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发帖数: 28 | 1 http://cellularinsights.com/iphone7/
iPhone 7 Plus: A Tale of Two Personalities
Like clockwork, every September the entire tech world gets excited for the
newest Apple device. The combination of a premium build, unmatched system
performance, and tightly integrated software and services delivers what’s
considered to be the gold standard in smartphone user experience.
Over the past five years, Apple’s modem supplier was Qualcomm, but this
year, Apple has taken a different approach with the decision to source two
instead of one baseband chipset suppliers: Qualcomm and Intel. This created
two distinct RF SKUs, one limited to GSM/WCDMA/LTE support (A1778, A1784),
powered by Intel’s modem, and one with GSM/CDMA/WCDMA/TD-SCDMA/LTE support
(A1660, A1661) powered by Qualcomm’s modem.
On the one hand, most high-end flagship devices launched this year are
powered by Qualcomm’s Snapdragon 820, with X12 Category 12 integrated modem
(MDM9645M discrete part). The X12 modem is capable of up to 600Mbps peak
downlink speeds, 3-Way Carrier Aggregation with 256 QAM, and also 4×4 MIMO
on a single component carrier. Note that it is up to the smartphone
manufacturers to decide which of these powerful capabilities will be
integrated into their final product.
The Verizon, Sprint and SIM Unlocked iPhone 7 and iPhone 7 Plus variants are
powered by Qualcomm’s MDM9645M modem, accompanied by two transceivers:
WTR3925 and WTR4905. Out of all supported features by Qualcomm’s solution,
Apple has chosen to implement 3-Way Carrier Aggregation on the downlink and
2-Way Carrier Aggregation on the uplink for contiguous Band 7 or Band 41.
Higher Order Modulation (DL-256QAM, UL-64QAM), and Higher Order MIMO (4×4
MIMO) have not been implemented. Therefore, the peak theoretical downlink
speeds are limited to 450Mbps when aggregating three 20MHz wide LTE
component carriers. We have achieved the maximum 450Mbps by aggregating
20MHz wide Band 20, Band 1, and Band 7. EVS (Enhanced Voice Services), also
known as Ultra HD Voice, offers significantly improved audio quality,
numerous efficiencies at the physical and IP layer, and is fully supported
by Qualcomm’s modem. However, Apple has made a decision to disable this
feature likely to level the playing field between the Qualcomm, and Intel
varaints.
On the other hand, the iPhone 7 represents Intel’s first major design win
in a long time. In many ways this iPhone appears to be Intel’s make or
break it in the cellular modem business. Similar to Samsung’s in house
Shannon LTE modem found in Exynos based devices, Intel has decided to
license CEVA DSP cores for the XMM7360 modem coupled with in-house SMARTi 5
RF Transceivers and X-PMU 736 RF Power Management. The Intel XMM7360 modem
also supports 3-Way Carrier Aggregation on the downlink and 2-Way Carrier
Aggregation on the uplink, but lacks support for EVS, DL-256QAM/UL-64QAM, 4
×4 MIMO. Ironically, mobile operators such as T-Mobile USA and Telstra
which have been offering these advanced LTE features, are being supplied
with the iPhone 7 with the Intel modem.
While there haven’t been a shortage of iPhone 7 unboxing videos, subjective
camera reviews, and more, we have been hard pressed to find any meaningful
mention of cellular performance. This goes for any other flagship device on
the market. In this day and age with mobile internet consumption at the all
time high, we believe that a mobile device is only as good as its ability to
seamlessly connect and maintain its connectivity with the mobile network.
Most of the time mobile operators get blamed for dropped calls or session
timeouts, but it’s often forgotten that the phone OEMs implementation of
baseband, RF Front-End (RFFE), and the antenna design could play its role.
