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Gigabit Cellular Networks Could Happen, With 24GHz Spectrum

YoopDaDum Re:too much multi pathing at that frequency (52 comments)

This is made for small cells indeed. Any time you see 5G with gigabit speed, it's only for high density areas covered with small cells. 4G will still be there for larger cells (coverage layer in high density areas, and less dense areas).

Also, there are ways to fight multipath. The primary one used in this scheme is beam-forming with a pretty dense array --- what I've seen on pre-5G tests typically use between 64 to 256 antennas. You then get a very narrow beam, and a primary path that is well above secondary reflections. Of course for this to work the base station must be able to precisely track the device, and that's another rarely mentioned limitation of such high-speed 5G scheme: it's mostly for static / pedestrian usage. You can extend this to vehicular (some demos are using cars) by having some smarts about anticipating movements (constrained to roads, etc.) and a less narrow beam (but then you loose SNR and reduce spectral efficiency). But mostly I would expect such 5G to be for the majority of slow moving devices, with fast moving ones pushed to an overlay of bigger 4G cells (so less HO too). This is consistent with small cells. And besides BF, I guess as 4G the waveform will use OFDM/OFDMA to also help fight multipath.

Last comment: as usual the marketing communication focuses on high bandwidth but the true interest is more capacity. So in real life instead of having a few users at super high throughput such a 5G network will be able to support more users at lower (but still very high) average throughput by multiplexing them.

4 days ago
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Internet Companies Want Wireless Net Neutrality Too

YoopDaDum Re: Wireless bandwidth is limited (38 comments)

Don't you want to discriminate voice over bulk data to make VoLTE calls work even when the cell is at full load during peak time? That is what is done, and it's not only QoS: at the radio level the way a voice connection is handled is different. To optimize for voice, even if it's voice over IP, LTE does use different techniques (SPS, ROHC, TTI bundling...) that adds complexity to the system.

And although overload doesn't always happen, it's something to be dealt with. We don't yet have the technology to offer unlimited capacity at peak time in dense areas at a price people are ready to pay for. So somewhere, sometimes, cells will be overloaded and we need to think about how to deal with this.

Not discriminating traffic like voice vs. download on a congested cell doesn't make sense to me as a user (I don't work for an operator). Net neutrality for wireless would need to be more subtle than "every packet is equal". Like supporting different traffic classes, with possibly different pricing, but making access to such classes open to all service providers under the same conditions. Today QoS is only for the operator services for example, an OTT player can only get special QoS if it has a deal with the operator. While this would be nice there is significant complexity there in term of access (need a standard API to let an application request some QoS level), access control (better to reject a call than to provide useless crippled voice for example. This is done today for voice, would likely need to be more powerful) and billing (need to be open, secure, simple).

It's already complex to make VoLTE works fine, I don't see this happen anytime soon just based on the underlying complexity. Seeing a reasoned discussion on this addressing the real challenges of wireless would be a good start to prepare the ground, but I don't think we're even close to this.

about a week ago
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Samsung Achieves Outdoor 5G Mobile Broadband Speed of 7.5Gbps

YoopDaDum Re:As a good Slashdotter I didn't RTFA (36 comments)

LTE is not done and is continuing its evolution. To give a rough idea recent products are LTE "release 10" (R10), and standard work will start in a few months on R13 that will not cover anything 5G yet. R13 should arrive in the field in ~2017. This Samsung demo is not a standard yet, it's more a technology evaluation / advanced work that will only land in real products in a few years.

It's likely that a real production 5G will come from within 3GPP, the organization that standardize 2G/3G/4G. At every big transition some people try to go for it with a completely different standard (for 4G: Qualcom UMD, WiMAX) and it may not be different with 5G, but it would be very unlikely to succeed IMHO. The technology demonstrated here is not universal: it can only work in very dense area. Which is fine, that's also where we need added capacity. But it means that whereas in time LTE can fully replace 2G and 3G, 5G will be designed to coexist with 4G and will never replace it. At best, you'll have LTE in low-density areas, and 5G in dense areas. And even in dense areas there may be a 4G coverage umbrella to provide service continuity.

