  The purpose of Green Communications is to reduce the energy consumption of
the communication system as much as possible without compromising the quality
of service (QoS) for users. An effective approach for Green Wireless
Communications is On-Demand strategy, which scales power consumption with the
volume and location of user demand. Applying the On-Demand Communications
model, we propose a novel scheme -- Wireless Resource Trading, which
characterizes the trading relationship among different wireless resources for a
given number of performance metrics. According to wireless resource trading
relationship, different wireless resources can be consumed for the same set of
performance metrics. Therefore, to minimize the energy consumption for given
performance metrics, we can trade the other type of wireless resources for the
energy resource under the demanded performance metrics. Based on the wireless
resource trading relationship, we derive the optimal energy-bandwidth and
energy-time wireless resource trading relationship for green wireless
communications. We also develop an adaptive trading strategy by using different
bandwidths or different delays for different transmission distances with
available bandwidths and acceptable delay bounds in wireless networks. Our
conducted simulations show that the energy consumption of wireless networks can
be significantly reduced with our proposed wireless resources trading scheme.
