Sharif Digital Repository

The voice channels present in cellular communication networks provide reliable, widespread and high priority communication mediums. Using these voice channels as a bearer for data transmission allows to deliver high Quality of Service data. But voice channels include vocoders that hinder the data flow by compressing the waveforms prior to transmission. Calculating vocoder channel capacity remains a challenging problem since no analytical model has been proposed for the vocoder channel so far. In this research, simplified models for the vocoder channel are proposed and bounds on vocoder channel capacity are derived based on them. In common cellular networks, the vocoder compression rate is... 

In this paper, we analyze and obtain performance of a multilevel Optical Code Division Multiple Access (OCDMA) system with Variable-Weight Optical Orthogonal Codes (VW-OOCs) under the same-bit-energy assumption. The exact error-probability of this system is derived for the Generalized VW-OOCs (codes with arbitrary cross-correlation) which is necessary for the optimum design of multilevel OCDMA systems. We show that the bit power has an important role on determining the performance of codes with different weights. Furthermore, the results reveal that the performance of low-weight codes depends on the weight of the low-weight codes and the code-weight ratio of two classes. Moreover, our exact... 

One of the most important issues in cognitive radio networks is to guarantee quality of service (QoS) constraints for primary users. In this paper, a relay-based cognitive radio network is considered in which secondary users compete in a selfish manner to use a relay to improve their utility function, while maintaining interference at the primary receiver to be lower than a certain threshold level. This problem is modeled as a non-cooperative game and by using a proper pricing function in the definition of the utility function, it is shown that despite the selfish behavior of the users, Nash equilibrium (NE) with sub-optimum property is achieved. A distributed and novel algorithm to update... 

Establishing high-quality communication in construction projects is essential to securing successful collaboration and maintaining understanding among project stakeholders. Indeed, poor communication results in low productivity, poor efficiency, and substandard deliverables. While high-quality communication is recognized as contingent on the interpersonal skills of workers, the impacts of communication quality on job performance remain unknown. This study addresses this deficiency by developing a method to evaluate construction workers' communication quality. A literature review is undertaken to capture salient interpersonal skills. Leadership style, listening, team building, and clarifying... 

In this paper, a low order recursive linear prediction method and recursive least square as an adaptive filter (LP-RLS) are introduced to predict the speech and the excitation signals. In real-time packet-based communication systems, one major problem is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid quality reduction due to packet loss, a suitable method and/or algorithm is needed to replace the missing segments of speech. The... 

In real-time packet-based communication systems, one major problem is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid quality reduction due to packet loss, a suitable method and/or algorithm is needed to replace the missing segments of speech. In this paper, we introduce a low order recursive linear prediction method for replacement of lost speech segment. In this method a normalized least mean square (NLMS) as an adaptive filter...