Recently, a number of techniques have been introduced to exploit multiuser diversity of a wireless multiple-input multiple-output (MIMO) broadcast channel (BC) that consists of a base station with t transmit antennas and K users with multiple antennas. However, prior works have ignored the rate overhead associated with feedback of MIMO BC channel state information at transmitter (CSIT), which is roughly K times larger than single-user MIMO CSIT (i.e., it is O(tr) where r = rk and rk is the number of antennas at the kth user). Considering the amount of feedback signaling, quantization is a necessity for effective feedback transmission as a form of partial CSIT. In this paper, we propose the greedy multi-channel selection diversity (greedy MCSD) scheme based on block MMSE QR decomposition with dirty paper coding (block MMSE-DP), where partial CSIT is almost sufficient. The sum-rate performance of our novel scheme approaches extremely close to the sum capacity of MIMO BC as the number of users increases, whereas the feedback overhead is reduced by a factor of 2t3/L(t2-t), in which L is the number of active channel vectors. Simulation results validate the expectation from the analysis. In addition, the proposed scheme is shown to be appropriate for reconfigurable implementation.

This paper clarifies a necessary condition and a sufficient condition for transmissibility for a given set of general sources and a given general broadcast channel. The approach is based on the information-spectrum methods introduced by Han and Verdu. Moreover, we consider the capacity region of the general broadcast channel with arbitrarily fixed error probabilities if we send independent private and common messages over the channel. Furthermore, we treat the capacity region for mixed broadcast channel.

Data broadcast has become a promising approach to achieving information dissemination in wireless environments due to the limited channel bandwidth and the power constraints of portable devices. In this paper, a restricted dynamic programming approach which generates broadcast programs is proposed to partition data items over multiple channels near optimally. In our approach, a function to predict the optimal average expected delay, in terms of the number of channels, the summation of the access frequencies of data items, and the ratio of the data items is developed by employing curve fitting. Applying this function, we can find a cut point that may be very close to the optimal cut. Thus, the search space in dynamic programming can be restricted to the interval around a determined cut point. Therefore, our approach only takes O(N log K) time, where N is number of data items and K is the number of broadcast channels. Simulation results show that the solution obtained by our proposed algorithm is near-optimal.

How to safely or reliably flood a packet via broadcast scheme to all nodes in computer networks is an important issue. However, it is a big challenge and critical problem to broadcast data packets over mobile ad hoc networks reliably due to the unsettled wireless links, high mobility, and the lack of the acknowledgment (ACK) scheme. Many solutions deal with this problem by adopting multiple unicast transmissions to achieve reliable broadcast transmission in network layer. Unfortunately, it will cause severe duplicate transmissions and thus rapidly consume the limited network bandwidth. One simplest way to solve this drawback is to broadcast data packets in data link layer. But a serious problem will be arisen that replied ACK frames will collide at the sending node if we enforce each mobile node to reply an ACK after receiving the broadcast data frame. Therefore, in order to overcome the thorny problem, we proposed a broadcast engagement ACK mechanism (BEAM), which is completely compatible with the IEEE 802.11 protocol, for reliable broadcast transmission in the data link layer. We also show that the overhead of raising the reliability of broadcast transmission in network layer would be significantly reduced in data link layer. Simulation results show that the proposed BEAM can reach approximate 100% reliability even in heavy traffic load. We also indicate that the BEAM could be combined with other network layer broadcast schemes to approach higher flooding ratio as well as reduce bandwidth consumption effectively.

Power saving is an important issue in the mobile computing environment. In this paper, we propose a broadcast mechanism that constructs the broadcast channels according to the access frequency of each type of message in order to save power in mobile stations. The pinwheel scheduling algorithm presented in this paper is used to organize all types of messages in the broadcast channels in the most symmetrical distribution in order to reduce both the tuning and access time. The multichannel broadcast mechanism is also discussed for use when the number of message types increases. The performance of the proposed mechanism is analyzed, and the improvement over existing methods is demonstrated numerically. The results show that the proposed mechanism is capable improving both the tuning and access time due to the presence of skewness in the access distribution among the disseminated messages. When the number of message types increase, both the tuning and access time can be further improved as long as a small number of broadcast channels are added.

In this letter, we study a hybrid Multimedia-on-Demand (MoD) system which provides broadcast, batch and interactive services. An analytical model for such an MoD system is provided. Numerical results show that with proper design, the system can provide better performance than those systems which only provide any subset of two services.

The measurement results of clear sky attenuation on an earth-satellite path at frequency Ku band in Laos are described. The measurement results show that diurnal clear sky noise vary with respect to humidity characteristics, which is a significant value in the early morning while low at daytime. The mean difference in variation is about 0.7 dB.

