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Visions of 5G Communications

Jaydip Sen (# 197587)

Innovation Lab, Tata Consultancy Services Ltd.Bengal Intelligent Park, Kolkata-700091

Email: Jaydip.Sen@tcs.com

1 Introduction

Pushing the envelope well beyond the state-of-the-art in broadband wireless while building on the

emerging generation of cognitive-radio and cooperative communication technologies, the 5th

Generation

(5G) communication system will aim at designing and developing novel technologies, systems and

networks that integrate into a flexible and dynamically-operating architecture. The architecture will

possibly allow up to 1 Tbit/s (1 terabit per second = 1012

bits/s) wireless link rate in burst-mode and at short

distances or as system aggregated traffic and, a sustainable symmetric link rate of approximately 300 Mbps

to mobile terminals at high speed. These demands are needed to meet the mega-communication demands of

futuristic applications such as immersive and tele-presence applications thus enabling human-centric

communicationsin 2020and beyond. With coverage ranging from the very-short distance in the personal

spaceat the home, the office or the car, to the mid-range in a metropolitan environment, the 5G system

will hopefully materialize G. Marconis vision articulated more than eighty years ago by the phrase: It is

dangerous to put limits on wireless.The realization of such a challenging goal calls for breakthroughs in a number of different areas

but, more importantly, requires the re-consideration and reformulation of the fundamental networking

design principles to take into account the dynamics of large interconnected systems. It will certainly take,

to put it in the words of Marconi, multiple syntoniesto achieve this task [1].

The challenging requirements of 5G can be attained designing new air interfaces and systems that

achieve a 3 to 5 times improvement over current wireless communications in terms of channel efficiency;

by using larger channel bandwidths in uncontested areas of the spectrum in higher frequency such as the

EHF band and/or considering spectrum co-existence and sharing; employing smaller size cells with

optimized dynamic spectrum management across different technologies; by developing novel cross-layer

and cross-network optimization technologies based on the principles of power efficient cognitive and

cooperative communications; by developing an end-to-end 5G system by jointly designing radio access

systems and network protocols across a number of heterogeneous network architectures including ad-hoc,

mesh and next-generation of cellular networks employing femto-cells and virtual-cells; and, by offering

improved wireless-wireline interfaces with lower overheads to achieve the aggregate bandwidth that is

needed to support the mega-communication demands of futuristic applications.

In this concept paper, we discuss some motivational aspects in 5G communication research and

discuss some specific challenges and techniques to overcome those challenges. The rest of the paper is

organized as follows. Section2 presets the motivation for 5G communication research. Section 3 presents

the concepts of 5G communication system. Section 4 depicts various scenarios in which 5G communication

will be deployed and discusses some specific architectural issues of a 5G network. Section 5 presents a

computational approach to illustrate how it is possible to achieve terabyte communication in 5G systems.

Section 6 concludes the paper.

2 Motivation for 5G Communication

In recent years we have witnessed an exponential increase in wireless access bandwidth that is

commercially available to the end user. We envision that the need for high throughput will continue toincrease in future wireless networks, fired by the rising needs of the mass market in the fields of bandwidth

demanding applications such as entertainment, multimedia, intelligent transport systems (ITS), tele-

medicine, emergency and safety/security applications. Futuristic applications such as: 3D Internet, virtual

and augmented reality that combines data for all senses, audio, visual, haptic, digital scent, (e.g., tele-haptic

applications, like planet or deep sea exploration), networked virtual reality (e.g., video streaming in social

networks - users stream their own reality), and tele-presence (e.g., immersive environments with

applications in both the commercial and military fields), can push the demand for real-time symmetric

wireless connectivity to an individual with a data rate of 300 Mbps.

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Another major driver for increased demands in wireless capacity is the growth in capabilities of

consumer devices. Some examples are 60 frames/s Ultra-HDTV appliances targeted for a mass market 10

years from now and requiring data rates of the order of Gbps, 50 Mpixel still-cameras having the same

resolution as photographic 35 mm film and, person-sized very-high resolution displays. This future

consumer-technology will create the psychological effect of presence orimmersion in the image and will

enable new applications that were hitherto unfeasible. For example true tele-presence will be a real

alternative to travelling and will make tele-working from the home, unlike present tele-conferencing, anenergy- and time-saving, quasi-equivalent to work at the office. It will make most private and business

travelling superfluous.

The drop in cost of 3D imaging and cave visualization technologies will open up new applications

in the consumer and professional sphere. The latter will demand consumer-level super-computing and

data storage. This in turn will demand the timely transfer of huge quantities of data between system

components, such as computers, display devices and storage servers in the house. Tbit/s communication

will be a strong enabler for such future systems.

