Welcome to the world of Telecom Terminologies, where we delve into the commonly used terms in the Telecom industry. In this installment, we will explore OFDMA and SC-FDMA, two techniques that have revolutionized mobile communications, allowing seamless connectivity between mobile phones and networks. So, let’s dive right in!
Contents
Understanding OFDMA and SC-FDMA
To better comprehend OFDMA (Orthogonal Frequency Division Multiple Access) and SC-FDMA (Single Carrier Frequency Division Multiple Access), let’s imagine a simplified diagram of how a cell phone connects to a mobile network.
The communication between a mobile network and a phone occurs in two directions: uplink and downlink. The downlink refers to communication sent from the network to the phone, while the uplink is the communication sent from the phone to the network.
In 4G LTE networks, the downlink communication employs OFDMA, while the uplink uses SC-FDMA. However, in 5G networks, both the downlink and uplink communication adopt OFDMA.
The Power of OFDM
OFDMA and SC-FDMA both utilize a waveform known as Orthogonal Frequency Division Multiplexing (OFDM). In 4G LTE, OFDM is a multi-carrier transmission scheme that divides the overall carrier bandwidth into smaller subcarriers, each measuring 15 kilohertz. This allows for efficient utilization of available bandwidth by simultaneously transmitting multiple data streams.
In OFDM, each frequency carrier is split into numerous smaller subcarriers. For example, a wideband 20 megahertz carrier can be divided into narrower 15 kilohertz subcarriers. These subcarriers are then tightly grouped and organized to ensure that the highest point or peak of each subcarrier only overlaps with the lowest point or zero of its neighboring subcarrier. This independence eliminates interference, making the subcarriers orthogonal to each other.
Subcarrier Allocation in OFDM
Let’s visualize the concept of subcarrier allocation used in OFDM. In the diagram below, we can see the time and frequency domains, with 12 subcarriers for simplicity. Each user is allocated a dedicated time slot, and all available subcarriers are assigned to them at different time intervals.
In OFDM, user allocation is flexible in the time domain but not in the frequency domain. This means that all subcarriers are assigned to all users at dedicated time intervals, regardless of their bandwidth requirements.
Making OFDM Flexible: OFDMA
OFDMA takes the flexibility of OFDM a step further by enabling dynamic subcarrier and time slot allocation in both the time and frequency domains. This flexibility allows for efficient multiple access, ensuring that each user is allocated the necessary bandwidth.
In LTE networks, mobile phone users can be assigned a specific number of subcarriers for a particular duration based on their data needs. For example, if one user is streaming a YouTube video while another is sending messages on WhatsApp, OFDMA can allocate more resources or subcarriers to the user streaming the video, as video streaming consumes more bandwidth. Additionally, the duration of time slots can be adjusted depending on the user’s bandwidth requirements.
SC-FDMA: Power Efficiency in Uplink Communication
While OFDMA handles downlink communication in 4G LTE networks, SC-FDMA steps in for uplink communication. SC-FDMA is a special version of the OFDM-based multiple access technique that utilizes a single carrier instead of multiple carriers.
The reason for using SC-FDMA in the uplink is its superior power efficiency. SC-FDMA consumes less power, thereby preserving the battery life of your cell phone. Moreover, SC-FDMA boasts a lower Peak to Average Power Ratio (PAPR) compared to OFDMA.
Conclusion
In this Telecom Terminologies video series, we have explored OFDMA and SC-FDMA, two groundbreaking techniques that have transformed mobile communications. OFDMA enables dynamic allocation of subcarriers and time slots, optimizing bandwidth usage, while SC-FDMA ensures power efficiency in the uplink communication.
Stay tuned for more exciting videos and articles that empower you with knowledge about the ever-evolving world of technology. For more information about “Techal,” visit our website Techal.
FAQs
Q: How does OFDMA differ from SC-FDMA?
A: OFDMA (Orthogonal Frequency Division Multiple Access) is primarily used in the downlink, while SC-FDMA (Single Carrier Frequency Division Multiple Access) is employed in the uplink for power efficiency.
Q: What is the advantage of OFDM in mobile communications?
A: OFDM allows for efficient utilization of available bandwidth by dividing the overall carrier bandwidth into smaller subcarriers, enabling simultaneous transmission of multiple data streams.
Q: How does OFDMA allocate resources in LTE networks?
A: OFDMA dynamically allocates subcarriers and time slots based on users’ data needs, ensuring optimal bandwidth allocation.
Q: Why is SC-FDMA power efficient in the uplink?
A: SC-FDMA consumes less power and has a lower Peak to Average Power Ratio (PAPR) compared to OFDMA, resulting in extended battery life for mobile phones.
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