The state-of-the-art design of the LTE air interface is characterised by OFDMA (DL) and SC-FDMA (UL) together with MIMO.
The downlink modulation is based on OFDMA (Orthogonal Frequency Division Multiple Access). OFDMA is a variant of OFDM which has the advantage that receiver complexity is at a reasonable level, it can handle scalable bandwidth requirements and it supports various modulation schemes from BPSK, QPSK,
16QAM to 64QAM. This allows adaptive modulation on a per user base.
In uplink direction a variant of OFDMA called SC-FDMA (Single Carrier Frequency Division Multiple Access) is used. It has the advantage against OFDMA to have a lower PAPR (Peak-to-Average Power Ratio), which leads to lower power consumption and less expensive RF amplifiers in the terminal.
LTE will support MIMO. It describes the possibility to have multiple transmitter and receiver antennas in a system. Other names are beam-forming or smart antennas.
Up to four antennas can be used by a single LTE cell. This allows having spatial
multiplexing and beam-forming. MIMO is considered to be the core technology to increase spectral efficiency. Currently the performance of MIMO for high mobility cases is still under investigation.
HARQ implements a protocol on layer 1/layer 2 that allows for fast retransmission. Furthermore blocks can be retransmitted with increased coding.
In contrast to UMTS where physical resources are either shared or dedicated, the Evolved Node B in EUTRAN handles all physical resource via a scheduler and assigns them dynamically to users and channels. This provides greater flexibility than the older system.
What technology is introduced in the LTE air interface?
The central topic of LTE is the technique of modulation and multiplexing of radio OFDMA and SC-FDMA, the operation of this technology is explained and the choice of technologies used for the LTE physical layer is justified.
How LTE Radio Air Interface Works
The LTE radio air interface is the communication link between the User Equipment (UE) and the Evolved NodeB (eNB), enabling wireless data transmission. It uses a frequency spectrum to carry user and control data between devices and the network. LTE’s radio air interface is based on Orthogonal Frequency Division Multiplexing (OFDM) for downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink. These techniques allow for high spectral efficiency and better handling of interference.
The air interface in LTE consists of several key components: the Physical Layer, which handles data transmission over the air; the MAC (Medium Access Control) layer, which manages scheduling and resource allocation; and the RLC (Radio Link Control) layer, which ensures reliable data transmission. Data is transmitted in the form of packets, and the radio interface dynamically allocates resources to optimize the quality of service, supporting both voice and data services.
Additionally, LTE uses advanced technologies such as MIMO (Multiple Input Multiple Output) and carrier aggregation to enhance the capacity and performance of the radio interface, providing faster speeds and improved connectivity for users.