Stefan Parkvall

Design aspects of network assisted device-to-device communications

Device-to-device (D2D) communications underlaying a cellular infrastructure has been proposed as a means of taking advantage of the physical proximity of communicating devices, increasing resource utilization, and improving cellular coverage. Relative to the traditional cellular methods, there is a need to design new peer discovery methods, physical layer procedures, and radio resource management algorithms that help realize the potential advantages of D2D communications. In this article we use the 3GPP Long Term Evolution system as a baseline for D2D design, review some of the key design challenges, and propose solution approaches that allow cellular devices and D2D pairs to share spectrum resources and thereby increase the spectrum and energy efficiency of traditional cellular networks. Simulation results illustrate the viability of the proposed design.

LTE: the evolution of mobile broadband

This article provides an overview of the LTE radio interface, recently approved by the 3GPP, together with a more in-depth description of its features such as spectrum flexibility, multi-antenna transmission, and inter-cell interference control. The performance of LTE and some of its key features is illustrated with simulation results. The article is concluded with an outlook into the future evolution of LTE.

Technical solutions for the 3G long-term evolution

Work has started in the 3GPP to define a long-term evolution for 3G, sometimes referred to as super-3G, which will stretch the performance of 3G technology, thereby meeting user expectations in a 10-year perspective and beyond. The fundamental targets of this evolution - to further reduce user and operator costs and to improve service provisioning - will be met through improved coverage and system capacity as well as increased data rates and reduced latency. This article presents promising technologies to fulfil these targets, including OFDM, multi-antenna solutions, evolved QoS and link layer concepts, and an evolved architecture. Furthermore, the results of a performance evaluation are presented, indicating that the requirements can indeed be reached using the proposed technologies.

Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems

In an asynchronous direct-sequence code-division multiple access (DS-CDMA) communication system, the parameter estimation problem, i.e., estimating the propagation delay, attenuation and phase shift of each users transmitted signal, may be complicated by the so-called near-far problem. The near-far problem occurs when the amplitudes of the users received signals are very dissimilar, as the case might be in many important applications. In particular, the standard method for estimating the propagation delays will fail in a near-far situation. Several new estimators, the maximum likelihood, an approximative maximum likelihood and a subspace-based estimator, are therefore proposed and are shown to be robust against the near-far problem. No knowledge of the transmitted bits is assumed, and the proposed estimators can thus be used for both acquisition and tracking. In addition, the Cramer-Rao bound is derived for the parameter estimation problem.

LTE-Advanced - Evolving LTE towards IMT-Advanced

This paper provides a high-level overview of some technology components currently considered for the evolution of LTE including complete fulfillment of the IMT-advanced requirements. These technology components include extended spectrum flexibility, multi-antenna solutions, coordinated multipoint transmission/reception, and the use of advanced repeaters/relaying. A simple performance assessment is also included, indicating potential for significantly increased performance.

Evolution of LTE toward IMT-advanced

This article provides a high-level overview of LTE Release 10, sometimes referred to as LTE-Advanced. First, a brief overview of the first release of LTE and some of its technology components is given, followed by a discussion on the IMT-Advanced requirements. The technology enhancements introduced to LTE in Release 10, carrier aggregation, improved multi-antenna support, relaying, and improved support for heterogeneous deployments, are described. The article is concluded with simulation results, showing that LTE Release 10 fulfills and even surpasses the requirements for IMT-Advanced.

Future-generation wireless networks

Starting with todays 3G standards, future-generation wireless networks are discussed. Two complementing major trends are identified: seamless roaming between different air interfaces, leading to the always best connected concept, and the continuous development of the current third-generation standards. The evolution of WCDMA toward high-speed downlink packet access. aiming for peak rates in the order of 8-10 Mb/s, is described as an example of air-interface evolution. Fourth-generation technologies such as ad hoc networking and multihop networks, still at the research level, are discussed and their impact on wireless communication systems addressed.

LTE release 12 and beyond [Accepted From Open Call]

As the specification of Release 11 of the LTE standards is approaching its completion, 3GPP is gradually moving its focus toward the next major step in the evolution of LTE. The drivers of the LTE evolution include the increasing demand for mobile broadband services and traffic volumes as well as emerging usage scenarios involving short-range and machine-type communications. In this article we provide an overview of the key technology areas/components that are currently considered by 3GPP for Rel-12, including support for further enhanced local area access by tight interaction between the wide area and local area layers, signaling solutions for wireless local area network integration, multi-antenna enhancements, improved support for massive MTC, and direct device-to-device communications.

Performance comparison of HARQ with Chase combining and incremental redundancy for HSDPA

We compare two hybrid automatic repeat request (HARQ) combining strategies that currently are considered for the high speed downlink packet access (HSDPA) evolution of WCDMA. The two HARQ combining schemes are Chase combining, where the retransmissions are identical copies of the original transmission, and incremental redundancy (IR), where the retransmissions consist of new parity bits from the channel encoder. We show that the link-level performance of a HARQ type-II system can be significantly better with IR compared to Chase combining. The largest gains are obtained for high channel-coding rates and high modulation orders. For low modulation and coding schemes (MCS), the link-level performance gains with IR are less significant. We further show that in a system that uses link adaptation we can not expect any large gains with IR as long as the link adaptation errors are reasonably small. Furthermore, we show that on fading channels there are situations when an IR system actually performs poorer than a Chase combining system.

Evolving 3G mobile systems: broadband and broadcast services in WCDMA

The third-generation WCDMA standard has been enhanced to offer significantly increased performance for packet data and broadcast services through the introduction of high-speed downlink packet access (HSDPA), enhanced uplink, and multimedia broadcast multicast services (MBMS). This article provides an overview of the key technologies used, the reasons behind their selection, and their integration into WCDMA. Performance results are also included to exemplify the performance possible in an evolved WCDMA network.