Joint Optimization of The two Tier Femto cells and Macro cell Users OFDMA Network

INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY
VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303
119
Joint Optimization of The two Tier Femto cells and
Macro cell Users OFDMA Network
P. Priya 1
1
varuvan vadivelan institute of technology, Anna University
Electronics and communication engineering,
priyanithu20@gmail.com
S. Ramani 2
2
varuvan vadivelan institute of technology, Anna University
Electronics and communication engineering,
Ramanivvit11@gmail.com
Abstract— We proposed a novel joint sub channel and resource allocation for the two-tier OFDMA network. The multi-cell
OFDMA network not only has to control the interference to the users, but also has to coordinate the cross-tier interference. A
resource allocation scheme for cross-channel Femto and Macro is proposed, aiming to maximize the capacity. We formulate this
joint optimization for both uplink and downlink in OFDMA network will be considered. To efficiently solve this problem using
dual decomposition and low complexity methods. The resulting schemes efficiently allocate the resource and data sharing in a
distributed way. The simulation results show that the less interference and provide significant throughput.
Index Terms — Dual decomposition, Femto cells and Macro cell, Resource allocation, Sub channel, Interference management.
——————————  ——————————
1 INTRODUCTION
Femtocells cover an even smaller space like a house or small
business. They are sold by the operator, but self-installed by the
customer. Some Femto cell may be autonomous implying that they
have the ability to determine the best frequency and power levels to
operate. The two arguments in favor of small cells are the reduced
capital and operational expenditure (CAPEX and OPEX) as
compared
techniques like cell splitting and ability of small cells to provide
adequate coverage in extremely densely populated areas. The idea of
merging small cells with the Macro cell network has the advantage
of offloading traffic from the bigger cell sites to the smallest cells.
This permits the Macro cells to operate at their normal capacity.
Such consolidation is transparent to the customer. It involves
seamless handoff between the multiple sized cells and facilitates
uninterrupted data services for the user. A key component of Het Net
which will help in meeting the above requirements is network
intelligence. Macro and Femto cells along with Wi-Fi have to be
integrated into a single framework in a manner which avoids
interference. As far as frequencies are concerned, all cells in
heterogeneous network need not be using the same spectrum.
Macro cells can operate at a lower frequency to boost
penetration. Higher bandwidth (bits/Hz) is desired for smaller cells,
so it would be best to allocate higher frequencies to such cells. Since
these works, joint sub channel and power allocation with QOS and
cross-tier interference consideration has rarely been studied. In a
non-cooperative power and sub channel allocation for co-channel
deployed Femto cells is proposed, together with Macro cell user
transmission protection. Femto cells networks should support
heterogeneous QOS for delay-sensitive services such as online
gaming and video phone calls, while maximizing the throughput of
delay-tolerant services. In resource allocation for mixed services
under a total power constraint in OFDMA systems is investigated.
Figure1. Femto and Macro cell operator network
In a dual decomposition method based sub channel selection and
power allocation, subject to interference temperature limit, is studied
in CR networks. In sub channel and power allocation based on
discrete stochastic optimization is proposed for CR networks
considering heterogeneous QOS users. In this paper, we focus on the
sub channel and power allocation problem in OFDMA based the
two-tier Femto cells networks, in which a central Macro cell is
overlaid with spectrum-sharing Femto cells. Moreover, the types of
interference in the two-tier networks are classified as follows:

