Wireless transmit/receive unit or base station for implementing space frequency block coding for orthogonal frequency multiplexing

Wireless transmitting/receiving unit or base station implementing orthogonal frequency multiplexing spatial frequency block coding

This creation is related to wireless communication systems. In more detail, this creation is related to a device and method for implementing spatial frequency block coding (hereinafter referred to as SFBC) in an orthogonal frequency division multiplexing (hereinafter referred to as OFDM) wireless communication system.

Creative background

Orthogonal frequency division multiplexing is a data transmission scheme in which the data is divided into multiple smaller data streams, and each data stream is transmitted using a subcarrier having a bandwidth smaller than the entire available bandwidth . The efficiency of the orthogonal frequency division multiplexing depends on the selected subcarriers that are orthogonal to each other. The said sub-carriers will not interfere with each other, and each sub-carrier carries a part of all user data.

The orthogonal frequency division multiplexing system has advantages over other wireless communication systems. When the user data is divided into data streams carried by different carriers, the effective data rate on each subcarrier will be relatively small. Therefore, the symbol duration will be much longer. A larger symbol duration can tolerate a larger delay profile. In other words, this comparison will not be severely affected by multiple paths. Therefore, the orthogonal frequency division multiplexing symbol can tolerate the delay profile without requiring a complicated receiver design. However, typical wireless systems require complex channel equalization schemes to combat the failure of multiple paths.

Another advantage of the described orthogonal frequency division multiplexing is that the generation of orthogonal subcarriers on the transmitter and receiver can use inverse fast Fourier transform (hereinafter referred to as IFFT) and fast Fourier transform (hereinafter referred to as FFT) engine. Because the implementation of the inverse fast Fourier transform and the fast Fourier transform are fairly well-known techniques, the orthogonal frequency division multiplexing can be easily implemented without using a complicated receiver.

Multiple input multiple output (hereinafter referred to as MIMO) is related to the type of wireless transmission and reception schemes, in which the included transmitter and receiver both use more than one antenna. A MIMO system takes advantage of spatial disparity or spatial multiplexing and improves the signal-to-noise ratio (hereinafter referred to as SNR) to increase the total processing capacity.

Space frequency block coding is a scheme of transmitting a spatially diverse code symbol on adjacent subcarriers instead of transmitting symbols on the same subcarrier in consecutive time slots. The space-frequency block coding avoids the problem of the first mutation in the space-time block coding. However, the channel needs to be maintained on the subcarriers where the combination occurs.

Creation content

A wireless transmitting/receiving unit or base station, which implements spatial frequency block coding of orthogonal frequency division multiplexing communication. The wireless transmitting/receiving unit or base station includes a channel encoder, a multiplexer coupled with the signal encoder, a power loading unit coupled with the multiplexer, and a power loading unit coupled with the power loading unit A plurality of spatial frequency block encoding and encoding units, a plurality of series-pair parallel converters coupled with the plurality of spatial frequency block encoding and encoding units, and a plurality of inherent beamforming coupled with the plurality of series-pair parallel converters And a plurality of inverse fast Fourier conversion units coupled with the plurality of inherent beamformers, and a plurality of antennas.

Detailed ways

In this specification, the technical term "base station (hereinafter referred to as STA)" includes, but is not limited to, depending on user equipment, a wireless transmitting/receiving unit, a fixed or mobile telephone subscriber unit, a pager, or Any other type of device that can operate in a wireless environment. In this specification, the technical term "Access Point (AP)" includes, but is not limited to, a Node B, a base station, an address controller, or any other type of interface device in a wireless environment.

This creation will be described in detail with reference to the drawings, in which the same symbols will be used to represent the same or similar elements. It is worth noting that the diagrams provided in this creation are high-level functional block diagrams, but these functional block diagrams can also be implemented with fewer or more blocks. The technical features described in this creation can also be integrated into an integrated circuit (IC) or configured on a circuit containing many interconnected components.

The specific embodiment of this creation provides a transmitter that performs SFBC MIMO encoding and a filter matched by the receiver. In specific embodiments, the functions of transmitter pre-coding, receiver antenna processing, and channel decomposition are also provided.

