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Broadband Powerline Communications Networks
Table 6.2
Parameters of the simulation model
Parameter
Value
Number of channels
15
Number of signaling channels
1
Channel data rate
64 kbps
Time-slot duration
4 ms
Segment size
32 bytes
= 4 bytes header + 28 bytes payload
The duration of a simulation run is chosen to correspond to the time needed for at least
10,000 events (generated packets) in the network. Also, 10 simulation runs and a warm-up
run are carried out for each simulation point the network load point is determined by
the number of stations (e.g. between 50 and 500). From the simulation runs, the mean
value, the upper bound, as well as the lower bound of the 95% confidence interval, are
computed and included in all diagrams representing the simulation results.
6.3 Investigation of Signaling MAC Protocols
An overview of the existing reservation MAC protocols, given in Sec. 6.1.4, shows that
there are many protocol solutions and their derivatives that are investigated for imple-
mentation in different communications technologies. However, according to the chosen
resource sharing strategy (MAC protocol) to be applied to the signaling channel, two
protocol solutions can be outlined as basic reservation protocols:
· protocols using random access to the signaling channel, mainly realized by slotted
ALOHA, and
· protocols with dedicated access, usually realized by polling.
Performance analysis of the basic protocols presented in Sec. 6.3.1 is carried out with the
following two aims: investigation of the basic protocols in a PLC transmission system
specified by its multiple access scheme (in this case OFDMA/TDMA) in a typical PLC
environment, characterized by unfavorable disturbance conditions, and validation of used
simulation model and chosen investigation procedure. Further, in Sec. 6.3.2, we analyze
several protocol extensions, and finally in Sec. 6.3.3, we present a performance analysis
of advanced polling-based reservation MAC protocols, which are outlined to achieve the
best performance in the case of per-packet reservation domain.
6.3.1 Basic Protocols
6.3.1.1 Description of Basic Reservation MAC Protocols
The transmission channels provided by the OFDMA/TDMA scheme are divided into
time slots that can carry exactly one data segment (Sec. 5.2.2). It is also the case in the
signaling channel, which is divided into request slots in its uplink part and control slots in
the downlink. The request slots are used for transfer of the transmission request from the