TECHNICAL FIELD

The present invention relates to mobile telecommunications technology, and in particular to a wireless communications process and an access point for Ultra-Reliable Low Latency Communication (URLLC).

BACKGROUND

While the current nominal communication latency in 4-th Generation ("4G") wireless networks is around 50 ms, the most critical requirement of 5-th generation ("5G") wireless networks is to reduce the latency to at most 1ms. In addition, this low latency has to be achieved with ultra- high reliability. This has led to an urgent need for the development of ultra-reliable and low- latency communication technologies, generally referred to in the art by the acronym "URLLC".

The main applications of URLLC include intelligent transportation, tele-surgery, and industrial automation. In intelligent transportation, vehicles need to exchange information with each other reliably and in a very short time period. Accordingly, URLLC is the crucial technology that can enable applications such as road safety, traffic efficiency, and fully automated driving to become a reality. Intelligent transportation requires the latency to be approximately 5-10 ms, and the block error rates (“BLER”) to be of the order of 10 ^-5 . In tele-surgery, surgery is performed by a robot that is controlled by a surgeon from a remote site, and it is critical for information from the surgeon to the robot to be sent reliably and with a low latency, leading to the need for URLLC. In such applications, the end-to-end delay should be less than 1 ms, and the required

BLER of the order of 10 ^-9 . The so-called 'Fourth Industrial Revolution' is also dependent on URLLC. Traditionally, wired communications networks are used in factories in order for the factory machines to receive instructions. However, wires limit the mobility of the industrial machines. As a result, wireless communication is needed in order to allow the industrial machines to be mobile. In order for such industrial automation to become a reality, the wireless communication latency should be around 1 ms, and the BLER of the order of 10

It is desired, therefore, to overcome or alleviate one or more difficulties of the prior art, or to at least provide a useful alternative.

SUMMARY

In accordance with some embodiments of the present invention, there is provided a wireless communications process executed by an access point of a wireless communications system, the process including the steps of: receiving, by a plurality of antennas of the access point, wireless signals representing pilot symbols transmitted by one or more antennas of respective transceivers of the wireless communications system; processing the received wireless signals to generate corresponding 1-bit CSI values for respective wireless communications channels between respective different antenna combinations, wherein each of the 1-bit CSI values represents channel state information of a corresponding wireless communications channel between a corresponding one of the plurality of antennas of the access point and a corresponding antenna of the one or more antennas of the one or more transceivers; processing the 1-bit CSI values for URLLC (ultra-reliable low-latency communications) between the access point and the one or more transceivers, the processing including: processing the 1 -bit CSI values and information symbols to generate corresponding transmit vectors for transmitting to the one or more transceivers in order to send the information symbols from the access point to the one or more transceivers; and processing the 1-bit CSI values and symbols received from the one or more transceivers to determine corresponding information symbols sent by the one or more transceivers to the access point.

In some embodiments, the one or more transceivers are a plurality of mobile transceivers that communicate with the access point on respective different frequency bands.

In some embodiments, the step of processing the received wireless signals generates a corresponding 1-bit CSI vector g for each antenna of the transceivers according to: where w _/ is a corresponding noise vector for the /-th pilot symbol transmission, h is a corresponding channel vector between the antennas of the access point and the antenna of the transceiver, P _p is the corresponding pilot power, and L is the corresponding total number of pilot symbols transmitted by the transceiver.

In some embodiments, the step of processing the 1-bit CSI values includes generating each transmit vector x of M elements x _m for each of the transceivers for transmission of a corresponding information symbol S Î { -1 - j,- + j, 1 - j, 1 +j} according to: where P _AP is the transmit power of the access point, M is the number of antennas of the access point, x _m is transmitted from the m-th antenna of the access point, for m = 1, 2, ..., M, and are the real and imaginary components of the m ^th element of g, s ^R and s ^I are the real and imaginary components of s; and wherein the transceiver processes a corresponding received vector y to determine a corresponding symbol according to: . where an error has occurred if .