We have been using the Rohde & Schwarz (R&S) CMWflexx setup containing two R
&S CMW500 and one R&S CMWC controller, as well as the R&S TS7124 RF Shielded
Box with four Vivaldi antennas. This study has been done entirely
independently, and Cellular Insights takes full responsibility for the
analysis and opinions in this report. We have self-funded the procurement of
iPhone 7 Plus units through commercial retail channels. All units have been
preloaded with the latest version of iOS (10.0.3)
20161004_173927
Consistent with our previous reviews, our focus has been on measuring the
highest achievable LTE throughput in clean channel state, starting at RSRP
value of -85dBm, and incrementally reducing radiated power level while
maintaining Block Error Rate (BLER) under 2%. This allows us to measure RF
sensitivity of the device under test while eliminating inter-cell
interference and fully controlling the radiated environment. This also
allows for high reproducibility and consistency of our tests, and takes into
account the performance of the entire RFFE subsystem.
We’ve tested three unique LTE frequency bands, Band 12 (10MHz), Band 4 (
20MHz), and Band 7 (20MHz) in 4×2 MIMO configuration using Transmission
Mode 4. While both devices achieved the maximum sustained data rates at the
cell center, simulating edge of cell scenarios by reducing power level did
cause each iPhone to display two very different personalities.
As the device attaches to eNodeB, it reports its LTE capability. To get this
out of the way, 4×4 MIMO and 256QAM features are not supported on the
iPhone 7 Plus.
mimocapability
FDD LTE Band 12 is part of the lower 700MHz band plan, covering 15 MHz of
contiguous spectrum across three blocks (A, B, C). Most LTE Band 12
deployments are either 5 MHz or 10 MHz wide even though Band 12 can
theoretically be deployed up to 15 MHz widths. Coincidentally, LTE Band 12
capable devices are only certified to support up to 10 MHz operation. As
opposed to mid and high band spectrum, low frequency such as 700MHz Band 12
can propagate further, penetrate the concrete structure better, and often
times is the only LTE layer reaching the device. For this particular reason,
high sensitivity of a smartphone receiver is extremely important in
challenging signal conditions, and it could make a difference between
completing and dropping a VoLTE call.
screen-shot-2016-10-20-at-2-15-37-am
Both iPhone 7 Plus variants perform similarly in ideal conditions. At -96dBm
the Intel variant needed to have Transport Block Size adjusted as BLER well
exceeded the 2% threshold. At -105dBm the gap widened to 20%, and at -
108dBm to a whopping 75%. As a result of such a huge performance delta
between the Intel and Qualcomm powered devices, we purchased another A1784 (
AT&T) iPhone 7 Plus, in order to eliminate any possibility of a faulty
device. The end result was virtually identical. We are hoping that this
sudden dip in performance at a specific RSRP value will be further
investigated by the engineering and hopefully resolved. At -121dBm, the
Intel variant performed more in line with its Qualcomm counterpart. Overall,
the average performance delta between the two is in the 30% range in favor
of the Qualcomm variant.
band12
Band 4 is the most commonly deployed LTE spectrum band in North America,
while Band 7 deployments are spread across the rest of the globe. Mid and
high spectrum bands are used to densify LTE networks and provide incremental
capacity. Just like during our Band 12 tests, the iPhone 7 Plus with the
Intel modem continues to struggle even at relatively higher RSRP values with
unexplainable sharp dips in performance. The gap between the two variants
is consistent and north of 30% again in favor of the Qualcomm variant.
band4
band7
To put this into perspective, we have compared the edge of cell performance
of a few other flagship devices to see how these iPhones compare in less
than favorable conditions
comparison
In all tests, the iPhone 7 Plus with the Qualcomm modem had a significant
performance edge over the iPhone 7 Plus with the Intel modem. We are not
sure what was the main reason behind Apple’s decision to source two
different modem suppliers for the newest iPhone. Considering that the iPhone
with the Qualcomm modem is being sold in China, Japan and in the United
States only, we can not imagine that modem performance was a deciding factor
. When all said and done, the iPhone 7 Plus is a beautifully designed
smartphone, with arguably the best-in-class camera and system performance.
It’s also the best iPhone ever. We hope that next year’s iPhone delivers
best-in-class LTE performance. |
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