Scheduling Versus Contention for Massive Random Access in Massive MIMO Systems

Abstract

Massive machine-type communications protocols have typically been designed under the assumption that coordination between users requires significant communication overhead and is thus impractical. Recent progress in efficient activity detection and collision-free scheduling, however, indicates that the cost of coordination can be much less than the naive scheme for scheduling. This work considers a scenario in which a massive number of devices with sporadic traffic seek to access a massive multiple-input multiple-output (MIMO) base-station (BS) and explores an approach in which device activity detection is followed by a single common feedback broadcast message, which is used both to schedule the active users to different transmission slots and to assign orthogonal pilots to the users for channel estimation. The proposed coordinated communication scheme is compared to two prevalent contention-based schemes: coded pilot access, which is based on the principle of coded slotted ALOHA, and an approximate message passing scheme for joint user activity detection and channel estimation. Numerical results indicate that scheduled massive access provides significant gains in the number of successful transmissions per slot and in sum rate, due to the reduced interference, at only a small cost of feedback.

Rainbow link beamforming technology and relevant analysis

“…The paper [7] proposed a scheduling-based method for massive random access in MIMO systems. The method is based on two discoveries that can significantly reduce downlink feedback for scheduling in order to avoid interference.…”

Effect of Waiting Time and Number of Slots on Vehicular Networking Employing Slotted ALOHA Protocol

“…Figs. [14][15][16][17][18][19] show the relationship between the delivered numbers of frames as a function of dynamically changing total number of slots (N), with Tw=200, while Figs. 20-24 show the same relationship for Tw=2000.…”

“…Thus, it is nowadays considered for general machine to machine (M2M) network applications. Due to the limitation of Slotted ALOHA regarding the size of network, the throughput of applying it is low at medium to high network densities [17,18].…”