rm[k]
The f (·) ∈ [0, 1] so as to force the UEto connect in the picocell, iff:
Dkm � Dk
pj∗
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Simulations (1/2)
0.01 0.02 0.04 0.06 0.08 0.1 0.120
0.1
0.2
0.3
0.4
0.5
λ
Averagedelay(sec)
Average delay for different NSU,m and NSU,pj = 10
Dp
Dm
NSU,m = 200
NSU,m = 400NSU,m = 600
0.01 0.02 0.04 0.06 0.08 0.1 0.120
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
λ
Cellassignmen
tprobability
Algorithms performance for different NSU,m and NSU,pj = 10
LA-Pr(u ∈ p)
LA-Pr(u ∈ m)
CONV-Pr(u ∈ p)
CONV-Pr(u ∈ m)
NSU,m = 400
NSU,m = 200
NSU,m = 600
Assumption: 1 mobile user (moves in 2D-RW) and 3 picocells
Remarks:
Comparison with the conventional (RSS-based) HO algorithm:
r dBmpj [k] > r dBm
m [k] + ∆ ∧ r dBmm [k] < r dBm
m,th
As the average delay gets sharper, Pr(u ∈ p)→ 1
Conventional HO keeps UE connected to the overloaded MC
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Simulations (2/2)
50 60 80 100 120 140 160 1800
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
dm(m)
Picocellassignmen
tprobability
Algorithms performance for NSU,m = 200 and NSU,pj = 10
LA-λ = 0.05LA-λ = 0.08LA-λ = 0.1LA-λ = 0.11LA-λ = 0.12DISTCONV
λ 0.05 0.08 0.1 0.11 0.12
¯DDIST/¯DLA 0.8861 0.8141 0.8798 1.3066 4.5235
¯DCONV/¯DLA 1.0596 1.1701 1.4790 2.4073 8.8547
Load ↑: DIST HO: ∼ 4CONV HO: ∼ 8
Assumption: 1 mobile user (moves across a line) and 1 picocell
Remarks:
Distance-based HO (DIST HO):Up to a distance threshold, UE is connected tooverloaded MC (Load ↑-Delay ↑)Load ↑: LA HO associates faster the UE with the picocell (Delay ↓)Load ↓: LA HO keeps UE to MC compared to the DIST HO
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Take away messages
� LA algorithm overcomes the HetNets power assymetries
� Such algorithm considers both the user (i.e., RSS) andnetwork (i.e., service delay) perspectives
� Conventional RSS and distance-based HO algorithms areinferior to the proposed scheme, esp. in high MC load
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Multi-connectivity resource allocationin evolved LTE
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Multi-connectivity in evolved LTE
Beyond HO: Seamless mobility
Single vs Multi-connectivity:
3GPP TS36.331: Legacy SC
Bandwidth and connectivityconstraintsOnly one RATNo seamless mobilitySet bounds on users QoS
Multi-connectivity framework
Wi-Fi
5G
4G LTE
Across any access node
Simultaneous connections in several technologies
Across Radio Access
Technologies
What about multi-connectivity in evolvedLTE?
X Component of 5G New Radio: DCextension (3GPP TS36.842)
X Multiple cell connections: single ormulti-RAT
X Several bands support
Goals & Challenges:
Optimized capacity coverage
Reliable high-speed data delivery
Effective resource utilization
Contrary to prior-art:
Users QoS requirements are
considered
Konstantinos Alexandris 24 / 52
Multi-connectivity in evolved LTE
Beyond HO: Seamless mobility
Single vs Multi-connectivity:
3GPP TS36.331: Legacy SC
Bandwidth and connectivityconstraintsOnly one RATNo seamless mobilitySet bounds on users QoS
Multi-connectivity framework
Wi-Fi
5G
4G LTE
Across any access node
Simultaneous connections in several technologies
Across Radio Access
Technologies
What about multi-connectivity in evolvedLTE?
X Component of 5G New Radio: DCextension (3GPP TS36.842)
X Multiple cell connections: single ormulti-RAT
X Several bands support
Goals & Challenges:
Optimized capacity coverage
Reliable high-speed data delivery
Effective resource utilization
Contrary to prior-art:
Users QoS requirements are
considered
Konstantinos Alexandris 24 / 52
Multi-connectivity in evolved LTE
Beyond HO: Seamless mobility
Single vs Multi-connectivity:
3GPP TS36.331: Legacy SC
Bandwidth and connectivityconstraintsOnly one RATNo seamless mobilitySet bounds on users QoS
Multi-connectivity framework
Wi-Fi
5G
4G LTE
Across any access node
Simultaneous connections in several technologies
Across Radio Access
Technologies
What about multi-connectivity in evolvedLTE?
X Component of 5G New Radio: DCextension (3GPP TS36.842)
X Multiple cell connections: single ormulti-RAT
X Several bands support
Goals & Challenges:
Optimized capacity coverage
Reliable high-speed data delivery
Effective resource utilization
Contrary to prior-art:
Users QoS requirements are
considered
Konstantinos Alexandris 24 / 52
Multi-connectivity in evolved LTE
Beyond HO: Seamless mobility
Single vs Multi-connectivity:
3GPP TS36.331: Legacy SC
Bandwidth and connectivityconstraintsOnly one RATNo seamless mobilitySet bounds on users QoS
Multi-connectivity framework
Wi-Fi
5G
4G LTE
Across any access node
Simultaneous connections in several technologies
Across Radio Access
Technologies
What about multi-connectivity in evolvedLTE?
