Jyri Hämäläinen

Effect of Relaying on Coverage in 3GPP LTE-Advanced

Current broadband wireless networks are characterized by large cell sizes. Yet, even in advanced networks that will be built using 3 GPP Long Term Evolution (LTE), also referred to as 3GPP LTE-Advanced, or mobile WiMAX radio interface, users on the cell edge will face relatively low signal-to-interference-plus-noise-ratio (SINR). An attractive solution for this problem is provided by multihop technologies. In this paper we consider the feasibility of Decode and Forward (DF) Relay Nodes (RNs) from 3GPP LTE-Advanced perspective. We propose a novel evaluation methodology that can be used to find a relation of RN transmission power, ratio between number of Base Stations (BSs) and RNs, and performance of the system. Evaluation of DF relays in 3GPP LTE-Advanced framework indicates a good performance gain.

System level analysis of vertical sectorization for 3GPP LTE

The aim of this paper is to evaluate the impact of a novel method for advanced antenna technologies for the downlink performance of the 3GPP Long Term Evolution (LTE) networks. The network performance impact of 3 × 2 vertical sectorization in different macro-cellular network scenarios for various combinations of antenna parameter configurations have been studied in terms of Signal to Interference plus Noise Ratio (SINR) and throughput performance. Simulation studies are performed for uniform UE distribution and full-buffer traffic by using LTE snap-shot simulator and three dimensional propagation modeling.

On the coverage extension and capacity enhancement of inband relay deployments in LTE-advanced networks

Decode-and-forward relaying is a promising enhancement to existing radio access networks and is currently being standardized in 3GPP to be part of the LTE-Advanced release 10. Two inband operation modes of relay nodes are to be supported, namely Type 1 and Type 1b. Relay nodes promise to offer considerable gain for system capacity or coverage depending on the deployment prioritization. However, the performance of relays, as any other radio access point, significantly depends on the propagation characteristics of the deployment environment. Hence, in this paper, we investigate the performance of Type 1 and Type 1b inband relaying within the LTE-Advanced framework in different propagation scenarios in terms of both coverage extension capabilities and capacity enhancements. A comparison between Type 1 and Type 1b relay nodes is as well presented to study the effect of the relaying overhead on the system performance in inband relay node deployments. System level simulations show that Type 1 and Type 1b inband relay deployments offer low to very high gains depending on the deployment environment. As well, it is shown that the effect of the relaying overhead is minimal on coverage extension whereas it is more evident on system throughput.

Performance analysis of downlink OFDMA resource allocation with limited feedback

Opportunistic resource allocation in orthogonal frequency division multiple access (OFDMA) with limited feedback improves the performance of wireless networks and it has been considered in several studies. However, the performances of reduced feedback schemes have not been characterized analytically. In this paper, the analysis of the resource allocation in downlink OFDMA with limited feedback is presented. OFDMA system with a practical resource fair round robin allocation and erroneous feedback channel is considered. The performances of the resource allocation based on three feedback methods are analyzed and compared. A resource-wise signal-to-noise ratio (SNR) quantization based feedback method is considered and two feedback strategies are based on the best-M method, where the M best resource blocks are informed to the transmitter. Analytical bit error probability (BEP) expressions are derived for binary phase-shift keying (BPSK) modulation for each feedback strategy. Furthermore, an asymptotic BEP performance for large SNR values is derived for the best-M feedback schemes. The outage capacity results are derived for the considered feedback schemes to illustrate performance with slow link adaptation. Numerical results based on the analysis are compared to those obtained by computer simulations to validate the correctness of the proposed analysis.

Outage Probabilities in Infrastructure-Based Single-Frequency Relay Links

This paper considers usage of a single-frequency mode for cell coverage extension in infrastructure-based relay links. We provide new closed-form expressions for outage probability by taking into account practical constraints such as interference due to frequency reuse and signal leakage between the relay transmitter and receiver. The analysis covers both decode-and-forward and amplify-and-forward protocols both in downlink and in uplink. For amplify-and-forward relaying, variable gain and fixed gain methods for transmit power normalization are discussed. Simulations show excellent agreement with theory and confirm that the single-frequency mode can be applied at the cost of tolerable signal degradation.

