Networking together hundreds or thousands of cheap microsensor nodes allows users to accurately monitor a remote environment by intelligently combining the data from the individual nodes. These networks require robust wireless communication protocols that are energy efficient and provide low latency. We develop and analyze low-energy adaptive clustering hierarchy (LEACH), a protocol architecture for microsensor networks that combines the ideas of energy-efficient cluster-based routing and media access together with application-specific data aggregation to achieve good performance in terms of system lifetime, latency, and application-perceived quality. LEACH includes a new, distributed cluster formation technique that enables self-organization of large numbers of nodes, algorithms for adapting clusters and rotating cluster head positions to evenly distribute the energy load among all the nodes, and techniques to enable distributed signal processing to save communication resources. Our results show that LEACH can improve system lifetime by an order of magnitude compared with general-purpose multihop approaches.

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An application-specific protocol architecture for wireless microsensor networks

Wireless Communications

We introduce space-time block coding, a new paradigm for communication over Rayleigh fading channels using multiple transmit antennas. Data is encoded using a space-time block code and the encoded data is split into n streams which are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. Maximum-likelihood decoding is achieved in a simple way through decoupling of the signals transmitted from different antennas rather than joint detection. This uses the orthogonal structure of the space-time block code and gives a maximum-likelihood decoding algorithm which is based only on linear processing at the receiver. Space-time block codes are designed to achieve the maximum diversity order for a given number of transmit and receive antennas subject to the constraint of having a simple decoding algorithm. The classical mathematical framework of orthogonal designs is applied to construct space-time block codes. It is shown that space-time block codes constructed in this way only exist for few sporadic values of n. Subsequently, a generalization of orthogonal designs is shown to provide space-time block codes for both real and complex constellations for any number of transmit antennas. These codes achieve the maximum possible transmission rate for any number of transmit antennas using any arbitrary real constellation such as PAM. For an arbitrary complex constellation such as PSK and QAM, space-time block codes are designed that achieve 1/2 of the maximum possible transmission rate for any number of transmit antennas. For the specific cases of two, three, and four transmit antennas, space-time block codes are designed that achieve, respectively, all, 3/4, and 3/4 of maximum possible transmission rate using arbitrary complex constellations. The best tradeoff between the decoding delay and the number of transmit antennas is also computed and it is shown that many of the codes presented here are optimal in this sense as well.

/pdf/space-time-block-codes-from-orthogonal-designs-1oj68nrilr.pdf

Space-time block codes from orthogonal designs

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.

Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

Convergence of Probability Measures. By P. Billingsley. Chichester, Sussex, Wiley, 1968. xii, 253 p. 9 1/4“. 117s.

Convergence of Probability Measures

The benefits of coding an optical communications system that employs binary on-off-keying heterodyne detection are shown. The system is impaired by laser phase noise as well as by additive white Gaussian noise (AWGN). A receiver structure especially designed to mitigate the effects of phase noise in the presence of AWGN is assumed. This special receiver structure requires a wider band front-end IF filter than would be required for a phase-noise-free signal. Results computed for several different coding schemes indicate that the benefits of coding are large and the costs are small. For a linewidth-to-bit-rate ratio of 0.64, a half-rate binary code that can correct three bit errors provides a 50% reduction in the required IF filter bandwidth (and therefore the required IF) and about 5 dB of reduction in required laser power. The benefits of coding are greatest under high- beta T conditions, corresponding to low bit rates, where coders and decoders are most practical to implement. The results obtained suggest the possibility that forward error correction could be used to improve the channel packing efficiency of FDMA (frequency division multiple access) networks. >

Coding of optical on-off-keying signals impaired by phase noise

In a representative embodiment, a multipath channel and an optical subcarrier modulation scheme are designed in concert to cause different modulated subcarriers of the optical communication signal to become substantially uncorrelated over the aggregate signal bandwidth. Provided that the employed FEC code has sufficient error-correcting capability for average channel conditions, breakdowns in the operation of the FEC decoder and the corresponding system outages can substantially be avoided.

Multipath channel for optical subcarrier modulation

We consider a packet switched network in the situation where communication resources are used close to capacity. Such heavy traffic may seem to present a dilemma. On one hand, at each node, the usefulness of status information about queues at other nodes is manifest. On the other hand, since the limitation of transmission resources causes backup, heavy load seems to be the worst situation in which to expend still more communication resources to convey status information. Under extremely general assumptions on inter-arrivals and services, a scaling appropriate for queueing processes in networks under heavy traffic has been established. Under these assumptions, we demonstrate that the status of the entire network can be communicated throughout the network, perfectly, in real time, without influencing the scaled queueing process. So, within a precise mathematical setting, we see that there is no dilemma: status can be conveyed at a negligible cost in a network operating at heavy load. Most of today's computer networks are designed for light-to-moderate loading. Yet heavy traffic analysis is growing in relevance, as is explained. A brief introduction to the subject of convergence of queueing systems is included.

Unintrusive communication of status in a packet network in heavy traffic

The present invention is directed to a formatter, a method of formatting encoded symbols and a wireless communication system employing the same. In one embodiment, the formatter includes a symbol generator that provides a plurality of encoded symbols from a bit stream. The formatter also includes a symbol mapping organizer that maps the plurality of encoded symbols into information cells, each having a unique space coordinate, time coordinate and degree of freedom within a frequency band. The information cells are arranged in a parallelopiped communication resource volume.

Formatter, method of formatting encoded symbols and wireless communication system employing the same

We present a simulation study of two relaying schemes in downlink cellular systems. We simulate the performance of two relaying strategies: (i) a collaborative power addition (CPA) scheme, cooperative scheme where the relay collaborates with the base station, and (ii) a simple orthogonal relaying strategy where base stations and relays transmit in orthogonal time slots. Evaluations are done in the context of a 19-cell, 57-sector set-up in which each of the served users must be delivered a message. The user messages are taken to have the same size and 90% of users in the network must be served. All simultaneous transmissions mutually interfere. Improvements due to relay deployments are measured as throughput improvements in terms of increase in common rate of users as well as power savings in terms of reduction in peak or average power transmitted by base stations. We observe that the simpler orthogonal relaying scheme performs nearly as well as the more complex collaborative relaying in producing throughput gains and power savings.

Gerard J. Foschini

Papers

Coding of optical on-off-keying signals impaired by phase noise

Multipath channel for optical subcarrier modulation

Unintrusive communication of status in a packet network in heavy traffic

Formatter, method of formatting encoded symbols and wireless communication system employing the same

Relaying in downlink cellular systems