Wednesday, September 12, 2018

[UPDATED] iPhone XS and XS Max mostly fail to impress in lab tested RF power output

Following Apple's keynote presentation yesterday, authorization filings for many of its newly announced mobile devices started being made publicly available in the FCC OET database.  Among others, this included the US variant iPhone XS (model A1920, FCC ID BCG-E3218A) and iPhone XS Max (model A1921, FCC ID BCG-E3219A).  The US variant iPhone XR (model A1984, FCC ID BCG-E3220A) was not included.  Its authorization documents likely will be disclosed closer to its October release, thus may be the subject of a later update or a different blog post.

Before proceeding any further, RF power figures to come represent best averaged and rounded estimates of maximum uplink EIRP test results provided to the FCC OET in individual device authorization filings.  Or in the case of ERP low band test measurements submitted in the filings, that ERP has been converted manually to EIRP for level comparison purposes.  All EIRP figures are normed against a baseline of 200 mW (23 dBm), which corresponds to a standard conducted power target with unity antenna gain and generally represents good RF transmission performance.  Caveats about lab testing versus real world capability and uplink versus downlink always apply.

Now, let the EIRP graphs speak for themselves...



As the blog post title indicates, the lab tested radiated output from the two new iPhone XS models does not set the world on fire.  Nearly all bands on both handsets fall short of the 200 mW benchmark.  Only band 41 HPUE on iPhone XS looks pretty good on paper, and even that comes with a conducted power asterisk to be analyzed later.

But first to nip in the bud one potential conspiracy theory, Apple's decision to forgo Qualcomm this year and source all cellular modems from Intel is not responsible for the RF power output limitations in the new iPhone models.  The cellular baseband modem is separate from and well upstream of the amplifiers that generate the conducted power and antennas that generate the radiated power being measured in lab testing.

Furthermore, conducted power is not the issue.  The standard conducted power target of 200 mW (23 dBm) is +/- 2 dB.  And Apple is using the +2 dB margin to enhance its figures, pushing 250-320 mW (24-25 dBm) conducted power across many included bands.  This extends to band 41 HPUE, which has a standard conducted power target of 400 mW (26 dBm).  Again using the +2 dB margin, Apple has upped that ante to 500 mW (27 dBm).  That inflated conducted power is fine.  But bear in mind that it assists only in transmission, never in reception.  Plus, it also can be used to mask some antenna shortcomings.

Yes, with often greater than standard conducted power being generated -- rhetorical questions ahead -- where is all that power going?  Where is it being diminished?  The answer lies in antenna gain.

Indeed, deeper analysis of the FCC OET authorization filings shows the underwhelming EIRP figures to be almost entirely products of negative antenna gain.  For every 3 dB drop in antenna gain, 50 percent of conducted power is attenuated.

To illustrate visually, look at a graph of the iPhone XS Max antenna gain (Ant. 1) across its entire uplink low band, mid band, and high band frequency range.  Antenna gain inevitably reduces conducted power by about 5-7 dB.


Now, both iPhone XS and XS Max this year incorporate four antennas operational across many but not all bands.  That antenna diversity in and of itself is a good thing.  However, even with the four antennas -- and possibly because of the four antennas crammed inside -- antenna gain is universally negative.  And simultaneous transmission from multiple antennas is not possible due to a "break before make" switching mechanism among the antennas.

For a partial look at all four antennas, see a snapshot from the iPhone XS Max authorization filing:


Lastly, for an interesting comparison and stronger RF output, see lab tested EIRP figures from last year's iPhone X (model A1865, FCC ID BCG-E3161A) and iPhone 8 Plus (model A1864, FCC ID BCG-E3160A).



The takeaway is that iPhone EIRP in the lab has not always been so compromised as it appears to be this year.  Real world RF performance comparisons when some users switch from the iPhone X and 8 generation to the iPhone XS generation, no doubt, will be interesting.

Also, see follow up articles (1, 2).

Source: FCC OET

21 comments:

  1. Very Insightful, AJ. It would appear that poor antenna design and or antenna tuning circuitry would be the likely culprit. The smoking gun to me is the fact that the Max variant is the poorest performer despite arguably more real estate to optimize the size and positioning of antennas within the handset. I look forward to teardowns to gain further information on the design and tuners used. Likewise, I look forward to a comparison of the Xr (with it's alleged omission of 4x4 MIMO) to see how it fares. Thanks for publishing your efforts.

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  2. This article is getting traction at the MacRumors website. Lots of reports of bad reception, dropped cell calls, poor performance when compared with prior iPhones.

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  3. Any news regarding the performance of the RF on the XR?
    That's the one im interest in.

