International Journal of Computer Networks and Communications Security VOL. 3, NO. 9, SEPTEMBER 2015, 378–383 Available online at: www.ijcncs.org E-ISSN 2308-9830 (Online) / ISSN 2410-0595 (Print) Decrease Interference Using Adaptive Modulation and Coding Osman Mudathir Elfadil 1 , Y. M. Alkasim 2 and Rayan. A. Ali 3 1, 2, 3 Department of Electrical and Electronics Engineering, Omdurman Islamic University E-mail: 1 osman7677@yahoo.com, 2 yasserm89@hotmail.com, 3 eng.ray2014@gmail.com ABSTRACT The limitations of channel bandwidth, time varying channel and fading are significant and fundamental problem in wireless communication, which leads to the difficulty of providing high Quality of Service. The traditional wireless communication systems are designed to provide good quality of services at the worst channel conditions. Wherein any attempts to increase the channel bandwidth, interference arises along with these attempts. And result in inefficient utilization of the full channel capacity. One of the efficient techniques to overcome to these problems is known as adaptive modulation and coding (AMC). This paper was prepared as simulation study of interference decreasing using AMC algorithm where a comparison between ordinary modulation techniques is compared to Multicarrier Modulation MCM and adaptive modulation, results of the simulation was observed and compared for above scenarios. Keywords: MCM, SCM, OFDM, AMC, BER, AWGN, Rayleigh. 1 INTRODUCTION Communication bandwidth is the range of frequencies passed by a wireless or wired medium, the bitrate supported is generally proportional to the bandwidth, and spectral efficiency is the ratio of bitrate to bandwidth. On these media spectral efficiency is limited by interference. In wireless radio any user’s communications typically share the same radio channel one user’s communication becomes unwanted interference to another user’s legitimate communication user’s cannot simply increase their transmitted power to overcome this interference because is increase interference as much as the wanted signal. One of the promising approaches to 4G is adaptive OFDM (AOFDM). In AOFDM, adaptive transmission scheme is employed according to channel fading condition with OFDM to improve the performance. In this paper we consider the use of AMC to decrease the interference and enhance data rate and bit error rate performance. The paper lies in five sections. In section 2 SCM is compared to MCM and investigating MCM and OFDM as MCM which maximum spectral efficiency obtained due to the use of orthogonality. Section 3 contains AMC block diagram and model the received signal and measured SNR for feedback purposes. The simulation was introduced in section 4 with simulation parameters and flow chart for AMC algorithm achieved, results obtained from the simulation was introduced and compared in figures and tables. The conclusion of the paper in section 5. 2 MULTI CARRIER MODULATION In this section, multi carrier modulation has been discussed. In single carrier modulation, data is sent serially over the channel at a bound rate of  symbols per second. The data   is then 1/. The time dispersion can be significant compared to the symbol period, in a multipath fading channel which results in inter symbol interference ISI. A complex equalizer is then needed to compensate for the channel distortion. The basic idea of multicarrier modulation is available bandwidth  is divided into a number of   of sub bands, commonly called subcarriers, each of width ∆ =    , as shown in fig. 1 the band width in single carrier modulation compared to MCM.