In 2009, Jeong et al. proposed a secure binding encryption scheme and an efficient secret broadcast scheme. This paper points out that the schemes have some errors and cannot operate correctly, contrary to their claims. In addition, this paper also proposes improvements of Jeong et al.'s scheme that can withstand the proposed attacks.

A Gaussian MIMO broadcast channel (GMBC) models the MIMO transmission of Gaussian signals from a transmitter to one or more receivers. Its capacity region and different precoding schemes for it have been well investigated, especially for the case wherein there are only transmit power constraints. In this paper, a special case of GMBC is investigated, wherein receive power constraints are also included. By imposing receive power constraints, the model, called protected GMBC (PGMBC), can be applied to certain scenarios in spatial spectrum sharing, secretive communications, mesh networks and base station cooperation. The sum capacity, capacity region, and application examples for the PGMBC are discussed in this paper. Sub-optimum precoding algorithms are also proposed for the PGMBC, where standard user precoding techniques are performed over a BC with a modified channel, which we refer to as the "protection-implied BC." In the protection-implied BC, the receiver protection constraints have been implied in the channel, which means that by satisfying the transmit power constraints on the protection implied channel, receiver protection constraints are guaranteed to be met. Any standard single-user or multi-user MIMO precoding scheme may then be performed on the protection-implied channel. When SINR-matching duality-based precoding is applied on the protection-implied channel, sum-capacity under full protection constraints (zero receive power), and near-sum-capacity under partial protection constraints (limited non-zero receive power) are achieved, and were verified by simulations.

This paper proposes a ternary subset difference method (SD method) that is resistant to coalition attacks. In order to realize a secure ternary SD method, we design a new cover-finding algorithm, label assignment algorithm and encryption algorithm. These algorithms are required to revoke one or two subtrees simultaneously while maintaining resistance against coalition attacks. We realize this two-way revocation mechanism by creatively using labels and hashed labels. Then, we evaluate the efficiency and security of the ternary SD method. We show that the number of labels on each client device can be reduced by about 20.4 percent. The simulation results show that the proposed scheme reduces the average header length by up to 15.0 percent in case where the total number of devices is 65,536. On the other hand, the computational cost imposed on a client device stays within O(log n). Finally, we prove that the ternary SD method is secure against coalition attacks.

Recently, broadcast services are introduced in cellular networks and macro diversity is an effective way to combat fading. In this paper, we propose a kind of distributed space-time block codes (STBCs) for macro diversity which is constructed from the total antennas of multiple cooperating base stations, and all the antennas form an equivalent multiple input multiple output (MIMO) system. This code is termed High-Dimension-Full-Rate-Quasi-Orthogonal STBC (HDFR-QOSTBC) which can be characterized as: (1) It can be applied with any number of transmit antennas especially when the number of transmit antennas is large; (2) The code is with full transmit rate of one; (3) The Maximum Likelihood (ML) decoding complexity of this code is controllable and limited to Nt/2-symbol-decodable for total Nt transmit antennas. Then, we completely analyze the structure of the equivalent channel for the kind of codes and reveal a property that the eigenvectors of the equivalent channel are constant and independent from the channel realization, and this characteristic can be exploited for a new transmission structure with single-symbol linear decoder. Furthermore, we analyze different macro diversity schemes and give a performance comparison. The simulation results show that the proposed scheme is practical for the broadcast systems with significant performance improvement comparing with soft-combination and cyclic delay diversity (CDD) methods.

Multi-source broadcasting is one of the information dissemination problems on interconnection networks such that some (but not all) units disseminate distinct information to all other units. In this paper, we discuss multi-source broadcasting on the Kautz digraph which is one of the models of interconnection networks. We decompose the Kautz digraph K(d,n) into isomorphic cycle-rooted trees whose root-cycle has length 2, then we present an algorithm for multi-source broadcasting using these cycle-rooted trees. This algorithm is able to treat d(d+1) messages simultaneously and takes the same order for required times as lower bound.

This paper is concerned with the packet transmission scheduling problem for repeating all-to-all broadcasts in Underwater Sensor Networks (USN) in which there are n nodes in a transmission range. All-to-all communication is one of the most dense communication patterns. It is assumed that each node has the same size packet. Unlike the terrestrial scenarios, the propagation time in underwater communications is not negligible. We define all-to-all broadcast as the one where every node transmits packets to all the other nodes in the network except itself. So, there are in total n(n - 1) packets to be transmitted for an all-to-all broadcast. The optimal transmission scheduling is to schedule in a way that all packets can be transmitted within the minimum time. In this paper, we propose an efficient packet transmission scheduling algorithm for underwater acoustic communications using the property of long propagation delay.

