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LTE _ graduation presentation

Education
by

Hasan Houji

on 2 May 2012

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Transcript of LTE _ graduation presentation

Channel
Osama Al Jundi
Yazan Abu Dames
Study and Implementation of 4G
LTE Technology
Definition of LTE


LTE, short for Long Term Evolution, is considered by many to be the obvious successor to the current generation of UMTS (Universal Mobile Technology System) 3G technologies



LTE is considered by many to be a "4G" technology, both because it is faster than 3G, and because it uses an "all-IP" architecture where everything (including voice) is handled as data, similar to the Internet.
Definition of LTE
The goal of LTE is to increase the capacity and speed of wireless data networks using new DSP (Digital Signal Processing) techniques

LTE represents a radical new step forward for the wireless industry, targeting order-of-magnitude increases in bit rates with respect to its predecessors by means of wider bandwidths and improved spectral efficiency. Beyond the improvement in bit rates


LTE aims to provide a highly efficient, low-latency, packet-optimized radio access technology offering enhanced spectrum flexibility.
Driving forces for LTE development
LTE Capabilities compared to HSPA Release 6

The performance targets in 3GPP are defined relative to HSPA in Release 6. The peak user throughput should be minimum 100 Mbps in downlink and 50 Mbps in uplink, which is ten times more than HSPA Release 6.

Also the latency must be reduced in order to improve the end user performance.

The terminal power consumption must be minimized to enable more usage of the multimedia applications without recharging the battery.
LTE Capabilities compared to HSPA Release 6
Features of LTE




LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz and supports both frequency division duplexing (FDD) and time-division duplexing (TDD).
Features of LTE

Peak download rates up to 299.6 Mbit/s and upload rates up to 75.4 Mbit/s depending on the user equipment category (with 4x4 antennas using 20 MHz of spectrum)

Low data transfer latencies (sub-5 ms latency for small IP packets in optimal conditions), lower latencies for handover and connection setup time than with
previous radio access technologies.


Improved support for mobility, exemplified by support for terminals moving at up to 350 km/h or 500 km/h depending on the frequency band.
Features of LTE

OFDMA (Orthogonal Frequency-Division Multiple Access) for the downlink SC-FDMA (Single-carrier frequency-division multiple access)for the uplink to conserve power.

Support for both FDD and TDD communication systems as well as half-duplex FDD with the same radio access technology.

Increased spectrum flexibility: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz wide cells are standardized.

Supports at least 200 active data clients in every 5 MHz cell.
OFDMA

In LTE the
downlink
multiple access is based on the Orthogonal Frequency Division Multiple Access (
OFDMA
) and the
uplink
multiple access is based on the Single Carrier Frequency Division Multiple Access (
SC-FDMA
).

the Frequency Division Multiple Access (FDMA) principle, different users would then be using different carriers or sub-carriers :
OFDMA

The use of the multi-carrier principle is shown, where
data are divided on the different sub-carriers of one transmitter
. In This example the filter bank which for practical solutions is usually replaced with Inverse Fast Fourier Transform (IFFT) for applications where the number of sub-carriers is high.
OFDMA

To address the resulting inefficiency from the possible guard band requirements, the approach is to choose the system parameters in such a way as to achieve
orthogonality between the different transmissions
, and to create the sub-carriers so that they
do not interfere
with each other but their spectrums
could still overlap
in the frequency domain.
OFDMA

The overall motivation for OFDMA in LTE and in other systems has been due to the following properties:

• Good performance in frequency selective fading channels.

• Low complexity of base-band receiver.

• Good spectral properties and handling of multiple bandwidths.

• Compatibility with advanced receiver and antenna technologies.
OFDMA Challenges



The OFDMA also has challenges, such as:

• Tolerance to frequency offset. This was tackled in LTE design by
choosing a
sub-carrier spacing of 15 kHz
, which gives a large enough tolerance for Doppler shift due to velocity and implementation imperfections.

