Signal Waveform Comparisons (Rev 3 + rev.FT R&D) Z. Sahinoglu, I. Guvenc, P. Orlik, S. Zhao Digital Communications and Networking Group, MERL Francois Chin, Sam Kwok, Zander Lei, Xiaoming Peng Digital Wireless Dept, I2R Patricia Martigne, Benoit Miscopein, Jean Schwoerer France Telecom R&D Saturday, May 04, 2019

Option-I One Bit The Other Bit Always Empty Always Empty Always Empty 100ns 8-chip times: 150ns 100ns 8-chip times: 150ns The Other Bit Always Empty Always Empty Always Empty 8-chip times: 150ns 100ns Enough long not to cause IFI : 100ns 8-chip times: 150ns

Coherent receivers exploit chip sequence patterns Features of Option-I Coherent receivers exploit chip sequence patterns Non-coherent receivers see in which half the energy arrives In ranging preamble, each piconet is assigned a different sequence of bits Symbol rate is 1Msps (after rate ½ code)

Example SOP preambles in Ranging with Option-I Piconet-I bit sequence: {1,0,0,1,1} Piconet-II bit sequence: {1,1,0,0,0}

Ranging Performance of Option-I Very resilient to SOP interference due to proper selection of preamble bit sequences For non-coherent radios, inter-pulse-interference due to multipath does not need to be resolved Statistical multiplexing is needed to increase SNR due to spreading bit energy over many pulses Preliminary results A train of 8-pulses EbN0 = 22dB, SIR = 0dB (randomly generated 30 symbols in the preambles of desired and interference) CM1 Integration interval: 4ns Ranging error: 3ns (72%) Better accuracy if narrower energy windows

Modulation with Option-I (I2R’s comments ) Additional time hopping of blocks is needed to support 2-SOP Ex: Another 160ns interval in each half of the frame [Zafer, can you illustrate this with a diagram?] Yes Francois, I could, but I now would like revise this statement and say that “it is better if a symbol consists of multiple frames with TH of a pulse (s) in each (See below please) to avoid catastrophic collisions in the communication mode (I think this is similar to what Ismail and Patricia have in their mind).  see Option IV - Patricia. OK, Zafer, there a whole lot of difference between the scheme shown in pp.4 and that shown below; the former in pp.4 is burst-PPM (the pulse are equally space, the energy detector does not care about the pulse details), while the latter, your preferred scheme, is pulse-PPM (the pulse are TH, energy detector cares about the pulse positions / details). Is my interpretation correct? Option-I with this additional time hopping blocks will be the only mode, since signaling is designed with SOP in mind Option-1 will also be the same signaling scheme for synchronisation for non-coherent receiver, as common preamble are used for both sync and ranging This will also be the common signaling scheme for the preamble in beacon packet Coherent receiver has to perform two layer of despreading (both time-hopping and code despreading) for synchronisation Ts <= 500ns

Option-II Ts = 500ns « 11 » 2-PPM + TR base M = 2 « 01 » « 11 » 2-PPM + TR base M = 2 One bit/symbol « 01 » « 10 » « 00 » (coherent decoding possible)

Option-II Features Pulses (or doublets) are spread over the entire 500ns symbol duration Non-coherent decoding and ranging with this waveform has not been simulated yet Has potentially better SOP isolation than Option-I in communication mode

Ternary Signaling for Synchronization & Ranging Option-III To compare fairly, with option-I, which has 8 pulses in 500ns, the PRI for option-III is 62.5ns Ternary Signaling for Synchronization & Ranging Pulse Repetition Interval ~ 62.5ns -Common signaling (Mode 1) for ALL Detectors -Receiver-specific signaling (Mode 2) for ED 1 2 3 4 5 6 7 8 30 31 ………………………… Non-inverted pulses are blue, Inverted pulses are green. Synchronisation / Ranging preamble = Binary Base Sequence repeated For K times… …………… …………… ................. Symbol Interval =1937.5ns Symbol Interval =1937.5ns Saturday, May 04, 2019

Option-III Criteria/Target – balance max post-despreading SNR and low auto-correlation side lobes Ternary Seq [+ - - 0 0 0 + - 0 + + + 0 + 0 - 0 0 0 0 + 0 0 - 0 - + 0 0 - - ] After Square Law & Integration in PRI Unipolar M-Seq [+ + + 0 0 0 + + 0 + + + 0 + 0 + 0 0 0 0 + 0 0 + 0 + + 0 0 + + ] In AWGN Soft output Noncoherent detection of OOK Sliding Correlator LPF / integrator BPF ( )2 ADC Sample Rate 1/Tc {1,-1} Binary Sequence Bipolar M-Seq [+ + + - - - + + - + + + - + - + - - - - + - - + - + + - - + + ]

