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: Comparison of D-PSK and FSK for Narrowband Systems Date Submitted: 22, September 2009 Source:David Davenport (1), Neal Seidl (2), Jeremy Moss (3), Maulin Patel (4),Anuj Batra (5), Jin-Meng Ho (5), Srinath Hosur (5), June Chul Roh (5), Tim Schmidl (5), Okundu Omeni (6), Alan Wong (6) (1) GE Global Research, davenport@research.ge.com, 518-387-5041, 1 Research Circle, Niskayuna, NY, USA (2) GE Healthcare, neal.seidl@med.ge.com, 414-362-3413, 8200 West Tower Ave., Milwaukee, WI, USA (3) Philips, j.moss@philips.com, +44 1223 427530, 101 Cambridge Science Park, Milton Road, Cambridge, UK (4) Philips, maulin.patel@philips.com, 914-945-6156, 345 Scarborough Rd., Briarcliff Manor, NY, USA (5) Texas Instruments, {batra, jinmengho, hosur, jroh, schmidl}@ti.com, 12500 TI Blvd, Dallas, TX, USA (6) Toumaz Technology, {okundu.omeni, alan.wong}@toumaz.com, Bldg 3, 115 Milton Park, Abingdon, Oxfordshire, UK Re: TG6 merger discussions Abstract: This presentation describes the advantages of differential PSK (D-PSK) over FSK for narrowband systems Purpose: For information 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. S. Hosur et al., TI et al.

2. Comparison of D-PSK and FSK for Narrowband Systems S. Hosur et al., TI et al.

3. D-PSK Scales Better To Higher Data Rates • D-PSK has better spectral efficiency than FSK • Since D-PSK has lower SNR requirements for a given bits/symbol, it will also better (lower) sensitivity numbers than FSK • Notes: • 4-FSK is very difficult to implement in real systems • D-PSK allows for future growth of technology, FSK limits technology, example Bluetooth, when they wanted to go to higher data rates, they switched from FSK to D-PSK  we should start with D-PSK, instead of making a difficult transition S. Hosur et al., TI et al.

4. Advantages of D-PSK over FSK • Obtain better out-of-band (OOB) emissions with D-PSK than with FSK • Better for coexistence with other BAN networks • FSK needs to be shaped with a Gaussian filter in order to achieve desired out-of-band emission. Gaussian filter introduces inter-symbol interference (ISI), which can lead to performance degradations • D-PSK uses a SRRC filter to shape spectrum. SRRC filter + matched filter does not introduce ISI. • D-PSK allows for higher data rate modes • With higher data rates, packets can be transmitted more quickly • Transmitting packets more quickly, leads to longer sleep times  lower power consumption (most of power consumed in RF/analog section, not much difference in power between 100 kbps and 1 Mbps) • D-PSK achieves same sensitivity as FSK, even with a lower transmit power of -10 dBm • Lower transmit power is better for coexistence with other networks, and battery life S. Hosur et al., TI et al.

5. A Way Forward to Compromise S. Hosur et al., TI et al.

6. Background • Took the groups suggestion on a common data rate / common mode very seriously • Investigated how a common signaling scheme could be achieved for D-PSK and FSK receivers • The next set of slides describes what we have learned and based on this knowledge, we will suggest a way forward S. Hosur et al., TI et al.

7. D-PSK Background • Constellation for p/2-DBPSK: • Phase change between symbols is limited to p/2 • Relationship between phase changes and instantaneous frequency: • Phase change by +p/2  positive instantaneous frequency • Phase change by –p/2  negative instantaneous frequency S. Hosur et al., TI et al.

8. Example • Relationship between transmitted data, phase change and instantaneous frequency for a p/2-DBPSK S. Hosur et al., TI et al.

9. Observations • From previous slide, we see that the sign of the instantaneous frequency gives the transmitted data • Therefore, an FM demodulator should be able to receive a p/2-DBPSK signal S. Hosur et al., TI et al.

10. Simulations • Transmitter: • A p/2-DBPSK signal with square-root raised cosine filter • Excess BW = 0.3 • Receiver #1: • A p/2-DBPSK receiver employing a matched filter (matched to transmitter) • Receiver #2: • FM receiver that measures the instantaneous frequency • VGA filter is a low-pass filter (not SRRC) • Instantaneous frequency of received signal r(t) = x(t) + jy(t) is obtained by: where ()’ denotes the derivative • Derivative is obtained by passing the signal through a simple 3 tap filter (other filters are also possible) S. Hosur et al., TI et al.

11. Results • Compared the un-coded BER for both receivers: • Operating point is around un-coded BER = ~10-3 (coded BER will be much lower) S. Hosur et al., TI et al.

12. Conclusions and Way Forward • A p/2-DBPSK results in frequency changes whenever the phase changes • Instantaneous frequency changes can be measured using an FM receiver • A simple FSK/FM receiver can decode a p/2-DBPSK signal: • Loss when compared to p/2-DBPSK receiver is negligible • A p/2-DBPSK signal should be the common mode signal for the narrowband PHYs: • Rates above the common mode should be based on DPSK S. Hosur et al., TI et al.