ACCP
Understanding ACCP (Adjacent Channel Co-Polarization)
If a cell tower runs out of internet capacity, the engineer must bolt a second microwave dish to the tower to double the speed. However, they cannot use the same frequency. They must use the Adjacent (next-door) frequency. How close can those frequencies be without crashing? That depends on Polarization.
The Polarization Defense
Radio waves have a physical orientation in the air (Polarization).
- If Dish A transmits Vertically (up and down) and Dish B transmits Horizontally (left and right), the physics of the waves ignore each other. This is called ACAP (Adjacent Channel Alternating Polarization). Because of this natural 30 dB physical isolation, engineers can squeeze the two frequency channels incredibly close together without any noise.
The ACCP Challenge
However, if the engineer is forced to use the exact same polarization for both dishes (e.g., both are transmitting Vertically), this is an ACCP configuration.
Because the physical waves are perfectly aligned, they are highly vulnerable to crashing into each other. Without the natural protection of cross-polarization, the RF engineer must mathematically push the two frequency channels significantly further apart on the spectrum analyzer to prevent the massive 'skirt' of Dish A's radio wave from bleeding into the delicate receiver of Dish B. Consequently, ACCP configurations are vastly less spectrally efficient than ACAP setups, consuming significantly more expensive licensed spectrum to achieve the exact same data speed.
Key Equations
Sample size: n from MIL-STD-1916 / ISO 2859
Accept: c or fewer defects in n
Reject: c+1 or more defects
OC curve:
P(accept) = Σk=0c C(n,k)pk(1−p)n−k
p = true defect rate
LTPD (lot tolerance):
P(accept|LTPD) = 0.10 (10% consumer risk)
Comparison
| AQL | n (Level II) | c | Application | Risk |
|---|---|---|---|---|
| 0.1% | 315 | 1 | Critical parameter | Very low |
| 0.25% | 200 | 1 | Important param | Low |
| 0.65% | 125 | 2 | Standard | Moderate |
| 1.0% | 80 | 2 | Non-critical | Standard |
| 2.5% | 50 | 3 | Cosmetic | Higher |
Frequently Asked Questions
Why would an engineer ever use ACCP?
Often, they have no choice. In many countries, the government telecom regulators strictly mandate that a specific microwave band can only be transmitted in Vertical polarization to protect a legacy military radar system operating nearby. Because the engineer is legally banned from using Horizontal polarization, they are forced to use the less efficient ACCP spacing rules to add more capacity to the tower.
How do RF filters fix ACCP noise?
Because the channels are forced close together with identical polarization, the radio hardware must be astronomically precise. The engineer must install highly expensive, aggressive 'Cavity Filters' on the back of the dishes. These massive metal tubes act as brutal brick walls, violently chopping off the bleeding edges of the radio wave to ensure it stays perfectly inside its designated channel.
What is Co-Channel Dual Polarization (CCDP)?
The ultimate spectral efficiency. CCDP uses the exact same frequency channel, but blasts two completely different data streams simultaneously: one Vertical, and one Horizontal. This mathematically doubles the speed of the link using zero extra spectrum. However, if it rains, the water droplets violently twist the waves, causing the Vertical and Horizontal data streams to crash into each other, requiring complex XPIC algorithms to untangle the mess.