Why isn't there a Modem-gate threat?

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macrumors regular
Original poster
Apr 4, 2015
Hermosa Beach, CA
Intel's XMM 7360 modem has been shown by independent scientific testing to have significantly (75% difference in some cases) worse reception and throughput on every single LTE band tested.

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)

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.

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.

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.

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.

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

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.


macrumors G4
Oct 31, 2009

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