There's a lot of hype and BS in wireless, so take all throughput / generation targets with a big grain of salt... LTE Advanced defines a "category 8" that goes up to 3 Gbps for example, but it's a joke to get the IMT 4G stamp. Already the initial LTE defined a category 5 that no product ever implemented. It was just there to match the WiMAX 2 peak target rate. It was bollocks and unpractical and nobody cared once WiMAX 2 died. Similarly, the people at IMT got over-excited and stuck in a hype loop, and defined real 4G has the ability to support 1 Gbps. It was nonsense at the time and still above what's practical. So what did LTE-A did? It introduced realistic new categories 6 and 7 with 300 Mbps down, and a BS category 8 at 3 Gbps. So on paper LTE-A is 4G, because of a category 8 that nobody will implement anytime soon if ever. I've seen pedants saying LTE is no real 4G but LTE-A is because only LTE-A makes the 1 Gbps IMT target: what a joke!

The high rates of 5G as demoed by Samsung use a very different approach. Much higher frequency allowing larger channels and data rates. Also the size of the antennas shrinks with a higher frequency, so it becomes possible to use many small antennas in a device. Each receive path is quite poor compared to LTE to keep the cost down, but it's compensated by a lot of them. These many antennas are not used for massive spatial multiplexing (SM) MIMO, which would be too computationally expensive, but for a few SM layers as today and beamforming as beamforming is cheap. It's a bit early to say it will work well in real life, but it looks promising and worth pursuing.

about a week ago
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Google Announces Motorola-Made Nexus 6 and HTC-Made Nexus 9

YoopDaDum Re:HTC (201 comments)

They've been sloppy with updates a few years back at their peak of popularity. I guess they had became complacent then. With their recent challenges it seems they have understood the importance of keeping your customers happy, and hence loyal long term, instead of pressuring them to update faster by not supporting old models and just succeeding in annoying people. It's long term vs. hypothetical short term gain. I'm glad they've taken the long view in the end.

Now I find they take updates of "old" phones seriously at least for their flagships (can't tell for the others). I have the first One (M7), it's about 18 months old now and I have Android 4.4.3 with Sense 6 on it, just as the latest One M8. I had a handful of updates since I bought the phone, tracking Google new versions closely. HTC announced Lollipop will be supported on the M7 too. Typically all the big updates are made available within 3 months or so of Google release. If they keep it like this (nice phones with updates), I'll probably stick with them when replacement time come.

One important point: I have an unlocked phone, bought without contract and independently from my operator. Updates may not be as fast when the phone is bought with a contract through an operator, but then the issue would be the operator not HTC.

about a week ago
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LTE Upgrade Will Let Phones Connect To Nearby Devices Without Towers

YoopDaDum Re:They've reinvented CB radio! (153 comments)

Yes it will. One of the driver for D2D is public safety, where the network may not be available. Think of a situation after a big earthquake or hurricane, where cell towers have been damaged and the cellular coverage is patchy or entirely gone in some areas. Then D2D can be used locally by public safety people to communicate with anyone having a LTE device supporting D2D (and the vision is that in time, everybody will). D2D will support both this offline / local mode and a network assisted mode when you're under cellular coverage. There's also a hybrid case where one party is under coverage and the other is not.

There are other use cases for D2D, but I must say I find most of the "end user" ones gimmicky. Besides public safety, which can potentially be really useful IMHO, there are other interesting use cases for M2M / infrastructure, like supporting car-to-car communications (assisted driving in the future) and coverage extension (mesh like, although the issue there is always the impact on the relay devices: would you like a meter in the basement draining your smartphone battery? You would need user acceptance, and then it gets complicated).

about three weeks ago
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EU, South Korea Collaborate On Superfast 5G Standards

YoopDaDum Re:How much more can we squeeze? (78 comments)

As said by others the fundamental limit is given by Shannon. This defines a maximum throughput given a spectrum bandwidth and S/N ratio. In current technologies we're pretty close to this. This also indicates how to increase the total throughput, which can comes from:

  • - Adding channels. This is what MIMO spatial multiplexing (SM) is about;
  • - Increasing the used spectrum bandwidth. There is a lot of spectrum at high frequencies, with new challenges, and one option for 5G is to use this;
  • - Increase the signal to noise ratio. This is what beam-forming is about.

