1. Interoperable NGV PHY Improvements
Month Year
doc.: IEEE yy/xxxxr0
July 2018
Interoperable NGV PHY Improvements
Date:
Authors:
Fischer-Filippi-Martinez, NXP
John Doe, Some Company

2. July 2018
Background
Thousands of cars equipped with IEEE p are already on the road, and several major auto manufacturers have announced massive p roll-outs [including Toyota, VW, and GM]
Improvements to IEEE p performance by NGV need to take into account the large number of p systems that will be in service by the time NGV is adopted and deployed
NGV needs to be fully interoperable with “legacy p”
Just having NGV stations be able to decode p signals is insufficient, especially for the safety channel
We cannot segment the safety critical V2X applications between “legacy” and “NGV users” – Millions of lives are at stake
Fischer-Filippi-Martinez, NXP

3. July 2018
Introduction
The goal of the NGV activity should be to improve the system-level performance of V2X communication, without limiting communication to and from already deployed IEEE p equipment
In this submission we will identify some opportunities to improve PHY performance while retaining full interoperability with the IEEE p PHY
Fischer-Filippi-Martinez, NXP

4. Suggested new PHY features for NGV
July 2018
Suggested new PHY features for NGV
The improvements can be classified into the following categories:
TX RF improvements
RX performance improvements
Waveform design improvements
Fischer-Filippi-Martinez, NXP

5. July 2018
TX RF improvements
Transmitter out-of-channel emissions can be reduced for better Multiple Channel Operation (MCO)
Full interoperability with IEEE p
The underlying waveform is not modified
Vehicles using different Spectrum Emission Masks (SEM) can exchange messages
Less interference between adjacent channels  better SINR  increased range & increased safety
The standard should control usage of adjacent service channels so that they never reduce performance of the safety channel
The more cars with a safer SEM, the safer the MCO
Fischer-Filippi-Martinez, NXP

6. RX performance improvements
July 2018
RX performance improvements
Provide better performance of deployed systems, especially in real-life (not only in the lab)
Fully backward-compatible
Minimum sensitivity in static channels can be increased by about 6dB
NGV should add various multipath fading sensitivity requirements for reliable mobility support in the field (with Doppler values aligned with application requirements up to 500 km/h)
Propose to use the ITS-G5 V2V channel model for acceptance criteria
Propose to use Doppler spectrum offset of 2731 Hz (500 km/h)
Fischer-Filippi-Martinez, NXP

7. Waveform design improvements
July 2018
Waveform design improvements
Retransmission of messages
The exact same PPDU is retransmitted one, two, or three times
Retransmissions are reduced as channel load increases (based on Channel Busy Ratio measurement) to avoid creating congestion
Fully interoperable – provides benefits to both p and NGV stations
Retransmissions seen as standalone messages by p stations
Performance improvement due to channel diversity (1 to 2 dB)
Additional messages will be naturally filtered by application
Filtering of duplicate messages is already performed by higher protocol layers – no software update needed
Message and retransmissions can be combined by NGV stations
Combining at LLR levels for example
+4 dB performance boost for 1 retransmission, +7 dB performance boost for 3 retransmissions
Fischer-Filippi-Martinez, NXP

8. Example with three retransmissions
July 2018
Example with three retransmissions
Fischer-Filippi-Martinez, NXP

9. Initial simulation results
July 2018
Initial simulation results
Simulations with one retransmission indicate ~1 dB improvement for p stations and ~4 dB improvement for NGV stations
Should be understood as « Boolean OR of the CRC-pass results », we take the best of the 2 tries:
- trans#1 FAIL + trans#2 FAIL = FAIL
- trans#1 FAIL + trans#2 PASS = PASS
- trans#1 PASS + trans#2 FAIL = PASS
- trans#1 PASS + trans#2 PASS = PASS
Fischer-Filippi-Martinez, NXP

10. Adaptive retransmission control
July 2018
Adaptive retransmission control
We propose to control the number of retransmissions (from 0 to 3) based on the congestion measurement of the channel, based on the Channel Busy Ratio (CBR, as described in ETSI TR )
Measured CBR
Number of retransmissions
Traffic increase (vs p)
Comment
≥ 0.6
No increase in traffic
Congested environment situation.
Retransmissions are disabled
[0.3 – 0.6[
0 or 1 (*)
x1 to x2
The number of retransmissions is gradually increased as the occupancy of the channel goes down.
[0.2 – 0.3[ 1 x2
[0.15 – 0.2[ 2 x3
< 0.15 3 x4
(*) Number of retransmissions = 0 or 1
Retransmission = random value with probability of retransmission = p = (0.6-CBR)/0.3
For example, CBR=0.30  p = ( )/0.3 = 0.3/0.3 = 1
For example, CBR=0.15  p = ( )/0.3 = 0.15/0.3 = 0.5
For example, CBR=0.60  p = ( )/0.3 = 0/0.3 = 0
Fischer-Filippi-Martinez, NXP

11. July 2018
Benefits
These techniques deliver performance improvements while maintaining full interoperability with p
These techniques provide improved communication even for p stations that do not implement NGV
These techniques do not increase channel load in congested environments
These techniques do not require changing higher layers of the ITS protocol stack
Fischer-Filippi-Martinez, NXP

12. July 2018
Summary
It is mandatory to maintain full interoperability with “legacy” p equipment
There are ways to improve overall channel efficiency for both the “legacy” users and NGV users
TX RF improvements
Reduce interference for better Multiple Channel Operation
RX performance improvements
Ensure better performance of deployed systems
Waveform design improvements
Retransmissions of messages, adaptive with channel loading
Fischer-Filippi-Martinez, NXP