CDMA cellular systems performance with fading, shadowing, andimperfect power control

This paper addresses capacity estimation for cellular code-division multiple-access (CDMA) systems, assuming the IS-95 standard as a reference. Extending a previous analytical method (Viterbi et al., 1994), we obtain a sequence of bounds on capacity, and then we introduce an accurate approximation to reduce computation complexity. The analysis accounts for interference internal and external to the reference cell, fading, shadowing, and imperfect power control. Outage probability is expressed in terms of the characteristic functions (cf's) of the interference and imperfect power control random variables (RV's). The interference contributions are computed on the basis of a Poisson distribution for the number of users in a lognormally shadowed channel. Results are provided for different channel conditions and are validated against Monte Carlo simulations. A comparison against previously published CDMA capacity estimates is carried out, aimed at clarifying some controversial issues. It is also confirmed that large system capacity is achievable under tight power control     

Outage probability of cellular CDMA systems with space diversity,Rayleigh fading, and power control error

It is well known that the capacity of code-division multiple-access (CDMA) systems degrades rapidly with the increase in power control error. The capacity is also affected by small-scale fading such as Rayleigh fading and by the voice activity. The main contribution of this paper is to provide a new simple approximation to the outage probability of the uplink of a CDMA system utilizing an antenna array for space diversity, taking into account stochastic models of the power control error, small-scale fading, and voice activity     

Outage probability comparisons for diversity systems with cochannel interference in Rayleigh fading

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.     

Stability of mobile slotted ALOHA network with Rayleigh fading,shadowing, and near-far effect

Dynamic network behavior is investigated using the classical ALOHA queueing model extended to mobile channels. The focus is on the assessment of receiver capture probabilities, based on a general propagation model for mobile radio communications. Queueing of packets in a mobile slotted ALOHA network with Rayleigh fading, shadowing, and UHF groundwave propagation is studied, using a finite Markov chain model. It is shown that receiver capture, assisted by all three propagation mechanisms, reduces bistability of the network substantially compared to the retransmission strategy. Results are presented for a uniform spatial distribution of the packet traffic ordered to the ALOHA channel. The near-far effect is highlighted, since the total network performance and the spatial distribution of the attempted traffic interact     

Analysis of transmit-receive diversity in Rayleigh fading

We analyze the error performance of a wireless communication system employing transmit-receive diversity in Rayleigh fading. By focusing on the complex Gaussian statistics of the independent and identically distributed entries of the channel matrix, we derive a formula for the characteristic function (c.f.) of the maximum output signal-to-noise ratio. We use this c.f. to obtain a closed-form expression of the symbol error probability (SEP) for coherent binary keying. The method is easily extended to obtain the SEP for the coherent reception of M-ary modulation schemes.     

TCM with preswitching diversity in slow Rayleigh fading forwardlink

The performance of trellis-coded modulation with finite interleaver size degrades in a very slow fading channel. In this case antenna diversity is effective. In personal communication systems, however, the limited size and complexity of the handset make diversity implementation at the handset difficult. The authors propose a scheme for obtaining interleaving effects by switching base station antennas in a forward link, without additional software or hardware in a small handset. Computer simulation shows that this scheme has significant performance gain in a slow fading forward link     

Error rates of DPSK systems with MIMO EGC diversity reception over Rayleigh fading channels

This paper analyzes the average bit error probability (BEP) of the differential binary and quaternary phase-shift keying (DBPSK and DQPSK respectively) with multiple-input multiple-output (MIMO) systems employing postdetection equal gain combining (MIMO EGC) diversity reception over Rayleigh fading channels. Finite closed-form expressions for the average BEP of DBPSK and DQPSK are presented. Two approaches are introduced to analyze the error rate of DQPSK. The proposed structure for the differential phase-shift keying (DPSK) with MIMO EGC provides a reduced-complexity and low-cost receiver for MIMO systems compared to the coherent phase-shift keying system (PSK) with MIMO employing maximal ratio combining (MIMO MRC) diversity reception. Finally, a useful procedure for computing the associated Legendre functions of the second kind with half-odd-integer order and arbitrarily degree is presented.     

