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| [[Category: Development Team Research Pages]] | | [[Category: Development Team Research Pages]][[Category: Johann's Research Pages]] |
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| I'm not sure if my stuff is really research, but this is some of the stuff that I'm busy with:
| | migrated to wireless dev |
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| == High Performance Node - WEP/WPA ==
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| One of the requirements of the High Performance Node is to have WEP or WPA enabled between the wireless links of the mesh nodes. This is one of the functionalities that we would like to sort out before we install any of the nodes in the field. It's very difficult to change the encryption mode after an installation because the mesh nodes will lose connectivity if one node is upgraded to use WEP, while another is still using older software without WEP.
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| WEP and WPA are both methods to enable the encryption of data that it is send over the air. WEP (Wired equivalence privacy) is an older standard and it makes use of a WEP encryption engine while the newer WPA standard added the use of an AES encryption engine. WEP encryption has some security flaws embedded into the protocol and there are several tools available on the Internet that can crack WEP keys. These tools are more effective with the cracking of 64bit WEP keys than with 128bit keys and they require a large amount of captured data and processing power to crack a key. Note that not all WEP keys can be cracked, but only weak keys and that flaw was addressed and fixed by WPA.
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| Wireless adapters on Unix Systems can operate in three different modes: Client, Hostap (Access Point) and Adhoc mode. Most of the implementations of wireless (802.11) networks are based on a model where there is one Access Point with several wireless clients attached to to it.
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| http://wirelessafrica.meraka.org.za/wiki/images/e/ec/AP-client.png
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| Wireless Mesh networks make use of the less tested Adhoc mode of 802.11.
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| http://wirelessafrica.meraka.org.za/wiki/images/2/26/Adhoc.png
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| WEP and WPA requires a couple of kld's to be loaded before they can be configured. The following kld's should be added to loader.conf
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| wlan_acl_load="YES"
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| wlan_amrr_load="YES"
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| wlan_ccmp_load="YES"
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| wlan_tkip_load="YES"
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| wlan_wep_load="YES"
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| wlan_xauth_load="YES"
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| ==== WEP ====
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| Enable and test WEP in Adhoc mode on the HPN.
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| WEP makes use of a single PSK that needs to be configured on all the wireless nodes. Any node or wireless device that is configured with this PSK will have the capability to crypt and decrypt these wireless packets. There are two methods to configure WEP in FreeBSD. You can use either use ifconfig directly or you can make use of the WPA supplicant utility.
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| ifconfig e.g.
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| mesh-9e69:~ # ifconfig ath0 10.10.1.2/24 wep deftxkey 1 wepkey 128bitwepison
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| mesh-9e69:~ # ifconfig ath0
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| ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
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| ether 00:80:48:50:9e:69
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| inet6 fe80::280:48ff:fe50:9e69%ath0 prefixlen 64 scopeid 0x1
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| inet6 fd9c:6829:597c:20:280:48ff:fe50:9e69 prefixlen 64
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| inet6 fd9c:6829:597c:20:: prefixlen 64 anycast
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| inet 10.10.1.2 netmask 0xffffff00 broadcast 10.10.1.255
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| media: IEEE 802.11 Wireless Ethernet autoselect mode 11g <adhoc>
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| status: associated
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| ssid ptamesh channel 13 (2472 Mhz 11g) bssid 56:e5:be:30:14:5a
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| authmode OPEN privacy ON deftxkey 1 wepkey 1:104-bit txpower 31.5
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| scanvalid 60 bgscan bgscanintvl 300 bgscanidle 250 roam:rssi11g 7
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| roam:rate11g 5 protmode CTS burst
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| Test configuration:
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| Host A ----- wep ------- Host B ----- wep Host C
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| Enable WEP on three mesh nodes and test connectivity.
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| mesh-9e69:~ # ping6 ff02::1%ath0
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| 16 bytes from fe80::280:48ff:fe50:9e69%ath0, icmp_seq=87 hlim=64 time=2.122 ms
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| 16 bytes from fe80::280:48ff:fe50:9ddd%ath0, icmp_seq=87 hlim=64 time=5.625 ms(DUP!)
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| 16 bytes from fe80::280:48ff:fe50:9a44%ath0, icmp_seq=87 hlim=64 time=32.358 ms(DUP!)
