Citation Context

... slots. Therefore, the tradeoff between high throughput and fairness is significant to opportunistic systems. Consequently, we analyze the fairness issue of the proposed scheme. Jain’s fairness index =-=[18]-=- is utilized to measure the fairness among STAs fairness index (30) where is the sum throughput of during the simulation round. The more this fairness index approaches the value of 1, the fairer the s...

Citation Context

...are not independent; thus, the optimization is aimed at the combination of and . The optimization in (29) is a mixed-integer nonlinear programming (MILNP) problem. Here, the branchand-bound algorithm =-=[16]-=- is adopted to solve this optimization problem. In the case where , frame collisions have a great impact on the system throughput. However, thanks to our opportunistic design and the optimization of t...

Citation Context

...ncorrelated, and the noise variance at the CCo is expressed as Here, the noise power spectral density (PSD) varies in different time frames, so the noise power spectrum at the CCo is time varying. In =-=[10]-=-–[12], the authors have investigated and confirmed the cyclostationary nature of noise in power lines. The noise power spectrum is observed to be periodic with the frequency of the power line cycle (5...

Citation Context

...elated, and the noise variance at the CCo is expressed as Here, the noise power spectral density (PSD) varies in different time frames, so the noise power spectrum at the CCo is time varying. In [10]–=-=[12]-=-, the authors have investigated and confirmed the cyclostationary nature of noise in power lines. The noise power spectrum is observed to be periodic with the frequency of the power line cycle (50 or ...

Citation Context

...OFDMA), power-line communication (PLC). I. INTRODUCTION P OWER-LINE communication (PLC) systems become increasingly viewed as an attractive two-fold solution to the “last mile” and “last inch” access =-=[1]-=-. By employing the orthogonal frequency-division multiplexing (OFDM) and other techniques, PLC systems can attain up to a 150-Mb/s information rate [2] at the physical (PHY) layer, which makes PLC net...

Citation Context

... not discussed. Compared with the aforementioned schemes, some randomaccess schemes are studied to take advantage of multiuser diversity in subchannel allocation and channel contention procedures. In =-=[7]-=- and [8], a backoff mechanism for OFDMA and CSMA/CA systems is presented. In this mechanism, the backoff counter is initialized as a random value between 0 and the minimum contention window size for t...

Citation Context

...cussed. Compared with the aforementioned schemes, some randomaccess schemes are studied to take advantage of multiuser diversity in subchannel allocation and channel contention procedures. In [7] and =-=[8]-=-, a backoff mechanism for OFDMA and CSMA/CA systems is presented. In this mechanism, the backoff counter is initialized as a random value between 0 and the minimum contention window size for the first...

Citation Context

...nnel set is not utilized by the contending users. This work gives the subchannel assignment solution from the opportunistic viewpoint, but collision resolution is not taken into account. Chang et al. =-=[4]-=- put forward a collision resolution policy for the opportunistic Aloha scheme of [3], where collided good subchannels are set with a random backoff time for future retrial, rather than discarded. Furt...

Citation Context

...y for the opportunistic Aloha scheme of [3], where collided good subchannels are set with a random backoff time for future retrial, rather than discarded. Furthermore, a backoff mechanism is shown in =-=[5]-=-, where all users estimate their channel power gains and compare them with a predefined 0885-8977/$31.00 © 2012 IEEE2074 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 4, OCTOBER 2012 backoff thre...

Citation Context

...h greater channel gain experience fewer numbers of backoff slots, which results in higher priority of the channel contention. Therefore, they are more likely to obtain their favorable subchannels. In =-=[6]-=-, another MAC protocol is proposed for OFDMA and CSMA/CA PLC networks. Similarly, the backoff time is decreased with the increasing gain of throughput for each user. Theses works provide the subchanne...

Citation Context

...requency of the power line cycle (50 or 60 Hz). Thereby, the channel signal-to-noise ratio (SNR) exhibits periodicity characteristics. Accordingly, the cyclostationary PLC channel noise is modeled in =-=[13]-=- using a time mask multiplied by the noise PSD [i.e., Mask ]. The time mask spans in an ac cycle period (20 ms for 50 Hz), and shows how the noise PSD varies (1)DONG et al.: OPPORTUNISTIC RANDOM-ACCE...

Citation Context

... the corresponding data rate. Here, is modeled by using the method of curve fitting based on the channel parameters in Section II. More details about the related curve-fitting process can be found in =-=[15]-=-. The cumulative distribution function (CDF) of is defined as . We suppose that achieves its maximum data rate over one subchannel among idle subchannels and, thus, the corresponding PDF of is calcula...