Showing papers by "Preben Mogensen published in 2010"

Carrier load balancing and packet scheduling for multi-carrier systems

Abstract: -In this paper we focus on resource allocation for next generation wireless communication systems with aggregation of multiple Component Carriers (CCs), i.e., how to assign the CCs to each user, and how to multiplex multiple users in each CC. We first investigate two carrier load balancing methods for allocating the CCs to the users- Round Robin (RR) and Mobile Hashing (MH) balancing by means of a simple theoretical formulation, as well as system level simulations. At Layer-2 we propose a simple cross-CC packet scheduling algorithm that improves the coverage performance and the resource allocation fairness among users, as compared to independent scheduling per CC. The Long Term Evolution (LTE)-Advanced is selected for the case study of a multi-carrier system. In such a system, RR provides better performance than MH balancing, and the proposed simple scheduling algorithm is shown to be effective in providing up to 90% coverage gain with no loss of the overall cell throughput, as compared to independent scheduling per CC.

Cell size breathing and possibilities to introduce cell sleep mode

Abstract: Global warming has put the energy consumption of all industries into focus. In 2005 mobile communications contributed to about 0.2% of global CO 2 emissions. Mobile operators have been reporting annual increases from 300% to 700% in 3G data traffic volumes. Such a steady growth in traffic requires regular upgrades in the infrastructure. While network equipment is in itself becoming more efficient, these upgrades still increase the overall energy consumption of the networks. This paper investigates the energy saving potential of exploiting cell size breathing by putting low loaded cells into sleep mode. The energy consumption and network performance of the resulting network are used to quantify the potential of this feature. The investigation is carried out on a tilt optimized network. Since putting cells into sleep mode results in a non- optimum antenna tilt configuration, this paper also investigates the possible gains of re-optimizing antenna tilting. The results show that by allowing sleep mode, over a restricted period of 12 hours, an energy saving of 33% is possible. While this energy saving comes at no expense of the overall network performance, the gain in average user data rate is noted to decrease by 21%.

High‐Speed Downlink Packet Access

Abstract: This chapter presents High-speed Downlink Packet Access (HSDPA) for WCDMA—the key new feature included in Release 5 specifications. The HSDPA concept has been designed to increase packet data throughput by means of fast physical layer (L1) retransmission and transmission combining as well as fast link adaptation controlled by the Node B (Base Transceiver Station (BTS)). This chapter is organised as follows: First, HSDPA key aspects are presented and a comparison to Release’99 downlink packet access possibilities is made. Next, the impact of HSDPA on the terminal uplink (user equipment (UE)) capability classes is summarised and an HSDPA performance analysis is presented, including a comparison to Release’99 packet data capabilities. The chapter is concluded with a short discussion of evolution possibilities of HSDPA.

A Scalable Spectrum-Sharing Mechanism for Local Area Network Deployment

Abstract: Current wireless access networks are able to provide relatively low data rates when compared with wired access. To extend the access to high-data-rate services to wireless users, the International Telecommunication Union (ITU) established new requirements for future wireless communication technologies of up to 100 Mb/s under high-mobility conditions and 1 Gb/s in low mobility. The low mobility goal can only be achieved through the use of highly optimized local area access networks operating at low range and low transmission power. The efficient sharing of radio resources among local area cells will be very difficult to achieve with a traditional network planning/dimensioning approach due to their intrinsic uncoordinated deployment characteristic. Cognitive radio (CR)-based networking methodologies are considered as the most promising solutions for such radio-resource-sharing problems, also enabling unlicensed/open spectrum operations. In this paper, a game-theory-inspired scalable algorithm for intercell dynamic spectrum access (IC-DSA) is introduced to enable distributed resource allocation in CR environments. Here, the new CR-based cell is called ?cognitive cell (C-cell),? and it is the minimal entity that allocates a resource set. The simulation results demonstrate the effectiveness of the proposed spectrum-sharing approach. This solution achieves a better overall performance in several load and interference scenarios in terms of both outage and average capacity when compared with fixed-frequency-reuse cases.

Dual-Cell HSDPA for Network Energy Saving

Abstract: The increasing demand for mobile broadband is pushing existing 3G networks closer to their capacity limit. Additional carriers together with new HSPA features (HSPA+) are expected to provide the next necessary boost in network capacity. One specific feature in HSPA+ is referred to as Dual-Cell HSDPA (or Dual-Carrier HSDPA). This feature allows for a single user to be simultaneously scheduled over two carriers, effectively doubling its achievable data rate. The addition of a secondary carrier will require additional radio equipment at the base station site, increasing the overall energy consumption. This paper proposes an energy saving feature that exploits variations in network traffic. Based on the individual load of each sector, the feature determines if the secondary carrier is detrimental for reaching some pre-set minimum requirements. Each sector is allowed to switch off one of its two carriers, during periods of low network traffic. It is concluded that an energy saving ranging between 14% and 36% is possible. This saving comes without degradation of network performance.

