| 1. |
- Eklund, Johan, 1966-, et al.
(author)
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Tuning SCTP failover for carrier grade telephony signaling
- 2010
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In: Computer Networks. - : Elsevier BV. - 1389-1286 .- 1872-7069. ; 54:1, s. 133-149
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Journal article (peer-reviewed)abstract
- The Stream Control Transmission Protocol (SCTP) has not only been selected as the signaling transport protocol of choice in IETF SIGTRAN, the architecture that bridges circuit-switched and IP-based mobile core networks, but also plays a pivotal role in SAE/LTE, the next-generation UMTS/HSPA networks. To meet the redundancy requirements of telecom signaling traffic, SCTP includes a failover mechanism that enables rerouting of traffic from an unreachable network path to a backup path. However, the recommendations provided by IETF on how to configure the SCTP failover mechanism to meet telecom signaling requirements are kept quite general and leave much of the tuning to the telecom equipment vendor and/or operator. Several works by us and others have been carried out to study the effect of different SCTP parameters on the failover performance. The main contribution of this paper is that it gives a coherent treatment of how to configure the SCTP failover mechanism for carrier-grade telephony signaling, and provides practically usable configuration recommendations. The paper also discusses an alternate or complementary way of optimizing the SCTP failover mechanism by relaxing the exponential backoff that foregoes a retransmission timeout in SCTP. Some results showing significantly reduced failover times by use of this mechanism, with only marginal deteriorating effects on a signaling network, are discussed and analyzed in the paper. (C) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Alayon Glazunov, Andres, et al.
(author)
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On the Physical Limitations of the Interaction of a Spherical Aperture and a Random Field
- 2011
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In: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 59:1, s. 119-128
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Journal article (peer-reviewed)abstract
- This paper derives physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. The derivation is based on the spherical vector wave expansion of the electromagnetic field outside a sphere circumscribing the antennas. The result is an extension of the seminal work of Chu on the classical limitations on maximum antenna gain and radiation Q. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e., the instantaneous effective gain G(i) and the mean effective gain G(e) if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, spectively. The obtained limitations are on the maximum of G(i)/Q and G(e)/Q, which establish a trade-off between link gain and Q.
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| 3. |
- Khanzadi, M Reza, 1983, et al.
(author)
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Calculation of the Performance of Communication Systems from Measured Oscillator Phase Noise
- 2014
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In: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328 .- 1558-0806. ; 61:5, s. 1553-1565
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Journal article (peer-reviewed)abstract
- Oscillator phase noise (PN) is one of the major problems that affect the performance of communication systems. In this paper, a direct connection between oscillator measurements, in terms of measured single-side band PN spectrum, and the optimal communication system performance, in terms of the resulting error vector magnitude (EVM) due to PN, is mathematically derived and analyzed. First, a statistical model of the PN, considering the effect of white and colored noise sources, is derived. Then, we utilize this model to derive the modified Bayesian Cramer-Rao bound on PN estimation, and use it to find an EVM bound for the system performance. Based on our analysis, it is found that the influence from different noise regions strongly depends on the communication bandwidth, i.e., the symbol rate. For high symbol rate communication systems, cumulative PN that appears near carrier is of relatively low importance compared to the white PN far from carrier. Our results also show that 1/f^3 noise is more predictable compared to 1/f^2 noise and in a fair comparison it affects the performance less.
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| 4. |
- Khanzadi, M Reza, 1983
(author)
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Modeling and Estimation of Phase Noise in Oscillators with Colored Noise Sources
- 2013
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Licentiate thesis (other academic/artistic)abstract
- The continuous increase in demand for higher data rates due to applications with massive number of users motivates the design of faster and more spectrum efficient communication systems. In theory, the current communication systems must be able to operate close to Shannon capacity bounds. However, the real systems perform below capacity limits, mainly due to channel estimation error and hardware impairments that have been neglected by idealistic or simplistic assumptions on the imperfections. Oscillator phase noise is one of the hardware impairments that is becoming a limiting factor in high data rate digital communication systems. Phase noise severely limits the performance of systems that employ dense constellations. Moreover, the level of phase noise (at a given off-set frequency) increases with carrier frequency which means that the problem of phase noise may be even more severe in systems with high carrier frequency.The focus of this thesis is on finding accurate statistical models of phase noise, as well as the design of efficient algorithms to mitigate the effect of this phenomenon on the performance of modern communication systems. First we derive the statistics of phase noise with white and colored noise sources in free-running and phase-locked-loop-stabilized oscillators. We investigate the relation between real oscillator phase noise measurements and the performance of communication systems by means of the proposed model. Our findings can be used by hardware and frequency generator designers to better understand the effect of phase noise with different sources on the system performance and optimize their design criteria respectively. Then, we study the design of algorithms for estimation of phase noise with colored noise sources. A soft-input maximum a posteriori phase noise estimator and a modified soft-input extended Kalman smoother are proposed. The performance of the proposed algorithms is compared against that of those studied in the literature, in terms of mean square error of phase noise estimation, and symbol error rate of the considered communication system. The comparisons show that considerable performance gains can be achieved by designing estimators that employ correct knowledge of the phase noise statistics. The performance improvement is more significant in low-SNR or low-pilot density scenarios.