Evolution of Limited-Feedback CoMP Systems from 4G to 5G: CoMP Features and Limited-Feedback Approaches

Coordinated multipoint (CoMP) transmission/reception has been adopted as a key technology to alleviate the intercell interference (ICI) in fourthgeneration (4G) mobile communication. This article reviews the state of the art in limited-feedback CoMP systems research. We first give an overview of recent related work in feedback-based coordinated transmission and then provide a performance analysis of typical feedback schemes and sensitivity to the channel state information (CSI) delay. To back up the discussion, we have validated the benefits of CoMP using field-test results from a CoMP trial network built at the Beijing University of Posts and Telecommunications (BUPT) campus. Furthermore, since mobile systems evolving to fifth generation (5G) have to bear a huge quantity of irregularly distributed wireless data traffic, cooperative communication will be more widely applied not only to address the ICI but also to improve the system resource utilization and data rate. We summarize the recent trend on 5G network architectures enabling the novel CoMP features, and we discuss the potential evolution directions of limited-feedback approaches motivated by CoMP development toward future 5G networks.

BEP Analysis of OFDM Relay Links with Nonlinear Power Amplifiers

This paper studies the performance of a two-hop infrastructure-based relay link. The relay operates in a half-duplex mode using an amplify-and-forward protocol. Considering transmission of OFDM signals with nonlinear power amplifiers (PAs), we determine exact closed-form expressions for end-to-end bit error probabilities (BEPs). The expressions allow us to analyze the effect of nonlinear distortion as well as the special case of linear PAs. Furthermore, we derive asymptotic BEP floor values which illustrate how the end-to-end performance is limited by both the nonlinear PA distortion and the weakest hop. Our discussion indicates that the influence of the nonlinear distortion can be mitigated by properly adjusting the PA back-offs.

Comparison of Relay and Pico eNB Deployments in LTE-Advanced

Relaying is one of the most important novel elements in 3GPP LTE-Advanced study item. It promises to offer significant gain for system capacity or coverage depending on the deployment prioritization. In this paper, we investigate the feasibility of relay node deployments in terms of system throughput and cell coverage area extension as compared to pico node deployments and traditional homogeneous single-hop macro cells. Relay backhaul link overhead is taken into consideration as a limiting factor in a relay deployment; nevertheless, results show that its effect on coverage extension is in most cases negligible. While the effect of relay backhaul overhead is small in coverage limited scenarios, the limitations on throughput due to relaying are evident, in particular, for 500m ISD scenarios. This study also demonstrates that both relay and pico node deployments outperform clearly traditional macro cell deployment in terms of coverage and network capacity.

Closed-loop transmit diversity for FDD WCDMA systems

Transmit diversity techniques provide attractive solutions for increasing the downlink capacity in 3G systems within low-mobility environments. Open-loop and closed-loop transmit diversity modes with two transmit antennas have already been included into 3GPP WCDMA Release 4, and at the moment schemes exploiting a larger number of transmit antennas are being developed. System capacity can be increased from that of open-loop modes if the transmitter is equipped with additional side information of the downlink channel. In an FDD system this means that the receiver has to provide the information through some feedback mechanism. We give a general algorithm by which it is possible to design a large variety of different closed-loop schemes depending on the feedback capacity of the system. The quantization of the transmit weights can be reduced to an eigenvalue problem by using linear functions of order statistics of the underlying probability distribution. This provides a simple analytical tool for the design of feedback algorithms. Furthermore, we provide analytical results for the transmit weights in the case of single-path Rayleigh fading channels.

Proposed operation of GSM packet radio networks

The standardization of the GSM General Packet Radio Service (GPRS) is progressing in European Telecommunications Standards Institute (ETSI). This paper describes the proposed architecture, signaling and protocols for the GPRS network. Also, the network layer interworking, mobility management, service establishment/management, as well as link layer issues are discussed here.