Efficient combination of MU-MIMO THP and user scheduling to achieve both high system capacity and fairness

Abstract

This letter proposes an efficient method for combining MU-MIMO Tomlinson Harashima precoding (THP) with user scheduling techniques to realize fairness among users as well as high system capacity. The concept of the proposed approach is to first adopt semiorthogonal user selection (SUS) for throughput maximization and then apply proportional fairness (PF) to the remaining users, which regains fairness lowered by using SUS for throughput maximization. Moreover, considering that THP adopted as a precoder for PF requires the calculation of ordering and precoding for each user combination, the proposed method adopts linear precoding (LP) instead of THP to relax the computational effort during operation of PF. This approach is inspired by the fact that LP achieves almost the same system capacity as THP with ordering when conducting PF. The effectiveness of the proposed method is demonstrated by comparing it to MU-MIMO THP with SUS or PF in terms of system capacity and fairness among users, by means of computer simulations. Keywords: MU-MIMO THP, semiorthogonal user selection (SUS), proportional fairness (PF), system capacity, fairness index (FI) Classification: Wireless Communication Technologies

Near Optimum User Selection for Minimum Mean Square Error Based Tomlinson Harashima Precoding

“…Let a composite channel matrix between the select user terminals and the access point be represented as , the composite channel matrix is defined in the following equation. (13) In the following, we describe user selection technique to choose the set s n to maximize the performance in terms of the transmission performance and the complexity.…”

“…Because transmission performance greatly depends on channel condition between user terminals and an access point, user terminal selection techniques for linear precoding have been investigated [9][10][11]. User selection techniques for non-linear precoding such as Tomlinson-Harashima precoding (THP) [12][13][14] also have been investigated, because the THP can be implemented with relatively lower complexity than the other non-liner precoding. For example, user selection techniques to maximize throughput have been investigated [12,14].…”

“…Where the water filling is used in conjunction with the THP. Even when nonlinear precoding is utilized, a user selection technique for a linear precoding has been shown to be useful [13].…”