X Component of 5G New Radio: DCextension (3GPP TS36.842)
X Multiple cell connections: single ormulti-RAT
X Several bands support
Goals & Challenges:
Optimized capacity coverage
Reliable high-speed data delivery
Effective resource utilization
Contrary to prior-art:
Users QoS requirements are
considered
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System assumptions
Air-interface
Downlink (DL):
Physical data rate:
RDbj ,ui
= BDbj︸︷︷︸
max #PRBs
· WDbj︸︷︷︸
BW per PRB
· log2(1 + SINRDbj ,ui︸ ︷︷ ︸
DL SINR
)
DL SINR based on:
RSRPDbj ,ui
: Pathloss + Shadowing + Antenna gain
Uplink (UL):
Same definitions hold for uplink + Power control
PU,dBmui ,bj
= min( Pmax,dBmui︸ ︷︷ ︸
max UE power
, PdBm0 + α · LU,dB
ui ,bj︸ ︷︷ ︸pathloss
)
a, P0: power control parameters
BSs
UEsu1
u3
u2
u4
b1 b3b2
Connection and Traffic
Multi-connectivity: UL/DL LTE FDD SISO
UE association: min(SINRUui ,bj
, SINRDbj ,ui
) >
threshold︷ ︸︸ ︷SINRth
Active UEs: Mobile and connected to multiple cells
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System assumptions
Air-interface
Downlink (DL):
Physical data rate:
RDbj ,ui
= BDbj︸︷︷︸
max #PRBs
· WDbj︸︷︷︸
BW per PRB
· log2(1 + SINRDbj ,ui︸ ︷︷ ︸
DL SINR
)
DL SINR based on:
RSRPDbj ,ui
: Pathloss + Shadowing + Antenna gain
Uplink (UL):
Same definitions hold for uplink + Power control
PU,dBmui ,bj
= min( Pmax,dBmui︸ ︷︷ ︸
max UE power
, PdBm0 + α · LU,dB
ui ,bj︸ ︷︷ ︸pathloss
)
a, P0: power control parameters
Connection and Traffic
Multi-connectivity: UL/DL LTE FDD SISO
UE association: min(SINRUui ,bj
, SINRDbj ,ui
) >
threshold︷ ︸︸ ︷SINRth
Active UEs: Mobile and connected to multiple cells
BSs
UEsu1
u3
u2
u4
b1 b3b2
U2U
Traffic type: User-to-user (U2U) traffic
Traffic routing: Locally routed via a common BS (2-hop)
2-hop routing offloads backhaul (EPC)
Public safety networks isolated BSs
Close community (U2U) apps: video sharing
Traffic requested rate: Rui ,uqE2E app target rate
Konstantinos Alexandris 25 / 52
Resource allocation
xU or Dbj ,(ui ,uq)
: Pct. of allocated PRBs
Utility functions:
PF: Proportional fairness
Φ (x) = log (x)
UPF: PF + QoS (R target rate)
Φ (x) = log
S(x,γ,R)︷ ︸︸ ︷(1
1 + e−γ(x−R)
)
γ impacts the shape of sigmoid
Non-linear: users perspective (QoS)
Linear: network perspective
0 1 2 3 4 5 6 7 8 9 10
106
0
0.2
0.4
0.6
0.8
1
Objective function:
U(
xUui ,uq
, xDui ,uq
),
Φ
∑bj∈B
Q
(xUbj ,(ui ,uq)
, xDbj ,(ui ,uq)
)where
Q
(xUbj ,(ui ,uq)
, xDbj ,(ui ,uq)
),
min
(xUbj ,(ui ,uq)
RUui ,bj
, xDbj ,(ui ,uq)
RDbj ,uq
)
Konstantinos Alexandris 26 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)s.t.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)
s.t. C1:∑
(ui ,uq )∈Cbj
xUbj ,(ui ,uq) ≤ 1, ∀ bj ,
C2:∑
(ui ,uq )∈Cbj
xDbj ,(ui ,uq) ≤ 1, ∀ bj ,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)
s.t. C1:∑
(ui ,uq )∈Cbj
xUbj ,(ui ,uq) ≤ 1, ∀ bj ,
C2:∑
(ui ,uq )∈Cbj
xDbj ,(ui ,uq) ≤ 1, ∀ bj ,
C3:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)B
Ubj≤ BU
ui, ∀ ui ,
C4:∑bj∈B
∑uq∈Sui
xDbj ,(uq ,ui )
BDbj≤ BD
ui, ∀ ui ,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)
s.t. C1:∑
(ui ,uq )∈Cbj
xUbj ,(ui ,uq) ≤ 1, ∀ bj ,
C2:∑
(ui ,uq )∈Cbj
xDbj ,(ui ,uq) ≤ 1, ∀ bj ,
C3:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)B
Ubj≤ BU
ui, ∀ ui ,
C4:∑bj∈B
∑uq∈Sui
xDbj ,(uq ,ui )
BDbj≤ BD
ui, ∀ ui ,
C5:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)P
Uui ,bj
BUbj≤ Pmax
ui, ∀ ui .
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Problem formulation
NUM problem is defined as:
maxX
∑(ui ,uq )∈C
U(
xUui ,uq
, xDui ,uq
)
s.t. C1:∑
(ui ,uq )∈Cbj
xUbj ,(ui ,uq) ≤ 1, ∀ bj ,
C2:∑
(ui ,uq )∈Cbj
xDbj ,(ui ,uq) ≤ 1, ∀ bj ,
C3:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)B
Ubj≤ BU
ui, ∀ ui ,
C4:∑bj∈B
∑uq∈Sui
xDbj ,(uq ,ui )
BDbj≤ BD
ui, ∀ ui ,
C5:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)P
Uui ,bj
BUbj≤ Pmax
ui, ∀ ui .
