User Manual

ADCP-62-504 • Issue 1 • November 2000 • Section 1: Introduction
Page 1-8
 2000, ADC Telecommunications, Inc.
5.1 WMU (Wireless Modem Unit)
The WMU is a DOCSIS-based wireless modem with specific wireless enhancements for
robustness. The system is connected to the subscriber equipment through a standard 10BaseT
Ethernet network interface card (NIC) or a hub or other Ethernet device for multiple users.
The WMU, which is installed adjacent to the computer, performs the data to IF signal
modulation and demodulation. It is housed in a complete, standalone enclosure.
5.2 Transverters and Antennas (Delete?)
Either a 17 dBi integrated planar antenna/transverter for typical installs or a 21 or 24 dBi grid
antenna with standalone transverter for high directivity installs or a 17 dBi planar array
antenna with attenuator and standalone transverter for close range installs can be used,
depending on the requirements of the site.
5.3 WMU Interaction
5.3.1 Channel Acquisition
After scanning for a downstream channel (frequency), the WMU obtains QAM lock and finds
the MPEG packets with the well-known PID associated with DOCSIS. Several downstream
channels may need to be searched before the WMU finds the one with DOCSIS data. Channel
acquisition is successful when the WMU decodes MPEG-2 frames that bear the DOCSIS well-
known PID. The MPEG-2 frames are then stripped away and the resulting MAC frames are
passed to the MAC layer for processing.
5.3.2 Obtaining Upstream Parameters
During this phase, the WMU looks for three MAC messages that are repeatedly sent by the
WMTS to provide a common time reference to all WMUs. The first message is the Time
Synchronization message (SYNC). The second one defines the Upstream Channel Descriptor
(UCD). The final message is an Upstream Bandwidth Allocation Map (MAP), which matches
the upstream channel described in the UCD.
5.3.3 Ranging
The WMU must be initially ranged into the system. During ranging the WMU must complete
the following three processes:
• Timing adjustment
• Transmit frequency tuning
• Transmit power adjustment