Comprehensive terminology reference for Automatic Link Establishment and related standards.
MIL-STD-188-141B Appendix A protocol. Uses 8-FSK modulation at 125 baud for automatic link establishment on HF radio. Provides robust calling, scanning, and channel selection.
MIL-STD-188-141C protocol. Enhanced version with higher data rates (up to 8000 bps), better LQA, and advanced features. Not yet implemented in PC-ALE 2.0.
Protocol for automatically establishing HF radio links without operator intervention. Handles frequency selection, calling, handshaking, and channel quality assessment.
Broadcast call to all stations monitoring ALE channels. Uses wildcard addressing (e.g., ***) to reach any listening station.
Short message (up to 90 characters) transmitted during ALE call. Displayed automatically on receiving station. Used for tactical messaging.
MIL-STD-188-141B Appendix C enhancements. Adds data elements (DE fields), CRC protection, slotted responses, and transaction codes to 2G ALE.
64-character subset of ASCII used in ALE words. Includes A-Z, 0-9, space, and 27 special characters. Encoded in 6 bits.
Positive acknowledgment that data was received correctly. In FS-1052, sent as ACK bitmap indicating which blocks were received.
Error control method where receiver requests retransmission of corrupted data. FS-1052 uses selective repeat ARQ.
One-way ARQ mode (FED-STD-1052). Transmitter sends data without waiting for acknowledgments. Used for point-to-multipoint.
Bidirectional ARQ mode (FED-STD-1052). Both stations can send data simultaneously. Not implemented in PC-ALE 2.0.
FED-STD-1052 mode with fixed block size (128 bytes). Simpler than Variable ARQ but less efficient. Not implemented in PC-ALE 2.0.
Federal Standard 1052: HF Radio Data Link Protocol. Defines ARQ modes, frame formats, and error recovery for HF data transmission.
Indicates data was received with errors. In selective repeat ARQ, NAK bitmap specifies which blocks need retransmission.
ARQ mode where only corrupted blocks are retransmitted. Uses bitmap to track which blocks were received correctly. Most efficient ARQ mode.
FED-STD-1052 mode with variable block size (1-1023 bytes). Adaptive to channel conditions. Fully implemented in PC-ALE 2.0 Phase 5.
Modulation used in 2G ALE. Eight tones spaced 125 Hz apart (750-1750 Hz) encode 3 bits per symbol. Symbol rate is 125 baud.
Percentage of bits received incorrectly. Used to measure channel quality. Lower BER indicates better quality.
Symbol rate (symbols per second). For 8-FSK at 125 baud, 3 bits per symbol = 375 bps.
Error detection code appended to data. PC-ALE uses:
- CRC-8 (AQC-ALE): Polynomial 0x07
- CRC-16 (AQC-ALE): Polynomial 0x1021 (CCITT)
- CRC-32 (FS-1052): Polynomial 0x04C11DB7 (FED-STD-1003A)
Error correction added before transmission. 2G ALE uses Golay (24,12) code with 3-bit error correction capability.
Algorithm for frequency analysis. Used in PC-ALE demodulator to detect which of 8 tones is present.
FEC code encoding 12 data bits into 24-bit codeword. Can correct up to 3 bit errors. Used in 2G ALE for robust transmission.
Ratio of signal power to noise power (in dB). Higher SNR indicates better signal quality. Used in LQA calculation.
Radio frequency used for communication. ALE scans multiple channels to find best one. Each channel has associated LQA.
Field in AQC-ALE word containing additional information:
- DE1: Reserved
- DE2: Slot position (0-7)
- DE3: Traffic class (0-15)
- DE4: LQA (0-31)
- DE5-DE8: Reserved
- DE9: Transaction code (0-7)
Time spent listening on each channel during scanning. Default is 200ms. Shorter dwell = faster scanning but more missed calls.
Exchange of messages establishing a link:
- Caller sends TO + FROM + TIS
- Called station responds with TIS
- Caller confirms with TWS
Measurement of channel quality (0-31 scale). Based on SNR and BER. Stored per-channel to guide frequency selection.
Group of stations sharing common address. Net calls reach all members. Example: NET1 includes ALPHA, BRAVO, CHARLIE.
3-bit field in ALE word indicating word type:
000= DATA001= THRU010= TO011= FROM100= TIS (This Is)101= TWS (This Was)110= CMD111= REP
Process of listening to multiple channels sequentially. ALE scanner dwells on each channel, looking for calls.
Transmission of TIS words on multiple channels to measure channel quality. Allows stations to build LQA table.
ALE word identifying a station. Used in handshakes and soundings. Contains station address.
ALE word confirming link establishment. Sent by caller after receiving TIS from called station.
Address pattern using * (match any characters) or ? (match single character). Example: ALF* matches ALFA, ALFRED, ALFONSO.
State machine state where station is transmitting a call (TO + FROM + TIS sequence). Waiting for TIS response.
State where station is responding to incoming call with TIS. Will transition to LINKED if caller sends TWS.
Initial state. Not scanning or calling. Waiting for command.
State where link is established. Can send AMD or transition to data mode. Link quality is known.
State where station is processing incoming ALE words. Parsing word sequence to determine action.
State where station is scanning channels. Listening for calls on each frequency in channel list.
256-bit field (32 bytes) in FS-1052 ACK frame. Each bit indicates whether corresponding sequence number was received correctly.
2-byte short address in FS-1052 control frames. Efficient for frequently-used addresses.
Unit of data transmission in ARQ. In Variable ARQ, block size is configurable (1-1023 bytes).
FS-1052 frame carrying control information (not user data). Four types: T1-T4.
FS-1052 frame carrying user payload. Up to 1023 bytes of data plus header and CRC-32.
