Abstract: An opportunistic hybrid-relay selection scheme for downlink transmission selects between cooperative relay and single relay schemes based on the channel conditions (e.g., signal-to-noise-ratio (SNR)) between the base station (BS) and RSs (i.e., BS-RSs link) and RSs and mobile station (MS) (i.e., RSs-MS link), respectively. In another selection scheme, a selection between the single relay (e.g., best-relay) transmission scheme or the cooperative-relay transmission scheme may be determined based on transmission paths (e.g., line-of-sight, obstructed-light-of-sight, non-light-of-sight) and channel conditions (e.g., SNR) between the BS-RSs link and the RSs-MS link, respectively.

Abstract: The following invention related to a dynamic on-off spectrum access scheme that will coordinate among different cells, sharing the same spectrum band and enhance spectrum efficiency. Based on the proposed scheme, in particular, the cells or sectors are classified to different types according to their geographical locations. Different types of cells or sectors occupy the total available frequency in a time-sharing fashion, and the duration or priority of the “on” state for each type is chosen based on users' quality of service (QoS) demand.

Abstract: A time-of-arrival (TOA) estimation method for multi-band orthogonal frequency division multiplexing (MB-OFDM) signals uses a simple equally-spaced channel model to recover the impulse response of the wireless channel, and locates the delay of the first channel path by minimizing the energy leakage from the first channel path. The TOA is estimated based on the delay. Such a method does not require channel information for TOA estimation at the receiver and does not require modification of the receiver structure. The method also avoids a sub-optimal solution known to occur in maximum likelihood (ML) estimation.

Abstract: A base station (BS) communicates with a mobile station (MS) through relay stations (RSs). In one exemplary reliable relay-associated transmission scheme, the BS transmits data to the RSs using multicast or unicast. From the received packets, each RS calculates its reliability value according to a reliability function, which it informs the MS. The BS then generates a reliability metric to identify the RSs that are considered reliable. The reliable RSs transmit their information to the MS under a cooperative multicast transmission mode. Meanwhile, the unreliable RSs overhear the transmissions between the reliable RSs and the target MS. If the MS is unable to receive information from reliable RSs, the unreliable RSs can join the cooperative transmission to provide a higher cooperative diversity gain to the target MS.

Abstract: In a geolocation application, a method is provided to jointly estimate the time-of-arrival (TOA) and the amplitude of a received signal based on super-resolution technique. The super-resolution joint TOA-amplitude estimators are provided based on either the expectation-maximization (EM), parallel-interference-cancellation space-alternating generalized expectation maximization (PIC-SAGE) or serial-interference-cancellation SAGE (SIC-SAGE). The SIC-SAGE estimator minimizes the ranging estimation error especially under a non-line-of-sight (NLOS) condition. The SIC-SAGE estimator is a simplified version of the maximum likelihood estimator with more stable performance in a multipath rich environment, such as the ultra-wideband (UWB) based applications. These techniques provide the following benefits: 1) it is generic, so that signal processing can be deployed on both time-domain (e.g., UWB impulse-radio) and frequency-domain (e.g.

Abstract: A wireless communication system experience interference from other wireless communication networks. A method for designing wireless communication systems subject to interference is proposed based on a realistic interference model which accounts for the propagation effects introduced by the wireless environment (such as path loss, shadowing, and multipath fading), and for the spatial scattering of transmitters (using a Poisson field). The method accounts for tradeoffs between network parameters, such as signal-to-noise ratio (SNR), interference-to-noise ratio (INR), path loss exponent, spatial density of the interferers, and error probability. Advantages of this method include: 1) a unified framework for designing a wireless system, subject to cumulative interference and noise, incorporating a wide range of performance metrics; and 2) a general application that covers a broad class of wireless communication systems and channel fading distributions.

Abstract: A wireless communication system and a detect-and-multiplex (DAM) spectrum sharing technique eliminate contention by secondary spectrum users by multiplexing multiple access methods. Suitable multiple access methods include time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), space division multiple access (SDMA), orthogonal frequency division multiple access (OFDMA), spectral nulling (SN) or a hybrid scheme (HS) based on a combination of two or more of the above techniques. Unlike, detect-and-avoid (DAA) multiple access methods, the DAM method increases spectrum usage efficiency, and allows more users to share the same region of the spectrum.

Abstract: The following invention relates to geolocation technology. In particular, the proposed method can be used to determine the optimum threshold value that minimizes the estimation error. The proposed method also allows the threshold value to be varied adaptively according to the signal-to-noise ratios (SNRs) under consideration. This is to ensure that the optimum threshold value is being selected under all channel conditions i.e., both line-of-sight (LOS) and non-LOS (NLOS) scenarios. Additionally, the proposed method is generic and system independent in which it can be applied to both coherent (e.g., match filter (MF)) and non-coherent receivers (e.g., energy detector (ED)).

Abstract: A method that estimates jointly and iteratively the first arriving path of a received signal and a mobile terminal location uses a residual location error. The method may include setting a ranging threshold to reduce residual location error. The method iteratively estimates the first arriving path of the received signals and mobile terminal location, with the estimate of mobile terminal location improving the estimate of the first arriving path, and vice versa. Initially, a peak selection method determines a rough time-of-arrival (TOA) for a signal received at each of a number of different fixed terminals. An estimate of the location of the mobile unit is then provided (e.g., based on a least-squares (LS) triangulation). If the residual error is unsatisfactory, the TOAs are refined, using a search-back algorithm, which searches back from the strongest paths of the received signals. The new TOAs are used to refine the estimate of the location of the mobile terminal.

Abstract: A method mitigates NLOS conditions based on weighted least squares (WLS) technique, in which the weights are derived from multipath components (MPCs) of the received signals. The weighting methodology can be used with both linear and non-linear least squares models, as well as different other NLOS mitigation schemes, such as residual based algorithms or maximum likelihood techniques.

Abstract: Non-line-of-sight (NLOS) identification and mitigation are carried out in a wireless positioning system based on channel statistics derived from multipath components of a received signal. The statistics may be based on the kurtosis, the mean excess delay spread, or the root mean square delay spread. The results are justified using IEEE 802.15.4a ultrawideband channel models. Amplitude and delay statistics based on the IEEE models are shown to be log-normal random variables. A joint likelihood ratio test is presented for the LOS and NLOS identification.