Outage probability analysis for microcell mobile radio systems with cochannel interferers in Rician/Rayleigh fading environment

A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied. This model is named a Rician/Rayleigh fading environment. Expressions of outage probabilities are presented for the mobile radio system in the Rician/Rayleigh fading environment.<>     

BPSK system with sounder to combat Rayleigh fading in mobile radio communication

A simple method is proposed to remove random FM from a fast Rayleigh faded binary phase shift keying (BPSK) signal and the great improved performance of reducing the irreducible error is presented. In the mobile radio environment, there happens inevitably a fast Rayleigh fading which causes random FM. The phase error of the reference signal due to random FM will degrade the bit error rate (BER) performance, even if the signal-to-noise ratio is sufficiently high. In the realization of reliable mobile communication, removal of this random FM is an unavoidable theme. Proposed strategy is to transmit a sounding continuous wave (CW) together with a BPSK signal, each phase being kept orthogonal and each power being kept the same. This CW wave is also used as the reference signal in coherent reception. The BER performance of this system is worse by 3 dB than that of the coherent BPSK in a slow Rayleigh fading environment.     

Direct sequence CDMA power control, interleaving, and coding

The authors develop and analyze models of power control that consider other aspects of code-division multiple access (CDMA) systems, such as interleaving and coding on the land mobile radio channel. The orientation is that a power control scheme keeps the received powers at the base station almost equal, and the performance degradation incurred if the powers are not exactly equal will be quantified. In doing so, the authors consider the performance implications of control latency and a maximum speech delay constraint. Because of positive correlations between the fading channel amplitudes, the effectiveness of the combination of interleaving and coding in combating the effects of power variations due to slow Rayleigh fading is reduced. It is shown that power control and interleaving/coding are most effective in complementary parameter regions, thus providing a degree of robustness for both fast and slow Rayleigh fading     

Performance of generalized selection combining for mobile radiocommunications with mixed cochannel interferers

The performance of generalized selection combining (GSC) space diversity for mobile radio systems in the presence of multiple cochannel interferers is studied. Two cochannel interference models are considered: (1) L cochannel interferers consisting of L-N Nakagami-m (1960) interferers and N Rayleigh interferers and (2) L cochannel interferers in which each interferer follows Nakagami-m distribution for a fraction of time and Rayleigh distribution for the remaining of time. The fading parameters of the Nakagami-m interferers are limited to integer values only. The desired signal is assumed to be Rayleigh faded. Also, all the desired signals and the cochannel interferers received on each branch are independent of each other. Closed-form expressions are derived for the probability density functions (PDFs) of the instantaneous signal-to-interference power ratio (SIR) at the output of the GSC for the two cochannel interference models. Using these SIR PDFs, closed-form expression for evaluating the outage probability and the average bit error probability (BEP) are subsequently derived. A differential phase-shift keying scheme is considered in the derivation. Numerical results showing the influences of various system parameters on the outage probability and the average BEP are then presented     

Transactions Letters - Outage Capacity and Optimal Power Allocation for Multiple Time-Scale Parallel Fading Channels

In this paper, we address the optimal power allocation problem for minimizing capacity outage probability in multiple time-scale parallel fading channels. Extending ideas from the work of Dey and Evans (2005), we derive the optimal power allocation scheme for parallel fading channels with fast Rayleigh fading, as a function of the slow fading gains. Numerical results are presented to demonstrate the outage performance of this scheme for lognormal slow fading on two parallel channels.     

Validation of an improved location-based handover algorithm using GSM measurement data

When a mobile station moves, the path loss and shadow fading contribute to the large-scale variation in the received signal strength. The variation of signal strength caused by shadow fadings is a random process, and handover decision mechanisms based on measurements of signal strength induce the "ping-pong effect." This paper proposes an improved handover algorithm, based on the estimates of location and velocity of the mobile station, to suppress the ping-pong effect in cellular systems. A practical approach based on GSM measurement data is used to estimate the location and velocity of mobile station to identify the correlation among shadowing components. The impact of location errors on handover performance was examined, and the proposed handover algorithm was applied to a real GSM system in urban Taipei city. The results indicate that the number of unnecessary handover can be reduced 18-26 percent by the proposed approach compared to the conventional method, while the signal outage probability remains similar. Besides, the computational complexity of the proposed algorithm is low, and the algorithm does not use a database or lookup table.     

