Rayleigh Channel

In this paper, the results of an on-body, line-ofsight (LOS), multiple-input, multiple-output (MIMO) channel sounding investigation are reported. Transmission takes place between on-body antennas and a uniform linear array, positioned at close range and within line-of-sight of each other. Due to the on-body location of the antennas, the influence of actual radio channel can no longer be separated from the effects of user behaviour and body proximity. This paper therefore argues that the composite channel must be considered. Post-processing of the recorded channels shows that their capacities outperform those from equivalent Rayleigh channels. Taking into account the clear LOS in the experiment, this appears counter-intuitive to the well-known fact that uncorrelated scattering results in high capacity. An analysis of the results highlights some less familiar facts and leads to an overview of capacity generating mechanisms in MIMO systems. The paper adds an analysis of the sensitivity of the capacity to the properties of the channel matrix, which is used for a discussion of the practical use of MIMO in personal and body area networks.

We consider discrete-time all-analog-processing joint sourcechannel coding, using non-linear spiral-like curves. We assume a Rayleigh channel, where the receiver may employ or not multiple antennas. Maximum Likelihood (ML) and Minimum Mean Square Error (MMSE) detection are considered. Our results show that MMSE performs much better than ML in high CSNR in single-antenna wireless systems, while diversity combining is able to significantly reduce such performance gap, therefore making the low complexity ML decoding very attractive in the case of multiple receive antennas.

A low-complexity high performance Rayleigh fading simulator and its Field Programmable Gate Array (FPGA) implementation are presented. This proposed method is a variant of the method of filtering of the white Gaussian noise where the filter design is accomplished in the analog domain and transferred into digital domain. The proposed method outperforms AR(20) filter and modified Jakes' generators in performance. Although IDFT method achieves the best performance, it brings a significant cost in storage. The proposed method achieves high performance with the lowest complexity, and its performance has been verified on commercially available FPGA platforms.

In this paper, we provide an exact closed-form expression of the effective signal-to-noise ratio (SNR) for orthogonal frequency division multiplexing (OFDM) performance under the combined effect of the phase noise, frequency offset, and amplifier nonlinearities of the soft envelope limiter (SEL). A simplified approximate expression is also obtained for the effective SNR under certain conditions. This formula describes explicitly the various parameters with the system performance. After deriving the effective SNR, we evaluate the bit-error-rate (BER) for slowly fading Rayleigh channel for QPSK and 16-QAM modulation formats. We also obtain the minimum total degradation (TD) versus phase noise rate for different values of frequency offset rate as a criterion of performance evaluation. We show that the degradation is increased as the phase noise levels and frequency offset levels are increased. For 16-QAM modulation format, we have obtained even worse results compared with QPSK modulation format.

In this paper, we provide an exact closed-form expression of the effective signal-to-noise ratio (SNR) for orthogonal frequency division multiplexing (OFDM) performance under the combined effect of the phase noise, frequency offset, and amplifier nonlinearities of the soft envelope limiter (SEL). A simplified approximate expression is also obtained for the effective SNR under certain conditions. This formula describes explicitly the various parameters with the system performance. After deriving the effective SNR, we evaluate the bit-error-rate (BER) for slowly fading Rayleigh channel for QPSK and 16-QAM modulation formats. We also obtain the minimum total degradation (TD) versus phase noise rate for different values of frequency offset rate as a criterion of performance evaluation. We show that the degradation is increased as the phase noise levels and frequency offset levels are increased. For 16-QAM modulation format, we have obtained even worse results compared with QPSK modulation format.

Due to the time-varying nature of the wireless channel and presence of limited resources for the signal transmission, which faces various detrimental effects such as path-loss, delay spread, Doppler spread, shadowing and interference make it very difficult to achieve sufficient data rates. To combat the effect of multi-path fading in the wireless communication system, the diversity combining mechanism has been introduced. In this paper, we have developed an algorithm for the performance evaluation of various spatial diversity combing techniques by using Matlab simulation. The developed new algorithm combine all three diversity techniques such as maximal ratio combining (MRC), selection combining (SC) and equal gain combing (EGC) techniques The combined diversity techniques algorithm computes and compares the MRC, SC, and EGC combing techniques theoretically by using the Matlab simulation.

