LTE: LONG TERM
EVOLUTION
Long Term Evolution (LTE) is a
radio platform technology that will allow operators to achieve even higher peak throughput than HSPA+ in higher spectrum bandwidth. Work on LTE began at 3GPP in
2004, with an official LTE work item started in 2006 and a completed 3GPP
Release 8 specification in March 2009. Initial deployments of LTE began in late
2009.
LTE is part of the GSM evolutionary path for mobile broadband, following EDGE, UMTS, HSPA (HSDPA and HSUPA combined) and HSPA Evolution (HSPA+). Although HSPA and its evolution are strongly positioned to be the dominant mobile data technology for the next decade, the 3GPP family of standards must evolve toward the future. HSPA+ will provide the stepping-stone to LTE for many operators.
The
overall objective for LTE is to provide an extremely high performance
radio-access technology that offers full vehicular speed mobility and that can
readily coexist with HSPA and earlier networks. Because of scalable bandwidth,
operators will be able to easily migrate their networks and users from HSPA to
LTE over time.
LTE assumes a full Internet Protocol (IP) network architecture and is designed to support voice in the packet domain. It incorporates top-of-the-line radio techniques to achieve performance levels beyond what will be practical with CDMA approaches, particularly in larger channel bandwidths. However, in the same way that 3G coexists with second generation (2G) systems in integrated networks, LTE systems will coexist with 3G and 2G systems. Multimode devices will function across LTE/3G or even LTE/3G/2G, depending on market circumstances.
Standards
development for LTE continued with 3GPP Release 9 (Rel-9), which was
functionally frozen in December 2009. 3GPP Rel-9 focuses on enhancements
to HSPA+ and LTE while Rel-10 focuses on the next
generation of LTE for the International Telecommunication Union’s (ITU) IMT-Advanced requirements and both were developed nearly
simultaneously by 3GPP standards working groups. Several milestones have been
achieved by vendors in recent years for both Rel-9 and Rel-10. Most significant
was the final ratification by the ITU of LTE-Advanced (Rel-10) as IMT-Advanced
in November 2010.
The first
commercial LTE networks were launched by TeliaSonera in Norway and Sweden in
December 2009; as of November 2012, there were 117 commercial LTE
networks in various stages of commercial service. Many trials are underway with
up to 130 LTE deployments expected in 2012.
LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) on the downlink, which is well
suited to achieve high peak data rates in high spectrum bandwidth. WCDMA radio
technology is, essentially, as efficient as Orthogonal Frequency Division
Multiplexing (OFDM) for delivering peak data rates of about 10 Mbps in 5
MHz of bandwidth. Achieving peak rates in the 100 Mbps range with wider radio
channels, however, would result in highly complex terminals and is not
practical with current technology. This is where OFDM provides a practical
implementation advantage.
LTE Network Architecture
The high-level network
architecture of LTE is comprised of following three main components:
·
The User
Equipment (UE).
·
The
Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
·
The
Evolved Packet Core (EPC).
The evolved packet core
communicates with packet data networks in the outside world such as the
internet, private corporate networks or the IP multimedia subsystem. The
interfaces between the different parts of the system are denoted Uu, S1 and SGi
as shown below:
Facts about LTE
- LTE is the successor technology not only of UMTS but also of CDMA 2000.
- LTE is important because it will bring up to 50 times performance improvement and much better spectral efficiency to cellular networks.
- LTE introduced to get higher data rates, 300Mbps peak downlink and 75 Mbps peak uplink. In a 20MHz carrier, data rates beyond 300Mbps can be achieved under very good signal conditions.
- LTE is an ideal technology to support high date rates for the services such as voice over IP (VOIP), streaming multimedia, videoconferencing or even a high-speed cellular modem.
- LTE uses both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) mode. In FDD uplink and downlink transmission used different frequency, while in TDD both uplink and downlink use the same carrier and are separated in Time.
- LTE supports flexible carrier bandwidths, from 1.4 MHz up to 20 MHz as well as both FDD and TDD. LTE designed with a scalable carrier bandwidth from 1.4 MHz up to 20 MHz which bandwidth is used depends on the frequency band and the amount of spectrum available with a network operator.
- All LTE devices have to support (MIMO) Multiple Input Multiple Output transmissions, which allow the base station to transmit several data streams over the same carrier simultaneously.
- All interfaces between network nodes in LTE are now IP based, including the backhaul connection to the radio base stations. This is great simplification compared to earlier technologies that were initially based on E1/T1, ATM and frame relay links, with most of them being narrowband and expensive.
- Quality of Service (QoS) mechanism have been standardized on all interfaces to ensure that the requirement of voice calls for a constant delay and bandwidth, can still be met when capacity limits are reached.
- Works with GSM/EDGE/UMTS systems utilizing existing 2G and 3G spectrum and new spectrum. Supports hand-over and roaming to existing mobile networks.
Advantages of LTE
- High throughput: High data rates can be achieved in both downlink as well as uplink. This causes high throughput.
- Low latency: Time required to connect to the network is in range of a few hundred milliseconds and power saving states can now be entered and exited very quickly.
- FDD and TDD in the same platform: Frequency Division Duplex (FDD) and Time Division Duplex (FDD), both schemes can be used on same platform.
- Superior end-user experience: Optimized signaling for connection establishment and other air interface and mobility management procedures have further improved the user experience. Reduced latency (to 10 ms) for better user experience.
- Seamless Connection: LTE will also support seamless connection to existing networks such as GSM, CDMA and WCDMA.
- Plug and play: The user does not have to manually install drivers for the device. Instead system automatically recognizes the device, loads new drivers for the hardware if needed, and begins to work with the newly connected device.
- Simple architecture: Because of Simple architecture low operating expenditure (OPEX).
Bibliography
HCIG Reference Guide
Ericsson LTE
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