| 1. |
- Ghoraishi, Mir, et al.
(author)
-
Towards versatile access networks (Chapter 3)
- 2023
-
In: Towards Sustainable and Trustworthy 6G: Challenges, Enablers, and Architectural Design. - 9781638282396 ; , s. 40-120
-
Book chapter (other academic/artistic)abstract
- Compared to its previous generations, the 5th generation (5G) cellular network features an additional type of densification, i.e., a large number of active antennas per access point (AP) can be deployed. This technique is known as massive multipleinput multiple-output (mMIMO) [1]. Meanwhile, multiple-input multiple-output (MIMO) evolution, e.g., in channel state information (CSI) enhancement, and also on the study of a larger number of orthogonal demodulation reference signal (DMRS) ports for MU-MIMO, was one of the Release 18 of 3rd generation partnership project (3GPP Rel-18) work item. This release (3GPP Rel-18) package approval, in the fourth quarter of 2021, marked the start of the 5G Advanced evolution in 3GPP. The other items in 3GPP Rel-18 are to study and add functionality in the areas of network energy savings, coverage, mobility support, multicast broadcast services, and positioning
|
|
| 2. |
- Mazloum, Nafiseh Seyed, et al.
(author)
-
Energy savings using wake-up receivers - An analysis of optimal designs
- 2019
-
In: 2019 IEEE 90th Vehicular Technology Conference, VTC 2019 Fall - Proceedings. - 1550-2252. - 9781728112206 ; 2019-September
-
Conference paper (peer-reviewed)abstract
- With increasing number of wirelessly connected devices having limited energy resources, energy efficient solutions become more and more important. Many studies have addressed schemes where low-power wake-up receivers are used to improve energy efficiency in networks with low traffic intensity (per node) and demands on availability. One such scheme is the duty-cycled wake-up receiver medium access (DCW-MAC) scheme, for which we have detailed understanding of achievable energy savings. In this paper we combine these with recent bounds on the characteristics of optimal low-power receiver designs. What we find is that network energy savings are always achievable with optimally designed wake-up receivers. Moreover, potential network energy savings increase as wake-up receiver power consumption decreases, despite the associated degradation in performance. The lowest network energy consumption, for this type of network, is reached for wake-up receivers pushed to the limit of functioning.
|
|
| 3. |
- Rodriguez Sanchez, Jesus, et al.
(author)
-
Decentralized Massive MIMO Processing Exploring Daisy-Chain Architecture and Recursive Algorithms
- 2020
-
In: IEEE Transactions on Signal Processing. - 1053-587X. ; 68, s. 687-700
-
Journal article (peer-reviewed)abstract
- Algorithms for Massive MIMO uplink detection and downlink precoding typically rely on a centralized approach, by which baseband data from all antenna modules are routed to a central node in order to be processed. In the case of Massive MIMO, where hundreds or thousands of antennas are expected in the base-station, said routing becomes a bottleneck since interconnection throughput is limited. This paper presents a fully decentralized architecture and an algorithm for Massive MIMO uplink detection and downlink precoding based on the Coordinate Descent (CD) method, which does not require a central node for these tasks. Through a recursive approach and very low complexity operations, the proposed algorithm provides a good trade-off between performance, interconnection throughput and latency. Further, our proposed solution achieves significantly lower interconnection data-rate than other architectures, enabling future scalability.
|
|
| 4. |
- Sánchez, Jesús Rodríguez, et al.
(author)
-
Fully Decentralized Massive MIMO Detection Based on Recursive Methods
- 2019
-
In: Proceedings of the IEEE Workshop on Signal Processing Systems, SiPS 2018. - 9781538663189 ; 2018-October, s. 53-58
-
Conference paper (peer-reviewed)abstract
- Algorithms for Massive MIMO uplink detection typically rely on a centralized approach, by which baseband data from all antennas modules are routed to a central node in order to be processed. In case of Massive MIMO, where hundreds or thousands of antennas are expected in the base-station, this architecture leads to a bottleneck, with critical limitations in terms of interconnection bandwidth requirements. This paper presents a fully decentralized architecture and algorithms for Massive MIMO uplink based on recursive methods, which do not require a central node for the detection process. Through a recursive approach and very low complexity operations, the proposed algorithms provide a sequence of estimates that converge asymptotically to the zero-forcing solution, without the need of specific hardware for matrix inversion. The proposed solution achieves significantly lower interconnection data-rate than other architectures, enabling future scalability.
|
|
| 5. |
- Sarajlic, Muris, et al.
