LTE FemtocellsCell Edge Detection Based Interference

AvoidanceScheme for Closed Mode LTE Femtocells

- Kushal Mall

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

Agenda

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

Femtocells

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

Problem Statement

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

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

Cross-Tier Interference Effects

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

Closed Mode Femtocell

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

Proposed Solution

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

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.

Simulation Results

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 userSINR

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 in18%, 13% and 2% better results than FFR, EFFR and PC respectively

Low complexity Scalability Minimum backhaul signaling required

( since femtocell location and power information is not required)

Advantages of the Proposed Scheme

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

Conclusion

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

Reference

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