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### 传输功率校准与管理 #### 1. 引言 ##### 1.1 概述本文档旨在提供关于传输功率校准与管理的相关技术细节，特别针对Decawave公司的DW1000芯片组。该文档适用于对无线通信系统设计、调试以及合规性测试感兴趣的工程师和技术人员。 ##### 1.2 什么是传输功率？传输功率是指发射机在工作过程中向天线馈送的有效功率。在无线通信系统中，传输功率是一个关键参数，它直接影响到信号的传播距离、接收质量以及系统的整体性能。 ##### 1.3 传输功率对链路预算的重要性链路预算是评估无线通信系统性能的一种方法，它考虑了信号从发射端到接收端整个过程中的各种增益和损耗因素。传输功率是链路预算中的一个核心要素，因为它直接决定了信号强度，进而影响到信号的传播范围和信噪比。适当的传输功率设置有助于确保通信链路的稳定性和可靠性。 ##### 1.4 DW1000帧结构 DW1000是一种用于短距离无线通信的芯片，支持IEEE 802.15.4a标准，该标准定义了一种名为脉冲调制超宽带（Pulse Modulation Ultra-Wideband, PMUWB）的物理层。DW1000帧结构包括前导码、同步头、数据包、CRC校验和后序等部分，这些部分共同构成了一个完整的数据包结构，用于实现可靠的数据传输。 #### 2. 如何测量传输功率以满足法规要求 ##### 2.1 概述为了确保无线设备符合相关的国际和国家标准，必须进行传输功率的测量。这些标准通常涉及到最大允许的辐射功率水平，以避免对人体健康造成不利影响，并防止对其他无线设备造成干扰。 ##### 2.2 辐射测量辐射测量是指通过专门的测试设备来检测无线设备在工作时产生的电磁辐射。这些测量包括平均辐射功率和峰值辐射功率。 ##### 2.3 测量窗口测量窗口是指在进行辐射测量时所选取的时间段或频谱范围。选择合适的测量窗口对于准确测量传输功率至关重要。 ##### 2.4 测量平均功率平均功率是指在一定时间间隔内发射机输出的功率的平均值。在进行合规性测试时，平均功率是一个重要的指标，因为它反映了设备在长时间内的辐射特性。 ##### 2.5 测量峰值功率峰值功率是指在短时间内发射机输出的最大功率。对于某些应用来说，峰值功率可能是更重要的指标，因为它可以揭示设备在瞬态条件下的行为。 #### 3. 优化传输功率优化传输功率是提高无线通信系统性能的关键步骤之一。通过调整传输功率，可以在不违反法规限制的情况下最大化通信距离和数据传输速率。 ##### 3.1 动态功率控制动态功率控制是一种根据实际通信环境自动调整传输功率的技术。通过实时监测链路质量并相应地调整传输功率，可以减少不必要的能量浪费，同时保持良好的通信质量。 ##### 3.2 传输功率的校准为了确保测量结果的准确性，需要定期对发射机进行校准。这通常涉及到使用标准参考信号和校准设备来验证发射机的实际输出功率是否与预期相符。 ##### 3.3 软件配置除了硬件校准之外，还需要通过软件配置来进一步优化传输功率。例如，可以通过修改芯片内部寄存器的设置来微调功率输出级别。 #### 结论传输功率是无线通信系统中一个至关重要的参数。通过对传输功率进行精确的测量、校准和管理，不仅可以确保设备符合法规要求，还可以显著提升通信系统的性能和效率。对于从事无线通信技术研发和产品开发的工程师而言，掌握传输功率的相关知识和技术是非常必要的。

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APS023: APPLICATION NOTE

AP- Transmit-Power-Calibration-and-Management -1.0

APS023: APPLICATION NOTE

Transmit Power Calibration

and Management

Version 1.0

This document is subject to change without

notice

APS023: APPLICATION NOTE

AP-Transmit-Power-Calibration-and-Management-1.0

Page 2

TABLE OF CONTENTS

1 INTRODUCTION ........................................................................................................................................ 4

