Energy Efficiency Optimization in Green Wireless Communications

The rising energy concern and the ubiquity of energy-consuming wireless applications have sparked a keen interest in the development and deployment of energy-efficient and eco-friendly wireless communication technology. Green Wireless Communications aims to find innovative solutions to improve energy efficiency, and to relieve/reduce the carbon footprint of wireless industry, while maintaining/improving performance metrics. Looking back at the wireless communications of the past decades, the air-interface design and network deployment had mainly focused on the spectral efficiency, instead of energy efficiency. From the cellular network to the personal area network, no matter what size the wireless network is, the milestones along the evolutions of wireless networks had always been higher-and-higher data rates throughout these years. Most of these throughput-oriented optimizations lead to a full-power operation to support a higher throughput or spectral efficiency, which is typically not energy-efficient. To qualify as green wireless communications, we believe that a candidate technology needs to be of high energy efficiency, reduced electromagnetic pollution, and low-complexity. In this dissertation research, towards the evolution of the green wireless communications, we have extended our efforts in two important aspects of the wireless communications system: air-interface and networking. In the first aspect of this work, we study a promising green communications technology, the time reversal system, as a novel air-interface of the future green wireless communications. We propose a concept of time reversal division multiple access (TRDMA) as a novel wireless media access scheme for wireless broadband networks, and investigate its fundamental theoretical limits. Motivated by the great energy-harvesting potential of the TRDMA, we develop an asymmetric architecture for the TRDMA based multiuser networks. The unique asymmetric architecture shifts the most complexity to the BS in both downlink and uplink schemes, facilitating very low-cost terminal users in the networks. To further enhance the system performance, a 2D parallel interference cancellation scheme is presented to explore the inherent structure of the interference signals, and therefore efficiently improve the resulting SINR and system performance. In the second aspect of this work, we explore the energy-saving potential of the cooperative networking for cellular systems. We propose a dynamic base-station switching strategy and incorporate the cooperative base-station operation to improve the energy-efficiency of the cellular networks without sacrificing the quality of service of the users. It is shown that significant energy saving potential can be achieved by the proposed scheme

Analisis Performansi Interference Cancellation Pada Sistem Komunikasi HF TRDMA

Komunikasi High Frequency (HF) adalah suatu sistem komunikasi yang mampu menjangkau jarak yang jauh tanpa menggunakan repeater atau relay, namun memanfaatkan lapisan ionosfer untuk memantulkan sinyalnya sehingga cocok digunakan di Indonesia sebagai negara kepulauan. Mengingat bahwa badwidth pada kanal HF terbatas yakni pada frekuensi 3 – 30 MHz, maka diperlukan metode akses jamak yang mampu meningkatkan efisiensi penggunaan kanal. Salah satu teknik akses jamak yang diterapkan pada sistem komunikasi HF adalah TRDMA (Time Reversal Division Multiple Access). Pada komunikasi TRDMA memungkinkan beberapa user berkomunikasi pada frekuensi yang sama, namun akses jamak ini akan menyebabkan terjadinya efek interferensi antar pengguna, Inter-User Interference (IUI) yang sedang aktif. Selain itu pengaruh pantulan ionosfer juga menyebabkan akses jamak yang dapat menimbulkan Intersymbol Inteference (ISI). Oleh karena itu penelitian ini menganalisa berapa banyak user penginterferensi yang dapat menggunakan satu frekuensi yang sama dan penerapan metode Interference Cancellation untuk mengurangi interferensi ISI dan IUI. Link referensi yang digunakan adalah Merauke - Surabaya dengan kota penginterferen berupa Dompu, Kupang, Maumere, Pulau Leti, Saumlaki, Ternate, dan Timika. Hasil tugas akhir ini menunjukkan bahwa sistem komunikasi TRDMA dapat digunakan pada kanal HF pukul 01.00 UTC dan 05.00 UTC yakni pada rentang waktu pagi hingga siang hari dengan 1 penginterferen selain itu dengan penggunaan interference Cancellation menunjukkan terjadinya penurunan nilai BER pada semua lintasan ================================================================= High Frequency Communications (HF) is a communication system that can reach long distances without using a repeater or relay, but utilize the abaility of ionosphere to reflect the signal, so it suitable for communication in indonesia as archipelago. Given that HF has limited badwidth channels at frequency of 3-30 MHz, it would require multiple access methods that can improve the efficiency of channell. One of multiple access technique that is applied to HF communication system is TRDMA (Time Reversal Division Multiple Access). In TRDMA communication allows multiple users to communicate on the same frequency, but this multiple access would lead to interference effects between users, Inter-User Interference (IUI). Besides the influence of the reflection of the ionosphere also causes multiple access which may cause intersymbol Inteference (ISI). Therefore, the present study will analyze how much user interference can allow using same frequency and implementation of Interference Cancellation methode to reduce interference ISI and IUI. Link reference used is Merauke – Surabaya with links of interference are Dompu, Kupang, Maumere, Pulau Leti, Saumlaki, Ternte, dan Timika. The results of this final project show that TRDMA communication system can be used on the HF channel at 01:00 UTC and 05:00 UTC on timescales that morning until noon with 1 interfere. In addition to the use of interference Cancellation showed that can reduce of Bit Erorr Rate on all links

