Intermittently Connected Mobile Ad Hoc Networks (ICMANs) are mobile networks in which complete so... more Intermittently Connected Mobile Ad Hoc Networks (ICMANs) are mobile networks in which complete source-todestination paths do not exist most of the time because of their sparse topology. Such networks enable communications among sparsely distributed moving objects, e.g. a network of ambulances. Traditional routing schemes are unsuitable in ICMANs because they only forward packets in connected paths. Recently, store-and-forward based routing (e.g. multi-copy relaying) have been proposed to address this. However, existing multi-copy strategies do not adapt to the frequent variations in network conditions as they rely heavily on the source to control the relaying process. In this paper, we propose an efficient store-andforward based scheme, Adaptive Multi-Copy Routing (AMR), for packet delivery in ICMANs. In this scheme, instead of relying on the source, each relay node independently decides whether to forward a packet according to the delivery delay target and current network conditions. Simulation results show that the proposed scheme always adapts to the varying network mobility and/or delivery probability that cannot be anticipated in the conventional source-defined strategies and delivers packets within specific delay targets with minimum traffic overhead.
IEEE Transactions on Wireless Communications, 2010
Retransmission (ReTX) mechanisms, i.e. Automatic Retransmission reQuest (ARQ) protocols are widel... more Retransmission (ReTX) mechanisms, i.e. Automatic Retransmission reQuest (ARQ) protocols are widely used for error control in mobile communications. Using ARQ, corrupted data frames are retransmitted in several attempts for eventual error recovery at the receiver. Error correction coding and soft combining have also been used in Hybrid ARQ (HARQ) protocols to increase efficiency. However, the evolution of ARQ protocols to
The relative velocity between mobile devices is one of the key factors that determine the quality... more The relative velocity between mobile devices is one of the key factors that determine the quality of communications in mobile ad hoc networks. Velocity estimation is useful in various aspects of ad hoc networking (e.g. predicting link lifetime, adapting routing strategies and measuring performance). Normally, velocity estimates can be obtained from localization systems such as GPS. If the characteristics of signal propagation can be identified, it is also possible to obtain the velocity estimates based on the statistics of the received signal. A recently proposed method makes use of the time-varying inter-node range information for velocity estimations provided that the range estimates are noise-free. In this paper, we propose a new Range-based method for relative Velocity Estimations (RVE). We derive two rangebased relative velocity estimators for both sparse and dense ad-hoc networks, i.e. RVEs and RVEd. In addition to being less dependent on the characteristics of the wireless channel, the proposed method is more tolerant of the multi-path or NLOS errors contained in range measurements. Thus, the new method is more robust than the existing method in noisy communication environments. An efficient analytical algorithm for predicting the expected node degree in networks with uniform/non-uniform node distributions is also given for examining the applicability of either of the two estimators. Simulation results show excellent match between the velocity estimates given by the proposed method and the actual values in both sparse and dense network cases regardless of the nodal speed limits or the distribution of noises. In comparison to the existing method, the proposed method is shown to achieve an improvement factor of about 33 (in terms of normalized bias) with Gaussian multi-path noises of 4m standard deviation, or 20 with Uniform NLOS noises of 32m maximum.
I would like to acknowledge all my classmates in MRes/Msc NSE and CE&SP, for their generous help ... more I would like to acknowledge all my classmates in MRes/Msc NSE and CE&SP, for their generous help and enlightening. With them, I really enjoyed the passed year in University of Plymouth. On the personal side, I would like to thank my parents, for their unending love and support. V Improving Perceived Speech Quality for Wireless VoIP by Cross-layer designs CHAPTER 1
2007 IEEE International Conference on Communications, 2007
The quality of communications in mobile ad-hoc networks is largely determined by the topological ... more The quality of communications in mobile ad-hoc networks is largely determined by the topological stability. Characterizing the mobility of mobile nodes (e.g. how often they move away from each other) would enable the measurement of the frequency of network reconfigurations for predicting stability. In this paper, we first define a triplet V, Θ, Ψ which consists of mobility parameters that are directly correlated with the stability of a network (e.g. inter-node relative speeds/orientations and epoch time). Based on our previous study on range-based velocity estimations, we then propose a new scheme to estimate the mobility parameters in realtime. In contrast to existing methods that are based on either localization systems or features of wireless channel, the proposed scheme estimates the parameters V, Θ, Ψ only from the time-varying inter-node distance information while retaining its reliability and accuracy even in noisy environments. The performance of the proposed scheme is validated in computer simulations against an existing method under different network settings. We also apply the proposed scheme to link availability estimation as a more lightweight way of obtaining mobility parameters using an existing tool. Preliminary results for various scenarios show that, with the proposed scheme, the tool achieved a comparable performance to when a priori knowledge of nodal mobility is used.
