# Advanced Wireless Service Interference Tests Results and Analysis

Federal Communications Commission

Office of Engineering and Technology

October 10, 2008

# Advanced Wireless Service Interference Tests Results and Analysis

# Introduction:

# The Commission has initiated a proceeding to consider provisions for Advanced Wireless Service (AWS) in the 2155--2175 MHz band, referred to as AWS-3.[^1] Concerns have been raised that, if the Commission were to allow time-division-duplex (TDD) operations in this spectrum under the proposed technical conditions, there is a significant risk of harmful interference from mobile devices operating in the AWS-3 band to mobile devices that receive signals in the adjacent 2110--2155 MHz band, referred to as AWS-1. The Commission also invited comment as to whether the proposed band might be expanded to 2155-2180 MHz to provide greater flexibility to mitigate harmful interference.

T‑Mobile submitted into the record test results which it claims shows
that under the proposed rules, harmful mobile-to-mobile interference is
likely to occur.[^2] To further inform the record, the Commission staff,
together with interested parties, performed laboratory bench tests to
investigate this interference potential on September 3-5 at a test
facility in Seattle, Washington.[^3] These laboratory bench tests were
designed to increase understanding of T-Mobile's previously conducted
tests including test setup, underlying assumptions, suitability of the
equipment used and the extent to which they may be relied upon to assess
the effect AWS-3 handset operations could have on AWS-1 handsets. We
previously published the raw data from these tests on September 12,
2008.[^4]

It is important to note that the laboratory bench tests were performed
with both the desired and interfering signals coupled directly into the
antenna connection of the AWS‑1 mobile device. The tests were conducted
at various AWS-1 receive signal levels and various frequency separations
from the AWS-3 signals. Tests were also performed to investigate whether
improved filtering of the AWS-1 receiver might reduce potential
interference. While these tests produced important information, they are
only one element in assessing the potential for harmful interference.
Other elements must be considered such as what signal levels are
appropriate to protect, what assumptions should be made about the
typical separations between the mobile devices, and various factors that
affect the coupling of signals between the devices under actual
operating conditions.

In this report, we present the test results from the joint testing,
provide an analysis of the potential for harmful interference, and make
tentative conclusions as to the standards necessary to control the
potential for harmful interference.[^5] This report tentatively
concludes that for the static case that is examined AWS-3 devices could
operate at a power level of up to 23 dBm/MHz equivalent isotropic
radiated power (EIRP) and with out-of-band emissions (OOBE) attenuated
by 60 + 10\*log(P) dB without a significant risk of harmful
interference. However, this report also notes that the Commission has in
the past adopted less stringent OOBE standards under flexible service
rules whereby the licensees and industry work together cooperatively to
manage potential interference.

# Laboratory testing:

# Test Setup: 

The joint tests consisted of a test setup identical to that described in
the T-Mobile Test Report. This is shown in Figure 1.

As shown in Figure 1, the link between the AWS-1 mobile station (MS),
depicted here as a UMTS mobile station, and its associated base station
(BS) was established using two signal generators (*i.e*., a serving BS
(CMU 200) and an AWGN noise generator) connected to the MS through a set
of combiners and step attenuators. The function of the AWGN noise
generator is to simulate the inherent noise typical within mobile
systems due to factors such as loading.[^6] A second signal generator is
also connected to the MS through a custom filter to simulate the
interfering signal (*i.e*., the AWS-3 transmitter).

The specific tests were conducted by first establishing a link between
the BS and the MS at various MS desired receive signal levels. Then, an
interfering signal was injected into the system and its level was
adjusted to determine the signal strength at which either a
Call-Setup-Failure (CFS) or Call-Drop (CD) occurred. This interfering
signal level was recorded for each combination of desired receive level
and frequency separation between the BS transmitter and MS receiver. We
note that parties have generally stated that UMTS or WiMAX based systems
are likely to be used in the AWS-3 band. Thus, the joint tests simulated
these signals as the interference sources.

![](media/image1.jpeg){width="4.675694444444445in"
height="2.5743055555555556in"}

**Figure 1:** Test setup

# Interference Mechanisms: 

The joint tests examined two interference mechanisms - in-band
interference and out-of-band (*i.e*., adjacent band) interference -- to
determine the level at which an AWS-3 mobile transmitter causes
interference to AWS-1 handsets. More specifically, AWS-1 in-band
interference is caused by out-of-band emissions from an AWS‑3 mobile
transmitter that, due to practical limitations affecting how quickly the
transmitter filter can roll-off or suppress emissions in the adjacent
band, are located in the receive band of the AWS-1 mobile receiver.
Correspondingly, AWS-1 out-of-band interference is caused by AWS-3
emissions within the AWS-3 mobile receive band that, due to the roll-off
of the AWS‑1 receiver filter, enter the front-end of AWS-1 receiver and
causes it to saturate. This is more commonly referred to as overload
interference. The specific interference scenarios of an AWS-3 mobile
transmitter and an AWS-1 mobile receiver are shown in Figure 2.

