4G TECHNOLOGY
JAY
SHRIRAM GROUP OF INSTITUTIONS
Dharapuram
Road, Avinashipalayam , Tirupur-638660
Ph:0421-2313335,9047098310,www.jayshriram.com
Presented by,
GANESH.P
EMAIL
ID: newmoonstars@gmail.com
Abstract
Third-generation (3G) mobile networks face a new rival:
so-called 4G. And, astonishingly, the new networks may even be profitable.
Alvin Toffler, an eminent futurologist, once said, “THE future always comes too fast, but in the wrong order”. The state of wireless telecoms is a
classic example. Even as 3G mobile networks are being switched on around the
world, a couple of years later than planned, attention is shifting to what
comes next: a group of newer technologies that are, inevitably, being called
Fourth Generation Mobile Networks (4G). 4G is all about an integrated, global
network that's based on an open systems approach.
The goal of 4G
is to replace the current proliferation of core cellular networks with a single
worldwide cellular core network standard based on IP for control, video, packet
data, and VoIP. This integrated 4Gmobile system provides wireless users an affordable
broadband mobile access solutions for the applications of secured wireless
mobile Internet services with value-added QoS. This paper gives the reasons for
the evolution of 4G, though 3G has not deployed completely. And then gives the
information on the structure of the transceiver for 4G followed by the
modulation techniques needed for the 4G. Later this gives the information about
the 4G Processing .Finally concludes with futuristic views for the quick
emergence of this emerging technology.
introduction
While 3G hasn't quite arrived,
designers are already thinking about 4G technology. With it comes challenging
RF and baseband design headaches. Cellular service providers are slowly
beginning to deploy third-generation (3G) cellular services. As access
technology increases, voice, video, multimedia, and broadband data services are
becoming integrated into the same network. The hope once envisioned for 3G as a
true broadband service has all but dwindled away. It is apparent that 3G systems,
while maintaining the possible 2-Mbps data rate in the standard, will
realistically achieve 384-kbps rates. To achieve the goals of true broadband
cellular service, the systems have to make the leap to a fourth-generation (4G)
network.
This is not merely a numbers game.
4G is intended to provide high speed, high capacity, low cost per bit, IP based
services. The goal is to have data rates up to 20 Mbps, even when used in such
scenarios as a vehicle traveling 200 kilometers per hour. The move to 4G is
complicated by attempts to standardize on a single 3G protocol. Without a
single standard on which to build, designers face significant additional
challenges.
What is 4G?
4G
takes on a number of equally true definitions, depending on who you are talking
to. In simplest terms, 4G is the next generation of wireless networks that will
replace 3G networks sometimes in future. In another context, 4G is simply an
initiative by academic R&D labs to move beyond the limitations and problems
of 3G which is having trouble getting deployed and meeting its promised
performance and throughput. In reality, as of first half of 2002, 4G is a
conceptual framework for or a discussion point to address future needs of a
universal high speed wireless network that will interface with wire line
backbone network seamlessly.
Motivation for 4G Research Before 3G Has Not
Been Deployed?
·
3G performance may not be sufficient to meet
needs of future high-performance applications like multi-media, full-motion
video, wireless teleconferencing. We need a network technology that extends 3G
capacity by an order of magnitude.
·
There are multiple standards for 3G making it
difficult to roam and interoperate across networks. we need global mobility and
service portability
·
3G is based on primarily a wide-area concept. We
need hybrid networks that utilize both wireless LAN (hot spot) concept and cell
or base-station wide area network design.
·
We need wider bandwidth
·
Researchers have come up with spectrally more
efficient modulation schemes that can not be retrofitted into 3G
infrastructure
·
We need all digital packet networks that utilize
IP in its fullest form with converged voice and data capability.
