Vector Signal Generator R&S ® SMU200A

Digital fading simulator with

unrivalled characteristics

Impairments and various problems

such as Doppler shifts and construc-

tive or destructive superposition of

multipath propagation with different

signal delays may occur during the

radio transmission of signals. The

mobile radio standards stipulate

appropriate measurements with

defined channel models to ensure

that radio systems are not impaired by

such channel characteristics.

Fading with all channel models

To perform these measurements, you

need a fading simulator that is able to

simulate the various channel models

that occur when a signal is transmit-

ted from the transmitter (e.g. a base sta-

tion) to the mobile receiver (e.g. a mobile

station). These channel models gen-

erally consist of superimposed single

paths that are independent of each

other and statistically modeled. With the

two fading options R&S ® SMU-B14 and

R&S ® SMU-B15 of the Vector Signal Gen-

erator R&S ® SMU200A (FIG 1), you can

model both stationary and dynamic sys-

tems (see box at right). In stationary sys-

tems – with constant delays in the paths

– you can set the individual fading paths

in the path profile and in the path delay

as required. Dynamic systems that may

suddenly be subject to new propagation

paths or to a change in delay are sim-

ulated in accordance with stipulations

laid down in the 3GPP standard. FIGs 2

and 3 show examples of baseband sig-

nals subjected to stationary and dynamic

fading.

Unrivalled signal quality

The purely digital fading simulator in the

R&S ® SMU200A offers numerous advan-

tages:

◆ Up/down conversion as well as A/D

and D/A conversion of a conventional

RF fading simulator are not required.

The result is excellent and unrivalled

signal quality even for signals with

additive noise.

◆ The fading simulator is integrated

into the vector signal generator. This

provides a system solution at low

cost, low weight and minimum space

requirements. For example, if you

install all options, you will have a

single instrument that contains two

independent signal generators. It will

include fading and noise generation

and occupy only four height units.

Thus, it will meet performance test

requirements for 3GPP FDD base sta-

tions in accordance with TS25.141.

◆ The fading simulators in the two

paths may be connected in many

different ways, thus significantly

increasing the range of applications

(e. g. for testing receive and transmit

diversity).

With up to 40 paths for multipath fading

and a delay resolution of up to 10 ps to

meet the highest requirements for spa-

tial resolution, the R&S ® SMU200A

fading simulator is ideal for all possible

FIG 1 The Vector Signal Generator R&S ® SMU200A offers two complete signal generators with

digital modulation capability in a single instrument.

43985/2

News from Rohde & Schwarz Number 184 (2004/IV)

MOBILE RADIO Signal generators

FIG 2

Baseband signal with QPSK modulation and rectangular filter

that has been subjected to Rice fading (one path, stationary

fading). As a result of the duration of luminescence set on the

oscilloscope, the variation of the constellation points in phase

and amplitude caused by the fading simulator is clearly visible.

FIG 3

Baseband signal with ASK modulation (only one 1 bit, then many

0 bits) that has been subjected to dynamic fading (moving prop-

agation). Path P1 remains still while path P2 moves in time rela-

tive to P1. This is clearly visible due to the long duration of lumi-

nance set on the oscilloscope.

Special features of the

R&S

SMU200A fading option

◆ Dual-channel fading with variable

connections and paths that can be

correlated

◆ Extremely high signal quality

◆ Visual overview of the fading

simulator configuration

◆ Easy operation

◆ Multipath fading with up to

40 fading paths

◆ Very high resolution of delay (up to

10 ps)

◆ Comprehensive selection of pre-

defined settings in accordance

with test specifications of all

important mobile radio standards

Fast fading profiles

Simulate fast signal level fluctuations that

arise due to shifts between constructive

and destructive interference during mul-

tipath propagation.

Pure Doppler fading Simulates a direct

transmission path on which a Doppler shift

occurs due to the receiver being in motion.

Rayleigh fading Simulates a radio hop

that arises as a result of scatter caused by

obstacles in the signal path (buildings, etc).

Rice fading Models a Rayleigh radio hop

along with a strong direct signal.

Slow fading profiles

Simulate slow variations in level that

can occur due to shadowing effects (e.g. in

tunnels).

Lognormal fading Simulates an addi-

tional slow fluctuation of the received

amplitude of a receiver in motion. This

can occur due to landscape or topograph-

ical features (e.g. when driving through a

depression). Lognormal fading has a multi-

plicative effect on the path loss. The multi-

plication factor is time-variable and lognor-

mally distributed.

Suzuki fading Suzuki fading is lognormal

fading while a Rayleigh profile is active.

Dynamic fading

Simulates dynamic propagation conditions

in accordance with test cases specified in

the 3GPP standard.

Birth death propagation Simulates

sudden variations in delay, e.g. with

sudden disappearance and reappear-

ance of a signal. This may occur, for exam-

ple, when a pedestrian making a call walks

around the corner of a building).

Moving propagation Simulates slow

variations in delay.

The R&S

SMU200A offers all fading profiles

News from Rohde & Schwarz Number 184 (2004/IV)