Philip V. Orlik

On the spectral and power requirements for ultra-wideband transmission

UWB systems based on impulse radio have the potential to provide very high data rates over short distances. In this paper, a new pulse shape is presented that satisfies the FCC spectral mask. Using this pulse, the link budget is calculated to quantify the relationship between data rate and distance. It is shown that UWB can be a good candidate for reliably transmitting 100 Mbps over distances at about 10 meters.

UWB Systems for Wireless Sensor Networks

Wireless sensor networks are emerging as an important area for communications. They enable a wealth of new applications including surveillance, building control, factory automation, and in-vehicle sensing. The sensor nodes have to operate under severe constraints on energy consumption and form factor, and provide the ability for precise self-location of the nodes. These requirements can be fulfilled very well by various forms of ultra-wide-band (UWB) transmission technology. We discuss various techniques and tradeoffs in UWB systems and indicate that time-hopping and frequency-hopping impulse radio physical layers combined with simple multiple-access techniques like ALOHA are suitable designs. We also describe the IEEE 802.15.4a standard, an important system that adopts UWB impulse radio to ensure robust data communications and precision ranging. In order to accommodate heterogeneous networks, it uses specific modulation, coding, and ranging waveforms that can be detected well by both coherent and noncoherent receivers.

TOA estimation for IR-UWB systems with different transceiver types

In this paper, performances of stored-reference, transmitted-reference (TR), and energy-detection (ED)-based time-of-arrival estimation techniques are analyzed for impulse-radio ultra-wideband (IR-UWB) systems at sub-Nyquist sampling rates. First, an additive white Gaussian noise channel is considered to emphasize certain fundamental issues related to these different transceivers. In particular, energy collection characteristics and decision statistics are presented. Probability of accurate peak detection is analyzed for each transceiver, and receiver operating characteristics for the leading edge are derived. Effects of number of pulses per symbol and number of averaging symbols are investigated in detail. Then, realistic multipath channels are addressed, and various maximum-likelihood estimation approaches are investigated. A new estimator that jointly exploits the noise statistics and power delay profile of the channel is proposed, and a Bayesian estimator that (ideally) gives a lower bound is analyzed. Simulation results show that while ED and TR have better energy collection capabilities at low-rate sampling, they suffer from distributing the energy over time.

Image transmission over IEEE 802.15.4 and ZigBee networks

An image sensor network platform is developed for testing transmission of images over ZigBee networks that support multi-hopping. The ZigBee is a low rate and low power networking technology for short range communications, and it currently uses IEEE 802.15.4 MAC and PHY layers. Both ZigBee networking (NWK) and IEEE 802.15.4 MAC layer protocols are implemented on a single M16C microprocessor. Transport layer functionalities such as fragmentation and reassembly are performed at the application layer, since the ZigBee NWK does not have a fragmentation support. The multiple access scheme is CSMA/CA, therefore only the best effort multi-hop transmission of JPEG and JPEG-2000 images are tested; observations and resulting statistics are presented, and open issues are discussed.

Tree-Based Data Broadcast in IEEE 802.15.4 and ZigBee Networks

This paper studies efficient and simple data broadcast in IEEE 802.15.4-based ad hoc networks (e.g., ZigBee). Since finding the minimum number of rebroadcast nodes in general ad hoc networks is NP-hard, current broadcast protocols either employ heuristic algorithms or assume extra knowledge such as position or two-hop neighbor table. However, the ZigBee network is characterized as low data rate and low cost. It cannot provide position or two-hop neighbor information, but it still requires an efficient broadcast algorithm that can reduce the number of rebroadcast nodes with limited computation complexity and storage space. To this end, this paper proposes self-pruning and forward node selection algorithms that exploit the hierarchical address space in ZigBee networks. Only one-hop neighbor information is needed; a partial list of two-hop neighbors is derived without exchanging messages between neighboring nodes. The ZigBee forward node selection algorithm finds the minimum rebroadcast nodes set with polynomial computation time and memory space. Using the proposed localized algorithms, it is proven that the entire network is covered. Simulations are conducted to evaluate the performance improvement in terms of the number of rebroadcast nodes, number of duplicated receivings, coverage time, and communication overhead

Dynamic resource control for high-speed downlink packet access wireless channel

It is a challenging task to provide Quality of Service (QoS) control for a shared high-speed downlink packet access (HSDPA) wireless channel. In this paper, we first propose a new dynamic resource control framework integrated with adaptive modulation and coding (AMC) and hybrid automatic repeat request (H-ARQ) to support class-based multimedia applications over HSDPA wireless channels. Then we present a new scheduling algorithm, Delay-sensitive Dynamic Fair Queueing (DSDFQ), to meet delay requirements of multimedia applications as well as maintain high network efficiency. The proposed approach can easily adapt to load fluctuations of different traffic classes and varying wireless channel conditions caused by user mobility, fading and shadowing. Performance evaluation shows the advantage of our proposed approach.

