Has SC-FDMA been used as a multiple access scheme in LTE systems?
Yes, SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in LTE systems specifically for the uplink. If you remember from our previous post on LTE protocol stacks, the uplink and downlink operate differently, and here you’re going to see why SC-FDMA is ideal for uplink use.
Understanding SC-FDMA in LTE
SC-FDMA is a single-carrier modulation technique, which means it transmits data over a single carrier with additional frequency division. While it may sound similar to OFDMA used in the downlink, there’s a reason LTE separates the two. OFDMA offers great performance for base stations, but for mobile devices—where power efficiency matters most—SC-FDMA is preferred.
Why LTE Uses SC-FDMA for Uplink
Mobile devices operate under strict power limitations. SC-FDMA offers a much lower peak-to-average power ratio (PAPR), which reduces the stress on a phone’s power amplifier and helps extend battery life. OFDMA, by contrast, can be very power-hungry due to its high PAPR.
This low PAPR is a major reason LTE adopted SC-FDMA as its uplink multiple access scheme, ensuring better battery efficiency and overall performance on user equipment.
SC-FDMA Operation Overview
| Step | What Happens |
|---|---|
| 1 | User data is mapped onto subcarriers using a Discrete Fourier Transform (DFT). |
| 2 | The transformed signal is then mapped to orthogonal subcarriers in the frequency domain. |
| 3 | An Inverse Fast Fourier Transform (IFFT) is applied to convert the data back to the time domain. |
| 4 | The resulting signal is transmitted over the air as a single-carrier signal. |
Advantages SC-FDMA Brings to LTE Uplink
SC-FDMA isn’t just used because it’s different from OFDMA—it brings tangible uplink benefits:
- Lower PAPR: This allows mobile devices to transmit efficiently without needing bulky or expensive hardware.
- Improved coverage: It performs better in conditions with interference or poor signal quality.
- Spectral efficiency: Enables more users to share limited frequency resources without major signal degradation.
Frame Structure in LTE Uplink
In the LTE uplink, each user’s data is slotted into a well-defined frame structure. These frames consist of time slots and subframes, and the eNodeB (base station) schedules who uses which subcarriers and when.
Using SC-FDMA, each mobile device sends its data using specific subcarriers that the eNodeB dynamically assigns. This scheduling helps ensure all users get fair access while also maximizing spectral efficiency.
So next time you’re analyzing uplink transmission, remember this: SC-FDMA is there to make sure the uplink remains energy-efficient, reliable, and able to scale with demand. It’s one of those technical choices that makes LTE such a balanced and optimized system.