Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Low Rate Sensitivity] Date Submitted: [10 October, 2001] Source: [Paul Gorday] Company: [Motorola] Address: [8000 W. Sunrise Blvd., M/S 2141, Plantation, FL 33322] Voice:[(954) 723-4047], FAX: [(954) 723-3712], E-Mail:[paul.gorday@motorola.com] Re: [IEEE 802.15.4 PHY Baseline; Doc. IEEE 802.15-01/358r0] Abstract: [This presentation describes the effect on low rate sensitivity of a proposed change to the TG4 PHY.] Purpose: [] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Paul Gorday, Motorola

2. Low Rate Sensitivity:IEEE 802.15.4D09 PHY Changes Leading to “Low-Rate” Sensitivity Loss Paul Gorday Oct. 10, 2001 Paul Gorday, Motorola

3. Previous Symbol Definition I-Channel 32-chip CPM symbol · · · Q-Channel 32-chip CPM symbol · · · Ts = 32 µs Rs = 31.25 kbaud d09 Symbol Definition I-Channel 32-chip CPM symbol · · · Q-Channel · · · Ts = 16 µs Rs = 62.5 kbaud PHY Changes in d09 Symbol Structure Paul Gorday, Motorola

4. Previous Chip Modulation Ts = 32 µs I-Channel cI0 cI1 cI2 cI30 cI31 Q-Channel cQ0 cQ1 cQ2 cQ30 cQ31 1 µs Complex Chip Rate = 1 Mchip/s d09 Chip Modulation Ts = 16 µs I-Channel c0 c2 c30 Q-Channel c1 c3 c31 1 µs Complex Chip Rate = 1 Mchip/s PHY Changes in d09 Chip Modulation Paul Gorday, Motorola

5. PHY Changes in d09 Symbol Structure (cont’d) • Previous Symbol Definition • Complex Symbol defined as two “real” 32-chip CPM symbols (I and Q) • Required two orthogonal PN codes • d09 Symbol Definition • Complex Symbol defined as one “real” 32-chip CPM symbol • Requires one PN code • Allows greater frequency drift since PN sequence spans less time • Alternative d09 Symbol Definition • For consistency, we could have defined a complex symbol as two “real” 32-chip symbols that are sequential in time, but this seems less simple. I-Channel 32-chip CPM symbol 32-chip CPM symbol · · · Q-Channel · · · Ts = 32 µs Rs = 31.25 kbaud Paul Gorday, Motorola

6. PHY Changes in d09 Base Rate Mode • In both modulation methods: • Each 32-chip CPM symbol represents 4 bits of data, and it both cases the net bit rate is Rb=250 kbps. • Each 32-chip CPM symbol is selected from a set of 24 = 16 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles 16-ary non-coherent orthogonal modulation (curves available from almost any communications textbook). • Simulated performance of the new modulation • Eb/No = 7.5 dB at 10-4 BER • 0.5 dB improvement (differential coding removed, I/Q cross-correlation reduced). • Receiver sensitivity (assuming 15 dB noise figure) • Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) • = -174 + 15 + 7.5 + 10log(250000) • = -97.5 Paul Gorday, Motorola

7. PHY Changes in d09 Low Rate Mode • Previous modulation method: • Each 32-chip CPM symbol represents 1 bit of data, but within a complex symbol, the I and Q component carried the same bit. The net bit rate was 31.25 kbps. • Each 32-chip CPM symbol is selected from a set of 21 = 2 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles binary non-coherent orthogonal modulation. • The 3 dB penalty from repeating each bit on I and Q was offset by coherently combining the I and Q correlation results prior to making the symbol decision. • Simulated performance of the old modulation • Eb/No = 13.5 dB at 10-4 BER • Receiver sensitivity (assuming 15 dB noise figure) • Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) • = -174 + 15 + 13.5 + 10log(31250) • = -100.5 Paul Gorday, Motorola

8. PHY Changes in d09 Low Rate Mode (cont’d) • New modulation method: • Each 32-chip CPM symbol represents 1 bit of data. New net bit rate is 62.5 kbps. • Each 32-chip CPM symbol is selected from a set of 21 = 2 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles binary non-coherent orthogonal modulation. • Symbol repetition was removed. • Simulated performance of the new modulation • Eb/No = 13 dB at 10-4 BER • 0.5 dB improvement (differential coding removed, I/Q cross-correlation reduced) • 3 dB loss (removal of symbol repetition) • Receiver sensitivity (assuming 15 dB noise figure) • Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) • = -174 + 15 + 13 + 10log(62500) • = -98 Paul Gorday, Motorola

9. PHY Changes in d09 Summary • High Rate • Net bit rate is the same as before • Sensitivity gain of 0.5 dB due to removal of differential coding and reduced I/Q cross-correlation. • Low Rate • Net bit rate increased due to removal of symbol repetition • Sensitivity gain of 0.5 dB due to removal of differential coding and reduced I/Q cross-correlation. • Sensitivity loss 3 dB due to removal of symbol repetition • Possible corrections for Low-Rate sensitivity loss • Put symbol repetition back in. Needs to be verified by simulation. • Run in high-rate mode (i.e., 4 bits/symbol), but use additional FEC coding to achieve “low-rate” sensitivity gain. (Complexity?) Paul Gorday, Motorola

10. BER Curves Conventional DSSS Decoding • Notes: • Theoretical refers to M-ary non-coherent orthogonal signaling • “New” refers to the latest d09 version • “Old” refers to all earlier versions Paul Gorday, Motorola