See Ho Ting

Nanyang Technological University, Tumasik, Singapore

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Publications (53)40.31 Total impact

  • Qiang Li, A. Pandharipande, See Ho Ting
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    ABSTRACT: We consider a cognitive spectrum sharing system on an interference channel with a cognitive relay (IFC-CR) assisting both the primary and secondary users in forwarding their messages to the respective destination nodes. The CR uses a successive interference cancelation scheme to decode the primary and secondary messages after a first transmission phase. The CR performs power allocation and in the second transmission phase, forwards a linear weighted combination of the decoded primary and secondary messages. We demonstrate that with a properly designed power allocation, secondary spectrum sharing is achieved and at the same time a better performance can be achieved for the primary user than the case without spectrum sharing. The proposed spectrum sharing scheme further does not require any non-causal knowledge of the primary message at the secondary user or at the CR.
    Wireless Communications and Networking Conference (WCNC), 2013 IEEE; 01/2013
  • Source
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    ABSTRACT: We consider the scenario in which multiple sensors send spatially correlated data to a fusion center (FC) via independent Rayleigh-fading channels with additive noise. Assuming that the sensor data is sparse in some basis, we show that the recovery of this sparse signal can be formulated as a compressive sensing (CS) problem. To model the scenario in which the sensors operate with intermittently available energy that is harvested from the environment, we propose that each sensor transmits independently with some probability, and adapts the transmit power to its harvested energy. Due to the probabilistic transmissions, the elements of the equivalent sensing matrix are not Gaussian. Besides, since the sensors have different energy harvesting rates and different sensor-to-FC distances, the FC has different receive signal-to-noise ratios (SNRs) for each sensor. This is referred to as the inhomogeneity of SNRs. Thus, the elements of the sensing matrix are also not identically distributed. For this unconventional setting, we provide theoretical guarantees on the number of measurements for reliable and computationally efficient recovery, by showing that the sensing matrix satisfies the restricted isometry property (RIP), under reasonable conditions. We then compute an achievable system delay under an allowable mean-squared-error (MSE). Furthermore, using techniques from large deviations theory, we analyze the impact of inhomogeneity of SNRs on the so-called k-restricted eigenvalues, which governs the number of measurements required for the RIP to hold. We conclude that the number of measurements required for the RIP is not sensitive to the inhomogeneity of SNRs, when the number of sensors n is large and the sparsity of the sensor data (signal) k grows slower than the square root of n. Our analysis is corroborated by extensive numerical results.
    IEEE Transactions on Signal Processing 11/2012; 61(18). · 2.81 Impact Factor
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    ABSTRACT: We consider spectrum sharing in a cognitive radio network where a secondary system co-exists with an automatic repeat-request (ARQ)-based primary system. A cooperate-and-access spectrum sharing protocol is proposed where the secondary system alternates between cooperation and access modes. In the cooperation mode, the secondary system serves as a relay to assist the primary transmission, and in return accumulates credits. The credits allow the secondary system to gain spectrum access by exploiting the ARQ retransmissions of the primary system. We show analytically that through the proposed credit system, as long as the credits accumulated in cooperation mode compensate for the degradation in primary performance during access mode, an equal or higher average throughput is achieved for the primary system than in the case without spectrum sharing, while providing spectrum access opportunities for the secondary system.
    IEEE Transactions on Communications 01/2012; 60(10):2861-2871. · 1.75 Impact Factor
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    ABSTRACT: In this paper, we propose an opportunistic spectrum sharing protocol that exploits the situation when the primary system is incapable of supporting its target transmission rate. Specifically, the secondary system tries to help the primary system to achieve its target rate via two-phase cooperative OFDM relaying, where the secondary system acts as an amplify-and-forward relay for the primary system by allocating a fraction of its subcarriers to forward the primary signal. At the same time, the secondary system uses the remaining subcarriers to transmit its own signal, and thus gaining opportunistic spectrum access. As a part of the protocol, if the primary system finds that outage will occur even when the secondary system serves as a pure relay, the primary system will cease transmission and the secondary system will be granted access to the primary spectrum. We study the joint optimization of the set of subcarriers used for cooperation, subcarrier pairing, and subcarrier power allocation such that the transmission rate of the secondary system is maximized, while helping the primary system, as a higher priority, to achieve its target rate. Simulation results demonstrate the performance of the proposed spectrum sharing protocol as well as the win-win solution for the primary and secondary systems.
    IEEE Transactions on Wireless Communications 01/2012; 11(6):2126-2135. · 2.42 Impact Factor
  • Source
