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Making heterogeneous network possible

Posted: 30 Nov 2011 ?? ?Print Version ?Bookmark and Share

Keywords:LTE? Evolved NodeB? heterogeneous network? HetNet?

Most cellular networks these days are now on their third generation (3G). Based on universal mobile telecommunications system (UMTS) or code division multiple access (CDMA) technologies, they support data rates of a few megabits per second (Mbps) under low-mobility conditions. During the last few years, these networks have been overwhelmed as the number of cellphones has dramatically increased. Meanwhile, most cellular service subscribers now also use the mobile Internet and, over the past three years, many new broadband mobile devices have been commercialized including smart phones, tablets and laptops with 3G capabilities. As a result, the amount of wireless data that cellular networks must support is exploding.

This avalanche of mobile data makes it increasingly difficult for operators to ensure sufficient network performance. Yet the only way they can remain competitive and continue offering unlimited data plans is to reduce the price/performance ratio for mobile data. In response, the industry has introduced the LTE standard as the first step toward a new 4G cellular network, which has recently entered the deployment phase. The latest releases of the LTE specifications also include the concept of the Heterogeneous Network (HetNet), which will rely heavily on System-on-Chip (SoC) integration to handle the computational complexity of many different types of small cell Evolved NodeB (eNodeB) LTE base stations.

In particular, a HetNet requires a special variation of application-specific SoCs that enable more robust, multilevel parallelism while delivering all the required eNodeB Layer 1-3 protocol stack software and managing its execution across multiple programmable processing cores.

LTE overview
Standardized by the 3G Partnership Project (3GPP), the first, LTE Release 8 specification was frozen in December 2008 before being published in March 2009. Release 8 offers downlink data rates of up to 150Mbit/sa promising solution for operators seeking an efficient way to evolve their network.

Because LTE technology is based on an evolution of the existing 3G network, operators will be able to deploy is more quickly than alternative wireless standards such as WiMAX. The first LTE deployment was executed during 2010 by TeliaSonera in three Norwegian cities and 25 Swedish cities. Since then, many other commercial deployments have been launched and are now underway around the world.

LTE introduces two major innovations beyond previous 3G techniques. First, in order to reduce network latencies, a flat, all-IP core network architecture is proposed. This new core network, called evolved packet core (EPC), introduces new interfaces that directly connect enhanced base stations (eNodeBs, or eNBs) together, and removes 3G's hierarchical approaches.

The second major enhancement proposed in LTE is a new radio access network called the evolved universal terrestrial radio access network (E-UTRAN). E-UTRAN is based on the orthogonal frequency division multiple access (OFDMA) technology for the downlink and single-carrier frequency division multiple access (SC-FDMA) technology for the uplink. LTE supports bandwidth of up to 20MHz making it a suitable standard for high data rates. An advantage of OFDMA and SC-FDMA is the orthogonality of neighboring subcarriers, which avoids interference between adjacent narrowband frequencies. SC-FDMA was chosen in the uplink (unlike WiMAX, for instance) because its transmit signal has a lower peak-to-average ratio.

A new frame structure is also proposed in LTE, in which resource elements called physical resource blocks (PRBs) are allocated in both the time and frequency domains, thus allowing the network to serve more users at higher data rates. Like all other new wireless technologies, LTE also generalizes the use of multiple antennas at both receiver and emitter side. Such systems, called multiple input multiple output (MIMO), also greatly increase performance, while making it possible for eNodeBs to perform beamforming and focus their signal in the optimal direction required by users, thus reducing interference between neighboring cells and users.

Release 9 of the LTE specification proposed several additional enhancements including architectural features for home eNBs (HeNBs). HeNBs are a new kind of small base station, also called femtocell, that are aimed at increasing radio coverage indoors.

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