This post originally appeared on Qualcomm Developer Network on April 6, 2023.
If you’re designing and developing for the Internet of Things, you live in a low-throughput, low-power world. You’re on the lookout for wireless standards that will keep things like parking meters, asset trackers, and energy meters connected on a tight power budget. You also value global coverage, accuracy in positioning, and a strong standards roadmap.
We’ve studied the low-power wide-area network (LPWAN) standards for IoT, going back to LTE Cat 1 in 3GPP Release 8. We’ve found that LTE Cat 1bis holds the most promise and ticks the most important boxes for IoT developers, designers and manufacturers. And it includes features that will accelerate IoT adoption worldwide.
That’s why we’ve released a new whitepaper entitled “Understanding the benefits of LTE Cat 1bis technology.” The goals of this post are to highlight the main points in the paper and to encourage you to evaluate LTE Cat 1bis for your IoT products.
No network changes required
eMTC technologies like LTE Cat NB2 (NB-IoT) and LTE-M require operators to upgrade software on their networks — a big speed bump on the road to adoption. LTE Cat 1bis devices, on the other hand, operate on the same LTE network on which our cell phones run. No network upgrade is necessary.
The LTE network treats a Cat 1bis device as it does a Cat 1 device, with one important difference: Cat 1bis requires a single receive- (Rx) antenna instead of the two antennas used in Cat 1.
And unlike eMTC, there is no need to reserve network capacity for coexistence with LTE. Cat 1bis devices do not need dedicated bandwidth; they coexist with regular LTE Cat 1 devices, Cat 4 devices and smartphones on the same network and spectrum.
Global connectivity and roaming
If your application tracks assets moving around the world, you won’t want to tie it to a patchwork of support for LTE-M and NB-IoT. Even with roaming tie-ups, coverage still won’t be global unless you resort to a multi-mode device, with higher manufacturing costs.
LTE data connectivity, however, is nearly ubiquitous thanks to extensive roaming relationships. LTE Cat 1bis devices run on those same networks and benefit from the roaming agreements for cell phones. Your IoT devices can rely on a single service provider, just as consumer devices do.
Lower power consumption
IoT devices such as energy meters and trackers remain inactive most of the time, waking only occasionally to send and receive data. 3GPP has introduced features like extended discontinuous reception (eDRX) and power-saving mode (PSM) for longer sleep cycles. Commonly used in NB-IoT and LTE-M networks, those features apply to Cat 1bis devices also.
But Cat 1bis devices have an advantage in the time that a device must be in active mode to complete a data transaction, or ON time. To upload or receive 500 bytes of data on NB-IoT and LTE-M, device ON time is 400 milliseconds and 40 ms respectively. In contrast, a Cat 1bis device can complete the same data transaction in 8 ms at 500 Kbps of throughput (Note that 500 kbps reflects the potential average data rate for Cat1bis devices).
The following table shows a comparison of Cat 1bis and LPWAN current/power consumption:
Coverage
Both LTE-M and NB technology use Layer-1 packet repetition (control, data channel included) to provide extended coverage compared to traditional LTE. However, their extended RF coverage comes at the cost of reduced spectral efficiency (reduced data rates) because operators have to allocate more resources for packet repetition and increased latency.
Due to the reduced number of antennas, LTE Cat 1bis carries an additional 2.5 to 3 dB of penalty compared to traditional LTE Cat 1.
More accurate positioning
Geolocation or positioning of devices is one of the key IoT use cases.
Positioning accuracy tends to improve as a function of the number of cells detected, and cell detection benefits from greater channel bandwidth. The envelope supported by Cat 1bis is 20 MHz, in contrast to the six resource blocks (1.4 MHz) in LTE Cat-M1.
As a result, the bell curve for cell towers detected by a Cat-M device operating on a 10 MHz channel peaks at four or five towers, as shown below.
The bell curve of cell towers detected by an LTE Cat 1 device increases from five towers and peaks at 10 towers. Thus, the chances of detecting LTE cells for positioning with Cat 1bis are greater than with Cat-M1. With more accurate positioning, LTE Cat 1bis is a better choice for asset tracking.
Lower cost than Cat 1 devices
LTE Cat 1bis modules and devices have a cost advantage over Cat 1 devices. In contrast to the two antennas needed for Cat 1 devices, Cat 1bis modules and devices have a single antenna and a single receive RF chain. Thus, it is easier and less expensive to build devices in smaller form factors.
LTE-M and NB-IoT have the cost advantage of needing no surface acoustic wave filter (i.e., SAW-less) due to the half-duplex nature of communication. Overall, though, the cost structure of Cat 1bis is comparable to that of LTE-M and NB-IoT.
In 2020, the average selling prices (ASP) of Cat 1bis and LPWAN modules sold worldwide were on the order of USD 10. Since then, the price of Cat 1bis modules has fallen to be comparable to that of Cat-M/NB-IoT devices.
Strong standards roadmap
What future does the standards roadmap hold for Cat 1bis?
The 3GPP has defined an option for network architecture that allows upgraded LTE (eLTE) devices to connect to a 5G core (5GC) network over upgraded eLTE NB (eNB). That will ensure service continuity for these devices in case operators should phase out 4G core networks. Cat 1bis user equipment (UE) can time-share or frequency-share spectrum with New Radio UE with dynamic spread spectrum (DSS). That will ensure continued service for Cat 1bis devices when operators re-farm LTE spectrum for other advanced technologies.
Before the end of 2023, 3GPP will freeze Rel-18 standards, among which is NR enhanced reduced capability (eRedCap), designed specifically for resource-constrained IoT devices. NR eRedCap will extend support for similar channel bandwidths of up to 20 MHz and provide data rates of around 10 Mbps using the same single-antenna architecture used by Cat 1bis. When eRedCap devices roll out, LTE will become their fallback technology, enabling operation in Cat 1bis mode on LTE.
Read the paper and stay tuned for part 2
You’re welcome to download our paper, “Understanding the benefits of LTE Cat 1bis technology.”
We’re convinced of the technical and business merits of Cat 1bis and we’re confident in its prospects for IoT devices worldwide. So much so, that we’ve launched the Qualcomm 216 LTE IoT modem, specifically optimized for LTE Cat 1bis.
The modem is in the certification process with several Tier-1 operators, making the modem and Cat1 bis viable candidates for your next round of innovation in IoT devices.
In part 2 of this series, I’ll have more details about the Qualcomm 216 LTE IoT Modem and the status of certification. Stay tuned.
