Increasing Throughput and Reducing Delay in Wireless Sensor Networks Using Interference Alignment

In recent years, several experimental studies have come out to validate the theoretical findings of interference alignment (IA), but only a handful of studies have focused on blind interference alignment. Unlike IA and other interference mitigation techniques, blind IA does not require channel state information at the transmitter (CSIT). The key insight is that the transmitter uses the knowledge of channel coherence intervals and receivers utilize reconfigurable antennas to create channel fluctuations exploited by the transmitter. In this work, we present a novel experimental evaluation of a reconfigurable antenna system for achieving blind IA. We present a blind IA technique based on reconfigurable antennas for a 2-user multipleinput single-output (MISO) broadcast channel implemented on a software defined radio platform where each of the receivers is equipped with a reconfigurable antenna. We further compare this blind IA implementation with traditional TDMA scheme for benchmarking purposes. We show that the achievable rates for blind IA can be realized in practice using measured channels under practical channel conditions. Additionally, the average error vector magnitude and bit error rate (BER) performances are evaluated.

Network densification enables ultra high capacity gains in 5G networks by shrinking cell sizes, thereby bringing users closer to base stations. However, this leads to severe levels of interference. A promising method to suppress interference in K-user MIMO networks is interference alignment. Massive MIMO is another technology that is expected to contribute to increased capacity by the deployment of hundreds of transmit and receive antenna elements. In this paper we describe a design methodology for evolved 5G dense networks using interference alignment and K-user MIMO techniques. Our contributions include mathematical models showing the extension of the interference alignment protocol for K > 3 users using a modified hypercube network structure. We also provide a model for interference alignment under Cramer-Rao bound channel estimation error constraints. Further, we show how large numbers of transmit and receive antennas can provide additional signal power gains and present a user scheduling protocol to maximize capacity.

Wireless Sensor Networks use battery-operated computing and sensing devices. It is often impractical or even impossible to charge/replace the exhausted batteries of the nodes. Thus, energy consumption is the main concern in a wireless sensor network. Moreover, a critical event detected by the sensor network should be delivered to the user as soon as possible. Thus, for sensor networks, both energy efficiency and transmission latency are important parameters. In this paper, we propose a novel asynchronous, duty cycled, energy efficient, and low transmission delay for wireless sensor networks, which addresses all the sources of energy waste to make the medium access more energy efficient, while keeping transmission delay low.The currently available asynchronous contention-based MAC protocols require that proper strategies for sender and receiver nodes are provided to rendezvous. However, the proposed protocol does not rely on any rendezvous between sender and receiver. For evaluating the novel MAC protocol, we have simulated this protocol and two very efficient and established MAC protocols, RTS/CTS IEEE 802.11 and S-MAC. The simulation results indicate that the proposed protocol has very good performance. In addition, as the results show, the novel protocol provides a very suitable balance between energy efficiency and transmission delay.

Wireless sensor networks are distributed event-based systems with severe energy constraints, variable quality links, low data-rate and many-to-one event-to-sink flows. Communication algorithms for sensor networks, such as directed diffusion, are designed to operate efficiently under these constraints. However, directed diffusion is not efficient in more challenging domains, such as video sensor networks, because of the high throughput and low delay requirements of multimedia data. Instead, we propose EDGE - a greedy algorithm based on directed diffusion that reinforces routes with high link quality and low latency, thus maximizing throughput and minimizing delay. ETX (Expected Transmission Count) is used as the metric for measuring link quality. This paper presents an improved method for computing aggregate ETX for a path that increases end-to-end throughput. Simulation results with CBR (constant bit rate) traffic show that our proposed distributed algorithm selects routes that give better throughput than those reinforced by standard directed diffusion, while maintaining low delay.

Interference alignment with receive antenna partitioning for SWIPT-enabled fog RANs