This paper proposes multipoint-to-multipoint (MPtoMP) real-time broadcast transmission using network coding for ad-hoc networks like video game networks. We aim to achieve highly reliable MPtoMP broadcasting using IEEE 802.11 media access control (MAC) that does not include a retransmission mechanism. When each node detects packets from the other nodes in a sequence, the correctly detected packets are network-encoded, and the encoded packet is broadcasted in the next sequence as a piggy-back for its native packet. To prevent increase of overhead in each packet due to piggy-back packet transmission, network coding vector for each node is exchanged between all nodes in the negotiation phase. Each user keeps using the same coding vector generated in the negotiation phase, and only coding information that represents which user signal is included in the network coding process is transmitted along with the piggy-back packet. Our simulation results show that the proposed method can provide higher reliability than other schemes using multi point relay (MPR) or redundant transmissions such as forward error correction (FEC). We also implement the proposed method in a wireless testbed, and show that the proposed method achieves high reliability in a real-world environment with a practical degree of complexity when installed on current wireless devices.

We investigate delay analysis of multi-hop wireless mesh network (WMN) where nodes have multi-channel and multiple transceivers to increase the network capacity. The functionality of the multi-channel and multiple transceivers allows the whole WMN to be decomposed into disjoint zones in such a way that i) nodes in a zone are within one-hop distance, and relay node and end nodes with different CWmins contend to access the channel based on IEEE 802.11e EDCA, ii) different channels are assigned to neighbor zones to prevent the hidden node problem, iii) relay nodes can transmit and receive the packets simultaneously by multi-channel and multiple transceivers. With this decomposition of the network, we focus on the delay at a single zone and then the end-to-end delay can be obtained as the sum of zone-delays. In order to have the location-independent end-to-end delay to the gateway regardless of source nodes' locations, we propose two packet management schemes, called the differentiated CW policy and the strict priority policy, at each relay node where relay packets with longer hop count are buffered in higher priority queues according to their experienced hop count. For the differentiated CW policy, a relay node adopts the functionality of IEEE 802.11e EDCA where a higher priority queue has a shorter minimum contention window. We model a typical zone as a one-hop IEEE 802.11e EDCA network under non-saturation condition where priority queues have different packet arrival rates and different minimum contention window sizes. First, we find the PGF (probability generating function) of the HoL-delay of packets at priority queues in a zone. Second, by modeling each queue as M/G/1 queue with the HoL-delay as a service time, we obtain the packet delay (the sum of the queueing delay and the HoL-delay) of each priority queue in a zone. Third, the average end-to-end delay of packet generated at end node in each zone is obtained by summing up the packet delays at each zone. For the strict priority policy, we regard a relay node as a single queueing system with multiple priority queues where relay packets in priority queues are served in the order of strict priority. Relay node has smaller CWmin than end node has and relay node competes with end nodes in a zone. Using the PGF of HoL-delay of packet at relay node and end node, we obtain the packet delay in a zone. The average end-to-end delay to the gateway generated at end node in each zone is obtained. Finally, for both the differentiated CW policy and strict priority policy, by equating all end-to-end delays to be approximately equal, we find the minimum contention window sizes of each priority queue numerically by trial and error method so that end-to-end delays of packets are almost equal regardless of their source's location, respectively. Numerical results show that proposed two methods obtain almost same end-to-end delay of packets regardless of their generated locations and our analytical results are shown to be well matched with the simulation results.

This paper considers an optimized limited feedback design for a multi-antenna system serving multiple users under different types of channels: Rayleigh distributed and line-of-sight distributed channels. Since the users are asymmetric, we propose an optimized feedback bandwidth allocation scheme for users under a total feedback rate constraint. The allocation scheme is designed according to the long-term channel type information of users, and thus it can be efficiently implemented. Numerical results verify the effectiveness of our proposed scheme.

Provider authentication is necessary in bidirectional broadcasting services, and a digital signature scheme is often used to prevent an adversary from attempting impersonation. The cost of secure signing key management is extremely high. In addition, the key has to be updated very often, since it is frequently used. The result is that the verification key also has to be updated very often, and its redistribution cost is huge. These costs are real and substantive problems, especially when the number of users is large. In this paper, we propose a system that dramatically reduces these costs. In the system, the signing key is updated, but the corresponding verification key does not have to be updated. This means that the signing key can be updated without any cost for redistributing the verification key and that the system is secure against the threat of signing key leakage, since the key can be frequently updated. Moreover, we propose a new key management method that divides a conventional key management server's role into two. The use of a key-insulated signature (KIS) scheme enables low-cost and more secure key management with two servers. Finally, to make a bidirectional broadcasting service more secure even if the signing key is leaked, we developed a new strong KIS scheme. We performed an experiment that assessed the cost of our strong KIS scheme and found that it is sufficiently low. Accordingly, a provider authentication system employing this scheme would be more efficient and would have lower key redistribution and network costs in comparison with conventional authentication systems.

