Antti Anttonen

Error Probability of Energy Detected Multilevel PAM Signals in Lognormal Multipath Fading Channels

Noncoherent multilevel systems have been typically analyzed with spectrally inefficient orthogonal modulation methods. In this paper, we present a novel error probability analysis of energy detected (ED) signals with spectrally efficient multilevel pulse amplitude modulation (PAM). One of the main challenges in the analysis of ED systems with the multilevel PAM is to find analytical methods to evaluate and optimize the performance of ED systems with respect to arbitrary system parameters, e.g., decision thresholds for chi-squared-distributed decision variables, integration time, bandwidth, and number of modulation levels. We propose analytically tractable methods that can be efficiently used to design spectrally efficient ED systems for short-range, wideband, and high data rate wireless communications in lognormal multipath fading channels with uncorrelated diversity paths.

Interruption Probability of Wireless Video Streaming With Limited Video Lengths

In this paper, we consider a simple queueing theoretic method to predict the video interruption probability for a given video length. Specifically, a mobile user is streaming a video with a limited length and variable bit rate video encoding. The playback interruptions are caused by random packet delays occurring in the wireless link between the source and destination nodes. The dynamics of the playback buffer in the user terminal is modeled as a G/G/1 queue. To evaluate the video interruption probability, a simple asymptotic method has been presented for the case in which the video length approaches infinity. However, in many practical cases, the video length is limited, hindering the usage of the asymptotic method. We obtain a simple and closed-form upper bound for the analysis of the interruption probability that incorporates the effect of finite video lengths with known statistical delay parameters. Furthermore, a useful method is presented to select between the proposed method and the asymptotic method whose relative accuracy changes with the video length and statistical properties of the buffer load size. The accuracy of the proposed analytical method is compared with the existing methods. Finally, we address some practical challenges in buffer dimensioning when the statistical delay parameters are unknown and estimated with a finite number of received packets.

Sensitivity of energy detected multilevel PAM systems to threshold mismatch

In this paper we theoretically evaluate the sensitivity resulted from a decision threshold mismatch with multilevel and energy detected pulse amplitude modulated (ED-PAM) signals. We quantify the relation between the threshold offset and the degradation in the required signal-to-noise ratio to preserve a desired symbol error rate. Based on the analysis we conclude some useful guidelines with respect to various system parameters. One of the main problems in an ED-PAM with arbitrary number of modulation levels, integration time, and bandwidth is to find a simple way to calculate the optimal threshold values. We rise to this challenge by proposing a new multilevel threshold calculation method which is attractive to use from both performance and complexity point of views for a wide range of system parameters. The results can be used, e.g., in an impulse radio for high data rate short-range wireless communications.

Energy detection of multilevel PAM signals with systematic threshold mismatch

We address a symbol decision problem with spectrally efficient energy detected multilevel pulse amplitude modulated (PAM) signals. First, we analytically quantify the relationship between a systematic threshold mismatch and the required increase of the average signal-to-noise ratio to preserve a desired symbol error rate. For the case in which such an increase is not tolerable, we present a novel near-optimal multilevel threshold selection scheme, which is accurate for a wide range of system parameters.

Full length article: Error performance of PAM systems using energy detection with optimal and suboptimal decision thresholds

In this paper, we consider the error probability for multilevel pulse amplitude modulated (PAM) signals, which are used with a multipath diversity combiner based on energy detection (ED). A distinctive feature of ED combined with nonconstant envelope signals is that the symbol decision thresholds need to be determined from a non-Gaussian distributed decision variable. We first present a novel theoretical analysis framework which provides a basis to predict the error performance of ED-PAM systems with optimal maximum likelihood decision thresholds in general multipath fading channels with arbitrary number of degrees of freedom. We then use frequency-selective lognormal fading channels as a case example and evaluate simple approximations for the error probability. Moreover, the analysis is extended to include the joint effect of systematic and random threshold deviation on the error probability with suboptimal but practical data-aided threshold estimation.

Nondata-Aided Hypothesis Testing of PAM Signals with Energy Detection

In this letter, we consider the problem of nondata-aided (NDA) detection of multilevel pulse-amplitude-modulated (PAM) signals combined with energy detection. We show that it is possible to estimate proper thresholds for the symbol decision without using redundant signals. Furthermore, we present an analytical method to evaluate the effect of pattern noise on the error performance of the NDA scheme with respect to the number of modulation levels and the convergence rate. With relatively low numbers of degrees of freedom and slow fading, which are typical for short-range systems using multiband modulation, the performance of the NDA scheme turns out to be asymptotically comparable to that of the optimal threshold selection.

