A Wireless Sensor Network (WSN, for short) is a distributed system consisting of n sensor nodes and a base station. In this paper, we propose an energy-efficient protocol to initialize the sensor nodes in a WSN, that is, to assign a unique ID to each sensor node. We show that if an upper bound u on the number n of sensor nodes is known beforehand, for any f 1 and any small µ (0<µ<1), a WSN without collision detection capability can be initialized in O((log (1/µ) + log f)u1+µ) time slots, with probability exceeding 1-(1/f), with no sensor node being awake for more than O(log (1/µ)+ log f) time slots.

A radio network is a distributed system with no central shared resource, consisting of n stations each equipped with a radio transceiver. One of the most important parameters to evaluate protocols in the radio networks is the number of awake time slots in which each individual station sends/receives a data packet. We are interested in devising energy-efficient initialization protocols in the single-hop radio network (RN, for short) that assign unique IDs in the range [1,n] to the n stations using few awake time slots. It is known that the RN can be initialized in O(log log n) awake time slots, with high probability, if every station knows the number n of stations in the RN. Also, it has been shown that the RN can be initialized in O(log n) awake time slots even if no station knows n. However, it has been open whether the initialization can be performed in O(log log n) awake time slots when no station knows n. Our main contribution is to provide the breakthrough: we show that even if no station knows n, the RN can be initialized by our protocol that terminates, with high probability, in O(n) time slots with no station being awake for more than O(log log n) time slots. We then go on to design an initialization protocol for the k-channel RN that terminates, with high probability, in O(n/k + (log n)2) time slots with no station being awake for more than O(log log n) time slots.

To reduce mutual coupling of a two-level nested array (TLNA) with an even number of sensors, we propose an improved array configuration that exhibits all the good properties of the prototype optimal configuration under the constraint of a fixed number of sensors N and achieves reduction of mutual coupling. Compared with the prototype optimal TLNA (POTLNA), which inner level and outer level both have N/2 sensors, those of the improved optimal TLNA (IOTLNA) are N/2-1 and N/2+1. It is proved that the physical aperture and uniform degrees of freedom (uDOFs) of IOTLNA are the same as those of POTLNA, and the number of sensor pairs with small separations of IOTLNA is reduced. We also construct an improved optimal second-order super nested array (SNA) by using the IOTLNA as the parent nested array, termed IOTLNA-SNA, which has the same physical aperture and the same uDOFs, as well as the IOTLNA. Numerical simulations demonstrate the better performance of the improved array configurations.

The main contribution of this work is to propose energy-efficient randomized initialization protocols for ad-hoc radio networks (ARN, for short). First, we show that if the number n of stations is known beforehand, the single-channel ARN can be initialized by a protocol that terminates, with high probability, in O(n) time slots with no station being awake for more than O(log n) time slots. We then go on to address the case where the number n of stations in the ARN is not known beforehand. We begin by discussing, an elegant protocol that provides a tight approximation of n. Interestingly, this protocol terminates, with high probability, in O((log n)2) time slots and no station has to be awake for more than O(log n) time slots. We use this protocol to design an energy-efficient initialization protocol that terminates, with high probability, in O(n) time slots with no station being awake for more than O(log n) time slots. Finally, we design an energy-efficient initialization protocol for the k-channel ARN that terminates, with high probability, in O(n/k+log n) time slots, with no station being awake for more than O(log n) time slots.

The main contribution of this work is to propose energy-efficient protocols that compute the sum of n numbers over any commutative and associative binary operator stored in n wireless sensor nodes arranged in a two-dimensional grid of size nn. We first present a protocol that computes the sum on a Wireless Sensor Network (WSN) in O(r2+(n/r2)1/3) time slots with no sensor node being awake for more than O(1) time slots, where r is the transmission range of the sensor nodes. We then go on to present a fault-tolerant protocol which computes the sum in the same number of time slots with no sensor node being awake for more than O(log r) time slots. Finally, we show that in a WSN where the sensor nodes are empowered with the ability to dynamically adjust their transmission range r during the execution of the protocol, the sum can be computed in O(log n) time slots and no sensor node needs to awake for more than O(log n) time slots.

Low-hit-zone frequency-hopping sequences (LHZ-FHSs) are frequency-hopping sequences with low Hamming correlation in a low-hit-zone (LHZ), which have important applications in quasi-synchronous communication systems. However, the strict quasi-synchronization may be hard to maintain at all times in practical FHMA networks, it is also necessary to minimize the Hamming correlation for time-shifts outside of the LHZ. The main objective of this letter is to propose a lower bound on the maximum correlation magnitude outside the low-hit-zone for LHZ-FHS sets. It turns out that the proposed bound is tight or almost tight in the sense that it can be achieved by some LHZ-FHS sets.

A Radio Network (RN, for short) is a distributed system with no central arbiter, consisting of p radio stations each of which is endowed with a radio transceiver. In this work we consider single-hop, single channel RNs, where each station S(i), (1ip), initially stores si items which are tagged with the unique destination they must be routed. Since each item must be transmitted at least once, every routing protocol must take at least n = s1 + s2 + + sp time slots to route each item to its final destination. Similarly, each station S(i), (1ip), must be awake for at least si + di time slots to broadcast si items and to receive di items, where di denotes the number of items destined for S(i). The main contribution of this work is to present a randomized time- and energy-optimal routing protocol on the RN. Let qi, (1ip), be the number of stations that have items destined for S(i), q=q1 +q2 ++ qp, and ri be the number of stations for which S(i) has items. When qi is known to station S(i), our routing protocol runs, with probability exceeding 1 - , (f > 1), in n + O(q + log f) time slots with each station S(i) being awake for at most si + di + O(qi + ri + log f) time slots. Since qidi, risi, and qn always hold, our randomized routing protocol is optimal. We also show that, when the value of di is known to S(i), our routing protocol runs, with probability exceeding 1 - , (f > 1), in O(n + log f) time slots with no station being awake for more than O(si + di + log f) time slots.