At the same time, it is expected that a trillion devices will be connected to the Internet of the (not

so distant) future creating great technological challenges in terms of the networking architecture. While

terabit wireless communications seems out-of-reach for todays technologies, according to Gilders Law,

which predicts a six-fold increase of the available bit-rate every 1.5 years, and given that gigabit wireless

bit-rate is attainable today under certain conditions, it should take approximately six years to achieve this 1

Tbit/s target.

Existing wireless technologies (3G+ cellular, WiMAX IEEE 802.16e, WiFi, WiMedia) as well asthe corresponding emerging next generation networks (LTE/LTE-advanced, IEEE 802.16m, IEEE 802.11n,

etc.) in the WWAN, WLAN and WPAN scales are not expected to meet such demanding needs for data

rates. Significant breakthroughs in the state-of-the-art are required to attain this level of performance

leading us to what can be characterized as a new paradigm for future systems.

Future home and building environments are a domain where, in the coming decade, large

quantitative and qualitative changes can be expected in services and applications that ultimately will benefit

from wireless Tbit/s communication technology. All-wireless indoor communication, or wireless,

supported by a basic infrastructural fiber-backbone, will be the solution of choice because it offers the

maximum amount of architectural freedom in designing new houses and buildings and in placing objects

within the buildings. Furthermore, the tremendous growth of the number of networked devices (1000 per

person expected in 2017), requires wireless solutions from a cost perspective and to support mobility, since

a large fraction of the devices will be associated with people and robots.

Ambient intelligencein the house or building will be supported by vast numbers of sensors (fromsimple ones to complex ones such as sophisticated cameras), building of user profiles, tracking of all

relevant data in very large history files, distributed computing and by artificial intelligence techniques.

Again there will be a need for fast and real-time transfer of huge amounts of data between system

components. This will be supported by Tbit/s communication technology.

To summarize, we expect that Tbit/s communication in 5G will be needed 10 to 15 years from

now for very high resolution multiple real-time multi-media streams and, for fast transfers of huge data

files among consumer and professional systems and devices. Moreover, this will not only be needed to

support the new application and services that are foreseen, but also to guarantee their provision.

3 The Concept of 5G Communication

The objective of the 5G system is to create the enabling wireless infrastructure for the human-

centric communications in 2020 and beyond. The drivers for the advancement in broadband wireless

communications are expected to be on the one hand, the increasing demand for ultra-high bit rate short

range links operating in burst mode (and reaching rates up to the terabit level over very short ranges), and

on the other hand, the need for delivering a sustainable rate of 300 Mbps to mobile terminals at high speed

for the needs of immersive applications and tele-presence [3].

In order to realize the 5G vision, major advancements and breakthroughs will be required in a

number of key technologies spanning all layers and system scales of the wireless networks of the future. In

general, a number of different technologies and systems are expected to provide the foundations of the

network of the future optimized to the particular requirements of different classes of applications. The three

founding pillars of the top-down design approach of 5G will be:

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An information theoreticperformance/capacity estimation of different types of networking paradigms.

Protocol design for end-to-end performance optimization rather than the ones based on the classical

layered design.

Self organizing / self healing networks based on cognitive networking principles essential for

managing the complexity induced by a variety of possible usage scenarios on the one hand and to

minimize the spectrum and energy requirements on the other.

As shown in Figure 1, development of 5G should be structured around the following three main

operational domains.

Short-range low mobility communications: Indoor/Outdoor Human-Centric Communications

Outdoor broadband wireless with full mobility: Wireless Wide-Area-Networks, WWANs.

Converged communications: Infrastructure Support, Integration with the Future Internet.

Figure 1. The concept diagram of 5G communication system

We envision the following revolutionary design paradigms for 5G:

Designing new air interfaces and systems that achieve a 3 to 5 times improvement over current

wireless communications in terms of channel efficiency.

Exploiting larger channel bandwidths in uncontested areas of the spectrum in higher frequency bands

and/or considering spectrum co-existence and sharing, while employing smaller size cells and

essentially overlapping coverage between the existing and future networks. The 5G mobile terminal

not only will be able to cognitively select an air interface over which to establish a connection but also

concurrently use several air interfaces (e.g., 5G new radio technologies, but also the emerging

generation of WiFi, LTE-Advanced and WiMAX systems) into the same end-to-end connection.

Making extensive use of small-sized cells and the concept of virtual cells, i.e., grouping a number of

small cells in a synchronized manner in a way that they all operate in the same channel and are seen bythe terminal as a single base station.

