Access Schemes

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Chi Wan Sung - One of the best experts on this subject based on the ideXlab platform.

  • Uncoordinated multiple Access Schemes for visible light communications and positioning
    2016 IEEE International Symposium on Information Theory (ISIT), 2016
    Co-Authors: Siu-wai Ho, Chi Wan Sung
    Abstract:

    In visible light communication (VLC) systems, information are conveyed by visible light instead of radio-frequency electromagnetic waves. Based on received signal strength, accurate indoor positioning systems can also be built. Since a receiver obtains the superposition of signals from all light sources within line of sight together with ambient light, a multiple Access scheme is necessary for the receiver to distinguish the received symbol and signal strength from each light source. This paper proposes two multiple Access Schemes for VLC. The first scheme supports information broadcast and positioning. By using 2N timeslots, N transmitters transmit 2N - 1 symbols in total. The second scheme supports positioning only but places emphasis on minimizing the required timeslots. In each 2N timeslots for an odd integer N, the channel gains of 3N - 1/2 transmitters can be estimated.

  • ISIT - Uncoordinated multiple Access Schemes for visible light communications and positioning
    2016 IEEE International Symposium on Information Theory (ISIT), 2016
    Co-Authors: Siu-wai Ho, Chi Wan Sung
    Abstract:

    In visible light communication (VLC) systems, information are conveyed by visible light instead of radio-frequency electromagnetic waves. Based on received signal strength, accurate indoor positioning systems can also be built. Since a receiver obtains the superposition of signals from all light sources within line of sight together with ambient light, a multiple Access scheme is necessary for the receiver to distinguish the received symbol and signal strength from each light source. This paper proposes two multiple Access Schemes for VLC. The first scheme supports information broadcast and positioning. By using 2N timeslots, N transmitters transmit 2N − 1 symbols in total. The second scheme supports positioning only but places emphasis on minimizing the required timeslots. In each 2N timeslots for an odd integer N, the channel gains of 3N − 1 over 2 transmitters can be estimated.

C.n. Georghiades - One of the best experts on this subject based on the ideXlab platform.

  • On a unified view of synchronous multiple-Access Schemes: a bandwidth efficiency perspective
    2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733), 2004
    Co-Authors: P.d. Papadimitriou, C.n. Georghiades
    Abstract:

    Due to complexity considerations, synchronous multiple-Access Schemes, such as TDMA, CDMA, and OFDM, have been mainly based on orthogonal (unitary) transformations of the multiuser signal, which makes the receiver less complex, at the cost of bandwidth efficiency. In future systems, however, it seems that the limiting factor will not be processing power, but rather bandwidth. Therefore there is a need for redesigning multiple-Access Schemes, or rather unifying their design, in a multiple-Access scheme that is bandwidth efficient. The efficiency in the bandwidth can he achieved by applying non-unitary transformations to the multiuser signal such that the multiuser interference can he handled by a reasonably complex receiver. In this paper we attempt to unify the design of the aforementioned multiple-Access Schemes to a scheme that efficiently utilities the bandwidth, given that receivers of reasonable complexity can be deployed.

  • WCNC - On a unified view of synchronous multiple-Access Schemes: a bandwidth efficiency perspective
    2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733), 2004
    Co-Authors: Panayiotis Papadimitriou, C.n. Georghiades
    Abstract:

    Due to complexity considerations, synchronous multiple-Access Schemes, such as TDMA, CDMA, and OFDM, have been mainly based on orthogonal (unitary) transformations of the multiuser signal, which makes the receiver less complex, at the cost of bandwidth efficiency. In future systems, however, it seems that the limiting factor will not be processing power, but rather bandwidth. Therefore there is a need for redesigning multiple-Access Schemes, or rather unifying their design, in a multiple-Access scheme that is bandwidth efficient. The efficiency in the bandwidth can he achieved by applying non-unitary transformations to the multiuser signal such that the multiuser interference can he handled by a reasonably complex receiver. In this paper we attempt to unify the design of the aforementioned multiple-Access Schemes to a scheme that efficiently utilities the bandwidth, given that receivers of reasonable complexity can be deployed.

Siu-wai Ho - One of the best experts on this subject based on the ideXlab platform.

  • Uncoordinated multiple Access Schemes for visible light communications and positioning
    2016 IEEE International Symposium on Information Theory (ISIT), 2016
    Co-Authors: Siu-wai Ho, Chi Wan Sung
    Abstract:

    In visible light communication (VLC) systems, information are conveyed by visible light instead of radio-frequency electromagnetic waves. Based on received signal strength, accurate indoor positioning systems can also be built. Since a receiver obtains the superposition of signals from all light sources within line of sight together with ambient light, a multiple Access scheme is necessary for the receiver to distinguish the received symbol and signal strength from each light source. This paper proposes two multiple Access Schemes for VLC. The first scheme supports information broadcast and positioning. By using 2N timeslots, N transmitters transmit 2N - 1 symbols in total. The second scheme supports positioning only but places emphasis on minimizing the required timeslots. In each 2N timeslots for an odd integer N, the channel gains of 3N - 1/2 transmitters can be estimated.

