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Further Investigation on WUR Performance

Further Investigation on WUR Performance. Date: 2016-09-12. Authors:. 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 802.11 OFDM transmitter K subcarriers are used ( K = 1, 13, 64)

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Further Investigation on WUR Performance

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  1. Further Investigation on WUR Performance Date: 2016-09-12 Authors: Eunsung Park, LG Electronics

  2. 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 802.11 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. 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 • 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 802.11 packet) • Furthermore, we should consider the coexistence issue with other 802.11 devices (or potentially with non-802.11 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) • 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 802.11 OFDM transmitter in slide 6 • Also, two options for a symbol structure according to the guard interval will be introduced in slide 7 Eunsung Park, LG Electronics

  6. 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 -32 -31 -30 … -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 … 30 31 Eunsung Park, LG Electronics

  7. 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 CP GI OFF sub-symbol 0us 0.8us 2.4us 4us 0us 0.8us 2.4us 4us ON sub-symbol OFF sub-symbol GI ON sub-symbol Information “0” Information “1” CP CP CP CP GI OFF sub-symbol GI OFF sub-symbol 0us 0.4us 2.0us 2.4us 4us 0us 0.4us 2.0us 2.4us 4us Information “1” Information “0” GI ON sub-symbol GI ON sub-symbol Eunsung Park, LG Electronics

  8. 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] Eunsung Park, LG Electronics

  9. 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 • Uncoded as in [1] • 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 Eunsung Park, LG Electronics

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

  12. 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 802.11 and non-802.11 devices Eunsung Park, LG Electronics

  13. References [1] IEEE 802.11-16-0865-01-0wur-performance-investigation-on-wake-up-receiver Eunsung Park, LG Electronics

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