![](media/image2.png){width="3.6041666666666665in"
height="2.6770833333333335in"}

**Figure 2:** Representation of in-band and out-of-band interference
mechanisms

![](media/image3.wmf){width="4.019444444444445in"
height="2.553472222222222in"}

**Figure 3:** Representation of test equipment vs. actual
performance.[^7]

![](media/image4.wmf){width="5.570833333333334in"
height="0.6145833333333334in"}

# Characterization of mobile handsets:

The ability of a mobile handset to either cause interference to or
tolerate a signal from a nearby handset is directly related to the
transmit power of the interfering handset and the filter characteristics
of the interferer and the victim handset. Interference potential is
reduced with lower power. Similarly, steeper roll-off of the receiver
and transmit filters reduces interference potential. Figure 2 shows that
interference can be significantly reduced by the combined effect of the
two devices' front end filters.[^8]

Figure 3 shows the situation of interest in this proceeding, where the
front end filter of the victim AWS-1 receiver is designed to operate
across the entire AWS-3 spectrum. In such a situation conventional
spectrum management practice suggests that interference can be avoided
or minimized by either setting a strict power limit on the AWS-3
transmitter, or improving the filtering of the AWS-1 device to better
reject signals outside the AWS-1 band.

For our testing, we did not have an actual AWS-3 handset and instead
used a signal generator to simulate the interfering signals. In this
regard, it is important to note that test equipment often does not
function exactly like an actual handset. This appears to be the
situation encountered during these tests. In practice, a transmitted RF
signal concentrates most of its energy within its desired channel;
outside of this channel the signal levels will fall as a function of
frequency separation from the desired channel. In contrast to the way an
actual handset would be expected to behave, we determined that the
signal generator used in these tests simulated the interfering
transmitter (*i.e.*, the AWS-3 transmitter) signals with a signal level
that remained essentially constant outside of the desired channel
regardless of frequency separation. This results in higher out-of-band
energy levels than would typically be produced using an actual handset.
The practical effect is that using the signal generator will tend to
overestimate the interference potential of an AWS-3 handset. To further
illustrate this point, Figure 4 shows the transmit spectrum of the AWS-1
mobile handset used in the joint testing and Figure 5 shows the spectrum
for five transmitters measured by OFCOM which were used as the basis for
their proposed rules in the 2.6 GHz band.[^9] These are distinctly
different from those generated by the UMTS/WiMAX signal generator as
shown in Figures 6 and 7.

![](media/image5.jpeg){width="4.125in" height="2.5006944444444446in"}

**Figure 4:** UMTS EU Transmit Spectrum

![](media/image6.wmf){width="5.030555555555556in"
height="3.1256944444444446in"}

**Figure 5:** 3GPP Transmit Mask and OFCOM Measured Transmit Spectrum @
2112.5 MHz[^10]

![](media/image7.jpeg){width="4.314583333333333in"
height="3.321527777777778in"}

**Figure 6.** Signal Generator UMTS Transmitter Spectrum (Interferer)

![](media/image8.jpeg){width="5.0in" height="3.2604166666666665in"}

**Figure 7:** Signal Generator WiMAX Transmitter Spectrum (Interferer)

# Analysis: 

# Measurement Results:

a.  AWS-1 In-Band Interference:

As described above, this interference scenario is characterized by the
AWS-3 out-of-band emissions (OOBE) that are directly in the pass band of
the AWS-1 receiver.

For these tests, identical signals (*i.e*., same frequency and
bandwidth) were used for the desired and undesired signals. The test was
conducted by setting the desired signal to a particular value (*e.g*.,
-90 dBm) and adjusting the signal level of the interferer until an
interference event -- call set-up failure or call drop - was observed.
The tests results are summarized in Table 1.

+-------------------------------+--------------------------------------+
| **Desired Signal: UMTS**      | **Interference Signal: UMTS**        |
|                               |                                      |
| **2152.5 MHz**                | **2152.5 MHz**                       |
|                               |                                      |
| **(dBm/5MHz)**                | **(dBm/5MHz)**                       |
+-------------------------------+--------------------------------------+
| -105                          | -96.2                                |
+-------------------------------+--------------------------------------+
| -100                          | -89.2                                |
+-------------------------------+--------------------------------------+
| **-95**[^11]                  | **-83.2**                            |
+-------------------------------+--------------------------------------+
| -90                           | -77.2                                |
+-------------------------------+--------------------------------------+
| -85                           | -72.2                                |
+-------------------------------+--------------------------------------+

**Table 1:** OOBE Test Results with a UMTS Interferer

We note that, though planned, OOBE measurement data with a WiMAX
interfering signal were not collected. We present results for the tests
we did conduct with a WiMAX interferer in Table 4 below. These tests
generally show that a WiMAX signal has less potential for causing
interference than a UMTS signal. Based on these observations, we can
reasonably expect that WiMAX in the AWS-3 band would have less impact on
an AWS-1 receiver than UMTS.

b.  Receiver Overload measurement:

This interference scenario is characterized by the amount of energy
within the AWS-3 channel that enters the AWS-1 receiver. In measuring
overload interference, it is important to ensure that all effects of
AWS-3 out-of-band interference are removed from the test. This is
accomplished by using an external filter with a steep roll-off as shown
in Figure 8.

The test results corresponding to overload from both UMTS and WiMAX
interferer signals are summarized in Tables 2-4.

