How to get signal strength

Hi,
my problem is:
I’ve got a simple senario: One acces point and one mobile node. The mobile node first is going into the radius of the acess point and then out of the radius. Now I want to know, the signal strength of the mobile node, when the link is going down.
In tcl I haven’t found a solution. I thougth there is something easy like “set strength [$node set signalstrength]” but it seems there isn’t such a think… 🙁
Because of that I go to the C++-Source-Code. After a little bit of searching I found the file “wireless-phy.cc” and there the function “sendUp”. I think there the variable “Pr” is the signal strength (because later in the function “Pr” is compared with “CSTresh_” and “RXTresh_” wich a used to simulated if a paket is recieved correct or not).
But now I had the problem that “Pr” alway had got the same value and I don’t know why. I went back to my tcl file and play a little bit with my settings. As I changed “set opt(prop) Propagation/TwoRayGround” to “set opt(prop) Propagation/FreeSpace” and start a simulation, I’ve got an output on my console like “time: 0.008566: d: 31.622777, Pr: 2.949347e-09” (and there the Pr is chaniging!). First I was wondered about that, but then I looked into the file “propagation.cc” and there I found in the function Pr() “printf(“%lf: d: %lf, Pr: %en”, Scheduler::instance().clock(), d, Pr);”. So I copy that and put it into the file “tworayground.cc” at the same position (the function Pr) and now it seems to work.
But I always have a question: Why is Pr in “tworayground” changing and in wireless-phy”
not? And is it the correct position to read out the signal strength?
I’ve alway looked into the file “mac-802_11.cc” and the function “send” but there “Pr” also seems not to work correct (there it is alwas “1.600278e-02” or “-1″…) What do I have to change?
And a last thing: I want to have the signal strength in dBm. Because of that I made “10*log10(Pr)” but I’m not sure if I have to use “10*log10(Pr/0.001)” instead (because 1mW is the referece value for dBm and I don’t know if it is include in Pr or not…)
I hope anybody can help me with my problem(s). Thanks!
Greets Daniel Rother

PS: Here is my tcl-Code. Maybe there is just a simple error…:
# ======================================================================
# Define options
# ======================================================================
set opt(chan) Channel/WirelessChannel ;# channel type
#set opt(prop) Propagation/FreeSpace ;# radio-propagation model
set opt(prop) Propagation/TwoRayGround ;
set opt(netif) Phy/WirelessPhy ;# network interface type
set opt(mac) Mac/802_11 ;# MAC type
set opt(ifq) Queue/DropTail/PriQueue ;# interface queue type
set opt(ll) LL ;# link layer type
set opt(ant) Antenna/OmniAntenna ;# antenna model
set opt(ifqlen) 50 ;# max packet in ifq
set opt(nn) 3 ;# number of mobilenodes
set opt(adhocRouting) DSDV ;# routing protocol

set opt(x) 300 ;# x coordinate of topology
set opt(y) 150 ;# y coordinate of topology

set opt(apX) 50 ;# x coordinate of the AP
set opt(apY) 50 ;# y coordinate of the AP

set opt(nodeX) 20 ;# start x coordinate of the wireless node
set opt(nodeY) 40 ;# start y coordinate of the wireless node
set opt(nTarX) 250 ;# target x coordinate of the node
set opt(nTarY) 40 ;# target y coordinate of the node
set opt(nSpeed) 5 ;# speed of the node

set opt(seed) 0.0 ;# seed for random number gen.
set opt(ftpstart) 5
set opt(dist) 200
set opt(stop) [expr $opt(dist) / $opt(nSpeed) + 10] ;# time to stop simulation
# time from start to target of the node

set num_wired_nodes 0
set num_bs_nodes 1

Antenna/OmniAntenna set Gt_ 1
Antenna/OmniAntenna set Gr_ 1

Mac/802_11 set basicRate_ 1Mb
Mac/802_11 set dataRate_ 11Mb

Phy/WirelessPhy set L_ 1.0
Phy/WirelessPhy set freq_ 2.472e9
Phy/WirelessPhy set bandwidth_ 11Mb ;

Phy/WirelessPhy set Pt_ 0.031622777
Phy/WirelessPhy set CPTresh_ 10.0
Phy/WirelessPhy set CSTresh_ 5.011872e-12
Phy/WirelessPhy set RXTresh_ 5.82587e-09