Self-Organizing Coalitions for Conflict Evaluation and Resolution in Femtocells

Abstract: The recent introduction of carrier aggregation in LTE-Advanced enables new possibilities in designing frequency domain interference reduction and management schemes. These methodologies are of extreme interest in the case of dense and uncoordinated deployments of femtocells. In such scenarios, dense deployment of cells coupled with the scarcity of frequency resources may lead to a potentially disruptive amount of interference, which severely affects the performance of the system. This contribution presents a novel method inspired by graph and coalitional game theories. The proposed algorithm consists of a set of distributed and scalable rules for building coalitions; these rules essentially resolve the conflicts among avid femtocells competing for a limited amount of resources. The proposed scheme has been designed by targeting localized reconfigurations, thus avoiding reconfiguration storms in the network. Furthermore, the rules governing the resource redistribution ensure overall system performance improvements while maintaining a certain degree of fairness among the competing nodes. Simulation results prove the effectiveness of the proposed method.

SVD-Based vs. Release 8 Codebooks for Single User MIMO LTE-A Uplink

Abstract: The ambitious data rate target of the Long Term Evolution - Advanced (LTE-A) systems, which are currently being standardized by the 3rd Generation Partnership Project (3GPP), can only be achieved by using advanced Multiple Input Multiple Output (MIMO) antenna techniques on both uplink and downlink. In this paper, the focus is on LTE-A uplink and we discuss the suitability of two options for the closed loop precoded MIMO transmission. The first option is to use the same codebook of precoding matrices defined for LTE downlink, while the second option exploits the Singular Value Decomposition (SVD) of the channel matrix, which could theoretically achieve the MIMO capacity. Qualitative benefits of both solutions are discussed. Link level simulation results show that, the SVD-based approach only lead to a poor performance gain in terms of spectral efficiency over the LTE downlink codebook because of the losses due to the quantization of the right singular vectors of the channel matrix. Since SVD-based solution doesn't even exploit some useful properties (e.g., power balance over the antennas) which LTE Release 8 codebook offers, the latter results to be a better candidate for the closed loop MIMO transmission in LTE-A uplink.

Power variations of wireless communication systems

Abstract: The use of wireless digital communication devices like GSM, WCDMA, HSPA, DECT, and WiFi changes the exposure of electromagnetic waves toward the user. Concentrating on the power variations on a slow and fast time scale, these new systems are discussed. Experimental results for both uplink and downlink are included for a sample of systems. The spectrum of the power fluctuations is seen as a convenient and compact way of describing very complex system behavior. The results are of interest for scientific studies of epidemiology and biological effects, and for general electromagnetic compatibility (EMC) aspects. Bioelectromagnetics 31:302–310, 2010. © 2010 Wiley-Liss, Inc.

On Open versus Closed LTE-Advanced Femtocells and Dynamic Interference Coordination

Abstract: Low-power home base stations, also known as femtocells, are one of the strong candidates for high data rate provisioning in indoor environments. Unfortunately, the benefits are not without new challenges in terms of interference management and efficient system operation. In this paper we take a closer look at several aspects associated with the deployment of LTE-Advanced home eNBs under two different access policies: closed subscriber group (CSG) and open subscriber group (OSG). Our results are derived from extensive downlink system level simulations. We limit our scope to dense-urban deployment of femtocells assuming dedicated carriers, i.e. no interference to/from the macro layer. Particularities of each access mode are discussed under different hard frequency re-use configurations. Our results indicate that an OSG deployment is indeed able to cut short the lower end of the SINR distribution when universal frequency re-use is employed. However, when other re-use configurations are considered, OSG no longer guarantees improved SINR conditions. In addition, we present additional results for the autonomous component carrier selection (ACCS) concept introduced in earlier contributions, providing strong suggestions that the scheme yields attractive performance benefits independently of the access policy selected by the operator. Finally, we point out that uplink results including realistic power control settings need to be considered before definitive conclusions can be safely drawn.

Uplink Coordinated Multi-Point for LTE-A in the Form of Macro-Scopic Combining

Abstract: For the future LTE-Advanced network, one of the requirements in the uplink (UL) direction is to enhance the celledge user performances. Coordinated multi-point reception in the UL is one of the techniques being investigated to further improve the performance of LTE networks. With the help of the information coordination through the links between the sites and advanced receivers the UL performance can be improved. The simulation results show that, with the ideal interference cancellation, inter-Site maximum ratio combining, and optimized closed-loop and open-loop fractional power control, there are about 27% gains for the 5% outage user throughput and 12% gains for the average user throughput. As shown in this paper, these gains from UL macro-scopic multi-cell combining between sites are achieved for optimized power control, ideal interference cancellation receivers, and X2 with no delay and high bandwidth.

A Site-Specific Study of In-Building Wireless Solutions

Abstract: This paper studies the different ways of extending wireless coverage for high data rates and improving the data capacity in a building. The solutions considered include deployments of single or multiple small base stations, i.e. Picocell or Femtocell, and distributed antenna system, operated on the same frequency as the macro cellular network. We look at the radio performance of each solution in a LTE downlink context with in-building path loss values retrieved from real-life measurements. The performance is compared by means of maximum supportable user numbers and average system throughput. Potential gains by hard frequency reuse in the building and QoS based packet scheduling are examined. Simulation results show the robustness of the proposed distributed antenna system and the conditions for multi-Femtocell deployment.

