Table of Contents
Table of Contents Chapter 1 – Introduction
1.1 Wireless Connectivity Alternatives
1.2 Goals
1.3 The Fundamental Problem
1.4 Audience
1.5 Recommended Reading
1.6 Can One Size Fit All?
1.7 Hardware History
1.8 On-the-Move Connectivity Problems
1.9 Reference Implementations
1.10 Reference Microcontroller/OS Platform
1.11 Reference Cellular Communication Modules (CCMs) Family
1.12 A Few Words on Advice, Practices and Efficiency
1.12.1 Best Practice or Good Practice
1.12.2 Efficiency Is a Large Umbrella
1.12.2.1 Spatial and Temporal Efficiency
1.12.2.2 Data Efficiency
1.12.2.3 Developmental Efficiency
1.13 3G, 4G, 5G, 6G
Chapter 2 - Platforms, Tools and Debugging
2.1 Importance of Tool-Chain Selection
2.2 An Expanded View of the Tool Chain
2.3 Computing/OS Platforms
2.4 Programming Language Choices
2.5 Running the Same Code on Development Computer and IoT Device
2.6 Running IoT Connectivity Code in a Debugger
Chapter 3 - Cellular Network Basics
3.1 Standards
3.2 What do Cellular Networks do?
3.3 Are Cellular Networks Wireless?
3.4 What is a Cell? What is a Sector?
3.5 Omnidirectional Cellular Coverage
3.6 Cell Towers
3.7 How are Cellular Networks Identified?
3.8 How Are IoT Devices Identified
3.9 eNodeB IDs, and Cell IDs
3.10 Tracking Areas and Paging
3.11 Frequency and Modulation
3.11.1 Modulation
3.11.1.1 Radio Telegraphy
3.11.1.2 Amplitude Modulation (AM Radio)
3.11.1.3 Frequency Modulation (FM Radio)
3.11.1.4 Phase Modulation
3.12 Spectral Efficiency
3.13 Error Detection
3.13.1 Luhn Algorithm
3.14 Error Correction
3.15 LTE Modulation Techniques
3.15.1 Binary Phase Shift Keying (BPSK)
3.15.2 Quadrature Phase Shift Keying (QPSK)
3.15.3 Quadrature Amplitude Modulation (QAM)
3.16 Bandwidth and Latency
3.17 Range
3.18 Frequency Bands
3.18.1 Frequency Affects Range
3.19 Radio Access Technologies (RAT) and Categories
3.20 SIM Cards
3.21 What Happens When a Cellular Modem Switches On?
3.21.1 Network Selection, Cell Selection, Camping, and Cell Reselection
3.21.2 Network Registration
3.22 Handoff (also called Handover)
3.22.1 Maintaining Connectivity
3.22.2 Load Balancing
3.23 Sharing the Air
3.24 Timing Advance
3.24.1 Why is Timing Advance Useful?
3.24.2 How Accurate are Distance Estimates Using Timing Advance?
3.24.3 Timing Advance Band Depth and Maximum Range
3.25 Expressing Power
Chapter 4 - SIM Card Basics
4.1 Mobile Virtual Network Operators (MVNOs)
4.2 Size
4.3 Native Versus Multi-SIMs or MNO Versus MVNO
4.4 Home Versus Roaming Access
4.5 SIM Factors Affecting Price and Coverage
4.5.1 How Much Do SIM Cards Cost?
4.5.2 Is there a Monthly Activation Fee?
4.5.3 Are There Fees for Activating and/or Deactivating SIM Cards?
4.5.4 How Much Does Data Cost
4.5.5 Is the Monthly Data FPooled”?
4.5.6 Are There Fees for Deactivated (but not Terminated) SIMS Cards?
4.5.7 Is There a Not-Yet-Activated Fee?
4.6 Text Messages (SMS)
4.7 Usage Limits
4.8 Firewalls
4.9 Replacing SIMs and/or Network Providers
4.10 Access Point Name (APN)
Chapter 5 - Verify Cellular Connectivity
5.1 Preparation
5.1.1 Adequate Power
5.1.2 Activated SIM Card
5.1.3 Base Station in Range
5.1.4 SIM Card Authorization
5.1.5 Band Configuration
5.1.6 RAT Configuration
5.1.7 Automatic Registration
5.2 Try to Auto-Register
5.3 What Can Go Wrong?
5.3.1 Operating System Interference
5.3.2 Communicating With Modem
5.3.3 Malformed AT commands
5.3.4 Parsing Responses to AT Commands
5.3.5 Timing Problems
5.3.6 Unset or Incorrect Access Point Name (APN)
5.4 Modem Configuration for Auto-Registration
Chapter 6 - Let’s Move Some Data
6.1 Low-level Sockets or High Level Protocols
6.2 Verify ServerServer is Running
6.3 Verify EchoServer is Running
6.4 USB or UART?
6.5 AT Commands — a Troubled Past
6.6 Unsolicited Response Codes (URCs)
6.7 A Handy Modem Program
6.8 AT Commands Manuals
6.9 Communicating with the Cellular Modem
6.10 Getting EchoServer Information from ServerServer
6.11 Bouncing Data off EchoServer
6.12 No Problems is Bad Luck
Chapter 7 - Cellular Connectivity Regions
7.1 How Geography, Topology and Population Density Affect Connectivity
7.1.1 Geography and Topology
7.1.2 Population Density
7.2 Region Categories
7.2.1 Rural
7.2.2 Rural Town
7.2.3 Flat Farmland/Flat Arid
7.2.4 Mountainous
7.2.5 Suburban
7.2.6 Dense City
7.2.7 Interstate Highway
7.2.8 Uninhabited
Chapter 8 - Cellular Communication Modules (CCMs)
8.1 CCM Worldwide Market Share
8.2 Frequency Band Usage
8.3 Protocol Implementation
8.4 Similarities and Differences Across CCMs
8.4.1 Single or Dual AT Command Channels
8.4.2 Different AT command Sets
8.4.3 Different Response Times for Similar or Identical Commands
8.4.4 Differing Response Formats
8.4.5 Differing Responses For Compound Statements
8.4.6 Different Timing Requirements
8.4.7 AT Command are not Thread-Safe
8.4.8 Support For Different Protocols
8.5 Consider the Whole CCM Family
8.6 CCM Firmware Bugs
8.7 CCMs, Are a Lot Like Sensors: Imprecise and not Entirely Reliable
Chapter 9 - AT Commands (a New Approach)