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| Everything seems to work fine (as expeted) with WEP enabled in the mesh.
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| '''WPA'''
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| WPA was designed to work in an environment where you have one AP and several clients and not for Adhoc (mesh) networks. On the AP you have the Authenticator software and on the client you have the supplicant software. This means that if one would like to use WPA to it's full then every mesh node needs to be an Authenticator for all the other nodes it can see, as well as a supplicant for every node it can see. According to the WPA design document http://wirelessafrica.meraka.org.za/wiki/images/3/39/Wpa_supplicant-devel-04.pdf one can use WPA in Adhoc mode only in a static way with PSK's:
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| IEEE 802.11 operation mode (Infrastucture/IBSS).
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| 0 = infrastructure (Managed) mode, i.e., associate with an AP.
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| 1 = IBSS (ad-hoc, peer-to-peer)
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| Note: IBSS can only be used with key_mgmt NONE (plaintext and static WEP) and key_mgmt=WPA-
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| NONE (fixed group key TKIP/CCMP). In addition, ap_scan has to be set to 2 for IBSS. WPA-None requires
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| following network block options: proto=WPA, key_mgmt=WPA-NONE, pairwise=NONE, group=TKIP
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| (or CCMP, but not both), and psk must also be set (either directly or using ASCII passphrase).
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| This is methods is very similar to the way that WEP is being used. This means the the only advantage of using WPA over WEP is that one can make use of the AES encryption engine that comes with WPA. Please note that with this mode of WPA and with WEP that anyone can decrypt the data being send over the air if they get hold of the mesh-wide PSK that is configured on every node in the network. If security is of importance them end users should consider the use of point-to-point security mechanisms like VPN's.
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| The configuration of WPA is not supported in command line mode, but only with the wpa_supplicant software. This is an example of a wpa_supplicant.conf file to enable WPA in Adhoc mode:
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| ap_scan=2
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| #
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| network={
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| ssid="ptamesh"
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| # Channel 13 : 2472 Mhz 11g
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| frequency=2472
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| mode=1
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| proto=WPA
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| key_mgmt=WPA-NONE
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| pairwise=NONE
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| group=TKIP
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| psk="mesh-ipv6"
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| }
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| To start the WPA software during boot-up one needs to add WPA to the ifconfig line in rc.conf. E.g.
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| ifconfig_ath0="WPA 10.10.1.1/24 mode 11g mediaopt adhoc channel 13 ssid ptamesh"
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| Test configuration:
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| Host A ----- wep ------- Host B ----- wep Host C
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| Unfortunately WPA did not work as easy as WEP, so it's off to debugging.
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| Starting wpa_supplicant in the foreground with debugging enabled. E.g
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| wpa_supplicant -d -i ath0 -c /etc/wpa_supplicant.conf
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| The debugging output shows that something happens that initiates a wlan scan operation, while the card is in Adhoc mode. This should not happen and wpa_supplicant software never completes the configuration due to this error.
