This document provides an overview of orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) systems. It discusses the basic principles of OFDM, including signal representation and pulse shaping. It also compares single-carrier and multi-carrier modulation schemes. The document then describes the long-term evolution (LTE) architecture, including components like the eNodeB base station and the evolved packet core. It explains voice over LTE (VoLTE) technology and time-division duplexing used in TD-LTE systems.

1. UNIT VI: Orthogonal Frequency
Division Multiplexing and MIMO
System
M V K Gayatri Shivani
Assistant Professor

2. Syllabus
• Basic Principles of Orthogonality
• Single vs Multicarrier Systems
• OFDM Block Diagram and Its Explanation
• OFDM Signal Mathematical Representation,
• Pulse shaping in OFDM,
• Space Diversity and System
• MIMO Based System Architecture,
• Long-Term Evolution:, LTE Architecture, Enhanced Node B,
Core network, Radio channel components, TD-LTE,VoLTE

3. Basic Principals of Orthogonality
• Signals Vs Vectors
There is a strong connection between signals and vectors. Signals
that are defined for only a finite number of time instants (say N) can
be written as vectors ( of dimension N)
This relationship clearly shows that continuous time signals are
straightforward generalizations of finite dimension vectors. Thus,
basic definitions and operations in a vector space can be applied to
continuous time signals as well

4. • Component of one vector along the other

6. Decomposition of Signals and Signal
Components

7. To minimize the error, differentiate the error signal

9. Single Vs Multicarrier Systems
• Single-carrier modulation systems exploit only
one signal frequency to transmit data symbols.
• Differently, multicarrier modulation systems
divide the whole frequency channel into many
subcarriers and the high-rate data stream is
divided into many low-rate ones transmitted in
parallel on subcarriers

10. Compared with multicarrier modulations, single-carrier
modulations have some advantages:
(1) the peak to average power ration (PAPR) in single-carrier
modulation systems is very low, which is very helpful for the
stability of systems and the adoption of low-cost devices in the
design of wireless communication systems;
(2) compared with multicarrier modulations, single-carrier
modulation systems are less sensitive to frequency shift and phase
noise, which makes it easier for the time and frequency
synchronizations in wireless communication systems, especially
for point-to-point communication systems.

11. Multi Carrier Modulation
Multicarrier modulation (MCM) is a derivative of frequency-
division multiplexing.
MCM is a baseband process that uses parallel equal bandwidth
subchannels to transmit information and is normally
implemented with fast Fourier transform (FFT) techniques.
MCM’s advantages are better performance in the inter-symbol-
interference environment, and avoidance of single-frequency
interferers.
The increase in PAPR in between single and MCM system is
N is number of subcarriers

12. Any increase in the peak-to-average ratio of a signal requires an
increase in linearity of the system to reduce distortion.
Linearization techniques can be used, but they increase the cost
of the system.
x(n), is parsed into N relatively slower streams and modulated
using a prescribed signal constellation. The modulated streams,
d(k) (n), k = 0, ... ,N −1, are then up-sampled by a factor N,
yielding the signals y(k) (n), k = 0, ... ,N − 1. They are then
filtered by a bank of synthesis filters, g(k) (n), k = 0, ... ,N − 1,
and the filtered signals are summed to form the composite
transmit signal, s(n):

15. OFDM
• There exist a number of MCM implementations
• The implementations have been divided into two categories,
depending on the choice of filters employed by the analysis and
synthesis filter banks.
• The first category contains implementations that use the discrete
Fourier transform in the filter bank
• The other category is based on employing bandpass filters at the
synthesis and analysis filter banks
• The first implementation is an extremely popular one due to its
efficient hardware implementation using the FFT and the inverse
FFT (IFFT). Known in wireless applications as orthogonal
frequency division multiplexing (OFDM) or in wireline
applications as discrete multitone (DMT)

17. Signal Representation for OFDM

19. Pulse Shaping OFDM
• Pulse-shaped OFDM is closely related to windowed OFDM and
filtered multitone (FMT) .
• It exploits the pulse shape as an additional degree of freedom for
multicarrier modulation systems.

22. Pulse shape categorization
In OFDM systems with pulse shaping, the ISI and ICI are determined by the transmit pulse g(t)
and the receive pulse γ(t). In this paper, we use the pulse shape categorization according to the
correlation property
Orthogonal pulse design is the pulse shaping scheme where perfect reconstruction condition is
fulfilled and matched filtering is employed.
Bi-orthogonal pulse design is the pulse shaping scheme where perfect reconstruction condition is
fulfilled and mis-matched filtering is employed.
Non-orthogonal pulse design is the pulse shaping scheme where perfect reconstruction condition
is not fulfilled.
Design criteria
Depending on the specific criteria for pulse-shaped OFDM systems, pulse shapes are constructed
to satisfy diverse requirements. Herein, we discuss several commonly applied conditions that the
pulse shape design needs to fulfill.

