Transcript Fourth generation (4g) wireless systems

FOURTH GENERATION (4G)
WIRELESS SYSTEMS
Mobile & Wireless Systems (DVAD04)
17 July 2015
Jesús Moreno Arques
Introduction
Definition (I)
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4G system is defined as systems that support low to high
mobility applications, a wide range of data rates and
capabilities for high-quality multimedia applications (by ITU in
the IMT-Advanced).
Some key features of IMT-Advanced are:
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Compatibility of services within IMT and with fixed networks;
Capability of interworking with other radio access systems;
High-quality mobile services;
User equipment suitable for worldwide use;
Worldwide roaming capability;
Enhanced peak data rates to support advanced services and
applications (100 Mbit/s for high and 1 Gbit/s for low mobility
were established as targets for research).
Definition (II)
Technologies for the 4G
MIMO
•Beamforming
•OFDM
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MIMO (I)
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In point to point wireless links, Multiple Input
Multiple Output (MIMO) system uses several
antennas at the transmitter end and multiple
antennas at the receiver end.
MIMO (II)
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MIMO systems take
advantage of the
multipath signals and
beamforming to improve
the signal quality (Bit
Error Rate or BER) and
increase the data rate
(bits/sec) of the
communication.
Average data rate versus SNR for different
antenna configurations.
The channel bandwidth is 100 kHz.
MIMO (III)
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Techniques streams:
 Spatial
multiplexing (SM)
 Space-Time coding
MIMO (IV) Spatial Multiplexing
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Each antenna transmits different
signals which are rearranged in
the receiver.
Maximum data rate  number
of independent data streams.
Number of transmit (Tx)
antennas ≥ data streams.
With a linear receiver: number
of receive (Rx) antennas ≥ data
streams.
Data rate of the system
increases by min(Tx antennas,
Rx antennas, data streams)
Three TX and three RX antennas yielding three-fold
improvement in spectral efficiency. Ai, Bi, and Ci represent
symbol constellations for the three inputs at the various
stages of transmission and reception.
MIMO (V) Space-Time Coding
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Each antenna transmits
the same signal, causing
the receiver improve
the quality and
reliability of reception.
Space-Time coding
serves to offset the
effects of channel
fading.
Space-Time coding schema
Beamforming (I)
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The beamforming is the process of concentrate
the array to signals coming from one particular
direction.
Sending radio signals at specific relative
phases, beamforming creates a narrower
antenna beam than that generated by a
baseline fixed-beam antenna, with the beam
acting as a powerful adaptive directional
antenna.
The signal with its transmitted energy is
physically formed and directed to a particular
subscriber, resulting in higher gain, greater
throughput and less interference.
Beamforming Alternatives
Video: MIMO + Beamforming
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http://www.youtube.com/watch?v=Sq_moM4objE
Orthogonal Frequency Division
Multiplexing (OFDM)
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OFDM is a frequencydivision multiplexing (FDM)
scheme utilized as a digital
multi-carrier modulation
method
OFDM is a communication
technique that
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Divides a channel
(frequency channel) in a
certain number of equally
spaced frequency bands
Each band transmitting a
subcarrier which carries a
portion of user information.
The fact that each subcarrier
is orthogonal to the rest
allows the spectrum of each
are overlapping.
Frequency-time representation of an OFDM signal
4G Standards
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Standards to investigate
 IEEE
802.11n
 3GPP LTE Advanced
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Both standards are based on MIMO, BF & OFDM
IEEE 802.11 N
IEEE 802.11N - Introduction
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IEEE 802.11n is a 4G wireless LAN technology
with higher data rates, longer range and more
reliable coverage than 802.11 a/b/g
networks.
Mechanisms:
 Physical
layer diversity (MIMO technology)
 Channel bonding
 Frame aggregation
Physical layer diversity (MIMO technology)
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IEEE 802.11n employs a variety of physical layer
diversity mechanisms for achieving higher
throughput and improved packet reception
capabilities. In 802.11n, receiver diversity is
implemented by using Maximum Ratio Combining
(MRC), a technique which optimally combines signals
from multiple antennas taking into account the
signal-to-noise ratio (SNR) of the signals received at
different antennas.
