Method for wireless data communication and a communication apparatus

The present application discloses a method for operating a wireless communication system. The method includes receiving a series of input data bits in a current timeslot by a transmitter and encoding the input data bits with a cross-Gray coding scheme to obtain coded information bits. Additionally, the method includes mapping the coded information bits to obtain respective multiple transmission symbols Xt for the current timeslot in a constellation diagram. Furthermore, the method includes converting the multiple transmission symbols Xt to generate a space-time matrix St of the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1 of a previous timeslot. Moreover, the method includes transmitting a respective one of elements in the space-time matrix St using a respective one transmitting antenna activated in the transmitter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/CN2019/123894 filed Dec. 9, 2019, which claims priority to Chinese Patent Application No. 201910058663.1, filed Jan. 22, 2019, the contents of which are incorporated by reference in the entirety.

TECHNICAL FIELD

The present invention relates to communication technology, more particularly, to a method for wireless data communication, and a communication apparatus.

BACKGROUND

Multiple-Input Multiple-Output (MIMO) technology has been widely applied with relative high diversity gain and multiplexing gain in wireless communication system in which multiple antennas are used at both the source (transmitter) and the destination (receiver). The antennas at each end of the communications circuit are combined to minimize errors and optimize data speed. However, channel-channel interference becomes more and more a serious problem, the reliability of data transmission gradually drops. Spatial modulation (SM) is introduced as a branch technology of MIMO to activate only one transmitting antenna during one timeslot, thus avoiding the channel-channel interference completely. Compared to traditional MIMO technology, SM technology adds space dimension. Therefore, spectrum efficiency of communication with SM technology is enhanced over traditional communication with MIMO technology. On the other hand, SM technology has its own limitation. In the SM system, receiver terminal requires to know the channel state information first, which makes channel estimation even more difficult. Especially for high-speed data flow through channels, the reliability associated with channel state information is even harder to be guaranteed. Improved communication technology is desired.

SUMMARY

In an aspect, the present disclosure provides a method for operating a wireless communication system for data communication. The method includes a step of receiving a series of input data bits in a current timeslot by a transmitter of the wireless communication system. The method further includes a step of encoding the input data bits with a cross-Gray coding scheme to obtain coded information bits. Additionally, the method includes a step of mapping the coded information bits to respectively obtain multiple transmission symbols Xtfor the current timeslot in a constellation diagram, including θ degree rotation within the constellation diagram. Furthermore, the method includes a step of converting the multiple transmission symbols Xtto generate a space-time matrix Stof the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1of a previous timeslot. Moreover, the method includes transmitting a respective one of elements in the space-time matrix Stusing a respective one transmitting antenna being activated.

Optionally, the step of encoding the input data bits with the cross-Gray coding scheme includes receiving the input data bits including a series of bit-elements of {p1, p2, p3, . . . , pn-1, pn}. The step further includes inserting pnevery other one bit-element in a sub-sequence of {p1, p2, p3, . . . , pn-1}, either from left to right or from right to left of the input data bits to obtain the coded information bits.

Optionally, the step of mapping the coded information bits includes mapping the coded information bits to obtain multiple initial constellation symbols Xt′ of the current timeslot at multiple constellation nodes (i,j) in the constellation diagram, Xt′=XijR+XijI, wherein XijRis a real part of and XijIis an imaginary part of a respective one initial constellation symbol Xt′(i,j)at a respective one of the multiple constellation nodes (i,j). The step further includes rotating the multiple initial constellation symbols Xt′ by θ degree rotation to obtain the multiple transmission symbols Xtas

Optionally, the step of mapping the coded information bits includes modulating the coded information bits by Quadrature Amplitude Modulation (QAM) protocol, or Phase shift Keying (PSK) protocol, or Amplitude-Phase shift Keying (APSK) protocol to obtain modulated bits in terms of the multiple transmission symbols Xt.

Optionally, the step of converting the multiple transmission symbols Xtto generate a space-time matrix Stof the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1of a previous timeslot includes performing a convolution operation of the multiple transmission symbols Xtfor the current timeslot with the space-time matrix St-1generated in the previous timeslot.

Optionally, the space-time matrix Stof the current timeslot includes a real matrix with one element per column denoting a to-be-transmitted information bit including a respective one of the modulated bits and a respective one of the spatial bits for activating a respective one transmitting antenna and only one to-be-transmitted information bit per row associated with only one transmitting antenna being activated once in the current timeslot.

Optionally, the step of performing a convolution operation includes estimating a channel transmission matrix Htof the current timeslot, Ht=Yt-1Xt−Nt-1Xt, based on multiple reception symbols Yt-1received in the previous timeslot by a receiver of the wireless communication system, Yt-1=Ht-1St-1+Nt-1, where Ht-1is a channel transmission matrix of the previous timeslot and Nt-1is a noise vector in the previous timeslot. Additionally, the step includes converting both the multiple transmission symbols Xtand the channel transmission matrix Htfrom a complex field to a real field. Furthermore, the step includes performing an orthogonal triangulation decomposition to the channel transmission matrix Ht.

Optionally, the step of transmitting a respective one of elements in the space-time matrix Stincludes activating a respective one transmitting antenna for transmitting a respective one to-be-transmitted information bit to a respective one receiving antenna based on an estimated channel transmission matrix.

In another aspect, the present disclosure provides a method for operating a wireless communication system for data communication. The method includes a step of transmitting a respective one of elements in a space-time matrix Stusing an activated one of ntnumber of transmitting antennas of the wireless communication system through respective one of channels based on an additive white Gaussian noise (AWGN) model. The method further includes a step of receiving multiple reception symbols Ytrespectively by nrnumber of receiving antennas of the wireless communication system, wherein Yt=HtSt+Nt, Htis a channel transmission matrix at a current timeslot with a dimension of (nr×nt) and respective elements representing channel gains associated with respective nrnumber of receiving antennas and ntnumber of transmitting antennas. Htis estimated from multiple symbols Yt-1received during a previous timeslot by a receiver via Yt-1Xt−Nt-1Xt, the space-time matrix Stis generated by the transmitter from multiple transmission symbols Xtin a constellation diagram mapped from coded information bits for the current timeslot. Ntis a transmission noise vector in the current timeslot based on the AWGN model. Nt-1is a transmission noise vector in the previous timeslot. Furthermore, the method includes a step of demodulating the multiple reception symbols Ytto obtain demodulated information bits. Moreover, the method includes a step of decoding a respective one of the demodulated information bits to obtain a respective one decoded constellation symbol.

Optionally, the step of decoding a respective one of the demodulated information bits includes decoding by a sphere decoding detection algorithm to obtain corresponding spatial bits or demodulated data bits in decoded constellation symbols.

Optionally, the step of decoding includes using a receiver-centric sphere decoding detection algorithm to decode the demodulated information bits to obtain decoded constellation symbols independent from a channel transmission matrix of the current timeslot.

Optionally, the decoded constellation symbols are represented by
[{circumflex over (X)}DSMRx-SD]=argmaxtraceS∈Xt{Re(YtH−Yt-1Xt)≤CR2},
where argmaxtrace{.} is to output an argmax value within a search radius CRfor the current timeslot. YtHare conjugate transposition of multiple reception symbols Ytrespectively received in the current timeslot by nrnumber of antennas in the receiver of the wireless communication system. Yt-1is reception symbols received in a previous timeslot.

Optionally, the method further includes a step of converting both the multiple transmission symbols Xtin a transmitter of the wireless communication system and an estimated channel transmission matrix Htfrom a complex field to a real field. Additionally, the method includes a step of performing an orthogonal triangulation decomposition to the estimated channel transmission matrix Ht. The method further includes a step of converting the multiple transmission symbols Xtto a space-time matrix St. Furthermore, the method includes a step of transmitting an information bit made by a respective one of elements in the space-time matrix Stusing a respective activated transmitter antenna. Moreover, the method includes a step of decoding the multiple reception symbols Yt=HtSt+Ntreceived by the receiver based on a transmitter-centric sphere decoding detection algorithm to decode the demodulated information bits to obtain decoded constellation symbols.

Optionally, the decoded constellation symbols are represented by
[{circumflex over (X)}DSMTx-SD]=argminX∈Oc{∥YtQ−RXt∥2≤CR2},
where argmin{.} is a function for obtaining a minimum value in a group OcofXwithin a search radius CRfor the current timeslot.YtQrepresents multiple reception symbols Ytleft-multiplying a positive definite matrix Q.

Optionally, the step of decoding the multiple reception symbols Ytincludes searching through a shortest searching path {circumflex over (T)} among a group of searching paths Tiin the constellation diagram to obtain the decoded constellation symbols. The shortest searching path is represented by

Optionally, the step of decoding a respective one of the demodulated information bits includes decoding the demodulated information bit of the current timeslot to obtain an output data bit containing a spatial bit and/or modulated bit, and storing the output data bit, if the spatial bit and/or modulated bit in a to-be-transmitted information bit of the current timeslot is different from a spatial bit and/or modulated bit in a to-be-transmitted information bit of a previous timeslot. The step further includes obtaining and storing an output data bit associated with the to-be-transmitted information bit of the previous timeslot to be the output data bit for the current timeslot, if the spatial bit and/or modulated bit in the to-be-transmitted information bit of the current timeslot is same as a spatial bit and/or modulated bit in the to-be-transmitted information bit of the previous timeslot.

