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

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

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

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

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

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

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

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

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

Flowchart of the Proposed Scheme

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.

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

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

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

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

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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