Improved Baseband - No Deathgrip

We’ve mentioned already that the 4S is more of an evolution of the CDMA iPhone 4 than the GSM/UMTS iPhone 4, and where that’s most obvious is again is its cellular architecture. When we reviewed the GSM/UMTS iPhone 4, we investigated and explained why its design made it especially prone to unintended attenuation when held a certain way. Apple remedied the situation somewhat by giving away free cases, but only in the case of the CDMA iPhone 4 was the fundamental design issue remedied by adding receive diversity with a second cellular antenna at the top.

The 4S builds on this architecture by incorporating the same diverse receive path with two U shaped antennas at top and bottom, and adding transmit diversity to the equation. I’m being a bit fast and loose with the term “diversity” here, since the 4S cannot transmit simultaneously on both antennas, but rather switches between the two antennas based on which has the least receive fading. Receive diversity is a bit more interesting to explain, since the 4S appears to be able to dynamically decide whether to select one of the two receive paths (in the case that one is much more faded than the other), or combine the two (using something like maximal-ratio combining) and get a better quality equivalent signal.

When I talked about the CDMA 4’s receive diversity scheme, I went into detail to prove that this feature was present. With the 4S, these diversity features are much easier to talk about because Apple has been directly forthcoming about the feature this time. In addition, the transmit switching part of the equation is discussed at length in Apple’s FCC disclosure (since the FCC is interested in scrutinizing transmitters), and even includes a nice diagram.

The device is capable of switching between the Primary/ANT1 and Secondary/ANT2 Antennas. The antenna switching is implemented with a physical, "break-before-make" switch such that only one antenna can be used for cellular transmission at a time.

To re-state the evolution that Apple has taken with this design, the GSM/UMTS 4 had one transmit and receive chain, the CDMA 4 added a second receive chain for diversity, and the 4S now has two receive chains and the ability to switch between two transmit chains. The result is that the phone no longer is prone to fading on either the forward or reverse link due to being held near the feed points for one chain.

To be totally thorough, you can immediately see that the 4S still incorporates the same overall design however, complete with a a U.FL connector at the bottom and a feed cable that runs up the side of the PCB to the top. From here it obviously terminates somewhere that makes contact with the top antenna.


Encircled in red: Top antenna feed cable (Original photo courtesy iFixit)

When we saw that the CDMA iPhone used Qualcomm’s MDM6600, we made an educated guess that the next device would likely be based on the same baseband. It turned out that this was pretty close to the case, as the iPhone 4S uses an unannounced Qualcomm MDM6610.


Encircled in blue: Qualcomm MDM6610 and PM8028, Red: Bottom antenna U.FL connector. Note to the right the two test pads for the two chains. (Original photo courtesy iFixit)

There are some immediate differences that stick out about MDM6610 versus MDM6600. First, 6610 doesn’t appear to include an internal transceiver, unlike MDM6600 which previously included a transceiver in its package. MDM6610’s package is correspondingly smaller, at 10x10 mm, compared to 6600’s 9.8x12.2 mm, but again you have to factor in the fact that the transceiver isn’t inside that package anymore. Based on those facts and the state of 28nm maturity, it’s almost certain that MDM6610 is still a 45nm part. The 4S uses Qualcomm’s RTR8605 IntelliCeiver transceiver for cellular RF management and also for GLONASS/GPS. We’ve seen RTR8600 before, and RTR8605 appears to just be an improvement upon that part with the same functionality. In fact, inside the MDM6610’s AMSS it’s just referred to as RTR8600.

Qualcomm isn’t ready to talk at all about MDM6610, but I’ve done a little digging and know more about this part. First off, it’s referred to as codename “Trek” inside the Qualcomm AMSS (Advanced Mobile Subscriber Software), whereas MDM6600 in the CDMA iPhone was referred to as “Phoenix.” When we first saw that the 4S was using a baseband that hasn’t been announced, we assumed it was an Apple specific one-off. However, after some digging I uncovered a reference to a GSM/UMTS only part as well: “MDM6210MDM6610”. For those that aren’t familiar, the 2 connotes GSM/UMTS compatibility, 6 adds 1x/EVDO. Apple appears to have secured MDM6610 exclusivity for the time being, but I expect we’ll see a more formal announcement of the MDM6x10 family down the road. This is pretty much par for the course for Apple when it comes to component sourcing.

iPhone 4S - Network Support
GSM/EDGE Support 850 / 900 / 1800 / 1900 MHz
UMTS/HSDPA/HSUPA Support 850 / 900 / 1900 / 2100 MHz
HSDPA/HSUPA Speeds 14.4 Mbps / 5.76 Mbps
CDMA2000 1x/EVDO Support EVDO Rev.A (800 / 1900 MHz)
Baseband Hardware Qualcomm MDM6610

MDM6610 also appears to inherit all the air interfaces that MDM6600 had, including WCDMA/HSPA+ with HSDPA 14.4, HSUPA 5.76, GSM, CDMA 1x/EVDO (up to Rev.B, though Apple notes only A is used at present), and finally GPS/GLONASS. Superficially, there don’t appear to be any major differences beyond using an external transceiver to accommodate diversity and transmit switching. In addition, the 4S contains all the same bands as the GSM/UMTS iPhone 4.

