Preface xix
Acknowledgement xxi
1 Introduction 1
1.1 Wireless Connectivity Alternatives 1
1.2 Goals 2
1.3 The Fundamental Problem 3
1.4 Audience 4
1.5 Recommended Reading 5
1.6 Can One Size Fit All? 6
1.7 Hardware History 6
1.8 On-the-move Connectivity Problems 7
1.9 Reference Implementations 8
1.10 Reference Microcontroller/OS Platform 9
1.11 Reference Cellular Communication Modules (CCMs) Family 11
1.12 A Few Words on Advice, Practices, and Efficiency 13
1.12.1 Best Practice or Good Practice 14
1.12.2 Efficiency Is a Large Umbrella 14
1.12.2.1 Spatial and Temporal Efficiency 14
1.12.2.2 Data Efficiency 15
1.12.2.3 Developmental Efficiency 17
1.13 3G, 4G, 5G, and 6G 17
2 Platforms, Tools, and Debugging 19
2.1 Importance of Toolchain Selection 19
2.2 An Expanded View of the Tool Chain 21
2.3 Computing/OS Platforms 21
2.4 Programming Language Choices 23
2.5 Running the Same Code on Development Computer and IoT Device 23
2.6 Running IoT Connectivity Code in a Debugger 24
3 Cellular Network Basics 27
3.1 Standards 27
3.2 What Do Cellular Networks Do? 28
3.3 Are Cellular Networks Wireless? 29
3.4 What Is a Cell? What Is a Sector? 30
3.5 Omnidirectional Cellular Coverage 33
3.6 Cell Towers 34
3.7 How Are Cellular Networks Identified? 37
3.8 How Are IoT Devices Identified? 39
3.9 eNodeB IDs and Cell # 40
3.10 Tracking Areas and Paging 40
3.11 Frequency and Modulation 42
3.11.1 Modulation 43
3.11.1.1 Radio Telegraphy 43
3.11.1.2 Amplitude Modulation (AM Radio) 44
3.11.1.3 Frequency Modulation (FM Radio) 45
3.11.1.4 Phase Modulation 47
3.12 Spectral Efficiency 48
3.13 Error Detection 49
3.13.1 Luhn Algorithm 50
3.14 Error Correction 52
3.15 LTE Modulation Techniques 54
3.15.1 Binary Phase Shift Keying (BPSK) 56
3.15.2 Quadrature Phase Shift Keying (QPSK) 57
3.15.3 Quadrature Amplitude Modulation (QAM) 57
3.16 Bandwidth and Latency 57
3.17 Range 58
3.18 Frequency Bands 59
3.18.1 Frequency Affects Range 60
3.19 Radio Access Technologies (RAT) and Categories 61
3.20 SIM Cards 63
3.21 What Happens When a Cellular Modem Switches On? 64
3.21.1 Network Selection, Cell Selection, Camping, and Cell Reselection 64
3.21.2 Network Registration 65
3.22 Handoff (Also Called Handover) 67
3.22.1 Maintaining Connectivity 67
3.22.2 Load Balancing 69
3.23 Multiple Access 70
3.24 Timing Advance 70
3.24.1 Why Is Timing Advance Useful? 73
3.24.2 How Accurate Are Distance Estimates Using Timing Advance? 73
3.24.3 Timing Advance Band Depth and Maximum Range 77
3.25 Expressing Power 77
4 SIM/USIM Card Basics 81
4.1 Mobile Virtual Network Operators (MVNOs) 81
4.2 Size 82
4.3 Native Versus Multi-SIMs or MNO Versus MVNO 84
4.4 Home Versus Roaming Access 85
4.5 SIM Factors Affecting Price and Coverage 86
4.5.1 How Much Do SIM Cards Cost? 88
4.5.2 Is There a Monthly Activation Fee? 88
4.5.3 Are There Fees for Activating and/or Deactivating SIM Cards? 88
4.5.4 How Much Does Data Cost? 88
4.5.5 Is the Monthly Data "Pooled"? 89
4.5.6 Are There Fees for Deactivated (but Not Terminated) SIMs Cards? 90
4.5.7 Is There a Not-yet-activated Fee? 90
4.6 Text Messages (SMS) 91
4.7 Usage Limits 91
4.8 Firewalls 92
4.9 Replacing SIMs and/or Network Providers 94
4.10 Access Point Name (APN) 96
5 Verify Cellular Connectivity 97
5.1 Preparation 98
5.1.1 Adequate Power 98
5.1.2 Activated SIM Card 100
5.1.3 Base Station in Range 100
5.1.4 SIM Card Authorization 100
