Page 73 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 6 – Wireless communication systems in beyond 5G era

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 6

3.1 Network players 3. Cat. III: Similarly, the set of slice users requesting for
eMBB, and mMTC slices subscribed to SP ∈ and
Herein, a set of InP numbered as ℐ = { | ∈ , 1 ≤ ≤ under the coverage of a picocell ∈ are indexed
|ℐ|}, with unique and independent resources; that is, ≠
′ by ℰ , , and ℳ , , .
, provide services to a set of MVNOs . Where the set of
MVNOs is indexed as = { | ∈ , 1 ≤ ≤ | |}. An
MVNO is independent and manages its own acquired or 4. Cat. IV: Lastly, slice users under the coverage of a
′
leased resources; that is, ≠ , offers virtual services to clustered femtocell ∈ ℱ and subscribed to SP

service providers. Similarly, the set of service providers is ∈ , are denoted by ℰ , , and ℳ , , .
numbered as = { | ∈ , 1 ≤ ≤ | |}. Following the
′
assumptions for InPs and MVNOs, it is given that ≠ . 3.4 V2X communication model
A service provider offer a set of slice use‑case services
denoted to subscribers. Herein, = {ℰ ∪ ℳ ∪ ℛ}, We model slice users in the V2X‑tier as having similar

where ℰ, ℳ, and ℛ denote the eMBB, mMTC, and URLLC URLLC QoS requirements due to their uniqueness [49,
slice use cases, respectively. 50, 51, 52]. Two widely known approaches to V2X‑
communications are namely [53, 54]: (1) Cellular‑V2X
3.2 Physical network (C‑V2X), and (2) Dedicated Short Range Communications
(DSRC) which is premised on the IEEE 802:11:P standard.
Additionally, we examine the physical network of the M‑ Owing to the growing popularity of C‑V2X in the com‑
TTSD network. In this work, the multi‑tier network con‑ munications and automobile industry and coupled with
sists of macro‑cells, picocells, clustered femtocells, non‑ other numerous reasons discussed in [55, 56, 57, 58], we
clustered femtocells, and a Vehicle‑to‑everything (V2X) adopt the C‑V2X approach in modelling C‑V2X users in
tier whose resources are owned and managed by the re‑ this work. The set of paired vehicles in the V2V communi‑
spective InPs. Furthermore, we index the tiers by pro‑ cation layer is indexed as = { | ∈ , 1 ≤ ≤ | |}.
ceeding with macro‑cells. The set of macro‑cells owned The PC5 sidelink [55] is employed in the communication
by InP is indexed as = { | ∈ , 1 ≤ ≤ | |}. of paired vehicles in the V2V layer. Additionally, the set

Moreover, the set of non‑clustered femtocells owned by of vehicles in the V2I layer (otherwise known as V2N) is
an InP is denoted as ℱ = { | ∈ , 1 ≤ ≤ |ℱ |}. numbered as ℛ = { | ∈ , 1 ≤ ≤ |ℛ|}. These vehicles

The set of picocells owned by InP is numbered as = are connected to macro‑base‑stations alone to reduce the

{ | ∈ , 1 ≤ ≤ | |}. Besides, a cluster of a femto‑ handover signalling overhead, owing to the large cover‑

cells is under the coverage area of a picocell and therefore, age area of the macro‑base‑stations [59].
the number of clusters is equal to | |. Finally, we de ine

the V2X tier by categorising this tier into two: (i) vehi‑
cles engaged in Vehicle‑to‑Infrastructure (V2I) communi‑ 3.5 Channel model
cation layer, and (ii) those engaged in Vehicle‑to‑Vehicle This paper focuses on the downlink of the M‑TTSD net‑
(V2V) communication layer [47, 48]. Furthermore, it is work. Speci ically, we employ the link‑layer model de‑
important to note that in this paper, we identify users or
scribed in [60, 61], and the mobility characterisation of
vehicles in the V2X tier as URLLC users owing to the pe‑
slice users. To this end, the channel modelling stage is
culiarities of V2X communications [49, 50, 51, 52]. More‑
categorised, respectively, into two: (i) static or moder‑
over, we give a detailed explanation of the V2X layer in
ately mobile slice users, and; (ii) highly mobile slice users.
Subsection 3.4.
Without loss of generality, eMBB and mMTC slice users
are assumed to be static or moderately mobile, while
3.3 Slice‑user categorisation URLLC slice users are categorised as highly mobile.
In this subsection, the slice users in the M‑TTSD network
are categorised primarily according to their slice use‑case 3.5.1 Static slice users
type, slice users’ SP, and the location of the slice user in
the M‑TTSD network. Therefore, the categorisation is as The channel modelling for static slice users , ∈ {ℰ ∪
follows. ℳ} is dependent on large‑scale fading components such
as path loss, shadow fading, and the tier in consideration.
1. Cat. I: The set of eMBB, mMTC, and URLLC users sub‑ The propagation model is expressed as [62]:
scribed to an SP ∈ under the coverage of a macro‑
tier ∈ belonging to an InP ∈ ℐ are denoted by = Λ + 35 log(d ) (1)

ℰ , , , ℳ , , , and ℛ , , . , , , , , ,
2. Cat. II: The set of eMBB and mMTC slice users sub‑ where d , , , is the distance of a slice user , from an ac‑
scribed to SP ∈ under the coverage of a non‑ cess point belonging to InP . Λ denotes the tier depen‑

clustered femtocell ∈ ℱ managed by an InP ∈ ℐ dent variable. The parameters for the respective tiers are

are denoted by ℰ , , and ℳ , , . given in Table 2. The spectrum ef iciency of the categories
of users described in Subsection 3.3 is given as:
© International Telecommunication Union, 2021 61