> ![](media/image9.wmf){width="5.15in" height="2.75in"}
>
> **Figure 8:** Filter Response for External AWS-3 Transmit Filter for
> the Upper Band Edge

+----------------------+----------------------+------------------------+
| **Desired Signal:    | **Interference       |                        |
| UMTS**               | Signal: UMTS**       |                        |
|                      |                      |                        |
| **2152.5 MHz**       | **2157.5 MHz**       |                        |
|                      |                      |                        |
| **(dBm/5MHz)**       | **(dBm/5MHz)**       |                        |
+----------------------+----------------------+------------------------+
|                      | **Combined effect of | **Overload             |
|                      | OOBE and overload    | interference only**    |
|                      | interference**       |                        |
|                      |                      | **(WITH EXTERNAL       |
|                      | **(WITHOUT FILTER)** | FILTER)**              |
+----------------------+----------------------+------------------------+
| -105                 | -44.2                | -34.2                  |
+----------------------+----------------------+------------------------+
| -100                 | -37.2                | -30.2                  |
+----------------------+----------------------+------------------------+
| **-95**              | **-33.2**            | **-28.2**              |
+----------------------+----------------------+------------------------+
| -90                  | -29.2                | -26.2                  |
+----------------------+----------------------+------------------------+
| -85                  | -27.2                | -25.2                  |
+----------------------+----------------------+------------------------+
| -75                  | -11.2                | N/A                    |
+----------------------+----------------------+------------------------+

> **Table 2:** Results of overload tests (with filter) versus the
> combined OOBE and overload interference (without filter) using a
> serving UMTS signal at 2152.5 MHz and a UMTS interfering signal at
> 2157.5 MHz.

+----------------------+----------------------+------------------------+
| **Desired Signal:    | **Interference       |                        |
| UMTS**               | Signal: UMTS**       |                        |
|                      |                      |                        |
| **2142.5 MHz**       | **2157.5 MHz**       |                        |
|                      |                      |                        |
| **(dBm/5MHz)**       | **(dBm/5MHz)**       |                        |
+----------------------+----------------------+------------------------+
|                      | **Combined effect of | **Overload             |
|                      | OOBE and overload    | interference only**    |
|                      | interference**       |                        |
|                      |                      | **(WITH EXTERNAL       |
|                      | **(WITHOUT FILTER)** | FILTER)**              |
+----------------------+----------------------+------------------------+
| -105                 | -43.2                | -27.2                  |
+----------------------+----------------------+------------------------+
| -100                 | -35.2                | -23.2                  |
+----------------------+----------------------+------------------------+
| **-95**              | **-29.2**            | **-19.7**              |
+----------------------+----------------------+------------------------+
| -90                  | -23.2                | -16.2                  |
+----------------------+----------------------+------------------------+

> **Table 3:** Results of overload tests (with filter) versus the
> combined OOBE and overload interference (without filter) using a
> serving UMTS signal at 2142.5 MHz and a UMTS interfering signal at
> 2157.5 MHz.

+----------------------+---------------------+------------------------+
| **Desired Signal:    | **Interference      |                        |
| UMTS**               | Signal: WiMAX**     |                        |
|                      |                     |                        |
| **2142.5 MHz**       | **2160 MHz**        |                        |
|                      |                     |                        |
| **(dBm/5MHz)**       | **(dBm/5MHz)**      |                        |
+----------------------+---------------------+------------------------+
|                      | **Combined effect   | **Overload             |
|                      | of OOBE and         | interference only**    |
|                      | overload            |                        |
|                      | interference**      | **(ESTIMATED)\***      |
|                      |                     |                        |
|                      | **(WITHOUT          |                        |
|                      | FILTER)**           |                        |
+----------------------+---------------------+------------------------+
| -105                 | -30.2               | -19.7                  |
+----------------------+---------------------+------------------------+
| -100                 | -25.2               | -17.2                  |
+----------------------+---------------------+------------------------+
| **-95**              | **-22.2**           | **-16.2**              |
+----------------------+---------------------+------------------------+
| -90                  | -21.2               | -15.2                  |
+----------------------+---------------------+------------------------+
| -85                  | -19.2               | -14.2                  |
+----------------------+---------------------+------------------------+

> \* As noted above, the tests only recorded data for a WiMAX interferer
> without a filter. Based on comparisons of the UMTS and WiMAX
> measurements for the combined effect of OOBE and overload
> interference, which show about a 5 to 10 dB difference between the
> UMTS measurements with and without the filter, we estimate the effect
> of overload interference from a WiMAX interferer would be about 6 dB
> less.
>
> **Table 4:** Results of overload tests (with filter) versus the
> combined OOBE and overload interference (without filter) using a
> serving UMTS signal at 2142.5 MHz and a WiMAX interfering signal at
> 2160 MHz.

These tests result in the following observations:

1.  Tables 2 and 3 show that overload interference improves with
    increased frequency separation.

2.  Tables 2 and 3 show that OOBE improves with increased desired signal
    level.

3.  Table 4 shows that the WiMAX signal provides more protection against
    overload interference than UMTS.

# Interference analyses and link budget calculations:

In this section we use a classical link budget calculation to analyze
potential interference between an AWS-1 receiver and an AWS-3
transmitter. Figure 9 shows the scenario used for this analysis. An
AWS-1 mobile receiver establishes a link with a serving base station
(desired signal) and a nearby AWS-3 mobile transmitter is also operating
(interferer). The signal level that reaches the AWS-1 device from the
AWS-3 transmitter must not exceed the interference threshold level that
would cause harmful interference.

