= Investigating Physical Carrier Sensing in the DCF with Multiple Traffic Flows =

The purpose of the 802.11 Distributed Coordination Function (DCF) is to allow multiple traffic flows to contend for a shared wireless medium. In this application note we investigate how the Mango 802.11 Reference Design behaves when subjected to multiple traffic flows. This note provides a case study on how the design's experiments framework can be used to control and analyze the performance of 802.11 Reference Design nodes.


=== Experimental Setup ===

The experiments described below used 3 Mango WARP v3 kits, each running the [wiki:../../../Changelog#a0.91BetaRelease 802.11 Reference Design (version v0.91)].

Each node's RF interface was connected to an antenna with a toroidal pattern with 5dBi gain in all horizontal directions ([http://www.l-com.com/wireless-antenna-24-ghz-7-dbi-desktop-omni-antenna-4ft-sma-male-connector L-Com RE07U-SM]).

The nodes were indoors in a small office environment with limited mobility.

||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:experimental_setup_photo.jpg, width=600)]]  ||
||  '''Experimental Setup'''  ||

We use 4 traffic flows in our experiments:
 * '''Flow 1:''' Backlogged traffic from AP to STA_1
 * '''Flow 2:''' Backlogged traffic from AP to STA_2
 * '''Flow 3:''' Backlogged traffic from STA_1 to AP
 * '''Flow 4:''' Backlogged traffic from STA_2 to AP

 [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:experimental_flows.png, width=600)]] 

The colors in the figure above are used throughout this app note to denote each flow.

== Experiment 1: Physical Carrier Sensing Enabled ==

The first experiment enables physical carrier sensing at all 3 nodes. This experiment highlights the expected behavior of the DCF in an environment with heavy contention for the medium.

=== Experiment Details ===
 * Packet Length: 1400 byte payloads (1428 bytes OTA with MAC header and FCS)
 * PHY Rate: 18 Mbps (QPSK, code rate 3/4)
 * Tx Power: -5 dBm
 * Trial Duration: 300 seconds
 * 2.4GHz channel 1
 * Physical Carrier Sensing Threshold: 250/1023 (approximately -70 dBm)

=== Results ===


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_xput_vs_time.png, width=600)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_xput_hist.png, width=600)]]  ||
 ||  '''Throughput vs. Time'''  || '''Throughput Histogram'''  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_pow_vs_time.png, width=600)]]  ||
||  '''Rx Power vs. Time''  ||

||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_cw_vs_time.png, width=600)]]  ||
||  '''Rx Power vs. Time''  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_coll_flow_1.png, width=300)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_coll_flow_2.png, width=300)]]  ||
||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_coll_flow_3.png, width=300)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_coll_flow_4.png, width=300)]]  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_collision_retx.png, width=600)]]  ||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:cs_1sec.png, width=600)]]  ||
||  '''Collisions (Zoomed)'''  ||  '''Collisions (1 second)'''  ||

== Experiment 2: Disabled Physical Carrier Sensing ==

=== Experiment Details ===
 * Packet Length: 1400 byte payloads (1428 bytes OTA with MAC header and FCS)
 * PHY Rate: 18 Mbps
 * Tx Power: -5 dBm
 * Trial Duration: 300 seconds
 * Channel 1
 * Physical Carrier Sensing Threshold: 1023/1023


=== Results ===


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_xput_vs_time.png, width=600)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_xput_hist.png, width=600)]]  ||
 ||  '''Throughput vs. Time'''  || '''Throughput Histogram'''  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_pow_vs_time.png, width=600)]]  ||
||  '''Rx Power vs. Time''  ||

||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_cw_vs_time.png, width=600)]]  ||
||  '''Rx Power vs. Time''  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_coll_flow_1.png, width=300)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_coll_flow_2.png, width=300)]]  ||
||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_coll_flow_3.png, width=300)]]  || [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_coll_flow_4.png, width=300)]]  ||


||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_collisions_zoom.png, width=600)]]  ||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:no_cs_1sec.png, width=600)]]  ||
||  '''Collisions (Zoomed)'''  ||  '''Collisions (1 second)'''  ||

== Resources ==

Links to the data sets and experiment scripts used to perform this study will be posted shortly.