Partial Detection for Multiple Antenna Cooperation

Multi-antenna relays can significantly increase the speed and reliability of wireless systems. However, because of the complexity of MIMO detection, there is considerable overhead in implementing a MIMO relay if the conventional detect-and-forward strategy is used. To address this challenge, we propose a novel cooperative partial detection (CPO) strategy that partitions the detection task between the relay and the destination. CPO leverages the structure of the tree-based c1ose-toML MIMO detectors, and modifies the tree traversal so that instead of visiting all the levels of the tree, only a subset of the levels, thus a subset of the transmitted streams, are visited. This novel approach reduces the tree levels, i.e. dimensions, in both the relay and the destination. Moreover, CPO provides a flexible method to control the level of partitioning between the relay and the destination, and thus, adjust the detection computational complexity in the relay and the destination. Monte-Carlo simulation results show that, under equal transmit power and complexity constraint in the destination, CPO achieves a better BER performance compared to the non-relay scenario, with limited computational overhead in the relay.NokiaNational Science Foundatio

Cooperative Partial Detection for MIMO Relay Networks

This paper was submitted by the author prior to final official version. For official version please see http://hdl.handle.net/1911/64372Cooperative communication has recently re-emerged as a possible paradigm shift to realize the promises of the ever increasing wireless communication market; how- ever, there have been few, if any, studies to translate theoretical results into feasi- ble schemes with their particular practical challenges. The multiple-input multiple- output (MIMO) technique is another method that has been recently employed in different standards and protocols, often as an optional scenario, to further improve the reliability and data rate of different wireless communication applications. In this work, we look into possible methods and algorithms for combining these two tech- niques to take advantage of the benefits of both. In this thesis, we will consider methods that consider the limitations of practical solutions, which, to the best of our knowledge, are the first time to be considered in this context. We will present complexity reduction techniques for MIMO systems in cooperative systems. Furthermore, we will present architectures for flexible and configurable MIMO detectors. These architectures could support a range of data rates, modulation orders and numbers of antennas, and therefore, are crucial in the different nodes of cooperative systems. The breadth-first search employed in our realization presents a large opportunity to exploit the parallelism of the FPGA in order to achieve high data rates. Algorithmic modifications to address potential sequential bottlenecks in the traditional bread-first search-based SD are highlighted in the thesis. We will present a novel Cooperative Partial Detection (CPD) approach in MIMO relay channels, where instead of applying the conventional full detection in the relay, the relay performs a partial detection and forwards the detected parts of the message to the destination. We will demonstrate how this approach leads to controlling the complexity in the relay and helping it choose how much it is willing to cooperate based on its available resources. We will discuss the complexity implications of this method, and more importantly, present hardware verification and over-the-air experimentation of CPD using the Wireless Open-access Research Platform (WARP).NSF grants EIA-0321266, CCF-0541363, CNS-0551692, CNS-0619767, EECS-0925942, and CNS-0923479, Nokia, Xilinx, Nokia Siemens Networks, Texas Instruments, and Azimuth Systems

Architecture and Algorithm for a Stochastic Soft-output MIMO Detector

In this paper, we propose a novel architecture for a soft-output stochastic detector in multiple-input, multiple-output (MIMO) systems. The stochastic properties of this detector are studied and derived in this work, and several complexity reduction techniques are proposed to significantly reduce its cost from an architecture-implementation perspective. We also propose an efficient architecture to implement this detector. Finally, this detector is incorporated into an iterative detectiondecoding structure, and through simulations, it is shown that the overall frame error rate (FER) performance and complexity is of the same order as that of the conventional K-best sphere detector.Nokia CorporationXilinx Inc.National Science Foundatio

Prevalence of Mycoplasma Pneumoniae Infection in Patients with COPD Exacerbation; a Letter to the Editor

