How to Implement Network Spatial Modulation in NS2

To implement Spatial Modulation (SM) in NS2, we need to replicate a system in which the multiple antennas are used, and the information is routed using both the antenna index (spatial dimension) and the modulated symbols (traditional modulation).

Spatial modulation utilizes solitary one antenna to route at a given time that creating it energy-efficient and mitigating an inter-antenna interference. The antenna index itself carries part of the information that adds a new dimension to the transmitted data.

Here’s how we can simulate Network Spatial Modulation in NS2:

Step-by-Step Implementation:

  1. Understanding Spatial Modulation (SM)
  • In spatial modulation, only one antenna is activated during each transmission time slot. The index of the active antenna is used as part of the transmitted data.
  • The data is divided into two parts: one part for modulated symbols such as QAM or PSK symbols, and the other part are used to choose the active antenna.
  • This technique permits the transmission of more bits without increasing the signal constellation or leads an inter-antenna interference.
  1. Steps for Implementing Spatial Modulation in NS2
  1. Modify the Physical Layer (WirelessPhy) to Support Multiple Antennas.
  2. Activate a Single Antenna at a Time Based on Data.
  3. Modify the Receiver to Decode Both Antenna Index and Modulated Symbols.

Step 1: Modify the Physical Layer to Support Multiple Antennas

In NS2, the physical layer manages the transmission and reception of signals. We need to adjust this layer to support multiple antennas and choose one antenna based on the data to be transmitted.

Define Antenna Configuration

In the wireless-phy.tcl or the physical layer, we will describe the number of antennas and a function to choose one antenna at a time for transmission.

# Define the number of antennas for spatial modulation

set WirelessPhy/num_antennas 4  ;# Number of antennas (e.g., 4 antennas)

# Function to select the transmitting antenna based on the input data

proc select_transmitting_antenna {input_data} {

set num_antennas [WirelessPhy set num_antennas]

# Use part of the input data to select the antenna index

set antenna_index [expr $input_data % $num_antennas]

return $antenna_index

}

Step 2: Modify the Packet Transmission Logic to Use Spatial Modulation

In this step, the packet transmission function is adapted to use only one antenna during each transmission. The antenna is choosen based on the part of the data that carries the antenna index.

# Packet transmission function with spatial modulation

proc Phy/WirelessPhy::transmit_packet {packet} {

# Get the data to be transmitted

set data [$packet data]

# Select the transmitting antenna based on part of the data

set antenna_index [select_transmitting_antenna $data]

# Transmit using only the selected antenna

puts “Transmitting on antenna index: $antenna_index”

# Perform the actual transmission using the selected antenna

$self send_packet_via_antenna $packet $antenna_index

}

# Function to simulate packet transmission via the selected antenna

proc Phy/WirelessPhy::send_packet_via_antenna {packet antenna_index} {

# Simulate the transmission via the selected antenna (abstracted)

# You can add more complex transmission logic if needed

puts “Sending packet via antenna $antenna_index”

# Call the send function (existing) to handle the actual transmission

$self send_up $packet

}

Step 3: Modify the Packet Reception to Decode the Antenna Index and Data

At the receiver, the system needs to decode both the antenna index (to know that antenna was used for transmission) and the authentic data (modulated symbols).

# Packet reception with spatial modulation

proc Phy/WirelessPhy::recv_packet {packet} {

# Get the received signal strength or data

set received_signal [$packet data]

# Decode the antenna index from the received data

set antenna_index [select_transmitting_antenna $received_signal]

# Decode the actual data (modulated symbols)

set decoded_data [decode_data $received_signal]

puts “Received on antenna index: $antenna_index with data: $decoded_data”

# Pass the decoded data to the upper layers

$self send_up $decoded_data

}

# Simple function to decode modulated symbols from the data (abstracted)

proc decode_data {signal} {

# Simulate decoding of modulated data (e.g., QAM or PSK)

set decoded_data [expr $signal / 10]  ;# Example decoding logic

return $decoded_data

}

Step 4: Define a TCL Simulation Script to Simulate Spatial Modulation

Generate a TCL simulation script that configures the wireless network, setting up the multiple antennas, and allows spatial modulation for data transmission.

# Create a simulator instance

set ns [new Simulator]

# Define trace and nam files for output

set tracefile [open spatial_modulation.tr w]

set namfile [open spatial_modulation.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define the network topology (e.g., 1000×1000 meters)

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Create the General Operations Director (GOD)

set god_ [create-god 5]  ;# 5 nodes in the network

# Define node parameters for wireless communication

set opt(chan)       Channel/WirelessChannel

set opt(prop)       Propagation/TwoRayGround

set opt(netif)      Phy/WirelessPhy

set opt(mac)        Mac/802_11

set opt(ifq)        Queue/DropTail/PriQueue

set opt(ll)         LL

set opt(ant)        Antenna/OmniAntenna

set opt(x)          1000

set opt(y)          1000

# Create nodes and set initial positions

for {set i 0} {$i < 5} {incr i} {

set node_($i) [$ns node]

set x [expr rand() * $opt(x)]

set y [expr rand() * $opt(y)]

$node_($i) set X_ $x

$node_($i) set Y_ $y

$node_($i) set Z_ 0.0

}

# Set up traffic generation

proc start_traffic {} {

global ns node_

# Create UDP agents and attach them to nodes

for {set i 0} {$i < 5} {incr i} {

set udp_($i) [new Agent/UDP]

set null_($i) [new Agent/Null]

$ns attach-agent $node_($i) $udp_($i)

$ns attach-agent $node_($i) $null_($i)

# Generate CBR traffic (constant bit rate)

set cbr_($i) [new Application/Traffic/CBR]

$cbr_($i) set packetSize_ 512

$cbr_($i) set interval_ 0.1

$cbr_($i) attach-agent $udp_($i)

# Connect the UDP agent to the null agent

$ns connect $udp_($i) $null_($i)

}

}

# Start the traffic at 1 second

$ns at 1.0 “start_traffic”

# End simulation after 100 seconds

$ns at 100.0 “finish”

# End simulation procedure

proc finish {} {

global ns tracefile namfile

close $tracefile

close $namfile

$ns halt

}

# Run the simulation

$ns run

  1. Explanation of the Script
  • Multiple Antennas: We describe multiple antennas in the WirelessPhy layer and execute logic to choose one antenna for transmission according to part of the input data.
  • Packet Transmission: During each transmission, the selected antenna is used to transfer the packet, since the data is modulated using traditional modulation schemes such as QAM.
  • Packet Reception: The receiver decodes both the antenna index and the modulated data that replicates spatial modulation.
  • Traffic Generation: The script mimic traffic generation among nodes, in which spatial modulation is applied to each transmission.
  1. Running the Simulation
  1. Save the modified wireless-phy.tcl and the TCL script (spatial_modulation.tcl).
  2. Execute the simulation using:

ns spatial_modulation.tcl

  1. Further Enhancements
  • Advanced Modulation Schemes: execute more advanced modulation schemes such as 16-QAM, 64-QAM along with spatial modulation.
  • Adaptive Antenna Selection: Add logic to adaptively choose the antenna according to signal strength or network conditions.
  • Interference and Noise: Combined interference and noise models to mimic more realistic wireless environments with spatial modulation.

In this demonstration, we can see the clear information on how to implement and setup the network scenarios for network spatial modulation that establish it with ns2 simulator tool. More information will shared regarding this process in another manual. Our team of specialists is prepared to assist you in generating optimal thesis ideas and topics that align with your interests. For effective implementation results of Network Spatial Modulation using the NS2 tool, you may consult the team at ns2project.com.