Sven-Gustav Häggman

Sensitivity to Doppler shift and carrier frequency errors in OFDM systems-the consequences and solutions

Due to the intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) mobile radio communication systems, the bit error rate (BER) of the received signals are extremely sensitive to Doppler frequency shifts and carrier synchronization errors. This paper studies the mechanism of the ICI signals, and then proposes a new method to overcome such problems without any equalization procedures. The results show that by using the self ICI cancellation scheme proposed, the ICI can be reduced significantly. Therefore this OFDM system suffers much less from performance degradation caused by frequency errors than the normal OFDM systems.

Wideband radio channel measurement system at 2 GHz

This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements. Implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented. Limitations and accuracy of radio channel measurements are discussed. Typically, delay resolution of about 20 ns is achieved with 100 MHz bandwidth. With a sliding correlator, a dynamic range of 25 dB was obtained with maximum Doppler bandwidth of 25 Hz and maximum excess delay of 19 /spl mu/s. Digital matched filtering with a maximum sampling rate of 125 MHz can be used in real-time measurements with Doppler shifts of several kilohertz and 30 dB dynamic range. Using matched filter deconvolution as a resolution enhancement technique is discussed. Examples of the time-variant complex impulse response measurements are given.

Effect of Mutual Coupling on Capacity of MIMO Wireless Channels in High SNR Scenario

Theoretical results on the effect of antenna mutual coupling (MC) on capacity of multiple-input multiple-output (MIMO) wireless channels are presented in this paper with particular emphasis on the case of high signal to noise ratio (SNR) scenario. Two cases are considered, 1- channel capacity variations due to MC effect on correlation properties and target average receive SNR and 2- channel capacity variations due to MC effect on correlation properties at fixed average receive SNR. It is shown that the effect of MC on MIMO channel capacity can be positive or negative depending on the propagation environment spatial correlation properties and the characteristics of the transmitter and receiver MC matrices. Conditions where MC has positive and negative effects on MIMO channel capacity in the two considered cases are identified. Numerical results for half wavelength dipole antenna supporting the theoretical observations are presented.

System aspects of smart-antenna technology in cellular wireless communications-an overview

In this paper, we surveyed the three main system aspects of smart-antenna (SA) technology in wireless communications, i.e., SA receiver, wireless network control, and planning with SAs. A classification of SA receivers and their algorithms is given in order to simplify orientation in a very large amount of structures and algorithms. We discuss system integration of SA receivers, taking into consideration expected propagation conditions, user mobility, and offered traffic. Several radio network planning and upgrading concepts associated with SAs are evaluated. We describe possible radio networks architectures when SAs are used at the mobiles, base stations, or at both ends. Radio network control functions with SAs at different layers are briefly examined. Existing experimental and commercially available SAs and their performance are surveyed.

GPRS performance estimation in GSM circuit switched services and GPRS shared resource systems

GPRS is designed for transmitting packet data and supposed to take its radio resource from the pool of channels unused by GSM voice services. The number of channels allocated to GPRS is a random variable depending on the voice traffic. In this paper, an approximation method is used for evaluating the GPRS performance of single-slot service in the variable radio resource. The method could be used for evaluating the GPRS performance when the average service time of circuit switched services is much longer than that of GPRS. The multi-slot services cause higher blocking probability and longer delay to the network than the single-slot service. However, those effects can be reduced by implementing a GPRS resource allocation scheme with flexible multi-slot services.

New aspects on nonlinear power amplifier modeling in radio communication system simulations

A new semi-physical behavioral amplifier model to characterize the AM/AM conversion of a bipolar solid-state high power amplifier in a mobile phone is introduced. The functional model is able to copy the low-voltage features of a real amplifier causing crossover distortion. Hence it gives an improved description of the nonlinearity of Class AB amplifiers widely used in mobile phones employing a linear modulation scheme. The AM/AM conversion model is accompanied by an AM/PM conversion model function to complete the amplifier model. The model is utilized in mobile communication system studies to investigate the increase of common channel and adjacent channel interference due to the nonlinear behavior of the amplifier. The new model is compared to the existing widely used functional models, and it is found to give an excellent match to the two-tone performance of a measured amplifier.

