Browsing by Author "Heidarpour, M. R."

Now showing 1 - 7 of 7

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Cooperative BICM-OFDM systems for frequency-selective relay channels
(IEEE, 2011) Heidarpour, M. R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we consider a cooperative multi-carrier multi-relay system over frequency-selective fading channels. Specifically, we adopt the orthogonal frequency division multiplexing (OFDM) with bit-interleaved coded-modulation (BICM) as the physical layer signalling platform. Under the assumption of amplify-and-forward relaying, we first present a diversity order analysis through the derivation of pairwise error probability (PEP) for an orthogonal scheme in which relays scale and transmit their received OFDM signals in non-overlapping time slots. Based on the derived PEP expression, we further propose a relay selection rule to improve the spectral efficiency. We also investigate some suboptimal (heuristic) selection methods as low-complexity alternatives. We present extensive Mont Carlo simulations to confirm the analytical derivations and provide performance comparisons among competing schemes.
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Cooperative communication techniques for future-generation HF radios
(IEEE, 2012-10) Uysal, Murat; Heidarpour, M. R.; Electrical & Electronics Engineering; UYSAL, Murat
When Hurricane Katrina hit the Gulf Coast of the United States in 2005, it severely damaged the telecommunications infrastructure, isolating the area from the outside world. With all the high-end emergency communication gear in its path being knocked out by the hurricane, highfrequency (HF) amateur radio systems played a critical role in rescue and recovery operations. Such tragic incidents have resulted in re-appreciation of the "good old" HF technology that has been an essential part of worldwide information transmission since the advent of radio. HF systems traditionally have been associated with analog voice and very-low-rate data transmission. With the shift from analog to digital in voice communication and increasing demands for high-rate data transmission (e.g., email, Internet, FTP), HF communication has been going through a renaissance. Innovative techniques are required to push the capacity limits of the HF band. Our tutorial provides a contemporary overview of HF communication and discusses cooperative diversity as an enabler to support the challenging expectations of future-generation HF communication systems.
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Design and analysis of broadband amplify-and-forward cooperative systems: A fractionally-spaced sampling approach
(IEEE, 2016-10-01) Heidarpour, M. R.; Uysal, Murat; Damen, M. O.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we propose novel fractionally-spaced frequency-domain equalizers for the amplify-and-forward cooperative systems. In the proposed equalization schemes, the sampling rate of the received signal remains at least as high as the Nyquist rate within the digital processing chain of the relay node(s), upon which a true fractionally-spaced equalization becomes feasible at the destination. Based on minimum-mean-square-error (MMSE) criterion, different equalization structures (linear and non-linear) are designed, and approximations for their bit error rate (BER) performance are presented. The BER performance of the proposed schemes are further lower bounded through a matched-filter bound (MFB) analysis which provides insight into system design such as optimum power allocation and relay selection strategy. Our results show that, under certain channel realizations and sampling phase errors (that may occur in the relay and destination terminals), the performance of the conventional symbol-spaced cooperative systems reduces to that of no relay scenario. However, the performance of cooperative systems with the proposed fractionally-spaced equalizers is independent of the samplers' phases, and as a result, full benefit of cooperation is retained.
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Fractionally spaced equalization for broadband amplify-and-forward cooperative systems
(IEEE, 2013) Heidarpour, M. R.; Uysal, Murat; Damen, M. O.; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we revisit the concept of fractionally spaced equalization (FSE) for broadband single-carrier amplify-and-forward (AaF) cooperative systems. Particularly, we investigate fractionally spaced frequency domain equalization (FS-FDE) for cooperative multi-relay systems. Our motivation stems from the elegant properties reported for the FSE in the point-to-point communication systems (i.e., its robustness to sampling phases and potential in achieving the optimum performance) and the scalability of the FDEs. In particular, we propose a TS/2-spaced equalizer that transforms the temporal sample sequence of the received signal to the frequency domain, applies linear/decision-feedback equalization, and returns the resulting signal back to the time domain for detection. The vital importance of using FS-FDE method in cooperative systems is disclosed in practical scenarios where the transmitted signals have nonzero roll-off components and sampling phase error may occur in relay(s) and destination terminals. Our results demonstrate that, under specific channel realizations and sampling errors, the cooperative systems with symbol spaced FDE (SS-FDE) fail to harvest the available cooperative diversity and the performance approaches to that of no relay scenario. On the other hand, the performance of cooperative system with FS-FDE method becomes independent of sampling phase errors and full benefit of cooperation is retained.
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Joint lifetime-outage optimization in relay-enabled IoT networks—A deep reinforcement learning approach
(IEEE, 2023-01) Heidarpour, A. R.; Heidarpour, M. R.; Ardakani, M.; Tellambura, C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Network lifetime maximization in Internet of things (IoT) is of paramount importance to ensure uninterrupted data transmission and reduce the frequency of battery replacement. This letter deals with the joint lifetime-outage optimization in relay-enabled IoT networks employing a multiple relay selection (MRS) scheme. The considered MRS problem is essentially a general nonlinear 0-1 programming which is NP-hard. In this work, we use the application of the double deep Q network (DDQN) algorithm to solve the MRS problem. Our results reveal that the proposed DDQN-MRS scheme can achieve superior performance than the benchmark MRS schemes.
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Multicarrier HF communications with amplify-and-forward relaying
(IEEE, 2011) Heidarpour, M. R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
High-frequency (HF) radio communication has been recognized as the primary means for long-range wireless communications since the advent of radio. With its unique features, HF communication continues to be used for a wide range of civilian, government and military applications as a powerful alternative to a myriad of more sophisticated communication systems. However demanding requirements of high-speed data communications impose new requirements on the HF system design and innovative approaches are required. In this paper, building upon the promising concept of cooperative transmission, we investigate the performance of a multicarrier coded HF system with amplify-and-forward relaying. Specifically, we consider orthogonal frequency division multiplexing (OFDM) with bit-interleaved coded modulation (BICM) and demonstrate the achievable diversity through the derivation of pairwise error probability. We also conduct Monte Carlo simulations to confirm the analytical derivations and present performance comparisons.
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Soft actor-critic-based computation offloading in multiuser MEC-enabled IoT-A lifetime maximization perspective
(IEEE, 2023-10-15) Heidarpour, A. R.; Heidarpour, M. R.; Ardakani, M.; Tellambura, C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
This article studies the network lifetime optimization problem in a multiuser mobile-edge computing (MEC)-enabled Internet of Things (IoT) system comprising an access point (AP), a MEC server, and a set of K mobile devices (MDs) with limited battery capacity. Considering the residual battery energy at the MDs, stochastic task arrivals, and time-varying wireless fading channels, a soft actor-critic (SAC)-based deep reinforcement learning (DRL) lifetime maximization, called DeepLM, is proposed to jointly optimize the task splitting ratio, the local CPU-cycle frequencies at the MDs, the bandwidth allocation, and the CPU-cycle frequency allocation at the MEC server subject to the task queuing backlogs constraint, the bandwidth constraint, and maximum CPU-cycle frequency constraints at the MDs and the MEC server. Our results reveal that DeepLM enjoys a fast convergence rate and a small oscillation amplitude. We also compare the performance of DeepLM with three benchmark offloading schemes, namely, fully edge computing (FEC), fully local computing (FLC), and random computation offloading (RCO). DeepLM increases the network lifetime by 496% and 229% compared to the FLC and RCO schemes. Interestingly, it achieves such a colossal lifetime improvement when its nonbacklog probability is 0.99, while that of FEC, FLC, and RCO is 0.69, 0.53, and 0.25, respectively, showing a significant performance gain of 30%, 46%, and 74%.