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    ABSTRACT: We consider a sensor communication scenario where a sensor node communicates information to a data sink. To aid the sensor, the data sink transmits channel state information (CSI). To obtain the CSI, however, a fixed receive processing energy is incurred by the sensor node. Given a choice, the sensor node may choose not to obtain the CSI if the receive processing energy does not lead to a larger reduction in the transmit energy. In this paper, we study the tradeoff involved in this choice. Specifically, we design the optimal transmit strategy so that the total expected transmit and receive power of the sensor are minimized subject to a target outage probability. We focus on the case in which the feedback packet conveys one bit of CSI to the sensor nodes. Closed-form expressions of suboptimal solutions are obtained and shown to perform close to the optimal solution.
    Wireless Communications Letters, IEEE. 01/2012; 1(3).
  • Source
    Jian Tian, Qi Zhang, See Ho Ting
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    ABSTRACT: The second-order statistics are of significance for the design of wireless relay networks. In this correspondence, we have theoretically derived the second-order statistics, level crossing rate (LCR) and average fade duration (AFD), of the Nth best proactive and reactive decode-and-forward (DaF) relaying schemes in Rayleigh fading channels. The above two schemes choose different relaying nodes to assist the signal transmission. It is shown that the theoretically derived LCR and AFD performances match the simulation results. It is also shown that for the Nth best DaF relaying, both proactive and reactive schemes have the same LCR and AFD performances.
    Wireless Communications Letters, IEEE. 01/2012; 1(4):380-383.
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    ABSTRACT: In this paper, we consider a hidden terminal scenario where two transmitters A and B, hidden to each other, wish to communicate to a common access point, AP. When a collision occurs at AP, due to the inherent asynchrony between the colliding packets, the mutual interference between them is effectively decreased. This achieves a higher signal-to-interference-plus-noise (SINR) ratio which improves the probability of successfully decoding both colliding packets through conventional successive interference cancellation (SIC). When neither colliding packet can be decoded first through SIC, we propose an enhanced SIC (ESIC) scheme. The proposed decoding scheme does not require synchronization, coordination or power control between the transmitters or a sophisticated coding design. By exploiting the inherent asynchrony between the two colliding packets, there exists, with high probability, an interference-free chunk together with an interfered chunk in a packet ready for decoding. Thus it is still possible for both colliding packets to be recovered eventually from a single collision. Our results demonstrate that through the proposed ESIC scheme, both colliding packets can be recovered with a higher probability thus improving the system throughput.
    Global Communications Conference (GLOBECOM), 2012 IEEE; 01/2012
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    ABSTRACT: In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a selective relaying primary system. The primary system comprises of a transmitter-receiver pair PT-PR and M relays R_i, i∈{1,2,..., M}. The secondary system is a multi-user system with N transmitters R_i, i∈{M+1,M+2,...,M+N} which intend to communicate with a common receiver SR. In the proposed protocol, terminals R_i, i∈ M_1={1, 2,...,M+Q} are designated as possible candidates for assisting the primary system while the remaining secondary transmitters R_{i^\prime}, {i^\prime}∈M_2= {M+Q+1, M+Q+2,...,M+N} are chosen as possible candidates for secondary spectrum access, where 0≤ Q< N. The relaying terminal R_p, p∈ M_1 which achieves the request target rate for the primary system and has the best channel to PR, is first selected from M_1 to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of R_p, the primary system is able to tolerate some interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter R_s, s∈ M_2 which satisfies this interference constraint and optimizes the outage performance for the secondary system, is then selected from M_2 to access the spectrum band simultaneously when R_p is relaying the primary signal. Analytical and simulation results confirm the efficiency of the proposed spectrum sharing protocol. We show that there exists an optimal value for Q and both primary and secondary systems are able to achieve better outage performance with increasing N.
    IEEE Transactions on Communications 01/2012; 60:62-67. · 1.75 Impact Factor
  • Xiao Hong Mao, Yee Hui Lee, See Ho Ting
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    ABSTRACT: Path loss along the Line-of-Sight and the Non Line-of-Sight routes in an urban environment are examined for the application of urban warfare in the military UHF band. Based on the experimental results, frequency dependency of the path loss, the path loss exponent and the corner loss are studied.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
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    ABSTRACT: Two-path or successive relaying has recently emerged as a promising cooperative communication protocol to improve spectral efficiency in half-duplex relaying networks. In this paper, we consider decode-and-forward (DF) version of the two-path relaying protocol. We analyze the fundamental performance of this protocol in terms of the diversity-multiplexing tradeoff (DMT). We first derive the DMT for this protocol, where perfect decoding at the relays is assumed, and show that it approaches the 3 x 1 multiple-input single-output (MISO) DMT. We then remove the assumption of perfect decoding at the relays and derive the closed-form expression of the achievable DMT based on the relative distances between nodes. Specifically, we found that for sufficiently long transmission length, if the average source-relay SNR is at least 2.5 times (measured in dB) of other links, the 3 x 1 MISO DMT is achieved. Successive interference cancellation at the relays is also proposed to further improve the performance of the DMT.
