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LTE IN FEMTOCELL

LTE IN FEMTOCELL. PRAVIN MORCHHALE. What is Femtocell. Femtocells are used to provide licensed indoor coverage. Femtocells are small mobile towers at home. Femtocells combine the internet access technologies like DSL and cable with mobile technologies.

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LTE IN FEMTOCELL

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  1. LTE IN FEMTOCELL PRAVIN MORCHHALE

  2. What is Femtocell • Femtocells are used to provide licensed indoor coverage. • Femtocells are small mobile towers at home. • Femtocells combine the internet access technologies like DSL and cable with mobile technologies. • Mobile radio signals are generated indoor using Femtocells and connects the operator via internet providing excellent radio conditions.

  3. Need for Femtocells • LTE aims for: • Very high data rates for mobile phones and data terminals. • Improved capacity. • Low data transfer latencies. • Challenges: • Poor coverage: • Indoor : because the signals travel very poorly through the walls. • Outdoor: As a result of 2.5 GHz frequency use by LTE the signal attenuates much more compared to 3g systems. • Attenuation also hinders the use 64 QAM on which LTE relies for high data rates. • Increasing the power level to overcome penetration loss will increase the interference to other users. • Large coverage area and large number of users of Macro cell leads to average spectral efficiency.

  4. How does FEMTOCELL address these challenges • Improvement in capacity: • The increase in capacity can be validated using Shannon's Capacity formula: •  C = B log2 (1+SINR) • SINR is a function of desired and interfering transmit antennas and path loss, • As, • Path loss  ∝ Distance (d) between transmit and receive antennas • It causes the transmitted signal to decay as Ad-n ; where n is the path loss exponent. • To increase the capacity SINR should be increased. • this can be achieved by reducing the distance between the antennas and Path loss exponent.

  5. Femtocellantennas transmit at a low power while maintaining excellent indoor radio conditions. • Excellent Radio conditions allow the use of 64 QAM for DL and 16 QAM for UL • Penetration losses aid Femtocell by acting as insulation between neighboring Femtocell and Macrocell. • Low interference better Signal to noise ratio. • Femtocell servers around 4-5 subscribers so large resources are available per user. • Very good multipath signal factor and NxN MIMO increases data rate.

  6. Femtocell Architecture HeNB Logical Architecture X2 interface: For communication and information exchange between HeNBs. S1 interface :Femtocellsare connected to the Evolved packet core via HeNB GW through S interface S1 Interface is logically further divided into: S1-MME : carries control plane plane information. S1-U: for data plane.

  7. Synchronization and Timing • Synchronization and timing are very critical • What makes it difficult to achieve in Femtocells • Timing and synchronization depends on reliable receipt and delivery of RF signals. • Number of Femtocells and location of each femtocell is unpredictable. • One of the reason for femtocell deployment is to cover the shadow regions and poor radio areas of the Macro-cell. • 1) There can be areas where there are no macro cells nearby. • 2) Macro cell with very bad radio condition. • Service provider has minimal control on the location and placement of femtocell.

  8. Methods for Synchronization in LTE Femtocell • GPS: • Location tracking via GPS is popular but GPS can also be used for synchronization purposes. • GPS makes use of multiple continuously moving satellite for synchronization. • GPS L1 band 1.5 GHz which has a precision code is used. • each satellite spreading code and carrier frequency is already known to UE. • The UE scans waveform from each satellites using a large number of codes and frequency offset.

  9. Methods for Synchronization in LTE Femtocell • once the signal is received from four or more satellites the receiver enters a tracking loop. • Periodic measurements of carrier frequency and pseudo ranges is made. • pseudo range = speed of light x round trip time • Information from pseudo range is used to determine time and location with reference to the satellite's coordinates and time. • Cellular Network Listen • This works in the same way as the UE gets downlink synchronized to a MacrocelleNB. • HeNBlisten to the synchronization information from other cells transmitted in the SIB block 1 on the broadcast channels.

  10. Methods for Synchronization in LTE Femtocell Femtocell synchronization and timing from the Internet • The femtocell access point can use the backhaul connection to access the clock of the network operator - time servers. • IEEE 1588 which uses Precession time protocol PTP for synchronization. • NTP is used along with PTP. • PTP establishes a master to slave protocol • Clock nomenclature: • Ordinary clock : End device clock • Transparent clock: clocks of transmission components like switches. • Master is controlled via radio clock or a GPS • Master synchronizes Slaves connected to it.

  11. IEEE 1588 functional principal The correction information are provided in the PTP correction field. • Synchronization takes place in two phases : • Offset correction : time difference between master and the slave • Master sends a SYNC message to the slaves periodically • The SYNC message contains precise transmission timing information • The Slave measures the exact receive time of theses SYNC messages. • The difference is the offset. • The Salve is corrected by this offset • Delay measurement : propagation delay between master and slave. • The propagation delay is between nodes is calculated using delay request and delay response messages of PTP.

  12. Interference in LTE Femtocell • Femtocell can be deployed to use the spectrum in two ways considering Macro cells • Dedicated channel: • On an totally different channel frequency as compared to Macro cells • No interference with neighboring Macro cells. • Spectrum being limited and costly, this method is very unfeasible. • 2. Co-channel Deployment: • Using the same frequency channels as the macro cells. • But this method leads to Co-channel interference issues that need to addressed. • Scenarios: • Cross-tier • Interference between femtocells and Macro cells work working on the same frequency may interfere with each other. • Co-tier: • Interference among neighboring femtocells may cause interference. • UE transmitted signal Reaching more than one femtocell

  13. Solutions for interference • Adaptive Pilot power control: • Open loop: • Each HeNB proactively detects the signals from neighboring HeNB listening to its pilot channel and reduces the its power level to mitigate the interference but still maintaining its coverage area. • Closed loop: • Power adjustment to HeNB is decided by Macro Cell NodeB • Femto-aware spectrum arrangement: • Available frequencies for macro cells are divided into by the Mobile operator: • Macro cell Dedicated Spectrum. • Macro cell Femtocell shared spectrum. • An Interference pool is maintained for the set of frequencies which can interfere with the Femtocells • Therefore assigning Macro cell dedicated spectrum to UE nearby the Femtocells will reduce the interference.

  14. Solutions for interference Fractional Frequency Reuse (FFR) and resource partitioning The Macro cell is divided into sectors: The whole band for Macro cell is divided into sub-bands. Choosing 3 sub-bands separated from each other and deployed as: Band 1 to Macrocell Band 2 and 3 to Femo-cell Will mitigated interference issue maintaining the overall capacity and throughput.

  15. REFERENCES • Femtocell Synchronization and Location by Femto forum • FemtocellNetworks: A Survey, by Vikram Chandrasekhar and Jeffrey G. Andrews, The University of Texas at Austin and Alan Gatherer, Texas Instruments • A study on Efficiency of Femtocellsby Rajesh Vaka. • FemtocellTutorial : Fanny Mlinarsky; President, octoScope. • Femtocelltechnology tutorial : radio-electronics.com • http://lteworld.org/Femtocell-whitepapers-tutorials • http://www.ieee1588.com/

  16. Thank You

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