Table 33 - Tdd Structure In Tdm Mode - Motorola PTP 600 Series User Manual

In IP Mode, the PTP 600 product runs an Adaptive TDD scheme. Basically an unloaded link
runs 10:10 mode (10 OFDM bursts alternately in each direction). A sustained traffic load in
one direction for example may cause a threshold to be reached where the TDD mode
automatically adapts to say 20:10. If the load continues to increase, then the TDD structure
may adapt even further through 30:10 to 40:10. This is a state of maximum link asymmetry
(40 OFDM bursts in one direction compared with 10 in the other). If the load increases in
BOTH directions, then the TDD structure can adapt from 10:10, through 20:20, 30:30 and
finally 40:40. This is a state of maximum aggregate throughput. So if three out of these
combinations are considered; 10:10, 40:10 and 40:40 they would give the following
characteristics:
x
10:10 equal performance in each direction, lowest aggregate throughput and lowest
Latency.
x
40:10 achieves maximum one way throughput performance, to the detriment of both
latency and throughput in the opposite direction.
x
40:40 Maximum link aggregate rate, balanced performance in each direction, higher
latency.
NOTE: There is an engineering trade-off between the flexibility of ATDD and Latency as
follows: When the TDD structure changes, there will be a short term impact on Latency for a
few Frames. This would not affect the steady state long term average latency, but could be
recorded as a Maximum latency. This affect may be amplified for short Latency tests or if the
traffic loading is oscillating either side of a boundary condition. As the TDD burst length
increases, Traffic in each direction will have to wait longer before a Transmit window is
available, but more data can be sent during the burst. There is an impact on latency but it
varies depending upon installation range, Frame size and modulation mode.
In TDM mode, two major differences in link behavior occur compared with IP mode. First the
TDD structure is fixed symmetrically. Either 10:10, 20:20, 30:30 or 40:40 based upon the
installed range, as shown in Table 33.
Table 33 – TDD Structure in TDM Mode
OFDM Radar
Bursts Avoidance
Range (km)
10:10 1-20
20:20 21-63
30:30 64 -145
40:40 146 -200
30 MHz 15 MHz
Band Range Band Range
(km) (km)
1-43 1-60
44-95 61-130
96 -150 131 -200
151 -200 N/A
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10 MHz 5 MHz Band
Band Range Range (km)
(km)
1-94 1 -200
95-200 N/A
N/A N/A
N/A N/A