Having more MIMO SM layers (i.e. concurrent channels) is not practical. The complexity of a MMSE decoder isO(L^3) with L the number of layers, so it gets ugly quickly. Today MIMO SM is typically limited to 2 layers in practice, with 4 likely coming and 8 the practical limit (and that may not be so practical really...).

Using very high frequencies (above 10 GHz) gives access to a lot of free spectrum, but the higher one go the lower the reach for a given power budget. To compensate for the high attenuation this is coupled with massive multi-antennas, the talk for 5G is 64 to 256. This is split between a few very costly MIMO SM layers and the rest for cheap beam-forming. So for example 256 antennas would behave like four 64 patches BF antennas for 4 layers MIMO. Of course with that many antennas and RF transceiver you have to compromise in cost and quality. So it's a lot of poor receive chains, vs. a few very high quality ones today. But there's still the potential to gain overall.
It has challenges though: it will still be for small cells (low reach) and rather low mobility (the beam steering cannot track high speed mobiles, plus small cells don't work wall for highly mobile devices: too many handovers). But because most people are low speed and the places where capacity is most needed are urban centers where small cells are ok, it still can be a win.

But as one can see, high speed 5G won't be universal like 4G is. By this I mean that 4G can (and will) completely replace 2G and 3G in time, while this high frequencies / massive BF 5G could only complement 4G is high density urban places, but will never be suitable for lower density parts (rural) where 4G would stay.

And then there's the elephant in the room: a lot of the improvements in telecoms have been riding on Moore's law. With the scaling problems that start now to be more openly discussed, how much more processing power we can use for 5G and what the users are prepared to pay (cost and power) for all these improvements are interesting questions.

about 4 months ago
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How MIT and Caltech's Coding Breakthrough Could Accelerate Mobile Network Speeds

YoopDaDum Re:what the FEC... (129 comments)

FEC is commonly used in streaming over IP applications to support lost packets, see for example the "above IP" FEC used in LTE multicast (eMBMS) or DVB-H, Raptor. In those applications the L2 transport has its own error detection scheme, so IP packets will typically be either fully lost or ok (in other words, the probability of having a corrupt packet is very low).

about 5 months ago
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Linux 3.15 Will Suspend & Resume Much Faster

YoopDaDum Re:not fast (117 comments)

The sloppiness in the PC ACPI world can also bite Windows too. You can find nice Asrock mini PCs based on laptop hardware. If you look at a Tom's hardware review of the Asrock VisionX 420, with a mobile core and mobile AMD GPU, you'll see that it consumes 28W at idle. This is crazy high for what's in effect a mobile laptop in small form factor box. One of the big reason is that the system ACPI says that PCIe ASPM (the low-power mode of PCIe) is not supported. Configuring laptop-mode on Linux and forcing ASPM results in idling at ~12.5W only, and a quieter box. Enabling ASPM in power saving mode alone saves ~8W, the rest is due to other suboptimal Windows defaults I guess.

So IMHO the "let's do the minimum and ship" to save a buck approach of PC vendors hurts Windows and linux both. On the Windows side you'll usually get something considered good enough for its product class (here power was not considered as relevant for an HTPC it seems) but likely not optimal. On Linux you will get a mess by default because as you say vendors can't be bothered with it. But with some work you can actually get something quite good.

about 6 months ago
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New MU-MIMO Standard Could Allow For Gigabit WiFi Throughput

YoopDaDum Re:The title is a bit misleading (32 comments)

Absolutely, and that's why I'm talking about "peak throughput" above and not only throughput. Increasing capacity allows to either offering higher average throughput, or offering the same average throughput to more devices concurrently, or any mix in between. It does matter, and actually changing field a bit capacity in the wireless cellular world is what really matters: stretching things a bit to make a point you could say that in cellular peak throughput is for marketing, capacity improvements are for real life concerns (increasing average throughput / reducing cost per bit). Unfortunately the later is more complicated to sell so is often not put forward, but that's where the real work is.

