1. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Jan 2013
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Low Power Transceiver Data Rate Analysis]
Date Submitted: [Jan 15th, 2013]
Source: [Andy Bottomley]
Company [Microsemi-Zarlink]
Address [15822 Bernardo Center Dr, Ste B, San Diego, CA, 92127]
Voice:[ ]
FAX :[ ] ]
Re: [In response to TG4q PAR]
Abstract: [This presentation attempts to provide some justification for defining the optimal data rate for a low power transceiver]
Notice: This document has been prepared to assist the IEEE P 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 P
Andy Bottomley (Microsemi)
Rick Powell (Microsemi)

2. Analysis of Optimal Data Rate for Low Power Transceivers (802.15.4q)
July 2012
doc.: IEEE q
Jan 2013
Analysis of Optimal Data Rate for Low Power Transceivers ( q)
Jan 14th 2013, Andy Bottomley, Microsemi
Andy Bottomley (Microsemi)
Rick Powell (Microsemi)

3. Jan 2013
Abstract
This presentation attempts to provide some justification for defining the optimal data rate for a low power transceiver.
Andy Bottomley (Microsemi)

4. Example of a Low Power FSK TX
Jan 2013
Example of a Low Power FSK TX
Direct modulation of a synthesizer VCO offers a low power TX system for FSK modulation.
FSK modulation does not require a linear PA.
For a first order approximation the system current consumption can be considered to be somewhat in-sensitive to different data rates.
Andy Bottomley (Microsemi)

5. Example of a low power FSK RX
Jan 2013
Example of a low power FSK RX
The current consumption of an RX system is sensitive to the data rate. To accommodate higher data rates requires higher bandwidths in various blocks and higher sampling clocks in the digital baseband blocks.
The following diagram shows the blocks that have a current consumption sensitivity to data rate.
Andy Bottomley (Microsemi)

6. Current Consumption and Data Rates (1)
Jan 2013
Current Consumption and Data Rates (1)
The amplifier bandwidths have to be increased to accommodate higher occupied bandwidths due to higher data rates.
The amplifier current consumption is related to the UGBW and hence data rate by the following simple relationship (assuming strong inversion in the transistors):
Andy Bottomley (Microsemi)

7. Current Consumption and Data Rates (2)
Jan 2013
Current Consumption and Data Rates (2)
The sampling rate of the digital demodulator scales with the low-IF frequency.
Andy Bottomley (Microsemi)

8. Context for Current Consumption Analysis (1)
Jan 2013
Context for Current Consumption Analysis (1)
The number of payload bits is kept constant as the data rate is varied and the duty cycling of the RX is kept constant to meet an overall required throughput of data.
A fixed startup time is built into the system that does not scale with data rate. This is related to the synthesizer start up and other miscellaneous currents.
The peak current consumption is calculated as a function of data rate.
Andy Bottomley (Microsemi)

9. Context for Current Consumption Analysis (2)
July 2012
doc.: IEEE /0626r0
Jan 2013
Context for Current Consumption Analysis (2)
4-FSK is used in the analysis in preference to 2-FSK for the maximum data rate in order to improve spectral efficiency and reduce the RX bandwidth.
An occupied BW of 600kHz with 400kbps is used as the reference for the analysis. The occupied BW is considered to scale proportionally with the data rate along with the amplifier bandwidths (the Modulation Index is assumed to be constant for this analysis).
Block current consumption is referenced to prior IP. Scaling of current consumption is based on the aforementioned relationships with data rate.
Andy Bottomley (Microsemi)
Rick Powell (Microsemi)

10. Context for Current Consumption Analysis (3)
Jan 2013
Context for Current Consumption Analysis (3)
No TX Acks are included for the current consumption analysis only RX duty cycled events are considered.
A constant overall data throughput of 10kbps is used at each payload data rate.
The goal of the analysis is to compare apples with apples and observe if an optimal data rate exists that provides the lowest relative average power for an RX PHY. Please note that this analysis does not aim to accurately define absolute current consumption levels, but only seeks to provide a relative means to compare and contrast different data rates.
Andy Bottomley (Microsemi)

11. RX Idd Analysis Results
Jan 2013
RX Idd Analysis Results
Andy Bottomley (Microsemi)

12. Jan 2013
Observations
The optimal 4-FSK data rate appears to be around 500kbps for the lowest overall current consumption.
Using a 1Mbps payload data rate does not seem to offer a benefit for reducing overall current consumption.
In this example, the peak current consumption increases by a factor of 2 when the data rate changes from 500kbps to 1Mbps. It should be noted that peak power consumption is often a critical concern for many energy harvesting applications.
Andy Bottomley (Microsemi)

13. Jan 2013
Recommendations
An FSK PHY is recommended for q to facilitate a low power transceiver design.
Based on the analysis in this presentation it is not recommended that a maximum payload data rate >500kbps is used for q in order to limit the peak current consumption.
It is not recommended that a maximum payload data rate of <200kbps is used for q in order to optimize the average current consumption.
Andy Bottomley (Microsemi)

14. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Jan
500kHz channelization
Provides multiple narrowband channels for interference mitigation
Coexistence with O-QPSK 2MHz channelization
Filtered FSK
Data rates:
Symbol Rate (ksps) SF
Data Rate (kbps)
Modulation
Type
200 1
400
4-FSK
2-FSK 2
100 4 50 8 25
Data rates in-line with current ‘g’ and ‘k’ FSK PHY proposals
Andy Bottomley
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