Page 82 - Kaleidoscope Academic Conference Proceedings 2020

2020 ITU Kaleidoscope Academic Conference

large gain when there is a near-far effect, e.g., a near and scheduling (SPS) [22] is employed, and every user sensing
strong user can reuse the channel used by a far and weak user, the spectrum resources randomly selects idle resources in a
which greatly improves the spectrum efficiency. Therefore, given period. A sensing-based method is also studied and a
the near-far effect is included in comparison. As shown in potential candidate in 5G V2V [24]. The problem of a
Figure 2, the outage performances of two different sensing-based method is that it is not friendly to multiple
contention-based grant-free NOMA schemes [12] [18] are antennas, and the reliability is relatively low in ultra-dense
compared. As mentioned before, power domain NOMA with environments. To solve these problems, [24] proposes a
a contention-based feature requires extra sensing of channel novel distributed antenna deployment and full-duplex
gain and power control according to estimated channel gain. contention-based NOMA transceiver scheme which jointly
The aim is to make the receive power belong to some use power, code and spatial domain to achieve an ultra-low
predetermined power levels. It results in an extremely high latency and high reliability V2V communication in ultra-
transmission power, and [12] provides sub-channel selection dense scenarios. The block error rate (BLER) comparison is
and distance-based methods to solve it. As a comparison, shown in Figure 3. The channel model is based on LTE-V
code domain NOMA [18] is just required to randomly select standards [22], and 1500 and 700 vehicles are dropped in the
the spread code and can work without power control. urban and freeway scenarios defined in [10], respectively.

The simulation results show that code domain NOMA In Figure 3, three protocol-defined scenarios are all
performs better than power domain. For a target outage rate considered, including urban non-line-of-sight (UN), urban
of 0.1, the achievable arrival rate of power domain NOMA line-of-sight (UL) and freeway line-of-sight (FL). In this
is less than 1 while that of code domain NOMA is greater comparison, the full-duplex NOMA scheme achieves a much
than 2. Also, when combined with the SIC of the diversity higher reliability than the method in the current protocol.
-2
strategy, the achievable arrival rates at the outage of 10 are Also, the overheads of the full-duplex NOMA scheme are
2.4 and 3.4 for power domain and code domain NOMA. In reduced only 1/5, which means a much more frequent
this comparison, power domain NOMA plus SIC of diversity transmission of 250 packets per second (pps) can be
achieves a lower error floor because perfect sensing and supposed, which helps to reduce the end-to-end latency once
power control are assumed. The outage performance of code the information is generated. In this case, NOMA turns the
domain NOMA is bounded by a corresponding orthogonal near-far effect into advantages, and achieves a high spectrum
multiple access (OMA) transmission of perfect scheduling. efficiency and ultra-high reliability of near vehicles.
As the near-far effect is utilized, code domain NOMA plus
SIC of diversity achieves an arrival rate greater than 3 with
the outage performance very close to the OMA bound.

Figure 3 – The BLER comparison of sensing-based SPS in
current protocols and full-duplex contention-based NOMA
using novel access technologies
Figure 2 – The outage comparison of contention-based
NOMA and their combination with SIC of diversity. PD 6. CONCLUSIONS
and CD denote power domain and code domain
To fulfill digital transformations, it is necessary to make
5.2 Case Study of V2V some great modifications in current protocols. One crucial
aspect is to enhance the access protocols as it is a bottleneck
This case study is for vehicle-to-vehicle (V2V) of seamless and instant digital services. This paper provides
communicati without central control. V2V several novel access technologies, and potential impacts on
communication should be extremely reliable for safety, and protocols are also briefly analyzed. Moreover, some typical
V2V without central control is especially important due to use cases are shown to verify the necessity of these
the robustness in a non-cellular domain and ultra-low latency modifications of future protocols. The standardization
requirement. In LTE-V, sensing-based semi-persistent process of novel access technologies to boost digital

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