5decawave產(chǎn)品化應(yīng)用設(shè)計(jì)參考

1、APPLICATION NOTE: APS001APS001 APPLICATION NOTEDW1000 POWER CONSUMPTIONSystem related aspects of Power Consumption and how to optimize them when using the DW1000Version 2.1This document is subject to change without notice© Decawave 2015 This document isand contains information which is propriet

2、ary toDecawave Limited. No reproduction is permitted without prior express written permission of the authorAPS001: System Aspects of Power ConsumptionTABLE OF CONTENTS12INTRODUCTION4POWER CONSUMPTION OF WIRELESS TRANSCEIVERS IN GENERAL52.12.2INTRODUCTION5THE IMPLICATIONS OF PROTOCOL CHOICE52.2.12.2.

3、2“No Synchronization” case5“Synchronized” Case83POWER CONSUMPTION IN TWO WAY RANGING APPLICATIONS103.13.2INTRODUCTION TO TWO-WAY RANGING SCHEMES10TIME & POWER103.2.13.2.2Introduction10Overall time to derive a location123.3IMPACT OF THE ABOVE ON POWER CONSUMPTION143.3.1Reducing ranging power cons

4、umption144POWER CONSUMPTION IN TDOA RTLS APPLICATIONS154.14.2INTRODUCTION TO TDOA SYSTEMS15TIME & POWER154.2.14.2.2Introduction15Overall time to derive a location155COMMON POWER CONSUMPTION CONTROL METHODOLOGIES185.15.2INTRODUCTION18TAG MESSAGE LENGTH OPTIMIZATION / DYNAMIC MODIFICATION185.2.15.

5、2.25.2.3Introduction18Message Preamble Optimization18Message Payload optimization185.35.4TAG UPDATE-RATE OPTIMIZATION20OPTIMIZING THE RECEIVE WINDOW IN THE TAG205.4.15.4.2Two-way ranging20TDOA206REFERENCES21789REVISION HISTORY21MAJOR CHANGES21ABOUT DECAWAVE22APPENDIX 1: DW1000 OPERATING STATES23TABL

6、E OF FIGURESFIGURE 1: ASYNCHRONOUS POLLING SINGLE SLAVE6FIGURE 2: ASYNCHRONOUS POLLING MULTIPLE SLAVE7FIGURE 3: SYNCHRONOUS POLLING SINGLE SLAVE8FIGURE 4: SYNCHRONOUS POLLING MULTIPLE SLAVES9FIGURE 5: TWO-WAY RANGING EXCHANGE10FIGURE 6: OVERALL LOCATION SCHEME USING TWO-WAY RANGING11FIGURE 7: SINGLE

7、 TWO-WAY RANGING TRANION WITH COMMUNICATIONS TO LOCATION ENGINE12FIGURE 8: OVERALL LOCATION SCHEME USING TDOA16FIGURE 9: TAG TRANION WITH INDIVIDUAL ANCHOR NODE17FIGURE 10: DYNAMIC MESSAGE PAYLOAD MODIFICATION19© Decawave 2015 This document isand contains information which is proprietary toPage

8、: 2 of 23Decawave Limited. No reproduction is permitted without prior express written permission of the authorAPS001: System Aspects of Power ConsumptionFIGURE 11: TAG DYNAMIC UPDATE RATE MODIFICATION19LIST OF TABLESTABLE 1: POWER CONSUMPTION ELEMENTS5TABLE 2: COMPONENTS OF TIME TAKEN TO PERFORM A S

9、INGLE TWO-WAY RANGING EXCHANGE13TABLE 4: REFERENCES21TABLE 3: REVISION HISTORY21TABLE 5: POWER CONSUMPTION OF VARIOUS DEVICE STATES IN DECREASING ORDER23© Decawave 2015 This document isand contains information which is proprietary toPage: 3 of 23Decawave Limited. No reproduction is permitted wi

10、thout prior express written permission of the authorAPS001: System Aspects of Power Consumption1INTRODUCTIONThis is one in a series of notes on the use and application of Decawaves Ultra Wideband technology.This note examines some of the system-related concepts and tradeoffs that need to be consider

