-
8/4/2019 PhyLayer
1/3
Physical Layer (in MiXiM)
The physical layer, which is implemented by the MiXiM framework,
will be used in the
simulation. The PhyLayer is the core part of the wireless node
in MiXiM. Its responsible for
sending and receiving messages and models the physical channel
(attenuation and BER). The
PhyLayer contains three main components: (1) The PhyLayer
OMNeT++ Module itself,
providing interface to upper layer and the channel (2)
AnalogueModel as attenuation filter (3)Decidercalculates BER.
The PhyLayer is the only OMNeT module in the PhyLayer, while all
the components are pure
C++ classes, which can be easily substituted with other
components.
BasePhyLayerDecider
Inheritance
Inheritance
PhyLayer
MACToPhyInterface
AnalogueModelAnalogueModel
Listdecider
Figure 1: Physical Layer Collaboration Diagram
PhyLayer OMNeT++ class
The PhyLayer OMNeT++ class provides an interface to the MAC
layer. It is directly connected
to the MAC layer via OMNeT++ gates. In addition PhyLayer is able
to send messages to other
physical layers using ChannelAccess which provides an access to
the channel. Two important
entities are encapsulated by this class; the AnalogueModel used
to calculate attenuation of the
received message and Decider which decides whether the received
signal is receivable message
or noise/interference. In addition it calculates BER for the
receivable messages. In addition it
holds parameters such as, thermal noise value, sensitivity for
receiving messages and information
regarding all messages currently transmitted on its entire
channels.
PhyLayer phases:
1. Module initialing: reads NED parameters and initializing
module, Decider andAnalogueModels.
2. Message handling: Receives AirFrames from MAC layer and send
them to the channel.
-
8/4/2019 PhyLayer
2/3
Receives AirFrames from channel, hand them to the AnalogueModels
forfiltering and for the Decider for evaluating. The PhyLayer can
forward the packet
up to the MAC layer.
Analogue ModelThe AnalogueModel module is a filter, responsible
for simulating the attenuation of received
signals. One PhyLayer may hold a list of AnalogueModel filters
for the receiving signals, and all
can be applied on the received message. This is the place to set
different radio propagation
models for the channels. A filter can attenuate the signal by
simulating fading, shadowing, path
loss and more. All the operations are done on the Signal module
(see MiXiM API) within the
AirFrame. The Signal holds some parameters which are used by the
AnalogueModel, such as
starting and ending time of the signal, the sender position at a
given time, the transmitter power,
propagation delay and bit-rate. The Signal also has a member
which describes the attenuation. To
add attenuation to the Signal, the physical layer module
iterates all the AnalogueModels on every
Signal. For each AnalogueModel the filterSignal(signal& S)
method is invoked. This method
makes the desired mathematics evaluations according to a
theoretical channel model, andinvokes
S.addAttenuation(ConstMapping* att) method when finished. The
attenuation value
inside
Three Analogue models are already implemented in MiXiM:
JakesFading,
LogNormalShadowing and SimplePathlossModel (see 2.2.1.2).
This function has to be overridden by every implementation:
virtual void filterSignal(signal&)=0: Filters a specific
signal by adding attenuation to the signal.
The steps to add a new channel model goes as follow:
Create new ChannelModel class, which publics the AnalogueModel
class. Implement the filterSignal(signal& S) method. Make sure
to update the signals
attenuation at the end.
Initialize the new ChannelModel from the physical layer
module.Decider
The Decider provides the main functionality of the physical
later, like signal classification and
demodulation. The Decider evaluates received signals and
categorizes them to interference/noise
or receivable message, with a given bit error rate (BER). The
channel modulation in MiXiM is
represented by the relation between BER to SINR (signal to
interference and noise ratio), anddepends on the Decider
implementation. Additionally, the Decider provides channel
carrier
sensing information for the MAC layer. Two Deciders are already
implemented in MiXiM:
Decider80211 and SNRThresholdDecider.
The next function has to be overridden in new
implementations:
virtual simtime_t processSignal(AirFrame*): Processes an
AirFrame given by the PhyLayer.
-
8/4/2019 PhyLayer
3/3
AirFrame
This packet format is used to send messages from the physical
layer to the channel. All other
physical layers that can 'hear' (within its maximal interference
distance) this message can
evaluate noise, interference and the payload. The payload is
carried by a Signal class.
Signal class stores the physical representation of the payload
of an AirFrame. This includes
propagation delay, the sender host move pattern, the
transmission power, bit rate, attenuation and
more. The signal is created at the sender MAC layer.
Some class methods (for all methods see MiXiM API):
simtime_t getSignalLength() - Returns the length of the signal
transmission.
simtime_t getPropagationDelay() - Returns the propagation delay
of the signal.
void setBitrate(Mapping* bitrate) - Sets the function
representing the bit rate of the signal.
void addAttenuation(ConstMapping* att) - Adds a function
representing the attenuation of the
signal.
const ConstMapping* getTransmissionPower() - Returns a function
representing the
transmission power of the signal
This Message class is taken directly from the MiXiM framework
without any modifications.
http://c/Documents%20and%20Settings/efraima/Desktop/MiXiM-1.1/MiXiM/doc/doxy/a00017.html%236de2ca07018de313a7147a03e6d77bffhttp://c/Documents%20and%20Settings/efraima/Desktop/MiXiM-1.1/MiXiM/doc/doxy/a00017.html%236de2ca07018de313a7147a03e6d77bffhttp://c/Documents%20and%20Settings/efraima/Desktop/MiXiM-1.1/MiXiM/doc/doxy/a00017.html%236de2ca07018de313a7147a03e6d77bffhttp://c/Documents%20and%20Settings/efraima/Desktop/MiXiM-1.1/MiXiM/doc/doxy/a00017.html%236de2ca07018de313a7147a03e6d77bff
