Nowadays the demand for communication over the wireless medium is significantly increasing, while the available wireless spectrum is already limited. In this thesis, we introduce new practical physical layer designs that employ node cooperation for more efficient wireless spectrum utilization. First, a cooperative scheme is introduced that takes advantage of the existence of simultaneous multiple frequency band operation in modern wireless devices. The main idea of this scheme is to use one frequency band for sharing data among collaborating nodes, and another one for cooperatively transmitting to a common destination. The benefits of such a cooperative design across frequency bands are evaluated on a testbed of software-defined radios, where we investigate and identify the possible network conditions under which our scheme enables better throughput compared to the traditional operation. Second, we present a practical design that facilitates physical layer cooperation in Long Term Evolution (LTE) networks. The main idea here is to adapt the inherent Hybrid Automatic Repeat-reQuest (H-ARQ) in standard LTE operation, so that multiple relays can cooperate over the transmission of one encoded block. Performance evaluation of the design reveals significant throughout gains under asymmetric channel conditions for parallel relay networks in LTE framework. Finally, we look at the node cooperation from a privacy perspective in wireless sensor networks. To this end, we design and evaluate a low-overhead message encryption protocol based on network coding. The main idea of the protocol is to employ node cooperation to increase the inherent weak security that network coding offers. Results show up to 60% increase in terms of extra security added on top of the inherent one.