With the growing demand for high-performance multimedia applications over wireless channels, we need to develop a Medium Access Control (MAC) system that supports high throughput and quality of service enhancements. This paper presents the standard analysis, design architecture and design issues leading to the implementation of an IEEE 802.11e based MAC system that supports MAC throughput of over 100 Mbps. In order to meet the MAC layer timing constraints, a hardware/software co-design approach is adopted. The proposed MAC architecture is implemented on the Xilinx Virtex-II Pro Field-Programmable Gate Array (FPGA) (XC2VP70-5FF1704C) prototype, and connected to a host computer through an external Universal Serial Bus (USB) interface. The total FPGA resource utilization is 11,508 out of 33,088 (34%) available slices. The measured MAC throughput is 100.7 Mbps and 109.2 Mbps for voice and video access categories, transmitted at a data rate of 260 Mbps based on IEEE 802.11n Physical Layer (PHY), using the contention-based hybrid coordination function channel access mechanism.

A multicast content service, including numerous devices, requires an efficient group key management scheme as one of its core components. The purpose of group key management is to provide a secure key-sharing scheme among the members of a group so that messages transmitted via broadcasting or multicasting are not exposed to non-members. The Chinese Remaindering Group Key (CRGK) is an efficient group key management scheme based on the Chinese Remainder Theorem (CRT). It optimizes the number of re-key messages, the user-side key computation cost, and the number of stored keys. However, CRGK is not fit for a group with a large number of members because of the high computation complexity of the CRT. In this paper, we propose a Hierarchical CRGK (HCRGK) scheme that supports a group with a large number of members. We improved CRGK by adopting it to include an n-ary tree structure. The tree approach simplifies the group key management by distributing the group key computation to subgroups. Our scheme requires at most (log m N + 1) re-key messages for a group with N members and a short computation time even when the group is very large.

Recently, network coding has been applied to the loss recovery of reliable multicast in wireless networks, where multiple lost packets are XOR-ed together as one packet and forwarded via single retransmission, resulting in a significant reduction of bandwidth consumption. In this paper, we first prove that maximizing the number of lost packets for XOR-ing, which is the key part of the available network coding-based reliable multicast schemes, is actually a complex NP-complete problem. To address this limitation, we then propose an efficient heuristic algorithm for finding an approximately optimal solution of this optimization problem. Furthermore, we show that the packet coding principle of maximizing the number of lost packets for XOR-ing sometimes cannot fully exploit the potential coding opportunities, and we then further propose new heuristic-based schemes with a new coding principle. Simulation results demonstrate that the heuristic-based schemes have very low computational complexity and can achieve almost the same transmission efficiency as the current coding-based high-complexity schemes. Furthermore, the heuristic-based schemes with the new coding principle not only have very low complexity, but also slightly outperform the current high-complexity ones.

We present a 60-GHz wireless through-repeater system based on self-heterodyne transmission scheme with the potential to optimize the carrier-to-interference and noise ratio (CINR) performance according to the transmission distance. The phase-noise degradation through a 60-GHz repeater link is not a serious concern when we employ the self-heterodyne transmission scheme. Multichannel interferences caused by third-order intermodulation distortions are efficiently suppressed by setting a high power ratio of LO carrier to RF signals in the self-heterodyne transmission. However, this high power ratio results in a lower carrier-to-noise ratio (CNR) and becomes unsuitable for improving link performance if the transmission distance increases. In order to facilitate a solution, we propose and make an embodiment of 60 GHz self-heterodyne transmitters that provide flexible control over the power ratio of LO to RF in a range of 10 dB ranges. With them, we successfully demonstrate terrestrial digital broadcasting signals on five channels and optimize their performance for wireless through-repeater applications.

In the IEEE 802.11 MAC protocol, access points (APs) are given the same priority as wireless terminals in terms of acquiring the wireless link, even though they aggregate several downlink flows. This feature leads to a serious throughput degradation of downlink flows, compared with uplink flows. In this paper, we propose a dynamic contention window control scheme for the IEEE 802.11e EDCA-based wireless LANs, in order to achieve fairness between uplink and downlink TCP flows while guaranteeing QoS requirements for real-time traffic. The proposed scheme first determines the minimum contention window size in the best-effort access category at APs, based on the number of TCP flows. It then determines the minimum and maximum contention window sizes in higher priority access categories, such as voice and video, so as to guarantee QoS requirements for these real-time traffic. Note that the proposed scheme does not require any modification to the MAC protocol at wireless terminals. Through simulation experiments, we show the effectiveness of the proposed scheme.