In some embodiments, each of the transceivers generates a corresponding transmit vector x for a corresponding information symbol s Î {-1 - j, -1 + j, 1 - j, 1 + j} according to: where Pu is the total transmit power of the transceiver, and wherein the step of processing the 1-bit CSI values includes processing a corresponding receive vector and the corresponding 1- bit CSI values to determine that a corresponding symbol s has been transmitted by the transceiver according to: where and are the real and imaginary components of , and and and and

where and are the real and imaginary components of the m ^th element of g, and and are the real and imaginary components of the m* element of y.

In some embodiments, the one or more transceivers are a plurality of transceivers that communicate with the access point on the same frequency band but using respective different and non-overlapping subsets of the plurality of antennas of the access point.

In some embodiments, the one or more transceivers are a plurality of transceivers that communicate with the access point on the same frequency band.

In some embodiments, the step of processing the received wireless signals includes generating a noisy 1-bit CSI matrix G for each of the transceivers according to: where W _/ is an N x M noise matrix, H is a two-dimensional matrix of communications channels between the access point antennas and the transceivers wherein the ( m , n)-\h element of H is a communications channel between the n ^th transceiver antenna and the m ^th antenna of the access point, for m = 1, 2, ..., M, P _p is the pilot power, and L is the number of orthogonal pilots transmitted by each of the transceiver antennas. In some embodiments, the step of processing the 1-bit CSI values includes generating transmit vectors for each of the transceivers according to: where P _AP is the transmit power of the access point, and | · | denotes amplitude of a complex- valued number, where and are the real and imaginary components of the ( n , m)- th element of G, and are the real and imaginary components of s _n , being the complex-valued information symbol to be sent to the n ^th antenna of the transceivers, and wherein the transceiver can process corresponding received wireless signals to determine a corresponding symbol according to:

In some embodiments, each of the N transceivers can generate a corresponding transmit vector x _n according to: where P _U is the total transmit power of the corresponding transceiver, s _n being the complex- valued information symbol to be sent from the n- th antenna of the transceivers, and wherein the step of processing the 1-bit CSI values includes processing a corresponding receive vector and the corresponding 1-bit CSI values to determine that a corresponding symbol has been transmitted from the n- th transceiver antenna, for n = 1, 2, ... , N, according to: where and and and where and are the real and imaginary components of the (m,n) ^th element of the 1-bit CSI matrix G, wherein an error has occurred if .

In some embodiments, the plurality of antennas of the access point includes at least 100 antennas. In some embodiments, the plurality of antennas of the access point includes at least 1000 antennas. In accordance with some embodiments of the present invention, there is provided an access point for a wireless communications system, the access point including a plurality of communications channels, each said communications channel including:

(i) a corresponding antenna;

(ii) a corresponding DAC;

(iii) a corresponding ADC; and

(iv) a digital baseband processing component configured to execute any one of the above processes.

In some embodiments, the communications channels number M, and the access point further includes, for each of the antennas, a corresponding set of M 1-bit phase shifters, wherein the m- th phase shifters of the M antennas are coupled to a corresponding m-th analogue adder of a set of M analogue adders, the m-th analogue adder being coupled in turn to an m-th 1-bit ADC of a set of M ADCs.

In some embodiments, the antennas of the access point number at least 100 antennas. In some embodiments, the antennas of the access point number at least 1000 antennas..

In accordance with some embodiments of the present invention, there is provided an electronic data storage medium having stored thereon configuration data or processor-executable instructions (or both) that, when used to configure an FPGA or when executed by at least one processor of an access point of a wireless communications system, cause the access point to execute any one of the above processes. Also described herein is a wireless communications process executed by an access point of a wireless communications system, the process including the steps of: receiving, by a plurality of antennas of the access point, wireless signals representing pilot symbols transmitted by one or more antennas of respective transceivers of the wireless communications system; processing the received wireless signals to generate corresponding 1-bit CSI values for respective wireless communications channels between respective different antenna combinations, wherein each of the 1-bit CSI values represents channel state information of a corresponding wireless communications channel between a corresponding one of the plurality of antennas of the access point and a corresponding antenna of the one or more antennas of the transceiver; processing the 1-bit CSI values for URLLC (ultra -reliable low-latency communications) between the access point and the one or more transceivers, the processing including: generating transmit vectors for transmitting information symbols from the access point to the one or more transceivers; and processing the 1-bit CSI values to determine information symbols received from the one or more transceivers.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, wherein:

