Despite the fact that time-division multiplexed switching (TDMS) based multiple-input multiple-output (MIMO) wireless channel sounders are cost effective implementation techniques, they may result in significant measurement errors due to phase noise (PN) in the local oscillators. In this paper the impact of PN on the accuracy of measured MIMO channel capacity is studied by considering its effect on both the spatial multiplexing gain and on the power gain. We show that in case of a low rank physical channel matrix the PN impact is more pronounced on the spatial multiplexing gain than on the power gain. Based on that we propose an eigenvalue filtering (EVF) technique to improve the accuracy of measured channel capacity. Numerical results supporting our theoretical observations are presented.

In this paper, the performance of the widely used stochastic Kronecker multiple-input multiple-output (MIMO) radio channel model is investigated based on non-line of sight (NLOS) measured data in urban microcellular environment at 5.3 GHz carrier frequency. The channel transfer matrices rendered by the Kronecker model are compared to the measured ones in terms of the distribution of the channel coefficients and the distribution of the eigenvalues of the channel correlation matrix. Furthermore, the channel capacity and the symbol error rate performance achievable over the measured and modeled channels are also compared. Good agreement in terms of symbol error rate performance is found while 4.16% error in the median channel capacity at 20 dB signal to noise ratio (SNR) is observed

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 correlation properties of MIMO channel highly depend on the propagation environment and the antenna array geometry. In this paper the impact of different antenna array geometries on MIMO channel eigenvalues is investigated in realistic microcellular propagation environment under different scenarios. Four different antenna array geometries are considered, namely, uniform linear array, uniform circular array, uniform rectangular array and uniform cubic array. All the considered geometries have same number of elements and fixed inter-element spacing. The uniform linear array geometry shows superiority to the other considered geometries.

In this paper, we present an algorithm for the nonlinear equalisation in OFDM transmission systems. We suggest to apply a disjoint iterative method for the linear multipath channel estimation and the nonlinearly distorted transmitted data recovery. A simple technique is proposed for the channel re-estimation on the basis of the recovered transmitted data. For the nonlinear noise cancellation, we use a procedure of the nonlinear noise estimation at the receiver. The presented simulation results confirm the efficiency of the proposed algorithm.

For orthogonal frequency-division multiplexing (OFDM) communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in intercarrier interference (ICI). This paper studies an efficient ICI cancellation method termed ICI self-cancellation scheme. The scheme works in two very simple steps. At the transmitter side, one data symbol is modulated onto a group of adjacent subcarriers with a group of weighting coefficients. The weighting coefficients are designed so that the ICI caused by the channel frequency errors can be minimized. At the receiver side, by linearly combining the received signals on these subcarriers with proposed coefficients, the residual ICI contained in the received signals can then be further reduced. The carrier-to-interference power ratio (CIR) can be increased by 15 and 30 dB when the group size is two or three, respectively, for a channel with a constant frequency offset. Although the redundant modulation causes a reduction in bandwidth efficiency, it can be compensated, for example, by using larger signal alphabet sizes. Simulations show that OFDM systems using the proposed ICI self-cancellation scheme perform much better than standard systems while having the same bandwidth efficiency in multipath mobile radio channels with large Doppler frequencies.

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.

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.

We have shown previously that matched filter deconvolution (MFD) is a powerful inverse filtering technique for increasing time resolution in direct-sequence (DS) type radio channel sounding. A drawback of the technique anyhow is an SNR floor that is caused by deconvolution noise (DN). The DN is correlative with the channel impulse response (IR) and can appear also in noiseless channels. We suggest that the reason for the DN is in spectral zeros of the sounding code. The concept is studied by deriving an approximation for the MFD IR. We observe that the accuracy of this expression is proportional to the deconvolution constant. Based on this scenario we then suggest a spectral interpolation technique for compensation of the DN. We simulate its performance as the function of uniformly distributed delay and Gaussian amplitude components (UDDGAC) channel tap number and post channel SNR and record the respective instantaneous radio channel impulse response estimate (IRCIRE) SNR. Our simulations indicate that the higher the channel tap number is, the higher degree curve fit should be applied to replace the missing frequency domain data. For example we note that the fifth degree polynomial fit can yield IRCIRE SNR improvement varying between 4 dB to 11 dB in a line-of-sight (LOS) channel having 9 to 1 in average 20 dB smaller UDDGAC taps respectively. If the degree of the spectral fit is smaller than what is required by the actual channel taps, we note that the spectral interpolation can potentially deteriorate the MFD performance.