9.1 Purpose of AT Commands
9.2 Problems of AT Commands
9.2.1 Maximum Response Time for an AT Command
9.3 Traditional Solution to Executing AT Commands and Extracting Responses
9.4 Command Independent Processing (CIP)
9.4.1 The Central Observation Underlying CIP
9.4.2 Fundamental Elements of CIP
9.4.2.1 AtParams
9.4.2.2 AtCommand
9.4.3 AT Command in CIP
9.4.3.1 Step 1 – Define a Name for a Command
9.4.3.2 Step 2 - Create a Set of Parameters for Each Command
9.4.3.3 Step 3 - Store the Command Name and AtParams Object in a Map
9.4.3.4 Step 4 - Create a Command Object
9.4.3.5 Step 5 - Pass Arguments to the Command Object (if necessary)
9.4.3.6 Step 6 - Perform the Command
9.4.3.7 Step 7 – Verify Success or Failure
9.4.3.8 Step 8 - Extract Response Information
9.4.3.9 AT Commands with Parameters
9.4.3.10 Timing Out
9.4.4 Using CIP Across CCM Families and Across Manufacturers
Chapter 10 - CIP Design and Details
10.1 Pseudocode Conventions
10.1.1 Identifier Names
10.1.2 Angle Brackets
10.1.3 Constructors
10.1.4 Dot Operator
10.1.5 Unified Modeling Language (UML)
10.2 A Note on Objected-Orientation and Threads
10.3 AT Command Basics
10.3.1 Echoing
10.3.2 Enable/Disable Response Codes
10.3.3 Short or Long Response Codes
10.3.4 Line Terminators
10.3.5 Housekeeping
10.4 Categories of Responses to AT Commands
10.4.1 OK_ONLY
10.4.2 TEXT_OK
10.4.3 AFTER_COLON
10.4.3 OK_PLUS_AFTER_COLON
10.4.5 MULTI_RECEIVE
10.4.6 MULTI_SEND
10.4.7 MULTI_AFTER_COLON
10.5 Details of Command Independent Processing (CIP)
10.5.1 AtStep Purpose
10.5.2 AtStep Attributes
10.6 A “Factory Method” for Creating AtCommand Objects
10.7 Performing AT Commands
10.7.1 Why AT Commands Fail
10.7.2 Timing Out
10.7.3 Details of the Execute Method
10.7.4 Response Length
10.7.5 Hardware Timing
10.7.6 Combining Parameter Settings - Method Chaining
10.7.7 Assessing Success, and Multiple Tries
10.7.8 Multi-Line AT Commands - AtStep
10.7.9 A Second Example With a Regular Expressions
10.7.10 Integrating AtStep Into the execute Methods
10.8 AT Commands For Multiple Modems
10.8.1 The Simplest Case
10.8.2 Connectors
10.13.2.1 All Connectors Are Also Threads
10.13.2.2 Connectors Are Created Using a Factory Method
10.13.2.3 Custom AT Commands are Added In Static Blocks of Connectors
10.13.2.4 Where to Override Methods or Parts of Methods
10.8.3 An Asymmetrical Case – AtParamsNoOp
Chapter 11 - Geographical Coverage, Signal Strength and Quality
11.1 Radio Technologies (RATs)
11.2 Cellular Network Coverage Maps
11.3 Signal Strength and Quality: RSSI, RSRP, RSRQ, SINR
11.3.1 RSSI and RSRP
11.3.2 RSRQ
11.3.3 SINR
11.3.4 Using Modem For to Report Signal Strength and Quality
11.4 Antenna Selection and Performance
11.4.1 Antenna Size
11.4.2 Passive Versus Active Antennas
11.4.3 Antenna Connectors
11.4.4 Antenna Placement
11.5 Antenna Testing
11.6 Geography and Signal Strength Must Be Considered Together
Chapter 12 - Network Selection and Registration
12.1 Network Registration
12.2 Radio Access Technology (RAT)
12.3 Network Frequency Band Selection
12.4 PLMN Selection
12.4.1 Manual PLMN Selection
12.4.2 Automatic PLMN Selection
12.5 How to Create Your Own User Preference List
12.5.1 Reading the UPL and OPL
