along with their corresponding code
names. The icons for the cell sites represent
three-sector cells. The heatmap colors are
the coverage or serving areas for each cell
sector. The boundary area between colors
is where the handoffs occur from one cell
sector to the next. If a mobile phone was
being served by the sector indicated by the
black arrow, then it would be deemed to
be located within the red area indicated by
the red arrow.
As Figure 7 demonstrates, the coverage
areas of the cells look nothing like circles
or arcs. Most coverage areas are shown
generally downstream from the antenna,
but the shape and size are dependent on
all the factors mentioned previously. This
modeling is based on scientific calculations
and real-world data.
Figure 7: Best server coverage plot
Measured Data
Drive testing can be performed to further improve the RF coverage
model. Drive testing uses a device such as the one in Figure 8. The
drive test equipment consists of a high speed cellular scanner, GPS
receiver, cellphones, and a tablet or laptop computer. The equipment
is installed in a vehicle and then driven around the area of interest to
gather actual signal strength measurements being received from the
cell sites.
The scanner collects signal strength and cell site parameters for
multiple technologies simultaneously. The GPS receiver tags a
location to the signal data once per second and stores it on the hard
drive of the tablet or laptop computer.
A phone can be connected
Figure 8: Drive
to the equipment in
test equipment
order to simulate a user
experience and try to
duplicate the mobile
phone in question.
Network data collected
from the phone indicates
the serving cell, signal
levels, and a host of other
data. While it is desired
to use the same model of
phone as the defendant
used, it is not necessary
because most phones use
similar technology. In
addition, radio frequency
specifications for the mobile phone are set by FCC requirements.8
The resulting signal strength measurements and their GPS locations
are imported into the modeling software. The modeling software uses
the actual measured data to fine tune the model and make it more
accurate.
Network-related parameters are also collected via a proprietary
interface to the USB port on the cellphone. This provides
information equivalent to the mobile phone of interest and provides
the best duplication of the RF experience.
Information Requested from
Wireless Operators
When requesting information from the mobile wireless operator
with a subpoena, it is important to be proactive and timely. Records
may be stored for a few months up to several years, depending on the
wireless operator. The subpoena should contain the following in order
to determine the phone’s location:
All subscriber information, call detail(s), caller identification(s), cell
site location information, call detail records.
List of cell sites within a *** radius of *** containing the following for
each cell sector (required for RF modeling of actual coverage):
· Latitude
· Longitude
· Ground Elevation (feet)
· Antenna Centerline (feet)
· Antenna Azimuth (degrees from True North)
· Antenna Model
· Antenna Mechanical Down tilt
· Antenna Electrical Down tilt
· Cable Losses (dBm)
· EiRP (Watts)
· Technology (LTE, UMTS, CDMA, EVDO, GSM, etc.)
· MIMO configuration (2 x 2, none, etc.)
· Frequency Band
· Channel Number (Channel number for CDMA, UARFCN for
UMTS, EARFCN for LTE)
· Cell site identification code per technology (PN for CDMA,
PSC for UMTS, PCI for LTE)
SPRING 2019 23