March, 2000IEEE 802.15-00/051r1

IEEE P802.15

Wireless Personal Area Networks

Project / IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Title / Desirable PHY Modulation Characteristics with respect to the PAN High Rate Selection Criteria.
Date Submitted / 7 March, 2000
Source / Richard Roberts / Bruce Kraemer
Intersil Corporation
P.O. Box 883
MS 62A-028
Melbourne, Fl. 32902-0883
USA / Voice:+407.724.7022 or
+407.729.5683
Fax:+407.724.7094
E-mail: /
Re: / Revision to 00051r0P802-15.doc
Abstract / In this contribution we qualitatively discuss performance of three likely candidate PHY waveforms: CP-BFSK (continuous phase binary frequency shift keying), a single carrier waveform such as SQPSK (staggered quadraphase shift keying), and OFDM (orthogonal frequency division multiplexing). It is suggested that CP-BFSK is not robust enough and that OFDM, while having adequate robustness, is too complex. It is then suggested that single carrier SQPSK offers the right trade-off between complexity and performance.
Purpose / Recommendations to working group P802.15 High Rate
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.

Desired Waveform Characteristics and Candidate Waveforms

For a WPAN high rate application, it seems reasonable that the candidate air waveform should offer the following characteristics:

  • Not require high linearity in the transmitter and the receiver
  • Offer a low BER at a reasonable SNR
  • Have a reasonably low degree of implementation complexity

Waveform Selection Tree

Three candidate waveform were considered:

  • CPBFSK (continuous phase binary frequency shift keying such as GFSK)
  • Constant envelope waveform, very tolerant of nonlinearity
  • TX PA can be compressed, RX can use a limiter instead of AGC
  • Spectral shape is controlled by TX prefiltering and adjusting the deviation
  • In general demodulation is noncoherent … limiter/discriminator combination
  • Single carrier waveform such as SQPSK (staggered QPSK)
  • Nearly constant envelope waveform, reasonable tolerance of nonlinearities
  • TX PA nearly compressed (small backoff), RX can use a limiter instead of AGC
  • Spectral shape can be solely determined by baseband TX prefiltering
  • Demodulation can be coherent
  • Multi-carrier OFDM (orthogonal frequency division multiplexing)
  • Not constant envelope waveform, can not tolerate much nonlinearity
  • TX and RX must be linear, need an AGC stage instead of limiter in the RX
  • TX spectral shape is controlled by baseband shaping
  • Demodulation is coherent

Subjective Evaluation (1-worse … 5-best)

CP-BFSK
(GFSK) / Single Carrier (SQPSK) / Multi-carrier
(OFDM)
Range / 2 / 5 / 4
Multipath Tolerance / 2 / 4 / 5
Power Consumption / 5 / 3 / 2
Low Complexity (includes linearity) / 5 / 3[1] / 1
Bits/Hz/Watt[2]
(efficiency) / 1 / 4 / 4
Score / 15/25 / 19/25 / 16/25

Hypothesis

Of the three classes of waveforms rated here, we believe that the single carrier, coherently demodulated waveform offers the best trade-off between performance and complexity. We believe that CP-BFSK, while having low implementation complexity, can not meet the QoS (quality of service) criteria. In addition, we believe that multi-carrier OFDM, while having more than adequate robutiness, can not meet the low complexity criteria. Therefore, our hypothesis is that the single carrier (e.g. SQPSK) will be the best candidate waveform.

Submissionpage 1Rick Roberts, Intersil

[1] One can argue that the baseband of OFDM is no more complex then that of a single carrier system if the single carrier system needs significant equalization. However, this argument becomes weaker when the analog chips are included in the complexity discussion.

[2] This is a measure of modulation efficiency. For example, for a given path loss and a given transmit output power, how many bits per Hertz can be achieved for a desired bit error rate. CP-FSK becomes very unrobust at low deviation ratios, OFDM has a constant occupied bandwidth regardless of the data rate (poor efficiency at low data rates) and SQPSK has an occupied bandwidth that is proportional to the data rate.