Packet Coding Research Articles

Cooperative spatial multiplexing for ad hoc networks with hybrid ARQ: system design and performance analysis

For a network where each node has multiple antennas, we propose a transmission mode and a cooperation protocol, with the aim of maximizing the network throughput. The distinctive feature of the work is that the focus in both the design and the evaluation is at the network level, rather than on a single link. To this end, we propose the use of spatial multiplexing and code division multiple access (CDMA) to increase the parallelism of transmissions in the network, thus improving throughput. Cooperation is also implemented by spatial multiplexing and CDMA, together with an adaptive hybrid automatic repeat request mechanism that adapts the retransmissions to the actual channel conditions. Spatial multiplexing allows frame-asynchronous transmissions and a flexible cooperation protocol that minimizes the signaling overhead. The resulting scheme is named layered coded cooperative system (LCCS). We propose an implementation of LCCS based on linear erasure packet codes, where cooperation is transparent to the receiver, and we assess the performance of LCCS both by analyzing a simple network with three nodes and by simulating a more complex network.

Layer 2 and 3 Contention Resolution and Radio-Over-Fiber in OCDMA PON for Transparent Optical Access in Personal Networks

In this paper, we analyze, for the first time, the eminent role of optical transparent networking in personal networks. We show how an optical access network mitigates many issues with respect to connectivity and mobility management. A concrete personal network user-scenario deduces requirements for such an architecture. A combination of passive optical network, optical code-division multiple access (OCDMA), and radio-over-fiber exhibits minimal cost and complexity because of centralized network control and management, resource sharing, and simplified network nodes. We enable transparent peer-to-peer communication between optical networking units in the OCDMA passive optical network subnet of the central office. We use, for the first time, simultaneously optical code-sense medium access control and optical code packet switching for contention resolution.

Distributed Rate Adaptive Packet Access (DRAPA) for Multicell Wireless Networks

Fueled by the explosive growth of the Internet, applications are demanding higher data rates and better services. Given the scarcity of radio resources, higher network capacities need to be achieved through more efficient use of the available bandwidth. Current cellular networks utilize frequency planning schemes that are optimized for circuit-switched applications, and thus is inherently problematic for future wireless packet networks with bursty, high peak-rate traffics. Random access schemes such as the ALOHA are seen as better solutions for packet networks. However, co-channel interference may significantly reduce the network throughput when the multicell load is heavy. In this paper, we propose a distributed rate adaptive packet access (DRAPA) scheme to combine the advantages of rate adaptation (in circuit-switched networks) and random access (in packet-switched networks). In particular, DRAPA allows terminal stations to transmit packets in random access fashion in the presence of brusty interference from neighboring cells. The packet code rate is adjusted according to interference level so that the retransmisson is controlled at an acceptable level. The DRAPA scheme subsumes two traditional schemes as the extreme cases, and has superior performance over the traditional schemes in terms of throughput and stability.

Code reservation CDMA for integrated voice and data service in cellular environment

A new media access control (MAC) protocol for packet code division multiple access (CDMA) in a cellular environment is proposed. When the overall system load remains low, the proposed protocol is shown to yield improvement over conventional ones for both voice and data traffic at the expense of introducing code reservation and modification of contention mechanism.

Quantum wave packet approach to the Eley–Rideal reactive scattering between a gas phase atom and an adsorbate

A quantum wave packet code for studying Eley–Rideal scattering reactions of gas phase atoms with atoms adsorbed onto a rigid substrate is described. The flat surface approximation reduces the full treatment to three-dimensional (3D) numerical resolutions. The time evolution relies on the split operator propagator in a discrete, cylindrical coordinate representation. A pseudospectral strategy is used to evaluate efficiently the Hamiltonian operation by means of sequential 1D transformations between coordinate and momentum spaces. Fast Fourier transforms are performed for the two Cartesian coordinates whereas a discrete Bessel transform is applied for the cylindrical radius. The potential energy representation is based on the so-called LEPS model. Flux analysis in the product molecular region yields energy-resolved reaction cross sections and rovibrational distributions.

