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We consider several aspects of delay diversity in coded OFDM. The cyclic properties of the FFT allow to do delay diversity in a cyclic manner without exceeding the guard interval. We investigate the impact of different cyclic delays in terms of achievable diversity level, information theory and BER performance. Furthermore, we propose an interleaving and user assignment strategy which allows multiple users to exploit the full spatial diversity in an OFDMA system with appropriately chosen cyclic delays. Finally, we introduce a scheme with low delay and low reference symbol overhead for differential modulation in frequency direction which can be detected non-coherently and is able to cope with the increased frequency-selectivity which is caused by the cyclic delays.

Signal distortions in communication systems
occur between the transmitter and the receiver; these
distortions normally cause bit errors at the receiver. In
addition interference by other signals may add to the
deterioration in performance of the communication link. In
order to achieve reliable communication, the effects of the
communication channel distortion and interfering signals
must be reduced using different techniques. The aim of this
paper is to introduce the fundamentals of Orthogonal
Frequency Division Multiplexing (OFDM) and Orthogonal
Frequency Division Multiple Access (OFDMA), to review
and examine the effects of interference in a digital data
communication link and to explore methods for mitigating
or compensating for these effects.

Orthogonal Frequency Division Multiplexing (OFDM) technology has become widespread in civil and military radio systems, especially in channels with frequency selective fading. Due to the large number of OFDM signal schemes, an urgent task for modern radio monitoring systems is development of methods and algorithms for detecting such signals that will be stable in the uncertainty of OFDM signal structure and electromagnetic environment. At the stage of detection, the characteristic feature of OFDM signal is presence of frequency channels in its spectrum envelope. In this research, an algorithm for detecting an OFDM signal in the frequency domain and for estimating the number of frequency channels and duration of the interval of orthogonality was developed. To make a decision whether signal is present in realization of the normalized to the energy spectrum, its variation was used. This approach avoids estimating noise power. In case of signal samples detecting spectrum is double-smoothed using moving average. This provides better smoothing than with a single long window. Thereafter, double thresholding is performed. The second threshold is calculated using samples that have not exceeded the first threshold. Samples that have exceeded the second threshold are considered signal. Next, a search is made for occupied frequencies with a given bandwidth. The samples located in this band are re-smoothed and give spectrum trend, which is used as a threshold to determine the boundaries of frequency channels. OFDM signal is considered detected if equidistant frequency channels were found. After that, duration of the interval of orthogonality is calculated. The proposed method requires a slight complication of the spectral analysis procedure based on the fast Fourier transform. Proposed method can be used for improving broadband radio monitoring systems and provide practically simultaneously implementation procedure of OFDM signal detection-recognition. ; В настоящее время в радиосистемах гражданского и военного назначения широкое распространение получило использование технологии OFDM, особенно при работе в каналах с частотно-селективными замираниями. Из-за большого количества схем построения OFDM сигналов актуальной задачей для современных систем радиомониторинга является разработка методов и алгоритмов обнаружения таких сигналов, устойчивых относительно неопределенности структуры OFDM сигнала и электромагнитной обстановки. На этапе обнаружения характерным признаком OFDM сигнала выбрано наличие частотных каналов в огибающей его спектра. Разработан алгоритм обнаружения OFDM сигнала в частотной области, а также оценки количества частотных каналов и длительности интервала ортогональности. Для принятия решения о наличии сигнальных отсчетов в рассчитанной реализации нормированного к энергии спектра использовано его вариацию. Такой подход позволяет избежать оценки мощности шума. В случае обнаружения частотных отсчетов проводится двойное сглаживание спектра с помощью скользящего среднего. Это обеспечивает лучшее сглаживание чем с помощью одного окна большой длины. После этого выполняется двойная пороговая обработка. Второй порог рассчитывается с использованием отсчетов, которые не превысили первый порог. Отсчеты, превысившие второй порог, считаются сигнальными. Далее производится поиск занятых участков частот с заданной шириной полосы. Отсчеты, находящиеся в этой полосе повторно сглаживаются, что позволяет получить тренд спектра, который используется как порог для определения границ частотных каналов. OFDM сигнал считается обнаруженным, если были найдены эквидистантные частотные каналы. После этого рассчитывается длительность интервала ортогональности. Предложенный метод требует незначительного усложнения процедуры спектрального анализа на основе быстрого преобразования Фурье. Метод может быть использован для повышения эффективности работы широкополосных систем радиомониторинга, а именно практически одновременной реализации функции обнаружения-распознавания OFDM сигнала. ; На даний час в радіосистемах цивільного та військового призначення широкого поширення набуло використання технології OFDM, особливо при роботі в каналах із частотно-селективними завмираннями. Через значну кількість схем побудови OFDM сигналів актуальним завданням для сучасних систем радіомоніторингу є розроблення методів та алгоритмів виявлення таких сигналів, які будуть стійкими щодо невизначеності структури OFDM сигналу та електромагнітної обстановки. На етапі виявлення характерною ознакою OFDM сигналу обрано наявність частотних каналів в згинаючій його спектра. Розроблено алгоритм виявлення OFDM сигналу в частотній області, а також оцінюванні кількості частотних каналів і тривалості інтервалу ортогональності. Для прийняття рішення про наявність сигнальних відліків у розрахованій реалізації нормованого до енергії спектра використано його варіацію. Такий підхід дозволяє уникнути оцінювання потужності шуму. У разі виявлення частотних відліків проводиться подвійне згладжування спектра за допомогою ковзаючого середнього. Це забезпечує краще згладжування ніж за допомогою одного вікна великої довжини. Після цього проводиться подвійна порогова обробка. Другий поріг розраховується із використанням відліків, що не перевищили перший поріг. Відліки, що перевищили другий поріг вважаються сигнальними. Далі проводиться пошук зайнятих ділянок частот із заданою шириною смуги. Відліки, що знаходяться у цій смузі ще раз згладжуються, що дозволяє отримати тренд спектра, який використовується як поріг для визначення меж частотних каналів. OFDM сигнал вважається виявленим, якщо було знайдено еквідистантні частотні канали. Після цього розраховується тривалість інтервалу ортогональності. Запропонований метод потребує незначного ускладнення процедури спектрального аналізу на основі швидкого перетворення Фур'є. Метод може бути використаний для підвищення ефективності роботи широкосмугових систем радіомоніторингу, а саме практично одночасної реалізації функції виявлення-розпізнавання OFDM сигналу.