Analisis Efek Near Far Terhadap Interferensi Pada Sistem Komunikasi HF TRDMA

Sistem komunikasi radio High Frequency (HF) memiliki kelebihan yakni dapat memberikan transmisi jarak jauh, biaya relatif murah serta fleksibel. Namun, karena bandwidth kanal yang digunakan pada sistem komunikasi HF terbatas yaitu pada frekuensi 3-30 MHz, diperlukan suatu metode akses jamak yang mampu meningkatkan efisiensi penggunaan kanal. Salah satunya adalah dengan menggunakan metode Time-Reversal Division Multiple Access (TRDMA) pada komunikasi HF. Salah satu permasalahan yang perlu diatasi dalam mengimplementasikan TRDMA pada komunikasi HF adalah efek nearfar. Efek near-far adalah fenomena saat terdapat dua pemancar (atau lebih) yang memancarkan sinyal ke satu penerima yang sama, dalam konteks uplink pada proses multiple-access, yang bekerja dengan frekuensi yang sama. Karena bekerja di frekuensi yang sama, tentu akan ada efek interferensi antara keduanya, sehingga mempengaruhi kualitas sinyal pemancar utama, yang diukur menggunakan parameter signal to interference ratio (SIR). Pengaruh jarak setiap pemancar terhadap kualitas sinyal dari masing-masing pemancar tersebut itulah yang disebut sebagai efek near-far. Pada penelitian ini digunakan data dari rekomendasi ITU-R P.533 untuk mendapatkan kinerja komunikasi pada band HF. Dilakukan mekanisme kontrol daya pancar untuk mendapat hasil SIR ideal untuk semua user, dengan cara menyamakan daya di penerima untuk setiap pemancar, mendekati -120 dBW. Lalu dilakukan perhitungan SIR untuk pemancar utama Kupang dan Merauke, dengan penerima di Surabaya. Didapatkan hasil kinerja SIR komunikasi HF TRDMA, cukup baik hanya jika hanya ada 1 peng-interferensi. Sedangkan lebih dari itu nilainya sudah dibawah 0 dB, sehingga perlu digabungkan dengan teknik spread spectrum, dengan level yang rendah, agar tidak boros dalam penggunaan bandwidth. ========================================================================================================= High frequency (HF) radio communication systems has an advantage, that it can provide a long distances transmission, relatively cheap, and flexible. But consider that the channel bandwidth of HF frequency band was limited, from 3-30 MHz, it is necessary to use an multiple access method to increase channel usage efficiency. Once of it was by apllied Time Reversal Division Multiple Access (TRDMA) method for HF communication systems. One of the problem to be solved to implements TRDMA on HF communications system is near far effect. Near far effect is a phenomenon when there was two transmitter (or more) that propagates a signal to a same receiver, in an uplink context of a multiple access process, using a same frequency. Because of using a same frequency, there was an interference effect between them, that affect to signal quality of the main trasmitter, which caltulated by signal to interference ratio (SIR) parameter. The affection of distances and signal quality of each transmitter is named near far effect. In this research, is using data from ITU-R P.533 to get information about communication performance at high frequency band. We applied transmission power control to get an ideal SIR performance for each user, by equate received power for each user, approach -120 dBW for each user. Then SIR performance was calculated, with the receiver in Surabaya, and two main transmitter at Kupang and Merauke. So we get SIR performance of HF communication systems. It found that SIR performance of HF TRDMA communication systems is only have positive value in dB scale, when only has 1 interference link. When the interference link was 2 or more, the value was negative. So it need to be combined with other techniques such as spread spectrum with a low sequence level, that enough to increase SIR performance, but still efficient in using bandwidth

COMPRESSIVE QUANTIZATION FOR SCALABLE CLOUD RADIO ACCESS NETWORKS

With the proliferation of new mobile devices and applications, the demand for ubiquitous wireless services has increased dramatically in recent years. The explosive growth in the wireless traffic requires the wireless networks to be scalable so that they can be efficiently extended to meet the wireless communication demands. In a wireless network, the interference power typically grows with the number of devices without necessary coordination among them. On the other hand, large scale coordination is always difficult due to the low-bandwidth and high-latency interfaces between access points (APs) in traditional wireless networks. To address this challenge, cloud radio access network (C-RAN) has been proposed, where a pool of base band units (BBUs) are connected to the distributed remote radio heads (RRHs) via high bandwidth and low latency links (i.e., the front-haul) and are responsible for all the baseband processing. But the insufficient front-haul link capacity may limit the scale of C-RAN and prevent it from fully utilizing the benefits made possible by the centralized baseband processing. As a result, the front-haul link capacity becomes a bottleneck in the scalability of C-RAN. In this dissertation, we explore the scalable C-RAN in the effort of tackling this challenge. In the first aspect of this dissertation, we investigate the scalability issues in the existing wireless networks and propose a novel time-reversal (TR) based scalable wireless network in which the interference power is naturally mitigated by the focusing effects of TR communications without coordination among APs or terminal devices (TDs). Due to this nice feature, it is shown that the system can be easily extended to serve more TDs. Motivated by the nice properties of TR communications in providing scalable wireless networking solutions, in the second aspect of this dissertation, we apply the TR based communications to the C-RAN and discover the TR tunneling effects which alleviate the traffic load in the front-haul links caused by the increment of TDs. We further design waveforming schemes to optimize the downlink and uplink transmissions in the TR based C-RAN, which are shown to improve the downlink and uplink transmission accuracies. Consequently, the traffic load in the front-haul links is further alleviated by the reducing re-transmissions caused by transmission errors. Moreover, inspired by the TR-based C-RAN, we propose the compressive quantization scheme which applies to the uplink of multi-antenna C-RAN so that more antennas can be utilized with the limited front-haul capacity, which provide rich spatial diversity such that the massive TDs can be served more efficiently

