iCORE Student Seminars in Communications
In late 2001, the iCORE Wireless Communications Laboratory created a student seminar series. The purpose of these seminars is the dissemination of information, ideas, and research among the graduate students in communications at the University of Alberta.
For the iCORE Student Seminars, students generally present seminars based on their research results or their upcoming conference presentations. Some students present seminars based on publications that are relevant to their research. In all cases, the iCORE Student Seminars in Communications serve as a good conduit of information for students. Besides, it's a good excuse to get students out of the lab.
Back to Student Seminars
Seminars in Fall 2008
| Time: | 3:30 - 4:30 P.M., Wednesday, October 15th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Dr. Zhonshan Zhang University of Alberta |
| Topic: | Cooperative OFDM Channel Estimation with Frequency Offsets |
| Abstract: | This paper discusses channel estimation in a cooperative orthogonal frequency-division multiplexing (OFDM) network in the presence of frequency offsets. Both the amplify-and-forward (AF) and decode-and-forward (DF) relaying modes are analyzed. In order to eliminate the multiple access interference (MAI), the maximum number of active AF and DF relays are N/(2L-1) and N/L, respectively, where N is the total number of subcarriers, L is the channel order. The pairwise error probability (PEP) of orthogonal space-time coding in cooperative OFDM due to both the frequency offset and channel estimation errors is also evaluated. The optimal power allocation ratio between the source and the set of the relays to minimize the PEP is derived for both the relay modes. When L<16, the DF mode always outperforms the AF mode in terms of PEP. Given 16 active relays and with L=4, the proposed DF mode outperforms the AF mode by about 9dB for a frequency offset error variance of 0.001, and this gap increases to about 11.3dB when the variance increases to 0.01. |
| Time: | 3:30 - 4:30 P.M., Wednesday, October 15th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Dr. Zhonshan Zhang University of Alberta |
| Topic: | Improved OFDMA Uplink Transmission via Cooperation in the Presence of Frequency Offsets |
| Abstract: | In this paper, we evaluate the performance improvement in an Orthogonal Frequency-Division Multiple Access (OFDMA) uplink achievable with cooperative relaying in the presence of frequency offsets. We consider both the amplify-and-forward (AF) and decode-and-forward (DF) relays. In each transmission, each node plays two roles i.e., the source node and relay, simultaneously, but at different subcarriers. The proposed scheme improves performance without sacrificing the transmission rate and power of the cooperative relays, and the total power used to transmit each symbol, including the power consumed in node the source node and the relays, is kept constant. The outage information rates of the proposed cooperative transmission scheme are derived, and the diversity gain of each forwarding mode in an interference-limited environment is analyzed in this paper. Numerical results illustrate the superior performance of the proposed scheme over the conventional transmission with regard to outage information rate. |
| Time: | 3:30 - 4:30 P.M., Wednesday, October 22nd, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Amir Masoud Rabiei University of Alberta |
| Topic: | ISI-free cochannel interference whitening for bandlimited fading channels |
| Abstract: | The problem of cochannel interference mitigation using interference-plus-noise whitening receiver design in the presence of intersymbol interference (ISI) is considered. The effect of ISI on the signal-to-interference-plus-noise ratio (SINR) of the interference whitening receiver is examined. Then, two methods are proposed to maximize the SINR without introducing ISI. In the first method, the transmitter and receiver filters are designed to maximize the SINR while their overall spectrum maintains a given Nyquist spectrum to avoid ISI. In the second method, the transmitter filter is assumed to be fixed and only the receiver filter is designed to achieve maximum SINR without introducing ISI. The SINR of the ISI-free SINR-maximizing filter is then analytically compared with that of the conventional matched filter receiver and the interference whitening receiver. Numerical results are presented for the cases when standard raised-cosine and Beaulieu-Tan-Damen pulses are used in the system. |
| Time: | 3:30 - 4:30 P.M., Wednesday, October 22nd, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Dr. Zhonshan Zhang University of Alberta |
| Topic: | Optimal Pilots for Frequency Offsets and Channel Estimation in OFDMA Uplink |
| Abstract: | Optimal pilots design and placement for the frequency offsets and channel estimation in Orthogonal Frequency- Division Multiplexing Access (OFDMA) uplink systems are proposed. The received pilots of multiple users can always be demodulated, even if they are totally overlapped due to the large frequency offsets. The proposed frequency offset estimation is also independent of the actual frequency offset. With the knowledge of channel state information (CSI) at the receiver, the performance of the proposed frequency offset estimation is robust to the channel estimation errors. The frequency offset and CSI can be jointly estimated by employing the proposed pilots. |
| Time: | 3:30 - 4:30 P.M., Wednesday, October 29th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Reza Nikjah University of Alberta |
| Topic: | On Optimal Power Allocation for Source-Orthogonal Relay-Nonorthogonal Amplify-and-Forward Relaying |
| Abstract: | An amplify-and-forward relaying network where the source is orthogonal to all the relays but the relays are nonorthogonal (SORNAF) is studied. The problem of relay power optimization in a SORNAF relaying scheme is formulated as a nonconcave fractional program. Selection amplify-and-forward (SAF) relaying is a possible power allocation strategy previously proposed for the SORNAF scheme. A necessary condition for the optimality of the SAF power allocation is derived in terms of instantaneous channel coefficients, based on which, an upper bound on the SAF optimality probability is calculated. The upper bound approaches zero almost exponentially as the number of relays increases, showing that SAF relaying is asymptotically strictly suboptimal. A suboptimal power allocation, which is significantly superior to the SAF algorithm in terms of outage performance, is also proposed for SORNAF relaying. |