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| 5. |
- Wang, Chao, et al.
(author)
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On the Degrees of Freedom of Parallel Relay Networks
- 2010
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In: 2010 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE GLOBECOM 2010. - 1930-529X. - 9781424456383 - 9781424456369
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Conference paper (peer-reviewed)abstract
- We study the degrees of freedom (DOF) of a single-antenna M-user time-varying parallel relay network, where the communications between M pairs of unconnected sources and destinations are provided by a large number of half-duplex decode-and-forward (DF) relays. Unlike the conventional relaying strategy which demands all the relays to simultaneously assist the sources, we divide the relays into two clusters and permit them to take turns forwarding the source messages. With appropriate interference alignment design, it is proved that the M-user time-varying relay network has M DOF, provided that the number of relays is infinitely large.
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| 6. |
- ur Réhman, Shafiq, 1978-
(author)
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Expressing emotions through vibration for perception and control
- 2010
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Doctoral thesis (other academic/artistic)abstract
- This thesis addresses a challenging problem: “how to let the visually impaired ‘see’ others emotions”. We, human beings, are heavily dependent on facial expressions to express ourselves. A smile shows that the person you are talking to is pleased, amused, relieved etc. People use emotional information from facial expressions to switch between conversation topics and to determine attitudes of individuals. Missing emotional information from facial expressions and head gestures makes the visually impaired extremely difficult to interact with others in social events. To enhance the visually impaired’s social interactive ability, in this thesis we have been working on the scientific topic of ‘expressing human emotions through vibrotactile patterns’. It is quite challenging to deliver human emotions through touch since our touch channel is very limited. We first investigated how to render emotions through a vibrator. We developed a real time “lipless” tracking system to extract dynamic emotions from the mouth and employed mobile phones as a platform for the visually impaired to perceive primary emotion types. Later on, we extended the system to render more general dynamic media signals: for example, render live football games through vibration in the mobile for improving mobile user communication and entertainment experience. To display more natural emotions (i.e. emotion type plus emotion intensity), we developed the technology to enable the visually impaired to directly interpret human emotions. This was achieved by use of machine vision techniques and vibrotactile display. The display is comprised of a ‘vibration actuators matrix’ mounted on the back of a chair and the actuators are sequentially activated to provide dynamic emotional information. The research focus has been on finding a global, analytical, and semantic representation for facial expressions to replace state of the art facial action coding systems (FACS) approach. We proposed to use the manifold of facial expressions to characterize dynamic emotions. The basic emotional expressions with increasing intensity become curves on the manifold extended from the center. The blends of emotions lie between those curves, which could be defined analytically by the positions of the main curves. The manifold is the “Braille Code” of emotions. The developed methodology and technology has been extended for building assistive wheelchair systems to aid a specific group of disabled people, cerebral palsy or stroke patients (i.e. lacking fine motor control skills), who don’t have ability to access and control the wheelchair with conventional means, such as joystick or chin stick. The solution is to extract the manifold of the head or the tongue gestures for controlling the wheelchair. The manifold is rendered by a 2D vibration array to provide user of the wheelchair with action information from gestures and system status information, which is very important in enhancing usability of such an assistive system. Current research work not only provides a foundation stone for vibrotactile rendering system based on object localization but also a concrete step to a new dimension of human-machine interaction.
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| 7. |
- Alhashimi, Anas, 1978-
(author)
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The application of auto regressive spectrum modeling for identification of the intercepted radar signal frequency modulation
- 2012
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In: Inventi Impact - Telecom. - Bhopal, India : Inventi Journals Pvt.Ltd.. - 2249-1414 .- 2230-8172. ; 2012:3
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Journal article (peer-reviewed)abstract
- In the Electronic Warfare receivers, it is important to know the type of modulation of the intercepted Radar signals (MOP modulation on pulse). This information can be very helpful in identifying the type of Radar present and to take the appropriate actions against it. In this paper, a new signal processing method is presented to identify the FM (Frequency Modulation) pattern from the received Radar pulses. The proposed processing method based on Auto Regressive Spectrum Modelling used for digital modulation classification [1]. This model uses the instantaneous frequency and instantaneous bandwidth as obtained from the roots of the autoregressive polynomial. The instantaneous frequency and instantaneous bandwidth together were used to identify the type of modulation in the Radar pulse. Another feature derived from the instantaneous frequency is the frequency rate of change. The frequency rate of change was used to extract the pattern of the frequency change. Results show that this method works properly even for low signal to noise ratios.