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    Replies
    1. No news on iPhone XR A1984 (BCG-E3220A). A device does not require an FCC authorization filing until the device becomes available for sale to the public. That is why iPhone XS and XS Max filings were released just shortly before preorders started.

      AJ

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  4. You can completely dismiss the data blow in my post because it's anecdotal speed testing, but it showed me why this phone is going back to Apple after reading this article and understanding a fix is not likely possible through software (which sucks, this is the 1st phone I've been excited about in a very long time, XS Max 64GB

    On my desk, 25 feet from a R7000 router

    Ipad2015(190 Down, 15.2 Up_
    Iphone 8Plus(152 Down, 21.1 Up)
    XS Max 64GB (23.8Down 11.7Up)

    Now my wifi signal is not amazing, but that's important because it mimics so much of my life here in NYC. I can imagine my ability to use my device effectively in many situations is going to be substantially worse off. Ugh....just why Apple? Did you really think the steel was going to sell so many more phones it was worth the risk? Upping the power is a dead giveaway there is a large and difficult to overcome design flaw working here.

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    Replies
    1. Are you sure the Max isn’t grabbing the 2.4 GHz band? As opposed to the 5GHz less congested one...

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  5. You say speed test between apple's iPhone is faster than my note I tried both and my note is greatly appreciated it's got the best wifi calls and my signal strength is always 5 bars.

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  6. Thank you for the insightful post. Seeing some serious correlation with real life performance and this scientific analysis.

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  7. I ran both my iPhone X, and XS Max on my 5GHz wifi (Netgear R6300) at home and I get:

    iPhone X (147 Down, 12.65up)
    iPhone XS Max (155 Down, 12.5up)

    I ran this 10 time and the Max always beats the X by just a few points. The last time I ran it was exactly the same on download and upload was .2 Mbps faster on the Max.

    Now my cell service with AT&T fluctuate with mostly the X ahead of the Max...

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  8. Just received my Max, considering whether to return it. We got very poor Tmobile signal around our house. It looks iPhone 8 Plus is the best for Tmoible.

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  9. Yup Apple received a big No Thank You from me. I hope there is a landslide pushback on this and the many other issues people are experiencing. This type of garbage is gross negligence in my opinion at these price tags.

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  10. Coming from an LG V30, my XS Max has MUCH worse mobile data reception at my office desk and elsewhere.

    I haven't really noticed if there's an issue with the Wi-Fi. I've called T-Mobile and troubleshooted with them. I've done a network reset. I've updated to iOS 12.1 Beta today with no change.

    I'm using the same SIM card that I was using with my LG V30.

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  11. Great Analysis. But intel modem beong the issue cannot be ruled out because of the following reason. Modem and RF transceiver come together - meaning you cannot have an intel modem and RF tranceiver from someone else. If the output power from tranceiver is poor, then the overall power output at antenna would be poor too

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    Replies
    1. No, the issue is not the power input to the antenna. Carefully read my post, and note that the conducted power levels are fine, even a bit on the high side (~25 dBm). That conducted power would be downstream of the Intel baseband modem and RF transceiver. So, while the Intel chipsets could be responsible for some of the cellular performance problems being reported, the Intel chipsets are not the cause of lower than expected antenna gain and EIRP.

      AJ

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  12. Did the iPhone XS and XR drop support for Band 4? I see band 4 results for the earlier iPhone models, but not the current generation.

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    Replies
    1. The FCC is tasked with regulating its own licensed frequency bands, not 3GPP LTE bands. Band 66 encompasses all of band 4. Apple or its certified testing lab opted to submit only band 66 test measurements. That is sufficient for the FCC, since band 66 covers both AWS-1 and AWS-3 bands.

      AJ

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  13. So is this affecting received data or transmitted data?

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    Replies
    1. One, both, and neither. The question and answer are not that simple.

      The FCC regulates transmitters, rarely receivers. So, the certified lab testing submitted to the FCC reflects only the device's uplink transmission capabilities, not downlink reception capabilities.

      That certified lab testing submitted to the FCC as part of the authorization process does not measure uplink data transmitted, but uplink power transmitted, though that power ultimately is demodulated into data.

      Lastly, while certified lab testing submitted to the FCC does not include downlink reception measurements, the uplink transmission measurements are relevant to downlink reception performance as well. Cellular communication always is two way communication, not broadcast communication. The uplink is required for the downlink and vice versa. And the uplink tends to be the weaker link of the two. For example, if the uplink fails because of limited radiated power output capabilities, then the downlink drops, too, resulting in a complete loss of signal.

      AJ

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  14. Mr. Shepherd:

    Appreciate your article and your explanation of this situation and its possible ramifications.

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  15. Is there a hope to solve it with a software update??

    ReplyDelete