23. Zhao, Z., Schellmann, M., Gong, X. et al. Pulse shaping design for OFDM systems. J Wireless
Com Network 2017, 74 (2017). https://doi.org/10.1186/s13638-017-0849-8

30. LONG TERM EVALUATION
LTE stands for Long Term Evolution and it was started as a project in 2004 by
telecommunication body known as the Third Generation Partnership Project (3GPP).
SAE (System Architecture Evolution) is the corresponding evolution of the GPRS/3G packet
core network evolution. The term LTE is typically used to represent both LTE and SAE.
LTE evolved from an earlier 3GPP system known as the Universal Mobile
Telecommunication System (UMTS), which in turn evolved from the Global System for
Mobile Communications (GSM).
Even related specifications were formally known as the evolved UMTS terrestrial radio
access (E-UTRA) and evolved UMTS terrestrial radio access network (E-UTRAN). First
version of LTE was documented in Release 8 of the 3GPP specifications.

32. LTE ARCHITECTURE

38. The eNodeB is a part of the E-UTRAN radio access network
and is the component that allows UEs to connect to the LTE
network. An eNodeB typically communicates with the UE, with
other eNodeBs, and with the EPC through various interfaces:
the Uu, X2 and S1.
eNODE B

39. The eNodeB performs the following functions:
a) Radio resource management, which includes:
• radio bearer control – is responsible for the setup, maintenance and the release of
radio bearers and its resource configuration
•mobility management – handles the radio resource management for UEs in both idle
and connected modes
•admission control – allows or denies radio bearer setup requests
•dynamic resource allocation, covering the release and allocation of radio resources in
both the user plane and the control plane
b) MME selection, which includes:
•enabling the UE to be served by an MME while the UE is in the “attach” procedure
• enabling the UE to be served by a different MME while being in a network
c) Packet compression and ciphering, which includes encryption and decryption of
packets through ciphering algorithms , header compression for downlink packets and
header decompression for uplink packets
d) Message scheduling and transmission

40. The Mobility Management Entity (MME)
S-GW (Serving Gateway)
P-GW (Packet Data Network Gateway
Home Subscriber Server (HSS)
The Policy and Charging Rules Function (PCRF),
he Policy and Charging Enforcement Function
(PCEF

41. VoLTE
•Voice over LTE, or VoLTE, is a digital packet technology that uses 4G LTE
networks to route voice traffic and transmit data. This voice service is the
standard for high-speed wireless communications in devices such as smart
phones, data terminals, IoT devices and wearable's.
•VoLTE is important for network operators, vendors, original equipment
manufacturers and consumers. Since LTE is a data-only networking
technology, VoLTE provides higher quality calls, better service, and the
ability to use voice and data simultaneously.

42. How does VoLTE Work
•VoLTE is based on the IP Multimedia Subsystem framework. This enables
the service to deliver multimedia as data flows using a common IP interface
that can use but doesn't depend on a legacy circuit-switched voice network.
•For example, a user might initiate a call using the LTE network. If they
wander outside an LTE coverage area, the call will go back to the legacy
network. This functionality is known as Single Radio Voice Call Continuity,
where the LTE network simultaneously maintains two connections until the
LTE signal disconnects.
•Additionally, the recommended speech codec for VoLTE is adaptive multi-
rate wideband, or HD voice. HD voice increases the audio frequency range
for voice calls and raises sound quality

43. Benefits of VoLTE
VoLTE can provide service providers and device users with multiple
benefits:
Uses spectrum more efficiently than traditional voice technology.
Increases battery life when compared to VoIP.
Provides a superior audio quality and a clear calling experience.
Offers reliable services and interoperability.
Lets users make calls and use data simultaneously.
Enables up to six-way conference calls.
Deploys alongside multimedia services, such as video sharing and
multimedia messaging.
Simplifies network management and developer accessibility.
Frees up network bandwidth due to a smaller packet.

44. TD-LTE
TDD (time division duplex) version of LTE is known as TD-LTE.
There are two major differences between LTE-TDD and LTE-FDD
While LTE-FDD uses paired frequencies to upload and download
data, LTE-TDD uses a single frequency, alternating between uploading
and downloading data through time.
The ratio between uploads and downloads on a LTE-TDD network can
be changed dynamically, depending on whether more data needs to be
sent or received.
LTE-TDD and LTE-FDD also operate on different frequency
bands, with LTE-TDD working better at higher frequencies, and LTE-
FDD working better at lower frequencies.

45. Frequencies used for LTE-TDD range from 1850 MHz to 3800 MHz, with several
different bands being used. The LTE-TDD spectrum is generally cheaper to access,
and has less traffic. Further, the bands for LTE-TDD overlap with those used
for WiMAX, which can easily be upgraded to support LTE-TDD
TD LTE is more efficient in its spectrum usage. However, using the same
channel means that a guard interval is required between the TD LTE uplink
and downlinks to separate them.
In terms of coverage, FD LTE is thought to be superior to TD LTE due to its
power efficiency. A report by Qualcomm claims that FD LTE covers an area
80% larger than TD LTE for 2:1 downlink/uplink allocation on 2.6GHz
frequency