Optimum Selection of Modes Set for Adaptive Modulation and Coding based on Imperfect Channel State Information Mehrdad Taki Department of Electrical Engineering University of Qom Qom, Iran E-mail: m.taki@qom.ac.ir Reza Mahin Zaeem - Tehran, Iran E-mail: reza.zaeem@gmail.com Received: September 28, 2016- Accepted: December 19, 2016 Abstract—Complexity issues and limited feedback rate strictly constrain the number of transmission modes in discrete link adaptation. A new algorithm is designed for selecting an optimum set of modes out of all the possible transmission modes based on the link’s characteristics and the constraints, meanwhile, imperfect channel state information (CSI) is available. The design goal is to maximize the average spectral efficiency and the selection is done using a combination of nonlinear quantization and integer programming. As numerical evaluations for adaptive LDPC or convolutional coded, QAM modulated transmission show, performance of the proposed scheme is considerably improved in comparison with the benchmark schemes. Keywords-component; Link Adaptation; Adaptive Modulation and Coding; Integer programming I. INTRODUCTION Link adaptation is an efficient tool to conquest multipath fading in wireless communication systems where transmission rate is adapted based on the received SNR [1]. In practice, a limited set of modes may be utilized where each mode is implemented with a modulation and a coding scheme resulting in a specific transmission rate, i.e., adaptive modulation and coding (AMC). Obviously, the more the number of transmission modes are, the better the performance of the system would be. However, the implementation of each mode requires the use of appropriate hardware/software in the transmitter and the receiver while the hardware complexity and processing capability are limited especially in user end systems. In addition, another obstacle in which practical systems may be confront is that adapting rate based on perfect channel state information (CSI) is impossible. That CSI is not existing because of error in channel estimation and time variant essence of channels. Eventually, the index of appropriate mode must be sent back to the transmitter, as regards, increasing the number of modes would increase the feedback rate, so limited number of transmission modes must be considered. AMC is implemented in IEEE 802.11 [2] and DVB [3] standards. Not only it is shown that the performance of different systems is improved by using AMC with perfect CSI [4]-[13], but also it can be observed that AMC increase system's performance with imperfect CSI [14]-[15]. In the mentioned articles, a limited number of transmission modes are selected randomly and the selected set remains unchanged, although, by the change of the link’s characteristics or constraints. Based on the author's knowledge, no Downloaded from journal.itrc.ac.ir at 15:06 IRST on Wednesday February 17th 2021