This proceding at: IEEE 80th Vehicular Technology Conference (VTC)Fall. Took place 2014, September 15-19, in Vancouver (Canada). ; Radio over Fiber (RoF) distribution aided co-operation of Remote Access Points (RAPs) is proposed for jointly transmitting data to the users in the downlink (DL) of a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Joint transmission is performed with the aid of Block Diagonalization (BD), where the transmitted signal is pre-distorted in order to overcome the non-linearity imposed by the optical modulator. We demonstrate that with adequate design, the users can obtain high data rates with very small degradation introduced by the RoF transmission. Quantitatively, when M=7 RAPs, each equipped with t=2 transmit antennas (TAs) each, cooperate to serve N=7 simultaneous users, also equipped with r=2 receive antennas (RAs), the SNR degradation is kept below 0.1 dB compared to a system assuming a perfect RoF channel. On the other hand, the SNR performance degradation is around 1.2 dB, when the number of antennas at the transmitters and the receivers is increased to t=r=8. ; This work was supported by projects CSD2008-00010, TEC2011-29006- C03-03 and by a mobility grant of Spanish Ministry of Education. The financial support of the UK Government's Engineering & Physical Sciences Research Council (EPSRC) as well as that of the Research Councils UK (RCUK) and of the European Research Council's Senior Research Fellow Grant is also gratefully acknowledged. ; Publicado

