The latest mobile WiMAX standard promises to deliver high data rates over extensive areas and to large user densities. More specifically, data rates are expected to exceed those of conventional cellular technologies. The IEEE 802.16e WiMAX standard enables the deployment of metropolitan area networks to mobile terminals in non-line-of-sight radio environments. Current concerns include leveraging high data rates, increasing area coverage, and competing with beyond 3G networks. Based on the IEEE 802.16e wirelessMAN-OFDMA (orthogonal frequency division multiple access) physical (PHY) layer air-interface, this paper presents a physical layer study of MIMO enabled mobile WiMAX in an urban environment. The radio channels are based on those developed in the European Union IST-WINNER project. Results are given in terms of system throughput and outage probability with and without relays for a range of SISO, MISO and MIMO architectures. Results show that satisfactory performance cannot be achieved in macrocells unless radio relays are used in combination with MIMO-STBC.

The challenge at millimeter-wave frequencies is that the propagation characteristics approximates to that of light. In a nonline-of-sight scenario, when even the mobile station (MS) is near the base station, the attenuation may be tens of dBs due to shadowing and obstructions. Increasing the number of base stations reduces such effects but at the expense of cost and complexity. An attractive method to mitigate such shadowing effects is to use dedicated active or passive relay stations. Proposed here is a network infrastructure in the form of a 3D pyramid. It consists of a single access point with four (but not restricted to) active relays operating in parallel in a medium sized room of 400 m/sup 2/. Simulation is performed in a sophisticated 3D ray tracing tool. Human shadowing densities of 1 person/400 m/sup 2/ up to 1 person/1 m/sup 2/ are set to test the robustness of such a system. Results show that comparing to a normal system with just a single access point either mounted on the ceiling or at the same level as a MS; the pyramid relaying system provides superior coverage and capacity.

Adaptive modulation and coding scheme (AMC) is an effective way to achieve high data rate communication. In AMC system, the key issue is to determine the switching rule for different modulation and coding scheme (MCS). In this paper, adaptive threshold controlling scheme for AMC is proposed. The proposed scheme controls switching thresholds according to target block error rate. Simulation results have shown that the throughput performance of the proposed scheme is very close to the performance, which obtained by the optimum SIR thresholds.

Substantial progress has been made in the receiver signal-processing algorithms for wireless communications to minimize the requirements on signal-to-noise (and/or interference) power ratio and computational complexities for the same quality of service. In cellular infrastructure systems, one of the key system design objectives in the base stations is to maximize the receiver sensitivity, so that the required signal level from the mobile stations can be minimized. The use of advance signal-processing algorithms, based on maximum a posteriori (MAP) estimation, iterative (turbo) channel estimation, equalization, and decoding, allows for a reduction of the required transmitter power by one-third to one-half. Lower computational complexities in the terminals, which implies a reduced power drain on the digital circuits, can be achieved by using techniques that adapt the state complexity of the receiver to the propagation channel. We give an in-depth review of these algorithms, and discuss their performance and implementation requirements.

In this paper we investigate source controlled channel decoding with a hard output channel decoder. Various methods have been devised in the past for source controlled channel decoding, but most of them assume that a soft output channel decoder is used. Most receivers in mobile wireless communications have a standard Viterbi channel decoder which produces only hard outputs. It is shown that a simple sliding histogram is capable of improving the speech quality significantly. The ideas and methods in this paper are applied for the full-rate and enhanced full-rate speech codecs in the GSM system.

The problem of active noise control in a linear duct is examined. Essentially, a nonlinear inverse to a nonminimum phase actuator is proposed. The nonlinear inverse exploits the non-Gaussian nature of some chaotic and stochastic noise sources. The architecture of the controller is derived using Bayesian estimation theory and is shown to be a combination of a linear adaptive network and a radial basis function (RBF) or Volterra series (VS) network. Because of the nonlinear nature of the controller, the filtered-x least means square (LMS) architecture cannot be used. Hence a modified active noise controller is proposed. Simulation results demonstrate the improvements in performance achievable with the combined linear and nonlinear controller.