User's Manual

Link Management

The SkyPilot system supports variable modulation types and encoding rates. Differing rates can be utilized for each individual link

within the network, including each of the multiple individual links possible for any given node. The various modulation types and

rates are shown in the table below. Note that the payload traffic capacity will be less than the stated data rates due to packet

header and protocol overhead.

Per-link Data Rates for Different Modulation Types

Raw Data

Rate

(Mbps)

Modulation

Type

Coding Rate Coded bits

per Subcarrier

Coded bits

per OFDM

Symbol

Data bits per OFDM Symbol

6 BPSK ½ 1 48 24

9 BPSK ¾ 1 48 36

12 QPSK ½ 2 96 48

18 QPSK ¾ 2 96 72

24 16QAM ½ 4 192 96

36 16QAM ¾ 4 192 144

48 64QAM ½ 6 288 192

54 64QAM ¾ 6 288 216

Each link within a SkyPilot network is optimized for maximum performance. This optimization occurs both at the point of link

creation and as an ongoing process in the case of active links utilized for subscriber traffic.

RSSI vs. Modulation Level

The modulation level of a link will generally relate directly to the Received Signal Strength Indicator (RSSI). RSSI values are

available via the SkyPilot MIB or CLI. Interference within a channel can cause a reduced modulation level.

The chart below shows test data mapping packet throughput against the Receive Signal Strength Indicator (RSSI). 10,000 packets

were transmitted for each combination of modulation and RSSI level. Note that this test was performed in the lab, free from

interference and multipath reflections, for both SkyGateway/SkyExtender and SkyExtender/SkyExtender links. The thick horizontal

line indicates a 90% packet success rate. The current link optimization algorithm requires a 95% packet success rate in order to

select the modulation level.

Based on these test results, the table below can be used to map RSSI to modulation levels:

RSSI Modulation Level (Mbps)

7 6

8 9

9-11 12

12-13 18

14-18 24

19-30 36

31+ 48