October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

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

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

Low Rate Sensitivity:IEEE 802.15.4

D09 PHY Changes Leading to “Low-Rate” Sensitivity Loss

Paul Gorday

Oct. 10, 2001

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Symbol Structure

32-chip CPM

symbol · · ·

· · ·I-Channel

Q-Channel

Ts = 16 µs

d09 Symbol Definition

Rs = 62.5 kbaud

Previous Symbol Definition

32-chip CPM symbol

32-chip CPM symbol · · ·

· · ·I-Channel

Q-Channel

Ts = 32 µs

Rs = 31.25 kbaud

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Chip Modulation

I-Channel

Q-Channel

Ts = 16 µs

d09 Chip Modulation

Complex Chip Rate = 1 Mchip/s1 µs

c0 c2 c30

c1 c3 c31

Previous Chip Modulation

I-Channel

Q-Channel

Ts = 32 µs

Complex Chip Rate = 1 Mchip/s1 µs

cI0 cI

1 cI2 cI

31

cQ0 cQ

1 cQ2 cQ

31

cI30

cQ30

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Symbol 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.

32-chip CPM

symbol · · ·

· · ·I-Channel

Q-Channel

32-chip CPM

symbol

Ts = 32 µs

Rs = 31.25 kbaud

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Base 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

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Low 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

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Low 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

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

PHY Changes in d09Summary

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?)

October 2001

Paul Gorday, Motorola

doc.: IEEE 802.15-01/478r0

Submission

0 2 4 6 8 10 12 14

10-4

10-3

10-2

10-1

100

Eb/No (dB)

BE

R

Simulated IEEE 802.15.4 PHY performance in ideal AWGN channel

Theory (16-ary)4 bits/symb (New)4 bits/symb (Old)Theory (2-ary)1 bit/symb (New)1 bit/symb (Old)

BER CurvesConventional DSSS Decoding

Notes: (1) Theoretical refers to M-ary

non-coherent orthogonal signaling

(2) “New” refers to the latest d09 version

(3) “Old” refers to all earlier versions