I was initially worried that Apple would go the same route that it did with both iPhone 4 launches and initially not include FieldTest. Thankfully, the 4S includes FieldTest right out of launch, which works for both CDMA and GSM/UMTS provisioned 4Ses.

 
iPhone 4S Field Test under CDMA Mode

There’s a corresponding difference in the interface for the two modes. On CDMA iPhone 4S mode, there are tabs for 1x and EVDO, and Rx signal strength fields for both receive paths, as well as the current transmit power. What’s interesting here is that when using the 4S in CDMA mode, you can see the receive strength change for each antenna when held.

 
iPhone 4S Field Test under UMTS/GSM Mode

On the GSM/UMTS provisioned iPhone 4S, you don’t get individual receive strength for each chain, instead just the effective RSCP from either the selected chain or combined. If you grip the phone while watching this, you can sometimes watch RSCP race to –130 dBm and then switch entirely to the other antenna and race back up to an acceptable number. As a reminder, to get into FieldTest dial *3001#12345#* - you can then keep numerics instead of bars in the top left by force quitting FieldTest after launching it (hold down power/lock until power off appears, then hold the home button).

So how does the 4S do in our actual attenuation testing? Very well actually. I watched the RSCP of one NodeB and held the 4S all the same ways we’ve done since the 4, recorded a bunch of data, and averaged it together. What we’re measuring here is reported in dBm, and less attenuation is better (0 dBm = 1 mW).

Signal Attenuation Comparison in dB - Lower is Better
  Cupping Tightly Holding Naturally Holding in Case On an Open Palm
iPhone 4S 10.8 8.8 - 4.3
CDMA iPhone 4 16.5 15.5 9.0 7.9
GSM/UMTS iPhone 4 24.6 19.8 7.2 9.2
Samsung Galaxy S 2 18.4 5.9 - 12.2
Droid 3 16.0 11.3 - 5.0
HTC Sensation 15.0 10.0 8.0 0.0
Samsung Droid Charge 10.0 10.0 5.0 0.0
HTC Thunderbolt - LTE 5.3 2.5 - 4.4
HTC THunderbolt - EVDO 6.5 0.8 - 7.2
LG Optimus 2X 13.7 9.3 - 5.9
Nexus S 13.3 6.1 - 4.3
Droid 2 11.5 5.1 - 4.5
BlackBerry Torch 15.9 7.1 - 3.7
Dell Streak 14.0 8.7 - 4.0
Droid X 15.0 5.1 - 4.5
iPhone 3GS 14.3 1.9 3.2 0.2
HTC Nexus One 17.7 10.7 7.7 6.7

When we reviewed the CDMA iPhone 4, I made mention of the fact that this was the first iPhone 4 I felt comfortable using without a case. This same confidence continues with the 4S, which is in practice completely usable without a case, unlike the GSM/UMTS iPhone 4. Since launch time, Anand and myself have been using our 4Ses without cases, and the difference is dramatic.

Introduction Faster Throughput on WCDMA
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  • Formul - Monday, October 31, 2011 - link

    There is about a dozen fairly similar android phones every month. As iPhone gets refreshed just once every year (this time year and a half) and has bigger market than any single android phone out there it makes sense to make the review thorough. I guess Nexus Prime and even Razer will get similar lengthy reviewsa ... as did many other android phones before that (galaxy s2 for example had about the same as this one).

    You are the one biased here. Counting the number of android articles on any gadget blog will seriously outpace the iPhone by far. You should shut up and read what you want, no one is forcing you to read this blog or any particular article on it. I dont read android articles, i dont care about android all that much. Why do you have to troll here if it does not interest you after all?
    Reply
  • Anand Lal Shimpi - Monday, October 31, 2011 - link

    I believe we did just that for the Galaxy S 2 review:

    http://www.anandtech.com/show/4686/samsung-galaxy-...

    We don't have the RAZR, Galaxy Nexus or S2 Skyrocket, but we typically do a deep dive whenever there's a new platform transition or something truly unique to look at.

    Take care,
    Anand
    Reply
  • LordSojar - Tuesday, November 1, 2011 - link

    Hmm, touche Anand, I had forgotten about how detailed the S2 review was.

    The RAZR doesn't warrant a particularly detailed review I suppose, but I think the S2 Skyrocket might warrant a detailed antenna review etc considering the transition to LTE along with, what should be a major change to the antenna and should (I think) have QC's MDM9615 or MDM8215 chips in it... which is a big deal considering those could yield not only significant speed gains along with an antenna update, but some major throughput.