Mechanism preventing buffer overflow. FS-1052 uses flow control bit in ACK bitmap to pause transmission.
18-byte long address in FS-1052 control frames. Used for extended addressing or routing.
List of blocks that failed to send or were NAKed. Blocks in queue are retransmitted.
ARQ mechanism where receiver NAKs specific blocks (not entire window). More efficient than go-back-N.
8-bit identifier for each data block (0-255). Wraps around after 255. Used to detect duplicates and order blocks.
Flow control mechanism. Sender can have up to window_size blocks outstanding. Default window size is 16.
FS-1052 control frame: Link setup request. Contains source/destination addresses and mode.
FS-1052 control frame: Link setup confirmation. Acknowledges T1 and confirms link.
FS-1052 control frame: Link termination request. Cleanly closes link.
FS-1052 control frame: Link status. Exchanges state information (not implemented in PC-ALE 2.0).
3-bit AQC-ALE field indicating next action:
- 0: BUSY
- 1: MS_141A (MIL-STD messaging)
- 2: NAK
- 3: ACK
- 4: TERMINATE
- 5: Reserved
- 6: AQC_CMD
- 7: Reserved
4-bit AQC-ALE field indicating data type:
- 0: Clear voice
- 1-4: Digital voice modes
- 8: ALE messaging
- 9-11: Data modes (PSK, 39-tone, HF email)
- 15: Emergency
Maximum number of unacknowledged blocks allowed in flight. Larger windows improve throughput but require more memory.
Function pointer registered with PC-ALE libraries. Called when events occur (word received, link established, data received).
Software written from specifications without reference to existing code. Avoids copyright issues. PC-ALE 2.0 is 100% clean-room.
Code that runs on multiple operating systems without modification. PC-ALE 2.0 supports Windows, Linux, macOS.
Component extracting digital data from analog signal. PC-ALE uses FFT demodulator for 8-FSK.
Error correction technique. Golay decoder uses triple redundancy: transmit 3 copies, decode using majority rule.
Component converting digital data to analog signal. PC-ALE uses tone generator for 8-FSK.
Development stage in PC-ALE project:
- Phase 1: FSK modem (FFT, Golay, tones)
- Phase 2: Protocol layer (words, messages, addressing)
- Phase 3: Link state machine (scanning, calling, LQA)
- Phase 4: AQC-ALE extensions (DE, CRC, slots)
- Phase 5: FS-1052 ARQ (selective repeat, CRC-32)
- Phase 6: Audio I/O integration (planned)
Unit of modulation. In 8-FSK, one symbol encodes 3 bits. Symbol duration is 1/125 second = 8ms.
Test of single component in isolation. PC-ALE has 54 unit tests covering all phases.
Federal Standard 1003A: CRC-32 polynomial and implementation. Used in FS-1052 for data integrity.
See FS-1052 above.
Military Standard 188-110A: HF modem specification. Defines PSK and QAM modes. Used with ALE for data transmission.
Military Standard 188-141B: HF ALE specification. Defines 2G ALE (Appendix A) and AQC-ALE (Appendix C).
Military Standard 188-141C: Enhanced ALE specification. Defines 3G ALE with higher data rates. Not implemented in PC-ALE 2.0.
Serial or USB interface for controlling radio (frequency, mode, power, etc.). Hamlib library provides CAT support.
Windows API for low-latency audio I/O. Used in PC-ALE for real-time audio processing.
Open-source library for radio CAT control. Supports 200+ radio models. Planned for PC-ALE Phase 6.
Radio frequency range 3-30 MHz. Long-distance propagation via ionosphere. ALE is designed for HF operation.
Radio capable of both transmitting and receiving. ALE requires PTT control to switch between modes.
Signal controlling transmitter. ALE must activate PTT before transmitting, deactivate after.
Modern Windows audio API. Provides lower latency than DirectSound. Supported in PC-ALE Phase 6.
| Acronym | Full Name | Description |
|---|---|---|
| ACK | Acknowledgment | Positive response to data |
| ALE | Automatic Link Establishment | Automated radio linking protocol |
| AMD | Auto Message Display | Short message in ALE call |
| AQC | Advanced Quick Call | Enhanced ALE with DE fields |
| ARQ | Automatic Repeat Request | Error recovery through retransmission |
| BER | Bit Error Rate | Percentage of bit errors |
| CAT | Computer Aided Transceiver | Radio control interface |
| CRC | Cyclic Redundancy Check | Error detection code |
| DE | Data Element | AQC-ALE extension field |
| FEC | Forward Error Correction | Error correction before transmission |
| FFT | Fast Fourier Transform | Frequency analysis algorithm |
| FS | Federal Standard | U.S. federal technical standard |
| FSK | Frequency Shift Keying | Frequency modulation scheme |
| HF | High Frequency | 3-30 MHz radio band |
| LQA | Link Quality Analysis | Channel quality measurement |
| MIL-STD | Military Standard | U.S. military technical standard |
| NAK | Negative Acknowledgment | Indicates error in reception |
| PTT | Push-To-Talk | Transmitter control signal |
| QAM | Quadrature Amplitude Modulation | Advanced modulation (188-110A) |
| SNR | Signal-to-Noise Ratio | Signal quality metric (dB) |
| TIS | This Is | ALE identification word |
| TWS | This Was | ALE confirmation word |
- ARCHITECTURE.md - System architecture and design
- API_REFERENCE.md - Complete API documentation
- MIL_STD_COMPLIANCE.md - Standards compliance matrix
- INTEGRATION_GUIDE.md - Integration with audio/radio
- TESTING.md - Testing guide and coverage
Last Updated: December 2024
Version: PC-ALE 2.0 Phase 5