Showing papers by "Raymond Knopp published in 2005"

A practical method for wireless channel reciprocity exploitation through relative calibration

Abstract: We present a relative calibration method for a wireless TDD link, which, after a calibration phase involving feedback, lets the transmitter acquire knowledge of the downlink channel state from the uplink channel estimates, through proper modeling and estimation of the RF circuitry impulse responses. Contrarily to previous methods, relative calibration does not require specific calibration hardware. Experimental results confirm the validity of the proposed linear reciprocity model, and of the calibration approach.

Subspace analysis of indoor UWB channels

Abstract: This work aims at characterizing the second-order statistics of indoor ultra-wideband (UWB) channels using channel sounding techniques We present measurement results for different scenarios conducted in a laboratory setting at Institut Eurecom These are based on an eigendecomposition of the channel autocovariance matrix, which allows for the analysis of the growth in the number of significant degrees of freedom of the channel process as a function of the signaling bandwidth as well as the statistical correlation between different propagation paths We show empirical eigenvalue distributions as a function of the signal bandwidth for both line-of-sight and non-line-of-sight situations Furthermore, we give examples where paths from different propagation clusters (possibly arising from reflection or diffraction) show strong statistical dependence

Achievable diversity-multiplexing-delay tradeoff in half-duplex ARQ relay channels

Abstract: In this paper, we present an efficient protocol for the delay-limited fading automatic retransmission request single relay channel. The source is using an ARQ retransmission protocol to send data to the relay and the destination. When the relay is able to decode, both the relay and the source send the same data to the destination providing additional gains. The proposed protocol exploits two kinds of diversity: (i) space diversity available through the cooperative (relay) terminal, which retransmits the source's signals, (ii) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (snr) regime

Process for estimating the channel state in a transmitter of a digital communication system and apparatus for doing the same

Abstract: 1. Process for determining the channel characteristics in a digital communication system comprising a first Communication Unit (CUA 100) and a second Communication Unit B (200) communicating through a transmission medium (140). The first unit 100 includes a first signal signal processor (110), and at least one first conversion and RF module (120) and a first antenna (130). The second unit (200) includes a second signal processor (170), and at least one second conversion and RF module (160) and at least one second antenna (150). The process comprises the steps of: executing a first loop based on the successive transmission of a first training information generated by said first unit (100) and the retransmission of a feedback signal combined with a second training information generated by said second unit (200) back to said first unit (100) in order to let said first unit compute relationship characteristics (P A ,P B ) between the transfer function of said first and second conversion and RF modules (120, 160); upon completion of said first loop, executing a second loop for the purpose of continuously deriving the knowledge of the G channel within the emitter of said first Unit (100) from the sole knowledge of the estimated H channel together with said relationship characteristics (P A ,P B ).

Resource allocation in wideband wireless systems

Abstract: We consider the problem of resource allocation in multiuser single-antenna wideband OFDM(A) systems The key advantage of such systems with respect to narrow band systems is the possibility of considering frequency as an additional resource to be allocated Although the maximum normalized average throughput is not increased with respect to that in a narrowband system, a more efficient use of resources is possible especially if the bandwidth is considerably larger than the coherence bandwidth of the channel and the channel is varying slowly with respect to the scheduling updates This is mainly because randomness in the system is increased by the wideband resources The work presented in this paper analyzes the effects of bandwidth on the delay characteristics To this end, the relationship between ergodic information rates, stability and delay in multiuser communications systems is studied and candidate resource allocation policies are presented and simulated

Code constructions for non-coherent on-off ultra-wideband systems

Abstract: We consider coding schemes for non-coherent on-off signaling over ultra-wideband channels. Different code constructions are proposed and optimized using an exit chart based methodology. The performance of proposed codes is then measured using both an exit chart based analysis and Monte Carlo simulations. The optimized codes are shown to perform close to information-theoretic limits.

ResourceAllocation inWideband WirelessSystems

Abstract: We consider theproblem ofresource allocation in multiuser single-antenna wideband OFDM(A)systems. Thekey advantage ofsuchsystems withrespect tonarrowbandsystems isthepossibility ofconsidering frequency asanadditional re- source tobeallocated. Although themaximumnormalized aver- agethroughput isnotincreased withrespect tothatinanarrow- bandsystem, amoreefficient useofresources ispossible especially ifthebandwidth isconsiderably larger thanthecoherence band- width ofthechannel andthechannel isvarying slowly withrespect tothescheduling updates. Thisismainly because randomness in thesystem isincreased bythewideband resources. Theworkpre- sented inthis paperanalyzes theeffects ofbandwidth onthedelay characteristics. Tothis end,therelationship between ergodic in- formation rates, stability anddelay inmultiuser communications systems isstudied andcandidate resource allocation policies are presented andsimulated.