Performance of HARQ in Device-to-Device Communication

doi:10.4236/cn.2013.53B2061

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Communications and Network, 2013, 5, 333-337

http://dx.doi.org/10.4236/cn.2013.53B2061 Published Online September 2013 (http://www.scirp.org/journal/cn)

Performance of HARQ in Device-to-Device

Communication

Wenji Feng, Yafeng Wang, Lei Yang

Wireless Theory & Technology lab (WT&T), Beijing University of Posts and Telecommunications, Beijing, China

[email protected], [email protected]

Email: [email protected], wangyf@bupt.edu.cn, [email protected]

Received July, 2013

ABSTRACT

In this paper, we study D2D (Device-to-Device) communication underlying LTE-Advanced uplink system. Since D2D

communication reuses uplink resources with cellular communication in this scenario, it’s hard for D2D users to avoid

the interference from cellular users while cellular users are communication with eNB (evolved Node B). HARQ (Hy-

brid Automatic Repeat reQuest) is widely used in LTE-Advanced system in order to improve the accurate rate of cellu-

lar communication. Hence, we consider studying the integration of D2D with HARQ, so as to achieve the purpose of

improving the throughput of D2D communication and the performance of overall system. Synchronous HARQ is con-

sidered to introduce into D2D communicatio n procedures. What’s more, this idea will be taken into system-level simu-

lation. From the simulation results, we can see that the throughput of D2D communication gets a lot of gain and the

performance of overall system is improved as well. In addition, Synchronous HARQ technique can significantly de-

crease the BLER (Block Error Rate) of D2D communication, especially for which in a bad channel condition.

Keywords: D2D Communication; Synchronous HARQ; LTE-Advanced System; Uplink; BLER

1. Introduction

3GPP Long Term Evolution (LTE) technology has been

proved to have outstanding performance, especially in

the measures of spectral efficiency and throughput, cell

edge and peak values in a cellular, frequency reuse one

network [1,2]. Hence, major efforts have been spent on

the development of LTE. Currently the further evolu-tion

of such systems has been started under the scope of

IMT-Advanced [3-5].

The device-to-device communication (D2D) tech-

nol-ogy, also known as proximity-based services (ProSe),

is introduced to the LTE-Advanced system [6-7]. How-

ever, the D2D communication is sharing authorized fre-

quency band with cellular communication by the way of

or-thogonal method or multiplexing method. The intro-

duc-tion of D2D communication is to improve the

throughput of the whole cellular system. It contributes to

higher sys-tem spectrum efficiency as well. When D2D

users reuse cellular frequency resources, it is hard to

avoid the inter-ference from other cellular users in the

same cell. It may affect the performance of D2D com-

munication to some extent.

Hybrid automatic repeat request technology (HARQ)

is widely used in LTE-Advanced. HARQ can be divided

into synchronous HARQ and asynchronous HARQ in

accordance with the time of occurrence of the re-

trans-mission [8]. Synchronous HARQ means the trans-

mission of a HARQ process (retransmission) occurs at a

fixed moment. Asynchronous HARQ refers to a retrans-

mission that the HARQ process can occur at any time.

Synchro-nous HARQ is considered to introduce into

D2D com-munication procedures.

This paper focuses on studying the integration of D2D

with synchronous HARQ, and analysis the overall sys-

tem performance after joining the mechanism.

This paper is organized as follows: Section 2 describes

the simulation platform. Section 3 compares and analysis

the overall system performance with or without D2D

communication. Finally concluding remarks are made in

Section 4.

2. Procedures and Simulation Platform

We usually use HARQ to guarantee the accuracy of data

communication in LTE-Advanced system. Thus, we as

well consider adding HARQ into D2D communication to

guarantee the accuracy, and improve the performance of

overall system.

D2D communication reuses uplink resources of

LTE-Advanced in our simulation. It means that D2D

users only communicate during uplink slot. Figure 1

shows the procedures of the integration of D2D with

HARQ.

W. J. FENG ET AL.

334

Figure 1. Flow chart of synchronous HARQ for D2D.

Where CQI denotes Channel Quality Indicator, ACK

denotes Acknow ledgement, and NA CK denotes Negative

Acknowledgement.