In this paper, the performances of a multicarrier modulation (COFDM) system in an urban mobile radio channel is analyzed using a computer-aided analysis tool called SPW. This multicarrier modulation system, with convolutional coding and interleaving, provides an extremely bandwidth efficient and multipath resistant transmission method. COFDM gives a remarkable performance in selective Rayleigh channels at a much higher bit rate than conventional systems.

We derive closed-form expressions for the ergodic capacity and symbol error rate (SER) of MIMO beamforming with maximum ratio combining (MRC) receivers in uncorrelated and semi-correlated Rayleigh channels. Our results are exact, finite expressions, applying for arbitrary numbers of antennas, and all SNRs. Based on the analytical results, we examine the effect of spatial correlation on the capacity and SER.

A Channel estimation technique has been proposed with the least square (LS) based on comb-type pilots for orthogonal frequency division multiplexing (OFDM). An interpolator should be used to obtain the channel information between adjacent pilots for a comb-type pattern. However, an interpolation method causes additional errors due to the interpolation properties of not detecting long delayed paths and generating fictitious paths. OFDM has its strength in realistic possibility of constructing the single frequency network (SFN). However, synchronization and channel estimation errors are revealed by multi-path fading with long delayed paths in SFN channels. We propose a robust channel estimator overcoming the adverse effects of long delayed signals in SFNs. A new channel estimator is proposed with the interpolated LS by applying phase shifted samples in the frequency-domain. In particular, the proposed channel estimator is more robust to the single frequency network (SFN) whenever the delay spread is less than the cyclic prefix length. For a Rayleigh channel, the proposed estimator has an almost 3 dB gain comparing to conventional estimator. 1

A two-way relaying (TWR) system is analyzed, where two source terminals with unequal numbers of antennas exchange data via an amplify-and-forward relay terminal with a single antenna. In the system considered herein, the link quality between the sources and relay can generally be asymmetric due to the nonidentical antenna configuration, power allocation, and relay location. In such a general setup, accurate bounds on the average sum rate (ASR) are derived when beamforming or orthogonal space time block coding is employed at the sources. We show that the proposed bounds are almost indistinguishable from the exact ASR under various system configurations. It is also observed that the ASR performance of the TWR system with unequal numbers of source antennas is more sensitive to the relay location than to the power allocation.

A noncoherent, bandwidth-efficient modulation scheme is proposed for frequency-hopping multiple-access (FH-MA) networks. The proposed scheme is a combination of noncoherent-ary amplitude-shift keying (NMASK) and orthogonal frequency-division multiplexing (OFDM). Using this scheme will minimize the required data bandwidth. The number of frequency slots available to the users will increase significantly for a fixed spread-spectrum bandwidth (BW 55). The effect of the multiple-access interference will be reduced. Simple and accurate bit error rate expressions have been derived for FH-OFDM-MASK in additive white Gaussian noise channels and for FH-OFDM-ASK in Rayleigh fading channels.

A noncoherent, bandwidth-efficient modulation scheme is proposed for frequency-hopping multiple-access (FH-MA) networks. The proposed scheme is a combination of noncoherent-ary amplitude-shift keying (NMASK) and orthogonal frequency-division multiplexing (OFDM). Using this scheme will minimize the required data bandwidth. The number of frequency slots available to the users will increase significantly for a fixed spread-spectrum bandwidth (BW 55). The effect of the multiple-access interference will be reduced. Simple and accurate bit error rate expressions have been derived for FH-OFDM-MASK in additive white Gaussian noise channels and for FH-OFDM-ASK in Rayleigh fading channels.