In yet another aspect, the present disclosure provides a wireless communication apparatus. The wireless communication apparatus includes an encoder configured to encode input data bits of a current timeslot with a cross-Gray coding scheme to obtain coded information bits. The wireless communication apparatus further includes a modulator configured to map the coded information bits to respectively obtain multiple transmission symbols Xtfor the current timeslot in a constellation diagram, including θ degree rotation within the constellation diagram. Additionally, the wireless communication apparatus includes a processor configured to convert the multiple transmission symbols Xtto generate a space-time matrix Stof the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1of a previous timeslot. The wireless communication apparatus further includes a transmitter configured to activate a respective one of ntnumber of transmitting antennas to transmit a respective one of elements in the space-time matrix St. Furthermore, the wireless communication apparatus includes a receiver configured to have a respective one of nrnumber of receiving antennas to receive a respective one of multiple reception symbols Yt=HtSt+Ntbased on channel gain defined by a channel transmission matrix Ht. The wireless communication apparatus further includes a demodulator configured to demodulate the multiple reception symbols Ytto obtain demodulated information bits. Moreover, the wireless communication apparatus includes a decoder configured to decode a respective one of the demodulated information bits to obtain a respective one decoded constellation symbol from which an output data bit can be extracted and stored.

Optionally, the modulator includes one selected from a Quadrature Amplitude Modulation (QAM) modulator, or a Phase shift Keying (PSK) modulator, or an Amplitude-Phase shift Keying (APSK) modulator to obtain modulated bits in terms of the multiple transmission symbols Xt. The processor is configured to perform a convolution operation of the multiple transmission symbols Xtof the current timeslot with the space-time matrix St-1of the previous timeslot to generate the space-time matrix Stof the current timeslot.

Optionally, the decoder includes a detector storing a receiver-centric sphere decoding detection algorithm executed to decode demodulated information bits to obtain decoded constellation symbols when the transmitter directly transmits the elements in the space-time matrix Stof the current timeslot without having the processor to perform extra digital-data operations to the multiple transmission symbols Xt.

Optionally, the decoder includes a detector storing a transmitter-centric sphere decoding detection algorithm executed to decode demodulated information bits to obtain decoded constellation symbols when the transmitter transmits to-be-transmitted information bits after the processor performs extra digital-data operations of these steps: estimating a channel transmission matrix Htof the current timeslot, Ht=Yt-1Xt−Nt-1Xt, based on multiple reception symbols Yt-1received in the previous timeslot by a receiver of the wireless communication apparatus, Yt-1=Ht-1St-1+Nt-1. Ht-1is a channel transmission matrix of the previous timeslot and Nt-1is a noise vector in the previous timeslot; converting both the multiple transmission symbols Xtand the channel transmission matrix Htfrom a complex field to a real field; and performing an orthogonal triangulation decomposition to the channel transmission matrix Ht.

DETAILED DESCRIPTION

Accordingly, the present disclosure provides, inter alia, a wireless communication method, a communication apparatus utilizing differential spatial modulation (DSM) without need of channel transmission estimation, that possesses advantages with simplified system processing and enhanced system reliability for data transmission substantially to obviate one or more of the problems due to limitations of the related art. For example, the method of the present disclosure can be applied in an electronic price-tag updating system.

In one aspect, a wireless communication method is provided. Optionally, the wireless communication method is implemented thorough a wireless communication system illustrated inFIG. 1as an example. The method is shown by a flow chart shown inFIG. 2based on the wireless communication system shown inFIG. 1. Referring toFIG. 1, the wireless communication system is configured to receive a series of input data bits that are subjected for wirelessly transmitting via a transmitter to a receiver in the communication system. Optionally, the series of input data bits include information generated in a server device which is associated with the transmitter configured to transmit the input data bits in terms of multiple transmission symbols that are processed before transmission via an activated one of multiple transmitting antennas. The data processing operation of the input data bits includes encoding the input data bits to coded bits via an encoder based on a certain encoding scheme and modulating the coded bits via a modulator according to a certain modulation scheme. Optionally, a differential spatial modulation scheme is used. Optionally, the wireless transmission is achieved through one of multiple channels controlled by a channel transmission matrix. For example, Multiple-Input Multiple-Output (MIMO) technology has been widely applied with relative high diversity gain and multiplexing gain in wireless communication system in which multiple antennas are used at both a transmitter and a receiver of the wireless communication system. The receiver is part of a user device configured to receive the multiple reception symbols wirelessly via at least one receiving antenna. The multiple reception symbols are related to the multiple transmission symbols processed through the channel transmission matrix plus certain channel noises. The multiple reception symbols are then demodulated by a demodulator to obtain demodulated information bits and decoded by a decoder/detector to generate decoded symbols, from which an output data bit can be deduced.

Optionally, the transmitter side and the receiver side of the wireless communication system can be switched in positions, i.e., the receiver can include multiple antennas configured to transmit signals and the transmitter also can include multiple antennas configured to receive the signals from the receiver.

