物联网时代：低功耗广域网技术的关键进展与挑战

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随着物联网（IoT）设备数量的爆炸性增长，对网络连接的需求也在不断演变，特别是对于电池寿命、部署成本和覆盖范围的要求，以确保这些设备之间的有效通信。针对这一挑战，新兴的低功耗广域（LPWA）网络技术应运而生。LPWA技术的核心目标是提供经济高效的连通性，尤其适合那些对能源效率有极高需求且部署在广阔地域的应用场景，如智慧城市、环境监测、农业传感和远程监控等。 LPWA技术主要包括以下几种类型： 1. **LoRaWAN（Long Range Wide Area Network）**：由Semtech公司开发，它利用扩频技术，提供超长距离通信和低功耗特性，适用于大规模部署的物联网应用。LoRaWAN支持星型和网状拓扑结构，确保信号稳定且覆盖广泛，同时保持低功耗以延长电池寿命。 2. **NB-IoT（Narrowband Internet of Things）**：这是蜂窝网络运营商如中国移动、AT&T等推出的一种窄带物联网技术。NB-IoT通过优化频率资源和传输速率，实现了低功耗和高连接密度，特别适合那些需要接入现有移动网络的设备。 3. **Sigfox**：这是一种法国公司开发的LPWA技术，强调短数据包传输和极低的数据速率，非常适合传感器数据的收集和上报。其特点是通信效率高，但数据处理能力相对较弱。 4. **Zigbee/Thread**：虽然主要作为局域网技术，但它们在某些情况下也被用作LPWA解决方案，尤其是在智能家居和工业自动化领域，能够与其他LPWA技术配合使用，实现多层网络架构。 5. **LTE-M（Long Term Evolution for Machines）**：基于4G LTE网络的LPWA技术，提供了高速数据传输的同时保持低功耗，适合对实时性和可靠性的要求较高的应用。这些LPWA技术的优势在于它们能够在大范围地理区域提供稳定的连接，同时减少设备的能耗，这对于那些需要长时间运行且难以更换电池的物联网设备尤为重要。然而，选择哪种技术取决于具体的应用场景、预算、数据传输需求以及对网络稳定性和覆盖范围的要求。研究论文深入探讨了LPWA技术的性能比较、标准规范、部署策略和未来发展趋势，旨在为设计者和开发者提供一个全面的参考框架，推动LPWA技术在物联网领域的广泛应用和发展。

cellular networks, such as LTE, Global System for Mobile Communica-

tions (GSM), etc. can achieve long-distance transmission through

multi-hop mesh networking, it is not the most ideal solution, because the

cost of network deployment and communication is too high (Finnegan

and Brown, 2018). In order to lower the cost of long-range communi-

cation, LPWA technologies, which can achieve a long range of a few to

tens of kilometers, and battery life of ten years and beyond at the expense

of low data rate (about 10 kb/s), are proposed for connecting ubiquitous

IoT devices (Petajajarvi et al., 2015). Note that LPWA technologies

achieve long transmission range and low power consumption at the

expense of low transmission rate (typically tens of kb/s) and high latency

(typically a few seconds or minutes). In summary, LPWA technologies are

only suitable for these use cases that are tolerance to the network delay,

require low power consumption and low cost, and have no need on the

transmission rate.

2.2. Design goals

LPWA technologies are designed to offer low power connectivity for

large number of devices over a wide area at low cost. Low power refers to

using a cheap power source (e.g., a button cell or a pair of AA batteries) to

enable the IoT devices to function autonomously for a long period of time

(up to 10 years). Wide area refers to a long direct communication dis-

tance between two IoT devices, which enables the coverage of city or

rural area without using complex mesh networking technique. In this

section, we like to highlight the design goals of LPWA technologies,

including long range, low power, low cost, and scalability.

Long Range. Wide area coverage is an important design goal of

LPWA technologies, which can be achieved by exploiting several factors,

such as sub 1 GHz, special modulation schemes, etc. The deployment

environment (rural, urban, etc.) also has an impact on the communica-

tion range from a few to tens of kilometers.

