Patent application publication US20070274411, entitled SIGNAL GENERATION USING PHASE-SHIFT BASED PRE-CODING, is a candidate for LTE DL MIMO essential patent.
Information communication services have become more popular and with the introduction of various multimedia services and high quality services, there is an increased demand for enhanced wireless (radio) communication services. In order to actively meet such demands, the capacity and data transmission reliability of the communication system should be increased. To increase communication capacity in a wireless (radio) communication environment, one method would be to find newly usable bandwidth and another would be to improve the efficiency of given resources. As some examples of the latter method, multiple antenna transmitting/receiving (transceiving) techniques are recently gaining attention and being actively developed, whereby a plurality of antennas are provided at the transceiver in order to obtain diversity gain by additionally securing spatial domain for resource utilization, or increasing transmission capacity by transmitting data in parallel via each antenna. Among such multiple antenna transceving techniques, an example would be Multiple-Input Multiple-Output (MIMO) system based on Orthogonal Frequency Division Multiplexing (OFDM).
Certain multi-carrier based wireless access techniques do not adequately support mobile communication systems with various types of antenna structures:
The space-time code (STC) technique, for a multiple antenna environment, relates to continuously (sequentially) transmitting the same signal, but in case of repetitive transmissions, transmitting through different antennas is performed, in order to obtain spatial diversity gain. Such space-time code technique has some shortcoming. For example, respectively different forms of space-time codes are required according to how the antenna structure changes, the transmitting side and receiving side have increased complexity because data symbols are repeatedly transmitted through a plurality of time slots in order to obtain spatial diversity, and has respectively lower performance compared to that of other closed-loop systems because data is transmitted without using feedback information.
Cyclic Delay Diversity (CDD) is a method in which frequency diversity gain is obtained at the receiving side, by using the antennas to respectively transmit signals with different delays or different magnitudes when transmitting OFDM signals in a system having multiple transceiving antennas. Upon separating and delivering the OFDM symbols to each antenna via a serial-to-parallel converter and a multiple antenna encoder, an Inverse Fast Fourier Transform (IFFT) for changing a frequency domain signal into a time domain signal and a cyclic prefix (CP) for minimizing interference between channels are added and transmitted to the receiving side. Here, the data sequence delivered to the first antenna is transmitted to the receiving side as is (i.e., without any changes), while the data sequence transmitted from other transmit antennas is delayed in cyclic shift manner when compared to a first antenna. By using the phase-shift diversity method, the flat fading channel may be changed to a frequency selectivity channel, and frequency diversity gain or frequency scheduling gain may be obtained according to a cyclic delay sample. However, despite some benefits of the above-described cyclic delay diversity scheme or phase-shift diversity scheme, because the spatial multiplexing rate is 1, the data transmission rate cannot be increased as desired.
The pre-coding scheme may include a codebook based pre-coding method used when there is a finite (or limited) amount of feedback information in a closed-loop system and may include a method of performing feedback upon quantization of channel information. Here, codebook based pre-coding refers to obtaining signal-to-noise ratio (SNR) gain by feeding back, to the transmitting side, an index of a pre-coding matrix that is already known by both the transmitting side and the receiving side. Such codebook based pre-coding scheme is beneficial in that effective data transmission is possible due to feedback of the index. However, because a stable channel is necessary, such codebook based pre-coding may not be fully appropriate for a mobile environment with severe channel changes. Also, some loss in the uplink transmission rate may occur due to the feedback overhead for the preceding matrix index. Additionally, because a codebook is needed in both the transmitting side and the receiving side, increased memory usage may be required.
The present invention recognized certain shortcomings related to certain multi-carrier based multiple antenna transmitting and/or receiving techniques. Based upon such recognition, several new features have been conceived to address and/or to solve such issues.
A phase-shift based pre-coding scheme used in a transmitting side and a receiving side that has less complexity than those of a space-time coding scheme, that can support various spatial multiplexing rates while maintaining the advantages of the phase-shift diversity scheme, that has less channel sensitivity than that of the pre-coding scheme, and that only requires a low capacity codebook has been conceived and provided herein. In particular, the matrix used for performing phase-shift based pre-coding can be more easily expanded and implemented according to any changes in the number of antennas being employed.
14. An apparatus to perform downlink baseband signal generation for a multiple antenna system with multiple antenna ports, the apparatus comprising: a layer mapper that performs layer mapping of complex-valued modulation symbols for each code word to be transmitted; a precoder that performs a precoding procedure on a first set of complex-valued modulation symbols received from the layer mapper to generate a second set of complex-valued modulation symbols to be mapped onto resources related to the antenna ports; and a transmitter that performs signal transmission via the antenna ports based upon the second set of complex-valued modulation symbols generated by the precoder. :
DL MIMO specification in 3GPP TS36.211, V890, Section 6.3 for general structure for downlink physical channels & Figure 6.3-1: Overview of physical channel processing.
26. The apparatus of claim 15, wherein the preceding is performed according to y(i)=W(i)D(i)U(i).times.(i),where a pre-coding matrix W(i) has a size of P.times..upsilon., and D(i) is a diagonal matrix to support cyclic delay diversity, and a unitary matrix U(i) has a size of .upsilon..times..upsilon.. :
DL MIMO specification in 3GPP TS36.211, V890, Section 220.127.116.11.2 for precoding for large delay CDD
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