WO2024058761A1 - A retransmission method for multiple access networks - Google Patents

Abstract

A computer implemented retransmission method for network characterized by; sending a data package to a network by a base station, determining a reliability level of the data, sending a negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value, splitting as a private data and a common data, sending to the common data based on NOMA by a base station in response to the negative acknowledgment, determining the reliability level of the received common data, sending the negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value, sending to the private data based on SDMA by a base station in response to the negative acknowledgment, determining a reliability level of the received private data.

Description

DESCRIPTION

A RETRANSMISSION METHOD FOR MULTIPLE ACCESS NETWORKS Technical Field

The invention is related to a computer-implemented method for retransmission of the wireless networks, especially on 5G and B5G networks, preferably wireless networks that use ratesplitting as a multi access approach to serving multi-users and and system configured to carry out said method.

Prior Art

Multi-access techniques are approaches that are allowing the simultaneous connection of many users to some resources in the wireless networks such as time, frequency, or space in an orthogonal and non-orthogonal manner. Recently, non-orthogonal approaches such as non- orthogonal multiple access (NOMA) and rate splitting multiple access (RSMA) have a potential interest among researchers for several reasons.

First of these reasons, serving multiple users simultaneously provides several efficiencies can be achieved, such as spectral, and energy. Concurrently, an interference management mechanism has to be applied to prevent the multi-user interference problem.

Second of these reasons, serving multiple users simultaneously provides system capacity increases which means an increase in the number of users who can use the resources.

Finally, effective multiple access provides effective resource management where these resources are the basic components of any communication system that play an active role in obtaining its efficiencies, such as energy, bandwidth, time, and space.

NOMA is one of the most promising radio access techniques in next-generation wireless communications. Compared to orthogonal frequency division multiple access (OFDMA), which is the current effective standard orthogonal multiple access (OMA) technique, NOMA offers a set of desirable potential benefits, such as enhanced spectrum efficiency, reduced latency with high reliability, and massive connectivity. OFDMA is a multi-user version of the orthogonal Frequency Division Multiplexing (OFDM) digital modulation technology. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users. This allows concurrent low-data-rate transmission from several users. The fundamental idea of NOMA is to serve multiple users non-orthogonally using the same resources in terms of time, frequency, and space. NOMA techniques can divide into two major categories, i.e., code-domain NOMA and power-domain NOMA. Power-domain NOMA based on Superposition Coding (SC) at the transmitter and Successive Interference Cancellation (SIC) at the receivers has been recognized as a promising multiple access scheme for future mobile networks. Since the principle of NOMA allows multiple users to be superimposed on the same resource, this leads to interference for such systems. Consequently, existing resource management and interference mitigation techniques, especially for ultra- dense networks, need to be revisited due to the incorporation of additional interference this new technology brings.

NOMA has several known disadvantages.

First of these advantages is increase of the receiver complexity (i.e., the number of SIC layers) and aggravation of the SIC error propagation, when the number of users increases. Furthermore, for the K-user SISO (single-input-single-output) BC (broadcast channel), the user with the strongest channel requires K-l layers of SIC to decode and remove the interference from the K-l messages of all other co-scheduled users before being able to access its intended message.

