4G演进：从LTE到LTE-A的关键技术详解

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本文深入探讨了从3G向4G演进的过程中，特别是针对LTE-Advanced（长期演进-高级）的先进技术。文章首先概述了从3G到4G的技术转变，重点在于性能需求和关键特性，强调了4G在移动通信领域的革命性提升。4G，即第四代移动通信系统，旨在提供更高的数据速率、更低的延迟以及更大的容量，以满足日益增长的移动互联网用户需求。 3GPP（第三代合作伙伴计划）在推动这一演进中起着核心作用，通过其新的网络架构，旨在整合现有的和未来的无线接入技术，确保无缝的升级和未来扩展能力。在LTE-Advanced的诸多关键技术中，文章特别提到了： 1. 频谱带宽管理：随着频谱资源的有限性和需求的增长，如何高效利用和共享频谱成为关键。这包括载波聚合（Carrier Aggregation），通过合并多个载波来扩大整体带宽，以支持更高的数据传输速率。 2. 增强型MIMO（Multiple-Input Multiple-Output）：MIMO技术通过多个天线进行信号传输和接收，增强了信号质量并提高了吞吐量。增强型MIMO不仅提升了单用户的性能，还引入了空间分集和空间复用等高级技术，以实现更高的网络效率。 3. 协作多点传输与接收（CoMP）：这是一种多小区协作技术，通过多个基站之间的协同工作，共同为一个用户服务，从而改善信号覆盖和容量，减少干扰，提高整体系统性能。 4. 中继（Relay）：在某些情况下，中继技术被用来增强信号覆盖，特别是在广袤区域或建筑物内部信号较弱的地方。它通过中继节点转发信号，延长了通信距离，增加了网络的可达性。文章指出，这些技术的发展和应用既带来了显著的优势，也面临着挑战，如频谱效率、信道估计、功率控制等问题。此外，为了应对这些挑战，研究者们正在不断探索创新方法和解决方案。阅读这篇论文对于理解4G LTE-Advanced技术的发展历程、核心要素及其潜在影响是十分有价值的，它为通信行业的专业人士提供了深入了解下一代移动通信系统的关键见解。

222 I.F. Akyildiz et al. / Physical Communication 3 (2010) 217–244

Table 2

Primary LTE-Advanced deployment scenarios.

Scenario

no.

Description Transmission BWs of

LTE-A carriers

No. of LTE-A CCs Bands for LTE-A carriers Duplex

modes

Single-band contiguous spec.

alloc. @ 3.5 GHz band for FDD

UL: 40 MHz UL: Contiguos 2 × 20 MHz

CCs

3.5 GHz band FDD

DL: 80 MHz DL: Contiguos 4 × 20 MHz

CCs

B Single-band contiguous spec.

alloc. @ Band 40 for TDD

100 MHz Contiguous 5 × 20 MHz

CCs

Band 40 (3.5 GHz band) TDD

Multi-band non-contiguous

spec. alloc. @ Bands 1, 3 and 7

for FDD

UL: 40 MHz UL/DL: Non-contiguous

10 MHz CC@Band

1 + 10 MHz CC@Band

3 + 20 MHz CC@Band 7

Band 3 (1.8 GHz), Band 1

(2.1 GHz), Band 7

(2.6 GHz)

FDD

DL: 40 MHz

D Multi-band non-contiguous

spec. alloc. @ Bands 39, 34,

and 40 for TDD

90 MHz Non-contiguous 2 × 20 +

10 + 2 × 20 MHz CCs

Band 39 (1.8 GHz), Band

34 (2.1 GHz), Band 40

(2.3 GHz)

TDD

In the uplink, LTE uses DFT-precoded OFDM. For LTE-

Advanced there is one DFT per component carrier, support-

ing contiguous and frequency-non-contiguous resource

allocation on each CC. As for the downlink, the objective

is to reuse and extend most of what has already been de-

veloped for LTE [13].

3.1.3. Transceiver architecture

To utilize these wider spectrum bands, LTE-Advanced

devices must use wideband transceivers. As described

in [16], the two basic approaches for wideband communi-

cation transceivers are as follows.

• Multiple single-band transceivers: For n spectrum bands,

n transceivers are used, one for each spectrum band.

In this case, the transceivers work simultaneously,

allowing the use of all the spectrum bands simultane-

ously. As described at the beginning of Section 3, LTE-

Advanced is considering the use of six spectrum bands,

which would require at least six transceivers through

this scheme. This concept is feasible in the sense that

only requires the addition of parallel paths to process

each spectrum band, as in current multi-band devices.

However, this translates into an increase of the size

and cost of the mobile device. There exists a point at

which the transceivers join in the processing of the

signals. In Fig. 7, we show an example of a high-level

block diagram for a receiver [16], where the digital

signal processing is the point of union of the parallel

transceivers. The receiver has a single antenna, and sev-

eral RF branches. Each branch has an RF band pass fil-

ter for a specific spectrum band, an RF frontend, and

an analog-to-digital converter. In general, as the point

of union moves toward the antenna the number of ele-

ments reduces, which translates into a reduction of the

size and the cost of the device.

• Wideband transceiver: In this case, a single transceiver

processes all the spectrum bands of interest, and the fil-

tering of each individual spectrum band is usually done

in the digital domain. As described at the beginning of

Section 3, LTE-Advanced would process the spectrum

band from 450 MHz to 4.99 GHz through this scheme. In

Fig. 7. Multiple single-band receivers [16].

Fig. 8. Wideband receiver [16].

Fig. 8, we show an example of a wideband receiver high-

level block diagram [16]. It is composed of an RF band-

pass filter, RF frontend, analog-to-digital converter, and

digital signal processing blocks. Due to the wideband

nature of this type of transceivers, most of the RF com-

ponents used need to be wideband. Since the RF signal is

digitally filtered, very high-speed, high-resolution, and

high-dynamic range linear analog-to-digital converters

(ADCs) are needed.

Based on these two general classifications, 3GPP further

specifies subclassifications of transceiver structures for

LTE-Advanced, which can be found in [13].

3.2. Spectrum sharing

Carrier/spectrum aggregation allows a service provider

to offer up to 100 MHz of bandwidth to its LTE-Adva-

nced clients by aggregating dedicated spectra in order

to increase performance. However, in certain scenarios,

sharing of the spectrum becomes another attractive option

to achieve this objective.

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