Developing novel cross-layer and cross-network-domain optimization technologies based on the

principles of power efficient cognitive and cooperative communications.

For optimization of system performance, a comprehensive approach should be taken in developing a

converged 5G system by jointly designing radio access systems and network protocols across a number of

heterogeneous network architectures including ad hoc, vehicular, mesh and femto-cell networks, efficiently

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connected to the wired internet of the future. The complexity of networking will have to be autonomously

managed.

4 Different Usage Scenarios in 5G Communication

This section provides a detailed account for a usage scenario of transaction between the present and the

5G communication environment.

4.1 Short-Range Communications

The human-centric vision of 5G is to provide each user with ubiquitous, personalized network

access, at very high sustainable data rates approaching the Ethernet current state-of-the-art (10+ Gbit/s)

reaching up to 1 Tbit/s in bursty mode. A ubiquitous and pervasive wireless network offering consistently

10 Gbit/s can be used as an alternative to Ethernet and an access network to Tbit/s fibre networks. A

possible scenario to be demonstrated in 5G for this operational domain is the sync-n-go application, or

"your own pocket Internet" on a burst, with very fast downloads from hotspots, e.g., a movie about 10GB,

transmitted in less than one second when you pass with your "multimedia cell" over a portal. The whole

network becomes a fast burst intelligent environment, thanks to the high-speed short range portals widely

available.

5G communication will achieve this level of performance by exploiting millimetre wave

communication links, by improving the bandwidth efficiency via MIMO and highly directional antennas

and by the concurrent and seamless utilization of different frequency bands and air interfaces into the sameconnection. The concurrent utilization of existing air interfaces into the same connection will be possible.

One of the key challenges for 5G is to identify the particular bands in the spectrum range from the

EHF band, that allow for the design of systems that yield high data rate and significant bandwidth

efficiency, as required for Tbit/s communications. In particular, the band ranging from 70GHz up to

300GHz may be considered. At those high carrier frequencies, the specific propagation conditions together

with the devices characteristics in term of non-linearities and phase noise as well as limitations on the

passband of digital devices (A/D converters), limit the efficient use to achieve Tbit/s when traditional

design approaches are considered. Therefore, novel and unconventional solutions, both for RF and

baseband design should be considered. Moreover, the high absorption rate at those high carrier frequencies

poses great challenges for their utilization in non-LOS and mobile connections.

On the other hand, the high directionality attained in this band can be used to increase spatial

multiplexing. 5G short-range communications will be based on multiple directional antennas transmitting

to the same terminal in order to create spatial diversity and mitigate LOS blocking. Moreover, 5G willrequire not only novel PHY layer technologies but also advances towards cognitive networkarchitecture.

Progress towards such a cognitive network, which is a step ahead of the cognitive radio concept, can be

achieved through collaborative research in a series of interrelated fields such as: directional links, adaptive

modulation and coding, medium independent handover, cognitive radio and cooperative techniques at

different layers of the protocol stack. Furthermore, the human-centric paradigm is requesting a huge

interaction of the user with the environment in order to interchange information related to the context,

profile, role and other relevant information which in general may help to optimize the whole network

behaviour as well as the user perception.

4.2 Outdoor Broadband Wireless (Full Mobility)

At the WMAN scale, 5G should aim at the 1 Gbit/s milestone at the down-link and at a

sustainable, symmetric rate of 300 Mbps to a mobile terminal at high speed, while the vision of the 1 Tbit/s

rate corresponds to aggregate capacity of a large number of users served in a metropolitan area. This targetcalls for a revolutionary step also for the techniques to be adopted: 5G shall consider new communication

systems, based on the suitable transmission, signalling and modulation techniques, to be implemented also

in new bands.

Increased data rates may be achieved by decreasing the communication range through the use of

femto-cells (mini home base stations that dynamically share the resources with macro-cells), by the use of

cognitive and cooperative techniques, true MIMO (on both sides of the link) and various types of beam-

forming for establishing highly directional links. This allows for a significant positive effect, i.e. a

reduction of the overall energy consumption of wireless networks. The solution that we propose for the 5G

system is based on the virtual cellconcept. The key advantage of virtual cells is that mobility signalling is

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not increased compared to larger cell systems and therefore management overhead and terminal complexity

are in the same order of magnitude. At the same time, the solution retains the advantages of a small cell

system since the short distance between the terminal and the nearest cell allows high bandwidth

communications.

4.3 Converged 5G Systems

In addition to developing the enabling technologies and network components, 5G will also design

a converged architecture and network and enable ubiquitous terabit wireless connectivity for human-

centric communications over the network of the future. In this context, 5G should design and develop

wireless/wired interfaces and network protocols in order to integrate the wireless access networks to the

fixed infrastructure as well as the core optical part of the network of the future.

