WiMAX System Performance with Multiple Transmit and Multiple Receive Antennas
In this paper, the performance of WiMAX networks using multiple transmit and multiple receiver antennas are analyzed via system simulations. For downlink, two kinds of technologies are studied: i) open loop: where the base station has no knowledge of channel and uses mobile mode selection feedback to switch between single data stream STBC and multi-stream spatial multiplexing MIMO (SM-MIMO); ii) closed loop: where base station has explicit knowledge of downlink channel and transmits using adaptive beamforming. This paper compares the WiMAX downlink system performance using open loop and closed loop MIMO technologies with various frequency reuse factors and different data traffic models. The performance of WiMAX uplink is also analyzed with multiple receive antennas and using both single input multiple output (SIMO) and multi-user MIMO (MU-MIMO, a.k.a. SDMA).

title: HRPD-A downlink voice/IP and data throughput and delay analysis
abstract: HRPD-A adds new forward and reverse link rates and a forward link multi-user packet capability at the MAC layer. Completed simulations reveal the performance characteristics of this system in the 1.9 GHz frequency band. These characteristics consist of capacities of voice/IP traffic and mixed data and voice/IP traffic. Downlink data traffic models consist of FTP, HTTP (Web browsing), WAP, and video streaming models. The simulation assumptions include the ITU channel models and 3GPP2 data traffic models

title: Link Performance of WiMAX PUSC
abstract: Link performance of WiMAX (802.16e) downlink and uplink using partial usage subchannelization (PUSC) is evaluated through link-level simulations. WiMAX using single transmit and two receive antennas is compared to a WiMAX system with four transmit and two receive antennas with closed-loop beamforming in the downlink and one transmit and eight receive antennas in the uplink. Two dimensional channel estimators are applied to estimate the channel frequency response using pilot symbols. Spatial channel modeling method is used to model the antenna correlations between multiple transmit and the multiple receive antennas. Link simulations demonstrate that significant link performance improvements can be achieved using closed-loop beamforming for downlink and using more receive antennas for uplink.

title: WiMAX Overview and System Performance
abstract: In this paper, the performance of WiMax network with DL SIMO, DL MIMO and UL SIMO is analyzed via system simulations. Two data traffic models are considered, namely Web browsing (HTTP) and full buffer sessions, operating in multi path fading channels such as the ITU pedestrian-B and vehicular-A channels. The control channel coverage and reliability of WiMAX using realistic overhead is also analyzed in this paper.

title: Throughput-oriented MAC for mobile ad hoc networks: A game-theoretic approach
abstract: The conservative nature of the 802.11 channel access scheme has instigated extensive research whose goal is to improve the spatial reuse and/or energy consumption of a mobile ad hoc network. Transmission power control (TPC) was shown to be effective in achieving this goal. Despite their demonstrated performance gains, previously proposed power-controlled channel access protocols often incur extra hardware cost (e.g., require multiple transceivers). Furthermore, they do not fully exploit the potential of power control due to the heuristic nature of power allocation. In this paper, we propose a distributed, single-channel MAC protocol (GMAC) that is inspired by game theory. In GMAC, each transmitter computes a utility function that maximizes the link's achievable throughput. The utility function includes a pricing factor that accounts for energy consumption. GMAC allows multiple potential transmitters to contend through an admission phase that enables them to determine the transmission powers that achieve the Nash equilibrium (NE). Simulation results indicate that GMAC significantly improves the network throughput over the 802.11 scheme and over another single-channel power-controlled MAC protocol (POWMAC). These gains are achieved at no extra energy cost. Our results also indicate that GMAC performs best under high node densities and large data packet sizes.

title: A Bidirectional Adaptive Sequential Gaussian Approximation for MIMO Systems
abstract: A bidirectional adaptive detection method was proposed to prevent error propagation based on sequential Gaussian approximation algorithm for MIMO systems. Conventional sequential Gaussian approximation detection executes a tree search at the receiver, when the number of searching paths is large, error propagation is well prevented at the cost of high complexity, when few paths are searched, serious error propagation may occur. In the new method, transmitted symbols were estimated parallel both in sequential order and inverse order, and the number of searching paths was determined by comparing the results of bidirectional detection, which can effectively prevent error propagation at reduced complexity. The novel algorithm can be executed at low delay because of parallel computing, and shows good performance at low complexity.

title: Handling Grammatical Errors, Ambiguity and Impreciseness in GIS Natural Language Queries
abstract: A natural language query interface is very desirable for a geographic information system (GIS). It converts natural language queries (sentences) into a formal query language. A key task in building a natural language query interface is handling uncertainty and impreciseness. Grammatical errors and parsing ambiguity cause uncertainty. A natural language query may contain imprecise terms that have to be processed before an executable query can be generated. In this paper, a three–step technique is presented that can be used to correct grammatically incomplete natural language queries, solve parsing ambiguity, and translate imprecise conditions into executable selection conditions.

title: The shortest route cut and fill problem in linear topological structure
abstract: In this paper, we study the Shortest Route Cut and Fill (SRCF) problem where a fleet of vehicles with fixed capacities travel between cut and fill points to finish all cut and fill requirements so that the travel time of the fleet is minimized. We state and classify the SRCF problem and present a complete view of its computational complexities with NP-hardness proof for the basic linear topological structure. Moreover, a simple cycle-based optimization method is proposed to solve the SRCF in linear time complexity, for the version of single vehicle in linear structure without time window constraint.

title: An Adaptive MIMO System Based on Unified Belief Propagation Detection
abstract: An adaptive multiple input and multiple output (MIMO) system based on the unified belief propagation (BP) detection is proposed. A BP detector composed of a serial of component detectors is first presented. With a unified design of the BP detector, a multi-rate MIMO system adaptive to channel variations is then developed, which aims at achieving the maximal throughput performance. The usage of the unified BP detector eliminates the multiple detector modules at the receiver in conventional multi-mode adaptive MIMO systems. Further, the linear complexity to space time block length and parallel operation of the unified BP detection provide the advantages of low complexity, low detection delay and smooth switching between different data rates. With the average receiving signal-to-noise ratio (SNR) based switching mechanism, the proposed adaptive MIMO framework adaptively chooses the appropriate rate for the transmission. Simulation results are provided to show the BER and complexity performance of a specific BP detector as well as the throughput performance of the adaptive scheme.