Digital Front End Algorithms for Sub-Band Full Duplex

Abstract

Sub-band full duplex is a new communication scheme technology, where a single frequency band is partitioned into sub-bands for downlink (DL) and up-link(UL) transmissions, and both can take place simultaneously. The idea behind the sub-band full duplex development is to improve the throughput, and coverage and reduce the latency of the UL communication by allowing the UL reception during the DL transmission. Several integrated ways enable sub-band frequency isolation, such as antenna’s spatial isolation and signal processing techniques to mitigate interferences.
The main challenge for a gNodeB, capable of a full duplex, is self-interference mitigation. A self-interference mitigation technique enables a radio transceiver to transmit and receive simultaneously on a single channel.
During the design process, the Digital Front End (DFE) of the Radio Near algorithm (RNA) is considered the main part of the study (with certain limitations) as it involves the algorithms with the use of MATLAB, which are used to mitigate the distortion caused by radio hardware imperfections. Signal processing algorithms are performed on the transmitter side and receiver side of DFE. The transmitter side includes the Crest Factor Reduction (CFR) block followed by Digital Pre-Distortion (DPD) block before the Power amplifier (PA) to linearize PA output. The transmit path also includes the feedback path for DPD which is used to linearize PA. The algorithms for CFR block namely Turbo Clipping and Peak Cancelation Crest Factor Reduction (PC-CFR) were developed and compared for the performance in terms of Adjacent Channel Leakage Ratio (ACLR) and Error Vector Magnitude (EVM). The algorithm for DPD namely 2-stage frequency selective DPD is implemented along with the legacy DPD technique, and the performance was evaluated in terms of ACLR and EVM.
Finally, the Self-interference cancelation (SIC) algorithm is implemented at the receiver chain side. Signal to Interference Noise Ratio (SINR) is measured for different Signal to Noise Ratios (SNRs) and different RF cancellations levels to evaluate the system performance at gNodeB.

Popular Abstract

Popular Science Summary
Wireless communication is a way to transfer information from a sender to a receiver, without any wire or fiber, in the form of electromagnetic waves. The information can be sound, text data, images, etc. The radio spectrum is part of the electromagnetic spectrum with frequencies from 1 Hz to 3,000 GHz and is used in modern telecommunication. Cellular communication is one of these wireless radio technologies that has changed modern society. Users are no longer limited to text messages or voice calls. The use of social media, live video streaming, online gaming, shopping, etc are now in trend which results in the consumption of more and more data. According to the Ericsson Mobility Report Nov. 2022, the average data consumption per smartphone is expected to exceed 19 GB per month in 2023, while only new generation mobile subscriptions will hit 5 billion alone in 2028. To fulfil this demand, new technologies are required, along with the improvement of existing ones.
The evolution of wireless communication is based on providing a better-quality experience and more reliable transmission with the fastest possible speed. With every 10 years passing there is a new generation of communications known as generation G-terminology. This journey of evolution started in 1981 as 1G, and now since 2020, we are in the era of 5G. The next generation is now in the research phase and is expected to be launched in the 2030s. Growing from 5G to 6G with the aim of learning from live 5G networks will play a key role in the standardization and development of 6G.
Modern communication systems send and receive simultaneously to exchange information, this concept of two-way transmission is called full duplex. Frequency division duplex (FDD) and time division duplex (TDD) are two fundamental concepts for full-duplex communication. In FDD, separate frequency bands are used for uplink (phone to the network) and downlink (network to the phone) while in TDD, the same frequency band is used for uplink and downlink but only one link can communicate at a time. Both technologies are used in present communication systems. In FDD, a portion of the frequency spectrum is used as a guard band to separate the uplink data and downlink, which is not an efficient use of an expensive spectrum while TDD deployment is very complex, and longer guard periods are required to separate the uplink and downlink which affects the capacity of the network.
Sub-band full duplex is a novel idea that has the potential to outperform other duplexing schemes and is one of the candidate technologies for 6G advancements. The idea of the sub-band full duplex technique is to utilize the spectrum efficiently without adding any guard band. This new technique has flavors of both duplexing schemes in terms of benefits and challenges which integrates the FDD scheme inside the TDD scheme to enable simultaneous downlink and uplink transmissions.
Sub-band full duplex has many challenges to consider coming up with some practical solutions. One of the challenges is self-interference when spectral sharing is being deployed for two radios operating in the same frequency band simultaneously. Another challenge lies with the digital front-end electronic devices, like power amplifiers’ non-linear behavior that degrades the overall system’s efficiency. A digital pre-distortion (DPD) algorithm can be used to correct the non-linearity effect and achieve high power efficiency. This technique helps linearize the power amplifier, minimizing in-band distortion and out-of-band emissions and eventually reaching a reduced bit error rate. Before this technique, another signal processing technique, known as crest factor reduction (CFR), could be required to reduce the peak-to-average power ratio of the downlink signal such that the distortion into the other sub-bands is eliminated or reduced.
This thesis investigates an optimization strategy of DPD and CFR algorithms to reduce the self-interference and hence contribute to a better signal quality at the receiver end.

• author: Rizvi, Midhat and Al-Khateeb, Khaled
• supervisor: Aleksei Fedorov
• organization: Department of Electrical and Information Technology
• course: EITM02 20221
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Adjacent Channel Leakage Ratio, Bit Error Rate, Clipping and Filtering, Crest Factor Reduction, Digital front end, Digital Pre-Distortion Error Vector Magnitude, Frequency Division Duplex, Power Amplifier, Peak to Average Power Ratio, Peak Cancellation Crest Factor Reduction, Sub Band Full Duplex, Self-Interference Cancellation, Signal-to-Interference Noise Ratio, Signal-to-Noise Ratio, Turbo Clipping, Time Division Duplex
• report number: LU/LTH-EIT 2023-913
• language: English
• id: 9111900
• date added to LUP: 2023-03-09 14:25:52
• date last changed: 2023-03-09 14:25:52