In this paper, we propose an efficient route discovery scheme for mobile ad hoc networks called Hop-Wise Limited broadcast (HoWL). Since nodes do not identify the location of other nodes, some of the routing protocols proposed for mobile ad hoc networks use network-wide broadcasts to discover a route. In contrast, HoWL limits the area of a route discovery by predicting the current location of the destination node using history of hop counts of previously used routes. We also introduce Characterized Environmental Indicators (CEI) which characterize environments for networks of mobile nodes. Specifically, environments can be characterized by three indicators: node density, average hop count of utilized routes, and frequency of link failure. We have implemented HoWL as an extension to DSR on GloMoSim network simulator. Quantitative and qualitative performance comparisons were evaluated between HoWL and its related work, Expanding Ring Search (RING) and LAR. The simulations show that HoWL performs best when low communication overhead is desired where up to 20% decrease over RING and three-fold decrease over LAR in the overhead were demonstrated. Thus, HoWL is most effective in overhead sensitive environments such as battery-limited sensor networks.

Energy-efficient operations are essential to prolonging the lifetime of wireless sensor networks. Clustering sensor nodes is one approach that can reduce energy consumption by aggregating data, controlling transmission power levels, and putting redundant sensor nodes to sleep. To distribute the role of a cluster head, clustering approaches should be based on efficient cluster configuration schemes. Therefore, low overhead in the cluster configuration process is one of the key constraints for energy-efficient clustering. In this paper, we present an autonomous clustering approach using a coverage estimation-based self-pruning algorithm. Our strategy for clustering is to allow the best candidate node within its own cluster range to declare itself as a cluster head and to dominate the other nodes in the range. This same self-declaration strategy is also used in the active sensor election process. As a result, the proposed scheme can minimize clustering overheads by obviating both the requirements of collecting neighbor information beforehand and the iterative negotiating steps of electing cluster heads. The proposed scheme allows any type of sensor network application, including spatial query execution or periodic environment monitoring, to operate in an energy-efficient manner.

The complete subtree (CS) method is widely accepted for the broadcast encryption. A new method for assigning keys in the CS method is proposed in this paper. The essential idea behind the proposed method is to use two trapdoor permutations. Using the trapdoor information, the key management center computes and assigns a key to each terminal so that the terminal can derive all information necessary in the CS method. A terminal has to keep just one key, while log2 N + 1 keys were needed in the original CS method where N is the number of all terminals. The permutations to be used need to satisfy a certain property which is similar to but slightly different from the claw-free property. The needed property, named strongly semi-claw-free property, is formalized in terms of probabilistic polynomial time algorithm, and its relation to the claw-free property is discussed. It is also shown that if the used permutations fulfill the strongly semi-claw-free property, then the proposed method is secure against attacks of malicious users.

Δ-Timed Atomic Broadcast is the broadcast ensuring that all correct processes deliver the same messages in the same order, and that delivery latency of any message broadcast by any correct process is some predetermined time Δ or less. In this paper, we propose a Δ-timed atomic broadcast algorithm in a synchronous system where communication delay is bounded by a known constant d and processes suffer both crash faults and timing faults. The proposed algorithm can tolerate fc crash faults and ft timing faults as long as at least ft + 1 processes are correct, and its maximum delivery latency Δ is (2f' + 7)d where f' is the actual number of (crash or timing) faulty processes. That is, the algorithm attains the early-delivery in the sense that its delivery latency depends on the actual number of faults rather than the maximum number of faults that the algorithm can tolerate. Moreover, the algorithm has a distinct advantage of guaranteeing that timing-faulty processes also deliver the same messages in the same order as the correct processes (Uniformity). We also investigate the maximum number of faulty processes that can be tolerated. We show that no Δ-timed atomic broadcast algorithm can tolerate ft timing faults, if at most ft processes are correct. The impossibility result implies that the proposed algorithm achieves the maximum fault-resilience with respect to the number of faulty processes.

This paper proposes a scattered-pilot-OFDM reception scheme employing turbo inter-carrier interference (ICI) cancellation in the fast varying fading environments of mobile communications. In the OFDM transmission, the orthogonality among the subcarriers cannot hold due to large Doppler shift, and the OFDM signal suffers from severe degradation due to ICI. The proposed receiver carries out two modes: (i) a coherent detection (CD) mode, and (ii) a turbo ICI cancellation (TC) mode. Initially, the receiver performs the CD mode. When any decision errors are detected, it shifts from the CD mode to the TC one that carries out both the ICI cancellation and the channel estimation by using the decoder output (the log likelihood ratio). In addition, the iteration of the TC mode can improve the accuracy of the channel estimation and ICI cancellation ability. Computer simulations following specifications for the mobile reception mode in the digital terrestrial television broadcasting demonstrate that the receiver can effectively cancel ICI due to the fast varying fading, and that its average BER performance is much better than that of CD.

