Dr. Geoff Knagge
Publications
Selected Publications.
- A VLSI 8x8 MIMO Near-ML Decoder with Preprocessing
- G. Knagge, M. Bickerstaff, B. Ninness, S.R. Weller, G. Woodward
- Journal of Signal Processing Systems Special Issue on SiPS06, to appear 2008
- BibTeX | Full Text
- Multiple-Input Multiple-Output (MIMO) systems are of significant interest due to their
ability to increase the capacity of wireless communications systems, but for these to be
useful they must also be practical for implementation in VLSI circuits. A particularly
difficult part of these systems is the detector, where the optimal maximum-likelihood
(ML) solution is desirable, but cannot be directly implemented due to its exponential
complexity.
This paper addresses this challenge and presents a digital circuit design for an 8x8 MIMO
detection problem. A key feature is the integrated channel preprocessing unit, which
performs the channel decomposition functions that are either omitted or performed
``off-line'' in other designs. The proposed device achieves near maximum
likelihood bit error rate results at 57.6Mbps. Other novelties include a high speed sorting
mechanism and power saving features.
- Silicon Complexity for Maximum Likelihood MIMO Detection Using Spherical Decoding
- D. Garrett, L. Davis, S. ten Brink, B. Hochwald, G. Knagge
- IEEE Journal of Solid-State Circuits Vol. 39, No. 9, 2004
- BibTeX
- A VLSI 8x8 MIMO near-ML decoder engine
- G. Knagge, M. Bickerstaff, B. Ninness, S.R. Weller, G. Woodward
- IEEE 2006 Workshop on Signal Processing Systems (SiPS'06) 2006
- BibTeX | Full Text
- Multiple-Input Multiple-Output (MIMO) systems are of significant interest due to their ability to increase the capacity of wireless communications systems, but for these to be useful they must also be practical for implementation in VLSI circuits. A particularly difficult part of these systemsis the decoder, where the optimal maximum-likelihood (ML) solution is desirable, but cannot be directly implemented due to its exponential complexity.
The paper presents the first published 8×8 MIMO detection engine with an integrated channel preprocessing unit, achieving near-ML BER results at 57.6Mbps, using QPSK in an extended HSDPA application. Other novelties include the high speed sorting mechanism and power saving features.
- VLSI Preprocessing techniques for MUD and MIMO Sphere Detection
- G. Knagge, L. Davis, G. Woodward, S.R. Weller
- Australian Communications Theory Workshop 2005
- BibTeX | Full Text
- While it has been shown that sphere detectors for multiuser detection (MUD) and multiple-input multiple-output (MIMO) systems can be efficiently designed, a significant hindrance to their feasibility arises from the preprocessing requirements of these algorithms. This paper investigates a number of approaches that may be taken to address this issue, and evaluates their performance in fixed point and reduced precision floating point simulations to determine the most suitable approach. A very large scale integrated circuit (VLSI) implementation strategy is also proposed to show how the chosen method may be efficiently built in hardware.
- A VLSI Optimised Parallel Tree Search for MIMO
- G. Knagge, G. Woodward, S.R. Weller, B. Ninness
- Australian Communications Theory Workshop 2005
- BibTeX | Full Text
- Multiple Input-Multiple Output (MIMO) systems are of great interest due to their ability to significantly increase the capacity of wireless communications systems, but for these to be useful they must also be practical for implementation in very large scale integrated (VLSI) circuits. A particularly difficult part of these systems is the detector, where the maximum-likelihood (ML) solution cannot be directly implemented due to its exponential complexity.
Lattice decoders, such as the sphere search, exhibit near-ML performance with reduced complexity, but their application is still limited by computational requirements. Here, a number of optimisations are presented, designed to reduce the computational cost of the sphere search in the context of VLSI implementation for MIMO applications. We also propose parallel implementation strategies for such a detector, suitable for implementation in VLSI. This is then combined with a single-pass tree search approach and it is demonstrated that it can be designed so that the error-rate performance is not significantly impaired.
- An Optimised Parallel Tree Search for Multiuser Detection with VLSI Implementation Strategy
- G. Knagge, G. Woodward, B. Ninness, S.R. Weller
- IEEE Global Telecommunications Conference 2004
- BibTeX | Full Text
- Multiuser detection (MUD) strategies have the potential to significantly increase the capacity of wireless communications systems, but for these to be useful they must also be practical for implementation in very large scale integrated (VLSI) circuits. In particular, while the maximum-likelihood (ML) solution is optimal in bit error rate, it cannot be directly implemented due to its exponential computational complexity.
Lattice decoders, such as the sphere search, exhibit near-optimal ML performance with reduced complexity, but their application is still limited by computational requirements. Here, we present a number of optimisations designed to reduce the computational cost of the sphere search, in the context of VLSI implementation. We also propose parallel implementation strategies for such a detector, suitable for implementation in VLSI. We then combine this with a single-pass tree search approach that can be designed to not significantly impair error-rate performance. While our design is targeted towards a MUD application, the concepts may also be applied to a multiple-input multiple-output (MIMO) system, or similar applications.
- A Highly-Parallel VLSI Architecture for a List Sphere Detector
- B. Widdup, G. Woodward, G. Knagge
- IEEE International Communications Conference 2004
- BibTeX
- A 28.8 Mb/s 4x4 MIMO 3G High-Speed Downlink Packet Access Receiver with Normalized Least Mean Square Equalization
- D. Garrett, G. Woodward, L. Davis, G. Knagge, C. Nicol
- IEEE International Solid-State Circuits Conference (ISSCC) 2004
- BibTeX
- A Greedy Iterative Algorithm and VLSI Implementation Strategy for Multiuser Detection
- G. Knagge
- Australian Communications Theory Workshop 2004
- BibTeX | Full Text
- Multiuser detection (MUD) strategies have the potential to significantly increase the capacity of wireless communications systems, but for these to be useful they must also be practical for implementation in VLSI circuits that cope with real world situations and process data in real time. The application of the optimal Maximum Likelihood (ML) solution is limited by its exponential computational complexity. Current near-ML algorithms such as the spherical detector offer significantly reduced complexity, but are still likely to be impractical for larger problems. Simpler MUD algorithms, such as the interference canceller (IC), are more practical but offer poor performance in some cases of interest.
In this paper, we present a unique algorithm that shares aspects of these well known techniques, but offers higher performance than the simpler methods, while remaining practical. Our approach involves a series of iterations that that gradually converge to a decision, by choosing the estimates that produce lower values for our ML cost function. While this is more complex than well known methods, it offers higher bit error rate performance and is lower in complexity that other methods with comparable performance. We also show how to further reduce the complexity to make our algorithm suitable for VLSI implementation.
- Matrix Datapath Architecture for an Iterative 4x4 MIMO Noise Whitening Algorithm
- G. Knagge, D. Garrett, S. Venkatesan, C. Nicol
- Great Lakes Symposium on VLSI Circuits (GLSVLSI) 2003
- BibTeX | Full Text
- Algorithms and Application Specific Integrated Circuits for Combinatorial Optimisation in Wireless Communications
- G. Knagge
- 2007
- BibTeX
- thesis