LTE-Advanced: The leading technology in the new MBB era
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In 1Q 2011, 3GPP released the first version of the LTE-Advanced (LTE-A) protocol:
LTE-A Release10. LTE-A has evolved from LTE technology to meet the
requirements of IMT-Advanced, the fourth generation of mobile communications
systems. LTE-A technology can dramatically increase the peak rate, peak spectral
efficiency, average rate, average spectral efficiency, and cell-edge user performance.
It improves networking efficiency across the entire network and will become the
mainstream future wireless communications technology, riding the wave of the new
MBB era.
The number of mobile users and mobile broadband users continues to grow rapidly,
with the CAGR of the latter group increasing by 104% between 2007 and 2011.
Infonetics estimates that the number of global mobile users will reach 5.2 billion in
2011, mobile broadband users will hit 5 billion, and traffic growth per user per year
will exceed 50% over the next 10 years. As such, network traffic will grow by a
staggering 500 times, requiring LTE-A to step in and underpin the required huge
network capacity.
Key technologies of LTE-A
LTE-A expands and enhances the basic LTE platform. It is characterized by flexible
and effective spectrum utilization, higher spectral efficiency, simpler and optimized
network architecture, and the ability to cut TCO and provide more services. LTE-A is
backward compatible with LTE and represents its smooth evolution.
LTE-A needs to support a bandwidth of up to 100MHz, a downlink peak rate of
1Gbps with an increased spectral efficiency of 30bps/Hz, an uplink peak rate of
500Mbps with an increased spectral efficiency of 15bps/Hz, and expand downlink and
uplink MIMOs to 8×8 and 4×4 respectively.
Introducing the following key technologies into LTE-A realizes these requirements:
Carrier Aggregation (CA), Enhanced MIMO, Coordinated Multi-point Tx/Rx (CoMP),
Heterogeneous Network (HetNet), and Self-Organization Network (SON).
CA
To meet peak rate requirements – an uplink speed of 500Mbps and downlink speed of
1Gbps – LTE-A must support a bandwidth of up to 100MHz. However, it is
extremely difficult to find such high continuous bandwidth in currently available
spectrum resources. Therefore, LTE-A integrates the key technology, Carrier
Aggregation (CA), to fully utilize the spectrum resources scattered in multiple
frequency bands. This not only enables high bandwidth, but also ensures backwards
compatibility with LTE.
The highest bandwidth currently supported by LTE is 20MHz. LTE-A aggregates
multiple carriers that are backward compatible with LTE to support a bandwidth of up
to 100MHz. LTE-A adopts three forms of CA – continuous CA within the band,
non-continuous CA within the band, and non-continuous CA outside of the band – to
aggregate multiple continuous or non-continuous component carriers. Given the
asymmetry of uplink and downlink traffic, LTE-A can also aggregate asymmetric
carriers in the typical scenario that downlink bandwidth is greater than uplink
bandwidth.
CA not only dramatically increases spectrum resource utilization, but also helps
operators flexibly combine bandwidth and solve spectra discontinuity to increase the
user’s peak rate and network throughput. CA also poses no additional requirements on
terminals’ receiving ability. Therefore, LTE-A terminals with a receiving ability of
over 20MHz can receive multiple component carriers simultaneously, while LTE
Rel.8 terminals can normally receive one component carrier.
Enhanced MIMO
Given that frequency resources are increasingly scarce, increasing channel capacity
through multi-antennas has been widely adopted in multiple standards. Notably, this
is a key way of increasing LTE-A’s peak and average spectral efficiencies.
LTE Rel.8 supports one, two, or four transmitting antennas on the downlink, two or
four receiving antennas on the terminals, and a maximum of four layers of
transmission on the downlink. On the uplink, LTE Rel.8 supports a single transmitting
antenna on terminals and a maximum of four receiving antennas at base stations. The
multi-antenna transmission mode of LTE Rel.8 includes open-loop MIMO, close-loop
MIMO, beam forming, and transmission diversity. In addition to single-user MIMO,
LTE also uses a multi-antenna transmission approach – multi-user MIMO – to
increase spectral efficiency, which enables multiple users to use the same wireless
transmission resource through space division.
Based on LTE Rel.8, LTE-A supports a maximum of four transmitting antennas on
the uplink. If the physical uplink shared channel (PUSC) adopts the single-user
MIMO, LTE-A can support up to two codeword streams and four transmission layers.
The PUSC can also improve transmission quality and coverage of uplink control
information through transmission diversity. LTE-A supports up to eight transmitting
antennas on the downlink and can transmit two codeword streams and a maximum of
eight transmission layers. This further increases the throughput and spectral efficiency
of both uplink and downlink transmissions. On the downlink, LTE-A supports
dynamic switching between single-user MIMO and multi-user MIMO, and further
boosts the performance of downlink multi-user MIMO through enhanced channel
state information feedback and a new codebook design.
LTE-A multi-antenna technology increases the peak and average spectral efficiencies
and dramatically enhances capacity and coverage to improve network performance.