This involves addressing seamless and efficient wired/wireless network integration as the access

part of the 5G approach will possibly be based on a high capacity wireless network solution while the

metro-core network of the future is clearly expected to be an optical fiber based infrastructure.To ensure an

optimized convergedwireless/wireline network, research on 5G should study and propose novel solutions

addressing the overall network architecture and the interconnection of the different technology parts of the

network with emphasis on the functional interfaces as well as the associated protocol and control plane

issues. Specifically, the focus in 5G will be on the design of the wireless/wireline interfacing network

nodes, i.e., the nodes that will facilitate the integration of wireless and wired (optical) network segments.

These nodes will play the role of edge devices as far as the optical network is concerned and will provide

aggregation, traffic shaping and traffic engineering capabilities. In order to globally optimize the end-to-end connectivity, research on 5G should also aim to design, develop and evaluate novel transport protocols

suitable for the wired part (optical fiber) of the network that are able to support the characteristics of both

the metro and the core part of the network offering abundant bandwidth in an efficient and cost effective

manner. A high level description of the converged 5G network architecture is shown in Figure. 2.

Figure 2. The converged 5G network architecture

The converged 5G architecture will consist of a number of self-organizing / self-healing wireless access

networks that are seamlessly connected to the core network of the future. These access networks will bedesigned based on cognitive and cooperation networking principles. At the local scale, these cognitive

access networks can be isolated from each other but by co-existing in a certain area, they can operate in co-

operation with each other in order to satisfy in-aggregation the mega-communication needs of the users.

The key building blocks of the 5G access networks will be: the 5G-node and the 5G-station. We envision

5G node as an intelligent cognitive multi-radio, multi-band, MIMO mobile device capable of operating in a

variety of spectrum allocation and interference conditions by selecting cross-layer, cross-network

optimized physical and network layer parameters often in collaboration with other radios even if they

belong to different co-located networks. The extreme flexibility of the 5G-node has significant implications

for the design of network algorithms and protocols at the local/access network and global internetworking

5G BS & UE

5G Architecture

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used approaches. With multi antenna optimizations a bandwidth efficiency of 6 to 8 could be achieved.

This, however shows that bandwidth efficiency is inversely related with the carrier frequency, i.e. the

higher the chosen band the lower the achievable efficiency, at least if current concepts (and not innovative

concepts) are used also to those high frequency bands.

To reach around 100Gb/s we have to find a band with enough bandwidth at reasonable bandwidth

efficiency looking at the frequency allocation map and assuming an achievable bandwidth efficiency of

4bit/s/Hz at frequencies above 100 GHz. In that case we need 25 GHz bandwidth and the first band that

provides such a wide spectrum is at 250 GHz. From 250 - 300 GHz we have 50 GHz free which fulfils the

requirements. Therefore natural choice to achieve 1Tbit/s, very high frequency bands (above 200GHz)

should be utilised but also guarantee at those frequency bands a spectral efficiency close to the ones

achievable today (around 10 at least) (10bit/s/Hz*100GHz=1Tbit/s).

The use of so high frequency bands opens many challenges such as: (1) available technology, (2)

channel characterization at those frequencies is lacking, (3) design of robust modulation and transmission

techniques considering CMOS components limitations, (4) passband of digital device do not allow to use

one channel with a bandwidth higher than 2GHz today.

About the available technology, a lot of progress has been already done and is foreseen. However,

with respect to point (4) above, we should explore the possibility to send the information over large

bandwidth using low precision ADC and also the possibility to send the information over several narrower

sub-bands to be aggregated.

Exploiting parallel channels in higher frequency bands will also be an interesting research

direction. If we consider the use of parallel Gaussian channels to increase the capacity, then the total poweris distributed over K parallel Gaussian channels. In this case, the channel capacity is given by: C = KW ld

(1 + P/(No K W)) / bits per second; when the channel is unknown to the receiver. For example for P = 10

W, No = 1e-9 W/Hz, C = 1 Tb/s; one might choose K=20 parallel channels and W = 10 GHz.

Roughly, we need to exploit 20 parallel channels when the bandwidth is 10GHz. Those parallel

channels must be found in the spatial domain (MIMO) or in other domains (for instance, Code Division

Multiplexing). 5G may aim to attain even higher rates by the use of more sophisticated MIMO techniques

at the baseband (e.g., linear transmit pre-coding along the channel Eigen modes, assuming channel

feedback, or with nonlinear equalization techniques at the receiver). In which case, overall re-use efficiency

(bits per Hz per m3) is more relevant than simple spectral efficiency (bits per Hz).

