1. Further Investigation on WUR Performance
Month Year
doc.: IEEE yy/xxxxr0
September 2016
Further Investigation on WUR Performance
Date:
Authors:
Name
Affiliation
Address
Phone
Eunsung Park
LG Electronics
19, Yangjae-daero 11gil, Seocho-gu, Seoul , Korea
Jinsoo Choi
Dongguk Lim
HanGyu Cho
Eunsung Park, LG Electronics
John Doe, Some Company

2. Recap on [1] Uncoded PER performance for the wake-up receiver is shown
September 2016
Recap on [1]
Uncoded PER performance for the wake-up receiver is shown
Wake-up packet is computed by the OOK modulation
OOK symbol is generated using OFDM transmitter
K subcarriers are used (K = 1, 13, 64)
Coefficients of all available subcarriers are set to 0 (off) and 1 (on) for information “0” and “1”, respectively
Two decoding methods are applied to the receiver
Coherent decoding
Non-coherent decoding
Eunsung Park, LG Electronics

3. September 2016
Overview (1/2)
In this contribution, WUR performance is further investigated by applying some schemes such as coding and symbol repetition
Coherent decoding
As shown in [1], the coherent decoding method offers good performance even in the uncoded case, but the performance can be degraded due to several impairments such as CFO and TO
Thus, we may need to further enhance the performance, and in this contribution, we additionally check on the performance for the coded case as a reference
BCC with ½ code rate using random interleaver is applied
Eunsung Park, LG Electronics

4. Overview (2/2) Non-coherent decoding
September 2016
Overview (2/2)
Non-coherent decoding
WUR performance can be worse than the L-SIG performance as shown in [1], and impairment factors may lead to a further performance degradation
Thus, the performance enhancement is imperative in order to achieve a similar performance with the L-SIG (i.e., align the transmission range between the wake-up packet and conventional packet)
Furthermore, we should consider the coexistence issue with other devices (or potentially with non devices)
Consecutive OFF symbols in a wake-up packet may have a coexistence problem
To this end, we apply several schemes as follows
Manchester code
Symbol repetition
We will demonstrate PER performance for both decoding methods
The number of information bits is set to 48 (e.g. MAC address)
Eunsung Park, LG Electronics

5. OOK Modulation with Manchester Code (1/3)
September 2016
OOK Modulation with Manchester Code (1/3)
If Manchester code is applied to the OOK modulation, envelope transition occurs from on/off to off/on in the middle of the symbol time
This process can prevent consecutive OFF symbols
Then, we can consider that each OOK symbol (information “0” or “1”) is composed of two 1.6us sub-symbols and 0.8us guard interval
4us symbol time is the same as the uncoded case in [1] and thus the data rate is also the same
Each sub-symbol for each information is as follows
We denote 1.6us sub-symbols “0” and “1” as OFF and ON sub-symbols, respectively, and we will give an example how to generate them using OFDM transmitter in slide 6
Also, two options for a symbol structure according to the guard interval will be introduced in slide 7
Information
First sub-symbol (1.6us)
Second sub-symbol (1.6us)
“0”
1 (ON)
0 (OFF)
“1”
Eunsung Park, LG Electronics

6. OOK Modulation with Manchester Code (2/3)
September 2016
OOK Modulation with Manchester Code (2/3)
OFF sub-symbol
The signal for the 4us OFF symbol is described in [1] and either the first or second half of this signal except the guard interval can be used (i.e. OFF during 1.6us)
ON sub-symbol
Set the coefficients as follows
Every other available subcarrier : 1
Others : 0
E.g.) indices of available subcarriers are -6 to 6
By doing this, we can generate a 3.2us signal that has 1.6us periodicity
Choose either the first or second 1.6us part
… …
Subcarrier index
Eunsung Park, LG Electronics

7. OOK Modulation with Manchester Code (3/3)
September 2016
OOK Modulation with Manchester Code (3/3)
Symbol structure
Option 1 : 0.8us guard interval is used at the front of each symbol
Option 1 may lead to a severe inter sub-symbol interference especially in an outdoor environment
Option 2 : 0.4us guard interval is used at the front of each sub-symbol
Option 2 can reduce the inter sub-symbol interference compared to option 1 CP
Information “0”
0us us us us
Information “1”
0us us us us CP GI
OFF sub-symbol GI
ON sub-symbol
OFF sub-symbol
ON sub-symbol CP
Information “0”
0us 0.4us us 2.4us us CP
Information “1”
0us 0.4us us 2.4us us GI
OFF sub-symbol GI
OFF sub-symbol GI
ON sub-symbol GI
ON sub-symbol
Eunsung Park, LG Electronics

8. September 2016
Symbol Repetition
For non-coherent decoding, we also consider a symbol repetition in the time domain for a better performance
Two symbols are used to indicate information “0” and “1”
The more symbols for each information, the better performance
However, given a latency issue, we should minimize the overhead the most, and thus we only use two symbols for each information
In order to avoid consecutive OFF symbols, we use different symbols between two symbols as follows
ON/OFF symbols are depicted in [1]
Information
First symbol (4us)
Second symbol (4us)
“0”
1 (ON)
0 (OFF)
“1”
Eunsung Park, LG Electronics

9. Simulation Environment
September 2016
Simulation Environment
Preamble : 11 symbols as in [1]
Information bits : 48 bits (e.g. MAC address)
Number of available subcarriers : 13
Channel : TGn D, UMi NLOS
No CFO/TO
Decoding methods
Coherent
Uncoded as in [1]
Coded : BCC w/ ½ code rate and random interleaver
We do not consider Manchester code
Non-coherent
Two options for Manchester code
Symbol repetition
We do not apply two options for Manchester code to each symbol for the symbol repetition method in the simulation
Eunsung Park, LG Electronics

10. Coherent Decoding TGn D UMi NLOS September 2016
Eunsung Park, LG Electronics

11. Non-coherent Decoding
September 2016
Non-coherent Decoding
TGn D
UMi NLOS
Eunsung Park, LG Electronics

12. September 2016
Conclusion
We investigated the PER performance for the WUR by using several schemes
In coherent decoding, we verified that the uncoded case already has a better performance than the L-SIG case and the coded case can further enhance the performance
It seems that we don’t have to apply the channel code which causes large overhead and high power consumption
However, we need to check on the performance by taking into account several factors which yield performance degradation
In non-coherent decoding, we verified that the WUR with several schemes can obtain a better performance than the L-SIG case
In both channels, the symbol repetition method offers the best performance at the cost of the overhead
Option 2 for Manchester code can provide a comparable performance comparing with the L-SIG performance in the TGn D channel
However, both options for Manchester code have poor performance in the UMi channel, and thus we can confirm that they are vulnerable to the inter symbol/sub-symbol interference
Therefore, it seems that we need to apply the symbol repetition method at least even considering the impairment factors
Or, we can consider other options for Manchester code which have a better performance with a slight overhead increase (i.e. longer guard interval for ISI reduction)
Note that those options for Manchester code and symbol repetition can avoid the coexistence problem with other and non devices
Eunsung Park, LG Electronics

13. September 2016
References
[1] IEEE wur-performance-investigation-on-wake-up-receiver
Eunsung Park, LG Electronics