Figure 1 is a simplified block diagram of an access point in a 1-bit CSI (channel state information) generation mode, in accordance with an embodiment of the present invention;

Figure 2 is a simplified block diagram of the access point in a transmission mode;

Figure 3 is a simplified block diagram of the access point in a receiver mode; Ligure 4 is a simplified block diagram of an access point in a transmission mode, in accordance with an alternative embodiment of the present invention;

Ligure 5 is a simplified block diagram of the access point in a 1-bit CSI generation mode;

Ligure 6 is a simplified block diagram of the access point in a receiver mode;

Ligure 7 is a graph of the bit error rate (BER) of the access point communications with transceivers as a function of the signal-to-noise ratio (SNR) for different numbers of access point transmit and receive antennas and

Ligure 8 is a flow diagram of a wireless communications process executed by the access point.

DETAILED DESCRIPTION

Embodiments of the present invention include a wireless communications process and a wireless communications access point that enable Ultra-Reliable Low Latency Communication (“URLLC”) at/to transceivers by using multiple antennas at an access point in combination with 1 -bit channel state information (“CSI”) for the communications channel between each antenna of the access point and each antenna of the transceiver devices. The use of 1-bit CSI information allows extremely fast channel estimation to be implemented at the multi-antenna access point. This allows the access point to use low- cost and fast 1-bit ADCs (analogue-to-digital converters), 1-bit DACs (digital-to-analogue converters), and 1-bit phase shifters.

In some embodiments, the access point communicates with multiple transceivers using respective different frequency bands. In other embodiments, the access point communicates with multiple transceivers using the same frequency band to communicate with all transceivers. These arrangements allow URLLC to be achieved in the physical communication layer, without requiring resource-intensive processing in the higher communication layers.

Single-Antenna Transceivers

In some embodiments, an access point ("AP") with a multiple number (M > 1) of antennas communicates with multiple single- antenna wireless transceivers (also variously referred to herein for convenience of description as "devices" or "users"). Each of these users requires URLLC for both reception and transmission. The user transmits information to the AP in one frequency band, and receives information from the AP in another frequency band, or alternatively in the same frequency band where the reception and transmission are multiplexed in time.

The described embodiments of the present invention implement communication methodologies that achieve URLLC for each user in both the reception and the transmission directions. Sufficient conditions for achieving URLLC at the user are the following:

1) The AP has multiple antennas;

2) when acquiring channel state information (CSI), the AP acquires only 1-bit CSI of the channel between the m-th antenna at the AP and the user's antenna, for m = 1, 2, M ; and

3) the AP uses the 1-bit CSI vector to beamform/process its transmit vector, as well as to beamform/process its received vector for the purposes of achieving URLLC for the user in both the reception and the transmission directions. Access Point Modes of operation

The AP operates in three modes: 1) a 1-bit CSI generation mode, used for the AP to generate a 1-bit CSI vector of a communications channel; 2) a transmitter mode, used for the AP to transmit information symbols to the user; and 3) a receiver mode, used for the AP to receive information symbols from the user. Each of these operating modes of the AP is described below.

1 -bit CSI Generation Mode

In the 1-bit CSI generation mode, the user sends L pilot symbols to the AP in a time-division duplex fashion, where L > 1. At the AP, the received analogue pilot signal on the m-th antenna is digitized to 1 -bit of information which represents the 1 -bit CSI of the channel between the m-th antenna at the AP and the user's antenna for the l- th pilot symbol, for m = 1, 2, ..., M and 1=1, 2, L. Such digitization of the received analogue pilot signal can be performed by passing the received analogue pilot signal to a 1 -bit ADC. Then, the output of the 1 -bit ADC represents the 1-bit CSI of the channel between the m-th antenna at the AP and the user's antenna for the l- th pilot symbol, for m = 1, 2, ..., M and l=1, 2, ... , L. The generated L 1-bit CSI values for the m-th antenna of the AP are then processed in order to obtain only one 1-bit CSI value for the m-th antenna of the AP. This processing can, for example, be to sum the L 1- bit CSI values and then take the sign of the sum as the 1 -bit CSI value for the m-th antenna of the AP. This process can be modeled mathematically as follows.

