A transmission method for rate-splitting multiple access relay networks

Abstract

The invention is related to a transmission method designed for rate-splitting multiple access (RSMA) networks in the context of amplify-and-forward (AF) relay scenarios.

Description

[0001] A TRANSMISSION METHOD FOR RATE-SPLITTING MULTIPLE ACCESS RELAY NETWORKS

[0002] Technical Field

[0003] The invention is related to a transmission method designed for rate-splitting multiple access (RSMA) networks in the context of amplify-and-forward (AF) relay scenarios.

[0004] Prior Art

[0005] Multiple access (MA) techniques are crucial for optimizing the utilization of resources in communication systems, especially in the context of emerging technologies like 6G and beyond. RSMA has recently gained attention as a versatile MA scheme, enabling non- orthogonal transmission of common and private messages [1], However, RSMA introduces challenges related to successive interference cancellation (SIC) at the receiver, particularly in the presence of imperfect channel state information at the receiver (CSIR). To address these challenges, there is a need to enhance SIC performance for ensuring the reliability of the transmitted stream [2],

[0006] Relay-assisted communication is a promising technology for overcoming wireless channel fading by leveraging spatial diversity through relays or users that receive and forward signals [3], The conventional relays can be categorized into amplify-and-forward (AF) relays, and decode-and-forward (DF) relays. AF relays are preferred due to their low power consumption and latency. However, RSMA is not directly applicable to basic AF relays, requiring the development of an intelligent multiplexing scheme for RSMA in AF relay scenarios.

[0007] The application of RSMA for DF relays has been explored in a single paper [4], focusing on scenarios with a single user served by the relay. However, there is a notable gap in the literature regarding the application of RSMA in AF relay scenarios, particularly for multiple users served by the relay.

[0008] To tackle the residual error issue stemming from Channel State Information at the Receiver (CSIR) in SIC, various approaches have been introduced in the literature. One such method involves the design of a practical RSMA receiver based on Model-Based Deep Learning (MBDL) techniques [5], The proposed solution in this study [4] strives to amalgamate the simplicity found in traditional SIC receivers with the robustness and model-agnostic nature of deep learning methods however, this approach introduces additional complexity through the incorporation of machine learning techniques.

[0009] Another work [6] proposed different receiver structures categorized as SIC and SIC-free receivers. However, their approach to SIC involves considerations of decoding complexity and latency. While they explore using soft symbols at the receiver as an SIC-free approach, this structure still relies on information from the demodulation of the common stream. Joint decoding structures, while potentially optimal, increase the complexity due to the multiplication of modulation order amounts and do not necessarily introduce significant spectral efficiency improvements. Their approach to SIC involves considerations of decoding complexity and latency. While exploring the use of soft symbols as an SIC-free approach, this structure still relies on information obtained from the demodulation of the common stream. Joint decoding structures, although potentially optimal, escalate complexity due to the multiplication of modulation order amounts and do not necessarily yield significant improvements in spectral efficiency.

[0010] As a result, all of the problem mentioned above has made it necessary to provide a novelty in the related field.

[0011] Brief Description and Objects of the Invention

[0012] The main object of the present invention is to establish a transmission method for rate-splitting multiple access (RSMA) networks which is directly applicable to AF relays, where relays lack the ability to decode and precode.

[0013] Another object of the invention is to eliminate residual errors from successive interference cancellation for RSMA networks. To address the residual error problem inherent in RSMA, the disclosed method uses a diversity scheme for cell edge users. This involves storing the initially transmitted common stream in a buffer and applying known diversity techniques to both the first and second transmission phase common streams. This approach increases the reliability of the common stream, improving SIC performance and reducing residual errors. Overall, by leveraging the already transmitted signal, the total reliability of cell edge users enhanced.

[0014] Another object of the invention is to reduce the interference between the common and private parts of the different users. Through the encoding of the private streams of cell edge users, interference originating from these users to cell center users is minimized. Furthermore, the conditions for already challenging cell edge users are improved by minimizing interference among them.

