4g what`s next

8/3/2019 4g what`s next

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Abstract --Currently 2G and 3G are widely used around the

world. One problem with these technologies is that the data rates

are rather limited. To increase the speed, different new

technologies are under development among others WiMAX and

LTE that might be the next generation wireless communication

called 4G. These new technologies use functions like VoIP, Ipv6

and OFDM (Orthogonal Frequency Division Multiplexing).

Unlike 3G that is both circuit and packet switched the next

generation will be fully packet switched. This gives a lot of new

opportunities but also some problems that has to be taken care of

before it can reach commercial use worldwide.

1. I NTRODUCTION

The term 4G refers to the next generation wireless

communication system. Exactly how the next generation

will look like is hard to predict. There is no formal

definition for standards in 4G, more objectives that the

developers are working towards:

- Higher transmission rate

- Higher capacity

- Higher frequencies

- Next-generation Internet support

- Lower system costs

One thing that is certain is that 4G will be IP-based

and fully packet switched like it is on the Internet.

Different 4G technologies are already on its way and

hopefully it will be in commercial use worldwide in afew years.

In this paper we will briefly discuss the background of

previous mobile generations. The evolution from 3G to

4G and the user requirements for 4G, for instance what

the next generation must be able to handle will be

discussed. Later in the article the architecture for 4G,

how it may look like is presented. In 4G it should be

possible to switch between different networks and

therefore a new technology for transferring calls is

needed. This technology is called VoIP and sets new

demands on today’s WLANs. This paper also briefly

presents new access schemes that are needed to be able

to transfer data at very high transmission rates. Finally

WiMAX and LTE are two 4G technologies that are on

its way and there future survival and advantages will be

analyzed.

2. BACKGROUND

In the early 1980s the first generation wireless mobile

communication was introduced and completed around

ten years later. This was an analogue system that

provided voice transmission using frequencies around

900 MHz and had a speed of 2.4 kbps [1].

The second generation wireless mobile

communication was introduced in the late 1980s and

finished in the late 1990s. This was based on a low band

digital data signalling and the most popular technologyin this generation is known as GSM (Global System of

Mobile communications, originally from Groupe

Spéciale Mobile). The 2G uses a combination of TDMA

(Time Division Multiple Access), FDMA (Frequency

Division Multiple Access) and SDMA (Space Division

Multiple Access). Most of the GSM networks today

operate in the 900 MHz and 1800 MHz band. The

problem with 2G was that is was mainly planned for

voice transmissions with the speed of 64 kbps which

wasn’t enough for data transmissions that became more

and more popular.

The third generation of wireless systems wasdeveloped in the late 1990s and introduced a new

technology called CDMA (Code Division Multiple

Access). The main features of 3G are better voice

quality because of new codec’s and higher and more

flexible data rates. 3G operates at approximately 2 GHz

band and has a speed up to 2 Mbps for stationary users

[2].

Kristian Sylwander, Johan Rahnboy

4G or So what's next?



3. EVOLUTION FROM 3G TO 4G

The difference between 3G and 4G is that 3Gs

objective was to develop a new technology and a new

protocol while 4G are integrating already existing

technologies. The evolution of the next generation

wireless technology is both to move beyond the problems and limitations of 3G and to achieve a higher

data rate, reduce the cost and enhance the QoS (Quality

of Service). Unlike the third generation that is both

circuit and packet switched the forthcoming generation

will only be based on packet switching. The next

generation will also operate in a higher frequency band.

In figure 1 the evolution between 3G to 4G can be seen.

There is a big difference in the data rates and other

major improvements of the next generation that will be

discussed later in this article [3].

Figure 1: 3G and 4G Parameters [3]

4. R EQUIREMENTS FOR 4G

As the expectations on the mobile communicationsystem grows beyond the limitations of the 3G mobile

system new demands for the upcoming 4G is a fact. First

of all the data rates has to become much higher as a

result of the improvement in media communication

quality. Most noted by the customers are the size and

resolution of LCD (Liquid Crystal Display) screens, the

number of pixels in built-in cameras and the possibility

to view high-quality video streams directly in the mobile

phone. As stated by Toshio Miki et al. there are three

main directions for improving media communication

quality. These are 3D audio communications, 3D visual

communications and biological information

communication, as shown in Figure 2 [4]. After

analyzing these main directions a result (showed in

Table 1) intended that the future user will need from 1

Mbit/s up to 100Mbit/s [5].

To be able to achieve data rates that are tens of timesfaster than the data rates of today we will need a

completely new transmission system.