Let h denote the M -length channel vector of the channel between the AP and the user, where the m-th element of h is the channel between the m-th antenna at the AP and the user's antenna, for m = 1, 2, ..., M . The 1-bit CSI vector g of the channel vector h is given by: where w _l is the noise vector at the AP for the /-th pilot transmission, P _p is the user's transmit power used to transmit the pilot symbols, and L is the total number of pilot symbols transmitted by the user.

Transmission Mode Operation

Let be the complex- valued symbol that the AP wants to transmit: to the user in one channel use, where with Let denote the real-valued and imaginary-valued parts of . The 1 -bit CSI vector g, given by ( 1), is known at the AP, Let denote the real- valued and imaginary-valued parts of the m-th element of g for m — 3.2. · · · , M. Using * and g, the AP constructs a vector x comprised of M elements, where the m-th element of x , denoted by for , is constructed as follows where P _AP is the transmit power of the AP. Next, the resulting vector x is transmitted from the AP, where the m-th element of x is transmitted from the m-th antenna, for m = 1, 2, ..., M. As a result of this transmission, the symbol received at the user's antenna is y. To decode the symbol s from y, the receiving user constructs a symbol as follows:

Thus the user determines that is the symbol transmitted from the AP. If , then an error has occurred. Receiver Mode Operation

Let .v be a complex-valued symbol that the user wants to transmit to the AP in one channel use

(i.e., in one symbol duration), where s Î {-1 - j, -1 + j, 1 - _j , 1 + j} with j =Ö-1. Next, s is transformed into x, according to: where P _U is the transmit power of the user. Linally, x is transmitted from the user to the AP.

As a result of this transmission, the AP receives a complex-valued symbol on each of its antennas. Let y _m denote the complex-valued symbol received at the AP on its m -th antenna, for m = 1, 2, ..., M .

Let and be the real and imaginary components of y _m the m ^th element of y, respectively. The 1-bit CSI vector g, given by Equation (1) above, is known at the AP. Let and be the real and imaginary components of the 777 ^th element of g. Then, using and for m = 1, 2, . . . , M , the AP constructs:

and

Using the AP constructs and as and

The AF then decides that the symbol has been transmitted by the user. Hence an error happens if occurs.

Multiple Users on Different Frequency Bands

The most common (but not the only) wireless communications network configuration is where one AP communicates with multiple users, each of which has one or more antennas. In some embodiments, different frequency bands are allocated for communications between respective different users and the AP. Hence for N users, or N antennas at the users, N distinct frequency bands are allocated. Then, the communication in each frequency band is a communication between the AP and a single user antenna, and the processes described above are applied to each frequency band.

As will be appreciated by those skilled in the art, an access point (AP) implementing the communications processes described above can itself be implemented in any of a variety of different possible hardware configurations. Figure 1 is a simplified block diagram showing the components of an embodiment of an access point to implement the 1-bit CSI generation mode described above. In order for the AP to generate a 1-bit CSI, it is sufficient for the AP to have a corresponding 1-bit ADC for each of its antennas, at least when it is operating in the 1-bit CSI generation mode.

Similarly, Figure 2 is a simplified block diagram showing the components of the access point to implement the transmission mode described above. When the AP operates as a transmitter of information, it is sufficient for it to have a corresponding 1 -bit DAC for each of its antennas. Figure 3 is a simplified block diagram showing components of the access point to implement the receiver mode described above. When the AP operates as a receiver of information, it is sufficient for the AP to have a corresponding 1-bit analog phase-shifter for each antenna, as shown in Figure 3.

Multiple Users on the Same Frequency Band

In the embodiments described above, the AP communicates with multiple user antennas over respective different and dedicated frequency bands. In other embodiments described below, the access point communicates with multiple transceivers using the same frequency band to communicate with all transceivers. Thus in the following, an AP having M antennas communicates with K users over only one frequency band. However, such communication comes at the expense of increased latency, due to 1-bit CSI generation from K users in one frequency band, and at the expense of added complexity at the AP.