Time-Reversal Massive Multipath Effect and Bandwidth Heterogeneity

The proliferation of new mobile communication devices, such as smartphones and tablets, has led to an exponential growth in network traffic. The demand for supporting the fast-growing consumer data rates urges the wireless service providers and researchers to seek a new efficient radio access technology, which is the so-called 5G technology, beyond what current 4G LTE can provide. On the other hand, ubiquitous RFID tags, sensors, actuators, mobile phones and etc. cut across many areas of modern-day living, which offers the ability to measure, infer and understand the environmental indicators. The proliferation of these devices creates the term of the Internet of Things (IoT). For the researchers and engineers in the field of wireless communication, the exploration of new effective techniques to support 5G communication and the IoT becomes an urgent task, which not only leads to fruitful research but also enhance the quality of our everyday life. Massive MIMO, which has shown the great potential in improving the achievable rate with a very large number of antennas, has become a popular candidate. However, the requirement of deploying a large number of antennas at the base station may not be feasible in indoor scenarios. Does there exist a good alternative that can achieve similar system performance to massive MIMO for indoor environment? In this dissertation, we address this question by proposing the time-reversal technique as a counterpart of massive MIMO in indoor scenario with the massive multipath effect. It is well known that radio signals will experience many multipaths due to the reflection from various scatters, especially in indoor environments. The traditional TR waveform is able to create a focusing effect at the intended receiver with very low transmitter complexity in a severe multipath channel. TR's focusing effect is in essence a spatial-temporal resonance effect that brings all the multipaths to arrive at a particular location at a specific moment. We show that by using time-reversal signal processing, with a sufficiently large bandwidth, one can harvest the massive multipaths naturally existing in a rich-scattering environment to form a large number of virtual antennas and achieve the desired massive multipath effect with a single antenna. Further, we explore the optimal bandwidth for TR system to achieve maximal spectral efficiency. Through evaluating the spectral efficiency, the optimal bandwidth for TR system is found determined by the system parameters, e.g., the number of users and backoff factor, instead of the waveform types. Moreover, we investigate the tradeoff between complexity and performance through establishing a generalized relationship between the system performance and waveform quantization in a practical communication system. It is shown that a 4-bit quantized waveforms can be used to achieve the similar bit-error-rate compared to the TR system with perfect precision waveforms. Besides 5G technology, Internet of Things (IoT) is another terminology that recently attracts more and more attention from both academia and industry. In the second part of this dissertation, the heterogeneity issue within the IoT is explored. One of the significant heterogeneity considering the massive amount of devices in the IoT is the device heterogeneity, i.e., the heterogeneous bandwidths and associated radio-frequency (RF) components. The traditional middleware techniques result in the fragmentation of the whole network, hampering the objects interoperability and slowing down the development of a unified reference model for the IoT. We propose a novel TR-based heterogeneous system, which can address the bandwidth heterogeneity and maintain the benefit of TR at the same time. The increase of complexity in the proposed system lies in the digital processing at the access point (AP), instead of at the devices' ends, which can be easily handled with more powerful digital signal processor (DSP). Meanwhile, the complexity of the terminal devices stays low and therefore satisfies the low-complexity and scalability requirement of the IoT. Since there is no middleware in the proposed scheme and the additional physical layer complexity concentrates on the AP side, the proposed heterogeneous TR system better satisfies the low-complexity and energy-efficiency requirement for the terminal devices (TDs) compared with the middleware approach