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| 8. |
- Gustavsson, Ulf, 1975
(author)
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From Noise-Shaped Coding to Energy Efficiency - One bit at the time
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Three parameters that drive the research and development of future RF transmitter technologies for high speed wireless communication today are energy efficiency, flexibility and reduction of the physical footprint. This thesis treats the use of single-bit quantization in conjunction with a method called Noise-Shaped Coding (NSC), as an enabler for these parameters, foremost in terms of energy efficiency.The first part of the thesis provides a short introduction to the common Radio Frequency Power Amplifier (RFPA) power efficiency enhancement techniques. The pulsed RF transmitter is introduced in which the RFPA is used as a switch, modulated by a single-bit quantized signal which allows it to operate solely at its two most efficient states.The second part of the thesis provides an introduction to the concept of NSC and the underlying idea of how high signal quality can be achieved with one bit quantization of the signal amplitude. A particular method of implementing NSC, namely the ΣΔ-modulator, is introduced and some common methods for design and analysis are discussed. An optimization-based approach to ΣΔ-modulator design is proposed and benchmarked against conventional methods in terms of its ability to shape the power spectral density of the quantization noise according to a given reconstruction filter response, minimizing the reconstructed error metric.The third and final part of the thesis focuses specifically on the application of ΣΔ-modulation in a pulsed RF transmitter context. The concepts of band-pass and baseband ΣΔ-modulation are introduced. A few important challenges related to the use of ΣΔ-modulation in a pulsed RF-transmitter context are identified. A ΣΔ-modulator topology which handles a complex input signal is investigated in great detail and advantages compared to conventional methods for using ΣΔ-modulation are unveiled by means of theoretical analysis and simulations. A method for suppressing the quantization noise within a frequency band surrounding the modulated RF carrier, enabling the use of more wideband reconstruction filter and moderate pulse-rates, is also presented. A detailed theoretical analysis reveals how optimized Noise-Shaped Coding, as provided by the optimization method introduced in the second part, can be deployed in order to improve the system performance. Finally, the method is validated by experimental measurements on two different high efficiency RFPAs at 1 and 3.5 GHz respectively, showing promising results.
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| 9. |
- Chen, Jingjing, 1982, et al.
(author)
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10 Gbps 16QAM transmission over a 70/80 GHz (E-band) radio test-bed
- 2012
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In: European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 7th European Microwave Integrated Circuits Conference, EuMIC 2012. - : IEEE. - 9782874870286 - 9781467323024 - 9782874870262 ; , s. 556-559
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Conference paper (peer-reviewed)abstract
- A millimeter-wave radio test-bed is implemented which demonstrates 16QAM transmission over 70/80 GHz band for data rate up to 10 Gbps. Performance of the 16QAM transmitter and receiver is evaluated in a loop-back lab set-up. With the proposed 10 Gbps on single carrier system architecture, it is possible to achieve 40 Gbps over a 5 GHz bandwidth when combined with polarization and spatial multiplexing.
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| 10. |
- Farhadi, Hamed, 1983
(author)
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On the throughput of wireless interference networks with limited feedback
- 2011
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In: IEEE International Symposium on Information Theory Proceedings (ISIT'11). - 2157-8095. - 9781457705960 ; , s. 762 - 766
-
Conference paper (peer-reviewed)abstract
- Considering a single-antenna M-user interference channel with symmetrically distributed channel gains, when the channel state information (CSI) is globally available, applying the ergodic interference alignment scheme, each transmitter-receiver pair achieves a rate proportional to ½ of a single user's interference-free achievable rate. This is substantially higher than the achievable rate of the conventional orthogonal transmission schemes such as TDMA. Since the rigid requirement on the CSI may be difficult to realize in practice, in this paper we investigate the performance of applying the ergodic interference alignment scheme when the estimation of each channel gain is made globally known through exploiting only a limited feedback signal from the associated receiver of that channel. Under a block fading environment, we provide a lower bound on the achievable average throughput of the network. Our results imply that the better performance of interference alignment over TDMA may still exist even without the assumption of perfect CSI. Also, the trade off between allocating feedback rate of each receiver to the desired channel or the interference channels at deferent SNR region investigated.
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