1. Consideration on Features for 11bd
Jan 2019
Consideration on Features for 11bd
Date:
Authors:
Name
Affiliation
Address
Phone
Dongguk Lim
LG Electronics
19, Yangjae-daero 11gil, Seocho-gu, Seoul , Korea
Insun Jang
Eunsung Park
Suhwook Kim
Jeongki Kim
Jinsoo choi
Dongguk Lim, LG Electronics

2. Jan 2019
Introduction
In order to support the increasing needs from the future V2X applications, the following scopes for Next Generation V2X (i.e., NGV) were defined in PAR doc [1].
Higher throughput
Lower sensitivity level (i.e., longer range)
Interoperability, Backward compatibility, Coexistence, Fairness
In this contribution, we discuss the features to be considered for achieving the above goals.
We approach these features primarily from PHY perspective.
Dongguk Lim, LG Electronics

3. Considerations for High Throughput (1/2)
Jan 2019
Considerations for High Throughput (1/2)
To increase the throughput, we can consider the following various features which are already applied to other WLAN systems (e.g., 11n, 11ac and 11ax).
Higher MCS
For enhanced throughput, high modulation level such as 256 QAM or 1024QAM adopted in WLAN systems can be considered.
Max Modulation level adopted in 11p is 64 QAM.
Due to the high mobility of vehicles, the adaptation of high modulation level can be restricted.
Because it can require low constellation error and high complexity, we need to check the feasibility to apply in 11bd.
Supporting of Multi-Spatial stream
Contrary to 11p which only supports a single spatial stream, multiple spatial streams can be considered.
Extensibility up to 2 spatial streams may be considered.
But, because it is highly affected by the transmission environment, it is important to consider whether or not it is suitable for high mobility environment. Also, it should be also considered how the STA does reception of multi-spatial streams.
Dongguk Lim, LG Electronics

4. Considerations for High Throughput (2/2)
Jan 2019
Considerations for High Throughput (2/2)
Wider bandwidth
Generally, conventional WLAN systems used the wider bandwidth to improve the throughput performance.
extensibility up to 40MHz in 2.4GHz and up to 160MHz in 5GHz band.
Total 75MHz bandwidth as a ITS band had been allocated in 5.9GHz band.
There are two 20MHz channels available in the 5.9GHz band
For example, Ch. 175 and Ch. 181.
So, we can take wider bandwidth into account such as 20MHz bandwidth for throughput enhancement.
Additional bandwidth can consist of continuous / Non-continuous 20MHz within the 5.9GHz band.
We need to develop the following features to efficiently use the wider bandwidth (i.e., 20MHz).
Tone Plan for 20MHz
NGV-STF / NGV- LTF sequence
Control field (e.g., NGV SIG)
Phase rotation for 20MHz
Dongguk Lim, LG Electronics

5. PHY features for Wider bandwidth: Tone Plan
Jan 2019
PHY features for Wider bandwidth: Tone Plan
The conventional tone plan was designed by reusing the tone plan of 11a and applying 2x down-clocking to achieve the reliable and stable transmission.
For the 20MHz transmission, we can consider the two methods to form the tone plan.
By reusing the construction method of conventional tone plan.
As the most simple design way, we can consider the duplication of conventional tone plan (i.e., 10MHz + 10MHz).
Another is to reuse the tone plans for other WLAN systems (e.g., 40MHz of 11n and 11ac or 20MHz of 11ax) in a 20MHz BW.
For example, if the tone plan for 40MHz of 11ac is applied to 20MHz of 11bd, then tone plan consists with below.
Also, we can consider the new tone plan for 20MHz to improve efficiency and throughput.
In this new tone plan, various factors (e.g., DC tones, Guard tones, pilot tones) can be considered.
Dongguk Lim, LG Electronics

6. PHY features for Wider bandwidth: NGV-STF / NGV- LTF sequence
Jan 2019
PHY features for Wider bandwidth: NGV-STF / NGV- LTF sequence
NGV-STF /NGV-LTF sequence appropriate for 20MHz BW need to be examined closely.
The conventional sequences for STF and LTF were well designed to be optimized in terms of PAPR.
But, due to the impact of high mobility, it may cause performance degradation of channel estimation and correlation.
So, to reduce the performance degradation, we may need to consider a way to compensate the degradation by well utilizing those training fields or inserting mid-amble, etc.
The Design for NGV-STF/LTF field is also dependent on tone plan.
Dongguk Lim, LG Electronics

7. PHY features for Wider bandwidth : Control fields
Jan 2019
PHY features for Wider bandwidth : Control fields
To support the various bandwidth, i.e., 10 / 20MHz, we need to define the control fields for the indication of this information.
Basically, the information for BW is transmitted by using the SIGA field in conventional WLAN system.
NGV-SIG can contain the common control information and early indicated information.
This field may be constructed by using conventional 10MHz tone plan and transmitted by using duplication of 10MHz within 20MHz.
In addition to common control information, we can consider user-specific information to support the new V2V applications, e.g., autonomous driving, sensor sharing.
11p mainly focused on the broadcasting of some information related to transportation. So, to reinforce the intercommunication between vehicles, related control information can be considered in 11bd.
User-specific information can be conveyed by using the common control field or the user-specific field.
If the user-specific field exists on one of the frame formats for 11bd, this field may be constructed like a common signal field by using the same way.
Dongguk Lim, LG Electronics

