This work is presented resource allocation algorithm dor D2D communication. https://ieeexplore.ieee.org/abstract/document/8292187

1. D2D Resources Allocation underlaying
(2-tier) Heterogeneous Cellular Networks
By: Amal Algedir

2. Outline
Introduction
Motivation
Contribution
System Model & Problem Formulation
Sequential Max Search Algorithm
Results & Conclusion
2

3.  The growth of data traffic has dramatically increased in recent years, primarily due to wireless smart devices
(e.g., smartphones, mobile PC, tablet) and their applications.
 The tremendous amount of data traffic has motivated researchers to develop new technologies for
enhancing user experience and network performance.
 Long Term Evolution-Advanced (LTE-A) release 12 introduced a new technology named Device-to-Device
communication (D2D).
 D2D communication enables direct communication between user equipment located within close proximity
without go throughout cellular base stations (BS).
Introduction
3

4. 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
Challenging
 control of level of interference.
 High complication of resource allocation
procedure and power control
WhyD2DCommunications
Underlay:
 Cellular and D2D communication share the same
radio resources.
Overlay :
 Cellular and D2D are given dedicated resources
Direct link
4
Direct link

5. Motivation
• The coexistence of D2D communication with small cells in HetNets is still an open area
for research.
• Most of existing work consider D2D in Uplink spectrum sharing under conventional
cellular network; a few works study the Downlink sharing under HetNets.
• In DL sharing spectrum, the interference from the cellular transmission to the D2D
originates from the BS and depends only on the D2D receiver location. Therefore, D2D
interference to the DL users can be controlled by an efficient resource allocation.
5

6. LTE resourcesgridstructure
• Resources are grouped into two dimensional Resources Blocks (RBs).
• RB contains 12 subcarriers (180kHz in total) and 7 consecutive symbols (normal CP) or
6 symbols (extended CP).
• A pair of RBs (in time domain) is minimum unit an eNodeB scheduler can allocate.
• Number of resource blocks attached to a user defines the user data rate.
One subframe 6

7. 7
 In this work, Adaptive D2D resources allocation algorithm, a Sequential Max Search
(SMS) algorithm, is developed. (SMS) is a less computationally demanding approach
 Our proposed algorithm accounts for co-channel interference between different tier
users as well as satisfying various rate requirements for cellular and D2D users
 Based on space search reduction from SMS algorithm, we applied Brute-force search
to find the optimal resources allocation
 The results from SMS were compared to Brute-force search results
Contribution

8. SystemModel
• HetNets consists of one cell serving by one macro base
station (MB) located at the center.
• A small base station (SB) is placed within the converge of
the macro cell.
• There are N users uniformly distributed within the coverage
of MB.
• Total bandwidth B is divided to K Physical Resource Blocks
(PRBs).
• frequency reuse of one between the SB and MB stations
• The MB, SB, and D2D_TX will transmit at their maximum
power
• Fully loaded network.
• Downlink spectrum sharing.
• Users under the same BS are assigned orthogonal RBs,
one RB per cellular user.
• Only one D2D pair can share RB with preassigned
cellular user. One RB is assigned for D2D user
• Cellular users allocation is not considered in this work.
Assumption
8

9. MB
Um
Us
UD
TxRx
SB
Interference from MB
Interference from SB Interference from (D2D-TX)
Communication link in RB-k
𝑥 𝑑,𝑘 = 1 𝑖𝑓 𝑘 𝑡ℎ
𝑅𝐵 𝑎𝑠𝑠𝑖𝑔𝑛 𝑡𝑜 𝑝𝑎𝑖𝑟 𝑑
0 𝑜𝑤
Problemformulation
𝑥 𝑑,𝑘 ≡ 𝑏𝑖𝑛𝑎𝑟𝑦 𝑖𝑛𝑑𝑖𝑐𝑡𝑜𝑟 𝑓𝑜𝑟 𝐷2𝐷 𝑝𝑎𝑖𝑟
Systemmodelofin-bandD2Dcommunications
underlayingHetNetsindownlinkperiod
𝜸 𝑼𝒎
𝒌
=
𝑃 𝑀𝐵 ∗ 𝐺 𝑀𝐵,𝑈𝑚
𝑁0 + 𝑑=1
𝐷
𝑥 𝑘,𝑑 ∗ 𝑃𝑑 ∗ 𝐺 𝑑,𝑈𝑚 + 𝑏=1
𝐵
𝑅𝐵𝑆𝐵 ∗ 𝑃𝑆𝑀 ∗ 𝐺𝑆𝐵,𝑈𝑚
𝛾 𝑈𝑠
𝑘
=
𝑃𝑆𝐵 ∗ 𝐺𝑆𝐵,𝑈𝑠
𝑁0 + 𝑑=1
𝐷
𝑥 𝑘,𝑑 ∗ 𝑃𝑑 ∗ 𝐺 𝑑,𝑈𝑠 + 𝑐=1
𝐶
𝑅𝐵 𝑀𝐵 ∗ 𝑃 𝑀𝐵 ∗ 𝐺 𝑀𝐵,𝑈𝑠
𝛾 𝑈𝑠
𝑘
=
𝑥 𝑘,𝑑 ∗ 𝑃𝑑 ∗ 𝐺 𝑑,𝑑
𝑁0 + 𝑐=1
𝐶
𝑅𝐵 𝑀𝐵 ∗ 𝑃 𝑀𝐵 ∗ 𝐺 𝑀𝐵,𝑑 + 𝑏=1
𝐵
𝑅𝐵𝑆𝐵 ∗ 𝑃𝑆𝑀 ∗ 𝐺𝑆𝐵,𝑑
9

