Data capture and storage
When you consider the raw data that needs to be collected with a wideband measurement system that also has multi-channel capability, an eight-channel, 1 GHz bandwidth measurement can consume gigabytes of data in just one second, quickly filling disk drives. In addition, consider how to get this data from the ADC to a storage device. It's nearly impossible for the data to be captured and streamed in real-time. Disk drive manufacturers might like this because they will sell more storage, but it's just not practical. Instead, there are two other data capture-methods to consider that can reduce the amount of collected data:
- If the sounding signal is less than one transmitting period, you can capture only the effective data or only the data needed to perform the CIR calculations. This method can greatly reduce the data collection.
- Taking this one step further, you can perform the wideband measurement with real-time autocorrelation and signal processing with an onboard FPGA to produce the effective CIR data within the measurement system, now only the CIR results need to be saved. Thus, significantly saving storage space and providing the CIR results much faster.
Channel parameter estimations
Much of the research to date has focused on a single channel. MIMO (multiple input, multiple output) channels, however, introduce spatial and correlation information. The key issue with MIMO channels is how to estimate the spatial parameters. This includes parameters such as AoA (angle of arrive), AoD (angle of departure), and AS (angular spread). There are several channel parameter estimation algorithms that can be considered including beamforming based, subspace based, and ML (Maximum Likelihood) based. For consistency, coherence, and estimation performance, the ML-based estimation algorithms provide the very good performance for MIMO channel parameter estimations. Specifically, the SAGE (space-alternating generalized expectation-maximization) algorithm (ML based) with relativity low computing, is widely accepted by the research community.
Next: Calibrate and synchronize