Abstract
The combination of multiuser multiple-input multiple-output (MU-MIMO) technology with orthogonal frequency division multiplexing (OFDM) is an attractive solution for next generation of wireless local area networks (WLANs), currently standardized within IEEE 802.11ac, and the fourth-generation (4G) mobile cellular wireless systems to achieve a very high system throughput while satisfying quality of service (QoS) constraints. In particular, Block Diagonalization (BD) scheme is a low-complexity precoding technique for MU-MIMO downlink channels, which completely pre-cancels the multiuser interference. The major issue of the BD scheme is that the number of users that can be simultaneously supported is limited by the ratio of the number of base station transmit antennas to the number of user receive antennas. When the number of users is large, a subset of users must be selected, and selection algorithms should be designed to maximize the total system throughput. In this paper, the BD technique is extended to MU-MIMO-OFDM systems and a low complexity user scheduling algorithm is proposed to find the optimal subset of users that should transmit simultaneously, in light of the instantaneous channel state information (CSI), such that the total system sum-rate capacity is maximized. Simulation results show that the proposed scheduling algorithm achieves a good trade-off between sum-rate capacity performance and computational complexity.
Highlights
The forthcoming breed of wireless standards, commonly referred to as fourth generation (4G) systems (LTE-Advanced, WiMAX or IEEE 802.11ac), are expected to satisfy the increasing demand for high data rates while satisfying quality of service (QoS) constraints
It is well known that multiuser multiple-input multiple-output (MIMO) (MU-MIMO) techniques are capable of significantly increasing capacity compared to traditional MIMO wireless systems [5]
We propose a low-complexity multicarrier user selection algorithm for Block Diagonalization (BD)
Summary
The forthcoming breed of wireless standards, commonly referred to as fourth generation (4G) systems (LTE-Advanced, WiMAX or IEEE 802.11ac), are expected to satisfy the increasing demand for high data rates while satisfying quality of service (QoS) constraints. It is assumed that the sum-rate capacity of MIMO broadcast channels can be achieved by applying dirty paper coding (DPC) at the transmitter [7] Implementing this technique in practice is still a challenging task because of the complicated encoding and decoding schemes [8], especially when the number of users is large. As the number of users grows, the size of the search space becomes computationally very complex To reduce this complexity, a large number of existing user selection approaches (e.g., [10], [11], [12]) has been employed to achieve a sum-rate capacity close to the one promised by DPC. The BD technique for inter-user interference pre-cancelation is extended to MU-MIMO-OFDM systems and a low-complexity scheduling algorithm, based on [13], is developed considering the availability of multiple-antenna receivers. The operation and represent the transpose and the Hermitian transpose of a matrix, respectively, and denote the Frobenius-norm (F-norm) of a matrix . is the cardinality of subset , denotes the expectation operator, Tr(.) is the trace and is the set of complex numbers
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