![](media/image10.wmf){width="5.176388888888889in"
height="3.060416666666667in"}

**Figure 9**: Interference Scenario for Link Budget Analysis

The following assumptions are used for the analysis:

-   Desired AWS-1 serving signal to be protected is -95 dBm.[^12]^,^
    [^13]

-   Interference criterion is call setup failure[^14]

-   Separation distance = 2 meters[^15]

-   Free Space Propagation Model[^16]

-   Head-body loss of 6 dB[^17]

-   Loss due to antenna mismatch of 2 dB[^18]

-   No loss was considered due to antenna efficiency[^19]

-   AWS-1 OOBE slope of 3 dB[^20]

-   Multipath/Shadowing loss of 3.5 dB[^21]

-   Signal Bandwidth = 5 megahertz

-   Technologies: UMTS and WiMAX

The following acronyms will be used in the equations to follow:

> EIRP \-- Equivalent isotropic radiated power (dBm)
>
> I~OOBE~ \-- AWS-3 in-band interference (dBm)
>
> HBL \-- Head and body loss (dB)
>
> FR \-- Front end receiver filter rejection (dB)
>
> FSL \-- Free space loss (dB)
>
> AM \-- Antenna polarization and impedance mismatch (dB).
>
> MF \-- Multipath fading and shadowing (dB)
>
> L~slope~ \-- AWS-1 OOBE slope (dB)

CSF \-- Call setup failure (dB)

CD \-- Call drop (dB)

BCF \-- Bandwidth correction factor[^22] (dB)

A.  **Required OOBE:**

> The following formula is used to determine the out-of-band emission
> levels of an AWS-3 handset that correspond to an interference event in
> an AWS-1 handset. All of the calculations shown in this section are
> based on the minimum desired received signal level of ‑95 dBm.
>
> OOBE = I~OOBE~ + ∑losses - BCF, where
>
> ∑losses = FSL~\@2M~ + HBL + AM + MF + L~slope~
>
> **- UMTS Interferer:**

From Table 1, for the desired received signal level of ‑95 dBm,
interference occurs when the interferer reaches a level of ‑83.2 dBm/5
MHz. Substituting this into the formula results in:

OOBE~AWS-3~ = -83.2~dBm/5\ MHz~ + 45.12 + 6 + 2 + 3.5 + 3 - 10\*log(5) =
-30.56 ~dBm/MHz~

This level of OOBE translates to a requirement for an AWS-3 handset to
reduce its OOBE by about (60 + 10\*log(P) dB) or more to avoid causing
interference to AWS-1 handsets.

The following observations can be made:

1.  A UMTS AWS-3 handset can safely operate with an OOBE limit of about
    --30 dBm/MHz (or attenuation of 60 + 10\*log(P) dB) without causing
    disruption of service to nearby AWS‑1 handsets.

2.  As noted, we do not have OOBE measurement data for a WiMAX
    interferer. However, based on the WiMAX tests we conducted and our
    observations from those tests, we expect that a WiMAX AWS-3 handset
    would provide a margin of improvement over that observed for a UMTS
    handset.

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B.  **Maximum Power of AWS-3 to prevent interference:**

To calculate overload interference, we consider that the maximum
overload interference (I~OL~) is related to the AWS-3 handset EIRP as
follows:

> EIRP~AWS-3~ = I~OL~ + ∑losses - BCF, where ∑losses = FSL~2M~ + HBL +
> AM + MF + FR[^23]

a)  **UMTS desired vs. UMTS Interferer:** Serving UMTS @ 2152.5 MHz and
    interferer UMTS at 2157 MHz

> From table 2(a), desired signal level of -95 dBm corresponds to an
> I~OL~= -28.2dBm. Substituting this into the formula results in:

EIRP~AWS-3~ = -28.2 + 45.12 + 6 + 2 + 3.5 - 10\*log(5) ≈ 21.4 ~dBm/MHz~

b)  **UMTS desired vs. UMTS Interferer:** Serving UMTS @ 2142.5 MHz and
    interferer UMTS at 2157 MHz

> From table 2(b), desired signal level of -95 dBm corresponds to I~OL~
> = -19.7 dBm. Substituting this into the formula results in:

EIRP~AWS-3~ = -19.7 + 45.12 + 6 + 2 + 3.5 - 10\*log(5) ≈ 30 ~dBm/MHz~

c)  **UMTS desired vs. WiMAX Interferer:** Serving UMTS @ 2152.5 MHz and
    interferer WiMAX at 2160 MHz

For the WiMAX interferer case, the only measured data available is that
for the combined effect of OOBE and Overload interference. Data for the
overload interference can therefore only be inferred from the UMTS
interferer measurements case, summarized in Tables 2 and 3. From table
4, the desired signal level of ‑95 dBm corresponds to I~OL~ of -22.2
dBm. With OOBE removed, we estimate I~OL~ to be about -16.2 dBm.
Substituting this into the formula results in:

EIRP~AWS-3~ = -16.2 + 45.1 + 6 + 2 + 3.5 - 10\*log(5) ≈ 33.4 ~dBm/MHz~

The following observations can be made:[^24]

1.  For a desired signal level of -95 dBm or greater, a UMTS AWS‑3
    handset, under static conditions, can safely operate with maximum
    EIRP of about 23 dBm/MHz without causing disruption of service to
    nearby AWS-1 handsets.

2.  A WiMAX AWS-3 handset, under static conditions, can safely operate
    with an EIRP of about 33 dBm/MHz without causing disruption of
    service to nearby AWS‑1 handsets.

