Channel Parameters
Channel Width (MHz)
?
Total OFDM channel bandwidth. DOCSIS 3.1 supports 24–192 MHz downstream channels in multiples of the subcarrier spacing. Max is 192 MHz per CM-SP-PHYv3.1.
Must be 24–192 MHz
Subcarrier Spacing
?
50 kHz → 4096-point FFT at 204.8 MHz sample rate (20 µs symbol). 25 kHz → 8192-point FFT (40 µs symbol). 50 kHz is most commonly deployed. [DOCSIS 3.1 §7.4.2]
Modulation Order
?
Average modulation per data subcarrier. DOCSIS 3.1 supports QPSK through 4096-QAM. Higher orders require better SNR. [CM-SP-PHYv3.1 §7.6]
Guard Band (MHz)
?
Total guard band removed from the occupied spectrum (both edges combined). Prevents interference with adjacent channels. Typical: 1 MHz. Range: 0–4 MHz.
Must be 0–4 MHz
Excluded Spectrum (MHz)
?
Spectrum notched out within the channel (e.g., for legacy analog or narrowband interference). Reduces usable subcarriers. Range: 0–20 MHz.
Must be 0–20 MHz
Cyclic Prefix (samples)
?
CP duration in samples at 204.8 MHz sample rate. 512 samples = 2.5 µs, sufficient for most HFC plant delay spreads. Larger CP wastes spectral efficiency but improves multipath tolerance. [CM-SP-PHYv3.1 §7.4.4]
Downstream Results
Aggregate Throughput
—Gbps
Spectral Efficiency
—
Data Subcarriers
—
Symbol Period
—
LDPC CWs / Symbol
—
CP Overhead
—
Symbol Rate
—
DOCSIS 3.1 reference: At 192 MHz, 50 kHz spacing, 4096-QAM, 512-sample CP,
this model yields ~1.73 Gbps — consistent with the PHY specification after accounting for
PLC, continuous pilots, scattered pilots, and NCP overhead.
CableLabs' ~1.89 Gbps headline figure omits LDPC and NCP framing overhead.
Channel Parameters
Channel Width (MHz)
?
Total OFDMA upstream channel width. DOCSIS 3.1 supports 6.4–96 MHz for low-split, up to 684 MHz for extended high-split. Common deployments: 48 or 96 MHz. [CM-SP-PHYv3.1 §8.1]
Must be 6.4–684 MHz
Subcarrier Spacing
?
OFDMA upstream supports 6.25, 25, or 50 kHz subcarrier spacing. 25 kHz is most common. 6.25 kHz is used for extended reach. [CM-SP-PHYv3.1 §8.4.2]
Modulation Order
?
Upstream modulation order per data subcarrier. DOCSIS 3.1 supports QPSK through 4096-QAM upstream. 1024-QAM is a practical limit for many plant conditions.
Minislot Size (subcarriers)
?
Number of subcarriers per minislot. For 50 kHz spacing: 8 subcarriers/minislot. For 25 kHz spacing: 16 subcarriers/minislot. Minislots are the fundamental upstream allocation unit. [CM-SP-PHYv3.1 §8.5]
Guard Band (MHz)
?
Guard band at channel edges (both sides combined). Prevents interference with adjacent upstream bands. Typical: 0.4–1 MHz total.
Must be 0–4 MHz
Excluded Spectrum (MHz)
?
Spectrum notched out within the upstream channel (e.g., for ingress avoidance or narrowband RFI). Range: 0–10 MHz.
Must be 0–10 MHz
Upstream Results
Aggregate Throughput
—Gbps
Per-Minislot Rate
—
Minislots / Channel
—
Spectral Efficiency
—
Symbol Period
—
Total Subcarriers
—
Data Subcarriers
—
DOCSIS 3.1 upstream note: OFDMA uses minislot-based resource allocation.
Throughput shown is the aggregate channel capacity assuming full allocation to a single
upstream profile. Actual per-CM throughput depends on scheduling and RF conditions.