Core Concepts
The authors settle the communication complexity necessary to achieve any approximation guarantee via maximal-in-range (VCG-based) mechanisms for combinatorial auctions, providing tight bounds for both submodular and general valuations.
Abstract
The paper analyzes the communication complexity of maximal-in-range (MIR) mechanisms, which are a class of truthful mechanisms that leverage the VCG mechanism to trade off approximation guarantees for efficiency. The key findings are:
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For submodular valuations:
- For all k = Ω(log(m)), the best approximation guarantee achievable by an MIR mechanism using 2k communication is Θ(√m/k). This improves the previous best lower bound from Ω(m^(1/3)/log^(2/3)(m)) to Ω(√m/log(m)).
- The authors provide a mechanism that achieves this Θ(√m/k) approximation guarantee using 2^O(k) simultaneous value queries or computation.
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For general (monotone) valuations:
- For all k = Ω(log(m)), the best approximation guarantee achievable by an MIR mechanism using 2k communication is Θ(m/k). This improves the previous best lower bound from Ω(m/log^2(m)) to Ω(m/log(m)).
- The authors provide a mechanism that achieves this Θ(m/k) approximation guarantee using 2^O(k) simultaneous value queries or computation.
The key technical ideas are:
- For general valuations, using multiple random partitions of the items to improve the approximation guarantee.
- For submodular valuations, combining a bucketing approach with the chunking mechanism for general valuations to achieve the optimal Θ(√m/k) approximation.
The authors also show that their MIR mechanisms are optimal among all deterministic truthful mechanisms in the value query and computational/succinct representation models.
Stats
For submodular valuations, the best approximation guarantee achievable by an MIR mechanism using 2^k communication is Ω(√m/(k log(m/k))) when n = Ω(√m/k).
For general valuations, the best approximation guarantee achievable by an MIR mechanism using 2^k communication is Θ(m/k).
Quotes
"Let MIRSubMod(m, k) denote the best approximation guarantee achievable by an MIR mechanism using 2k communication between bidders with submodular valuations over m items. Then for all k = Ω(log(m)), MIRSubMod(m, k) = Ω(√m/(k log(m/k)))."
"Let also MIRGen(m, k) denote the best approximation guarantee achievable by an MIR mechanism using 2k communication between bidders with general valuations over m items. Then for all k = Ω(log(m)), MIRGen(m, k) = Θ(m/k)."