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| mesh-9ddd:~ # wpa_supplicant -d -i ath0 -c /etc/wpa_supplicant.conf
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| Initializing interface 'ath0' conf '/etc/wpa_supplicant.conf' driver 'default'
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| ctrl_interface 'N/A' bridge 'N/A'
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| Configuration file '/etc/wpa_supplicant.conf' -> '/etc/wpa_supplicant.conf'
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| Reading configuration file '/etc/wpa_supplicant.conf'
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| ap_scan=2
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| Priority group 0
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| id=0 ssid='ptamesh'
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| Initializing interface (2) 'ath0'
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| EAPOL: SUPP_PAE entering state DISCONNECTED
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| EAPOL: KEY_RX entering state NO_KEY_RECEIVE
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| EAPOL: SUPP_BE entering state INITIALIZE
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| EAP: EAP entering state DISABLED
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| EAPOL: External notification - portEnabled=0
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| EAPOL: External notification - portValid=0
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| Own MAC address: 00:80:48:50:9d:dd
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| wpa_driver_bsd_set_wpa: enabled=1
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| wpa_driver_bsd_set_wpa_internal: wpa=3 privacy=1
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| wpa_driver_bsd_del_key: keyidx=0
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| wpa_driver_bsd_del_key: keyidx=1
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| wpa_driver_bsd_del_key: keyidx=2
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| wpa_driver_bsd_del_key: keyidx=3
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| wpa_driver_bsd_set_countermeasures: enabled=0
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| wpa_driver_bsd_set_drop_unencrypted: enabled=1
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| Setting scan request: 0 sec 100000 usec
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| Added interface ath0
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| State: DISCONNECTED -> SCANNING
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| Trying to associate with SSID 'ptamesh'
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| Cancelling scan request
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| WPA: clearing own WPA/RSN IE
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| Automatic auth_alg selection: 0x1
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| wpa_driver_bsd_set_auth_alg alg 0x1 authmode 1
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| WPA: No WPA/RSN IE available from association info
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| WPA: Set cipher suites based on configuration
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| WPA: Selected cipher suites: group 8 pairwise 1 key_mgmt 16 proto 1
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| WPA: clearing AP WPA IE
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| WPA: clearing AP RSN IE
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| WPA: using GTK TKIP
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| WPA: using PTK NONE
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| WPA: using KEY_MGMT WPA-NONE
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| WPA: Set own WPA IE default - hexdump(len=24): dd 16 00 50 f2 01 01 00 00 50
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| f2 02 01 00 00 50 f2 00 01 00 00 50 f2 00
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| No keys have been configured - skip key clearing
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| wpa_driver_bsd_set_key: alg=TKIP addr=ff:ff:ff:ff:ff:ff key_idx=0 set_tx=1
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| seq_len=6 key_len=32
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| wpa_driver_bsd_set_drop_unencrypted: enabled=1
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| State: SCANNING -> ASSOCIATING
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| wpa_driver_bsd_associate: ssid 'ptamesh' wpa ie len 24 pairwise 0 group 2 key
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| mgmt 4
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| ioctl[SIOCS80211, op 22, len 24]: Invalid argument
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| Association request to the driver failed
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| wpa_driver_bsd_set_key: alg=TKIP addr=ff:ff:ff:ff:ff:ff key_idx=0 set_tx=1
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| seq_len=6 key_len=32
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| Cancelling authentication timeout
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| State: ASSOCIATING -> COMPLETED
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| CTRL-EVENT-CONNECTED - Connection to 00:00:00:00:00:00 completed (auth) [id=-1
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| id_str=]
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| EAPOL: External notification - portControl=ForceAuthorized
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| Next was to install fresh copy of the FreeBSD src code onto my PC. I found the wpa_supplicant source code under /usr/src/usr.sbin/wpa/wpa_supplicant/driver_freebsd.c Build a new driver from source code and run it on a router. After that I've added in a lot of printf statements to trace how the driver works and to locate the code that puts the wifi card in scanning mode. In the end I found out that wpa_supplicant driver did not put the card in scanning mode, but it somehow caused the 802.11 stack to start the scanning. Unfortunately I don't know enough about the 802.11 code in FreeBSD to do any mode debugging. I've send a mail about the problem to one of the FreeBSD mailing lists and the originator of most of the 802.11 code in FreeBSD (Sam Leffler) said I must log a problem report. So I logged a problem report with FreeBSD and now we have to wait and see if someone to take responsibility to fix this problem. More information on the problem report can be found at: http://www.freebsd.org/cgi/query-pr.cgi?pr=126822
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| For now I recommend that we make use of WEP instead of WPA in our implementation as it is working and there isn't such a big advantage in using WPA over WEP in this mode except for the encryption algorithm that changes from WEP to AES.
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| == Voip - IP04 ==
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| == High performance node - Antenna calculations ==
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| Every HP-node has two 5.15-5.6 GHz antennas. The one as a build in patch antenna and the other is an 5.1-5.8 GHz omni-directional antenna. The idea is that the patch antenna of a node will either be aligned to the omni or the patch antenna of another node. The following calculations is to get an feeling of what distances should be possible between these antennas.
