The
contrast in capabilities between IMT-Advanced and its predecessor is remarkably
exciting. IMT Advanced was designed to address the increasing demand for mobile
traffic. To put the demand expectations into perspective, it is helpful to note
that a 26-fold increase in mobile data traffic is expected by 2015, reaching a
rate of 6.3 exabytes per month. With the world population estimated to grow to
a range of 7.2 to 7.5 Billion people, an estimate is made there will be as much
as 1 mobile unit or device per capita connecting wirelessly. Estimates are also
predicting that 1.3GB per month generated per smartphone, with video taking up
to two thirds of the traffic. In 2020, more than 50 Billion devices will be
connected to the Internet and serving a population in the range of 7.5 to 7.9
Billion – almost six devices per capita .
Towards
this vision, the earlier deployments of IMT-Advanced would have been made, with
great advancements made in both the wireless and the wired Internet. The
deployments will provide substantial understanding and experience of how OFDMA
operates in practice, which is currently lacking. The use of heterogeneous
access networks is also projected to be the norm, with different access technologies
aimed at different connection requirements. In the meantime, policies and
technologies currently investigated for combating spectrum will slowly emerge,
and initial large scale realizations of the adaptive and opportunistic
software-defined or cognitive radios will be made. Together with these physical
layer advances, especially in cooperative MIMO communication, dynamic spectrum
access and allocation will open the door for higher capacity communication.
It is these capacities that will make possible high bandwidth transmissions,
both in the downlink and the uplink, in addition to supporting the transport of
massive amounts of information. At the radio access interworking and backhaul
level, advances will facilitate a more capable network-end management of
network functionalities that is fitting to the multitude of devices to be
communicating through the network.
At a larger scale, earlier forms of network intelligence will appear that
will facilitate much desirable characteristics of network autonomy. Such characteristics
include the currently deliberated aspects of self-optimization and self
healing.
This autonomy will depend on processing massive amount of information that
will be already traversing the network, generated either by passive sensing or
through active Machine-to-Machine (M2M) communications. Many of the recently
starting initiatives will ensures that such processing is made in a manner that
preserves the integrity and privacy of the processed information, while achieving
the desired network performance and user satisfaction objectives. At the same
time, operators and vendors will begin employing mechanisms for reducing energy
requirements, both per-unit and for networks as a whole. Such “greener
operation”, however, will not be at the cost of network reliability.
In this the enablers of this vision, together with the challenges faced to
realize its practicality are discussed;
Network Capacity
Several technologies have been sought in order to enhance the capacity of
access networks at a cost efficient manner.Without doubt, the choice of
multi-carrier access techniques will offer both great flexibility and
reliability in such direction. However, it is in advanced antenna and network
configurations that substantial capacity gains are achieved. Already, the
notion of small cells – through the in-band femtocells or out-of-band WiFi
networks – are already beginning to play an important role in today’s networks.
The importance of small cells in the next few years can be highlighted by
estimates of the amount of data they are expected to support −800 million
terabytes per month by 2015.
Other advances will come at higher costs, including the use of relaying
techniques and cooperative MIMO. It is generally understood that such “meshed”
wireless communications can provide substantial gains. Relaying, for example,
combats path loss and shadowing loss through the breaking down of the wireless
link into smaller and reliable segments. Similarly with MIMO, which have shown
great versatility in either mitigating interference or enhancing the
reliability of the wireless link. And while for some of these advances the
limits on possible gains are yet to be figured , the practicality of achieving
these gains will be slowly evaluated over the next ten years as they are
introduced to actual deployments. Certain issues, such as finding deployable
mechanisms for resource allocations, remain unresolved. More critically, it
will be important to demonstrate that capacity gains made exhibit reliability
and cost efficiency.
LTE and LTE-Advanced are complemented by an IP-based network core, the EPC.
There is also strong IP-based internetworking in WiMAX. Such support will be
crucial in creating heterogeneous network composites – not only for user
access, but for generalized device access. Work within the 3GPP and 3GPP2, in
addition to the efforts in IEEE 802.21 or Media Independent Handover, are all
aimed at supporting inter-technology handovers at the access level. There are
also efforts including those of the IEEE P1900 working group that are aimed at,
among other things, enhancing operational coexistence between the different
radio technologies.
