Showing papers by "Raymond Knopp published in 2003"

On the achievable rates of ultra-wideband PPM with non-coherent detection in multipath environments

Abstract: In this work we investigate the achievable rates of ultra-wideband (UWB) systems using a m-ary pulse position modulation (PPM) with non-coherent receivers in multipath fading environments. We derive a random coding bound on the achievable information rates and highlight the influence of system parameters (bandwidth, delay spread). We also investigate the effect of the use of hard decisions prior to channel decoding and characterize its impact on system performance.

Coding strategies for UWB interference-limited peer-to-peer networks

Abstract: In this work we study the achievable rates of memoryless sig-naling strategies adapted to UltraWideBand (UWB) multi-path fading channels. We focus on strategies which do nothave explicit knowledge of the instantaneous channel realiza-tion, but may have knowledge of the channel statistics. Weevaluate the average mutual information of general binaryash-signaling and achievable rates for m -PPM as a functionof the channel statistics. Finally, we briey examine the ro-bustness of ash-signaling for interference-limited systems.NotationsThroughout the paper, small letters 0 a will be used for scalars,capital letters 0 A for vectors, and bold capital letters 0 A formatrices.1. IntroductionIn this work, we consider achievable rates for transmissionstrategies suited to Ultra-wideband (UWB) systems and focusnon-coherent receivers (i.e. those which do not perform chan-nel estimation, but may have prior knowledge of the second-order channel statistics). Here we take a UWB system to beloosely de ned as any wireless transmission scheme that occu-pies a bandwidth between 1 and 10 GHz and more than 25%of it's carrier frequency in the case of a passband system.The most common UWB transmission scheme is based ontransmitting information through the use of short-term im-pulses, whose positions are modulated by a binary informa-tion source [1]. This can be seen as a special case of ashsignaling coined by Verdu in [6]. Similar to direct-sequencespread-spectrum, the positions can further be modulated bya non-binary sequence (known as a time-hopping sequence )for mitigating inter-user interference in a multiuser setting[2]. This type of UWB signaling is a promising candidatefor military imaging systems as well as other non-commercialsensor network applications because of its robustness to in-terference from signals (potentially from other non-UWB sys-

On the achievable rates of ultra-wideband systems in multipath fading environments

Abstract: In this work, we consider achievable rates for transmission strategies suited to Ultra-wideband (UWB) systems and focus non-coherent receivers (i.e. those which do not perform channel estimation, but may have prior knowledge of the secondorder channel statistics). Here we take a UWB system to be loosely defined as any wireless transmission scheme that occupies a bandwidth between 1 and 10 GHz and more than 25% of it’s carrier frequency in the case of a passband system. The most common UWB transmission scheme is based on transmitting information through the use of short-term impulses, whose positions are modulated by a binary information source [3]. This can be seen as a special case of gash signaling coined by Verdu in [2]. We focus on the case of non-coherent detection since it is well known [l] that coherent detection is not required to achieve the wideband AWGN channel capacity C,. In [2] Verdu addresses the spectral efficiency of signaling strategies in the wideband regime under different assumptions regarding channel knowledge a t the transmitter and receiver. He shows that approaching C, with non-cohcrent detection is impossible for practical data rates (>lo0 kbit/s) even for the vanishing spectral efficiency of UWB systems. This is due to the fact that the slope SO of the curve representing (Eb/No),i, versus spectral efficiency, is zero at the origin for non-coherent detection. We restrict our study to strictly time-limited memoryless real-valued signals, both at the transmitter and receivcr. The transmitted pulse, of duration Tp, is passed through a linear channel, h(t , U) of duration Td and corrupted by additive white Gaussian noise with power spectral density No/2. The transmitted signal is written as z( t ) = E,”=, S ( U k ) f i p ( t where k is the symbol index, T, the symbol duration, E, = PT, the transmitted symbol energy, uk E (1,. . . , m} is the transmitted symbol at time k , p ( t ) and s ( u ~ ) are the assigned pulse and amplitude for symbol U k . For all k, p ( t ) is a unit-energy pulse of duration Tp. The considered model encompasses modulation schemes such as flash signaling, mary PPM, amplitude, and differential modulations. A guard interval of length Td is left a t the end of each symbol (from our memoryless assumption) so that T, 2 T, + T d . We characterize UWB propagation channel in terms of statistical eigenvalue distributions and optimal transmit pulse shapes, and highlight the “no-fading”, or constant received energy, behavior these channels.

On the Achievable Rates of Multiband Ultra-Wideband Systems

Abstract: In this work we study the achievable rates of memoryless signaling strategies adapted to ultra-wideband (UWB) multipath fading channels. We focus on strategies that do not have explicit knowledge of the instentaneous channel realization, but may have knowledge of the channel statistics. We evaluate the average mutual information of the general binary flash-signaling rates as a function of channel statistics and derive random coding bounds for m-ary PPM using different noncoherent receivers as well as an imperfect coherent receiver. Then we extend the results to multiband m-PPM signaling and show that for data rates on the order of 400 Mbits/s, at 4 m distance between the transmitter and the receiver, can be achieved using simple noncoherent receivers.