Jukka Rinne

Pilot spacing in orthogonal frequency division multiplexing systems on practical channels

Performances of two different channel interpolation methods to be used with Orthogonal Frequency Division Multiplexing (FDM) systems are investigated. The considered scheme uses constant pilot frequencies for channel response estimation. The interpolation techniques are piecewise-constant and piecewise-linear methods which due to their inherent simplicity are straightforward to implement. The results are given as error probability vs. pilot separation for a channel with exponential type power-delay profile and M-ary quadrature amplitude submodulation with M=4, 16 and 64.

Feasibility study of IΕΕΕ 802.11ah radio technology for IoT and M2M use cases

In this paper we study the feasibility of IEEE 802.11ah radio technology for internet of things (IoT) and machine to machine (M2M) use cases. Devices in internet of things and machine to machine networks are foreseen to communicate wirelessly. Therefore, it is of foremost importance to have a reliable, low-energy wireless technology available that may be used anywhere and anytime without draining the device battery and could achieve satisfactory coverage and data rate. Here we study the link budget, achievable data rate and packet size design of the IEEE 802.11ah radio technology in different channel scenarios. System design and simulation results show that when using this technology the system parameters can be selected to satisfy in most of the cases a reliable communication link while providing better coverage and relatively comparable throughput when compared to other existing solutions like ZigBee.

Phase noise modelling and mitigation techniques in ofdm communications systems

This paper addresses the analysis and mitigation of the signal distortion caused by oscillator phase noise (PN) in OFDM communications systems. Two new PN mitigation techniques are proposed, especially targeted for reducing the intercarrier interference (ICI) effects due to PN. The first proposed method is a fairly simple one, stemming from the idea of linearly interpolating between two consecutive common phase error (CPE) estimates to obtain a linearized estimate of the time-varying phase characteristics. The second technique, in turn, is an extension to the existing state-of-the-art ICI estimation methods. Here the idea is to use an additional interpolation stage to improve the phase estimation performance around the boundaries of two consecutive OFDM symbols. The paper also verifies the performance improvement of these new PN estimation techniques by comparing them to the existing state-of-the-art techniques using extensive computer simulations. To emphasize practicality, the simulations are carried out in 3GPP-LTE downlink -like system context, covering both additive white Gaussian noise (AWGN) and extended ITU-R Vehicular A multipath channel types.

The behavior of orthogonal frequency division multiplexing signals in an amplitude limiting channel

This paper presents an investigation of orthogonal frequency division multiplexing (OFDM) signal distortion in an amplitude limited channel. In the presence of both limiter distortion and channel noise, the back-off can be optimized to give maximum signal-to-noise ratio for a given system.<<ETX>>

An equalization method for orthogonal frequency division multiplexing systems in channels with multipath propagation, frequency offset and phase noise

We present an improved equalizing scheme to be used with orthogonal frequency division multiplexing (OFDM) systems in multipath channels with frequency offset and phase noise. We compare the performance of this method with methods that have been proposed to be used earlier with OFDM. For the performance evaluation we apply a random walk phase noise model with a typical terrestrial TV multipath channel.

Equalization of orthogonal frequency division multiplexing signals

An equalizer is generally a transversal filter which can be used either at the passband or the baseband. Adaptive equalizers adapt filter coefficients to cancel the channel response. We study two different frequency domain adaptive equalizers for orthogonal frequency division multiplexing systems (OFDM). After introducing some theoretical aspects we derive a lower bound for the signal-to-noise ratio reduction due to equalization. Comparisons between two different equalizer structures, the least-mean square (LMS) and proportional equalizers, are presented and tested by simulation in a terrestrial TV channel with strong microreflections.

Comparison of efficient interpolation techniques for symbol timing recovery

There is a trend of using digital receivers where the sampling of the received signal is not synchronized to the incoming data symbols. In these receivers, timing adjustment must be done after sampling using interpolation. There are many different interpolation methods which can be used. We compare three different polynomial-based interpolation methods which can be efficiently implemented using the so-called Farrow (1988) structure. Methods to be compared are the linear and cubic Lagrange interpolation and a new interpolation method proposed earlier by the authors.

Impulse burst position detection and channel estimation schemes for OFDM systems

A new method for compensating the effects of impulse noise in OFDM systems has been presented by Rinne, Henriksson and Hazmi (see Proc. 7th International OFDM Workshop, Hamburg. Germany, p.183-187, Sept. 2002). It is shown that in the AWGN case, the method can effectively cancel the impulse noise. However in the time-frequency selective channel further measures are needed. The purpose of this paper is to present an enhanced channel estimation scheme for the standard method to overcome its sensitivity to the time frequency selective channel estimates. The scheme uses the impulse free pilots to estimate the corrupted ones. Three different alternatives are discussed. Their performances in mean squared error (MSE) versus Doppler frequency are studied analytically. Bit error rate ratio (BER) simulations results are given, in the cases of SFN hilly terrain static and mobile channels. Additionally, results on simple practical impulse burst position detection method are also presented.

Subcarrier-based selection diversity reception of DVB-T in a mobile environment

Some comparative results on simple diversity combining schemes are presented to be used with orthogonal frequency division multiplexing (OFDM) systems and especially in DVB-T in multipath channels with time selective fading. A comprehensive performance evaluation of these methods is given.

On the performance of filter bank based multicarrier systems in xDSL and WLAN applications

We consider filter bank based multicarrier systems which have been considered for fast digital subscriber line applications and possibly could be interesting also for broadband wireless LAN applications. In addition to being resistant to narrowband interference, these systems provide better spectral shaping than DFT-based OFDM and DMT systems for the subchannels, as well as for the overall signal. Furthermore, they provide better efficiency because the time-domain guard interval is not needed and the guard-band in frequency domain can be reduced. The channel equalization for such systems has been an open problem, but the paper demonstrates that it can be solved, at least in principle, even though effective adaptive equalization algorithms are still under development. Another open question is the performance when nonlinearities are included in the chain, especially in the transmitter power amplifier. In the paper, it is demonstrated that the performance of filter bank based systems with nonlinear power amplifiers is only slightly worse than in the corresponding OFDM/DMT systems. When the number of channels is the same, no more than 1 dB higher input backoff is required.