Ghost Femtocells: a Novel Radio Resource Management Scheme for OFDMA Based Networks WCNC 2011

Ghost Femtocells: a Novel Radio ResourceManagement Scheme for OFDMA Based Networks

WCNC 2011

OutlineIntroductionSystem ModelGhost Femtocells: The Proposed Resource Allocation

AlgorithmSimulationConclusions

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Introduction

The femtocell deployment in 3GPP/LTE sets new challenges to interference mitigation techniques and Radio Resource Management (RRM).

The goal of this paper is to achieve effective spectral reuse between macrocells and femtocells while guaranteeing the QoS of users served by both macro and femto base stations.

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System Model

OFDM symbols are organized into a number of physical RBs consisting of

12 contiguous sub-carriers7 consecutive OFDM symbolsbandwidth of 10 MHz 50 RBs are available for data transmission

4

System Model

5

System Model: Deployment

6

System Model: Path loss

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System Model: Fading channels

The information theoretical limit is established by defining an outage probability

Pout that the instantaneous mutual information for a given fading instance is smaller than the spectral efficiency R associated with the transmitted packet

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Proposed Resource Allocation Algorithm

In this paper vision, femtocells should be invisible in terms of interference generated to neighbour cellular users.

Femtocells deployment presents a very challenging issue: while H-BSs power consumption and interference range should be small, the coverage range at which UEs can meet their QoS constraints should be large.

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Step 1: [Classification of Interferers] H-UEs overhear the broadcast channel (BCH) and

estimate which neighbour HBSs are strong interferers.

Step 2: [Feedback to H-BS] H-UE feedbacks to the H-BS its QoS constraints the momentary Channel State Indicator (CSI) and the cell-IDs of the H-BSs perceived as strong interferers

Step 3: [Feedback to Control Unit] Each H-BS reports this information

to the Control Unit (CU). CU stores the set of its neighbours Vi.


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Step 4: [Computing Scheduling Matrices] CU computes scheduling metric λi

j for every user i on every RB j.

RRMghost implements a Proportional Fair based scheduler,

that is

RRMghost uses this metric to build the scheduling

matrices MTx and Mrep

MTx : scheduler allocates to each user the minimum number

of RBs that meets QoS and power constraints.

Mrep: to allocate to the served users additional available RBs.


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RB1

RB2

RB6

RB16

RB9

U1

U2

U3

U1U2 U3

RB1

RB2

RB16

Step 5: [Scheduling] The CU selects for each user to serve, the minimum number of RBs that meets

QoS and power constraints.

Step 5-a: selects the best user-available RB pair (i,j)

with the best metric in MTx

Step 5-b: Each user-available RB pair (i,j), the

algorithm checks the set of RBs allotted to user

i (RBi) and selects the highest possible Modulation

and Coding Scheme (MCSi), accordingly.


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RB1

RB2

RB6

RB16

RB9

U1

U2

U3

Step 5-c: The controller estimates the sum of the Mutual Information

I given by set RBi and MCSi.


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RB1

RB2

RB6

RB16

RB9

U1

U2

U3

Step 6: [MCS Scaling] Given the set of RBs (RBi) allocated each served user i, the algorithm finds the

MCS* of the minimum order that meets the QoS target. If MCS* is different from MCSi, the MCS of user i (MCSi) is set equal to MCS*.

Step 7: [Repetition] The CU allocates unused RBs to repeat the original message and improve the

transmission robustness.

Step 7-a: The scheduler selects the user-available RB pair (i,j) that has the best metric in

MRep.

Step 7-b: If I < Rtg, repetitions would cause outage, hence the values of the row

corresponding to user I in MRep are set to zero. When I ¸ Rtg, the original message is repeated in the additional RB and MRep(i; j)

as well as MRep(k; j), where k ∈ Vi, are set to zero.


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Step 8: [Power Scaling] The algorithm estimates the SINR perceived at each served user and reduces the

allocated transmission power to meet the SINR threshold given by the target PER and the selected MCS.

Step 9: [Message Reception] Finally, each user collects the information received in each of its allotted RBs and

combines these RBs using the chase combining scheme


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Simulation

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Conclusions

RRMghost, a novel radio resource management scheme that efficiently uses the available wireless spectrum in a two-tier network.

It limits the undesired effects of interference by reducing the power budget PT required at femtocells to meet target QoS constraints.

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每周一句On the contrary, in Scenarios Traf:3 and Traf:4 under

RRMghost, H-UEs achieve performance beyond 90% of Ttg.

on the contrary: 恰恰相反in contrast: 一定是相反，非常不一樣即可on the other hand: 換句話說

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Documents

Ghost Femtocells: a Novel Radio Resource Management Scheme for OFDMA Based Networks WCNC 2011