[0015] This necessitates a novel multiplexing scheme for AF relays serving multiple destinations. The disclosed RSMA multiplexing scheme has two key steps. First one is encoding private parts together. Private parts of multiple destinations are encoded together at the source node, allowing the relay to solely amplify and forward the signal. This provides each user with a NOMA-like signal. Similar to splitting the common part, destinations also split their respective private parts.

[0016] Second one is utilizing the common stream. The invention introduces the utilization of the common stream transmitted from the source node initially. Traditionally overlooked in the literature, this signal is employed for diversity, enhancing the reliability of the common stream. This, in turn, increases the reliability of the private stream — an area of concern in NOMA-type transmission schemes.

[0017] Moreover, if the relay employs multiple-input multiple-output (MIMO) technology, hybrid precoding can be implemented at both source and relay node.

[0018] Description of the Figures of the Invention

[0019] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0020] Figure 1. A schematic view of rate-splitting multiple access (RSMA) network.

[0021] Figure 2. A transmitter model of source node

[0022] Figure 3. Receiver model of center node in the first transmission.

[0023] Figure 4. Receiver model of edge node in the first transmission.

[0024] Figure 5. Receiver model of edge node in the second transmission.

[0025] Figure 6. Flowchart of the first and the second transmission for the edge node.

[0026] Reference Numbers

[0027] The parts and components are given in the figures are referenced for the subject matter of the invention to be understood better.

[0028] 101. Source node

[0029] 102a. Center node 102b. Edge node

[0030] 103. Relay node

[0031] 104. Common signal

[0032] 105. Private signal of center node

[0033] 106. Prive signal of relay node

[0034] 107. Edge node signal

[0035] 201. Scheduler

[0036] 202. Message splitter

[0037] 203a. Common combiner

[0038] 203b. Private combiner

[0039] 204. Encoder

[0040] 205. Precoder

[0041] 206. Transmit antenna

[0042] 207. Wireless channel

[0043] 301a. Common decoder

[0044] 301b. Private decoder

[0045] 302. Successive interference cancellation

[0046] 303a. Common splitter

[0047] 303b. Private splitter

[0048] 304. Combiner

[0049] 305. Receive antenna

[0050] 401. Buffer

[0051] 501. Diversity mean

[0052] Detailed Description of the Invention

[0053] The invention is related to a transmission method designed for rate-splitting multiple access (RSMA) networks in the context of amplify-and-forward (AF) relay scenarios. The disclosed method is applicable to various scenarios involving a source, amplify-and- forward (AF) relay, and destinations. The sources can include base stations (BSs), user equipment (UEs), unmanned aerial vehicles (UAVs), integrated access and backhauls (lABs), and any transmitter node capable of RSMA transmission. AF relays encompass network- controlled repeaters (NCRs), radio frequency (RF) repeaters, and any node with AF capabilities. Destination nodes may also be BSs, UEs, UAVs, and any receiver node.

[0054] Figure 1 illustrates an example scenario with one source node (101), one cell center node(102a), two cell edge node (102b), and one relay node (103) selected. Common signals (104) are shown by solid arrows, private signal of center node (105) and private signal of relay node (106) are shown by dashed arrows, and edge node signal (107) is shown by dotted arrows (107). The depiction also includes indications of cell edge and cell coverage area.

[0055] The disclosed method operates under a two-phase transmission model. The first phase involves transmission from the source node (101) to the relay node (103), and the second phase encompasses transmission from the relay node (103) to the cell edge nodes (102b). It is essential to note that this approach is flexible and can be extended to accommodate multiple source nodes (101), relay nodes (103), cell center nodes, and edge nodes. In the first transmission phase, signals are represented by solid and dashed arrows, while in the second transmission phase, signals are denoted by dotted lines (107).

[0056] The device operates as the source node (101), emitting an RSMA signal during the first transmission phase. The common signal (104) is transmitted omnidirectionally, while the private signal of the center node (105) is conveyed using space division multiple access (SDMA), following the conventional RSMA transmission. Similarly, the private signals of the edge nodes (106) are collectively sent to the relay node using SDMA.

