Subject: [NEXTEL-1] 60GHz wireless channel measurement and statistical analysis

From: [email-masked]
Date: Thu, 23 Oct 2003 09:40:55 -0400

60GHz wireless channel measurement and statistical analysis
By Haewoon Nam

Haewoon Nam is a WNCG graduate student currently working on his Ph.D. in
electrical and computer engineering. His research focuses are wireless channel
modeling and wideband system design. His current research includes the statistical
analysis and modeling of 60GHz wireless channels. For the summer of 2003, he
worked at the IBM T.J. Watson Research Center, Yorktown Heights, NY as a co-op
student. His responsibilities included the investigation of 60GHz wireless channel
characteristics. The following article is his synopsis of the research he did as a
part of his summer experience.

The rising importance of multimedia and computer communications in today’s society
creates new challenges for those working in related research areas. The data rate
required for future mobile communication systems is increasing. The first step
towards implementing such a system is frequency selection, and the second is to
understand the channel characteristics and develop a channel model.
The 60GHz frequency band is very attractive for broadband and portable mobile
communications for many reasons.  Since this frequency band experiences more
attenuation because of oxygen absorption, it allows better frequency reuse.  This
may seem to be a negative factor; however, it actually increases the network
capacity, dramatically reducing interference.  This band is not being used by any
other communication technology, and 5GHz of consecutive bandwidth is available. An
additional benefit is the very small antenna size, due to the small wavelength.
This will result in more compact equipment.  To use 60GHz for the future WPAN
(Wireless Personal Area Network), the channel characteristics at the specific
frequency have to be studied in advance.  There are two main approaches to channel
measurements. One is time-domain measurement using a sliding correlator channel
sounder, and the other is frequency-domain measurement, which sweeps the whole
bandwidth using a vector network analyzer.
The channel sounder at IBM consists of mostly off-the-shelf equipment. For
example, an Arbitrary Waveform Generator generates PN sequences. It provides a
more reliable environment and some additional flexibility, although the size of
system is bigger.

To get meaningful data for a statistical analysis, measurement environments and
scenarios must be correctly defined. The definition involves characterizing where
measurements are done, the location of the BS (Base Station) antenna and the MS
(Mobile Station) antennas, and the structural composition of the building,
including the material used for the walls, size of the rooms, and so on. Almost
all research at 60GHz to date uses directive antennas for measurements. The
channel sounder should be accurately calibrated in advance and carefully handled
as even small movement of the cables can affect the result, especially at very
high frequencies.  Key parameters for statistical analysis such as RMS delay
spread and path loss are then extracted from various measurement scenarios, and a
mathematical channel model is derived and validated based on the analysis and
measurement data. We are currently analyzing data collected at IBM to achieve a
better understanding of 60GHz channel characteristics.

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