MiXiM - Physical Layer
Karl Wessel: wessel@tkn.tu-berlin.de
Michael Swigulski: swigulski@tkn.tu-berlin.de
20. Novemb e r 2007
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1 requirement specificatio n
1.1 Overview
• provide status information to MAC
• switch radiostate (RX, TX, SLEEP)
• send packets to air/channel
• receive packets / listen for packets
• provide hooks for statistical information
• configurable settings
1.2 provide status information to MAC
In addition to received packets the physical layer has to provide some other
information to the MAC layer. Some of this information has to be provided
passively on demand (e.g. current channelstate) and some should be delivered
actively to the MAC layer on certain events (e.g. transmission of a packet
complete).
Information which has to be provided to MAC on demand:
• channelstate: busy/idle (boolean) or RSSI
• current radiostate (RX, TX, SLEEP)
Information which has to be provided to MAC the moment it occurs:
• transmission over (se nd)
1.3 switch radiostate
The physical layer has to be able to switch between the following things:
• current radiostate (RX, TX, SLEEP)
Switching from one state to another may take some time. Whereas the switching
time may depends to whitch state we are switching.
Figure 1: State machine for radiostate
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1.4 send packets
The physical layer has to be able to send packets from the MAC layer to the
channel. We also want to support the possibility to control the sending process
after it has been started.
Before we can send packets the following things have to be assured:
• the radio has to be in TX state
• we are not already sending
The above items should be controlled by the MAC layer so the physical layer
would only throw an error if they are not set.
The following information has to be attached by the MAC layer to the packet:
• channel dimensions (frequency/space)
• bitrate (for all dimensions) over time
Note: Most cases will be covered by header and payload bitrate.
• TX power for all dimensions over time
• size of packet
The sending process itself is made up of the following steps:
1. MAC layer gives packet and control info to physical layer
2. check requirements for sending, throw error if they are not fulfilled
3. add information needed by the receiving physical layer to packet (see be-
low)
4. add signal to packet
5. packet is s ent to channel by physical layer
6. schedule transmission over message for MAC layer
The following information is needed by the receiving physical layer:
• signal
– TX power (for all dimensions) over time
– the bitrate (for all dimensions) over time
– the channel(dimensions)
– the duration the signal would nee d to be transmitted
– the duration of the preamble
• position, move direction and speed of the sending host
• size of packet
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1.5 receive packets
Because the packets arrive immediately at every receiving node we have to
simulate the receiving process:
1. simulate propagation delay (if needed)
2. simulate preamble duration
3. simulate payload duration
We also have to simulate the attenuation of the signal strength. This should be
done by filtering the signal with the analogue models directly after a message
arrives (since we already have it then). The AnalogueModels will add an atten-
uation matrix to the Signal.
signal or noise. The decision is made by the Decider. Therefore the preamble
has to be filtered previously by the analogue models.
The packet has to be classified as signal or noise. The decision is made by the
Decider.
If the transmission of a signal is over we have to decide if it was received cor-
rectly. This is also done by the Decider by evaluating the signal to noise ratio
short SNR. If the signal was received correctly we pass it to the MAC layer. It
is also possible to pass the signal to the MAC layer anyway, marked as biter-
ror/collision.
1.5.1 the analogue model
The analogue model simulates the attenuation of the signal strength by filtering
the receiving power function.
There should be models to simulate the following things:
• pathloss
• shadowing
• fading
Further we set the following requirements to the analogue models:
• physical layer should be able to apply multiple analogue models to a signal
• you should be able to set the analogue models independent from physical
layer
• you should be able to add your own analogue models
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1.5.2 the Decider
As mentioned already above the Decider has to decide the following things:
• classify packet as signal or noise
• decide if a packet was received correctly on the basis of the signal and
interfering noise
We set the following requirements to the Decider:
• you should be able to set the Decider independently from physical layer
• you should be able to add your own Decider
• the Decider should be able to return bitwise correctness of the signal (on
demand)
1.6 statistical informatio n
You should be able to get the following statistical information (the physical layer
should not evaluate it but has to provide access to the according information):
• packet count
• received signal strength
• signal to noise ratio
• bit error ratio
• collisions
1.7 parameters
The following parameters of the physical layer should b e freely configurable:
• simulate propagation delay? (boolean)
• which analogue models should be used
• the parameters for the analogue models
• which Decider should be used
• the parameters for the decider
• thermal noise
• sensitivity
• maximum TX power
• switching times between states (RX, TX, SLEEP)
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