6.5 Summary and Conclusions
This chapter provided an overview of the LTE radio interface, emphasizing the hierarchical channel structure and the radio resource in both downlink and uplink. The material covered should be adequate for the reader to get the unique characteristics of the LTE physical layer and understand the detailed physical layer procedures in the following chapters.
- LTE is the next step in the evolution of mobile cellular systems, and is a packet-switched network from end to end that is designed with a clean slate approach.
- LTE adopts the hierarchical channel structure from UTRA/HSPA. It simplifies the channel structure and is based totally on the shared channel transmission, which improves the efficiency of the air interface.
- LTE applies OFDMA in the downlink and SC-FDMA in the uplink, both of which have similar radio resource structures in the time-frequency plane. The capability of scheduling in both time and frequency domain provides a higher spectral efficiency in LTE than what is achieved in HSPA. Both localized and distributed resource allocations are supported in the downlink, while only localized resource allocation is supported in the uplink.
- MIMO transmission is a key component of LTE. In current specifications, downlink transmission supports a variety of MIMO modes, while uplink transmission has a limited MIMO support considering cost and complexity.