ABSTRACT To evaluate mobile communication systems, it is important to develop accurate and concise fading channel models. However, fading encountered in mobile communication is usually non‐stationary, and the existing methods can only model quasi‐stationary or piecewise‐stationary fading instead of general non‐stationary fading. To address this, this paper proposes an evolutionary spectrum (ES)‐based approach to modeling non‐stationary fading channels. Our ES approach is more general than the existing piecewise‐stationary models and is capable of characterizing a general non‐stationary fading channel that has an arbitrary ES (or time‐varying power spectral density); our ES approach is parsimonious and is also able to generate stationary fading processes. As an example, we show how to apply our ES approach to generating stationary and non‐stationary correlated Nakagami‐mfading channel processes. Simulation results show that the ES of the channel gain process produced by our ES‐based channel model agrees well with the user‐specified ES, indicating the accuracy of our ES‐based channel model. Copyright © 2011 John Wiley & Sons, Ltd.

Modeling of wireless channels, especially non-stationary fading channels, is important for design and performance analysis of wireless communication systems. Recently, we proposed a new approach to modeling non-stationary fading channels, based on the theory of evolutionary spectrum ES. In this paper, we develop a time-varying autoregressive AR model for a non-stationary flat fading channel; specifically, we develop a method to determine the time-varying coefficients of the AR channel model, given the ES of a non-stationary process. Furthermore, with the ES theory, we develop a trace-driven time-varying AR channel simulator to generate a non-stationary flat fading process. Simulation results show that the ES of the channel gain process produced by our joint ES-and-AR-based channel model agrees well with the user-specified ES, indicating the accuracy of our joint ES-and-AR-based channel model. Copyright © 2012 John Wiley & Sons, Ltd.

In the paper, we study the service process S(t) of an independent and identically distributed (i.i.d.) Nakagami-m fading channel, which is defined as the amount of service provided, i.e., the integral of the instantaneous channel capacity over time t. By using the Moment Generation Function (MGF) approach and the infinitely divisible law, it is proved that, other than certain generally recognized curve form or a stochastic process, the channel service process S(t) is a deterministic linear function of time t, namely, S(t)=c_m* \cdot t where c_m* is a constant determined by the fading parameter m. Furthermore, we extend it to general i.i.d. fading channels and present an explicit form of the constant service rate c_p*. The obtained work provides such a new insight on the system design of joint source/channel coding that there exists a coding scheme such that a receiver can decode with zero error probability and zero high layer queuing delay, if the transmitter maintains a constant data rate no more than c_p*. Finally, we verify our analysis through Monte Carlo simulations.

ABSTRACT The grail of next‐generation wireless networks is providing real‐time services for delay‐sensitive applications, which require that the wireless networks provide QoS guarantees. The effective capacity (EC) proposed by Wu and Negi provides a powerful tool for design of QoS provisioning mechanisms. In this paper, we intend to generalize their formula for the effective capacity of a correlated Rayleigh fading channel; specifically, we derive a closed form approximate EC formula for a special correlated Nakagami‐m fading channel, for which the inverse of the correlation coefficient matrix is tridiagonal. To verify its accuracy via simulation, we develop a Green‐matrix based approach, which allows us to analytically obtain the effective capacity (given the joint probability density function of a correlated Nakagami‐m fading channel) while being able to simulate the corresponding channel gain process. Simulation results show that our EC formula is accurate. Furthermore, to facilitate the application of the EC theory to the design of practical QoS provisioning mechanisms, we propose a simple algorithm for estimating the EC of an arbitrary correlated Nakagami‐m fading channel, given channel measurements; simulation results demonstrate the accuracy of our proposed EC estimation algorithm showing its suitability in practice. Copyright © 2011 John Wiley & Sons, Ltd.

In the paper, we consider the end-to-end routing and link scheduling problem for multi-hop wireless sensor networks. The efficient link scheduler under our consideration is intended to assign time slots to different users so as to minimize channel usage subject to constraints on data rate, delay bound, and delay bound violation probability. We also present a coupled robust multi-path routing structure satisfying the restriction of flows over fading channels based on an SINR-based interference model. Here the effective capacity (EC) model is used and then the joint routing and link scheduling can be formulated as a mixed integer optimization problem. Moreover, because the mixed integer optimization problem is NP-complete, we propose a computationally feasible EC-based Column-Generation-Algorithm (EC-CGA) to search for a sub-optimal solution. Simulation results are given to evaluate the performance of our proposed scheme.

In the paper, we study the channel service process of an independent and identically distributed (i.i.d.) Rayleigh channel. The channel service process S(t) is defined as the amount of service provided by the channel, i.e., integral of the instantaneous channel capacity over a time interval of length t. The channel side information (CSI) is assumed available at the receiver. Using the Moment Generation Function (MGF) approach and the infinitely divisible law, it is proved that the channel service process S(t) is a deterministic linear function of time t other than the generally recognized certain curve form, namely, S(t) = c* · t, where c* is a constant.

