LTE Femtocells

Cell Edge Detection Based Interference
Scheme for Closed Mode LTE Femtocells
Kushal Mall
Problem Statement
Cross-Tier Interference
Closed-Mode Femtocell
Proposed Solution
Simulation Results
Advantages of the Proposed Scheme
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
Cross-tier interference caused by non–
subscribed users at the edge cell in the closed
mode Femtocell
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
High deterioration of the femtocell capacity
QoS of users and
Decrease in cell throughput
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
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
Flowchart of the Proposed Scheme
The proposed scheme has been compared
with the FFR scheme
For simplicity, a two cell scenario has been
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.
 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
 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
Low complexity
Minimum backhaul signaling required ( since
femtocell location and power information is
not required)
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
“Cell Edge Detection Based Interference
Avoidance Scheme for Closed Mode LTE
Femtocells” by Syed Muhammad Ali and
Adnan Khalid Kiani

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