Rohde&Schwarz SMW200A等设备支持的802.11n从SISO到MIMO应用指南

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本应用笔记详细介绍了Wi-Fi标准IEEE 802.11n的发展历程，从单一输入/输出(SISO)模式向多输入/多输出(MIMO)技术的转变。802.11n是目前无线局域网(WLAN)中最常用的标准，它不断扩展以满足日益增长的数据速率需求，尤其是在非蜂窝网络环境中。MIMO技术通过利用多个天线进行同时传输和接收，显著提升了数据传输的效率和容量。该文档首先概述了802.11n的重要增强，包括对先前版本的修正以及其在无线通信中的雄心勃勃的新测量任务。重点在于如何使用罗德与施瓦茨(Rohde & Schwarz)公司的各种仪器，如SMW200A、SMU200A、AMU200A等，来处理这些复杂的MIMO相关任务。这些仪器不仅能够支持信号生成，包括多标准信号构建，还提供了802.11n信号分析的能力，通过屏幕截图展示了在实际信号上的操作演示。应用笔记作者Detlev Liebl在1MA179_10e版本中，以清晰的结构组织内容，包括目录，帮助用户了解MIMO在802.11n标准中的实施策略和仪器使用方法。对于无线工程师和测试人员来说，这是一份极具价值的参考资料，它不仅介绍了理论知识，还提供了实用的工具和技术指导，以便他们在设计和测试过程中充分利用MIMO技术提升无线网络性能。无论是理论学习还是实践操作，这份应用笔记都是深入理解并应用802.11n MIMO的关键资源。

Principles of MIMO Testing

Common WLAN Settings

1MA179_10e Rohde & Schwarz WLAN 802.11n: From SISO to MIMO 10

4 Principles of MIMO Testing

Multiple input / multiple output (MIMO) is now being used in many wireless

communication systems to increase data throughput and to improve the robustness of

the transmission. MIMO is used with LTE and WiMAX

, as well as for WLAN since the

introduction of IEEE 802.11n. An overview of the theory and T&M requirements for

MIMO can be found in the application note "Introduction to MIMO" [4], and more in-

depth explanations are provided in [5], for example.

This chapter is limited to the use of MIMO for WLAN, the implementation in line with

IEEE 802.11n, and the available T&M solutions.

Unlike previous radio transmission methods, MIMO uses multiple transmit and receive

antennas. And unlike antenna diversity, true MIMO transmits different signals over the

individual antennas. These signals are also subjected to different coding, delay, and

amplitude and phase control during processing.

The MIMO terminology emphasizes the transmission medium between the stations,

not the stations themselves. In other words, "n x m" MIMO means that n antennas feed

into the transmission medium between the stations (STAs) and m antennas read from

it.

IEEE 802.11n specifies up to four RX/TX antenna pairs.

As a result of the large number of manufacturers and the wide range of equipment

configurations, a station with a specific number of transmit and receive antennas is

often paired with a station with a different number of transmit and receive antennas.

For example, Fig. 2 shows a combination of one station with four TX and RX antennas

and another station with two TX and three RX antennas.

Fig. 2:Combination of two different stations.

When STA1 in the example above operates as the transmitter and STA2 as the

receiver, this is considered to be 4x3 MIMO; the view is from left to right. When STA2

works as the transmitter and STA1 as the receiver, it is considered to be 2x4 MIMO;

the view is from right to left.

Principles of MIMO Testing

Common WLAN Settings

1MA179_10e Rohde & Schwarz WLAN 802.11n: From SISO to MIMO 11

802.11n specifies to use the same number of RX and TX antennas during testing.

However, when assessing a receiver in R&D, measurements must be performed using

all possible combinations.

802.11n also specifies a direct cable connection between the transmit and receive

antennas. During receiver development, however, it is essential that the transmission

medium along with its characteristics be included. Therefore, in addition to pure signal

generation, Rohde & Schwarz generators also permit a flexible simulation of the

transmission medium: multipath propagation / fading simulation is an option for SMU or

the combination of AMU and SMATE, additional white Gaussian noise (AWGN) is

available for all generators mentioned in this application note.

Receiver tests

In the WLAN standard, the formats of the RX and the TX frames (packets) are the

same. RX and TX tests use the same packets, either in legacy, in mixed mode, or in

Greenfield format.

Fig. 3 on page 12 shows how the Rohde & Schwarz generators process the TX

signals. This figure shows the block diagram for 4x4 MIMO; i.e. the maximum number

of TX and RX antennas, with a static simulation of the transmission medium. This type

of configuration is needed for the receiver test receiver minimum input sensitivity

(20.3.22.1), for example.

For every RX input on the DUT, a separate generator is provided that generates all

four TX antenna signals, simulates the transmission medium in an antenna matrix, and

carries out RF upconversion.

The baseband configuration is exactly the same for generators A to D (in the red

blocks) so that TX signals with the same index are always identical. Signal processing

is carried out the same as in every 802.11n module.

The green blocks represent an additional transmission medium simulation function

available with Rohde & Schwarz generators, which provides every DUT antenna with

portions of all four TX signals over four individual paths in the transmission medium.

You can define the parameters for these paths by magnitude and phase using the

complex elements w

νµ

of antenna matrix W.

The signals are processed and combined in the baseband; afterwards the resulting

signals are upconverted to the RF band.

This means that the following sum signals are present at the outputs of generators O1

to O4 instead of TX1 to TX4:

O1 = w

.TX1 + w

.TX2 + w

.TX3 + w

.TX4

O2 = w

.TX1 + w

.TX2 + w

.TX3 + w

.TX4

O3 = w

.TX1 + w

.TX2 + w

.TX3 + w

.TX4

O4 = w

.TX1 + w

.TX2 + w

.TX3 + w

.TX4

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Rohde&Schwarz SMW200A等设备支持的802.11n从SISO到MIMO应用指南

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