A definite trend that is to grow over the coming years is the addition of
satellite networks to the existing heterogeneity. Traditionally, and despite
their great bandwidths, satellites have been avoided for user- and device level
access due to both their cost and delay characteristics. However, there is
currently great interest in near-space (17∼22 km) satellites called High Altitude Platforms (HAP).
The delay characteristics for HAPs will be functional for terrestrial
application. HAPs will also be characterized by wide coverage, offering
reasonable coverage overlays for IMT-Advanced networks. Already, the ITU-R has
issued the minimum performance requirements for HAPs providing 3G service in
certain regions.
Cognitive Radio and Dynamic Spectrum
Software-Defined Radios (SDR) were initially defined so as to facilitate
changing the characteristics and capabilities of a radio interface simply
through reprogramming. Its evolution, Cognitive Radio (CR), was one where the
programmability of the SDR can be made over-the-air and on-the-fly. What is
more, however, is that a CR had sufficient processing capability to
autonomously understand and react to various elements of the radio’s context of
operation. Among other things, these characteristics include identifying
whether the current spectrum band of operation is the best spectrum available
for the radio’s active communication, and whether there are bands that are available
and, for example, would offer greater bandwidth or better transmission quality.
For CR to perform, it requires more than simply identifying whether or not a
particular spectrum band is busy – rather, it becomes important that the radio
recognizes what entity is utilizing that spectrum, and know for how long will
this utilization will take place.
Such distinction is greatly important, especially in light of recent
international cooperation between the different Telecommunications Regulatory
Authorities (TRA) of the different countries and the ITU-R. These cooperations
are at spectrum harmonization, refarming and reallocation. In addition, many
countries now recognize primary and secondary users for certain bands, allowing
for cooperative arrangements and coexistences between the different spectrum
users, both licensed and unlicensed. It thus becomes possible for a secondary
user to utilize spectrum “holes” or “empty spots” in a primary user’s band or,
depending on the band and mode of communication, for both primary and secondary
users to operate in the same band. Such cognition, however, is not limited to
licensed bands. Bluetooth, for example, is already instilled with adaptability
so as to overcome from other devices in the ISM band such as WiFi network
elements or microwaves.
Network Intelligence
Services utilizing network and location analytics are already emerging in
the smartphone applications market. Meanwhile, the proliferation of various
sensing and actuating platforms, for example, ANT+ and IQRF, that interface directly with mainstream smartphone and network
access types will soon allow for more valuable services that are more prompt,
reliable and relevant. In this interweaved connectivity between context and
personal preferences (both through settings and through non-invasive
profiling), in addition to the service infrastructure of social networking
platforms, the users’ wireless and mobile experience will become much more
enhanced. Another dimension of interest is that of utilizing network
information to discern physical properties. Many examples of this have been
displayed, both in research and industry. One of the commercial examples
involves utilizing network traffic levels in recognizing actual street
congestions.
For the considerations of access network operation, however,
functionalities that employ network analytics include instilling reliable
wireless communication, interference management and mitigation, power
management, resource allocation, and reduced energy. Both LTE and WiMAX support
various mechanisms for autonomous operation of network entities, and have made
provisions for selfoptimization in various aspects of their respective
standards. For example, the operation of femtocells cannot do without autonomy,
especially given the ad hoc nature of their deployment. Another example
involves the required processing capabilities for Coordinated Multipoint
Transmission (CoMP).
Access Network Architecture
The introduction of 3GPP’s X2 interface marked a particular evolutionary
step in the design of access network infrastructure. Traditionally, base
stations were connected to network cores in centralized star configuration,
with each base station directly and independently connected to the access core.
Such configuration, exercised up until the earlier releases of UTRAN, results
in substantial handover latencies, especially when it came to IP-based
mobility. Similarly with WiMAX, which is neutral to the choice of network core,
support has been made to realizing flat architectures. A direct advantage of
flat architecture is greatly reduced handover latency times, which was mandated
by the IMT-Advanced requirements letter.
This advantage, consequently, results in reduced disruptions for multimedia
IP handover as the users traverse the network. Through internetworking base
stations, user context can be transported from a serving base station to the
target one without having to go back to the network core. As was observed,
additional optimizations are also possible in instances where the user terminal
moved between a base station and its children relay stations.