The system of this creation has two modes of operation: a closed loop and an open loop. When channel state information (hereinafter referred to as CSI) can be used in the transmitter, a closed loop is used, and when the channel state information cannot be used, an open loop is used. A variant can be used to transmit to a conventional base station, where this variant provides different benefits.

In the closed loop mode, the channel state information is used and a virtual independent channel is established by decomposing and diagonalizing the channel matrix and pre-coding in the transmitter. Given the inherent value distribution of the TGn channel, this creation uses a spatial frequency orthogonal multiple input multiple output code in the transmitter at the input to the channel pre-coding to increase reliability at the cost of reducing the data rate. Spend. Any coding scheme in the multiple input multiple output described must deal with the trade-off between multiplex gain and diversity. It is best to have a compromise solution that is most suitable for the specific channel statistics. Due to the low mobility and long channel coherent time, a spatial frequency block coding will be selected. Such a scheme allows the receiver to perform simpler than an MMSE receiver. The combined decoupling method allows a higher processing capacity in a larger range. The specific embodiment of the present invention allows each sub-carrier power/bit to load and maintain a sustainable and reliable link through the closed loop operation with channel state feedback. Another possible benefit is that it is easy to add any number of antennas in the transmitter or receiver.

The channel state information can be obtained in the transmitter by feedback from the receiver or by developing channel reciprocity. Channel reciprocity is particularly effective for systems based mainly on Time Division Duplex (TDD). In this example, it is possible for the transmitter and receiver to estimate and decompose the channel independently. When the signal-to-noise ratio is high enough to cause a reduced feedback bandwidth load, the channel update rate can become lower. The potential needs and the feedback data rate are usually less important for the non-selective intrinsic value of the natural frequency.

The closed loop mode requires the classification of the transmitter to compensate for the amplitude, and the estimated channel phase difference in the uplink and downlink directions. This situation does not often occur, for example, in the process of STA association or in the case of application control, and it is possible to use channel equivalence to evaluate the channels at both ends. In addition, the CQI (or SNR) of each inherent beam is fed back to the transmitter to support proper rate control.

Figure 1 is a block diagram of an OFDM MIMO system 100 using a closed loop mode. The system 100 includes a transmitter 110 and a receiver 130. The transmitter 110 includes a channel encoder 112, a multiplexer 114, a power loading unit 116, a plurality of SFBC encoding units 118, a plurality of parallel-to-serial (S/P) converters 120, and a plurality of inherent beam forming Adapter 122, multiple IFFT units 124, and multiple transmitting antennas (not shown). In a better case, the channel encoder 112 encodes the data according to the channel quality index (hereinafter referred to as CQI) sent by the receiver 130. The CQI is used to determine the code rate and modulation scheme of each subcarrier or group of subcarriers. The encoded data string is multiplexed into two or more data strings through the multiplexer 114.

The transmission power level of each data string is adjusted by the power loading unit 116 based on feedback. The power loading unit 116 adjusts the power level related to the data rate of each inherent beam to balance the entire transmission power passing through all the inherent beams (or subcarriers), which will be described in detail later.

The SFBC encoding unit 118 performs SFBC encoding on the data string. For each transmitted data rate, all inherent beams and subcarriers are SFBC encoded. The natural beam and subcarrier pairs are selected in order to determine independent channels. OFDM symbols are carried on the K subcarriers. In order to comply with SFBC, the subcarriers are divided into L pairs of subcarriers (or subcarrier groups). The bandwidth of each subcarrier group should be smaller than the coherent bandwidth of the channel. However, when combined with the natural beam formation, this limitation can be loosened due to the frequency dullness of the natural beam.

The pair of subcarrier groups used by the block code is considered to be independent. The following is an example of Alamouti form SFBC applied to OFDM symbols:<maths><img file="TWM287552U_D0001.tif" /></maths>

Once the SFBC encoding unit 118 constructs OFDM symbols for all subcarriers, the encoded blocks are multiplexed by the S/P converter 120 and input to the inherent beamformer 122. The inherent beam former 122 distributes the beam to the transmitting antenna. The IFFT unit 124 converts data in the frequency domain into data in the time domain.

