Internet of Things connectivity must reach a middle ground between coverage and bandwidth to provide for applications with very different requirements.
While it’s true that tracking, measurement, control, or monitoring systems in rural or remote areas have lower traffic and rely on low-bandwidth technologies such as GSM, a different trend is growing. A whole range of M2M and IoT applications using live video, rich media, on-the-go content, multi-user sharing, demand a high network capacity that can be provided today with LTE.
Carrier aggregation (CA), the key concept in LTE-Advanced, allows operators to supply even higher bandwidth than LTE, to support such connected devices. As its name suggests, carrier aggregation combines two or more carriers in order to offer a greater throughput.
Using CA, new transmission channels can be created using the operators’ existing frequency spectrum. It is available in both TDD and FDD systems, and can be achieved by combining carriers from the same frequency band or from different frequency bands, as shown below.
Capacity is essential for IoT, as hundreds of devices are in constant communication with the network. In CA systems, up to 100 MHz bandwidth can be reached, as each component carrier can have a maximum bandwidth of 20 MHz, and a maximum of 5 carriers could be aggregated. In practice though only two carriers have been used so far.
Operators may also opt to combine carriers from different spectrum bands, as some are already reported to be doing, and this can be very practical given that LTE networks are currently being deployed on distinct frequency bands.
For carrier aggregation to work on both ends, devices must be able to detect and read the multiple frequencies sent by the radio network. In theory, a peak speed of 500Mbps for uplink and 1Gbps for downlink could be achieved with carrier aggregation.
In commercial deployments so far, as reported recently by the GSA, a maximum downlink 300Mbps has been achieved on a number of devices including smartphones and mobile hotspots. According to the same report, only 88 commercial implementations of carrier aggregation systems have been launched so far in 45 countries, but others are underway.
Carrier aggregation can be used to offer increased bandwidth for IoT, and it can also improve coverage by combining low frequency carriers with high frequency ones. Trade-offs of this system include battery life, but we’ll talk more about LTE for IoT next week during IoT Evolution Expo.