ANALISIS CAKUPAN SISTEM KOMUNIKASI SELULER HF TRDMA

Sistem komunikasi radio High Frequency (HF) merupakan sistem komunikasi memiliki kelebihan yaitu memanfaatkan lapisan ionosfer untuk memantulkan sianyalnya, sehingga system komunikasi HF dapat menjangkau jarak yang jauh. Sistem Komunikasi HF menggunakan bandwidth kanal yang bekerja pada frekuensi 3-30 MHz, karena bandwidth kanal yang digunakan terbatas, maka kapasitas dari kanal HF kecil. Oleh karena itu diperlukan suatu metode yang dapat diterapkan untuk memaksimalkan penggunaan kanal HF, salah satunya dengan menggunakan metode Time-Reversal Division Multiple Access (TRDMA). Salah satu yang perlu diteliti adalah cakupan dari jaringan radio seluler dengan relay pada masing-masing unit pemancar dan penerima menerapkan TRDMA. Pemancar dan penerima menggunakan antena dipole yang berpolarisasi horizontal dengan arah radiasi maksimum yang saling tegak lurus, yaitu Timur-Barat (di mana antenna dipole dipasang membentang Utara-Selatan) dan Utara-Selatan (antenna dipole membentang Timur-Barat) yang menggunakan frekuensi kerja yang berbeda untuk meminimalisasi efek interferensi antar terminal yang saling berkomunikasi menggunakan kanal HF ionosferik. Penelitian ini menggunakan acuan kriteria SIR yang dialami oleh terminal pengguna pada kondisi terburuk. Dalam pengerjaannya menggunakan data dari rekomendasi ITU-R P.533 untuk mendapatkan kinerja komunikasi dari band HF. Perhitungan kinerja SIR dilakukan dengan kondisi jarak antar relay dan jumlah pemancar interferensi yang berbeda. Didapatkan hasil bahwa pemodelan terbaik dengan menggunakan jarak antar relay sejauh 2828 Km dan jumlah maksimum pemancar yang dapat aktif secara bersamaan adalah 3, dimana bagi setiap user terdapat 2 penginterferensi. "=============================================================================================" High Frequency radio communication systems is a system that has advantages of utilizing the ionosphere to reflec to reflect its own transmission signal, so this communication systems can be used as a long distance communication. HF Communication System uses bandwidth channel running at a frequency within 3-30 MHz, due to the limited bandwidth of the channels, HF communication systems has small capacity of HF channel. Therefore we need a method that can be applied to maximize the use of HF channels, one of them is Time- Reversal Division Multiple Access (TRDMA). One that needs to be examined is the coverage of a cellular radio network with a relay in each transmitter and receiver units that use TRDMA. The transmitter and receiver using a dipole antenna which is polarized horizontally with the direction of maximum radiation perpendicular to each other, the East- West (where the dipole antenna facing North-South) and North-South (dipole antenna facing east-west) that use different frequency to minimize the effects of interference between terminals communicating using HF ionospheric channel. This research use SIR as refences that experienced by the user terminal in the worst conditions. In the process, using data from ITU-R P.533, to get the performance of HF communications band. SIR performance calculation is done with different conditions of the distance between the relay and the number of transmitter interference. Showed that the best model by using the distance between relay as far as 2828 km and maximum number of transmitters that can be active simultaneously is 3, which is one user and two transmitter interference

Time-Reversal Indoor Positioning System and Medium Access Control

With the rapid expansion of the wireless communication, there has been a rapid growth in the demand for the mobile traffic. Moreover, the wireless traffic not only expands in traffic volume but also in the diversity of applications and requirements with the rise of the Internet of Things (IoT) concept. The insatiable demand for both the traffic volume and the ever-expanding IoT applications poses a great challenge on the design of the next generation, i.e. the 5G, communication system. Time reversal (TR) technology has been proposed as a promising candidate for the 5G system with several promising characteristics, such as easy densification, asymmetric and heterogeneous design. TR system utilizes large bandwidth and observes detailed, location-specific channel impulse responses (CIR). With the detail CIR information, the TR system designs waveforms to concentrate transmitted energy to the intended users via the unique spatial temporal focusing effect. In this dissertation, we propose a TR indoor positioning system and medium access control design based on this unique effect. We begin by proposing the time reversal resonating strength (TRRS) to quantify the similarity between the location information embedded CIRs. The TR indoor positioning system identifies the unknown users by calculating the TRRS between the CIR of the unknown user and the CIRs in the database. We built the system prototype and are the first-ever to perform precise indoor positioning at 1 to 2 cm resolution in both line-of-sight and non-line-of-sight scenario using one pair of transmitter and receiver both equipped with a single antenna. Based on the positioning system, we propose an indoor tracking system by collecting CIRs at several regions of interest and track unknown users when they pass it. To facilitate deployment, we built a prototype to automate CIR collection and the experiments show that the system detects the users correctly with very low false alarm rate. In the second part, we design the medium access control scheme to maximize system sum rate and guarantee quality of service to the users in a downlink scenario. The system objective and constraints are transformed into a mixed integer quadratically constraint quadratic programming and can be solved efficiently. We then investigate rate adaptation scheme via selection of optimal backoff factors in TR system. The rate adaptation scheme effectively increases the system-wise performance and the fairness among users

Interference mitigation using group decoding in multiantenna systems

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