Multicarrier Code Division Multiple Access (MC-CDMA) techniques were originally proposed at mid of 90's for wideband multi-user communications in wireless environments characterized by hostile propagation characteristics. In this work, 1 the design of a MC-CDMA-based infrastructure is considered for VBR broadband indoor connections with real-time asynchronous multiple access. At the present time, Broadband Fixed Wireless Access (BFWA) standards like IEEE 802.16 and HIPERMAN can bring broadband services inside buildings, but indoor access should be conveniently provided by a local area connection. The capability of MC-CDMA of supporting asynchronous multi-user variable-bit-rate (VBR) transmission is exploited jointly with an efficient and real-time Medium Access Control (MAC) strategy in order to allow a significant number of indoor VBR users to transmit information in CDMA modality with different quality of service (QoS) profiles. Different classes of users are defined at the MAC level. The available radio resources (i.e. the orthogonal subchannels) are selectively attributed to transmitting users depending on their performance achieved at MAC level and measured by an "intelligent" gateway. When the quality level is not satisfactory for one or more users, the AP issues a decrease of the data rate for such users while providing them with an increased number of subcarriers, guaranteeing a slower transmission fostered against frequency-selective channel distortions. The paper presents an overview of the system and tests its performance through extensive simulations. The proposed joint MAC-PHY approach demonstrates good performance in terms of achieved throughput and high flexibility in radio resource management.

In this work 1 , a novel methodology for the efficient multiplexing and streaming of MPEG4 video over wireless networks is presented and discussed. The proposed cross-layer adaptation jointly exploits variable-bitrate (VBR) multi-carrier code-division multiplexing (MC-CDM) and MPEG4 Fine-GrainScalability (FGS) in order to provide unequal error protection to the transmitted video stream. A shared bandwidth is partitioned into orthogonal sub-channels in order to multiplex different layers of MPEG4-coded signals. Lower layers are assigned a higher number of sub-channels (and hence an increased frequency diversity) as compared to FGS enhancement layers, in order to provide a differentiated protection against channel degradations. Results achieved in terms of PSNR show that the VBR MC-CDM technique can provide better results than conventional MPEG4 single-layer multicarrier Spread Spectrum transmission.

MapReduce job execution typically occurs in sequential phases of parallel steps. These phases can experience unpredictable delays when available computing and network capacities fluctuate or when there are large disparities in inter-node communication delays, as can occur on shared compute clouds. We propose a pipeline-based scheduling strategy, called speculative pipelining, which uses speculative prefetching and computing to minimize execution delays in subsequent stages due to varying resource availability. Our proposed method can mask the time required to perform speculative operations by overlapping with other ongoing operations. We introduce the notion of "open-option" prefetching, which, via coding techniques, allows speculative prefetching to begin even before knowing exactly which input will be needed. On a compute cloud testbed, we apply speculative pipelining to the Hadoop sorting benchmark and show that sorting time is shortened significantly.

In this work 1 , the capability of MC-CDMA to support asynchronous multi-user variable-bit-rate (VBR) transmission over multipath channel is exploited, jointly with an efficient Medium Access Control (MAC) strategy, in order to allow a significant number of VBR users to share the same bandwidth with different quality of service profiles. An application scenario related to WLAN transmission has been considered in order to assess the proposed MAC methodology. Available radio resources (i.e. the orthogonal subchannels) are selectively attributed to transmitting users depending on their achieved performance at the MAC level, measured by an "intelligent" Access Point (AP). When quality level is not satisfactory for one or more users, the AP issues a decrease of the data rate for such users while providing them with an increased number of subcarriers, in order to guarantee a lower bitrate fostered against frequency-selective channel distortions. Performance is evaluated through extensive simulation, demonstrating good performance and high flexibility of the approach.