Cellular wireless communication is on the threshold of its 5th generation of evolution. From diverse region-specific standards in its 1st generation during the late 1970’s, the industry across the world has come together under the aegis of 3GPP for LTE as a unified 4th generation standard adopted today. The focus of services offered has evolved from being voice centric to pure packet data where voice is also offered over a packet network in VoLTE. With increasing relevance of Machine-to-Machine (M2M) communication enabling the Internet of Things (IoT), 3GPP has recognized the need to enable ultra-low cost wireless devices serviced by ubiquitous cellular networks. The result is Narrowband-IoT (NB-IoT), a variant of LTE technology that is being specified in Release 13 of 3GPP.
LTE has been optimized for high bandwidth performance, during its evolution, till Release 12 of 3GPP specifications. Devices with capability ranging from 1 Mbps up to 450 Mbps of data throughput are supported but overheads are high for devices which should handle low data rates. Notable is the need for all LTE devices to have RF capability to simultaneously receive 20 MHz of signal bandwidth. This is partially addressed by the introduction of enhanced Machine Type Communication (eMTC) support in 3GPP Release 13, where required RF capability is reduced to 1.08 MHz.
NB-IoT aims to enable a category of ultra-low cost devices which require modest data rates, are delay tolerant, have low or no mobility, operate in very poor signal coverage, and enable long battery life. The RF capability is limited to 180 KHz, enabling peak data rates in excess of 100 Kbps in normal coverage. In extreme signal coverage of 164 dB, data rates less than 360 bps with latency of the order of seconds is considered. For devices which transmit a few 100 bytes once a day, batteries are expected to last several years. Minimal mobility support is factored to adapt to changes in network coverage at the locations where devices are deployed.
Choice of 180 KHz RF bandwidth for NB-IoT provides flexibility for operators to deploy this over currently used spectrum assets. NB-IoT is being specified to be deployable within the operating bandwidth of a legacy LTE cell or in guard bands of LTE cells. Standalone operation in 200 KHz frequency bands re-farmed from GSM deployments is also possible. This facilitates rollout of NB-IoT as an increment over the existing networks deployed by cellular operators.
Narrowband-IOT provides a viable option for applications such as metering, over cellular wireless infrastructure. The devices could be in extreme coverage areas such as basements or manholes, which are not serviceable by currently deployed cellular networks. This is also an application segment addressable with short-range connectivity technologies such as Wi-Fi, Bluetooth or Zigbee. The overhead in short-range solutions is the need for backhaul connectivity to a location close to the devices. NB-IoT provides an advantage here by offering long range connectivity to the wireless network infrastructure. This could be especially relevant in semi-urban scenarios where the density of devices is not high.
The challenge to NB-IoT arises from LPWA technologies such as Sigfox and LoRa. With NB-IoT specifications still being drafted by 3GPP, Sigfox and LoRa offer almost a year of lead time in deployment readiness. While Sigfox/LoRa offers an advantage for early deployments in unlicensed spectrum, the value offered by NB-IoT is more to existing cellular operators. Cellular operators will find this an attractive migration option for offering IOT-related services over the licensed spectrum they currently hold. This may resemble the situation of some years ago where WiMax provided a potential alternative to HSPA/EVDO for wireless data. A well-defined migration path for HSPA/EVDO evolution towards LTE was provided by 3GPP. This has been largely influential in shaping the current scenario where LTE remains the predominant technology for long range data connectivity. A key consideration in NB-IoT specification process in 3GPP is the reuse of techniques and protocols that have proved efficient in LTE deployment. This will aid accelerated rollout once the specifications are frozen in early 2016.
Services delivered over licensed spectrum have advantage of higher data traffic handling capacity. This could be a significant differentiator as the number of devices deployed in networks grows. With support from Ericsson, Nokia, Huawei, Qualcomm and Intel, NB-IoT is poised to be a lead contender for enabling devices for the Internet of Things.
Authors: Roney Kurien (Architect), Krishna Kishore (Senior Architect), and Ashok Vasudevan (Technical Account Manager – Europe)
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