移动数字多媒体的原模图LDPC码设计

提出一种用于移动数字多媒体的原模图LDPC码,提出的LDPC码的编码算法可以简化编码器的硬件。在AWGN信道仿真结果表明,提出的LDPC码的性能要优于GB20600 LDPC码。

Construction of protograph LDPC codes with circular generator matrices

The application of protograph low density parity check （LDPC） codes involves the encoding complexity problem. Since the generator matrices are dense, and if the positions of ＂1＂ s are irregularity, the encoder needs to store every ＂1＂ of the generator matrices by using huge chip area. In order to solve this problem, we need to design the protograph LDPC codes with circular generator matrices. A theorem concerning the circulating property of generator matrices of nonsingular protograph LDPC codes is proposed. The circulating property of generator matrix of nonsingular protograph LDPC codes can be obtained from the corresponding quasi-cyclic parity check matrix. This paper gives a scheme of constructing protograph LDPC codes with circulating generator matrices, and it reveals that the fast encoding algorithm of protograph LDPC codes has lower encoding complexity under the condition of the proposed theorem. Simulation results in ad- ditive white Gaussian noise （AWGN） channels show that the bit error rate （BER） performance of the designed codes based on the proposed theorem is much better than that of GB20600 LDPC codes and Tanner LDPC codes.

The QoS of the Edge Router based on DiffServ

Internet real-time multimedia communication brings a further challenge to Quality of Service(QoS).A higher QoS in communication is required increasingly.As a new framework for providing QoS services,Differentiated Services (DiffServ)is undergoing a speedily standardization process at the IETF.DiffServ not only can offer classified level of services,but also can provide guaranteed QoS in a certain extent.In order to provide QoS,DiffServ must be properly configured.The traditional DiffServ mechanism provides classifier for edge router to mark the different traffic streams,and then the core router uses different Drop Packet Mechanisms to drop packets or transmit data packets according to these classified markers.When multiple edge routers or other core routers transmit data packets high speedily to a single core router,the core router will emerge bottleneck bandwidth.The most valid solution to this problem is that the edge router adopts drop packet mechanism.This paper proposes an Modified Edge Router Mechanism that let the edge router achieve marking,dropping and transmitting packets of hybrid traffic streams based on DiffServ in a given bandwidth,the core router will only transmits packets but won’t drop packets.By the simulation of ns2,the modified mechanism ensure the QoS of high priority traffics and simplify the core router,it is a valid method to solve the congestion of the core router.

Construction of time-frequency codes based on protograph LDPC codes in OFDM communication systems

This paper proposes a scheme to construct time- frequency codes based on protograph low density parity check （LDPC） codes in orthogonal frequency division multiplexing （OFDM） communication systems. This approach synthesizes two techniques： protograph LDPC codes and OFDM. One symbol of encoded information by protograph LDPC codes corresponds to one sub-carrier, namely the length of encoded information equals to the number of sub-carriers. The design of good protograph LDPC codes with short lengths is given, and the proposed proto- graph LDPC codes can be of fast encoding, which can reduce the encoding complexity and simplify encoder hardware implementa- tion. The proposed approach provides a higher coding gain in the Rayleigh fading channel. The simulation results in the Rayleigh fading channel show that the bit error rate （BER） performance of the proposed time-frequency codes is as good as random LDPC- OFDM codes and is better than Tanner LDPC-OFDM codes under the condition of different fading coefficients.

Diffserv AQM algorithm for edge and core routers

The existing active queue management （AQM） algorithm acts on subscribers and edge routers only, it does not support differentiate-serve （Diffserv） quality of service （QoS）, while the existing diffserv QoS has not considered the link capacities between edge routers and connected core routers. When a core router in a two layers’ network experiences congestion, the connected edge routers have no ability to adjust their access data rates. Thus, it is difficult to achieve the congestion control for the large scale network with many edge routers and core routers. To solve these problems, two difffserve AQM algorithms are proposed for the congestion control of multilayer network. One diffserv AQM algorithm implements fair link capacities of edge routers, and the other one implements unequal link capacities of edge routers, but it requires the core routers to have multi-queues buffers and Diffserv AQM to support. The proposed algorithms achieve the network congestion control by operating AQM parameters on the conditions of proposed three theorems for core and edge routers. The dynamic simulation results demonstrate the proposed control algorithms for core and edge routers to be valid.

MCHOKeM algorithm with assured bandwidth allocation in DiffServ networks

An active queue management（AQM） algorithm called MCHOKeM is presented,which is borrowed from CHOKeW that draws multi-packets at random from the buffer,the multi-packets are compared with an arriving packet and abandoned if they are from the same flow.But MCHOKeM uses multiple virtual queues for different priority packets and enhances the drawing function by adjusting the maximum number of draws based on the current status of virtual queue length.The number of parameters that MCHOKeM needs to maintain is determined by the number of priority levels being supported by the router,which usually has a small limited value.In order to explain the features of MCHOKeM,an analytical model is used.A series of simulation tests to evaluate the performance are given.

Huber's Minimax Approach in Distribution Classes with Bounded Variances and Subranges with Applications to Robust Detection of Signals

A brief survey of former and recent results on Hubers minimax approach inrobust statistics is given. The least informative distributions minimizing Fisher information forlocation over several distribution classes with upper-bounded variances and subranges are writtendown. These least informative distributions are qualitatively different from classical Huberssolution and have the following common structure: (i) with relatively small variances they areshort-tailed, in particular normal; (ii) with relatively large variances they are heavy-tailed, inparticular the Laplace; (iii) they are compromise with relatively moderate variances. These resultsallow to raise the efficiency of minimax robust procedures retaining high stability as compared toclassical Hubers procedure for contaminated normal populations. In application to signal detectionproblems, the proposed minimax detection rule has proved to be robust and close to Hubers forheavy-tailed distributions and more efficient than Hubers for short-tailed ones both in asymptoticsand on finite samples.