5.1.5 Band Configuration 100
5.1.6 RAT Configuration 101
5.1.7 Automatic Registration 101
5.2 Try to Auto-register 101
5.3 What Can Go Wrong? 102
5.3.1 Operating System Interference 102
5.3.2 Communicating with Modem 103
5.3.3 Malformed AT Commands 103
5.3.4 Parsing Responses to AT Commands 103
5.3.5 Timing Problems 104
5.3.6 Unset or Incorrect Access Point Name (APN) 107
5.3.6.1 Pitfall: Failing to Explicitly Set the APN 107
5.4 Modem Configuration for Auto-registration 108
6 Let's Move Some Data 111
6.1 Low-level Sockets or High-level Protocols 112
6.2 Verify ServerServer Is Running 116
6.3 Verify EchoServer Is Running 117
6.4 USB or UART? 117
6.4.1 Pitfall: USB Device Names Are Not Fixed and Should Not Be Hard Coded 118
6.5 AT Commands-A Troubled Past 119
6.6 Unsolicited Response Codes (URCs) 120
6.7 A Handy Modem Program 123
6.8 AT Commands Manuals 130
6.9 Communicating with the Cellular Modem 131
6.10 Getting EchoServer Information from ServerServer 134
6.10.1 Before Step 1: Enable Unsolicited Response Codes (URCs) 135
6.10.2 Step 1: Configure PDP Context for HTTP GET 136
6.10.3 Step 2: Configure a PDP Context 136
6.10.3.1 Test Commands 137
6.10.3.2 Read Commands 137
6.10.3.3 Write Commands 137
6.10.4 Step 3: Activate the PDP Context 139
6.10.5 Step 4: Allow/Disallow Response Header for HTTP GET 140
6.10.6 Step 5: Set HTTP(S) URL 141
6.10.7 Step 6: Send HTTP(S) GET Request 141
6.10.8 Step 7: Read HTTP(S) Response 142
6.10.9 After Step 7: Deactivate the PDP Context 143
6.10.10 Using Modem to Interact with ServerServer 143
6.11 Bouncing Data Off EchoServer 145
6.11.1 Before Step 1: Enable Unsolicited Response Codes (URCs) 145
6.11.2 Step 4: Open a TCP Client Socket Connection 146
6.11.3 Step 5: Send Mixed-case Text to EchoServer 146
6.11.4 Step 6: Read (Uppercase) Response from EchoServer 148
6.11.5 Step 7: Close TCP Client Socket Connection 151
6.11.6 Step 8: Deactivate PDP Context 151
6.12 No Problems Is Bad Luck 151
7 Cellular Connectivity Regions 153
7.1 How Geography, Topology, and Population Density Affect Connectivity 154
7.1.1 Geography and Topology 154
7.1.2 Population Density 154
7.2 Region Categories 156
7.2.1 Rural 156
7.2.2 Rural Town 156
7.2.3 Flat Farmland/Flat Arid 156
7.2.4 Mountainous 157
7.2.5 Suburban 157
7.2.6 Dense City 157
7.2.7 Interstate Highway 157
7.2.8 Uninhabited 158
8 Cellular Communication Modules (CCMs) 159
8.1 CCM Worldwide Market Share 162
8.2 Frequency Band Usage 162
8.3 Protocol Implementation 164
8.4 Similarities and Differences Across CCMs 165
8.4.1 Single or Dual AT Command Channels 165
8.4.2 Different AT Command Sets 166
8.4.3 Different Response Times for Similar or Identical Commands 167
8.4.4 Differing Response Formats 167
8.4.5 Differing Responses for Compound Statements 167
8.4.6 Different Timing Requirements 168
8.4.7 AT Commands Are Not Thread-safe 168
8.4.8 Support for Different Protocols 168
8.5 Consider the Whole CCM Family 169
8.6 CCM Firmware Bugs 169
8.7 CCMs Are a Lot Like Sensors: Imprecise and Not Entirely Reliable 170
9 AT Commands (A New Approach) 171
9.1 Purpose of AT Commands 171
9.2 Problems of AT Commands 173
9.2.1 Maximum Response Time for an AT Command 174
9.3 Traditional Solution to Executing AT Commands and Extracting Responses 175
9.4 Command Independent Processing (CIP) 179
9.4.1 The Central Observation Underlying CIP 180
9.4.2 Fundamental Elements of CIP 181
