Telecom Techniques Guide


LTE SC-FDMA and LTE Uplink

LTE SC-FDMA and LTE Uplink

LTE (Long-Term Evolution) utilizes a specific modulation scheme for the uplink known as Single-Carrier Frequency Division Multiple Access (SC-FDMA). SC-FDMA is a modulation and access scheme that provides advantages for uplink transmission in LTE networks.

  • Introduction to SC-FDMA and uplink frame structure
  • Marriage of single carrier transmission and FDMA
  • Uplink SC-FDMA tranmsit and receive chains
  • Peak to Average Power Ratio (PAPR) comparison with SC-FDMA and OFDMA

Here are some key aspects of LTE SC-FDMA and the LTE uplink:

SC-FDMA in LTE Uplink:

In the uplink direction of LTE, SC-FDMA is used as the modulation scheme. SC-FDMA is a form of Frequency Division Multiple Access (FDMA) where each user is assigned a specific subset of subcarriers for transmission.

SC-FDMA offers advantages over traditional FDMA schemes by reducing the Peak-to-Average Power Ratio (PAPR) and improving power efficiency. This is especially important for mobile devices with limited battery power.

Uplink Resource Allocation:

In LTE, the uplink resources are dynamically allocated to different users based on their channel conditions and quality. The uplink resource allocation is performed by the base station (eNodeB) using techniques like uplink scheduling and power control.

The uplink resources are allocated in the frequency domain and time domain, specifying the subset of subcarriers and the duration of transmission for each user.

Random Access Procedure:

The LTE uplink includes a random access procedure that allows UEs to request access to the network and initiate an uplink transmission. This procedure is used for initial connection establishment, handovers, and other signaling exchanges.

During the random access procedure, the UE transmits a preamble on a specific set of subcarriers, and the eNodeB responds with a grant for uplink transmission resources.

Uplink Channel Quality Reporting:

Uplink channel quality reporting is an essential part of LTE uplink operations. UEs periodically measure the quality of the uplink channel and report it to the eNodeB. This information is used for resource allocation, scheduling, and power control optimization.

By employing SC-FDMA in the uplink, LTE achieves a balance between power efficiency, spectral efficiency, and robustness. SC-FDMA reduces the PAPR compared to other modulation schemes like Orthogonal Frequency Division Multiple Access (OFDMA), making it suitable for uplink transmissions from battery-powered devices. The dynamic allocation of uplink resources, random access procedures, and channel quality reporting contribute to the efficient and reliable operation of the LTE uplink.

Why is SC-FDMA used in uplink for LTE?

SC-FDMA (Single-Carrier Frequency Division Multiple Access) is used in the uplink for LTE (Long-Term Evolution) due to several advantages it offers over other modulation schemes. Here are the key reasons why SC-FDMA is utilized in the uplink for LTE:

Power Efficiency:

SC-FDMA provides better power efficiency compared to other modulation schemes like OFDMA (Orthogonal Frequency Division Multiple Access). It exhibits a lower Peak-to-Average Power Ratio (PAPR), which means the power amplifiers in user devices can operate more efficiently, reducing power consumption and extending battery life. This is particularly important for uplink transmissions from battery-powered devices such as smartphones and IoT devices.

Lower Interference:

SC-FDMA offers a lower level of out-of-band and in-band interference compared to OFDMA. It achieves this by distributing the energy of a transmitted signal over a narrower frequency range, resulting in reduced interference to adjacent subcarriers. Lower interference levels enhance the overall system performance and enable better coexistence with neighboring frequency bands.

Better Receiver Performance:

SC-FDMA exhibits better receiver performance in terms of receiver complexity and tolerance to frequency errors and phase noise. The receiver complexity is reduced because SC-FDMA uses a single carrier instead of multiple carriers like OFDMA. Additionally, SC-FDMA has improved tolerance to frequency-selective fading and Doppler effects, which can degrade the performance of the receiver.

Contiguous Resource Allocation:

SC-FDMA enables contiguous resource allocation, meaning the assigned subcarriers are adjacent to each other in the frequency domain. This is particularly beneficial for uplink transmission, as it allows for more efficient implementation of frequency-domain equalization and simplifies the receiver processing.

Compatibility with Existing Technologies:

SC-FDMA provides a smooth transition from legacy technologies like WCDMA (Wideband Code Division Multiple Access). It enables backward compatibility by reusing the existing WCDMA infrastructure and radio frequency components, minimizing the need for costly upgrades.

By utilizing SC-FDMA in the uplink, LTE achieves a good balance between power efficiency, spectral efficiency, receiver performance, and compatibility with legacy technologies. These advantages make SC-FDMA well-suited for uplink transmissions in LTE, providing efficient and reliable communication for various devices in the network.