    IEEE Transactions on Communications 08/2011; · 1.75 Impact Factor
  • V.A. Bohara, See Ho Ting
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    ABSTRACT: Although much research has been devoted to the theoretical performance evaluation of cognitive spectrum sharing (CSS) protocols, there are few measurement results available to demonstrate the practical performance of such protocols. In this paper, we have designed and developed a testbed for proof-of-concept demonstration and performance assessment of our proposed CSS protocol. The packet error rate (PER) for both primary and secondary systems are measured to quantify their respective performance. Spectrum access probability for the secondary system is also measured. Measurement results proved that the proposed CSS protocol is able to assist the primary system to achieve a better PER and at the same time allows spectrum access for the secondary system.
    IEEE Transactions on Wireless Communications 08/2011; · 2.42 Impact Factor
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    ABSTRACT: Dynamic spectrum-sharing protocols are gaining attention due to the need for improved spectrum utilization. We propose a spectrum-sharing protocol with two-way relaying systems, where two licensed primary users A and B communicate with each other with the assistance of an unlicensed secondary transceiver C, which acts as a relay. The secondary transceiver C gains spectrum sharing by using a decode-and-forward (DF) relay protocol and superposing the secondary transmission on network-coded primary signals. We analytically derive the outage probabilities for both the primary and secondary systems under the proposed cognitive two-way relaying (CTR) protocol. Our results show that a spectrum-sharing region exists such that, as long as C is located within this region, there will be a power-allocation threshold above which the proposed CTR protocol is able to provide a better (or an equal) outage performance for the primary system and, at the same time, achieve secondary spectrum sharing.
    IEEE Transactions on Vehicular Technology 04/2011; · 2.06 Impact Factor
  • Source
    Qiang Li, See Ho Ting, Chin Keong Ho
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    ABSTRACT: In this paper, we analyze how different amount of receiver side information (RSI) available at the receivers of a broadcast channel will affect the overall network throughput. Two transmission schemes, namely random linear network coding (RLNC) and round robin scheduling (RRS), are considered. Taking into account the differing amount of RSI available at each receiver, closed-form expressions of network throughput and asymptotic throughput at high SNR are obtained for a broadcast channel. Our results show that the asymptotic throughput of RLNC is always no worse than RRS no matter how much RSI is available at each receiver. With a sum constraint for the overall arrival rate of receiver side information in the broadcast channel, we show that the maximum throughput is achieved for RLNC if each receiver accumulates the same amount of RSI. Index Terms—Broadcast channel, wireless network coding, receiver side information (RSI).
    Proceedings of IEEE International Conference on Communications, ICC 2011, Kyoto, Japan, 5-9 June, 2011; 01/2011
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    ABSTRACT: We consider spectrum sharing in a cognitive radio network where a secondary user co-exists with an ARQ-based primary user. A spectrum sharing protocol is proposed where the secondary user switches between cooperation and access modes. In the cooperation mode, the secondary system serves as a relay to assist the primary transmission, and in return accumulates credits. The credits allow the secondary user to gain spectrum access by exploiting the ARQ redundant retransmission of the primary user in access mode. We show analytically that as long as the credits accumulated in cooperation mode compensate for the degradation in primary performance during access mode, the proposed protocol achieves an equal (or higher) average throughput for the primary system than the case without spectrum sharing, while providing spectrum access opportunities for the secondary user.
    01/2011;
  • Y. Han, S.H. Ting, A. Pandharipande
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    ABSTRACT: In this study, the authors consider a cognitive radio scenario and focus on the spectrum efficiency of sensing-transmission protocols for a secondary dual-hop relay system. A straightforward dedicated sensing protocol is first considered as a benchmark, where sensing is performed in dedicated sensing periods at both the source (S) and the relay (R) before their respective transmissions. This, however, leads to a substantial loss in spectrum efficiency for the secondary system. In view of the spectrum efficiency loss in the dedicated sensing protocol, the authors propose an alternative approach, namely simultaneous sensing protocol. In this protocol, sensing is only performed at S, during the period when R transmits to destination (D), by cancelling out the self-interference component that is known a priori. The authors derive the closed-form expression of the average probability of detection for the proposed simultaneous sensing protocol. Furthermore, by deriving the average collision time and average utilisation time for both the dedicated and simultaneous sensing protocols, the authors show that the simultaneous sensing protocol significantly improves the spectrum efficiency for the secondary system and also achieves a higher overall spectrum utilisation of the spectrum band, compared to the dedicated sensing protocol.
