Protocol | Icd-gps-153

ICD-GPS-153 is the formal Interface Control Document (ICD) that defines the GPS Standard Serial Interface Protocol (GSSIP). It is primarily used to control the input and output of data between military GPS receivers—such as the Defense Advanced GPS Receiver (DAGR) and the Precision Lightweight GPS Receiver (PLGR)—and other systems, typically military aircraft and vehicles. Purpose and Scope

Tactical Data Exchange: It facilitates data messaging capabilities between receivers and host platforms.

Military Standard: Unlike the civilian NMEA-0183 protocol, which uses text-based ASCII messages, ICD-GPS-153 is a more robust protocol designed for military and government data streams.

Secure Operations: It supports communication for Selective Availability Anti-Spoofing Module (SAASM) receivers, providing protection against jamming and spoofing. Technical Characteristics

B-286466,B-286466.2 [Protest of Air Force Rejection of ... - GAO

This guide outlines the purpose, structure, and availability of ICD-GPS-153 icd-gps-153 protocol

, the official interface control document for communicating with standard Department of Defense (DoD) GPS receivers. 1. Overview of ICD-GPS-153 ICD-GPS-153

is a technical specification that defines the serial interface protocol (RS-232/RS-422) used by DoD standard GPS User Equipment (UE). It allows external devices to communicate with receivers like the (Precision Lightweight GPS Receiver) and

-based units to exchange timing, position, and status information. Safran - Navigation & Timing 2. Key Message Types

While the full protocol is controlled, common implementation examples (such as those used in timing systems) utilize specific message subsets: Safran - Navigation & Timing Current Status (Message 5040):

Transmitted at 1 Hz; provides the receiver's operational health and status. Time Transfer (Message 5101): ICD-GPS-153 is the formal Interface Control Document (ICD)

Transmitted at 1 Hz; delivers precise GPS time synchronized with a 1PPS (Pulse Per Second) signal. Buffer Box (Message 253):

Transmitted at 1/6 Hz; used for legacy compatibility with SINCGARS (Single Channel Ground and Airborne Radio System) interfaces. 3. Protocol Applications Military Integration:

Primarily used to interface GPS receivers with battle command systems, tactical radios (like Link 16), and navigation systems. Emulation & Testing:

Modern timing equipment can emulate ICD-GPS-153 messages to provide legacy systems with time and 1PPS signals as if they were connected to a standard military receiver. Synchronization:

Essential for systems requiring decimeter-level accuracy and precise orbital/clock updates through a network. Safran - Navigation & Timing 4. How to Access the Document Unlike public specifications (like IS-GPS-200 ICD-GPS-153 Step 3: Implement the Message Parser Write a

is not typically available for direct public download because it contains sensitive information for military receivers. Public Release Policy: GPS.gov only hosts documents cleared for public release. Requesting Access: Authorized personnel or contractors must submit a GPS Technical Library Document Request form, signed by a GPS Program representative, via the U.S. Coast Guard Navigation Center Historical Reference:

Step 3: Implement the Message Parser

Write a state machine to parse the binary sync words. Do not search for ASCII strings (like $GPGGA). Use a circular buffer and check CRC before processing.

Pseudo-code example:

while (serial_available()) 
    byte = read_byte();
    if (byte == SYNC1 && next_byte() == SYNC2) 
        msg_type = read_byte();
        length = read_word();
        payload = read_bytes(length);
        crc = read_word();
        if (crc == calculate_crc(payload, length)) 
            process_message(msg_type, payload);

Feature draft — ICD-GPS-153 protocol

4. The SAASM and M-Code Security Layer

The most complex aspect of ICD-GPS-153 is its integration with military GPS security. Standard ICD-GPS-153 messages are not inherently encrypted—the protocol defines the container. However, the payloads for precision data (Type 1, 2, 26) can be encrypted using the GPS security architecture.

When a host system sends a command to the receiver, the receiver uses its internal SAASM or M-Code module to decrypt the GPS signals. The results are then repackaged into ICD-GPS-153 messages. The host never sees the raw classified keys.

Critical Security Commands in ICD-GPS-153:

Zeroize: A command to destroy all cryptographic keys within the receiver (used before maintenance or loss of equipment).
Key Fill: Interface to accept new keys from a programmable fill device (like the AN/CYZ-10 or SKL).
Anti-Spoofing (A-S) Mode: Enable/disable the use of encrypted P(Y) code.