One practical approach to address this issue is to restrict the number of SIC layers at each user by clustering users into smaller groups, applying SC-SIC in each group, and scheduling user groups via OMA. Such an approach, however, may cause a loss in performance and increase latency. Also, NOMA has several limitations in multi-antenna networks, such as multiantenna NOMA can suffer from a loss of DoF due to the inefficient use of SIC, and multiantenna NOMA can impose significant computational burdens on the transmitter and the receivers. Besides the multiple SIC layers required at each user for decoding interference, the transmitter also requires a joint optimization of the precoders, user grouping, and decoding orders as they are coupled with each other. Multi-antenna NOMA can be sensitive to user deployment. It is generally most suitable for highly overloaded scenarios where the user channels are nearly aligned in each user group and are relatively orthogonal among different user groups. Multi-antenna NOMA can be vulnerable to CSIT inaccuracies as the inter-group interference is managed in the same manner as in SDMA. Space division multiple access (SDMA) is the unprecedentedly exploding demand for wireless communications and the scarcity of spectrum resources has motivated the adoption of multiple-input multiple-output (MIMO) communication in modern wireless networks by deploying multiple antennas at all access points. MIMO has become one of the most essential and indispensable technologies for current wireless networks and is included in virtually all high-rate wireless standards (e.g., 5G New Radio-NR, 4G Long Term Evolution-LTE, IEEE 802.1 In, WiMAX). MIMO networks create the spatial dimension, which opens the door for SDMA. By properly utilizing the spatial resources and multi-antenna processing, SDMA can serve multiple users at the same time-frequency resource, and therefore boosts SE. MIMO is inherently connected to the information-theoretic literature on the multi-antenna broadcast channel (BC) and the multiple access channel (MAC). But SDMA has some disadvantages such as it is only suitable for underloaded systems, and the performance drops significantly when the network becomes overloaded as having enough transmit antennas is a prerequisite for successful interference management based on using SDMA. A common method to handle overloaded settings is to separate users into different groups, schedule user groups via OMA, and perform SDMA in each user group, which, however, reduces the QoS and increases latency. Second SDMA is sensitive to the user deployment (including the angles and strengths of the user channels), which therefore imposes a stricter requirement on the scheduler. SDMA requires the scheduler to pair users with nearly orthogonal channels and relatively similar channel strengths. The last one, SDMA is sensitive to CSIT inaccuracy. In contrast to its good performance in the perfect CSIT setting, SDMA cannot achieve the maximal DoFs when CSIT is imperfect. In fact, its performance decreases dramatically in the presence of imperfect CSIT. This is due to the fact that SDMA is designed for perfect CSIT. Applying a framework motivated by perfect CSIT under imperfect CSIT conditions results in residual multi-user interference caused by the imprecise interference mitigation at the transmitter (via imperfect linear precoding).

RSMA is a general and powerful candidate for multiple access frameworks for downlink multiantenna systems, and it is including both SDMA and NOMA as special cases. RSMA relies on linearly precoded rate-splitting with SIC to decode part of the interference and treat the remaining part of the interference as noise. Recently, RSMA has been shown to outperform both SDMA and NOMA rate-wise in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel directions, and channel strengths and qualities of channel state information at the transmitter). As a consequence, RSMA bridges and unifies the two extremes of SDMA and NOMA. To partially decode interference, various messages of users are split into common and private parts in rate splitting (RS). The common parts are jointly encoded and decoded by multiple users while the private parts are decoded by the corresponding users only. RSMA has been shown in to be more spectrally efficient than SDMA and NOMA in a wide range of user deployments, and in the presence of perfect and imperfect CSI at the Transmitter (CSIT). On the other hand, in interference management strategies, one of the big needs is to apply RSMA or introduce an efficient multi-access approach that is compatible with beyond 5G (B5G) networks. It is between when fully decoding the interference and when treating interference as noise.

One of the big reasons to use RSMA in 5G/6G networks is the ability to overcome the imperfection in CSIT where one major source of multi-user interference is the imperfection of CSIT. In the presence of imperfect CSIT, interference management is further impeded because CSIT imperfections imply that interference cannot be managed easily by the precoders at the transmitter anymore, e.g., interference cannot be eliminated since the channel is not known accurately. Unfortunately, the acquisition of accurate CSIT is challenging due to many inevitable sources of impairment. This imperfection introduces additional multi-user interference and has become the primary performance bottleneck in MIMO networks. Such severe multi-user interference, however, is simply treated as noise by both SDMA and multiantenna NOMA (with multiple user groups). The classical approach for dealing with this practical limitation of imperfect CSIT takes a “robustification” stance where the precoders for SDMA and NOMA that have been designed under the assumption of perfect CSIT are tweaked to account for imperfect CSIT. As a result, all of the problem mentioned above has made it necessary to provide a novelty in the related field.

