Conference Paper

Reduced-Complexity Power-Efficient Wireless OFDMA using an Equally Probable CSI Quantizer

Univ. Rey Juan Carlos. Fuenlabrada, Madrid
DOI: 10.1109/ICC.2007.484 Conference: Communications, 2007. ICC '07. IEEE International Conference on
Source: IEEE Xplore


Emerging applications involving low-cost wireless sensor networks motivate well optimization of multi-user orthogonal frequency-division multiple access (OFDMA) in the power-limited regime. In this context, the present paper relies on limited- rate feedback (LRF) sent from the access point to terminals to acquire quantized channel state information (CSI) in order to minimize the total average transmit-power under individual average rate and error probability constraints. Specifically, we introduce two suboptimal reduced-complexity schemes to: (i) allocate power, rate and subcarriers across users; and (ii) design accordingly the channel quantizer. The latter relies on the solution of (i) to design equally probable quantization regions per subcarrier and user. Numerical examples corroborate the analytical claims and reveal that the power savings achieved by our reduced-complexity LRF designs are close to those achieved by the optimal solution.

Download full-text


Available from: Javier Ramos, Apr 01, 2015
  • Source
    • "This limited-rate feedback enables channel-adaptive operation based on a finite number of possible transmit-configurations. Let S denote a set containing a finite number of adaptive modulation, coding, and power (AMCP) modes [2], [4]. Specifically, let the mth AMCP mode for the jth user on subcarrier k consist of a discrete rate (modulation and coding) r j,m,k ; and a discrete power level p j,m,k . "
    [Show abstract] [Hide abstract]
    ABSTRACT: The present paper deals with dynamic resource management based on quantized channel state information (CSI) for multi-carrier cognitive radio networks comprising primary and secondary wireless users. For each subcarrier, users rely on adaptive modulation, coding and power modes that they select in accordance with the limited-rate feedback they receive from the access point. The access point uses CSI to maximize the sum of generic concave utilities of the individual average rates in the network while respecting rate and power constraints on the primary and secondary users. Using a stochastic dual approach, optimum dual prices are found to optimally allocate resources across users per channel realization without requiring knowledge of the channel distribution.
    Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2008, March 30 - April 4, 2008, Caesars Palace, Las Vegas, Nevada, USA; 01/2008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tesis Doctoral leída en la Universidad Carlos III de Madrid en enero de 2007. Directores de la Tesis: Francisco Javier Ramos López y Georgios B. Giannakis
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Los sistemas de comunicación operando en canales (móviles) inalámbricos degradan considerablemente sus prestaciones (tasa de transmisión, consumo de potencia o probabilidad de error) debido a los desvanecimientos que sufre el medio inalámbrico. Esta degradación puede mitigarse aprovechando el conocimiento del estado canal (CSI) en el receptor y en el transmisor. El CSI puede ser perfecto si el error de estimación del canal es despreciable o cuantificado si no se conoce el valor exacto del canal sino únicamente la categoría (región) a la que el canal pertenece. La presente disertación tiene como objetivo diseñar y utilizar de manera óptima la cuantificación del CSI a fin de minimizar la potencia transmitida satisfaciendo requisitos de calidad de servicio en términos tasa de transmisión y probabilidad de error. El escenario básico de aplicación consiste en sistemas de comunicaciones móviles con transmisores adaptativos en los que el receptor tiene conocimiento perfecto del canal mientras que el transmisor, típicamente a través de un canal de control de retorno, únicamente conoce una versión cuantificada del mismo. Las contribuciones de esta tesis cubren sistemas de comunicaciones de distinta complejidad, operando sobre distintos tipos de canales, para uno o múltiples usuarios. Simulaciones numéricas validarán las derivaciones analíticas y mostrarán el significativo ahorro energético cuando se implementan los esquemas propuestos. Las principales contribuciones de esta tesis pueden resumirse como sigue: (i) se derivan esquemas de cuantificación y de adaptación como la solución de un problema de minimización con ligaduras; (ii) se prueba que los esquemas de cuantificación de canal corresponden al menos a un óptimo local; (iii) se prueba que los esquemas de adaptación son globalmente óptimos; (iv) se demuestra que la complejidad computacional por cada realización del canal requerida para implementar los esquemas adaptativos es moderada o despreciable; (v) se demuestra que las necesidades de envío de información de control del receptor al transmisor son sorprendentemente pequeñas y (vi) se muestra que la potencia consumida por los esquemas adaptativos basados en CSI cuantificado es considerablemente menor que la potencia consumida por sistemas no adaptativos y a su vez que la pérdida de prestaciones de aquellos frente a los que hacen uso de CSI perfecto es pequeña. Estas contribuciones motivan la implantación práctica de esquemas similares a los propuestos en sistemas reales de comunicaciones que, con un incremento moderado de la complejidad, obtienen significativas mejoras en sus prestaciones. _____________________________________________ Performance of wireless communication systems (quantified in terms of transmission rate, power e±ciency or error probability) degrades severely due to fading effects introduced by the shared air-interface. This degradation can be mitigated if channel state information (CSI) is available at the receiver and/or the transmitter side. Full CSI can be assumed when sufficient training allows for essentially perfect channel estimation, while quantized CSI can be used when only the class (cluster or region) that the channel belongs to is known. This dissertation aims at optimally designing and exploiting quantized CSI to minimize transmit-power under rate and error probability constraints. The setup comprises a wireless communication system with channel-adaptive modulation; where the receiver has available perfect CSI while the transmitter has only quantized CSI. In this context, innovative claims from a high-level vantage point pertain to novel schemes with variable complexity, under different channel types shared by single or multiple users. Simulated numerical tests corroborate the analytical claims and reveal that significant power savings result when implementing the proposed schemes. Specific contributions can be summarized as follows: (i) the quantization and adaptive transmission parameters can be obtained as the solution of a judiciously formulated constrained minimization problem; (ii) the channel quantization algorithms developed attain at least a local optimum of the objective function; (iii)the adaptive schemes reach the global optimum; (iv) the required computational complexity per channel realization for the adaptive schemes ranks from moderate to negligible; (v) the amount of feedback transmitters need from the receiver is stunningly small; and (vi) power consumed by adaptive schemes based on quantized CSI is significantly less than that required by non-adaptive alternatives, and closely approaches the power savings achieved by the benchmark perfect transmit-CSI design. These features encourage practical deployment of the proposed schemes that, with moderate computational overhead, offer a significant performance improvement.