Curated by Vinay Prabhakar Minj
Many communication standards which started off with non-IoT applications are now evolving to help IoT.
Internet of Things (IoT) thrives on communication standards and these standards are evolving rapidly to support IoT better.
IoT applications ranges from building & home automation to smart cities, smart manufacturing, wearables, automotive and agriculture. It doesn’t stop here, the scope of IoT is immense. However, depending on the use case, IoT applications can pose different challenges for wireless communication standards.
Building a wireless communication standard for IoT is really hard with all the available communication standards. It’s not that easy to decide which one is best suited for our IoT application. We have standards spanning from personal area network (PAN) and proximity sensors to wide area networks (WAN) and low-powered wide area networks(LPWAN) which are specifically meant for IoT. And in between we also have wireless LAN (WLAN). So different communication standards offer different specifications to help IoT in different ways. These communication standards are evolving and enabling new and future IoT applications.
IOT drives communication standard on both opposite ends. It wants low latency, which is a fast response time, as well as low power. Some applications require high data rate and wide range. These are conflicting goals and it is very difficult for a single wired standard to achieve all of this. To add on top of this, we have other things to resolve such as security, low cost, network capacity and reliability. This is a real challenge for the wireless communication standard.
Evolving Wireless Standards in IoT Communication
Some of the wireless standards that are evolving to help IoT include 802.11 for wireless LANs (802.11 ax and 802.11 bx are coming up as new standards), Bluetooth 5, SUB-1GHz and NB-IoT, which is meant specifically for IoT.
The 802.11ba is also called as the ‘Wake-up Receiver’. Usually, WLAN is used for applications which require very high data rate and where power is not a concern. But to enable IoT, the WLAN has to reduce its power consumption. The new standard of WLAN, called as 802.11ba, works with its previous Gen WiFi 5 or WiFi 6 standard to help achieve low power.
Low power is usually achieved by keeping your wireless device in the sleeping mode most of the time, but that increases latency which makes the response time of your system very slow. In many applications that is not possible because we want faster response time, data rates and low power.
Our goal is to achieve both low power and low latency. This is achieved by low-power wake-up receiver called LPWUR. It works in conjunction with the normal WLAN transceiver (TRx). The basic function of this Wake-up Receiver is to sniff the air for wake-up packets. Once it receives the wake-up packets, it turns ON the main transceiver.
The classic example of this is the video doorbell. The video doorbell needs high data (because it’s video) and if it’s battery operated you would want to save power. A video doorbell needs to continuously sniff the air for online commands to operate the lock and that drains power. So, instead of keeping the main WLAN receiver ON all the time (which is actually meant for high data rate), just for sniffing purpose, we can keep the Wireless Wake-up-Receiver which will check for wake-up packets and then turn ON the main WLAN receiver. This saves a considerable amount of power and this helps IoT get high data rate, low latency as well as low power.
The main IoT enablers possible by 802.11ba are:-
- Low Power- Battery life can be increased by 10 times because the Wake-up Receiver is a very simple receiver. It is just a sniffing radio and can consume less than 10 per cent of the actual WLAN receiver power.
- Low Latency – You can keep the Wake-up Receiver ON all the times. Thus its response time can be in milliseconds.
- It can be always connected – Suppose the sensors on the move, like the mobile application which have sensors moving around. If there is a disconnection from the AP, then instead of keeping your WLAN receiver ON to sniff whether you are within the AP coverage, you can use this Wake-up Receiver to sniff for the AP coverage. This again saves considerable power.
There are future advances planned for 11ba. The wake-up packet consists of a legacy field and a data field. The data field can be used to selectively turn ON the devices that you want, so you can have addresses for specific devices and selectively turn ON devices that you want with the wake-up packet. Other uses of the data packet can be:-
- Indoor location scan – This can be implemented by using data packets from neighbouring APs to figure out your location.
- Roaming scan – When you move out of coverage of your AP, the WLAN receivers turn ON a scan for checking new, available networks. This can be done on a wake-up receiver which will substantially reduce power consumption for your WLAN device.
WiFi 6 is the latest upgrade for WLAN. It is also called as 802.11ax. This is a substantial improvement over the previous standard which was WiFi 5 or 11ac. Previously, WiFi 5 was mostly focussed on increasing data throughput in favourable conditions. WiFi 6 tries to achieve the best possible average data output from your WLAN. Though WLAN is capable of Gigabits/sec kind of data rate, we normally don’t get it. The data rate substantially drops when there are multiple connections to the same AP. WiFi 6 is trying to address this issue.
Comparison Between 802.11ac and 802.11ax
There are two major changes between ac and ax:-
- The technology has changed from OFDM to OFDMA.
- The subcarrier data spacing (frequencies which carry the data symbols) has reduced from 312 KHz to 78 KHz. 78 KHz means that you have data bins/data carriers closely packed together.
Usually, the WLAN channel is 20 MHz long which can pack four times more data carriers using lower subcarrier spacing.
Symbol length and subcarrier frequency are interlinked, which means if frequency reduces, symbol length increases.