  • ISIT - Uncoordinated multiple Access Schemes for visible light communications and positioning
    2016 IEEE International Symposium on Information Theory (ISIT), 2016
    Co-Authors: Siu-wai Ho, Chi Wan Sung
    Abstract:

    In visible light communication (VLC) systems, information are conveyed by visible light instead of radio-frequency electromagnetic waves. Based on received signal strength, accurate indoor positioning systems can also be built. Since a receiver obtains the superposition of signals from all light sources within line of sight together with ambient light, a multiple Access scheme is necessary for the receiver to distinguish the received symbol and signal strength from each light source. This paper proposes two multiple Access Schemes for VLC. The first scheme supports information broadcast and positioning. By using 2N timeslots, N transmitters transmit 2N − 1 symbols in total. The second scheme supports positioning only but places emphasis on minimizing the required timeslots. In each 2N timeslots for an odd integer N, the channel gains of 3N − 1 over 2 transmitters can be estimated.

Anthony Ephremides - One of the best experts on this subject based on the ideXlab platform.

  • Access Schemes for Mitigating the Effects of Sensing Errors in Cognitive Wireless Networks
    IEEE Transactions on Wireless Communications, 2014
    Co-Authors: Anthony Fanous, Anthony Ephremides
    Abstract:

    We study from a cross-layer perspective a cognitive network consisting of one primary user (PU) and one secondary user (SU). In contrast with the oversimplified collision channel model, we assume that simultaneous PU and SU transmissions are successful with some positive probability. We propose and analyze two Access Schemes at the SU aiming at maximizing its stable throughput while guaranteeing the stability of the PU's queue. These Schemes exploit the SU's knowledge of the channel statistics and of the average arrival rate to the PU. In the first scheme, the SU Accesses the channel at all slots with fixed probability p^* without sensing. In the second scheme, the SU Accesses the channel with probabilities p_1^* and p_2^* when the PU is sensed to be idle and busy, respectively. The analysis shows that if simultaneous PU and SU transmissions are likely to be successful, Schemes with no sensing outperform Schemes with sensing. Otherwise, Schemes with sensing are preferred. Therefore, using complex receivers capable of handling interference, alleviates the need of complex SU transmitters with strong sensing capabilities. We then extend the analysis to the case where the PU has an average delay constraint which is more restrictive than the stability constraint.

  • Comparison of Two Low Complexity Multiple Access Schemes
    2006 IEEE International Symposium on Information Theory, 2006
    Co-Authors: Anthony Ephremides
    Abstract:

    This paper studies multiple Access channels with additive Gaussian noise in the low signal to noise ratio (SNR) regime. We compare the spectral efficiencies of the optimal superposition channel sharing scheme and two simple alternatives: the time division multiple Access (TDMA) scheme and the parallel multiple Access scheme with single user decoding (PMAS). We consider the situation when the receiver has multiple receive antennas while each transmitter only has single antenna. We show that, due to TDMA's inefficiency in exploiting the multiuser multiplex gain, the relative spectral efficiency of PMAS over TDMA grows drastically as the number of receive antennas increase. The relative spectral efficiency of PMAS over the optimal scheme is approximately 1/2, irrespective of the number of receive antennas. Since the simplicities of PMAS and TDMA are similar, our results suggest that PMAS is a better alternative to TDMA for multiple Access system in the low SNR regime

Krishna R Narayanan - One of the best experts on this subject based on the ideXlab platform.

  • on the design of universal Schemes for massive uncoordinated multiple Access
    International Symposium on Information Theory, 2016
    Co-Authors: Austin Taghavi, Jeanfrancois Chamberland, Krishna R Narayanan
    Abstract:

    Future wireless Access points may have to support sporadic transmissions from a massive number of unattended machines. Recently, there has been a lot of interest in the design of massive uncoordinated multiple Access Schemes for such systems based on clever enhancements to slotted ALOHA. A close connection has been established between the design of the multiple Access scheme and the design of low density generator matrix codes. Based on this connection, optimal multiple Access Schemes have been designed based on slotted ALOHA and successive interference cancellation, assuming that the number of users in the network is known at the transmitters. In this paper, we extend this work and consider the design of universal uncoordinated multiple Access Schemes that are agnostic to the number of users in the network. We design Markov chain based transmission policies and numerical results show that substantial improvement to slotted ALOHA is possible.