Downlink transmit (Tx) power calibration techniques are vital in self-organizing femtocell networks to achieve a good tradeoff between femtocell coverage and interference impact to nearby macrocells and femtocells. In this paper, we present two power calibration techniques that adapt to a wide variety of residential deployment scenarios: (1) Over a long term, Tx power is adapted by learning required coverage range, RF profile inside the home and interference outside using feedback from home users and macro users; (2) Tx power is adapted in real-time based on short term dynamic variations in traffic such as arrival of active macro users (guest or passer-by). The presence of nearby active macro users is detected by sensing their uplink channel. The algorithms are shown to provide superior performance compared to conventional techniques in wide variety of deployment scenarios.

Downlink transmit (Tx) power calibration is necessary in femtocell deployments to achieve a good tradeoff between downlink femtocell coverage and interference to other macrocells and femtocells. Developing a practical Tx power calibration scheme that provides excellent performance in different deployment scenarios is challenging. In this paper, we present an enterprise deployment framework that consists of coverage planning and Tx power calibration using technician assistance. The Tx power calibration algorithms presented here use mobile feedback to learn key information such as surrounding RF environment, required coverage range, and interference impact to other cells to adapt to different deployments. Both centralized and distributed Tx power calibration algorithms are evaluated for multi-femto enterprise. It is shown that the distributed algorithm, is simple, efficient and performs very close to the centralized algorithm. Furthermore, over-the-air field tests highlight the practical efficacy of the distributed algorithm in providing excellent femtocell coverage indoors with minimal leakage to outdoors.

The paper presents MIMO field performance results observed using a ultra mobile broadband (UMB) testbed network. We evaluate metrics such as antenna correlations and channel condition number to characterize the MIMO channel. Results show that low condition numbers, which are beneficial to MIMO, are prevalent for a majority of the coverage area in our network. We demonstrate that the use of MIMO provides gains of the order of 20-40% over SIMO transmissions. These gains are made possible by the use of cross-polarized transmit antennas and advanced UMB features that allow dynamic MIMO vs. SIMO transmission selection based on channel conditions. These results are obtained in a truly mobile, wireless wide-area deployment, which makes them unique. Our results point to the viability and value of MIMO in future mobile wireless networks.

Cooperation diversity schemes have been proposed for cellular networks that permit a base station (or a mobile station) to relay signals to a destination receiver, thereby increasing the network coverage and reliability. The mobile relays either decode and forward (DF) or amplify and forward (AF) the received signal. Most existing analyses of cooperation diversity assumes perfect channel information at the receiver. A realistic assessment should consider the effects of practical channel estimation schemes. This paper considers pilot symbol aided channel estimation for cooperation diversity systems. Since the overall channel in AF systems is different from conventional cellular channels, the channel estimation problem is interesting and challenging and therefore our focus is on AF systems. The paper addresses issues such as the estimator design, pilot symbol spacing based upon realistic channel models, and an approximate bit error rate (BER) analysis that accounts for imperfect channel estimation.

System-on-Package (SOP) based on silicon carriers has the potential to provide modular design flexibility and high-performance integration of heterogeneous chip technologies for a wide range of two- and three-dimensional product applications. Key technology enablers include silicon through-vias, high-density wiring, high-I/O chip interconnection, and supporting test and assembly technologies. This paper describes the electrical characterization of key technical elements of the silicon carrier and discusses the significance of those elements in enhancing the overall system performance. The paper also discusses some methodologies that may allow silicon carrier technical elements to be easily integrated within existing EDA tools.

We present performance analysis of handoffs on the forward link (i.e., downlink) of packet-switched 1xEV-DO Rev. A systems by a combination of theoretical analysis and simulation results. A theoretical approach is developed to evaluate slot error probability (SEP) relevant to 1xEV-DO Rev. A. The novelty of the theoretical analysis lies in the fact that unlike the existing literature we consider the combined effects of Rayleigh and shadow fading, filtering, and handoff delay on the handoff algorithm. Contrary to the general assumption, a practical filter cannot eliminate Rayleigh fading completely. We evaluate the handoff performance by considering the effects of filtering, hysteresis, and other system parameters. Tradeoffs in choosing handoff algorithm parameters are studied in terms of the SEP, packet error rate (PER), and number of handoffs.

Several new "sum-of-sinusoids" models have recently been introduced for the simulation of Rayleigh fading channels. These models are statistical in nature implying that their simulation parameters such as the Doppler frequencies are random. They have been shown to accurately reproduce some of the desired statistical properties of the faded envelope such as the time autocorrelation and the level crossing rate. However, a comparative analysis of these models, hitherto scattered throughout the literature, is not available. This paper compares these models in terms of their complexity and performance. The performance assessment is based upon the variance of the time average statistical properties from their ideal ensemble averages.

Mobile-to-mobile channels find increasing applications in futuristic intelligent transport systems, ad hoc mobile wireless networks, and relay-based cellular networks. Their statistical properties are quite different from typical cellular radio channels, thereby requiring new methods for their simulation. This paper proposes a "double-ring" model to simulate the mobile-to-mobile local scattering environment, and develops sum-of-sinusoids (SoS)-based models for simulating such channels. The proposed models produce waveforms having desired statistical properties with good accuracy, and also remove some drawbacks of an existing model derived by using the discrete line spectrum simulation method.

The BER degradation caused by imperfect channel estimation as well as the adverse effect of jamming on pilot symbols, which are used for the channel estimation (CE), is often neglected while analyzing OFDM und MC-CDMA systems leading to over-optimistic results. Therefore, to provide a more realistic analysis, we analyze the vulnerability of pilot symbol aided CE schemes for OFDM/MC-CDMA systems to narrowband and partial band jamming. We derive closed form BER expressions for studying the effect of imperfect CE for OFDMA/MC-CDMA in the absence of jamming in a frequency selective Rayleigh fading environment. We extend these results via simulations and theory (wherever permitted by mathematical tractability) to account for jamming. Some possible solutions such as the use of boosted pilots and the use of jamming side information, whenever available, to excise the jammed pilots or provide MMSE equalization are proposed to reduce the impact of jamming on the CE.

The paper considers the power constrained design of orthogonal multiprocessor interconnection networks. The authors present a detailed model of message latency as a function of topology, technology architecture, and power. This model is then used to analyze a number of interesting scenarios, providing a sound engineering basis for interconnection network design in these cases. For example, they have observed that under a fixed power constraint, the network dimension which achieves minimal latency is a slowly growing function of system size. In addition, as they increase the available power per node for a fixed system size, the dimension at which message latency is minimized shifts towards higher dimensional networks.