Research
Massive Machine-Type Communications
The Internet of Things (IoT) has been envisioned as a key application scenario in the fifth-generation (5G) wireless networks. It aims to interconnect large numbers of devices (more than 1M devices / km2 defined by the 3GPP) to support emerging applications, such as e-health, smart homes, and industrial Internet. However, IoT also poses new challenges to networking and communication protocols because of its unique features. First, unlike the existing data communication system where most data transmission takes place in the downlink (DL), much of the communication in IoT takes place in the uplink (UL). As a result, a vast number of devices pose a considerable challenge to how to coordinate UL data transmission with limited spectrum resources. Second, in most IoT applications, each device generates intermittent data with a very short message payload. Therefore, existing data communication protocols (e.g., 4G LTE) are not suitable for IoT traffic due to considerable signal overhead before data transmission.
The Massive Machine-Type Communication project focuses on developing IoT UL communication protocols with low overhead and high spectral efficiency. Common random access (RA) protocol, such as ALOHA, CA-ALOHA, and CSMA, enables multiple access in a distributed manner, but they do not aim to exploit MIMO multiplexing gains and the benefit of CSMA over ALOHA type RA is limited when the IoT payload is short and . Even though significant progress has been made in designing non-orthogonal multiple access (NOMA) such as sparse code multiple access (SCMA) for multiplexing users using different codebooks, it overlooked the use of MIMO technology, a key driver of the performance gains of 4G LTE systems due to the complexity of MIMO. Besides, a centralized MIMO scheme results in high overhead because it requires the collection of channel state information (CSI) from all users. Therefore, how to design the UL IoT multiple access systems that can exploit MIMO gains with low complexity and low overhead remained unsolved. We propose UL random access protocols using pseudo-random beamforming. Specifically, for 1) infinite backlog systems, uniform loads, and channel conditions, and 2) finite backlog systems, uneven loads, and channel conditions, we develop joint beam selection and random access schemes that can provably achieve fractions of the optimal capacity region with low overhead regardless of the number of interfering devices.
Publications
Y. Zou, K. T. Kim, X. Lin, M. Chiang, Z. Ding, R. Wichman, and J. Ha ̈ma ̈la ̈inen, “Low-overhead multi-antenna-enabled uplink random access for massive machine-type communications with low mobility,” Proc. IEEE GLOBECOM Conf., Puako, HI, December 2019