Source: http://www.google.com/patents/US20020115473?dq=oakley+D523,461&ei=qiI4T-CjGqXf0QHz_PSUCA
Timestamp: 2014-12-28 08:51:48
Document Index: 662732765

Matched Legal Cases: ['arts 104', 'arts 104', 'arts 104', 'arts 108', 'arts 104', 'art 104']

PRIORITY [0001] This application claims priority to an application entitled �Transmit Antenna Diversity Apparatus and Method for Base Station in a CDMA Mobile Communication System� filed in the Korean Industrial Property Office on Dec. 21, 2000 and assigned Serial No. 2000-79713, the contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to a communication apparatus and method in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a forward transmit antenna diversity apparatus and method in a CDMA mobile communication system. [0004] 2. Description of the Related Art [0005] An existing CDMA mobile communication system that mainly supports voice service, has been developed into a future (CDMA mobile communication system which provides high-speed data service as well as voice service. The future CDMA mobile communication system supports voice, moving image and Internet search services. In the mobile communication system, communication links existing between a base station and a mobile station are classified into a forward link for transmitting a signal from the base station to the mobile station, and a reverse link for transmitting a signal from the mobile station to the base station. [0006] The mobile communication system must resolve a fading problem in order to transmit high-speed data. The fading causes a reduction in the amplitude of a received signal from several dB to several tens dB. In order to solve the fading problem, a variety of diversity techniques are used. [0007] One of the techniques used in the CDMA system employs a Rake receiver, which receives a signal on a diversity basis using delay spread of a channel and the Rake receiver supports a reception diversity technique for receiving a multi-path signal. However, this diversity technique is disadvantageous in that it is not operable when the delay spread is low in level. [0008] Also, a time diversity technique utilizing interleaving and coding is used in a Doppler spread channel. However, this technique is not effective in a low-speed Doppler spread channel. It is possible, though, to effectually solve the fading problem using a space diversity technique, in an indoor channel with a low Doppler spread level and a pedestrian channel, a low-speed Doppler channel. [0009] The space diversity technique uses two or more antennas. In this technique, even though a signal transmitted through one antenna is attenuated due to the fading, it is possible to compensate for the attenuation using a signal transmitted through the other antennas. The space antenna diversity technique is divided into a reception antenna diversity using a plurality of reception antennas and a transmit (transmission) antenna diversity using a plurality of transmission antennas. It is hard to install the reception antenna diversity in the mobile station in light of its size and cost. Thus, the use of the transmit antenna diversity for the base station is recommended. [0010] The transmit antenna diversity includes a �closed loop transmit diversity� transmitting a signal based on forward channel information fed back from the mobile station, and an �open loop transmit diversity� receiving no feedback information from the mobile station. In the closed loop transmit diversity scheme, the base station applies weights to transmission signals of the respective transmission antennas based on the channel information measured and fed back by the mobile station to maximize a signal-to-noise ratio (SNR) of an antenna at the mobile station. In the open loop transmit diversity scheme, the base station transmits the same signal through two quadrature (or orthogonal) paths without using the feedback information. The quadrature paths can be provided by time division, frequency division or code division. [0011]FIG. 1 illustrates a structure of a base station transmitter using an open loop transmit diversity scheme according to the prior art. Referring to FIG. 1, an input bit stream is encoded by a channel encoder 101, and an output sequence of the channel encoder 101 is mapped into an M-ary symbol by an M-ary symbol modulator 102. The M-ary symbol modulator 102 serves as a QPSK (Quadrature Phase Shift Keying), 8-PSK (8-ary Phase Shift Keying) or 16-QAM (16-ary Quadrature Amplitude Modulation) modulator according to its data rate, and its modulation mode can be changed in a physical layer packet unit where the data rate can be changed. I and Q sequences of the M-ary symbol output from the M-ary symbol modulator 102 are modulated into two different complex symbols by an STTD/STS (Space-Time Transmit Diversity/Space Time Spreader) modulator 103. A detailed description of the STTD/STS modulator 103 will be made with reference to FIGS. 4 and 5. Walsh cover parts 104 and 105 orthogonally spread their input symbols using a Walsh orthogonal code WN i assigned to the mobile station. A detailed structure of the Walsh cover parts 104 and 105 is illustrated in FIG. 2. The two complex symbols spread by the Walsh cover parts 104 and 105 are subject to complex spreading by their associated complex spreaders 106 and 107, respectively. An internal operation of the complex spreaders 106 and 107 is illustrated in FIG. 3. The output signals of the complex spreaders 106 and 107 are shifted to RF (Radio Frequency) band signals by associated RF parts 108 and 109, and then radiated through first and second antennas ANT1 and ANT2. [0012]FIG. 2 illustrates a detailed structure of the Walsh cover parts 104 and 105 illustrated in FIG. 1. Each Walsh cover part 104 and 105 spreads its input complex symbol to a transmission bandwidth, using a Walsh code assigned to a transmission channel. FIG. 3 illustrates an internal operation of the complex spreaders 106 and 107 shown in FIG. 1. Each of the complex spreaders 106 and 107 complex-spreads its input complex signal into an I-channel (or I-ann) signal and a Q-channel (or Q-arm) signal, using a spreading sequence comprised of an I-channel spreading sequence PNI and a Q-channel spreading sequence PNQ. [0013]FIG. 4 illustrates an internal operation of the STTD/STS modulator 103 of FIG. 1 when it operates in an STTD (Space-Time Transmit Diversity) mode. In the STTD mode, the STTD/STS modulator 103 operates as shown in Table 1. TABLE 1 Input to Antenna #1 Antenna #2 Time t S0 S0 −S*1 Time t+T S1 S1 S*0 [0014] In Table 1, S0 and S1 represent complex symbols, and are represented by S0 =Si 0 +jSq 0 S