Dear editor;Currently, control and prevention of respiratory illnesses is considered a health priority in most developed countries and managing the risk factors is necessary for improving the population’s health. Chronic obstructive pulmonary disease (COPD) is the 5th cause of death around the world and estimations have indicated that due to an increase in environmental pollution, this disease will become the 3rd cause of death in the future.In previous studies, pulmonary infection with mycoplasma pneumoniae has been introduced as one of the causes for COPD exacerbation. Mycoplasma pneumoniae affects the upper and lower respiratory tract and its clinical manifestation is trachea-bronchitis accompanied by restlessness and dry coughs. The pathogenesis spectrum of this bacterium ranges from mild pharyngitis and trachea-bronchitis to acute pneumonia. Epidemiologic studies have shown that this bacterium is responsible for more than 20% of community acquired pneumonias.In a cross-sectional study by the authors of the present letter, 66 patients over the age of 18 years who had presented to the emergency department of Imam Reza Hospital, Mashhad, Iran, with diagnosis of COPD exacerbation were evaluated. Sputum sample of the patients was obtained and sent to the laboratory for performing polymerase chain reaction (PCR). Mean age of the patients participating in this study was 67.28 ± 13.68 years (60.6% male). The result of PCR was positive in 6 patients out of the total of 66 patients (9.1%). The results of the present study showed that there was no correlation between age (p=0.18), sex (p=0.25), duration of being affected with COPD (p=0.20), consumption of antibiotics (p=0.35), smoking (p=0.62), opioid abuse (p=0.44), corticosteroid use (p=0.57), underlying illness (p=0.94) and health care—associated pneumonia (HCAP) (p=0.46) with mycoplasma infection. However, prevalence of leukocytosis (p=0.01) and myalgia (p=0.02) was significantly higher in the mycoplasma group.Numerous studies have confirmed the presence of mycoplasma pneumoniae in exacerbation of COPD using serologic diagnosis. For instance, in a study by Lieberman et al. prevalence of mycoplasma pneumoniae in patients with COPD exacerbation was reported as 14.2% and in Meloni et al. study the prevalence of this infection was expressed to be 6.7%. These rates were reported between 5% and 14% in other studies.Thus, it seems that prevalence of mycoplasma is high in COPD exacerbation, but there is still no answer to the question if this infection results in exacerbation of COPD or not and there is controversy between the studies in this regard. Therefore, it is suggested to design case-control or cohort studies to find the answer to this question

Reduced Complexity Soft MMSE MIMO Detector Architecture

Computing the soft LLR values in MMSE receivers of MIMO systems requires a very large complexity. In this paper, we propose a reduced complexity soft MMSE detector for MIMO systems. We use different complexity reductions techniques and propose an architecture based on the new reduced-complexity method. We also compare the complexity and show more than 2x complexity reduction using this method. We present complexity/performance tradeoffs to demonstrate the efficacy of our techniques. More importantly, these techniques give the receivers the flexibility to choose how accurately they perform the detection based on the available resources.XilinxNational Science Foundatio

Cooperative Partial Detection Using MIMO Relays

Using multiple-input multiple-output (MIMO) relays in cooperative communication improves the data rate and reliability of the communication. The MIMO transmission, however, requires considerable resources for the detection in the relay. In particular, if a full detect-and-forward (FDF) strategy is employed, the relay needs to spend considerable resources to perform the full MIMO detection. We propose a novel cooperative partial detection (CPD) strategy to partition the detection task between the relay and the destination. CPD modifies the tree traversal of the tree-based sphere detectors in a way where there is no need to visit all the levels of the tree and only a subset of the levels; thus, a subset of the transmitted streams are visited. The destination, then, combines the source signal and the partial relay signal to perform the final detection step and recover the transmitted vector. We study and compare the performance and complexity of FDF and CPD and show that by using the CPD approach, the relay can avoid the considerable overhead of MIMO detection while helping the source-destination link to improve its performance. More specifically, in the case of a 4X4 system, the relay complexity can be reduced by up to 80% of the conventional relaying scheme

Physical Layer Algorithm and Hardware Verification of MIMO Relays Using Cooperative Partial Detection

