Selahattin Gokceli

OFDMA-based network-coded cooperation: design and implementation using software-defined radio nodes

Benefits of network coding towards enhancing communication quality, both in terms of robustness or data transmission rates, make it a significant candidate as a future networking technology. Conventionally, network coding is mostly used in wired infrastructures, where transmission errors between nodes are negligible. Capturing the provided benefits of network coding via straightforward extension from wired networks to wireless networks is not trivial. In addition to the challenges introduced through the wireless channel impairments, we can also capture the spatial diversity gain provided by the broadcast nature of the wireless channels. In this work, we design and implement a network-coded cooperation (NCC) system that operates in real time through the use of software-defined radio (SDR) nodes for the first time in the literature. We specifically target wireless networks. Our system is based on orthogonal frequency division multiple access (OFDMA) that provides a practical means to enable high transmission rates through the use of narrowband subcarriers. The developed testbed is composed of three source nodes, a relay node and two destination nodes. The transmission of the proposed NCC-OFDMA system is completed in two phases; the broadcast and the relaying phases. Multiplexing of source nodes’ signals is achieved through OFDMA technique. In the broadcast phase, an OFDMA signal is transmitted to relay and destination nodes. In the relaying phase, the relay node first detects the OFDMA signal, generates network-coded symbols, and then transmits these symbols to destination nodes. At the end of these two phases, the destination nodes determine the source nodes’ signals by using network decoders. The destination nodes make use of both the uncoded and network-coded symbols, which are received in broadcast and relaying phases, respectively. Destination nodes then perform network decoding. Through real-time bit error rate and error vector magnitude measurements, we show that the NCC-OFDMA system can significantly improve the communication quality and robustness, while enabling data transmission between multiple users, as known from theoretical analyses. Some features of this implemented NCC-OFDMA system have the potential to be included in 5G standards, due to the improved radio resource usage efficiency.

IoT in Action

With the development of sensor technologies, various application areas have emerged. The usage of these technologies and exploitation of recent improvements have clear benefits on building applications. Such use-cases can improve smart functions of buildings and can increase the end-user comfort. As a similar notion, building automation systems (BAS) are smart systems that target to provide automated management of various control services and to improve resource usage efficiency. However, buildings generally contain hardware and control services from a diverse set of characteristics. The automated and central management of such functions can be challenging. In order to overcome such issues, an Emergency Evacuation Service is proposed for BAS, where requirements of such central management model are analyzed and model content and subservice definitions are prepared. A crucial scenario, which could be a necessity for future BAS, is defined and an approach for evacuation of people in the buildings at emergency situations is proposed. For real-life scenarios, the Evacuation Service is implemented by using a low-cost design, which is appropriate for Internet of Things (IoT) based BAS applications. As demonstrated, the proposed service model can provide effective performance in real-life deployments.

Cognitive Radio Testbeds: State of the Art and an Implementation

Cognitive radio (CR) technology is a potential solution to the spectrum scarcity problem. In CR systems, the availability of the licensed spectrum portion is monitored by the spectrum sensing process and strategies are applied to use this licensed portion without interfering with active primary users (PU). CR provides a flexible system that secondary users (SU) can make decisions about the spectrum usage at any time by simply configuring corresponding transmission parameters. However, implementation of CR systems can be a challenging task due to characteristic difficulties of the wireless channels introduced by fading. Especially spectrum sensing process is affected by changing channel conditions, which should be considered in order to create a high performance CR system. Robust spectrum sensing is essential for a CR system due to its vital role in the efficient usage of the spectrum. Therefore, several algorithms that are proposed for this issue should contain suitable properties considering realistic channel conditions. Implementation of these algorithms can be realized through software defined radios (SDRs). SDR is a core component of the CR technology and it allows a practical development process with modification on the software rather than hardware. Thus, SDR based approaches to CR problems are quite effective. In this chapter, the state of the art of CR systems are explained in detail by highlighting essential components of the existing studies. Effective approaches to the implementation using SDR systems are given. Moreover, an energy detection based spectrum sensing implementation for 2.4 GHz ISM band is given as an implementation example and channel based spectrum usage is analyzed by using SDR tools LabVIEW and NI USRP-2921 hardware in real-time.

Universal filtered multicarrier systems: Testbed deployment of a 5G waveform candidate

Orthogonal frequency division multiplexing (OFDM) technique, with a broad usage in recent communication technologies, provides a good performance that is mostly appropriate for target quality of service levels. Yet, it will not be effective for future requirements due to its synchronization and spectral efficiency related communication system drawbacks. To address these issues, universal filtered multi-carrier (UFMC) technique has been proposed. Specifically, UFMCs less strict synchronization requirements and its increased spectral efficiency compared to the OFDM render it very desirable for 5G. In this study, UFMC is implemented by using software defined radios in real-time for the first time in the literature. With an effective synchronization solution, UFMCs design issues are tackled and a proper design model that is feasible for 5G requirements is demonstrated. Two methods are proposed for improvement of channel estimation and pilot usage for synchronization process. Moreover, as shown with real-time experiments, by carefully adjusting UFMC parameters, UFMC outperforms OFDM that is implemented in same configuration.