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| South African Wifi channels:
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| Channel 1 : 2412 Mhz 11g Channel 48 : 5240 Mhz 11a
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| Channel 2 : 2417 Mhz 11g Channel 52 : 5260* Mhz 11a
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| Channel 3 : 2422 Mhz 11g Channel 56 : 5280* Mhz 11a
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| Channel 4 : 2427 Mhz 11g Channel 60 : 5300* Mhz 11a
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| Channel 5 : 2432 Mhz 11g Channel 64 : 5320* Mhz 11a
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| Channel 6 : 2437 Mhz 11g Channel 100 : 5500* Mhz 11a
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| Channel 7 : 2442 Mhz 11g Channel 104 : 5520* Mhz 11a
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| Channel 8 : 2447 Mhz 11g Channel 108 : 5540* Mhz 11a
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| Channel 9 : 2452 Mhz 11g Channel 112 : 5560* Mhz 11a
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| Channel 10 : 2457 Mhz 11g Channel 116 : 5580* Mhz 11a
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| Channel 11 : 2462 Mhz 11g Channel 120 : 5600* Mhz 11a
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| Channel 12 : 2467 Mhz 11g Channel 124 : 5620* Mhz 11a
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| Channel 13 : 2472 Mhz 11g Channel 128 : 5640* Mhz 11a
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| Channel 36 : 5180 Mhz 11a Channel 132 : 5660* Mhz 11a
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| Channel 40 : 5200 Mhz 11a Channel 136 : 5680* Mhz 11a
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| Channel 44 : 5220 Mhz 11a Channel 140 : 5700* Mhz 11a
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| HP-Node detailed specs: http://wirelessafrica.meraka.org.za/wiki/images/0/07/WLAN-A0033.pdf
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| Pigtail detail specs: http://wirelessafrica.meraka.org.za/wiki/images/0/0a/Ca178_cable_assemblies_datasheet.pdf
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| Wireless adapter detail specs: http://wirelessafrica.meraka.org.za/wiki/images/2/21/Wlm54sag23.pdf
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| Node specs summary:
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| Patch antenna - 21-23 dBi, 16 deg H, 11 deg V, 5.15 -5.6 GHz
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| 5Ghz Omni antenna - 8-11 dBi, 360 deg H, 10 deg V, 5.1 - 5.85 GHz
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| 2.4Ghz Omni antenna - 7.5-8.5 dBi, 360 deg H, 12 deg V, 2.4 - 2.5 GHz
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| 30mm U.FL-SMA pigtail - RG178 cable insertion loss, 2.4 GHZ = -1.1dB, 5.6 GHz = -2dB
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| Compex WLM54AG23 adapter - IEEE 802.11a/b/g (2.4/5GHz)
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| - AR5413/5414(AR5006X/XS) Atheros Chipset
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| - RECEIVER SENSITIVITY 802.11a -
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| -90 dBm @ 6Mbps
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| -70 dBm @ 54Mbps
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| - OUTPUT POWER 802.11a
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| 23dBm @ 6-24Mbps
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| 22dBm @ 36Mbps
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| 19dBm @ 48Mbps
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| 17dBm @ 54Mbps
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| I could not find any receive sensitivity info for ranges between 6Mbps and 54Mbps for the WLM54AG23. The closest I could find was the specs of another manufacturer card, using the same Atheros chipset as the WLM54AG23. Here is the receive sensitivity info for a WMIA-166AG Dual-Band miniPCI module (802.11a/g)
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| Nominal Temp Range:
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| 6Mbps 10-5 BER @ -90 dBm, typical
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| 9Mbps 10-5 BER @ -89 dBm, typical
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| 12Mbps 10-5 BER @ -88 dBm, typical
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| 18Mbps 10-5 BER @ -86 dBm, typical
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| 24Mbps 10-5 BER @ -82 dBm, typical
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| 36Mbps 10-5 BER @ -78 dBm, typical
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| 48Mbps 10-5 BER @ -72 dBm, typical
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| 54Mbps 10-5 BER @ -68 dBm, typical
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| The WLM54AG23 is not the best wifi adapter in the market, but it gives a good compromise between price vs performance. If one need to push the limits of a specific link then I would probable select the SR5 from Ubiquity. They have excellent TX power and RX sensitivity.
