MULTICARRIER TECHNOLOGIES IN LTE
Adopting a multicarrier approach for multiple access in LTE was the first major design choice. The choice of multiple-access schemes was made in December 2005, with OFDMA being selected for the downlink, and SC-FDMA for the uplink.
Both of these schemes open up the frequency domain as a new dimension of flexibility in the system, as illustrated schematically in Figure below.
OFDMA extends the multicarrier technology OFDM to provide a very flexible multipleaccess scheme. In OFDMA, the subdivision of the available bandwidth is exploited in sharing the subcarriers among multiple users.
This resulting flexibility can be used in various ways:
• Different spectrum bandwidths can be utilized without changing the fundamental system parameters or equipment design.
• Transmission resources of variable bandwidth can be allocated to different users and scheduled freely in the frequency domain.
• Fractional frequency re-use and interference coordination between cells are facilitated.
SC-FDMA has a significantly lower PAPR. It therefore resolves to some extent the dilemma of how the uplink can benefit from the advantages of multicarrier technology while avoiding excessive cost for the mobile terminal transmitter and retaining a reasonable degree of commonality between uplink and downlink
technologies
Multicarrier Technologies in LTE
Multicarrier technologies in LTE are used to enhance the capacity and flexibility of the radio interface by enabling the use of multiple frequency bands. These technologies help LTE networks efficiently utilize the available spectrum and improve data throughput. Here’s how multicarrier technologies work in LTE:
Carrier Aggregation (CA): Carrier Aggregation is a key feature in LTE-Advanced that allows the combination of multiple component carriers (CCs) to form a wider transmission bandwidth. Each component carrier typically operates in a separate frequency band, and the aggregation of these carriers results in higher data rates and improved network performance. Carrier Aggregation can combine up to 5 carriers, supporting bandwidths up to 100 MHz, which enables faster download and upload speeds.
Types of Carrier Aggregation: There are different types of carrier aggregation based on the frequency band configuration:
- Intra-band Contiguous CA: Multiple carriers within the same frequency band are aggregated in a continuous manner.
- Intra-band Non-contiguous CA: Multiple carriers within the same frequency band are aggregated, but they are not adjacent to each other.
- Inter-band CA: Carriers from different frequency bands are aggregated, providing flexibility in spectrum usage.
Orthogonal Frequency Division Multiple Access (OFDMA): OFDMA is used in the downlink (DL) of LTE, where the frequency spectrum is divided into several subcarriers. This allows multiple users to be served simultaneously without interference. Each user is assigned a set of subcarriers, and multicarrier transmission increases the total capacity and data rates.
Single Carrier Frequency Division Multiple Access (SC-FDMA): SC-FDMA is used in the uplink (UL) of LTE. It provides low PAPR (Peak-to-Average Power Ratio), which is beneficial for mobile devices with limited battery life. By using SC-FDMA, LTE ensures efficient uplink transmission even when multiple carriers are involved.
Benefits of Multicarrier Technologies:
- Increased Data Rates: By aggregating multiple carriers, LTE can achieve higher data rates, supporting bandwidth-intensive applications like HD video streaming and large file downloads.
- Better Spectrum Utilization: Multicarrier technologies allow LTE to use the available spectrum more efficiently, including fragmented spectrum across different bands.
- Enhanced Network Capacity: Carrier aggregation increases the number of users that can be served simultaneously, improving the overall capacity of the LTE network.
In summary, multicarrier technologies like Carrier Aggregation, OFDMA, and SC-FDMA enhance LTE’s performance by increasing data throughput, maximizing spectrum utilization, and improving overall network capacity. These technologies are fundamental in supporting the high data rates and efficiency required by modern mobile applications.