Bit error rate (BER) analysis of orthogonal frequency division multiplexing (OFDM) systems over frequency-selective Nakagami-fading channels is considered in this work. The provided analyses are applicable for multipath channels with any number of taps and the Nakagami-fading parameter can be finite or infinite. The results obtained demonstrate that the Gaussian approximation (GA) can be inaccurate if the number of channel taps is less than five. The analytical results confirmed by simulation demonstrated that the probability distribution functions for infinite fading parameter are substantially different from those where is finite. It was also found that the effect of depends on the number of multipath components . For even values of , increasing decreases the BER while the opposite happens for odd values. Therefore, the worst case scenario for even values occurs for = 1, while for odd values it occurs for = , i.e., the amplitudes of the multipath components are constants and equal.

Multicarrier code-division multiple access (MC-CDMA) combines multicarrier transmission with direct sequence spread spectrum. Recently, different approaches have been adopted which do not assume a perfectly known channel. In this paper, we examine the forward-link performance of decision-directed adaptive detection schemes, with and without explicit channel estimation, for MC-CDMA systems operating in fast fading channels. We analyze theoretically the impact of channel estimation errors by first considering a simpler system employing a threshold orthogonality restoring combining (TORC) detector with a Kalman channel estimator. We show that the performance deteriorates significantly as the channel fading rate increases and that the fading rate affects the selection of system parameters. We examine the performance of more realistic schemes based on the minimum mean square error (MMSE) criterion using least mean square (LMS) and recursive least square (RLS) adaptation. We present a discussion which compares the decision-directed and pilot-aided approaches and explores the tradeoffs between channel estimation overhead and performance. We find that there is a fading rate range where each method provides a good tradeoff between performance and overhead. We conclude that the MMSE per carrier decision-directed detector with RLS estimation combines good performance in low to moderate fading rates, robustness in parameter variations, and relatively low complexity and overhead. For higher fading rates, however, only pilot-symbol-aided detectors are appropriate.

This paper extends a recently proposed space-time model for Rayleigh fading to include an arbitrary transmit antenna configuration of any shape and size transmitting simultaneously in a multiple-input multiple-output (MIMO) channel. The space-time correlation function and space-frequency cross spectrum function for a non-isotropic scatterer distribution around the receiver is derived for the arbitrary configuration as a further extension of a previous result of a multiple-input single-output Rayleigh wireless channel which used a ring of uniformly distributed scatterers model. Analysis based on achievable spectral efficiency for typical arbitrary transmit antenna configurations is given. The analysis demonstrates the utility of the correlation function.

A low-complexity high performance Rayleigh fading simulator and its Field Programmable Gate Array (FPGA) implementation are presented. This proposed method is a variant of the method of filtering of the white Gaussian noise where the filter design is accomplished in the analog domain and transferred into digital domain. The proposed method outperforms AR(20) filter and modified Jakes' generators in performance. Although IDFT method achieves the best performance, it brings a significant cost in storage. The proposed method achieves high performance with the lowest complexity, and its performance has been verified on commercially available FPGA platforms.

Space diversity is an effective method to combat fading and cochannel interference (CCI) in wireless systems. In this paper, outage performances of several diversity schemes, including a practical variation of maximal-ratio combining that does not require signal-to-noise ratios at different antennas, equal-gain combining, and selection combining, are compared analytically for an interference-limited environment in a Rayleigh fading channel. Our analysis provides insight into the performance of diversity schemes in the presence of CCI as well as assesses the impact of cochannel interferer power distributions.

In this paper, the principles of a MIMO system are analyzed, in addition to how it can be used with OFDM modulation to obtain both frequency and space diversity in a terrestrial multipath Rayleigh channel. Toward this aim, an Alamouti encoder and decoder are employed, in conjunction with QPSK and 16QAM modulation schemes. From the simulation results, it is observed that MIMO, with two transmit and two receive antennas using OFDM and 16QAM, performs well in terms of received BER.