CoMP
CoMP enables cell-edge users to coordinate and simultaneously receive signals from
and send signals to users of multiple cells. Downlink performance can be dramatically
improved if the transmitted signals from multiple cells coordinate to avoid mutual
interference. On the uplink, the signals of multiple cells are received and combined. If
multiple cells are coordinated and scheduled simultaneously, inter-cell interference
can be suppressed and the signal-to-noise ratio of the received signals can increase.
Based on the relationships between the nodes to be coordinated, CoMP is mainly
divided into two modes: intra-site CoMP and inter-site CoMP. Intra-site CoMP covers
collaboration within a single site. As there is no restriction on backhaul capacity, large
volumes of information can be exchanged between multiple cells within a site.
Inter-site CoMP covers multiple site collaboration, which has higher requirements on
backhaul capacity and delay. Currently, the performance of inter-site CoMP is limited
by backhaul capacity and delays.
CoMP includes downlink CoMP transmission and uplink CoMP reception. Uplink
CoMP reception increases a cell-edge user’s throughput by receiving the user’s data
by coordinating multiple cells. Downlink CoMP transmission adopts two forms of
collaboration – joint processing and co-scheduling/beamforming – depending on
whether service data is obtained on multiple coordinated points.
Joint processing occurs when multiple cells coordinate and act as a single virtual cell
to serve terminals together. This usually obtains better transmission gains but has
higher requirements on backhaul capacity and delay.
Collaborative dispatch/beam forming dynamically exchanges information among
multiple cells and coordinates the corresponding scheduling and transmission weights
to minimize interference among multiple cells. The terminals must measure the
channels of multiple cells and provide feedback, including the expected precoding
vector from the serving cell and the interference precoding vector from the
neighboring cells that produce strong interference. Coordinating the schedulers of
multiple cells assists each cell to reduce interference on its neighboring cells when
transmitting beams. This ensures the signal strength expected by the users of a cell.
CoMP is a key LTE-A technology that effectively increases the average capacity of
cells and the signal-to-noise ratio for cell-edge users. Although CoMP increases
system complexity, its capacity and coverage advantages greatly outweigh its
disadvantages.
HetNet
Statistics show that 80% to 90% of future network throughput will take place in
indoor and hotspot nomadic scenarios. Indoor, low-speed, and hotspot application
scenarios will rise in importance in the mobile Internet era, requiring operators to use
new technologies to enhance the user experience of traditional cellular networks in
hotspot scenarios.
In a traditional macrocell network, operators can obtain more spectra or add base
stations (such as cell splitting) to increase supply capacity. Alternatively, they can
deploy more base station antennas to realize advanced MIMO technology. These
measures raise expenditure and deployment complexity, greatly limiting the network
performance evolution potential of a traditional macrocell.
HetNet technology significantly increases network throughput and overall network
efficiency by distributing low-power nodes in areas covered by macro base stations to
form a heterogeneous system with different node types offering the same coverage.
Low-power nodes include micro, pico, remote radio head (RRH), relay, and
femtocell. Increasing small, low-power stations is cheap, flexible, and effectively
increases network throughput. Small stations not only accurately offload the hotspots
of the macrocell, but also cover macrocell blind spots.
The key to HetNet is the collaboration of macro base stations and micro base stations,
especially in terms of interference coordination and interoperability.
Huawei’s innovations
Huawei is actively involved in the 3GPP work group with 1 chair, 3 vice chairs, and
32 reporters. Huawei standard body comprising many senior experts continually
contributes to core LTE/LTE-A technologies, based on their specialist knowledge of
market demands, and rich product R&D and commercialization experience.
At CTIA Wireless 2010, Huawei demonstrated LTE-advanced. Offering the world’s
fastest downlink data transmission rate at 1.2Gbps – over 40 times faster than current
commercial 3G networks – Huawei again set a new speed record for mobile
broadband networks.
On the path of LTE evolution to LTE-A, Huawei has fully addressed the main
challenges facing mobile broadband networks. It has also designed and developed a
range of leading products and solutions including the 3mRRU solution which features
the lightest and smallest dual-transmission module in the industry, with ease of
installation and maintenance; the 4mRRU solution which helps reduce the number of
sites and modules to be configured, cut down combination insertion loss, simplify
antenna system, save on TCO and support 5-band and 3-mode; adaptive antenna
system (AAS) & adaptive antenna array (AAA) which, through integration of RF
module and antenna, boast the simplest site installation, with improved site efficiency,
saved TCO, enhanced network performance via beamforming, and boosted network
capacity via cell splitting; and the HetNet with micro & pico & femtocell solution,
which effectively offloads hotspots and covers blind zones in supplementing macro
network, featuring easy and cost-efficient deployment of low-power nodes. These
solutions offer multiple advantages including smaller and lighter modules, lower TCO,
and the full utilization of available frequency bands to increase spectral efficiency and
enhance system capacity.
In the future, LTE-A will become the mainstream MBB technology. Huawei will
continue to innovate and lay a solid foundation for LTE and LTE-A products and
solutions to ensure MBB becomes “broader and smarter”.
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