Referring toFIG. 2, in the embodiment, the method includes receiving a series of input data bits in a current timeslot by a transmitter of the wireless communication system. The method further includes a step of encoding the input data bits with a cross-Gray coding scheme to obtain coded information bits. Optionally, the input data bits can be encoded via various encoding schemes. Optionally, the input data bits can be encoded using Gray encoding scheme. In the embodiment, the input data bits are encoded using Cross-Gray encoding scheme, enhancing encoding efficiency for subsequent differential spatial modulation operation. The cross-Gray encoding scheme can be achieved, for example, on an input bits sequence {p1, p2, p3. . . . , pn-1, pn}. The encoding is performed by inserting pnevery other bit from left to right or from right to left of a bit sequence {p1, p2, p3, . . . , pn-1} to obtain coded bit sequence. In an example, the input data bits are formed by a sequence of binary digits 0 and 1. Any two neighboring digits in the coded bit sequence, only two are different. Inserting pnfrom left to right every other digit into a bit sequence {p1, p2, p3, . . . , pn-1} leads to a coded bit sequence {pn, p1, pnp2, pn, p3, . . . , pn, pn-1}. Inserting pnfrom right to left every other digit into a bit sequence {p1, p2, p3, . . . , pn-1} leads to another coded bit sequence {p1, pnp2, pn, p3, . . . , pn, pn-1, pn}. Cross-Gray encoding scheme changes a length of the bit sequence with a simple encoding rule, enhancing encoding efficiency comparing to traditional gray encoding scheme. Correspondingly, a receiver of the wireless communication system can perform a decoding operation from left to right or from right to left according to a same manner.

Referring toFIG. 2, the method additionally includes a step of mapping the coded information bits to obtain respective multiple transmission symbols Xtfor the current timeslot in a constellation diagram. In the embodiment, the step of mapping the coded information bits to a constellation diagram includes performing a modulation operation to the coded information bits to obtain modulated bits in terms of multiple transmission symbols Xtin the constellation diagram. Optionally, the modulation operation includes one selected from Quadrature Amplitude Modulation (QAM). Phase Shift Keying (SK) or Amplitude-Phase Shift Keying (APSK) modulation techniques. For example, the symbols are encoded in the difference in phase between successive sample information bits, this is called differential phase-shift keying (DPSK). A convenient method to represent PSK schemes is on a constellation diagram. This shows the points in the complex plane where, in this context, the real and imaginary axes are termed the in-phase and quadrature axes respectively due to their 90° separation. Such a representation on perpendicular axes lends itself to straightforward implementation. The amplitude of each point along the in-phase axis is used to modulate a cosine (or sine) wave and the amplitude along the quadrature axis to modulate a sine (or cosine) wave. For example, BPSK uses two phases which are separated by 180° and so can also be termed 2-PSK. For example, QPSK uses four points on the constellation diagram, equi-spaced around a circle. In the constellation diagram each symbol X is a complex number having a real portion XRand an imaginary portion XI.

Optionally, if the cross-Gray coding scheme is used only on the transmitter of the wireless communication system, a higher error rate may be caused. For example, the transmitter transmits symbols (0+j) and (1+0j) (where j is the imaginary part symbol). After cross-Gray coding, two different symbols (1+j) and (0+0j) are obtained with corresponding real part symbol being crossed on the constellation diagram. In this case, it results in one of the transmitting antennas to transmit a symbol (0+0j), corresponding to 0 for both the real part and the imaginary part. Thus, the antenna has no corresponding transmission information to transmit, causing a large error in the encoding process. Additionally, after the transmission symbols are encoded via the cross-Gray coding scheme, the Euclidean distance of the transmission symbols also changes, causing reliability of the communication system to drop.

Accordingly, a rotation coordinates cross-Gray encoding scheme is adopted. In particular, after encoding to obtain the coded information bits, the mapping of the coded information bits to the constellation diagram leads to multiple initial constellation symbols Xt′ of the current timeslot at multiple constellation nodes with coordinates of (i, j). In this case, Xt′=XijR+XijI, wherein XijRis a real part of and XijIis an imaginary part of a respective one symbol Xt′(i,j) at the node (i, j) in the constellation diagram. Then, a rotation operation is performed to rotate the multiple initial constellation symbols Xt′ by θ degrees to obtain the multiple transmission symbols Xtas

Xt=[cos⁢⁢θsin⁢⁢θ-s⁢in⁢⁢0cos⁢⁢θ]⁡[XijRXijI],
where 0°<θ<360° and is different per usage of different modulation scheme during the constellation mapping operation. Optionally, a simulation is performed and verified by experiment to select an optimum value of θ to determine final transmission symbol Xtto reduce error-bit rate. In some embodiments, nPSK modulation scheme is employed to modulate coded information bits through the constellation mapping and rotation. A spectral efficiency at the transmitter can be given as

mDSM=1nt⁢log2⁡(nt!)+n,
where ntis the number of transmitting antennas and n is the order of the nPSK modulation scheme.

Referring toFIG. 2, the method additionally includes a step of converting the multiple transmission symbols Xtto generate a space-time matrix Stof the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1of a previous timeslot. In the embodiment, the differential spatial modulation operation in the wireless communication system introduces a space-time field in which the transmission symbol X is converted to a space-time matrix S with dimensions of nt×ntwith each element S(m, t) of the space-time matrix represents a transmission symbol being transmitted in time t within the timeslot by the m-th antenna of the nttransmitting antennas in the transmitter. Each element of the space-time matrix S becomes a to-be-transmitted symbol by the transmitter at a specific time using one activated transmitting antenna during the current timeslot. The method includes a step of transmitting a respective one of elements in the space-time matrix Stusing a respective one transmitting antenna being activated.

