OQAM-OFDM：未来物联网无线通信的关键技术与挑战

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本文是一篇关于未来物联网（IoT）中无线通信的关键技术及挑战的调查报告，主要聚焦于基于偏置正交幅度调制（Offset Quadrature Amplitude Modulation, OQAM）的正交频分复用（Orthogonal Frequency Division Multiplexing, OFDM）系统。首先，报告详细介绍了OQAM-OFDM在IoT无线通信中的应用，强调了它相较于传统的OFDM技术所具有的优势，如可能带来的更高效的频谱利用率和抗多径衰落能力。文章深入探讨了几个关键技术领域： 1. **原型滤波器设计**：OQAM-OFDM的滤波器设计对于系统的性能至关重要，因为它决定了信号的传输质量和带宽效率。研究者对不同类型的滤波器结构及其对系统性能的影响进行了深入分析。 2. **峰值到平均功率比（Peak-to-Average Power Ratio, PAPR）降低**：PAPR是衡量无线通信系统信号稳定性的重要指标。通过优化算法或特殊的调制方式，OQAM-OFDM能够有效降低PAPR，从而减少功放的动态范围要求，提升系统效率。 3. **尾部降低**：OQAM-OFDM信号的尾部特性对其频谱效率和抗干扰能力有直接影响。文章中可能讨论了如何通过合理的信号处理技术来减少信号的尾部衰减，提高信号质量。 4. **信道估计**：在无线通信中，精确的信道估计是至关重要的。OQAM-OFDM可能会采用新的信道估计算法，以适应其特有的调制方式，提升信道估计的精度和鲁棒性。 5. **多输入多输出（Multiple-Input Multiple-Output, MIMO）结合**：MIMO技术在增强数据传输速率和可靠性方面表现出色。对于OQAM-OFDM，研究者可能探讨了如何有效地利用多天线进行空间多址和数据传输，以实现更高的系统容量和抗干扰能力。报告通过大量的仿真验证了OQAM-OFDM在这些关键技术领域的性能，并对比了与OFDM在相同条件下的表现，揭示了OQAM-OFDM作为未来IoT无线通信潜在方案的潜力和挑战。这篇调查提供了对未来IoT环境下OQAM-OFDM技术应用的深入理解，对于相关研究人员和工程师来说具有很高的参考价值。

3792 IEEE INTERNET OF THINGS JOURNAL, VOL. 5, NO. 5, OCTOBER 2018

(a)

(b)

Fig. 3. OQAM-OFDM versus OFDM for discontinuous spectrum.

C. Superiority of OQAM-OFDM-Based Wireless

Communications for IoT

The major spectral drawback of OFDM originates from the

use of the time domain rectangular pulse shaping. Therefore,

as the evolution of OFDM, OQAM-OFDM uses a well

designed prototype ﬁlter on each subcarrier to obtain ultralow

frequency domain sidelobes. With the improved spectral char-

acteristics, OQAM-OFDM has much better compatibility with

the following IoT scenarios than OFDM.

1) Discontinuous Spectrum: Some applications in IoT

transmit small data packets such as sensors and data acquisi-

tion, or transmit even several bits of control information such

as the smart home. For the above applications, allocating ﬁxed

spectrum resources to IoT terminals is not the best way since

the resources are idle in most time. Therefore, ﬂexibly utiliz-

ing the spectrum holes and the unlicensed spectrum is a good

choice. Note that, the spectrum bands in the spectrum holes

and unlicensed spectrum are typically discontinuous and the

leaked interferences should be strictly controlled in order not

to interfere other users.

In Fig. 3, OQAM-OFDM is compared with OFDM for

the discontinuous spectrum. We can see that there are max-

imum three continuous sub-bands available for the current

user. The neighboring sub-bands are unavailable due to the

usage by other users. Since OFDM has very high frequency

domain sidelobes, large guard bands are required at both the

two sides of the available spectrum bands to avoid the leaked

out-of-band interferences to other users. As a result, two sub-

bands are wasted and only one sub-band can be utilized in

the OFDM-based wireless communication system. On the con-

trary, OQAM-OFDM has ultralow frequency domain sidelobes

and is able to further control the out-of-band interferences

through the prototype ﬁlter design. Therefore, almost no guard

band is needed in the OQAM-OFDM-based wireless com-

munication system, which greatly improves the utilization

efﬁciency of spectrum resources.

2) Asynchronous Transmission: Since the objective of IoT

is to connect everything in the word, it is expected that the

number of IoT terminals will be dramatically increasing year

by year. Different from traditional cellular users, it is difﬁ-

cult to manage the IoT terminals in a synchronous way due

to the large number of terminals and their uncertain activities.

(a)

(b)

Fig. 4. OQAM-OFDM versus OFDM for asynchronous transmission.

Moreover, many IoT terminals only transmit a few of bits as

the control information. The signaling used in the synchronous

transmission is a signiﬁcant overhead for those terminals with

small data packets. Therefore, the asynchronous transmission

can signiﬁcantly improve the system capacities for IoT termi-

nals. In addition, some applications in IoT require real-time

and accurate information, and their tolerances on the latency

are very low. Note that, the asynchronous transmission dis-

cards the synchronization signaling and waiting, which greatly

reduces the signal overhead and decreases the transmission

latency.

In Fig. 4, OQAM-OFDM is compared with OFDM for

the asynchronous transmission. As an orthogonal technique,

OFDM strongly relies on the strict time synchronization

between all users to ensure their signals arrive at the BS simul-

taneously. Otherwise, the orthogonality among the received

signals from different users will be damaged by the high

frequency domain sidelobes, resulting in strong interferences

among asynchronous users. Even with long CP inserted in

OFDM signals, the time offsets originated from large num-

ber of IoT terminals cannot be fully absorbed. Moreover, the

CP insertion will decrease the effective data rate. Therefore,

OFDM cannot support the asynchronous transmission, and

the overhead of signaling and waiting greatly increases

the transmission latency. On the contrary, OQAM-OFDM

is a nonorthogonal technique and depends on the ultralow

frequency domain sidelobes to reconstruct signals. Then, a

certain range of time offsets among received signals from

different users at the BS is affordable for the OQAM-

OFDM-based wireless communication system, and the strict

time synchronization among users is unnecessary. Therefore,

OQAM-OFDM can well support the asynchronous transmis-

sion and greatly reduce the transmission latency caused by the

signaling and waiting.

3) Various Types of Services: In the future, more and more

IoT terminals will be connected to the IoT. Various types of

services have different requirements on the communication

performances such as the data rate and transmission latency.

For example, the rate requirement of wearable devices is on the

level of 10 Mb/s, while the rate requirement of the automation

and monitoring is about 50–500 kb/s. Regarding the tolerance

of the communication latency, most IoT applications require

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OQAM-OFDM：未来物联网无线通信的关键技术与挑战

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