QVBR-MAC: A QoS-Oriented MAC Protocol for Variable-Bit-Rate MC-CDMA Wireless LANs

Multicarrier Code Division Multiple Access (MC-CDMA) techniques were originally proposed at mid of 90’s for wideband multi-user communications in wireless environments characterised by hostile propagation characteristics. Problems still to be solved are related to the provision of efficient resource channel allocation in variable-bit-rate transmission. In this work, the design of a MC-CDMA-based WLAN infrastructure is considered. The great advantage of MC-CDMA, i.e. the capability of supporting asynchronous multi-user variable-bit-rate (VBR) transmission over multipath channel with conventional detection, is exploited, jointly with an efficient and real-time Medium Access Control (MAC) strategy, in order to allow a significant number of VBR users to share the same bandwidth with different QoS profiles. Different classes of users will be labeled by the MAC level that has to plan a controlled access to the channel on the basis of the users’ requests and to check the possibility of assuring to them a certain Qos degree. The paper presents an overview of the system and tests its performance through extensive simulation

Multi-Carrier Code Division Multiplexing of Multi-Layered MPEG4 Video Signals for Real-time Mobile Streaming Applications

In this report, a novel methodology for the efficient multiplexing and transmission of MPEG4- coded video signals over wireless networks will be presented and discussed. The proposed approach relies on the joint exploitation of variable-bit-rate (VBR) multicarrier code-division multiplexing (MC-CDM), together with MPEG4 coding with Fine-Grain-Scalability (FGS) in order to provide unequal error protection to the transmitted video stream.The innovative scheme proposed employs a shared bandwidth partitioned into orthogonal sub-channels in order to multiplex different layers of MPEG-4-coded signals. The highest number of sub-channels (and hence an increased frequency diversity) is assigned to the lowest-bit-rate base layer and the lowest number of sub-channels is assigned to the highest bit-rate enhancement layer. In such a way, base layer information contents are more protected against channel degradations than information contained in FGS enhancement layers, which can only yield a refinement of the quality of the decoded streams. A 2GHz LEO multicast satellite transmission to mobile users has been regarded as the application testbed for the proposed method. Results achieved in terms of PSNR point out that the VBR MC-CDM technique can provide better results than a conventional MPEG-4 single-layer MC-SS transmission.In the framework of a full-digital implementation of reconfigurable multimedia transceivers, the proposed VBR MC-CDM technique may be regarded as an interesting solution for reliable multimedia transmissions in mobile environments

Cross-Layer Adaptation of MPEG4 Video Streaming Over Wireless Networks Using Unequal Error Protection and MC-CDMA

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-Grain-Scalability (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. A 2-GHz LEO multicast satellite transmission system has been considered as a application testbed of the proposed methodology. Results achieved in terms of PSNR show that the VBR MC-CDM technique can provide better results than conventional MPEG4 single-layer MC-SS transmission. In the framework of a full-digital implementation of reconfigurable multimedia transceivers, the proposed VBR MC-CDM technique may be regarded as a convenient solution for reliable multimedia transmissions in mobile environments