Throughput scaling laws of an ad hoc network equipping directional antennas at each node are analyzed. More specifically, this paper considers a general framework in which the beam width of each node can scale at an arbitrary rate relative to the number of nodes. We introduce an elastic routing protocol, which enables to increase per-hop distance elastically according to the beam width, while maintaining an average signal-to-interference-and-noise ratio at each receiver as a constant. We then identify fundamental operating regimes characterized according to the beam width scaling and analyze throughput scaling laws for each of the regimes. The elastic routing is shown to achieve a much better throughput scaling law than that of the conventional nearest-neighbor multihop for all operating regimes. The gain comes from the fact that more source-destination pairs can be simultaneously activated as the beam width becomes narrower, which eventually leads to a linear throughput scaling law. In addition, our framework is applied to a hybrid network consisting of both wireless ad hoc nodes and infrastructure nodes. As a result, in the hybrid network, we analyze a further improved throughput scaling law and identify the operating regime where the use of directional antennas is beneficial. In addition, we perform numerical evaluation in both ad hoc and hybrid networks, which completely validates our analytical results.

Opportunistic interference alignment (OIA) is known to achieve the optimal degrees-of-freedom (DoF) in the interfering multiple-access channel (IMAC) with independent and identically distributed (i.i.d.) Rayleigh fading, provided that a certain user scaling condition is satisfied. We analyze the performance of OIA in a poor scattering K-cell single-input multiple-output IMAC, where there exist finite paths between the transmitter and receiver sides. Under the feasible model, we derive a new fundamental user scaling law, required to achieve a target DoF, which generalizes the existing achievability result shown for the i.i.d. Rayleigh fading case. Our main result indicates that KS DoF is achievable if the number of per-cell mobile stations (MSs) scales at least as SNR(K-1)min(L,S), where L denotes the number of paths and S denotes the number of simultaneously transmitting MSs per cell. To verify our achievability result for finite system parameters, computer simulations are performed along with comparison to the i.i.d. Rayleigh channel case. The amount of leakage of interference is numerically evaluated and is shown to be consistent with our theoretical result. The achievable sum-rates are also evaluated.

Throughput scaling law of a large wireless network equipping directional antennas at each node is analyzed based on the information-theoretic approach. More specifically, this paper considers a general framework in which the beamwidth of each node can scale at an arbitrary rate relative to the number of nodes in the network. We introduce an elastic routing protocol, which enables to increase per-hop distance elastically according to the beamwidth, while maintaining an average signal-to-interference-and-noise ratio at each receiver as a constant. This elastic routing is shown to achieve a much better throughput scaling law than that of the conventional nearest-neighbor multihop routing. The gain comes from the fact that more source-destination pairs can be activated simultaneously as the beamwidth becomes narrower, which eventually leads to a linear throughput scaling law.

BACKGROUND: Health information technology (HIT) certification and meaningful use are interventions encouraging the adoption of electronic health records (EHRs) in the USA. However, these initiatives also constitute a significant intervention which will change the structure of the EHR market. OBJECTIVE: To describe quantitatively recent changes to both the demand and supply sides of the EHR market. MATERIALS AND METHODS: A cohort of 3447 of hospitals from the HIMSS Analytics Database (2006-10) was created. Using hospital referral regions to define the local market, we determined the percentage of hospitals using paper records, the number of vendors, and local EHR vendor competition using the Herfindahl-Hirschman Index. Changes over time were assessed using a series of regression equations and geographic information systems analyses. RESULTS: Overall, there was movement away from paper records, upward trends in the number of EHR vendors, and greater competition. However, changes differed according to hospital size and region of the country. Changes were greatest for small hospitals, whereas competition and the number of vendors did not change dramatically for large hospitals. DISCUSSION: The EHR market is changing most dramatically for those least equipped to handle broad technological transformation, which underscores the need for continued targeted support. Furthermore, wide variations across the nation indicate a continued role for states in the support of EHR utilization. CONCLUSION: The structure of the EHR market is undergoing substantial changes as desired by the proponents and architects of HIT certification and meaningful use. However, these transformations are not uniform for all hospitals or all the country.

In this paper, we investigate a joint scheduling and power control for a multi-cell cognitive radio network (CRN) in coexistence with a cellular primary radio network (PRN). The PRN uses a set of licensed orthogonal channels for transmission. This set of channels is also accessed in an opportunistic manner by a set of cognitive radio base stations (CR-BSs) to support secondary users (SUs). The problem is formulated to maximize the spectrum utilization of SUs without causing excessive interference to active primary users (PUs) of the PRN. In addition, all the served SUs must meet a certain QoS. A centralized solution for joint scheduling and power control is derived to give the global accessing decision for all unserved SUs. With the assumption that the knowledge of all subscribers is available, the coordinator of the CRN can use the joint scheduling and power control algorithm to maximize the spectrum utilization of served SUs by solving a mixed-integer linear programming (MILP) with an NP-hard complexity. To avoid the NP-hard complexity, we propose a sub-optimal heuristic algorithm that can be obtained at a much lower complexity based on the coloring interference graph among unserved SUs effected by served SUs and active PUs. Simulation results show that the proposed algorithm can yield the performance close to the optimal solution's.

In this paper, we propose dynamic spectrum sharing methods for femto base stations (BSs) operated within a macro BS's spectrum area. As the spectrum sharing methods, we provide traffic pattern based resource hopping schemes of the femto BSs. Traffic pattern information which reflects channel activities for each subband used by the macro BS is utilized by the femto BSs to select proper resources. We evaluate our proposed method compared with pure random hopping method in terms of resource hit probabilities. Also we evaluate our proposed method combined with direct interference measurement results, compared with pure interference measurement based random hopping method. Since traffic pattern information reflects future channel activities, simulation results show that the proposed methods can outperform pure random hopping and conventional methods which utilize past information such as interference measurement results only.

A Femto base station (BS) is connected to operator's network using a residential DSL or cable broadband connection and provides service in the licensed spectrum. When a BS operates with time division duplex mode (TDD), synchronization of the transmission time at the BS is important to avoid inter-slot interference with adjacent BSs. Because femto BSs are generally located indoor, they may not receive the global positioning system (GPS) signal which is used to synchronize the wireless cellular network. We propose a multi-hop based network synchronization scheme for femtocell systems. In the femtocell system, synchronization can be achieved by aligning its frame start point with the neighbor cell's preamble signal hop-by-hop. We evaluate the performance of the multi-hop synchronization and compare it to the single-hop synchronization.

The band adaptive modulation and coding (band AMC) scheme is used in orthogonal frequency division multiple access (OFDMA) systems to increase mobile communication system throughput, however, an amount of feedback overhead degrades uplink system performance. In this paper, we propose an adaptive feedback method that can significantly reduce the amount of channel feedback information when a femto base station (BS) and mobile stations (MS) communicate in the band AMC mode. Since the channel variation of the MS in the femto cell is relatively small, instead of informing the femto BS of the channel quality information (CQI) periodically, MSs only send CQI feedback to the femto BS when channel condition changes above a threshold. Simulation results show that the proposed scheme can reduce feedback overhead up to 70% without resulting in system throughput degradation compared to the conventional best-M feedback scheme.