IoT connectivity solutions: Media access control layer and network topology

161-Datalink-MAC

Media access control layer and network topology

For IoT applications, the main characteristics of the media access layer control (MAC) that need to be considered are multiple access, synchronization, and network topology.

Multiple Access. Looking back at decades of successful cellular system deployment, one can safely conclude that TDMA is a good fit for the IoT. TDMA is suited for low-power operation with a decent number of devices, as it allows for optimal scheduling of inactive periods. Hence, TDMA is selected for multiple access in the MAC layer.

Synchronization. In IoT applications, there are potentially a very large number of power-sensitive devices with moderate throughput requirements. In such a configuration, it is essential to maintain a reasonably consistent time base across the entire network and potentially across different networks. Given that throughput is not the most critical requirement, it is suitable to follow a beacon-enabled approach, with a flexible beacon period to accommodate different types of services.

Network topology. Mobile networks using a cellular topology have efficiently been servicing a large number of devices with a high level of security and reliability, e.g., 5,000+ per base station for LTE in urban areas. This typology is based on a star topology in each cell, while the cells are connected in a hierarchical tree in the network backhaul. This approach is regarded suitable for the IoT and is therefore selected.

The network layer and interface to applications

The network layer (NWK) and the interface to applications are less fundamental as far as power-efficiency and reliability is concerned. In addition, there is more variation in the field of IoT applications. Nevertheless, it is widely acknowledged that IoT applications need to support the Internet Protocol (IP), whether it is IPv4 or IPv6. In addition, the User Datagram Protocol (UDP) and Constrained Application Protocol (CoAP) could provide the relevant trade-off between flexibility and implementation-complexity on resource-constrained devices.

Furthermore, the IoT will represent an immense security challenge, and it is likely that state-of-the-art security features will become necessary. As of today, we can assume 128 bits Advanced Encryption Standard (AES) for encryption and Diffie-Hellman (DH), or the Elliptic Curve Diffie-Hellman (ECDH) variants, can become the baseline for securing communication.

4 Main ‘Must Haves’ for the Physical Layer of Internet of Things Wireless Connectivity

image0011210155736818

Analysis of the physical layer of wireless communication solutions for IoT application.

For IoT applications, the main characteristics of the physical layer that need to be considered are modulation, data rate, transmission mode, and channel encoding.

Modulation. The nature of IoT applications, some involve infrequent data transmission that need low-cost low-complexity devices, preclude the use of high-order modulation or advanced channel coding like trellis-coded modulation. Unless mandatory, due to a harsh radio environment with narrowband interferers or regulatory constraints, spread spectrum, e.g., Direct Sequence Spread Spectrum (DSSS), is to be avoided as it increases the channel bandwidth, requiring a more costly and power-consuming RF frontend, with no data rate improvement. Allowing non-coherent demodulation relaxes the constraint on the device complexity, so (Gaussian) Frequency Shift Keying ((G)FSK) is a proven and suitable choice, similarly as in Bluetooth radio. It is considered that the most sensible choice upon availability would be Gaussian Minimum Shift Keying (GMSK), as the modulation index of ½ allows for lower complexity, or better sensitivity at a given complexity. When available bandwidth is restricted, GFSK with lower modulation index is still appropriate, with the next best being 1/3 as it still allows for near-optimal demodulation at reasonable complexity.

Data rate. IoT applications need to mix very low data rate requirements, e.g., a sensor or an actuator with limited data size either uplink or downlink, with more demanding requirements, e.g., a 6-inch 3-color ePaper display in a home that updates the daily weather forecast or the shopping list, easily amounting to more than 196 kB worth of data. Yet even for small data amounts, a carefully chosen higher data rate actually improves power-consumption thanks to shorter transmission time and reduced probability of collision. Similar reasoning is applied to Bluetooth Low Energy, a.k.a., BLE or Bluetooth Smart, formerly Nokia’s WiBree, which uses 1 Mbps with much lower data throughput. The latter is aimed at proximity communication and its high gross data rate of 1 Mbps sacrifices the range considerably. Even when operating at sub-GHz frequencies, which offer better range than 2.4 GHz for a given transmit power, the 1 Mbps is considered to be the absolute upper limit. On the higher end, the transceiver complexity and power increase do not improve the actual useable throughput, as the overhead of packet acknowledgement and packet processing time become the bottleneck.