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
Objective is non-differentiable!
Contains the min (·) function
Concave but non-differentiable
Transformation needs to be applied
The problem is shown to be convex
Konstantinos Alexandris 27 / 52
Simulations (1/3): Single vs Multi-connectivity
BSs
UEsu1
u3
u2
u4
b1 b3b2
Performance metric
User pairs aggregated rate:
ζui ,uq ,∑bj∈B
Q
(x?Ubj ,(ui ,uq), x
?Dbj ,(ui ,uq)
)
where
x?Ubj ,(ui ,uq)
, x?Dbj ,(ui ,uq)
: optimal for UL/DL
PF for different load cases (#UEs)
Comparison of Single/Multi-connectivityUE number Performance Single- Multi-in BS z/z/z metric connected connected
Connected BS 1 2.07Under-loaded Connected UE pairs 6 17.52case: 2/2/2 Aggregated user rate 0.99 Mbps 20.04 Mbps
Connected BS 1 1.34Uneven-loaded Connected UE pairs 34 49.95
case: 6/2/2 Aggregated user rate 11.68 Mbps 46.73 MbpsConnected BS 1 1.45
Over-loaded Connected UE pairs 90 162.22case: 6/6/6 Aggregated user rate 55.04 Mbps 57.01 Mbps
Remarks:
X Connectivity increases with the loaddecrement
X Higher number of UE pairs: trafficdiversity
X Gain in aggregated rate
X Advantages to both user andnetwork perspective
Konstantinos Alexandris 28 / 52
Simulations (2/3): Performance analysis of PF & UPF
Performance metric
Satisfaction ratio:
Mui ,uq= Prob
{ζui ,uq ≥ Rui ,uq
}.
Unsatisfied normalized error:
Eui ,uq =
∥∥∥∥∥ ζui ,uq − Rui ,uq
Rui ,uq
∥∥∥∥∥ , if ζui ,uq < Rui ,uq,
0 , o/w.
PF vs UPF: A trade-off between networkaggregated rate and users satisfaction
PF provides fairness and maximizesthe network aggregated rate
UPF extends PF and takes intoaccount the users QoS
Multi-connectivity case with 4 UEs/BS
QoS metrics comparison of PF and UPFMetric Requested rate PF problem UPF problem
0.1Mbps 68.72% 91.39%0.5Mbps 42.07% 58.03%
Satisfaction 1Mbps 25.15% 35.33%ratio 5Mbps 6.42% 23.10%
10Mbps < 1% <1%0.1Mbps 0.2122 0.0625
Unsatisfied 0.5Mbps 0.4131 0.2317normalized 1Mbps 0.5483 0.3906
error 5Mbps 0.7949 0.660710Mbps 0.8833 0.8441
Remarks:
UPF redistributes the resources toboost the user pairs satisfaction
Both of QoS metrics are decreasingwith the requested rate increment
Even in high R, UPF satisfies moreuser pairs (constrained by resources)
Konstantinos Alexandris 29 / 52
Simulations (3/3): Impact on γ on UPF
PDF plot of ζ for the UPF utility function with several γ
Remarks:
Sigmoid function approximates the step function (in UPF) when γ ↑Linear (PF case) vs Step (ideal UPF case) → (more/less) Network aggregatedrate vs (worse/better) user pairs QoS
Consequently:
X QoS requirements are more fulfilled with the increment of γ
X PDF tail decrement: less network aggregated rate-better users QoS
Konstantinos Alexandris 30 / 52
Take away messages
� Multi-connectivity outperforms the legacy single-connectivity
� Multi-connectivity can boost the aggregated rate, especially inunder-loaded scenarios
� UPF can increase the users satisfaction ratio when they areavailable network resources compared to PF
� Operators can impact the users network performance via UPFfunction shape (network vs user perspective)
Konstantinos Alexandris 31 / 52
Multi-connectivity resource allocationwith limited backhaul capacity in
evolved LTE
Konstantinos Alexandris 32 / 52
System model-Resource allocation
Air-interface
Uplink/Downlink (UL/DL):
Carrier frequency: Inter-frequency deployment
SINR: UL/DL based on RSRP
UL: Power control
Connection and Traffic
Multi-connectivity: UL/DL LTE FDD SISO
UE association: min(SINRUi,j , SINRD
j,i ) >
threshold︷ ︸︸ ︷SINRth
Active UEs: Connected to multiple cells
BSs
UEsu1
u3
u2
u4
b1 b3b2
Core network
Internet
Backhaul
links
xU or Dj,q : Pct. of allocated PRBs
Utility functions: PF + UPF
Objective functions:
UL:
U1
(xUi
), Φ
∑bj∈B
xUi,jR
Ui,j
DL:U2
(xDq
), Φ
∑bj∈B
xDj,qR
Dj,q
Konstantinos Alexandris 33 / 52
System model-Resource allocation
Air-interface
Uplink/Downlink (UL/DL):
Carrier frequency: Inter-frequency deployment
SINR: UL/DL based on RSRP
UL: Power control
Connection and Traffic
Multi-connectivity: UL/DL LTE FDD SISO
UE association: min(SINRUi,j , SINRD
j,i ) >
threshold︷ ︸︸ ︷SINRth
Active UEs: Connected to multiple cells
Traffic type: From/to (UL/DL) remote server traffic
