To maximize throughput and to make efficient use of the available spectrum, wireless communications systems use multiple-input multiple-output (MIMO) operations and RF beamforming. The Analog Devices® FMCOMMS5 radio hardware combines two AD9361 chips to satisfy these requirements. Using the FMCOMMS5 radio hardware, you can develop and implement larger MIMO communications systems of up to four transmit and receive channels.
Multi-chip synchronization is required when you use channels from different chips driven by different timing sources. It comprises baseband synchronization and RF (phase) synchronization. For more information, see Synchronizing multiple AD9361 devices and the Baseband Synchronization section of the AD9361 User Guide.
Baseband synchronization involves aligning the baseband sampling and data clocks of each chip. When using the FMCOMMS5 System objects and blocks, this synchronization is performed automatically when required.
RF synchronization ensures that the internal RF oscillators of each chip are aligned. Since the AD9361 chip does not include internal RF synchronization, some external means must be provided. For example, you can achieve RF synchronization by measuring the carrier phase difference of the internal local oscillators (LOs) and correcting the resulting samples. For an example, see the Direction of Arrival Estimation Using the MUSIC Algorithm and Analog Devices FMCOMMS5 example. The example transmits a 10 kHz signal from a suitable transmitter and calculates the direction of arrival of the signal by using functionality from the Phase Array System Toolbox™. This example shows how to implement RF synchronization at the application level, where each sample is corrected with the measured phase offset.