April 11, 2023 1

Mobile Computing COE 446

Network PlanningTarek Sheltami

KFUPMCCSECOE

http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm

Principles of Wireless Networks

K. Pahlavan and P. Krishnamurth

April 11, 2023 2

Outline Architectural Methods for Capacity Expansion

Cell splitting

Using directional Antennas for Cell Sectoring

Lee’s Microcell Method

Split-Band Analog Systems

Reuse Partitioning

Using Smart Antenna

April 11, 2023 3

Architectural Methods for Capacity Expansion

Cell Splitting

Splitting cell into smaller cells and allow additional channels in the smaller cells

Let us consider a cellular architecture with cluster size of 7

When traffic load increases, a smaller cell is introduced such that it has half the area of the larger cells

In practice only a single small cell will be introduced such that it is midway between two cocahnnels

Let suppose that the radius of the smaller split cell is R/2

Let the transmit power of the BS of the smaller cell be the same as the transmit power of the larger cell

April 11, 2023 4

April 11, 2023 5

Architectural Methods for Capacity Expansion..

From the smaller cell side, Sr is maintained

From the larger cochannel cell side:

The cochannel reuse ratio is now DL/2R with respect to the smaller cell

In order to maintain same level of interference the transmit power of BS in the small cell should be reduced, but this will increase the interference observed by MTs in the smaller cell

Another alternative is to divide the channels allocated to larger cells into two parts, some of them can be used by smaller cell and some of them can not be used

The channels used by the smaller cell in the larger cell only within radius R/2 from the center of the cell, so that the cochannel reuse ratio will be maintained

April 11, 2023 6

Architectural Methods for Capacity Expansion..

This is called overlaid cell concept where larger macrocell coexists with a smaller microcell

The disadvantage of this approach is that the capacity of the larger cells is reduced. Also the BS in the larger cells will become more complex and there will need for handoffs between the overlays

April 11, 2023 7

Architectural Methods for Capacity Expansion..

Using directional Antennas for Cell Sectoring

The simplest and most popular scheme for expanding the capacity of cellular systems

Reduces the interference and cluster size and increasing capacity

The radio propagation is focused in only one direction where it is required, which reduces the interference

April 11, 2023 8

Architectural Methods for Capacity Expansion..

The coverage of the cell BS antenna is restricted to part of a cell called a sector by making the antenna directional

Cell site locations remain unchanged, and only the antenna used in the site will be changed

Increases Sr, which enables using lower frequency reuse factor

Lower frequency reuse factor allows a larger number of channels per cell, which increases overall capacity

April 11, 2023 9

Architectural Methods for Capacity Expansion..

Where Js is the number of interfering cell sites

The most popular directional antenna employed in cellular systems are 120o directional antennas

In some cases 60o directional antennas are employed

42L

rs s

D1 9S N

J R J

April 11, 2023 10

April 11, 2023 11

April 11, 2023 12

April 11, 2023 13

April 11, 2023 14

It is possible to use a cluster size of 4 or 3 with 6-sector cells, because Sr will be 21.58 dB or 19.1 dB respectively, which has sufficient margin for AMPS

April 11, 2023 15

Architectural Methods for Capacity Expansion..

Disadvantages of Using Sectors

Each sector is a new cell with different shape

Channels are partitioned between different sectors

More handoffs

April 11, 2023 16

Architectural Methods for Capacity Expansion..

Lee’s Microcell Method

One BS per cell with three zone-sites located at the corners of the cell

Directional antennas that span 135o are employed at these zone-sites

All three zone-sites act as receivers for signals transmitted by an MT

The BS determines which of the zone-sites has the best reception from the MT and uses that zone-site to transmit the signal on the downlink

The zone-sites are connected to the BS by high speed fiber links to avoid congestion and delay

April 11, 2023 17

Architectural Methods for Capacity Expansion..

Lee’s Microcell Method..

Only a single zone site is active at a time to reduce the cochannel interference

Cluster size is reduced to three and a capacity of gain of 2.33 is obtained over seven-cell cluster scheme

April 11, 2023 18

April 11, 2023 19

Architectural Methods for Capacity Expansion

Read example 5.12 page 246 in the handouts

Using Overlaid Cells Channels are divided among a larger macrocell that

coexists with microcell contained entirely in the macrocell

BS serves both the maco- microcells

R1, D1, R2, and D2

D2/R2 is larger than D1/R1 so Sr for the microcell will be grater than that of the macocell

The microcell is called overlay cell and macrocell is call underlay cell

Two methods to exploit this situation to increase the capacity

April 11, 2023 20

Architectural Methods for Capacity Expansion..

Split-Band Analog Systems

BW efficient modulation is used within overlay cells, which is FM

S/N is inversely proportional to BW2

If BW is reduced to half the original value, S/N will be increased four times (by 6dB)

If we arrange R2 and D2 to have a cochannel reuse ratio that is four times larger than usual, we end up with Sr that remains unchanged

The overlay cell then can use the FM with half BW of the underlay cell doubling the capacity within the overlay

April 11, 2023 21

Architectural Methods for Capacity Expansion..

MTs and BSs need minor changes to cope up with multiple BWs

April 11, 2023 22

April 11, 2023 23

service provider has 12.5 MHz of band-

April 11, 2023 24

Architectural Methods for Capacity Expansion..

Reuse Partitioning

Channels are divided among a macrocell and a microcell contained entirely in the macrocell

BW in both cells remain the same

Sr for the overlay cell is larger than that of the underlay cell

Channels allocated to the microcell may be used in every 3rd or 4th microcell

Channel allocated to the marcocell may be used in every 7th or 12th macrocell

This requires additional complexity at the BS and handoffs when an MT moves from microcell to macrocell

April 11, 2023 25

Example Reuse partitioning of 7 and 3

If we have AMPS network operating on the infrastructure in the next figure, the required Sr is 18 dB.

D1/R1 = D2/R2 = 4.6 (EQ. 5.2 in the handouts)

Since R2 < R1 D2 < D1 improvement in cochannel reuse ratio because the microcells are not contiguous

April 11, 2023 26

April 11, 2023 27

April 11, 2023 28