Outage rates and outage durations of opportunistic relaying systems

Opportunistic relaying is a simple yet efficient cooperation scheme that achieves full diversity and preserves the spectral efficiency among the spatially distributed stations. However, the stations? mobility causes temporal correlation of the system?s capacity outage events, which gives rise to its important second-order outage statistical parameters, such as the average outage rate (AOR) and the average outage duration (AOD). This letter presents exact analytical expressions for the AOR and the AOD of an opportunistic relaying system, which employs a mobile source and a mobile destination (without a direct path), and an arbitrary number of (fixed-gain amplify-and-forward or decodeand- forward) mobile relays in Rayleigh fading environment.     

DS/CDMAM-ary orthogonal signalling in a shadowed Rayleigh channel for mobile communications

In this paper a modified RAKE receiver is studied for a frequency selective mobile radio channel. The reverse link (Mobile to base station) is analysed, assuming lognormal shadowing and Rayleigh fading andK asynchronous users, withM orthogonal sequences per user. The analysis is based on the consideration of the quadrature components of the signal and noise, taking advantage of the multipath effects. The performance evaluation is carried out in terms of both the bit error rate and outage probability in order to qualify completely the proposed receiver. The positive results assure the possibility of applying this system in a microcellular mobile radio environment.     

Exact outage probability for equal gain combining with cochannel interference in Rayleigh fading

Equal gain combining (EGC) diversity has performance close to that of maximal ratio combining but at lower implementation complexity. We present a new outage performance analysis for EGC in mobile cellular radio systems that are limited by cochannel interference and undergo Rayleigh fading. We utilize a new model where interfering signals add in amplitude and phase across antenna array elements. In addition, the interfering signals may each have a different power. In comparing our analysis to an existing method, we find that: 1) as much as 1.5 dB difference in signal-to-interference ratio may exist at the same probability of outage; 2) the existing method can lead to overly optimistic outage performance prediction in certain situations.     

Outage Probability Analysis of Dual-Hop Decode-and-Forward Relaying Over Mixed Rayleigh and Generalized Gamma Fading Channels

In this letter, outage probability of dual-hop decode-and-forward (DF) relaying scheme is analyzed over mixed Rayleigh and generalized Gamma fading channels. Cooperation model considered in this work consists of a source, a relay and a destination. It is assumed that source-relay and relay-destination channels experience Rayleigh fading and generalized Gamma fading, respectively. Exact outage probability expression is derived and outage performance is illustrated for both direct transmission and DF relaying scheme.     

Computing the outage probability in mobile radio networks using thesampling theorem

This article provides a novel, efficient numerical solution to evaluate the moment generating function of a Suzuki probability density function using the sampling theorem. Applications include outage probability calculations for mobile radio networks in Rayleigh fading and shadowing     

Optimal power control in interference-limited fading wirelesschannels with outage-probability specifications

We propose a new method of power control for interference-limited wireless networks with Rayleigh fading of both the desired and interference signals. Our method explicitly takes into account the statistical variation of both the received signal and interference power and optimally allocates power subject to constraints on the probability of fading induced outage for each transmitter/receiver pair. We establish several results for this type of problem. We establish tight bounds that relate the outage probability caused by channel fading to the signal-to-interference margin calculated when the statistical variation of the signal and interference powers is ignored. This allows us to show that well-known methods for allocating power, based on Perron-Frobenius eigenvalue theory, can be used to determine power allocations that are provably close to achieving optimal (i.e., minimal) outage probability. We show that the problems of minimizing the transmitter power subject to constraints on outage probability and minimizing outage probability subject to power constraints can be posed as a geometric program (GP). A GP is a special type of optimization problem that can be transformed to a nonlinear convex optimization problem by a change of variables and therefore solved globally and efficiently by interior-point methods. We also give a fast iterative method for finding the optimal power allocation to minimize the outage probability     

Joint Impact of Co-Channel Interference and Channel Estimation Error on Outage Performance of Cellular Two-Way Relay Networks

This paper investigates the joint impact of co-channel interference and channel estimation error (CEE) on the performance of cellular multiuser two-way relay network, wherein a multi-antenna base station communicates with one of the several single-antenna mobile stations via a single-antenna relay. Specifically, we derive a tight lower bound closed-form expression for the overall outage probability under Rayleigh fading channels. We also evaluate an asymptotic outage expression in the high signal-to-noise ratio regime. Based on the asymptotic analysis, we study some practical cases of interest under both interference-limited and interference-free scenarios with CEE, from which various insights into the system diversity order are presented. Numerical and simulation results corroborate our theoretical findings.     