(author)
-
An Energy Efficiency Perspective on Massive MIMO Quantization
- 2017
-
In: Proceedings of the 50th Asilomar Conference on Signals, Systems and Computers. - 9781538639542 ; , s. 473-478
-
Conference paper (other academic/artistic)abstract
- One of the basic aspects of Massive MIMO (MaMi) that is in the focus of current investigations is its potential of using low-cost and energy-efficient hardware. It is often claimed that MaMi will allow for using analog-to-digital converters(ADCs) with very low resolutions and that this will result in overall improvement of energy efficiency. In this contribution, we perform a parametric energy efficiency analysis of MaMi uplink for the entire base station receiver system with varyingADC resolutions. The analysis shows that, for a wide variety of system parameters, ADCs with intermediate bit resolutions (4 - 10 bits) are optimal in energy efficiency sense, and that using very low bit resolutions results in degradation of energy efficiency.
|
|
| 6. |
- Sarajlić, Muris, et al.
(author)
-
Fully Decentralized Approximate Zero-Forcing Precoding for Massive MIMO Systems
- 2019
-
In: IEEE Wireless Communications Letters. - 2162-2337. ; 8:3, s. 773-776
-
Journal article (peer-reviewed)abstract
- We analyze the downlink of a massive multiuser multiple input, multiple output (MIMO) system where antenna units at the base station are connected in a daisy chain without a central processing unit and only possess local channel knowledge. For this setup, we develop and analyze a linear precoding algorithm for suppressing interuser interference. It is demonstrated that the algorithm is close to zero-forcing precoding in terms of performance for a large number of antennas. Moreover, we show that with careful scheduling of processing across antennas, requirements for interconnection throughput are reduced compared with the fully centralized solution. Favorable tradeoff between performance and interconnection throughput makes the daisy chain a viable candidate topology for real-life implementations of base stations in MIMO systems where the number of antennas is very large.
|
|
| 7. |
- Sarajlic, Muris
(author)
-
Hardware-Conscious Wireless Communication System Design
- 2019
-
Doctoral thesis (other academic/artistic)abstract
- The work at hand is a selection of topics in efficient wireless communication system design, with topics logically divided into two groups.One group can be described as hardware designs conscious of their possibilities and limitations. In other words, it is about hardware that chooses its configuration and properties depending on the performance that needs to be delivered and the influence of external factors, with the goal of keeping the energy consumption as low as possible. Design parameters that trade off power with complexity are identified for analog, mixed signal and digital circuits, and implications of these tradeoffs are analyzed in detail. An analog front end and an LDPC channel decoder that adapt their parameters to the environment (e.g. fluctuating power level due to fading) are proposed, and it is analyzed how much power/energy these environment-adaptive structures save compared to non-adaptive designs made for the worst-case scenario. Additionally, the impact of ADC bit resolution on the energy efficiency of a massive MIMO system is examined in detail, with the goal of finding bit resolutions that maximize the energy efficiency under various system setups.In another group of themes, one can recognize systems where the system architect was conscious of fundamental limitations stemming from hardware.Put in another way, in these designs there is no attempt of tweaking or tuning the hardware. On the contrary, system design is performed so as to work around an existing and unchangeable hardware limitation. As a workaround for the problematic centralized topology, a massive MIMO base station based on the daisy chain topology is proposed and a method for signal processing tailored to the daisy chain setup is designed. In another example, a large group of cooperating relays is split into several smaller groups, each cooperatively performing relaying independently of the others. As cooperation consumes resources (such as bandwidth), splitting the system into smaller, independent cooperative parts helps save resources and is again an example of a workaround for an inherent limitation.From the analyses performed in this thesis, promising observations about hardware consciousness can be made. Adapting the structure of a hardware block to the environment can bring massive savings in energy, and simple workarounds prove to perform almost as good as the inherently limited designs, but with the limitation being successfully bypassed. As a general observation, it can be concluded that hardware consciousness pays off.
|
|
| 8. |
- Sarajlic, Muris, et al.
