RESEARCH ARTICLE Multiple access based on different lengths super orthogonal codes to support QoS of M2M communications in next generation networks Fayezeh Ghavimi 1 | Hsiao‐Hwa Chen 2 1 Engineering Science, National Cheng Kung University, Floor 4, No. 41404, Engineering Science Dep, National Cheng Kung University, 1 Da‐Xue Rd, Tainan 70101, Taiwan 2 National Cheng Kung University, Tainan, Taiwan Correspondence Fayezeh Ghavimi, Engineering Science, National Cheng Kung University, Floor 4, No. 41404, Engineering Science Dep, National Cheng Kung University, 1 Da‐Xue Rd., Tainan 70101, Taiwan. Email: faiezeh.ghavimi@gmail.com Summary Global connectivity, low latency, and ready‐to‐use infrastructure of next generation wireless (NGW) networks provide a platform for machine‐to‐machine (M2M) communications on a large scale. However, M2M communications over NGW net- works pose significant challenges because of different data rates, diverse applica- tions, and a large number of connections. In this paper, we address M2M challenges over NGW networks, and in particular, we focus on random access over- load issue and diverse quality‐of‐service (QoS) requirements to enable M2M com- munications in the context of NGW networks. To enable massive M2M access while QoS guarantees, we propose group‐based M2M communications on the basis of identical transmission protocols and QoS requirements. Furthermore, to guarantee low energy consumption for M2M devices in the same group, we propose a decentralized group‐head selection scheme. In addition, a solution is proposed by using an effective capacity concept to provide QoS guarantees for M2M devices with a strict time constraint. A new random access approach based on different lengths super orthogonal codes is proposed to ease massive random access challenges with provisioning diverse QoS requirements of M2M communications in heterogeneous NGW networks. KEYWORDS grouping, LTE‐advanced, M2M communications, quality‐of‐service (QoS), random access, super orthogonal code 1 | INTRODUCTION Machine‐to‐machine (M2M) communications refer to the ways enabling the applications that provide connectivity among machines or devices without any human interven- tion. 1 Because of global connectivity and wide coverage of cellular systems, they are expected to play a significant role in the successful deployment of M2M communications, thus constituting a platform for ubiquitous communications among all M2M devices. As the ultimate goal of M2M com- munications is to construct all devices, the scenarios defined by 3GPP give the directions to find solutions to enable M2M communications. 2,3 In Third‐Generation Partnership Project (3GPP) Long‐Term Evolution‐Advanced (LTE‐A), various stations can be configured as evolved universal terrestrial radio access NodeBs (eNBs) in macrocells or picocells, home eNBs in femtocells, and relay nodes in relay networks to pro- vide wireless access in both outdoor and indoor environ- ments. 1 Through attaching to those stations, higher‐layer connections among all M2M devices can be provided. How- ever, connections of M2M devices via 3GPP NGW networks brings in new challenges, which needed to be tackled. One of the most important issues in enabling M2M in next generation wireless (NGW) networks is congestion and system overload problem. Congestion due to concurrent transmit messages from a large number of M2M devices can be overwhelming, thus impacting on the operations of a whole mobile network. In the context of M2M Received: 21 October 2016 Revised: 9 January 2017 Accepted: 17 January 2017 DOI 10.1002/dac.3297 Int J Commun Syst 2017;e3297. https://doi.org/10.1002/dac.3297 Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/dac 1 of 15