Figure 2: Three main directions for improving media

communication [4]

Table 1: Requirements for future networks [4]

When the data rates are increased this much it would

be necessary to lower the cost for data transmission to

make it affordable for the customer. For the 4G system

this means that a broadband channel and a lower bit cost

is required. But how can this be done when we probably

will use a higher frequency band to achieve higher data

rates which will reduce the radius of the cell and hence

more base stations are needed which is costly. A

possible solution is to expand the cell with more



effective radio transmission and improved

modulation/demodulation. Another important topic will

concern the delay of the 4G system. When the data rates

are increased it would be necessary to lower the delay to

a time of 50 ms to achieve a highly real-time

communication [4].

Future mobile communication should be able to

handle a variety of services in addition to the ordinarytelephone services. Services like e-mail, music, video

streaming, Internet browsing, camera, GPS, text

processors, diary, calendar etc should all work in

harmony with each other and be easy to use. Below

some scenarios for the radio access infrastructure is

shown. The explanations of the abbreviation in figures

3-6 is shown in figure 7.

Scenario 1: Outdoor – It’s a requirement that the

upcoming mobile communication system can handle

speeds over 100 km/h for moving mobile phones,

preferably up to about 300 km/h to make it possible for

good communication in fast trains. Another importantaspect is that the cell radius should be about 500 meters

in urban areas and several kilometres for suburban areas

and as stated above the use of higher frequencies means

that technologies for radio transmission has to be

improved to keep the radius of a cell at the given value.

According to research the delay in urban environment is

0.5 to 2 μs [6]. Hence the 4G mobile communication

system has to cope with this delay resulting in a speed of

20Mbit/s uplink and 100Mbit/s downlink channel for a

moving device. A stationary device should be able to

handle speed of about 100Mbit/s uplink and 1Gbit/s

downlink [6]. Figure 3 shows this scenario.Scenario 2: Indoor - Inside buildings, houses and

malls it is necessary to have base stations which mobile

devices can communicate with. There has to be two

types of base stations. First an isolated cell which is

suitable for small houses and second a multi-cell for

malls and larger buildings. When the mobile devices are

used inside a building the speed parameter has nearly no

effect on the communication (only pedestrian speed as

people walks through the buildings) hence the transfer

rates will be approximately the same as for stationary

devices around 100Mbit/s uplink and 1Gbit/s downlink.

The cell radius should be around 30-100 metersdepending on which situation (different sizes on

buildings) [6]. This scenario is illustrated in figure 4.

Figure 3: Scenario 1: Mobile Access (outdoor) [6]

Figure 4: Scenario 2, Mobile Access (indoor) [6]

Figure 5: Scenario 3, Moving devices [6]



Scenario 3: Moving Cell - It should also be possible

for users that are travelling at higher speeds like in

trains, busses and cars to be connected to the network.

This can be done with the moving cell which allows this

kind of radio communication. These cells make it

possible to connect a moving user to a fixed network.

This is illustrated in figure 5.

Scenario 4: Ad-hoc Communication – One way toeliminate dead spots and areas where the transmission

power is low is the Ad-hoc network (see figure 6). In an

ad-hoc network terminals can both communicate with

each other (setup own small network without any

connection with a base station) and communicate with

the fixed network using the base stations. Concerning

speed it should be sufficient that the Ad-hoc network

supports the speed of a stationary mode stated above.

The distance that should be supported between devices

should be around 10 to 100 meters. One big advantage

with the Ad-hoc network is that it can still work in case

of a disaster when the fixed network is out of service.

Figure 6: Scenario 4 Ad-hoc network [6]

Figure 7: Explanation of abbreviations in figures 4-7 [6]

5. ARCHITECTURE OF NEXT GENERATION NETWORKS

Exactly how the mobile communications will look

like in the future is hard to predict however it’s known

that Next Generation Networking (NGN) will be fully

packet switched like it is on the Internet. There are some

main features that may mark the future networks.

Smart antennas - In the next generation networkswireless mobiles will use several smart antennas to

benefit from multipath propogation and can use

Beamforming to follow a single wireless mobile [7].

Beamforming is a technique used for directional signal

transmission or reception [8].

Core network - The core network becomes more and

more based on IP (Internet Protocol) [2]. For the future

generations the core network will use IPv6 (a new

internet protocol version that has a much larger address

space) and maybe the next generation will be all-IP

based which has many advantages. "IP tolerates a

variety of radio protocols. It lets you design a corenetwork that gives you complete flexibility as to what

the access network is," says Sun Microsystems

Laboratories engineers James Kempf. "You could be a

core network provider that supports many different

access technologies, 802.11, WCDMA, Bluetooth,

HyperLAN, and some that we haven't even invented yet,

such as some new CDMA protocols. The core [IP]

network can evolve independently from the access

network. That's the key for using all IP," says Kempf

[9].