Still, it's too bad that on a geek site one has to pass a capacity improvement as a peak improvement to make it more sexy. Let's learn to love capacity for its own sake ;)

about 7 months ago
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New MU-MIMO Standard Could Allow For Gigabit WiFi Throughput

YoopDaDum Re:A rare sight (32 comments)

Thanks! The MAC layer principles are the same in 802.11ac than in 802.11n. The MU-MIMO feature is really made for the AP to stations direction (downlink). The AP can decide on the combined transmission on its own, based on queued packets: if the AP has packets buffered for several stations that can be sent using MU-MIMO, it can merge them into a single PHY access. There's a gotcha for the ACK part, you don't want the receiving stations to ACK at the same time but for this block ACK is used for all stations but one. So those other stations will wait for a block ACK request from the AP, and the AP makes sure there is no collision.

For more details I can recommend "Next Generation Wireless LANs" by E. Perahia and R. Stacey. I have no relation to the authors, but I've used their book and found it good. Warning: it's only if you really want to go into the details (but it beats the IEEE spec handily on readability ;)

about 7 months ago
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New MU-MIMO Standard Could Allow For Gigabit WiFi Throughput

YoopDaDum The title is a bit misleading (32 comments)

The title could lead some to believe that MU-MIMO is increasing the peak throughput, which is not the case. Spatial multiplexing (SM) MIMO allows to have as many independent concurrent streams as there are antennas on receiver and transceiver (the min of both sides actually). So with 4 antennas on the AP and 3 on the station for example, you can have 3 streams. With SU-MIMO, all three streams are used between the AP and a single station. With MU-MIMO the AP can use its streams with more stations: for example 1 stream to station A, and 2 streams to station B. There is a little bit of degradation of course compared to single use. It's a win when you have for example a 4 antennas AP and only 2 antennas stations, then instead of leaving half the capacity on the floor you can make use of all the streams. But it doesn't increase the peak rate possible with SU-MIMO, it increases the AP capacity when devices do not have as many antennas as the AP, which is the usual case.

about 7 months ago
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Shuttleworth Wants To Get Rid of Proprietary Firmware

YoopDaDum Re:Some context from a hardware perspective. (147 comments)

True, but at least on a PC the main CPU could protect itself against any device being an IOMMU. And in smartphones ARM also has an IOMMU IP (called SMU). I don't think it's commonly used yet, but on principle at least it is possible to hook any smart peripheral with an embedded processor (or several nowadays for a 4G cellular modem for example) to the SMU, and then the SMU to the SoC NoC providing access to the system memory. Then the user application processor (AP) can restrict any memory access from those devices.

So even if such a smart peripheral is exploited, if it sit behind an IOMMU/SMU the AP can restrict to which parts of the memory it can access, just like a MMU provides such protection between processes. The peripheral, even if inside the SoC die, can be sandboxed.

Is this how it is done today? I guess not. For SoCs, I'm not sure a lot of chip vendors pay for the additional SMU IP, unless they have another use-case that requires it (like supporting virtualization). And even if the hardware is there, I'm not sure it is actually used for security containment as I described. Could a linux expert comment on that for the PC world at least?

Now of course an IOMMU/SMU will never protect against an embedded chip purposefully designed to be able to take control of the chip and access system memory without restriction, like the management chip on some Intel chips (vPro feature IIRC). But as you point out there are a lot of smart peripherals, and if we could at least mitigate exploits from them it'd be that many less potential holes.