The diamond relay network is an efficient cooperative networking configuration in which the source node cooperates with two selected neighbors. For such networks, we investigate the impact of the relay positioning on the performance. In particular, considering an opportunistic protocol based on the use of relaying buffers, we provide sets of constraints which, when satisfied, give sufficient conditions for simultaneously guaranteeing network stability and throughput improvement. These results are given for both symmetric and asymmetric relay locations. In contrast to prior work dealing with the diamond relay network, we also break the strong hypothesis of no interlink interference between the source and relay transmissions. Our results provide design guidelines for relay selection by establishing areas of feasible relay locations, whilst also identifying optimal positions which lead to maximum throughput gain.

Abstract The next generation wireless networks call for quality of service (QoS) support. The effective capacity (EC) proposed by Wu and Negi provides a powerful tool for the design of QoS provisioning mechanisms. In their previous work, Wu and Negi derived a formula for effective capacity of a Rayleigh fading channel with arbitrary Doppler spectrum. However, their paper did not provide simulation results to verify the accuracy of the EC formula derived in their paper. This is due to difficulty in simulating a Rayleigh fading channel with a Doppler spectrum of continuous frequency, required by the EC formula. To address this difficulty, we develop a verification methodology based on a new discrete‐frequency EC formula; different from the EC formula developed by Wu and Negi, our new discrete‐frequency EC formula can be used in practice. Through simulation, we verify that the EC formula developed by Wu and Negi is accurate. Furthermore, to facilitate the application of the EC theory to the design of practical QoS provisioning mechanisms in wireless networks, we propose a spectral‐estimation‐based algorithm to estimate the EC function, given channel measurements; we also analyze the effect of spectral estimation error on the accuracy of EC estimation. Simulation results show that our proposed spectral‐estimation‐based EC estimation algorithm is accurate, indicating the excellent practicality of our algorithm. Copyright © 2010 John Wiley & Sons, Ltd.

Diamond relay network is a kind of efficient cooperative network, in which the source user selects two neighbors as relays and cooperates with both of them. In our previous work, we have studied its transmission rates for different coding and relaying schemes and proved that the performance of SRP scheme (Spatial Reuse Pattern) is better than others. To further improve the performance, we incorporated the opportunistic scheduling and studied how to use buffers adapted to the time varying Rayleigh fading channel. However, the position information of users has not been considered yet which actually has a great influence on the performance of the diamond relay channel. Thus, in this paper, it is the first time that we study how to select the position of two relays to guarantee the performance of the throughput and delay constraint. This study facilitates the practical application of diamond relay networks since the source user knows that from where selecting neighbors as relays will bring nice performance. Finally, the simulation results confirm our analysis and some interesting illustrations show much novelty.

Abstract The diamond relay channel, or diamond relay network, is a kind of efficient cooperative network in which the source node cooperates with two neighbors. In this paper, we study the impact on the performance of such a network caused by the relays' position for a general Nakagami‐m fading channel, which extends the previous work for a special Rayleigh fading case. In particular, the symmetric scenario for the two relays is investigated but the channel conditions of the two source‐relay‐destination links may have great difference due to the different values of m for the four Nakagami‐m fading channels. We study how to select the position of the two relays and give clear restrictions of their positions based on the requirement of the throughout improvement and network stability. Finally, we show how to find the optimal position to achieve the largest throughput improvement. The numerical results confirm our analysis and the interesting illustrations show much insight on the cooperative neighbor selections. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract Diamond relay network model, as a basic transmission model, has recently been attracting considerable attention in wireless ad hoc networks. Node cooperation and opportunistic scheduling scheme are two important techniques to improve the performance in wireless scenarios. In the paper we consider such a problem how to efficiently combine opportunistic scheduling and cooperative modes for the Rayleigh fading scenario in the diamond relay network. To do so, we first compare the throughput of SRP (Spatial Reused Pattern) and AFP (Amplify Forwarding Pattern) in the half‐duplex case with the assumption that channel side information is known to all and then come up with a new scheduling scheme. It will be verified that only switching between SRP and AFP simply does little help to obtain an expected improvement because SRP is always superior to AFP on average due to its efficient spatial reuse. To improve the throughput further, we put forward a new processing strategy in which buffers are employed at both relays in SRP mode. By efficiently utilizing the links with relatively higher gains, the throughput can be greatly improved at a cost of queuing delay. Furthermore, we shall quantitatively evaluate the queuing delay and the tradeoff between the throughput and the additional queuing delay. Finally, to realize our developed strategy and make sure it always run at stable status, we present two criteria and an algorithm on the selection and adjustment of the switching thresholds. Copyright © 2009 John Wiley & Sons, Ltd.

In this paper, we consider two fundamental problems in log-normal fading networks. One is the energy efficiency. The other is the characterization of the internode interferences and spacial reuse. We first introduce a power efficiency factor as a new parameter to measure the transmit efficiency and obtain an optimal transmit power allocation of the concurrent transmitters in such fading environment. The internode interference caused by the simultaneous transmissions within a local area is then analyzed. The analysis will also be extended to the whole network within unlimited region where the interference accumulative impact is taken into account. By doing so, we set up a direct link between the interference double disc model with the statistical accumulative interference model and derive the optimal spatial reuse distance to guarantee the network efficiency. Finally, we propose a concurrent access strategy, OCMAC (opportunistic concurrent MAC), which can efficiently mitigate the internode interference through the node coordination before the simultaneous transmissions while keeping a relatively low transmit power and high spatial reuse efficiency.