Device-to-Device Communications
Underlying Cellular Networks
Geoffrey Ye Li
School of ECE, Georgia Institute of
Technology
Outline
• Why D2D Communications?
• Topic 1: QoS-Aware Resource Allocation
• Topic 2: EE/SE Mode Switching
• Future Work
1/40
Why D2D Communications?
• 5G Perspective: Common View
– Challenges
 High connection density
 High date rate
 High traffic volume
 High mobility
 Low latency
– Design principles
 Spectrum efficiency
 Energy efficiency
 Cost efficiency
Source：IMT-2020
2/40
Why D2D Communications? (cont.)
• Advantages of D2D Communications
– Proximity gain
– Hop gain
– Reuse gain
• Potential Benefits
–
–
–
–
Higher date rate /capacity
Lower latency
Higher spectrum-, energy-, and cost-efficiency
Better robustness
3/40
Why D2D Communications? (cont.)
• Main Features of Short Range Techniques
Feature
Name
Standardizat
ion
Frequency
band
D2D
Wi-Fi Direct
NFC
ZigBee
Bluetooth4.0
UWB
3GPP LTEAdvanced
802.11
ISO 13157
802.15.4
Bluetooth SIG
802.15.3a
13.56 MHz
868/915MHz,
2.4GHz
2.4GHz
3.1-10.6 GHz
200m
0.2m
10-100m
10-100m
10m
250Mbps
424kbps
250kbps
24Mbps
480Mbps
Radio-frequency
identification
ID broadcast or
coordinator
assistant
Manual
pairing
Manual pairing
Licensed band
2.4 GHz, 5GHz
for LTE-Advanced
Max
transmission 10-1000m
distance
Max data
1Gbps
rate
Device
discovery
BS coordination
ID broadcast
and embed soft
access point
Uniformity
of service
provision
Yes
No
No
No
No
No
Application
Public safety,
Content sharing,
Local advertising,
Cellular relay
Content
sharing, Group
gaming, Device
connection
Contactless
payment systems,
Bluetooth and WiFi connections
Home
Entertainment
and Control,
Environmental
monitoring
OBject
EXchange,
Peripherals
connection
Wireless USB,
High-definition
video,
Auto Radar
4/40
Why D2D Communications? (cont.)
• Applications
Standard UE-BS
communication
D2D based multi-hop
transmission
D2D based vehicle
communication
Pico BS
Macro BS
Public safety service
Local
advertising
Traditional UE-BS Link
Content sharing/
Local multicasting
D2D link
D.-Q. Feng, L. Lu, Y. Yuan-Wu, G. Y. Li, S.-Q. Li and G. Feng, “Device-to-Device
5/40
communications in cellular networks,” IEEE Commun. Mag., Apr. 2014.
Outline
• Why D2D Communications?
• Topic 1: QoS-Aware Resource Allocation
• Topic 2: EE/SE Mode Switching
• Future Work
6/40
QoS-Aware Resource Allocation
• System Model
• Problem Formulation
• Proposed Three-Step Solution
• Network Performance
7/40
System Model
• System Assumption
–
–
–
–
Fully loaded network
Uplink spectrum sharing
A minimum SINR for each user
Perfect CSI at BS
• Motivation
– Access more users
– Without effecting existing cellular users
D.-Q. Feng, L. Lu, Y. Yuan-Wu, G. Y. Li, G. Feng and S.-Q. Li, “Device-to-Device communications
underlaying cellular networks ” , IEEE Trans. Commun., vol. 61, no. 8, 2013.
8/40
System Model of QoS-Aware Resource
Allocation (cont.)
• System Model
Is this D2D pair
admissible?
If accessible, which
channel will be reused?
9/40
Problem Formulation
• Optimization Problem
– Objective: maximize overall throughput
– Variables: power allocation and channel assignment
– Constraints: minimum SINR and peak power of users

c
d 
max
[log(1


)


log(1



i
i, j
j )] ,
i , j , Pic , Pjd iC jS


Pi c gi , B
c
s.t. i  2
 ic,min , i  C ,
d
(i )
 N  i , j Pj h j
 jd 
Pjd g j (i )
 N  i , j Pi hi , j
2
i , j { 0,1} ,
c

