3LTE Advance _ MIMO

• LTE Advanced


  4G cellular services with advanced features that enable higher data rates and better performance, particularly at cell edges
• Basic LTE services launched

  Around 2010
• LTE was never envisaged to provide the full performance intended, requiring additional elements in LTE Advanced
• LTE Advanced


  • Incorporated new techniques to provide very much higher data rates and better performance, particularly at cell edges
• LTE Advanced took a few more years to fully develop and roll out across the networks
• IMT-Advanced


  4G mobile technology defined by ITU-R, with higher speed requirements than 3GPP release 8 LTE
• Key requirements of IMT-Advanced

  • Higher speeds than UE can achieve from 3GPP release 8
• OFDM


  Radio access technology basis, used with OFDMA and SC-FDMA in a hybrid format
• LTE downlink


  Uses OFDMA
• LTE uplink


  Uses SC-FDMA
• LTE-Advanced in release 10 allows frequency-selective scheduling in uplink, unlike release 8 SC-FDMA
• LTE-Advanced MIMO


  • Allows up to 8x8 MIMO in downlink and 4x4 MIMO in uplink
• Relay nodes


  Low power eNBs extending coverage of main eNB in low coverage environments, connected to Donor eNB through Un interface
• eICIC


  Enhanced inter-cell interference coordination introduced in release 10 to mitigate interference in Heterogeneous Networks, using power, frequency and time domain
• ICIC


  eNB sends "load information" message to neighbor eNB about interference level per physical resource block, neighbor adjusts DL power levels
• Almost Blank Subframes (ABS)


  Only control channels and cell-specific pilots, no user data, allows UEs in CRE region to mitigate macro-cell interference
• Carrier Aggregation (CA)


  Combines multiple RF carriers to increase channel bandwidth, each carrier is a Component Carrier, up to 5 CCs supported in release 10
• Component Carriers in CA are backwards compatible to be used by release 8 and 9 devices
• Goals of Carrier Aggregation

  • Improve end user throughput, utilize fragmented spectrum across different or same bands
• Heterogeneous networks combine large macro cells with small cells
• CoMP


  Coordinated Multipoint transmission in downlink and reception in uplink, to improve cell edge throughput and spectrum efficiency
• Release 11 includes enhancements to LTE Advanced features standardized in release 10
• Carrier Aggregation enhancements in release 11

  • Multiple timing advances for uplink, non-contiguous intra-band CA, physical layer changes for TDD support
• ePDCCH


  New enhanced PDCCH introduced in release 11 to increase control channel capacity, using PDSCH resources unlike release 8 PDCCH
• Network-based positioning


  Support for uplink positioning added in release 11, utilizing sounding reference signals for time difference measurements by multiple eNBs
• MIMO


  Multiple Input Multiple Output technology using multiple antennas to make use of reflected signals, providing gains in channel robustness and throughput
• MIMO diversity modes


  • Time diversity, frequency diversity, space diversity
• Spatial diversity


  Transmit and receive diversity, improving signal-to-noise ratio and reliability
• Spatial multiplexing


  Utilizes different paths to carry additional traffic, increasing data throughput
• MIMO can linearly increase channel throughput with every pair of antennas added
• Shannon's Law


  Defines the maximum rate of error-free data transmission over a channel with given bandwidth and noise
• MIMO spatial multiplexing increases data rates beyond those possible on a single channel, without breaking Shannon's Law
• Shannon's law


  Defines the maximum rate at which error free data can be transmitted over a given bandwidth in the presence of noise
• Shannon's law


  • There is an ultimate limit on the capacity of a channel with a given bandwidth
  • Capacity is also limited by the signal to noise ratio of the received signal
• Modulation scheme


  • Can play a major part in increasing channel capacity
  • Higher order modulation schemes require better signal to noise ratio than lower order modulation schemes
• There is a balance between data rate, allowable error rate, signal to noise ratio and power that can be transmitted
• MIMO


  Utilises several sets of antennas to increase throughput capability
• MIMO spatial multiplexing


  1. Transmit data streams t1, t2, ..tn from antennas 1, 2, ..n

  2. Receiver differentiates between data streams using channel properties h12, h21, etc

  3. Receiver reconstructs transmitted data streams by multiplying received vector with inverse of transfer matrix [H]
• MIMO coding


  • Necessary to add coding to different channels so receiver can detect correct data
  • Includes Space-Time Block Coding, MIMO precoding, MIMO coding, Alamouti codes
• Space-time block coding


  Transmits multiple copies of data stream across antennas to exploit spatial and temporal diversity and improve data transfer reliability