We compare the energy efficiency of some transmission

schemes in wireless sensor networks. By constraining

the system to end-to-end throughput requirements, we assume

that the nodes in multi-hop and cooperative schemes operate

at a spectral efficiency which is twice that of the single-hop

transmission. By taking into account the energy consumption of

the RF circuitry, we show that cooperation may be considerably

more energy efficient than non-cooperative schemes even in small

transmission ranges, specially if a feedback channel is available.