Comparing Key Parameters of 4G with 3G
3G
(including2.5G,sub3G)
|
4G
|
|
Major Requirement Driving Architecture
|
Predominantly voice driven - data was always add on
|
Converged data and voice over IP
|
Network Architecture
|
Wide area cell-based
|
Hybrid - Integration of Wireless LAN (WiFi,
Bluetooth) and wide area
|
Speeds
|
384 Kbps to 2 Mbps
|
20 to 100 Mbps in mobile mode
|
Frequency Band
|
Dependent on country or continent
(1800-2400 MHz)
|
Higher frequency bands (2-8 GHz)
|
Bandwidth
|
5-20 MHz
|
100 MHz (or more)
|
Switching Design Basis
|
Circuit and Packet
|
All digital with packetized voice
|
Access Technologies
|
W-CDMA, 1xRTT, Edge
|
OFDM and MC-CDMA (Multi Carrier CDMA)
|
Forward Error Correction
|
Convolutional rate 1/2, 1/3
|
Concatenated coding scheme
|
Component Design
|
Optimized antenna design, multi-band
adapters
|
Smarter Antennas, software multiband and
wideband radios
|
IP
|
A number of air link protocols, including
IP 5.0
|
All IP (IP6.0)
|
Table 1
What is needed to Build 4G Networks of
Future?
To achieve a 4G
standard, a new approach is needed to avoid the divisiveness we've seen in the
3G realm. One promising underlying technology to accomplish this is
multicarrier modulation (MCM), a derivative of frequency-division multiplexing.
Forms of multicarrier systems are currently used in digital subscriber line
(DSL) modems, and digital audio/video broadcast (DAB/DVB). MCM is a baseband
process that uses parallel equal bandwidth subchannels to transmit information.
Normally implemented with Fast Fourier transform (FFT) techniques, MCM's
advantages include better performance in the inter symbol interference (ISI)
environment, and avoidance of single-frequency interferers. However, MCM
increases the peak-to-average ratio (PAVR) of the signal, and to overcome ISI a
cyclic extension or guard band must be added to the data.
Cyclic extension works as
follows: If N is the original length of a block, and the channel's response is
of length M, the cyclically extended symbol has a new length of N + M - 1. The
image presented by this sequence, to the convolution with the channel, looks as
if it was convolved with a periodic sequence consisting of a repetition of the
original block of N. Therefore, the new symbol of length N + M - 1 sampling
periods has no ISI. The cost is an increase in energy and uncoded bits added to
the data. At the MCM receiver, only N samples are processed, and M - 1 samples
are discarded, resulting in a loss in signal-to-noise ratio (SNR) as shown in Equation 1.
SNR loss=10
log ((N+M-1)/N) db-------- (1)
Two different types of MCM are
likely candidates for 4G as listed in Table
1. These include multicarrier code division multiple access (MC-CDMA)
and orthogonal frequency division multiplexing (OFDM) using time division
multiple access (TDMA). MC-CDMA is actually OFDM with a CDMA overlay. Similar
to single-carrier CDMA systems, the users are multiplexed with orthogonal codes
to distinguish users in MC-CDMA. However, in MC-CDMA, each user can be
allocated several codes, where the data is spread in time or frequency. Either
way, multiple users access the system simultaneously. In OFDM with TDMA, the
users are allocated time intervals to transmit and receive data. As with 3G
systems, 4G systems have to deal with issues of multiple access interference
and timing.
Why OFDM?
OFDM
overcomes most of the problems with both FDMA and TDMA (ie ICI and ISI). OFDM
splits the available bandwidth in to many narrow band channels. The carriers
for each channel are orthogonal to one another allowing them to be spaced very
close together, with no overhead as in the FDMA. Because of this there is no great
need for users to be time multiplexed as in TDMA, thus there is no overhead
associated with switching between the users. Each carrier in an OFDM signal has
a very narrow bandwidth (ie 1 K Hz), thus the resulting symbol rate is low.
This results in signal having a high tolerance to multipath delay spread, as a
delay spread must be very long to cause ISI ( i.e. >500 μsec).
THE 4G TRANSCEIVER:
The structure of a 4G
transceiver is similar to any other wideband wireless transceiver. Variances
from a typical transceiver are mainly in the baseband processing. A
multicarrier modulated signal appears to the RF/IF section of the transceiver
as a broadband high PAVR signal. Base stations and mobiles are distinguished in
that base stations transmit and receive/ decode more than one mobile, while a
mobile is for a single user. A mobile may be a cell phone, a computer, or other
personal communication device.