11、ed to achieve best possible power consumption.It assumes theer is familiar with the concepts and principlesWireless Communications ingeneral and the DW1000 in particular for more information see the Decawave website.Other notes in this series, also available on, include technicals of theDW1000 and e

12、xamine the application of Decawave technology to market areas such as Electronic Shelf Labeling, Process Automation, Healthcare, Logistics and so on.© Decawave 2015 This document isand contains information which is proprietary toPage: 4 of 23Decawave Limited. No reproduction is permitted withou

13、t prior express written permission of the authorAPS001: System Aspects of Power Consumption22.1POWER CONSUMPTION OF WIRELESS TRANSCEIVERS IN GENERALIntroductionThe accurate determination of the power consumption of a wireless transceiver from a systems pointof view iually a very tricky thing to do.

14、It depends primarily on two things: -··The actual power consumed by the wireless subsystem in its various modes of operation The amount of time spent in each of those modesTo minimize power consumption requires that the wireless subsystem spend as little time as possible operating and when

15、 it is operating it spends as little time as possible in higher-power states and as much time as possible in lower-power states.The first is mainly determined by the designers of the wireless technology used (chips, modules or subsystems) and the system designer generally has little control here apa

16、rt from, perhaps, reducing the transmitted RF power when long range operation is not necessary thereby reducing power consumption.The second, however, is heavily influenced by protocol choicesby the system designer.2.2The implications of protocol choiceThe protocol and system configuration choices t

17、he system designer makes can have major implications for the power consumption of individual elements of the system.Consider two different scenarios illustrated in Figures 1 & 2 below. Both involve a master polling a slave for a responseFor both Master and Slave the average power consumption ove

18、r o considering the time spent in the various modes of operation: -cond can be calculated byTable 1: Power consumption elements2.2.1“No Synchronization” caseIn the first of these scenarios there is no synchronization between the master and slave. The master polls the slave at random intervals requir

19、ing the slave to continually listen for polls and respond when a suitably addressed poll is received.The power consumption of the Master is entirely under its own control. It sleeps, wakes, polls the slave, waits for a response and goes back to sleepSlave power consumption is dictated by the duty cy

20、cle of the master. The longer between polls the longer the slave spends listening.© Decawave 2015 This document isand contains information which is proprietary toPage: 5 of 23Decawave Limited. No reproduction is permitted without prior express written permission of the authorTimeAssociated Powe

21、r ConsumptionTs: Time spent sleePS: Sleep powerTTX: Time in Transmit ModePTX: Transmit powerTL: Time listening for responsePL: Power in Listen modeTRX: Time receiving responsePRX: Receive powerAPS001: System Aspects of Power ConsumptionCASE 1: ASYNCHRONOUS POLLING CONFIGURATION1st Message Exchange2n

22、d Message ExchangeMASTERSleepSleepSleepRX1RX ACKRX ACKTX1TXTXPSPTXPLPRXPSPTXPLPRXPS1st Message Exchange2nd Message ExchangeSLAVEListenListen for Next MessageListenRX2LISTENRXLISTENRXLISTENTX2TX ACKTX ACKPLPRXPIPTXPLPRXPIPTXPLt0Figure 1: Asynchronous Polling Single SlaveBecause the slave does not kno

23、w when messages will arrive it needs to listen constantly. When it does receive a message it responds and then returns to listening mode.The relationship between Idd in listening mode vs. Idd in Rx & Tx modes is very importn determining overall consumption.© Decawave 2015 This document ispr

24、ior express written permission of the authorand contains information which is proprietary to Decawave Limited. No reproduction is permitted withoutPage: 6 of 23APS001: System Aspects of Power ConsumptionThe situation becomes even more complex from a power consumption point of view when there are mul

25、tiple slaves because all slaves receive all messages.Each slave analyses the received messages to determine which adressed to it and then either accepts or discards them. Having each slave receivepolls that are not addressed to it is a complete waste of power as we can see in Figure 2.CASE 2: ASYNCH

26、RONOUS POLLING CONFIGURATION MULTIPLE SLAVES1st Message Exchange2nd Message Exchange3 rd Message ExchangeMASTERRXSleepSSSleepLISRX ACK1LISRX ACKLISRX ACKTXTX1TX2TX3PSPTXPLPRXPSPTXPLPRXPSPTXPLPRXPS1st Message Exchange2nd Message Exchange3rd Message ExchangeSLAVE 1ListenLisLisListenRX1LISTENRX1LISRX2L

