DOCOMO Communications Laboratories United States Inc.

United States

DOCOMO Communications Laboratories United States Inc.

United States
SEARCH FILTERS
Time filter
Source Type

Yen P.,University of Texas at Dallas | Minn H.,University of Texas at Dallas | Chong C.-C.,DOCOMO Communications Laboratories United States Inc.
2011 IEEE Wireless Communications and Networking Conference, WCNC 2011 | Year: 2011

Next generation wireless systems require much higher data rate supports and hence larger bandwidths than the existing systems. Due to the compatibility requirement with the existing legacy systems and the constraints on the availability of contiguous spectrum, bandwidth (or carrier) aggregation has recently emerged as a practical means for supporting high data rate requirement of next-generation systems. A practical issue associated with the bandwidth or carrier aggregation is the significant increase of the peak-to-average power ratio (PAPR) of the time-domain signal. This paper proposes a low-complexity PAPR reduction method for bandwidth aggregated systems with orthogonal frequency division multiplexing / multiple-access (OFDM/OFDMA) or single-carrier frequency division multiple access (SC-FDMA). The proposed approach adopts the existing selective mapping concept, but with some modifications for substantially reducing complexity and signaling overhead, while adapting to carrier-aggregated systems. Performance evaluation under 3GPP LTE-Advanced environment shows PAPR reduction advantage of the proposed method while not requiring any signaling overhead. © 2011 IEEE.


Lopez-Perez D.,King's College London | Guvenc I.,DOCOMO Communications Laboratories United States Inc. | De La Roche G.,University of Bedfordshire | Kountouris M.,Supelec | And 2 more authors.
IEEE Wireless Communications | Year: 2011

3GPP LTE-Advanced has recently been investigating heterogeneous network (HetNet) deployments as a cost effective way to deal with the unrelenting traffic demand. HetNets consist of a mix of macrocells, remote radio heads, and low-power nodes such as picocells, femtocells, and relays. Leveraging network topology, increasing the proximity between the access network and the end users, has the potential to provide the next significant performance leap in wireless networks, improving spatial spectrum reuse and enhancing indoor coverage. Nevertheless, deployment of a large number of small cells overlaying the macrocells is not without new technical challenges. In this article, we present the concept of heterogeneous networks and also describe the major technical challenges associated with such network architecture. We focus in particular on the standardization activities within the 3GPP related to enhanced intercell interference coordination. © 2006 IEEE.


Guvenc I.,DOCOMO Communications Laboratories United States Inc. | Gezici S.,Bilkent University | Sahinoglu Z.,MItsubishi Electric
Wireless Communications and Mobile Computing | Year: 2012

In this paper, theoretical lower bounds on performance of linear least-squares (LLS) position estimators are obtained, and performance differences between LLS and nonlinear least-squares (NLS) position estimators are quantified. In addition, two techniques are proposed in order to improve the performance of the LLS approach. First, a reference selection algorithm is proposed to optimally select the measurement that is used for linearizing the other measurements in an LLS estimator. Then, a maximum likelihood approach is proposed, which takes correlations between different measurements into account in order to reduce average position estimation errors. Simulations are performed to evaluate the theoretical limits and to compare performance of various LLS estimators. Copyright © 2010 John Wiley & Sons, Ltd.


Hua G.,Texas Instruments | Guleryuz O.G.,DoCoMo Communications Laboratories United States Inc.
IEEE Transactions on Image Processing | Year: 2011

We propose a prediction technique that is geared toward forming successful estimates of a signal based on a correlated anchor signal that is contaminated with complex interference. The corruption in the anchor signal involves intensity modulations, linear distortions, structured interference, clutter, and noise just to name a few. The proposed setup reflects nontrivial prediction scenarios involving images and video frames where statistically related data is rendered ineffective for traditional methods due to cross-fades, blends, clutter, brightness variations, focus changes, and other complex transitions. Rather than trying to solve a difficult estimation problem involving nonstationary signal statistics, we obtain simple predictors in linear transform domain where the underlying signals are assumed to be sparse. We show that these simple predictors achieve surprisingly good performance and seamlessly allow successful predictions even under complicated cases. None of the interference parameters are estimated as our algorithm provides completely blind and automated operation. We provide a general formulation that allows for nonlinearities in the prediction loop and we consider prediction optimal decompositions. Beyond an extensive set of results on prediction and registration, the proposed method is also implemented to operate inside a state-of-the-art compression codec and results show significant improvements on scenes that are difficult to encode using traditional prediction techniques. © 2011 IEEE.


Lin T.-L.,University of California at San Diego | Kanumuri S.,DoCoMo Communications Laboratories United States Inc. | Zhi Y.,Texas Instruments | Poole D.,AT and T Labs Research | And 2 more authors.
IEEE Transactions on Image Processing | Year: 2010

In this paper, we propose a generalized linear model for video packet loss visibility that is applicable to different group-of-picture structures. We develop the model using three subjective experiment data sets that span various encoding standards (H.264 and MPEG-2), group-of-picture structures, and decoder error concealment choices. We consider factors not only within a packet, but also in its vicinity, to account for possible temporal and spatial masking effects. We discover that the factors of scene cuts, camera motion, and reference distance are highly significant to the packet loss visibility. We apply our visibility model to packet prioritization for a video stream; when the network gets congested at an intermediate router, the router is able to decide which packets to drop such that visual quality of the video is minimally impacted. To show the effectiveness of our visibility model and its corresponding packet prioritization method, experiments are done to compare our perceptual-quality-based packet prioritization approach with existing Drop-Tail and Hint-Track-inspired cumulative-MSE-based prioritization methods. The result shows that our prioritization method produces videos of higher perceptual quality for different network conditions and group-of-picture structures. Our model was developed using data from high encoding-rate videos, and designed for high-quality video transported over a mostly reliable network; however, the experiments show the model is applicable to different encoding rates. © 2010 IEEE.


