Search

We present a new selective retransmission method for orthogonal space-time block (OSTB) coded orthogonal frequency division multiplexing (OFDM) systems at modulation layer. The proposed method is independent of the conventional hybrid automatic repeat request (HARQ) methods and improves throughput by selectively retransmitting of OSTB codes corresponding to the poor quality subcarriers. A typical failed packet has fewer corrupt bits and retransmission of partial packet can help receiver to recover from bit errors. Thus, the proposed method allows selective retransmission correspond to the poor quality subcarriers of multiple-input multiple-output (MIMO) OFDM system. The receiver performs Chase combining (joint detection) of retransmitted OSTB codes by combining observations from the first transmission (preserved before retransmission request) and ensuing selective retransmission. Due to the structure of the OSTB codes, we use ℓ 2 -norm of the MIMO channel matrix as a channel quality metric. We also present union bound on the bit-error rate (BER) for the proposed selective Chase combining (SCC) approach. [ABSTRACT FROM AUTHOR]

Abstract: The IEEE 802.11n standard is defined to achieve a high throughput at the MAC layer. This high throughput is accomplished via many enhancements in both the physical and MAC layers. A key enhancement introduced in the 802.11n standard is frame aggregation. Two types of aggregation defined by the 802.11n standard, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). Frame aggregation reduces both the headers and timing overheads at the MAC layer by aggregating multiple frames into a single large frame before being transmitted. The aggregation headers themselves still have a negative impact on the network performance especially when aggregating frames of small payload. Moreover, the lack of partial retransmission in the A-MSDU aggregation is behind its poor performance in error-prone channels. In this paper we proposed an optimized header A-MSDU frame aggregation (OHA-MSDU) with subframes retransmission capability at the MSDU level. The simulation results show the significance of the proposed scheme, especially for applications that have a small frame size such as VoIP. [Copyright &y& Elsevier]

Abstract: Three-dimensional (3D) meshes are used intensively in distributed graphics applications where model data are transmitted on demand to users’ terminals and rendered for interactive manipulation. For real-time rendering and high-resolution visualization, the transmission system should adapt to both data properties and transport link characteristics while providing scalability to accommodate terminals with disparate rendering capabilities. This paper presents a transmission system using hybrid unequal-error-protection and selective-retransmission for 3D meshes which are encoded with multi-resolutions. Based on the distortion-rate performance of the 3D data, the end-to-end channel statistics and the network parameters, transmission policies that maximize the service quality for a client-specific constraint is determined with linear computation complexity. A TCP-friendly protocol is utilized to further provide performance stability over time as well as bandwidth fairness for parallel flows in the network. Simulation results show the efficacy of the proposed transmission system in reducing transmission latency and providing smooth performance for interactive applications. For example, for a fixed rendering quality, the proposed system achieves 20–30% reduction in transmission latency compared to the system based on 3TP, which is a recently presented 3D application protocol using hybrid TCP and UDP. [Copyright &y& Elsevier]