The R&D in satellite communications in Korea has been driven mainly by KCC (Korea Communications Commission) but in a small scale compared to Korea space development program organized by MEST (Ministry of Education, Science and Technology). Public and civilian satcom sector R&D has been led mainly by ETRI with small/medium companies contrary to rare investment in private sector while military sector R&D has been orchestrated by ADD with defense industry. By the COMS (Communication, Ocean and Meteorological Satellite) experimental Ka-band payload, Korea pursues a space qualification of own technology for national infrastructure evolution as well as industrialization of space R&D results. Once COMS launched and space qualified in 2009, subsequent application experiments and new technology R&D like UHDTV will entail service and industry promotion. The payload technology is expected for the next Korean commercial satellites or for new OBP satellites. The COMS ground control system and GNSS ground station technologies are under development for COMS operation and enhanced GNSS services along with advent of Galileo respectively. Satellite broadband mobile VSAT based on DVB-S2/RCS (+M) and low profile tracking antennas have been developed for trains, ships, and planes. While APSI is developing GMR-1 based Thuraya handset functions, ETRI is designing IMT-Advanced satellite radio interface for satellite and terrestrial dual-mode handheld communication system like Japanese STICS, with universities' satellite OFDM researches. A 21 GHz Ka-band higher-availability scalable HD broadcasting technology and SkyLife's hybrid satellite IPTV technology are being developed. In near term Korea will extend R&D programs to upgrade the space communication infrastructure for universal access to digital opportunity and safer daily life from disaster, and to promote space green IT industrialization, national security, and space resources sovereign. Japanese stakeholders are invited to establish a collaborative R&D with Korea for mutual benefit of the future.

It is an almost classical problem to develop an efficient broadcast mechanism in multi-hop networks. However, the problem is far from solved though a lot of research till recently has been focused on it. In this letter, we analyze the optimal distribution of forwarding nodes that can doubly cover the network with the minimum transmission overlapped area in a multi-hop wireless network where nodes are ideally distributed. On this basis we propose a simple and effective broadcast method to significantly increase the transmission efficiency and deliverability. In this method, the total number of retransmissions is quite low since each node only needs to select three forwarding nodes, and high deliverability can be achieved for the set of forwarding nodes provide nearly double coverage to the whole network. In addition, the method has excellent scalability in large scale networks and highly dynamic environment.

Wireless LAN access is now being offered by small personal terminals in addition to laptops. Since these terminals have very limited battery capacity, wireless LAN interfaces that offer some form of power saving are essential. IEEE802.11. specifies PSM (Power save management); it reduces power consumption by suspending some communications functions. However, since Multicasting and Broadcasting are invariably received by all terminals regardless of PSM, the terminals unnecessarily consume electric power, even if the terminal is not multicast subscriber. This paper clarifies this problem, and proposes a scheme for reducing power consumption. The results of an experiment confirm its excellent performance.

Multi-source broadcasting is one of the information dissemination problems on communication networks such that some units disseminate distinct messages to all other units. In this paper, we study multi-source broadcasting on the de Bruijn and Kautz digraphs which are the models of interconnection networks. In [8] and [12], a cycle-rooted tree which has a large root-cycle is constructed by composition of isomorphic factors, and the multi-source broadcasting is executed on the cycle-rooted tree. On the other side, we execute multi-source broadcasting on each isomorphic factors at the same time. We present a method for multi-source broadcasting using isomorphic cycle-rooted trees which factorize these digraphs, and investigate its efficiency.

This paper assesses application-level QoS and Quality of Experience (QoE) in the case where audio and video streams are transferred with the enhanced distributed channel access (EDCA) of the IEEE 802.11e MAC. In EDCA, a station can transmit multiple MAC frames during a transmission opportunity (TXOP); this is referred to as TXOP-bursting. By simulation, we first compare application-level QoS with the TXOP-bursting scheme and that without the scheme for various distances between access point (AP) and stations. In this paper, we suppose that the bit error rate (BER) becomes larger as the distance increases. Numerical results show that TXOP-bursting can improve many metrics of video quality such as average media unit (MU) delay, MU loss ratio, and media synchronization quality, particularly when the AP sends audio and video streams to stations in the downlink direction. We then examine the effect of TXOPLimit on the video quality. Simulation results show that the video quality can be degraded if the value of TXOPLimit is too small. Furthermore, we assess QoE by the method of successive categories, which is a psychometric method. Numerical results show that TXOP-bursting can also improve the QoE. We also perform QoS mapping between application-level and user-level with principal component analysis and multiple regression analysis.