On-Demand LoRa: Asynchronous TDMA for Energy Efficient and Low Latency Communication in IoT
- Energy efficient: during periods of inactivity, i.e., when there are no data to be transmitted, the end devices must reside in a deep sleep state to maximize device and overall network lifetime.
- Responsive: data must be delivered to the gateway and vice versa in both a timely and reliable manner.
- a new network architecture leveraging short- and long-range technologies for enabling low-latency and energy efficient data collection over a two-hop network.
- the design and implementation of a new receiver-initiated on-demand TDMA MAC for managing channel access and packet collisions. The proposed MAC offers two modalities for node triggering and allows slot allocation for combating packet collisions. On-demand TDMA achieves an improvement of at least 1.72× in terms of latency and an extended node lifetime of 1.4× with 100% system reliability over the traditional channel sensing scheme for LoRa. This new feature still works with the standard LoRa, but improves overall performance with an on-demand TDMA scheme.
- introduce an analytical model to quantify the data collection latency for on-demand TDMA in broadcast and unicast mode.
- the performance evaluation of the proposed network architecture and MAC using an indoor testbed composed of 11 sensor nodes.
2.1. Low-Power Long-Range Communication: LoRa
2.2. Wake-Up Radios
3. Related Work
3.1. Long-Range Communication Schemes
3.2. Wake-Up Radio-Enabled MAC
4. Energy-Efficient Data Communication Network and Protocol
4.1. Network Architecture
- The end device (ED) is responsible for sensing and equipped with both a wake-up receiver and a LoRa transceiver. The EDs are battery powered and, therefore, will spend most of the time in a low-power mode, i.e., deep sleep state.
- The cluster head (CH) is in charge of managing the nodes in the cluster and relaying commands from the gateway to the EDs. Depending on the application scenario and the energy availability, the CH can either operate in a duty cycle mode or can always be listening. The nodes designated as CHs are also equipped with both radios. Each CH is assigned a unique ID address allowing the sink to query each CH at a time, thus reducing the interference from other clusters.
- The sink acts as a gateway and is assumed to have no energy constraints and will be wall-powered. Therefore, the sink can be always on and listening for any incoming data. Unlike ED and CH, the sink only offers long-range communication without the wake-up radio interface.
4.2. On-Demand TDMA MAC Design
4.2.1. Unicast TDMA
4.2.2. Broadcast TDMA
4.2.3. Slot Allocation
5. Experimental Evaluation
5.1. Experimental Setup
5.1.2. Radio Settings
5.1.3. Ambient Noise Floor
5.2. Evaluation Metrics
5.3. Network Performance Analysis
5.3.1. Packet Delivery Ratio
Broadcast TDMA vs. LBT
Unicast TDMA vs. Broadcast TDMA
5.3.3. Energy Efficiency
Broadcast TDMA vs. LBT
Unicast TDMA vs. Broadcast TDMA
Conflicts of Interest
|IoT||Internet of Things|
|TDMA||time division multiple access|
|MAC||medium access control|
|ISM||Industrial, Scientific and Medical|
|LPWAN||low power wide area network|
|CSS||chirp spread spectrum|
|CSMA/CA||carrier sense multiple access with collision avoidance|
|LBT||listen before talk|
|CAD||channel activity detection|
|PTW||pipelined tone wake-up|
|W-MAC||wake-up radio MAC|
|ToA||time on air|
|PDR||packet delivery ratio|
|RDC||radio duty cycle|
|RTT||round trip time|
|NB-IoT||Narrow Band Internet of Things|
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- is the symbol rate
- is the payload length in bytes (1–255)
- is the LoRa spreading factor (6–12)
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- is the data rate optimizer, one when enabled, zero otherwise
- is the LoRa coding rate [1: 4/5, 2: 4/6, 3: 4/7, 4: 4/8]
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|SX1276 in listening mode||50 mW|
|SX1276 transmitting at +14 dBm (LoRa mode)||250 mW|
|Mote in deep sleep mode, wake-up receiver listening||1.83 W|
|Wake-up receiver (receiving + address decoding)||284 W|
|Wake-up transmitter at +14 dBm||260 mW|
|Wake-up radio data rate||1 kbps|
|Wake-up beacon packet size||2 B|
|LoRa Radio Setting||SET 1||SET 2||SET 3|
|Data Rate (kb/s)||0.976||7.03||21.87|
|Transmission Power (dBm)||10||10||10|
|Preamble Length (symbols)||8||8||8|
|Carrier Frequency (MHz)||868||868||868|
|Time-on-air (measured (ms))||264||31||9|
|LoRa Radio Setting||SET 1||SET 2||SET 3|
|TDMA Mode||No. of EDs||Sink (mJ)||CH (mJ)||ED (mJ)||RTT Latency (ms)||Sink (mJ)||CH (mJ)||ED (mJ)||RTT Latency (ms)||Sink (mJ)||CH (mJ)||ED (mJ)||RTT Latency (ms)|
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Piyare, R.; Murphy, A.L.; Magno, M.; Benini, L. On-Demand LoRa: Asynchronous TDMA for Energy Efficient and Low Latency Communication in IoT. Sensors 2018, 18, 3718. https://doi.org/10.3390/s18113718
Piyare R, Murphy AL, Magno M, Benini L. On-Demand LoRa: Asynchronous TDMA for Energy Efficient and Low Latency Communication in IoT. Sensors. 2018; 18(11):3718. https://doi.org/10.3390/s18113718Chicago/Turabian Style
Piyare, Rajeev, Amy L. Murphy, Michele Magno, and Luca Benini. 2018. "On-Demand LoRa: Asynchronous TDMA for Energy Efficient and Low Latency Communication in IoT" Sensors 18, no. 11: 3718. https://doi.org/10.3390/s18113718