The technique of retransmission is an effective way to improve system performance, and packet retransmission is often requested when a received packet is detected to be in error. This scheme, termed the automatic retransmission request (ARQ), is intended to ensure an extremely low packet error rate. The efficiency of ARQ can be improved by reusing the data from the previous (re)transmissions instead of discarding them. This technique, termed the hybrid ARQ (HARQ), includes the Chase Combining (CC) and Incremental Redundancy (IR). HARQ is supported in the LTE system for reliable data transmission together with Multiple Input Multiple Output (MIMO). The combined with HARQ, MIMO can potentially provide higher throughput packet data services with higher reliability.

HARQ retransmissions at MAC react faster to channel conditions and improve performance for delay- sensitive applications. HARQ is adaptive. Retransmissions can use different coding rates and redundancy bits. The receiver doesn't discard erroneous packets but stores them in its buffer. All versions are used to improve decoding. HARQ doesn't discard erroneous packets. They're stored in a buffer and combined with retransmitted packets that will be received later. This is called Hybrid ARQ with Soft-Combining. With Incremental Redundancy, retransmitted packets are related to the same information bits although each packet carries a different subset of information and parity bits. 8 uplink HARQ processes are running on both the user side and base station with 4 processes delay. HARQ process length is the same as a subframe (1 ms). When the user sends data to the base station, the base station decodes data and checks CRC. The base station then sends an acknowledgment (ACK) or not- acknowledged (NACK) to the user after 4 subframes. Based on the base station response, the user will send new data or retransmit the data again. Soft Combining is an error correction technique in which the bad packets are not discarded but stored in a buffer. The basic idea is that 2 or more packets received with insufficient information can be combined in such a way that the total signal can be decoded.

The two types of HARQ are chase combining also known as type 1 HARQ and incremental redundancy also known as type 2 HARQ. In the chase combining, the combining approach uses the data, error detection bits, and forward error correction bits (FEC). FEC bits are added to each message before sending. If the channel quality is good, errors are detected and corrected. But if the channel quality is bad, not all errors may be corrected, and the receiver asks for re-transmission (like ARQ). FEC adds a large overhead. In the case of incremental redundancy, the combining approach uses data, error detection bits, and FEC bits. But a different subset of data, a different subset of error detection, and a different subset of FEC are sent on each re-transmission. For example, in the first transmission, a subset of information is sent. Re-transmissions are made with a different set of data, error detection, and FEC.

Error-control coding, or channel coding, plays a crucial role in modem digital communication systems. A simplified block diagram of a digital communication system is depicted in Figure 1. Channel coding is performed on the information data in such a way as to mitigate the negative effects of noise and interference incurred in the communications channel by involving redundancy, where the extra bits are included for future error correction or error detection at the receiver. The capability of the demodulator to restore the transmitted signals is hampered by different channel factors including noise, interference, Doppler shift, multipath fading, etc. These factors result in demodulation errors and hinder reliable communication. The purpose of a channel encoder is, therefore, to facilitate a way to combat these errors caused by unfavorable channel conditions. Today’s error correction codes can be generally classified into two major categories: (i) block codes and (ii) convolutional codes. Both can be used by HARQ.

More recently, a general multiple access framework, called rate-splitting multiple access (RS MA), where the transmitter adopts linearly precoded rate splitting (RS) and the receivers use SIC, has been proposed as shown in Figures 2 and 3. The RSMA is viewed as a technique to bridge the commonly used space division multiple access (SDMA) of treating interference as pure noise and nonorthogonal multiple access (NOMA) of decoding interference. In RSMA, the transmitted signal is split into a common and private signal, where the common signal is required to be first decoded by all the receivers and removed from the received signal using SIC, then each receiver decodes its intended private signal by treating the unintended private signals as noise. The idea of RS was first introduced in Carleial’s work in a two-user interference channel model. Figure 2 represents the transmitter structure based RSMA approach where the data of the users are splitted into two parts common and private, respectively, where CP 1 and CP 2 represent the common part of data for user 1 and user 2, respectively. PP 1 and PP 2 represent the private part of data for user 1 and user 2, respectively. CP 1 is the combination of the common parts of both users. XC is the common stream for both users. XP1 and XP2 are the private streams for user 1 and user 2, respectively.

