Link Quality Metrics Research Articles

Modeling ordered subcarrier SNR in MIMO-OFDM wireless links

Recent research has shown that the detected bit error-rate of coded and bit-interleaved multiple-input, multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) links is characterized by the ordered post-processing signal-to-noise ratio (SNR). In this paper, we show that the per-stream ordered SNR converges asymptotically (with delay spread) to the inverse, marginal cumulative distribution function (CDF) of post-processing SNR. We derive a new approximation of the post-processing SNR inverse marginal CDF through an approximation of the marginal CDF for ordered eigenvalues in Wishart random matrices. By evaluating the independence of subcarriers in terms of the power delay profile, we show that the inverse marginal CDF is also an important characterization of post-processing SNR in practice. We exploit this structure to improve principal component regression algorithms that empirically infer a low-dimension basis for ordered SNR. Numerical simulations show high accuracy of this basis with just three dimensions for arbitrary power delay profiles. The consequences of this work include high-resolution limited channel feedback, simpler channel models for system simulation and algorithm design, as well as the reduction of dimension in link quality metrics for link adaptation. Simulations demonstrate the application to link adaptation in IEEE 802.11n with constellations that may be adapted per spatial stream.

On the Suitability of Using ANT Colony Optimization for Routing Multimedia Content over Wireless Sensor Networks

This paper studies the suitability of using a meta-heuristic ant colony technique in routing multimedia content over wireless sensor networks. The presented technique is both energy and QoS-aware. Ant colony algorithm is used to find the optimal routing path. Optimality is in the sense of minimizing energy consumption and increasing link quality and reliability. The proposed approach results in minimizing energy consumption and prolonging the lifetime of the network. Moreover, the optimal path has a high link quality and reliability which enhances video frame quality and ensures high probability of successful delivery of video frames. The importance given to energy consumption, link quality, and link reliability metrics can be varied depending on the multimedia application requirements.

Value-Aware Resource Allocation for Service Guarantees in Networks

The traditional formulation of the total value of information transfer is a multi-commodity flow problem. Each data source is seen as generating a commodity along a fixed route, and the objective is to maximize the total system throughput under some concept of fairness, subject to capacity constraints of the links used. This problem is well studied under the framework of network utility maximization and has led to several different distributed congestion control schemes. However, this view of value does not capture the fact that flows may associate value, not just with throughput, but with link-quality metrics such as packet delay and jitter. In this work, the congestion control problem is redefined to include individual source preferences. It is assumed that degradation in link quality seen by a flow adds up on the links it traverses, and the total utility is maximized in such a way that the end-to-end quality degradation seen by each source is bounded by a value that it declares. Decoupling source-dissatisfaction and link-degradation through an effective capacity variable, a distributed and provably optimal resource allocation algorithm is designed to maximize system utility subject to these quality constraints. The applicability of the controller in different situations is supported by numerical simulations, and a protocol developed using the controller is simulated on ns-2 to illustrate its performance.

Comparative analysis of link quality metrics and routing protocols for optimal route construction in wireless mesh networks

We provide a comparative analysis of various routing strategies that affect the end-to-end performance in wireless mesh networks. We first improve well-known link quality metrics and routing algorithms to enhance performance in wireless mesh environments. We then investigate the route optimality, i.e., whether the best end-to-end route with respect to a given link quality metric is established, and its impact on the network performance. Network topologies, number of concurrent flows, and interference types are varied in our evaluation and we find that a non-optimal route is often established because of the routing protocol’s misbehavior, inaccurate link metric design, interflow interference, and their interplay. Through extensive simulation analysis, we present insights on how to design wireless link metrics and routing algorithms to enhance the network capacity and provide reliable connectivity.

Link quality analysis and measurement in wireless mesh networks

Protocols and applications in wireless mesh networks often optimize their performance by measuring the quality of wireless links. However, measuring and characterizing link-quality is a challenging task due to the nature of wireless channel and device-specific properties of radios. The paper proposes two aspects of link-quality measurement and estimation in realistic networks that benefit higher-layer protocols. First, we analyze the statistical properties of link-quality metrics, such as received signal strength and packet error rates, in an indoor IEEE 802.11 mesh network. We show that the statistical distribution and memory properties vary across different links, but are predictable. The next contribution of the paper is a real-time measurement framework that enables higher-level protocols in wireless mesh networks. We discuss the architectural requirements and our implementation experiences of a measurement framework. In addition, we provide three concrete applications that use the measured link-quality and statistical inference to better adapt their behavior.

A Hybrid Mesh Routing protocol for ubiquitous internet connectivity in hierarchical Wireless Mesh Networks

We propose a cross-layer-aware Hybrid Mesh Routing (HMR) protocol for the ubiquitous Internet connectivity in hierarchical Wireless Mesh Networks (WMNs) that can provide the Internet access for users by mesh routers. The HMR protocol applies two independent routing metrics to obtain high performance. The HMR is able to take advantage of each of those protocols strengths depending on the situation, and more suitable than other protocols in hierarchical hybrid WMNs by providing the benefits of both hop count and link quality metrics. Through simulations, we show that our schemes perform better than existing mechanisms in terms of various performance measures.

