The keyhole phenomenon, i.e., non-fully correlated but rank-deficient fading, can lead to significant performance degradations in multiple-input multiple-output (MIMO) systems and has to be carefully taken into account for system design. In this paper, we consider generalized keyhole fading including Rayleigh, Ricean, Nakagami-q, Nakagami-m, and Weibull fading. We derive simple and elegant closed-form expressions for the asymptotic pairwise error probability (PEP) of both single-antenna transmission and space-time coded transmission with two transmit antennas. The obtained PEP expressions provide significant insight into the impact of various system and channel parameters such as the types of fading at the transmitter and receiver side, the numbers of transmit and receive antennas, and the space-time code design on performance. This insight can be exploited for system design and to explain the differences in the performance of space-time codes in non-keyhole and keyhole fading channels. Furthermore, the presented asymptotic PEP expressions can be utilized to obtain tight asymptotic approximations for the bit, symbol, and frame error probabilities of arbitrary, not necessarily orthogonal, space-time codes. Simulation results confirm the accuracy and usefulness of the derived results.

The keyhole phenomenon, i.e., uncorrelated but rank-deficient fading, can lead to significant performance degradations in multiple-input multiple-output (MIMO) systems and has to be carefully taken into account for system design. In this paper, considering the practically important case of two transmit and an arbitrary number of receive antennas, we provide a simple closed-form expression for the asymptotic pairwise error probability (PEP) of space-time codes (STCs) in generalized keyhole fading channels including Rayleigh, Ricean, Nakagami-q, Nakagami-m, and Weibull fading. We show how the number of transmit and receive antennas as well as the fading parameters affect the diversity gain. The presented analysis provides new insights into STC design and can be used to obtain tight asymptotic upper bounds for the bit, symbol, and frame error probabilities of arbitrary STCs in keyhole fading.

In this paper, we introduce an adaptive Lp-norm metric for robust coherent diversity combining in non-Gaussian noise and interference. We derive a general closed-form expression for the asymptotic bit error rate (BER) for Lp-norm combining in independent non-identically distributed Ricean fading and non-Gaussian noise and interference with finite moments. Based on this asymptotic BER expression, the metric parameters can be adapted to the underlying type of noise and interference using a finite difference stochastic approximation (FDSA) algorithm. Simulation results confirm the validity of the derived asymptotic BER expression and the excellent performance of the proposed adaptive Lp-norm metric.

In this paper, we study the asymptotic behavior of the bit-error probability (BEP) and the symbol-error probability (SEP) of quadratic diversity combining schemes such as coherent maximum-ratio combining (MRC), differential equal-gain combining (EGC), and noncoherent combining (NC) in correlated Ricean fading and non-Gaussian noise, which in our definition also includes interference. We provide simple and easy-to-evaluate asymptotic BEP and SEP expressions which show that at high signal-to-noise ratios (SNRs) the performance of the considered combining schemes depends on certain moments of the noise and interference impairing the transmission. We derive general rules for calculation of these moments and we provide closed-form expressions for the moments of several practically important types of noise such as spatially dependent and spatially independent Gaussian mixture noise, correlated synchronous and asynchronous co-channel interference, and correlated Gaussian interference. From our asymptotic results we conclude that (a) the asymptotic performance loss of binary frequency-shift keying (BFSK) with NC compared to binary phase-shift keying (BPSK) with MRC is always 6 dB independent of the type of noise and the number of diversity branches, (b) the asymptotic performance loss of differential EGC compared to MRC is always 3 dB for additive white Gaussian noise but depends on the number of diversity branches and may be larger or smaller than 3 dB for other types of noise, and (c) not only fading correlation but also noise correlation negatively affects the performance of quadratic diversity combiners.

In this paper, we provide a unified framework for the asymptotic performance analysis of space-time codes (STCs) in correlated Ricean fading and non-Gaussian noise and interference. In particular, we derive simple and asymptotically tight expressions for the pairwise error probability (PEP) of coherent and differential STCs which are valid for any type of noise and interference with finite moments and detection with general Mahalonobis distance (MD) metrics including Euclidean distance (ED) and noise decorrelating (ND) metrics. These PEP expressions can be combined with truncated union bounds to obtain accurate asymptotic approximations for the bit, symbol, and frame error probabilities of STCs. We show that while the diversity gain of an STC is independent of the type of noise and the type of MD metric used, the coding gain is not and depends on certain moments of the noise and interference. We provide closed-form expressions for these moments for several practically relevant types of noise and interference. We show that for correlated noise significant performance gains can be achieved with the ND metric compared to the ED metric. While noise correlations are beneficial at high signal-to-noise ratios if they can be exploited by the metric, they are harmful if this is not the case and the simple ED metric is employed. All our analytical findings are confirmed by simulations for various popular STCs and several different types of noise and interference.