For example, a space-time matrix

S=[S1100S22]
representing two transmission symbols S11and S22respectively transmitted y a 1-st and a 2-nd transmitting antenna during 1-st time and 2-nd time. Other elements being equal to 0 indicate that other transmitting antennas transmit no symbols. In an embodiment, the space-time matrix S is obtained by incorporating spatial bits information associated with orders of transmitting antennas being activated for transmission through wireless channels. The space-time matrix S must meet two following conditions: 1) every column of the space-time matrix S only has one element (effectively) so that every time it activates one transmitting antennas; 2) every row of the space-time matrix Shas one element (effectively) so that one transmitting antenna must be activated only once for one time during the timeslot.

FIG. 3is schematic diagram of encoded spatial bits corresponding to arrangements of transmitting antennas according to an embodiment of the present disclosure. The spatial bit information is represented respectively in real part and imaginary part of the transmission symbol corresponding to orders of the transmitting antennas in the transmitter. In a case that there are two transmitting antennas in the transmitter, the mapping order of the antennas is 1, 2 corresponds to a spatial bit of 0; the mapping order of the antennas is 2, 1 corresponds to another spatial bit of 1. Referring toFIG. 3, the number of transmitting antennas is nt=4. In this case, spatial bits can adopt at least 8 codes to represent the four transmitting antennas. Extra 4 codes shown inFIG. 3are discarded. Diversity gain is significantly enhanced.

FIG. 4is a table of using BPSK modulation in differential spatial modulation (DSM) mapping according to an embodiment of the present disclosure. The Input data bit may be encoded information bit after performing encoding operation via cross-Gray encoding scheme. Two transmitting antennas are involved, denoted by serial number #1 and #2, respectively. BPSK modulation scheme is employed in this case. When the antennas are activated in the order of serial number #1 and serial number #2, as shown inFIG. 4, the corresponding spatial bit would be 0. When the spatial bit is 0, and the to-be-transmitted space-time matrix is

[+100+1],
the BPSK modulated bit is 11. Correspondingly, the transmitted information bit will be 011.

In an embodiment, the space-time matrix Stof a current timeslot is obtained by performing a convolution operation of the multiple transmission symbols Xtfor the current timeslot with the space-time matrix St-1generated in the previous timeslot. Referring toFIG. 1, a channel model is needed to properly assess a multi-input multi-output channel for the wireless communication system containing ntnumber of transmitting antennas and nrnumber of receiving antennas, wherein nt=nr=M. Each receiving antenna receives not only the direct transmission symbol intended for it, but also receives a fraction of signal from other propagation paths. The channel response is expressed as a channel transmission matrix H with dimension of (nr×nt). For example, a direct path formed between antenna1at the transmitter and the antenna1at the receiver is represented by the channel response as an element h11. The channel response of the path formed between antenna1in the transmitter and antenna2in the receiver is expressed as another element h21and so on.

In the embodiment, a channel transmission matrix Htfor the current timeslot needs to be estimated based on a Ht-1for a previous timeslot, which is feedback from a receiver of the wireless communication system that is linked through channels between nrnumber of receiving antennas and ntnumber of transmitting antennas. Optionally, the channels are access points based on an additive white Gaussian noise (AWGN) model. The modulation operation of the coded information bits (mapped to multiple transmission symbols Xtthrough the constellation mapping operation and coordinates rotation operation) at the transmitter can be performed without need of the channel transmission state of the current timeslot, thereby simplifying system processing on the transmission data and enhancing reliability of data transmission through the wireless communication system. Specifically, the step of modulating the coded information bits includes estimating a channel transmission matrix Htof the current timeslot, Ht=Yt-1Xt−Nt-1Xt, based on multiple reception symbols Yt-1received in the previous timeslot by a receiver of the wireless communication system, Yt-1=Ht-1St-1+Nt-1, where Ht-1is a channel transmission matrix of the previous timeslot and Nt-1is a noise vector in the previous timeslot. Referring toFIG. 2, the step of transmitting a respective one of elements in the space-time matrix Stincludes activating a respective one transmitting antenna for transmitting the respective one to-be-transmitted information bit to a respective one receiving antenna based on the estimated channel transmission matrix.

Both the multiple transmission symbols Xtand channel transmission matrix Htcontain complex elements that describe both the amplitude and phase variations of the coded information bits and the channel link between the transmitter and the receiver of the wireless communication system. In a specific embodiment, the modulation operation at the transmitter side of the wireless communication system further includes converting both the multiple transmission symbols Xtand the channel transmission matrix Htfrom a complex field to a real field and performing an orthogonal triangulation (QR) decomposition to the channel transmission matrix Htto obtain a QR-decomposed channel transmission matrix that is used for transmitting multiple transmission symbols during the current timeslot. The QR decomposition of the channel transmission matrix can be performed before or after it is converted from the complex field to the real field. When the above modulation operation to convert both the transmission symbols and channel transmission matrix from complex field to real field is performed at the transmitter side of the wireless communication system, the decoding complexity at the receiver side of the wireless communication system can be reduced.