On the lower end, data rates below 40 kbps are actually impractical, as it would rule out using standard off-the-shelf 20 parts per million (ppm) crystals. Indeed, the frequency accuracy of these crystals is not sufficient: 20 ppm translates into a 18 kHz frequency error when operating in sub-GHz bands, while it is 48 kHz when operating at 2.4GHz. A narrow channel requires an accurate crystal like temperature-compensated TCXO on both ends, including the client, which is more costly, power-consuming, and bulky [36].The optimal baseline gross data rate is considered to be 500 kbps. Depending on the scale of the network, e.g., home, building, district, or city, the applications, and the number of devices, we expect different trade-offs with actual deployments ranging from 100 kbps to 500 kbps.

Transmission mode. Full duplex communication is challenging, as it requires good isolation and does not allow for resource sharing between transmit and receive. Full duplex also typically involves different frequencies for downlink and uplink. Since the radio resource is a scarce resource, half-duplex is therefore selected, preferably on the same radio channel.

Channel coding. There is the potential for improving link quality and performance with a limited complexity increase by using (adaptive) channel coding together with Automatic Repeat-Request (ARQ) retry mechanism. As of today, this is considered optional due to complexity-cost-performance trade-offs achieved with current technologies. However, provisions have to be made for future implementation. As of today, flexible packet length is considered a sufficient means of adapting to the link quality variations.


Media access control layer and network topology

For IoT applications, the main characteristics of the media access layer control (MAC) that need to be considered are multiple access, synchronization, and network topology.

Multiple Access. Looking back at decades of successful cellular system deployment, one can safely conclude that TDMA is a good fit for the IoT. TDMA is suited for low-power operation with a decent number of devices, as it allows for optimal scheduling of inactive periods. Hence, TDMA is selected for multiple access in the MAC layer.

Synchronization. In IoT applications, there are potentially a very large number of power-sensitive devices with moderate throughput requirements. In such a configuration, it is essential to maintain a reasonably consistent time base across the entire network and potentially across different networks. Given that throughput is not the most critical requirement, it is suitable to follow a beacon-enabled approach, with a flexible beacon period to accommodate different types of services.

Network topology. Mobile networks using a cellular topology have efficiently been servicing a large number of devices with a high level of security and reliability, e.g., 5,000+ per base station for LTE in urban areas. This typology is based on a star topology in each cell, while the cells are connected in a hierarchical tree in the network backhaul. This approach is regarded suitable for the IoT and is therefore selected.

The network layer and interface to applications

The network layer (NWK) and the interface to applications are less fundamental as far as power-efficiency and reliability is concerned. In addition, there is more variation in the field of IoT applications. Nevertheless, it is widely acknowledged that IoT applications need to support the Internet Protocol (IP), whether it is IPv4 or IPv6. In addition, the User Datagram Protocol (UDP) and Constrained Application Protocol (CoAP) could provide the relevant trade-off between flexibility and implementation-complexity on resource-constrained devices.

Furthermore, the IoT will represent an immense security challenge, and it is likely that state-of-the-art security features will become necessary. As of today, we can assume 128 bits Advanced Encryption Standard (AES) for encryption and Diffie-Hellman (DH), or the Elliptic Curve Diffie-Hellman (ECDH) variants, can become the baseline for securing communication.

Internet of Things Wireless Connectivity Option: Wi-Fi Pros and Cons

Wifi-Hotspots
Today one of the most common connectivity technologies for consumer products is Wi-Fi, whose 802.11b/g flavors are using the license-free 2.4 GHz frequency band. A Wi-Fi access point (or hotspot) has a range of about 20 meters (66 feet) indoors and a slightly greater range outdoors. Wi-Fi has the benefit of a large spectrum allowing high data rates, 54 Mbps and still increasing with 802.11n and 802.11ac, in a license-free frequency band that is almost harmonized worldwide1 [17]. Wi-Fi has been widely adopted and it is a great way to provide wireless broadband internet access. However, Wi-Fi is designed for high data rates needed for multimedia contents, as opposed to many IoT applications. There has been some effort to promote low-power Wi-Fi; however, it remains an order of magnitude hungrier than what battery-powered devices in IoT application can afford such as battery powered sensors. In short, Wi-Fi is not a suitable candidate for many IoT applications. It is overkill on the data rate for most applications and an absolute power guzzler.  Wi-Fi is likely to remain the major smartphone and Internet connectivity medium. One can envision that the IoT network gateway would be embedded in the Wi-Fi hub already present in most homes, commercial spaces, factories, and offices.

Great Write Up about Pebble and Apple Iwatch

Pebble vs. Apple: David and Goliath This Ain’tapple-watch-6_1

By 

By this time next week Apple will have, once again, sucked all the oxygen out of the room. Next Monday, at one of the company’s time-tested high-profile events, we’ll all be attending the coming out party for Apple Watch.

