S-band Multiple Access (SMA)

S-Band Multiple Access (SMA) is a technology used by The Tracking and Data Relay Satellite System (TDRSS) for providing S-band services.

TDRSS offers S-band services by means of the SMA phased array. The SMA array includes two antennas, where one is for transmitting to and the other one is for receiving from users.

The SMA phased array antennas are built to get signals from five different spacecraft simultaneously, while transmitting signals to one.

In the SMA array, every element employed to support spread-spectrum Code Division Multiple Access (CDMA) returns link transmissions from users.

A multitude of self-sufficient, high-gain antenna beams can be formed at the TDRS Ground Terminal. The subset of elements is used in TDRS forward link transmission to the users.

The SMA array is remarkably effective, with hardly any element failures.

SMA characteristics:

• Offers five multiple access return channels and one multiple access forward channel per spacecraft.
• Includes return services, which make use of the same frequency (i.e., 2287.5 MHz) and CDMA to avoid interference.
• Has been enhanced to 3 Mbps return for TDRS trio TDRS-H, -I, -J, versus the 100 Kbps of earlier TDRS.
• Has been upgraded up to 300 Kbps forward.
• As well as the S-band multiple access service, the TDRS trio offer services such as S-band Single Access (SSA) and Ku-band single access (KuSA).