 Using Sub 1 GHz bands: Most LPWA technologies use sub 1 GHz to

offer robust and reliable wireless communication with a few excep-

tion (e.g. Weightless-W ( Weightless, 2019) and Ingenu (Ingenu,

2019a)). Because when encountering obstacles, the communication

signal with lower frequency has less attenuation and multiple path

fading. Moreover, sub 1 GHz is less congested than 2.4 GHz, in which

multiple protocols (e.g., Bluetooth, ZigBee, WiFi, etc.) are running

simultaneously. As a result, using sub 1 GHz can lower the possibility

of interference between different communication techniques

(Andreev et al., 2015).

 Modulation Schemes: In LPWA technologies, the modulation rate and

data rate are slowed down to save more energy to transmit the data

and then the receivers can decode the attenuated signals correctly.

Generally speaking, there are two types of modulation schemes

adapted in different LPWA technologies, including narrowband and

wideband techniques. Narrowband technology ﬁrst compresses

sensed data into ultra-narrow bands and then uses signal processing

techniques to decompress data (Reynders et al., 2016; Goursaud and

Gorce, 2015), while wideband technology adopts a larger bandwidth

than needed and utilizes frequency diversity to express the sensed

data.

Low Power. LPWA technologies also need to be run with a cheap

power source (e.g., a button cell or a pair of AA batteries) as they either

do not or cannot easily replace the power source. As a result, under the

low power circumstances, the longer the lifetime of power source, the

more suitable for LPWA connectivity. To lower the energy consumption

in designing LPWA technologies, some of the following aspects should be

taken into consideration.

 Topology. In short range wireless networks, mesh networking tech-

nique is adapted to extend the transmission range, which will cause a

high deployment cost. In addition, the data will be transmitted to the

end devices through multiple hops, resulting in quick depletion of the

batteries (Oppermann et al., 2014). To address this limitation, most

LPWA technologies adapt a star topology, where the sensed nodes

connect to a base station directly. There is no need for the dense and

expensive deployments of relays and gateways altogether. In this

case, it saves the energy for the communication and provides a quick

access to the end devices (Raza et al., 2017).

 Duty Cycling. In order to further save energy consumption, LPWA

devices are designed to turn off the power hungry components

opportunistically. Speciﬁcally, when the data is to be transmitted or

received, the device is turned on. In LPWA networks, the duty cycling

mechanisms are used according to several factors, such as the appli-

cations, communication pattern, type of power source, etc. By

designing a listening schedule between the end device and base sta-

tion, different components of IoT devices (e.g., uplink module or

downlink module) could be wakeup accordingly (Sornin et al., 2015).

In addition, duty cycling is also a legislative requirement that a

transmitter is limited to occupy the channel at a certain time to ensure

the coexistence with other devices (Burns et al., 2015).

 Lightweight Medium Access Control. The most popular Medium Access

Control (MAC) protocol in cellular networks and short-range wireless

networks is exploiting frequency and time diversity to synchronize

base stations and the User Equipment (UE) accurately (Zhang et al.,

2015). However, this MAC protocol is not suitable for LPWA networks

as the cheap end devices (less than 5$) do not have high quality os-

cillators to achieve the function. Therefore, a simple random access

scheme – ALOHA is adapted and performs well in LPWA technologies,

because it keeps the transceiver simple and low cost (Sinha et al.,

2017). Moreover, TDMA-based protocols are also adapted by several

LPWA technologies to improve the efﬁciency (Cano et al., 2017).

 Ofﬂoading Complexity. Many complex components of the application

are ofﬂoaded to the base stations for simplifying the design of end

devices (Gu et al., 2018). Thus the base stations have to exploit

hardware diversity to be capable of receiving and transmitting mul-

tiple tasks from different end devices. However, it brings a high

communication consumption for the whole network. To address the

challenge, we have to make a trade-off between of ﬂoading the tasks

to the base stations and running on local devices because different IoT

applications have different requirements, such as bandwidth, data

rate, latency, etc.

Low Cost. Low cost is also a key design goal of LPWA technologies.

LPWA networks have success in connecting a large number of end

Fig. 3. LPWA network architecture (Sanchez-Iborra and Cano, 2016).

F. Gu et al. Journal of Network and Computer Applications 149 (2020) 102459

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