Channel bonding
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IEEE 802.11n introduces two different channel
bandwidths: 20 MHz and 40 MHz
Using a 40 MHz band should double the amount
of throughput achieved using a 20 MHz band.
Frame aggregation (I)
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An option of combining multiple data frames ready
for transmission into an aggregate frame.
Helps amortize the channel contention and backoff
delays by transmitting the aggregated frame (i.e.
multiple data frames) in a single transmission
opportunity on the channel.
Frame aggregation (II)
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Aggregation methods
 A-MSDU
(MSDU added): At the start of the MAC layer,
which adds MSDUs as a first step in the formation of
the MPDU.
 A-MPDU (MPDU added): Completed at the end of the
MAC layer, to form aggregates multiple MPDUs PSDU
that is then passed to the PHY layer to form the
payload for transmission.
Long Term Evolution Advanced
LTE Advanced - Introduction
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3GPP Long Term Evolution (LTE):
 Flexible
radio interface whose deployment was
realized in 2009.
 While LTE deployment was underway, the focus of
research gradually changed towards greater progress
of LTE, called LTE-Advanced.
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Objective of LTE-A
 Reach
and even exceed the requirements of IMTAdvanced, which are defined by ITU-R.
Evolution of 3GPP capabilities
Ericsson whitepaper: Optimizing global mobility through seamless coexistence and evolution of GSM, WCDMA and LTE. Feb 2009.
LTE Advanced
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The link performance of LTE is close to the Shannon
limit
LTE-Advanced require higher SNR than is usually
experienced in cellular wide area networks to
obtain very high data rates
Is necessary to find tools to improve the SNR
Technologies considered for LTE-Advanced
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Wider-band transmission and spectrum sharing
Multi-antenna solutions
Coordinated multi-point transmission
Relay nodes
Repeaters
Wider-band transmission and spectrum sharing (I)
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To get the peak data rate expected for LTE-A
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Increase transmission bandwidth
LTE-A bandwidth  transmit up to 100 MHz
Multiple LTE component carriers (CC) are aggregated
into the physical layer to provide the bandwidth
needed
Compatibility with a LTE spectrum and other similar
technologies
Resource sharing between LTE and LTE-Advanced
LTE for UMTS - OFDMA and SC-FDMA Based Radio Access. AvHarri Holma,Antti Toskala.
Wider-band transmission and spectrum sharing(II)
Characteristics
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Entire system bandwidth up to
100 MHz comprises multiple
basic frequency blocks
(component carriers)
Each CC can be configured in
a backward compatible way
with Rel-8 LTE
Carrier aggregation supports
both contiguous and noncontiguous spectrum, and
asymmetric bandwidth for
FDD
Goals
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Satisfy requirements
for peak data rate
Maintain backward
compatibility with Rel8 LTE
Achieve flexible
spectrum usage
Multi-antenna solutions
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The number of MIMO antennas affects the gain
of the signals
Example:
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To use an 8x8 system for the eNB, and 4x4 for the
UE.
Important to consider:
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The cost of increasing the antennas
Extra energy expenditure.
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To find an arrangement:
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A good ratio between the number of antennas per
sector and number of sectors per cell (6 cells with 4
antennas or 3 cells with 8 antennas?).
Problem: the size of the UE device
windowsil.org
Coordinated multi-point transmission
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Coordinated Multi Point (CoMP) technique
is a cooperative communication strategies
for distributed antennas.
Allow cooperation between several
distributed antennas
Offers advantages from the spatial
structure of the wireless propagation
medium.
Significantly increased spectral efficiency
is expecetd by the use of spatial diversity
and reduced co-channel interference.
Relay nodes
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Purpose: To extend the coverage to allow UE
farther from the base station to send data via relay
nodes that play the best eNodeB
Network with relay nodes.
Repeaters
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Consists of two way amplifier with
duplex filter.
It has two antennas:
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One for the connection to the parent
base station (donor antenna)
Other one for service area to the
users(service antenna)
The repeater receives signal from
donor antenna, filters the signal,
amplifies the signal and directs to the
other antenna to be transmitted.
It is located in the cells and is used to
improve the cell coverage and cell
capacity in certain areas.
A repeater configuration.
Questions?