Heterogeneous Path Loss Research Articles

Generalised uplink model for cellular and D2D transmissions

This study investigates a hybrid wireless communication network consisting of both regular cellular users and device-to-device (D2D) users. A generalised uplink model is developed. The model is based on stochastic geometry and encompasses several new features, including heterogeneous pathloss links, non-singular law, configurable pathloss-compensation, and offset uniform distribution. A set of closed-form solutions is derived for the coverage probability and ergodic capacity. Many recently proposed models can be regarded as special cases of the model presented in this study.

Adaptive limited feedback for interference alignment in MIMO interference channels.

It is very important that the radar sensor network has autonomous capabilities such as self-managing, etc. Quite often, MIMO interference channels are applied to radar sensor networks, and for self-managing purpose, interference management in MIMO interference channels is critical. Interference alignment (IA) has the potential to dramatically improve system throughput by effectively mitigating interference in multi-user networks at high signal-to-noise (SNR). However, the implementation of IA predominantly relays on perfect and global channel state information (CSI) at all transceivers. A large amount of CSI has to be fed back to all transmitters, resulting in a proliferation of feedback bits. Thus, IA with limited feedback has been introduced to reduce the sum feedback overhead. In this paper, by exploiting the advantage of heterogeneous path loss, we first investigate the throughput of IA with limited feedback in interference channels while each user transmits multi-streams simultaneously, then we get the upper bound of sum rate in terms of the transmit power and feedback bits. Moreover, we propose a dynamic feedback scheme via bit allocation to reduce the throughput loss due to limited feedback. Simulation results demonstrate that the dynamic feedback scheme achieves better performance in terms of sum rate.

Maximum WSN coverage in environments of heterogeneous path loss

We study wireless sensor network (WSN) node placement in an environment where RF signal losses vary with position. This reflects real-world outdoor environments where vegetation and topography cause nonuniform path loss. Many techniques that solve for a variety of objective functions subject to various constraints have previously been proposed for node placement. However, many of these methods make simplifying assumptions such as all nodes having the same transmission range. Our goal is to take the insights and approaches of this previous ork and extend it to real-world environments. The present work assumes we have a map that quantifies the path loss behaviour of the real environment. Based on this map, and a path loss model that accounts for spatial variations in the path loss exponent, we propose a node placement algorithm for two-tiered WSNs that maximises the area covered by a specified number of relay nodes and sensor nodes.

Limited Feedback Design for Interference Alignment on MIMO Interference Networks With Heterogeneous Path Loss and Spatial Correlations

Interference alignment is degree of freedom optimal on -user MIMO interference channels and many previous works have studied the transceiver designs. However, these works predominantly focus on networks with perfect channel state information at the transmitters and symmetrical interference topology. In this paper, we consider a limited feedback system with heterogeneous path loss and spatial correlations and investigate how the dynamics of the interference topology can be exploited to improve the feedback efficiency. We propose a novel spatial codebook design and perform dynamic quantization via bit allocations to adapt to the asymmetry of the interference topology. We bound the system throughput under the proposed dynamic scheme in terms of the transmit SNR, feedback bits, and the interference topology parameters. It is shown that when the number of feedback bits scales with SNR as C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ·log SNR +O(1), the sum degrees of freedom of the network are preserved. Moreover, the value of scaling coefficient C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> can be significantly reduced in networks with asymmetric interference topology.

Distributed Interference Cancellation for Cognitive Radios Using Periodic Signals of the Primary System

This paper considers secondary usage of spectrum resources that are allocated to frequency division duplexing (FDD)-based cellular systems. We propose an interference cancellation technique using the concept of distributed antenna array. We show that the interference from the primary cellular system can be cancelled at a secondary node equipped with single antenna by introducing a helper that decodes the interference and transfers it to the secondary node. Interference is forwarded during the time periods in which training signals are transmitted within the primary cellular system. Since the duration of those intervals is short relative to periods for data transmission in the primary system, we introduce a scheme by which the helper compresses the interference before forwarding it. The performance advantage of our scheme is verified by computer simulation, where both analytical and measured channel models are used. The measurement data used in evaluations have been obtained through outdoor experiments while assuming a short-range secondary system. The results indicate that the proposed method for distributed interference cancellation leads to performance benefit, in particular under heterogeneous path loss conditions between the helper and the primary/secondary nodes.

Spectrally Efficient Incremental Relaying for Coverage Expansion in Cellular Networks with Heterogeneous Path Loss Conditions

In this paper we propose a cooperative scheme in which fixed relays operate with a higher spectral efficiency than the source. The relay transmits L times faster than the source with L times the spectral efficiency, reducing the loss inherent to the orthogonal cooperation. We assume a large scale path loss model which is capable of handling with heterogeneous conditions between the nodes of the network: the source, the relay and the base-station antennas can be at different heights. Our results show that the proposed scheme consumes less energy while achieving up to 3 dB of gain, in terms of throughput, when compared to the baseline cooperative scheme. In addition, a coverage area analysis shows that the proposed scheme increases considerably the cell area when compared to the non-cooperative transmission and to the baseline cooperative scheme. Finally, we show that the proposed scheme, with a single relay, outperforms in the high signal to noise ratio region the regular cooperative scheme using multiple relays.

Cognitive Radio Operation under Directional Primary Interference and Practical Path Loss Models

This paper discusses the possibility of deploying a short-range cognitive radio (secondary communication system) within the service area of a primary system. Although the secondary system interferes with the primary system, there are certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without causing harmful interference to it and being disturbed by the primary system. These locations are referred to as having a spatial opportunity for communications in the secondary system, since it can reuse the frequency of the primary system. Simulation results indicate that the antenna gain, beamwidth, and propagation path loss greatly affect the spatial opportunity of frequency reuse for the secondary users. The results show that spatial spectrum reuse can be significantly increased when the primary system users are equipped with directional antennas. An important component in this study is the heterogeneous path loss model, i.e., the path loss model within the primary system is different from the model used to calculate the interference between the primary and the secondary systems. Our results show that the propagation models corresponding to the actual antenna heights in the primary/secondary system can largely impact the possibilities for spectrum reuse by the cognitive radios.

A Scalable Limited Feedback Design for Network MIMO Using Per-Cell Product Codebook

In network MIMO systems, channel state information is required at the transmitter side to multiplex users in the spatial domain. Since perfect channel knowledge is difficult to obtain in practice, limited feedback is a widely accepted solution. The dynamic number of cooperating BSs and heterogeneous path loss effects of network MIMO systems pose new challenges on limited feedback design. In this paper, we propose a scalable limited feedback design for network MIMO systems with multiple base stations, multiple users and multiple data streams for each user. We propose a limited feedback framework using per-cell product codebooks, along with a low-complexity feedback indices selection algorithm. We show that the proposed per-cell product codebook limited feedback design can asymptotically achieve the same performance as the joint-cell codebook approach. We also derive an asymptotic per-user throughput loss due to limited feedback with per-cell product codebooks. Based on that, we show that when the number of per-user feedback-bits Bk is {O}( NnTnR log2(ρgksum)), the system operates in the noise-limited regime in which the per-user throughput is {O} ( nR log2 (nRρgksum/NnT)). On the other hand, when the number of per-user feedback-bits Bk does not scale with the system SNR ρ, the system operates in the interference-limited regime where the per-user throughput is {O}(nRBk/(NnT)2). Numerical results show that the proposed design is very flexible to accommodate dynamic number of cooperating BSs and achieves much better performance compared with other baselines (such as the Givens rotation approach).