Outage Probability in GSM-GPRS Cellular Systems With and Without Frequency Hopping

General packet radio service(GPRS) is designed for transmitting packet data andis supposed to take its radio resource from the pool ofunused channels of GSM voice services. Obviously, theintroduction of GPRS has an impact on the voice services.In this paper, we present a method to calculate theoutage probability of the GSM-GPRS network for bothnon-frequency hopping and frequency hoppingsystems. This method takes into account Rayleighfading, power control (with error), discontinuoustransmission, and frequency hopping (if applied). Theoutage probability of voice services affected by theintroduction of GPRS is discussed. The number ofunused voice channels allocated to GPRS depends on thedifference between the outage level of the existingGSM network and the maximum acceptable level. Thefrequency hopping system can accommodate more GPRStraffic than the non-frequency hopping system. Thepower control error has more impact on systemperformance when more channels are allocated to GPRS.Beyond our expectations, for the non-frequency hoppingsystem, the channels provided for GPRS are not muchdifferent between high channel occupancy and lowchannel occupancy of voice services. In contrast, for thefrequency hopping system, the system can provide morechannels for GPRS at low channel occupancy. The cellservice area decreases by about 10% ∼ 20% for eachadditional channel allocated to GPRS.

IEEE 802.11b/g WLAN tolerance to jamming

In this paper, the performance of IEEE 802.11b and 802.11g wireless local area networks (WLANs) performance under barrage jamming is evaluated theoretically and using measurements. Single WLAN ad-hoc link performance is measured when receiver station is jammed. WLAN link vulnerability assessment is based on throughput and packet error rate (PER), which depends on different physical (PHY) layer characteristic. WLAN system is found to be more tolerant to narrow-band jamming than to wideband-band jamming. In 802.11b WLAN, processing gain increases the tolerance to jamming whereas coding and different modulations are used to improve the link performance in 802.11g WLAN. Measured link throughputs are far from theoretical values, especially when high data rate modes are used.

Performance of IEEE802.16-2004 Based System in Jamming Environment and its Improvement with Link Adaptation

As the first standard for WiMAX product, IEEE802.16-2004 is facing different threats in the physical layer, including radio frequency jamming. In this paper, the performance of an IEEE 802.16-2004 based system in jamming environment is evaluated by computer simulations. Two categories of jamming, multitone pilot jamming and partial-band jamming, are investigated. The results reveal that, the system exposed to multitone pilot jamming suffers greater throughput loss than the system exposed to partial-band jamming, when the same total jamming power is applied. The system tolerance to multitone pilot jamming increases with decreasing number of jammed pilots, whereas the system performance under partial-band jamming is more complicated and can be divided into three stages depending on the power level of jamming. A carrier-to-interference-noise ratio (CINR) based link adaptation algorithm is also proposed to enhance the system resistance to jamming. According to the simulations, the system performance is improved by applying the algorithm

Spatial Smoothing Effect on Kronecker Mimo Channel Model in Urban Microcells

In this paper, the effect of spatial smoothing on performance of widely used stochastic narrowband multiple-input multiple-output (MIMO) radio channel model, namely the Kronecker model, is investigated based on data measured in urban microcellular environment at 5.3 GHz carrier frequency. Results from non-line of sight (NLOS) and line of sight (LOS) traveling routes are analyzed. It is noticed that in NLOS traveling route spatial smoothing improves the accuracy of the large eigenvalues of the channel correlation matrix and significantly enhances the applicability of the Kronecker structure. Under LOS condition both the Kronecker model and its smoothed version fail to render the eigenvalues of the measured channel correlation matrix but spatial smoothing slightly improves the applicability of the Kronecker structure.