| Summary: | With the explosive growth of wireless communications, frequency resources have become scarcer, considering the dramatically increasing demands for higher communication rates. However, by examining the existing duplex modes, e.g., time division duplex (TDD) and frequency division duplex (FDD), it is observed that more than half of the resources are wasted due to the “half-duplex” constraints, as well as the uses of guard zones in the time or frequency domain to avoid interference from neighbor time slots or frequency bands. Therefore, efficiently utilizing the expensive frequency resources to provide high spectrum-efficient communications becomes one of the most important challenges in the design of the next generation wireless communication systems.
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