The advantage of having a longer symbol length is that you are more immune to delays of your signal reception. So when multiple signal reflections are coming into you, each of that reflection would be slightly delayed. When that happens, longer the symbol length you have, you are more robust and don’t have inter-symbol interference. Longer symbol length helps you have a bigger guard interval which is 3.2µs versus 0.8 µs. Bigger guard interval safeguards you from multiple reflections and you get more reliable data.
Apart from these two major changes, the speed has increased, which is the main purpose of WLAN. 256 QAM has gone upto 1024 QAM, which is almost a 30 per cent increase in the data rate.
Data rates possible for a 600 Mbps for a single spatial stream. For all eight streams, multiple Gigabits/sec data rates are possible for a WLAN.
Subcarrier spacing reduction had enabled us to pack more subcarriers in the 20 MHz channel bandwith.
Initially, for 11ac we had only 52 subcarriers. Now, we have 242 subcarriers, which is a substantial increase. And these subcarriers can be further divided into nine parts which are called Resource Units (RUs). Each RU has 26 subcarriers and 2 MHz bandwidth.
Each of these can have different data or different devices can have different RUs.
In 11ac, we had a 20 MHz channel dedicated to a single user all the time. There was no choice to give that entire 20 MHz space to each of the users doing different activities (texting, video streaming, etc).
With 11ax, we can pack that data in the same 20 MHz channel. This helps us in two ways:-
- For a limited data transfer, you can pack your data together and send it in one go. This helps your system sleep for the rest of the time. This helps reduce power consumption.
- Since you are done with that data transfer in one go, you are now free to address other users. No matter where you are, you will get good speeds.
The 11ax features that enable IoT are:-
- OFDMA (Orthogonal Frequency Division Multiple Access) for both Uplink as well as Downlink. You get more spectrum efficiency and more network capacity. More users can be served at one time.
- 8×8 Multi-User- MIMO Uplink and Downlink. So you can transmit to eight users together for both transmission and reception.
- Long OFDM symbol duration.
- Power save modes with longer sleep intervals and scheduled wake up times.
In terms of future IoT use cases that 11ax enables, you can have battery operated devices for video surveillance, remote diagnostics, disaster management. All these use cases require low power, long range, low latency as well as good data rates.
There are augmented and virtual reality kind of applications which WiFi 6 enables in high data rate modes. For example, virtual training, virtual diagnostics, robotic surgery, augmented reality tourism. All these new applications become possible with WiFi 6.
Bluetooth 5: The latest technology from Bluetooth
In the previous generation, we had BT 4. It had two subparts: classic and low energy. Classic was mostly used in headsets and sound-buds. Low-energy is used in wearables, fitness bands and similar kind of applications.
BT 5 has new features which enables IoT. These include –
Longer Range: You get 4x longer range for low data rates. This is enabled by adding more Forward Error Correction to the data you send. So, for every bit of data you send, this mode will send two more error correction codes which will improve the chances of detecting that bit. And therefore you get four times the range. But this is only for low data rates.
Faster Data: With BT 5, we can achieve 2 Mbps data rate. Faster data rate is achieved by doubling the symbol rate. This helps with faster pairing, connection and download speed.
In BT 4, there were 31 bytes available for advertising which is basically just broadcast messages. Now, that has been increased to eight times, thus helping achieve more richer advertising content.
Various applications of BT 5 include health & fitness (heart rate monitors, smart bands), wireless audio (soundbars, speakers, headsets), retail (location-based ads). Most of them is similar to BT 4 but their specifications have improved, with lower power and better range.
Wireless standards that are specifically meant for IoT
SUB 1GHz is specifically meant for IoT application. It gives you a very long range (as the band is from 750 MHz to 950 MHz), possibly upto 20 km distance. It can run for multiple years on a single coin battery. This is a robust technology because this uses frequency hopping and is less susceptible to interference and also avoids the crowded 2.4 GHz space.
Its applications include street light control, e-meters, smoke detectors, toll road tax, irrigation systems, etc.
Narrow Band IoT (NB-IoT) is the latest LTE standard. It is the lowest data rate LTE version. In LTE, there is the high-performance mode which offers upto 1 Gbit/s kind of data rates. This is where the 5G is going to come. At the other end of the spectrum, it has low cost, power and throughput. The range is of 20 km with data rates of 250 Kbps. Use cases are similar to SUB 1 GHz.
Choose the right wireless standard for your IoT solution
Depending on your use case, you can choose your communication technology. Except for NB-IoT, which is subscription-based, all others are licence free.
While NB-IoT and SUB-1GHz offer a good range, WiFi is the best choice for speed. BT, SUB-1GHz, and NB-IoT will give you similar battery life.
As per Digikey report, the cost is highest for NB-IoT at Rs 1000. The cost for WiFi and BT is similar at Rs 300, while SUB-1GHz is higher at Rs 350. These are module costs, including antenna.
802.11ba standard has not been ratified yet. There are still issues that need to be resolved. However, the new 11ax will have these capabilities, but again whether it will be backward compatible or not is not cleared yet.
About the author
The above article is an extract from the speech given by Rittu Sachdev, RF engineer, Texas Instruments, at IEW/IOTSHOW.IN 2019.
Q. Can SUB-1GHz penetrate through walls and buildings? Is it reliable?
Yes, SUB-1GHz is very reliable. With 20 km range it offers, it can easily penetrate through walls and buildings.