ADVANCED COMMUNICATION TECHNOLOGY (ELEE1085)

Research PresentationLTE (Long Term Evolution)Group # 10

Name: Samit BasakBanner ID: 000524091

Place: University of Greenwich, Medway

Date: 23rd November’2011

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

INTRODUCTIONWhat 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

LTE CHARACTERISTICSLTE 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)

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)

LTE GRAPHS

Expected LTE subscriberComparison of speeds for different

standards

LTE ARCHITECTURELTE 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

LTE MULTIPLE ACCESS TECHNIQUESLTE 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.

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 / LWhere, 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

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

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

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

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

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

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

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

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.

Thank You AllAny Questions?