WCNC

Resource Allocation Strategy using Optimal Power Control for Mitigating Two-Tier Interference in Heterogeneous Networks

Shovon pal, Shifath Shams, Atiqur Rahman

North South University

Electrical Engineering and Computer Science DepartmentBangladesh

Toha Ardi Nugraha

IT Convergence Department, Kumoh National Institute of Technology,

South Korea

111Presented by

Shovon Pal, Shifath Shams

North South University

IEEE WCNC WORKSHOP 2014 1

Table Of Contents

• Introduction • Why next generation networks• HETNET• Interference Scenarios• Solution schemes for interference problems• System model designing• Simulations and results• Conclusion• Further Contribution


Introduction


Evolution of Wireless devices


Traffic Growth of Cellular network

Transition to LTE will increase capacity trough more spectrum, better scheduling, and MIMO, but these gains are not sufficient.

Energy consumption of networks will become an increasing problem. “More ofthe same” will not be good enough.


The Exponential Market GrowthNo other industry has ever seen a growth as fast as that seen in the mobile telecommunications sector.

This has also made the mobile phone the single most widespread information and communication technology (ICT) to date.

Within a span of five years, the proportion of mobile subscriptions originating from the developing world exploded to 64%


Capacity gains in wireless network

Wireless Network CapacityGains 1950-2000

15x by using more spectrum (3 GHz vs 150 Mhz)

5x from better voice coding

5x from better MAC and modulation methods

2700x from smaller cells

Total gain 1 million fold

Source: William Webb, Ofcom.


Why next generation networkHigh data rate and improved quality-of-services to

subscribers

Eliminate dead holes in existing network footprint

Mobility Optimization

Extended battery life of mobile phones

Mitigate spectrum underutilization problem

Taking DATA network to the very next level to get connected 24/7


Heterogeneous Networks


Heterogeneous Networks Heterogeneous networks (Hetnets) consisting of Macro-cells

and Small-cells (e.g. Femto-,Metro-, Pico-cell) are capable of extending cellular coverage and increasing capacity

The Macro-eNBs are used to offer coverage over a widearea, while the low power Small-cells are typically deployedin hot-spots and indoor are to offload traffic from the Macrolayer


Multi-tire Cellular NetworkImprovement of cell coverage, network capacity, and betterquality-of-service (QoS) provisioning are some of the major challenges for next generation cellular networks.

Universal frequency reuse and make transmitters and receivers closer

Hierarchical layering of cells, an efficient solution to improve cell coverage and network capacity

Adopted in the evolving Long Term Evolution (LTE)/LTE-Advanced (LTE-A) systems 3GPP Release-8 (LTE), 3GPP Release 10 onwards (LTE-Advanced)


LTE-A NetworkLTE-Advanced systems are designed to support high-speed packet-switched services in 4G cellular wireless networks.

The cells or radio base stations in LTE-A can be classified as: i) macrocell base station (referred as MeNB), and ii) small cells (e.g., microcells, picocells, femtocells).

“Small cell” is an umbrella term for low-power radio access nodes that operate in both licensed and unlicensed spectrum and have a range of 10 meter to several hundred meters.

Small cells will improve the cell coverage and area spectral-efficiency (capacity per unit area).


LTE-A Network


Small Cells - A Necessary Topology Evolutionfor Future Data Growth

Moving to hierarchical cell

structures with small cells can:

Significantly increase the

capacity in the same bandwidth

Significantly reduce the energy

consumption of networks


Interference Scenarios


Macro-Femto Interference

This type of interference commonly

occurs when a Macro Base Station is

very near to a Femtocell region. The

Femtocell operates at 20mW, whereas a

Macrocell operates way over the kW

range. Considering they both relate to

the same network,


Femto-Femto Interference

When two femtocells are close to each other,

it tends to effect the Femtocell’s cell edge

user the most. Although the users are in their

respective region, the neighboring

Femtocell’s transmission power interferes

with the cell edge user.


Macrocell User Interference

When a macrocell user (MU) is in a

Femtocell region, the downlink signal of

MU will interfere with any FUE near the

MU.