27、ISRX3LISTENTX1TX1 ACKPLPRXPIPTXPIPLPRXPSLEEPPLPRXPSLEEPPL1st Message Exchange2nd Message Exchange3rd Message ExchangeSLAVE 2ListenLisLisListenRX2LISTENRX1LISRX2LISRX3LISTENTX2TX2 ACKPLPRXPSPLPRXPIPTXPIPLPRXPSLEEPPL1st Message Exchange2nd Message Exchange3rd Message ExchangeSLAVE 3ListenLisLisListenR

28、X3TX3LISTENRX1LISRX2LISRX3LISTENTX3 ACKPLPRXPSPLPRXPSPLPRXPIPTXPIPLt0Figure 2: Asynchronous Polling Multiple Slave© Decawave 2015 This document isprior express written permission of the authorand contains information which is proprietary to Decawave Limited. No reproduction is permitted without

29、Page: 7 of 23APS001: System Aspects of Power ConsumptionWe can make one compromise here in that once a slave realizes a poll is not addressed to it, it can sleep for the period of the acknowledgment from the slave to which the poll is addressed. If we dont do this then all slaves will receive acknow

30、ledgments from all the other slave nodes making the power consumption situation even worse.2.2.2“Synchronized” CaseNow consider the case of a synchronous polling configuration: -CASE 3: SYNCHRONOUS POLLING CONFIGURATION1st Message Exchange2nd Message ExchangeSleepSleepSleepMASTERRX1 TX1RX ACKRX ACKT

31、XTXPSPTXPLPRXPSPTXPLPRXPS1st Message Exchange2nd Message ExchangeSLAVESleepLisSleepLisSleepRX2RXRXTX2TX ACKTX ACKPSPLPRXPIPTXPSPLPRXPIPTXPLt0Figure 3: Synchronous Polling Single SlaveIn this scheme, the Master and Slave are synchronized in one of a number of different ways so that the Slave knows wh

32、en to expect a poll from the Master. In this case the Slave can wake up shortly before a poll is due, receive the poll, respond and return to sleep. Clearly this has a very large & beneficial impact on power consumption. The effect, from a system point of view, is even more dramatic when we exte

33、nd this concept to multiple nodes.© Decawave 2015 This document isprior express written permission of the authorand contains information which is proprietary to Decawave Limited. No reproduction is permitted withoutPage: 8 of 23APS001: System Aspects of Power ConsumptionCASE 4: SYNCHRONOUS POLL

34、ING CONFIGURATION MULTIPLE SLAVES1st Message Exchange2nd Message Exchange3 rd Message ExchangeSleepSSSleepLISRX ACK1LISRX ACKLISRX ACKTX1TX2TX3PSPTXPLPRXPSPTXPLPRXPSPTXPLPRXPS1st Message ExchangeSleepLisSleepLISRX1TX1 ACKPSPLPRXPIPTXPSLEEP2nd Message ExchangeSleepLisSleepLISRX2TX2 ACKPSPLPRXPIPTXPSL

35、EEP3rd Message ExchangeSleepLisSleepLISRX3TX3 ACKPSPLPRXPIPTXPSLEEPt0Figure 4: Synchronous Polling Multiple SlavesHere, once synchronized, each slave only receives the poll addressed to it thereby significantly reducing power consumption over the unsynchronized case.It is not the purpose of this not

36、e to discuss the implementations of such schemes, particularly the synchronization scheme; there is awealth of literature available on these topics. The intention here is simply to illustrate the very significant effect that the choice of system architecture can have on individual node power consump

37、tion.© Decawave 2015 This document isprior express written permission of the authorand contains information which is proprietary to Decawave Limited. No reproduction is permitted withoutPage: 9 of 23APS001: System Aspects of Power Consumption33.1POWER CONSUMPTION IN TWO WAY RANGING APPLICATIONS

38、Introduction to Two-Way Ranging SchemesTwo Way Ranging systems are a class of RTLS in which a tag and a fixed node exchange information and by doing so can calculate the distance between themselves knowing the speed of light.These are more fully described in 5.An overview of Decawaves implementation

39、 of this scheme is given in Figure 5There are some obvious observations here: -1.Ranging to 3 anchors sequentially in time is a relatively slow process and significant motion of the tag between ranges can result in a location errorTo derive one location requires a minimum of 3 ranging measurements.