Clerckx et al. introduced a rate- splitting strategy and highlighted the benefits of RSMA in terms of reliability, spectral and energy efficiencies, and reduction of channel state information (CSI) feedback overhead. Joudeh and Clerckx investigated the max-min fairness problem through transmitting BF amongst multiple co-channel multicast groups with RSMA. To achieve better spectral and energy efficiencies, Mao et al. investigated the rate- splitting, nonorthogonal, unicast, and multicast strategies. More recently, Yin and Clerckx applied RSMA to a multi-beam satellite system and studied the BF design to achieve max-min fairness. However, the error correction mechanism due to the uncertainty of the wireless channel conditions is not studied and investigated for RSMA networks.

Brief Description and Objects of the Invention

The main object of the present invention is to provide a retransmission method which is more flexible and more adaptive than known methods for 5G and B5G networks.

The main object of the present invention is to solve latency, saving resources, improving the quality of service (QoS), and increasing the reliability, and capacity of the system problems in retransmission of the network.

Another object of the invention is to solve error propagation, propagation delay, Errors from interference and noise and especially imperfect channel state information at the transmitter problems specifically the transmitter problems in retransmission method based rate splitting multiple access.

Mentioned problems are solved in the present invention by proposing an adaptive/intelligent/ awareness retransmission approach using the hybrid automatic repeat request (HARQ) protocol. HARQ combines the medium access control (MAC)-layer acknowledgement (ACK)- negative acknowledgement (NACK) feedback mechanism with channel coding to obtain an efficient re-transmission scheme for recovering messages with missing packets.

A HARQ approach that is suitable for RSMA networks by intelligently retransmitting the common packet as a response to the first NACK and the private part as a response to the second NACK. And, if the receiver sends a third NACK, the base station will send the whole data as a response. By proposing such a protocol, it minimizes the number of retransmissions tries to 3 which reduces the retransmission latency in the system, increase the reliability level at the receiver, and overcomes the imperfect channel state information (CSI).

The core of this invention is proposing an adaptive multi-access approach based on HARQ protocol that is suitable for 5G and beyond networks by intelligently making the retransmission according to three strategies when the errors happened in the network. The first strategy is to retransmit the common data part-based NOMA approach. The second strategy is to retransmit the private part based on the SDMA approach. The third one is to retransmit the whole data based on the RSMA approach which is contained both common and private parts. By proposing such an adaptive retransmission approach, it utilizes effectively the resources in the network either power, rate, reduces the retransmission latency in the system, increases the reliability level at the receiver, and overcomes the imperfect channel state information (CSI).

The main contributions of the present application to the prior art as follows;

A unique approach of retransmission is introduced where the data of several users are mixed and combined.

Minimizing the number of retransmissions tries to 3 and reducing the retransmission latency in the system. This RSMA approach as a base will provide higher flexibility to split the data which can be considered as the IR approach that is used in HARQ. IR approach is highly recommended in 3 GPP to be used in LTE.

By proposing such an approach, three aspects can be designed nicely and effectively which are best scheduling, link adaption, and error control approach. This will make a good utilization to save the communication resources such as power, rate, as well as add more levels of adaptivity and flexibility to the network.

Increasing the reliability level at the receiver and overcome the imperfect CSI. Then, more flexibility at the transmitter and simplifying the receiver structure, because of using it is combiner to do combining based on what we have in it. Furthermore, it is compatible with various approaches in the MAC layer such as link adaptation, and scheduling.

The user equipment has one antenna, and multiple copies at the receiver will be available. This will give a diversity gain where the Virtual combining (VC) between these copies can be done. By doing that, VC will be done based on the proposed approach. We can apply any optimization method based on what we need/want for the reliability of the system, this provides the flexibility of using several methods of combining based on the system requirements.

Lastly, getting the channel gain as well as diversity gain to improve the system performance where the users who have the less acceptable error, will use the retransmission to increase it. But on the other hand, the users who don’t want they can use it to increase the diversity at the receiver side by getting more independent copies.

Description of the Figures of the Invention The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

Figure 1. Block diagram of a typical digital communication.

Figure 2. Transmitter model of RSMA in MIMO networks.

