Mark C. Reed

Coverage and Throughput Analysis with a Non-Uniform Small Cell Deployment

Small cell network (SCN) offers, for the first time, a low-cost and scalable mechanism to meet the forecast data-traffic demand. In this paper, we propose a non-uniform SCN deployment scheme. The small cell base stations (BSs) in this scheme will not be utilized in the region within a prescribed distance away from any macrocell BSs, defined as the inner region. Based upon the analytical framework provided in this work, the downlink coverage and single user throughput are precisely characterized. Provided that the inner region size is appropriately chosen, we find that the proposed non-uniform SCN deployment scheme can maintain the same level of cellular coverage performance even with 50% less small cell BSs used than the uniform SCN deployment, which is commonly considered in the literature. Furthermore, both the coverage and the single user throughput performance will significantly benefit from the proposed scheme, if its average small cell density is kept identical to the uniform SCN deployment. This work demonstrates the benefits obtained from a simple non-uniform SCN deployment, thus highlighting the importance of deploying small cells selectively.

Tractable model for heterogeneous cellular networks with directional antennas

Heterogeneous cellular networks consisting of microcell, picocell, femtocell, distributed antennas and relays codeployed in space and frequency with carefully planned tower-mounted base stations, increase the complexity of the cellular network structure, which makes a tractable analysis model difficult to obtain. In this paper, we extend the original tractable model for downlink heterogeneous cellular network to the scenario with directional antennas, from which the coverage probability (or equivalently outage probability) for a randomly located mobile user in this network can be derived. By using this tractable model, the impact of implementing directional antenna for certain heterogeneous tiers can be demonstrated and utilized as a deployment guideline.

Efficient Robust Broadband Antenna Array Processor in the Presence of Look Direction Errors

The performance of adaptive antenna array processors is known to decline severely in the presence of array imperfections and uncertainties. Hence the robustness of an array processor against uncertainties is an important issue. Diagonal loading of the correlation matrix is a popular technique applied to the standard Frost processor to increase robustness of the array system. This paper presents a number of robust beamforming algorithms using efficient realization techniques. The techniques do not use a presteered array and allow an array designer to specify the frequency response of the processor in the look direction and steer the main beam of specified frequency response in an arbitrary direction. The proposed techniques are computationally efficient and applicable in environments with strong mutual coupling. Simulation results show the effectiveness of the proposed beamforming algorithms and compare the performance of the beamformer using the proposed techniques with that of existing methods.

Coverage Analysis of Packet Multi-Tier Networks With Asynchronous Slots

Using stochastic geometry, the downlink (DL) and uplink (UL) coverage probabilities are derived for co-channel packet multi-tier heterogeneous cellular networks (HCNs). The spatial locations of base stations (BSs) as well as user equipments (UEs) are modeled as independent spatial homogeneous Poisson point processes. The decoupled association is evaluated where the UE may connect to different BSs in the UL and DL transmissions. Unlike most of the existing works, the packet transmission slots are not synchronized, that is, the starting and ending points of the slots are not aligned. We investigate fundamental performance metrics of dynamic packet HCN for two traffic models, namely, the slotted-asynchronous and exponential-interarrival. Furthermore, tight lower bounds for the DL and UL coverage probabilities for two traffic models are obtained. The derived bounds are tight especially in high data rate regimes. The analysis provided herein enables us to determine the performance limits of packet-based HCNs with possible asynchronous time-slots. Simulation results are conducted to verify the analytical derivations. Furthermore, the performance comparison between pure synchronous and asynchronous packet-based systems is provided. The results confirm that the synchronous case outperforms the asynchronous one in terms of the UL and DL coverage probabilities at the cost of higher computational complexity.

Recovering signals with variable sparsity levels from the noisy 1-bit compressive measurements

In this paper, we consider the 1-bit compressive sensing reconstruction problem in a scenario that the sparsity level of the signal is unknown and time variant, and the binary measurements are contaminated with the noise. We introduce a new reconstruction algorithm which we refer to as Noise-Adaptive Restricted Step Shrinkage (NARSS). NARSS is superior in terms of performance, complexity and speed of convergence to the algorithms already introduced in the literature for 1-bit compressive sensing reconstruction from the noisy binary measurements.

Joint Low-Power Transmit and Cell Association in Heterogeneous Networks

In heterogeneous networks (HetNets), mobile users are proactively offloaded to small cells by association bias. To alleviate the signal-to-interference-plus-noise-ratio (SINR) degradation to offloaded users, resource partitioning and transmit power reduction are proposed in Long Term Evolution-Advanced (LTE-A), which is known as enhanced inter-cell interference coordination (eICIC). In this paper, we develop a tractable framework for performance analysis of eICIC with joint cell association, resource partitioning, and transmit power reduction by using stochastic geometry. We derive the downlink coverage probability of the network. Numerical results are provided and we give some valuable insights and guidelines for eICIC in cochannel HetNets.

Robust Efficient Broadband Antenna Array Pattern Synthesis Techniques

This paper presents efficient robust broadband antenna array pattern synthesis techniques with interference cancellation capabilities. The synthesis techniques are able to place multiple broad nulls and isolated point nulls at regions of interest for interference cancellation. The new synthesis algorithms result in improved performance broadband antenna array processors. The presented synthesis techniques are computationally more efficient than the existing synthesis techniques. The paper includes numerical simulations that demonstrate the performance of the new techniques compared to existing methods.

On Capacity and Association Area Characterization in Small Cell-Based Multi-Tier Networks

A mathematical framework is developed for statistical characterization of association cell and channel capacity in co-channel two-tier networks. The cell association and capacity derivation are based on maximum instantaneous received power (IRP) or equivalently Max-SIR in the downlink. We consider two-tier networks consisting of Macro cell base station (MBS) and small cell base station (SCBS). Characterizing coverage in multi-tier networks is critical as it is connected directly to network throughput and load. Two channel models, Log-normal shadowing and Nakagmi- m fading are considered to account for multipath fading. It is shown that in both channel models the cell association areas of SCBS have different behavior compared to path-loss only case. Numerical results provided herein confirm the validity of analytical results.

Iterative detection for compressive sensing: Turbo CS

We consider compressive sensing as a source coding method for signal transmission. We concatenate a convolutional coding system with 1-bit compressive sensing to obtain a serial concatenated system model for sparse signal transmission over an AWGN channel. The proposed source/channel decoder, which we refer to as turbo CS, is robust against channel noise and its signal reconstruction performance at the receiver increases considerably through iterations. We show 12 dB improvement with six turbo CS iterations compared to a non-iterative concatenated source/channel decoder.

Efficient robust broadband beamforming using circular antenna arrays

Broadband antenna arrays can suffer significant performance degradation when the array response vector for the desired signal is not known exactly. Diagonal loading of the correlation matrix is a popular technique applied to the beamformer to increase robustness of the array system. This paper presents two robust beamforming algorithms for circular broadband arrays using efficient realization techniques. These techniques do not use presteering, and allow an array designer to arbitrarily specify the main beam look direction and frequency response. The circular array processor is able to scan a beam azimuthally through 3600 with little change in either the beam width or the sidelobe level. Simulation results exhibit enhanced robustness performance of the processor.