Last point, security always has a cost: someone needs to handle the IOMMU/SMU management to do the sandboxing. And a sandbox may prevent zero copy, requiring extra copying from the AP in some cases (to move data from AP reserved memory to/from a given device sandbox).

about 7 months ago
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Stop Trying To 'Innovate' Keyboards, You're Just Making Them Worse

YoopDaDum Re:Bad example. (459 comments)

But it has a very bad idea, which cannot be fixed: the mechanical functions keys are gone. Instead you have touche sensitive keys, with no travel. One can adapt toa new layout for a product one use often and long (ok, after some grumbling...), and with some utilities remap keys if needed (switching ctrl/caps lock is very common). But you can't add real keys where there are none here. And you can't select an alternative keyboard with the usual functions keys either.

It's very ironic that their new slogan is "Thinkpad, for those who do". I guess it's for those who don't do enough to remember each function key role in the applications they work with, and need an icon on the key to remember it. And use all this infrequently enough not to care about touch sensitive keys.

I'm for one very disappointed with this nonsense. I was looking forward to treat myself with a high definition screen, long battery life light laptop with this update. I guess Asus or somebody else can thank the "innovators" at Lenovo who pushed this crap through.

about 9 months ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:All the other OS, too. (352 comments)

Then criticize such designs for being insecure, I'm fine with that. But rightfully criticizing a weak design, and condemning the whole of the cellular world are two different things. The article does the later and that's why I think there is exaggeration (with some errors and misunderstandings too).

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:All the other OS, too. (352 comments)

In theory it is possible. In practice the network operator would see the extra traffic (so the NSA too it seems ;), so the risk to get caught red handed seems way too high to me. It could kill a brand.

It's up to everyone to decide on their paranoia threshold and what they feel they need to protect against. But anyone who really cares about its own security and would trust 1) it's smartphone including a lot of closed source software even with Android 2) a complex baseband stack 3) a hugely complex operator network or even many for an international call, just doesn't get security. You want real secure? You need a trusted terminal host stack and and end-to-end secure connection (SRTP, or VoIP over a VPN, etc.). Then you don't have to trust anything in between as anything else just see encrypted traffic. You still have to trust the terminal host stack, so best if one can audit it. This is overkill for most. But that's what secure phones are, with a price to match.

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:Over-the-air Security Protocols (352 comments)

Encryption is optional but typically always set in production network.

For the downgrade attack, I completely agree and mention this elsewhere. When a next gen cellular technology is out there's not much changes/updates on the previous ones as operator focus their investments in the latest. And due to this we still have the 2G issue you mention. That's unfortunate, but in practice I believe the only solution to this will come when 2G will be phased out. It's still a few years away in most countries, and has been done already in some places (some big operators in Japan, South Korea).

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:Exploits for baseband processors (352 comments)

"Certification requirements" is the key thing here, and it's a lot of work for vendors (can't really be lazy and succeed in this space ;).

Spectrum is a shared medium, and the worst jammer is a buggy device. Because of this there are strict certification requirements before being legally allowed to put a device over the air. And going through all the associated tests cost a lot of money: it's a lot of time with expensive testing hardware and in the field (after passing the "safe for network" part). It's expensive both for operators and vendors by the way. This cost make everyone quite conservative. Any change will go through a cost assessment. So it's not that they don't care about security, they do and even if there has been holes in the old versions a lot of work go into making the system secure. But not at any price.

To be practical, the target is good enough security for the average person. And that's ok. If you really have higher protection requirements than this, there is no way but having your own controlled end-to-end scheme. I would expect anyone claiming security is critical and taking this seriously to have figured this out.

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:Over-the-air Security Protocols (352 comments)

Hi there. I'm not following 3G closely but in LTE the encryption schemes are secure. You have two options, both 128 bits: SNOW 3G (inherited from 3G as you can guess ;) and an AES scheme. Both secure as of today. In R10 or R11 a Chinese scheme called ZUC has been added too, also 128 bits. The operator decides on which scheme is used, and the device must support both SNOW 3G and AES today.