FIG. 5shows a flow chart of another wireless communication method according to an embodiment of the present disclosure. Referring toFIG. 1andFIG. 5, the wireless communication method includes transmitting a respective one of elements in a space-time matrix Stusing an activated one of ntnumber of transmitting antennas of the wireless communication system through respective one of channels based on an additive white Gaussian noise (AWGN) model. X1represents a first transmission symbol in the constellation diagram. XMrepresents a M-th transmission symbol in the constellation diagram. In an example, 1≤M≤nr. nris the number of receiving antennas in the receiver of the wireless communication system. The method further includes a step of receiving multiple reception symbols Ytrespectively by nrnumber of receiving antennas of the wireless communication system, where Yt=HtSt+Nt. Htis a channel transmission matrix at a current timeslot and is estimated from multiple symbols Yt-1received during a previous timeslot by the receiver via a relationship of Yt-1Xt−Nt-1Xt. Ntis a transmission noise vector in the current timeslot based on the AWGN model. Nt-1is a transmission noise vector in the previous timeslot.

Referring toFIG. 5, the method further includes a step of demodulating the multiple reception symbols Ytto obtain demodulated information bits. In the embodiment, the receiver of the wireless communication system does not need information of wireless channel state information through estimation of the channel transmission matrix of the current timeslot. Instead, the demodulation can be performed based on channel transmission matrix obtained for the previous timeslot.

Additionally, referring toFIG. 5, the method includes another step of decoding a respective one of the demodulated information bits to obtain a respective one decoded constellation symbol. Optionally, the wireless communication system can adopt various different decoding algorithms to decode the demodulated information bits. For example, maximum likelihood detection (ML) algorithm is used. In another example, sphere decoding detection (SD) algorithm is used. The ML algorithm is to perform a complete searching through all grids in the constellation diagram to detect the transmission symbols. Its computational complexity grows exponentially with the increase in the number of transmitting antennas. The sphere decoding detection (SD) algorithm is applied to limit a range of searching space under a foundation of the ML algorithm by limiting numbers of grids to be searched.

In a preferred embodiment, an improved sphere decoding detection (SD) algorithm is provided to reduce calculation complexity in the detection process. In particular, each constellation grid is calculated through multiple layers within a sphere with a given radius and the search of transmission symbols is performed from bottom up in the sphere. When a layer associated with a grid currently being searched is beyond the radius of the sphere, the grid is then discarded. Instead, simply searching for the symbol on a grid with minimum Euclidean distance as the symbol for decoding.

In the embodiment, decoding scheme for a respective one of the demodulated information bits includes a decoding operation performed via a sphere decoding detection algorithm to obtain corresponding spatial bits or demodulated data bits in the decoded constellation symbols.

In the embodiment, the decoding scheme includes a receiver-centric sphere decoding detection algorithm configured to decode the demodulated information bits to obtain decoded constellation symbols independent from a channel transmission matrix of the current timeslot.

In a specific embodiment, the decoded constellation symbols {circumflex over (X)}DSMRx-SDobtained by using the receiver-centric sphere decoding detection algorithm are represented by

As shown above, based on the receiver-centric sphere decoding detection algorithm the receiver side of the wireless communication system can demodulate and decode the transmitted information bits to obtain decoded symbol without need to know information about the wireless channel transmission state information.

In another specific embodiment, the decoding scheme includes a transmitter-centric sphere decoding detection algorithm configured to decode the demodulated information bits to obtain decoded constellation symbols. Before performing the decoding operation, two following steps are executed at the transmitter side of the wireless communication system: 1) a step includes converting both the multiple transmission symbols Xtand an estimated channel transmission matrix Htfrom a complex field to a real field; 2) and a second step includes performing an orthogonal triangulation decomposition to the estimated channel transmission matrix Ht. Based on the QR decomposition analysis on the estimated channel transmission matrix and upper-triangular characteristics of R matrix, the constellation grids at upper layer are made to be sequentially dependent to grids in lower layers. This reduces number of elements in the channel transmission matrix and reduces calculation complexity. Then, the transmitter side further execute steps of converting the multiple transmission symbols Xtto a space-time matrix Stand transmitting an information bit made by a respective one of elements in the space-time matrix Stusing a respective activated transmitter antenna. After the receiver receives the information bits in terms of multiple reception symbols Yt=HtSt+Ntbased on which demodulated information bits are obtained, the transmitter-centric sphere decoding detection algorithm is executed to decode the demodulated information bits to obtain decoded constellation symbols.