• The high Peak-to-Average Ratio (PAR) of the transmitted signal, which requires high linearity in the transmitter. The linear amplifiers have low power conversion efficiency and therefore are not ideal for mobile uplinks. In LTE this was solved by using the SC-FDMA, which enables better power amplifier efficiency.
Simulation


OFDM

OFDM is a special case of
multicarrier
transmission, where a
single data stream is transmitted over a number of lower-rate subcarriers (SCs).
It is worth mentioning here that OFDM can be seen as either a modulation technique or a multiplexing technique.



One of the main reasons to use OFDM is to
increase immunity against frequency-selective fading
or narrowband interference. In a single-carrier system, a single fade or interferer can cause the entire link to fail, but in a multicarrier system, only a small percentage of the SCs will be affected.


OFDM



The
bandwidth of the SCs becomes small compared with the coherence bandwidth
of the channel; that is, the individual SCs experience flat fading, which allows for simple equalization.


.
OFDM

Unlike single carrier systems, OFDM communication systems do not rely on increased symbol rates in order to achieve higher data rates.

This makes the task of managing ISI much simpler. OFDM systems break the available bandwidth into many narrower sub-carriers and transmit the data in parallel streams.

Each subcarrier is modulated using varying levels of
QAM
modulation, e.g.
QPSK, 16QAM, 64QAM
or possibly higher orders depending on signal quality (
Adaptive modulation
) .
Blocks of OFDM System
Spark
(cc) image by nuonsolarteam on Flickr
Blocks of OFDM System

We will focus of the OFDM modulation and demodulation blocks, also will assume that the original data is digital so DAC and DAC are not needed, we will also ignore up conversion for simplicity.

The
IDFT and the DFT
are used for, respectively,
modulating and demodulating
the data constellations on the orthogonal SCs.

At the beginning of the transmission IDFT (Inverse Discreet Fourier Transform) is performed of the data, thus giving the time domain representation of the data.

Next a cyclic prefix as a guard interval (GI) is added, the addition of the cyclic prefix as the guard interval (GI) is used to overcome the effect of the multipath effect of channel.
Blocks of OFDM System

The multipath effect causes Inter Symbol Interference (ISI), the cyclic prefix eliminates this interference (Explained Later) .

Next the data is transmitted through the channel; the length of the cyclic prefix is longer than the length of the channel, this causes the effect of the ISI to be eliminated.


At the receiver the cyclic prefix and the guard interval (GI) are removed and Demodulation using DFT (Discreet Fourier Transform) is accomplished.

Finally removing the effects of the channel is done by what so called “Channel-Estimation” .
Data Generation
Transmitter
Reciever
Results of OFDM Simulation

A simulation of the block diagram of OFDM system were made , and the results we obtained were very close to actual world performance, Next is a sample of our
simulation results :

MIMO

One of the fundamental technologies introduced together with the first LTE Release is the
Multiple Input Multiple Output (MIMO)

(MIMO) operation include
spatial multiplexing
as well as
transmit diversity
.

The basic principle in
spatial multiplexing
is sending signals from
two or more
different
antennas
with different data streams and by signal processing means in the receiver separating the data streams, hence increasing the peak data rates by a factor of 2 (or 4 with 4-by-4 antenna configuration).


Transmit diversity relies on sending the
same signal
from
multiple antennas
with
some coding
in order to
exploit the gains from independent fading
between the antennas.
MIMO

So Why MIMO ??

MIMO can be used to
increase data rate
by sending
two data streams in the same band
and separating them at the receiver .

MIMO
enables
antenna diversity
so the bit error rate is decreased .
MIMO

The OFDMA nature is well suited for MIMO operation. As the
successful MIMO operation
requires reasonably
high SNR
, with an OFDMA system it can benefit from the locally (in the frequency/time domain) high SNR that is achievable.

Principle with
two-by-two antenna configuration
:
MIMO

The
reference symbols
(also called
pilots
) enable the receiver to
separate different antennas
from each other.

To avoid transmission from another antenna corrupting the
channel estimation
needed for separating the MIMO streams, one needs to have each reference symbol resource used by a single transmit antenna only.

