The code words and spreading algorithm of synchronous code division multiple access (S-CDMA) enable simultaneous transmission of up to how many modems on the same RF return channel?

The correct answer is derived from the principles of synchronous code division multiple access (S-CDMA) technology, which utilizes unique spreading codes to allow multiple users to transmit simultaneously over the same frequency channel.

In S-CDMA, each modem is assigned a unique spreading code that helps to distinguish its signal from those of other modems, even when they are all using the same frequency. The number of simultaneous users that can be accommodated over the same RF return channel is determined by the length and complexity of these spreading codes.

For S-CDMA systems, a commonly used configuration allows for the assignment of up to 128 unique spreading codes, enabling the simultaneous transmission of 128 different modems. This is due to the fact that the system can effectively separate and decode multiple signals by utilizing these unique codes without interference. The correct answer reflects the maximum capacity that is typically achievable under standard conditions for S-CDMA technology.

Understanding the limits of simultaneous transmissions is crucial for planning bandwidth and capacity in communication systems. This capacity consideration is why option B stands out as the correct choice.