Ad-hoc technologies - In the future different

communication layers will support ad-hoc mode. For anexample can this technology extend the battery life time

by transmitting to devices nearby instead of transmitting

directly to the base station which cost a lot of energy

[2].

Figure 8 shows an example over an IP-based fourth

generation mobile communication network. A user will

be able to connect to different technologies through an

IP-based core network. There are still many problems

with this network for example that only a few systems

for an example that only a few systems support IPv6

which is probably a requirement.



Figure 8: Example IP-based fourth generation mobile

communication network [2]

6. MOBILE VOIP

The benefits with voice over IP (VoIP) are among

operators and customers quite large. If this technology

can be implemented in the 4G system it will be a huge

advantage if it’s not already a prerequisite. This will

mean that a customer can setup a call with another

phone anywhere in the world where an internet network

exists. In other words the call will be routed as packets

and use the same network as other regular data packets,

same architecture which benefits from lower prices and

easier administration.The problem at hand lies in the implementation of

Mobile VoIP. An efficient way to converge this

technology with WiFi and WLAN networks is

necessary. Figure 9 illustrates the VoWLAN

architecture. Voice transmission over IP puts some new

demands on WLANs that data transmissions doesn’t.

Keep in mind that WLAN was originally designed for

data-only transmission. The dream would be to begin a

call at home, continue the call in the car and finish it at

work switching between several different WiFi, WLANs

and phone networks on the way. Sadly we are not quite

there yet. Tony Rybczynski, director of strategic

enterprise technology at Brampton, Ontario-based

Nortel Networks Ltd claims that it’s of most importance

when companies starting to plan their WiFi networks to

keep voice usage in mind [10]. One big difference

between voice usage and data-only transmission is that

the coverage has to be ubiquitous (anytime, anywhere)

for voice usage to ensure that no calls will drop. One

huge debate concerning VoIP regards which Standard to

be used. Today it’s generally between WLAN 802.11b/g

and 802.11a. By using the 802.11g you will get the

advantage of greater range and legacy support because

802.11g networks have the capability to handle 802.11b

users. When using voice over IP you must have a

coverage that is ubiquitous as stated above, which in

theory means to add several more access points (AP) to

the network. However each new AP is a source for

interference which in addition with other metal objectsin a room, such as refrigerator, can block and reflect

signals causing multi-path interference. Devices such as

a microwave oven that operates at the same frequency as

the WLAN will also contribute to the interference. It’s

said that the frequencies of WLAN 802.11b has more

devices that could interfere with the network [10]. One

way that 802.11 use to mitigate interference is to allow

different access points to use several channels that don’t

interfere with each other. 802.11g/b both uses three

channels and 802.11a uses 12 channels hence the

802.11a standard would be a good choice for a high

quality system. More channels means that an AP canminimize interference. Another advantage of 802.11a is

that it operates in a less crowded frequency spectrum. In

short you can say that 802.11g/b offers a better range or

coverage area than 802.11a, however 802.11a is a more

reliable scheme or has better capacity than 802.11g/b.

"WiFi spectrum is scarce, so why choose one standard

and its corresponding spectrum swath over the other

when you can deploy both? If wired networking has

taught us anything, it's that you can never have enough

bandwidth” says Scott Lindsay, VP of Marketing for

Engim, a manufacturer of multi-channel WLAN chipsets

[11]. This company believes in a future where access points can handle many different standards like

802.11g/b and 802.11a at the same time. He also claims

that a multi-channel design has several benefits like

consolidation of roaming, Qos (quality of service) and

security.

Figure 9: VoWLAN illustration [22]



Today WLANs uses best-effort for QoS and are

designed to handle bursty and unpredictable data. This is

maybe approved for data application when little delay

doesn’t cause to much problem. However if voice would

be transmitted in this fashion even the smallest delay

will degrade the call quality or even drop the call

completely. Engim suggests that putting the data and

voice on separate channels would be the right thing todo while Meru (another vendor like Engim) will put

WLAN traffic in a time-sensitive way in an attempt to

improve QoS which is a requirement if Mobile VoIP

should work satisfying [11].

What about roaming? Apparently two types of

roaming are present, switching between the mobile

network and a WLAN or intra-WLAN (switching

between APs within a WLAN). One of the largest draw-

backs today and the one problem causing lot of

headaches among the developers is power consumption.