1.1 OVERVIEW ................................................................................................................................................. 4

1.2 WHAT DO WE MEAN BY TRANSMIT POWER? ...................................................................................................... 4

1.3 THE IMPORTANCE OF TRANSMIT POWER TO LINK BUDGET ..................................................................................... 4

1.4 THE DW1000 FRAME STRUCTURE .................................................................................................................. 5

2 HOW TRANSMIT POWER IS MEASURED FOR REGULATORY COMPLIANCE ................................................ 6

2.1 OVERVIEW ................................................................................................................................................. 6

2.2 RADIATED MEASUREMENTS ............................................................................................................................ 6

2.3 MEASUREMENT WINDOW ............................................................................................................................. 6

2.4 MEASURING MEAN POWER ............................................................................................................................ 7

2.5 MEASURING PEAK POWER ............................................................................................................................. 7

3 OPTIMIZING TRANSMIT POWER FOR SHORT FRAMES .............................................................................. 8

3.1 INTRODUCTION ........................................................................................................................................... 8

3.2 THE BASIC PRINCIPLE .................................................................................................................................... 8

4 ADJUSTING & CALIBRATING TRANSMIT POWER IN THE DW1000 ........................................................... 11

4.1 INTRODUCTION ......................................................................................................................................... 11

4.2 THE IMPORTANCE OF CALIBRATING THE TRANSMIT POWER ................................................................................. 11

4.3 TRANSMITTER MODES OF OPERATION ............................................................................................................ 11

4.4 ADJUSTING TRANSMIT POWER IN THE DW1000 .............................................................................................. 11

5 MANUAL MODE ..................................................................................................................................... 13

5.1 INTRODUCTION ......................................................................................................................................... 13

5.2 ADJUSTING TRANSMIT POWER IN MANUAL MODE .......................................................................................... 13

5.3 CALIBRATING TRANSMIT POWER IN MANUAL MODE ....................................................................................... 14

5.3.1 Introduction .................................................................................................................................. 14

5.3.2 Frames always longer than one millisecond ................................................................................. 15

5.3.3 More than 1 frame transmitted per millisecond ........................................................................... 16

5.3.4 Only one frame transmitted per millisecond and frame duration constant ................................. 16

5.3.5 Only one frame transmitted per millisecond but with variable duration ...................................... 16

5.4 ENABLING MANUAL MODE ........................................................................................................................ 16

6 SMARTTX POWER MODE ....................................................................................................................... 17

6.1 INTRODUCTION ......................................................................................................................................... 17

6.2 ADJUSTING TRANSMIT POWER IN SMARTTX POWER MODE ............................................................................ 17

6.3 CALIBRATING TRANSMIT POWER IN SMARTTX POWER MODE ......................................................................... 19

6.4 ENABLING SMARTTX POWER MODE .......................................................................................................... 19

7 CALIBRATING A DW1000 TRANSMITTER WITH BOOST ........................................................................... 20

8 MANAGING TRANSMIT POWER DURING NORMAL OPERATION ............................................................. 23

8.1 INTRODUCTION ......................................................................................................................................... 23

8.2 VARIATION OF TRANSMIT POWER WITH TEMPERATURE AND VOLTAGE .................................................................. 23

8.3 MAINTAINING TRANSMIT POWER OVER TEMPERATURE AND VOLTAGE .................................................................. 23

8.3.1 Is it necessary? .............................................................................................................................. 23

8.3.2 How do I implement it? ................................................................................................................. 24

9 REFERENCES ........................................................................................................................................... 27

9.1 LISTING .................................................................................................................................................... 27

10 DOCUMENT HISTORY ......................................................................................................................... 27

10.1 REVISION HISTORY ..................................................................................................................................... 27

11 CHANGE LOG ...................................................................................................................................... 27

APS023: APPLICATION NOTE

AP-Transmit-Power-Calibration-and-Management-1.0

Page 3

12 ABOUT DECAWAVE ............................................................................................................................ 28