Intermittently Connected Mobile Ad Hoc Networks (ICMANs) are mobile networks in which complete so... more Intermittently Connected Mobile Ad Hoc Networks (ICMANs) are mobile networks in which complete source-todestination paths do not exist most of the time because of their sparse topology. Such networks enable communications among sparsely distributed moving objects, e.g. a network of ambulances. Traditional routing schemes are unsuitable in ICMANs because they only forward packets in connected paths. Recently, store-and-forward based routing (e.g. multi-copy relaying) have been proposed to address this. However, existing multi-copy strategies do not adapt to the frequent variations in network conditions as they rely heavily on the source to control the relaying process. In this paper, we propose an efficient store-andforward based scheme, Adaptive Multi-Copy Routing (AMR), for packet delivery in ICMANs. In this scheme, instead of relying on the source, each relay node independently decides whether to forward a packet according to the delivery delay target and current network conditions. Simulation results show that the proposed scheme always adapts to the varying network mobility and/or delivery probability that cannot be anticipated in the conventional source-defined strategies and delivers packets within specific delay targets with minimum traffic overhead.
IEEE Transactions on Wireless Communications, 2010
Retransmission (ReTX) mechanisms, i.e. Automatic Retransmission reQuest (ARQ) protocols are widel... more Retransmission (ReTX) mechanisms, i.e. Automatic Retransmission reQuest (ARQ) protocols are widely used for error control in mobile communications. Using ARQ, corrupted data frames are retransmitted in several attempts for eventual error recovery at the receiver. Error correction coding and soft combining have also been used in Hybrid ARQ (HARQ) protocols to increase efficiency. However, the evolution of ARQ protocols to
The relative velocity between mobile devices is one of the key factors that determine the quality... more The relative velocity between mobile devices is one of the key factors that determine the quality of communications in mobile ad hoc networks. Velocity estimation is useful in various aspects of ad hoc networking (e.g. predicting link lifetime, adapting routing strategies and measuring performance). Normally, velocity estimates can be obtained from localization systems such as GPS. If the characteristics of signal propagation can be identified, it is also possible to obtain the velocity estimates based on the statistics of the received signal. A recently proposed method makes use of the time-varying inter-node range information for velocity estimations provided that the range estimates are noise-free. In this paper, we propose a new Range-based method for relative Velocity Estimations (RVE). We derive two rangebased relative velocity estimators for both sparse and dense ad-hoc networks, i.e. RVEs and RVEd. In addition to being less dependent on the characteristics of the wireless channel, the proposed method is more tolerant of the multi-path or NLOS errors contained in range measurements. Thus, the new method is more robust than the existing method in noisy communication environments. An efficient analytical algorithm for predicting the expected node degree in networks with uniform/non-uniform node distributions is also given for examining the applicability of either of the two estimators. Simulation results show excellent match between the velocity estimates given by the proposed method and the actual values in both sparse and dense network cases regardless of the nodal speed limits or the distribution of noises. In comparison to the existing method, the proposed method is shown to achieve an improvement factor of about 33 (in terms of normalized bias) with Gaussian multi-path noises of 4m standard deviation, or 20 with Uniform NLOS noises of 32m maximum.
I would like to acknowledge all my classmates in MRes/Msc NSE and CE&SP, for their generous help ... more I would like to acknowledge all my classmates in MRes/Msc NSE and CE&SP, for their generous help and enlightening. With them, I really enjoyed the passed year in University of Plymouth. On the personal side, I would like to thank my parents, for their unending love and support. V Improving Perceived Speech Quality for Wireless VoIP by Cross-layer designs CHAPTER 1
2007 IEEE International Conference on Communications, 2007
The quality of communications in mobile ad-hoc networks is largely determined by the topological ... more The quality of communications in mobile ad-hoc networks is largely determined by the topological stability. Characterizing the mobility of mobile nodes (e.g. how often they move away from each other) would enable the measurement of the frequency of network reconfigurations for predicting stability. In this paper, we first define a triplet V, Θ, Ψ which consists of mobility parameters that are directly correlated with the stability of a network (e.g. inter-node relative speeds/orientations and epoch time). Based on our previous study on range-based velocity estimations, we then propose a new scheme to estimate the mobility parameters in realtime. In contrast to existing methods that are based on either localization systems or features of wireless channel, the proposed scheme estimates the parameters V, Θ, Ψ only from the time-varying inter-node distance information while retaining its reliability and accuracy even in noisy environments. The performance of the proposed scheme is validated in computer simulations against an existing method under different network settings. We also apply the proposed scheme to link availability estimation as a more lightweight way of obtaining mobility parameters using an existing tool. Preliminary results for various scenarios show that, with the proposed scheme, the tool achieved a comparable performance to when a priori knowledge of nodal mobility is used.
Uploads
Papers by Zhuoqun Li