The explosive demand for high data rates and the need ubiquitous wireless connectivity has led to the phenomenon of network densification, the deployment of large number of base station within a geographic area. Since the radio spectrum is limited, wireless transmissions need to share a common resource which results in interference. Interference in turn creates a bottleneck on the communication rate. Recently three breakthroughs have been made to increase the capacity of wireless networks while mitigating interference : multiple input multiple output (MIMO) beamforming, interference alignment (IA) and pattern reconfigurable antennas (PRA). While a great deal of progress has been made on understanding each individually, relatively little is known about how to use these techniques in combination to increase system performance. In this dissertation, we analyze and experimentally evaluate how these new technologies can be leveraged to enhance the rate performance of communication networks. Specifically, we address three problems: i) enhancing multi-user MIMO performance with PRA, ii) improving IA performance with PRA-based antenna selection, and iii) enabling practical blind IA with PRA. To understand the impact PRAs on MU-MIMO and IA, it is necessary to evaluate their performance through measurements. Simulation-based studies often reiterate over set of simplistic channel models and unrealistic assumptions. This dissertation focuses on a measurement-based evaluation approach. For each of these problems, a hardware testbed implementation and measurement methodology is developed for evaluating the performance of the aforementioned technologies through efficient and repeatable experiments. The first two major contributions of this dissertation focus on multi-user MIMO (MU-MIMO) and IA. While the theoretical rate gains of MU-MIMO and IA are substantial, the performance gains in practical systems and measured channels have been limited. One of the key limiting factors are spatially correlated user channels. In this work, we propose MU-MIMO and IA transmission schemes that leverage the pattern diversity provided by PRAs to mitigate the effects of spatial correlation in wireless channels. PRAs are capable of dynamically adjusting their radiation pattern, providing an additional degree of freedom that can be exploited to improve MU-MIMO and IA performance by treating the array configuration and radiation characteristics as additional components in the joint optimization of adaptive system parameters. We quantify the benefits of pattern diversity on the rate performance of MU-MIMO and IA systems through extensive measurements. Furthermore, we develop efficient antenna mode selection algorithms to realize those benefits without increasing the system complexity or overhead, making these techniques suitable for practical implementation. The third contribution of this dissertation focuses on a transmission technique known as blind IA. In contrast to MU-MIMO and conventional IA, blind IA is signaling scheme that suppresses interference in multi-user systems, without the knowledge of channel state information at the transmitter (CSIT). The key to performing IA without CSIT is the use of PRAs that are capable of dynamically switching among a fixed number of radiation patterns to introduce artificial fluctuations in the channel. In this dissertation, we develop a novel implementation of a blind IA system on a software defined radio platform where each of the receivers is equipped with a PRA. Our work provides the first experimental evaluation of PRA-based blind IA schemes and demonstrates significant gains in rate and reliability over traditional orthogonal transmission schemes such as TDMA.

As a novel method to increase channel capacity of networks, interference alignment (IA) technique has attracted wide attention in fifth-generation wireless networks (5G). However, when it is applied in interference networks, the problem regarding information delay arises which has not been well addressed yet. In this paper, we formally propose the novel concepts of degree of delay (DoD) to quantify the issue of information delay and analyze its determining factors, i.e., delay sensitive factor, queueing delay slot and size of dataset. To reduce DoD, three novel joint IA schemes are proposed for broadcast channel (BC) networks with different amounts of users, i.e., hybrid antenna array based partial interference elimination and retrospective interference regeneration scheme (HAA-PIE-RIR), HAA based improved PIE and RIR scheme (HAA-IPIE-RIR) and HAA based cyclic interference elimination and RIR scheme (HAA-CIE-RIR). Among the three, the second scheme extends the application scenarios of the first scheme from 2-user to K-user while bringing huge computational complexity burden. The third scheme relieves the burden but it leads to slight degree of freedom (DoF) loss. Overall, the proposed schemes achieve higher DoF and lower DoD than the existing IA schemes.

Wireless sensor Networks (WSNs), is one of the most rapidly growing scientific domain. This is because of the development of advanced sensor nodes with extremely low cost One of the characteristic feature of WSNs compared to the traditional wireless communication networks to reduce “delay” in such networks we introduce replication or “spraying” methods that can reduce the overhead of flooding-based schemes by distributing a small number of copies to only a few relays, whereas 20% energy efficiency in large number of source nodes. To route messages efficiently in such networks, we propose a scheme that also distributes a small number of copies to few relays. However, each relay can then forward its copy, instead of naively waiting to deliver it to the destination itself. This scheme exploits all the advantages of controlled replication, and could deliver the message faster thereby reducing delay. Simulation results for traditional mobility models, as well as for a more realistic “community-based” model, indicate that our scheme can reduce the delay 20 times compared to existing techniques.

In this paper, we consider the two-hop MIMO interference network, where T source-destination pairs communicate via T×K relays selected from G alternative relays. Based on optimal relay selection, each source-destination pair selected K relays to transmit data streams. In the first time slot, the source node transmits data steams to the selected relays by adaptive beam forming. In the second time slot, the selected relays forward the data streams by interference alignment technique. Compared the beam forming and interference alignment transmission mechanism based on fairness relay selection, our scheme can achieve higher system capacity.

We study the K-user Gaussian interference wiretap channel with N external eavesdroppers. All the transmitters, receivers and eavesdroppers have a single antenna each. We propose an achievable scheme to lower bound the secure degrees of freedom (d.o.f.) for each transmitter-receiver pair. Our approach is based on the (real) interference alignment technique. Our achievable scheme not only aligns the interference at each receiver to prevent the d.o.f. from vanishing, but also aligns the signals observed by the eavesdroppers to reduce the secrecy penalty. The achievable secure d.o.f. of each transmitter-receiver pair is shown to be equations for almost all channel gains.

