Wireless Communication Techniques: OFDM, OFDMA, SISO, MIMO, and More

This section will cover the fundamentals of Virtual Reality (VR) systems and how they function.

Difference Between OFDM and OFDMA

Here, we’ll delve into the distinctions between Orthogonal Frequency-Division Multiplexing (OFDM) and Orthogonal Frequency-Division Multiple Access (OFDMA).

Difference Between SC-FDMA and OFDM

This section explains the differences between Single-Carrier Frequency-Division Multiple Access (SC-FDMA) and Orthogonal Frequency-Division Multiplexing (OFDM).

Difference Between SISO and MIMO

A comparison of Single-Input Single-Output (SISO) and Multiple-Input Multiple-Output (MIMO) systems.

Difference Between TDD and FDD

An explanation of the differences between Time-Division Duplexing (TDD) and Frequency-Division Duplexing (FDD).

FDMA vs TDMA vs CDMA

This section provides a comparative analysis of Frequency-Division Multiple Access (FDMA), Time-Division Multiple Access (TDMA), and Code-Division Multiple Access (CDMA).

FDM vs TDM

Here, we’ll explore the distinctions between Frequency-Division Multiplexing (FDM) and Time-Division Multiplexing (TDM).

CDMA vs GSM

A comparison between Code-Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM).

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## Difference Between OFDM and OFDMA

OFDM (Orthogonal Frequency-Division Multiplexing) is a modulation technique that divides a high-rate data stream into multiple lower-rate streams that are transmitted simultaneously over a number of subcarriers. These subcarriers are orthogonal to each other, minimizing interference.

OFDMA (Orthogonal Frequency-Division Multiple Access) builds upon OFDM by adding a multiple access component. This means that different users can be assigned different subcarriers or groups of subcarriers, allowing for simultaneous access to the communication channel.

Here's a table summarizing the key differences:

| Feature          | OFDM                                       | OFDMA                                        |
| ---------------- | ------------------------------------------ | -------------------------------------------- |
| Access Method    | Single-user (typically)                    | Multiple access (multiple users)             |
| Subcarrier Usage | All subcarriers used by a single user      | Subcarriers allocated to different users     |
| Applications     | Digital TV broadcasting, Wi-Fi (sometimes) | Mobile broadband (LTE, WiMAX), Wi-Fi (often) |

The bandwidth $B$ is divided into $N$ orthogonal subcarriers. Each subcarrier has a bandwidth of $\Delta f = \frac{B}{N}$.