12.5.2 Modifying the UPL
12.6 Once a PLMN is Auto-Selected, Is it Always Selected?
12.7 Forcing the CCM Back to the PLMN Preference List
12.8 A Mysterious PLMN Selection Behavior
12.9 Troubleshooting Registration Problems
12.9.1 New Modem, Never Registered
12.9.2 Old Modem, Previously Registered
12.10 Anomalous Behavior
Chapter 13 - Communication Protocols: TCP, UDP, PPP and Hybrids
13.1 Internet Protocol (IP)
13.2 Transmission Control Protocol (TCP)
13.3 Considering Data Consumption
13.4 User Datagram Protocol (UDP)
13.5 TCP Pros and Cons
13.6 Point-to-Point Protocol (PPP)
13.7 AT Commands for Data Transfer are Completely Unstandardized
13.8 PPP on Linux
13.8.1 Debugging PPP
13.9 Alternatives to PPP
Chapter 14 - Thin Air
14.1 A Most Dramatic Case
14.1.1 Watching the Server
14.1.2 Packets Not Getting to the Server
14.2 What Was Going On? Thin Air
14.3 Why Did Thin Air Persist Over Hundreds of Miles?
14.4 How to Detect Thin Air
14.5 What to Do About Thin Air
14.6 Minimizing the Size of a Thin Air Region
14.7 A Hybrid UDP Protocol For Detecting Thin Air
14.8 Reducing (or Eliminating) Thin Air by PLMN or Band Selection
14.8.1 The Most Direct Approach
14.9 Putting the Hybrid Protocol to a Second Use
Chapter 15 - Time and Location (GNSS)
15.1 Clarifying Terminology
15.2 Time
15.3 Location
15.4 Obtaining Time information
15.4.1 Real-Time Clock (RTC)
15.4.2 Cellular Modem
15.4.2.1 Additional Configuration
15.4.2.2 Local Time or UTC
15.4.2.3 Daylight Saving Time
15.4.2.4 Using Modem to Read the Clock
15.4.3 Get Time From a GNSS Receiver
15.4.4 Get Time From a Server
15.5 Sources of Location Information
15.6 Pros and Cons of CCM’s GNSS Receiver Versus Stand-Alone GNSS Receiver
15.7 Cold Start, Warm Start, Hot Start
15.8 Assisted GPS (A-GPS)
15.9 GNSS Antenna Selection
15.10 GNSS Receiver Placement
15.11 GNSS Accuracy and Precision
15.11.1 Improving Accuracy
15.12 NMEA Sentences
15.12.1 Using Modem to Read GNSS Sentences
15.13 Three Ways to Obtain Location Information
15.13.1 Simple AT Command Request for Location
15.13.2 Read Streaming Data From gpsd Daemon
15.13.2.1 For a Stand-Alone GNSS Receiver
15.13.2.2 For a CCM’s GNSS Receiver
15.13.3 Read Streaming Data Directly From CCM’s GNSS receiver
15.14 Understanding gpsd JSON Output
15.15 Writing Software To Capture and Process gpsd Output
15.16 GNSS Data Streamed From a CCM
15.17 NMEA 0183
15.17.1 Talker Sentence Format
15.17.1.2 RMC Sentence Format
15.17.1.3 GSV Sentence Format
15.17.2 NMEA Checksums
15.17.3 CCM GNSS Receivers Only Stream Some NMEA Sentences
15.18 Some Additional gpsd Utilities
15.19 Setting System Time From Cellular Network, GNSS Time, or Server
Chapter 16 - Establishing and Maintaining a Cellular Connection
16.1 Modem Selection
16.2 Foundational Tasks
16.2.1 State 1 - Detecting CCM
16.2.1.1 Using Modem to Detect a CCM
16.2.2 State 2a - Initializing CMM
16.2.2.1 Viewing Modem’s Initializations
16.2.3 State 2b - Waiting to Retry
16.2.4 State 3 - Set MNO
16.2.5 State 4 - Checking Registration Status
16.2.5.1 Using Modem to Check Registration Status
16.2.6 State 5 - Connecting
16.2.7 State 6 - Manage Connection
Chapter 17 - Sending and Receiving Text Messages (SMS)