Option-III Features (I2R’s comments) Zero autocorrelation side lobe sequences (very important for leading edge detection, as the leading edge can be 6 ~ 10 dB below peak) Under SOP interference, correlator peak is 3dB degraded in non-coherent reception due to suboptimal correlation This makes identification of weak multipath components difficult Suboptimal correlation sequence is chosen to achieve Zero autocorrelation side lobe, which is considered more crucial in ranging After the square-law device, the integrator integrates over the PRI (~30ns) (simplest architecture for data comm. mode) In option-I, integration interval is 2ns or 4ns. Longer integration interval collects more noise Longer integration interval collects more interference energy After the square-law device, the integrator integrates over the 2 ~ 4ns (for ranging mode) Same as option-I After the square-law device, the integrator integrates over the 2 ~ 4ns (for comm. Mode with selective rake combining) Less energy capture Less noise capture too

Option-IV (FT R&D – derived from Option-I) The idea exposed in Option-I with Zafer's comments on "additional time hopping to avoid catastrophic collisions in the communication mode" is illustrated below 4 pulses per symbol are used Use of an 8-ary Time Hopping code of length 4 Use of such a TH code combined with the band plan may allow to handle the SOP issue Code order and length are scalable to meet different requirements Tp = 4ns, Tc = 20 ns, Tf = 160 ns, Tsymbol = 640 ns PRP ± TH Tp Tc Tf

Recommended Architecture for Ranging with Non-Coherent Rx (MERL) (No FFT routine is needed, being different from doc#0269) Energy image generation Removes interference 2-4ns Length-3 Vertical Median or Minimum Filtering 1D to 2D Conversion LPF / integrator BPF ( )2 ADC 2D to 1D Conversion with Energy Combining TOA Estimator

Recommended Architecture for Ranging with Non-Coherent Rx (FT R&D) Time base 1-2ns accurate 4ns Time-stamping LPF / integrator Analog Comparator "Path-arrival dates" table BPF ( )2 1D to 2D Conversion Filtering + Assumption/path selection Assumption path synchronization Matrix TOA measure

Recommended Architecture for Ranging with Non-Coherent Rx (I2R) TOA Estimator 2D-1D conver-sion Energy image generation interference suppression 2-4ns Energy combining across symbols 1D-2D conver-sion Sliding Correlator LPF / integrator BPF ( )2 ADC Bipolar Sequence Francois, could you elaborate on sliding correlator and energy combining blocks please, when the integration is at 4ns intervals ? . Thanks When I tried the sliding correlator, I got results on slide 22. How would you generate your images? Zafer, I have put in details block diagram above with text in next slide….

Sliding correlator Architecture (I2R) Explained using 2D energy map …. 1D-2D conversion Form 2D energy map with 16 rows energy window size = 3.90625ns (16 energy window within PRI of 62.5ns) Sliding correlate each row with bipolar sequence Combine / average over symbols (each symbol = 16x31 map) 2D-1D conversion into (16 x 31 1D-linear map) (to get almost exact Channel impulse response in absence of noise and SOP interference)

Energy Map for Sliding Correlator (I2R) Simulation parameters CM1 channel energy window size = channel tap separation = 3.90625ns (16 energy window within PRI of 62.5ns) 16 preamble symbol, each consists 31-chip ternary sequence Combine / average over symbols (each symbol = 16x31 map) 3 cases Eb/No = 20 dB, no interference Eb/No = 10 dB, no interference Eb/No = 20 dB, SIR = -6dB CM1 Channel Leading edge

Energy Map with Sliding Correlator (I2R) Leading edge Eb/No = 22dB, no interference Energy image generation interference suppression Energy combining across symbols 1D-2D conver-sion Sliding Correlator Bipolar Sequence Symbol Period

Energy Map for Sliding Correlator (I2R) Leading edge Eb/No = 15dB, no interference Energy image generation interference suppression Energy combining across symbols 1D-2D conver-sion Sliding Correlator Bipolar Sequence Symbol Period

Energy Map for Sliding Correlator (I2R) Leading edge Eb/No = 22dB, SIR = -6dB Energy image generation interference suppression Energy combining across symbols 1D-2D conver-sion Sliding Correlator Bipolar Sequence Symbol Period

Ranging with Option – III (I2R’s) Transmit signaling is pure equally spaced pulses Method used is sliding correlator, energy detector and coherent detector alike The sliding correlator output, after symbol combining, has the energy content of the close to channel impulse response, even in the presence of AWGN and SOP interference

