| 3 | | |
| 4 | | == Timing == |
| 5 | | The basic packet exchange which defines the maximum throughput for CSMA is DATA-ACK-DATA. The timing of this exchange is our implementation is illustrated below. Please note the figure is ''not'' drawn to scale. |
| 6 | | |
| 7 | | [[Image(OFDMReferenceDesign/Applications/CSMA/Benchmarks/Files:csma_pktExchangeTiming.png)]] |
| 8 | | |
| 9 | | This figure assumes the following parameters: |
| 10 | | * SISO antenna configuration |
| 11 | | * 2 OFDM symbols for channel training per packet |
| 12 | | * 24 byte MAC header at QPSK (2 OFDM symbols) |
| 13 | | * Full rate modulation of QPSK (12 bytes per OFDM symbol) or 16-QAM (24 bytes per OFDM symbol) |
| 14 | | * 1484 byte payloads (1470 byte IP datagram + 14 byte Ethernet header) |
| 15 | | |
| 16 | | This figure includes a random backoff period imposed after a node receives an ACK. This period is designed to prevent two fully-backlogged nodes from simultaneously attempting to transmit a new packet immediately after the previous DATA-ACK exchange completes. The backoff imposes a wait of an integral number of slot durations (a slot is 22µs in v14), with the slot count drawn randomly from ![0,7]. |
| 17 | | |
| 18 | | Given this timing, the average minimum period for transmitting a new DATA packet is 1263µs (for QPSK full rate) or 775µs (for 16-QAM full rate), implying a peak data throughput of 9.31Mbps for QPSK and 15.2Mbps for 16-QAM. |
