Distributed media access control (MAC) architecture has many merits to make it a favorable candidate for high-data-rate wireless personal area networks (WPANs) with physical layer (PHY) based on ultrawideband (UWB) technology. This paper focuses on the WiMedia MAC, which is the first distributed MAC for WPANs, approved as a standard. In such a MAC, all devices transmit their beacons to provide timing reference and to broadcast control and reservation information, that is, to maintain device synchronization. We investigate problems related to beacon collisions, which occur when multiple devices join a piconet almost at the same time. To join a piconet or to resolve a collision, a device chooses a slot for its beacon randomly within some window. We show that an improper slot choice scheme leads to repeated collisions, increasing the time overhead to achieve device synchronization. It also leads devices into trouble in joining and collision resolution, even into deadlocks, when devices have no chance to escape repeated collisions. We develop an analytical model to evaluate the performance of various slot choice schemes for multihop WPANs. The model is employed to compare the efficiency of these choice schemes and to optimize their parameters to achieve the best performance.

In the paper we propose and study a novel packet transmission scheme aimed to overcome a fundamental overhead of WPAN MAC/PHY protocols and to improve ARQ performance. Specifically, we propose to combine two well- known techniques: fragmentation and aggregation by adding multiple Frame Control Sums (FCS) to each fragment. We show analytically and by simulation that the proposed scheme increases WiMedia MAC efficiency greatly. Although the WiMedia MAC has been used as a design base, this novel packet transmission scheme can be extended to other high rate wireless communication systems to cover mmWave.

In this paper, we investigate beaconing problems in Wireless Personal Area Networks (WPANs) with distributed control, which is being developed by Multi-Band OFDM Alliance. The problems are related to collision that is caused by multiple access to a piconet; and the collision resolution that is used in the MBOA MAC, i.e. random slot allocation for devices’ beacons. The collision problem and the current resolution may cause deadlock and prevent other devices from joining a piconet. We propose new solutions to resolve the collision without causing potential deadlock. We develop an analytical model to evaluate performance of the new schemes. The model can also be employed to determine parameters to achieve optimized performance.

A variety of algorithms have been developed for Blind Search (BS) over peer-to-peer (P2P) overlay networks, i.e., search of resources without any routing information for the exact location of the target resource. All these algorithms generate significant amount of duplicate query messages to increase the success rate. In this paper, we introduce tag routing search - a novel framework for BS over P2P overlay networks structured by Distributed Hash Tables (DHTs). A query message in this framework contains a tag that affect the selection of next hop nodes. We propose two specific algorithms: Zigzag Modified Breadth First Search with Local Indices (ZMBFS+L) and Recursive Partitioning Search (RPS). ZMBFS+L achieves high success rate with less duplications compared to other known BS algorithms. RPS, taking advantage of the DHT structure, does not generate any message duplication by design, thus is a very efficient broadcasting algorithm, and can achieve 100% success rate efficiently.

Typical blind search algorithms in P2P networks generate a significant amount of duplicate query messages to increase the success rate. We present a framework, named Recursive Partitioning Search (RPS), for blind search over structured peer-to-peer (P2P) networks, by which the query message duplication can be avoided. Two realizations of the framework for Chord and Pastry are presented. With simulation model, we compare success rate, lookup delay and overlay network load of RPS and various well-known blind search algorithms, and show RPS is the superior blind search algorithm running over a DHT. The algorithm guarantees that with high probability the lookup delay to visit every peer is of O(log N) hops, comparable to the delay of the exact match search over the DHTs. With RPS, every node in the overlay network is visited not more than once by design. These characteristics qualify the Recursive Partitioning Search over DHT as an efficient broadcasting algorithm. We investigate RPS scalability and propose the way to choose an appropriate Time-to-Live (TTL) parameter value to maintain the balance between high success rate and reasonable network load.

Ultra wide-band (UWB) radio uses base-band pulses of very short duration, thereby spreading the energy of radio signal very thinly over gigahertz. Power spectral density (PSD) of UWB signals consists of continuous component and discrete component. Generally speaking, the discrete component contributes more to the PSD than the continuous component, thus presents greater interference to narrow-band wireless systems. In 2002, the FCC approved commercial deployment of UWB systems. In order to ensure negligible interference to other narrow-band wireless systems, the FCC has specified emission limits for UWB applications. UWB is now under consideration as an alternative physical layer technology for wireless PAN in IEEE 802.15.3a. However, little study has been reported on how to contain the PSD of UWB signals in IEEE 802.15.3a. This paper presents base-band data whitening schemes to reduce the PSD of UWB signals in IEEE 802.15.3a.

Ultra wide-band (UWB) radio uses base-band pulses of very short duration, thereby spreading the energy of radio signal very thinly over gigahertz. Power spectral density (PSD) of UWB signals consists of continuous and discrete components. Since the discrete component contributes more to PSD than continuous component, it presents greater interference to other narrow-band wireless systems. UWB was approved by the FCC for commercial deployment in 2002. In order to ensure negligible mutual interference, the FCC has specified emission limits for UWB applications. UWB is now under consideration as an alternative physical layer technology for wireless PAN in IEEE 802.15.3a. However, little study has been reported on PSD issues in IEEE 802.15.3a. This paper presents analysis on PSD of UWB signals in IEEE 802.15.3a systems, and on what frame reversion can achieve in reducing the PSD.

Ultra wide-band (UWB) is now under consideration as an alternative physical layer technology for wireless PAN. UWB radio uses base-band pulses of very short duration, thereby spreading the energy of radio signal very thinly over gigahertz. The power spectral density (PSD) of UWB signals consists of a continuous component and discrete component. Generally speaking, the discrete component presents greater interference to narrow-band communication systems than the continuous component. Frame synchronization is commonly used in multiple access systems, including wireless PAN systems. The sync word will generate strong PSD. In this paper, we devise a more efficient and better performance mechanism to suppress the discrete component of the PSD of UWB signals by randomizing the pattern of UWB signals. The mechanism can also be applied to payload data to smooth the PSD of USB signals.

In this paper, we study the performance of a real-time transport protocol in an interactive multimedia data network. Access multiplexers, which support groups of users, and digital media servers (MS) are interconnected by a star-topology asynchronous transfer mode (ATM) virtual path crossconnect (VPX) network. The network traffic is generated by data retrieval requests from data on demand (DOD) and video on demand (VOD) users. Typical DOD applications are interactive games, interactive home shopping, etc. Some VOD (like a start up) and all DOD data transfers are caused by user action. Transmissions of information packets from MSs to users are scheduled by the multitoken exchange (MTEX) protocol which represents a deadline priority on-the-fly virtual path rereservation scheme. Statistically guaranteed quality of service (QoS) is assigned to all data transmissions caused by user actions, while deterministic performance requirements are imposed to ensure the integrity of video signals. The performance of the proposed protocol is evaluated in terms of meeting the deterministic and statistical QoS requirements by means of the probability of missing the data delivery deadline and the average response time correspondingly. We show that the attainable statistical multiplexing gain depends on the number of active VOD users and on a number of other traffic related parameters.

An analysis is presented of a fiber-optic random-access network suitable for real-time communication. It is based on pure Aloha access discipline of a hybrid, time-wavelength, code-division-multiplexed channel. The network performance is determined as a function of the signaling parameters, number of active users, and their information rates. It is shown that the network throughput can be significantly increased if users allow a few bit errors per packet. Thus, users have the freedom of trading off throughput for bit error rate and vice-versa.>