Bandwidth Efficient Channel Coding Scheme for Non-cooperative Overloaded Multiuser MIMO Systems Muhammad Bilal Janjua The University of Lahore, Lahore, Pakistan bilal.janjua@es.uol.edu.pk Muhammad Amish Hasan The University of Lahore, Lahore, Pakistan amish.hassan@es.uol.edu.pk Muhammad Zafrullah The University of Lahore, Lahore, Pakistan muhammad.zafrullah@ee.uol.edu.pk Abstract Multiple Input Multiple Output (MIMO) system provides the high data transmission with spectral efficiency under Or- thogonal Frequency Division Multiplexing (OFDM). Multiuser detection becomes complex when there exists a large number of non-cooperative co-channel users in the system. In this scenario, it is difficult to accommodate each user with a separate physical antenna at a receiver. It leads the MIMO-OFDM system to an overloaded condition, where Multi-User Detection (MUD) becomes a challenging problem. In this article, we design an efficient receiver that reduces the complex- ity of an overloaded MIMO-OFDM system with the efficient MUD. In order to achieve the proficient outcomes, Chase Combining Hybrid Automatic Repeat Request (CC-HARQ) protocol is used for the re-transmissions in the receiver to create virtual antennas, which converts an overloaded system into an underloaded or a critically loaded system. Using this technique, the suboptimal detection algorithms can be applied in an overloaded condition. The significant performance improvements in terms of throughput, low Bit Error Rate (BER) and Packet Drop Rate (PDR) are computed analytically and presented through MATLAB simulations. 1 Introduction During last two decades, services and applications of the wireless systems have been increasing drastically along with an exponential increase in the number of users mak- ing it complicated for service providers to satisfy the de- mands of clients. However, multiple antenna systems have brought the revolution in the field of wireless communi- cation by providing ways to enhance spectral efficiency within a limited amount of resources. One of the key fea- tures of MIMO systems is to make wireless communica- tion systems more efficient in terms of capacity, coverage and reliability [1]. MIMO systems are used as underline key technology in all advanced wireless systems, such as Long Term Evolution (LTE), LTE-advance and Worldwide Inter-operability for Microwave Access (WiMax) for better data rates and robustness [2,3]. However, inclusion of mul- tiple co-channel users leads the system to overloaded state, when there is a shortage of receiving antennas as compared to transmitting antennas. This state causes the suboptimal and optimal MUD algorithms to perform poorly and results in high complexity [4]. OFDM technology has made it possible to construct an efficacious receiver with low complexity and frequency di- versity for better resource allocation [5]. It allows optimal decoding algorithms to decode adroitly in MIMO systems. However, the complexity of the algorithm increases with increase in constellation size and number of transmitting antennas. Consequently, suboptimal algorithms compro- mise on performance for low complexity. Despite the fact that MIMO-OFDM offers high capacity and diversity gains in wireless communication, but the presence of channel distortion and multipath fading induce errors in the pack- ets is still a severe problem [6–8]. In order to negate the adverse aspects of multipath fading and channel distortion, retransmissions of erroneous packets are necessary. Au- tomatic repeat request (ARQ) is found to be an appropri- ate protocol to retransmit the erroneous data, but retrans- mission of the whole data is required, even if the smaller amount of bits is corrupted. To reduce the number of re- transmissions, Forward error correction (FEC) codes are combined with ARQ when the channel quality is good [9, 10]. In multiuser MIMO systems, when the receiver has less number of receiving antennas than co-channel users, the system turns to overload and detection algorithms re- sult in poor performance. In recent research work, some multiuser detection algorithms have been proposed using HARQ [11, 12]. In [11], authors designed an optimal mul- tiuser detection algorithm for overloaded MIMO system using HARQ and Network coding (NC) but these are not suitable for the practical situation because these algorithms