Anke Schmeink

Adaptive Distributed Space-Time Coding Based on Adjustable Code Matrices for Cooperative MIMO Relaying Systems

An adaptive distributed space-time coding (DSTC) scheme is proposed for two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE) receive filters and adjustable code matrices are considered subject to a power constraint with an amplify-and-forward (AF) cooperation strategy. In the proposed adaptive DSTC scheme, an adjustable code matrix obtained by a feedback channel is employed to transform the space-time coded matrix at the relay node. The effects of the limited feedback and the feedback errors are assessed. Linear MMSE expressions are devised to compute the parameters of the adjustable code matrix and the linear receive filters. Stochastic gradient (SG) and least-squares (LS) algorithms are also developed with reduced computational complexity. An upper bound on the pairwise error probability analysis is derived and indicates the advantage of employing the adjustable code matrices at the relay nodes. An alternative optimization algorithm for the adaptive DSTC scheme is also derived in order to eliminate the need for the feedback. The algorithm provides a fully distributed scheme for the adaptive DSTC at the relay node based on the minimization of the error probability. Simulation results show that the proposed algorithms obtain significant performance gains as compared to existing DSTC schemes.

Joint Linear Receiver Design and Power Allocation Using Alternating Optimization Algorithms for Wireless Sensor Networks

In this paper, we consider a two-hop wireless sensor network (WSN) with multiple relay nodes where the amplify-and-forward (AF) scheme is employed. We present strategies to design jointly linear receivers and the power-allocation parameters via an alternating optimization approach subject to global, individual, and neighbor-based power constraints. Two design criteria are considered: The first criterion minimizes the mean-square error (MSE), and the second criterion maximizes the sum-rate (SR) of the WSN. We derive constrained minimum mean-square error (MMSE) and constrained maximum sum-rate (MSR) expressions for the linear receivers and the power-allocation parameters that contain the optimal complex amplification coefficients for each relay node. Computer simulations show good performance of our proposed methods in terms of bit error rate (BER) or SR compared with the method with equal power allocation and to a two-stage power-allocation technique. Furthermore, the methods with neighbor-based constraints bring flexibility to balance the performance against the computational complexity and the need for feedback information, which is desirable for WSNs to extend their lifetime.

Blocklength-Limited Performance of Relaying Under Quasi-Static Rayleigh Channels

In this paper, the blocklength-limited performance of a relaying system is studied, where channels are assumed to experience quasi-static Rayleigh fading while at the same time only the average channel state information (CSI) is available at the source. Both the physical-layer performance (blocklength-limited throughput) and the link-layer performance (effective capacity) of the relaying system are investigated. We propose a simple system operation by introducing a factor based on which we weight the average CSI and let the source determine the coding rate accordingly. We show that both the blocklength-limited throughput and the effective capacity are quasi-concave in the weight factor. Through numerical analysis, we investigate the relaying performance with average CSI while considering perfect CSI scenario and direct transmission as comparison schemes. We observe that relaying is more efficient than direct transmission in the finite blocklength regime. Moreover, this performance advantage of relaying under the average CSI scenario is more significant than under the perfect CSI scenario. Finally, the speed of convergence (between the blocklength-limited performance and the performance with infinite blocklengths) in relaying system is faster in comparison to the direct transmission under both the average CSI scenario and the perfect CSI scenario.

QoS-Constrained Energy Efficiency of Cooperative ARQ in Multiple DF Relay Systems

In this paper, we study the higher layer performance as well as the “throughput, delay, energy consumption” tradeoff problem for multirelay-assisted cooperative automatic repeat request (C-ARQ) protocols. We study a practical scenario where only the average channel state information (CSI) is available at the source and relays. We consider four multirelay C-ARQ protocols and derive closed-form expressions for the transmission delay distribution, the energy consumption, and the higher layer queuing performance. Furthermore, we analyze the quality of service (QoS)-constrained energy efficiency performances of the protocols. Our analysis is validated by simulations. In addition, we evaluate the system performance under these C-ARQ protocols and for different topologies. We conclude several guidelines for the design of efficient C-ARQ protocols. Finally, a simple extension of the studied C-ARQ protocols is proposed, which improves the QoS-constrained energy efficiency by 4%.

