User Manual

ADCP-XX-XXX • November 2000 • Section 3: WMTS Functional Description
Page 3-8
 2000, ADC Telecommunications, Inc.
5 UPSTREAM
5.1 Overview
The return path information is transmitted from the WMU, in the network over the upstream channel
toward the base station. An allocated time slot is assigned to each WMU to send the information. The
WMTS converts the received information to digital data.
5.2 Return Channel
The WMU modulator provides QPSK modulation at symbol rates and channel widths, as described in
table 5.1.
Table 5-1. WMTS Upstream Performance Requirements
REQUIREMENT SPECIFICATION
MODULATION
QPSK
SYMBOL RATES
0.320, 0.640, 1.28 Ms/s
RECEIVE LEVEL
-13 to +17, -10 to +20, -7 to +23 dBmV (respective to symbol rates)
CHANNEL BANDWIDTHS
400 KHz, 800 KHz, and 1.6 MHz
FREQUENCY RANGE
5 to 65 MHz
CNR THRESHOLD FOR 1X10
-6
B
E
12.5 dB @ QPSK
THROUGHPUT
1
400 KHz: 520 Kb/s
800 KHz: 1.0 Mb/s
1.6 MHz: 2.0 Mb/s
INPUT IMPEDANCE
75 ohms
FORWARD ERROR CORRECTION
Reed-Solomon codes over GF(256) with T= 1 to 10, Codeword size
K = 16 to 253
DESCAMBLER
Pseudo Random Binary Sequence based on the polynomial x
15
+x
14
+
the seed is variable
TRACKING RANGE
+/- 32 KHz
CHANNELS SUPPORTED
Up to 5
As can be seen from the above table, each upstream channel has an assigned bandwidth associated
with it. The occupied bandwidth is directly related to the channel's data rate. The DOCSIS compliant
upstream channels, occupies bandwidths of 400, 800 or 1600 KHz. This corresponds to channel data
rates of 320, 640 or 1280 kilosymbols per second (ksym/sec).