    Cheers
    Reply
  • doobydoo - Tuesday, November 1, 2011 - link

    'Samsung releases a new phone that has overall better features, faster CPU, faster NAND, a different and arguably better (or at least equal) screen'

    I hope you are comparing to the OLD Samsung, in this sentence, rather than comparing to the iPhone 4S.

    The CPU/GPU performance of the iPhone 4S is not comparable to the Galaxy S2, and I would argue the features are very much superior too.

    Which, incidentally, along with the dual-antenna design, Siri, brand new camera, makes the iPhone 4S much more of a step up than the Samsung Galaxy to Samsung Galaxy S2. (The Galaxy S was about the same performance as the iPhone 4. The Galaxy S2 is slower than the iPhone 4S, therefore iPhone 4S is a bigger upgrade).

    And of course, as Anand said, they thoroughly review most phones, and as the other poster says, the Android phones come out way more often so over the same length of time they get at least as much if not more coverage.
    Reply
  • Tetracycloide - Tuesday, November 1, 2011 - link

    The Galaxy S2 released in May. The 4S released in October. The next Galaxy phone, the generation the 4S is actually going to compete with, is the Galaxy Nexus. What I'm saying is your point would hold more water (or any at all) if Samsung didn't make 2 upgrades in the space of time it took Apple to do 1 so the differential between generations is hardly an apples to apples comparison (pun intended). Reply
  • thunng8 - Tuesday, November 1, 2011 - link

    But the Galaxy Nexus isn't any faster than the S2. The main benefit is the new operating system and higher resolution screen.

    The Nexus is actually a significant step backwards from the S2 in terms of camera (likely from the samples on the prototype) and GPU (definitely since it is using the SGX540) performance
    Reply
  • doobydoo - Wednesday, November 2, 2011 - link

    Release dates will not stop phone users comparing the iPhone 4S to the Androids released in March 2012, just like they compared all the Androids over the last 17 months to the iPhone 4.

    The iPhone 4S, right now, is competing with the Galaxy S2 directly.

    The Nexus Prime, as the other comment alluded to, is a significant downgrade from the Samsung Galaxy S2. Indeed, it uses the same GPU as used in the much older Samsung Galaxy S (albeit clocked higher).

    The Galaxy S to S2 took approximately a year inbetween generations (June 2010 to May 2011), which is very much in line with the typical Apple release cycle of annually (this year was the exception). Even this year, with the extended timeline between iPhone 4 and 4S, Samsung didn't make 2 upgrades during that time. Your point would hold more water (or any at all) if it had.
    Reply
  • Tetracycloide - Wednesday, November 2, 2011 - link

    It's obvious you're not making a real comparison between current products but instead of admitting that you pretend it's a non-issue and then strangely fought that issue anyway by suggesting I'm not actually right to call you out on these shenanigans. So thanks for being obtuse about this, it makes it much easier to dismiss your position as that of an irrational fan-boy (at least it does when combined with the condescension in some of the other threads you've commented on here). Reply
  • doobydoo - Friday, December 2, 2011 - link

    'It's obvious you're not making a real comparison between current products'

    Erm, huh?

    That's EXACTLY what I'm doing.

    What YOU'RE doing is asking is to compare a phone which isn't even out yet with a phone which is. You're trying to 'pretend it's a non-issue' that the phone you say the iPhone 4S should be compared with wasn't even out when this discussion started. THAT is the definition of fanboy-ism. It's like the constant like of Android fans 'x WILL be better when it eventually comes out' - and THAT is obtuse.

    So, the only comments which can be dismissed are YOUR fanboy comments about 'x phone released in x months will be better'. Turns out you were wrong anyway, but that's irrelevant - the bottom line is you don't want iPhone to be compared to CURRENT Android phones, but instead compared to FUTURE ones.

    Rational, much?

    As it happens, it's out now, and isn't even much of an improvement on the Samsung Galaxy S2
    Reply
  • Lucian Armasu - Wednesday, November 2, 2011 - link

    The cameras seem to be about the same, according to Anand. I've actually found the SGS II camera to be a bit better in photo comparisons. Siri? I still think it's more of a gimmick for now. Maybe in 5-10 years it will be actually useful. Once the novelty expires, people will barely even use it in a few months. The same happened with FaceTime which everyone went crazy about at launch, and then they stopped using it completely.

    The CPU of the SGS2 IS faster than iPhone 4S CPU. There's no way Apple managed to get a 50% performance improvement for the same Cortex A9 chip that Samsung is using.

    I think Anand can confirm this. He wasn't very clear in the review. He was only talking about the improvements it gets over the old Cortex A8.
    Reply

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