Introduction to Modulation and Multiplexing 2

Which statement best explains why digital modulation is preferred for satellite links carrying mixed voice and data traffic?

• Digital modulation allows digitized analog signals and digital data to share a channel, enabling a mix of voice and data.

• Analog modulation provides higher carrier-to-noise ratio for all traffic types without additional processing.

• Digital modulation only supports audio subcarriers and cannot carry data simultaneously.

• Analog modulation is required for time division multiplexing of baseband channels.

A satellite system must transmit voice, video, and data from multiple senders with minimal interference while maximizing medium utilization. Which approach most strategically meets this requirement?

• Assign separate carriers for each sender to avoid multiplexing.

• Use time division multiplexing to interleave digital signals from different channels, then modulate the combined stream.

• Convert all signals to analog and send them simultaneously over a single unmodulated channel.

• Increase transmitter power to overcome interference without changing the channel structure.

A system must transmit digital data over optical fiber with minimal complexity. Which modulation choice aligns with varying the carrier’s amplitude to encode bits, and why is it appropriate for this medium?

• Amplitude-shift modulation (keying), because it varies signal amplitude such as voltage to encode data

• Frequency-shift modulation, because it uses multiple tones near the carrier

• Phase-shift modulation, because it uniformly shifts the carrier wave at set intervals

• Time division multiplexing, because it slices time among users

An operator must multiplex several users over a single channel where idle users should not consume bandwidth. Which technique best meets this requirement, and what is the rationale?

• Frequency division multiplexing (FDM), since each user gets a fixed subchannel even when idle

• Time division multiplexing (TDM), since each user gets full bandwidth only during a time slice that is wasted if the user has nothing to send

• Statistical multiplexing, since bandwidth is allocated on demand to arriving packets, carrying only useful data

• Digital Video Broadcasting (DVB), since it is synonymous with digital television

A mobile network must support two-way communication between the base station (BS) and mobiles. Which duplexing approach uses two distinct frequency bands—one for the forward (downlink) channel and one for the reverse (uplink) channel—and requires careful frequency separation to minimize interference?

• Time Division Duplexing (TDD)

• Frequency Division Duplexing (FDD)

• Single Access

• Code Division Multiple Access (CDMA)

In a system where both directions of transmission share one contiguous frequency allocation but alternate in time slots between forward and reverse links (often called “ping pong”), what consequence does using the same band have on the communication quality in both directions?

• Quality differs: downlink is better than uplink

• Quality is the same in both directions

• Quality is unpredictable and varies randomly

• Quality is worse than FDD by definition

A satellite earth station on a heavy-traffic route uses a single modulated carrier that occupies the whole transponder bandwidth. This operation is called single access. What infrastructure characteristic is specifically required for such single-access operation?

• Small earth station antennas and low G/T

• Large earth station antennas and high G/T (e.g., minimum 37.5 dB/K)

• Multiple small carriers sharing bandwidth

• Separate uplink and downlink transponders

Which statement best explains the purpose of multiple access in satellite communication?

• It increases a satellite’s transmit power to reach distant users.

• It divides satellite resources into nonoverlapping segments so many earth stations can communicate without interfering.

• It reduces the number of earth stations needed by combining them into one.

• It encrypts signals so only authorized users can decode them.

A network designer must minimize performance degradation while allowing many users to share finite radio spectrum resources. Which multiple access approach classification is most relevant to this goal according to the material?

• Broadcast-only downlink access

• Preassigned multiple access vs. demand-assigned multiple access

• Analog modulation schemes

• Single-user narrowband access

A satellite network uses Frequency Division Multiple Access (FDMA) to serve multiple earth stations. Which planning decision best ensures that no two users interfere with each other during a call?

• Allocate unique frequency bands to each user and include guard bands between adjacent channels.

• Increase the transmit power of weaker stations so their signals dominate shared frequency bands.

• Allow users to time-share the same frequency while using narrowband filters.

• Use wider channels without guard bands to simplify allocation.