2.2 - MULTIPLE ACCESS - FDMA/TDMA/CDMA/OFDMA

Summary

This video delves into the evolution of wireless communication, explaining multiplexing and multiple access techniques. It covers FDMA, TDMA, CDMA, and W-CDMA, highlighting their roles in 1G to 3G networks. The focus then shifts to OFDMA, a key technology in 4G LTE, known for its bandwidth scalability, carrier aggregation, and low ISI. The video promises to explore OFDMA and SC-FDMA in detail in the next installment, inviting viewers to subscribe for more.

Takeaways

• 📶 Multiplexing is the process of combining multiple signals and transmitting them over a common channel.
• 🤝 Multiple Access refers to the use of multiplexing to allow multiple users to communicate over a single channel.
• 📡 Wifi hotspots exemplify multiple access by sharing internet connections among users through frequency blocks.
• 📈 FDMA (Frequency Division Multiple Access) allocates specific frequency bands to users for data transmission.
• 🕒 TDMA (Time Division Multiple Access) shares a common frequency band by assigning different time slots to multiple users.
• 🔐 CDMA (Code Division Multiple Access) uses a high-frequency code to spread signals over a wide frequency band, enhancing security and robustness.
• 🌐 W-CDMA (Wideband CDMA) spreads signals over an even higher bandwidth, used in 3G standards like UMTS and HSPA+.
• 🚀 OFDMA (Orthogonal Frequency Division Multiple Access) improves spectral efficiency and reduces interference with its use of orthogonal subcarriers.
• 📱 The evolution of wireless communication has seen significant improvements in spectral efficiency and data rates, from 1G to 4G.
• 🔄 OFDMA's variable bandwidth allocation and lack of guard bands between subcarriers make it a key technology in modern mobile networks like LTE.

Q & A

What is the main topic of the video script?

The main topic of the video script is the evolution of multiple access techniques in wireless communication networks, focusing on how multiple users can access a network simultaneously through various multiplexing methods.

What is multiplexing?

Multiplexing is the process of combining multiple signals and transmitting them over a common channel.

How is multiple access different from multiplexing?

Multiple access refers specifically to the use of multiplexing to allow multiple users to communicate over a single common channel.

What is the role of a frequency block in a Wi-Fi hotspot?

In a Wi-Fi hotspot, a frequency block is provided to multiple users over which they can transmit and receive data, with the size of the block affecting the throughput.

What is FDMA and how was it used in telecommunication?

FDMA (Frequency Division Multiple Access) uses frequency division multiplexing to provide chunks of the frequency spectrum to each user for data transmission, avoiding interference with guard bands. It was used in first-generation analog systems like AMPS.

How does TDMA allocate resources to multiple users?

TDMA (Time Division Multiple Access) allows multiple users to share a common frequency band by allocating different time slots, with signals from each user transmitted at intervals determined by the number of channels and time slot duration.

What is CDMA and how does it ensure security and robustness?

CDMA (Code Division Multiple Access) modulates data bits with a high-frequency orthogonal sequence or pseudo-random code to spread signals over a large frequency band. The same spreading sequence is required at the receiver to retrieve the signal, making CDMA secure and robust.

What is the difference between CDMA and W-CDMA?

CDMA spreads signals over a certain frequency band, while W-CDMA (Wideband CDMA) spreads signals over an even higher bandwidth, used in 3G standards like UMTS to HSPA+ with a bandwidth of 5MHz compared to 1.25 MHz in CDMA.

Why did the evolution of communication networks lead to OFDMA?

The evolution to OFDMA was driven by the need for higher data rates, spectral efficiency, and to address issues like spectrum exhaustion, congestion at peak hours, resource wastage, and poor spectral efficiency.

What are the advantages of OFDMA over W-CDMA?

OFDMA (Orthogonal Frequency Division Multiple Access) offers advantages like bandwidth scalability, carrier aggregation, and low ISI (Inter Symbol Interference). It uses orthogonal subcarriers, allowing variable bandwidth access and no need for guard bands.

How does OFDMA allocate subcarriers to users for data transmission?

OFDMA provides users with a subset of orthogonal subcarriers for data transmission, allowing access to variable bandwidth depending on resource availability.