1. LTE Femtocells Cell Edge Detection Based Interference Avoidance
Scheme for Closed Mode LTE Femtocells
- Kushal Mall

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

3. 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 m

4. Problem Statement
Cross-tier interference caused by non– subscribed users at the edge cell in the closed mode Femtocell

5. 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

6. Cross-Tier Interference Effects
High deterioration of the femtocell capacity
QoS of users and
Decrease in cell throughput

7. 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

8. 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

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

10. Flowchart of the Proposed Scheme

11. 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.

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

13. 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

14. Advantages of the Proposed Scheme
Low complexity
Scalability
Minimum backhaul signaling required ( since femtocell location and power information is not required)

15. 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

16. Reference
“Cell Edge Detection Based Interference Avoidance Scheme for Closed Mode LTE Femtocells” by Syed Muhammad Ali and Adnan Khalid Kiani

17. Thank You