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Lightweight Ethernet Switch

Employing Xilinx wireless connectivity IP and FPGAs enables integration of multiple devices connecting baseband channel cards to remote radio heads into a single device based I/Q switch. An integrated CPRI I/Q switch on an FPGA supports all line rates, I/Q data switching and combining, and multiple Ethernet control messaging channels and switching to allow highly flexible and granular interconnect to ease deployment, reconfiguration, and field enhancements.

Proof of Concept Summary

This Proof of Concept (PoC) design provides a six port Lightweight Ethernet Switch for use in CPRI-based wireless systems. The switch is implemented as a four port gigabit switch and a three port aggregator to minimize resource utilization. The aggregator can be scaled to support more ports, if required.

Key Features

  • Six ports consisting of
    •  Four port gigabit switch
      • Port 1 - Upstream CPRI
      • Port 2 - Local microprocessor
      • Port 3 - Debug
      • Port 4 - Aggregator/de-aggregator
  • Three port aggregator/deaggregator for downstream CPRI ports operating at 100 Mb/s maximum
  • Maximum Ethernet frame size of 2048 bytes
  • Automatic and manual address learning
  • 64 entry address table
  • 1.6 Mframes/s per port (max 6 Mframes/s)

Applications

The Lightweight Ethernet Switch is targeted at wireless systems and uses an architecture that supports a scalable number of radio connections using a port aggregator to reduce the resource requirements. A simplified application is shown in Figure 1 and consists of the following Ethernet ports:

  • One upstream CPRI link to the baseband unit
  • Three downstream CPRI links to radios
  • One external debug and control port through an external PHY
  • One internal connection to a CPU
Click to expand

Figure 1 – Typical Application System

Architecture

The Lightweight Ethernet Switch architecture is based on sharing the available bandwidth between multiple downstream (radio) links where little Ethernet traffic is required during normal operation of the system. In the PoC example the three downstream CPRI links are connected through the aggregator/de-aggregator and share a single connection to the main switch as shown in Figure 2. This enables support for an increased number of downstream links.

Figure 2 – Lightweight Ethernet Switch Architecture
Figure 2 – Lightweight Ethernet Switch Architecture

Resource Utilization

The resource utilization and approximate bandwidth available at each aggregated downstream port for selected configurations is shown in Table 1

Table 1: Resource Utlization

Configuration RAMB18s LUTs FFs Downstream
Bandwidth
6 Ports 28 4000 6000 100 Mbit/s
12 Ports 52 6000 10000 25 Mbit/s
18 Ports 60 8000 14000 10 Mbit/s

Delivery

The Lightweight Ethernet Switch PoC design is delivered as a zip file available in the Xilinx lounge (registration required). The zip file contains encrypted source for the switch and a example design delivered with the switch, demonstrating simple pattern generation and checking. In addition a test bench and implementation and simulation scripts for use in the Vivado® Design Suite are provided. The switch has a static configuration of six ports.

Verification

The IQ switch has been verified using the UVM methodology.

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