Peter von Wrycza

Spectrum allocation for decentralized transmission strategies: properties of Nash equilibria

The interaction of two transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum is analyzed from a game theoretic perspective. Each pair utilizes a decentralized iterative water-filling scheme to greedily maximize the individual rate. We study the dynamics of such a game and find properties of the resulting Nash equilibria. The region of achievable operating points is characterized for both low- and high-interference systems, and the dependence on the various system parameters is explicitly shown. We derive the region of possible signal space partitioning for the iterative water-filling scheme and show how the individual utility functions can be modified to alter its range. Utilizing global system knowledge, we design a modified game encouraging better operating points in terms of sum rate compared to those obtained using the iterative water-filling algorithm and show how such a game can be imitated in a decentralized noncooperative setting. Although we restrict the analysis to a two player game, analogous concepts can be used to design decentralized algorithms for scenarios with more players. The performance of the modified decentralized game is evaluated and compared to the iterative water-filling algorithm by numerical simulations.

On Convergence Properties of Joint Optimal Power Control and Transmit-Receive Beamforming in Multi-User MIMO Systems

We consider SDMA in a multi-user downlink MIMO system with several access points, each serving one or more users. The problem of minimizing the total transmitted power satisfying the SINR requirements at all users is considered. This is a non-linear and non-convex optimization problem with three sets of variables: the transmitter powers, the transmitter weights and the receiver weights. Global system knowledge will be assumed at the access points and the provided results can be seen as benchmarks in system performance. We present a new initialization strategy and investigate its convergence behavior for a proposed algorithm. A numerical study is performed to analyze the dependence of the target SINRs on the optimal solution. The performance of this initialization process is evaluated and compared to an existing beamforming algorithm

MMSE Criteria for Downlink Beamforming in CDMA Wireless Systems

In wireless systems with multiple antennas at the access points, the downlink power has to be spatially optimized to allow several simultaneous users. We consider two different MMSE criteria for a multi-user downlink CDMA system and determine the optimal transmit beamforming weights. The MMSE criteria with and without receiver gain control are compared for a system where the transmitter is equipped with an antenna array and the receivers have single antennas. The MMSE and SINR versus different number of users is shown and the effect of including the gain control in the MMSE criteria is clearly demonstrated

5G systems: The mmMAGIC project perspective on use cases and challenges between 6–100 GHz

mmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is an EU funded 5G-PPP project, whose overall objective is to design and pre-develop a mobile radio access technology (RAT) operating in the 6–100 GHz range, capable of impacting standards and other relevant fora. The focus of the project is on extreme Mobile Broadband, which is expected to drive the 5G requirements for massive increase in capacity and data-rates. This paper elaborates on some 5G key research areas such as: identification of the most compelling use-cases and Key Performance Indicators (KPIs) for future 5G systems, advantages and challenges of millimeter-wave (mmWave) technologies, channel measurements and channel modeling, network architecture; and the design of a new mobile radio interface including multi-node and multi-antenna transceiver architecture.

A Game Theoretic Approach to Multi-User Spectrum Allocation

We consider the interaction of several transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum. Using a game theoretic framework, each pair is regarded as a player whose payoff function is the individual link rate and power is allocated using the iterative water-filling algorithm. We find properties of the resulting Nash equilibria and derive conditions for when various operating points are achievable. The analysis presented herein extends previous work by characterizing the set of stable solutions for a multi-user system. Also, we show how the game can be modified to obtain better operating points in terms of sum rate compared to the iterative water-filling algorithm. The increase in performance corresponding to one such modification is evaluated and compared to the iterative water-filling algorithm by numerical simulations.

Convergence of the iterativewater-filling algorithm with sequential updates in spectrum sharing scenarios

Spectrum sharing between two independent, co-existing transmit-receive pairs (TRPs) is formulated as a non-cooperative game with the TRPs as players, their individual link rates as payoffs and power allocation over the utilized spectral bands as the strategy. A Nash Equilibrium (NE) corresponds to the outcome of such a game and TRPs iteratively use the water-filling algorithm according to an agreed order for achieving the NE. Dynamics of this distributed algorithm is studied to determine the conditions for convergence and characterize the resulting NE. A sufficient condition on global convergence is derived and is shown to be tighter than existing ones. Further, a novel characterization of the globally achievable NE based on necessary conditions is presented. Some of these results are also extended to multiple NE scenarios where local convergence is exhibited.

From 3G to 4G: background and motivation of 3G evolution

This introductory chapter provides an overview of the research and standardization background behind today’s HSPA technologies. A review of WCDMA development and standardization is provided in order for the reader to understand the framework upon which the 3G specifications have been built. This is followed by an insight into the workings of the standardization organizations that relate to WCDMA and HSPA, in particular 3GPP and ITU. The motivations and constraints behind the continuing evolution of HSPA are reviewed. This provides the reader with a framework with which to understand the drivers and processes behind the evolution features described in Part III of the book. In addition, a brief insight into the spectrum allocations and availability for HSPA is given.

Overview of release 99 WCDMA

This chapter provides a brief overview of WCDMA release 99 to serve as a background to subsequent chapters. WCDMA is a versatile and highly flexible radio interface that can be configured to meet the requirements from a large number of services, but the focus for the description is the functionality commonly used to support packet-data transmissions. The goal of this description is to provide sufficient background to the underlying release 99 WCDMA specifications such that HSPA and the HSPA enhancements that are described in subsequent chapters can be seen in context.

Chapter 18 – HSPA system performance

The performance of HSPA is driven by a complex mix of aspects such as, among other things, traffic behaviors, connectivity states, user population and positions, propagation environment effects, algorithmic effects, operator policies, intercell and inter-UE interference, signaling error levels, reporting accuracies, and user behavior. These factors interact in a nontrivial manner. A proportion of the factors relate to human behavior. Thus, the performance of an HSPA deployment is never analytically predictable. Nonetheless, statistical analysis and simulation of system behavior is needed for understanding performance drivers and benchmarking improvements. To properly characterize HSPA performance in terms of capacity and user experience, it is necessary to model system behavior to some extent. In this context, the term “system” refers to the interaction of all factors that impact capacity and user experience. This chapter reviews the principles behind modeling HSPA performance, the factors that drive performance, and the performance observed when modeling typical deployments.

Chapter 8 – High-speed downlink packet access

The introduction of High-Speed Downlink Packet Access (HSDPA) in release 5 implied a major extension of the WCDMA radio interface, significantly enhancing the WCDMA downlink packet-data performance and capabilities in terms of higher peak data rate, reduced latency, and increased capacity. The enhancements were achieved through the introduction of several techniques, including higher-order modulation , rate control , channel-dependent scheduling , and hybrid-ARQ with soft combining . Some of the responsibility for managing radio resources was moved from the RNC to the Node B, in order to enable decisions relating to the air interface to be made closer to the interface and faster. HSDPA is the fundamental downlink building block of the subsequent HSPA evolution. Release 5 HSDPA is described in detail in this chapter, whereas enhancements that have followed in later releases are described in subsequent chapters.