Final report on link level and system level channel models - Winner

WINNER D5.4 v. 1.4
5. Measurements and Literature Review
Our models are based on 3 pillars, namely existing (spatial) channel models, new publications regarding
all kind of channel modelling aspects, and finally measurements conducted within the work of WINNER.
5.1 Measurement systems
5.1.1 Principle of channel sounding
The operation principle of a channel sounder is to transmit a known signal using one antenna in one place
and to receive it using another antenna in another place. The operation is thus very similar to that of a
vector network analyzer. The key difference is that the transmitter and receiver are separate units. For this
reason, both the receiver and transmitter must be phase locked to accurate frequency standards (typically
Rubidium clocks) in order to maintain phase coherence.
In simplest form the channel can be sounded by generating a CW RF signal with a signal generator at the
transmitter, and mixing it down at the receiver using another generator tuned to the same frequency. The
voltage at the mixer output gives the narrowband radio channel as a function of time. In practice
amplifiers and filters are also needed in the system. The advantage of this type of channel sounder is that
it can be easily built using standard laboratory equipment. However, the drawback is that the wideband
channel properties can’t be measured. KTH used this type of channel sounder in their WINNER
measurements.
In order to solve the wideband properties of the radio channel, also the sounding itself needs to be done
using a wideband signal. The wideband signal can be generated either using direct signal spreading (used
e.g. in PropSound and HUT sounders) or OFDM-type of transmission (used in RUSK sounder).
Naturally, also the receiver needs to be wideband. The radio channel is estimated either in time or
frequency domain by cross-correlating the received signal with a replica of the original transmitted signal.
Typically this is done numerically after sampling the wideband signal at the output of a vector
demodulator. The result is either the complex impulse response or frequency transfer function of the
channel (these two are connected by a Fourier transform). In addition, the effects of the transmitter and
receiver need to be removed from the result using e.g. inverse filtering methods.
MIMO channel sounding requires transmission and reception using multiple antennas. In all wideband
sounder systems used in WINNER measurements this was achieved with a single transmitter – receiver
pair through time multiplexing with synchronous antenna switches in the transmitter and receiver. Using
electronic RF switches the switching can be made fast enough to capture essentially the same radio
channel with all antennas even in mobile measurements. In KTH measurement system the MIMO
measurement was done using four parallel transmitters tuned at slightly different frequencies and four
parallel receivers each receiving all transmitted frequency tones.
5.1.2 Channel sounders employed
Four different radio channel measurement systems were used in the measurement campaigns. The results
obtained with the HUT sounder in campaigns outside WINNER are used as background data in the
channel model. The measurement systems are listed in Table 5.1.
Partner
Table 5.1: Measurement systems used in channel measurements.
Measurement
system type
Manufacturer
Hyperlink
EBIT Propsound Elektrobit http://www.propsim.com/
NOK
Propsound
+ HUT antennas
Elektrobit
http://www.propsim.com/
TUI RUSK Medav http://www.channelsounder.de/
KTH KTH specific N/A N/A
HUT HUT specific N/A http://www.tkk.fi/Units/Radio/research/
rf_applications_in_mobile_communication/radio_channel/
radio_channel_sounder.htm
The PropSound TM and RUSK channel sounders are commercial wideband radio channel measurements
systems, while the HUT wideband channel sounder is mainly self-made. The narrowband measurement
Page 56 (167)