The hybrid medium access control (MAC) protocol, which was first adopted in the IEEE 802.11ax standard, combines contention-based random access (UORA) and contention-free scheduled access (SA) transmissions over orthogonal resource units (RUs). We present a novel fixed-point analysis of saturation throughput and average access delay of hybrid access that accounts for discrete rate adaptation, packet decoding errors, and scheduling. Using this analysis and Markov decision process (MDP) theory, we design a novel dynamic RU allocation policy (ODRAP) for hybrid access. Our analysis and policy design are the first to capture the dynamic flow of users between UORA and SA, and its dependence on the RU allocation. The existing literature has modeled UORA or SA, but not both, or has assumed a fixed number of SA users. We first develop the analysis when the number of packets reported in the buffer status report (BSR) of a user is a geometric random variable. We then present an iterative approach to handle application-specific general distributions. Our numerical results verify the accuracy of the analysis despite its simplicity. Furthermore, they highlight the impact of the number of allocated RUs on the scheduler. ODRAP optimally trades off the throughput with the access delay compared to several benchmark policies.

Current generation wireless local area networks (WLANs) based on the IEEE 802.11ax standard employ a novel hybrid medium access control (MAC) protocol, which combines contention-based random access (UORA) and contention-free scheduled access (SA) transmissions over orthogonal resource units (RUs). We present a novel fixed-point analysis of the saturation throughput of IEEE 802.11ax that accounts for hybrid access, discrete rate adaptation, and schedulers. Our analysis captures the dynamic flow of users between UORA and SA in hybrid access. The variability in the number of users, which depends on the number of RUs allocated to UORA and the MAC contention protocol, affects the performance of the scheduler. Our approach differs from the literature, which models either UORA or SA (but not both) or assumes a fixed number of SA users. Our results verify the accuracy of the analysis despite its simplicity and reveal that the conventional approaches can overestimate the UORA and SA throughputs.

A study of rendering natural instrument sounds and vocals as an ensemble is presented. Using a single channel musical recording, a multi-channel signal is created by introducing delays and rendered in spatially distributed loudspeaker array. Three listeners participate in a listening experiment. We observed that the perceived width of the ensemble varies with the signal timbre. We find that spectro-temporal properties of the musical instruments play a significant role in the perception of source width. On an average, sustained sounds (like vocal) create wider percept than transients like percussion. Also, low pitched sounds (like male bass voice, saxophone, tuba) create wider percept than high pitched signals.

In this paper, the effect of time-varying pitch-glides on timbre perception of vowels is studied experimentally. While earlier studies show that stationary pitch is observed to be a significant dimension of timbre, we explore the effect of non-stationary pitch changes on the perception of vowel timbre using synthesized vowels. In each trial, three listeners rate perceptual timbre change using a MUSHRA-like (MUltiple Stimuli with Hidden Reference and Anchor) methodology. Results show that perceived timbre change is affected by the pitch-shift and nature of pitch-glide. Timbre change is observed to be monotonic with pitch-shift for all types of pitch-glides, implying larger the pitch-shift, higher the perceived timbre change. When the excitation is a pitch-glide, the vowel spectral centroid and the nature of pitch-glide interact. We observe that for vowels of higher spectral centroid, decreasing pitch-glides cause higher timbre change than the timbre change caused by increasing pitch-glides; vice- versa for vowel of lower spectral centroid. Thus, “incoherent” pitch-glides cause higher timbre change than the “coherent” pitch-glides.