Advanced Wireless Local Area Networks in the Unlicensed Sub - 1 GHz ISM - bands

This dissertation addresses the challenges of wireless local area networks (WLANs) that operate in the unlicensed sub-1GHz industrial, scientific, and medical (ISM) band. Frequencies in the 900MHz spectrum enable a wider coverage due to the longer propagation characteristics of the radio waves. To utilize globally available sub-1GHz (S1G) ISM-bands, the IEEE 802.11ah Task Group started to standardize a new WLAN protocol in 2010. The IEEE 802.11ah WLAN protocol enables moderate data rates over a wider coverage area. However, this introduces newer challenges that need to be addressed in such a system. They are, reduction of energy consumption and the network performance in high density WLANs. Additionally, the presence of short-range wireless personal networks (WPANs) in the S1G ISM radio-band is of paramount importance. Coexistence problems between WLANs and WPANs compromise the data transmission performance in both networks due to numerous data retransmissions. However, the fact that no IEEE 802.11ahWLAN currently exists limits the discussion on potential system improvements. Therefore, a novel wireless prototype is proposed in this thesis that enables the testing of S1G WLANs. This dissertation is organized into two parts. The first part outlines the motivation for S1G WLANs (Chapter 1) and introduces the emerging IEEE 802.11ah WLAN protocol amendment (Chapter 2). It includes the fundamentals of the S1G physical layer (PHY) and media access control (MAC) strategies, followed by an introduction of the IEEE 802.11ah WLAN protocol functions. The second part includes the building of such a network and testing it on a testbed. To obtain over-the-air evaluation results of the new S1G WLAN, a novel narrow-band multiple-input multiple-output (MIMO) IEEE 802.11ah WLAN prototype is proposed (Chapter 3). This prototype consists of software-defined radio (SDR) hardware and software components operating at 900MHz. In general, the prototype allows first-hand experiments using carrier frequencies in the licenseexempt 915 to 930MHz ISM-band in Japan. The motivation is to obtain performance results of data transmission under controlled environmental conditions and to evaluate the findings, including the signal characteristics, upper bound of throughput, and coexistence issues. The prototype utilizes the 802.11ah PHY and MAC scheme along with the limited channel bandwidth of 1MHz. Additionally, a novel