Effect of Number of Pulses on Performance for Non-Coherent Modulation and Ranging: An Example M: (Degree of freedom/2) = (BWxT) N: Number of pulses NsEb = symbol energy No: Noise psd Case 1: Single Pulse Per Symbol N = 1 s = 0 s = 1 μ1 MN0 MN0+2NsEb σ12 MN02 MN20+4N20NsEb PDF s = 0 s = 1 Transmitting one pulse with large energy Energy Energy of this pulse is NsEb μ1

Effect of Number of Pulses on Performance for Non-Coherent Modulation and Ranging: An Example Case 2: Multiple Pulses Per Symbol N = Ns s = 0 s = 1 μ2 NsMN0 Ns(MN0+2Eb) σ22 NsMN02 Ns(MN02+4N0Eb) Transmitting many pulses with less energies PDF s = 0 s = 1 Energy Energy of each pulse is Eb, and there are Ns number of pulses μ2

Effect of Number of Pulses on Performance for Non-Coherent Modulation and Ranging The energy per symbol can be collected in a single pulse (N=1), or in Ns pulses The means and variances statistics of the square-law device outputs can be observed in the absence and presence of signal The Euclidean distance between the means for s=0, and s=1 are the same for both cases (2NsEb) However, the variance term when using larger number of pulses increases

Current Status MERL is simulating Option-III according to the recommended block diagram, and will share the observations soon Preliminary Option-I results are shared on slide 5 There are still unincorporated optimization techniques to improve edge detection performance Adaptive threshold selection Search back window selection etc

Pulse OOK vs Burst PPM (MERL Comment) Pulse OOK (option-III) Burst PPM (option-I) Signaling Spaced out pulse seq Clustered pulse seq Energy Integration period (for ranging) 2~4ns Energy Integration period (for data comm.) 2ns ~ PRI (30ns) Half Symbol period Performance @1Mbps without SOP TBD Performance @1Mbps with SOP Good in com. mode (Sufficient processing gain to handle) good in ranging mode (Not much processing gain to handle the comm. mode) Common signaling for preamble No Time hopping Time Hopping Additional complexity for Coherent receiver to receive preamble with common signaling No Yes (2 layer sync, TH then code de-spreading) Agreed

Pulse OOK vs Burst PPM (MERL I2R Comment) Pulse OOK (option-III) Burst PPM (option-I) Inter-pulse interference during ranging operation Less due to high PRI (30ns @ 33MHz PRF or ~60ns @ ~16MHz PRF) More due to small inter pulse interval (Yes, but IPI is not deleterious to ranging performance in burst PPM) (but, this could be an issue for the coherent detector, which will look into the pulses….) Sampling rate (Comms) Low in receiver Low in transmitter (Isnt it different in com and ranging 4ns vs. 30ns?) (let’s break it into comms and ranging ….) High in transmitter Sampling rate (Ranging) High in receiver

Illustrations of Energy Image Generation To better understand how images are created, just shift the mask below over desired user and interferer signals one block at a time in the animation mode, and populate the matrix from open windows in the mask In I2R scheme, it will be masked onto +1 and -1 positions in a symbol Symbol duration in Option-I Desired user code-2 {2,1,2,1} Interference code {1,3,1,2} User Energy matrix Interference Energy Matrix

A look Into Energy Images of Option-I EBN0 = 22dB, SIR = 0dB, no statistical multiplexing Strong SOP interference is easily suppressed by the way the image is created and by means of length-3 minimum filtering (in ranging) Multi-user Interference Desired User Energy Minimum Filtering {Length 3 Vertical} Symbol Index Symbol Index Block Index Block Index

Ternary Energy Image Simulation Results Case-A: Images are generated before the Unipolar correlator The mask is formed from positions of +1 and -1 in the sequence Settings: 4ns block sizes Observing the signal in 16 windows at +/- 1’s of the ternary code Eb/N0 = 30dB No clear sign of signal paths under AWGN + Interference, when imaging is used on data before the bipolar correlator We will test it on samples after Unipolar correlation in the next round. I expect it to improve the images and to ease edge detection Pls see clarification of receiver mechanism and performance in pp.13-18 Desired edge is here Noise and interference free Noise + interference (after min-3 filtering)

Autocorrelation of Ternary Sequences @4ns Sampling (MERL) A sequence of 4 Ternary symbols are passed through a CM1 channel (no AWGN and no SOP Interference) Received signal energies are integrated over 4ns intervals The sequence of energy samples are correlated with a Unipolar template (output of the correlator is plotted below) We are studying how correlator outputs can be best exploited for ranging under AWGN and SOP interference Pls see clarification of receiver mechanism and performance in pp.13-18