Power Aware Communications for Wireless OptiMised personel Area Network

Traditionally upper and lower layers of the OSI model have been implemented and integrated following independent paths. In order to make the user centric concept a reality, we think that by embedding a transparent layer just bellow the TCP/IP stack interacting with the wireless platform it can facilitate the realization of that concept. Furthermore, we do not constraint the interaction just to the IP layer but we extend it to the middleware, so providing the tools for the ambient intelligence. In this sense, the PACWOMAN project introduces the PAN and CAN Optimisation Layer (PCOL) as an enabling technology, with three main functionalities: Battery consumption optimisation, based on link layer considerations Alleviating the impairments introduced by the multihop wireless scenario Providing information to the ad hoc routing algorithms for achieving an optimised performance. Furthermore, the PCOL, as an add-on functionality, will also support upper layers operation, in particular the middleware entity that could be partially responsible for achieving concepts related to location sensitivity, adaptive applications and application-level energy management. This goes in line with the Cross Layer Optimisation concept that is likely to play a fundamental role on the near future communication topologies and scenarios.

The starting point was the establishment of a FCC compliant solution for a centre frequency of 4 GHz using OOK modulation and capable of a maximum raw bit rate of 5Mbit/s. Two main criteria were taken in account for such design: simplicity of the implementation and low power consumption of the system. A scaled-down version of the FCC compliant design was proposed as operating at a lower centre frequency. The transmitter and receiver designs implementing the scaled-down frequency demonstration were deduced. A novel reduced-complexity synchronization mechanism was proposed for the UWB receiver.

Trust management is becoming a necessity for a large variety of groups of IP interconnected of devices. Networked devices both wireless and fixed, sometimes heterogeneous, create an internet grid capable of sharing services for the benefit of users. Sensors, mobile phones, media centers, home equipment including white goods, along with mainstream devices such as PDAs, laptops, desktop and public servers, are examples of providers and consumers of services. The problem of ownership and trust within and between such groups is becoming a crucial factor; networks should now be identified on the basis of trust rather than on physical or other connectivity criteria. A Network of Trust (NT) can be any set of IP networked devices identified on the basis of a certificate signed by an owner. In an offline manner, the originator and owner of a NT: - Creates a root key-pair consisting of a public and a private key, - Creates a root certificate, - Signs the certificates of all devices to be included in the NT with the root private key and - Stores the private root key in a secure place under his responsibility. An IP networked device presenting a certificate signed by the root private key, has as owner the issuer of the root certificate and is said to belong to a Network of Trust (NT). Within a set of IP networked devices we can distinguish: - The home NT, consisting of all devices presenting a certificate signed by the owner of this NT. - One or several foreign NTs. A foreign NT consists of devices on which a foreign owner has conducted steps (a) (d) with his own root key-pair and this foreign owner is trusted by the owner of the home NT. - Any number of (un-trusted) devices not being able to present any certificate signed either by the owner of the home NT or by any trusted owner of a foreign NT TruMan is a centralized solution regarding Trust Management within and across NTs; it enables the formation of a NT as well as its operation in an environment of trust. TruMan relies on a dynamically configurable Trust Manager (TM) that is able to enforce authentication and authorization of IP networked devices. The role of the manager is to authenticate devices newly entering the domain of concern, distribute state information and maintain the trusted presence of these devices under various modes of trust.

Methodology to design power management strategies across the traditional OSI layers has been proposed. The approach is to analyse at design-time the performance/cost trade-off and to exploit the analysis results at run-time.

An FPGA-based flexible convolutional encoder has been developed which supports power saving by shutting down unused parts through specific enable logic. In order to cover a wide range of convolutional codes there should be a certain number of polynomials generated simultaneously. The memory of a single encoder will be 10, and we have chosen up to 16 data streams that can be emitted in parallel or, by proper configuration, can be joined to form code rates of 1/c; c = 2&16.

During the PACWOMAN project, Lund University has designed and implemented a flexible OFDM transmitter. The FFT processor is a central part of an OFDM transceiver, and has been fabricated both as a stand alone chip and as part of an OFDM transmitter chip. The transmitter chip includes in addition to the FFT, a signal mapper and a cyclic prefix inserter. It is shown that high flexibility is obtained in the transmitter with a reasonable amount of extra hardware. Comprehensive measurements on power consumption are presented for both chips. A scheme to reduce hardware and delay in an OFDM transceiver is found. The scheme shows that the data buffers in an OFDM transceiver, due to a cyclic prefix and a bit reversing pipelined FFT processor, can be significantly reduced with a cyclic suffix and a bidirectional FFT processor.

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