OFDM Reference Design - Wireless/Wired Bridge

This simple application uses the OFDM Reference Design to build a wired-to-wireless bridge. It utilizes two WARP nodes, each connected via Ethernet to a separate PC. Every packet received on the WARP node's Ethernet interface is transmitted over the air. Every packet received over the air is copied to the node's Ethernet interface. This bridging "tricks" the two PCs into believing they are connected directly over Ethernet.

In this application, the WARP nodes have no MAC or IP addresses. Both nodes run the same program. There is no medium access control protocol; every packet is transmitted wirelessly immediately, and no retransmissions or ACKs are generated.

Requirements

• 2 WARP SISO or MIMO kits
• 2 PCs with Ethernet interfaces

Setup

1. Connect each WARP node directly to the Ethernet interface of the PCs
2. Configure the PC Ethernet interfaces with IP address on the same subnet (10.0.0.1 and 10.0.0.2, for example)
3. Generate the FPGA configuration file for the design using the OFDM Reference Design project and the noMAC software project
4. Configure both WARP nodes using the same download.bit
5. When it's working, the PCs will be able to ping each other, stream video (using VLC, for example), or any other point-to-point network application

Code

The code for this application is provided in noMAC.c​. The default OFDM Reference Design project includes noMAC as a software project.

Timing

The values below correspond to OFDM Reference Design v14

The timing of noMac is defined by the minimum delay between sequential packet transmissions. The idle time between transmissions is imposed by packet and state handling in the noMac application. The figure below illustrates the timing of bak-to-back packet transmissions by noMac.

This figure assumes the following parameters:

• SISO antenna configuration
• 2 OFDM symbols for channel training per packet
• 24 byte MAC header at QPSK (2 OFDM symbols)
• Full rate modulation of QPSK (12 bytes per OFDM symbol) or 16-QAM (24 bytes per OFDM symbol)
• 1484 byte payloads (1470 byte IP datagram + 14 byte Ethernet header)

Given this timing, the minimum period for transmitting a new full-length packet is XXµs (for QPSK full rate) or XXµs (for 16-QAM full rate), implying a peak data throughput of 9.31Mbps for QPSK and 15.2Mbps for 16-QAM.

Benchmarks

Detailed benchmarks are available for the latest (v14) reference design's noMac implementation.