The receiver 130 includes a plurality of receiving antennas (not shown), a plurality of FFT units 132, an intrinsic beamformer 134, an SFBC decoding unit 136, a combiner 138, a channel decoder 144, a channel estimator 140, a CSI generator 142, and CQI generator.

The FFT unit 132 converts the received samples into the frequency domain and the intrinsic beamformer 134, and the SFBC decoding unit 136 and the channel decoder 144 perform operations opposite to those performed on the transmitter 110. The combiner 138 uses Maximum Radio Combination (MRC) to combine the SFBC decoding results.

The channel estimator 140 uses a training sequence transmitted by the transmitter to generate a channel matrix, and divides each subcarrier (or each subcarrier group) by single value decomposition (SVD) or dual value decomposition. The channel matrix is divided into a number of beamforming unit matrices U and V (for transmitting and V for receiving), and a diagonal matrix D.

The channel matrix H between nT transmitting antennas and nR receiving antennas can be expressed by the following formula:<maths><img file="TWM287552U_D0002.tif" /></maths>

Decompose the channel matrix H by SVD into:<i>H=UDV</i>^<i>H</i>, Where U and V are beamforming unit matrices and D is a diagonal matrix.<i>U</i><img file="TWM287552U_D0003.tif" />CnRxnR while<i>V</i><img file="TWM287552U_D0004.tif" />CnTxnT. Then, for the transmission vector s, the transmission precoding is simply performed as follows:<i>x=Vs</i>(transmitted signal).

The received signal becomes the following formula:<i>y=HVs+n</i>, Where n is the noise introduced into the channel. The receiver completes the decomposition by using a matching router:<i>V</i>^<i>H</i><i>H</i>^<i>H</i><i>=V</i>^<i>H</i><i>VD</i>^<i>H</i><i>U</i>^<i>H</i><i>=D</i>^<i>H</i><i>U</i>^<i>H</i>.

After normalizing the channel gain of the inherent beam, the estimate of the transmitted symbol s becomes:<maths><img file="TWM287552U_D0005.tif" /></maths>

It detects s without performing continuous interface cancellation or MMSE type detector. DHD is a diagonal matrix formed by the intrinsic value of H passing through the diagonal. Therefore, the normalization factor α=<i>D</i>^－².U is the intrinsic vector of HHH, V is the intrinsic vector of HHH, and D is the diagonal matrix of the single value of H (the square root of the intrinsic value of HHH).

Figure 2 is a block diagram of a system 200 using the open loop mode obtained according to this case. The system 200 includes a transmitter 210 and a receiver 230. In the open loop mode, the combination of space-frequency coding and spatial spreading in the transmitter 210 will provide diversity without requesting CSI. When operating with a legal 802.11a/g STA, a variation of this scheme can be used.

The transmitter 210 includes a channel encoder 212, a multiplexer 214, a power loading unit 216, a plurality of SFBC encoding units 218, a plurality of parallel-to-serial (S/P) converters 220, and an inherent beamformer Network (BFN) 222, multiple IFFT units 224, and multiple transmitting antennas 226. As in the closed loop mode, the channel encoder 212 uses the channel quality index (CQI) to determine the coding rate and modulation for each subcarrier or each subcarrier group. The CQI is used to determine the code rate and modulation scheme of each subcarrier or group of subcarriers. The encoded data string is multiplexed into two or more data strings through the multiplexer 114.

In the open loop, a beamforming network (BFN) 222 is used to replace the inherent beamformer. The BFN222 forms N beams in space, where N is the number of antennas 226. The beam is constructed pseudo-randomly through BFN matrix operations. The independent subcarrier groups used for SFBC coding are transmitted on individual beams.

For statutory support, SFBC encoding may not be implemented. Implementing beam changes to replace diversity will improve diversity and the performance of statutory 802.11 a/g devices.