The big thing is that the encryption is between the device and cell (base station). The assumption is that the cell is secure, and behind the operator network is secured by other means. So it's important to protect the cell (eNB in LTE) against compromises. A fake cell won't work as in LTE the authentication is mutual: the UE won't work with any cell, except for an emergency call.

For more details have a look at the 3GPP 33.401 spec, for example the latest R9 version.

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:Old silent SIM firmware (352 comments)

No. The SIM is powered from the baseband, and when the baseband is off the SIM has no power supply and can't do anything. Plus the SIM can only communicate with cell towers through the baseband, never on its own. The SIM cannot wake-up the baseband on its own, enabling the radio subsystem can only be done from the host processor. So what you described is not possible.

What is possible however is that when your device cellular radio is on and the baseband is enabled, then the SIM can directly use the baseband to communicate with the network using what is called the SIM Toolkit (STK). This can be done with or without the user being informed. The STK also many features like transforming the numbers you dialed (to seamlessly add a routing prefix, or redirect), filter calls (block or accept), get and report a location, etc. The specs are public, look for 3GPP TS 31.048 and ETSI 102.223 (using USAT and CAT instead of STK, but it's all the same under different names).

about a year ago
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The Second Operating System Hiding In Every Mobile Phone

YoopDaDum Re:All the other OS, too. (352 comments)

I believe the article has some gross exaggerations, and I'm in the baseband business. Of course I can't speak for all implementations, so this is my opinion only.

When the baseband is in a separate die, connected with some interface like SDIO for QCOM, HSI, USB HSIC, ... there is no way that the baseband will control any host resources (unless it can exploit a bug in the host software of course). When the baseband is in the same die as the application processor (AP) and its resources, it becomes at least possible in theory for the BB to access AP resources. But think about it: why do we have process memory isolation and MMUs in the first place? And a kernel sitting between hardware and user space? For security and fault isolation. Do you really want to be the poor engineer having to debug a complex system on chip (SoC) where a bug in the BB part can create weird bugs in completely unrelated parts of the system handled by different teams? That looks like a recipe for disaster. In the systems I work on you have hardware isolation between subsystems to prevent just this. And then a compromised BB can't do a lot of damage (same as for a separate die BB).

I believe the article is a bit sensationalistic and miss the real danger: a compromised base station. That's what the source articles quoted talk about. If you can compromise a cell you can spy traffic without any attack on the UE (encryption is only between device and cell). A fake cell is an issue with 2G but since then authentication is mutual: in LTE a device do authenticate the cell too, and won't work with a fake one. But that doesn't protect against a compromised cell. This is a risk with small and femto cells mostly, as macro cells are easier to protect. The only interest as see in compromising the BB is to use it as a vector to attack the host processor (which has been done), where you have access to much more interesting stuff. This requires a security exploit on the host side too. On its own the BB isn't really very interesting as an attack target.

While I'm at it, there are others not very serious claims here. The fact that one can redirect calls to voice mail with an AT command has nothing to do with baseband security. An baseband support a control interface, and even usually two: 1) a modern but proprietary interface and 2) the standard but old fashioned AT interface. You can do a lot with these commands, no need to compromise the BB. But normally such access is limited to trusted applications, so if anyone can access this it's a host security issue, not a baseband issue.
The baseband doesn't contain one RTOS but usually several instances. There's at least one RISC core (typically ARM), possibly more. At least one DSP, possibly more. With likely more than one OS: having an instance running linux is common, with other(s) on RTOS or even bare bone schedulers (depending on the complexity of the task at hand and timing constraints). That can vary a lot depending on each BB design, but as a rule of thumb for a modern LTE capable BB expect two RISC cores and two DSPs (YMMV).
The mutual authentication I've talked about already. Here the practical issue is that when the next gen is out there's not much interest in doing big upgrades to previous generations. So the lack of network authentication in 2G will stay with us until 2G is phased out, which is still a few years away in most places (big Japan networks have already killed 2G however).

about a year ago

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