Now showing 1 - 10 of 61
  • Placeholder Image
    Publication
    Downlink throughput enhancement of an OFDMA cellular system with closed-access indoor relays
    (22-10-2013)
    Karthik, K. S.
    ;
    We propose user-deployable closed-access indoor relays for throughput improvements in the downlink of LTE (long-term evolution) cellular system. The relays are assumed to be placed proximate to the destination user equipments (UEs). We propose a two-hop non-regenerative relaying scheme where the relay, equipped with multiple antennas, performs optimum combining to maximize the SINR (signal-to-interference-plus-noise ratio) before forwarding to a UE. The relaying is performed in a concurrent manner, where the base station (BS) transmits to some other receiver simultaneously when the relay is transmitting, and is therefore spectrally efficient. In order that the users served by a BS do not experience additional co-channel interference (CCI) because of the transmissions of the closed-access relays, we present an interference management scheme that can be implemented with minimal changes in the scheduling algorithm of a BS. Computer simulations, performed with large-scale deployment of indoor relays in the LTE framework, show that the UEs served by the relays see an improvement of over 100% in their respective throughputs, while the average cellular throughput improves by 24% when compared with a baseline system without relays. Also, the UEs served by the BSs do not experience any loss in their throughputs. © 2013 IEEE.
  • Placeholder Image
    Publication
    An efficient suboptimum detector based on linear prediction in Rayleigh flat-fading channels
    It is well known that the optimum detector based on linear prediction, for frequency-nonselective (flat) fading channels, requires MP states for M-ary signalling, where P is the order of the prediction filter required to decorrelate the received signal. In this paper, we first derive a suboptimal linear predictive-based (SLP) detector for M-ary PSK by making a high SNR assumption. We then demonstrate using the concept of isometry that for M-ary PSK signalling, only MP-1 states are required for this SLP detector. The complexity reduction is achieved with no loss in symbol-error-rate performance compared to the case where MP states are used. As a corollary, we also show that for a first-order prediction filter and M-ary PSK signalling, the SLP detector is identical to the conventional differential detector. © 2001 Elsevier Science B.V.
  • Placeholder Image
    Publication
    Distributed cooperative precoding with SINR-based Co-Channel user grouping for enhanced cell edge performance
    (01-09-2011)
    James, J. Vinosh Babu
    ;
    We consider the problem of cooperative precoding for controlling interference in the downlink of a multiple-input and multiple-output (MIMO) interference channel. A model for the multicell, multiuser, MIMO system is analyzed, and a criterion to simultaneously maximize the SINRs of users sharing a common spectral resource is provided. An asymptotically optimal solution is then proposed as the number of users per sector (U) and the number of resources (B) in the system become large, within a specific framework for scheduling co-channel users in interfering cells. Based on this, a heuristic algorithm for distributed cooperative precoder selection (CPS) is proposed for application in practical systems with finite B and U values. System performance gains measured in terms of mean cell throughput and cell-edge spectral efficiency values are estimated using numerical simulations. The proposed technique takes into account practical constraints such as limiting the information exchanged from the user equipments to the serving base stations, and amongst the cooperating base stations, to a modest level. © 2006 IEEE.
  • Placeholder Image
    Publication
    Distributed cooperative precoding in cellular systems
    (01-01-2014)
    James, Vinosh Babu
    ;
    We consider the problem of cooperative precoder selection for interference management in a broadband cellular wireless system. The problem is posed as a sum-rate maximization problem and a solution employing distributed scheduling and precoder selection is proposed. The solution is then shown to be optimal under certain asymptotic conditions. This is also verified using system simulations. © 2014 IEEE.
  • Placeholder Image
    Publication
    A two-hop AF relaying scheme with interference suppression at the relay
    (01-09-2014)
    Ks, Karthik
    ;
    We consider a system with a source, a relay, and a destination with an arbitrary number of cochannel interferers and thermal noise at both the relay and the destination. The relay is equipped with multiple antennas, whereas the destination has a single antenna with limited interference mitigation capabilities. For such a system, we propose a two-hop amplify-and-forward (AF) relaying scheme, where the relay performs optimum combining to maximize the signal-to-interference-plus-noise ratio (SINR) and forwards the soft symbols to the destination. We derive the cumulative distribution function of an upper bound on the end-to-end SINR achievable with such relay in Rayleigh fading channels. The achievable diversity and outage probability performance are analyzed using the bound and simulations. Block error rate performance at the destination is studied and a practical application in cellular networks is discussed. The results show that the proposed relay can assist a destination with a single antenna, which was experiencing lower SINR in the absence of the relay, to achieve higher values of SINR.
