Specifications

sacrificing performance. 99.999 percent link availability is planned into the standard. By

making these adjustments the throughput on the link is always maximized for the given

conditions. This “self tuning” of the link will provide for the ability to quickly establish links

with out having to manually adjust the equipment.

In the 2-11 GHz frequencies the MAC layer also issues automatic repeat requests (ARQ) to

insure higher data reliability. The MAC also includes a privacy sub layer that provides

authentication of network access and connection establishment to avoid theft of signal.

Encryption and key exchange are also built into the MAC for added security.

Orthogonal frequency division multiplexing (OFDM) is used in the unlicensed bands with the

media access being by time division multiplexing. The system is also time division duplex. This

makes for efficient use of the spectrum in that the up and down links can be asymmetric with no

loss of efficiency. The use of OFDM also has the effect that each of the OFDM signals occupies

a narrow bandwidth. This loosens the requirement for coherence bandwidth considerably, and

helps with the problems of time domain dispersion caused by multipath interference.

2.2 Redline Equipment: For the purpose of these tests Redline AN-50 radios were purchased.

64 QAM modulation is an option on these radios; it brings the advertised throughput up to

48Mbps measured at the Ethernet port. This option was purchased on three of the radios. A total

of four radios were purchased so that point to point operation could be tested, as well as point to

multipoint operation. The point to multipoint testing did not get completed, as there was a

hardware problem on the base station terminal that has to be resolved under warranty. The four

modulation types that are implemented in the AN-50 are BPSK, QPSK, 16 QAM and 64 QAM.

The AN-50 radios include a forward error-correcting scheme that is identified by the number of

data bits to the total number of bits. For example a ¾ code would contain 3 bits of data for every

4 bits transmitted. The other bit is used for error correction purposes. The coding rate is varied

along with the modulation format to provide the highest level of throughput possible. The table

below shows the various settings for modulation type and coding scheme that are used in the

AN-50 radios, along with the data rates that are achievable for each.