5G之路：毫米波技术的挑战与机遇

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"The path to 5G: mmWave aspects" 5G通信技术是当前移动通信领域的热点，其中毫米波（mmWave）技术是实现高速、大容量和广覆盖的关键技术之一。毫米波指的是频率在30 GHz至300 GHz之间的电磁波，这一频段具有极大的带宽资源，为5G提供了前所未有的传输速率潜力。 1. 毫米波的特性与挑战毫米波的宽频谱特性使得它可以支持更高速的数据传输，适合于高密度的城市环境和密集用户场景。然而，毫米波的传播特性也带来了挑战，如短距离传播、易受雨衰和建筑物阻挡的影响，以及大气吸收等。因此，设计高效的mmWave系统需要对这些特性有深入理解，并针对性地创新。 2. RF系统架构与电路创新为了克服毫米波传播的限制，5G系统需要创新的射频（RF）系统架构。这包括采用多输入多输出（MIMO）技术，通过多个天线同时发送和接收信号，提高数据传输速率和系统容量。此外，波束成形技术也被广泛应用，通过动态调整天线阵列的相位，将能量集中到特定方向，增强信号强度并提高通信距离。 3. 接收机与发射机设计毫米波接收机和发射机的设计是5G技术中的重要环节。发射机需要高效地产生毫米波信号，同时保持低功耗和高线性度。接收机则需要有高灵敏度，能从噪声中提取微弱的毫米波信号。这通常涉及复杂的前端设计，包括低噪声放大器（LNA）、混频器、本振（LO）和数字信号处理单元。 4. 天线与封装技术毫米波通信对天线设计提出了新的要求。小型化、多元素的天线阵列是必要的，以实现波束成形和空间分集。同时，封装技术也需革新，以集成更多的元器件并减小体积。例如，三维集成电路（3D IC）和片上系统（SoC）技术可以将天线、射频组件和基带处理单元紧密集成，降低互连线损耗。 5. 关键技术综述论文还回顾了mmWave通信中的其他关键技术，如频率选择性滤波器、相控阵天线设计、信道建模和跟踪算法等。这些技术共同推动了毫米波在5G中的实际应用。 "The path to 5G: mmWave aspects"这篇论文深入探讨了毫米波在5G通信中的应用，分析了其独特优势和设计挑战，强调了创新的RF系统架构、电路、天线和封装设计的重要性。随着5G技术的不断发展，毫米波将在未来的无线通信中发挥越来越重要的作用。

Journal of Communications and Information Networks

2.3 System architecture

Considering the unique characteristics of the

mmWave frequency, an advanced RF transceiver

architecture is needed to improve the system speed,

energy efciency, and spectral efciency. With the high

integration level in the chip and very compact antenna

array, it is suitable to realize a mmWave system using

MIMO and beamforming techniques

[15-18]

As shown in Fig.2 and Fig.3, for mmWave comm-

unication, there are two typical transceiver

architectures, namely direct conversion and dual-

conversion

[9,19,20]

; both of these have their advantages

and disadvantages. Direct conversion, which is

popular in GHz RF radio, can achieve compact and

low power implementation, as well as operation

exibilities. However, for mmWave applications, its

high-frequency quadrature modulation/demodulation

typically gives rise to severe distortion, such as I/

Q imbalance and LO (Low Oscillator) feedthrough.

Moreover, the indispensable quadrature PLL (Phase-

Locked Loop) has introduced several implementation

issues. These are the trade-off between the phase

noise, tuning range, and phase error, as well as the

frequency pulling/pushing caused by the power

amplier

[20]

To overcome the above-mentioned design issues

and improve the SNR, an alternative solution is to

use the dual-conversion architecture (also referred to

as sliding-IF), as shown in Fig.3. In this architecture,

the quadrature modulation and demodulation working

frequency is significantly reduced. Moreover, the

tuning range and operating frequency of the LO are

reduced, simplifying the system design. Therefore,

the sliding-IF architecture is very popular in mmWave

systems

[19, 21-23]

Combined with the beamforming technique, based

on the above transceiver architecture, we can realize

the phased-array system, thus achieving beam-

scanning capability, which is good for LOS and

NLOS communication scenarios. With the above

features, mmWave wireless access and wireless

backhaul can be simultaneously supported, increasing

the system exibility

[2-4]

. Moreover, with a large-scale

antenna array, we can realize a large antenna array

gain, compensating the large path loss associated

with high frequency and increasing the coverage

Accordingly, we can establish a stable wireless link.

To be more specific, from an implementation

perspective, mmWave can achieve a high directivity

using a large array antenna, and the actual power

that is required to deliver a certain EIRP (Equivalent

Isotropic Radiated Power) is significantly reduced.

Accordingly, the requirements on each RF front-

end component, such as the antenna gain and PA

output power, can be relaxed, thereby increasing the

system energy efciency. On the other hand, we can

achieve a small beam, increasing the signal spatial

isolation and simultaneously accommodating many

co-channel users. In other words, a kind of spatial

ltering on the co-channel signal is achieved, and the

spectrum efciency can be improved. Combined with

the mmWave large path loss feature, the interference

can be relaxed and the frequency can be reused by

using small-cell techniques, as well as increasing the

spectrum efficiency and communication capacity.

Figure 2 Direct-conversion architecture

Figure 3 Dual-conversion architecture

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