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I.  **Probability of Interference and Impact on AWS-1 System
    Performance**

The interference analyses presented above are based on a static case
where all of the elements are assumed to be fixed. Most importantly,
even under these conditions, the analysis shows that an AWS-1 and AWS-3
device operating in close proximity does not necessarily result in
interference. And when factoring in actual operation under non-static
conditions, the situation only improves.

For example, as detailed above, in most cases an AWS-1 device will
receive a stronger signal than -95 dBm, which results in a vastly
reduced interference risk. Similarly, our analysis assumes an AWS-3
handset transmitting at its maximum power, which will occur only a small
portion of the time;[^25] a reasonable assumption especially if AWS-3
signal patterns are similar to those cited by T-Mobile in their Test
Report.[^26] This too would reduce the interference potential predicted
here. In addition, we note that modern wireless phones operate across
multiple frequency bands and channels. Our static analysis only
considers the case where the AWS-1 and AWS-3 handsets are operating on
directly adjacent channels and in close proximity. Under likely
scenarios where this is not the case, the potential for interference
would be reduced from that predicted in this report.

Thus, the static case as tested here provides insight as an upper bound
on interference. The statistical nature of calling patterns, frequency
selection, transmitter and receiver location, and signal levels only
serves to improve the predicted performance and results in fewer
instances of interference than would be predicted by this static case.
We do not here analyze the various arguments in the record regarding the
probability of interference and its impact on overall AWS‑1 reliability
or performance, but do note that this must be considered in a
comprehensive analysis.

II. **Comparison with other Analyses and OOBE standards**

We note that commenters in the record have cited analyses conducted by
the United Kingdom's Office of Communications (OFCOM) assessing
potential interference between TDD and FDD mobile handsets in adjacent
bands operating in the 2.5 GHz region of the spectrum.[^27] The
situation analyzed by OFCOM is very similar to the situation we are
considering here, although there are some differences. OFCOM determined
that TDD and FDD mobile handsets can operate in adjacent bands with
appropriate technical constraints. Notably, OFCOM restricted base
station power in the first adjacent 5 megahertz TDD channel as a means
to ensure that operations would be restricted to small cells where the
TDD handset power would tend to be reduced. OFCOM established an OOBE
limit equivalent to 49 + 10\*log(P) dB**.** We note that OFCOM's
analysis found there was virtually no risk of interference beyond the
first adjacent 5 megahertz channel.

The Commission has previously adopted standards for OOBE based on
flexible rules that permit TDD or FDD operation. For example, in the
upper 700 MHz band, the Commission permitted TDD operation in the
commercial spectrum subject to an OOBE attenuation standard of
43 + 10\*log(P) dB.[^28] Indeed the Commission specifically amended its
rules to provide for TDD operation, recognized the possibility of
mobile-to-mobile interference, and adopted and maintained an OOBE limit
of 43 + 10\*log(P) dB. In considering rules for the lower 700 MHz band,
the Commission specifically rejected a proposal to adopt a stricter OOBE
standard for TDD operations and affirmed the 43 + 10\*log(P) dB
standard.[^29] While many participants in the Commission's proceeding
argue that such operation was not realistically contemplated, presumably
because the Commission decided to continue to auction paired spectrum,
the fact remains that the rules specifically contemplated the
possibility of mobile-to-mobile interference using an OOBE standard of
43 + 10\*log(P) dB and continue to provide for implementation of such
technology in these bands if licensees were to choose to do so. In
establishing rules for flexible operation in the 2.5 GHz band, the
Commission adopted an OOBE attenuation standard for mobile digital
stations of 43 + 10\*log(P) dB and 55 + 10\*log(P) dB at 5.5 megahertz
from the channel edges.[^30]

Notably, when establishing OOBE limits for frequency bands where
flexible use is permitted the Commission has generally indicated that it
expected the licensees to work together to mitigate any potential for
harmful interference. Indeed the wireless industry often has established
its own standards that are stricter than the FCC regulations. This
cooperation has been a cornerstone in enabling a shift from command and
control regulation whereby separate interference protection limits must
be tailored to each technology and situation to one where industry has
the flexibility to adopt the technologies and services of its choosing
along with standards to practices to control harmful interference. We
note also that the Commission has generally reserved the right to apply
more stringent OOBE standards in the event that harmful interference may
occur and cannot be resolved among the parties.

III. **Remarks and conclusions:**

The appropriate power limits and OOBE limits are a function of the
underlying assumptions of any analysis. The Commission has generally
adopted standards that balance the risk of potential interference
against a variety of other factors, including the impact those standards
may have on the potential uses of spectrum. The analysis above is based
on reasonable assumptions that support allowing power levels of up to 23
dBm/MHz and an OOBE limit of 60 + 10\*log(P) dB. Alternatively, a
standard of 43 + 10\*log(P) dB would be consistent with past practice
and would encourage the parties to work together to adopt whatever
further measures may be necessary to control interference.[^31]

# Annex

The following are the underlining assumptions behind our study:

-   Desired AWS-1 serving signal to be protected is -95 dBm

-   Interference criterion is call setup failure

-   Separation distance = 2 meters

-   Free Space Propagation Model

-   Head-body loss of 6 dB

-   Loss due to antenna mismatch of 2 dB

-   No loss was considered due to antenna efficiency

-   AWS-1 OOBE slope of 3 dB

-   Multipath/Shadowing loss of 3.5 dB

-   Signal Bandwidth = 5 megahertz

-   Technologies considered are UMTS and WiMAX

1.  **AWS-3 EIRP**:

**Table 1:** EIRP Results for UMTS Interferer

  --------------------------- ------------ -------- -------- -------- -------- -----------
  **Parameters**              **Values**                                       **Units**

  **Desired Signal**          -105.0       -100.0   -95.0    -90.0    -85.0    dBm/5 MHz

  **Frequency**               2152.5       2152.5   2152.5   2152.5   2152.5   MHz

  **UMTS Interferer Signal**  -34.2        -30.2    -28.2    -26.2    -25.2    dBm/5 MHz

  **Obstructions**                                                             dB

  **Multipath/Shadowing       3.5          3.5      3.5      3.5      3.5      dB
  loss**                                                                       

  **Mobile Antenna Gain**                                                      dBi

  **AWS-1 Rx Filter                                                            dB
  Rejection**                                                                  

  **Head/body loss**          6.0          6.0      6.0      6.0      6.0      dB

  **AWS-1/AWS-3 Antenna       2.0          2.0      2.0      2.0      2.0      dB
  Impedance & Polarization                                                     
  Mismatch**                                                                   

  **Separation Distance**     2.0          2.0      2.0      2.0      2.0      Meters

  **EIRP**                    22.4         26.4     28.4     30.4     31.4     dBm/5 MHz

                              15.4         19.4     21.4     23.4     24.4     dBm/MHz
  --------------------------- ------------ -------- -------- -------- -------- -----------

**Table 2:** EIRP Results for WiMAX Interferer

  -------------------------- ------------ -------- -------- -------- -------- -----------
  **Parameters**             **Values**                                       **Units**

  **Desired Signal**         -105.0       -100.0   -95.0    -90.0    -85.0    dBm/5 MHz

  **Frequency**              2152.5       2152.5   2152.5   2152.5   2152.5   MHz

  **WiMAX Interferer         -19.7        -17.2    -16.2    -15.2    -14.2    dBm/5 MHz
  Signal**                                                                    

  **Obstructions**                                                            dB

  **Multipath/Shadowing      3.5          3.5      3.5      3.5      3.5      dB
  loss**                                                                      

  **Mobile Antenna Gain**                                                     dBi

  **AWS-1 Rx Filter                                                           dB
  Rejection**                                                                 

  **Head/body loss**         6.0          6.0      6.0      6.0      6.0      dB

  **AWS-1/AWS-3 Antenna      2.0          2.0      2.0      2.0      2.0      dB
  Impedance & Polarization                                                    
  Mismatch**                                                                  

  **Separation Distance**    2.0          2.0      2.0      2.0      2.0      Meters

  **EIRP**                   36.9         39.4     40.4     41.4     42.4     dBm/5 MHz

                             29.9         32.4     33.4     34.4     35.4     dBm/MHz
  -------------------------- ------------ -------- -------- -------- -------- -----------

2.  **Out of Band Emission limit:**

**Table 3:** OOBE Results for UMTS Interferer

  --------------------------- --------------------------------------- -------- -------- -------- -------- ------------
  **Parameters**              **Values**                                                                  **Units**

  **Desired Signal**          -105.0                                  -100.0   -95.0    -90.0    -85.0    dBm/5 MHz

  **Frequency**               2152.5                                  2152.5   2152.5   2152.5   2152.5   MHz

  **UMTS Interferer Signal**  -96.2                                   -89.2    -83.2    -77.2    -72.2    dBm/5 MHz

  **Obstructions**            ![](media/image11.jpeg){width="0.0in"                                       dB
                              height="2.1145833333333335in"}                                              

  **Multipath/Shadowing        3.5                                    3.5      3.5      3.5      3.5      dB
  loss**                                                                                                  

  **AWS-3 Antenna Gain**                                                                                  dBi

  **AWS-1 OOBE Slope**        3.0                                     3.0      3.0      3.0      3.0      dB

  **Head/Body loss**          6.0                                     6.0      6.0      6.0      6.0      dB

  **AWS-1/AWS-3 Antenna       2                                       2        2        2        2        dB
  impedance & polarization                                                                                
  mismatch loss**                                                                                         

  **Separation Distance**     2.0                                     2.0      2.0      2.0      2.0      Meters

  **OOBE**                    -36.6                                   -29.6    -23.6    -17.6    -12.6    dBm/5 MHz

                              -43.6                                   -36.6    -30.6    -24.6    -19.6    dBm/MHz

                              73.6                                    66.6     60.6     54.6     49.6     \+ 10\*log
                                                                                                          (P) dB
  --------------------------- --------------------------------------- -------- -------- -------- -------- ------------

[^1]: *See* Service Rules for Advanced Wireless Services, WT Docket Nos.
    07-195 and 05-356, *Further Notice of Proposed Rulemaking*, 23 FCC
    Rcd 35995 (2008).

[^2]: *See*
    <http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6520035719>.
    T‑Mobile submitted a report titled "AWS‑3 to AWS-1 Interference
    Laboratory Test Report" (T-Mobile Test Report) on July 28, 2008.

[^3]: The joint tests were open to the public and conducted at Boeing's
    test facility in Seattle Washington.

[^4]: *See*:
    <http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6520067726>.

[^5]: This report focuses only on the potential for mobile-to-mobile
    interference. Other interference scenarios, such as mobile-to-base,
    base-to-base and base-to-mobile are well understood and mitigation
    techniques are well established and are routinely employed by
    network designers.

