5G Oscillators Requirements Soar In the Wake of Stringent Timing & Synchronization Requirements
Though 5G comes with many promises of a ubiquitous high-speed experience with dramatically improved performance over 4G systems, there are several necessary upgrades to underlying technology and infrastructure that are necessary to achieve those desired ends. One such area is with timing and synchronization. In order to realize the desired 5G network responsiveness for high order modulation techniques, intra-band carrier aggregation (CA), multi-input multi-output (MIMO), downlink coordinated multi-point transmission/reception (CoMP), and uplink CoMP, the synchronization between the various circuits that drive the transmitters, receivers, and modulators/demodulators functions require tighter synchronization specifications.
Adding in the ultra-reliable low-latency communications (URLLC) aspect of 5G, this means that the entire synchronization chain from the air interface at the remote radio units (RRUs) through the entire network infrastructure and to the end-device must be taken into account to achieve a tight end-to-end (E2E) latency. For 5G time-domain duplex (TDD) networks alone the initial target for E2E is 1.4 microseconds, which will likely become more stringent over time.
A key component of the synchronization chain, and a limiting factor to timing and synchronization, is the RF oscillator. Hence, Oscillators for 5G applications must now meet more stringent standards of phase noise and other forms of noise to achieve a tighter maximum time interval error in order to maintain timing within a local customer of RRUs. Specifically for MIMO, the phase noise for a local oscillator (LO) contributes directly to channel aging which negatively impacts the linear precoding of the MIMO signals. The result of which is substantial performance degradation. The same goes for phase noise with high order quadrature amplitude modulation (QAM), for which the higher order QAM techniques require even lower jitter and phase noise requirements to meet specified bit-error rate (BER) and other signal quality parameters.
Lastly, energy millimeter-wave 5G applications are requiring LOs with higher base frequencies, as upconverting and LO signal requires both amplification and a mixer at the output of the LO signal. These components not only add noise, phase noise, and contribute to jitter, but they also introduce undesirable non-linearities and spurious behavior. Therefore, there is likely to be an increasing need for higher performance oscillators for telecoms applications on the infrastructure side that may be similar to oscillators required for military and aerospace radar and communications applications.