Cooperative communication can reduce energy consumption effectively due to its superior diversity gain. To further prolong network lifetime and improve the energy efficiency, this paper studies energy-efficient packet transmission in wireless ad-hoc networks and proposes a novel cluster-based cooperative packet transmission (CCPT) protocol to mitigate the packet loss and balance the energy consumption of networks. The proposed CCPT protocol first constructs a highly energy-efficient initial routing path based on the required energy cost of non-cooperative transmission. Then an iterative cluster recruitment algorithm is proposed that selects cooperative nodes and organizing them into clusters, which can create transmit diversity in each hop of communication. Finally, a novel two-step cluster-to-cluster cooperative transmission scheme is designed, where all cluster members cooperatively forward the packet to the next-hop cluster. Simulation results show that the CCPT protocol effectively reduces the energy cost and prolongs the network lifetime compared with the previous CwR and noC schemes. The results also have shown that the proposed CCPT protocol outperforms the traditional CwR protocol in terms of transmit efficiency per energy, which indicates that CCPT protocol has achieved a better trade-off between energy and packet arrival ratio.

Simultaneous recordings of eight channel surface myoelectric signals (EMGs) of the biceps brachii muscles of seven subjects were measured in isovelocity elbow flexion against constant load torque. The velocity was 10, 15, 20 and 25 degree/s and the load torque was 5-15 % of the torque obtained at the maximum voluntary contraction (MVC). Individual motor units were identified from the eight-channel surface EMG, by tracking the waveform change which originated from the change of relative position of muscle fiber and electrode. In the low-load (5 and 7% MVC) experiment, 36 examples of recruitment and 22 examples of derecruitment were measured. In the middle-load (10 and 15% MVC) experiment, most of the motor units did not show an obvious change in the firing rate with the elbow joint angle. Average of the firing rates of all the motor units measured at the elbow angle of 0 to 120 degree (13.3-14.7 Hz) did not depend on flexion velocity between 10 to 25 degree/s. It was concluded that the firing rates of the activated MUs were almost constant and that some MUs were recruited and derecruited during the isovelocity flexion movements. These are the first findings.