Link Parameters Bundling across Multiple Component Carriers in LTE-A Uplink

Abstract: A multiple component carrier (CC) solution has been agreed as the underlying structure of the Long Term Evolution - Advanced (LTE-A) systems, which are currently being standardized by the 3rd Generation Partnership Project (3GPP). In this deployment, the bundling of Modulation and Coding Scheme (MCS) and Hybrid Automatic Repeat Request (HARQ) parameters across multiple CCs is foreseen to maintain the feedback signaling comparable with the one of the previous LTE Release 8. This paper focuses on the transmission over multiple CCs in LTE-A Uplink. Issues related to the bundling of the link level parameters is discussed and a simple Codeword (CW) mixing strategy is proposed to boost the spectral efficiency performance while keeping low feedback overhead. Results show that, combined HARQ/MCS bundling can achieve the same performance of HARQ only bundling when used together with our proposed CW mixing strategy, with the advantage of a lower feedback overhead. CW mixing also leads to similar spectral efficiency when the bundling is performed over 2 and 3 CCs. The use of a turbo Successive Interference Cancellation (turbo SIC) receiver further improves the spectral efficiency, especially when antenna gain imbalance (AGI) occurs.

Uplink Performance of Dynamic Interference Coordination under Fractional Power Control for LTE-Advanced Femtocells

Abstract: It has been identified in numerous contributions that dynamic interference coordination is very appealing in case of dense and uncoordinated deployments of home eNBs, also known as femtocells. One of the proposed schemes for LTE-Advanced is known as Autonomous Component Carrier Selection (ACCS). Previous contributions presented extensive downlink performance results attesting the effectiveness of ACCS. Nonetheless, the uplink has its own set of specificities, such as the use of Fractional Power Control (FPC). In this light, the purpose of this paper is two-fold: (i) Provide qualitative and quantitative answers to questions such as what is the impact of FPC on femtocells and how to best configure it. (ii) Evaluate in detail the uplink performance of ACCS under realistic power control settings. Using results derived from extensive uplink system level simulations we show that the behavior of FPC when applied to femtocells is significantly different from that seen on macrocells. In addition we demonstrate that ACCS is equally attractive and applicable to the uplink even though most decisions are based on UE downlink measurements.

Downlink Transmission in Multi-Carrier Systems with Reduced Feedback

Abstract: in this paper we address the problem of reducing the feedback for the downlink transmission in multi-carrier systems. In these systems multiple Component Carriers (CCs) are aggregated together to form a wide spectrum. Consequently, a large feedback overhead is required to report the channel quality information over such a wide bandwidth. We first generalize two existing feedback reduction techniques, and then propose a new one. These techniques use different feedback schemes across the CCs, or allow some CCs to be un-reported, for the purpose of reducing the amount of feedback. Performance for the investigated techniques is evaluated in a realistic system setting with different traffic conditions and terminal categories. Based on the obtained results, the selection of proper feedback reduction technique under different load conditions can be made. The findings are useful for reducing the feedback overhead in future generation wireless communication systems that operate over multiple CCs.

Device, method and computer software for operation of transmission antenna with feedback for systems using several antennae

Abstract: FIELD: physics; communication. ^ SUBSTANCE: method involves determination of weight coefficients corresponding to each antenna from several antennae used for transmitting data signals. Each weight coefficient is suitable for changing the corresponding data signal before transmission using the corresponding antenna; and transmission of information corresponding to at least one weight coefficient and enabling determination of at least the said weight coefficient. Another method involves receiving information corresponding to at least one of several weight coefficients corresponding to several first antennae used for transmitting first data signals, where each weight coefficient is used for changing the corresponding one of first data signals before transmission using the corresponding one of first antennae; using the received information to determine several weight coefficients corresponding to several first antennae, and using at least several weight coefficients to decode second data signals received using several second antennae to generate at least one output signal. ^ EFFECT: transmission of return line information for antenna transmission with a closed loop over an uplink. ^ 37 cl, 6 dwg

Open loop transmit diversity solutions for LTE-A uplink

Abstract: Transmit diversity (TD) techniques are expected to be included in the uplink of the upcoming Long Term Evolution — Advanced (LTE-A) systems to boost the user performance in low Signal-to-Noise Ratio (SNR) conditions. In this paper, several open loop TD solutions based on both space frequency coding (SFC) and space time coding (STC) are evaluated in a Single Carrier Frequency Division Multiplexing (SC-FDM) system with the aim of discussing their suitability for the upcoming standard. Traditional SFC is shown to increase the Peak-to-Average Power Ratio (PAPR) of the SC-FDM signal but it also outperforms STC for high speed and high order modulation and coding schemes (MCSs). Moreover, STC suffers from reduced flexibility in the time domain encoding. Starting from the single carrier sequences in the time domain, a SFC solution keeping low PAPR is derived; it is shown to be a valid option for low delay spread channels and small amount of data to be transmitted.