1.Introduction
The single-emitter analysis model (SEAM) estimates the signal levels received at a specified propagation distance in terms of the field strength or emitter power of a single emitter. The estimated signal levels are field strength, power flux density, power and voltage. An inverse computation estimates the propagation distance required for the received signal level to meet a threshold value specified by the user.
A propagation model option is included in the package as a subroutine for path loss versus distance determination as a function of emission frequency in both direct and inverse modes. The user selects free-space or smooth-earth propagation, with the Integrated Propagation System (IPS) model representing the smooth-earth option.
The user also selects the computation mode: Direct or Inverse and the user is prompted only for those input parameters needed for the selected computation mode. In the Direct mode, the received signal parameters, such as, propagation loss Lp in dB, field strength in mV/m and dBmV/m, power density Pd in mW/m2 and dBm/m2, received power Pr in mW and dBm and received voltage Vr in mV and dBmV, are computed and displayed for specified emission frequency, emission level and propagation distance. In the Inverse mode, propagation loss Lp in dB and the propagation distance D in km are computed and displayed for specified emission frequency and received signal threshold selected by the user.
The user can also select Field strength E0 at reference distance D0 or the emitter power to specify the emission level in either direct or inverse mode. The emitter can be expressed in either equivalent isotropic radiated power (EIRP) or the transmitter power Pt and transmitter antenna gain Gt, where EIRP = PtGt.
In the inverse mode, the received signal threshold can be specified in terms of one of the following: received voltage threshold Vrt, received power threshold Prt, power density threshold Pdt or field strength threshold Et.
2. Input parameters
The input parameters for direct mode are emission frequency F in MHz, EIRP and transmitter power Pt in W, mW, nW, dBm or dBW, transmitter and receiver antenna gains Gt and Gr respectively in dBi, field strength E0 in mV/m or mV/m, receiver antenna diameter Dr in m, and, reference and propagation distances D0 and D respectively in m.
The input parameters for the inverse mode include the received signal threshold instead of the propagation distance. The threshold values of either the received voltage Vrt in dBmV/m or received power Prt in dBm or power flux density Pdt in dBm/m2 or field strength Et in dBmV/m.
The IPS model also requires transmitter and receiver antenna heights, transmitter antenna polarization and environmental data as input parameters, which are entered through a dedicated screen that includes parameter ranges and helpful suggestions. The environmental data needed are ground conductivity (0.0001– 5.0 mho/m), ground dielectric constant (1.00–81.00) and atmospheric refractivity (200.00 – 450.00). The suggested values of electrical ground constants are given below.
Conductivity (mho/m) Dielectric Constant
Average ground 0.005 15.0
Poor ground 0.001 4.0
Good ground 0.020 25.0
Fresh water 0.010 81.0
Sea water 5.000 81.0
3. Analysis
The input/output computations are performed with a set of standard units and formulas. Any unit conversion is done before or after the input/output formulas are applied. This permits the potential modification of the input and output units without affecting the set of input/output formulas implemented in the package. The EIRP is automatically derived if the transmitter power and antenna gain are specified. The receiver antenna gain is automatically derived if the receiver antenna diameter is specified, assuming a parabolic dish with an efficiency factor n = 0.55. If neither the receiver gain nor the receiver antenna diameter is given, a default value of Gr = 0.0 dBi is provided.
The input/output formulas employed in the direct and the inverse mode computations are summarized in Tables 1 and 2 respectively. Each table consists of two sets of formulas, with one set corresponding to the field strength input option and the other to the emitter power input option. The formulas assume a medium characteristic impedance of 377 ohms and a receiver load impedance of 50 ohms.
The IPS propagation model is hard wired to its envelope mode (minimum path loss magnitude) and median signal attenuation (50% path loss percentile).
TABLE 1
SEAM DIRECT MODE INPUT/OUTPUT FORMULAS
Case of Field Strength (E0, D0) Input Parameter
E (dBmV/m) = -27.6 + E0 (dBmV/m) + 20 log D0 (m) + 20 log F (MHz) – Lp (dB)
Vr (dBmV) = 2.2 + E0 (dBmV/m) + 20 log D0 (m) + Gr (dBi) - Lp (dB)
Pr (dBm) =-104.8+ E0 (dBmV/m) + 20 log D0 (m) + Gr (dBi) - Lp (dB)
Pd (dBm/m2) =-143.3+ E0 (dBmV/m) + 20 log D0 (m) + 20 log F (MHz) – Lp (dB)
Lp (dB) = Propagation Model evaluated at D (m) in Direct Mode
Case of EIRP Input Parameter
E (dBmV/m) = 77.2 + EIRP (dBm) + 20 log F (MHz) – Lp (dB)
Vr (dBmV) =107.0 + EIRP (dBm) + Gr (dBi) – Lp (dB)
Pr (dBm) = EIRP (dBm) + Gr (dBi) – Lp (dB)
Pd (dBm/m2) = -38.5 + EIRP (dBm) + 20 log F (MHz) – Lp (dB)
Lp (dB) = Propagation Model evaluated at D (m) in Direct Mode
Note: The conversion algorithm between the two cases above is
EIRP (dBm) = -104.8 + E0 (dBmV/m) + 20 log D0 (m),
based on free space propagation at the reference distance D0 (m)
TABLE 2
SEAM INVERSE MODE INPUT/OUTPUT FORMULAS
Case of Field Strength (E0, D0) Input Parameter
Lp (dB) = -104.8 + E0 (dBmV/m) + 20 log D0 (m) + Gr (dBi) – Prt (dBm)
= -143.3 + E0 (dBmV/m) + 20 log D0 (m) + 20 log F (MHz) – Pdt (dBm/m2)
= -27.6 + E0 (dBmV/m) + 20 log D0 (m) + 20 log F (MHz) – Et (dBmV/m)
= 2.2 + E0 (dBmV/m) + 20 log D0 (m) + Gr (dBi) – Vr (dBmV)
D (m) = Propagation Model evaluated at Lp (dB) in Inverse Mode
Case of EIRP Input Parameter
Lp (dB) = EIRP (dBm) + Gr (dBi) –Prt (dBm)
= -38.5 + EIRP (dBm) + 20 log F (MHz) - Pdt (dBm/m2)
= 77.2 + EIRP (dBm) + 20 log F (MHz) + Et (dBmV/m)
=107.0 + EIRP (dBm) + Gr (dBi) –Vr (dBmV)
D (m) = Propagation Model evaluated at Lp (dB) in Inverse Mode
Note: The conversion algorithm between the two cases above is
EIRP (dBm) = -104.8 + E0 (dBmV/m) + 20 log D0 (m),
based on free space propagation at the reference distance D0 (m)
4. Output
The direct mode outputs are Propagation Loss Lp in dB, Field Strength E in mV/m or dBmV/m, Power Flux Density Pd in mW/m2 or dBm/m2, Received Power Pr in mW or dBm and Received Voltage Vr in mV or dBmV.
The inverse mode outputs are Propagation Loss Lp in dB and Propagation Distance D in km.
No comments:
Post a Comment