Backhaul network: Star topology
Traffic requested rate: Ri app target rate
BSs
UEsu1
u3
u2
u4
b1 b3b2
Core network
Internet
Backhaul links
UL/DL
xU or Dj,q : Pct. of allocated PRBs
Utility functions: PF + UPF
Objective functions:
UL:
U1
(xUi
), Φ
∑bj∈B
xUi,jR
Ui,j
DL:U2
(xDq
), Φ
∑bj∈B
xDj,qR
Dj,q
Konstantinos Alexandris 33 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t. C1:
∑ui∈S,
(ui ,bj
)∈E
xUi,j ≤ 1, ∀ bj ∈ B,
C2:∑
uq∈D,(bj ,uq
)∈E
xDj,q ≤ 1, ∀ bj ∈ B,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t. C1:
∑ui∈S,
(ui ,bj
)∈E
xUi,j ≤ 1, ∀ bj ∈ B,
C2:∑
uq∈D,(bj ,uq
)∈E
xDj,q ≤ 1, ∀ bj ∈ B,
C3:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj ≤ MU
i , ∀ ui ∈ U,
C4:∑
bj∈B,(bj ,uq
)∈E
xDj,qB
Dj ≤ MD
q , ∀ uq ∈ U,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t. C1:
∑ui∈S,
(ui ,bj
)∈E
xUi,j ≤ 1, ∀ bj ∈ B,
C2:∑
uq∈D,(bj ,uq
)∈E
xDj,q ≤ 1, ∀ bj ∈ B,
C3:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj ≤ MU
i , ∀ ui ∈ U,
C4:∑
bj∈B,(bj ,uq
)∈E
xDj,qB
Dj ≤ MD
q , ∀ uq ∈ U,
C5:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj PU
i,j ≤ Pmaxi , ∀ ui ∈ U,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t. C1:
∑ui∈S,
(ui ,bj
)∈E
xUi,j ≤ 1, ∀ bj ∈ B,
C2:∑
uq∈D,(bj ,uq
)∈E
xDj,q ≤ 1, ∀ bj ∈ B,
C3:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj ≤ MU
i , ∀ ui ∈ U,
C4:∑
bj∈B,(bj ,uq
)∈E
xDj,qB
Dj ≤ MD
q , ∀ uq ∈ U,
C5:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj PU
i,j ≤ Pmaxi , ∀ ui ∈ U,
C6:∑
ui∈S,(ui ,bj
)∈E
xUi,jR
Ui,j ≤ CU
h,j , ∀ bj ∈ B,
C7:∑
uq∈D,(bj ,uq
)∈E
xDj,qR
Dj,q ≤ CD
h,j , ∀ bj ∈ B.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Problem formulation
NUM problem is defined as:
maxX
∑ui∈S
U1
(xUi
)+∑
uq∈DU2
(xDq
)s.t. C1:
∑ui∈S,
(ui ,bj
)∈E
xUi,j ≤ 1, ∀ bj ∈ B,
C2:∑
uq∈D,(bj ,uq
)∈E
xDj,q ≤ 1, ∀ bj ∈ B,
C3:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj ≤ MU
i , ∀ ui ∈ U,
C4:∑
bj∈B,(bj ,uq
)∈E
xDj,qB
Dj ≤ MD
q , ∀ uq ∈ U,
C5:∑
bj∈B,(ui ,bj
)∈E
xUi,jB
Uj PU
i,j ≤ Pmaxi , ∀ ui ∈ U,
C6:∑
ui∈S,(ui ,bj
)∈E
xUi,jR
Ui,j ≤ CU
h,j , ∀ bj ∈ B,
C7:∑
uq∈D,(bj ,uq
)∈E
xDj,qR
Dj,q ≤ CD
h,j , ∀ bj ∈ B.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1-C2: maximum PRBs at BS (UL/DL)
C3-C4: maximum PRBs at UE (UL/DL)
C5: Power control in UL
C6-C7: maximum BH capacity (UL/DL)
Objective is differentiable!
Concave function + Linear constraints
Convex problem→Interior point method
Konstantinos Alexandris 34 / 52
Simulations (1/5): Performance metrics
Simulation scenarios
3GPP TR 25.927:
Scenario A-Empty cell: 0/z/z
BSs
UEsz
b1 b3b2
Core network
Internet
Backhaul
links
more
resourcesz
Konstantinos Alexandris 35 / 52
Simulations (1/5): Performance metrics
Simulation scenarios
3GPP TR 25.927:
Scenario A-Empty cell: 0/z/zScenario B-Loaded cell: z/z/z
BSs
UEsz
b1 b3b2
Core network
Internet
Backhaul
links
zz
Konstantinos Alexandris 35 / 52
Simulations (1/5): Performance metrics
Simulation scenarios
3GPP TR 25.927:
Scenario A-Empty cell: 0/z/zScenario B-Loaded cell: z/z/z
BSs
UEsz
b1 b3b2
Core network
Internet
Backhaul
links
zz
Performance metrics
Network aggregated rate:
RD ,∑
uq∈D
∑bj∈B
(xDj,q
)?RDj,q
User satisfaction ratio:
SD , Prob
∑bj∈B
(xDj,q
)?RDj,q ≥ RD
q
where x?D
j,q : optimal for DL (id. in UL)
Konstantinos Alexandris 35 / 52
Simulations (1/5): Performance metrics
Simulation scenarios
3GPP TR 25.927:
Scenario A-Empty cell: 0/z/zScenario B-Loaded cell: z/z/z
BSs
UEsz
b1 b3b2
Core network
Internet
Backhaul
links
zz
Performance metrics
Network aggregated rate:
RD ,∑
uq∈D
∑bj∈B
(xDj,q
)?RDj,q
User satisfaction ratio:
SD , Prob
∑bj∈B
(xDj,q
)?RDj,q ≥ RD
q
where x?D
j,q : optimal for DL (id. in UL)
Use cases:
, Infinite BH
/ Finite BH
Remarks:
X Single vs Multi cells: Cell diversity
X BH limitations
Konstantinos Alexandris 35 / 52
Simulations (2/5): Infinite BH-0/z/z Scenario
Single-PF-0/2/2 Multi-PF-0/2/2 Single-UPF-0/2/2 Multi-UPF-0/2/2400500600700800900
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario A
Single-PF-0/4/4 Multi-PF-0/4/4 Single-UPF-0/4/4 Multi-UPF-0/4/4400500600700800900
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario A
Single-PF-0/2/2 Multi-PF-0/2/2 Single-UPF-0/2/2 Multi-UPF-0/2/20
20406080
100
Per
cent
age
