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The growing demand of high data rates requires much energy consumption. For this, in this paper we examine energy efficiency (EE) through total energy expenditure per bit characterization when the joint coupling between Modulation and Coding Scheme (MCS) related to the physical layer and Selective Repeat (SR) truncated Hybrid Automatic Repeat reQuest (HARQ) type I protocol of data link layer is performed into Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra-Wideband (UWB) system. The optimization is based on total energy expenditure per bit diminishing constrained by MCS rate and Packet Error Rate (PER). We propose an algorithm to identify the optimal MCS rate basing on dichotomy policy. Thus, analytical analysis highlights a closed-form expression of the optimal MCS rate allowing energy per bit minimization. In addition, in measuring the energy consumption per useful information the hardware components of MB-OFDM UWB (MB-UWB) crosslayer structure are considered. Further, the analytical framework is validated through computer results which reveal the effectiveness of our method in terms of energy saving.

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A new scheme for error-free transmission is presented which uses optimized combination of adaptive modulation and coding (AMC) and automatic repeat request (ARQ). Using conventional error correction codes with finite length, a limited value of packet error rate (PER) is inevitable. More powerful codes with more extra parity bits results in lower PER, however, at the cost of more transmit power per bit which is limited by average power constraint. Remained erroneous packets may be detected by error detection codes and be substituted by retransmission request in ARQ. However, when error correction capability is weak, throughput decreases due to increase of required retransmissions. In this article a method for optimum combination of error correction codes in AMC and error detection codes in ARQ is provided. In practice, due to estimation error and time variant channels, noisy and outdated channel state information (imperfect CSI) is available which restricts providing exact instantaneous PER constraint. To satisfy instantaneous PER constraint based on imperfect CSI, a novel technique is designed in this paper.Numerical evaluations indicate the efficiency of the proposed design.

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