This paper deals with broadcast encryption schemes, in which a sender can send information securely to a group of receivers excluding some receivers over a broadcast channel. In this paper we propose modifications of the Complete Subtree (CS), the Subset Difference (SD) and the Layered Subset Difference (LSD) methods based on the Master Key Tree (MKT). Our modifications eliminate log N keys or labels from receivers' storage, in exchange for an increase in the computational overhead, where N is the total number of receivers. We also propose modifications of the SD and LSD methods by applying the Trapdoor One-way Permutation Tree (TOPT) which is originally proposed in order to modify the CS method. Our modifications based on TOPT also eliminate log N labels, and the computational cost is much smaller than MKT based methods.

The complete subtree (CS) method is one of the most well-known broadcast encryptions which do not enforce the receivers to keep "online." This paper is to reduce the size of secret information which must be stored in a terminal of the method. In the original CS method, the size of the secret information increases as the number of terminals increases. It is shown in this paper that, by making use of a one-way trapdoor permutation, we can make the size constant regardless of the number of terminals. The security of the proposed scheme is investigated, and detailed comparison with other similar schemes is presented. The proposed scheme is suitable for practical implementations of the CS method.

This paper considers a neighborhood broadcasting protocol in undirected de Bruijn and Kautz networks. The neighborhood broadcasting problem(NBP) is the problem of disseminating a message from an originator vertex to only its neighbors. Our protocol works under the single-port and half-duplex model and solves NBP in 5log2(n+1) + O(1) time units on the undirected de Bruijn graph UB(n,d) with nd vertices and the undirected Kautz graph UK(n,d) with nd + nd-1 vertices, where 2n is the maximum degree of these graphs. This completion time is asymptotically optimal in this model.

We design a DAB system using space-time coding for reliable transmission in the multipath fading channel. This letter assess the performance evaluation of space-time coded DAB system. For channel estimation in the space-time coded DAB system, we introduce two training sequences and derive the mean square error of each training sequence. We then represent the average symbol error rate of the space-time coded DAB system for the specific cases of two, three, four transmit antennas.

In providing video programs to a number of clients through networks, a broadcasting approach is more appropriate than a true-video-on-demand approach in efficient use of bandwidth. However, the broadcasting approach also needs excessively wide bandwidth if many video programs are to be transmitted. This study presents a very simple but novel architecture called dynamic channel broadcasting, for video-on-demand systems. The proposed architecture uses both static and dynamic broadcasting channels to improve the efficiency of channels. The proposed architecture eliminates the necessity of dividing each video into segments and switching channels frequently unlike the pyramid broadcasting, the skyscraper broadcasting and the harmonic broadcasting. Also this new architecture needs a smaller buffer size. The numerical results demonstrate that the newly proposed approach in some cases requires only 14% of the bandwidth required for the conventional broadcasting while maintaining the start-up latency.

In this paper, we propose a set of broadcast streaming protocols designed for unidirectional radio channels. Considering the limited size and implementation overhead on a mobile terminal, the proposed protocol set is almost compliant with the current mobile streaming protocols, i.e. 3GPP PSS (Packet-switched Streaming Service), except for that the proposed protocols are designed to work on a unidirectional downlink channel. This protocol set enables flexible layout rendering by SMIL (Synchronized Multimedia Integration Language) in combination with SDP (Session Description Protocol), and reliable and synchronized static media (including still image and text) delivery by RTP (Real-time Transport Protocol) carousel. We present the prototype of this protocol set and measure its performance of video quality and waiting time for video presentation through a W-CDMA radio channel emulator and header compression nodes. From the experimental results, we show 1) trade-off between video quality and waiting time, 2) advantage and disadvantage of header compression, 3) effectiveness of synchronized transmission of SDP, SMIL, and I-frames of video objects, and 4) reliability of RTP-carousel. This protocol set is applicable to 3G MBMS (Multimedia Broadcast/Multicast Service) streaming service.

The advanced satellite broadcasting system in the 21 GHz band or higher frequency bands is expected to be suitable for use in high quality multimedia services in the future. To establish this system, rain attenuation mitigation is very important and the time diversity system has been proposed as an appropriate technology for this purpose. This paper shows principle of time diversity as an attenuation mitigation technology and also shows the effect of time diversity. We also propose a method for predicting time diversity gain as a function of the rain attenuation, cumulative time percentage, and time delay of two data contents or broadcasts.

A good channel assignment scheme in a multihop ad hoc network should not only guarantee successful data transmissions without collisions, but also enhance the channel spatial reuse to maximize the system throughput. It becomes very inefficient to use fixed channel assignment when the network size grows. Therefore, spatial reuse of channels become more important in a large multihop ad hoc network. In this paper, we consider an ad hoc network with an overlaid CDMA/TDMA structure. We divide each code into time slots to form the channels. A dynamic channel assignment (DCA) strategies called Greedy-Based DCA (GB-DCA) is proposed in a clustered wireless multihop ad hoc network. This DCA strategy is designed to make better use of available channels by taking advantage of the spatial reuse concept. In GB-DCA, the increase in spatial reuse is achieved by adding certain control overhead. We show that the bandwidth saving due to channel spatial reuse is higher than the additional bandwidth spent on the control overhead.