Careful network design, however, is required in order to achieve these
desirable characteristics. Design considerations would include aspects such as
where is it best to connect the access network to the core or the identifying
topology configurations that match the projected traffic load while achieving
certain levels of reliability. Looking beyond IMT-Advanced networks, interest
has already started in what is called “ultra-flat architectures”, wherein
substantial processing is migrated from the network core to the network edges –
the base stations.
Such migration, however, will largely depend on substantial advances taking
place not in terms (of) processing capabilities, but also in inference
frameworks. In such instances, the issues such as identifying the best location
for a certain functionality, become more prominent.
Radio Resource Management
Radio resource management (RRM) functionalities oversee the allocation and
maintenance of network resource to the various devices during network
operation. RRM functionalities in IMT-Advanced comprise both traditional and
emerging modules, including modules for admission control, scheduling, resource
reservation (for various prioritization objectives), spectrum management,
ARQ/HARQ, and routing. The various modules comprise different elements of an
overall framework, and are expected to operate in a cohesive manner, serving
specific overall operational objectives. Designing frameworks for IMT-Advanced
networks, however, is not without challenges. By requirements, IMT-Advanced
networks are expected to deal with certain characteristics among which are an
immense magnitude of traffic from both users and devices, a range of traffic
requirements for various services and applications, a range of mobility speeds,
and different types of access technologies and modes. A definite problem of
traditional framework designs is that they do not scale.
Complexity, hence, becomes a key issue to overcome when designing such
frameworks, and one that is prominent at the different levels of network
management. For example, there is
difficulty of scheduling multi-carrier access techniques, both OFDMA and
SC-FDMA.
And while the separation of the time and frequency aspects of resource
allocations does lead to significant operational optimization, scheduling
becomes more cumbersome when introducing advances such as MIMO, either at the
single cell or the multiple cell level. Another example of complexity can be found
at a higher management level, and has to do with admission control of
connections or flows. IMT-Advanced networks will employ different modes of
operation, including point-to-multipoint, where a base station communicates
directly to the device, relaying where the base stations communicate with the
devices through one or more relay stations, or femtocells where the devices
connect through the Internet.
Meanwhile, IMT-Advanced networks will support access heterogeneity, which
adds the selection of access technology to the possible connection choices. In
addition, the flexibility in spectrum allocations will also make possible
varying the spectrum band through which the device is connected, that is, a
spectrum handover. Considering that more than 50 Billion devices will be
connected in the future, the importance of simplifying network selection
mechanisms becomes more pressing.
This complexity issue has already been tackled in several ways. For
example, the above noted notion of small cells “opens up” the capacities at the
network end – a strong leverage when considering different connection
possibilities. At the same time, the introduction of flat architectures have
also simplified the considerations of the RRM as they have forced the decision
making to be more localized, focusing only at users within the cell and the
technologies overlaying the cell’s coverage. Within the research, much work has
addressed the possibility of Common RRM, whereby the resources of overlaid
access technologies can be jointly managed – a powerful advance that is viable
for technologies administered by a single operator. Advances are expected in
the AAA that would further facilitate inter-operator resource agreements and
management. These advances, however, will take a longer time to realize.
Green Wireless Access
By some estimates, cellular networks consume 0.5% of world-wide energy
consumption, with 1% consumed by the user handsets and 99% consumed by the
network. Meanwhile, multiple-interface phones (Cellular with WiFI, Bluetooth,
ANT+, etc.) have been observed to deplete their batteries much faster when all
the radios are active all the time. Not surprisingly, then, that several
initiatives and research projects have focused on reducing the energy
requirements of wireless and mobile networks over the past few years. The
projects, in general, vary in their approaches and their objectives. Some, for
example, have focused on energy reduction through interference management –
reducing the energy requirements of mobile handsets to reliably transmit its
data. Network design plays an important role, whereby the location of the fixed
base stations and the trajectory of the mobile stations are decided in a manner
that also reduces handset energy expenditure. Meanwhile, energy can definitely
be added to the considerations of network selection. Advances in dynamic
spectrum allocation will also play a major role.
These enhancements, however, focus on handset energy expenditure. To
alleviate some of the network expenditure, it is possible (to) utilize
renewable energy sources such as solar and wind turbines. More advanced
mechanisms, however, can also be employed. For example, it is possible to
deploy high density access configurations whereby the all base stations would
be turned in instances of high demand, and only a portion of the base stations
would operate when the demand decreases. Naturally, a small coverage would be
used when all base stations are turned on, and a wider coverage when only a
portion is operating.
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