CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH*

T/R switch

Ante

nna

Low Noise Amplifier

Mixing

stages

Power Amplifier

Problem Statement

The in-forest communication between multi-antenna mobile transmit-receive units is considered. Issues to address :

• Forest propagation and multi-path (FDTD modeling requires enormous resources) .

• Effect of arbitrary platform (MoM requires extremely complex Green’s function).

• Operation of transceiver electronics under cosite interference conditions (MoM incompatible with SPICE type solvers as TRANSIM).

Modeling Approach

• Use the Method of Moments [Sarabandi and Koh, IEEE AP-49, Feb. 2001] to model wave propagation through the forest.

• Enclose the vehicular transceivers in an FDTD mesh to model rigorously the effect of the platform and the transceiver architecture as in [Sarris et al., Proc. 2001 IEEE AP-S].

*Joint CEN-5/FCS work. Contributors : CEN-5 C. D. Sarris, W. Thiel , L. P. Katehi FCS I.-S. Koh, K. Sarabandi

1CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

humvee.net

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

FDTD / MoM CONNECTION ALGORITHM

Forest propagation of a transmitted signal is modeled

by MoM for multiple frequency points in a band of

interest.

Time domain waveform of the incident (transmitted) field on the rectangular FDTD

domain is extracted via Fourier transform.

Time domain MoM data are interpolated / extrapolated

(via system identification) to provide an FDTD excitation

signal at the FDTD time step.

FDTD simulation of the rectangular domain including the vehicular transceivers is

executed. Large signal transceiver model is used.

INHERENT ASSUMPTION : Reflected waves from the FDTD domain towards the forest and back have a secondary effect on the solution.

FUTURE WORK : Take this effect into account by coupling the two codes.

2CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

Validation

A 2x2x2 FDTD mesh is used to model free space within the forest (in the absence of any vehicles).

The same problem is solved by a pure MoM code.

Results of the two methods are in excellent agreement.

(y)

(z)(x)

2x2x2 FDTD mesh and electric field component that is plotted in the figure on the right.

FDTD simulation conditions :

x = y = z = 0.3 m

t = 0.314 nsec

3CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

Application :

Two monopoles (1.2 m long) on a

Humvee vehicle loaded with realistic

MESFET based receiver models

• A 10x20x10 FDTD mesh (3mx6mx3m)

is used to model a platform with two

antennas within a forest.

• Both antennas are on receive-mode.

• Bandpass filters of the antennas are

tuned at 49 and 50 MHz.

Equivalent circuit for Yee-cell

2 section Chebychev band-pass

filter

Impedance matching

Impedance matching

MESFET-transistor

Single balanced

mixer

3 section Chebychev low-pass

filter

Rectangular FDTD domain and FDTD/MoM interfacepoints

0.9m3 m

6m

Remote transmitter :

10-100 MHz pulse

FDTD domain

4CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

EFFECT OF PLATFORM

5CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

Humvee.net

Staircase model for vehicle in FDTD

• The signal received by a monopole on the platform is compared to the signal received by the corresponding dipole above ground.

• The transmitter, the receiving monopole and the FDTD domain are specified as before.

• The difference between the two waveforms reveals platform-induced multi-path effects.

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

6CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

MUTUAL TRANSCEIVER INTERFERENCE AND LO LEAKAGE

• The operation of the two transceivers on a common platform under no external excitation is simulated.

• Levels of LO power leakage between the two transceivers are thus determined.

• System specifications can lead to largely different LO isolations (e.g. 3 dBs compared to 23 dBs in the two cases).

Own LO Interfering LO

Own LO

Interfering LO

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

7CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

COSITE INTERFERENCE

The following two cases are simulated and compared :

• One antenna (with input filter tuned at 49 MHz) receives while its neighbor transmits a 1-V amplitude tone at 50 MHz.

• The amplitude of the sinusoidal transmitter is set to zero.

In both cases a transmitted 10-100 MHz from a remote in-forest transmitter excites the domain.

0.9m

Sinusoidal

transmitter

Receiver communicating with an in-forest transmitter

Input voltage at the receiving antenna

CEN-5 Numerical Solutions to Large Scale CEN-5 Numerical Solutions to Large Scale Tactical Comm Problems via a Scalable Time Domain MethodTactical Comm Problems via a Scalable Time Domain Method

COSITE INTERFERENCE IN A VEHICULAR TRANSCEIVER NETWORK WITHIN A FOREST ENVIRONMENT : A HYBRID FDTD/MOM APPROACH

8CC ENENComputational Electronics and NanoelectronicsComputational Electronics and Nanoelectronics CCHSSIHSSI

COSITE INTERFERENCE : IF CURRENT

• The IF current in the two previous cases is derived and plotted in the time and frequency domain (based on 50,000 time steps).

• In the presence of the interfering signal, a 2 MHz IF corresponding to the detection of the 50 MHz tone dominates the IF spectrum.

• The IF current in the two previous cases is derived and plotted in the time and frequency domain (based on 50,000 time steps).

• In the presence of the interfering signal, a 2 MHz IF corresponding to the detection of the 50 MHz tone dominates the IF spectrum.