Null-forming SDMA scheme based on channel responses correlation coefficient

The explosive growth in wireless communications has resulted in a demand for increased capacity on the existing infrastructure. Spatial division multiple access (SDMA) has been under investigation to improve cell capacity in the spatial domain. Conventionally, antenna arrays are deployed at the base stations, and, with beam-forming algorithms, spot beams are directed to desired mobile terminals. Terminals served under different spot beam areas can be allocated the same physical channel. For a beam-forming based SDMA, mobile terminal direction of arrival (DOA) information is usually required for pointing the beam to the right direction. However, it is difficult to estimate the DOA information in a multipath environment; side lobes also induce interference from the same physical channel. Instead of using beam-forming algorithms, we investigate the SDMA scheme with a null-forming algorithm. Nulls are formed toward other users in the same physical channel as the desired user. The channel response correlation coefficient is proposed as the criterion for channel duplication. The performance with respect to probability of bit errors (PBE) is discussed based on a multipath ray-tracing model.