Fast Link Adaptation for MIMO OFDM

We investigate link-quality metrics (LQMs) based on raw bit-error-rate, effective signal-to-interference-plus-noise ratio, and mutual information (MI) for the purpose of fast link adaptation (LA) in communication systems employing orthogonal frequency-division multiplexing and multiple-input-multiple-output (MIMO) antenna technology. From these LQMs, the packet error rate (PER) can be estimated and exploited to select the modulation and coding scheme (MCS) among a class of candidate MCSs that achieves the maximum throughput for the current channel state under a specified target PER objective. We propose a novel MI-based LQM and compare the PER-estimation accuracy obtained with this LQM with that resulting from using other LQMs by means of comprehensive Monte Carlo simulations. Search methods for the MCS in the class that is most suitable for a given channel state are presented. An algorithm for obtaining a practical upper bound on the throughput of any LA scheme is proposed. The investigated LQMs are applied to the IEEE 802.11n standard with a 2 × 2 MIMO configuration and practical channel estimation. The proposed MI-based LQM yields the highest PER estimation accuracy, and its throughput shows only 1.7 dB signal-to-noise-ratio (SNR) loss with respect to the upper bound but up to 9.5 dB SNR gain, compared to the MCS maximizing the throughput for the current noise variance.

Energy and Link Quality Based Routing for Data Gathering Tree in Wireless Sensor Networks Under TINYOS - 2.X

Energy is one of the most important and scarce resources in Wireless Sensor Networks (WSN). WSN nodes work with the embedded operating system called TinyOS, which addresses the constrains of the WSN nodes such as limited processing power, memory, energy, etc and it uses the collection Tree Protocol (CTP) to collect the data from the sensor nodes. It uses either the four-bit link estimation or Link Estimation Exchange Protocol (LEEP) to predict the bi directional quality of the wireless link between the nodes and the next hop candidate is based on the estimated link quality. The residual energy of the node is an important key factor, which plays a vital role in the lifetime of the network and hence this has to taken as one of the metric in the parent selection. In this work, we consider the remaining energy of the node as one of the metric to decide the parent in addition to the link quality metrics. The proposed protocol was compared with CTP protocol in terms of number of packets forwarded by each node and packet reception ratio (PRR) of the network. This work was simulated in TOSSIM simulator and the same was tested in Crossbow IRIS radio test bed. The results show that our algorithm performs better than CTP in terms of load distribution and hence the increased lifetime

Using fuzzy link cost and dynamic choice of link quality metrics to achieve QoS and QoE in wireless mesh networks

The growth of multimedia applications and wireless systems requires a new behavior of routing protocols for wireless mesh networks (WMNs). It is necessary to provide not only the minimum requirements for quality of service (QoS), but also to assure the quality of experience (QoE) support for multimedia applications. In this context, the usage of only one link quality metric for routing different types of packets within the network is not enough to ensure applications with suitable QoS and QoE levels. This paper presents a variation of the WMN routing protocol optimized link state routing (OLSR), to achieve QoS and QoE requirements for multimedia applications. It is based on the dynamic choice of metrics and in a fuzzy link cost (FLC) to determine the best routes for multimedia packets. The proposed FLC metric is based on a fuzzy system that uses two link quality metrics, namely expected transmission count (ETX) and minimum delay (MD), to define a new metric. Simulations were performed to demonstrate the performance of the proposed metric compared to the ones present in the original OLSR and other current versions of this protocol. For comparison purposes, it was considered different performance evaluation QoS metrics and the quality of videos received by the user in a higher competition scenario.

Adaptation in Convolutionally Coded MIMO-OFDM Wireless Systems Through Supervised Learning and SNR Ordering

Multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) wireless systems use link adaptation to exploit the dynamic nature of wireless environments. Link adaptation maximizes throughput while maintaining target reliability by adaptively selecting the modulation order and coding rate. Link adaptation is extremely challenging, however, due to the difficulty in predicting error rates in OFDM with binary convolutional codes, bit interleaving, MIMO processing, and real channel impairments. This paper proposes a new machine-learning framework that exploits past observations of the error rate and the associated channel-state information to predict the best modulation order and coding rate for new realizations of the channel state without modeling the input-output relationship of the wireless transceiver. Our approach is enabled through our new error-rate expression that is only parameterized by postprocessing signal-to-noise ratios (SNRs), ordered over subcarriers and spatial streams. Using ordered SNRs, we propose a low-dimensional feature set that enables machine learning to increase the accuracy of link adaptation. An IEEE 802.11n simulation study validates the application of this machine-learning framework in real channels and demonstrates the improved performance of SNR ordering as it compares with competing link-quality metrics.

From Experience with Indoor Wireless Networks: A Link Quality Metric that Captures Channel Memory

With ARQ based link-layer schemes, energy consumption on a link increases with packet retransmissions. We define the inefficiency of a link as the expected number of transmissions before a packet is successfully received on that link. Memory in the packet success process, caused by long indoor coherence times, strongly influences inefficiency. Based on measurements, we build a simple model for the packet success process that incorporates memory and predicts our metric practically and accurately. In particular, inefficiency is asymptotically linear in the memory duration when there is a nonzero probability of a deep fade, and approximately logarithmic otherwise.

