ScenarioScenario

Spectrum Measurements

-100

-95

-90

-85

-80

-75

-70

-65

21 26 31 36 41 46 51 56 61

dBm

Channel

Roof Intermediate Basement

-100

-95

-90

-85

-80

-75

-70

-65

21 26 31 36 41 46 51 56 61

dBm

Channel

Roof Intermediate Basement

-100

-95

-90

-85

-80

-75

-70

-65

21 26 31 36 41 46 51 56 61

dBm

Channel

Roof Intermediate Basement

Analytical model to study the interference that indoor devices Analytical model to study the interference that indoor devices generate on the DTV receiver. The evaluation of the model is done generate on the DTV receiver. The evaluation of the model is done

with extensive Omnet++ simulations.with extensive Omnet++ simulations.

ηJi =max∀k∈J (P

iktx −PL[d Jik ]+µ)

ηi = P itx −PL[diI ]− (n f +1)×α

I Ktot =max∀i∈K (ηi )+

J∈N∑ ηI

k

k∈J∑

Building heightBuilding height

Street size

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 6 11 16 21 26 31 36

Free channels ratio

λ (meters)

4 buildings9 buildings

16 buildings

ConclusionConclusion-Availability of TVWS both indoor and outdoorAvailability of TVWS both indoor and outdoor-Great availability of indoor TVGSGreat availability of indoor TVGS- Heavy shadowing leads to low interferenceHeavy shadowing leads to low interference

This work has been made with the support of Telecom Italia and the Italian PRIN project STEM-NET.This work has been made with the support of Telecom Italia and the Italian PRIN project STEM-NET.

Map of Turin with the Map of Turin with the measurement sites measurement sites

The scarcity of available frequencies is a well known problem for a multitude of services. Several bands have been licensed for a variety of services, and nowadays it is difficult to find unused spectrum to accomodate new requests.

Cognitive radio networks have been proposed as a possible solution to contrast the experienced spectrum scarcity. One case of particular interest come from the scarce utilization of TV frequencies, which form the so-called TV White Spaces. After the analog TV switch to digital TV, several channels are often free, and could be utilized by opportunistic devices. However, in dense populated areas it is not always easy to find unused spectrum.

In this paper, we investigate the utilization of occupied frequencies by secondary devices for short range communication. We conduct spectrum measurements to quantify the availability of spectrum, and study how short range communications could impact the DTV receiver. We show that these portions of spectrum, called gray spaces, can be utilized under certain circumstances, for example in highly populated areas, which is the scenario in which it is more difficult to find TV White Spaces. Simulation studies show the impact grey spaces can have on the available spectrum for opportunistic use.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

Free channels ratio

Street size (meters)

4 buildings9 buildings

16 buildings

PL[d Ii ]=10β log10 (dIi )+10β log10 ( f )+ Χg

The DTV signal is received as interference (red line) by the indoor device, which produce interference to the DTV receiver while transmitting (yellow line). It is important that the signal received by the DTV receiver (green line) guarantees a decent SINR.