An enhanced very high data rate UWB airinterface based on the WIMEDIA standard - An European View -

The existing UWB standard based on OFDM developed by the WIMEDIA industrial consortium can support data rates up to 480 MBit/s for a distance of up to 2m. The initial focus and key application driver of the WIMEDIA standard implementation will be the replacement of USB 2 cables in PC peripherals using the certified wireless USB protocol. Typical usage scenarios for this implementation will be the connection of a PC to hard disk drives, digital cameras, printers, etc. For future deployments of UWB technologies in multimedia and network centric consumer electronics applications higher data rates are needed. The goal of work package WP2a in the PULSERS II project is the definition and evaluation of an air interface and the corresponding building blocks that can provide data rates in the range 3GBit/s over a distance of around 2m. In order to achieve this goal the OFDM based air interface of the WIMEDIA system will be upgraded in an evolutionary manner with strong considerations for the backward compatibility of the future devices. This paper will give an overview of the state of the definition of this enhanced air-interface developed in the PULSERS II project. The concepts and the evaluation results coming out of this activity should be used as an input to the future standardization activities in the WIMEDIA group starting in 2007 with an initial step towards a lGbit/s enhancement of the air interface.

Why Will Computing Power Need Particular Attention in Future Wireless Devices

In this tutorial particular attention is given to the computing power in the physical layer of wireless devices, which are energy and power limited. Communication uses the power in the analog radio frequency parts and computation uses power in the signal processing and other tasks required during communication, both in the transmitter and in the receiver. Example applications include sensor networks and mobile devices in ultra-dense small cell networks where the link distances are below about 10 m, and the computing power is larger than the communication power. The computation-communication tradeoff means that if one of the powers is increased, the other one must be decreased, otherwise the total power increases. Energy efficiency is a challenging multidisciplinary topic, and the consequences of the interrelated fundamental limits are not well understood. According to Edholm?s prediction, the link bit rates are increasing exponentially each year, which implies that there must be a corresponding exponential trend in improving energy efficiency, defined as number of bits per energy unit, both in computation and communication. It is well known that for communications, due to noise, the Shannon limit forms the fundamental limit for the received energy per bit, but in computation there is a similar limit called Landauer limit for the switching energy of a transistor. Near the two fundamental limits the energy efficiency cannot be improved any more exponentially. Our main contribution is to elaborate the connections between the various technology predictions, different fundamental limits and possible design trade-offs. Specifically, we show that because of the aforementioned fundamental limits, the exponential trends in bit rates cannot continue without a compensating exponential trend in energy efficiency. We also revisit the concept of crossover distance and derive it from the fundamental limits to give some further system-level insight on the energy consumption bottlenecks.

Timing and Phase Offset Sensitivity of Autocorrelation Based Frequency Estimation in an FH-OFDM System

In this paper, a new aspect on the problem of carrier frequency offset (CFO) estimation is studied in a frequency-hopping (FH) orthogonal frequency division multiplexing (OFDM) system. Unlike in a traditional nonhopped OFDM system, in FH-OFDM system it is important to verify how accurately frequency-switching must be performed before the CFO estimation can take place with adequate performance. The accuracy of frequency-switching is evaluated through frequency-hopping timing offset (FHO) and frequency-hopping phase offset (PHO) between the received signal and the signal produced by the local frequency-hopping synthesizer of the receiver. The target system uses ultra-wideband (UWB) in order to achieve very high data rate of 1.6 Gbit/s. The performance of selected autocorrelation based algorithms is simulated in multipath fading channel under the FHO and PHO, and the results are compared to the performance of ideal frequency-switching and the corresponding analytical Cramer-Rao bound. It is found that the CFO estimators based on autocorrelation principle are quite robust to the FHO less than half the hopping period. Furthermore, simple methods are proposed to compensate the degradation caused by the FHO. The estimators are, however, sensitive to the PHO caused by the possible lack of phase memory in the frequency-hopping synthesizer resulting in a significant bias to the CFO estimate.

Design and implementation of advanced algorithms for MIMO-UWB wireless communications

This paper describes the design and implementation of low-complexity multiple-input multiple-output (MIMO) signal processing techniques suitable for ultra-wideband (UWB) wireless communications. It provides the general system concept, description of the measurement set-up and modular FPGA platform for test and verification of the proposed multiple antenna schemes under real air-interface environment. We validate the performance of selected spatial multiplexing and diversity approaches applied to Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) and demonstrate the enhancements in capacity and link reliability of existing WiMedia devices through algorithm- and implementation-level investigations.