i, j
  jd,min , j  S ,
 1, i  C ,
j
i , j { 0,1} ,

i, j
 1, j  S ,
i
c
Pi c  Pmax
, i  C ,
d
Pjd  Pmax
, j  S
MINLP Problem!
Pi c
Pjd
i , j
C
S
transmit power of CU i
transmit power of D2D pair j
channel reuse indicator for CUi and D2D pair j
set of exisiting cellular user
set of admittable D2D pair
10/40
Proposed Three-Step Solution
• Step 1: Distance-Based Admission Control
• Step 2: Optimal Power Control
• Step 3: Maximum Weighted Matching
11/40
Step1：Distance-Based Admission
• Admissible Area
Admissible
area
Admissible
conditions
Pi c
Pi c
lc
ld
ic 
 jd 
c
Pi gi , B
 N 2  Pjd h j , B
Pjd g（j i）
 N 2  Pi c hi , j
c
Pmax
ld
lc
A
c
Pmax
 ic,min ,
A
  jd,min ,
c
Pi ,min
c
Pi ,min
c
d
Pi c  Pmax
, Pjd  Pmax
.
Pjd,min
(a) with admissible area
d
Pmax
Pjd
Pjd,min
d
Pmax
Pjd
(b) without admissible area
12/40
Step1：Distance-Based Admission
Control (cont.)
• Admission Criteria
Li , j  Li , j ,
min
Lmin
i, j
c
1

C i , j i , jic,min jd,min Pmax
]
[ c
c
2
c
d
2
 ( Pmax gi  i ,min N )   i ,min j ,min N

d
C i , j i , jic,min jd,min ( N 2  Pmax
h j (i ) ) 1

[
]
(i )
d
2

gi ( Pmax g j   j ,min N )

Li , j
if
if
c
Pmax
gi , B
d
 N 2  Pmax
h j (i )
c
Pmax
gi , B
d
 N 2  Pmax
h j (i )
 ic,min ,
 ic,min .
denotes the distance between CU i and the receiver of D2D pair j
13/40
Step 2 : Optimal Power Allocation
• Power Allocation Optimization Problem
c
d
(Pi c* , Pjd * ) = arg max{log
(1


)

log
(1


2
i
2
j )},
c
d
Pi , Pj
s.t. ic 
 jd 
Pi c gi , B
 N 2  Pjd h j , B
Pjd g（j i）
 N 2  Pi c hi , j
c
Pi c  Pmax
,
 ic,min ,
  jd,min ,
NP-hard!
d
Pjd  Pmax
.
Z.-Q. Luo and S. Zhang, “Dynamic spectrum management: Complexity and duality,” IEEE J. Sel.
Topics Signal Process., vol. 2, no. 1, pp. 57–73, 2008.
14/40
Step 2 : Optimal Power Allocation (cont.)
• Method for Finding Optimal Power
Optimal
point on this
line
c
log 2 (1 
d
j
f(Pi , P )
Pi c gi , B
 N 2  Pjd h j , B
)  log 2 (1 
Pjd g（j i）
 N 2  Pi c hi , j
),
 Pjd g（i）
 Pi c gi , B
f( Pi ,  P )= log 2 (1  2
)  log 2 (1  2
)
 N   Pjd h j , B
 N   Pi c hi , j
c
d
j
j
 log 2 (1 
Pi c gi , B
 N 2   Pjd h j , B
> f(Pi c , Pjd ),
)  log 2 (1 
Pjd g（j i）
 N 2   Pi c hi , j
)
(  1)
At least one of the D2D pair and the
cellular user transmit at the
maximum power
15/40
Step 2 : Optimal Power Allocation (cont.)
• Optimal Power
potential
operation
points
Pi c
lc
ld
c
Pmax
Pi c
C
potential
operation
points
ld
c
Pmax
D
E
A
F
lc
A
c
Pi ,min
c
Pi ,min
Pjd,min
d
Pmax
Pjd
d
Pmax
Pjd,min
(a)
Pjd
(b)
potential
operation
points
Pi c
ld
c
Pmax
C
O
F
lc
A
c
Pi ,min
Pjd,min
d
Pmax
(c)
Pjd
16/40
Step 3:Optimal Reuse Partner Selection
• D2D Throughput Gain
Ti ,Gj  log 2 (1 
Pi c* gi , B
 N  P hj
2
d*
j
(i )
)  log 2 (1 
Date rate of cellular
user with D2D
Pjd * g j (i )
 N  Pi hi , j
2
c*
Date rate of D2D
)  log 2 (1 
c
Pmax
gi , B
N
2
)
Date rate of cellular
user without D2D
– Single D2D pair scenario
i*  arg max Ti ,Gj
iR j
– Multiple D2D pairs scenario
G
max

T
i, j i, j ,
'
iC ,jS
s.t.
'


