Wireless communication systems employ various techniques for supporting two-way communications. For example, a wireless communications system may support Time Division Duplex (TDD) communications, where the same operating frequency band is time multiplexed to support two-way communications. A wireless communication system may support Frequency Division Duplex (FDD) communications, where distinct frequency bands are used for the distinct directions of the duplex communications.
A system designer may take several factors into account when deciding on the manner in which duplex communications is to be supported. In some systems, the manner of duplexing communications is set forth in a standard or specification.
However, the duplexing configuration set forth in a standard may pose design issues for optimizing communications within a given frequency spectrum. For example, a wireless communication standard may specify FDD operation in symmetric transmit and receive bands. However, the actual frequency spectrum that is licensed by a government entity may consist of two bands that may have different bandwidths. The distinct bandwidths of the licensed bands make it difficult to support the symmetric FDD operation specified in the standard.
Additionally, one or more of the licensed bands may border a band that is licensed to support some other type of communications. There may be severe emissions constraints placed on transmitters operating adjacent the band supporting other types of communications. The emissions constraints may require a system designer to implement a large guard band adjacent the other band supporting other types of communications. In such situations, symmetric FDD uplink and downlink bands may be licensed to a system provider, but the effective usable bands may be asymmetric if the large guard band is implemented in one of the licensed bands but not another. Alternatively, the system capacity may be unnecessarily limited if both the licensed uplink and downlink bands implement the guard band, but only one of the uplink or downlink bands is adjacent the band supporting other types of communications.
A system designer may select from any one of several duplexing implementations, but is constrained by spectrum allocation, operating standards, and adjacent band emissions constraints. The combination of design and operational constraints may make it difficult to optimize system capacity across operating bands.