[0057] The first step involves encoding both users' private data together as the common signal (104), subsequently transmitted to the relay node (103). The second innovation that distinguishes our novel approach is the utilization of the common signal (104) that has already been transmitted to the cell edge destinations during the first transmission phase.

[0058] Figure 2 illustrates the transmitter model at the source node (101). The scheduler (201) selects destinations requesting transmission and forwards their data, 1 / 1^, I2, W3, to the message splitter (202). Here, 14^ represents the data of the cell center node (102a), and I2, 3 are the data of cell edge node (102b), respectively. The message splitter (202) then divides the user messages into common and private parts as foreach edge node (102a, 102b), respectively. The common combiner (203a) combines the common messages for each user using conventional RSMA to obtain C. The novelty in the transmitter model lies in the private combiner (203b), where the private messages (P2> P-3) of cell edge node (102b) users are combined as PR. Subsequently, the combined common message C, the private message P of destination node 1, and the combined private message PRof cell edge users are encoded as sc, Si, sfi, respectively, at the encoder (204). Any coding scheme, such as Polar coding, LDPC (Low-Density Parity-Check) coding, Turbo coding, etc., can be employed at the source and destination nodes in the disclosed system. These encoded messages are then precoded with precoders (205) pc, plfpR, respectively. Subsequently, transmitted to transmit antenna (206) through the channel (207) as part of the RSMA transmission to the two destinations, similar to the scenario where the relay node (103) is considered as another destination.

[0059] First and second transmission phases are represented as super indices (-)^ and (-)^, respectively. The transmitted signal at the source node (101) is given by: til S = PcSc + P1S1 + PRSR.

[0060] Til

[0061] The center node (102a) receives RSMA signal y^1by receive antenna (305) and decodes it by common decoder (301a) to obtain common stream C as depicted in Figure 3. Subsequently, SIC (302) is applied on y^1and C to obtain y^ . Then, yD^ is decoded by the private decoder (301b) to obtain15and after splitting its common message as by common splitter (303a), they are combined to form W±by combiner (304). These steps closely mirror conventional RSMA and are presented here for the purpose of comparison. In scenarios with multiple cell center destinations, all destinations in the cell center decode their signals in a similar way. The received signal at the center node (102a) is given by: where the hS D1denotes the channel between the source node and destination node 1. Thanks to the RSMA feature, the common signal (104) is broadcasted to all destinations through omnidirectional transmission. Cell edge node (102b) destination also receive this signal as yD, albeit with a low signal-to-noise ratio (SNR). Relying solely on this signal is insufficient for meeting their quality of service (QoS) requirements. However, this received common signal (104) can be leveraged for diversity. In the first transmission phase, cell edge destination nodes Til receive the signal yD^ and perform decoding by the common decoder (301a) to extract the common stream C, subsequently storing fW in the buffer (401) as depicted in Figure 4. The received signals at the edge nodes (102b) in the first transmission phase are given by: y[1]D2= hs,D2pcscy[1]D3= hs,D3pcsc, where the hS D2, hS D3denote the channels between source node (101) and edge nodes (102b), respectively. The received and transmitted signal at the relay node (103) in the first and second transmission phase are given by:

[0062] J[1]R= hS,RPcSc+ hS,RPRsR where the hs Rdenotes the channel between the source node and relay node. The received and transmitted signals are essentially identical, differing only in the amplification introduced by the AF relay. This discrepancy arises during the second transmission phase when the relay node amplifies and forwards the incoming signal from the source node.