1,


{
0,1
}
,

i

C`
,
 i, j
i, j
j

i, j
Maximum weight bipartite
matching problem!
 1, i , j { 0,1} , j  S ,
i
17/40
Step 3:Optimal Reuse Partner Selection (cont.)
• Multiple D2D Pairs and Reuse Candidate
Matching
T1,G1
T2,G 1
T2,G 2
T1,G2
Reuse candidate
1
...
2
1
D2D pair
2
M-1
G
TM-1,
1
G
TM-1,
3
3
M
G
TM,
3
G
TM,
K-2
...
K-2
G
TM,
K
G
TM-1,
K-1
K-1
K
Maximum weight bipartite matching: Classic Kuhn-Munkres algorithm
18/40
Summary of Proposed Three-Step Solution
• Step 1: Distance-Based Admission Control
– Find all the admissible D2D pair
– Find all the reuse candidates for each admissible D2D pair
• Step 2: Optimal Power Control
– Optimal power allocation for each D2D pair and its reuse
partner
• Step 3: Maximum weighted matching
– Find the optimal D2D pairs and reuse partners matching
19/40
Network Performance
• Simulation Parameters
Cell radius
500 m
Uplink bandwidth
5 MHz
Pathloss exponent
4
Pathloss constant
0.01
Noise power
-174 dBm/Hz
Maximum D2D Tx power
21, 24 dBm
Maximum RCU Tx power
24 dBm
Minimum SINR of RCU
[0, 25] dB
Minimum SINR of D2D,
[0, 25] dB
Multiple-path fading
Exponential distribution with unit
mean
Shadowing
Log-normal distribution with
standard deviation of 8dB
20/40
Network Performance (cont.)
• Effect of D2D Cluster Radius
(a)
(b)
100%
10
90%
9
8
Throughput gain (Mbps)
80%
Access rate
70%
60%
50%
40%
30%
20%
10%
20
 =4, Proposed
 =4, Heuristic
 =4, Fixed margin
 =3.5, Proposed
 =3.5, Heuristic
 =3.5, Fixed margin
 =4, Proposed
 =4, Heuristic
 =4, Fixed margin
 =3.5, Proposed
 =3.5, Heuristic
 =3.5, Fixed margin
30
40
50
7
6
5
4
3
2
1
60
r (m)
70
80
90
100
0
20
30
40
50
60
r (m)
70
80
90
100
Performance decrease with the radius of D2D cluster
21/40
Network Performance (cont.)
• Effect of The Number of Active Cellular Users
and D2D Pairs
(a)
(b)
100%
40
90%
35
80%
Throughput gain (Mbps)
30
Access rate
70%
60%
50%
40%
N=20,
N=20,
N=20,
N=40,
N=40,
N=40,
30%
20%
10%
0.1
0.2
Proposed
Heuristic
Fixed margin
Proposed
Heuristic
Fixed margin
0.3
0.4
N=20,
N=20,
N=20,
N=40,
N=40,
N=40,
Proposed
Heuristic
Fixed margin
Proposed
Heuristic
Fixed margin
25
20
15
10
5
0.5
0.6
M/N
0.7
0.8
0.9
1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
M/N
Existing a saturation point for the D2D pairs
22/40
Outline
• Why D2D Communications?
• Topic 1: QoS-Aware Resource Allocation
• Topic 2: EE/SE Mode Switching
• Future Work
23/40
EE/SE Mode Switching
• Motivation
• System Model
• Problem Formulation
• EE/SE Optimization
• Network Performance
24/40
Motivation
• New Freedom For Potential D2D Users
– Three transmission modes
 Dedicated mode : Dedicated resource with direct link
 Reusing mode : Reusing resource with direct link
 Cellular mode : Conventional BS-relaying link
UE
UE
BS
UE
BS
D2D Tx
BS
D2D Tx
D2D Tx
D2D Rx
UE
D2D Rx
D2D Rx
UEUE
α
α
UE+D2D
D2D
(1-α)
Dedicated mode
Reusing mode
D2D UL
D2D DL
(1-α)β
(1-α)(1-β)
Cellular mode
25/40
System Model
• Basic User Scenario:
– Single D2D pair and single cellular user
• Prioritized Traffic:
– Weighted user throughput
• Uplink Spectrum Sharing
• Guaranteed QoS
• Perfect CSI at BS
D.-Q. Feng, G.-D. Yu, Y. Yuan-Wu, G. Y. Li, S.-Q. Li and G. Feng, “Mode switching for device-todevice communications in cellular networks,” （invited paper), IEEE GlobalSIP'14, Atlanta, 2014.
26/40
Problem Formulation
• Objective:
– Maximize overall EE(SE)
• EE(SE) Metric:
– Sum of weighted throughput/total power consumption
(bandwidth)
• Mode Selection:
–
M  arg max( D ,  R , C )
*
M { D,R,C }
D , R , and C denote the max EE(SE) in dedicated mode, reusing mode
and cellular mode, respectively.
27/40
EE Optimization at Dedicated Mode
• EE Optimization Problem
– Variables: spectrum and power
c
d
W
c
d
Pc
Pd
gc, B
g d ,d
weight of RCU
weight of D2D pair
total bandwidth
percentage of spectrum resource for RCU
percentage of spectrum resource for D2D pair
transmit power of RCU
transmit power of D2D pair
channel gain from RCU to the BS
channel gain of D2D pair
28/40
EE Optimization at Dedicated Mode (cont.)
• Parametric Transformation For Nonlinear
Fractional Programing (NFP)
• Dinkelbach Algorithm for NFP
– The critical step : Subproblem
W. Dinkelbach, “On nonlinear fractional programming,” Management Science, 1967,
13(7): 492-498.
29/40
EE Optimization at Dedicated Mode (cont.)
• EE Subproblem at Dedicated Mode
– Standard convex optimization problem
– Interior point method
 Logarithmic barrier function to remove inequality constraints
 Quasi-Newton method to obtain search direction
 Backtracking line search for step size
S. P. Boyd and L. Vandenberghe, Convex optimization. Cambridge university press, 2004.
30/40
EE Optimization at Reusing Mode
• EE optimization problem
– Variables：power
hd , B
channel gain of the interference link
hc , d
from D2D transmitter to the BS
channel gain of the interference link
from RCU to D2D receiver
31/40
EE Optimization at Reusing Mode (cont.)
• Parametric Transformation for NFP
• EE Subproblem at Reusing Mode
– NP hard, however, objective function with difference of convex
(D. C.) structure,
G. R. Lanckriet and B. K. Sriperumbudur, “On the convergence of the concave-convex
procedure,” in Proc. Advances in Neural Inform. Process. Syst., 2009, pp. 1759–1767.
32/40
EE Optimization at Reusing Mode (cont.)
• Concave-Convex Procedure (CCCP) for D.C.
Optimization
– Objective function differentiable
– Sequential convex approximation
– Properties