120
 Co-tier interference: This type of interference occurs between
network elements that belong to the same tier in the network. In
case of a Femto cells network. Co-tier interference occurs
between neighboring Femto cells.
 Cross-tier interference: This type of interference occurs
between network elements that belong to the different tiers of
the network, i.e., interference between Femto cells and Macro
cells.
 Femto cell interfering with Macro cell on the same spectrum.
 Macro cell interfering with Femto cells on the same spectrum.
 Neighboring Femto cell that are close, interfering with each
other on the same spectrum.
 User hand-equipment transmitting with high power may reach
the Macro cell that influences the level of noises received by the
Macro cell.
The designers claim that Femto cells can provide the best
coverage within a range of 40m and can support connection to users
who are travelling at speed up to 120 Km/h. So the optimum distance
between the two Femto cell should be around 80m. Though based on
the Femto cell class (1–3), the coverage range varies from 10–40 m.
The classes of the Femto cells variation among these three based
on its operation in residential and enterprise application. In an ideal
heterogeneous network, there is very little chance of co-tier
interference if Femto cell are deployed with proper planning.
However, the ―plug and play‖ feature that Femto cells offers cannot
be included in any network planning. So mitigating interference in
heterogeneous network is a big problem for network planners. In the
heterogeneous network, the target is to use minimum frequency
reuse factor.
2 SYSTEM MODEL
2.1 Interference Mitigation Techniques
Many techniques have been tested and deployed to mitigate the
interferences in Femto cells network. They can be classified based on
different criteria and according to their ability to improve the link
reliability as well as the capacity. The user centric approach imitates
the satisfaction of the users on the service of the network. The users
get the main focus and the resources are allocated to guarantee user
satisfaction. As a result, it maximizes the available resources of the
system that can before matted as:
𝑚𝑎𝑥 𝑝(𝑛) 𝑞 𝑘
(𝑛)
1
𝐾𝑈 𝑟𝑘
𝑛
𝑞 𝑘
𝑛
𝑁
𝑛=1
𝐾
𝑘=1
𝑃(𝑛)
𝑁
𝑛=1
≤ 𝑃𝑚𝑎𝑥 , 𝑞(𝑛)
≤ 1
𝐾
𝑘=1
Where, q (n) k and U(r (n) k) are the variable sub-carrier
assignment variable and the unity function, respectively.
When sub-carrier is assigned to users, the value of is 1 otherwise
its 0. On the other hand, system centric approach concentrates on the
QOS of the system. Instead of monitoring individual’s satisfaction, it
studies the overall performance of the network. System centric
arrangement can be classified into the two sub-systems: Radio,
adaptive system and The margin adaptive system. In radio, adaptive
system, the QOS of the users are maximized which can be formatters
𝑃(𝑛)
𝑁
𝑛=1
≤ 𝑃𝑚𝑎𝑥 , 𝑃(𝑛)
> 1
Where, p (n), G (n) and N are the total bandwidth, transmitting
power, channel gain and the number of subscribers, respectively.
Conversely, The margin adaptive system emphasizes on minimizing
the transmission power of FBS that can be expressed as where R is
the required data rate of the user.
TABLE 1
UNITS FOR MAGNETIC PROPERTIES
Statements that serve as captions for the entire table do not need footnote letters.
Gaussian units are the same as cgs emu for magneto statics; Mx = Maxwell, G =
Gauss, OE = Oersted; Wb = Weber, V = volt, s = second, T = tesla, m = meter, A
= ampere, J = joule, kg = kilogram, H = Henry.
Increasing BTS capacity and tuning parameters of the resources
are also included in the hardware approach in terms of dealing
interferences. Based on resource partitioning and power
management, self-organized approaches can be categorized as
centralized method and distributed method. Below some of the
algorithms which based on interference mitigation are discussed.
2.2 Resources Allocation
A core building block enables Femto cell to find the available
resources in a completely distributed resource management
framework that effectively manages the interference. A frequency
splitting techniques to solve the interference problem in Femto cell
network where multiple access interference (MAI) and Inter-Carrier
Interference (ICI) influence the system’s performance. Clustering
Algorithms are proposed in where the whole bandwidth is allotted
into the two bands. One is dedicatedly assigned to Femto-users and
another is for Macro-users. The ratio of the bands is fixed by the
given ―Clustering‖ technique.

121
Fig. 2 Resource Allocation
3 SIMULATION RESULTS
Simulation results are given in this section to evaluate the
performance of the proposed resource allocation algorithms.
Fig. 3 Uplink total capacity of all Femto cell versus the number of Femto
cell K.
In the simulations, spectrum-sharing Femto cell are uniformly
distributed in the Macro cell coverage area and, Femto users are a
distributed in the coverage area of their serving Femto cells.
Uniformly distributed in the coverage area of their serving Femto
cells. The coverage radius of the Macro cell is 500 m, and that of a
Femto cells is 10 m. A round-robin scheme is adopted for Macro user
scheduling in the simulation. The MBS-Macro user’s lognormal
shadowing is 8 dB.
Fig. 4 Total downlink capacity of all Femto cell versus the number of
Femto cell K.
The Macro users maximum transmit powers are uniformly set at
23 dB, which means equal power allocation at the Macro side.
4 CONCLUSIONS
In this paper interference is limiting both outdoor and indoor
throughputs (e.g. for edge SNR of 30 dB), it is shown that indoor
throughputs can even exceed outdoor throughputs due to the
asymmetric shielding effects of the walls for different base stations,
which can result increased indoor SINR. Since increase the data
sharing capacity using OFDMA network.
ACKNOWLEDGMENT
A large number of people generously contributed to this special
issue, including the authors, reviewers, parents, friends and IJTET
staffs.
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Author Profile:
Priya.P is currently pursuing a master degree programs in Applied
Electronics in a varuvan vadivelan institute of technology, Anna
University, India, E-mail:priyanithu20@gmail.com

Joint Optimization of The two Tier Femto cells and Macro cell Users OFDMA Network

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