High-throughput multicast routing metrics in wireless mesh networks

The stationary nature of nodes in a mesh network has shifted the main design goal of routing protocols from maintaining connectivity between source and destination nodes to finding high-throughput paths between them. Numerous link-quality-based routing metrics have been proposed for choosing high-throughput routing paths in recent years. In this paper, we study routing metrics for high-throughput tree or mesh construction in multicast protocols. We show that there is a fundamental difference between unicast and multicast routing in how data packets are transmitted at the link layer, and accordingly how the routing metrics for unicast routing should be adapted for high-throughput multicast routing. We propose a low-overhead adaptive online algorithm to incorporate link-quality metrics to a representative multicast routing protocol. We then study the performance improvement achieved by using different link-quality-based routing metrics via extensive simulation and experiments on a mesh-network testbed, using ODMRP as a representative multicast protocol. Our extensive simulation studies show that: (1) ODMRP equipped with any of the link-quality-based routing metrics can achieve higher throughput than the original ODMRP. In particular, under a tree topology, on average, ODMRP enhanced with link-quality routing metrics achieve up to 34% higher throughput than the original ODMRP under low multicast sending rate; (2) the improvement reduces to 21% under high multicast sending rate due to higher interference experienced by the data packets from the probe packets; (3) heavily penalizing lossy links is an effective way in the link-quality metric design to avoid low-throughput paths; and (4) the path redundancy from a mesh data dissemination topology in mesh-based multicast protocols provides another degree of robustness to link characteristics and reduces the additional throughput gain achieved by using link-quality-based routing metrics. Finally, our experiments on an eight-node testbed show that on average, ODMRP using SPP and PP achieves 14% and 17% higher throughput over ODMRP, respectively, validating the simulation results.

Interference-aware fast path adaptation in wireless mesh networks

Existing multihop wireless routing protocols are incapable of reacting quickly to transient degradation of link quality rendering them unsuitable for supporting real-time applications such as streaming/interactive voice and video. This limitation in the sensitivity of the routing protocols to link quality is difficult to overcome due to the following reasons. All link quality metrics used in routing, such as ETX [1, 2] require active probing. Too frequent probing results in high overhead and can interfere with the actual traffic. Further, a time window of 5 to 10 seconds is required to gather enough probe samples to allow reasonable confidence in the statistics and avoid load sensitivity. Additional latency is also incurred in propagating routing updates.

Operation and Performance of Link-Quality Based Channel Assignment Schemes in Adaptive Packet-Switched Mobile Radio Systems

This paper proposes and evaluates a set of physical level assisted cross-layer channel assignment schemes. These schemes allocate an incoming call the available channel that experienced the best channel quality conditions during previous transmissions. To estimate such conditions, three different link quality metrics have been considered. The performance of the proposed schemes has been compared to that of the commonly employed random allocation mechanism. The obtained results show that the proposed schemes improve the system performance of an adaptive packet-switched mobile radio system while also exhibiting the long-term channel uniform use characteristic of the random allocation mechanism. The higher performance attained with the proposed schemes is due to their short-term channel use pattern that results in an implicit cooperation among co-channel interfering cells during the channel allocation process. With the proposed schemes, interfering cells avoid assigning the same channels to simultaneous incoming calls, therefore reducing the experienced interference and increasing the system performance.

Error prediction for adaptive modulation and coding in multiple-antenna OFDM systems

In this paper, the problem of packet error rate (PER) prediction is addressed in the multiple-antenna broadband OFDM context, and its impact on adaptive modulation and coding (AMC) is quantified. The analysis is based on a physical layer comprising various modulation and coding schemes, ranging from robust space–time block coding (STBC) modes to high bit rate spatial division multiplexing (SDM) modes, and also hybrid SDM–STBC schemes. For each mode the expression of several link quality metrics (LQM) enabling PER prediction in the broadband OFDM channel, such as instantaneous signal-to-noise ratio (SNR), capacity, or exponential effective SNR metrics are provided. Their advantages and limitations are investigated. Finally, their performance is benchmarked in the IEEE 802.11a/g/n context. It is shown that the choice of the LQM has a significant impact on the throughput performance of the AMC algorithm.

Comparison of routing metrics for static multi-hop wireless networks

Routing protocols for wireless ad hoc networks have traditionally focused on finding paths with minimum hop count. However, such paths can include slow or lossy links, leading to poor throughput. A routing algorithm can select better paths by explicitly taking the quality of the wireless links into account. In this paper, we conduct a detailed, empirical evaluation of the performance of three link-quality metrics---ETX, per-hop RTT, and per-hop packet pair---and compare them against minimum hop count. We study these metrics using a DSR-based routing protocol running in a wireless testbed. We find that the ETX metric has the best performance when all nodes are stationary. We also find that the per-hop RTT and per-hop packet-pair metrics perform poorly due to self-interference. Interestingly, the hop-count metric outperforms all of the link-quality metrics in a scenario where the sender is mobile.