9.4.2.1 AtParams 181
9.4.2.2 AtCommand 181
9.4.3 AT Commands in CIP 182
9.4.3.1 Step 1: Define a Name for a Command 183
9.4.3.2 Step 2: Create a Set of Parameters for Each Command 183
9.4.3.3 Step 3: Store the Command Name and AtParams Object in a Map 184
9.4.3.4 Step 4: Create a Command Object 185
9.4.3.5 Step 5: Pass Arguments to the Command Object (if Necessary) 185
9.4.3.6 Step 6: Perform the Command 185
9.4.3.7 Step 7: Verify Success or Failure 186
9.4.3.8 Step 8: Extract Response Information 187
9.4.3.9 AT Commands with Parameters 192
9.4.3.10 Timing Out 194
9.4.4 Using CIP Across CCM Families and Across Manufacturers 196
10 CIP Design and Details 197
10.1 Pseudocode Conventions 198
10.1.1 Identifier Names 198
10.1.2 Angle Brackets 198
10.1.3 Constructors 199
10.1.4 Dot Operator 199
10.1.5 Unified Modeling Language (UML) 199
10.2 A Note on Objected-orientation and Threads 199
10.3 AT Command Basics 200
10.3.1 Echoing 200
10.3.2 Enable/Disable Response Codes 201
10.3.3 Short or Long Response Codes 201
10.3.4 Line Terminators 201
10.3.5 Housekeeping 201
10.4 Categories of Responses to AT Commands 202
10.4.1 Ok_only 203
10.4.2 Text_ok 203
10.4.3 After_colon 203
10.4.4 Ok_plus_after_colon 204
10.4.5 MULTI_RECEIVE, MULTI_SEND, and Multi_after_colon 205
10.5 Details of Command Independent Processing (CIP) 205
10.5.1 AtStep Purpose 205
10.5.2 AtStep Attributes 207
10.6 A "Factory Method" for Creating AtCommand Objects 208
10.7 Performing AT Commands 210
10.7.1 Why AT Commands Fail 212
10.7.2 Timing Out 212
10.7.3 Details of the Execute Method 217
10.7.4 Response Length 219
10.7.5 Hardware Timing 220
10.7.6 Combining Parameter Settings-Method Chaining 221
10.7.7 Assessing Success and Multiple Tries 221
10.7.8 Multi-line AT Commands-AtStep 223
10.7.9 A Second Example with Regular Expressions 225
10.7.10 Integrating AtStep into the Execute Methods 227
10.8 AT Commands for Multiple Modems 228
10.8.1 The Simplest Case 230
10.8.2 Connectors 231
10.8.2.1 All Connectors Are Also Threads 234
10.8.2.2 Connectors Are Created Using a Factory Method 235
10.8.2.3 Custom AT Commands Are Added in Static Blocks of Connectors 236
10.8.2.4 Where to Override Methods or Parts of Methods 237
10.8.3 An Asymmetrical Case-AtParamsNoOp 239
11 Geographical Coverage, Signal Strength, and Quality 243
11.1 Radio Access Technologies (RATs) 243
11.2 Cellular Network Coverage Maps 245
11.3 Signal Strength and Quality: RSSI, RSRP, RSRQ , SINR 246
11.3.1 RSSI and RSRP 247
11.3.2 Rsrq 249
11.3.3 Sinr 249
11.3.4 Using Modem to Report Signal Strength and Quality 250
11.4 Antenna Selection and Performance 251
11.4.1 Antenna Size 253
11.4.2 Passive Versus Active Antennas 255
11.4.3 Antenna Connectors 256
11.4.4 Antenna Placement 257
11.5 Antenna Testing 258
11.6 Geography and Signal Strength Must Be Considered Together 259
12 Network Selection and Registration 261
12.1 Network Registration 261
12.2 Radio Access Technology (RAT) 262
12.3 Network Frequency Band Selection 264
12.4 PLMN Selection 266
12.4.1 Manual PLMN Selection 267
12.4.2 Automatic PLMN Selection 267
12.5 How to Create Your Own User Preference List 268
12.5.1 Reading the UPL and OPL 269
12.5.2 Modifying the UPL 271
12.6 Once a PLMN Is Auto-selected, Is It Always Selected? 273
12.7 Forcing the CCM Back to the PLMN Preference List 274
12.8 A Mysterious PLMN Selection Behavior 275