40、A single ranging measurement requires 3 messages; therefore 9 messages are required in total; so two way ranging occupies 9 times more air time than a simple tag-blink and therefore the tag density achievable in TWR is approximately 9 times less than that achievable with TDOA although other factors

41、do play a part also.The tag must be both a transmitter and receiver; as a result its power consumption is higher than one which is just a transmitter2.3.Tag sees Round Trip, TRT, of (TRR - TSB)er sees Round Trip, RRT, of (TRF - TSR)Tag TimesTSBer Timeser knows all times, so it can:(a) remove its res

42、ponse time: (TSR - TRB) from the Tags TRT,Tag blink (ID)T(b) remove tags response time: (TSF - TRR) from to give antenna to antenna round trip timeser RRT,RBsimple ACK responseer then can combine these two resultant round trip times (by averaging) to remove by effects of each ends clock differences,

43、 and then divide by 2 to get one way trip time.TSRTRRFinal Message( ID, TSB, TRR, TSF )Multiplying by c the speed of light (and radio waves) gives the distance (or range) between the two devices:( (TRR - TSB) - (TSR - TRB) + (TRF - TSR) (TSF - TRR) ) / 4cTSFTRFor ( 2TRR - TSB - 2TSR + TRB + TRF - TS

44、F ) / 4c.Figure 5: Two-Way Ranging exchangeThis section examines some of the system issues that contribute to tag power consumption in a two- way ranging system. For the purposes of this discussion it is assumed that the anchor nodes are mains powered and their power consumption is not so much of an

45、 issue compared to tag power consumption.3.2Time & Power3.2.1IntroductionPower consumption of a tag in a two-way ranging scheme depends on the time it spends in each of its operating states and the power consumption of each of those states. So in order to address theissue of power consumption it

46、 is necessary to first consider thes involved.© Decawave 2015 This document isand contains information which isPage: 10 of 23proprietary to Decawave Limited. No reproduction is permitted without prior express written permission of the authorAPS001 System Aspects of Power ConsumptionOVERALL SCHE

47、ME TO DERIVE A LOCATION FROM 3 TWO-WAY RANGING EXCHANGESSleepExchange with Anchor1Exchange with Anchor 2Exchange with Anchor 3TAGAnchor calculationComms to Locn EngineANCHOR 1Listen for TagExchange with TagAnchor calculationComms to Locn EngineANCHOR 2Listen for TagExchange with TagAnchor calculatio

48、nComms to Locn EngineANCHOR 3Listen for TagExchange with TagLOCATION ENGINEComms with Anchor 1Comms with Anchor 2Comms with Anchor 3Calculate LocationLOCATION AVAILABLEFigure 6: Overall location scheme using two-way ranging© Decawave 2015 This document isprior express written permission of the

49、authorand contains information which is proprietary to Decawave Limited. No reproduction is permitted withoutPage: 11 of 23APS001: System Aspects of Power Consumption3.2.2Overall time to derive a locationThe calculation of one location involves the following steps: -1.The tag ranges to the first anc

50、hor the first anchor provides the resulting distance measurement to the location engineThe tag ranges to the second anchor - the second anchor provides the resulting distance measurement to the location engineThe tag ranges to the third anchor - the third anchor provides the resulting distance measu

51、rement to the location engineThe Location Engine calculates the location of the tag2.3.4.The total time to establish a location for one tag therefore depends on: -1.2.3.4.The time take to perform each range The time between rangesThe time taken to calculate the range at the last anchorThe time taken

52、 to communicate that last range to the location engine (on the assumption thatmeasurements from the other previous anchors have aly reached the location engine)5.The time taken for the location engine to solve between the resulting spheres.This overall sequence is shown in Figure 6.The breakdown of a single ranging exchange is discussed in 3.2.2.1 and presented in Figure 73.2.2.1Time taken to perform each rangeThe time taken to perform a single range measurement depends on