17.1 Why Send/Receive Text Messages?
17.1.1 Need to “Push” Information to an IoT Device
17.1.2 Serverless IoT Devices That Interact With End-Users
17.2 Cost of Text Messaging via Cellular Modem
17.3 Application-to-Person (A2P) Messaging is Often Regulated
17.4 Overview of Sending/Receiving Text Messages
17.5 Sending Text Messages
17.5.1 Set the Message Format
17.5.2 Set Parameters for Sending
17.5.3 Specify the Destination Phone Number and the Text to Send
17.5.4 What if Sending an SM Fails?
17.5.5 Using Modem to Send a Text Message
17.6 Receiving and Reading a Text Messages
17.6.1 Configure the CCM
17.6.1.1 Set the Message Format
17.6.1.2 Configure SMS Storage
Pitfall: Don’t Forget to Align Memory Blocks
17.6.1.3 Check for a Received Text Messages
17.6.1.4 Using Modem to List Text Messages
17.6.1.5 Delete a Text Messages
17.6.1.6 Using Modem to Delete a Text Message
17.7 SMS with Constrained Devices
17.7.1 Set the Message Format
17.7.2 Set Parameters for Writing to mem-2
17.7.3 Specify the Destination Phone Number and Text to Store
17.7.4 Send a Text Message Already Stored in mem-2
17.7.5 Verifying a Text Message Was Sent From mem-2
17.8 Integrating SMS into CIP
Chapter 18 - Power Saving Modes and Techniques
18.1 What are Low-Power CCMs (LP-CCMs)
18.2 Plenty of Power, Most of the Time
18.3 Low-Power IoT Devices
18.3.1 Microcontroller Energy Consumption
18.3.2 Temperature Sensor Energy Consumption
18.4 Battery Capacity
18.5 Transmitter Power
18.6 Legacy (GSM) Power Consumption
18.7 Cellular Modem Energy Consumption
18.7.1 Additional Energy Consumption
18.8 Network Registration States – RRC_CONNECTED and RRC_IDLE
18.8.1 RRC_CONNECTED (without DRX)
18.8.1.1 Scenario 1 – Sending a Location Packet
18.8.1.2 Scenario 2 – Fetching an Over the Air Update
18.8.2 RRC_IDLE (without DRX)
18.8.3 Discontinuous Reception (DRX)
18.8.3.1 Discontinuous Reception in RRC_IDLE (iDRX)
18.8.3.2 Discontinuous Reception in RRC_CONNECTED (cDRX)
18.8.4 Registration Characteristics Summary
18.9 Latency
18.10 Using Low-Power CCM – Cat M and NB-IoT and Cat 1 bis
18.11 Power Saving Mode (PSM)
18.11.1 How to Enable PSM
18.11.1.1 Using Modem to Enter PSM
18.11.2 Verifying PSM and Possible Problems or Surprises
18.11.2.1 Using Modem to Check PSM Status
18.11.3 Actual PSM Cycle Length
18.11.4 Exiting PSM
18.11.4.1 Using Modem to Exit PSM
18.11.5 Sending Data From PSM Inactive
18.11.6 PSM Effectiveness
18.11.7 Integrating PSM into CIP
18.12 Extended Discontinuous Reception (eDRX)
18.12.1 How to Enable eDRX
18.12.1.1 Using Modem to Enable eDRX
18.12.2 Verifying eDRX Cycle Length
18.12.2.1 Using Modem to Check eDRX Status
18.12.3 Disabling eDRX
18.12.3.1 Using Modem to Disable eDRX
18.12.4 Integrating eDRX into CIP
18.13 When to Use PSM, eDRX or Both
18.14 Don't Trust the Numbers
Appendix A - A UML Primer
A.1 Assumptions
A.2 UML Syntax
A.3 Visibility (private, protected, public)
A.4 Attribute/Parameter/Method Names and Types
A.5 Class Attributes and Methods
A.6 Aggregation
A.7 Multiplicities
A.8 Inheritance
A.9 Interfaces
A.10 Hidden Attributes
A.11 Layout
Closing Notes
Appendix B - 3GPP AT Commands Used in This Book
Appendix C - The Modem Utility
Glossary
