In this paper, we propose a simultaneously transmitting and reflecting intelligent reflecting surface (STAR-IRS) assisted multi-user communication system in the terahertz (THz) band. To overcome the potential blockage of direct links from the base station (BS) towards users or the possibility of users located out of the reach of the BS, the STAR-IRS assisted link can help enhancing the performance of the system. We derive closed-form expressions for the signal-to-noise ratio (SNR) outage probability for optimal and non-optimal STAR-IRS phase shifts with considering the users' statistical distribution within the service area. We conduct our analysis assuming the combined$\alpha-\mu$distribution, pointing errors, and molecular absorption that are inherent in THz transmission. The derived expressions are validated through Monte Carlo simulations and the effect of various system parameters on the outage probability is studied. Results show that the proposed system can achieve acceptable outage performance even with the existence of phase shift errors. Moreover, the performance can be further enhanced with increasing the number of STAR-IRS elements, which is practical in the THz band due to the very small wavelength.

Pulse position modulation (PPM) presents several advantages in free-space optical systems, unrepeatered fiber transmission, and passive optical networks. In this paper, we study the error performance in direct-detection optically preamplified M-ary PPM optical communication systems. We consider the impact of the amplifier spontaneous emission noise, as well of the finite extinction ratio of the transmitter, on the probability of bit error at the receiver. We derive expressions for the probability of bit error under both assumptions of noise polarization, namely, single- and dual-polarized amplifier noise, and compute it numerically for different symbol sizes M and extinction ratios. In addition, we present the power penalty due to the transmitter finite extinction ratio for systems with and without forward error correction. Our findings show that, in the cases of practically achievable finite extinction ratios, systems with smaller M may perform equally well when compared to those using higher values of M. We also show that there is little benefit, if any, associated with using a polarization filter in the receiver since the additional size, weight, and power consumption requirements outweigh the error performance improvement.

Delivery of multimedia contents over unreliable channels poses several challenges. In particular, video streaming has strict requirements on bandwidth, delay, and loss rate. In this paper, we propose the integration of several approaches to overcome these challenges. These approaches are adaptive modulation, adaptive channel coding, adaptive playback, and bitstream switching. The proposed adaptive scheme significantly improves the effective channel bitrate. It also accommodates variations in the channel condition and subsequently ensuring uninterrupted video playback.

Abstract Efficient resource allocation is a key factor to improve the efficiency of video transmission over wireless channels. To increase the number of correctly received video frames at the decoder, it is desirable to reduce the video source rate while increasing error protection when the wireless channel is anticipated to be bad or when the receiver buffer is approaching starvation. In this study, we introduce a retransmission‐based adaptive source‐channel rate control scheme for video transmission over wireless packet networks. In this scheme, the level of adaptiveness is optimized to reduce the bandwidth requirement while guaranteeing delay and loss bounds. The proposed scheme has the advantage of providing closed‐form expressions of the near‐optimum parameters of the proposed model, which are then fed back to the transmitter to scale both the source and channel rates adaptively. Simulation and numerical investigations are carried out to verify the adequacy of the analysis and study the impact of the adaptive process on the continuity of the video playback process. Copyright © 2009 John Wiley & Sons, Ltd.

In this paper we propose a fair-scheduling algorithm for the transmission of video frames over wireless links. The scheme is based on the occupancy of the video decoder buffer. When the occupancy of the decoder buffer of a given video client becomes increasingly small and approaches a starvation threshold, it gets treated with a higher priority and gets serviced more frequently than other clients who may not be approaching the starvation point. When compared to other commonly-used scheduling algorithms, ours shows a better performance in terms of the end-to-end delay experienced by the video frames.