[^6]: This noise is known in the standards as In-Cell and Out-of-Cell
    Interference.

[^7]: If the difference is significant, as is the case here, between the
    predictable performance of an actual device and test equipment
    (emulator) the results of the test are faulty, unless the difference
    is accounted for somehow.

[^8]: This is most pronounced under static conditions such as those
    under which these tests were conducted. These effects also affect
    interference potential in a mobile environment. However, in a mobile
    environment we note that the occurrence of mobile‑to‑mobile
    interference is also subject to a large number of variables. Thus,
    such interference is affected by the statistical nature of these
    variables and often will only occur under the unlikely condition
    that several low probability events occur simultaneously. *See*
    Section V., *infra*.

[^9]: *See* OFCOM technical reports available at:
    [[http://www.ofcom.org.uk/consult/condocs/2ghzawards/2ghzawards.pdf]{.underline}](http://www.ofcom.org.uk/consult/condocs/2ghzawards/2ghzawards.pdf)
    and
    [[http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf]{.underline}](http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf).

[^10]: *See* OFCOM report, figure 17 page 41
    at:[[http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf]{.underline}](http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf).

[^11]: Measurements were not taken for a desired received signal level
    of -95 dBm. The interference signal levels shown here and below are
    interpolated from the results of the measurements taken.

[^12]: The received signal code power (RSCP) measured by the user
    equipment (UE) receiver on the primary common pilot channel (CPICH)
    must be greater than -95 dBm. This is known as the high quality
    criterion (*i.e*., CPICH RSCP \> -95 dBm). For more information,
    see: Kruger and Heinz Mellein (2004). *UMTS Introduction and
    Measurement*. Germany: Rohde & Schwarz. 131 and Jukka Lempiäinen,
    Matti Manninen (2004). *UMTS Radio Network Planning, Optimization
    and QOSUMTS Radio Network Planning, Optimization and QOS Management:
    For Practical Engineering Tasks*. Michigan: Kluwer Academic
    Publishers. 141.

[^13]: The choice to protect a desired receive signal level of -95 dBm
    or greater is a reasonable assumption. In its Test Report, T-Mobile
    provides statistics relating to drive tests it conducted in two
    markets to assess the received signal strength that users may
    experience. The statistics presented in their Test Report show that
    for both markets, approximately 85 percent of the locations measured
    experience received signal levels of -95 dBm or greater. *See*
    T‑Mobile Test Report at 13-16. We note that this data was collected
    from drive tests where users may use their mobile phones and not
    data based on actual calling patterns or locations. Nevertheless,
    given that most locations receive signal levels greater than -95 dBm
    coupled with the conservative static case analysis conducted herein,
    we believe that basing protection criteria on this received signal
    level is sufficient to protect the vast majority of AWS-1 users from
    interference. With respect to the -95 dBm signal level, we note that
    our calculations assume a reference bandwidth of 5 megahertz.
    However, in standards documents, protected signal levels are
    generally referenced to a bandwidth of 3.84 MHz. For example, the
    standards 3GPP TS 25.133 & 304 (pg.15) indicate: 1. for an FDD cell,
    the measured primary CPICH RSCP value shall be greater than or equal
    to -95 dBm/3.84 MHz and 2. for a TDD cell, the measured P‑CCPCH RSCP
    shall be greater than or equal to -84 dBm/3.84 MHz. For a signal
    bandwidth of 3.84 megahertz, the bandwidth correction factor would
    be 1.15 dB (*i.e*., 10\*log(5/3.84)).

[^14]: The choice of a particular interference criterion is important as
    it is a major determinant of the signal levels that lead to an
    interference event. We used the more conservative criterion of call
    setup failure rather than a call drop criterion. The difference
    between the two is about 4 dB -- that is, an active call has about 4
    dB of margin before it is severed completely either because of
    interference or some other phenomenon.

[^15]: A 2 meter separation distance is consistent with prior studies
    and proceedings, including UWB and H-Block, among others. We
    recognize that situations will exist where users may be attempting
    to communicate at separation distances less than 2 meters. However,
    in many locations where there are expected to be a high
    concentration of users, additional cell sites are used to ensure
    good coverage by relatively strong signals which will reduce the
    potential for harmful interference between the users.

[^16]: We note that free space propagation yields conservative results
    as it is a worst case model. In practice the mobile operating
    environment will result in losses that exceed those predicted by
    free space propagation. For example, the proximity of the handset to
    the human body/head, irrespective of angle of incident wave,
    introduces multipath components -- that is because of the inherent
    ability of the human body/head to reflect energy at certain
    frequencies. We note that any increase in propagation loss results
    in reducing the required separation distance between the devices
    under study. Free Space Propagation loss (FSL) can be calculated
    using the following formula:
    FSL = 20\*log(4\*PI\*d(m)\*Freq(MHz)/300). Thus, FSL at 2152.5 MHz
    with a 2 meter separation distance is 45.12 dB.

