D.K.C. So

University of Engineering and Technology, Taxila, Islāmābād, Islamabad Capital Territory, Pakistan

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Publications (37)17.7 Total impact

  • Warit Prawatmuang, Daniel K.C. So, Emad Alsusa
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    ABSTRACT: Cognitive radio opportunistically accesses the spectrum while the licensed user is idle. A spectrum sensing procedure to monitor primary users' existence is therefore vital to cognitive radios. In this paper, we investigate the energy detection based sequential cooperative spectrum sensing technique in time varying channels. By utilizing past local observations from previous sensing slots, cognitive radio nodes can aggregate the current and previously received energy values to improve the detection performance. We propose the weighted sequential energy detector (SED) in which a fixed number of past observations are taken for decision making. In addition, we propose two adaptive schemes, namely the Two-Stage SED and the Differential SED, where a cognitive radio user uses previously received energy values until it detects a change in primary user's activity. The probability of false alarm and detection for the Weighted SED and Two-Stage SED schemes are derived. The results show that the proposed schemes achieve better detection performance over the conventional cooperative energy detection technique. In particular, the Two-Stage SED and Differential SED schemes can satisfy the IEEE 802.22 standard's requirement of 10% false alarm and 90% detection in scenarios that conventional techniques cannot accommodate.
    IEEE Transactions on Wireless Communications 01/2014; 13(6):3394-3405. · 2.42 Impact Factor
  • S. Sohaib, D.K.C. So
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    ABSTRACT: Cooperative diversity exploits the broadcast nature of wireless channels and uses relays to improve link reliability. Most of the cooperative communication protocols are assumed to be synchronous in nature, which is not always possible in vehicle-to-vehicle (V2V) communication due to fast moving nature of the nodes. Also the relay nodes are assumed to be half duplex which in turn reduces the spectral efficiency. In this paper, we propose an asynchronous cooperative communication protocol exploiting polarization diversity, which does not require synchronization at the relay node. Dual polarized antennas are employed at the relay node to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased throughput rate. Capacity analysis of the proposed scheme ascertains the high data rate as compared to conventional ANF. Bit error rate (BER) simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes. Considering channel path loss, the proposed scheme consumes less total transmission energy as compared to the conventional ANF and non-cooperative scheme. Thus the proposed scheme is suitable for high rate and energy efficient relay-enabled communication.
    IEEE Transactions on Communications 01/2013; 61(5):1732-1738. · 1.75 Impact Factor
  • Juei-chin Shen, Emad Alsusa, Daniel K.C. So
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    ABSTRACT: Cyclostationary feature detection enables a cognitive radio system to reliably sensing the existence of licensed users. A statistical test based on the second-order cyclostationary features has been widely used. This paper evaluates the detection performance of this 2nd-order feature based technique subject to Nakagami fading. The analytical upper and lower bounds on the detection probability are derived by exploiting some available series expansion and exponential-type bound of the generalized Marcum Q-function. As a result, the preliminary detection performance can be acquired without relying on Monte Carlo simulations.
    Wireless Communications and Networking Conference (WCNC), 2013 IEEE; 01/2013
  • Warit Prawatmuang, Daniel K.C. So
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    ABSTRACT: Cognitive Radio (CR) is proposed to maximize spectrum utilization. When the licensed user is not using the spectrum, CR will then use it to communicate among each other. Hence, spectrum sensing, a procedure to observe primary user's existence, is important to CR. In this paper, we investigate the energy detection based cooperative spectrum sensing technique as it offers low complexity and significantly improves the sensing performance for CR. Conventional soft decision combining (SDC) scheme assumes that CR's local observation is perfectly forwarded to the fusion center. This forwarding procedure requires bandwidth, and increasingly so with more sensing nodes. By carefully applying quantization to this local observation, we could significantly reduce the number of bits required for this communication and thus reduce the overall system overhead. Uniform and non-uniform quantization approaches for SDC are investigated. We further propose a low complexity scheme based on an approximation of the cumulative density function. Simulation results show that these schemes can achieve a good detection performance comparable to the conventional SDC scheme, with reduced communication overhead.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on; 01/2013