The line between RF and baseband
will be closer for a 4G system. Data will be converted from analog to digital
or vice versa at high data rates to increase the flexibility of the system.
Also, typical RF components such as power amplifiers and antennas will require
sophisticated signal processing techniques to create the capabilities needed
for broadband high data rate signals. Figure
1 shows a typical RF/IF section for a transceiver. In the transmit path
inphase and quadrature (I&Q) signals are upconverted to an IF, and then
converted to RF and amplified for transmission. In the receive path the data is
taken from the antenna at RF, filtered, amplified, and downconverted for
baseband processing. The transceiver provides power control, timing and
synchronization, and frequency information. When multicarrier modulation is
used, frequency information is crucial. If the data is not synchronized
properly the transceiver will not be able to decode it.
4G processing:
Figure 2 shows a high-level block diagram of the transceiver
baseband processing section. Given that 4G is based on a multicarrier
technique, key baseband components for the transmitter and receiver are the FFT
and its inverse (IFFT). In the transmit path the data is generated, coded,
modulated, transformed, cyclically extended, and then passed to the RF/IF
section. In the receive path the cyclic extension is removed, the data is
transformed, detected, and decoded. If the data is voice, it goes to a vocoder.
The baseband subsystem will be implemented with a number of ICs, including
digital signal processors (DSPs), microcontrollers, and ASICs. Software, an
important part of the transceiver, implements the different algorithms, coding,
and overall state machine of the transceiver. The base station could have
numerous DSPs. For example, if smart antennas are used, each user needs access
to a DSP to perform the needed adjustments to the antenna beam.
Receiver section:
4G will require an improved receiver
section, compared to 3G, to achieve the desired performance in data rates and
reliability of communication. As shown in Equation 2, Shannon's Theorem specifies the minimum required SNR
for reliable communication:
SNR=2C/BW--------------
(3)
where C is the channel capacity
(which is the data rate), and BW is the bandwidth For 3G, using the 2-Mbps data
rate in a 5-MHz bandwidth, the SNR is only 1.2 dB. In 4G, approximately 12-dB
SNR is required for a 20-Mbps data rate in a 5-MHz bandwidth. This shows that
for the increased data rates of 4G, the transceiver system must perform
significantly better than 3G. The receiver front end provides a signal path
from the antenna to the baseband processor. It consists of a bandpass filter, a
low-noise amplifier (LNA), and a downconverter. De-pending on the type of
receiver there could be two downconversions (as in a super-heterodyne
receiver), where one downconversion converts the signal to an IF. The signal is
then filtered and then downconverted to or near baseband to be sampled.
The other configuration has one
downconversion, as in a homodyne (zero IF or ZIF) receiver, where the data is
converted directly to baseband.The challenge in the receiver design is to
achieve the required sensitivity, intermodulation, and spurious rejection,
while operating at low power.
Baseband processing:
The error correction coding of 4G
has not yet been proposed, however, it is known that 4G will provide different
levels of QoS, including data rates and bit error rates. It is likely that a
form of concatenated coding will also be used, and this could be a turbo code
as used in 3G, or a combination of a block code and a convolutional code. This
increases the complexity of the baseband processing in the receive section. 4G
baseband signal-processing components will include ASICs, DSPs,
microcontrollers, and FPGAs. Baseband processing techniques such as smart
antennas and multi-user detection will be required to reduce interference.
MCM is a baseband process. The
subcarriers are created using IFFT in the transmitter, and FFT is used in the
receiver to recover the data. A fast DSP is needed for parsing and processing
the data. Multi-user detection (MUD) is used to eliminate the multiple access
interference (MAI) present in CDMA systems.