  • Placeholder Image
    Publication
    A Case for Large Cells for Affordable Rural Cellular Coverage
    (01-04-2020)
    Amuru, Saidhiraj
    ;
    ;
    Kuchi, Kiran
    ;
    Milleth, J. Klutto
    ;
    In most developing countries across the world, cellular rural users are predominantly pedestrian and indoor users within village homes, and much less from vehicles, let alone fast-moving ones. Specifically, in India, 85% of the villages in the plains are spaced 2–3 km apart uniformly in every direction. The base station required for providing coverage in rural areas is starkly different from the base station along highways to provide coverage for fast-moving vehicles. Till IMT-2020, ITU did not have a rural use case suited to rural needs of developing countries. Hence, the IMT advanced technology development (such as 4G LTE) did not meet the rural requirements in countries like India. To avoid such a situation for 5G, a new test case requirement, named low-mobility large cell (LMLC) was included as a mandatory use case with performance requirements that must be met by every specification that is approved as an IMT-2020 compliant standard. In this paper, we describe the reasons why such a test case requirement is crucial by taking a case study from the Indian rural setting. In addition, we also describe various technical solutions that can be considered to satisfy such stringent requirements. In particular, we look at a new waveform with low peak-to-average power ratio that has been introduced in 5G for coverage enhancement.
  • Placeholder Image
    Publication
    Packet Reservation Multiple Access for Local Wireless Communications
    (01-01-1989)
    Goodman, D. J.
    ;
    Valenzuela, R. A.
    ;
    Gayliard, K. T.
    ;
    Packet reservation multiple access (PRMA) allows a variety of information sources to share the same wireless access channel. Some of the sources, such as speech terminals, are classified as “periodic” and others, such as signaling, are classified as “random.” Packets from all sources contend for access to channel time slots. When a periodic information terminal succeeds in gaining access, it reserves subsequent time slots for uncontested transmission. Computer simulations and a listening test reveal that PRMA achieves a promising combination of voice quality and bandwidth efficiency. © 1989 IEEE
  • Placeholder Image
    Publication
    Joint Transceiver Design for Non-Concurrent MIMO Two-Way AF Relaying
    (01-10-2015)
    Budhiraja, Rohit
    ;
    We consider an amplify-and-forward infrastructure non-concurrent two-way relaying (ncTWR) scenario where a base station serves a transmit-only user TUE and a receive-only user RUE. Unlike conventional two-way relaying, the RUE in ncTWR experiences back-propagating interference (BI). Uniform channel decomposition and Tomlinson-Harashima precoding improve the bit error rate (BER) of multiple-antenna-multiple-output (MIMO) systems. Inspired by these techniques, we design a transceiver to reduce BER of both users in MIMO ncTWR. This transceiver cancels BI of the RUE and uses spatial noise whitening filters, designed herein, to uniformly decompose MIMO channels of both TUE and RUE. This letter quantifies the improved BER of the proposed transceiver.
  • Placeholder Image
    Publication
    Precoder design for asymmetric two-way AF shared relay
    (01-01-2013)
    Budhiraja, Rohit
    ;
    Two-way relaying (TWR) reduces the loss in spectral efficiency caused in a conventional half-duplex relay. TWR is possible when two nodes exchange data simultaneously through a relay. In the case of cellular systems, data exchange between base station (BS) and users is usually not symmetric, e.g., a user might have uplink data to transmit during multiple access (MAC) phase, but might not have downlink data to receive during broadcast (BC) phase. This asymmetry in data exchange will reduce the gains of TWR. With infrastructure relays, where multiple users communicate through a relay, the BC phase following the MAC phase of a transmitting user (UE1) can be used by the relay to transmit downlink data to a second user (UE2). This will result in the receiving user UE2 not being able to cancel the back-propagating interference in the usual way. Precoders are designed in [1] to mitigate the back-propagating interference at UE2 for an amplify-and-forward (AF) relay. The present work studies the asymmetric data-flow problem for a shared AF relay, wherein multiple BS and users communicate using a common relay with multiple antennas. In this case, UE2 will observe inter-user interference (IUI) in addition to the back-propagating interference. Also, BS will now observe the IUI. We propose a precoder to jointly mitigate the back-propagating interference for UE2 and IUI for BS and UE2. It is shown that the sum-rate performance is better for the proposed precoder than the conventional zero-forcing precoder. © 2013 IEEE.
  • Placeholder Image
    Publication
    Robust LLR aided low feedback precoding for interference alignment
    (18-05-2010)
    Vinoth, N.
    ;
    Ayyar, Arun
    ;
    ;
    Interference alignment, as proposed in [1], is a joint multi-base-station precoding technique where each interfering base-station determines its precoder so as to obtain aligned interfering signals at each user. Determination of such precoders requires complete channel state information of all the interfering links to be present at all the base-stations. In this paper, we present a modified form of interference alignment based on locally-available channel state information at the user equipment. We consider the downlink of a wireless system where basestations and user equipments are equiped with two antennas each and scheduling of users is done based on Fractional Frequency Reuse. Assuming an MMSE receiver at the user equipment, an expression for the optimal precoder to be used by the interfering base-stations is derived so that there is zero interference after MMSE equalization. We also give an example for the case where there is uncancelled interference despite the use of these precoders. The effect of this uncancelled interference is overcome by the use of a robust LLR developed in [2]. Simulation results that demonstrate the performance of the proposed technique are presented. ©2010 IEEE.