Building upon the previous idea of using several parallel channels in order to achieve spatial

diversity through the use of high-order MIMO arrays, we can achieve even higher aggregate data rates once

we use parallel channels in different bands and radio/technology domains. This is also one of the design

directions that may be undertaken in 5G. At this point, we need to notice that systems exploiting highfrequency bands, such as 60 GHz and E-Bands and more, tend to concentrate radiated power in a very

narrow path and have considerable attenuation at much shorter distances than occurs in the lower

microwave bands. Due to this aspect, these systems are designed to operate in the phase of co-frequency

and with very short re-use distances.

A quick computation along these lines (utilizing the concept of frequency re-use) gives the

following results.

Capacity assessment

1) 64 -128QAM

2) the 19 + 19 channel wide 250 MHz available in 71-76 and 81-86 GHz

(ECC/Rec(05)07)

3) Frequency reuse H/V concept

4) Horizontal Spatial reuse due to antenna beam narrow (1 @E_band)

5) As point 4 but Vertical Spatial reuse

Figure 4. Horizontal section of a 5G node

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If we also exploit the concept of the space-reuse, as shown in Figure 5, we design a pylon with x5

previous scenario, exploiting space re-use.

Capacity assessment

H distance 10meter and Pylon of 100m

H Reuse factor let put x 5

Aggregated capacity= 760*5 =3.8 Tbit/s

Links 1 Km

Area = 10.000 m2

Volume = about 10.000m3 Efficiency= 3.8T/10.000= 100 Mbps/m3

Figure 5. Exploitation of space re-use

However, Terabit communications also poses challenges at higher layers, i.e. at the link and MAC layer.

One such challenge is extremely fast data packet aggregation. Today the average payload of a data packet

for a wireless communication system is between 1500 bits to some kilobytes. The short packet size has

been chosen due to the inherent high bit error rate. In extremely fast communication systems, however, the

ratio between the header and the payload becomes an important issue. To achieve high throughput, one has

to aggregate several messages to avoid large header overhead. Therefore new methods for buffer controland flow control have to be realized. Moreover high speed also implies very short reaction time to avoid

reduced throughput. Today the generation of an ACK messages requires approximately 5 s. In 100 Gb/s

systems 5 s equals 500 kb of data. A reduction to approximately 0.5 s seems to be necessary. In addition,

cognitiveness, efficient resource management, joint PHY and higher layer optimization, different topology

architectures are some of the concepts that must be investigated to allow terabit/s communications.

6 Conclusion

Responding to the need of the society of 2020 and beyond, 5G communication system shall offer

ubiquitous terabit wireless connectivity that will enable the human-centric mega-communication

applications over the network of the future. It will enable people to seamlessly bridge the virtual and

physical worlds offering the same level of all-senses, rich communication experience over fixed and

wireless networks. Applications envisaged over 5G systems will include networked virtual and augmentedreality, and tele-presence delivered to the mobile users. Additional applications would include data

collection in disseminated sensor networks in urban environments, e.g., for micro-climate control of public

health. 5G communication will synergistically exploit higher spectrum efficiencies in smaller cell sizes

with optimized dynamic spectrum management across different technologies, cognitive concepts using

newly freed and higher carrier frequencies in the EHF band (30-300 GHz) and improved wireless-wireline

interfaces with lower overheads to achieve the needed aggregate bandwidth. Some of the important areas in

which major research breakthrough will be required for success of 5G are: design of efficient multi-link

aggregation mechanism, guaranteeing QoS requirements taking advantage of heterogeneous access

technologies, selection of available resources, multilink-multiband-multinetwork communication,

disruptive solution exploiting heterogeneity in terms of availability of networks, design of suitable MIMO

strategies, cooperative communication and network coding techniques, equalization and channel

impairment mitigation techniques, multi-user MIMO, scheduling for MIMO systems, distributed MIMO

systems etc. By pushing the envelope well beyond the state of the art, 5G will make the vision ofwireless/wired convergence a reality in the network of the future.

References

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H.G.J Aitken, Syntony and Spark: The Origin of Radio, Princeton University Press, 1985.

[2]

S. Cherry, Edholms law of bandwidth- telecommunications data rates are as predictable as Moores

law, IEEE Spectrum, July 2004.

[3] R. Prasad, P. Pruthi and K. Ramareddy, The top 10 list for terabit speed wireless personal services,

in Springer Journal on Wireless Personal Communications, Special issue on GIMCV, 2009.