User's Manual

Overview
Trango Broadband Wireless — Atlas5055 page 7
Chapter 1 Overview
The Atlas5055 is a point-to-point (PtP) wireless Ethernet transmission system which provides network connectivity at
speeds up to 45 Mbps depending on the transmission distance and noise floor. The Atlas5055 utilizes OFDM technology
and is designed for use in long range backhaul and wide area data networking applications.
Users are required to simply specify one P5055M unit type as master unit (MU) and one unit as remote unit (RU) to
establish a link. Each unit utilizes power-over-Ethernet (PoE) and is designed for outdoor environments. The cable
entry point can accommodate both Shielded twisted pair Cat5 (STP) and unshielded twisted pair Cat5 (UTP), with the
addition of conduit for tower mounting.
DFS
One of the key features of the Atlas5055 is that it has Dynamic Frequency Selection (DFS) which allows it to be
operated in the 5.25 to 5.35 GHz and 5.47 to 5.7 GHz frequency ranges depending upon the regulatory requirements.
When operating in these frequency ranges the MU will monitor the channel for radar transmissions and switch to a new
channel automatically if radar is detected. The RU will switch to the new channel as well and the link will be
automatically reconnected, typically in about 1 minute.
Each radio unit has a different threshold for detecting radar that corresponds to the radio’s antenna gain. For the
P5055M-19-xx models, the threshold is –46 dBm. Any radar signal arriving at the antenna on the operating channel that
has an amplitude greater than –46 dBm will cause the MU and it’s associated RU to switch to a randomly selected
channel that is tagged as a DFS channel in the channel table. For the P5055M-23-xx units, the threshold is is –42 dBm,
and for the P5055M-EXT-xx units the threshold is –37 dBm.
IMPORTANT NOTE: When operating in the DFS frequencies, the radio units will use automatic transmit power
control (ATPC) to maintain the RSSI at a level of approximately –62 dBm. For very short link distances it may not be
possible for the transmit power to be reduced below the Radar detection threshold and the radio may not be able to
establish a reliable link. Trango recommends that careful link budget planning be done to ensure that this
condition does not exist.
OFDM
The Atlas platform utilizes Orthogonal Frequency Division Duplex (OFDM) processing which offers link stability and
performance in the presence of multipath interference.
Adaptive Modulation
One of the key advantages of the Atlas series radio platform is utilization of multiple modulation schemes including the
following:
• Binary Phase Shift Keying (BPSK)
• Quadrature Phase Shift Keying (QPSK)
• 16 Quadrature Amplitude Modulation (16QAM)
• 64 Quadrature Amplitude Modulation (64QAM)
The Atlas system allows individual selection of the upstream and downstream modulation schemes. The modulation
schemes can be adjusted manually or automatically (automatic rate shifting) for changing propagation and interference
conditions. The higher order modulation schemes (64QAM) are typically deployed at reduced ranges while lower order
modulation schemes (BPSK) are implemented at long distances.
ARQ
Another key advantage of the Atlas platform is its Automatic Repeat Request (ARQ) transmission correction scheme.
The ARQ algorithm detects packet loss due to fading and interference conditions and requests the remote radio to re-
transmit specific packets.