In the following description, K non-cooperating wireless transceivers, referred to as users, require URLLC for both reception and transmission. In general, it is assumed that there are N > K antennas in total at the users (each transceiver can have more than one antenna), indexed by 1, 2, ..., N . The K users transmit information to the AP in one frequency band, and receive information from the AP in another frequency band, or in the same frequency band where the reception and transmission are multiplexed in time. The following describes how the AP can achieve URLLC for the users in both the reception and transmission directions. In a special case, the transmit antennas at the AP are divided into N groups of M/N >1 antennas each. Each group of antennas is used as though it is a separate AP that serves only one of the users' antennas. Accordingly, the communication processes described above for the multiple frequency band embodiments are independently applied to each group of AP antennas.

Other embodiments operate as described below.

Sufficient conditions for achieving URLLC at the users are the following:

1) the AP has multiple antennas;

2) when acquiring CSI, the AP acquires only a 1-bit CSI of the channel between the m-th antenna at the AP and the n- th user’s antenna, for m = 1, 2, ..., M and n = 1, 2, ..., N ; and

3) the AP uses a 1-bit CSI matrix to beamform/process its transmit vector, as well as to beamform/process its received vector to achieve URLLC for the users in both the reception and the transmission directions.

Access Point Modes of operation

In the embodiments described below, the AP has the same three operating modes as the multiple frequency band embodiments described above, namely: 1) a 1-bit CSI generation mode, used for the AP to generate a 1-bit CSI matrix of a communications channel; 2) a transmitter mode, used for the AP to transmit information symbols to the user; and 3) a receiver mode, used for the AP to receive information symbols from the user. Each of these operating modes of the AP is described below.

1 -bit CSI Generation

In the 1-bit CSI generation mode, each antenna of the users sends L pilot symbols to the AP in a time-division duplex fashion, where L ³ 1. Assuming that the n-th antenna of the users transmitted a pilot symbol, for n = 1, 2, ..., N, then the received analogue pilot signal on the m- th antenna of the AP is digitized to 1 -bit of information which then represents the 1 -bit CSI of the channel between the m-th antenna of the AP and the n- th antenna of the users for the l- th pilot symbol from the n- th antenna of the users, for m = 1, 2, ..., M and n = 1, 2, ..., N and l= 1,2,... ,L. Such digitization of the received analogue pilot signal can be performed by passing the received analogue pilot signal through a 1-bit ADC. Then, the output of the 1-bit ADC represents the 1-bit CSI of the channel between the m-th antenna of the AP and the n- th antenna of the users for the l- th pilot symbol from the n- th antenna of the users, for m = 1, 2, ..., M and n = 1, 2, ..., N and l= 1,2,... ,L. The generated L 1-bit CSI values for the channel between the m-th antenna of the AP and the n- th antenna of the users are then processed in order to obtain only one 1-bit CSI value for the channel between the m-th antenna of the AP and the n- th antenna of the users. This processing can, for example, be to sum the L 1-bit CSI values and then take the sign of the sum as the 1-bit CSI value for the channel between the m-th antenna of the AP and the n- th antenna of the users. This process can be modeled mathematically as follows.

Let H denote a two-dimensional matrix of the communication channels between the AP and the users, where the (m, n)- th element of H is the channel between the n- th antenna of the users and the m-th antenna of the AP, for m = 1, 2, ..., M and n = 1, 2, ..., N . The noisy 1-bit CSI of the channel matrix H is given by: where W _l is an N x M noise matrix, Pp is the pilot power, and L is the number of orthogonal pilot symbols transmitted by each of the users' antennas. Transmission Mode Operation

Let be the complex- valued symbols that the AP wants to transmit to the users’ 1-st,

2-nd, 3-rd, ..... N-th antenna respectively. In one channel use, where , for , where . Let and denote the real-valued and imaginary-valued parts of respectively, i.e., and for The 1-bit CSI matrix G, given by (10), is known at the AP. Let. and denote the real-valued and imaginary- valued parts of the (n, m) element of G. Using and G, the AP constructs a vector x comprised of M elements, where the m-th element of , denoted by , for m — 1, 2, ,.., M, is constructed as follows

Using the AP generates a corresponding transmit vector x of M elements, where the m-th element of x is to be transmitted from the m-th antenna, for m = 1, 2, M , and x is constructed as follows: where P _AP is the transmit power of the AP, and | · | denotes the amplitude of a complex-valued number. Next, for each channel use, x is transmitted from the AP, where the m-th element of x is transmitted from the m-th antenna, for m = 1, 2, ..., M . As a result of this transmission, the symbol received at the n- th antenna of the users is y _n , for n = 1, 2, · · · , N . To decode s _n from y _n , the corresponding user generates s _n as follows:

Thus the user decides that the symbol transmitted from the AP is , then an error has occurred.

