Page 41 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 2

AZ DZ
CCZ
period
time
Fig. 4 – Clustering and Cache Placement Zone (CCZ), Access Zone (AZ) frequency
and Delivery Zone (DZ) ‑ Periodic allocation
During an MP, indicates that user sends discov‑
,
ery/advertisement beacons in the ℎ time slot using ℎ
RB.
In the case of multiple access attempts for an RB, inter‑
ference at the receiver is inevitable. If the SINR value 1 ms
at the receiver does not exceed the required threshold 1,1
for any user, the corresponding advertisement/discovery MP 5 ms RP 5 ms
message cannot be successfully received. As an outcome, time
overlapped users encounter outage, are unable to create Fig. 6 – Illustration of AZ Part 1 for N=10 ms
D2D links and cannot make a contribution to the of load‑
ing. On the other hand, if the SINR value meets the thresh‑ this beacon is transmitted via . Similarly, bea‑
1,1
old for a user, the corresponding user occupies the RB cons which are indicated by vertical lines and
3,9
during the entire AZ and gets a response in the same time dots also received successfully since these
5,6
slot and over the same RB during the following RP. The RBs are not selected by any other user and replied
SINR threshold depends on the modulation and coding over the corresponding RBs in RP.
rate [50]
• is selected by two users indicated by horizon‑
4,8
tal and vertical lines. As mentioned previously, this
Part 1 Part 2 Part 3
overlap causes an interference at the receiver. Since
ms ms ms none of the users ful ill the SINR threshold condition,
2 × + ms
a reply message is not sent in the RP.
Fig. 5 – Access Zone (AZ) Structure
• Another particular case for multiple access to the

same RB occurs at 1,5 . This time, the SINR
The irst half of the partitions (1 and 3) is used for trans‑ threshold condition is ful illed by one of the users
mitting discovery/advertisement beacons and called a and a reply is sent over .
Messaging Period (MP). On the other hand, the second 1,5
half is called a Reply Period (RP) and used to reply to ad‑ Moreover, in D2D communication users aim to be aware
vertisement/discovery messages. It is assumed that all of each other in an extended range. This might be possible
users stay in the cellular network coverage during the with increasing the transmission power but in dense net‑
simulations. Therefore, the time synchronization of users works with limited spectrum allocation, this causes inter‑
is provided by the network. ference, outage, and drains the battery. Therefore, simi‑
lar to the LTE D2D technology, it is assumed that all users
For D2D links Winner B1 Line of Sight (LOS) pathloss
model (6) is used which is also considered in technical re‑ have ixed (23 dBm, 200 mW) transmission power [49].
ports prepared by 3GPP for the case of outdoor users [47]. In LTE Direct, ixed output power of user equipment pre‑
vents usage of Orthogonal Frequency Division Multiple
, = 40 log 10 ( , ) + 2.7 log 10 ( /5) Access (OFDMA). Therefore, the Single Carrier Frequency

− 17.3 log (ℎ ) − 17.3 log (ℎ ) + 9.45 Division Multiple Access (SC‑FDMA) technique is used
10 10
(6) for uplink to avoid a high Peak‑to‑Average Power Ratio
(PAPR). On the other hand, the OFDMA technique is used
As mentioned beforehand, when a discovery or advertise‑ for the downlink which provides better spectral ef iciency
ment beacon is successfully received, the corresponding compared to SC‑FDMA.
response beacon is sent in the same time slot and over
the same RB in the RP. Thus, randomness in the RB se‑ In the proposed network model, the discovery beacon
lection is avoided and successful delivery of the response of an OU might be received by multiple CHs or IHUs for
message is ensured. In Fig. 6 the structure of an AZ and DBD2D. Similarly, the advertisement beacon of a CH or
some particular cases are illustrated. IHU also might be received by multiple OUs in ABD2D. In
such cases sending reply beacons using the same RB is not
• Discovery/advertisement beacon transmitted over possible because SC‑FDMA does not allow multiple access
is indicated by horizontal lines and reply to to an RB. Since nearby users will attempt to access a com‑
1,1

© International Telecommunication Union, 2021 27