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| There are lots of wifi/antenna/distance calculators available on the WEB. Most of these calculators cannot calculate the max distance for a link, you have to specify the distance and it will calculate you dBm margin. Links to a couple of Wifi/antenna/distance calculators:
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| http://www.radiolabs.com/stations/wifi_calc.html
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| http://www.zytrax.com/tech/wireless/calc.htm
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| http://www.widgetbox.com/widget/wifi-link-calculator
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| http://www.wifiextreme.com.au/index.php?main_page=page_5
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| http://www.rflinx.com/help/calculations
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| http://www.olotwireless.net/castella/radio.htm
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| Here are some formulas use to calculate a link budget:
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| Free space loss = 36.56 + 20Log10(Frequency) + 20Log10(Dist in miles)
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| mW to dBm = 10Log10(milliWatts) + 30
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| dBm to mW = 10(dBm/10)
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| RX Power = Margin - RX sensitivity
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| Theoretical margin = TX power budget + RX power budget - free space loss
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| SAD factor = Theoretical margin/TX power budget * 100 and shows the percentage of spare power on transmission.
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| (Free Space Loss) = 92.5 + (20 Log fequency) + (20 log km distance)
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| Free space loss @ 5400GHz:
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| 1km = -107.07dB 11km = -128.028dB
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| 2km = -113.09dB 12km = -128.784dB
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| 3km = -116.61dB 13km = -129.479dB
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| 4km = -119.11dB 14km = -130.123dB
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| 5km = -121.05dB 15km = -130.722dB
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| 6km = -122.63dB 16km = -131.282dB
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| 7km = -123.97dB 17km = -131.809dB
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| 8km = -125.13dB 18km = -132.305dB
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| 9km = -126.15dB 19km = -132.775dB
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| 10km = -127.07dB 20km = -133.221dB
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| The following are the minimum and maximum link calculations for our HPNode with a 5Ghz patch to omni link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.
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| Patch - Omni:
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| Min link distance @ 54Mbps 0.9km: Max link distance @ 54Mbps 1.55km:
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| patch min = 21dBi patch max = 23dBm
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| omni min = 8dBi omni max = 11dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 17dBm TX power = 17dBm
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| RX sensitivity = -70dBm RX sensitivity = -70dBm
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| Free space loss = -106dB Free space loss = -111dB
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| link margin = 6dB link margin = 6dB
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| Min link distance @ 24Mbps 6.9km: Max link distance @ 24Mbps 12.3km:
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| patch min = 21dBi patch max = 23dBm
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| omni min = 8dBi omni max = 11dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 23dBm TX power = 23dBm
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| RX sensitivity = -82dBm RX sensitivity = -82dBm
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| 34km free space = -124dB Free space loss = -129dB
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| link margin = 6dB link margin = 6dB
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| Min link distance @ 6Mbps 17km: Max link distance @ 6Mbps 30.9km:
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| patch min = 21dBi patch max = 23dBm
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| omni min = 8dBi omni max = 11dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 23dBm TX power = 23dBm
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| RX sensitivity = -90dBm RX sensitivity = -90dBm
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| 34km free space = -132dB Free space loss = -137dB
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| link margin = 6dB link margin = 6dB
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| The following are the minimum and maximum link calculations for our HPnodes with a 5Ghz patch to patch link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.
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| Patch - Patch:
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| Min link distance @ 54Mbps 3.9km: Max link distance @ 54Mbps 6km:
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| patch min = 21dBi patch max = 23dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 17dBm TX power = 17dBm
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| RX sensitivity = -70dBm RX sensitivity = -70dBm
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| Free space loss = -119dB Free space loss = -123dB
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| link margin = 6dB link margin = 6dB
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| Min link distance @ 24Mbps 30.9km: Max link distance @ 24Mbps 38.9km:
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| patch min = 21dBi patch max = 23dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 23dBm TX power = 23dBm
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| RX sensitivity = -82dBm RX sensitivity = -82dBm
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| Free space loss = -137dB Free space loss = -139dB
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| link margin = 6dB link margin = 6dB
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| Min link distance @ 6Mbps 77.6km: Max link distance @ 6Mbps 123km:
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| patch min = 21dBi patch max = 23dBm
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| pigtail = -2dBm pigtail = -2dBm
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| TX power = 23dBm TX power = 23dBm
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| RX sensitivity = -90dBm RX sensitivity = -90dBm
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| Free space loss = -145dB Free space loss = -149dB
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| link margin = 6dB link margin = 6dB
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