Basics of LTE

Basics of LTE

• 1.
  ADVANCED COMMUNICATION TECHNOLOGY (ELEE1085) ResearchPresentation 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 willallow 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 LTEsubscriber Comparison of speeds for different standards
• 7.
  LTE ARCHITECTURE LTE requiresnew 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 ACCESSTECHNIQUES 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 ACCESSTECHNIQUES (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 AVERAGEPOWER 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  CPis 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 OFLTE 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 FURTHERRESEARCH  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 AnyQuestions?