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    ABSTRACT: Data traffic demand in cellular networks continues to increase exponentially leading to high capital expenditure and operational costs such as electricity cost. Femtocells have been proposed as a solution to enhance network capacity without significantly increasing energy consumption and associated network deployment costs. In this paper, we analyze the network capacity and energy consumption aspects of a joint macrocell and femtocell network based on the LTE standard. Femtocells and macrocells are operated in the same frequency band to enhance spectral efficiency. Femtocell users are secondary users who only access the channel opportunistically when macrocell users are idle. We propose the use of cooperative spectrum sensing to manage adverse interference emanating from the co-channel operation of both macrocells and femtocells. Simulation results show that cooperative sensing is very effective at managing this cross-tier interference to maximize the throughput of both the macrocell and femtocell layers. This throughput maximization allows the lowest energy consumption ratio of such a heterogeneous network.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on; 01/2013
  • W. Prawatmuang, D.K.C. So
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    ABSTRACT: Cognitive radio is proposed to opportunistically access the spectrum while the licensed user is idle. As a result, spectrum sensing procedure to observe primary user's existence is vital to cognitive radio. In this paper, we investigate the energy detection based sequential cooperative spectrum sensing technique in time varying channel. By utilizing past local observations from previous sensing slots, cognitive radio nodes can aggregate the current and previously received energy values to improve the detection performance. We explored the moving-average technique using equal and exponential weighting. Simulation results show that this technique provides better detection performance compared to conventional energy detection based cooperative technique. Equal weighting provides the best performance when primary user's activity is not varying. If the primary users often change states, the proposed exponential weighting approach provides better detection performance.
    Vehicular Technology Conference (VTC Spring), 2012 IEEE 75th; 01/2012
  • W. Prawatmuang, D.K.C. So
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    ABSTRACT: Cognitive radio is proposed to opportunistically access the spectrum while the licensed user is idle. As a result, spectrum sensing procedure to observe primary user's existence is vital to cognitive radio. In this paper, we propose two adaptive sequential cooperative spectrum sensing techniques in time varying channel, namely the Two Stage Sequential Energy Detector and Differential Sequential Energy Detector. By utilizing past local observations from previous sensing slots, cognitive radio nodes can aggregate the current and previously received energy values to improve the detection performance. We explore the adaptive schemes, where cognitive radio user takes in previously received energy values when it thinks that the primary user's activity remains unchanged. Simulation results show that both proposed schemes provide better detection over conventional energy detection based cooperative technique. Additionally, both proposed schemes can satisfy the IEEE 802.22 standard's requirement of 10% false alarm and 90% detection in scenario that conventional techniques can not accommodate.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on; 01/2012
  • A. Phasouliotis, D.K.C. So
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    ABSTRACT: Multi-carrier code division multiple access (MC-CDMA) allows multiuser communication with frequency diversity. To increase the system data rates, spatial multiplexing for multiple-input multiple-output (MIMO) MC-CDMA has been investigated. This study proposes a chip level layered space-time (LST) receiver architecture for coded downlink MIMO MC-CDMA systems. As the conventional chip level ordered successive interference cancellation (OSIC) receiver is unable to overcome multiple access interference and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference in an ordered LST detection process by requiring only the knowledge of the desired user-s spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors but also outperforms both the chip and symbol level OSIC receivers. In this study the authors also compare the error rate performance between the proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and they justify the comparisons by deriving and analysing the pairwise error probability (PEP) for both systems. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system load. If all users- spreading sequences are known, multiuser interference can be reduced and MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.
    IET Communications 10/2011; · 0.72 Impact Factor
  • Source
    S. Sohaib, D.K.C. So
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    ABSTRACT: Nodes in most cooperative networks are powered by batteries and some of which are even non-rechargeable. Therefore, power allocation schemes must be developed to save the transmit power and improve the life-time of the system. In this context, we present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.
    Communications (ICC), 2011 IEEE International Conference on; 07/2011
  • Source
