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حرية الوصول المقاله
1 - Video Transmission Using New Adaptive Modulation and Coding Scheme in OFDM based Cognitive Radio
حسن فرسی Farid JafarianAs Cognitive Radio (CR) used in video applications, user-comprehended video quality practiced by secondary users is an important metric to judge effectiveness of CR technologies. We propose a new adaptive modulation and coding (AMC) scheme for CR, which is OFDM based sy أکثرAs Cognitive Radio (CR) used in video applications, user-comprehended video quality practiced by secondary users is an important metric to judge effectiveness of CR technologies. We propose a new adaptive modulation and coding (AMC) scheme for CR, which is OFDM based system that is compliant with the IEEE.802.16. The proposed CR alters its modulation and coding rate to provide high quality system. In this scheme, CR using its ability to consciousness of various parameters including knowledge of the white holes in the channel spectrum via channel sensing, SNR, carrier to interference and noise ratio (CINR), and Modulation order Product code Rate (MPR) selects an optimum modulation and coding rate. In this scheme, we model the AMC function using Artificial Neural Network (ANN). Since AMC is naturally a non-liner function, ANN is selected to model this function. In order to achieve more accurate model, Genetic algorithm (GA) and Particle Swarm Optimization (PSO) are selected to optimize the function representing relationship between inputs and outputs of ANN, i.e., AMC model. Inputs of ANN are CR knowledge parameters, and the outputs are modulation type and coding rate. Presenting a perfect AMC model is advantage of this scheme because of considering all impressive parameters including CINR, available bandwidth, SNR and MPR to select optimum modulation and coding rate. Also, we show that in this application, GA rather than PSO is better choice for optimization algorithm. تفاصيل المقالة -
حرية الوصول المقاله
2 - Joint Source and Channel Analysis for Scalable Video Coding Using Vector Quantization over OFDM System
Farid Jafarian Hassan FarsiConventional wireless video encoders employ variable-length entropy encoding and predictive coding to achieve high compression ratio but these techniques render the extremely sensitive encoded bit-stream to channel errors. To prevent error propagation, it is necessary t أکثرConventional wireless video encoders employ variable-length entropy encoding and predictive coding to achieve high compression ratio but these techniques render the extremely sensitive encoded bit-stream to channel errors. To prevent error propagation, it is necessary to employ various additional error correction techniques. In contrast, alternative technique, vector quantization (VQ), which doesn’t use variable-length entropy encoding, have the ability to impede such an error through the use of fix-length code-words. In this paper, we address the problem of analysis of joint source and channel for VQ based scalable video coding (VQ-SVC). We introduce intra-mode VQ-SVC and VQ-3D-DCT SVC, which offer similar compression performance to intra-mode H.264 and 3D-DCT respectively, while offering inherent error resilience. In intra-mode VQ-SVC, 2D-DCT and in VQ-3D-DCT SVC, 3D-DCT is applied on video frames to exploit DCT coefficients then VQ is employed to prepare the codebook of DCT coefficients. In this low bitrate video codecs, high level robustness is needed against the wireless channel fluctuations. To achieve such robustness, we propose and calculate optimal codebook of VQ-SVC and optimal channel code rate using joint source and channel coding (JSCC) technique. Next, the analysis is developed for transmission of video using an OFDM system over multipath Rayleigh fading and AWGN channel. Finally, we report the performance of these schemes to minimize end-to-end distortion over the wireless channel. تفاصيل المقالة -
حرية الوصول المقاله
3 - Balancing Agility and Stability of Wireless Link Quality Estimators
MohammadJavad Tanakian Mehri MehrjooThe performance of many wireless protocols is tied to a quick Link Quality Estimation (LQE). However, some wireless applications need the estimation to respond quickly only to the persistent changes and ignore the transient changes of the channel, i.e., be agile and sta أکثرThe performance of many wireless protocols is tied to a quick Link Quality Estimation (LQE). However, some wireless applications need the estimation to respond quickly only to the persistent changes and ignore the transient changes of the channel, i.e., be agile and stable, respectively. In this paper, we propose an adaptive fuzzy filter to balance the stability and agility of LQE by mitigating the transient variation of it. The heart of the fuzzy filter is an Exponentially Weighted Moving Average (EWMA) low-pass filter that its smoothing factor is changed dynamically with fuzzy rules. We apply the adaptive fuzzy filter and a non-adaptive one, i.e., an EWMA with a constant smoothing factor, to several types of channels from short-term to long-term transitive channels. The comparison of the filters outputs shows that the non-adaptive filter is stable for large values of the smoothing factor and is agile for small values of smoothing factor, while the proposed adaptive filter outperforms the other ones in terms of balancing the agility and stability measured by the settling time and coefficient of variation, respectively. Notably, the proposed adaptive fuzzy filter performs in real time and its complexity is low, because of using limited number of fuzzy rules and membership functions. تفاصيل المقالة -
حرية الوصول المقاله
4 - بررسی اثر تخمینگر کانال MIMO در طراحی پیشکدگذار روی شبکههای حسگر بیسیم
هستی رستمی ابوالفضل فلاحتییکی از مهمترین کاربردهای شبکههای حسگر بیسیم تخمین پدیده ناشناخته میباشد. در تخمین توزیعشده روی شبکه حسگر بیسیم از فعالیت مشارکتی و اطلاعات پراکنده گرههای حسگرها استفاده میشود. طراحی پیشکدگذارها در گرههای حسگر به منظور ارائه تخمینی نزدیکتر به مقدار واقعی استفا أکثریکی از مهمترین کاربردهای شبکههای حسگر بیسیم تخمین پدیده ناشناخته میباشد. در تخمین توزیعشده روی شبکه حسگر بیسیم از فعالیت مشارکتی و اطلاعات پراکنده گرههای حسگرها استفاده میشود. طراحی پیشکدگذارها در گرههای حسگر به منظور ارائه تخمینی نزدیکتر به مقدار واقعی استفاده میشود. مسئله طراحی پیشکدگذار یک مسئله بهینهسازی است. از آنجایی که کانال در این شبکهها لینک بیسیم است که طبیعتی تصادفی دارد لذا فرض دسترسبودن اطلاعات کامل کانال در این نوع شبکهها فرض صحیحی به نظر نمیرسد. در فرایند طراحی ماتریسهای پیشکدگذار در گرههای حسگر به اطلاعات کامل کانال نیاز میباشد. در این تحقیق اثر تخمین کانال بر فرایند طراحی ماتریس پیشکدگذار و تخمین پدیده ناشناخته بررسی میشود. در مسئله تخمین کانال از روش تخمین با دنباله آموزشی استفاده میشود و کانال با دو معیار LS و MMSE تخمین زده خواهد شد. از آنجایی که توان در شبکههای حسگر بیسیم قید اساسی میباشد لذا در این بررسی دنباله آموزشی بهینه و پیشکدگذار بهینه تحت قید توان طراحی میشوند. تفاصيل المقالة