Joint Preprocessing Techniques for Downlink CoMP Transmission in Multipath Fading Channels

An elaborate coordination among multiple cells called coordinated multipoint (CoMP) transmission/reception is adopted by LTE-A to improve coverage and cell-edge throughput. This paper derives various joint precoding techniques among coordinated cell sites to address the serious co-channel interference (CCI) for downlink CoMP broadband transmission. They include joint time-division multiple access (J-TDMA), joint zero-forcing (J-ZF), joint minimum mean square error (J-MMSE), and joint null-space decomposition (J-NSD). The J-TDMA scheme is automatically free from CCI at the cost of sacrificing spectral efficiency. The J-ZF scheme enables complete suppression of interference, but is at the expense of demanding higher transmitter power on precoding process. The performance of J-MMSE is close to the J-TDMA since it makes a good tradeoff between interference suppression and transmitter power efficiency. In J-NSD, the CCI is completely removed but it comes with a penalty in that a user´s transmission is constrained to a smaller subspace. The precoding is done under the perfect channel state information and thus the simulation results in this paper provide an upper-bound reference for these precoding schemes.