Power control and diversity in mobile radio cellular systems in thepresence of Ricean fading and log-normal shadowing

The performance of a cellular mobile radio system with frequency reuse is evaluated in terms of outage probability. Deterministic path loss, log-normal shadowing, and Ricean fading are accounted for, and the use of diversity and power control is considered in order to enhance system performance. Both hexagonal and lineal cells are considered. Particular attention is given to the sensitivity of the outage probability to the system parameters, especially those related to the propagation model (fading, shadowing, and path loss). It is seen that diversity and power control can improve the system behavior. The performance is sensitive to the fading parameter (i.e., the Rice factor) of the intended user, but is relatively independent of that of the interferers. Also, a significant dependence is observed on the shadowing parameter, whereas a limited dependence is seen on the outage threshold and the channel utilization. Finally, the presence of a dual path loss law degrades the performance, and the outage probability increases as the breakpoint distance gets larger     

The impact of fading correlation on the error performance of MIMO systems over Rayleigh fading channels

This paper analyzes the impact of receive fading correlation on the error performance of a multiple-input multiple-output (MIMO) system that employs a zero-forcing detection scheme over frequency-nonselective Rayleigh fading channels. Error rate expressions as a function of the eigenvalues of the fading correlation matrix and the number of transmit and receive antennas are derived. Numerical results indicate that MIMO systems are resistant to receive fading correlation.     

Probability of bit error for MPSK modulation with diversityreception in Rayleigh fading and log-normal shadowing channel

In an additive white Gaussian noise channel subject to Rayleigh fading and log-normal shadowing, consideration is given to diversity reception with K-port macroscopic selection and L-branch microscopic maximal-ratio combining, and analytical expressions are derived for upper and lower bounds on the bit error probabilities for BPSK, QPSK, 8-PSK, and 16-PSK modulations. The derived expressions can be evaluated at any location in the serving cell. Error-probability can be calculated by averaging over all possible locations within the serving cell. By evaluating these bounds, numerical results for the following cases are presented: without diversity reception, microdiversity combining, macrodiversity selection, and simultaneous use of macrodiversity selection and microdiversity combining. For symmetrical arrangement of macrodiversity ports against the lognormal shadowing, error probability at the equidistant point gives upper bounds on the error probabilities for most of the area in the serving cell. Error probability at the equidistant point is a good estimate of the error probability obtained by averaging over all possible locations in the cell     

Transmit diversity for arrays in correlated Rayleigh fading

Transmit diversity is usually presented for the case of independently faded channels. In this paper the structure of a linear transmitter that can be optimized for a Rayleigh-fading environment in which the fading may be correlated is derived. The transmitter achieves the best mix of array gain-obtained by beamforming, and diversity gain-obtained by using multiple transmit beamformers and space-time coding. The authors use a multiinput single output (MISO) transmitter and receiver structure to present a detailed performance analysis, that shows the array gain versus diversity gain tradeoff as the fading correlation changes. This analysis is validated by simulation results.     

Performance of feedback and switch space diversity 900 MHz FM mobile radio systems with Rayleigh fading

A theoretical and experimental comparison of performance has been made between two types of predetection switching space diversity mobile radio systems. This comparison was made at a frequency of 840 MHz using simulated Rayleigh fading for a vehicle speed of about 80 mi/h. The switch diversity system was a conventional receiver antenna switching technique with two simulated physically separated receiving antennas and a single transmitting antenna. The feedback diversity system used a single receiving antenna with two simulated physically separated transmitting antennas. The transmitting antennas were switched remotely from the receiver. The difference in the performance of the two systems was shown to be primarily due to time delay inherent in the remote antenna switching technique.     

Throughput analysis of a CSMA based WLAN with successive interference cancellation under Rayleigh fading and shadowing

In this paper, we consider a carrier sense multiple access based wireless local area network (WLAN) with a successive interference cancellation (SIC) technique. We develop an analytical model to compute the average throughput of a user in a WLAN with the SIC technique in presence of path loss, Rayleigh fading and log-normal shadowing. We then validate the model via simulation. By means of the developed analytical model, we compute the average throughput of a user in WLAN systems without and with the SIC technique and evaluate the throughput gain provided by the SIC technique. We find that the throughput gain provided by the SIC technique is significant. However, the throughput gain varies significantly depending on the parameters of network and wireless channel. We find that the throughput gain provided by the SIC technique increases with increasing the number of users in WLAN, medium access rate of the users and the variance in shadowing and it decreases with increasing the data transmission rate. We also investigate the effect of the decoding capability of the SIC technique on the throughput performance. We find that throughputs obtained with decoding capability of 2 and 3 packets are very close.     

Adaptive orthogonal signaling with diversity in a frequency-nonselective Rayleigh fading channel

Power and rate adaptations with diversity are considered for M-ary orthogonal signals in a frequency-nonselective Rayleigh fading channel. We derived the minimum required E~/sub b//N/sub 0/ for a given probability of error, the maximum average data rate, and the outage probability, when maximal-ratio combining is performed with an imperfect channel estimation. We analyzed the effects of channel estimation errors on the required E~/sub b//N/sub 0/ and outage probability, as a function of diversity order and adaptation methods. The relative benefits of rate and power control techniques are further presented in terms of channel estimation error, diversity order, and outage probability. The minimum required E~/sub b//N/sub 0/ with Reed-Solomon codes is also presented for comparison purposes.     

