VoIP Şebekesindeki Ses Kalitesinin Çok Katmanlı Yapay Sinir Ağları ile Modellenmesi

Öz

Son yıllarda internet ağının, çok yaygınlaşması, esnek olması, hızlı ve yüksek kapasite erişimi sunabilmesine bağlı olarak farklı tipteki birçok servis internet protokolü (IP) üzerinden iletilmeye başlanmıştır. Bu servis tiplerinden birisi de ses trafiği olup bu durum klasik haberleşme sistemlerini doğrudan etkilemektedir. Ses iletimi, genel anahtarlamalı telefon ağları (public switched telephone network, PSTN) yerine IP üzerinden yapılmaya başlanmıştır. Bu yeni haberleşme teknolojisi, IP üzerinden ses iletimi (voice over IP, VoIP) olarak adlandırılmıştır. VoIP teknolojisinde, ses iletiminin kullanıcı tarafından algılanma kalitesi ise ortalama görüş puanı (mean opinion score, MOS) ile belirlenir. MOS değerinin üretilmesi birçok parametreye bağlıdır. ITU-T (international telecommunications union -telecommunication standardization sector) tarafından MOS değerinin belirlenmesi için PSQM (perceptual speech quality measure), PESQ (perceptual evaluation of speech quality), POLQA (perceptual objective listening quality analysis) gibi birçok model standartlaştırılmıştır. Fakat bu model yapıları, birçok avantaja sahip olmasının yanında referans işaret gereksiniminden dolayı uygulamalarda pratik zorluklar oluşturmaktadır. Buyüzden bu çalışmada, ses iletimindeki MOS kalite değerlerini tahmin etmek amacıyla referans sinyal gerektirmeyen çok katmanlı yapay sinir ağları (YSA) tabanlı bir model yapısı tasarlanmıştır. Bu modelde, giriş olarak IP trafiğine ait servis kalite (quality of service, QoS) parametreleri ve çıkış olarak ise elde edilen MOS değerleri kullanılmıştır. Giriş olarak kullanılan bu QoS parametreleri ise paket kaybı (packet loss) ve gecikme (delay) değerleridir. Böylece 2 giriş ve 1 çıkışa sahip bir model oluşturulmuştur. Ayrıca model, farklı QoS parametresi kullanılarak MOS tahmini yapabildiği için esnek bir yapıya da sahiptir. Literatürdeki çalışmalardan farklı olarak bu çalışmada, POLQA yöntemi ile ölçülen MOS değerlerinin YSA model ile tahmin edilmesine çalışılmıştır. YSA modelin eğitim ve test sürecinde LMB (levenberg-marquardt backpropagation), BRB (bayesian regulation backpropagation) ve RSB (Resilient backpropagation) algoritması kullanılmıştır. Simülasyon sonucunda elde edilen sonuçlar tablolar ve şekiller vasıtasıyla sunulmuştur. Sonuçlara göre geliştirilen bu metodun ITU-T tarafından önerilen modeller ile karşılaştırılabilir seviyede olduğu gösterilmiştir.

Anahtar Kelimeler

• VoIP
• Ortalama Görüş Puanı
• POLQA Model
• Yapay Sinir Ağları

Modeling of Sound Quality in VoIP Network with Multi-Layer Artificial Neural Networks

Öz

In recent years, different types of services have been started to be transmitted over the internet protocol (IP), due to the widespread use of the internet network, its flexibility and the ability to offer fast and high capacity access. One of these service types is voice traffic and this directly affects classical communication systems. Voice transmission is started over IP instead of public switched telephone network (PSTN). This new communication technology is called voice over IP (VoIP). In VoIP technology, the quality of the perception of the voice transmission by the user is determined by the mean opinion score (MOS). Generation of the MOS value depends on many parameters. Many models such as PSQM (Perceptual Speech Quality Measure), PESQ (Perceptual Evaluation of Speech Quality), POLQA (Perceptual Objective Listening Quality Analysis) have been standardized by ITU-T (International Telecommunications Union -Telecommunication Standardization Sector) to determine the MOS value. However, besides having many advantages these model structures also create practical difficulties in applications due to the need of a reference signal. Therefore, in this study, a multi-layered artificial neural networks (ANN) based model structure that does not need a reference signal is designed to estimate MOS quality values in voice transmission. In this model, quality of service (QoS) parameters of IP traffic are used as input and obtained MOS values are used as output. These QoS parameters used as input are packet loss and delay values. Thus, a model with 2 inputs and 1 output was created. In addition, the model has a flexible structure as it can estimate MOS using different QoS parameters. Different from the studies in the literature, in this study, it was tried to estimate MOS values measured by the POLQA method with ANN model. LM (Levenberg Marquardt), BR (Bayesian Regulation) and RPROP (Resilient Backpropagation) algorithm was used in the training and testing process of the ANN model. The results obtained from the simulations are presented by tables and figures. The method, developed according to the results, has been shown to be comparable to the models recommended by ITU-T.

Anahtar Kelimeler

• Artificial Neural Networks
• POLQA Model
• Mean Opinion Score
• VoIP

Kaynakça

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