    Sarmad Sohaib, Daniel K. C. So
    04/2011; , ISBN: 978-953-307-241-8
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    ABSTRACT: Energy efficiency has become increasingly important in wireless communications nowadays. Saving energy will not only reduce operating cost but also reduces greenhouse gas emissions, which is important for combating climate change. The authors propose energy-efficient user grouping algorithms to provide power minimisation of grouped multi-carrier code division multiple access (MC-CDMA) and space-time block coding MC-CDMA systems in a cellular environment. Depending on the channel fading conditions, power control is utilised to minimise the total transmitted power under a bit error rate constraint. When the allocation is performed without a fair data rate requirement, the authors provide the optimal solution to the minimisation problem. However, when some fairness is considered, the optimal solution requires high computational complexity. Thus, the authors solve the problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.
    IET Communications 01/2011; 5(18):2640-2647. · 0.72 Impact Factor
  • S. Sohaib, D.K.C. So
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    ABSTRACT: Cooperative communication exploits the broadcast nature of wireless channel and uses relay nodes to provide better reliability and higher data rates without increasing power and bandwidth. In this paper, the energy analysis of the asynchronous polarized cooperative (APC) scheme is performed. APC employs multiple antennas at the relay and destination nodes to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased spectral efficiency. Considering channel path loss, the APC scheme consumes less total transmission energy as compared to ANF and non-cooperative scheme over more practical distance between the nodes. Thus the APC scheme is both spectral and energy efficient, and is suitable for the cooperative communication systems.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on; 10/2010
  • Antonis Phasouliotis, Daniel K. C. So
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    ABSTRACT: In this paper, we propose user grouping algorithms to provide power minimization in grouped MC-CDMA systems. Depending on the channel fading conditions, power control is utilized to minimize the total transmitted power under a bit error rate (BER) constraint. When the allocation is performed without a fair data rate requirement, we provide the optimal solution to the minimization problem. However when some fairness is considered, the optimal solution requires high computational complexity. Thus, we solve the problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.
    Proceedings of the IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2010, 26-29 September 2010, Istanbul, Turkey; 01/2010
  • Imran Rashid, Daniel K. C. So
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    ABSTRACT: Multiple Input Multiple Output (MIMO) systems use multiple transmit and receive antennas to achieve higher data rates by transmitting multiple independent data systems. Transmission errors can be reduced by using Hybrid Automatic Repeat request (HARQ) combining techniques with MIMO systems. We propose two novel MIMO HARQ combining methods which are based on using pre-combining only and a joint post and pre-combining techniques. In addition to conventional direct transmission, HARQ schemes for MIMO Multi-hop relay systems are also investigated. A novel approach is proposed to deal with the parallel HARQ processes in MIMO relay scenario. The simulation results show that the proposed methods can enhance the overall throughput performance of MIMO Single-hop and multi-hop relay systems.
    Proceedings of the IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2010, 26-29 September 2010, Istanbul, Turkey; 01/2010
  • A. Phasouliotis, D.K.C. So
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    ABSTRACT: In this paper, we propose user grouping algorithms to provide power minimization in grouped STBC MC-CDMA systems. Depending on the channel fading conditions, power control is utilized to minimize the total transmitted power under a BER constraint. When the allocation is performed without a fair data rate requirement, we provide the optimal solution to the minimization problem. However when some fairness is considered, the optimal solution requires high computational complexity. We solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.
    Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on; 01/2010
  • Source
    S. Sohaib, D.K.C. So, J. Ahmed
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    ABSTRACT: Cooperative communication achieves diversity through spatially separated cooperating nodes, which are battery powered in most applications. Therefore the energy consumption must be minimized without compromising the transmission quality (bit error rate). In this context, we present a novel power allocation scheme that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is explored to maximize the capacity.
    Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
  • S. Sohaib, D.K.C. So
