The document discusses different resource allocation schemes for femtocell networks using OFDMA. It presents a system model using fractional frequency reuse to control interference between macrocells and femtocells. Simulation results show that allocating 50% of resources to the macrocell and the remaining resources equally among femtocells (MF-Reuse2a) increases cell edge throughput the most. The total throughput is highest when allocating 40% of resources to the macrocell and 20% to each femtocell (MF-Reuse2b).

1. Different Resource Allocation Schemes
In Femtocell Network
Toha Ardi Nugraha

2. Overview
• Introduction
• System Model
– OFDMA-System (sub carrier)
– Using Fractional Frequency Reuse (Interference Control)
– Resource Allocation Scheme
• Simulation Result
– Throughput (cell edge and total)
• Conclusion

3. Introduction
Problems
• The growth of mobile subscribers increase the number of data traffic.
• Weak network signal in the building/home (indoor areas).
• In other case, subscribers in the cell edge are usually not getting good
signal from serving macro cell.
Solution
• That condition will be improved
by using the femtocell.
– Problems
; Co Channel Interferences
[Pic] Small Cell/Femto Forum
Proposes
Subcarrier allocation by using difference reuse schemes.

4. Fractional Frequency Reuse (FFR)
• OFDMA-based (Sub Carrier)
• FFR (Fractional Frequency Reuse) is one effective solution of inter-cell
interference control.
• FFR can control the interference in cell edges to enhance the frequency
reuse factor and performance in the cell edges.
Cell Center Cell Center Cell Center
Power Cell 1 Power Cell 1 Power Cell 1
Frequency Frequency Frequency
Cell Edge Cell Edge Cell Edge
Total System Total System Total System
BW BW BW

5. System Model

6. System Model
The allocation of subcarriers use two scenarios
A. Macro Reuse only (M-Reuse)
B. Macro-Femto Reuse (MF-Reuse).

7. System Model
• Formula (SINR)
Where m is the macro cell users and k is the sub-carrier. and
are transmit power of serving and neighbor macrocell . in the
subcarrier k. is the channel gain between macro user m and neighbor
femtocell F in the sub-carrier k.
For No is the white noise power spectral density, and is the subcarrier
spacing.
PLind = where
• Lwalls=7 dB, if d in(0-10m)
• Lwalls=10 dB, if d in(10-20m)
• Lwalls=15 dB, if d in(20-30m)

8. System Model
• Model Propagation Outdoor (SUI)
Where do = 100 m, = wavelength, d = cell radius, and s = shadow
fading.
And calculation of the capacity of macrocell users can be written as;
Where is a constant of Bit Error Rate (BER) and can be defined
= -1.5/ln (5BER).
So, the setting of BER is 10-6.

9. System Model
• Throughput
Where represents the sub-carrier assignment for macrocell users.
When = 1 means that sub-carrier k is assigned to macrocell user .
Otherwise, = 0. From the characteristics of the OFDMA-system, each sub-carrier
is allocated only one macro user in a macrocell in every time slot.
This implies that
Where is the number of macro users in a macrocell. Similar expression is used for
femtocell.

10. Simulation Result : Throughput in Cell Edge
Throughput vs. Number of femtocell, for different resource
allocation and schemes in the cell edge
Based on the simulation, M-Reuse
scheme had higher interference
than the proposed scheme (MF-
Reuse).
MF-Reuse2a (50% BA for macrocell, and
the other BA for each femtocell) is the
effective scheme to increase
performance but in the cell edge.
(increases throughput gradually
amount 20 percent every adding
five femtocells)

11. Simulation Result : Total Throughput
Total Throughput vs. Number of femtocell, for different resource
allocation and schemes in the cell
For the total throughput,
Macro-Femto Reuse (2b schemes,
40% BA for macrocell, and 20% BA
for each femtocell)
is the best performance for the
network compared with the
other scheme.

12. Conclusion
• Resource allocation schemes can provide a solution to
improve the network performances
• The best result reuse scheme based on the simulation is
about 20 percent of total bandwidth allocated for each
femtocell in the cell.

13. References
1. M. Assaad, “Optimal Fractional Frequency reuse (FFR) in Multicellular Of
dma System,” in Vehicular Technology Conference, 2008. VTC 2008-Fall. I
EEE 68th, Sept 2008, pp. 1–5.
2. A. Dalal, H. Li, and D. Agrawal, “A Novel Multi-cell Ofdma System Structur
e Using Fractional Frequency Reuse,” in Personal, Indoor and Mobile Radi
o Communications, 2007. PIMRC 2007. IEEE 18th Inter-national Symposi
um on, Sept 2007, pp. 1–5.
3. L. Poongup, L. Taeyoung, J. Jangkeu, and S. Jitae, “Interference Managem
ent In LTE Femtocell Systems Using Fractional Frequency Reuse,” in Adva
nced Communication Technology (ICACT), Feb 2010, pp. 1047–1051.