12.9 Troubleshooting Registration Problems 276
12.9.1 New Modem, Never Registered 276
12.9.2 Old Modem, Previously Registered 278
12.10 Anomalous Behavior 278
13 Communication Protocols TCP, UDP, and PPP 281
13.1 Internet Protocol 281
13.2 Transmission Control Protocol (TCP) 283
13.3 Considering Data Consumption 285
13.4 User Datagram Protocol (UDP) 285
13.5 TCP Pros and Cons 287
13.6 Point-to-point Protocol (PPP) 290
13.7 AT Commands for Data Transfer Are Completely Unstandardized 292
13.8 PPP on Linux 292
13.8.1 Debugging PPP 295
13.9 Alternatives to PPP 298
14 Thin Air 301
14.1 A Most Dramatic Case 302
14.1.1 Watching the Server 304
14.1.2 Packets Not Getting to the Server 305
14.2 What Was Going On? Thin Air 306
14.3 Why Did Thin Air Persist Over Hundreds of Miles? 308
14.4 How to Detect Thin Air 312
14.5 What to Do About Thin Air 313
14.6 Minimizing the Size of a Thin Air Region 313
14.7 A Hybrid UDP Protocol for Detecting Thin Air 314
14.8 Reducing (or Eliminating) Thin Air by PLMN or Band Selection 315
14.8.1 The Most Direct Approach 316
14.9 Putting the Hybrid Protocol to Second Use 322
15 Time and Location (GNSS) 325
15.1 Clarifying Terminology 325
15.2 Time 326
15.3 Location 328
15.4 Obtaining Time Information 331
15.4.1 Real-time Clock 331
15.4.2 Cellular Modem 332
15.4.2.1 Additional Configuration 333
15.4.2.2 Local Time or UTC 333
15.4.2.3 Daylight Saving Time 335
15.4.2.4 Using Modem to Read the Clock 336
15.4.3 Get Time from a GNSS Receiver 336
15.4.4 Get Time from a Server 337
15.5 Sources of Location Information 337
15.6 Pros and Cons of CCM's GNSS Receiver Versus Stand-alone GNSS Receiver 338
15.7 Cold Start, Warm Start, Hot Start 339
15.8 Assisted GPS 340
15.9 GNSS Antenna Selection 340
15.10 GNSS Receiver Placement 341
15.11 GNSS Accuracy and Precision 342
15.11.1 Improving Accuracy 345
15.12 NMEA Sentences 346
15.12.1 Using Modem to Read GNSS Sentences 347
15.13 Three Ways to Obtain Location Information 348
15.13.1 Simple AT Command Request for Location 348
15.13.2 Read Streaming Data from gpsd 350
15.13.2.1 For a Stand-alone GNSS Receiver 350
15.13.2.2 For a CCM's GNSS Receiver 351
15.13.3 Read Streaming Data Directly from CCM's GNSS receiver 355
15.14 Understanding gpsd JSON Output 356
15.15 Writing Software to Capture and Process gpsd Output 358
15.16 GNSS Data Streamed from a CCM 359
15.17 Nmea 0183 359
15.17.1 Talker Sentence Format 360
15.17.1.1 GSA Sentence Format 361
15.17.1.2 RMC Sentence Format 362
15.17.1.3 GSV Sentence Format 362
15.17.2 NMEA Checksums 364
15.17.3 CCM GNSS Receivers Only Stream Some NMEA Sentences 365
15.18 Some Additional gpsd Utilities 366
16 Establishing and Maintaining a Cellular Connection 369
16.1 Modem Selection 370
16.2 Foundational Tasks 371
16.2.1 State 1: Detecting CCM 373
16.2.1.1 Using Modem to Detect a CCM 373
16.2.2 State 2a: Initializing CMM 374
16.2.2.1 Viewing Modem's Initializations 374
16.2.3 State 2b: Waiting to Retry 376
16.2.4 State 3: Set Mobile Network Operator 376
16.2.5 State 4: Checking Registration Status 376
16.2.5.1 Using Modem to Check Registration Status 377
16.2.6 State 5: Connecting 378
16.2.7 State 6: Manage Connection 378
17 Sending and Receiving Text Messages (SMS) 379
17.1 Why Send/Receive Text Messages? 380
17.1.1 Need to "Push" Information to an IoT Device 380
17.1.2 Serverless IoT Devices That Interact with End-users 383
17.2 Cost of Text Messaging via Cellular Modem 383
