In wireless applications, a fundamental path is the Remote Radio Head (RRH) to Base Station (BTS) path. In the downlink, an analog radio signal is translated into a digital format in which it can then be processed and manipulated. In the uplink direction, the opposite processing is applied. This example design will showcase three of three of the functions that are part of these data paths: compression, mapping of IQ samples into a CPRI Frame, and a CPRI link that carries Control and IQ Payload between the RRH and the BTS. The modules/functions showcased in this design example are part of Altera's solution for wireless applications.
Arria 10 PCIe Development Kit
FMC Loopback Card
Quartus II 16.0
Arria 10 PCIe Development Kit ClockControl GUI
CPRI v6 IP License
ModelSim 10.1b or newer version
A high-level block diagram of the design is shown in Figure 1.0. This design example connects Compression/DeCompression, IQ Mapper/DeMapper, and CPRI IP modules. IQ samples are generated by Linear Feedback Shift Registers (LFSR) and are driven into the Compression Modules. After compression the IQ samples are mapped by the IQ Mapper module and are then driven into the CPRI IP. The CPRI module implements the CPRI protocol. It loads the IQ samples unto the CPRI IQ Data Plane. In this example the CPRI transmit serial link is routed back to the receive serial link, implementing an electrical serial loopback. In the receive direction (uplink), the IQ samples are extracted from the CPRI Frame by the CPRI module and are sent to the IQ DeMapper. From the DeMapper, the IQ samples go to the DeCompression modules. To show the integrity of the IQ data and the impact of compression on the IQ data, this design example uses an Error Vector Magnitude module. The uncompressed IQ Data, generated by the LFSRs, and the De-Compressed IQ Data received in the uplink direction (output of the DeCompression modules) are sent into the EVM module which calculates a difference in magnitude between the two.
Figure 1.0 High-Level Block Diagram
Direct IQ Mapper Interface
AxC0 : No Compression
AxC1 : 16:12 Compression
AxC2 : 16:10 Compression
AxC3 : 16:8 Compression
AxC4 : 16:7 Compression
AxC5 : 16:6 Compression
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Full Design Documentation
The full document can be downloaded using the following link.