# ============================================================================
# create simulator instance
set ns_ [new Simulator]

# Open tracefiles
$ns_ use-newtrace
set tracefd [open out.tr w]
set namtrace [open out.nam w]
set nodetr [open nodetrace.tr w]
$ns_ trace-all $tracefd
$ns_ namtrace-all-wireless $namtrace $opt(x) $opt(y)

proc record {} {
global node nodetr sink
#Get an instance of the simulator
set ns_ [Simulator instance]
#Set the time after which the procedure should be called again
set time 0.5
#How many bytes have been received by the traffic sinks?
set bw [$sink set bytes_]
#Get the current time
set now [$ns_ now]

#Get the signal strength
# is there anythong I can put here?

# just for test…
#Calculate the bandwidth (in MBit/s) and write it to the files
puts $nodetr “$now [expr $bw/$time*8/1000000]”
#Reset the bytes_ values on the traffic sinks
$sink set bytes_ 0
#Re-schedule the procedure
$ns_ at [expr $now+$time] “record”
}

# ============================================================================
# check for boundary parameters and random seed
if { $opt(x) == 0 || $opt(y) == 0 } {
puts “No X-Y boundary values given for wireless topologyn”
}
if {$opt(seed) > 0} {
puts “Seeding Random number generator with $opt(seed)n”
ns-random $opt(seed)
}

# set up for hierarchical routing
$ns_ node-config -addressType hierarchical
AddrParams set domain_num_ 1 ;# number of domains
lappend cluster_num 1 ;# number of clusters in each domain
AddrParams set cluster_num_ $cluster_num
lappend eilastlevel 2 ;# number of nodes in each cluster
AddrParams set nodes_num_ $eilastlevel ;# of each domain

# Create topography object
set topo [new Topography]

# define topology
$topo load_flatgrid $opt(x) $opt(y)

# create God
create-god [expr $opt(nn) + $num_bs_nodes]

# Create channel
set chan_1_ [new $opt(chan)]

# configure for base-station node
$ns_ node-config -mobileIP ON
-adhocRouting $opt(adhocRouting)
-llType $opt(ll)
-macType $opt(mac)
-ifqType $opt(ifq)
-ifqLen $opt(ifqlen)
-antType $opt(ant)
-propType $opt(prop)
-phyType $opt(netif)
-channel $chan_1_
-topoInstance $topo
-wiredRouting ON
-agentTrace ON
-routerTrace OFF
-macTrace OFF

#create base-station node
set BS [$ns_ node 0.0.0]
$BS random-motion 0 ;# disable random motion

#provide some co-ord (fixed) to base station node
$BS set X_ $opt(apX)
$BS set Y_ $opt(apY)
$BS set Z_ 0.0

# create mobilenodes in the same domain as BS
#configure for mobilenodes
$ns_ node-config -wiredRouting OFF

# configure for mobilehost

set node [ $ns_ node 0.0.1 ]
set node_(0) $node
$node base-station [AddrParams addr2id
[$BS node-addr]]

$node set X_ $opt(nodeX)
$node set Y_ $opt(nodeY)
$node set Z_ 0

# setup TCP connections
set tcp [new Agent/TCP]
$tcp set class_ 2
set sink [new Agent/TCPSink]
$ns_ attach-agent $BS $tcp
$ns_ attach-agent $node $sink
$ns_ connect $tcp $sink
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ns_ at $opt(ftpstart) “$ftp start”

# Define initial node position in nam

#$ns_ initial_node_pos $node 20

# Start movement
$ns_ at 10.0 “$node setdest $opt(nTarX) $opt(nTarY) $opt(nSpeed)”

# Tell all nodes when the simulation ends
$ns_ at 0.0 “record”
$ns_ at $opt(stop).0 “$node reset”
$ns_ at $opt(stop).0 “$BS reset”

$ns_ at $opt(stop).0001 “stop”
$ns_ at $opt(stop).0002 “puts “NS EXITING…” ; $ns_ halt”

proc stop {} {
global ns_ tracefd namtrace
$ns_ flush-trace
close $tracefd
close $namtrace
}

# informative headers for Node-Tracefile
puts $nodetr “time Datarate”

puts “Starting Simulation…”
$ns_ run