Mukherjee S.,DOCOMO Communications Laboratories United States Inc. | Guvenc I.,DOCOMO Communications Laboratories United States Inc.
Conference Record - Asilomar Conference on Signals, Systems and Computers | Year: 2011

Range expansion and inter-cell interference coordination can improve the capacity and fairness of heterogeneous networks by off-loading macrocell users to low-power nodes like picocells. In contrast to previous studies, which rely mostly on simulations, we here consider analytical models for base station and user (UE) locations in a macro network with pico-cell overlay and derive closed-form expressions for the distribution of the signal to interference plus noise ratio (SINR) and spectral efficiencies (SEs) of UEs associated with macro- and pico-cells. These results illuminate the effects on SE of (i) duration of the macro almost blank subframes (ABSs), (ii) the SINR threshold for a UE to be served by a picocell during ABSs, and (iii) the range expansion bias. They also help determine the optimum settings of these parameters. © 2011 IEEE.


Mukherjee S.,DOCOMO Communications Laboratories United States Inc.
IEEE International Conference on Communications | Year: 2011

Downlink coverage issues for macrocellular users (UEs) in a macrocellular network with Closed Subscriber Group (CSG) femtocellular overlay have so far been investigated almost exclusively via simulation. However, consideration of specific scenarios via simulation may not provide general insights applicable to long-term planning for femto-macro deployments. In this paper, we employ general models for macro Node B and femto access point (AP) locations to derive analytical expressions for the probability that an arbitrary UE cannot be served a macro Node B because of interference on the downlink from a nearby femto AP under CSG, and for the probability that the UE is served by the femto AP instead, if the femto AP operates with Open Access (OA). These expressions depend only on the ranges and densities of the macro Node Bs and femto APs, and on the parameters of the wireless channel model. We then show how to apply these results to compute measures of the fraction of overall macrocellular traffic that could be offloaded to an OA femtocellular network, thereby reducing the load on the macrocellular backhaul and increasing overall system capacity. These results are of interest to operators weighing the capacity vs. coverage tradeoff of a femtocellular overlay on a macrocellular network. © 2011 IEEE.


Mukherjee S.,DOCOMO Communications Laboratories United States Inc.
IEEE International Conference on Communications | Year: 2011

Downlink coverage issues for users (UEs) in a macrocellular network with femtocellular overlay have so far been investigated almost exclusively via simulation [1]. In this paper, we employ general models for macro Node B and femto access point (AP) locations to get closed-form expressions for the probability that an arbitrary UE can camp on a macro Node B or an open access (OA) femto AP. These expressions depend only on the relative densities and transmit powers of the macro Node Bs and femto APs, the fraction of femto APs operating in OA vs. Closed Subscriber Group (CSG) mode, and on the parameters of the wireless channel model. For a macrocellular operator considering a femtocellular overlay on a macrocellular network, we show how a set of universal curves could be used to choose the parameters of the femtocellular deployment. © 2011 IEEE.


Sahin M.E.,University of South Florida | Guvenc I.,DOCOMO Communications Laboratories United States Inc. | Arslan H.,University of South Florida
Physical Communication | Year: 2011

Coexistence of narrowband (NB) and multicarrier technologies will be a major concern in next generation wireless communication systems due to the co-channel interference (CCI) problem. In this paper, an efficient CCI cancellation method is proposed that may be utilized for improved coexistence of NB and multicarrier technologies. The method treats both co-channel signals as desired signals and enhances them in an iterative manner. In every iteration, the signals are demodulated, regenerated, and subtracted from the received signal successively in order to obtain a better estimate of the other co-channel signal. Computational complexity of the proposed method is compared in detail with the joint demodulation technique. Through computer simulations, it is shown that the proposed method has lower complexity compared to joint demodulation, and it yields significant gains in the symbol error rate (SER) performance of both the NB and multicarrier systems. © 2010 Elsevier B.V.


Demirdogen I.,University of South Florida | Guvenc I.,DOCOMO Communications Laboratories United States Inc. | Arslan H.,University of South Florida
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2010

Open access is one of the access options for femtocell networks, where the mobile stations (MSs) are allowed to make hand-off to the femtocell base stations (fBSs) in their vicinity. In this paper, several performance trade-offs that are related to the deployment of open access femtocell networks are presented through computer simulations. In particular, first, impact of a capacity-based cell selection method (rather than a cell selection that is based on the link quality) on the capacity of macrocell MSs is studied. Then, cumulative distribution functions (CDFs) of the capacities of macrocell and femtocell users in open access femtocells are investigated for different dedicated channel ratios. This is followed by evaluation of the impact of femtocell deployment ratio on the system performance. ©2010 IEEE.

Loading DOCOMO Communications Laboratories United States Inc. collaborators
Loading DOCOMO Communications Laboratories United States Inc. collaborators