But this week, the smart watch news is all about Pebble, which can reasonably claim to have energized the space three years ago in a very Apple way: Exploding onto the scene with a breakthrough device someone else thought of first.

Pebble returned to Kickstarter last week in a bald attempt to capitalize on the smart watch buzz created by Apple’s imminent entry into the space with Pebble Time, a sportier model with a new approach to notifications it calls Timeline. They’ve promised a month of news, timed to the 30-day campaign, which includes today’s reveal of — surprise! — an upgrade option to Pebble Time Steel, a steal at only $80 more than the (long since taken) $170 batch (Yes, I’m in. Again).

Pebble and Apple isn’t David and Goliath, at least not as far as Pebble CEO Eric Migicovsky is concerned. “Whether delusional, manically focused or simply well-rehearsed, Migicovsky chose to view the Apple announcement as a plus for Pebble,” Steven Levy writes in Backchannel. ‘It’s pretty incredible to see the world’s largest company come into the watch space,’ he said. ‘It’s validating something I’ve known for the last six and a half years — that the next generation of computing will be on your body.'”

What is undeniably true is that Pebble has sold more than one million watches in three years, and six days into a 30-day Kickstarter campaign, has sold another $14 million worth. With that, the company has re-claimed the title (it first took with the original Pebble) as the most funded Kickstarter project ever.

So, there is that.

I first took notice of Pebble in my Reuters column when they broke all records on their first Kickstarter campaign, in April 2012:

A Kickstarter project for a device you wear on your wrist, but that needs a smartphone to do anything really interesting, has raised more than $5.3 million in eight days. This is this far and away the most anyone has ever raised on Kickstarter, and it’s happening – with a gadget in a category that has a pretty dismal track record – at a sales pace that would make even Apple sit up and take notice.

As much as I like to dine out on those last words, I’m not really sure Apple did “sit up take notice” as much as it might have already been working on the idea for quite some time.

The smart watch has all the earmarks of the sort of device-that-time-forgot Apple often manages to turn into something relevant. Microsoft had tried and failed with it a decade before the first Pebble (note the similarities to the tablet, which Apple reinvented a decade after the Redmond giant tried to market its own). Various kinds of smart watch have been around ever since, getting little love. Even Pebble was going nowhere fast as a developer of a device tethered to Blackberry phones, which were about to fall off a cliff.

What changed? Two very important, intertwined things.

Smart watches were originally conceived of as stand-alone devices. The limitations are now pretty obvious, chiefly the tiny screen. Remember, though, at the time ofMicrosoft’s SPOT, screens on mobile phones were also pretty tiny.

But they didn’t do all that much. Unlike the Dick Tracy device people of a certain age remember fondly you couldn’t even talk to anyone with it. I mean, we KNEW that watches were communications devices in the early 1960s. So why aren’t they in the year 2002?!

Apple went a long way towards setting the stage for the emergence of the smart phone as must-have mobile device in 2007, with the first iPhone. Among the new features was a ginormous screen, which made activities like web surfing credible on a mobile device. So successful was the smart phone that it created a new version of a problem futurist Alvin Toffler had identified in 1970: information overload. Hard core techies, like Gigaom’s Mathew Ingram, would soon argue that you should choose a smart phone based on how well they wrangled notifications above all other features.

And that was the new opening for the resurgence of the smart watch. The trick, from my perspective, is to avoid mission creep. It is to remember that the opportunity lies in extending the utility of the smart phone, not replacing it.

But the existential question about whether smart watches are a mainstream consumer item is valid. Notification management is pretty hard core. One new use case: There are unique health monitoring opportunities for something strapped to your wrist. Pebble steals a little of that thunder today — surprise! — with a reveal of the smartstrap, which can “contain electronics and sensors to interface directly with apps running on Pebble Time.” That is another open invitation to developers, who have already flocked to the Pebble platform in very respectable numbers — 26,000 have written 6,000 apps.

Apple may bury Pebble, or its entry into the smart watch space might lift all boats — even Android, whose fans will tell you already boasts a range of excellent choices with features Apple will reinvent, or steal, depending on your point of view.

So, for a smart watch aficionado these are exciting times. If Apple is wildly successful, look to them to even extend coverage to Android devices, like iTunes spread to Windows. Apple’s entry is a make-or-break event which will answer whether there is a massive, pent-up hunger for this kind of device, or whether it’s only a play thing for people like me.

Either way, it’s about time.