Implementation of real time channel based spectrum monitoring for 2.4 GHz ISM band

In communication applications, frequency spectrum management has become an important issue due to rapid increase in the number of devices that use the limited frequency spectrum. Efficient spectrum management is a necessity due to resource scarcity. Cognitive radios are emerged as one of the most prominent for solutions for this problem. Recently, the frequency spectrum management implementations of cognitive radios has increased. In this study, channel based spectrum monitoring of 2.4 GHz ISM band is implemented using energy detection method and also software defined radio technology. The channel based usage density of ISM band is shown consistently as the outcome of this study.

A building automation system demonstration

This paper presents a building automation system based on the Arduino hardware and Android software. The system supports various sensor functions with a very practical and low cost system configuration. Android blocks that control the Arduino components and sensors are developed with MIT App Inventor 2 software. Additionally, all Arduino components and sensors are put into an unique demonstration model with the purpose of test of the system and the presentation in real-time. With this model, smart building environment is animated and correspondent functions become more understandable. Presented system that supports comprehensive functions has also potential for educational usage and teaching activities due to its practical configuration.

A Tutorial on Nonorthogonal Multiple Access for 5G and Beyond

Today’s wireless networks allocate radio resources to users based on the orthogonal multiple access (OMA) principle. However, as the number of users increases, OMA based approaches may not meet the stringent emerging requirements including very high spectral efficiency, very low latency, and massive device connectivity. Nonorthogonal multiple access (NOMA) principle emerges as a solution to improve the spectral efficiency while allowing some degree of multiple access interference at receivers. In this tutorial style paper, we target providing a unified model for NOMA, including uplink and downlink transmissions, along with the extensions to multiple input multiple output and cooperative communication scenarios. Through numerical examples, we compare the performances of OMA and NOMA networks. Implementation aspects and open issues are also detailed.

Implementation of Network Coding in Wireless Systems

In this chapter, we target to give extensive performance analyses about application of network coding (NC) in wireless systems, referred to as network coded cooperation (NCC), brings both diversity and multiplexing gains. We use the diversity-multiplexing trade-off (DMT) to determine performance bounds of NCC systems. Within the scope of this study, NCC is integrated with orthogonal frequency division multiple access (OFDMA) and the corresponding system model is characterized by specifically focusing on frequency diversity gain. DMT expressions of the NCC-OFDMA system is given. A real-time implementation of the NCC-OFDMA system is presented by creating a testbed NI USRP-2921, NI PXIe-5644R, NI PXI-6683H software defined radio (SDR) modules and LabVIEW software. Obtained real-time performance measurements are essential to demonstrate the practical advantages or disadvantages of the usage of the NCC-OFDMA system. Overall, we aim to present a detailed overview of the fundamental performance bounds of NCC and its extension to the practical applicability of NCC in wireless networks.

Error Performance Analysis of Random Network Coded Cooperation Systems

This paper presents a framework for computing successful decoding probability of random network coding (RNC) in wireless networks. As cooperation emerges due to the naturally occurring broadcasting in wireless links, the application of RNC in wireless networks enables random network coded cooperation (RNCC). The theoretical successful decoding probability of RNCC systems is derived by obtaining the ratio of the full rank and the rank deficient matrices. The full rank condition of the global encoding matrix indicates the successful decoding of source symbols. The results of a single relay along with a relay selection scheme are also investigated. The validity of the presented theoretical expressions is demonstrated through identical simulation results. An implementation scenario is also presented to demonstrate the practical usage effectiveness of RNC in real-time applications, by using software-defined radio nodes.

Practical Implementation of Index Modulation-Based Waveforms

Orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) technique has been recently proposed to provide performance improvements over conventional OFDM. OFDM-IM includes a different data transmission mechanism, where additional data bits are transmitted over subcarrier patterns by specifically activating selected subcarriers and nulling the others. However, such a mechanism inherently causes some inefficiency due to the inactive subcarriers. To improve the spectral efficiency of the OFDM-IM technique, dual-mode OFDM with index modulation (DM-OFDM) is proposed, where nulled subcarriers are activated by using a second signal constellation. With DM-OFDM, a significant data rate improvement can be obtained. As an important missing issue in the literature, OFDM-IM and its effective variations, such as DM-OFDM, have only been studied in terms of computer simulations and theoretical analysis. Therefore, their real-time performance is not yet investigated to assess their potential for next-generation networks. Addressing this gap, in this paper, OFDM-IM and DM-OFDM techniques are implemented in real-time by using software defined radio technology. National Instruments USRP-2921 nodes are used in a single-input single-output configuration. With this implementation, detailed real-time results and performance observations are provided. Moreover, a hybrid OFDM-IM (H-OFDM-IM) scheme, which can be seen as the combination of OFDM-IM and DM-OFDM, is proposed by targeting the limitations of both OFDM-IM and DM-OFDM in terms of spectral containment and error performance. With H-OFDM-IM, noticeable improvements in spectral containment and error performance can be obtained, and these observations show its suitability for real-time use and next-generation networks. With comprehensive computer simulation and test results, these claims are verified.