(author)
-
Impact of Relay Cooperation on the Performance of Large-Scale Multipair Two-Way Relay Networks
- 2019
-
In: 2018 IEEE Global Communications Conference, GLOBECOM 2018 - Proceedings. - 9781538647271
-
Conference paper (peer-reviewed)abstract
- We consider a multipair two-way relay communication network, where pairs of user devices exchange information via a relay system. The communication between users employs time division duplex, with all users transmitting simultaneously to relays in one time slot and relays sending the processed information to all users in the next time slot. The relay system consists of a large number of single antenna units that can form groups. Within each group, relays exchange channel state information (CSI), signals received in the uplink and signals intended for downlink transmission. On the other hand, per-group CSI and uplinkdownlink signals (data) are not exchanged between groups, which perform the data processing completely independently. Assuming that the groups perform zero-forcing in both uplink and downlink, we derive a lower bound for the ergodic sumrate of the described system as a function of the relay group size. By close observation of this lower bound, it is concluded that the sumrate is essentially independent of group size when the group size is much larger than the number of user pairs. This indicates that a very large group of cooperating relays can be substituted by a number of smaller groups, without incurring any significant performance reduction. Moreover, this result implies that relay cooperation is more efficient (in terms of resources spent on cooperation) when several smaller relay groups are used in contrast to a single, large group.
|
|
| 9. |
- Sarajlic, Muris, et al.
(author)
-
Modified Forced Convergence Decoding of LDPC Codes with Optimized Decoder Parameters
- 2015
-
In: 2015 IEEE 26th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC). - 9781467367820
-
Conference paper (peer-reviewed)abstract
- Reducing the complexity of decoding algorithms for LDPC codes is an important prerequisite for their practical implementation. In this work we propose a reduction of computational complexity targeting the highly reliable codeword bits and show that this approach can be seamlessly merged with the forced convergence scheme. We also show how the minimum achievable complexity of the resulting scheme for given performance constraints can be found by solving a constrained optimization problem, and successfully apply a gradient-descent based stochastic approximation (SA) method for solving this problem. The proposed methods are tested on LDPC codes from the IEEE 802.11n standard. Computational complexity reduction of 55% and a 75% reduction of memory access have been observed.
|
|
| 10. |
- Sarajlic, Muris, et al.
(author)
-
Power Scaling Laws for Radio Receiver Front Ends
- 2021
-
In: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328. ; 68:5, s. 2183-2195
-
Journal article (peer-reviewed)abstract
- In this paper, we combine practically verified results from circuit theory with communication-theoretic laws. As a result, we obtain closed-form theoretical expressions linking fundamental system design and environment parameters with the power consumption of analog front ends (AFEs) for communication receivers. This collection of scaling laws and bounds is meant to serve as a theoretical reference for practical low power AFE design. We show how AFE power consumption scales with bandwidth, SNDR, and SIR. We build our analysis based on two well established power consumption studies and show that although they have different design approaches, they lead to the same scaling laws. The obtained scaling laws are subsequently used to derive relations between AFE power consumption and several other important communication system parameters, namely, digital modulation constellation size, symbol error probability, error control coding gain, and coding rate. Such relations, in turn, can be used when deciding which system design strategies to adopt for low-power applications. For instance, we show how AFE power scales with environment parameters if the performance is kept constant and we use these results to illustrate that adapting to fading fluctuations can theoretically reduce AFE power consumption by at least 20x.
|
|