In this paper, we introduce an adaptive Lp-norm metric for robust coherent, differential, and noncoherent diversity combining in non-Gaussian noise and interference. We consider the general case where all diversity branches may use different combining weights and different Lp-norms. We derive a general closed-form expression for the asymptotic bit error rate (BER) for Lp-norm combining in independent non-identically distributed Ricean fading and non-Gaussian noise and interference with finite moments. The asymptotic BER expression reveals that the diversity gain of Lp-norm combining is independent of the type of noise and the metric parameters. In contrast, the combining gain depends on both the type of noise and the metric parameters. Thus, the asymptotic BER can be minimized by optimizing the Lp-norm metric parameters for the underlying type of noise. For this purpose finite difference stochastic approximation (FDSA) and localized random search (LRS) algorithms are developed. Both adaptive algorithms do not require any a priori knowledge about the underlying noise and are able to track changes in the noise statistics. Simulation results confirm the validity of the derived asymptotic BER expressions, the effectiveness of the proposed adaptive algorithms, and the excellent performance of the proposed adaptive Lp-norm metric compared to other popular metrics.

In this paper, we provide a framework for the asymptotic performance analysis of space-time codes (STCs) in correlated Ricean fading and non-Gaussian noise and interference. In particular, we derive a simple, asymptotically tight expression for the pairwise error probability (PEP) of coherent STCs which is valid for any type of noise and interference with finite moments. This PEP expression can be used to obtain accurate asymptotic approximations for the bit and symbol error probabilities of STCs. Our results show that while the diversity gain of an STC is independent of the type of noise, the coding gain is not and depends on certain moments of the noise and interference. We provide closed-form expressions for these moments for several practically relevant types of noise and interference. Our analytical findings are confirmed by simulations for Alamouti's ST block code and Tarokh's ST trellis code and several different types of noise and interference.

In this paper, we study the asymptotic behavior of the bit-error probability (BEP) and symbol-error probability (SEP) of differential M-ary phase-shift keying with differential equal gain combining (DEGC) in correlated Ricean fading and non-Gaussian noise, which in our definition also includes interference. We derive simple and easy-to-evaluate asymptotic BEP and SEP expressions which show that at high signal- to-noise ratios (SNRs) the performance of DEGC depends on certain moments of the noise and interference impairing the transmission. We provide closed-form expressions for these moments for practically important types of noise such as Gaussian noise, Gaussian mixture noise, and correlated co-channel interference. In addition, we show that the performance loss of DEGC compared to coherent maximum ratio combining (MRC) is always 3 dB independent of the type of noise if only one diversity branch is available but strongly depends on the type of noise if multiple diversity branches are combined.

In this paper, we study the asymptotic behavior of the bit-error probability (BEP) and symbol-error probability (SEP) of coherent maximum-ratio combining (MRC) in correlated Ricean fading and non-Gaussian noise, which in our definition also includes interference. We derive simple and easy- to-evaluate asymptotic BEP and SEP expressions which show that at high signal-to-noise ratios (SNRs) the performance of MRC depends on certain moments of the noise and interference impairing the transmission. We provide closed-form expressions for these moments for practically important types of noise such as Gaussian mixture noise, correlated co-channel interference, and correlated Gaussian interference. Interestingly, our results show that not only fading correlation but also noise correlation has an adverse effect on the asymptotic BEP and SEP.

A new time-hopping ultrawideband (TH–UWB) CDMA scheme for indoor wireless communications is presented. In the proposed method, the duration of each bit is divided into Ns1 frames, each one containing Ns2 subframes. Two pseudorandom sequences are assigned to each user. During each bit interval, based on the output of a super-orthogonal encoder and the user's first dedicated pseudorandom sequence, the transmitter selects one of the Ns1 frames and then transmits Ns2 narrow pulses in that frame, one in each of the Ns2 subframes. The location of the pulse in each subframe is determined by the user's second dedicated PN sequence. Four different detection techniques are considered at the receiver front end, namely thresholded hard decision, strict hard decision, soft decision and chip-based decision. Their performances are analysed and the results are compared with those of the previously introduced coded and uncoded TH–UWB systems. The results indicate that the proposed scheme has the best performance without requiring any extra bandwidth. It is also shown that the chip-based decoding technique works better in moderate and high SNRs while the soft decision method has better performance in low SNRs.