The paper describes an adaptive algorithm for power and bit allocations in a multiple user Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO OFDM) system with Space Division Multiple Access, which operates in a frequency selective fading channel. The zero forcing (ZF) technique is applied to accomplish multi user detection (MUD). A Lagrange multiplier method is applied to obtain a one-step solution for optimal power and bit allocations in this system. The resulting algorithm is advantageous over an alternative Greedy algorithm, because it does not require a time-consuming iterative procedure for its implementation. The algorithm assigns bits and power for all users according to the channel state information (CSI), which is assumed to be fully or partially available to the transmitter. The simulation results show the proposed algorithm operates successfully in multiple user access scenarios.

The demand for high-speed mobile wireless communications is growing at a very fast rate. OFDM technology is a key technique for achieving the high data rate and spectral efficiency requirements for wireless communication systems. Frequency division Multiplexing (OFDM) [3–6] has emerged as a successful air-interface technique. The Frequency division Multiplexing was originally developed from the multi-carrier modulation techniques used in high Frequency military radios. This thesis presents, a simulink based simulation system is implemented using Additive White Gaussian Noise channel (AWGN) to study the performance analysis of Bit Error rate (BER) Vs Signal to Noise ratio (SNR). The model of OFDM with Rician fading channel using simulink in MATLAB is discussed. This model is used for performance enhancement of the OFDM with QPSK and QAM modulation schemes and channel condition. The throughput and packet error rate are used to evaluate the performance of MAC layer with the change in physical layer parameter. The performance analysis of different technique used in the QAM OFDM is compared by visualizing the BER vs SNR curve

The demand for high-speed mobile wireless communications is growing at a very fast rate. OFDM technology is a key technique for achieving the high data rate and spectral efficiency requirements for wireless communication systems. Orthogonal Frequency Division Multiplexing (OFDM) [3–6] has emerged as a successful air-interface technique. The Orthogonal frequency division Multiplexing was originally developed from the multi-carrier modulation techniques used in high Frequency military radios. This paper presents, using Additive White Gaussian Noise channel (AWGN) and racian channel to studyand compair the performance analysis of Bit Error rate (BER) Vs Signal to Noise ratio (SNR). The model of OFDM with Rician fading channel using simulink in MATLAB is discussed. This model is used for performance enhancement of the OFDM with QPSK and QAM modulation schemes and channel condition. The throughput and packet error rate are used to evaluate the performance of communication with the change in physical layer parameter. The performance analysis of different technique used in the QAM OFDM is compared by visualizing the BER vs SNR curve.

Military communications require the rapid deployment of mobile, high-bandwidth systems. These systems must provide anytime, anywhere capabilities with minimal interference to existing military, private, and commercial communications. Ultra Wideband (UWB) technology is being advanced as the next generation radio technology and has the potential to revolutionize indoor wireless communications. The ability of UWB to mitigate multipath fading, provide high-throughput data rates (e.g., greater than 100 Mbps), provide excellent signal penetration (e.g., through walls), and low implementation costs makes it an ideal technology for a wide range of private and public sector applications. Preliminary UWB studies conducted by The Institute for Telecommunications Science (ITS) and the Defense Advanced Research Projects Agency (DARPA) have discovered that potential exists for harmful interference to occur. While these studies have provided initial performance estimates, the interference effects of UWB transmissions on coexisting spectral users are largely unknown. This research characterizes the electromagnetic interference (EMI) effects of UWB on the throughput performance of an IEEE 802.11a ad-hoc network. Radiated measurements in an anechoic chamber investigate interference performance using three modulation schemes (BPSK, BPPM, and OOK) and four pulse repetition frequencies over two Unlicensed National Information Infrastructure (U-NII) channels. Results indicate that OOK and BPPM can degrade throughput performance by up to 20% at lower pulse repetition frequencies (PRFs) in lower U-NII channels. Minimal performance degradation (less than one percent) due to interference was observed for BPSK at the lower PRFs and higher U-NII channels.