Receiver Mode Operation

Let he the complex-valued symbols that the users' , antenna wants to transmit to the _· AP in one channel use, respectively, where , for where Next, is transformed into given by when; P _U is the total transmit power of tire users. Finally, is transmitted from the n-th users’ antenna, where .

As a result of this transmission, the AP receives a complex-valued symbol on each of its antennas. Let denote the complex-valued symbol received at the AP on its m-th antenna, for . Let denote the real-valued and the imaginary-valued elements of respectively. The 1-bit CSI matrix G, given by (10), is knows at the AP. Let and denote the real-valued and imaginary- valued parts of the (n, m) element of G. Then, using and for and the AP constructs

Using and the AP constructs as

The AP then decides that the symbol has been transmited from the n-th users' antenna, Hence, an error happens if occurs for any .

As will be appreciated by those skilled in the art, an access point (AP) implementing the described communications processes can itself be implemented in any of a variety of different possible hardware configurations. Figure 5 is a simplified block diagram showing the components of an embodiment of an access point to implement the 1 -bit CSI generation mode. In order for the AP to generate a 1-bit CSI, it is sufficient for the AP to have a corresponding 1- bit ADC for each of its antennas, at least when it is operating in the 1-bit CSI generation mode.

Similarly, Figure 4 is a simplified block diagram showing components of an access point to implement the transmission mode process described above. When the AP operates as a transmitter of information, it is sufficient for it to have a corresponding q-bit DAC for each of its antennas, where q = log ₂ (N). Figure 6 is a simplified block diagram showing components of an access point to implement the receiver mode process described above. When the AP operates as a receiver of information, it is sufficient for the AP to have a corresponding set of N 1-bit analog phase-shifters for each antenna, followed by (for all antennas) N analog-adders and N 1-bit ADCs, as shown in Figure 6.

Error-Correction Codes

The description above has assumed data transmission without any error correction codes. If required, error correction coding can be applied to the input data before the processing steps described above in order to increase the reliability of the communication system, albeit at the expense of increasing the latency.

Maximum Latency

The maximum latency that the described embodiments achieve is equal to the number of channel uses required to estimate G at the AP, plus the one channel use needed for data transmission.

Numerical Example of Achieved BER

Figure 7 is a graph showing the bit error rate (BER) as a function of the signal-to noise-ratio (SNR) in dB for L = 1 and several different values of M and N. Due to the small BERs, the SNR is plotted only up to 15 dB. However, in practice, SNRs higher than 30 dB are normal.

Assuming that the allocated bandwidth is 20 kHz, each channel use lasts 1/(2B) = 5 × 10 ^-5 seconds. Then the corresponding delay for an AP with 1, 2, 3, 4, or 5 receive antennas will be 0.125, 0.250, 0.375, 0.500, or 0.625 ms, respectively, which are all well below the 1 ms maximum latency target for URLLC.

In another example, an access point with 1000 antennas distributed over an area of 1 m ² was used to communicate with a transceiver as described above, achieving a data rate of 4 Mbits per second with a latency of 1 ms or less, and bit error rate (BER) of 10 ^-9 or less over distances of at least 1 km and up to 60 km (depending on environment). Embodiments of the present invention require only simple hardware components for each antenna channel, which in turn allows a practical AP to have hundreds (if not thousands) of antennas. Additionally, the users’ transceivers can be simple, making the processes described herein applicable to sensor devices. The communications processes described herein achieve URLLC at the physical communication layer, without any need for the higher communication layers to perform intensive processing. This leads to minimal latency.

As will be apparent to those skilled in the art, in a wireless communications access point with the simple hardware components described above, the wireless communications processes described herein can be implemented in the form of configuration data of a field-programmable gate array (FPGA) or as processor-executable instructions ( e.g ., firmware) of one or more processors, or as a combination of both forms, electronically stored in at least one electronic data storage medium.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.