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The 2020 vision for LTE

22 июня 2012

The new mobile communications technologies invented and ensuing capabilities provided to operators and end users since inception of cellular around 30 years ago are outstanding. While development goals have evolved significantly over the decades, the pace of innovation continues unabated. At the heart of the world-leading mobile technology ecosystem, since 1998, is standardisation by the 3GPP producing a major release of technical specifications every year or two.

Following the introduction of an entirely new air interface with LTE in Release 8, and with various enhancements subsequently, upcoming Release 12 and beyond will be as significant as ever in the industry's quest to extend mobile broadband availability, provide much more consistent service quality, and economically satisfy demand for spiralling data growth in face of spectrum scarcity and other constraints.

The 3GPP Technical Specification Group responsible for Radio Access Network technologies met for a two-day workshop in Slovenia earlier this month to consider what should be evaluated for implementation in Release 12. Forty-five mobile technology vendors and operators took part, with 250 people attending the event. On the basis of consensus among this 3GPP membership and further study work, Release 12 will most likely be "frozen" in 2014, with commercial implementations beginning a couple of years later and extensive worldwide adoption toward 2020.

The generation game

Successive mobile generations are typically depicted in technological terms. For the world's mobile operators following the standards path, first laid by ETSI and then 3GPP, 1G analogue was followed by 2G TDMA-based GSM, then 3G wideband-CDMA-based UMTS and 3G/4G OFDMA-based LTE. However, concurrent with each generational shift have been profound advances in the capabilities, economics and availability of network, device and service offerings.

Outdoor coverage in urban areas and along highways for predominantly car phone use by a privileged minority was provided by 1G networks. Introduction of 2G since the early 1990s substantially increased voice capacity and reduced costs. Cellular soon became economic for mass-market consumer adoption in any nation. The result is 6 billion GSM subscriptions for voice and text worldwide today. The addition of 3G since the early 2000s provided further voice capacity and then, with HSPA, the higher speeds and lower latencies required to stimulate significant mobile broadband use. Enhancements to established 3G technologies and introduction of LTE with Releases 8-11 have made headline-grabbing news, with peak data speeds in the tens of megabits per second--1,000 times faster than a decade earlier with GPRS.  What more could anybody possibly need or want?

We are still at just the beginning of the mobile broadband revolution. The extent of market development and user adoption for mobile web, apps, multimedia and location capabilities, among others, is comparable to the early stages of the switch from 1G to 2G.  Mobile broadband, while impressive where available and for those who use it, was only a pursuit for a small minority until the last couple of years. Coverage remains patchy, with insufficient capacity in many places; and erratic service quality, including highly-variable data speeds--from cell-to-cell and from cell centre to cell edge.

While making major improvements on all these fronts to satisfy the current base of users and existing usage profiles, there is also the pressing need to satisfy massive growth in data traffic. This is widely-recognised, among 3GPP members and external observers, to have doubled each year and is set to continue growing rapidly. This will result from new services, such as highly connection-persistent cloud services, heavier usage per user all around and yet more people trading up from voice and text to mobile broadband devices and service plans. Virtually all commentators expect a 15 to 30-fold traffic increase over five years and several expect this growth trend to last a decade to 2020, representing a 250-1,000-fold increase. How can all that be achieved; and at low enough costs to cover and be afforded by half the world's population, plus billions more machine-to-machine connections?

 Alleviating the Capacity Crunch

The biggest challenge facing mobile operators and their technology suppliers is in satisfying this exponential growth in data traffic.  The proportion of users with smartphone and other mobile broadband devices is increasing. These users are already the majority in several developed nations. Per user data demands are escalating with always on, always with you access to a burgeoning array of applications and services including those delivered from network-intensive video and cloud services. LTE networks are already providing headline speeds approaching 100 Mbps, but these are only possible under ideal conditions on lightly loaded networks and where user equipment is close to the base station radio antenna.

Many technologies and features introduced in previous releases are being enhanced and supplemented with new additions in Releases 12 and 13.  These developments will increase network capacity, while also providing more consistent service quality, with the product of three compounding factors. Illustrative improvement figures of 3 x 6 x 56 = 1,008 were suggested by SK Telecom under three broad headings. The specifics were identified and described in contributions from many workshop participants.

3x increase in spectrum employed

Existing bands will be refarmed for more efficient use. New licensed bands, including higher frequencies for hot-spot demand zones will be introduced. This will all be used in combination with unlicensed spectrum, if suitable, while possibly exploiting cognitive radio techniques to access and manage the latter. TDD mode LTE is unleashing access to unpaired spectrum. Carrier aggregation including the combination of different bands and modes will increase total capacity, headline speeds and trunking efficiency.

6x improvement in spectral efficiency

A plethora of technologies are helping increase the amount of data transported per Hz of spectrum used, to reduce latency and increase speeds--with emphasis on average speeds achievable across the entire cell including cell edges. Improving consistency of service performance, rather than just peak speed--depending on time and place--is the key. Higher-order modulation to 256QAM, coordinated multiple point transmission and interference management techniques will improve cell-edge performance. 3D MIMO and massive antenna beamforming with arrays of as many as 64 antenna elements enable additional frequency reuse within cell sectors. With strong consensus in 3GPP to maintain LTE's OFDMA air interface in the downlink, some 3G participants favour introducing something similar to improve uplink performance.

56x higher average cell density

The addition of many small cells in HetNet configurations including macro, micro, pico femto, relay stations and even clouds of antennae will provide the biggest boost to capacity through extreme frequency reuse. With 70 per cent of traffic at home or in the office, buildings present both opportunities (e.g., access to power and backhaul) and difficulties (e.g., signal attenuation). Improved backhaul, and sidehauling via X2 interface (for inter-cell signalling), will support techniques such as baseband pooling and inter-cell coordination that can most efficiently and effectively orchestrate resources with the large arrays of radio heads that will be deployed in high-demand locations. There are initiatives to simplify management across cells with rationalised signalling and control maintained at the macro layer, and introduction of phantom cells in high-density small cell layers.

LTE takes centre stage

LTE has universal appeal and will soon predominate worldwide. The workshop participants overwhelmingly endorsed this as the definitive air interface standard for ongoing development.    LTE will provide the primary or only broadband access to billions of people in developing nations where fixed network alternatives are not available. LTE has become the target platform for machine-type communications (machine-to-machine), public safety use and proximity services (device-to-device). 

Meanwhile, operators wish to protect their investments in older technologies. They may not, for example, be able to refarm scarce spectrum from legacy technology use for several years. Release 12 will also include various enhancements that will improve spectral efficiency and service quality in UMTS networks using HSPA technologies.

By Phil Goldstein

Источник: FierceWireless:Europe

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