17.3 Application-to-person (A2P) Messaging Is Often Regulated 384
17.4 Overview of Sending/Receiving Text Messages 385
17.5 Sending Text Messages 386
17.5.1 Set the Message Format 386
17.5.2 Set Parameters for Sending 386
17.5.3 Specify the Destination Phone Number and the Text to Send 389
17.5.4 What If Sending an SM Fails? 390
17.5.5 Using Modem to Send a Text Message 390
17.6 Receiving and Reading a Text Message 391
17.6.1 Configure the CCM 392
17.6.1.1 Set the Message Format 392
17.6.1.2 Configure SMS Storage 392
17.6.1.3 Check for a Received Text Message 394
17.6.1.4 Using Modem to List Text Messages 395
17.6.1.5 Delete a Text Message 396
17.6.1.6 Using Modem to Delete a Text Message 396
17.7 SMS with Constrained Devices 397
17.7.1 Set the Message Format 397
17.7.2 Set Parameters for Writing to Mem- 2 397
17.7.3 Specify the Destination Phone Number and Text to Store 397
17.7.4 Send a Text Message Already Stored in Mem- 2 398
17.7.5 Verifying a Text Message Was Sent from Mem- 2 399
17.8 Integrating SMS into CIP 400
18 Power Saving Modes and Techniques 403
18.1 What Are Low-power CCMs (LP-CCMs) 404
18.2 Plenty of Power, Most of the Time 405
18.3 Low-power IoT Devices 407
18.3.1 Microcontroller Energy Consumption 407
18.3.2 Temperature Sensor Energy Consumption 408
18.4 Battery Capacity 408
18.5 Transmitter Power 409
18.6 Legacy (GSM) Power Consumption 410
18.7 Cellular Modem Energy Consumption 413
18.7.1 Additional Energy Consumption 414
18.8 Network Registration States-RRC_CONNECTED and Rrc_idle 414
18.8.1 RRC_CONNECTED (Without DRX) 416
18.8.1.1 Scenario 1-Sending a Location Packet 417
18.8.1.2 Scenario 2-Fetching an Over-the-air Update 418
18.8.2 RRC_IDLE (Without DRX) 420
18.8.3 Discontinuous Reception (DRX) 422
18.8.3.1 Discontinuous Reception in RRC_IDLE (iDRX) 423
18.8.3.2 Discontinuous Reception in RRC_CONNECTED (cDRX) 424
18.8.4 Registration Characteristics Summary 426
18.9 Latency 427
18.10 Using Low-power CCM-Cat M and NB-IoT and Cat 1 bis 429
18.11 Power Saving Mode (PSM) 431
18.11.1 How to Enable PSM 434
18.11.1.1 Using Modem to Enter PSM 436
18.11.2 Verifying PSM and Possible Problems or Surprises 437
18.11.2.1 Using Modem to Check PSM Status 439
18.11.3 Actual PSM Cycle Length 439
18.11.4 Exiting PSM 440
18.11.4.1 Using Modem to Exit PSM 441
18.11.5 Sending Data from PSM Inactive 442
18.11.6 PSM Effectiveness 442
18.11.7 Integrating PSM into CIP 443
18.12 Extended Discontinuous Reception (eDRX) 445
18.12.1 How to Enable eDRX 447
18.12.1.1 Using Modem to Enable eDRX 448
18.12.2 Verifying eDRX Cycle Length 449
18.12.2.1 Using Modem to Check eDRX Status 450
18.12.3 Disabling eDRX 451
18.12.3.1 Using Modem to Disable eDRX 451
18.12.4 Integrating eDRX into CIP 451
18.13 When to Use PSM, eDRX, or Both 454
18.14 Don't Trust the Numbers 454
A Unified Modeling Language (UML) Primer 455
A. 1 Assumptions 455
A. 2 UML Syntax 456
A. 3 Visibility (Private, Protected, Public) 457
A. 4 Attribute/Parameter/Method Names and Types 457
A. 5 Class Attributes and Methods 458
A. 6 Aggregation 459
A. 7 Multiplicities 459
A. 8 Inheritance 460
A. 9 Interfaces 460
A. 10 Hidden Attributes 461
A. 11 Layout 462
A. 12 State Diagrams 462
B 3GPP AT Commands Used in This Book 465
C The Modem Utility 469
C. 1 Invoking the Modem Program 470
C. 2 Flags 470
C. 3 Commands 471
Glossary 479
Closing Notes 485
Index 487
