Due to abundant frequency resources, millimeter wave (mm-wave) spectrum has drawn much attention as a solution to bandwidth scarcity. However, many characteristics of mm-wave transmissions, such as blockage and reduced coverage, make conventional network architectures very inefficient for use in mm-wave networks. A recently proposed multi-tier mm-wave network architecture allows for relaying around blockages and enlarges the coverage of each base station at an acceptable deployment cost. Nevertheless, this architecture introduces major challenges to the scheduling of each tier. The necessity of both enabling flexible user association and fully exploiting the wireless backhaul requires a cross-tier consideration of the multi-tier mm-wave network. We comprehensively analyze the scheduling problem of a downlink multi-tier mm-wave network by jointly regulating the transmissions in all tiers. The cross-tier optimization problem is NP-hard, but a sub-optimal scheme which iteratively optimizes the schedule in different tiers of the network is proposed with polynomial computational complexity. Simulation results show that our algorithm significantly outperforms the benchmarks in both spectral efficiency and fairness with various user distributions.

Migrating to higher frequencies using millimeter wave (mmWave) signaling will expand the networks capacity to satiate the current demand for higher throughput. However, the overhead cost required for a centralized scheduler to function in an mmWave network quickly becomes intractable as user and access point (AP) density increase. Alternatively, a decentralized approach where users in mmWave networks opportunistically transmit may greatly benefit from a higher AP density. Taking advantage of the AP diversity projected for mmWave networks a user may sequentially probe APs before selecting a destination AP for transmission. An opportunistic user in an mmWave network must balance the benefit of AP diversity against the overhead cost. We present an mmWave opportunistic network model encompassing the probability of an AP becoming unavailable and the cost of initial access. Our optimal opportunistic strategy is a set of thresholds, which are computable a priori. Bounds on average overhead, delay and throughput of our strategy are also presented. Via numerical analysis, we show that at finite and relatively small probings our proposed strategy outperforms practical alternatives.

Future millimeter wave (mmWave) frequency networks leveraging great swaths of unlicensed bandwidth, dense access point deployments, and beamforming may satiate the current demand for higher throughput. In a dense network, a centralized scheduling approach becomes infeasible. Therefore a user may opportunistically transmit to one of the multiple access points (AP) in its vicinity. Leveraging the AP diversity, a user may probe several APs before selecting a destination for the transmission. However, it is possible that the destination AP becomes unavailable or is in blockage when the user decides to transmit due to the density of the network. We present a novel mm Wave opportunistic network model which encompasses the probability of an AP becoming unavailable. Our optimal opportunistic transmission strategy maximizes the throughput of an opportunistic user. Results show that when users are unwilling to bear large delays, our strategy outperforms alternative methods. Additionally, our strategy performs equally to alternatives when users can shoulder the burden of delay.

In this paper, the radio parameters are designed for OFDM-based millimeter-wave (mmWave) communication systems. Firstly, design principles are presented to meet 5G requirements. Secondly, the radio parameters including TTI length, CP length and sub-carrier spacing for mmWave bands are discussed. In particular the impact of phase noise on subcarrier spacing is analyzed in detail. It shows that the phase noise dominates the sub-carrier spacing design. Based on the measured phase noise model, minimum sub-carrier spacing of 250 kHz and 500 kHz is inferred for typical mmWave bands (30 GHz and 70 GHz). At last a numerology with 600 kHz sub-carrier spacing and 512 OFDM symbols per subframe (1 millisecond) is proposed as a unified one for all mmWave bands, which can satisfy the design principles of mmWave systems.

Applying 6-100 GHz spectrum to mobile communications is a promising topic in 5G. In this paper, a hybrid network is presented where LTE system at low frequency works for seamless coverage and a mmWave system at 72 GHz works in hotspots for capacity enhancement. The scheme for the hybrid network includes: 1) frame structure and OFDM-based numerology for 72 GHz; 2) time-space beam switching method for beamforming; 3) zero-forcing MIMO precoding for interference cancellation; 4) a channel model based on measurements in [1] for simulation. System-level simulations show that the hybrid network can achieve the system throughput over 1600 times higher than that in 2 GHz frequency band in case of two streams. MIMO precoding is not mandatory for capacity enhancements because the effect of intra-cell interference is not severe. Thus, 72 GHz is a promising spectrum band that can well meet 5G requirements from the aspects of capacity and maximum data rate.

Spatial consistency is identified as an important feature for fifth generation (5G) channel model. In this paper, a geometry stochastic approach for spatial consistency is presented under the framework of spatial channel model. The extended stochastic channel model (SCM) realizes large-scale parameters(LSPs) and small- scale parameters (SSPs) in a continuous and realistic manner as a function of position. Channel measurements at 73 GHz are taken in an outdoor scenario, where correlation distances are analyzed, and observation on spatial consistency is found. Simulations of the extended channel model verify that the channel realizations can well present the properties of spatial consistency and match our measurements.

Millimeter-wave communication is deemed to be one of the promising solutions to meet the growing traffic explosion for the next generation wireless communication system. The compact design of millimeter-wave antenna makes it possible to form large number of narrow beams to cover a certain area. However, the number of beams that can be scheduled simultaneously is not as many as possible due to the hardware restriction of millimeter-wave. In this paper we proposed two beam scheduling schemes, namely Signal to Interference plus Noise Ratio (SINR) based scheduling scheme and Signal to Leakage plus Noise Ratio (SLNR) based scheduling scheme, targeting to suppress the interference between beams within one millimeter-wave pico station. The numerical simulation results indicate that the two proposed schemes significantly outperform the classical round robin scheduling scheme and proportionally fair scheduling schemes at both 28GHz and 72GHz frequency. The SINR based scheduling scheme achieves a gain about 120% at 28GHz and a gain about 75% at 72GHz respectively over the round robin scheduling scheme, in terms of cell average spectrum efficiency. The SLNR based scheduling scheme achieves a gain about 70% at 28GHz and a gain about 250% at 72GHz respectively over the round robin scheduling scheme, in terms of the cell-edge spectrum efficiency1.

In this paper, a mmWave unified access and back-haul (UAB) network is presented, where both radio access (RA) and backhaul (BH) share the same millimeter wave bands. Considering uniform resource allocation of RA and BH radio resource for all pico stations, which can well mitigate the interference among pico stations, the capacity of UAB is mainly influenced by the allocated resource ratio between RA and BH. Three dynamic resource allocation algorithms are proposed in this paper. The algorithms investigate maximization of network capacity and the fairness among stations, respectively. Results show that the proposed algorithms can well achieve a trade off between capacity and fairness guarantee. Compared to fixed resource allocation method, the system capacity can be improved up to 35% depending on the circumstance of traffic demands among pico stations.

Channel model is the fundamental issue to study and design millimeter wave communications, especially for beam-tracking evaluation where large-scale antenna array is applied. In this paper, a new channel model based on 3GPP spatial channel model (SCM) framework is proposed, which introduces variant arrival and departure angles. A linear variation with time is modeled to describe the angle changes where UE is assumed to move in a short range. The model well meets the requirements of beam-tracking evaluation where keeping spatial consistence. Simulations with ray-tracing tools verify the variant angles in indoor dining hall scenario.