Mobile radio slotted ALOHA with capture,diversity and retransmission control in the presence of shadowing

In this paper, the capture performance of a random access scheme in the presence of Rayleigh fading, shadowing and diversity is studied. The conditional throughput C_n, i.e., the average number of packets which are correctly received per slot, given the number of colliding packets, _n, is computed, as well as its limit as _n. Some different diversity schemes are compared. Also, retransmission control is considered as a means to enhance the system performance. The stability of the controlled system is directly proved. Finally, the effect of long-term attenuations on the system performance and stability is discussed.     

Necessary and sufficient conditions for full diversity order in correlated Rayleigh fading beamforming and combining systems

Transmit beamforming and receive combining are low complexity, linear techniques that make use of the spatial diversity advantage provided by transmitters and/or receivers employing multiple antennas. There has been a growing interest in designing beamforming schemes for frequency division duplexing systems that use a limited amount of feedback from the receiver to the transmitter. This limited feedback conveys a beamforming vector chosen from a finite set known to both the transmitter and receiver. These techniques often use a set of beamforming vectors where the probability of error expression can not be easily formulated or bounded. It is of utmost importance to guarantee that the sets of beamforming and combining vectors are chosen such that full diversity order is achieved. For this reason, necessary and sufficient conditions on the sets of possible beamformers and combiners are derived that guarantee full diversity order in correlated Rayleigh fading.     

Penalty of hybrid diversity for two-dimensional signaling in Rayleigh fading

Lower and upper bound expressions for the penalty of hybrid diversity used with any two-dimensional (2-D) signaling constellation with polygonal decision regions are derived. Using these bounds with well-known results for maximal ratio combining, the error probability performance of 2-D signaling with hybrid selection/maximal ratio combining can be approximated to a high accuracy.     

Performance analysis of equalized OFDM systems in Rayleigh fading

Channel estimation is usually needed to compensate for the amplitude and phase distortions associated with a received orthogonal frequency-division multiplexing (OFDM) waveform. This paper presents a systematic approach for analyzing the bit-error probability (BEP) of equalized OFDM signals in Rayleigh fading. Closed-form expressions for BEP performance of various signal constellations [phase-shift keying (PSK), differential phase-shift keying (DPSK), quaternary phase-shift keying (QPSK)] are provided for receivers that use a linear pilot-assisted channel estimate. We also derive the optimal linear channel estimates that yield the minimum BEP and show that some previous known results are special cases of our general formulae. The results obtained here can be applied to evaluate the performance of equalized single-carrier narrowband systems as well.     

On joint power-delay double packet capture in an SSMA network withRayleigh fading, shadowing, and propagation path loss

In this paper, joint power-delay double-capture probabilities of a spread-spectrum packet network are derived. What we mean in terms of "double-capture" is that a receiver can simultaneously capture the first two incoming packets (from different transmitters) encoded by the same spreading code. The power capture model concerned takes into account multiuser interference, multipath Rayleigh fading, shadowing, and propagation path loss. To derive delay capture probability with an arbitrary arrival delay, a discrete-time approximation is applied. The method of deriving double-capture probability can also be extended to calculating multiple-packet (more than two) capture probabilities. Performance of a common-code slotted ALOHA system is evaluated with the double-capture effect and the results are compared with those of a traditional ALOHA system. It is shown that the channel impairing factors can be greatly mitigated by exploiting joint power-delay double-capture effect     

Effect of coding in digital microcellular personal communicationsystems with co-channel interference, fading, shadowing, and noise

An analytical model is developed for the performance of a microcellular radio network in the presence of cochannel interference and additive white Gaussian noise. The modulation schemes considered are binary phase-shift keyed (BPSK), binary frequency-shift keyed (BFSK), and quadrature phase-shift keyed (QPSK). The multiple-access channel is statistically modeled by one Rician-distributed desired signal and several uncorrelated Rayleigh plus log-normally shadowed interfering signals, propagating according to dual path loss law with a turning point. The performance is determined in terms of bit error rate (BER), outage probability, block error probability, crosstalk probability, and spectrum efficiency, considering both fast and slow multipath fading. The effect of error correction codes, consisting of blocks with equal number of bits, on the performance parameters is also studied. The computational results show that the propagation loss exponents, Rician factor, turning point, and cell size all plays a major role in the design of an efficient microcellular system