Modern communication systems rely on multiple antennas that enhance the performance of network links using a series of techniques known as Multiple Input Multiple Output (MIMO). However, new technology is needed to meet the demands of a rapidly increasing number of wireless devices and enable the next generation of cellular systems. Known as Massive MIMO, this adaptation of traditional MIMO techniques presents challenges to research and development teams worldwide.
Device-to-device (D2D) communication that enables direct communication between nearby mobiles is an exciting and innovative feature of next-generation cellular networks. It will facilitate the interoperability between critical public safety networks and ubiquitous commercial networks based on e.g. LTE. How should we analyze and design such hybrid networks consisting of both cellular and ad hoc links? WNCG Profs.
Millimeter wave (mmWave) is a technology that can provide high bandwidth communication links in cellular systems. As mmWave uses larger bandwidths, the corresponding sampling rate of the analog-to-digital converter (ADC) scales up. Unfortunately, high speed, high resolution (e.g., 6-12 bits) ADCs are costly and power-hungry for portable devices. A possible solution is to use special ADC structures like a time interleaved ADC (TI-ADC) architecture where a number of low-speed, high-precision ADCs operate in parallel.
Millimeter Wave (mmWave) cellular will enable gigabit-per-second data rates thanks to the large bandwidth potentially available at this frequency band. Achieving these gains in practice, however, requires dealing with the severe propagation characteristics of high-frequency signals. To combat the enhanced path-loss in outdoor mmWave links and to provide sufficient received signal power, directional beamforming with large antenna arrays needs to be deployed at both the base station and mobile users.
Base station (BS) coordination is regarded as an effective approach to mitigate intercell interference. The idea is to allow multiple BSs to coordinate their transmit and receive strategies (e.g., beamforming, power control, and scheduling) by utilizing channel state information (CSI). A central concept in the implementation of BS coordination with low overheads is to form a cluster, defined as the set of BSs that a given user coordinates with. From the vantage of a user, only those BSs outside the cluster are sources of interference.
Due to the superposition and broadcast nature of the wireless medium, unmanaged interference results in diminishing data rates in wireless networks. With a recently developed network coding strategy, however, it was demonstrated that interference is no longer adverse in communication networks, provided that it can sagaciously be harnessed. This approach of exploiting interference has opened the possibility of better performance in the interference-limited communication regime than traditionally thought possible.
With advances in RF circuits, the era of operating cellular networks in millimeter wave (mmWave) bands is coming. The lightly licensed mmWave band offers the potential to solve the spectrum gridlock in current cellular networks. It is not clear, however, whether both high data rates and coverage in signal-to-noise-and-interference ratio (SINR) can be achieved in mmWave cellular networks; as the propagation conditions and hardware constraints become different, and prior microwave network models do not directly apply to mmWave systems.