BIP-102: Coin Emission Model
BIP: 102
Title: Coin Emission Model (CEM)
Author: Bitmark Development Team
Status: Final
Type: Standards Track
Created: 2018-06-01
Activated: Block 450,947
License: MIT
Abstract
This document specifies the Coin Emission Model (CEM) activated with Fork 1 at block 450,947. The CEM replaces height-based subsidy calculation with emission-based thresholds and introduces a dynamic scaling factor system that adjusts block rewards based on network hashrate.
Motivation
The original height-based reward schedule (BIP-100) had limitations in a multi-algorithm environment:
- Unequal Emission: Faster algorithms could emit more coins
- Hashrate Spikes: Temporary hashrate increases could accelerate emission
- Algorithm Imbalance: Popular algorithms would receive disproportionate rewards
The Coin Emission Model addresses these by:
- Basing reward thresholds on total emitted supply, not block height
- Distributing emission equally across all eight algorithms
- Introducing scaling factors that adjust rewards based on hashrate
Specification
Emission-Based Subsidy
Post-fork subsidy is determined by total coins emitted, not block height:
effective_emitted = NUM_ALGOS × previous_algo_money_supply
Where:
NUM_ALGOS= 8previous_algo_money_supply= total supply at last block of same algorithm
Subsidy Schedule
| Emitted (MARKS) | Base Subsidy | Note |
|---|---|---|
| 0 - 7,880,000 | 20.0 | Q1 H0 |
| 7.88M - 13.79M | 15.0 | Q1 H1 |
| 13.79M - 17.73M | 10.0 | Q2 H1 |
| 17.73M - 20.685M | 7.5 | Q2 H2 |
| 20.685M - 22.655M | 5.0 | Q3 H2 |
| 22.655M - 24.1325M | 3.75 | Q3 H3 |
| 24.1325M - 25.1175M | 2.5 | Q4 H3 |
| 25.1175M - 25.85625M | 1.875 | Q4 H4 |
| ... | ... | Continues |
Where Q = Quartering period, H = Halving period
Maximum Supply
Total Maximum Emission: 27,579,894.73108 MARKS
= 2,757,989,473,108,000 satoshis
Per-Algorithm Distribution
Each algorithm receives 1/8 of the emission:
algorithm_subsidy = base_subsidy / 8
With 8 algorithms each targeting 16-minute intervals:
- Each algorithm: ~90 blocks/day
- All algorithms: ~720 blocks/day
- Maintains 2-minute average block time
Scaling Factor System (SSF)
The Subsidy Scaling Factor adjusts rewards based on network hashrate.
Purpose:
- Smooth emission when hashrate varies
- Prevent hashrate spikes from accelerating emission
- Maintain predictable monetary policy
Calculation:
scaled_subsidy = base_subsidy - (base_subsidy × 100,000,000 / scaling_factor) / 2
Update Frequency:
- Updates approximately every 90 blocks per algorithm (~24 hours)
- Blocks with
BLOCK_VERSION_UPDATE_SSFflag trigger recalculation
Rationale
Why Emission-Based Thresholds?
Height-based thresholds assume predictable block times. With multiple algorithms:
- Block production rate varies
- Some algorithms may be faster/slower
- Total emission would be unpredictable
Emission-based thresholds ensure:
- Fixed maximum supply
- Predictable monetary policy
- Fair distribution regardless of algorithm popularity
Why 8x Multiplier?
effective_emitted = 8 × money_supply
This multiplier:
- Divides emission points by 8 (one per algorithm)
- Ensures each algorithm contributes equally
- Maintains original emission curve shape
Why Scaling Factors?
Without scaling:
- Hashrate spikes accelerate emission
- Mining profitability varies wildly
- Long-term supply becomes unpredictable
With scaling:
- High hashrate reduces per-block reward
- Low hashrate maintains minimum viability
- Total emission remains on schedule
Economic Analysis
Emission Curve
The combined halving/quartering schedule produces a smooth emission curve:
Year 1-3: 20 → 15 → 10 MARKS (base)
Year 4-6: 7.5 → 5 → 3.75 MARKS
Year 7-9: 2.5 → 1.875 → 1.25 MARKS
...
Final: Minimum ~0.015 MARKS
Distribution Timeline
| Percentage Emitted | Approximate Timeframe |
|---|---|
| 50% | ~6 years from genesis |
| 75% | ~12 years from genesis |
| 90% | ~20 years from genesis |
| 99% | ~35 years from genesis |
Comparison to Bitcoin
| Aspect | Bitmark | Bitcoin |
|---|---|---|
| Maximum Supply | ~27.58M | 21M |
| Halving Interval | ~3 years | ~4 years |
| Block Time | 2 minutes | 10 minutes |
| Additional Mechanism | Quartering, SSF | None |
Backward Compatibility
This is part of the Fork 1 hard fork (BIP-101). Pre-fork software:
- Uses height-based subsidy calculation
- Does not recognize scaling factors
- Will reject post-fork blocks
See Also
- BIP-100: Bitmark Original Design
- BIP-101: Multi-Algorithm Proof-of-Work
- Emission Model Technical Details
References
Copyright
This document is licensed under the MIT License.