| Time: | 3:30 - 4:30 P.M., Wednesday, October 29th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Reza Nikjah University of Alberta |
| Topic: | Novel Rateless Coded Selection Cooperation in Dual-Hop Relaying Systems |
| Abstract: | Selection cooperation is proposed for rateless coded relaying by developing a novel low-complexity protocol that exploits all source-destination, source-relay, and relay-destination link qualities for relay selection. The source or any decoding relay having a link to the destination with a gain greater than a preset threshold is a candidate for collaboration. When the number of candidates reaches a preset value, the best of them is selected for passing the source data to the destination. The source and relays are informed of the selected node by a broadcast feedback from the destination. Limited feedback is required only between the destination and the other nodes and merely for declaring success in decoding or selecting the next transmitting node. The system power and complexity are independent of the system parameters. Also, the system dispenses with internode synchronization at carrier or symbol levels, multireception combining, multiaccess interference, and multiuser detection. Assuming independent fading on different links, a general performance analysis of the new system is presented valid for any individual link fading model. It is shown through numerical results that the novel scheme is considerably more energy efficient, for diverse input conditions, than a more complex commensurate scheme previously proposed. Also, the energy efficiency is enhanced as the number of relays increases, such that despite an increase in the capacity, the energy expenditure diminishes. |
| Time: | 3:30 - 4:30 P.M., Wednesday, November 5th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Iraj Hosseini University of Alberta |
| Topic: | Optimal Error Rate Performance of Binary TH-UWB Receivers in Multiuser Interference |
| Abstract: | An exact mathematical model which explains the important characteristics of the probability density function (PDF) of the multiple access interference (MAI) in time-hopping UWB (TH-UWB) systems is discussed. The proposed model accurately foresees impulses, singularities, and heavy tails found in the distribution of the MAI. Also, it discloses precisely why a Gaussian approximation for the MAI in TH-UWB systems is highly inaccurate even in the presence of a large number of interferers. Then, using the maximum a posteriori (MAP) receiver rule and based on the obtained model for the PDF of the MAI, the optimal achievable BER performance of binary TH-UWB receivers is numerically determined. Finally, the performances of some recently proposed UWB receivers are benchmarked against the optimal performance. |
| Time: | 3:30 - 4:30 P.M., Wednesday, November 5, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Golnaz Farhadi University of Alberta |
| Topic: | Ergodic Capacity of Multi-Hop Wireless Relaying Systems in Rayleigh Fading |
| Abstract: | The ergodic capacity in Rayleigh fading of multi-hop wireless transmission systems employing either amplify-and-forward relaying or decode-and-forward relaying is studied, assuming channel state information is only known at the receiving terminals. Two upper bounds based on Jensen's inequality and the harmonic-geometric means inequality as well as an infinite series representation for the ergodic capacity of an amplify-and-forward multi-hop transmission system are derived. Numerical results indicate the upper bound obtained based on Jensen's inequality is tight. This upper bound is tighter than the upper bound based on harmonic and geometric means for larger numbers of hops and especially for systems in non-identical fading. Numerical results are provided to show the high accuracy of the infinite series approach. In addition, the ergodic capacity of a decode-and-forward multi-hop transmission system is obtained. It is shown that multi-hop transmission systems employing a decode-and-forward relaying scheme achieve higher ergodic capacities than multi-hop transmission systems with amplify-and-forward relaying schemes. |
| Time: | 3:30 - 4:30 P.M., Wednesday, November 12th, 2008 |
| Place: | Room ETLC E1-008 |
| Speaker: | Moslem Noori University of Alberta |
| Topic: | Characterizing the Traffic Distribution in Linear Wireless Sensor Networks |
| Abstract: | In a multi-hop wireless sensor network (WSN), the traffic load is not evenly distributed over the nodes. For example, the sensors which are one hop away from the sink relay the whole network traffic. This imbalanced traffic distribution can degrade the network lifetime and functionality. Here, an analysis is proposed to characterize the traffic load distribution over a randomly deployed linear WSN. The effect of the number of nodes and their distribution over the network is taken into account and the results are verified through computer simulation. |
| Time: | 3:30 - 4:30 PM, Wednesday, November 12th, 2008 |
| Place: | ETLC E1-008 |
| Speaker: | Mahdi Ramezani University of Alberta |
| Topic: | On the Design of Universal LDPC Codes |
| Abstract: | Low-density parity-check (LDPC) coding for a multitude of equal-capacity channels is studied. First, based on numerous observations, a conjecture is stated that when the belief propagation decoder converges on a set of equal-capacity channels, it would also converge on any convex combination of those channels. Then, it is proved that when the stability condition is satisfied for a number of channels, it is also satisfied for any channel in their convex hull. For the purpose of code design, a method is proposed which can decompose every symmetric channel with capacity C into a set of identical-capacity basis channels. We expect codes that work on the basis channels to be suitable for any channel with capacity C. Such codes are found and in comparison with existing LDPC codes that are designed for specific channels, our codes obtain considerable coding gains when used across a multitude of channels. |