Synchronous HARQ is introduced into simulation

platform. Different HARQ process ID is recorded by

system. In the same process, when the transmission oc-

curs, eNB merges SINR (Signal-to-Interference plus

Noise Ratio), and then determine whether to retransmit.

If there is no SINR data in the process, eNB can use cur-

rent SINR without merging. After deciding whether

needs to retransmit, there will be two branches:

1) Retransmit:

a) If system calls retransmission, the number of re-

transmission (ReTxNUM) will be recorded. The current

SINR, MCS and RB (Resource Block) ID will be re-

corded as well, which are merging data for next retrans-

mission.

b) If system calls retransmission, and current ReTx-

NUM is greater than Max-ReTxNUM, clear all data of

current process. System gives up transmitting this packet.

2) Non retransmit:

If the packet is successful transmitted, system clear all

data of current process.

The flow chart of synchronous HARQ for D2D simu-

lation platform is given in Figure 2.

The generation of retransmission probability in sys-

tem-level simulation is based on the mapping relation-

ship of SINR and BLER. Also the MCS and the size of

RB will affect this mapping relationship. In our HARQ

process the MCS is set to 28, and the size of RB is 10.

Table 1 shows the mapping relationship of SINR and

BLER.

The simulation platform consists of 7 base stations (21

sectors). The radius of each cell is 500 m. The distance

between transmitter and receiver is 10 m to 20 m. D2D

communication reuses UL resources of LTE-Advanced,

which contains 46 RB. The transmission power of D2D

transmitter is 20 dBm [9,10]. The system bandwidth is 10

MHz and the carrier frequency is 2 GHz. We distribute

210 cellular UEs into overall system so that there are 8 to

10 cellular UEs in each cell. Also we distribute one pair

Figure 2. Flow chart of synchronous HARQ for D2D.

of D2D UEs into one cell amount to 21 pairs of D2D

UEs. The permanent MCS of D2D communication is 28.

The path loss model and corresponding shadow fading

model of D2D communication are referred as model of

Urban Macro(UMa) in [11]，where it can be further

categorized as Line-of-sight (LOS) and Non-line-of-sight

(NLOS).

W. J. FENG ET AL. 335

Table 1. Mapping relationship of SINR and B LER.

MCS=28

SIZE OF RB=10

SINR BLER

17.2 1

17.4 0.96

17.6 0.864271

17.8 0.41018

18 0.103235

18.2 0.020804

18.4 0.00529

LOS:

10 10

16.9log ([])46.820log ([]/5.0)

PLd mfGHz (1)

NLOS:

10 10

40log([ ])30log([])49

PLd kmfMHz  (2)

The probability of LOS is as follow:

=exp((4) / 3),460

0, 60

LOS

Pdd





 







，

(3)

Where PL denotes the path loss, d is the distance be-

tween D2D users, fc is carrier frequency, and PLOS is the

probability of LOS.

The parameters of simulation are listed in Table 2.

3. Results and Analyses

Due to the introduction of synchronous HARQ for D2D

communication, the overall system throughput may have

been affected. We consider two different simulation sce-

narios:

a) Case BASIC:

This case will be the one that there is no HARQ in

D2D communication. This is a case used as the standard

of comparison system performance.

b) Case HARQ:

This case will be the one that joining HARQ into D2D

communication.

Both of these two simulation scenarios set the D2D

transmission power to 20 dBm. The scheduling mode of

D2D is the same and D2D communication reuse 10 RB

of cellular communication.

Figure 3 shows the results of two simulation cases.

As Figure 3 shows, the eNB throughput of both cases

is the same. It means that the integration of D2D with

HARQ does not affect the average throughput of eNB.

Since both cases’ throughput of cell-edge users are the

same as well, we can draw a conclusion that HARQ for

D2D communication does not affect the average

throughput either. Th e reasons are as follows:

In our simulation, the interference against eNB and

cellular UE is associated with D2D communication. As is

in both Case BASIC and Case HARQ, the interference

from D2D communication is just the same, th e results of

eNB throughput and cell edge user throughpu t turn ou t to

be the same.

