Synchronization of mutually coupled digital PLLs in massive MIMO systems

Oscillation Modes in Symmetrical Wireless-Locked Systems

“…IME synchronization between different devices is a usual requirement in engineering systems, such as computer networks, measurement systems, sensor networks and other [1]- [10]. For instance, the efficient data transmission in a multiple-input multiple output (MIMO) antenna systems, requires phase synchronization between the antennas, which is still a significant challenge [2]. In the case of sensor networks, a common time scale between the sensor nodes [10] enables applications such as cooperative transmissions, data-fusion of time-sensitive measurements or moving object tracking.…”

“…Alternative methods based on the wireless coupling of the oscillators in the network nodes [1]- [12] have been proposed. In pulsecoupled oscillators [6], [8]- [9], pulsed signals are transmitted and the nodes must detect the time of arrival of these pulses [1]- [2]. Two different time scales are involved [5]: the fast one corresponding to the short-duration pulse and the slow one corresponding to the phase evolution of each of the oscillator elements.…”

“…Although there are many previous works on wireless coupled oscillators [1]- [13], most of them rely on ideal models [2]- [3] of both the oscillator circuits, represented in terms of phase variables, and the coupling action, described with constant scalar coefficients and time delays. The work [14] presented a first detailed investigation of a system of three wireless-coupled oscillators, using a formulation that relies on linearized oscillator elements, extracted from harmonicbalance (HB) simulations, as well as detailed descriptions of the coupling effects, which consider the antenna gain and signal propagation.…”

“…The oscillator elements behave in an injection-locked mode, instead of being phase-locked loops (PLL). In the PLL case [2], the antenna signals enter the phase-detector of each oscillator and there is no clear solution to use a single antenna for both transmission and reception. This is easily achieved in the case of injection-locked operation, which should enable a simple testing of different network topologies.…”

On the Capacity and Transmission Techniques of Massive MIMO Systems

“…Further, malfunctioning of a few antennas will not affect the performance since the serving antennas are a dynamic group (can be hot swapped) [16]. Many of the recent literature on massive MIMO focuses on implementation issues such as carrier synchronization [17] and pilot contamination [18]. Increased hardware complexity due to the requirement of an analog radio frequency (RF) chain for each antenna also has been a concern.…”