Transmitter section:
As the data rate for 4G increases,
the need for a clean signal also increases. One way to increase capacity is to
increase frequency reuse. With the wider bandwidth system and high PAVR associated
with 4G, it will be difficult to achieve good performance without help of
linearity techniques (for example, predistortion of the signal to the PA). To
effectively accomplish this task, feedback between the RF and baseband is
required. The algorithm to perform the feedback is done in the DSP, which is
part of the baseband data processing.Power control will also be important in 4G
to help achieve the desired performance; this helps in controlling high PAVR -
different services need different levels of power due to the different rates
and QoS levels required.
The
digital-to-analog converter (DAC) is an important piece of the transmit chain.
It requires a high slew rate to minimize distortion, especially with the high
PAVR of the MCM signals. Generally, data is oversampled 2.5 to 4 times; by
increasing the oversampling ratio of the DAC, the step size between samples
decreases. This minimizes distortion. In the baseband processing section of the
transmit chain, the signal is encoded, modulated, transformed using an IFFT,
and then a cyclic extension is added. Dynamic packet assignment or dynamic
frequency selection are techniques which can increase the capacity of the
system. Feedback from the mobile is needed to accomplish these techniques. The
baseband processing will have to be fast to support the high data rates.
APPLICATIONS:
VIRTUAL
NAVIGATION AND TELEGEOPROCESSING:-
You will
be able to see the internal layout of a building during an emergency rescue.
This type of application is some time referred to as ‘telegeoprocessing’.
A remote
database will contain the graphical representation of streets, buildings and
physical characteristics of a large metropolis. Blocks of this database will be
transmitted in rapid sequence to a vehicle, where a rendering program will
permit the occupants to visualize the environment ahead. They may also ‘virtually’
see the internal layout of buildings to plan an emergency rescue or engage
hostile elements hidden in the building
.
TELEMEDICINE:-
A paramedic assisting a victim of a traffic
accident in a remote location could access medical records (X-rays) and
establish a video conference so that a remotely based surgeon could provide
‘on-scene’ assistance.
CRISIS
MANAGEMENT APPLICATION:-
In the
event of natural disasters where the entire communications infrastructure is in
disarray, restoring communications quickly is essential. With wideband wireless
mobile communications, limited and even total communication
capability(including Internet and video services) could be set up within hours
instead of days or even weeks required at present for restoration of wire line
communications.
ADVANTAGES OF 4G:-
1. Support for interactive multimedia services like teleconferencing and
wireless Internet.
2. Wider bandwidths and higher
bitrates.
3. Global mobility and service
portability.
4. Scalability of mobile network.
5. Entirely Packet-Switched
networks.
6. Digital network elements.
7. Higher band widths to provide
multimedia services at lower cost(up to 100 Mbps).
8. Tight network security
LIMITATIONS:-
Although the
concept of 4G communications shows much promise, there are still limitations
that must be addressed. A major concern is interoperability between the
signaling techniques that are planned for use in 4G (3XRTT and WCDMA).
Cost is another
factor that could hamper the progress of 4G technology. The equipment required
to implement the next-generation network are still very expensive.
A Key challenge
facing deployment of 4G technologies is how to make the network architectures
compatible with each other. This was one of the unmet goals of 3G.
AS regards the
operating area, rural areas and many buildings in metropolitan areas are not
being served well by existing wireless networks.
CONCLUSION:
.
System designers
and services providers are looking forward to a true wireless broadband
cellular system, or 4G. To achieve the goals of 4G, technology will need to
improve significantly in order to handle the intensive algorithms in the
baseband processing and the wide bandwidth of a high PAVR signal. Novel
techniques will also have to be employed to help the system achieve the desired
capacity and throughput. High-performance signal processing will have to be
used for the antenna systems, power amplifier, and detection of the signal. A
number of spectrum allocation decisions, spectrum standardization decisions,
spectrum availability decisions, technology innovations, component development,
signal processing and switching enhancements and inter-vendor cooperation have
to take place before the vision of 4G will materialize. We think that 3G
experiences - good or bad, technological or business - will be useful in
guiding the industry in this effort. To sketch out a world where mobile devices
and services are ubiquitous and the promise of future fourth generation (4G)
mobile networks enables things only dreamed of, we believe that 4G will
probably become an IP-based network today.