Figure 3 also shows that the integration of D2D with

HARQ increases 5.6% D2D communication throughput

gain. What’s more, the overall system gets 1.9% throughput

gain. In view of this, after joining the HARQ into D2D

communication, the performance of D2D communication

and overall system has certain promotion. In addition,

BLER of case HARQ is 20% smaller than that of case

BASIC. Thus it can be seen that the accuracy of D2D

communication gets e nhanced after using HARQ.

Table 2. List of simulation parameters.

Parameters Value

Number of eNB 7 base stations (21 sectors)

Radius of cell 500 m

Distance of D2D

communication 10 m to 20 m

System resources Uplink/D2D and cellular

communication reuse 46 RB

Transmission power of D2D 20 dBm

System bandwidth 10 MHz

Carrier freque nc y 2 GHz

Number of cellular U E 210

Number of D2D pairs 21

Distribution 8 to 10 cellular UEs in each cell;

one pair of D2D-U E into one cell

MCS of D2D 28

Thermal noise density ﹣174 dBm/Hz

Scheduling algorithm Proportional Fai r

AverageThroughputofeNB

4680.1173

(kbps)

4680.1173

(kbps)

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

BASIC HARQ

ThroughputofCell‐edgeUsers

4.452

(kbps )

4.452

kbps

0.5

1.5

2.5

3.5

4.5

BASIC HARQ

ThroughputofD2D

2350.3585

(kbps)

2481.864

(kbps)

2250

2300

2350

2400

2450

2500

BASIC HARQ

Throughputofoverallsystem

7030.4758

(kbps)

7161.9813

(kbps)

6950

7000

7050

7100

7150

7200

BASIC HARQ

BLER

0.2154

0.1715

0.05

0.1

0.15

0.2

0.25

BASIC HARQ

Figure 3. Results of two simulation case s.

W. J. FENG ET AL.

336

Figure 4 refers to the throughput CDF curves of both

case BASIC and case HARQ.

In Figure 4, the performance of D2D communication

throughput, which enables HARQ technique, is better

than the one without HARQ technique. The D2D UEs,

whose throughput is less than 1000 kbps, of case HARQ

are obviously less than those of case BASIC. It shows

that HARQ technique can increase the throughput of

low-throughput D2D UEs.

Since all parameters in both Case BASIC and Case

HARQ are the same, we consider comparing the

throughput of each D2D UE from different cases. Figure

5 shows the throughput difference between Case BASIC

and Case HARQ.

From Figure 5 we can find that after using HARQ

about 50% D2D UEs do not get any throughput gain,

because we set the transmission power to 20 dBm, which

is the maximal power for UE. At the same time, about

40% D2D UEs increase 0 to 500 kbps throughput gain.

What’s more, 10% D2D UEs after using HARQ get 500

to 1200 kbps throughput gain. We can assume that if

lower transmission power is set for D2D UEs, which

means D2D communication get lower SINR in the same

channel conditio n, the gain from HARQ will be greater.

0500 1000 15002000 25003000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Av er age R a t e ( kbps )

C D F

HARQ

BASIC

Figure 4. The throughput CDF curves.

0200 4006008001000 1200

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

T he Differ ence Bet w een BASI C an d H AR Q ( kbps)

C D F

Figure 5. Throughput difference CDF curves.

4. Conclusions

In this paper we introduce synchronous HARQ into D2D

communication, and we have Case BASIC and Case

HARQ for simulation. Case BASIC is the case used as

the standard of comparison system performance. In the

simulation of Case HARQ, the throughput of eNB and

cellular communication is not affected. At the same time,

the throughput of D2D communication g ets a lot of gain.

Due to the gain of D2D communication, the throughput

of overall system gets gain as well. What’s more, HARQ

technique can improve the accurate rate of D2D commu-

nication, espe cially for which in a bad channel condition .

Hence, the introduction of HARQ for D2D communica-

tion is viable and necessary. For further study, we should

further optimize HARQ of D2D communication, so that

we can make the overall system gain maximization.

5. Acknowledgements

This paper is supported by National Key Technology

R&D Program of China under grant No.

2012ZX03003011.

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