    IET Communications 01/2011; 5(5):709-718. · 0.72 Impact Factor
  • Source
    Qiang Li, See Ho Ting, Chin Keong Ho
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    ABSTRACT: In this paper, we consider a wireless multicast network with multiple sources, relays, and destinations. We adopt a multi-hop decode-and-forward relay protocol such that two canonical subnetworks are relevant, namely broadcast channel with receiver side information (BC-RSI) and orthogonal multiple access channel with correlated sources and receiver side information (MAC-CS-RSI). A joint network and channel coding (JNCC) strategy is proposed by exploiting ARQ, RSI, and correlated sources. The proposed JNCC strategy does not require the knowledge of RSI nor any transmit channel state information, such that each transmitter simply performs retransmissions until the intended receivers have accumulated enough mutual information to successfully decode all desired messages. This successful decoding is then conveyed from the receivers to the respective transmitters via an acknowledgement message. To measure the performance of the proposed JNCC strategy with ARQ, we derive closed-form expressions of network throughput by applying the renewal-reward theorem. Analytical results show that the proposed JNCC strategy outperforms, in terms of network throughput, the conventional separate network and channel coding strategy with random linear network coding.
    IEEE Transactions on Communications 01/2011; 59:181-193. · 1.75 Impact Factor
  • Vivek Ashok Bohara, See Ho Ting
    IEEE Transactions on Wireless Communications. 01/2011; 10:2052-2057.
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    ABSTRACT: In this paper, we propose a cooperative spectrum sharing protocol (CSSP) between two overlapping static ad hoc wireless networks where the primary and secondary networks consist of n and m randomly distributed nodes respectively. The secondary network achieves spectrum access along with the pri- mary network by allowing its nodes to relay the primary traffic. Taking advantage of the broadcast nature of wireless channels, the secondary nodes are able to forward primary and secondary packets simultaneously by transmitting a superimposed signal. We analyze the throughput and delay scaling performance of the proposed protocol and show that given mn, the primary network is able to achieve a per-node throughput scaling which is better than that of a stand-alone network with n nodes. At the same time, the secondary network achieves the same throughput scaling as a stand-alone network with m nodes. We also derive the throughput-delay tradeoff for both the primary and secondary systems in this scenario.
    01/2011;
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    ABSTRACT: In this paper, an amplify-and-forward (AF) two-path half-duplex relaying scheme is considered in which one of the relays additionally performs inter-relay interference cancellation. We first generalize lower bounds for the diversity-multiplexing tradeoff (DMT) of an arbitrary block lower triangular channel matrix. We then characterize the diversity-multiplexing tradeoff for the AF two-path relaying scheme and show that the DMT achieves the multiple-input single-output (MISO) upper bound. The analysis also demonstrates that, with a careful choice of the coding strategy, the DMT of this scheme is achievable for finite codeword lengths. We then propose using an equivalent linear space time code at the source, which does not require any form of channel state information, as a simple and effective coding strategy to achieve the full DMT of the scheme. From the DMT perspective, the proposed AF two-path relaying with the equivalent linear space time coding outperforms existing schemes. Our analysis is then extended to the slotted-amplify-and-forward (SAF) scheme with multiple relays, where we provide a stronger result by deriving the DMT while taking into account inter-relay interference.
    IEEE Transactions on Communications 01/2011; · 1.75 Impact Factor
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    ABSTRACT: In this paper, we have designed and developed a testbed for proof-of-concept demonstration and performance assessment of cooperative spectrum sharing (CSS) protocols. The performance of the testbed has been validated by obtaining both quantitative as well as qualitative results. Quantitative results are obtained by measuring the packet error rates for both primary and secondary systems during different times of the day whereas qualitative results are shown by utilizing a CSS protocol to successfully transmit two different images from primary transmitter (PT) to primary receiver (PR) and secondary transmitter (ST) to secondary receiver (SR) respectively. A parameter known as spectrum access probability which quantifies the probability of spectrum access for the secondary system is also measured.
    Proceedings of the Global Communications Conference, GLOBECOM 2011, 5-9 December 2011, Houston, Texas, USA; 01/2011

Publication Stats

427 Citations
40.31 Total Impact Points

Institutions

  • 2008–2010
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Tumasik, Singapore
  • 2009
    • Nanjing University of Science and Technology
      Nan-ching, Jiangsu Sheng, China
  • 2006
    • Nanyang Normal University
      Nan-yang-shih, Henan Sheng, China
  • 2004–2006
    • Tokyo Institute of Technology
      • Graduate School of Science and Engineering
      Tokyo, Tokyo-to, Japan