8. PHY features for Wider bandwidth : Phase rotation
Jan 2019
PHY features for Wider bandwidth : Phase rotation
The conventional Wi-Fi systems adapted the Phase rotation for Wider bandwidth (i.e., 40/80/160MHz) to optimize the PAPR.
NGV can reuse the phase rotation for 40MHz of 11n/11ac if tone plan consists with that of 11n/11ac for 40MHz or is constructed with repetition of that for 10MHz.
Or, we may need to design a new phase rotation for 20MHz by considering the new tone plan or adaptation of tone plan for 11ax 20MHz.
For example, the phase rotation was not applied to tone plan of 20MHz in 11ax. So, to reduce the PAPR, we may need to take phase rotation into account for NGV 20MHz transmission.
Dongguk Lim, LG Electronics

9. Considerations for Lower Sensitivity level
Jan 2019
Considerations for Lower Sensitivity level
To secure the reliability and robustness of 11bd transmission, we can look at the various methods such as repetition, power boosting, robust modulation scheme and etc.
In 11ax, for the extended range transmission, the dedicated frame format (i.e., ER-SU PPDU format) was defined. And, repetition of the control field and power boosting of the preamble part were applied to this frame format.
Similar to 11ax ER-SU PPDU, we can design the dedicated 11bd frame format for achieving the lower sensitivity(i.e., LS).
It needs a method to distinguish this frame format.
Also, as another method, the repetition of 11p PPDU as proposed in [2] can be considered.
It is a very simple method, but there is an increased memory requirement for storing additional information and it is hard to distinguish whether a received signal is repeated or not.
11ax ER SU PPDU format
Dongguk Lim, LG Electronics

10. PHY features for Lower Sensitivity level : Indication of frame format
Jan 2019
PHY features for Lower Sensitivity level : Indication of frame format
To use the different frame formats or transmission methods for LS, we need to develop the method for indication of this.
According to LS approaches, we can consider the following indication methods.
If the dedicated frame format for LS is defined, we can take into account using the early indication methods used in conventional Wi-Fi systems.
For example, length field of L-SIG and symbol repetition can be used like as that used in11ax.
If NGV frame is repeated for LS, we can consider using the information of control field, i.e., NGV-SIG.
This method also can applicable when LS frame format is used.
Dongguk Lim, LG Electronics

11. PHY features for Lower Sensitivity level : Robust transmission
Jan 2019
PHY features for Lower Sensitivity level : Robust transmission
For reliability and robust transmission of the data field, conventional Wi-Fi used the newly defined lowest MCS or additional modulation scheme.
For example, 11ah defined newly the lower MCS (i.e., MCS10) than MCS0 and 11ax used the Dual Carrier Modulation (i.e., DCM).
NGV can reuse the defined lowest MCS or additional modulation scheme to get the lower sensitivity.
Or, simply to achieve the LS, using repetition in aspect of frequency domain or time domain also can be considered.
Dongguk Lim, LG Electronics

12. Considerations for Interoperability (1/2)
Jan 2019
Considerations for Interoperability (1/2)
We agreed to follow the terminologies as described in [3].
i.e., Interoperability, Backward compatibility, Coexistence
By taking account to Coexistence between NGV and 11p, the Legacy preamble part (i.e., L-STF, L-LTF and L-SIG in 11p frame) can be included in the new NGV PPDU and this L-part is located before NGV part.
Since L-part is always transmitted firstly on NGV transmission, 11p device as well as NGV device can detect the transmitted signal on same channel.
That will ensure all NGV transmission will be detectable by 11p devices.
For example, the frame format of NGV for 10MHz transmission can be constructed with followings.
In addition to L-part, for identification of NGV transmission by NGV devices, we can consider some features which are compatible with 11p PHY features.
Dongguk Lim, LG Electronics

13. Considerations for Interoperability (2/2)
Jan 2019
Considerations for Interoperability (2/2)
To fully satisfy the interoperability where the 11p devices and NGV devices are blended, a NGV STA just needs to use an 11p PPDU, which limits the performance (i.e., 11p)
As an interoperable alternative for the better performance than 11p, the concept of consecutive 11p PPDU (with a certain time gap) has been proposed in [2]
If all PPDUs are the same, i.e., all PPDUs includes the information in common, the combining gain can be obtained
If different PPDUs are connected, it can improve the transmission efficiency.
We can introduce both of cases for 11bd, but it requires a signaling(e.g., field) for indicating whether the information of each PPDU is the same
For example, the figure as below
NGV or 11bd
Dongguk Lim, LG Electronics

14. Jan 2019
Conclusion
To improve the performance of V2X communication (i.e., 11p), we have considered several PHY features assuming the specified goals below in mind.
For Higher throughput
Wider bandwidth, i.e., 20MHz
For Lower sensitivity level (i.e., longer range)
Robust transmission method including a design of Frame format
For Interoperability and Coexistence
The inclusion of L-part and repetition of 11p PPDU
By taking account to these features in 11bd, the enhanced performance of 11bd will be ensured.
Dongguk Lim, LG Electronics

15. Reference [1] IEEE 802.11-18-0862/r5 , 802.11 NGV Proposed PAR
Jan 2019
Reference
[1] IEEE /r5 , NGV Proposed PAR
[2] IEEE /r0, Interoperable NGV PHY Improvement
[3] IEEE /r2, NGV SG Use Cases
Dongguk Lim, LG Electronics