CPRI
The Common Public Radio Interface, (CPRI), is an initiative to define a publicly available specification that standardizes the protocol interface between the radio equipment control (REC) and the radio equipment (RE) in wireless basestations. This allows interoperability of equipment from different vendors and preserves the software investment made by wireless service providers.
Conventional basestations are located adjacent to the antenna in a small hut at the base of the antenna tower. Finding suitable sites can be a challenge because of the footprint required for the hut, the need for structural reinforcement of rooftops, and the availability of both primary and backup power sources.
CPRI allows the use of a distributed architecture where basestations, containing the REC, are connected to remote radio heads via lossless fibre links that carry the CPRI traffic. This architecture reduces costs for service providers because only the remote radio heads containing the RE need to be situated in environmentally challenging locations. The basestations can be centrally located in less challenging locations where footprint, climate, and availability of power are more easily managed.
Figure 1 shows common CPRI network topologies.
Figure 1. CPRI Network Topologies
The CPRI specification addresses the details of the interface shown in Figure 2.
Figure 2. CPRI Interface
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As CPRI continues to evolve, implementing the link layer in an FPGA is the easiest and most flexible solution. Altera offers a number of FPGAs and ASICs with embedded transceivers that offer a high degree of programmability along with predictable latency.
Altera’s high-speed Stratix® IV GX FPGAs, HardCopy® IV GX ASICs, and Stratix II GX FPGAs, used in conjunction with a CPRI intellectual property (IP) core optimized for FPGAs, are ideal platforms for CPRI system implementation (see Table 1).
| Table 1. CPRI System Implementation |
| CPRI Line Rate (Mbps) |
Stratix IV GX FPGAs |
HardCopy IV GX ASICs |
Stratix II GX FPGAs |
| 614.4 |
 |
|
|
| 1228.8 |
|
|
|
| 2457.6 |
|
|
|
| 3072.0 |
|
|
|
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