Wireless Multimedia Sensor Networks (WMSNs) are spread systems of wirelessly networked devices that permit retrieving video and audio streams, still images, and scalar sensor data. WMSNs will be a crucial component of mission-critical networks to protect the operation of strategic national infra-structure, provide support to counteract emergencies and threats, and enhance infrastructure for tactical military operations. To enable these applications, WMSNs require the sensor network paradigm to be re-thought in view of the need for mechanism to deliver multimedia content with a pre-defined level of Quality of Service (QoS). In this paper, an improved cross-layer communication architecture based on the multiple-input and multiple-output (MIMO) – orthogonal frequency division multiplexing (OFDM) technology is described, whose goal is to reliably and flexibly bring QoS to various applications in WMSNs and also get better life cycle parameters, by leveraging and conniving connections between different layers of the protocol stack according to application requirements. Simulations get the recital objectives of WMSNs exclusive of sacrificing on the modularity of the overall design. Index Terms – Wireless multimedia sensor networks, improved cross-layer communication architecture, Quality of Service and life cycle improvement, multiple-input and multiple-output (MIMO) – orthogonal frequency division multiplexing (OFDM) .

Cover -- Advances in Communication Technology and Systems -- Copyright Page -- Preface -- Contents -- Section 1: Information and communication engineering -- The design and implementation of water conservancy information system based on WebGIS -- A sparse channel estimation method for OFDM systems based on parametric channel modelling -- Classification method of sulfur print image based on characteristics of intensity histogram -- A new information system using multimedia thin client and cloud architecture -- A high throughput satellite communication system based on the complex field network coding -- Performance analysis of genetic algorithm based downlink MIMO channel capacity enhancement for distributed antenna relay system in indoor line of-sight Wi-Fi environment -- The modeling and implementation of the sensor data acquisition device of the fall detection system -- Marsden identity of partial Said-Ball curve -- Communication relay testing and validation of unmanned aerial vehicles -- An improved real-time positioning method of indoor navigation system based on IEEE 802.11 Wlan -- Detected moving target using four-impulse cancelation cooperated with staggered pulse repetition frequency dealing with blind speed -- Design and implementation of the GSM soft modem on android smart terminals -- Research on communication cable features real-time detection technology -- Study on the characteristics of wave propagation in conductivity exponential-time-varying media by finite-difference method -- Joint transmit antenna selection and precoding in multiuser distributed MIMO systems -- An enhanced CSMA/CA algorithm based on collision avoidance after CCA deference in IEEE802.15.4 for wireless sensor network -- The design of a low offset bandgap reference -- The research on ultra wideband communication channel model of MAV

CMMB (China Multimedia Mobile Broadingcasting) is a wireless broadcastingchannel standard for low bandwidth, low cost hand-held digital TV is adopted byall continental Chinese government TV broadcasting companies and some HongKong private TV broadcasting companies. The business potential is high, yet thefuture is hard to predict because it might be replaced by GB200600 or DTMB. Thedigital modulation is based on OFDM with pilot supporting channel estimationand equalization and CP supporting multi-path induced ISI problems.This thesis investigates the implement a CMMB system using a SDR platform.Simulation chain was implemented using MATLAB with full data precision includingCMMB transmitter and receiver. The transmitter behavior model includes RSencoder, LDPC encoder, OFDM modulation, etc. The receiver behavior modelincludes OFDM demodulation, channel estimation, channel equalization, LDPCdecoder, RS decoder, etc. Different channel models emulating pathloss, whitenoise, multi-path, and glitch were modeled. Based on the simulation chain andchannel models, T-domain, F-domain channel estimator and equalizer were implemented,optimized. Optimized TD-FD models for different mobility scenarioswere proposed. The focus of the thesis is on 2D (FD-TD) channel estimation andequalization.