(%) DL user satisfaction ratio comparison of Scenario A
Single-PF-0/4/4 Multi-PF-0/4/4 Single-UPF-0/4/4 Multi-UPF-0/4/40
20406080
100
Per
cent
age
(%) DL user satisfaction ratio comparison of Scenario A
Remarks:
Downlink-Params: z =2 or 4 users, CDh,j =∞
Multi vs Single connectivity
Empty cell scenario: Utilizes more resourcesSuperior in network aggregated rate and user satisfaction
Further gain: PF vs UPF
Network aggregated rate: PF outperforms UPF (Aggegated rate boost)User satisfaction: UPF outperforms PF (Targets on users QoS)
Konstantinos Alexandris 36 / 52
Simulations (3/5): Infinite BH-z/z/z Scenario
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/2600
700
800
900
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario B
Singel-PF-4/4/4 Multi-PF-4/4/4 Singel-UPF-4/4/4 Multi-UPF-4/4/4650
750
850
950
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario B
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/20
20406080
100
Per
cent
age
(%) DL user satisfaction ratio comparison of Scenario B
Single-PF-4/4/4 Multi-PF-4/4/4 Single-UPF-4/4/4 Multi-UPF-4/4/40
20406080
100
Per
cent
age
(%) DL user satisfaction ratio comparison of Scenario B
Remarks:
Downlink-Params: z =2 or 4 users, CDh,j =∞
Multi vs Single connectivity
Loaded cell scenario: No extra resources to exploitNetwork aggregated rate: no such difference
Further gain: PF vs UPF
UPF can still increase the user satisfaction rateQoS aware-Better reshuffling the resources!
Konstantinos Alexandris 37 / 52
Simulations (4/5): Finite BH-0/z/z vs z/z/z Scenario
150 200 250 300 350 400Backhaul Capacity (Mbps)
200
300
400
500
600
700
800
Avg
dat
a ra
te (
Mbp
s)
DL average aggregated rate of Scenario A
Single-PF-0/2/2Multi-PF-0/2/2Single-UPF-0/2/2Multi-UPF-0/2/2
150 200 250 300 350 400Backhaul Capacity (Mbps)
400
500
600
700
800
Avg
dat
a ra
te (
Mbp
s)
DL average aggregated rate of Scenario B
Single-PF-2/2/2Multi-PF-2/2/2Single-UPF-2/2/2Multi-UPF-2/2/2
Remarks:
Downlink-Params: z =2 users, CDh,j <∞
Aggregated rate converges when BH capacity>300 Mbps
0/z/z Scenario: Multi-connectivity outperforms the single one
Even with limited BH (<300 Mbps) ⇒ i.e., more resources are utilized
z/z/z Scenario: Slightly better (Multi vs Single)-No extra resources
PF vs UPF: UPF in Multi performs the worst to satisfy users QoSTrade-off: Network and User perspective
Konstantinos Alexandris 38 / 52
Simulations (5/5): Finite BH-0/z/z vs z/z/z Scenario
DL user satisfaction ratio
Backhaul Single Multi Single MultiCapacity PF PF UPF UPF(Mbps) 0/2/2 2/2/2 0/2/2 2/2/2 0/2/2 2/2/2 0/2/2 2/2/2
150 ∼20 ∼20 63 ∼20 ∼20 ∼20 81 ∼20
200 49 ∼50 95 ∼50 51 54 100 55250 72 65 95 68 83 80 100 91300 81 72 95 73 90 84 100 93>350 81 72 95 73 90 84 100 93
Remarks:
Downlink-Params: z =2 users, CDh,j <∞
Single to Multi: Boosts the user satisfaction: esp. in 0/z/z
Gain in PF: 3-31% (esp. in limited BH)
PF to UPF: Accelerates more the performance: esp. in z/z/z
Additional gain: 8-16% (esp. in limited BH)
Operators can adjust their policy to such trade-offs!
Konstantinos Alexandris 39 / 52
Take away messages
� Multi-cell approach achieves better network aggregated rate inempty cell scenario
� Multi-connectivity boost user satisfaction even in loadedscenarios with limited BH capacity
� In such scenarios, UPF can offer additional gain to users QoSre-utilizing better the network resources
� Network vs User perspective (Network aggregated rate vs UserSatisfaction) trade-off determines the intended policy
Konstantinos Alexandris 40 / 52
Opportunistic scheduling undermulti-connectivity with limited
backhaul capacity
Konstantinos Alexandris 41 / 52
System model-Resource allocation
Air-interface
Downlink (DL):
Carrier frequency: Inter-frequency deployment
SINR: DL based on RSRP
Channel model: Large/Small scale fading
Connection and Traffic
Multi-connectivity: DL LTE FDD SISO
UE association:1
|K|
∑k∈K
SINRDj,k,i >
threshold︷ ︸︸ ︷SINRth
Active UEs: Connected to multiple cells
BSs
UEsu1
u3
u2
u4
b1 b3b2
Core network
Internet
Backhaul
links
Resource allocation
Opportunistic scheduling
Exploit channel variability (fast fading)
Realistic situation: Discrete resource blocks
Formulate an optimization problem with binary
variables (0/1)!
