Basics of Long Term Evolution (LTE).

1. ADVANCED COMMUNICATION
TECHNOLOGY (ELEE1085)
Research Presentation
LTE (Long Term Evolution)
Group # 10
Name: Samit Basak
Banner ID: 000524091
Place: University of
Greenwich, Medway
Date: 23rd
November’2011

2. PRESENTATION OUTLINE
 Introduction
 LTE Characteristics
 LTE Graphs
 LTE Architecture
 LTE Multiple Access Techniques
 Physical Layer of LTE
 FDD and TDD
 Summary and Further Research
 References

3. INTRODUCTION
What is LTE ?
 LTE (Long Term Evolution) is a 4th generation (4G) standard
for mobile communication
 Currently 17 communication companies worldwide have
adopted LTE, more than 100 more are about to follow
 Faster speeds for mobile wireless users and lower costs
and enhanced capacity
 Uses more radio waves to allow more data to be transferred
over the same bandwidth
 Introduced a number of new technologies when compared
to the previous cellular systems

4. LTE CHARACTERISTICS
LTE will allow operators to achieve even greater peak
throughputs in higher spectrum bandwidth, and to
benefit from greater capacity at a reduced cost.
LTE characteristics include:
 Peak LTE throughputs
• DL: 100 Mb/s SISO
• 173 Mb/s 2x2 MIMO or 326 Mb/s MIMO [20MHz]
• UL: 58 Mb/s 16 QAM or 86 Mb/s 64 QAM
 Increased spectrum efficiency
• DL: 3-4 times HSDPA for MIMO (2,2)
• UL: 2-3 times E-DCH for MIMO (1,2)

5. LTE CHARACTERISTICS (CONT.)
 Ultra low Latency
• Less than 10 msec for RTD from UE to Server
• Reduced call setup times (50-100ms)
 Capacity per cell
• 200 users for 5 MHz, 400 users in larger spectrum
allocations
 Flexible spectrum use maximizes flexibility
• 1.4, 3/3.2, 5, 10, 15, 20 MHz
• All frequencies of IMT-2000 (450MHz – 2.6GHz)

6. LTE GRAPHS
Expected LTE subscriber Comparison of speeds for different standards

7. LTE ARCHITECTURE
LTE requires new network architecture, with the main
functional entities being: the e-node B on the access side, and
the Serving (S) and Packet Data Network (PDN) gateways and
the Mobile Management Entity (MME) in the core network.
LTE is a pure packet system, with no support for legacy circuit
switched voice/data. This shift allows a significant
simplification of the network, reducing the number of nodes
and improving operational efficiencies

8. LTE MULTIPLE ACCESS TECHNIQUES
LTE have selected different transmission schemes in uplink
and downlink like OFDMA has been selected for downlink i.e.
from eNodeB to UE and SC-FDMA has been selected for
uplink i.e. for transmission from UE to eNodeB
 Downlink – OFDMA
• Employed by WiMAX and WLAN
• Spectral efficient transmission-Divide into orthogonal
sub-carriers.

9. LTE MULTIPLE ACCESS TECHNIQUES (CONT.)
• The first carrier is selected so that its frequency contains
integer number of cycles in a symbol period. In order to
make sub-carriers orthogonal to each other, adjacent
subcarriers are spaced by
BSC = B / L
Where, B: nominal bandwidth of high-bit-rate data stream
L: number of sub-carriers
• To make transmission completely ISI free we also need to
place a time guard in between the sub-carriers and their
spacing. Making this time guard enough, larger than the
maximum expected delay spread, makes transmission
completely ISI free

10. PEAK TO AVERAGE POWER RATIO AND FREQUENCY
RATIO
 PAPR is defined as the peak power within one OFDM
symbol normalized by the average signal power. When
several OFDM sub-carriers align themselves in phase there
occur a large PAPR which is the most difficult concern in RF
engineering of traditional OFDM. The value of PAPR is
directly proportional to the number of sub-carriers, given by
PAPR(dB) ∞10log(N)
 In OFDM, the uncertainty in carrier frequency, which is due
to the difference in the frequencies of local oscillators in the
transmitter and receiver, give rise to a shift in frequency
domain which is also called frequency offset

11. UPLINK – SC-FDMA
 Uplink transmission technique (MS to eNodeB) and it is a
modified form of OFDMA but it transmits on subcarriers in
sequence not in parallel like OFDM which prevents power
fluctuations (Low PAPR)
 SC-FDMA signals might cause ISI at the BS
 Perform frequency domain equalization at BS rather than a
burden like linear power amplification on mobile terminal

12. SC-FDMA TRANSMITTER
 Transmitter
• Binary input is modulated using QPSK, 16QAM or
64QAM
• Divided into blocks of N-symbols using N-point DFT to
convert to frequency domain representation Xk
• Modulated on one of orthogonal subcarriers that can be
transmitted which results in a set Xl of complex
subcarrier amplitudes
• M-Point inverse DFT is applied to convert Xl to a time
domain signal Xm
• Then each Xm modulated on a single carrier

13. SC-FDMA RECEIVER
 CP is removed by shaping the received signal
 Signal is converted to frequency domain using M-Point DFT
 Frequency domain equalization is performed and then these
equalized symbols are transformed to time domain using
Npoint IDFT

14. PHYSICAL LAYER OF LTE
LTE radio resource management is concerned mainly with
physical layer. It provides data transport services to the higher
layers with the help of transport channel.
 Functions-
• Transport channel error detection and report to the higher layers
• FEC encoding and decoding
• Physical channel modulation/demodulation
• Synchronization of time and frequency
• Reporting radio channel measurements to higher layers
• MIMO antenna signals processing, transmit diversity, and beam
forming

15. FDD AND TDD
 Both of them are supported on physical layer in LTE
 Both of the share the same frame structure which has a
duration of 10 ms and consists of 20 time slots
 LTE physical layer transmission is deployable in two
different modes:
• FDD: downlink and uplink are identified with two different
frequency bands
• TDD: downlink and uplink signals are transmitted in different
time slots

16. SUMMARY AND FURTHER RESEARCH
 This presentation addressed starting from the LTE basics
and its architectures. Then some important technical
aspects of LTE like uplink and downlink multiple access
techniques, physical layer were described.
 Research on LTE layer 2 which consists of three sub layers
named as MAC, RLC, and PDCP
 Research on the mobility, coverage and enhanced MBMS

17. REFERENCES
1. M.Rinne, O.Tirkkonen (2010), ‘LTE, the radio technology
path towards 4G’, Computer Communications, ELSEVIER.
2. Alcatel-Lucent (2008), ‘Long Term Evolution (LTE)’,
Obtained from: http://www.alcatel-lucent.com [Date
accessed: 20/11/11]
3. M. Sawahashi, Y. Kishiyama, T. Nakamura (2009),
‘Broadband Radio Access: LTE and LTE-Advanced’,
ISPACS, IEEE.

18. Thank You All
Any Questions?