Solution schemes for interference problems

Femto-Aware Spectrum Arrangement Scheme

Fractional Frequency Reuse (FFR)

Strict Fractional Frequency Reuse (Strict FFR)

Soft Frequency Reuse (SFR)

Poisson Point Process (PPP)


Soft Fractional Frequency Reuse (SFFR)

SFFR (Soft Fractional Frequency Reuse) is one effective solution of inter-cell interference control.

SFFR can control the interference in cell edges to enhance the frequency reuse factor and performance in the cell edges.

System Layout Model


Scenario SFFR

Sub-Carrier

Identification User Femto Femto

Center A 50 % 40% 60%

Sector 1 B (50/3 )% (60/3) % (40/3)% Random

Sector 2 C (50/3 )% (60/3) % (40/3)% Random

Sector 3 D (50/3 )% (60/3) % (40/3)% Random

Cell Edge

Cell Center

Total System

BW

Frequency

Cell 1Power

Frequency

Cell 1Power

Cell Edge

Cell Center

Total System

BW

Frequency

Cell 1Power

Frequency

Cell 1Power

Cell Edge

Cell Center

Total System

BW

Frequency

Cell 1Power

Frequency

Cell 1Power

Bandwidth : 10 MHz = 600 sub-carrierEx : 50%, cell center 300 subcarrier,

cell edge @100 sub-carrier


Point Process

A stochastic point process is a type ofrandom process for which any onerealization consists of a set of isolatedpoints either in time or geographical space,or in even more general spaces.


Usefulness of PPP

PPP provides tractable results that help understanding the relationship among the performance metrics and the design parameters.

PPP can model random network with randomized channel access.

Provides tight bound for networks with planned deployment and networks with coordinated spectrum access.

Most of the available literature assume that the nodes are distributed according to a PPP.

Results obtained using PPP are accurate (within 1-2dB) with those obtained for legacy cellular networks as well as multi-tier cellular networks.


Definition of PPP


Cellular networks and the PPP


SPPP on small cell deployment


System model designing

Considering two-tier Macro/Femto or

with combination C of |C| Macro-cells and |C| -1

underlying channels in the Femto-cells which are

denoted as Cc. The active mobile users are in the

areas have been denoted through j of |j| sets.

If the set of users |S| of S are denoted users which

are served by the base stations then 1

...o CJ S S


SINR Modeling(Stochastic geometry model)

,1 , S( ,..., )

cc c c

P P P

1 10( , ,..., )CP P P P

• Power allocation vector by

• Two-tier vector

So SINR from the User form is

Range of the base station, the users communicates with the with its corresponding base stations at the transmission power

𝛾𝑐,𝑗 =𝐺𝑐,𝑗𝑃𝑐,𝑗

𝐺𝑐,𝑗

𝑗′≠𝑗

𝑗′∈𝑆𝑐

𝑃𝑐,𝑗 + 𝑐′≠𝐶

𝑐′∈𝐶

𝐺𝑐′,𝑗( 𝑘∈𝑆𝑐′𝑃𝑐′,𝑘) + 𝑛0

𝑃𝑐


SINR Modeling(Stochastic geometry model)

Transmitting power vector

, 2 ,

1( ( )) log (1 ( ))j c j c jU P K P

T


Cell segmentation1. Small coverage is divided into two

sectors.( Cell center, Cell edge)

2. Determines the location of each user periodically.

3. Adaptive “Smart” small cell chooses best scheme for the user.


SON PRB(Physical resource Block) Initialization

Neighboring Cell Info

Neighboring Cell Info Update

QoS Guarantee PRB Allocation


Cell Edge optimization on SFFRo In order to improve the performance in

cell-edge, Soft Fractional Frequency Reuse

(SFFR) scheme is introduced, which is

based on Soft Frequency Reuse (SFR).

o Users in each cell are divided into two

major groups according to their geometry

factors.


Adaptive Power Algorithm

,varcP

Step 1

At the center of the Small-cells, there is no specified

interference reduction technique.