No relaxation applies: Problems in rounding
Konstantinos Alexandris 42 / 52
System model-Resource allocation
Air-interface
Downlink (DL):
Carrier frequency: Inter-frequency deployment
SINR: DL based on RSRP
Channel model: Large/Small scale fading
Connection and Traffic
Multi-connectivity: DL LTE FDD SISO
UE association:1
|K|
∑k∈K
SINRDj,k,i >
threshold︷ ︸︸ ︷SINRth
Active UEs: Connected to multiple cells
Traffic type: From (DL) remote server traffic
Backhaul network: Star topology
Traffic requested rate: Ri app target rate
BSs
UEsu1
u3
u2
u4
b1 b3b2
Core network
Internet
Backhaul links
DL
Resource allocation
Opportunistic scheduling
Exploit channel variability (fast fading)
Realistic situation: Discrete resource blocks
Formulate an optimization problem with binary
variables (0/1)!
No relaxation applies: Problems in rounding
Konstantinos Alexandris 42 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)s.t.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)s.t.
C1:∑ui∈U
∑k∈K
xDj,k,i ≤ BD
j , ∀ bj ∈ B,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)s.t.
C1:∑ui∈U
∑k∈K
xDj,k,i ≤ BD
j , ∀ bj ∈ B,
C2:∑bj∈B
∑k∈K
xDj,k,i ≤ MD
i , ∀ ui ∈ U,
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)s.t.
C1:∑ui∈U
∑k∈K
xDj,k,i ≤ BD
j , ∀ bj ∈ B,
C2:∑bj∈B
∑k∈K
xDj,k,i ≤ MD
i , ∀ ui ∈ U,
C3:∑ui∈U
xDj,k,i ≤ 1, ∀ bj ∈ B, k ∈ K.
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Problem formulation
xDj,k,i ∈ {0, 1}: Binary variable (PRB)
NUM problem is defined as:
maxxDi∈{0,1}|B|×|K|
∑ui∈U
U(
xDi
)s.t.
C1:∑ui∈U
∑k∈K
xDj,k,i ≤ BD
j , ∀ bj ∈ B,
C2:∑bj∈B
∑k∈K
xDj,k,i ≤ MD
i , ∀ ui ∈ U,
C3:∑ui∈U
xDj,k,i ≤ 1, ∀ bj ∈ B, k ∈ K.
User rate constrained by BH capacity:
RDi ,
∑bj∈B
∑k∈K
(xDj,k,i
)?RDj,k,i×
min
CDh,j∑
ui∈U∑
k∈K
(xDj,k,i
)?RDj,k,i
, 1
Objective function: Maximize network utility
The proposed utilities Φ(·) are applied
Allocation can be based on PF or UPF
Constraints:
C1: maximum PRBs at BS
C2: maximum PRBs at UE
C3: sub-channel exclusivity at UE
Combinatorial problem difficult to be solved!
Non-linear Integer Programming
Sub-modularity argument
Find efficient algorithms to solve it!
Any performance guarantee?
Konstantinos Alexandris 43 / 52
Proposed algorithm
The proposed optimization problem is NP-hard!
The optimization problem is proved to be with:
submodular and monotone function3 matroid constraints
Theorem (Alexandris et al. 2018)
Let OPT be the optimal solution of the formulated problem andS? be the output of the greedy algorithm. Then, it holds that
f (S?) ≥ 1
4OPT.
A greedy algorithm exists with an explicit bound on theoptimal solution
S? ∈ {0, 1}B×K×U the set of the exported solution
Konstantinos Alexandris 44 / 52
Simulations
100 120 140 160 180 200Backhaul Capacity (Mbps)
0
0.05
0.1
0.15
Avg
uns
atis
fied
n
orm
err
or
Non-opportunistic UPF-Multi (Min SINR) (Avg 1.76 connections per UE)Non-opportunistic UPF-Multi (Avg SINR) (Avg 1.89 connections per UE)Opportunistic UPF-Multi (Avg 2.19 connections per UE)
Permormance metric
Unsatisfied norm error: EDi =
∥∥∥∥∥R
Di − RD
i
RDi
∥∥∥∥∥ , if RDi < RD
i ,
0 , o/w.