A New Transmitted Reference Pulse Cluster System for UWB Communications

A new form of transmitted reference technique is proposed in this paper, where compactly spaced or even multiple contiguous reference and data pulses are used for transmission. This structure enables a simple, robust and practical autocorrelation detector to be implemented in the receiver. It is also compatible with the signal format proposed within IEEE 802.15.4a working group for coherent and non-coherent systems. The performance of the proposed receiver and a simple noncoherent energy detector are analyzed and compared. Simulation results show that this new transmitted reference system outperforms the non-coherent system by about 1.3-1.9 dB for 802.15.4a channel model 1 and 1.3-2.3 dB for channel model 8, while offering similar implementation complexity compared to that of the non-coherent system.

Load balanced routing for low power and lossy networks

The RPL routing protocol published in RFC 6550 was designed for efficient and reliable data collection in low-power and lossy networks. Specifically, it constructs a Destination Oriented Directed Acyclic Graph (DODAG) for data forwarding. However, due to the uneven deployment of sensor nodes in large areas, and the heterogeneous traffic patterns in the network, some sensor nodes may have much heavier workload in terms of packets forwarded than others. Such unbalanced workload distribution will result in these sensor nodes quickly exhausting their energy, and therefore shorten the overall network lifetime. In this paper, we propose a load balanced routing protocol based on the RPL protocol, named LB-RPL, to achieve balanced workload distribution in the network. Targeted at the low-power and lossy network environments, LB-RPL detects workload imbalance in a distributed and non-intrusive fashion. In addition, it optimizes the data forwarding path by jointly considering both workload distribution and link-layer communication qualities. We demonstrate the performance superiority of our LB-RPL protocol over original RPL through extensive simulations.

Pilot Matrix Design for Estimating Cascaded Channels in Two-Hop MIMO Amplify-and-Forward Relay Systems

In this paper, we consider a two-hop multi-input-multi-output (MIMO) amplify-and-forward (AF) relay system consisting of a source node (SN), a destination node (DN), and a relay node (RN) that simply amplifies and forwards its received signal to the DN without any further processing. In this system, the overall channel from the SN to the DN is a cascade of the backward relay channel over the SN-RN hop, the amplifying matrix at the RN, and the forward relay channel over the RN-DN hop. We investigate the estimation of the two cascaded relay channels at the DN based on the predefined amplifying matrix applied at the RN and the corresponding overall channel obtained through the conventional channel estimation algorithms with the help of pilots transmitted by the SN. In particular, we find necessary and sufficient conditions on the pilot amplifying matrix sequence at the RN to ensure feasible relay channel estimation at the DN. Based on these conditions, we present rules to design diagonal or quasi-diagonal pilot amplifying matrices so that the cascaded relay channels can be estimated with minimum complexity at the RN. In the presence of imperfect overall channel state information at the DN, we further develop the approximate linear least-square estimation of the relay channels based on the designed pilot matrix sequence and demonstrate its performance by simulation results.

Reliable broadcast in ZigBee networks

ZigBee is a new industrial standard for ad hoc networks based on IEEE 802.15.4. It is used for low data rate wireless networks and sensor networks. The data broadcast algorithms for ZigBee networks have been recently studied in (21), where the major task is to reduce the number of rebroadcast nodes. A broadcast algorithm should be robust, which can be achievable by introducing redundant transmissions to some extent. This issue will be studied by this paper. Results presented here extend the forward node selection algorithm in (21) for ZigBee networks. The tree neighbor information is exploited to make sure that every node is covered by at least one of its tree neighbors. A non-random rebroadcast timer is set according to the number of neighbors to be covered, distance and link quality to trigger rebroadcast times. The complexity of the proposed algorithm is polynomial in terms of both computation time and memory space. Simulations are conducted to evaluate the broadcast redundancy, coverage time, and coverage ratio, when the number of nodes varies and there is packet loss. Keywords—ZigBee; broadcast; reliability; ad hoc network