13 APPENDIX 1: IS IT NECESSARY TO MEASURE PEAK POWER IN PRODUCTION? .................................... 29

LIST OF TABLES

TABLE 1: TYPICAL USE CASE EXAMPLES ........................................................................................................................... 23

TABLE 2: APPROXIMATE RATES OF CHANGE OF TX POWER WITH TEMPERATURE AND VOLTAGE .................................................. 24

TABLE 3: TABLE OF REFERENCES .................................................................................................................................. 27

TABLE 4: DOCUMENT HISTORY ..................................................................................................................................... 27

LIST OF FIGURES

FIGURE 1: TRANSMIT POWER AT VARIOUS DIFFERENT POINTS IN THE SIGNAL PATH .................................................................... 4

FIGURE 2: DW1000 FRAME STRUCTURE ......................................................................................................................... 5

FIGURE 3: REGULATORY TRANSMIT POWER MEASUREMENT WINDOW – LONG FRAMES .............................................................. 6

FIGURE 4: REGULATORY TRANSMIT POWER MEASUREMENT WINDOW – SHORT FRAMES ............................................................ 6

FIGURE 5: FRAME DURATION LESS THAN MEASUREMENT WINDOW ........................................................................................ 8

FIGURE 6: OPERATION OF THE PRINCIPLE .......................................................................................................................... 8

FIGURE 7: CALIBRATION WITH FRAMES SHORTER THAN 1 MS ................................................................................................ 9

FIGURE 8: RELATIONSHIP BETWEEN FRAME DURATION AND ADDITIONAL TRANSMIT POWER........................................................ 9

FIGURE 9: TRANSMITTER POWER CONTROL REGISTER ........................................................................................................ 11

FIGURE 10: STRUCTURE OF THE 8-BIT TRANSMIT POWER CONTROL BYTE .............................................................................. 12

FIGURE 11: TRANSMIT POWER CONTROL REGISTER IN MANUAL MODE OF OPERATION ............................................................. 13

FIGURE 12: TIME DOMAIN PLOT OF FRAME SHOWING INCREASED POWER IN PREAMBLE AND PAYLOAD PORTIONS OF THE FRAME ..... 14

FIGURE 13: DECISION TREE FOR TRANSMIT POWER CALIBRATION IN MANUAL MODE ............................................................ 15

FIGURE 14: THE FOUR FRAME-DURATION “BINS” ............................................................................................................. 17

FIGURE 15: TRANSMIT POWER CONTROL REGISTER FOR FRAMES WITH DURATION > 500µS ...................................................... 18

FIGURE 16: TRANSMIT POWER CONTROL REGISTER FOR FRAMES WITH DURATION BETWEEN 250 µS & 500 µS ............................ 18

FIGURE 17: TRANSMIT POWER CONTROL REGISTER FOR FRAMES WITH DURATION BETWEEN 125 µS & 250 µS ............................ 18

FIGURE 18: TRANSMIT POWER CONTROL REGISTER FOR FRAMES WITH DURATION LESS THAN 125 µS ......................................... 19

FIGURE 19: SPECTRUM OF CORRECTLY CALIBRATED TRANSMITTER AT DATA RATE OF 6.8 MB/S WITH PRF16 AND NO BOOST APPLIED

...................................................................................................................................................................... 20

FIGURE 20: TRANSMITTING ONE FRAME PER MILLISECOND ................................................................................................ 21

FIGURE 21: SPECTRUM OF CORRECTLY CALIBRATED TRANSMITTER AT 6.8 MB/S DATA RATE WITH PRF16 AND 7 DB BOOST APPLIED 21

FIGURE 22: VARIATION OF TRANSMIT POWER OVER VOLTAGE AND TEMPERATURE .................................................................. 23

FIGURE 23: TRANSMIT POWER COMPENSATION SCHEME OVER TEMPERATURE & VOLTAGE ....................................................... 26

FIGURE 24: EXAMPLE OF PEAK POWER MARGIN WHEN PHR MEAN LIMIT SET TO -41.3 DBM / MHZ ......................................... 29

APS023: APPLICATION NOTE

AP-Transmit-Power-Calibration-and-Management-1.0

Page 4

1 INTRODUCTION

1.1 Overview

This application note deals with the whole area of the power of the RF signal transmitted by the

DW1000 / DWM1000: -

 What does it mean?