This principle is illustrated :
MIMO
With
MRC
, a signal
is received via two (or more) separate antenna/transceiver pairs
.

The
antennas are physically separated
, and therefore have distinct channel impulse responses.

When combined in this manner, the
received signals add coherently
within the baseband processor.

However, the
thermal noise
from each transceiver is
uncorrelated
.

Thus, linear combination of the channel compensated signals at the baseband processor results in an
increase in SNR of 3 dB
on average for a two-channel MRC receiver in a noise limited environment.
MIMO
How MRC increase the reliability of the received signal :
MIMO
SC-FDMA
Single Carrier Frequency Division Multiple Access (SC-FDMA)

Single Carrier Frequency Division Multiple Access (SC-FDMA) is a Scheme that is used in uplink transmission in the long term evolution (LTE) of cellular systems .

SC-FDMA its a modified version of A Single Carrier Modulation with Frequency Domain Equalization (SC/FDE)As equalizer .

Channel equalization aims to compensate for the distortion introduce by the multipath propagation channel and it’s basically an inverse filtering of that distortion.

it can be done by :
Single Carrier Modulation with Frequency Domain Equalization (SC/FDE)

The block diagrams of an SC/FDE system and, for comparison, an OFDM system. We can see that both systems use the same communication component blocks and the only difference between the two diagrams is the location of the IDFT block.
SC/FDE advantages over OFDM:

Low peak to average power ratio PAPR due to single carrier modulation at the transmitter.

Robustness to spectral null.

Lower sensitivity to carrier frequency offset.

Lower complexity at the transmitter that benefits the mobile terminal in cellular uplink communications.
SC-FDMA


A big disadvantage of OFDMA is the high peak to average power ratio (PARR) which implies a higher cost and less power efficiency for the a power amplifier.

In contrast, SC-FDMA where the PAPR is lower the power amplifier is simpler, lower in cost and more power efficient comparable to that in OFDMA but this difference in complexity is shifted to the receiver where the frequency domain equalizers (FDE) is way complicated comparable to that in OFDMA because of high signaling rate, but this is not a big deal because this complexity will be only at the base station and not at mobile terminals.
Subcarrier Mapping for SC-FDMA

there are two primary methods: Distributed subcarrier mapping (DFDMA) and localized subcarrier mapping (LFDMA). In the localized subcarrier mapping, the modulation symbols are assigned to M adjacent subcarriers, where in distributed subcarrier mapping, symbols are equally spaced across the entire channel bandwidth. In both modes, the IDFT in the transmitter assigns zero amplitude to the N − M unoccupied subcarriers.
Hisham Al Fayoumi
Summary

In this project we have studied and descried LTE system.

we have implemented the OFDM transmitter and receiver which is the basic enabling technology of LTE.

We have also implemented the second basic enabling technology which is the MIMO system in two modes of operation :

1- Spatial multiplexing for increasing the data rate.
2- Space-frequency block coding (SFBC) for achieving diversity gain over the MIMO channel.
Finally the results obtained from simulation were compared to results found in many scientific papers, and the results were reasonably close to real system performance
Future Work

We may continue our work in this important and developing technology in the following directions:

1-study and Implementation of OFDM synchronization techniques

2- Implement turbo codes and study the system performance with these codes.

3-Further study of performance in time-varying channels.

4- Study of various adaptive modulation techniques and their effect on the system performance and throughput.

5-Real time implementation of the system using field-programmable gate array (FPGA).
Linear filtering is a convolution operation in the time domain, but its not convenient where the channel impulse response is very long
So we use
frequency domain equalizers (FDE)
Thank You .
In LTE OFDMA is used only for downlink and SC-FDMA is used in uplink transmission .
Channel estimation
Results of OFDM Simulation
Contents
We will introduce in our presentation today the LTE, highlighting :

* A brief definition and historical info
* OFDMA, OFDM, definition and simulation
* MIMO technique
* SC_FDMA
* Future work for LTE

Wish you enjoy our presentation
Full transcript