Remarks:
Downlink-Params: z =2 users, z/z/z Scenario
Opportunistic scheduling increases connectivity
Nominal case: MIN SINR- Non-opportunistic, i.e., mink∈K
(SINRD
j,k,i
)QoS: Opportunistic outperforms the non-opportunitsic one even BH is limited
Konstantinos Alexandris 45 / 52
Take away messages
� Opportunistic scheduling exploits channel variability
� Discrete PRBs: NP-hard problem
� Problem is proved to be with sub-modular monotone functionand matroid constraints
� Greedy algorithm performs well with a guarantee solutionbound
� Non-opportunistic schemes perform worse in terms of usersQoS with limited BH
Konstantinos Alexandris 46 / 52
Conclusion
Konstantinos Alexandris 47 / 52
Summary
� X2 HO implementation in OAI emulator + real RF testbed
� Load-aware HO algorithm in next-generation HetNets
� Multi-connectivity resource allocation towards 5G
� Multi-connectivity resource allocation with limited BH
� Opportunistic scheduling in multi-connectivity with limited BH
Konstantinos Alexandris 48 / 52
Conclusion
Lessons learnt:
– Centralized mobility management can handle better HOprocess towards next-generation networks
– Transfer and service delay cost can be reduced with QoS-awarecross-layer mechanisms
– Centralized multi-connectivity resource allocation boostsnetwork aggregated rate as well as users QoS
– Multi-connectivity offers seamless mobility
– Connectivity failure: No need to re-establish connection– Support of user association towards 5G
– Such mobility and resource management centralized schemescan be directly applicable to SDN technology
Konstantinos Alexandris 49 / 52
Future directions
– Joint resource allocation and user association inmulti-connectivity under users QoS and BH limitations
– Resource allocation and beamforming in multi-connectednetworks
– Autonomous self-backhauling mesh network support undermulti-connectivity moving cells scenarios
– U2U-U2N-N2U: Local/Core routing
– Exploring multi-connectivity in disaggegated RAN
– C-RAN: CU-DU-RU
Konstantinos Alexandris 50 / 52
Publications
1 K. Alexandris, C.-Y. Chang, N. Nikaein and T. Spyropoulos “Utility-basedOpportunistic Scheduling under Multi-Connectivity with Limited BackhaulCapacity”, IEEE Wireless Communication Letter, 2018, under review.
2 K. Alexandris, C.-Y. Chang, N. Nikaein and T. Spyropoulos “Multi-ConnectivityResource Allocation with Limited Backhaul Capacity in Evolved LTE”, in 2018IEEE Wireless Communications and Networking Conference (WCNC), April2018, Barcelona, Spain, to appear.
3 K. Alexandris, C.-Y. Chang, K. Katsalis, N. Nikaein and T. Spyropoulos“Utility-Based Resource Allocation under Multi-Connectivity in Evolved LTE”,in 2017 IEEE 86th Vehicular Technology Conference (VTC-Fall), September2017, Toronto, Canada.
4 K. Alexandris, N. Nikaein, R. Knopp and C. Bonnet, “Analyzing X2 Handoverin LTE/LTE-A”, WINMEE 2016, Wireless Networks: Measurements andExperimentation, May 2016, Arizona State University, Tempe, Arizona, USA,invited.
5 K. Alexandris, N. Sapountzis, N. Nikaein and T. Spyropoulos, “Load-awareHandover Decision Algorithm in Next-generation HetNets”, in 2016 IEEEWireless Communications and Networking Conference (WCNC), April 2016,Doha, Qatar.
Konstantinos Alexandris 51 / 52
Questions?
Thank You!!!
Konstantinos Alexandris 52 / 52
Appendix
Konstantinos Alexandris 1 / 14
X2 Handover process
X2 HO request ACK
X2 HO request
Measurement report
Ho admission & resource
setup
SN Status transfer
Path switch request
HO decision
UE
Path switch request ACK
Release resource
HO complete (RRC connection reconfiguration complete)
RRC connected
RRC connected
RRC idle
RRC connected
Before handover
Handover preparation
Handover completion
Handover execution
RRC connected
After handover
RRC idle
RRC idle
RACH
UL grant
HO command (RRC connection reconfiguation)
Source eNB Target eNB EPC
Konstantinos Alexandris 2 / 14
OAI RF X2 Handover testbed schematic
Konstantinos Alexandris 3 / 14
Network topology
We assume a macrocell and a bunch of picocells at givendistances Dj from it, where j ∈ {1, . . . ,P}
Konstantinos Alexandris 4 / 14
Delay prediction
Assuming stationary M/G/1/PS:
Dki =
1
µik − λk
i
,
Service rate: µki = Rk
i /Y
The expected average rate is:
Rki =
NkMU,i Ci +
NkAU,i∑l=1
C (dl,i )
NkMU,i + Nk
AU,i
0 200 400 600 800 10000
200
400
600
dm(m)
Cb(dm)(M
bps)
Average Capacity bounds in macrocell
Lower boundUpper bound
0 50 100 150 200100
200
300
400
dpj(m)
Cb(dpj)(M
bps)
Average Capacity bounds in picocell
Lower boundUpper bound
Active users: Fixed capacity
C(dl,i ) ,[CL(dl,i ) + CU(dl,i )
]/2
Moving users: Average out distance
Ci =(C iL + C i
U
)/2
Konstantinos Alexandris 5 / 14
SDN framework
1 Controller tier: a) receives the respective λki and µki from BSs, b) computes
and sends the Dki to all BSs
2 Network tier: a) send the respective λki and µki , b) receive the Dki , c) send the
Dki to the UE
3 User tier: Each time k, the UE: a) receives the delays Dki , b) triggers the HO
procedure
Konstantinos Alexandris 6 / 14
Network topology
We consider an area L ⊂ R2 served by a set of BSsB = {b1, · · · , b|B|} and a set of UEs U = {u1, · · · , u|U|}
BSs
UEsu1
u3
u2
u4
b1 b3b2
Konstantinos Alexandris 7 / 14
Problem transformation
maxX ,Z
∑(ui ,uq )∈C
U
(zui ,uq
)
s.t. C1: zbj ,(ui ,uq) ≤ xUbj ,(ui ,uq)R
Uui ,bj
, ∀ bj ,
C2: zbj ,(ui ,uq) ≤ xDbj ,(ui ,uq)R
Dbj ,uq
, ∀ bj ,
C3:∑
(ui ,uq )∈Cbj
xUbj ,(ui ,uq) ≤ 1, ∀ bj ,
C4:∑
(ui ,uq )∈Cbj
xDbj ,(ui ,uq) ≤ 1, ∀ bj ,
C5:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)B
Ubj≤ BU
ui, ∀ ui ,
C6:∑bj∈B
∑uq∈Sui
xDbj ,(uq ,ui )
BDbj≤ BD
ui, ∀ ui ,
C7:∑bj∈B
∑uq∈Dui
xUbj ,(ui ,uq)P
Uui ,bj
BUbj≤ Pmax
ui, ∀ ui .