 Why is it important?

 How to calibrate it

 How to measure it

 How to use DW1000 features such as SMARTTX POWER to optimize it

1.2 What do we mean by transmit power?

It is important that we understand and define “transmit power” before we go any further.

Transmit power is generally used to refer to the signal power radiated from an antenna into the

surrounding environment. It can also refer to the signal power output from the DW1000 or at any

point in the chain between the DW1000 and the product’s antenna.

You should pay particular attention to the definition of transmit power in data sheets / manuals / test

specifications so that you understand exactly what is being referred to.

Figure 1: Transmit power at various different points in the signal path

Transmit power is generally measured in dBm; i.e. power expressed in dB relative to 1 mW. The

bandwidth over which the power is measured is very important so measurements are often quoted as

dBm / x MHz where x defines the bandwidth over which the power is measured.

For example, an ideal signal transmitted at -41.3 dBm / MHz into a 500 MHz wide channel is

equivalent to -14.3 dBm / 500 MHz. You should pay careful attention to the measurement bandwidth

to understand exactly what is being referred to.

This note uses the terms transmit power and transmitted power interchangeably throughout and

generally refers to signal power transmitted from a product’s antenna unless otherwise stated.

1.3 The importance of transmit power to link budget

The signal power that arrives at a receiver depends on a number of factors as seen by examining

RF Signal path inside productDW1000

Transmit

power at RF

output of

DW1000

Transmit

power just

prior to your

product’s

antenna

Transmit

power

radiated from

your

product’s

antenna

RF_P

RF_N

APS023: APPLICATION NOTE

AP-Transmit-Power-Calibration-and-Management-1.0

Page 5

Friis’ path loss formula: -

[dBm] = P

[dBm] + G [dB] – L[dB] - 20 log

(4πf

d / c)

Where: -

 P

is the received signal power;

 P

is the transmitted power from the DW1000 (note the definition here)

 G includes the antenna gains of the transmitting and receiving antennas, as well as any other

gain from external amplifiers.

 L includes any PCB, cable, connector and other losses in the system

 c is the speed of light, 299792458 m/s;

 f

is the center frequency of the channel used, expressed in Hertz;

 d is the distance in meters between the transmitter and receiver.

Provided P

is greater than the receiver sensitivity, the receiver will receive the signal correctly.

So, the power of the received signal level directly relates to the transmitted power. For each

additional dB of power transmitted by the DW1000 the power of the received signal increases by that

same amount.

1.4 The DW1000 frame structure

Before discussing transmit power any further we need to turn our attention to the DW1000 frame

structure illustrated in Figure 2 below.

Figure 2: DW1000 frame structure

[1] and [2] give further details but, in summary, each frame consists of three distinct parts: -

 The preamble followed by the start of frame delimiter (SFD) indicating the end of the

preamble sequence

 The PHY header (PHR)

 The payload or data portion

For the purposes of transmit power adjustment and calibration it is not necessary to know the detailed

functionality of each of these components. It is important to know that the modulation scheme applied

to the PHR is different to that applied to the Preamble / SFD and the payload portions of the frame.

The different modulation schemes used in the different parts of the frame have different peak to

average transmit power ratios. The PHR has a higher peak to average transmit power ratio than the

other two regions of the frame. This means that the mean transmit power setting of the PHR has the

most significant impact on the peak transmit power of the frame. This has important implications

when we are calibrating the transmit power and in particular when we come to exploit certain

characteristics of the power measurement process to allow us increase transmit power in certain

situations.

PREAMBLE PAYLOADPHR

64 to 4096 symbols 19 bits 127 Bytes

SFD

8 or 64 symbols

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