An improved UDP protocol for video transmission over Internet-to-wireless networks

Packet video will become a significant portion of emerging and future wireless/Internet traffic. However, network congestion and wireless channel error yields tremendous packet loss and degraded video quality. In this paper, we propose a new complete user datagram protocol (CUDP), which utilizes channel error information obtained from the physical and link layers to assist error recovery at the packet level. We propose several maximal distance separable (MDS) code-based packet level error control coding schemes and derive analytical formulas to estimate the equivalent video frame loss for different versions of user datagram protocol (UDP). We validate the proposed packet coding and CUDP protocol using MPEG-coded video under various Internet packet loss and wireless channel profiles. Theoretic and simulation results show that the video quality can be substantially improved by utilizing the frame error information at UDP and application layer.

An Integrated Voice Data Protocol for Slotted CDMA Personal Communication Networks

In this paper we propose a new protocol forintegrated voice/data traffic in personal communicationnetworks (PCNs) employing slotted packet code divisionmultiple access (CDMA). The concept of dynamic boundary is adopted in both code and timedomains to meet the different requirements for data andvoice traffic. This paper outlines and compares theperformance of three channel assignment policies. The network performance is measured in terms of theaverage voice blocking probability and average datadelay. A discrete-event simulation and a two-dimensionalMarkov model are developed for both the fixed boundary scheme and dynamic boundary scheme.The results indicate that an improved performance can beachieved by introducing the dynamic boundary scheme, andthe dynamic assignment policy results in a performance close to the optimal value. It isalso easier to be implemented.

Nonreactive atom/molecule-surface scattering within the finite basis wave packet method

A quantum wave packet code for studying nonreactive scattering of closed-shell atoms or diatomic molecules from a rigid surface is described. The time evolution relies on the Chebychev propagator. Up to 5 collider degrees of freedom, 3 in translation and 2 in rotation, are treated in a pseudospectral way with the momentum or finite basis representation as the primary space. Potential matrix elements are efficiently evaluated by means of sequential 1D transformations between momentum and coordinate spaces. Fast Fourier transforms are performed for the translational and azimuthal coordinates whereas a Gauss-Legendre transform is used for the polar coordinate. This pseudospectral strategy minimizes memory requirements because no off-diagonal Hamiltonian matrix elements need to be stored. In addition, a wide variety of physical systems can be studied since no particular functional form is imposed for the interaction potential.

Bit-rate control algorithm on video packet coding and its characteristics

A bit-rate control method based on a hybrid coding algorithm is proposed for packet video coding. Three types of bit-rate control modes, the constant bit-rate mode, the average bit-rate control mode and the free bit-rate mode, are investigated. According to the opinion test the latter two modes have an advantage in video quality over the constant bit-rate mode. A teleconference terminal, which includes this video codec, audio codec and packet adaptor, is implemented in actual hardware on High-speed Packet Switching system. On this system, video information are transmitted in UI frame (a packet format in X.25 protocol) at 64 K ∼ 800 Kbit/s.

Variable bit-rate coding of video signals for ATM networks

Statistical characteristics of video signals for video packet coding, are clarified and a variable-bit-rate coding method for asynchronous transfer mode (ATM) networks is described that is capable of compensating for packet loss. ATM capabilities are shown to be greatly affected by delay, delay jitter, and packet loss probability. Packet loss has the greatest influence on picture quality. Packets may be lost either due to random bit error in a cell header or to network control when traffic is congested. A layered coding technique using discrete-cosine transform (DCT) coding is presented which is suitable for packet loss compensation. The influence of packet loss on picture quality is discussed, and decoded pictures with packet loss are shown. The proposed algorithm was verified by computer simulations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Storage volume of computer tomography images can be reduced by a factor of five

The object of this study is the data compression of CT scans of the brain. A circle is first established which contains all pixels inside the head while minimizing the insignificant area, after which the portion outside the circle so obtained is eliminated. The data are then truncated at CT values of ± 127 and the differences of two consecutive pixel values are converted into variable length codes. The coding algorithms employed are the well-known Huffman code and our packet coding, both of which achieved a data compression ratio of 20%.