Abstract: The present invention discloses a volunteer search server, comprising a receiver, a database, an analyzer and a transmitter. The receiver is for receiving a request message from a requester, wherein the request message contains the location information of the requester. The database is for storing a matching mechanism and the location information of a plurality of volunteers. The analyzer is for exercising the matching mechanism to search at least one suitable volunteer according to the request message, wherein the matching mechanism considers both the location information of the requester and the volunteer. The transmitter is for transmitting a designate message to one designated volunteer. Additionally, the present invention discloses a search method of the volunteer search server and a volunteer search system thereof.

Abstract: Provided are a system and method for detecting air pollution, characterized by using an air pollution detecting device for detecting air pollutants, using a positioning device for locating the air pollution detecting device, and enabling a data transmission device to transmit air pollution data and position data to a data analysis and management device via a network system, and then enabling the data analysis and management device to perform analysis and management process on the data; accordingly, perceiving air pollution status at each area and thus proving air pollution information and improvement to air pollution areas in a shorter time.

Abstract: A preamble for an OFDM signal synchronizes (104) and estimates (106) the sub-channels with only one code. One polyphase code sequence is used repeatedly for the preamble. The preamble is spread out over the bandwidth, which is the same as an OFDM symbol in the frequency domain and has good autocorrelation characteristics in the time domain. All OFDM signals are added with this preamble at the beginning of the OFDM signal and transmitted on the channel at a transmitter (50). At the receiving end, the receiver (100) first does the autocorrelation process to find out a peak value for synchronization in the time domain. Then, since the polyphase code is known at the receiver, the signal to noise ratio for each sub-carrier is calculated in the frequency domain and smoothed using the normal (Gaussian) distribution to provide the channel estimation. Since the synchronization and channel estimation are processed with a single preamble, the overhead for these two functions is significantly reduced.

Abstract: An efficient system and method for modulation and demodulation to achieve a high data rate using Bit-Interleaved Coded Modulation and OFDM uses either a coherent or a non-coherent transmission scheme using differential modulation. In order to maintain a high data rate impervious to sudden phase changes, a communication system uses an efficient constellation having multiple rings with different sizes and modulation/demodulation schemes utilizing this constellation. In power line communications, the channel gain information is obtained easily at a receiver (100) while the phase information is not. Thus, the communication system uses an absolute magnitude and differential phase coding for modulation and demodulation of the signals.

Abstract: A method for conveying digitally encoded data within a Wireless Local Area Network (WLAN) using a contention based Media Access Control (MAC) protocol. In the method, a multi-beam access point can transmit a channel contention request and responsively receive channel contention responses. A set of nodes can be determined based upon the channel contention responses. Each node of the determined set can be assigned one beam of the multi-beam access point. The nodes can use the assigned beams to simultaneously communicate with said multi-beam access point in a collision-free fashion along an assigned beam.

Abstract: A method of simultaneously transmitting and receiving multiple data packets over wireless channels among the nodes of a wireless network is provided. The method includes automatically selecting a master sending node and corresponding master receiving node in response to an omni-directionally transmitted request to send during a contention period. The method also includes selecting a slave sending node and corresponding slave receiving node if a spatial reuse ratio correspond to the master-node pair is less than a predetermined threshold and if directional data transmissions between the slave sending node and corresponding slave receiving node avoid interfering with directional data transmissions between the master nodes and other pairs of slave nodes. The method further includes causing the master sending node and slave sending node to directionally transmit data packets during a coordination period.

Abstract: A preamble for an OFDM signal synchronizes (104) and estimates (106) the sub-channels with only one code. One polyphase code sequence is used repeatedly for the preamble. The preamble is spread out over the bandwidth, which is the same as an OFDM symbol in the frequency domain and has good autocorrelation characteristics in the time domain. All OFDM signals are added with this preamble at the beginning of the OFDM signal and transmitted on the channel at a transmitter (50). At the receiving end, the receiver (100) first does the autocorrelation process to find out a peak value for synchronization in the time domain. Then, since the polyphase code is known at the receiver, the signal to noise ratio for each sub-carrier is calculated in the frequency domain and smoothed using the normal (Gaussian) distribution to provide the channel estimation. Since the synchronization and channel estimation are processed with a single preamble, the overhead for these two functions is significantly reduced.

Abstract: An efficient system and method for modulation and demodulation to achieve a high data rate using Bit-Interleaved Coded Modulation and OFDM uses either a coherent or a non-coherent transmission scheme using differential modulation. In order to maintain a high data rate impervious to sudden phase changes, a communication system uses an efficient constellation having multiple rings with different sizes and modulation/demodulation schemes utilizing this constellation. In power line communications, the channel gain information is obtained easily at a receiver (100) while the phase information is not. Thus, the communication system uses an absolute magnitude and differential phase coding for modulation and demodulation of the signals.