Figure 3. Receiver model of RSMA in MIMO networks for the first user.

Figure 4. System model of RSMA network.

Figure 5. Schematic view of the retransmission of the common part-based NOMA

Figure 6. Schematic view of the retransmission of the common part-based NOMA

Figure 7. Retransmission process for the present invention.

Figure 8. Flowchart for the present invention.

Reference Numbers

The parts and components are given in the figures are referenced for the subject matter of the invention to be understood better.

BS. Base station

UE. User equipment

PD. Private data

CD. Common data

Detailed Description of the Invention

The invention is related to a computer-implemented method for retransmission on the wireless networks, especially on 5G and B5G network, preferably on the wireless networks that use rate splitting as a multi-access approach to serving multi-users and system configured to carry out said method.

The system model preferably comprises at least one base station (BS) that applies the MIMO (multiple-input and multiple-output) approach to serve several users in the network as shown in Figure 4. The base station (BS) uses RSMA to serve multiple users in the network and the BS has the capability to change RSMA to both SDMA and NOMA transmission approaches. Furthermore, assuming that the user equipment (UE) has one antenna. If the error happens at a user equipment (UE), and the user equipment (UE) asks for retransmission from the base station (BS). Mentioned error is occurred in the system due to low SNR (signal noise rate) at the intended receiver due to the imperfection channel estimation and user mobility, or from pilot contamination.

Referring to Figure 7; the data is sent from the base station (BS) to a user equipment (UE) via a network. The user equipment is a device having a communication unit capable of receiving transmitted data from the base station (BS). The communication unit can be compatible with wireless and/or wired communication.

In the present invention, the data is intended to send is split in two as a common data (CD) (also known as public) and a private data (PD) in accordance with RSMA protocol. The data is split by a splitter unit (not shown). The splitter unit is a device or a circuit is capable of split electronic data.

The private data (PD) may be read by all users who have access to the library with that data, but it may be modified only by the user who wrote the data initially. A common data (CD) is accessible for reading and updating by all users who may access the library with the data.

Referring to Figure 4 and 8; Firstly, the data is sent to the user equipment (UE) via the network. The user equipment (UE) can be a smart device (e.g. mobile phone, tablet) or a computer. The data is inspected to determine reliability level and compared predetermined value which is value with reliability level.

This determination is carried out error correction code (ECC), more specifically forward error correction (FEC). In the FEC, the base station (BS) encodes the message in a redundant way by using an error-correcting code. The redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to correct these errors without retransmission. FEC gives the receiver the ability to correct errors without needing a reverse channel to request retransmission of data, but at the cost of a fixed, higher forward channel bandwidth. Referring to Figure 5 and 8; If the data isn’t reliable according to above mention steps, the system, especially a control unit (not shown) creates a negative acknowledgment. The negative acknowledgment is response to be sent to the base station (BS). This negative acknowledgment asks for retransmission of the common data (CD) or private data (PD). In preferred embodiment of the present invention after first determination the control unit sends the negative acknowledgment which asks for retransmission of the common data (CD).

The control unit may be provided as integrated part of the network or the user equipment (UE). The control unit is a device or a circuit is capable of to determine a reliability level of the data and compare the reliability level of the data with a predetermined value and to create a negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value wherein the negative acknowledgment is response to make the base station sends the private data (PD) or the common data.

After first the negative acknowledgment is created, this acknowledgment is sent to the base station (BS) and in response to that base station sends the common data (CD) of the data package. This transmission of the common data (CD) is carried out based on a non- Orthogonal Multiple Access (NOMA).

The common data is inspected to determine reliability level and compared predetermined value which is value with reliability level. This determination is carried out error correction code (ECC), more specifically forward error correction (FEC). If the data isn’t reliable according to second determination step, the system, especially a control unit creates another negative acknowledgment. In preferred embodiment of the present invention, second acknowledgment is the negative acknowledgment which asks for retransmission of the private data (PD).