Proportional QoS adjustment for achieving feasible power allocation in CDMA systems

Resource management is the general topic of the present paper, particularly, we deal with capacity sharing for interference limited wireless networks by power control. Proportional reduction of the signal-to-interference ratio (SIR) requirements is suggested as the control mechanism to accommodate users in the case of overload. For this purpose, we carefully describe the geometrical structure and the asymptotic behavior of the set of feasible power vectors as a proportionality factor tends to its boundaries. In the case that there is no feasible power adjustment, the minimum proportional SIR reduction is determined under general power constraints. We conclude with developing a locally quadratic convergent algorithm for numerical computation of the optimum power assignment. The investigations provide both insight into the theoretical structure of optimum power allocation as well as a practical method for call admission control.

On the Capacity of Relaying With Finite Blocklength

In this paper, relaying performance is studied under the finite-blocklength regime. The overall error probability of relaying is derived. Moreover, we investigate the blocklength-limited capacity (BL-capacity) of relaying. We prove that the BL-capacity of relaying is quasiconcave in the overall error probability. Therefore, the BL-capacity has a global maximum value, which can be achieved by choosing an appropriate error probability. Through numerical investigations, we validate our analytical model and compare the performance of relaying under the finite-blocklength regime versus the Shannon capacity regime.

A robust optimisation model and cutting planes for the planning of energy-efficient wireless networks

In this paper, we present an optimisation model for the energy-efficient planning of future wireless networks. By applying robust optimisation, we extend this model to a robust formulation which considers demand uncertainties. The computability of the resulting model is moderate. Hence, we apply three different cutting plane approaches for an improvement. Furthermore, an extensive case study is performed to examine the price of robustness, to compare the robust solution to conventional planning, and to explore the performance of the cutting planes.

On fair rate adaption in interference-limited systems

A fair allocation of scarce resources is crucial in systems where multiple entities compete for the same goods. General interference-limited communication systems with rate adaption are investigated in this paper and the problem of fair resource allocation is addressed by two different approaches. First, a non game theoretic fairness approach is applied to the system model. Then bargaining theory is exploited to derive a game theoretic fairness concept. To compensate the information transmission necessary in the bargaining game, so-called incentive parameters are introduced. The solution of the thereby obtained local problem coincides with the Nash bargaining solution of the global problem if the incentive parameters are properly chosen. Numerical results show the advantage of the game theoretical modelling with respect to fairness and efficiency. Copyright

On the Performance Advantage of Relaying Under the Finite Blocklength Regime

We consider a two-phase relaying system with finite blocklengths. We study the performance difference of relaying under the finite blocklength regime as well as under the Shannon capacity regime. Most importantly, we are interested in the conditions that lead to a higher performance of relaying under the finite blocklength regime. We find that these situations are characterized by error probabilities of relaying, e.g., the overall error probability of relaying and the error probability of the bottleneck link of relaying. We identify scenarios where relaying outperforms direct transmission under the finite blocklength regime even if their performances are similar under the Shannon capacity regime. Moreover, we prove that under these scenarios the performance advantage of relaying is more significant with short blocklengths. Finally, numerical results are provided and discussed.

Alternating Optimization Algorithms for Power Adjustment and Receive Filter Design in Multihop Wireless Sensor Networks

In this paper, we consider a multihop wireless sensor network (WSN) with multiple relay nodes for each hop where the amplify-and-forward (AF) scheme is employed. We present algorithmic strategies to jointly design linear receivers and the power allocation parameters via an alternating optimization approach subject to different power constraints, which include global, local, and individual constraints. Two design criteria are considered: The first criterion minimizes the mean square error (MSE), and the second criterion maximizes the sum rate of the WSN. We derive constrained minimum mean square error (MMSE) and constrained maximum sum-rate expressions for the linear receivers and the power allocation parameters that contain the optimal complex amplification coefficients for each relay node. An analysis of the computational complexity and the convergence of the algorithms is also presented. Computer simulations show good performance of our proposed methods in terms of bit error rate (BER) and sum rate compared with the method with equal power allocation and an existing power allocation scheme.