SISO testing vs MIMO testing-SISO testing and MIMO testing basics

This article describes basics of SISO testing and MIMO testing. It mentions test setup used in SISO testing and MIMO testing. It describes RF compliance test specifications of transmitter and receiver used in SISO testing and MIMO testing.

SISO system vs MIMO system
Figure-1: SISO vs MIMO System basics

The figure-1 depicts SISO and MIMO systems. SISO stands for Single Input and Single Output. Hence it consists of one antenna for transmission and reception both. It uses duplexing technique such as TDD and FDD. In TDD, the system transmits and receive at different time instants but at the same frequency. In FDD, the system transmits and receive simultaneously at the same time but at two different frequencies.

MIMO system uses more than one antennas for transmission as well as reception. Figure depicts 2x2 MIMO configuration. The other popular MIMO configurations are 2x4, 4x4, 8x8 etc.

There are two major techniques used in MIMO viz. STBC and SM or SDM. In STBC both the antennas transmit different data symbols (s1,s2) at time t=t1, but at later point in time they transmit modified copies of the same data symbols (i.e. s1',s2') at t=t2. In SM (Spatial Multiplexing) or SDM (Space Division Multiplexing) both antennas transmit different set of data symbols at time instants t1 and t2.

Hence SM or SDM will serve high data rate compare to STBC. While STBC is suitable to enhance coverage distance requirement compare to SM due to redundancy concept used in transmission.

RF SISO Testing basics

SISO test setup
Figure-2: SISO test setup

The figure-1 depicts SISO test setup. As shown single transmitter can be tested by connecting its output to VSA (Vector Signal Analyzer) or Spectrum analyzer or SNA/VNA equipments. Similarly SISO receiver can be tested by feeding signal generated using VSG or any other RF signal generator equipments.

SISO RF Measurements

Following RF measurements are typically carried out for transmitter/receiver.

Transmitter measurements:
• Gain and Transmit Power or spectrum measurement
• 1dB Compression Point or TOI (Third Order Intercept) point measurement
• Phase Noise
• Spurious and Harmonics measurement
• CCDF measurement

Receiver measurements:
• Noise Figure measurement
• Gain measurement
• BER/SNR measurement
• Maximum Allowed input power
• Minimum detectable RF power
• EVM (Error Vector Magnitude)

RF MIMO Testing Transmitter part

MIMO Transmitter test setup
Figure-3: MIMO RF Transmitter test setup

The figure-1 depicts MIMO Transmitter test setup. As shown the testing can be done as per different test configurations viz. Parallel, Combined and Switched. We will understand 2x2 Antenna configuration based MIMO system.

Parallel VSA: Both the transmitters are connected simultaneously with two separate VSAs (Vector Signal Analyzers). Composite EVM test and interleaved sub-carrier test is carried out using this test setup.

Combined VSA: The output of both transmitters are combined using RF combiner and provided as input to single VSA. Here also combined EVM and STBC simulation results are obtained. SDM (Space Division Multiplexing) can not be simulated with this test setup.

Switched VSA: The transmitters are switched as input to single VSA sequencially as shown. Both STBC and SDM simulations can be obtained with this test setup.

MIMO Transmitter Measurements

Following MIMO transmitter measurements are carried out during MIMO compliance testing.
• Spectrum Mask
• Spectral Flatness
• Peak Power
• Center Frequency Error
• Symbol Clock Frequency Error
• Center Frequency Leakage
• Error Vector Magnitude (EVM)

RF MIMO Testing Receiver part

MIMO Receiver test setup
Figure-4: MIMO RF Receiver test setup

Here VSG consists of baseband signal generation software, AWG and RF upconverter. The different test configurations are used as shown viz. parallel, split and combined.

Separate VSG signal outputs are given as input in parallel VSG tests. Both SDM and STBC simulation can be carried out. Fading channel simulator is used to have channel emulation effect.

Input sensitivity gain and keyhole effect testing are carried out using Split VSG configuration. STBC and SDM can not be simulated with this test configuration.

Combined VSG is used for adjacent and non-adjacent channel testing. Broadband digital pre-distortion is also done using this setup.

MIMO Receiver Measurements

Following MIMO receiver measurements are carried out during MIMO compliance testing.
• Minimum Input Level Sensitivity
• Maximum Input Level
• Adjacent Channel Rejection (ACR)
• Non-Adjacent Channel Rejection
• Clear Channel Assessment (CCA) Sensitivity

What is difference between or comparison between

Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer