NB-IoT

Purpose and characteristics

Narrowband IoT is a new radio interface evolved from LTE for low-power, low-rate, intermittent IoT messages. It reuses the LTE core network and infrastructure but simplifies the radio interface; it is not backward-compatible with LTE at the radio interface.

Key properties from the lecture:

• licensed spectrum and high reliability;
• 180 kHz narrow bandwidth;
• roughly 200 kbit/s downlink and 144 kbit/s uplink peak rates;
• half-duplex communication, low complexity, and low-cost terminals;
• deep indoor/ubiquitous cellular coverage and high terminal capacity;
• bidirectional communication and long battery life (targeted at about ten years for suitable workloads).

It is appropriate for short, infrequent messages such as meters, tracking, environmental sensors, and alarms over a wide area. It is not a high-throughput or continuous-stream technology.

Network architecture

A UE communicates by radio with an eNodeB/eNB in its serving cell. The cellular core network provides system intelligence:

• MME: mobility management, paging, authentication-related and bearer management functions;
• HSS: subscriber/authentication database;
• S-GW/P-GW: forwarding user traffic through bearers toward the platform/application server.

Coverage is obtained by dividing a large region into cells served by fixed base stations. The cellular network manages attachment, tracking, paging, and cell reselection.

Deployment scenarios

NB-IoT can be deployed:

1. Standalone: one 200 kHz carrier in spectrum such as former GSM spectrum, independent of LTE.
2. Guard-band: one LTE physical resource block (PRB) in the unused guard band next to LTE.
3. In-band: one LTE PRB inside an LTE carrier, time-sharing resources with LTE.

Channels and multiplexing

• Signaling channels carry control information used to establish/access communication and manage radio resources.
• Data channels carry user traffic such as sensor readings.

Frequency multiplexing separates uplink and downlink resources (in FDD deployment); time multiplexing separates channels/resources within those directions. The eNB maps logical channels to physical channels. Paging is control/signaling traffic, not sensor user data.

Cell access and tracking

A newly powered-on UE:

1. scans/listens to broadcast information from candidate cells;
2. rejects cells that are not joinable;
3. compares signal strength/quality with the cell’s threshold;
4. selects the best acceptable cell and joins/attaches.

A UE does not hand over during an active short communication in the lecture model. If the serving cell becomes unsuitable, it performs cell reselection and may move between cells while idle.

A tracking area is a group of cells identified by a tracking-area identifier (TAI). If a UE enters a cell with a different TAI, it sends a tracking-area update (TAU). When downlink data arrives, the network pages all cells in the UE’s last known tracking area rather than tracking its exact cell continuously. TAU also acts as a keep-alive.

Power saving

• eDRX: the UE listens only at scheduled paging opportunities, including a 1.28-second paging window at the beginning of a hyperframe, and sleeps for a configured number of hyperframes. Longer sleep reduces energy but increases downlink latency; buffered data waits in the core network.
• PSM: the UE tells the core it will sleep indefinitely. It cannot be paged while asleep; when it wakes to transmit, it remains reachable briefly afterward.

Choosing NB-IoT vs 802.15.4

Prefer NB-IoT when devices are geographically dispersed/mobile, need cellular/deep-indoor coverage, or should avoid deploying and maintaining a local PAN/gateway. Prefer 802.15.4 for a local, short-range, low-cost network with many nearby devices and local coordination.

Sources

• master-cs/raw/iot/3.2-IoT_Internetworking-NB-IoT.md
• master-cs/raw/iot/Question Sheet Week 3.md
• master-cs/raw/iot/2021 alte klausur.md