The receiver 230 includes a receiving antenna 231, an FFT unit 232, a BFN234, an SFBC decoding and combining unit 236, and a channel decoder 238. The FFT unit 232 converts the received signal in the time domain to a signal in the frequency domain. The SFBC decoding and combining unit 23 decodes and combines the symbols received from the subcarrier group/intrinsic beam, and uses the prior knowledge of the cluster size to convert those symbols from parallel to serial. Use Maximum Radio Combination (MRC) to combine SFBC symbols. The channel decoder 238 decodes the combined symbols and generates CQI.

The following describes an embodiment of power loading. Spatial processing is a combination of spatial frequency coding and inherent beam forming. Performing the foregoing processing can achieve the best compromise between the redundancy gain provided by the SFBC and the spatial multiplexing provided by the inherent beamformer. The power loading scheme is operated by the inherent mode of the channel matrix. However, because of the interoperability within the encoder, SFBC will also cause a limitation, which means that no matter what input power is loaded, the output of the encoder has the same power loading.

Figure 3 is a block diagram of the transmitter 110 used to describe the power loading. Figure 3 depicts a 4x4 case as an example, and the first embodiment of the power loading scheme will be described later by referring to the 4x4 case shown. However, it should be noted that the 4x4 cases described will be extended to other cases.

For a specific subcarrier k, four data strings will be mapped to two pairs of power loading/AMC modes. In other words, the same number of modulation levels must be selected for each pair of inputs. Then, the modulation level is mapped to the intrinsic mode pair. The output of the power loading unit 116 is even connected to the dual 2x2 SFBC encoding unit 118 and then passed to the inherent beamformer 122. The natural beamformer 122 maps the input to the natural mode of the channel through preprocessing.

For all K subcarriers, the inherent value of the channel matrix is known to the transmitter. The channel energy of each inherent mode is defined as follows:<maths><img file="TWM287552U_D0006.tif" /></maths>

Where λ_<i>i,k</i>It is the i-th inherent value of the k-th subcarrier. For the two channel energies of the two coupled natural modes, it is defined as follows:<maths><img file="TWM287552U_D0007.tif" /></maths>

Where M is the number of inherent modes. In other words, the intrinsic modes are grouped, so that half of the intrinsic modes with strong channel energy (or SNIR) are divided into one group, and the other half with weaker channel energy are divided into another group. So SNIRs harmonics means the total channel energy of the stronger and weaker natural modes. The channel energy is an indicator of how strong the inherent modes are, so it can be known how strong the signals transmitted by these inherent modes will be. This information will be used to apply different adaptive modulation and coding (AMC) and/or the different power loading of each half which will be explained in more detail later. The separation of coupled SNIRs is defined as follows: _β= Β_m_o_d₁-Β_m_o_d₂During the closed loop operation, the transmitter 110 has the current CSI knowledge, so that it obtains the intrinsic value and the pre-processing matrix. The transmitter 110 can also infer from the CSI that the data rate can be supported on the link Rb. Then, the power loading of a given acceptable CSI is an optimization between the number of bits that can be transmitted per OFDM symbol and the modulation format that can be used for each mode.

It is used to calculate the channel energy as the inherent mode i described above to determine the maximum bit rate that can be supported by the channel condition. Then, the above-mentioned modes are calculated separately to determine how the bit rate must be distributed between the two pairs of modes. Figure 4 is a schematic diagram of exemplary power loading, adaptive modulation and coding mapping between two pairs of modes. In this embodiment, for a specific subcarrier, the supported bit rate is 24 bits per OFDM symbol. The lower bound of the modulation sequence that satisfies the bit rate is indicated by a dotted arrow in Figure 4. In this embodiment, the first and second modes (first coupling mode pair) will be used for 16QAM, and the third and fourth modes (second coupling mode pair) will be used by 256QAM.

It is worth noting that the mapping described is an acceptable CQI and a subcarrier mapping. In the examples of alternative MIMO configurations, such as 2x4, 2x2, etc., in addition to reducing the total number of bits in the table entry to indicate transmission feasibility, and in addition to reducing power loading on a single mode pair , The same power loading scheme can be used.

