Cambium Networks PMP 450 Series, Руководство по установке

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Chapter 1: Product description 38
Frame Period
The frame period or frame duration is the time between the beginning of a frame and the end of the frame.
The 450 Platform Family supports two frame periods: 2.5 ms and 5 ms.
The 5ms frame period configuration provides higher throughput as a result of reduced frame overhead
during transmission. In turn, the 2.5 ms frame period configuration affords reduced latency in the system,
half of that introduced by the 5 ms frame configuration.
Frame configurat ion - Dow nlink Dat a
The percentage of frame assigned to transport downlink data. The downlink data specifies the percentage
of the aggregate throughput for the downlink (frames transmitted from the AP/BHM to the subscriber).
The configurable range is 15% to 85%.
Note
For all 450 platform APs, the maximum configurable range is 34% to 66% for 40
MHz with 5 ms frame.
Link operat ion – Dynamic Rat e Adapt
The 450 Platform Family ODUs offer eight levels or speeds of operation – 2X MIMO- B and 1X MIMO- A
(QPSK), 4X MIMO-B and 2X MIMO-A (16-QAM), 6x MIMO-B and 3X MIMO-A (64-QAM) and 8X MIMO-B and
4X MIMO-A (256-QAM). If received power varies due to distance between the AP/BHM and the SM/BHS or
due to obstructions, or if interference affects the RF environment, the system automatically and
dynamically adjusts the links to the best operation level.
The system chooses its modulation rate dynamically, based on an internal ARQ (Automatic Repeat
reQuest) error control method. With ARQ, every data slot of every frame sent over the air (except
downlink broadcast) is expected to be acknowledged by the receiver, and if acknowledgement is not
received, the data is resent. The sending unit monitors these re- sends and adjusts the modulation rate
accordingly. It is normal to have links that change levels of operation as the RF environment changes.
Furthermore, the uplink or downlink portions of TDD duty cycle operate independently.
The various modulation levels used by 450 Platform Family are shown in below table.
Table 15 :Modulation levels
Rate MIMO-B MIMO-A
QPSK 2X MIMO-B 1X MIMO-A
16-QAM 4X MIMO-B 2X MIMO-A
64-QAM 6X MIMO-B 3X MIMO-A
256-QAM 8X MIMO-B 4X MIMO-A
Note
MIMO-A achieves half the throughput of MIMO-B but adds a combining diversity
(gain) which enhances the link budget or availability.