[Ns-developers] add WIFI_PHY_STANDARD_80211p_CCH and SCH

Thu Dec 17 08:16:07 PST 2009

Ramon,

-- I suppose the EDCA parameters are open to interpretation.  It is not 100%
clear which set of values to use.  Even in 1609.4 there is not one place to
look, I had to combine information from 3 different sections.  I read in
802.11p/D9.0, section 9.1.3.1 that "When communicating data frames outside
the context of a BSS (dot11OCBEnabled is true), the EDCA parameters are the
corresponding default values or are as set by the SME in the MIB attribute
table dot11EDCATable."  The MIB attribute table found in Annex D of 1609.4
says to "See the corresponding table in IEEE 1609.4."  The table in Annex B
of 1609.4 shows aCWmin = 15 and aCWmax = 511.  The cwMin and cwMax value
equations are in the "EDCA parameter set used on the CCH/SCH" table found in
section 6.3.1/2 of 1609.4.

  Does Section 7.3.2.29, Table 7-37a in 802.11p/D9.0 mean that only one set
of EDCA parameters are used now for both CCH and SCH? 

-- Is there a way to separate the channel bandwidth from the other
parameters (slot time, cwMin, cwMAX, AIFS, EDCA parameters)?  That way a
user can specify the channel bandwidth and then add on the 802.11p
parameters.  Or do you recommend developing code to allow selection of
5Mhz_80211p, 10Mhz_80211p, and 20Mhz_80211p?

-- I originally submitted the change only for Qadhoc, but another reviewer
recommended adding the change to Qap and Qsta as well.  I agree that 802.11p
will probably be used in the Qadhoc mode, but I don't see in 802.11p/D9.0,
section 5.2.6 and 5.2.10, that QoS AP and STAs are not allowed.  The WAVE
BSS mechanism in 1609.4 section 8 has some similarities to the AP/STA model
in that announcements,  join requests and join confirms are exchanged.  So
maybe it is ok to use the AP and STA modes in 802.11p for specific cases?  I
think that would be a rare occasion.

With the standards still in draft form for 802.11p, I think the parameters
will continue to change until the actual standard is agreed upon.

Michael

From: Ramon Bauza [mailto:monbauza at gmail.com] 
Sent: Thursday, December 17, 2009 4:06 AM
To: Michael Nowatkowski
Cc: ns-developers at isi.edu
Subject: Re: [Ns-developers] add WIFI_PHY_STANDARD_80211p_CCH and SCH

Hi Michael, all,

I am sorry but so far I haven't had time to look at the patch. Some comments
below:

- I have doubts about the correct values of the EDCA parameters. I know you
have considered those specified in IEEE 1609.4-2006. However, the values
provided in the last version of the 802.11p amendment (IEEE 802.11p/D9.0 Sep
09) seem to be slightly different. For example, it does not specify anything
about modifying the standard value of cwMax and thus I assume that a value
of 1023 should be employed. What is your opinion on this?

- Another question I have is whether 802.11p is limited to 10 Mhz channels.
I know that this channel spacing it is expected to be more suitable for
highly varying environments such as the vehicular. However, according to the
amendment, there are not any restricctions on channel spacings. In fact,
802.11p provides regulatory classes for channel spacings of 5, 10 and 20
Mhz.

- I wonder whether it is necessary to include modifications for 802.11p
operation in QapWifiMac and QstaWifiMac, since a 802.11p device operates
outside the context of a BSS (no AP involved in the communciations).

Thank you for the patch.

Best regards,

Ramon.

2009/11/11 Michael Nowatkowski <nowatkom at gmail.com>

Hello,

 This change adds WIFI_PHY_STANDARD_80211p_SCH and
WIFI_PHY_STANDARD_80211p_CCH as possible choices for WifiHelper::SetStandard
(enum WifiPhyStandard standard) when using QadhocWifiMac.

http://codereview.appspot.com/152058/show

 802.11p uses 10 MHz channels, so I tried to use as much existing
WIFI_PHY_STANDARD_80211_10Mhz code as possible.  802.11p also uses the
802.11e QOS model.  The SCH follows the default EDCA parameters, but the CCH
uses a different set of parameters.  I added some lines of code to add
802.11p specifications for the service channels (SCH) and the control
channel (CCH) per IEEE 1609.4-2006, sections 6.3.1 and 6.3.2.  cwMax for
both CCH and SCH is 511, versus 1023 in other standards.

Thanks!

 Michael Nowatkowski

 I modified the following files:

src/devices/wifi/qadhoc-wifi-mac.cc -- adds case statements for the added
standards.  CCH calls a new member function, ConfigureCCHDcf, because the
CCH Dcf parameters are different from the default 10Mhz parameters, and
cwMax is 511.  SCH uses the default Dcf parameters, but cwMax is 511.

src/devices/wifi/wifi-mac.h -- adds new member function prototypes
ConfigureCCHDcf, Configure80211p_CCH() and SCH().

src/devices/wifi/wifi-mac.cc -- adds case statements for the added standards
and adds new member functions Configure80211p_CCH() and SCH(), based on
10Mhz code, modifying the SetSlot time to 16 microseconds, per IEEE
P802.11p, and ConfigureCCHDcf, based on ConfigureDcf with CCH-specific
parameters set.

src/devices/wifi/yans-wifi-phy.h -- adds prototypes Configure80211p_CCH
(void) and SCH (void)

src/devices/wifi/yans-wifi-phy.cc -- adds case statements for the added
standards and adds new member functions Configure80211p_CCH(void) and
SCH(void), based on 10Mhz code.  I left m_channelStartingFrequency = 5e3.
The actual starting frequency is at 5.860 GHz for the first CCH (channel
number 172),  but I think using the actual channel number with
SetChannelNumber will account for that (5e3 + 172*5 = 5860).

src/devices/wifi/wifi-phy-standard.h -- adds the enumeration of the CCH and
SCH.

 **The changes can be tested by modifying a few lines in
/tutorial/third.cc:

 WifiHelper wifi = WifiHelper::Default ();

 wifi.SetStandard(WIFI_PHY_STANDARD_80211p_CCH); // added this line

 wifi.SetRemoteStationManager ("ns3::AarfWifiManager");

 QosWifiMacHelper mac = QosWifiMacHelper::Default (); // changed Nqos to
Qos

 mac.SetType ("ns3::QadhocWifiMac"); // changed to QadhocWifiMac

 NetDeviceContainer staDevices;

 staDevices = wifi.Install (phy, mac, wifiStaNodes);

 mac.SetType ("ns3::QadhocWifiMac"); // changed to QadhocWifiMac

 NetDeviceContainer apDevices;

 apDevices = wifi.Install (phy, mac, wifiApNode);

-- 
--------------------------------------------------------------------------
Ramon Bauza
Ubiquitous Wireless Communications Research Laboratory
Uwicore, http://www.uwicore.umh.es <http://www.uwicore.umh.es/>  
Signal Theory and Communications Division
University Miguel Hernández (Spain)
Tel: +34 96522 2031
Fax: +34 96665 8903
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