Referring to Figure 6 and 8; In response to the second negative acknowledgment, the base station (BS) sends the private data (PD. This transmission of the common data (CD) is carried out based on a Space-Division Multiple Access (SDMA). The private data (PD) is inspected to determine reliability level and compared predetermined value which is value with reliability level. This determination is carried out error correction code (ECC), more specifically forward error correction (FEC). According to the inspection, if the desired reliability level still doesn’t achieve yet, the third negative acknowledgment is created by the control unit. The third negative acknowledgment is the acknowledgment which asks for retransmission of the whole data. Transmission of the whole is carried out based on a Rate splitting multiple access (RSMA).

In the present invention, any point that desired reliability level is achieved the acknowledgment is created by the control unit wherein this acknowledgment is a response/command for combining the common data (CD) and the private data (PD). More clearly, after determination of the reliability level of the data or the common data (CD) or the private data (PD), if desired reliability level is achieved, the acknowledgment is created.

The combining step is carried out by a combiner unit (not shown). The combiner unit is a device or a circuit which is capable of combine of split electronic data.

In preferred embodiment of the invention, the user equipment (UE) has one antenna. By doing retransmission, multiple copies of the same data are data at the receiver. This provide a diversity gain as well as channel gain if the channel is not static. Consequently, Virtual combining (VC) between these copies will be done. Furthermore, it is not necessary to use a specific type of combining at the receiver as the conventional schemes do. Here, the optimum combining at the receiver might be based on the system requirements, it could be MMSE, selective combining, or a new design based on what is the system requirements.

Claims

CLAIMS A computer implemented retransmission method for network characterized by; a. Sending a data package to a network by a base station b. Determining a reliability level of the data, c. Sending a negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value, d. Splitting as a private data and a common data, e. Sending to the common data by a base station in response to the negative acknowledgment, f. Determining the reliability level of the received common data, g. Sending the negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value, h. Sending to the private data by a base station in response to the negative acknowledgment, i. Determining a reliability level of the received private data. A method according to claim 1, characterized in that method is for networks that use rate-splitting multiple access. A method according to claim 1 characterized in that in step (e) sending to the common data in based on NOMA and in step (h) sending to the private data is based on SDMA. A method according to any one of the claims 1-3, characterized by further comprising step of transmitting whole data based on RSMA to the network by the base station, if reliability level of the data of the private data is lower than predetermined value. A method according to the Claims 1-4, characterized by further comprising step of combining the private data and the common data, if reliability level of the data is higher than predetermined value. A method according to any one of the Claims 1-5, characterized by further comprising step of sending an acknowledgment to the network by the base station to combine the private data and the common data, if reliability level of the data is higher than predetermined value. A method according to any one of the Claims 1-6, characterized by determining error and reliability level of the data is carried out by error correction code. A method according any one of the Claims 1-7, characterized by determining error and reliability level of the data is carried out by forward error correction. A system for retransmission of the data on networks that uses rate- splitting multiple access characterized by;

A base station and user equipment configured to transmit and receive a data from each other,

A splitter unit configured to split the data as a private data and a common data,

A combiner unit configured to combine the private data and the common data,

A control unit configured to determine a reliability level of the data and compare the reliability level of the data with a predetermined value and to create a negative acknowledgment for retransmission of the data, if reliability level of the data is lower than predetermined value wherein the negative acknowledgment is response to make the base station sends the private data or the common data A system according to claim 9, characterized by the base station sends the private data based on SDMA or the common data based on NOMA. A system according to the Claim 9, characterized by the control unit is configured to create negative acknowledgment which is response to make the base station sends the whole data. A system according to the Claim 10, characterized by the control unit is configured to create negative acknowledgment which is response to make the base station sends the whole data based on RSMA. A system according to any one of the Claims 9-12, characterized by the control unit is configured to create an acknowledgment which is response for combining the private data and the common data, if reliability level of the data is higher than predetermined value. A system according to any one of the Claims 9-13, characterize by the control unit is configured to determine error and reliability level of the data is by error correction code. A system according to any one of the Claims 9-14, characterized by the control unit is configured to determine error and reliability level of the data is by forward error correction. A system according to any one of the Claims 9-15, characterized by the splitter is integrated with the control unit. A system according to any one of the Claims 9-16, characterized by the combiner is integrated with the control unit.