LTE AND LTE-A FEATURES
LTE and LTE-A have features that allow the operation of the radio channel instantaneous conditions in an efficient way. The result is a significant increase in system capacity by optimizing the power required.
In contrast, the simulation of this systems is difficult. A different approach to the one used in other mobile systems types is necessary, to address such networks plannings.
Main features of LTE and LTE-A are:
•Use of OFDMA (Orthogonal Frequency Division Multiplexing Access) in downlink. A technology that allows multiple access by dividing the channel into orthogonal subcarriers (subcarriers) that are divided into groups according to the needs of each user.
•Use of SC-FDMA (Single-Carrier OFDMA) in uplink. An OFDMA disadvantage is the existence of significant power variations in output signals. Therefore it is necessary to use specially linear amplifiers, which have low efficiency. Power consumption is especially important for uplink so SC-FDMA is used, a more power efficient alternative that retains most of OFDMA advantages.
•Spectrum flexibility. It is one of the key features. The existence of different regulatory frameworks depending on the deployment geographical area, as well as the coexistence with other operators or other services and systems, make necessary the flexibility in the bandwidth used within the deployment band. Ideally, any bandwidth may be used within this band (in 180 kHz steps corresponding to a PRB bandwidth). LTE defines a possible nominal bandwidth of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz.
LTE and LTE-A A are also capable of operating in both paired (FDD) and non-paired (TDD) bands.
The system also allows optimum use of the radio spectrum through Dynamic Spectrum Assignment (DSA) techniques. The system is able, depending on the channel conditions in each block of frequency and time, to select the users in better conditions.
•The use of multiples antennas. Benefits of using these techniques are varied:
oAdditional protection from radio channel fading by means of spatial diversity or polarization diversity techniques.
oPossibility of "shaping" the resulting radiation patterns in transmission and reception achieving, for example, increasing the gain in a desired direction, canceling some interference, etc
oObtaining very high data rates by using multiple parallel channels (spatial multiplexing), also called MIMO (Multiple Input - Multiple Output) techniques.
•Power control in uplink. Improving system capacity and reducing power consumption.
•Inter-Cell Interference Coordination (ICIC). LTE allows coordination between different base stations in order to identify which users are in the center or at the cell's edge. The use of different frequency reuse schemes allows the reduction of intercellular interference.
All above is valid for both LTE and LTE-A, although the LTE-A features allow greater flexibility in spectrum use thanks to the carrier aggregation technique.