 For a fixed point is a stationary point that satisfies the KKT
conditions of the D.C. problem
– CCCP Algorithm
33/40
EE Optimization at Cellular Mode
• EE optimization problem
– Variables: spectrum, power
1
Assuming   2 and R
the dedicated mode
dD
 RdU
, then, the same form as in
34/40
Network Performance
• Simulation Parameters
Cell radius
500 m
Uplink bandwidth
1.25 MHz
Pathloss exponent
4
Pathloss constant
0.01
Noise power
-174 dBm/Hz
Maximum D2D Tx power
125/250 mW
Maximum RCU Tx power
250 mW
QoS of RCU
[0, 1] Mbit
QoS of RCU of D2D
[0, 1] Mbit
Multiple-path fading
Exponential distribution with unit
mean
Shadowing
Log-normal distribution with
standard deviation of 8dB
35/40
Network Performance (cont.)
• Switching vs Single Mode Transmission
24
Optimal Mode
Dedicated Mode
Reusing Mode
Celluar Mode
22
Mode switching
Average SE (Bits/Hz)
20
18
Single mode
16
14
12
10
8
6
20
30
40
50
60
70
80
D2D cluster radius, r (m)
90
100
110
120
36/40
Network Performance (cont.)
• EE –SE Tradeoff
(a)
(b)
100
30
SE Switch, d=0.25
SE Switch, d=0.25
SE Switch, d=1
90
EE Switch, d=0.25
EE Switch, d=0.25
EE Switch, d=1
EE Switch, d=1
26
Higher EE but lower SE
80
24
Average throughput (Mbits)
Average energy efficiency (Mbits/joule)
SE Switch, d=1
28
70
60
EE gap
50
Higher SE but
lower EE
22
20
18
SE gap
16
40
14
30
20
20
12
30
40
50
60
70
80
D2D cluster radius, r (m)
90
100
110
120
10
20
30
40
50
60
70
80
D2D cluster radius, r (m)
90
100
110
120
37/40
Network Performance (cont.)
• Optimal Modes
Reusing Mode for EE
Dedicated Mode for SE
100
Percentage of selected optimal mode (%)
90
80
70
EE
EE
EE
SE
SE
SE
60
50
40
switch,
switch,
switch,
switch,
switch,
switch,
Dedicated Mode
Reusing mode
Celluar Mode
Dedicated Mode
Reusing mode
Celluar Mode
30
20
10
0
20
30
40
50
60
70
80
90
D2D cluster radius, r (m)
100
110
120
38/40
Future Work
• Full-Duplex D2D Communications
• Unlicensed- Band D2D Communications
• D2D-Aissitend Small Cell Deployment
• Cooperative D2D Caching
39/40
Thank you!
40/40