Hereinafter, a power loading scheme according to the second embodiment will be explained. Sort the intrinsic value of each subcarrier (λ1(k)&gt;λ2(k)&gt;...&gt;λnT(k)), and generate the intrinsic beams of all subcarriers by grouping the intrinsic values of the same order, As follows:<chemistry general="n"><img file="TWM287552U_D0008.tif" /></chemistry>

Among them, k is the number of subcarriers, nT is the number of transmitting antennas, and λi(j) is the i-th inherent value of the jth subcarrier, and nT is an even number.

The average value of the intrinsic value of each intrinsic beam is calculated as follows:<maths><img file="TWM287552U_D0009.tif" /></maths>

Pair the intrinsic beams to generate Alamouti spatial frequency blocks, such as {E1,E2}1,{E3,E4}2,...,{E2i-1,E2i}i...{EnT-1,EnT}nT/ 2. However, when the SNR of a pair is greater than SNRmax, the second inherent beam of the pair is replaced by the second lowest inherent value on average until its SNR is equal to or equal to SNRmin.

<maths><img file="TWM287552U_D0010.tif" /></maths>

in<img file="TWM287552U_D0011.tif" />Is noise variation, and SNRmin is the minimum required SNR of the highest data rate for the quality of service required. This step is repeated until all the inherent beams are paired. Figure 5 shows an example of the power/bit loading subcarrier pairing.

By mapping the SNR of a pair to a data rate of a given quality, a data rate of each inherent beam pair is determined. For each inherent beam pair, the required SNRs can be adjusted to compensate for measurement errors and to maintain the total transmit power at a constant value.

The weight vector of each inherent beam pair of each subcarrier can be calculated as follows:<maths><img file="TWM287552U_D0012.tif" /></maths>

Where i is the i-th inherent beam pair, and j is the j-th subcarrier.

Except for the first or second embodiment, according to the third embodiment, another power is applied to the sub-carrier group or sub-carrier of the weakened natural mode. In other words, instead of applying power loading to all the natural modes, it can only be applied to those weaker natural modes. Therefore, the most benefits can be obtained from power loading. In such an example, for example, those inherent modes without power loading can still have SFBC or other codes; or each can have different AMC settings. On the contrary, those inherent modes with power loading share the same AMC settings. Similarly, the inherent modes of the channel are usually sorted according to the power from strong to weak. By pairing inherent modes of similar power, the power loading of the channel can be improved.

A spatial processing scheme of any combination of receiving and transmitting antennas can be set. The combination of using SFBC and the inherent beamforming options depend on the number of antennas on each side. The following table sorts out the various settings that can be supported, the state of space processing, and the power loading of each implementable scheme.

<tables><img file="TWM287552U_D0013.tif" /></tables><tables><img file="TWM287552U_D0014.tif" /></tables>

Although the features and elements of this creation have been described in specific combinations in the preferred embodiment, each feature and element can be used alone, or there may be or Without the other features and elements in the preferred embodiment, the features and elements are used in various combinations.

<p>100, 200. . . system</p><p>110, 210. . . launcher</p><p>130, 230. . . receiver</p><p>110. . . Transmitter</p><p>S/P. . . Parallel</p><p>CSI. . . Channel status information</p><p>CQ. . . Channel Quality Index</p><p>MRC. . . Maximum wireless combination</p><p>SFBC. . . Spatial frequency block coding</p><p>IFFT. . . Inverse Fast Futura Conversion</p>

Figure 1: It is used to improve the multiple input multiple output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) communication system channel acoustic scheme flow chart.

Figure 1 shows a block diagram of an OFDM-MIMO system implementing a closed loop mode; Figure 2 shows a block diagram of a system implementing an open loop; Figure 3 shows a transmitter used to describe power loading Figure 4 shows a specific embodiment of power loading and adaptive modulation and coding mapping between two pairs of modes; and Figure 5 shows a specific embodiment of pairing of subcarrier groups for power/bit loading .