I thought I was the coolest college student in 2004, when I could check my e-mail during lectures with my Nokia 3650 mobile phone. However, GPRS network coverage was spotty in rural State College, Pennsylvania, and I don’t believe I ever experienced the 40-kb/s data rate I was promised. Fifteen years later, the behavioral patterns of you, I, and seven billion other mobile-phone users have largely driven today’s cellular technology to deliver higher data rates with today’s LTE-Advanced Pro and tomorrow’s 5G technologies.
A recent study by Juniper Research estimates that average smartphone consumption will rise from 2 GB per month in 2017 to 5 GB per month by 2021. We are the very reason why recent cellular modems like Qualcomm’s Snapdragon X20 and Intel’s XMN 7560 are designed to support up to 1-Gb/s downlink speeds using a combination of MIMO, carrier aggregation, and the 256-QAM modulation scheme.
However, applications like machine-type communication (i.e., the Internet of Things) are driving mobile standards in a completely different direction. These devices require lower power consumption and data rates with expectations of lower cost and higher reliability.
Today, several 3GPP technologies are evolving to address use cases that connect “things” instead of people—and with features that are very different than what we have grown accustomed to expect from the evolution of LTE. More specifically, some of the up-and-coming 3GPP technologies include LTE for machine-type communication (LTE-M), narrowband IoT (NB-IoT), and LTE Vehicle-to-Everything (LTE V2X).
LTE CAT-M1 and NB-IoT
LTE-M and NB-IoT are part of the LTE family. They’re designed to serve a wide range of low-power and low-data-rate devices as part of wide-area networks. LTE-M started as a simplification of the LTE radio and defined a new category 0 (LTE CAT-0) device in 3GPP Release 12.
1. NB-IoT can be deployed either adjacent to existing LTE transmissions or within unused resource blocks.
Today, in 3GPP Release 13 and 14, LTE-M is specifically referred to as LTE CAT-M1. These devices use half-duplex radios, transmit at lower output power (+20 dBm instead of +23 dBm), and are only required to support the 1.4-MHz LTE bandwidth configuration. In addition, the standard features an extended “discontinuous reception cycle,” which allows devices to extend battery life by sleeping for up to 40 minutes between transmissions. The target for LTE CAT-M1 devices is to consume approximately one-fifth of the power required by today’s most basic “traditional” LTE radios.
In parallel with LTE CAT-M1, another 3GPP technology called NB-IoT is a slightly longer-distance and lower-complexity cousin (Fig. 1). Although similar to LTE CAT-M1 in many aspects, one notable difference in NB-IoT is that it further reduces the transmission bandwidth to only 180 kHz, allowing for operation in reclaimed GSM spectrum and unused LTE resource blocks. Moreover, NB-IoT reduces the modulation complexity and only allows simple phase-shift-keyed (PSK) modulation schemes (QPSK, p/2-BPSK, p/4-QPSK). An important design attribute of NB-IoT is the improved link budget, which is several dB better than that of LTE-M and is 20 dB higher than legacy GPRS technology.
Cellular V2X vs. WAVE/802.11p/DRSC
The third emerging mobile technology that’s evolving to better connect “things” is LTE V2X, often referred to by the umbrella term “Cellular V2X.” Although the origins of LTE V2X started with LTE direct features for device-to-device communication in 3GPP Release 12, the standard will formally release as part of 3GPP Release 14.
LTE V2X is designed as an alternative to existing Wireless Access in Vehicular Environments (WAVE) technology (also known as also known as Direct Short Range Communications) based on the IEEE 802.11p. Unlike WAVE/802.11p/DRSC, LTE V2X allows for both direct vehicle-to-vehicle (V2V) communications and vehicle-to-network (V2N) communications (Fig. 2). In V2V mode, vehicles can tolerate relative velocity differences of up to 500 km/hr at a range of up to 450 meters.
2. LTE V2X supports both vehicle-to-vehicle (V2V) and vehicle-to-network (V2N) communications.
Today, the subject of 802.11p versus LTE V2X has sparked significant debate in the automotive industry, with each camp touting the merits of one technology over the other. In the end, one technology is likely to dominate, but it’s not clear which one that is just yet.
It should come as no surprise that wireless technologies continue to evolve at a pace that only seems to accelerate over time. Although the rapid rate of change is exciting for us as consumers, it creates significant challenges for engineers in the wireless industry.
At both the IC and device level, the introduction of new wireless technologies can add significant design complexity and test cost. As a result, engineers must continually find new methods to lower their cost of test with smarter test systems. With price of targets less than $5 for NB-IoT and LTE-M1 radios, along with wireless standards that change annually, the industry will continue to adopt flexible software-defined test equipment and new test approaches like parallel test.