In the specific embodiment, the decoded constellation symbols {circumflex over (X)}DSMTx-SDobtained by using the transmitter-centric sphere decoding detection algorithm are represented by

Here Re(.) represent real part of the matrix and Im(.) represents imaginary pan of the matrix. Under the transmitter-centric sphere decoding detection algorithm, every layer is updated with an updated searching radius CQ. After the conversion to real field,Ytis changed to a real matrix with a dimension of 2nr×2nt. R is changed to a real matrix with a dimension of 2nt×2nr.Xtis changed to a real matrix with a dimension of 2nt×1. Even though the dimensions of the channel transmission matrix have increased, but calculation volume during the process of decoding the demodulated information still becomes lighter since both the transmission and reception symbols are all represented by real matrices. And this transformation does not change the system transmission reliability or affect error-bit rate.

In the embodiment, the estimated channel transmission matrix is subjected a QR decomposition analysis for two conditions:

QH⁢Yt-1_=⁢QR=⁢{[Q1⁡[2⁢nr×2⁢nt]⁢Q2⁡[2⁢nr×2⁢(nr-nt)]]⁡[R1⁡[2⁢nt×2⁢nt]0[2⁢(nr-nt)×2⁢nt]]nr≥ntQ1⁡[2⁢nr×2⁢nr][R1⁡[2⁢nr×2⁢nr]R2⁡[2⁢nr×2⁢(nt-nr)]]nr<nt,
where QHis a conjugate transposition of matrix Q, Q1Q2=Q, R1R2=R; nrrepresents numbers of receiving antennas, and ntrepresent numbers of transmitting antennas. Under the condition of nr<nt, matrix Q2is a null matrix so that it is not shown in above formula. Thus, Q=Q1.

In an example for a case with two transmitting antennas (nt=2), a search scheme for every layer is shown inFIG. 6in a differential spatial modulation system adopting, e.g., a BPSK modulation scheme. For the transmitted information bit000and001, the spatial bit is the same during the search process. For the transmitted information bit000and100, the modulated bit is the same. In the decoding operation of using either receiver-centric sphere decoding detection algorithm or transmitter-centric sphere decoding detection algorithm, three searches are conducted, yet two of them are repeated searches.

In another specific embodiment, a “tree”-branching search scheme is introduced to be associated with the decoding operation employing the transmitter-centric sphere decoding algorithm to further reduce number of searches and calculation complexity. Optionally, decoding a respective one of the demodulated information bits includes decoding the demodulated information bit of the current timeslot to obtain an output data bit containing a spatial bit and/or modulated bit, and storing the output data bit, if the spatial bit and/or modulated bit in a to-be-transmitted information bit of the current timeslot is different from a spatial bit and/or modulated bit in a to-be-transmitted information bit of a previous timeslot. Optionally, decoding a respective one of the demodulated information bits includes obtaining and storing an output data bit associated with the to-be-transmitted information bit of the previous timeslot to be the output data bit for the current timeslot, if the spatial bit and/or modulated bit in the to-be-transmitted information bit of the current timeslot is same as a spatial bit and/or modulated bit in the to-be-transmitted information bit of the previous timeslot.

For example, in a case there are four transmitting antennas (nt=4), a searching process using a conventional sphere decoding detection algorithm versus an improved tree-branching sphere decoding detection algorithm is shown inFIG. 7andFIG. 8in a differential spatial modulation system adopting BPSK modulation scheme. Accordingly, by using the tree-branching transmitter-centric sphere decoding detection algorithm the number of calculations is substantially reduced. For searching a grid under conventional sphere decoding detection algorithm, total number of calculations is 16−3=48. While for searching a grid under the tree-branching transmitter-centric sphere decoding detection algorithm, total number of calculations becomes (2+4×2)×2=20, being reduced by more than half of original number.

In an embodiment under the tree-branching transmitter-centric sphere decoding detection algorithm, a shortest searching path for searching a grid is defined as a minimum Euclidean distance from the grid to a reception symbolYtafter conducting a mapping operation to the elements at grids of each layer through a upper-triangular matrix R. The shortest searching path is represented by

T^=arg⁢⁢min⁢[Q1HQ2H]⁢Y_t-[R10]×Ti2Ti∈TreeT^=arg⁢⁢min⁢{Q1H⁢Y_t-R×Ti2≤CQ2-Q2H⁢Y_t2}Ti∈Tree
where Tree is a group of all searching paths associated with the tree-branching search scheme. By implementing this algorithm for decoding detection, the complexity of calculations is reduced to more than half amount while without affecting reliability of the system. During the decoding detection, the decoding time is substantially reduced and hardware performance requirement by the system can be also relaxed.

