Data Modulation Title

It is not the intent of this page to provide a tutorial on communications theory but to provide information necessary for a potential customer to determine if TDRSS communications capabilities are consistent with the customer spacecraft telecommunication subsystem and mission requirements.

Modulation

Modulation is the process of impressing data onto an RF carrier for transmission. TDRSS supports three modulation schemes:

 

 

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BPSK Graphic

Binary Phase Shift Keying

Binary Phase Shift Keying- A single data channel modulates the carrier. A single bit transition, 1 to 0 or 0 to 1, causes a 180 degree phase shift in the carrier. Thus, the carrier is said to be modulated by the data. Most applicable for customers with a single data stream.

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QPSK Graphic

Quadrature Phase Shift Keying

Quadrature Phase Shift Keying - Two data channels modulate the carrier. Transitions in the data cause the carrier to shift by either 90 or 180 degrees. This allows customers to transmit two discrete data streams, identified as I channel (In phase) and Q channel (Quadrature) data.

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SQPSK Graphic

Staggered Quadrature Phase Shift Keying

Staggered Quadraphase Shift Keying - Two data channels modulate the carrier as in QPSK but the data channels are offset by 1/2 bit position so the carrier shifts 90 degrees. The data channels originate from a single stream with the data placed alternately on two channels. These streams are identified as I channel (In phase) and Q channel (Quadrature) data. The staggered nature of the modulation scheme provides easy identification of I channel and Q channel during recovery.

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