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    ABSTRACT: In cooperative wireless network, the users exploit spatial diversity by cooperating with each other. This alleviates the detrimental effects of fading and offers reliable data transfer. In this paper, we present a novel asynchronous cooperative multi-input multi-output (MIMO) communication scheme in the presence of polarization diversity which does not require synchronization at the relay node. Utilizing dual-polarized antennas, the relay node achieves full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is significantly reduced which in turn results into an increased throughput rate. Capacity analysis of the proposed system ascertains the high data rate as compared to the conventional ANF protocol. Bit error rate simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes.
    Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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    Yang Lan, D. So
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    ABSTRACT: In our earlier work, a novel concept of virtual receive antennas (VRA) was proposed and is a viable solution for single carrier spatial multiplexing system with less number of physical receive antennas. In this paper, we investigate the VRA system in spatially multiplexed orthogonal frequency-division multiplexing (OFDM) system, which is a promising scheme for next generation of downlink communication. To create VRA in OFDM, various fractionally spaced timing offset is imposed to each transmit substream, and oversampling at the receiver filter output. To explore the potential of the VRA-OFDM system, this paper analyzes its system capacity and error rate performance. Results show that the VRA-OFDM system can achieve higher ergodic capacity and outage rate, and lower outage probability than conventional MISO-OFDM system. Due to the created virtual antennas, ordered successive interference cancellation (OSIC) can be used in the VRA-OFDM system, which favours the use of VRA in downlink communication due to lower complexity. Meanwhile, if maximum likelihood (ML) detection is used, the VRA-OFDM system shows better BER performance than the conventional overloaded MISO-OFDM ML receiver.
    Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
  • Source
    A. Phasouliotis, D.K.C. So
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    ABSTRACT: In this paper, we analyze and compare the error rate performance of downlink coded multiple-input multiple-output multi-carrier code division multiple access (MIMO MC-CDMA) and coded MIMO orthogonal frequency division multiple access (MIMO OFDMA) systems under frequency selective fading channel conditions. In particular, the pairwise error probabilities (PEP) for both systems are derived. Simulation results illustrate that when the number of users, hence the system load is low, MIMO MC-CDMA outperforms MIMO OFDMA. However when the system load increases, the performance of MIMO MC-CDMA deteriorates and becomes worse than MIMO OFDMA. This can be explained by the PEP analysis of MIMO MC- CDMA which shows that when the number of users is small, the multiuser interference is also small and frequency diversity is better exploited. Conversely at high system load, MIMO OFDMA outperforms MIMO MC-CDMA as it is insensitive to multiuser interference. Nevertheless if the other users' spreading sequences are available at the receiver of the desired user, the impact of multiuser interference can be minimised and MIMO MC-CDMA outperforms MIMO OFDMA at all system loads.
    Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
  • Di Lu, D.K.C. So
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    ABSTRACT: Multiple antennas wireless systems can achieve large capacity at the expense of high hardware cost associated with the radio frequency chains. Antenna selection schemes make use of more antennas than RF chains and select a subset of antennas to effectively reduce the hardware cost and power consumption without much capacity loss. In this paper, the problem of receive antenna selection in V-BLAST systems is investigated. Two performance based selection criteria are proposed, namely the min-max MSE and min-first stage MSE criteria. The min-max criterion achieves the best performance at the expense of high computational complexity. Complexity reduced algorithms for this selection scheme are discussed. Analytical proof is provided to show the suboptimality of the capacity based selection to the performance based selection. The hybrid scheme, which combines the performance and capacity based selection approaches is proposed, it provides a good trade-off between performance and complexity. Computer simulations demonstrate that the complexity reduction algorithms and the hybrid scheme perform better and also with a lower complexity than the capacity based selection algorithm under most system configurations. Finally, robustness of the min-max MSE criterion under channel estimation errors is evaluated via computer simulations.
    IEEE Transactions on Wireless Communications 02/2009; · 2.42 Impact Factor

Publication Stats

92 Citations
17.70 Total Impact Points

Institutions

  • 2011
    • University of Engineering and Technology, Taxila
      • Department of Electrical Engineering
      Islāmābād, Islamabad Capital Territory, Pakistan
  • 2006–2008
    • The University of Manchester
      • School of Electrical and Electronic Engineering
      Manchester, ENG, United Kingdom
  • 2002–2004
    • The Hong Kong University of Science and Technology
      Chiu-lung, Kowloon City, Hong Kong