In an alternative aspect, the wireless communication method of the present disclosure can be applicated to different kinds of communication systems. In an example, the wireless communication system utilizing the method of the present disclosure is an electronic price-tag communication system.FIG. 9shows a schematic diagram of an electronic price-tag communication system. Referring toFIG. 9, a price-tag terminal serves as a transmitter to transmit information of price-tag back to a server. Alternatively, the price-tag terminal also can serve as a receiver to receive information from the server. Both the transmitter and the receiver are linked through wireless access point (AP) terminal for information communication. In some embodiments, differential spatial modulation and cross-Gray encoding scheme are incorporated with constellation symbols with mapping coordinate rotation technique to encode the information bits to obtain to-be-transmitted symbols for transmission from either the server or the price-tag terminal. Optionally, the AP terminal adopting Rayleigh flat fading channels with an estimated channel transmission matrix for transmitting the to-be-transmitted symbols, demodulating the reception symbols, and decoding the demodulated information bits to obtain the originally-modulated bits (plus spatial bits). In some embodiments, the method as disclosed in the present disclosure can effectively enhance diversity gain of the electronic price-tag communication system and secure reliability of data transmission through the communication system.

In another aspect, the present disclosure provides a wireless communication apparatus.FIG. 10is a block diagram of a wireless communication apparatus according to an embodiment of the present disclosure. Referring toFIG. 10, the wireless communication apparatus includes an encoder configured to encode the input data bits of a current timeslot with a cross-Gray coding scheme to obtain coded information bits. The wireless communication apparatus further includes a modulator configured to map the coded information bits to obtain respective multiple transmission symbols Xtfor the current timeslot in a constellation diagram. The mapping operation includes a rotation operation of an initial constellation symbol X′tby θ degree within the constellation diagram. Additionally, the wireless communication apparatus includes a processor configured to convert the multiple transmission symbols Xtto generate a space-time matrix Stof the current timeslot by incorporating spatial bits associated with orders of respective transmitting antennas based on a space-time matrix St-1of a previous timeslot. The wireless communication apparatus also includes a transmitter configured to activate a respective one of ntnumber of transmitting antennas to transmit a respective one of elements in the space-time matrix St. Furthermore, the wireless communication apparatus includes a receiver configured to have a respective one of nrnumber of receiving antennas to receive respective one of multiple reception symbols Yt=HtSt+Ntbased on channel gain defined by a channel transmission matrix Ht. The wireless communication apparatus still includes a demodulator configured to demodulate the multiple reception symbols Ytto obtain demodulated information bits. Moreover, the wireless communication apparatus includes a decoder configured to decode a respective one of the demodulated information bits to obtain a respective one decoded constellation symbol from which an output data bit can be extracted and stored or transmitted.

Optionally, the modulator of the wireless communication apparatus includes one of following modulators selected from a Quadrature Amplitude Modulation (QAM) modulator, or a Phase shift Keying (PSK) modulator, or an Amplitude-Phase shift Keying (APSK) modulator to obtain modulated bits in terms of the multiple transmission symbols Xt. The processor of the wireless communication apparatus is configured to perform a convolution operation of the multiple transmission symbols Xtof the current timeslot with the space-time matrix St-1of the precious timeslot to generate the space-time matrix Stof the current timeslot. Optionally, the processor includes a memory configured to store a computer-executable program designed to execute multiple steps of the method of operating the wireless communication system and store any coded information bits, perform data-processing operation and mapping constellation symbols. Optionally, the encoder, the modulator, and the processor are integrated with the transmitter to form a transmission terminal. Optionally, the transmission terminal is a server. Optionally, the transmission terminal is a user device or a field-deployed device.

Optionally, the decoder of the wireless communication apparatus includes a detector storing a receiver-centric sphere decoding detection algorithm executed to decode demodulated information bits to obtain decoded constellation symbols when the transmitter directly transmits the elements in the space-time matrix Stof the current timeslot without having the processor to perform extra digital-data operations to the multiple transmission symbols Xt.

Optionally, the decoder of the wireless communication apparatus includes a detector storing a transmitter-centric sphere decoding detection algorithm executed to decode demodulated information bits to obtain decoded constellation symbols when the transmitter transmits to-be-transmitted information bits after the processor performs extra digital-data operations. Optionally, the detector includes a memory configured to store a computer-executable program which includes the sphere decoding detection algorithm and store any decoded information bits or symbols. The extra operations are performed at the transmitter terminal, including 1) estimating a channel transmission matrix Htof the current timeslot, Ht=Yt-1Xt−Nt-1Xt, based on multiple reception symbols Yt-1received in the previous timeslot by a receiver of the wireless communication system, Yt-1=Ht-1St-1+Nt-1, where Ht-1is a channel transmission matrix of the previous timeslot and Nt-1is a noise vector in the previous timeslot; 2) converting both the multiple transmission symbols Xtand the channel transmission matrix Htfrom a complex field to a real field; and 3) performing an orthogonal triangulation decomposition to the channel transmission matrix Ht.

Optionally, the demodulator and the decoder are integrated within the receiver to form a receiving terminal. Optionally, the receiving terminal is a field deployed device. Optionally, the receiving terminal is a price-tag device. Optionally, the receiving terminal is also configured to transmit signal/data back to the transmission terminal or server. Optionally, the transmission between the transmission terminal and the receiving terminal is achieved through wireless channels acted as access points.