In an earlier article, we addressed LTE and measured it against the 4G standards published by the ITU-R. This article addresses LTE-A as the next logical step in the wireless network evolution. The 3rd Generation Partnership Project (3GPP) was motivated to enhance the LTE Release 8 specifications to achieve higher bit rates and greater network reliability while maintaining backward compatibility. These enhancements where published with LTE-A Release 10.
The enhanced requirements of LTE-A include:
Increasing peak data downlink rates to 1 Gbit/sIncreasing peak uplink rates to 500 MBit/sImproving downlink spectrum efficiency to 30 bps/HzReducing latenciesImproving coverage at the cell edgeSupporting non-contiguous carrier aggregationImproving user throughput
The new functionalities introduced in LTE-Advanced focus on the Evolved Universal Terrestrial Access Network (E-UTRAN). This is the air-interface. These functions include non-contiguous Carrier Aggregation, enhanced spatial multiplexing commonly known as Multiple-In, Multiple-Out (MIMO), the support for Relay Nodes and Coordinated Multi-Point Operation (CoMP).
LTE provided the ability to support multiple individual carrier bandwidths (1.4, 3, 5, 10, 15 or 20 MHz) and aggregate contiguous component carriers. LTE-A adds the capability to aggregate up to 5 non-contiguous uplink component carriers to a maximum bandwidth of 100 MHz. The number of aggregated uplink carriers will typically be less than for the downlink carriers.
Spatial Multiplexing or MIMO
LTE supports MIMO capabilities up to 4X4 for the downlink and 2X2 for uplink. LTE-A expands this to up 8X8 for the downlink and 4X4 for the uplink. This basically means that data can be transmitted and received over multiple bit streams simultaneously, thereby increasing peak bit rates.
Relay nodes introduce an efficient method to manage a network consisting of large and small cells or a heterogeneous network (Het-Net). Relay nodes are low power base stations that provide coverage at cell edges and support high data traffic spots. They communicate with an eNodeB via radio interface. Relay nodes eliminate the required physical fiber connection between it and the eNodeB site.
The last major enhancement is the CoMP that improves performance at the cell edge as well as adding some Het-Net capabilities. The CoMP enhances radio performance for a sector on the edge of multiple cells with overlapping coverage. It coordinates the transmitting and receiving between the user and multiple cell towers. It works with both homogeneous networks as well as Het-Nets.
The LTE-A enhancements truly make it a 4G technology in every way. The technology is already being deployed in multiple countries and by several carriers. It will surely be pervasive within a few years.