LTE Femtocells

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LTE Femtocells

• Cell Edge Detection Based Interference Avoidance
• Scheme for Closed Mode LTE Femtocells

- Kushal Mall
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Agenda

• Femtocells
• Problem Statement
• Cross-Tier Interference
• Closed-Mode Femtocell
• Proposed Solution
• Simulation Results
• Advantages of the Proposed Scheme
• Conclusion
• Reference

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Femtocells

• Femtocells are low power devices optimized for
  used in home and small businesses
• They connect via broadband infrastructure to
  provide enhanced network connectivity within the
  home and better QoS of the users
• Femtocells position and placement is independent
  of the operators planning
• The range for a femtocell is 30-40 m

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Problem Statement

• Cross-tier interference caused by nonsubscribed
  users at the edge cell in the closed mode
  Femtocell

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Cross-Tier Interference

• Occurs when a non-subscribed user operating at
  the same Resource Block(RB), but with a higher
  transmitting power comes in the vicinity of a
  femtocell
• The uplink cross-tier interference felt at closed
  mode femtocell is considered as the most common
  case

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Cross-Tier Interference Effects

• High deterioration of the femtocell capacity
• QoS of users and
• Decrease in cell throughput

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Closed Mode Femtocell

• The femtocells maintain a list of subscribed
  users which they use to authenticate the users.
  Any unsubscribed user cannot hand in to the
  closed mode femtocell.
• Does not alleviate the network load but can
  assure a dedicated bandwidth to the subscribed
  users. Hence, billing is much easier in this mode
  of femtocell

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Proposed Solution

• Is an effective threshold based interference
  avoidance scheme working on the principles of
  Universal Frequency Reuse to obtain higher cell
  throughput
• It is based on SINR thresholding and 9 dB has
  been considered the threshold
• Whenever the threshold is breached by Macro cell
  User Equipment (MUE), the interference avoidance
  mechanism begins

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• The orthogonal Resource Blocks (RBs) are
  allocated to the MUE based on the decision
  (Current Interference gt Initial Interference)
• Interference is avoided by orthogonal RB
  allocation to the MUEs
• Thus, all the RBs are utilized per TTI resulting
  in better overall cell throughput
• Co-tier interference among femtocells has been
  considered negligible in the proposed solution

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Flowchart of the Proposed Scheme
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Simulation Results

• The proposed scheme has been compared with the
  FFR scheme
• For simplicity, a two cell scenario has been
  considered
• One closed mode femtocell has been placed at the
  cell edge (distance from the center greater than
  650 m) of one of the macro cells
• The femtocell has one subscribed user connected
  to it.

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Femto User SINR Comparison

• The average SINR level for the mentioned schemes
  remains in the range
• (16.5-17.5dB). Increasing the MUE speed from
  3km/hr (pedestrian)
• to 30km/hr (vehicular) shows little effect on the
  femto user
• SINR

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Throughput Comparison (Urban)

• It can be seen that at MUE speed of 3km/hr, on
  average the UFR based
• scheme results in 22, 14 and 3 increase in
  the throughput than FFR,
• EFFR and PC respectively. At MUE speed of
  30km/hr, the UFR results in
• 18, 13 and 2 better results than FFR, EFFR and
  PC respectively

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Advantages of the Proposed Scheme

• Low complexity
• Scalability
• Minimum backhaul signaling required ( since
  femtocell location and power information is not
  required)

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Conclusion

• The proposed scheme results shows improvement in
  terms of
• macro cell throughput
• spectral efficiency
• SINR of the femtocell user
• However, a little tradeoff was observed in terms
  of slight increase in packet delay as compared to
  the FRR scheme

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Reference

• Cell Edge Detection Based Interference Avoidance
  Scheme for Closed Mode LTE Femtocells by Syed
  Muhammad Ali and Adnan Khalid Kiani

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Thank You