Especially Wi-fi systems suffer from this fact and

concern the second type of roaming, intra-WLAN.Switching between APs in a WLAN requires a lot from

the mobile device. First of all the device has to scan the

network and then determine which AP that is suitable

for the switch. These steps uses huge amount of power.

"The big problem with WLAN roaming today is that it's

not intelligent. Infrastructure needs to move away from

burdening clients to assisting them. If your network can

scan channels and available APs for the clients, telling

them where to go rather than forcing them to waste

power scanning the network themselves, you'll see much

better performance on the client side” says Lindsay

[11]. In short intra-WLAN roaming needs to beimproved and all power consumption functions

regarding switching APs has to be removed from the

mobile devices and implemented instead in the core

network.

Dual-mode phones - With voice over IP (VoIP) as a

future technology, phones that combines ordinary

mobile communication system with WiFi systems are

needed. These phones are called dual-mode phones and

use more than one technology to send and receive voice

and data transmissions.

The research firm ABI Research predicts that by the

year 2009 over 50 million dual-mode phones or smartphones are in circulation around the globe [12].

One major factor which works against the introduction

of these phones are the carriers themself. Due to the fact

that making calls from a WiFi network is a lot cheaper

than a regular phone call using the traditional mobile

network makes the carrier companies wonder how they

can make any money on these phones [12]. However the

large German telecommunication company T-mobile is

one of them that acts against the stream. They recently

introduced mobile phones that can use wireless Internet

connections both at home and in some of the companies

WiFi hotspots. This is considered as a bold move

because as stated above there is no money for the

company to gain here.

Recently TapRoot Systems announced software that

makes it possible to use WiFi-equipped Windows

Mobile phones as walking hotspot (WHS). This meansthat other devices can use these hotspots to connect to

Internet services. At present time the WHS allows up to

five 802.11b-equipped users (se figure 10) [13]. WHS

works just like an ordinary router which means that

these networks can be entirely ad hoc (a small network

between some devises including one or more WHS can

be setup without any special infrastructure needed).

Depending on the number of connected devices to a

WHS and the load they are putting on the network

performance can vary quite a lot. Keep in mind that the

bandwidth of the WHS is limited.

Figure 10: WalkingHotSpot connects up to five devices via a

WindowsMobile phone [13]

This is probably a step in the right direction if the

dream of a completely ad hoc mobile system should be

realised. Then it’s a requirement that these dual-phones

or smartphones has to be properly implemented. LikePhil Solis, Senior WiFi Analyst at ABI Research says

” Many enterprises now have established WiFi networks

and integrating voice-over-WiFi functionality is a

natural progression. As WiFi networks proliferate, it

only makes sense to give users the ability to switch from

the cellular carrier's network to the enterprise WiFi

network." [12]



7. POSSIBLE ACCESS SCHEMES FOR NEXT

GENERATIONS

For future generations of wireless communications new

access schemes are needed to be introduced to handle

the high expectations that are set for the next generation.

Two access schemes that are gaining more importance

are OFDMA (Orthogonal Frequency Division MultipleAccess) and MC-CDMA (Multi-Carrier Code Division

Multiple Access).

OFDMA - This access scheme is a multi user version

of OFDM modulation scheme. By assigning subsets of

subcarriers to each user multiple access can be achieved

(see figure 11). Different number of subcarriers can be

assigned to each user to guarantee QoS. Some

advantages with this technology is that it handles

multipath propagation without using training sequences

or equalizers and it also enables orthogonality in the

uplink by synchronizing users in time and frequency

[14].

Figure 11: OFDMA Technique [23]

MC-CDMA - The access scheme, which stands for

Multi-Carrier Code Division Multiple Access, supports

many users at the same time in the system. Each user

symbol is spread over the frequency domain. This means

that each one is carried over multiple parallel subcarriers

but its phase shifted with different code values. The

receiver can separate the user’s different signals with the

different code values [14, 15].

8. 4G TECHNOLOGIES

A. WiMAX

At 2006 Sprint which is one of the largest mobile

operators in the United States decided that they will use

WIMAX for their next generation wireless network.

Sprint told that they considered other 4G technologies

but choose WiMAX, ”because it believes it could build

an ecosystem of equipment makers around the

technology, which is based on the IEEE 802.16e

Standard”[16].

While the third generation technology has a specific

worldwide standard associated, the fourth generation

doesn’t have a specific standard more than that it should

be IP-based and use packet switching.WiMAX however has a specific technical standard

based on IEEE 802.16e. This standard will probably be

one type of a 4G technology in the future but this

doesn’t necessary mean that all 4G technologies will be

based on WiMAX. Because of mobile WiMAX

probably will be one of the first 4G technologies on the

market this article will do a brief presentation on

WiMAX based on IEEE 802.16e.

WiMAX stands for Worldwide Interoperability for

Microwave Access. The IEEE 802.16e standard added

support for mobility use so it is often referred as Mobile

WiMAX.WiMAX uses an algorithm in the MAC layer where

every unit that is connected to the AP (Access Point) has

a scheduled slot time. This slot time doesn’t always have

to be the same size but it’s always reserved for the

specific device. This makes it easier to get a better

connection and a better range with WiMAX than in

WiFi (Wireless Fidelity) where every device is

competing for the AP in a random way. Therefore

services like mobile VoIP that demands a constant QoS

works better with WiMAX than WiFi. In the physical

layer IEEE 802.16e uses a scalable OFDMA scheme

that was briefly presented earlier.Under perfect circumstances WiMAX could have a

range up to 110 km or handle speeds up to 70 Mbit/s

(for very short ranges).

Figure 12: Speed and Mobility for different technologies [24]



In figure 12 a plot is shown with the speed and

mobility for different technologies. As you can see

WiMAX operates in a pretty large interval both with

good mobility and speed while WiFi has a very high

speed but a low mobility.

Some thinks that WiMAX and WiFi are competing

standards but instead these can complement each other.

WiMAX can offer a more stable but slower connectionin a big area while WiFi gives a higher speed within a

smaller area. The WiMAX technology is also more

expensive then WiFi which doesn’t make WiMAX a

good alternative in smaller offices or at home.

One certain thing is that WiMAX could handle an IP-

based technology so it will be a good alternative for the

next generation technology [17, 18].

B. LTE

LTE stands for Long Term Evolution and it’s a

project to improve the now existing 3G technologyUMTS. LTE is not a standard but will result in 3GPP

(3rd Generation Partnership Project) release 8. The goals

for the LTE project are to improve the efficiency and

services, lower the cost and better integration with other

open standards.

In release 8 the architecture of UMTS has developed

into E-UTRAN (Evolved UTRAN) and EPC (Evolved

Packet Core). The E-UTRAN consist of eNBs (evolved

Node Bs) which are interconnected to each other by a

X2 interface and every eNB is connected to EPC by the

S1 interface (see figure 13). As an access scheme E-

UTRAN uses OFDM for downlink and SC-FDMA(Single-Carrier Frequency Division Multiple Access) for

uplink.

Figure 13: E-UTRAN architecture [19]

EPC (also called SAE – System Architecture

Evolution) is an evolution from the GPRS Core Network

with some differences. It has for an example a simplified

architecture, an all IP Network and support for lower

latency and higher throughput [19,20].

C. WiMAX or LTE for 4G?

Both WiMAX and LTE are two major technologies

that could offer a speed up to almost 100 Mbit/s and

could take the wireless mobile communication into the

next generation. It’s hard to predict which will prevail in

the future because they are in two different stages of

development. WiMAX is recognized over the entire

world as the first to be brought to the market while LTE

is some years after but have many advantages. For

instance that LTE will be able to evolve from the

existing infrastructure in UMTS. The UMTS

infrastructure is today used by 80 per cent of mobilesubscribers around the world. WiMAX however will

require building a new infrastructure. There is also a big

spectrum issue for WiMAX in Europe. In the US Sprint

that is launching WiMAX holds 2.5 GHz spectrum that

gives a great coverage. In Europe however this spectrum

is occupied by analogue TV and GSM mobile signals

and therefore European WiMAX has to be limited to 3.5

GHz spectrum which doesn’t give the same result. Not

before the analogue broadcasts have been switched off

in Europe and the 2.5 GHz becomes available, WiMAX

can give good results in Europe. But because of LTE is a

few years behind the analogue broadcasts may stop inEurope at the same time that LTE arrives which opens

up for both technologies. Maybe the mobile phones in

the future will be compatible with both WiMAX and

LTE [21].

9. CONCLUSION

There are a few 4G technologies that are here in a

near future but it’s still many years before we will see

these in a commercial use worldwide. Exactly how the

system architecture or which access scheme that will be

used isn’t fully decided for all upcoming technologies.

However the developers are working hard to overcome

the last problem with their technologies and be able to

offer transmission rates that is far beyond today’s

standards. Which 4G technology that will exist in the

future is hard to predict, probably it will be a

combination of many. But even when we so proudly are

standing there with our next generation mobile

communication system we will still face one of the



toughest challenges. To weave the new system into our

old ones. As of today the largest mobile communication

system used is still GSM and GPRS both part of the

second generation systems. The transfer to 4G has to be

calm and well-planned.

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4g what`s next