International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 2 Issue: 2 212 – 215 ______________________________________________________________________________________ 212 IJRITCC | February 2014, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Capacity Improvement in Multi-User MIMO System using Dirty Paper Coding Garima Saini, Assistant Professor (ECE Department) National Institute of Technical Teachers Training and Research Chandigarh, India garimasaini_18@rediffmail.com Shivkaran Meghwal, M.E. student (ECE Department) National Institute of Technical Teachers Training and Research Chandigarh, India shivkaran_sonel@yahoo.co.in Abstract —The capacity of Gaussian broadcast MIMO channel can be improved with Dirty Paper Coding. In this paper, the mean capacity for MU-MIMO (Multi-User Multiple Input, Multiple Output) is analyzed in terms of number of frames, available number of users at mobile station and number of packets. The analysis is done for 4x4 matrix. Dirty Paper Coding improves the degradation due to correlation and mutual coupling. In multi-user communication, multiple antennas allow users to transmit their data stream in the uplink and downlink Keywords- Multiple Input Multiple Output (MIMO), Broadcast Channel(BS), Multiple access Channel (MAC), Multi User Multiple Input Multiple Output (MU-MIMO), Dirty Paper Coding (DPC), Signal correlation, Mean capacity. __________________________________________________*****_________________________________________________ I. INTRODUCTION In conventional communication system, single antenna is used at two sides of communication link. In wireless communication system, multiple transmitting and receiving antennas are used for achieving greater system capacity [1]. The system capacity is bounded by correlation [2]. Correlation is due to closeness of antenna elements [3]. In multi path channel, the MIMO capacity for single user N R xN T system is proportional to N min =min(N T ,N R ) [4]. In single user MIMO system, a point to point high data rate transmission can be supported by spatial multiplexing while providing spatial diversity gain. In modern communication era, most communication system deals with multiple users, sharing the same radio sources [5]. For enjoying applications such as Wireless LAN, Cellular telephony, single base station must communicate with many users simultaneously. Therefore, the study of Multi-User MIMO systems has emerged as an important research topic recently [6]. In Figure 1. Multi-user communication is shown. The mobile stations are served by a single base station. Figure1. A Multi-user MIMO system for K=4 Here, four users (K=4) are connected to base station. Three users are selected and allocated communication resource such as time, frequency, and spatial stream. Base station and each mobile station are equipped with N B and N M antennas. In multi-user, K.NM antennas can communicate with a single base station (BS) with N B antenna. So, in multi-user MIMO system, multiple independent users can transmit data to base station (BS) and can decode data by each user simultaneously. Multi-user MIMO is attributed to increase in degree of freedom with multiple antennas as in the single user MIMO system [7]. Multi-user MIMO requires perfect data and power cooperation between the base stations. The sum capacity in a Multi-user MIMO is equivalent to maximum aggregation of user’s data rates. II. MATHEMATICAL MODEL FOR MULTI USER MIMO [7] A. Uplink Channel (Multiple access channel) In Figure 2. Uplink channel is mathematically modeled. As discussed earlier, base station and mobile station are equipped with N B and N M antennas. The received signal for uplink is given by z x H x H x H y K UL K UL UL MAC     .. .......... 2 2 1 1 (1)