[0063] Upon reaching the cell edge node (102b) destinations during the second transmission phase,

[0064] F21 the transmitted signal from the receive antenna (305), denoted as yD^ is decoded by common decoder (301a) and common stream C I2obtained. One of the diversity techniques such as maximal-ratio combining (MRC), equal-gain combiner (EGC) etc. can be applied to obtain C for both the common streams transmitted in the first and second transmission phases (fPl, Subsequently, SIC (302) is applied on the received signal and C to obtain y^ as depicted in Figure 5. This signal is then decoded by the private decoder (301b) to obtain the joint private stream PR, and similar to the common part, each destination takes its respective portion from this joint private stream by private splitter (303b). After splitting C by common splitter (303a), edge node (102) combines their respective portions as W2by combiner (304). The received signals at edge nodes (102b) during the second transmission phase are expressed as: y^D2=hR,D2hs,RPcsc + hR,D2hs,RPRsR where the hR D2, hR D3represent the channel between relay node and destination node 2 and 3, respectively.

[0065] Figure 6 illustrates the flowchart of the receiver model for cell edge destination node 2 in both

[0066] Til the first and second transmission phases. In the first transmission phase, the received signal yD^ by receive antenna (305) is decoded by the common decoder (301a) to obtain and this common signal (104) is then stored in the buffer (401). In the second transmission phase, the received signal yD^ by receive antenna (305) is decoded by the common decoder (301a) to obtain One of the diversity techniques can be applied to these two signals Subsequently, SIC (302) is applied to diversity output C and yD^ to obtain yD^, After decoding by the private decoder (301b) this signal, PRand C are split to extract corresponding common and private parts of the user. In the final step, these parts are combined by the combiner (304), resulting in W2.

[0067] This approach enhances the total SNR through diversity techniques, contributing to improved common stream decoding and consequently increasing the reliability of the private stream. This is particularly significant for superposition coding (SC)-SIC transmissions, where the reliability of the private stream (low power signal) is a critical aspect. In cases where the number of cell edge destinations exceeds two, the common stream encompasses the common parts of all users, while the private stream transmitted from the source to the relay comprises the private parts of all cell edge destinations.

[0068] For optimizing the RSMA signal, an additional approach for cell edge destinations involves power adjustment optimization for both channels hR>Dnand hs Rfor each destination in the cell edge. In terms of directional optimization, consideration can be limited to the relay by focusing on the channel hs R. In scenarios where more capable AF relays with multiple antennas and RF chains, along with beamforming capability, are employed, a hybrid precoding scheme can be applied. An illustrative example of such a scheme is provided in the context of millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (Mu-MIMO) relay systems [7],

[0069] Any wireless communication technology can utilize this invention to increase SIC performance for cell edge destinations. However, standards like 3GPP -based cellular and IEEE 802.11 based Wi-Fi networks, or any wireless network are particularly relevant to the invention due to the support of broadcast, multicast transmission provided in both standards. Furthermore, the described method in this invention can be implemented on any device, system or network capable of supporting any of the aforementioned standards, for instance: Global System for Mobile communications (GSM), GSM / General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Wideband-CDMA (W-CDMA), Evolution Data Optimized (EV- DO), High Speed Packet Access (HSPA), High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Evolved High Speed Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, 5GNew Radio (NR), or other known signals that are used to communicate within a wireless, cellular or internet of things (loT) networks.

[0070] This disclosed invention is used in any wireless network that uses rate splitting as a multi-access approach to serving multi-users in the relay network. The technical interest can be used in many areas such as (some examples but not strict in these only): link adaption and modulation, channel estimation and detection, enhanced throughput and reliability mechanisms, MAC layer management and specifications, non-orthogonal unicast and multicast transmission (NOUM), Multi-cell MIMO including coordinated multi-point (CoMP), cloud-radio access network (C- RAN), and fog-radio access network (F-RAN), cooperative user relaying networks, efficient precoding design aspects, Joint Radar and communication (JRC) applications, massive MIMO Networks, ultra-reliable and low-latency communications (URLLC) , millimeter-wave (mmWave) communication, unmanned aerial vehicles-aided communications (UAV) , physical layer security (PLS), massive machine-type communication (mMTC). REFERENCES

[0071] [1] Y. Mao et al., “Rate-splitting multiple access for downlink communication systems: Bridging, generalizing, and outperforming SDMA and NOMA,” EURASIP J. Wireless Commun. Netw., vol. 2018, no. 1, pp. 1-54, May 2018.