Assuming center cell signal is much stronger

Maximum two-tier utility performance is achieved if all of the resources of all the basestations are given to their respective cell users, and transmit at their maximum power

For a cell wϵC, at any given , power allocation vector such that

Which improves unity base power allocation and keeping h>1

,var

Min Max

C c CP P P c C


Adaptive Power Algorithm

The SINR gets a proper improvement and the SINR turns in to

, ,

,

, , , ,k 0

, , , ,

, , , ,k 0 , , , ,k 0

( )( )

. .

. ( ) . . ( ) .

c

c

c c

c c

c j c j

c j j S c C

c j c j c j cj j c C k S

c j c j c j c j

j S c C j S c C

c j c j c j c c j c j c j cj j c C k S j j c C k S

G PP

G P G P n

h G P h G P

h G P G P n h G P h G P h n


Step-2

𝑇𝐹𝑅

, ( ) 2 2

ˆ ˆ

( )y y

SFR e T FR FR

Z Z

Pg r g rF P T T T

PI PI

Cell Center: No interference and strong signal strengths so

The The coverage probability of an FFR cell center

user whose initial SINR is<

=

=

( , , , )

1 ( , , , )

c

c FR

Tp

p T

22(1 2 ( , , , )) ( )

0

, , ,1 ( )

FR FR

Tv T T T v

P

c TR

edv

p T

Where


Step 2(Cont)


Middle Outer regionThis midsector of small covers an area

10~20m away from the small BS. Here we use

the orthogonal frequency-division multiple

access (OFDMA) technology which is

intensely considered by the 3GPP LTE

[Resource allocation with Interference Avoidance – Yu-Shan Liang].

Assigning physical resource block

User classification

Increasing PRB efficiency

In OFDMA-based cellular system, the whole spectrum is split into orthogonal sub-channels. Achievable capacity (bps/Hz/cell),

Where Ṝ is the average delivered rate in the past, measured over a fixed window of

observation.


Sector 3: Cell Edge (20~25m)In order to improve the performance in cell-edge, the Soft fractional frequency reuse

(SFFR) scheme is introduced, which is based on soft frequency reuse but with a much

greater performance. Specially, users in each cell are divided into two major groups

according to their geometry factors. In cell-edge group, users are interference-limited

due to the neighboring cells, whereas in cell-centre group users are mainly noise-

limited.

Considering fo as the center

frequency and f1, f2, & f3 as non-

crossing frequencies the fractional

reuse factor Fr is,


Simulation and Results


Simulation Parameter


SFFR approach: Hexagonal grid simulations


Cell Edge improvement


Coverage probability

J. Andrews, F. Baccelli, and R. Ganti, “A Tractable Approach to Coverage and Rate in Cellular Networks,” IEEETransactions on Communications, vol. 59, no. 11, pp. 3122–3134 November 2011.


Improved Coverage probability


SINR Comparison


Result analysisAssumptions

1. We consider Hetnet with 3 Macro-cell as Tier-1 and 6 Femto-cell in Tier-2. The cell edge zone is 0.6 % of the coverage.

2. The path loss is being measured with different 3 different values which are 7dB, 10dB and 13dB for the three regions which have been discussed earlier in the paper.

3. TFR which is mentioned as FFR Threshold has been kept 3dB for this 2 tier HetNetdeployment.

Results1. Noticeable increase at the cell-edge Macro-cell, (SFFR technique)

2. Overall throughput increases by almost 15 %

3. At β= 4, SFFR provides the best coverage probability with the minimum SINR about -10dB compared to FFR.

4. Final results show that almost 16% development of the SINR distribution for the cell edge.


Conclusion

Here we proposed a Adaptive power algorithm with SFFR approach

This strategy is analyzed in a multi-cell systems with coexistence of Femto-cell

on the Macro-cells layers

network. With a better coverage probability we can conclude with the

enhancement in the SINR of the cell edge users. The final result shows

usalmost 16% development the SINR distribution for the cell edge.


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