A framework for analyzing the user membership in cellular CDMAnetworks

A theoretical framework is developed to analyze the user membership in cellular networks. The main interest is on code-division multiple-access (CDMA) networks, although the validity of the proposed approach is not restricted to these networks. The membership of a user terminal to a certain base station (BS) is established if the local mean attenuation to this BS is the lowest one among all surrounding BSs. The estimate of local mean attenuation on the radio links from a mobile terminal to each of the surrounding BSs is carried out through proper filtering of the sequences of received signal strength measurements taken on broadcast signals at regular time intervals. In CDMA networks, pilot channels can be considered, while broadcast control channels can be generically considered in narrow-band systems. A decision is made each time on whether the terminal is to be assigned to its “current” BS or if it would be better served by a different BS. Two performance measures are considered: the probability that the best BS is not selected and the average number of membership switchings per time unit. A channel model with log-normal shadowing and fast fading superimposed is considered. Analytical expressions for the above-mentioned performance measures are derived in a general system scenario. From numerical results, it is seen that a proper choice of filter parameters is required to achieve the lowest values for both performance measures. Moreover, these values are not negligible when the mobile terminal is close to a boundary cell region. The obtained results are considered to be of interest in handover and power control algorithms     

Outage probability for lognormal-shadowed Rician channels

A new general outage probability expression for a Rician signal received among L Rician interferers is derived. This result is shown to cover previous published expressions involving Rayleigh signal/interferers as special cases. A new method is then applied to further extend the result to include the effect of lognormal shadowing on the outage probability (for microcellular mobile radio systems in Rician/Rician fading environments). New Rician/Rician outage probability curves against the normalized reuse distance and cluster size with and without lognormal shadowing effect are presented and discussed     

The ALOHA systems in shadowed mobile radio channels with slow orfast fading

The influence of receiver capture on the performance of the ALOHA protocol in the presence of shadowing is investigated. The combined effect of Rayleigh fading, log-normal shadowing, and spatial distribution of mobile users is also studied. It is shown that shadowing is similar to fading and near/far phenomena, in that it makes the capture effect possible and provides ALOHA systems with substantial improvements in throughput. It is also confirmed that the superimposed Rayleigh fading, log-normal shadowing, and spatial distribution can further enhance the capture effect, resulting in a ALOHA system with higher throughput. The fast fading effect in ALOHA systems is explored. A very fast fading case is examined which may be considered to be equivalent to interleaving in slow fading. It is found that an ALOHA system under fast fading conditions also benefits from the capture results in higher throughput     

Performance analysis of cellular mobile systems with successive co-channel interference cancellation

This paper presents an analytical framework for the performance evaluation of cellular mobile radio systems equipped with smart antenna systems. In particular, the paper focuses on low-complexity systems which are able to successively suppress the strongest active interferers. The desired user fading statistics is assumed to be flat Rayleigh, Rician, or Nakagami, whereas the interfering signals are assumed to be independent and subject to slow flat Rayleigh fading. The paper starts by presenting generic closed-form expressions for the the carrier-to-interference ratio probability density function after interference cancellation. Based on that, exact closed-form expressions for the outage probability and average error rate formulas are derived. Finally, a comparison with a practical cancellation scheme and the impact of some practical considerations on the performance of successive interference cancellation are investigated. More specifically, the effect of traffic loading, the overall spectral efficiency gain, and the impact of time delay are studied.     

Two-relay distributed switch and stay combining

We study a distributed version of switch-and-stay combining (DSSC) for systems that utilize two relays. In particular, four different scenarios are considered, depending on a) whether or not the source-destination channel is taken into account, and b) the type of relaying, i.e., decode and forward or amplify and forward. A performance analysis in terms of outage and bit error probability is presented, when operating over Rayleigh fading channels. Numerical results demonstrate that two-relay DSSC achieves the same diversity gain and outage performance as if the best relay is selected for each transmission slot, albeit simpler.     

Performance analysis of microcellular mobile radio systems with shadowed cochannel interferers

A study is presented of microcellular mobile radio systems where the desired signal has Rician statistics and cochannel interferers experience lognormal shadowing as well as Rayleigh fading. This implies a Rician/Rayleigh-plus-lognormal microcell interference model. The probability density function of the signal-to-interference ratio is derived and used to evaluate the performance of microcellular systems in terms of the outage probability.<>     

A Relay-Assisted Handover Technique with Network Coding over Multihop Cellular Networks

A relay-assisted handover technique exploiting network coding for multihop cellular networks is described. In the scheme, each MS (mobile station) in the outer region receives data related to the home cell from the home BS (base station) as well as a coded version of data related to a neighboring BS from a relay node located in the cell boundary via the use of network coding. Thus, MSs can achieve more reliable macro diversity with the assistance of the relay-based handover technique. In a simulation, it is demonstrated that this technique is very effective in maintaining QoS (quality of service) in terms of outage probability over a multi-cell environment