[0072] [2] Mao, Y., Dizdar, O., Clerckx, B., Schober, R., Popovski, P. and Poor, H.V., 2022. Ratesplitting multiple access: Fundamentals, survey, and future research trends. IEEE Communications Surveys & Tutorials.

[0073] [3] J. N. Laneman, D. N. C. Tse, and G. W. Womell, “Cooperative diversity in wireless networks: Efficient protocols and outage behavior,” IEEE Trans. Inf. Theory, vol. 50, no. 12, pp. 3062-3080, Dec. 2004.

[0074] [4] Pang, H., Ji, F., Xu, L., Liu, Y. and Wen, M., 2022. Resource Allocation for RSMA-Based Coordinated Direct and Relay Transmission. IEEE Wireless Communications Letters, 12(3), pp.505-509.

[0075] [5] Loli, R.C., Dizdar, O., Clerckx, B. and Ling, C., 2023. Model-based deep learning receiver design for rate-splitting multiple access. IEEE Transactions on Wireless Communications.

[0076] [6] Zhang, S., Clerckx, B., Vargas, D., Haffenden, O. and Murphy, A., 2023. Rate- Splitting Multiple Access: Finite Constellations, Receiver Design, and SIC-free Implementation. arXiv preprint arXiv:2305.17178.

[0077] [7] M. Han et al., "Hybrid Beamforming With Sub-Connected Structure for MmWave Massive Multi-User MIMO Relay Systems," in IEEE Transactions on Green Communications and Networking, vol. 7, no. 2, pp. 772-786, June 2023, doi: 10.1109 / TGCN.2022.3226801.

Claims

CLAIMS1. A transmission method for rate-splitting multiple access (RSMA) networks comprising a source node (101) and at least one center node (102a) positioned inside the coverage area of the source node (101) and at least one edge node (102b) positioned at edge of the coverage area of the source node (101) and a relay node (103) characterized by,- Selecting destinations requesting transmission for the center node (102a) and the edge node (102b), splitting each message into common parts and private parts,Combining the common parts of all and the private parts of the edge node, Encoding all common parts together and the private parts and precoding encoded parts to form a transmit signal,- Sending the transmit signal directly to both the center node (102a) and the edge node (102b) as a first transmission signal,Decoding the first transmission signal to obtain combined common part and storing it at the edge node (102b),- Sending the transmit signal to the edge nodes (102b) over the relay node (103) as a second transmission signalDecoding the second transmission signal to obtain combined common part and private parts at the edge nodes (102b),Applying diversity to the combined common parts of the first transmission signal and the second transmission signal to obtain common part and splitting it to obtain common part to be sent to the edge node (102b),Applying Successive Interference Cancellation (SIC) to obtained common part and the second transmission signal to obtain a signal and decoding it to obtain combined private parts at the edge node and splitting it to obtain private part to be sent to the edge node (102b),Combining obtained common and private part.

2. A method according to Claim 1, characterized by decoding the first transmission to obtain the common part,Applying Successive Interference Cancellation (SIC) to the first transmission signal and common parts to obtain a signal and decoding it to obtain private parts at the edge node and splitting it to obtain private parts to be sent to the edge node (102a),3. A method according to Claim 1, characterized by combining the common parts of all and the private parts of the edge node by using RSMA.

4. A method according to Claim 1, characterized by encoding all common parts together and the private parts and precoding encoded parts by Polar coding, LDPC (Low-Density Parity-Check) coding or Turbo coding.

5. A method according to Claim 1 , wherein diversity technique is one of the maximal-ratio combining or equal-gain combiner.

6. A data processing device comprising means for carrying out the steps of the method of Claim 1 to 5.

7. A computer program comprising instructions which, when the program is executed by a data processing device, cause the data processing device to carry out the steps of the method of Claim 1 to 5.

8. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of Claim 1 to 5.

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