10. ProblemFormulation
• Objective: maximize overall throughput
• Variables: D2D channel allocation
• Constraints: minimum rate requirement of users all users
𝑃1: max
𝑋𝑘,𝐷
𝑘=1
𝐾
𝑇 𝑈 𝑀 𝑋 𝑘,𝑑 + 𝑇 𝑈 𝑆 𝑋 𝑘,𝑑 + 𝑇 𝑈 𝐷(𝑋 𝑘,𝑑) MINLP Problem
C2: indicates only one RB is assigned to each D2D pair.
C3: indicates RB cannot be used by more than one D2D pair.
10

11.  The problem (P1) is the Mixed Integer Nonlinear Problem (MINLP).
 Mixed Integer Nonlinear Program (MINLP) is (NP –hard) [1].
 The complexity of finding an optimal solution for MINLP is too high.
 A low complexity algorithm is proposed to allocate D2D users.
C4: C6 Represent various QoS requirements
For cellular and D2D users
11

12. • Maximum allowed interference threshold at 𝑘 𝑡ℎ
RB is calculated by solving the constraints (C4) and (C5)
Sequential MaxSearchAlgorithm
(𝑂. 𝐼) 𝑘is an accumulated interference in 𝑘 𝑡ℎ RB before allocating D2D pairs.
1- Set Maximum Interference Threshold
12

13. • Compute the interference imposed by D2D pairs at 𝑘 𝑡ℎ
RB for both SB users and MB users
• An initial set of reuse RBs for pair (d) is found by comparing Interference (𝐼 𝑑,𝑚
𝑘
, 𝐼 𝑑,𝑠
𝑘
) from equations with the maximum
threshold ( 𝐼 𝑘
𝑇ℎ
) ,The optimal set of RBs 𝜓 𝑅𝐵𝑠
∗
is found
2- Identify Optimal Resource Blocks Candidate
13

14. 2- Identify Optimal Resource Blocks Candidate
P1
PRB1
P2
P3
PRB2
PRB3
PRB5
PRB4
PRB5
PRB1
PRBk
Pn
T1,1
T2,1 T3,1
Tn,1
Multiple D2D Pairs and Reuse Candidate Matching
D2D Pairs Reuse Candidate
14

15. 3. Allocate Resources Block for D2D pairs.
• Compute achieved throughput allocated in the best candidate RBs
P1 PRB1
P2
P3
PRB2
PRB3
PRB6Pn
D2D Pairs
T2,2
Tn,6
Selected Resources
15

16. 16

17. BruteForceSearch
• By finding 𝜓 𝑅𝐵𝑠
∗
in the SMS algorithm, the search space for each D2D user is reduced
• The brute-force search is applied to determine the optimal allocation solution
17

18. NetworkPerformance
• Monte-Carlo is performed to evaluate the
algorithms.
• distance-dependent path loss and shadowing
fading presented in (3GPP).
Table (1) simulation parameters
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19. D2Duniformdistributedwithfixeddistanceseparation
D2D resource Allocation 19

20. As the separation distance between D2Dtx and
D2Drx increases, gain achieved from both
algorithms decreases
the separation
distance between D2Dtx and D2Drx increases, gain
achieved from both algorithms decreases. The
achieved
gain from D2D pairs in the guard distance topology
is
higher than the gain achieved in the no guard
distance
topology.
 Effect of The Number of D2D Pairs • Effect of D2D separation distance
 SMS shows an improvement in throughput with and without D2D
distance guard.
 Achieved gain with guard distance is higher than gain achieved
without guard distance.
 Results demonstrate that when compared with brute-force, SMS can
converge a suboptimal solution.
 Existing a saturation point for the D2D pairs
 The gain achieved from both algorithms decreases as the
separation distance increases.
 The achieved gain from D2D pairs in the guard distance topology
is higher than the gain achieved in the no guard distance
topology.
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21. D2DbasedonRSSvalues
 User association problem is formulated as (P1) to maximize RSS from users’ desire to communicate.
 𝑌𝑖,𝑗 binary indicator shows user 𝑖 connected to mode J= {𝐷, 𝑆, 𝑀} .
D= D2D communication S = assign with SB, M=assign with MB.
Subject to
21

22. Network Performance (cont.)
22

23. • The effect of number and position in
overall throughput is clear. Out of 250
users, there were 32 users
communicating via the D2D link.
• The majority of them were located at a
significant distance of MB (i.e., D2D
exposed to low interference). This
yields to a higher achieved throughput
• Alternatively, the majority of D2D
users in topologies N = (125, 200) were
located extremely close to MB and
exposed to high interference, which
results in low throughput.
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24. 24
Conclusion
 The overall (EE) optimization of HetNets –support D2D is performed in terms of
throughput maximization.
 D2D resources allocation algorithm is developed and named a Sequential Max Search
(SMS).
 The SMS algorithm maximizes the overall throughput and accounts for cross tiers
interference.
 The SMS fulfills various rate requirements for cellular and D2D users.

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