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The span‐restorable meta‐mesh model was previously designed as a cutting‐edge technique that enhanced the spare capacity efficiency in low average nodal degree networks. In this technique, lightpaths that fully traverse chains of degree‐2 nodes are provided with a logical express bypass span allowing a distinction between the internal and external working flow capacity that transit the chain. In the event of span failure, lightpaths which would normally traverse the chain in its entirety are allowed to fail back to its anchor nodes such that only the intrachain flow requires allocation of spare capacity. Previous work on the meta‐mesh design considered only single failure restorability. The work herein analyzes dual span failure situations by developing two new integer linear programming models. The first model provides the minimum total cost of designing a meta‐mesh network capable of withstanding dual span failure scenarios. The second model offers a maximization of the dual failure restorability by minimizing the number of nonrestored working capacities with a given limit of total spare capacity investment. Experiments are performed on six master test‐case networks of various topologies and scales.

One of the key challenges for future communication systems is to deal with fast changing channels due to the mobility of users. Having a robust protocol capable of handling transmission failures in unfavorable channel conditions is crucial, but the feedback capacity may be greatly limited due to strict latency requirements. This paper studies the hybrid automatic repeat request (HARQ) techniques involved in re-transmissions when decoding failures occur at the receiver and proposes a scheme that relies on codeword bundling and adaptive incremental redundancy (IR) to maximize the overall throughput in a limited feedback system. In addition to the traditional codeword extension IR bits, this paper introduces a new type of IR, bundle parity bits, obtained from an erasure code across all the codewords in a bundle. The type and number of IR bits to be sent as a response to a decoding failure is optimized through a Markov Decision Process. In addition to the single link analysis, the paper studies how the same techniques generalize to relay and multi-user broadcast systems. Simulation results show that the proposed schemes can provide a significant increase in throughput over traditional HARQ techniques.