High Performance Wireless Sensor Networks (HP-WSN) for critical, low latency applications such as traffic control, industrial process control, smart structures and smart vehicles has been a fast-growing field. Nevertheless, efforts towards new systems and circuit architectures to enable real-time, predictable and reliable HP-WSN have been limited, specially for reliable, low latency wireless links. This paper presents for the first time, to authors' knowledge, a low power, wideband, large delay, tunable, compact, CMOS-scalable and frequency-independent true time delay cell that enables wideband beamforming on HP-WSN. This new architecture, inspired on bucket brigade devices and N-path structure, is especially well suitable for sub-3 GHz ISM bands, where most of WSN transceivers work. Post-layout simulations of a circuit demonstrator has shown a continuous time delay between 100 − 1000 ps with 0.5% delay variation over 0 − 3 GHz band. The layout area is only 0.025 mm2 and it consumes 10 − 19 mW, including buffers. It has also established a record of delay-per-area density of 40000 ps/mm2

We describe a non-cooperative interference alignment (IA) technique which\nallows an opportunistic multiple input multiple output (MIMO) link (secondary)\nto harmlessly coexist with another MIMO link (primary) in the same frequency\nband. Assuming perfect channel knowledge at the primary receiver and\ntransmitter, capacity is achieved by transmiting along the spatial directions\n(SD) associated with the singular values of its channel matrix using a\nwater-filling power allocation (PA) scheme. Often, power limitations lead the\nprimary transmitter to leave some of its SD unused. Here, it is shown that the\nopportunistic link can transmit its own data if it is possible to align the\ninterference produced on the primary link with such unused SDs. We provide both\na processing scheme to perform IA and a PA scheme which maximizes the\ntransmission rate of the opportunistic link. The asymptotes of the achievable\ntransmission rates of the opportunistic link are obtained in the regime of\nlarge numbers of antennas. Using this result, it is shown that depending on the\nsignal-to-noise ratio and the number of transmit and receive antennas of the\nprimary and opportunistic links, both systems can achieve transmission rates of\nthe same order.\n

A Kt χ Kr cache-aided wireless interference network, in which both the transmitters and the receivers are equipped with cache memories is studied. Each user requests one file from a library of N popular files. The goal is to design the cache contents without the knowledge of the particular user demands, such that all possible demand combinations can be satisfied reliably over the interference channel. The achievable sum degrees-of-freedom (sDoF) and the normalized delivery time (NDT) are studied for centralized and decentralized network architectures, respectively. First, using a combination of interference alignment (IA), zero-forcing (ZF) and interference cancellation (IC) techniques, a novel caching and transmission scheme for centralized networks is introduced, and it is shown to improve the sDoF upon the state-of-the-art. Then, the NDT is studied when the content placement at the receiver caches is carried out in a decentralized manner. Our results indicate that, for this particular network architecture, caches located at the receiver side are more effective than those at the transmitter side in order to reduce the NDT.

Packet collision is the primary source of unnecessary energy usage in wireless sensor networks (WSNs). To address this issue, the advanced packet scheduling algorithm is presented. In real-time WSNs, some packet scheduling techniques can also affect and delay data transmission. Efficient packet scheduling is vital for minimizing energy consumption and data transmission delay in WSNs. It is crucial because it guarantees the fair and timely distribution of various kinds of data packets according to their priorities. Node will directly transmit the packet to its destination based on its priority. However, current approaches like first come first serve (FCFS) schedulers often result in significant latency, hindering timely data delivery to base stations (BS). To address this, we propose a novel dynamic multi-level round search mayfly optimizer-based priority packet scheduling technique (MRSMOPS). This technique utilizes a traffic-aware-weighted queue (TAWQ) model to schedule tasks based on priority, optimizing transmission slots for flowing packets. Our objective is to reduce overall transmission completion time while adhering to delay limits and energy budgets. By integrating the newly developed MRSMOPS method, the efficiency of packet scheduling is enhanced in WSNs. The proposed algorithm has demonstrated significant improvements in performance metrics, achieving a 15% reduction in packet delay and a 10% enhancement in energy efficiency compared to existing methods.

The LSTS algorithm is a kind of time synchronization algorithm which is directed to suppress the random bounded communication delay in wireless sensor networks (WSNs), Theoretical analysis shows that even under random delays, the drift estimations of all sensors given by this algorithm are asymptotically convergent to a common constant in a rate of $1/k$ , where $k$ is the discrete time, and the global synchronization error is bounded. In order to further verify the validity of the theoretical results and the practical feasibility of the LSTS algorithm, we autonomously design a hardware platform, and conduct physical experiments on this platform by comparing LSTS algorithm with some other algorithms like ATS and WMTS in several aspects including the convergent rate, the offset compensation error and the synchronization error. The result suggests that the LSTS algorithm is state of the art in most performance indices. Finally, the method of “synchronous second pulse(SSP) + synchronization time(ST)” is designed to provide timing service for WSNs, which makes the timing protocol very simple, and it's also convenient for the time acquisition for the underlying hardware, thus enhances the practicability and versatility.