Cooperative communication with multi-antenna relays can significantly increase the reliability and speed. However, cooperative MIMO detection would impose considerable complexity overhead onto the relay if a full detect-and-forward (FDF) strategy is employed. In order to address this challenge, we propose a novel cooperative partial detection (CPD) strategy to partition the detection task between the relay and the destination. CPD utilizes the inherent structure of the tree-based sphere detectors, and modifies the tree traversal so that instead of visiting all the levels of the tree, only a subset of the levels, thus a subset of the transmitted streams, are visited. Based on this methodology, the destination combines the source signal and the partial relay signal to perform the detection step. We show, in both simulation and hardware verification on the WARP platform, that using the CPD approach, the relay can avoid the considerable overhead of MIMO detection while helping the source-destination link to improve its performance.XilinxAzimuth SystemsNational Science Foundatio

Design and Architecture of Spatial Multiplexing MIMO Decoders for FPGAs

Spatial multiplexing multiple-input-multiple-output (MIMO) communication systems have recently drawn significant attention as a means to achieve tremendous gains in wireless system capacity and link reliability. The optimal hard decision detection for MIMO wireless systems is the maximum likelihood (ML) detector. ML detection is attractive due to its superior performance (in terms of BER). However, direct implementation grows exponentially with the number of antennas and the modulation scheme, making its ASIC or FPGA implementation infeasible for all but low-density modulation schemes using a small number of antennas. Sphere decoding (SD) solves the ML detection problem in a computationally efficient manner. However, even with this complexity reduction, real-time implementation on a DSP processor is generally not feasible and high-performance parallel computing platforms such as FPGAs are increasingly being employed for this class of applications. The sphere detection problem affords many opportunities for algorithm and micro-architecture optimizations and tradeoffs. This paper provides an overview of techniques to simplify and minimize FPGA resource utilization of sphere detectors for high performance low-latency systems

Reconfigurable Multi-Standard Uplink MIMO Receiver with Partial Interference Cancellation

As HSPA/HSPA+ and LTE/LTE-A evolve in parallel, the reconfigurability of a receiver to support multiple standards has become more and more important, especially for small cells. In this paper, we first suggest a reconfigurable multistandard uplink MIMO receiver based on a frequency domain equalizer. Then, to improve the performance, we propose two low-complexity partial iterative interference cancellation (IC) schemes to deal with the residual inter-chip and inter-antenna interference in HSPA/HSPA+ and the residual inter-symbol and inter-antenna interference in LTE/LTE-A. Compared with a receiver consisting of separate HSPA/HSPA+ and LTE/LTE-A uplink receivers, this reconfigurable receiver can save up to 66.9% complexity. Moreover, the two partial IC schemes have negligible performance loss compared with full IC scheme. They can achieve 2 dB gains in both standards with only 15.2% additional complexity to no IC scheme.Renesas MobileTexas InstrumentsXilinxSamsungHuaweiNational Science Foundatio

Flex-Sphere: An FPGA Configurable Sort-Free Sphere Detector For Multi-user MIMO Wireless Systems

Spatial division multiplexing (SDM) in MIMO technology significantly increases the spectral efficiency, and hence capacity, of a wireless communication system: it is a core component of the next generation wireless systems, e.g. WiMAX, 3GPP LTE and other OFDM-based communication schemes. Moreover, spatial division multiple access (SDMA) is one of the widely used techniques for sharing the wireless medium between different mobile devices. Sphere detection is a prominent method of simplifying the detection complexity in both SDM and SDMA systems while maintaining BER performance comparable with the optimum maximum-likelihood (ML) detection. There are several approaches for realizing sphere detectors, and the algorithmic landscape is rich with methods that enable the designer to make various tradeoffs between performance, e.g. throughput of the wireless channel, BER, and implementation complexity, e.g. silicon area for an ASIC implementation or FPGA resource envelope for an FPGA implementation. This paper describes the FPGA realization of a configurable and flexible sort-free sphere detector, Flex-Sphere, that supports 4;16;64-QAM modulations as well as a combination of 2;3 and 4 antenna/user configuration for uplink transmission. The detector provides a data rate of up to 849:9 Mbps. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed