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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?
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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
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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]
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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.
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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]
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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]
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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]
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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
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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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