ANU College ofEngineering & Computer Science

Multi-Tier Heterogeneous Cellular Networks for the FutureBy He Wang (Jackson)*†, ANU CECS ASP Group, He.Wang@anu.edu.au. Supervisor: Mark C. Reed*.

1 IntroductionThanks to the advances of wireless engineering techniques and evolutions of cellular networks, everyone has been “connected”, through smart phones, tablets, laptops ...

We ask ourselves:

1.1 Mobile Data Traffic• Global mobile data traffic grew 2.6-fold in 2010;

• New devices:

Android, iPhone, iPad …

• New services:

Cloud Storage, Cloud Music, …

• Data traffic demand will increase by up to 26 times in the next five years;

1.2 What should We Do?• 1,000,000x increase of capacity since late 1950’s;

• 1600x increased by spectrum re-usei.e. smaller cells, more base stations;

• Spectral efficiency per link is approaching theoretical limits (Shannon limits);

• MIMO, interference cancellation/alignment, BS cooperationhave NOT proven to scale to “practical needs”.

• Next step is to improve spectral efficiency per unit area.

1.3 Why Multi-Tier Heterogeneous Cellular Networks?• Utilizes a diverse set of base stations (BSs): Macrocell: Traditional, long-range, tower-mounted; Picocell: Medium-range (~100m), deployed, maintained by service providers; Femtocell: Short-range (~20m), user-deployed, closed-subscriber group; Relay: Extend coverage.

• Improves Wireless Spectrum Re-use;• Deployed according to the practical needs.

* Applied Signal Processing (ASP) Group, College of Engineering & Computer Science, Australian National University.† National ICT Australia (NICTA).

4 Planning/Optimization for Indoor Environment:Planning and Optimization Tools are being developed:

• Simulate indoor environment (enterprise buildings);

• Coverage/Interference Analysis.

2 What Cellular will Migrate to (and Already Is)?

Difficulties for modeling this network:

• Signal-to-Interference-Noise-Ratios (SINRs) vary a lot over space;

• Unplanned deployment:

Service provider optimized deployment nearly impossible;

User-deployed femtocells;

• No longer is the classical Voronoi (nearest neighbor) Tessellation:

Heterogeneous structures, as shown in Fig. 3;

Diverse transmit powers;

Possible different access biasing.

Fig.1: Data Traffic Demand

Fig.2: Multi-Tier HeterogeneousCellular Networks

Fig.3: Space divided by Heterogeneous Cellular Networks

3 Modeling Multi-Tier Heterogeneous NetworksTo model this network, we need a statistical model for BSs’ locations;

• Stochastic Geometry Model:

Poisson Point Process (“max entropy” for 2-D) as the starting point;

All BS locations are i.i.d.

Exponential PDF for # BS’s/Area;

Utilize the knowledge in the field of Stochastic Geometry.

• Coverage Probability & Throughput Results:

Adjust Transmit Powers

Adjust FemtocellAccess Points’ Number

and Locations

5 ConclusionMulti-tier Heterogeneous Cellular Networks will change and is changing the

mobile world. New analytical tools and theories for these new type of networks arerequired from the industrial and academic needs. New developments in analyzing,planning and optimizing indoor cellular environment are important for these networks’deployment.

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MoreSpectrum

FrequencyDivision

Modulationand Coding

Spectrumre-use

25 5 5

1600Capacity Increase Since 1950’s

The coverage probability of a typical randomly located mobile user is

where can be expressed as