[^17]: According to 3GPP TS 25.942, the body losses due to the close
    proximity of the user's head and also due to blockage of the hand on
    the UE may be as high as 12 dB. Other studies found the body losses
    can reach 9 to 15 dB. *See* H.-R Chuang, "Human operator coupling
    effects on radiation characteristics of a portable communication
    dipole antenna." IEEE Trans. Antennas Propagation, vol. 42 pp.
    556-560, April 1994. In another study by Sprint/Telecordia
    Technologies, head loss is found to be between 12 to 15 dB. For
    details *see*:
    [http://gullfoss2.fcc.gov/cgibin/websql/prod/ecfs/comsrch_v2.hts?ws_mode=retrieve_list&id_proceeding=98-153&applicant_name=sprint&start=31&end=32&first_time=N](http://gullfoss2.fcc.gov/cgi-bin/websql/prod/ecfs/comsrch_v2.hts?ws_mode=retrieve_list&id_proceeding=98-153&applicant_name=sprint&start=31&end=32&first_time=N).
    In addition, we note that the conservative 6 dB figure we use here
    accounts for two mobile devices -- the AWS-1 handset and the AWS-3
    handset.

[^18]: In general, users do not hold their handsets perfectly upright
    when in use. Thus, some antenna mismatch due to changes in
    polarization occurs (roughly 1.5 to 2.5 dB). *See* *Id*. at
    Attachment 2, page 3).

[^19]: Though important, antenna efficiency losses are difficult to
    characterize and thus not considered in this static analysis.

[^20]: This accounts for the fact that OOBE levels are not flat, but
    instead drop as frequency separation increases. We used a
    conservative 3 dB to offset this error in the measurement data,
    which is induced by the UMTS/WiMAX signal generators. This was shown
    in Figures 3-5.

[^21]: This is generally consistent with the values specified in the
    (IEEE 802.11-03/940r2)" High Throughput Task Group, IEEE P802.11, 15
    2004. We also note that this is the value OFCOM used for its
    analysis of FDD/TDD coexistence for the 2.6 GHz band. *See* the
    OFCOM report at page 35 available at:

    <http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf>.

[^22]: In all of our calculations, a bandwidth correction factor (BCF)
    is applied in order to normalize our results to 1 megahertz. The
    formula for the BCF = 10\*log(BW~ref~/1MHz). For a 5 megahertz
    reference bandwidth, the BCF is approximately 7 dB.

[^23]: FR is a measure of the victim receiver's filter rejection. Under
    normal circumstances, this term should be set appropriately high as
    a protection from OOBE. There is a case where a victim receiver is
    designed to operate in a band where it has no jurisdiction (*i.e*.,
    FR = 0 dB). A properly designed UMTS duplex filter will provide at
    least a couple of dB of attenuation. We do not consider any filter
    rejection in this analysis.

[^24]: We again point out that the standards specify that the RSCP value
    be referenced to a bandwidth of 3.84 megahertz and that our analysis
    is based on a 5 megahertz bandwidth. *See* note 13, *supra*.
    Analysis based on the smaller 3.84 megahertz bandwidth would provide
    additional margin allowing for higher AWS-3 power levels and/or less
    stringent OOBE levels than those calculated herein.

[^25]: We appreciate that there is a debate in the record as to whether
    they AWS-3 device would operate at maximum power most of the time,
    but also recognize that variable power control is a feature of
    virtually all current wireless technologies.

[^26]: *See* T-Mobile Test Report at 13-16.

[^27]: *See* United Kingdom's Office of Communications (OFCOM) *Award of
    Available Spectrum 2500--2690 MHz; 2010--2025 MHz* published on
    April 4, 2008 and available at:

    <http://www.ofcom.org.uk/consult/condocs/2ghzrules/statementim/statement/statement.pdf>.
    *See* also *On the Impact of Interference from TDD terminal stations
    to FDD terminal stations in the 2.6 GHz band* published on
    April 21, 2008 and available at
    <http://www.ofcom.org.uk/consult/condocs/2ghzregsnotice/tech.pdf>.

[^28]: See *Memorandum Opinion and Order and Further Notice of Proposed
    Rule Making* in WT Docket No. 99-168, CS Docket No. 98-120, and MM
    Docket No 00-83 available at:

    http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6511359021.

[^29]: See *Report and Order* in GN Docket No. 01-74 at para 122, where
    the Commission declined to adopt a stricter OOBE attenuation
    standard than 43 + 10\*log(P) dB and stated ".... in the absence of
    data and other support from the many parties to this proceeding, we
    should not increase OOBE limits given the potential adverse effects
    that may result on the commercial usefulness of the spectrum. If
    developments in the industry change significantly by 2006 or later
    we can reconsider our OOBE limits at that time. We note, however,
    that Section 27.53(f) currently states that in the event of harmful
    interference the Commission may, at its discretion, require greater
    attenuation than specified in the rules." available at:

    http://fjallfoss.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6513075423.

[^30]: See *Report and* *Order and Further Notice of Proposed Rule
    Making* in WT Docket No. 03-66, WT Docket No 03-67, MM Docket No.
    97-217; WT Docket No. 02-68, WT Docket No. 00-230, at para. 124--130
    adopting an out-of-band emissions mask for digital; mobile stations
    of 43 + 10\*log(P) dB at the channel edge and 55 + 10\*log(P) dB at
    5.5 megahertz from the band edge. The Commission noted that a
    tighter emissions mask may be needed to control adjacent channel
    interference between incompatible systems and provided for licensees
    to agree on a tighter mask upon a demonstration of harmful
    interference.

[^31]: It must be kept in mind that the technology the ultimate licensee
    of the AWS-3 chooses to use and corresponding system architecture
    are undetermined.