Objective function:
U(xUui ,uq
, xDui ,uq
) ,
Φ(∑bj∈B
Q(xUbj ,(ui ,uq), x
Dbj ,(ui ,uq))︸ ︷︷ ︸
zbj ,(ui ,uq)∈Z
)
Constraints:
min (·) is replaced by C1, C2 using the auxiliaryvariable z in the objective
Convexity:
U(
zui ,uq
)= Φ
(1T|B|zui ,uq
)Φ (·) is concave→ the objective is concave
Constraints are linear
Problem is convex!
Konstantinos Alexandris 8 / 14
Simulations-Performance analysis of PF & UPF
CDF plot of PF/UPF utility functions with different R
(a) R = 1 Mbps (b) R = 5 Mbps
(c) R = 10 Mbps
Remarks:
UPF outperforms PF in all cases: provides less network aggregated rateimproving user pairs QoS
Even in high requested rate in (c) still performs better (UPF CDF tail)
PF has the same CDF among different requested rates: QoS unaware
Konstantinos Alexandris 9 / 14
Network topology
We consider an area L ⊂ R2 served by a set of BSsB = {b1, · · · , b|B|} and a set of UEs U = {u1, · · · , u|U|}
BSs
UEsu1
u3
u2
u4
b1 b3b2
Core network
Internet
Backhaul
links
Konstantinos Alexandris 10 / 14
Simulations-Infinite BH-z/z/z Scenario
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/2500
600
700
800
Dat
a ra
te (
Mbp
s) UL aggregated rate comparison of Scenario B
UL user satisfaction ratio comparison of Scenario B
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/20
20406080
100
Per
cent
age
(%)
Remarks:
Uplink-Params: z =2 users, CUh,j = CD
h,j =∞Unallocated resources in each BS due to UL power control (C5constraint)
Multi-cell approach can make use of those resources
Higher gains in network aggregated rate + user satisfaction
Konstantinos Alexandris 11 / 14
Simulations-Dynamic BH
Single-PF-0/2/2 Multi-PF-0/2/2 Single-UPF-0/2/2 Multi-UPF-0/2/2200
400
600
800
1000
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario A
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/2500
600
700
800
900
Dat
a ra
te (
Mbp
s) DL aggregated rate comparison of Scenario B
DL user satisfaction ratio comparison of Scenario A
Single-PF-0/2/2 Multi-PF-0/2/2 Single-UPF-0/2/2 Multi-UPF-0/2/20
20406080
100
Per
cent
age
(%)
DL user satisfaction ratio comparison of Scenario B
Single-PF-2/2/2 Multi-PF-2/2/2 Single-UPF-2/2/2 Multi-UPF-2/2/20
20406080
100
Per
cent
age
(%)
Remarks:
Downlink-Params: z =2 users, CDh,j ∼ U [150, 350] Mbps
Multi vs Single connectivity
Loaded cell scenario: No extra resources to exploit compared to emptycell oneNetwork aggregated rate: no such difference
Further gain: PF vs UPF
UPF can still increase the user satisfaction ratePresented results closely lie in the range of finite BH gains
Konstantinos Alexandris 12 / 14
Simulations-Utilization ratio-Dynamic BH
Utilization Single Multi Single MultiRatio PF PF UPF UPF(%) 0/2/2 2/2/2 0/2/2 2/2/2 0/2/2 2/2/2 0/2/2 2/2/2
Air-interface 57 90 94 98 57 90 93 98
Backhaul 63 92 95 93 63 92 93 91
Remarks:
Downlink-Params: z =2 users, CDh,j ∼ U [150, 350] Mbps
Multi-connectivity utilizes better the unallocated resources both in air-interfaceand BH
Unlimited BH: Air-interface resources are fully used (100%) and BH utilizationratio is <100%
Limited BH: Air-interface resources are not fully used (< 100 %) and BHutilization ratio is 100 %
Konstantinos Alexandris 13 / 14
Simulations-Opportunistic Scheduling
120 140 160 180 200 220 240 260 280 300Backhaul Capacity (Mbps)
50
60
70
80
90
100
Avg
use
r sa
tisfa
ctio
n (%
)
PF-Multi with avg 2.21 connections per UEUPF-Multi with avg 2.49 connections per UE PF-Single with avg 1.00 connection per UEUPF-Single with avg 1.00 connection per UE
120 140 160 180 200 220 240 260 280 300Backhaul Capacity (Mbps)
50
60
70
80
90
100
Avg
use
r sa
tisfa
ctio
n (%
)
PF-Multi with avg 2.01 connections per UEUPF-Multi with avg 2.19 connections per UE PF-Single with avg 1.00 connection per UEUPF-Single with avg 1.00 connection per UE
Remarks:
Downlink-Params: z =2 users, CUh,j = CD
h,j <∞
0/z/z Scenario: Multi-connectivity outperforms the single one
Even with limited BH ⇒ i.e., more resources are utilizedConnectivity gain: multiple connection
z/z/z Scenario: Better (Multi vs Single)-No extra resources
PF vs UPF: UPF in Multi performs the best to satisfy users QoSAdditional gain: single to multi-cell comparisonTrade-off: Network and User perspective
Konstantinos Alexandris 14 / 14