Calculator conexiuni wireless

1. Puterea de transmisie efectiva (EIRP): [ puterea transmitatorului (dBm) ] + [ pierderi pe conectori (dB) ] + [ castig antena transmisie (dBi) ]
2. Pierderile datorita propagarii: [ Free space loss (dB) ]
3. Senzitivitatea efectiva a receptorului: [ castigul antenei de receptie (dBi) ] PLUS [ pierderi pe cablu (dB) ] PLUS [ senzitivitatea receptorului (dBm) ]

Avantajul calculelor in dB este ca putem configura si adauga echipamente cum dorim, ca si cand calculam un buget. Pentru o performanta cat mai precisa, avem nevoie in teorie de:

EIRP + Pierderi datorita propagarii + Senzitivitatea efectiva a receptorului trebuie sa fie MAI MARE DE 0

In realitate dorim o marja buna, intre 6 si 10 dB pentru a obtine o conexiune wireless de calitate. O legatura wireless este considerata functionala daca conexiunea functioneaza in AMBELE sensuri, de aceea calcularea conexiunii se face pentru fiecare capat al legaturii.

Aceasta pagina va ajuta sa considerati :

1. daca o conexiune wireless va functiona
2. Daca un link propus are transmitatori peste limita legala a EIRP-ului (36 dBm in 2.4 GHz si EIRP 30 dBm in 5.8 GHz).
3. Distanta maxima a unui link simetric*, in limitele legale a EIRP-ului, pentru un anumit transmitator si o anumita viteza.

1. Alegeti 802.11b/g sau 802.11a
2. Introduce-ti distanta in kilometri, si apasati pe  km -> dB.
3. Introduceti puterea transmitatorului si senzitivitatea de receptie a lui
4. Introduceti senzitivitatea receptorului si puterea de transmisie
5. Introduceti castigul antenelor pentru ambele capete
6. Alegeti pierderile pe cablu (sau introduceti manual o valoare negativa pentru ambele capete)
7. Apasati butonul  'Calculeaza' pentru a afla cat semnal ajunge in ambele capete. Semnalul trebuie sa fie mai mare de 10 pentru un link de calitate.
   
8. Verificati ulterior daca aveti alte pierderi datorate zonei Fresnel sau difractiei.

convertor dBm - miliWatti

Free Space Loss calculator

Alegeti frecventa (frecventa afecteaza calculele de mai jos)

The Link Budget Calculation

1. Pentru a obtine o conexiune de calitate, semnalul in capete trebuie sa fie de cel putin 10dB. This accommodates for local fading (ie variations of signal strength caused by refelections). A 4 to 6 dB margin is needed if the link reliability is moderate.
2. Check if Fresnel and/or diffraction limitations apply. Add extra losses to the required margin as needed.
3. *A symmetric link means the wireless card and antenna on both ends are identical.

A simple explanation of the role of the Fresnel ellispsoid in RF propagation is to visualise it as an elliptical "pipe" where most of the energy travels between the antennas. In order to avoid losses there should be NO obstacles inside this zone (forbidden region.)

For example, if half of the forbidden region is masked (aka antenna at the "limit of line of sight"), there will be a signal power loss of 6 dB. Thus 6 dB needs to be added to our base margin of 6-10 dB to account for this.

The bottom line is, the longer distance the link, the wider this forbidden region can become, therefore the taller the antenna towers need to be to prevent this being masked somewhere in the middle.

(The radius of forbidden region here is 0.6 x Radius of first Fresnel ellipsoid)

When an obstacle is located between the transmitter and the receiver some energy still passes through thanks to the diffraction phenomenon on the top edge of the obstacle. The higher the frequency of the transmission the higher the loss will be.

• These calculation are valid in the case of D1 and D2 far greater than h.
• Add this loss to the free space propagation loss.
• The loss is the same in the opposite direction (station B transmitting back to station.)
• Reference: S. Saunders, Antenna and propagation for wireless communication. systems.